Through the Smokescreen

For many years I was lucky enough to teach in a cancer biology course for third year natural science and medical students. Quite a few of those guys would already be eyeing up research careers and, within just a few months, some might be working on the very topics that came up in lectures. Nothing went down better, therefore, than talking about a nifty new method that had given easy-to-grasp results clearly of direct relevance to cancer.

Three cheers then for Mikhail Denissenko and friends who in 1996 published the first absolutely unequivocal evidence that a chemical in cigarette smoke could directly damage a bit of DNA that provides a major protection against cancer. The compound bound directly to several guanines in the DNA sequence that encodes P53 – the protein often called ‘the guardian of the genome’ – causing mutations. A pity poor old Fritz Lickint wasn’t around for a celebratory drink – it was he, back in the 1930s, that first spotted the link between smoking and lung cancer.

This was absolutely brilliant for showing how proteins switched on genes – and how that switch could be perturbed by mutations – because, just a couple of years earlier, Yunje Cho’s group at the Memorial Sloan-Kettering Cancer Center in New York had made crystals of P53 stuck to DNA and used X-rays to reveal the structure. This showed that six sites (amino acids) in the centre of the P53 protein poked like fingers into the groove of double-stranded DNA.

x-ray-picCentral core of P53 (grey ribbon) binding to the groove in double-stranded DNA (blue). The six amino acids (residues) most commonly mutated in p53 are shown in yellow (from Cho et al., 1994).

So that was how P53 ‘talked’ to DNA to control the expression of specific genes. What could be better then, in a talk on how DNA damage can lead to cancer, than the story of a specific chemical doing nasty things to a gene that encodes perhaps the most revered of anti-cancer proteins?

The only thing baffling the students must have been the tobacco companies insisting, as they continued to do for years, that smoking was good for you.

And twenty-something years on …?

Well, it’s taken a couple of revolutions (scientific, of course!) but in that time we’ve advanced to being able to sequence genomes at a fantastic speed for next to nothing in terms of cost. In that period too more and more data have accumulated showing the pervasive influence of the weed. In particular that not only does it cause cancer in tissues directly exposed to cigarette smoke (lung, oesophagus, larynx, mouth and throat) but it also promotes cancers in places that never see inhaled smoke: kidney, bladder, liver, pancreas, stomach, cervix, colon, rectum and white blood cells (acute myeloid leukemia). However, up until now we’ve had very little idea of what, if anything, these effects have in common in terms of molecular damage.

Applying the power of modern sequencing, Ludmil Alexandrov of the Los Alamos National Lab, along with the Wellcome Trust Sanger Institute’s Michael Stratton and their colleagues have pieced together whole-genome sequences and exome sequences (those are just the DNA that encode proteins – about 1% of the total) of over 5,000 tumours. These covered 17 smoking-associated forms of cancer and permitted comparison of tobacco smokers with never-smokers.

Let’s hear it for consistent science!

The most obvious question then is do the latest results confirm the efforts of Denissenko & Co., now some 20 years old? The latest work found that smoking could increase the mutation load in the form of multiple, distinct ‘mutational signatures’, each contributing to different extents in different cancers. And indeed in lung and larynx tumours they found the guanine-to-thymine base-pair change that Denissenko et al had observed as the result of a specific chemical attaching to DNA.

For lung cancer they concluded that, all told, about 150 mutations accumulate in a given lung cell as a result of smoking a pack of cigarettes a day for a year.

Turning to tissues that are not directly exposed to smoke, things are a bit less clear. In liver and kidney cancers smokers have a bigger load of mutations than non-smokers (as in the lung). However, and somewhat surprisingly, in other smoking-associated cancer types there were no clear differences. And even odder, there was no difference in the methylation of DNA between smokers and non-smokers – that’s the chemical tags that can be added to DNA to tune the process of transforming the genetic code into proteins. Which was strange because we know that such ‘epigenetic’ changes can occur in response to external factors, e.g., diet.

What’s going on?

Not clear beyond the clear fact that tissues directly exposed to smoke accumulate cancer-driving mutations – and the longer the exposure the bigger the burden. For tissues that don’t see smoke its effect must be indirect. A possible way for this to happen would be for smoke to cause mild inflammation that in turn causes chemical signals to be released into the circulation that in turn affect how efficiently cells repair damage to their DNA.

raleighs_first_pipe_in_england-jpeg

Sir Walt showing off on his return                         to England

Whose fault it is anyway?

So tobacco-promoted cancers still retain some of their molecular mystery as well as presenting an appalling and globally growing problem. These days a popular pastime is to find someone else to blame for anything and everything – and in the case of smoking we all know who the front-runner is. But although Sir Walter Raleigh brought tobacco to Europe (in 1578), it had clearly been in use by American natives long before he turned up and, going in the opposite direction (à la Marco Polo), the Chinese had been at it since at least the early 1500s. To its credit, China had an anti-smoking movement by 1639, during the Ming Dynasty. One of their Emperors decreed that tobacco addicts be executed and the Qing Emperor Kangxi went a step further by beheading anyone who even possessed tobacco.

And paying the price

And paying the price

If you’re thinking maybe we should get a touch more Draconian in our anti-smoking measures, it’s worth pointing out that the Chinese model hasn’t worked out too well so far. China’s currently heading for three million cancer deaths annually. About 400,000 of these are from lung cancer and the smoking trends mean this figure will be 700,000 annual deaths by 2020. The global cancer map is a great way to keep up with the stats of both lung cancer and the rest – though it’s not for those of a nervous disposition!

References

Denissenko, M.F. et al. ( (1996). Preferential Formation of Benzo[a]pyrene Adducts at Lung Cancer Mutational Hotspots in P53.Science 274, 430–432.

Cho, Y. et al. (1994). Crystal Structure of a p53 Tumor Suppressor-DNA Complex: Understanding Tumorigenic Mutations. Science, 265, 346-355.

Alexandrov, L.D. et al. (2016). Mutational signatures associated with tobacco smoking in human cancer. Science 354, 618-622.

Bigger is Better

“Nonsense!” most males would cry, quite logically, given that we spend much of our time trying to persuade the opposite sex that size doesn’t matter. But we want to have it both ways: in the macho world of rugby one of the oldest adages is that ‘a good big ’un will always beat a good little ’un’.  Beethoven doubtless had a view about size – albeit unrecorded by history – but after he’d written his Eroica symphony, perhaps the greatest revolutionary musical composition of all, his next offering in the genre was the magical Fourth – scored for the smallest orchestra used in any of his symphonies. And on the theme of small can be good, the British Medical Journal, no less, has just told us that if we cut the size of food portions and put ’em on smaller plates we’ll eat less and not get fat!

Is bigger better?

Is bigger better?

All of which suggests that whether bigger is better depends on what you have in mind. Needless to say, in these pages what we have in mind is ‘Does it apply to cancer?’ – that is, because cancers arise from the accumulation in cells of DNA damage (mutations), it would seem obvious that the bigger an animal (i.e. the more cells it has) and the longer it lives the more likely it will be to get cancer.

Obvious but, this being cancer, also wrong.

Peto’s Paradox

The first person to put his finger on this point was Sir Richard Peto, most famous for his work with Sir Richard Doll on cancer epidemiology. It was Doll, together with Austin Bradford Hill, who produced statistical proof (in the British Doctors’ Study published in 1956) that tobacco smoking increased the risk of lung cancer. Peto joined forces with Doll in 1971 and they went on to show that tobacco, infections and diet between them cause three quarters of all cancers.

Whenever this topic comes up I’m tempted to give a plug to the unfortunate Fritz Lickint – long forgotten German physician – who was actually the first to publish evidence that linked smoking and lung cancer and who coined the term ‘passive smoking’ – all some 30 years before the Doll study. Lickint’s findings were avidly taken up by the Nazi party as they promoted Draconian anti-smoking measures – presumably driven by the fact that their leader, Gröfaz (to use the derogatory acronym by which he became known in Germany as the war progressed – from Größter Feldherr aller ZeitenGreatest Field Commander of all Time) was a confirmed non-smoker. Despite his usefulness, Lickint’s political views didn’t fit the ideology of the times. He lost his job, was conscripted, survived the war as a medical orderly and only then was able to resume his life as a doctor – albeit never receiving the credit he deserved.

Returning to Richard Peto, it was he who in 1975 pointed out that across different species the incidence of cancer doesn’t appear to be linked to the number of cells in animal – i.e. its size.   He based his notion on the comparison of mice with men – we have about 1000 times the number of cells in a mouse and typically live 30 times as long. So we should be about a million times more likely to get cancer – but in fact cancer incidence is another of those things where we’re pretty similar to our little furry friends. That’s Peto’s Paradox.

It doesn’t seem to apply within members of the same species, a number of surveys having shown that cancer incidence increases with height both for men and women. The Women’s Health Initiative found that a four inch increase in height raised overall cancer risk by 13% although for some forms (kidney, rectum, thyroid and blood) the risk went up by about 25%. A later study found a similar association for ovarian cancer: women who are 5ft 6in tall have a 23% greater risk than those who only make it to 5 feet. A similar risk links ovarian cancer to obesity (i.e. a rise in body mass index from 20 (slim) to 30 (slightly overweight) puts the risk up by 23%). Statistically sound though these results appear to be, it’s worth nothing that, as my colleague Paul Pharoah has pointed out, these risk changes are small. For example, the ovarian cancer finding translates to a lifetime risk of about 16-in-a-1000 for shorter women going up to 20-in-a-1000 as they rise by 6 inches.

It’s true that there may be a contribution from larger animals having bigger cells (whale red blood cells are about twice as big as those of the mouse) that divide more slowly but at most that effect seems small and doesn’t fully account for the fact that across species the association of size and age with cancer breaks down: Peto’s Paradox rules – humans are much more likely to get cancer than whales.

What did we know?

Well, since Peto picked up the problem, almost nothing about underlying causes. The ‘almost’ has been confined to the very small end of the scale and we’ve already met the star of the show – the naked mole rat – a rather shy chap with a very long lifespan (up to 30 years) but who never seems to get cancer. In that piece we described the glimmerings of an explanation but, thanks to Xiao Tian and colleagues of the University of Rochester, New York we now know that these bald burrowers make an extraordinarily large version of a polysaccharide (a polymer of sugars). These long strings of glucose-like molecules (called hyaluronan) form part of the extracellular matrix and regulate cell proliferation and migration. They’re enormous molecules with tens of thousands of sugars linked together but the naked mole rat makes versions about four times larger than those of mice or humans – and it seems that these extra-large sugar strings restrict cell behaviour and block the development of tumours.

Going up!

Our ignorance has just been further lifted with two heavyweight studies, one from Lisa Abegglen, Joshua Schiffman and chums from the University of Utah School of Medicine who went to the zoo (San Diego Zoo, in fact) and looked at 36 different mammalian species, ranging in size from the striped grass mouse (weighing in at 50 grams) to the elephant – at 4,800 kilogram nearly 100,000 times larger. They found no relationship between body size and cancer incidence, a result that conforms to Peto’s paradox. Comparing cancer mortality rates it transpires that the figure for elephants is less than 5% compared with the human range of 11% to 25%.

107 final pic

Cancer incidence across species by body size and lifespan. A selection of 20 of the 36 species studied is shown. Sizes range from the striped grass mouse to the elephant. As the risk of cancer depends on both the number of cells in the body and the number of years over which those cells can accumulate mutations, cancer incidence is plotted as a function of size (i.e. mass in grams × life span, years: y axis: log scale). Each species is represented by at least 10 animals (from Abegglen et al., 2015).

It can be seen at a glance that cancer incidence is not associated with mass and life span.

The Tasmanian devil stands out as a remarkable example of susceptibility to cancer through its transmission by biting and licking.

How does Jumbo do it?

In a different approach to Peto’s Paradox, Michael Sulak, Vincent Lynch and colleagues at the University of Chicago looked mainly at elephants – more specifically they used DNA sequencing to get at how the largest extant land mammal manages to be super-resistant to cancer. In particular they focused on the tumor suppressor gene P53 (aka TP53) because its expression is exquisitely sensitive to DNA damage and when it’s switched on the actions of the P53 protein buy time for the cell to repair the damage or, failing that, bring about the death of the cell. That’s as good an anti-cancer defence as you can imagine – hence P53’s appellation as the ‘guardian of the genome’. It turned out that elephants have no fewer than 20 copies of P53 in their genome, whereas humans and other mammals have only one (i.e. one copy per set of (23) chromosomes). DNA from frozen mammoths had 14 copies of P53 but manatees and the small furry hyraxes, the elephant’s closest living relatives, like humans have only one.

The Utah group confirmed that elephants have, in addition to one normal P53 gene, 19 extra P53 genes (they’re actually retrogenes – one type of the pseudogenes that we met in the preceding post) that have been acquired as the animals have expanded in size during evolution. Several of these extra versions of P53 were shown to be switched on (transcribed) and translated into proteins.

Consistent with their extra P53 fire-power, elephant cells committed P53-dependent suicide (programmed cell death, aka apoptosis) more frequently than human cells when exposed to DNA-damaging radiation. This suggests that elephant cells are rather better than human cells when it comes to killing themselves to avoid the risk of uncontrolled growth arising from defective DNA.

More genes anyone?

Those keen on jumping on technological bandwagons may wish to sign up for an extra P53 gene or two, courtesy of genetic engineering, so that bingo! – they’ll be free of cancers. Aside from the elephant, they may be encouraged by ‘super P53’ mice that were genetically altered to express one extra version of P53 that indeed significantly protected from cancer when compared with normal mice – and did so without any evident ill-effects.

We do not wish to dampen your enthusiasm but would be in dereliction of our duty is we did not add a serious health warning. We now know a lot about P53 – for example, that the P53 gene encodes at least 15 different proteins (isoforms), some of which do indeed protect against cancer – but there are some that appear to act as tumour promoters. In other words we know enough about P53 to realize that we simply haven’t a clue. So we really would be playing with fire if we started tinkering with our P53 gene complement – and to emphasise practicalities, as Mel Greaves has put it, we just don’t know how well the elephants’ defences would stack up if they smoked.

Nevertheless, on the bright side, light is at long last beginning to be shed on Peto’s Paradox and who knows where that will eventually lead us. Meanwhile Richard Peto’s activities have evolved in a different direction and he now helps to run a Thai restaurant in Oxford, a cuisine known for small things that pack a prodigious punch. Bit like Beethoven’s Fourth you could say.

a-gem-of-a-find-in-oxford

References

Peto, R. et al. (1975). Cancer and ageing in mice and men. British Journal of Cancer 32, 411-426.

Doll, R. and Peto, R. (1976). Mortality in relation to smoking: 20 years’ observations on male British doctors. Br Med J. 2(6051):1525–36.

Maciak, S. and Michalak, P. (2015). “Cell size and cancer: A new solution to Peto’s paradox?”. Evolutionary Applications 8: 2.

Doll, R. and Hill, A.B. (1954). “The mortality of doctors in relation to their smoking habits”. BMJ 328 (7455): 1529.

Doll, R. and Hill, A.B. (November 1956). “Lung cancer and other causes of death in relation to smoking; a second report on the mortality of British doctors”. British Medical Journal 2 (5001): 1071–1081.

Tian, X. et al. (2013). High-molecular-mass hyaluronan mediates the cancer resistance of the naked mole rat. Nature 499, 346-349.

Abegglen, L.M., Schiffman, J.D. et al. (2015). Potential Mechanisms for Cancer Resistance in Elephants and Comparative Cellular Response to DNA Damage in Humans. JAMA. doi:10.1001/jama.2015.13134.

Sulak, M., Lindsey Fong, Katelyn Mika, Sravanthi Chigurupati, Lisa Yon, Nigel P. Mongan, Richard D. Emes, Vincent J. Lynch, V.J. (2015). TP53 copy number expansion correlates with the evolution of increased body size and an enhanced DNA damage response in elephants. doi: http://dx.doi.org/10.1101/028522.

García-Cao, I. et al. (2002). ‘Super p53’ mice exhibit enhanced DNA damage response, are tumor resistant and age normally. EMBO Journal 21, 6225–6235.

Dennis’s Pet Menace

As it happened, I’d already agreed to appear on Jeremy Sallis’ Lunchtime Live Show on BBC Radio Cambridgeshire – the plan being just to chat about cancery topics that might be of interest to listeners. Which would have been fine – if only The World Health Organization had left us in peace. But of course they chose last Tuesday to publish their lengthy cogitations on the subject of whether meat is bad for us – i.e. causes cancer.

Cue Press extremism: prime example The Times, quite predictably – they really aren’t great on biomedical science – who chucked kerosene on the barbie with the headline ‘Processed meats blamed for thousands of cancer deaths a year’.

But – to precise facts – and strictly it’s The International Agency for Research on Cancer, the cancer agency of the World Health Organization (WHO), that has ‘evaluated the carcinogenicity of the consumption of red meat and processed meat.’

But hang on … haven’t we been here before?

Indeed we have. As long ago as January 2012 in these pages we commented on the evidence that processed meat can cause pancreatic cancer and in May of the same year we reviewed the cogitations of the Harvard School of Public Health’s 28 year study of 120,000 people that concluded eating red meat contributes to cardiovascular disease, cancer and diabetes. To be fair, that history partially reflects why the WHO Working Group of 22 experts from 10 countries have taken so long to go public: they reviewed no fewer than 800 epidemiological studies! However, as the most frequent target for study was colorectal (bowel) cancer, that was the focus of their report released on 26th October 2015.

So what are we talking about?

Red meat, which means any unprocessed mammalian muscle meat, e.g., beef, veal, pork, lamb, mutton, horse or goat meat, that we usually cook before eating.

Processed meat: any meat not eaten fresh that has been salted, cured, smoked or whatever and commonly treated with chemicals to enhance flavour and colour and to prevent the growth of bacteria.

What did they say?

Processed meat is now classified as carcinogenic to humans – that is it goes into the top group (Group 1) of agents that cause cancer.

Red meat is probably carcinogenic to humans (Group 2A). Group 2B is for things that are possibly carcinogenic to humans.

Why?

Because 12 of the 18 studies they reviewed showed a link between consumption of processed meat and bowel cancer and because it’s known that agents commonly added to processed meat (nitrates and nitrites) can, when we eat them, turn into chemicals that can directly damage DNA, i.e. cause mutations and hence promote cancers.

For red meat 7 out of 15 studies showed positive associations of high versus low consumption with bowel cancer and there is strong mechanistic evidence for a carcinogenic effect i.e. when meat is cooked genotoxic (i.e. DNA-damaging) chemicals can be generated. They put red meat in the probably group because several of the studies that the Working Group couldn’t fault – and therefore couldn’t leave out – showed no association.

Stop woffling

My laptop likes to turn ‘woffling’ into ‘wolfing’. Maybe it’s trying to tell me something.

But is The WHO trying to tell us something specific about wolfing? To be fair, they have a go by estimating that every 50 gram portion of processed meat (say a couple of slices of bacon) eaten daily increases the risk of bowel cancer by about 18%. For red meat the data ‘suggest’ that the risk of bowel cancer could increase by 17% for every 100 gram portion eaten daily.

And what might that mean?

In the UK about 6 people in 100 get bowel cancer: if you take The WHO maximum estimate and have everyone eat 50 grams of processed meat every day of their lives such that 18% more of them would get bowel cancer, the upshot would be 7 people in 100 rather than 6. So it’s a small rise in a relatively small risk.

As the report points out, the Global Burden of Disease Project reckons diets high in processed meat cause about 34,000 cancer deaths per year worldwide and, if the reported associations hold up, the figure for red meat would be 50,000. Compare those figures with smoking that increases the risk of lung cancer by 20-fold and The WHO’s estimate of up to 6 million cancer deaths per year globally caused by tobacco use and 600,000 per year by alcohol consumption.

All of which suggests that it isn’t very helpful to lump meat eating, tobacco and asbestos in the same cancer-causing category and that The WHO could do worse than come up with a new classification system.

And the message?

Unchanged. Remember mankind evolved into the most successful species on the planet as a meat eater. As the advert used to say: It looks good, it tastes good and by golly it does you good – not least as a source of protein, vitamins and other nutrients. Do some exercise and eat a balanced diet – just in case you’ve forgotten, that means limit the amount of red meat (The WHO suggests no more than 30 grams a day for men, 25 g for women) so try fish, poultry, etc. Stick with the ‘good carbs’ (vegetables, fruits, whole grains, etc.), cut out the ‘bad’ (sugar – see Biting the Bitter Bullet), eat fishy fats not saturated fats and, to end on a technical note, don’t pig out.

_65259128_6136791400_49fc5aaece_b

‘The Divine Swine’ Castelnuovo Rangone, Italy

Meanwhile back on the Beeb

When the meat story broke I was a bit concerned that we might end up spending the whole of Lunchtime Live on how many bangers are lethal – especially as we were taking calls from listeners. Just in case things became a bit myopic I had Rasher up my sleeve. Rasher, you may recall, was Dennis the Menace‘s pet pig (in the The Beano‘s comic strip) who had a brother (Hamlet), a sister (Virginia Ham) and various other porky rellos. To bring it up to date we’d have introduced Sam Salami and Frank Furter and, of course, Rasher’s grandfather who was the model for the bronze statue named ‘The Divine Swine’ to be found in the little town of Castelnuovo Rangone in Pig Valley, Italy, the home of Parma ham.

But I shouldn’t have worried. All was well in the hands of Jeremy Sallis who, being a brilliant host, ensured that we mainly chatted about meatier matters than what to have for breakfast.

References

Press release: IARC Monographs evaluate consumption of red meat and processed meat.

Q&A on the carcinogenicity of the consumption of red meat and processed meat.

Carcinogenicity of consumption of red and processed meat. www.thelancet.com/oncology Published online October 26, 2015

Scandinavian Somersaults … or As You Were?

Talking about diets in the last post may have brought to mind the publicity about weight-reducing diets created by a recent Swedish study Dietary Treatment for Obesity.”

This report, incorrectly described by some of the press as providing national guidelines, has been interpreted as earth-shaking in turning conventional wisdom on its head by advocating a switch from low-fat to high-fat/low-carb nutrition.

lg-raspberry_chipotle_meatballsHelp yourself: Swedish meat balls:

pork and beef with lots of cream

But did it really say anything remotely revolutionary? Well, no. First, it was concerned only with diets aimed at reducing weight for obese people – and the central point was that a low-carbohydrate, high-fat diet, was the most effective in the short-term – over about 6 months – after which there’s not much difference compared with other dietary regimens.

So to summarise: eating lots of sugar and starch is bad for you – as anyone with much of a clue about metabolism knew anyway (see Biting the Bitter Bullet & A Small Helping For Australia) – and substituting artificial sweeteners won’t help either (The Best Laid Plans in Mice and Men..).

ShowImageVB.aspxA reminder from The Food Standards Agency

 References

SBU. Food in obesity. A systematic literature review. Stockholm: Swedish Council on Technology Assessment in Health Care (SBU); 2013. SBU Report No. 218. ISBN 978-91-85413-59-1.

http://healthimpactnews.com/2013/sweden-becomes-first-western-nation-to-reject-low-fat-diet-dogma-in-favor-of-low-carb-high-fat-nutrition/

Fast Food Fix Focuses on Fibre

If you’re like me you’re probably more bored than absorbed by the seemingly continuous stream of ‘studies’ telling us what we should and shouldn’t eat. No one’s going to argue it’s unimportant but gee, I wish they’d make their minds up. Of course the study of diet and its effects is tricky – as we noted in Betrayed by Nature – not least because you generally need enormous numbers of people to tease out significant effects.

Fortunately authoritative sources like The American Heart Association offer generally sane and simple advice: “eat a balanced diet and do enough exercise to match the number of calories you take in.”

A balanced diet includes fibre, sometimes called roughage, the stuff we eat but can’t digest that assists in taking up water and generally keeping our insides working. There’s much evidence that eating plenty of fibre helps to prevent bowel cancer – usually accumulated from vast numbers (e.g., the European Prospective Investigation into Cancer and Nutrition study involved over half a million people from ten European countries). But even for fibre, when you might just be thinking the answer’s clear-cut, there are other studies showing no protective effect.

So hooray for Stephen O’Keefe and friends from the University of Pittsburgh and Imperial College London for coming up with a dead simple experiment – and some pretty astonishing results (though to prevent panic we should reveal at the outset that they confirm that a high fibre diet can substantially reduce the risk of colon cancer).

Doing the obvious

The experiment compared what happened to two groups of 20, one African Americans, the other from rural South Africa, when they swapped diets for two weeks. So, in principle ‘dead simple’ but to describe it thus does a great injustice to the huge amount of effort involved – for a start they had to find two lots of 20 volunteers willing to have a colonoscopy examination before and after the diet swap. The Western diet was, of course, high protein, high fat, low fibre, whereas the typical African diet was high in fibre and low in fat and protein. Just to be clear, the American diet included beef sausage and pancakes for breakfast, burger and chips for lunch, etc. The traditional African diet comprises corn based products, vegetables, fruit and pulses, e.g., corn fritters, spinach and red pepper for breakfast.

B'fast jpegCompare and contrast.

A rural South African diet (corn fritters for breakfast) and the American diet (Getty images)

Shock – and horror

Almost incredibly, within the two weeks of these experiments there were significant, reciprocal changes in both markers for cancer development and in the bug army – the microbiota – inhabiting the digestive tracts of the volunteers. That is, the dreaded colonoscopy revealed polyps (tumour precursors) in nine Americans (that were removed) but none in the Africans. Cells sampled from bowel linings had significantly higher proliferation rates (a biomarker of cancer risk) in African Americans than in Africans. After the diet switch the proliferation rates flipped, decreasing in African Americans whilst the Africans now had rates even higher than in the starting African American group. These changes were paralled by an influx of inflammation-associated cells (lymphocytes and macrophages) in the now high-fat diet Africans whilst these decreased in the Americans on their new, high-fibre diet.

Equally amazing, these reciprocal shifts were also associated with corresponding changes in specific microbes and their metabolites. You may recall meeting our microbiota (in The Best Laid Plans of Mice and Men and It’s a Small World) – the 1000 or so assorted species of bacteria that have made you their home, mostly in your digestive tract, of which there are two major sub-families, Bacteroidetes and Firmicutes (Bs & Fs). We saw that artificial sweeteners in the form of saccharin shifts our bug balance: Fs down, Bs up. Here feeding Americans high-fibre diet was associated with a shift from Bs To Fs. As we noted before, the composition of the bug army is important because of the chemicals (metabolites) they produce – in this case the diet switch resulted in more short chain fatty acids (e.g., butyrate) in the American group and a reciprocal drop therein for the Africans.

The bottom line

It really is quite remarkable that these indicators of cancer risk manifest themselves so rapidly following a change to a typical Western diet. Of course ‘markers’ are one thing, cancer is another. As one of the authors, Jeremy Nicholson of Imperial College London, said: “We can’t definitively tell from these measurements that the change in their diet would have led to more cancer in the African group or less in the American group, but there is good evidence from other studies that the changes we observed are signs of cancer risk.”

Put less scientifically, “a nod’s as good as a wink to a blind horse.”

Reference

O’Keefe, S.J.D. et al. (2015). Fat, fibre and cancer risk in African Americans and rural Africans. Nature Communications 6, Article number: 6342 doi:10.1038/ncomms7342

Our Inner Self

Richard Gettner is the anti-hero of Christopher Fry’s wonderful play The Dark is Light Enough, set in the Austro-Hungarian war of 1848. Viewing himself as a failed author, failed husband and all-round disaster, he’s just absented himself from the Austrian Army on the basis of not being too nifty at soldiering either. Their minions are hot on his heels, intent on meting out the retribution that the military traditionally reserve for deserters, and he’s taken refuge in the family home of his former wife. In a tête á tête with her she rebukes him for his knack of self-destruction and points out that his book was actually quite well received and wasn’t really a failure. All Gettner’s frustration then bursts forth in a tirade of brutal philosphising:

‘Is there another

Word in the language so unnecessary

As ‘fail’ or ‘failure’?

No one has ever failed to fail in the end;

And for the very evident reason

That we’re made in no fit proportion

To the universal occasion; which, as all

Children, poets and myth-makers know,

Was made to be inhabited

By giants, fiends, and angels of such size

The whole volume of human generations

Could be cupped in their hands;

And very ludicrous it is to see us,

With no more than enough spirit to pray with,

If as much, swarming under gigantic

Stars and spaces.’

Fry deserves to be remembered as one of the great poetic wordsmiths of the English language, if only for The Dark is Light Enough but, had he known that nine out of ten cells in our bodies are bugs, he might have added a final blast to his demolition of the human condition:

Our failings should not surprise as we are but a sinister symbiosis,

More bacterial than human,

Helpfully poised such that when our hour is done

The microbial hordes surge forth to reduce us to our component parts.

bacteria and virus cartoon

The range of the hordes

Our rising preoccupation with the bug army (see it’s a small world & The Best Laid Plans In Mice and Men …) has been promoted by several recent studies that have propelled our ‘inner organism’ from the bowels of biology into the limelight. The story is somewhat fragmented but it’s a good time to see if we can make sense of the current threads.

We’ve known for many years that a motley collection of microorganisms are happy residents in most of our nooks and crannies, ranging from tummy buttons and through the skin, to saliva and our guts. They include bacteria and fungi, they’ve become known as the human microbiome (or microbiota), are said to outnumber human cells 10 to 1 and, all-told, can be viewed as a co-evolved ‘super-organism’ that has many benefits, including making our metabolism more efficient and hence improving nutrition. However, as with everything else in biology, this close relationship is a balancing act, the disturbance of which carries risks for disease development.

It’s critical to note that this vast microbial army, toiling away on our behalf in the dungeon of our innards, mostly dwelling in our gut, is a really mixed lot. It’s estimated to include about 700 different species of bacteria, of which perhaps thirty or forty species make up the bulk. It’s a bit like a mini Great Barrier Reef, well known as the world’s largest coral reef system and extraordinary in that, although it’s made up of billions of tiny organisms, the thing can behave in an integrated way, most dramatically illustrated by mass spawning.

Within the gut there are two major sub-families of microorganisms (Bacteroidetes (Bs) and Firmicutes (Fs)). Although more close-knit genetically speaking, each of these still includes many different classes of microbe. So, they’re a bit of a rabble but, by and large, not only are they harmless, they actually play a vital part in keeping us healthy.

Bacterial army manoeuvres

The power of DNA sequencing means that we can now interrogate our inner armies as to their make up under different conditions, because each type of microbe has a distinctive genome. The first thing to emerge is a dramatic shift in the balance between the major sub-families in obese individuals, be they mice or humans. That is, obese animals have about half the number of Bs and double that of Fs, compared to normal. And the link here is that the bug switch alters the pool of genes available, the upshot being increased energy harvest from nutrients consumed. In other words the switch helps animals get fatter.

It’s possible to breed mice that do not have any gut bugs and ask what happens when you transfer a colony from another animal. Bacteria-free mice on receipt of a normal gut army promptly double body fat: microbiota transferred from obese mice makes ’em twice as fat and, remarkably, human gut microbes from someone who’s obese also makes mice obese, if fed a high-fat rather than a normal diet.

Chemical warfare

Because we use antibiotics on a massive scale to control infections, we might ask whether they cause the good guys to suffer what the military call collateral damage – the point being that antibiotics don’t target bacteria on the basis of whether they’re good for us or potentially fatal. Inevitably, it turns out that ‘good guys’ do get hit by some antibiotics, and when this happens mice gain weight and build up fat. Unsurprisingly, a high-fat diet makes things worse. The sequence is that the drug changes the balance in microbiota before mice become obese and – a real shock – one course of antibiotic treatment imprints these effects on the animal permanently: it acts for life.

To clever for our own good

In our panic to avoid obesity and still pander to our sweet tooth, mankind has taken to using artificial sweeteners on a massive scale in the mistaken belief that these low-calorie agents do no harm. Only recently has this come to light as yet another example of the old adage about there being no such thing as a free lunch. It’s remarkable: saccharin, the most commonly used artificial sweetener, causes big shifts in the proportions of different types of gut bacteria – some increasing whilst others go down – the overall effect again being much more efficient energy harvesting from food. This is a direct effect of saccharin on the bugs, blocked by commonly used antibiotics.

The story so far

The regiments from which our foot soldiers are drawn (i.e. the species that form the microbiota) affect our metabolism and in particular can influence obesity – and that’s inextricably linked with type 2 diabetes and heart disease. With that in mind, it seems obvious that upsetting them with drugs is a risky business. What’s more, seemingly harmless food supplements can also be fraught with danger.

Marching to a beat

Yet another amazing feature of our inner army is that it keeps time. That is, the abundance of different sub-types fluctuates in synchrony with the day/night cycle. Put another way, it marches to a circadian rhythm along with many other physical, mental and behavioral changes that respond mainly to light – and hence roughly follow a 24-hour cycle. These can be big changes in composition: a particular type of bug can double in amount in 6 hours and return to its initial level by 6 hours later. One of the most familiar examples of the importance of biological rhythms comes from upsetting them by flying long distances on an east–west axis. Sure enough, mice have the same problem and, just like us, their clock is disturbed by jet lag (rather than shuttling them business class across the Atlantic you can simulate the effect simply by shifting the light-dark cycle under which they live forwards or backwards by 8 hours every three days). This largely blocks microbiota rhythmicity, the overall effect being to reduce the total number of bacteria. This in turn raises blood sugar level and the mice become obese. These events are absolutely dependent on what has happened to the microbiota because they are replicated in germ-free mice after transfer of jet-lagged faeces.

That’s more astonishing than might appear at first glance because it places the daily variation in gut bug populations alongside the basic circadian rhythms of the sleep-wake cycle, body temperature and other important functions. Circadian rhythms are driven by a ‘master clock’ in the brain that coordinates all the body clocks so that they are in synch. Four proteins are at the heart of the clock (CLOCK and BMAL1, highly expressed during the light phase, and cryptochromes (CRYs) and period proteins (PERs) expressed in the dark phase). These regulate the expression of many genes, thereby controlling the overall response (see Twenty More Winks). The implication is, therefore, that far from being a kind of add-on that occasionally gets upset, our microbiota play central role in a healthy body.

A recent example of it doing just that comes from another mouse model showing our ‘inner organism’ acting to protect against bacteria from the outside world. In response to infection, cells that line the small intestine switch on the production of a particular sugar (fucose): that is then released from the cells and consumed by members of the microbiota – this novel energy source seemingly helping the host to survive the onslaught of infectious microorganisms.

And finally …

All this stuff about germs being our best friends is riveting but what about the important question? Well, there appears to be a complex interaction between diet, microbial metabolism and colorectal cancer, with bacteria able to make some agents that protect against cancer and some others that drive carcinogenesis. There’s evidence that a wide range of tumours can be promoted by transferring microbiota to germ-free mice and, on the other hand, that depleting intestinal bacteria reduces the development of liver and colon cancers.

Space invaders

Personal space is, apparently, a big thing for many of us these days. So big that ‘scientists’ have had a go at measuring it – they never miss an opportunity do they? Actually, boffins being boffins, they measured something called the defensive peripersonal space (DPPS) – a ‘vital safety margin surrounding the body’ – by sticking a pair of electrodes to the wrists of volunteers who held their hands different distances from their faces whilst receiving bursts of current through the electrodes. That made them blink (!) and the nearer the hand to the face the more they blinked, as the shock was perceived to be a greater threat to their face. There is, seemingly, a sharp boundary: up to somewhere between 20 cm and 40 cm is a high-risk area where we get very aerated: beyond that we don’t much care – with large personal variations depending on how twitchy you are. Debrett’s, which styles itself as the arbiter of society etiquette, has a simpler test, its distilled wisdom revealing that if you can feel the warmth of someone’s anxious breath upon your face, then you’re standing too close.

With all this neurosis it’s probably a good job no one mentioned our inner army: a ten-to-one cellular takeover (albeit that bugs are much smaller) is not so much a bit of heavy breathing as a blitzkrieg. Even so, it’s a delicately poised occupation upon which we depend for survival – and it’s one that we disturb at our peril.

References

Sambo, C.F. and Iannetti, G.D. (2013). Better Safe Than Sorry? The Safety Margin Surrounding the Body Is Increased by Anxiety. The Journal of Neuroscience 33, 14225-14230; doi: 10.1523/JNEUROSCI.0706-13.2013.

The Best Laid Plans In Mice and Men …

I never thought I’d find myself indebted to one R. Burns, said to be Scotland’s national poet, but as a title for today’s piece it’s hard to avoid a mild bit of adaptive plagiarism. And after all, if John Steinbeck could do it …

Artificial sweeteners are wonderful things …

The next thing to do is to pass up all pretence at suspense and give the upshot of a remarkable new bit of work first. The story is of artificial sweeteners (non-caloric artificial sweeteners: NAS for short – most commonly saccharin) – among the most widely used food additives worldwide. Introduced over a century ago, they’ve long been considered great as they pander to our sweet teeth yet are low on calories – what can possibly go wrong?

Saccharin  StructureSweet'N Low

Well, according to Jotham Suez and his pals in The Weizmann Institute, Israel, quite a lot, once you get round to looking in the right places. They found that artificial sweeteners, particularly saccharin, make normal folk glucose intolerant (i.e. cause metabolic conditions – including diabetes – in which blood glucose levels are raised, aka hyperglycemia). Moreover, they do so by changing the make up of the bacteria in our gut (our intestinal microbiota – we’ve already met these guys in it’s a small world). The effects of NAS are reversed by antibiotics which, as we described in it’s a small world, can have drastic, permanent effects on our insides.

It’s a real shocker because, put another way, it shows NAS can dirDiet Coke etcectly drive the very outcomes we’re trying to avoid – diabetes and obesity.

How do they do it?

Suez & Co first showed that saccharin increases blood glucose in mice (glucose intolerance). Treatment with commonly used antibiotics (e.g., ciprofloxacin) blocks this effect. Sequencing DNA extracted from faeces revealed big shifts in the proportions of different types bacteria (taxa) – with some increasing whilst others went down. The overall effect is that the intestinal bugs (microbiota) as a whole became much more efficient at energy harvesting from food (e.g., producing more short-chain fatty acids) – an effect known to be associated with obesity in both mice and humans.

Obese miceDirect or indirect?

To show whether saccharin does this by directly acting on gut bugs they grew samples of faeces in the lab with and without added saccharin and – you’ve guessed it – the bug balance changed: Firmicutes down, Bacteroidetes up (from 89 to 79% and 6 to 22%, respectively). Transferring the saccharin-treated microbiota to germ-free (normal) mice made them glucose intolerant.

Lolli the Saccharin by Trinity FateRe-think required

The upshot of all this is that NAS may be doing the very thing we’re trying to avoid. Suez et al. note that the cult of NAS use has coincided with the epidemics of diabetes and obesity – but their results suggest very strongly that, far from being coincidence, it is yet another example of optimism and our hunger for easy solutions diverting our attention from our ignorance of the underlying science.

Grim reaperSo the message is there isn’t a short-cut to dealing with our sugar craving – if we aren’t to go on making ourselves very ill on a big scale we just have to show more self-discipline.

Reference

Suez , J. et al. (2014). Artificial sweeteners induce glucose intolerance by altering the gut microbiota. Nature 514, 181-186.

The Hay Festival

According to the Hay Festival  a recording of my talk ‘Demystifying Cancer’ on Wednesday 28th May should be available on their web site shortly and it can also be heard on the university site. However, I thought it might be helpful to post a version, not least for the for the rather breathless lady who arrived at the book signing session apologising for missing the lecture because she’d got stuck in mud. So for her and perhaps for many others I had the privilege of chatting to afterwards, read on …

 The Amazing World of Cells, Molecules … and CancerOpening pic

One of the biggest influences on my early years was the composer and conductor Antony Hopkins, who died a few days ago. Most of what I knew about music by the time I was 15 came from his wonderfully clear dissections of compositions in the series Talking About Music broadcast by the BBC Third Programme. When he was axed by the Beeb in 1992 for being ‘too elitist’ – yes, they talked that sort of drivel even then – Hopkins might have wished he’d been a biologist. After all, biology must be the easiest subject in the world to talk about. Your audience is hooked from the outset because they know it’s about them – if not directly then because all living things on the planet are interlinked – so even the BBC would struggle to make an ‘elitism’ charge stick. They know too that it’s beautiful, astonishing and often funny – both from what they see around them and also, of course, courtesy of David Attenborough. So it’s not a surprise when you show them that the micro-world of cells and molecules is every bit as wonderful.

The secret of life

What does come as a bit of a shock to most non-scientists is when you explain the secret of life. No, that’s not handing round pots of an immortalization elixir – much better, it’s outlining what’s sometimes rather ponderously called the central dogma of molecular biology – the fact that our genetic material (aka DNA) is made from only four basic units (most easily remembered by their initials: A, C, G and T – humans have over three thousand million of these stuck together). This is our ‘genome’ and the ‘genetic code’ enshrined in the DNA sequence makes us what we are – with small variations giving rise to the differences between individuals. The genetic code carries instructions for glueing together another set of small chemicals to make proteins. There are 20 of these (amino acids) and they can be assembled in any order to make proteins that can be thousands or even tens of thousands of amino acids long. These assemblies fold up into 3D shapes that give them specific activities. Proteins make living things what they are – they’re ‘the machines of life’ – and their infinite variety is responsible for all the different species to have appeared on earth. Can the basis of life really be so simple?

The paradox of cancer

Turning to cancer, a three word definition of ‘cells behaving badly’ would do fine. A more scientific version would be ‘cells proliferating abnormally.’ That is, cells reproducing either when they shouldn’t, or more rapidly than normal, or doing so in the wrong place. The cause of this unfriendly behavior is damaged DNA, that is, alteration in the genetic code – any such change being a ‘mutation’. If a mutation affects a protein so that it becomes, say, hyperactive at making cells proliferate (i.e. dividing to make more cells), you have a potential cancer ‘driver’. So at heart cancer’s very simple: it’s driven by mutations in DNA that affect proteins controlling proliferation. That’s true even of the 20% or so of cancers caused by chronic infection – because that provokes inflammation, which in turn leads to DNA damage.

The complexity of cancer arises because, in contrast to several thousand other genetic diseases in which just a single gene is abnormal (e.g., cystic fibrosis), tumour cells accumulate lots of mutations. Within this genetic mayhem, relatively small groups of potent mutations (half a dozen or so) emerge that do the ‘driving’. Though only a few ‘driver mutations’ are required, an almost limitless number of combinations can arise.

Accumulating mutations takes time, which is why cancers are predominantly diseases of old age. Even so, we should be aware that life is a game of genetic roulette in which each individual has to deal with the dice thrown by their parents. The genetic cards we’re dealt at birth may combine with mutations that we pick up all the time (due to radiation from the sun and the ground, from some foods and as a result of chemical reactions going on inside us) to cause cancers and, albeit rarely, in unlucky individuals these can arise at an early age. However, aside from what Mother Nature endows, humans are prone to giving things a helping hand through self-destructive life-style choices – the major culprits, of course, being tobacco, alcohol and poor diets, the latter being linked to becoming overweight and obese. Despite these appalling habits we’re living longer (twice as long as at the beginning of the twentieth century) which means that cancer incidence will inevitably rise as we have more time to pick up the necessary mutations. Nevertheless, if we could ban cigarettes, drastically reduce alcohol consumption and eat sensibly we could reduce the incidence of cancers by well over a half.

How are we doing?

Some readers may recall that forty-odd years ago in 1971 President Nixon famously committed the intellectual and technological might of the USA to a ‘War on Cancer’ saying, in effect, let’s give the boffins pots of money to sort it out pronto. Amazing discoveries and improved treatments have emerged in the wake of that dramatic challenge (not all from Uncle Sam, by the way!) but, had we used the first grant money to make a time machine from which we were able to report back that in 2013 nearly six hundred thousand Americans died from cancer, that the global death toll was over eight million people a year and will rise to more than 13 million by 2030 (according to the Union for International Cancer Control), rather less cash might subsequently have been doled out. Don’t get me wrong: Tricky Dicky was spot on to do what he did and scientists are wonderful – clever, dedicated, incredibly hard-working, totally uninterested in personal gain and almost always handsome and charming. But the point here is that, well, sometimes scientific questions are a little bit more difficult than they look.

Notwithstanding, there have been fantastic advances. The five year survival rates for breast and prostate cancers have gone from below 50% to around 90% – improvements to which many factors have contributed including greater public awareness (increasing the take-up of screening services), improved surgical and radiology methods and, of course, new drugs. But for all the inspiration, perspiration and fiscal lubrication, cancer still kills over one third of all people in what we like to refer to as the “developed” world, globally breast cancer killed over half a million in 2012 and for many types of cancer almost no impact has been made on the survival figures. In the light of that rather gloomy summary we might ask whether there is any light at the end of the tunnel.

The Greatest Revolution

From one perspective it’s surprising we’ve made much progress at all because until just a few years ago we had little idea about the molecular events that drive cancers and most of the advances in drug treatment have come about empirically, as the scientists say – in plain language by trial and error. But in 2003 there occurred one of the great moments in science – arguably the most influential event in the entire history of medical science – the unveiling of the first complete DNA sequence of a human genome. This was the product of a miraculous feat of international collaboration called The Human Genome Project that determined the order of the four units (A, C, G and T) that make up human DNA (i.e. the sequence). Set up in 1990, the project was completed by 2003, two years ahead of schedule and under budget.

If the human genome project was one of the most sensational triumphs in the history of science what has happened in the ensuing 10 years is perhaps even more dazzling. Quite breathtaking technical advances now mean that DNA can be sequenced on a truly industrial scale and it is possible to obtain the complete sequence of a human genome in a day or so at a cost of about $1,000.

These developments represent the greatest revolution because they are already having an impact on every facet of biological science: food production, microbiology and pesticides, biofuels – and medicine. But no field has been more dramatically affected by this technological broadside than cancer and already thousands of genomes have been sequenced from a wide range of tumours. The most striking result has been to reveal the full detail of the astonishing genetic mayhem that characterizes cancer cells. Tens of thousands or even hundreds of thousands of mutations featuring every kind of molecular gymnastics imaginable occur in a typical tumour cell, creating a landscape of stunning complexity. At first sight this makes the therapeutic challenge seem daunting, but all may not be lost because the vast majority of this genetic damage plays no role in cancer development (they’re ‘passenger’ mutations) and the power of sequencing now means they can be sifted from the much smaller hand of ‘driver’ mutations. From this distillation have emerged sets of ‘mutational signatures’ for most of the major types of cancers. This is a seismic shift from the traditional method of assessing tumours – looking directly at the cells after treating them with markers to highlight particular features – and this genetic approach, providing for the first time a rigorous molecular basis for classifying tumours, is already affecting clinical practice through its prognostic potential and informing decisions about treatment.

A new era

One of the first applications of genomics to cancer, was undertaken by a group at The Wellcome Trust Sanger Institute near Cambridge (where the UK part of the Human Genome Project had been carried out), who screened samples of the skin cancer known as malignant melanoma. This is now the fifth most common UK cancer – in young people (aged 15 to 34) it’s the second most common – and it killed over 2,200 in 2012. Remarkably, about half the tumours were found to have a hyperactivating mutation in a gene called BRAF, the effect being to switch on a signal pathway so that it drives cell proliferation continuously. It was a remarkable finding because up until then virtually nothing was known about the molecular biology of this cancer. Even more amazingly, within a few years it had lead to the development of drugs that caused substantial regression of melanomas that had spread to secondary sites (metastasized).

This was an early example of what has become known as personalized medicine – the concept that molecular analysis will permit treatment regimens to be tailored to the stage of development of an individual’s cancer. And maybe, at some distant time, the era of personalized medicine will truly come about. At the moment, however, we have very few drugs that are specific for cancer cells – and even when drugs work initially, patients almost invariably relapse as tumours become resistant and the cancer returns – one of the major challenges for cancer biology.

It behoves us therefore to think laterally, of impersonal medicine if you like, and one alternative approach to trying to hit the almost limitless range of targets revealed by genomics is to ask: do tumour cells have a molecular jugular – a master regulator through which all the signals telling it to proliferate have to pass. There’s an obvious candidate – a protein called MYC that is essential for cells to proliferate. The problem with stopping MYC working is that humans make about one million new cells a second, just to maintain the status quo – so informed opinion says that blocking MYC will kill so many cells the animal will die – which would certainly fix cancer but not quite in the way we’re aiming for. Astoundingly, it turns out in mice at least it doesn’t work like that. Normal cells tolerate attenuation of MYC activity pretty well but the tumour cells die. What a result!! We should, of course, bear in mind that the highway of cancer therapy is littered with successful mouse treatments that simply didn’t work in us – but maybe this time we’ll get lucky.

An Achilles’ heel?

In defining cancers we noted the possibility that tumour cells might proliferate in the wrong place. So important is this capacity that most cancer patients die as a result of tumour cells spreading around the body and founding secondary colonies at new sites – a phenomenon called metastasis. Well over 100 years ago a clever London physician by the name of Stephen Paget drew a parallel between the growth of tumours and plants: ‘When a plant goes to seed, its seeds are carried in all directions; but they can only live and grow if they fall on congenial soil.’ From this emerged the “seed and soil” theory as at least a step to explaining metastasis. Thus have things languished until very recent findings have begun to lift the metastatic veil. Quite unexpectedly, in mouse models, primary tumours dispatch chemical messengers into the blood stream long before any of their cells set sail. These protein news-bearers essentially tag a landing site within the circulatory system on which the tumour cells touch down. Which sites are tagged depends on the type of tumour – consistent with the fact that human cancers show different preferences in metastatic targets.

These revelations have been matched by stunning new video methods that permit tumour cells to be tracked inside live mice. For the first time this has shone a light on the mystery of how tumour cells get into the circulation – the first step in metastasis. Astonishingly tumour cells attach themselves to a type of normal cell, macrophages, whose usual job is to engulf and digest cellular debris and bugs. The upshot of this embrace is that the macrophages cause the cells that line blood vessels to lose contact with each other, creating gaps in the vessel wall through which tumour cells squeeze to make their escape. This extraordinary hijacking has prognostic value and is being used to develop a test for the risk of metastasis in breast cancers.

The very fact that cancers manifest their most devastating effects by spreading to other sites may lay bare an Achilles’ heel. Other remarkable technical developments mean that it’s now possible to fish out cancer cells (or DNA they’ve released) from a teaspoonful of circulating blood (that’s a pretty neat trick in itself, given we’re talking about fewer than 100 tumour cells in a sea of several billion cells for every cubic millimeter of blood). Coupling this to genome sequencing has already permitted the response of patients to drug therapy to be monitored but an even more exciting prospect is that through these methods we may be moving towards cancer detection perhaps years earlier than is possible by current techniques.

As we’ve seen, practically every aspect of cancer biology is now dominated by genomics. Last picIt’s so trendy that anyone can join in. Songs have been written about DNA and you can even make a musical of your own genetic code, French physicist Joel Sternheimer having come up with a new genre – protein music – in which sequence information is converted to musical notes. Antony Hopkins, ever receptive to new ideas, would have been enthralled and, with characteristic enthusiasm, been only too happy to devote an episode of Talking About Music to making tunes from nature.

it’s a small world

Once upon a time I went to Disneyland. My excuse is that it was a long time ago. So long, in fact, that I don’t need to specify where — it was before theme park cloning got going. Goodness knows why I went — given that if I was inclined to sticking pins in things, Mickey Mouse would be a prime target — though, logically, a model of Walt would come first. But one memory of that visit recurs unbidden to this day: the song ‘it’s a small world (after all).’ I know. I shouldn’t blame Disney as it was the Sherman Brothers greatest hit — and what with also writing the scores for Mary Poppins and Chitty Chitty Bang Bang, they’ve got a lot to answer for. Nevertheless and irritating though the jingle may be, it contains a rather profound line:

There’s so much that we share that it’s time we’re aware, It’s a small world after all’.

And that will do very well as our theme for the day.

SmallWorldFront83_wbYour inner self

A sobering thought about being human is that we’re mostly bugs – that’s to say on a cell to cell basis the microbes in our bodies outnumber us by ten to one. Ten to one: time for lunch, to recycle the old Goon Show gag, but first perhaps you should survey your microbiota – the 1000 or so assorted species of bacteria that have made you their home. Most of them (99%) reside in your digestive tract and we don’t notice them, of course, because they’re so much smaller than the cells of our body (they make up less than 3% of our mass). Sometimes called gut flora, they’re important in squeezing the last ounce of energy from what we eat by helping to digest sugars and they also make some vitamins that we need. You could, then, think of this unseen army of tiny cells as an organ in their own right. Unnoticed they may be but you upset them at your peril, as everyone knows who’s taken a course of antibiotics (e.g., penicillin) to get rid of unwanted bugs.

Bugs tummy

This vast force of bacteria, toiling away on our behalf in the dungeon of our innards, includes two major sub-families, Bacteroidetes and Firmicutes. Don’t worry about pronunciation: think of them as B & F. What’s important is that obese animals (including humans) have about half the number of Bs and double that of Fs, compared to normal. That’s a startling shift – the sort of result that gets scientists thinking: something fishy going on here. But what really gets their antennae twitching is the follow-up result. Each bug has its own genetic material (DNA) carrying a set of genes — different for each species. From faecal samples (i.e. stools) the total number of microbial genes can be estimated and — astonishingly — it turns out that there are several hundred times the number of our own genes. We have about 20,000, the bugs muster several million. But the really provocative result is that this total of microbial genes in our gut drops if we become obese:

Fewer genes = more body fat

More genes (a more diverse microbiome) = healthy status.

Cause or effect?

A good question — that can be answered by man’s best friend. Yes, I’m afraid it’s Mickey again. Mice born under aseptic conditions by Caesarean section don’t have any gut microbes — they’re ‘germ-free’ mice — and they grow up with less body fat than normal mice. However, give them the gut army from a normal mouse and they more than double their body fat in a couple of weeks. The microbiota from an obese mouse makes them gain twice as much fat. What happens if you colonise germ-free mice with human gut microbes? If they’re from someone who’s obese the mice also become obese, if fed a high-fat rather than a normal diet.

Because obesity is all about the balance between energy extracted from food and that expended, all this suggests that obesity-associated microbiomes increase the efficiency of extraction.

But if that’s the case maybe there are some slackers in the bug world – types that are pretty hopeless at food processing. Might they offset obesity? Well, at least one (by the name of Akkermansia muciniphila) does just that — again in mice — and its numbers are much reduced in obese people but go up after gastric bypass surgery that reduces the absorption of nutrients from food. This offers the seductive notion that some types of bug might help to reduce obesity.

Debugging

You may have spotted a bit of a cause for concern: if the make up of our gut bugs can affect how our bodies work — and especially whether we put on weight — what happens when we zap ourselves with antibiotics? The problem is, of course, that these drugs target a range of bacteria — they’re not particularly choosy — which is why you get diarrhœa when you take penicillin for a throat infection. And it’s not just you. In the UK we consume 30 million antibiotic prescriptions a year: Americans get through over 250 million and their children get an average of 15 courses of antibiotics in their early years.

The problem here is not about antibiotics being wonderful and saving millions of lives but the possibility that they might have long-term effects. Evidence for this has come from Martin Blaser’s group at New York University who showed that some antibiotics make mice put on weight and build up fat. What’s more, a high-fat diet adds to this effect. Remarkably, changes in the mice microbiota occur before they become obese — and the effects are for life. It seems extraordinary that a short drug pulse, such as we might give a child to cure an ear infection, can have permanent effects. The explanation may be that some gut bacteria are better at surviving the drug treatment resulting in a shift of microbiota balance to give more efficient digestion — i.e. greater energy provision.

It may not be coincidence that the escalation in antibiotic use since the 1940s has paralleled the obesity explosion. In 1989 no USA state had an obesity level above 14%; by 2010 none was below 20% — and the national average is now 30%.

Bugs and cancer: drivers or mirrors?

Those who follow this blog will know that where obesity lurks cancer looms. Indeed transferring microbiota to germ-free mice has been shown to promote a wide range of tumours and, conversely, depleting intestinal bacteria reduces the development of liver and colon cancers. It’s also worth noting that bowel cancer occurs more frequently in the large intestine than in the small — which may reflect the much higher microbial density.

Is it a small world after all?

All these findings suggest that our bug contingent can influence the onset of obesity and various cancers and that even brief drug treatments can have permanent effects on its make up. We have only the vaguest idea how this happens and most of the evidence so far comes from Mickey’s rellos. Even so, maybe in time we will be able to manipulate our personal gut micro-worlds to augment our defences against these potent foes.

Reference

Martin J. Blaser: Missing microbes, Henry Holt & Company 2014

http://www.amazon.com/Missing-Microbes-Overuse-Antibiotics-Fueling/dp/0805098100/ref=sr_1_1_ha?s=books&ie=UTF8&qid=1400478180&sr=1-1&keywords=missing+microbes

A Small Helping For Australia

There’s an awful lot of very good things in Australia. Australians for a start. They’re just so kind, open, welcoming and accommodating it makes touring round this vast land a joy. Not merely do they cheerfully find a way to fix anything you want but they’re so polite that no one’s drawn attention to my resemblance to a scientific version of those reconstructed geriatric pop groups (viz the Rolling Stones or whatever) staggering round the place on their Zimmer frames. And they say wonderful things about my talks – that’s how charming they are!!

Greater bilgy

Greater bilby

Of course, you could say of Australia what someone once said of America and Britain: two nations divided by a common language. In the case of Oz you could also add ‘and by a ferociously competitive obsession with sport.’ So it’s wonderfully not home. Even Easter’s different in that here you get chocolate Easter bilbies rather than rabbits. Bilbies, by the way, are a sort of marsupial desert rat related to bandicoots. The lesser version died out in the 1950s so only the greater bilby is left (up to 20 inches long + tail half as long again) and you have to go to the arid deserts to find those. Not the choccy versions obviously: they don’t do too well in the deserts but they’re all over Melbourne:

Easter bilby

Easter bilby

shops full of ’em – and a lot bigger than the real thing. So, together with the egg avalanche, there’s no limit to the number of calories you can consume in celebrating the resurrection of Christ. Coupled with the glorious fact that there’s scarcely any mention of wretched soccer, all these novelties mean you’re never going to be lulled into thinking you’re still in dear old Blighty (or back in the old country as they delightfully put it here).

Hors D’Oeuvres

Even so there are some marked similarities to make you feel at home. One of the least striking is that most people are overweight. That is, I scarcely notice it, coming from what I regard as the global fat capital, i.e. Cambridge. The stats say that that’s not true, of course. The USA does these things better than the UK. Of course it does. But there’s not much in it. More than two-thirds of American adults are overweight and one person in three is obese. For the UK the prediction is that one in three will be obese by 2020. Currently in Australia 63% of the adult population is overweight, a figure that includes 28% who are obese.

The essential point is that there’s stuff all difference between those countries and the really critical thing is that the rates go on soaring. In the U.S. between 1980 and 2000 obesity rates doubled among adults and since 1980 the number of overweight adolescents has tripled. By 2025 one Australian child in three will be in the overweight/obese category.

Main course

The meat in this piece is provided by a report written by a bunch of Australian heavyweights – all Profs from Sydney or wherever. It has the droll title ‘No Time To Weight’ – do I need to explain that or shall I merely apologise for the syntax? ‘Oh c’mon!’ I hear our Aussie readers protest. ‘We’re going to hell in a handcart and you’re wittering about grammar. Typical b***** academic.’ Quite so. Priorities and all that. So the boffins’ idea is to wake everyone up to obesity and get policy-makers and parliamentarians to do something effective.No Time to Weight report

Why is this so important? Probably unnecessary to explain but obesity causes a variety of disorders (diabetes, heart disease, age-related degenerative disease, sleep apnea, gallstones, etc.) but in particular it’s linked to a range of cancers. Avid followers of this BbN blog will recall obesity cropping up umpteen times already in our cancer-themed story (Rasher Than I Thought?/Biting the bitter bullet/Wake up at the back/Twenty winks/Obesity and Cancer/Isn’t Science Wonderful? Obesity Talks to Cancer) and that’s because it significantly promotes cancers of the bowel, kidney, liver, esophagus, pancreas, endometrium, gallbladder, ovaries and breast. The estimate is that if we all had a body mass index (BMI) of less than 25 (the overweight threshold) there would be 12,000 fewer UK cancers per year. Mostly the evidence is of the smoking gun variety: overweight/obese people get these cancers a lot more often than lesser folk but in Obesity Talks to Cancer we looked at recent evidence of a molecular link between obesity and breast cancer.

Entrée (à la French cuisine not North American as in Main course)

Or, as you might say, a side dish of genetics. The obvious question about obesity is ‘What causes it?’ The answer is both complicated and simple. The complexity comes from the gradual accumulation of evidence that there is a substantial genetic (i.e. inherited) component. Many people will have heard of the hormone leptin, a critical regulator of energy balance and therefore of body weight. Mutations in the leptin gene that reduce the level of the hormone cause a constant desire to eat with the predictable consequence. But only a very small number of families have been found who carry leptin mutations and, although other mutations can drive carriers to overeating, they are even rarer.

However, aside from mutations, everyone’s DNA is subtly different (see Policing DNA) – about 1 in every 1000 of the units (bases) that make up our genetic code differs between individuals. All told the guess is that in  90% of the population this type of genetic variation can contribute to their being overweight/obese.

Things are made more complicated by the fact that diet can cause changes in the DNA of pregnant mothers (what’s called an epigenetic effect). In short, if a pregnant woman is obese, diabetic, or consumes too many calories, the obesity trait is passed to her offspring. This DNA ‘imprinting’ activates hormone signaling to increase hunger and inhibit satiety, thereby passing the problem on to the child.Preg Ob

So the genetics is quite complex. But what is simple is the fact that since 1985 the proportion of obese Australians has gone up by over 10-fold. That’s not due to genes misbehaving. As David Katz, the director of Yale University’s Prevention Research Center puts it: ‘What has changed while obesity has gone from rare to pandemic is not within, but all around us. We are drowning in calories engineered to be irresistible.’

Desserts

We might hope that everyone gets theirs but for obesity that’s not the way it works. The boffos’ report estimates that in 2008 obesity and all its works cost Australia a staggering $58.2 billion. Which means, of course, that every man, woman and child is paying a small fortune as the epidemic continues on its unchecked way. The report talks formulaically of promoting ‘Australia-wide action to harmonise and complement efforts in prevention’ and of supporting treatment. It’s also keen that Australia should follow the American Medical Association’s 2013 decision to class obesity as a disease, the idea being that this will help ‘reduce the stigma associated with obesity i.e. that it is not purely a lifestyle choice as a result of eating habits or levels of physical activity.’ Unfortunately this very p.c. stance ignores that fact that obesity is very largely the result of eating habits coupled to levels of physical activity. The best way to lose weight is to eat less, eat more wisely and exercise more.

In 2008 Australian government sources forked out $932.7 million over 9 years for preventative health initiatives, including obesity. This latest report represents another effort in this drive. Everyone should read it but, clear and well written though it is, it looks like a government report, runs to 34 pages and almost no one will give it the time of day.

The problem is that in Australia, as in the UK and the USA, all the well-intentioned propaganda simply isn’t working. As with tobacco, car seat belts and alcohol driving limits, the only solution is legislation, vastly unpopular though that always is – until most folk see sense. Start with the two most obvious targets: ban the sale of foods with excessive sugar levels (especially soft drinks) and make everyone have a BMI measurement at regular intervals, say biannually. Then fine anyone over 25 in successive tests who isn’t receiving some sort of medical treatment.

Amuse bouche

I know: I’ll never get in on that manifesto. But two cheers for ‘No Time To Weight’ and I trust the luminaries who complied it appreciate my puny helping hand from Cambridge. In the meantime, not anticipating any progress on a national front, I’m going to start my own campaign – it’s going to be a bit labour-intensive, one target at a time, but here goes!

The other evening I had dinner in a splendid Italian restaurant (The Yak in Melbourne: very good!). And delightful it would have been had I not shared with two local girls at the next table. One was your archetypal tall, slender, blonde, 25-ish Aussie female – the sort you almost feel could do with a square meal. Her companion of similar age was one of the dirigible models. (You’ll understand I wasn’t looking at them at all: I was with my life’s companion so no chance of that – but I do have very good peripheral vision. Comes from playing a lot of rugby). Each had one of the splendid pasta dishes on offer – but, bizarrely, they also ordered a very large bowl of chips. No prizes for guessing who ate all the fries. Miss Slim didn’t have one – not a single one! (OK, by now I was counting). Her outsize friend had the lot. How could she do that with a shining example of gastronomic sanity sitting opposite?

So c’mon Miss Aussie Airship: you know who you are. Let’s have no more of it. Obesity is not a personal ‘issue.’ Regardless of your calorie intake in one meal, your disgraceful behavior ruined a delightful dining experience for me, and quite possibly several other folk within eyeshot, upset the charming waitress and insulted The Yak’s excellent chef. Just think in future: there’s a place in life for chips – but it’s not with everything.

Reference

“Obesity: A National Epidemic and its Impact on Australia”