Sonntag, 13. November 2016

Large ongoing Primary Prevention Studies

In this article I want to highlight large studies that are being performed in relatively healthy populations, or which provide relevant data to further the goal of delaying aging and age-related diseases.

To provide a complete picture I looked into various reviews and the notes and ideas I already had. Keeping track of new nutraceutical and health related developments used to be a big pastime of mine so I hope the below list is somewhat complete. In addition to literature search, I queried a large clinical trials database using various terms. One variation was for example a query for "Interventional Studies | mortality | Adult | Phase 3, 4 | Studies with safety issue outcome measures" yielding 1107 hits. From this list, I selected studies with n > 1000 which yielded approx. 255 results, which were then hand search. In this way the clinicaltrials database helped me to identify a few studies I would have missed otherwise and what follows are short notes on interesting trials.

Dienstag, 1. November 2016

Coffeehouse notes on GH/IGF-1, CR and life span

Both Ames and growth hormone receptor knock-out (GHRKO) mice have disruptions in the GH pathway (11).

Surprisingly, however, studies suggest that GHRKO mice show more robust life span extension than Ames dwarfs. For one, the GHRKO model holds the absolute longevity record for lab mice. Secondly, it is much less responsive to caloric restriction (CR), while reducing calories extends the lifespan of Ames dwarfs quite robustly. Third, Ames dwarfs lack TSH, which might be beneficial, yet do not outlive GHRKOs (alternatively, this means TSH is only a minor player).

However, this notion in itself is controversial, because these mice have defects in the same pathway. In Ames dwarfs growth hormone (GH) is absent and GHRKO mice simply lack the GH receptor.

The hypothesis of the highly robust GHRKO mouse has two important implications worth exploring. On the one hand, it suggests that if CR fails to increase lifespan in this model it may work exclusively through GH signaling, which I don't believe. In addition, it would mean that the GHR receptor might have functions independent of GH binding and that the GHRKO mouse is meaningfully different from the Ames dwarf. When I talked to researchers at the last conference, some were quite convinced that there is a "magic ingredient" to the GHRKO mouse responsible for its robustness. Let's call it magic, because no one really knows what it is.

So it is reasonable to hypothesize that GHRKO, with the magic pathway fully suppressed, imposed on top of Ames dwarfism, magic pathway still partly active, would further improve life span and healthspan. Before we discuss the paper by Gesing et al. 2016 (1) testing this proposition, I want to give an introduction to GH in aging and briefly review key studies and controversies.

Mittwoch, 28. September 2016

Millennium Development Goals (MDG) vs. Steven Pinker

In "The Better Angels of Our Nature: Why Violence Has Declined" Steven Pinker chronicles an unprecedented decline in violence and war over the last decades and centuries (c.f. [4]). After having read this book one has to wonder if the same trajectory applies to public health goals? Although, the answer is obvious to me I don't think it is evident from media reporting or even common knowledge that the world today is better than ever in almost all regards.

One key question is not just whether there is progress at all, but also the rate of change. Is progress accelerating leading to a singularity? Is progress constant, e.g. a fixed decrease in deaths per year or a fixed fraction? If the latter is true the total amount of suffering may be increasing while the incidence of suffering decreases, not exacly the best outcome.
Or is progress even slowing down because the last bit is the hardest, the remaining challenges being exponentially more complex - as has been suggested for biomedical research?

Can we expect a world without bloody internecine struggle in 2100? Will we live long enough to see a world without poverty, gender inequality and HIV? Will we eradicate cancer and solve aging one day in the far future?  How ridiculous are these questions and aspirations?

If we want to look at high level progress towards a better, utopian world, it seems prudent and most convenient to look at those who need the most help: poor, developing nations. The United Nation's "Millennium Development Goals Report" (1) provides a handy source documenting progress across the board with notable exceptions. In this post, I will discuss what we have achieved so far with some added commentary on biomedicine and Pinker's book and at some later point I plan to write a post focusing on the situation in developed nations.

The goals
Goal 1: Eradicate Extreme Hunger and Poverty
Goal 2: Achieve Universal Primary Education
Goal 3: Promote Gender Equality and Empower Women
Goal 4: Reduce Child Mortality
Goal 5: Improve Maternal Health
Goal 6: Combat HIV/AIDS, Malaria and other diseases
Goal 7: Ensure Environmental Sustainability
Goal 8: Develop a Global Partnership for Development

Mittwoch, 27. April 2016

Iron: focus on epidemiology and current studies relevant to CVD and all-cause mortality

Although, I believe that iron is more of a player in carcinogenesis than cardiovascular disease (CVD) I would like to do a brief review of the latter anyway. So far, the best evidence suggests that modest iron excess may promote atherosclerosis but not other types of CVD. But does it really?

1. Ferritin associates with all-cause mortality - does it matter?

2. Evidence against the iron-atherosclerosis hypothesis: ferritin & CVD incidence
3. Hemochromatosis: a special casse

4. Special epidemiology - beyond ferritin and CVD incidence

5. What are the problems with epidemiology?
6. The solution: best biomarker, best study design

7. Other studies of interest - biogerontology
8. References

1. Ferritin associates with all-cause mortality - does it matter?
A recent study by Ellervik et al. (2014) found a positive association of ferritin with total mortality (n~9000, 23y follow-up). They also performed a "meta-analysis", but in the end only three studies were included (4).
"...we conducted a meta analysis of our own study and 2 additional previous population-based studies on risk of increased total mortality according to ferritin concentrations in quartiles or tertiles, indirectly testing the hypothesis that using quartiles or tertiles for risk prediction hides an increased risk because the highest quartiles or tertiles often include part of the reference interval for ferritin concentrations, thereby diluting risk estimates."

Indeed, given these tertiles any significant result is unlikely using this approach:
"lowest tertile T1 (range 1–55 ug/L), second tertile T2 (56–126 ug/L), and highest tertile T3 (127–1524 ug/L)."
The normal range is 12-150 ng/mL or up to 300 for males. For comparison, male participants in the largest iron reduction study ever performed reached 50-70ng/ml and lower seemed better (10).

The critical discussion of the Ellervik study by several letters and editorials reminded me just how complicated iron-CVD epidemiology is (4a-4e). Below follow a few key Points.

Montag, 25. April 2016

Life extension - Calories or protein?

There are some major controverises left in the calorie restriction (CR) field: modest or null results in wild-dervied mice and ILSXISS strains, human epidemiology, rhesus monkey studies and recently CR vs. protein restriction (PR) (cf. IGF1 vs other pathways).

Recently, people started to wonder if protein restriction may drive the effect of CR in rodents. Speakman et al. provide a beautifully succint review and meta-analysis of the CR vs PR debate. A must read for everyone in the field, since Speakman is generally known for his diligent work.

Some background: Calorie restriction (CR) was discovered in the 1920s but Clive McCay's rigoros studies from the 30s are credited with starting the field of biogerontologic CR. Nevertheless the question whether CR or PR is more important was unresolved at that time, but after a few decades the consensus emerged that CR is not due to protein restriction. Many relevant papers were published including those by Ross et al. in the 1960s and Masoro et al. in the 1980s. However, when life extending essential amino acid restriction was discovered in the late 80s/early 90s, and secondly Linda Partridge (and many others) showed that insect lifespans are more responsive to PR than CR, this reignited the debate about mammalian CR vs PR.
Recent work on mice has involved varying the protein to carbohydrate ratio in ad libitum fed mice and then plotting their responses including lifespan in the context of a two-dimensional framework defined by the balance of intake of protein to non-protein components ( Solon-Biet et al., 2014). This massive experiment involved feeding mice 25 different diets that varied in their protein to non-protein ratios, and following cohorts of them until they died. The data clearly [and controversially] indicated that the key factor influencing longevity, as was observed in insects, was the protein to non-protein (carbohydrate) ratio in the diet. As the protein to carbohydrate ratio declined, lifespan increased, recapitulating the same finding detailed above (Ross, 1961).
To rephrase, Solon-Biet claim that protein restriction was the exclusive determinant of lifespan and not CR. This claim will be challenged by Speakman et al.

Methods. A shout-out to the free science crowd:
Occasionally (n = 4 papers) we could not extract data on the diet compositions, either because the full text of the papers were hidden behind pay-walls, or the specialised diet manufacturer appeared to be no longer in business, and the paper only cited the source of the diet rather than its composition. 
Speakman excluded studies with a null result in their analysis because they seek to explain changes in lifespan across macronutrient levels. There is nothing to explain if the experiment didn't work, even if these experiments have some relevance to CR per se. So they excluded the important studies on wild-derived mice and in the ILSXISS strains.

The idea was to derive a dose-response curve for CR w/o PR and contrast it with a curve for CR + PR.
The effect of ‘CR with PR’  [n~67]on rodent lifespan does not differ from the effect of ‘CR without PR’ [n~8]... the overlap of the fitted regressions was striking, and it is clear that this is not a situation where there is a trend for an effect that fails to reach significance because of the high variation in the responses within treatments.

Speakman and colleagues describe the problem with Solon-Biet et al. (2014) which is that in their hands 30% CR shortended lifespan in the B6 strain, in contrast with the vast majority of all studies ever performed (dozens!) Intriguingly, Solon-Biet et al. achieved CR via cellulose addition which could have reduced hunger signalling which is essential to the life extension effects. Thus it seems that Speakman et al. speculate along the same lines as I did when I first discussed Solon-Biet after a first glance review. Furthermore, "the mice ingested fewer calories, they did so while ingesting almost twice as much mass of food". Hence I would speculate that excess cellulose could be harmful, but I'm not sure about the natural cellulose content of mouse diets, much less if natural is optimal (4).

A second quick glance at the literature makes me wonder again if there is something wrong with the Solon-Biet paper. Kokkonen et al (1988) for instance claim that dietary dilution via cellulose extends lifespan (I have no full access to ref. 2 using two different university accounts, who doesn't love paywalls?). A review of all studies using cellulose to induce CR might be useful esp. when combined with macronutrient data.

"Effect of percentage protein composition of the diet on lifespan" in ad libitum animals
If 18-26E% protein is taken as the baseline an extension of LS is seen especially with lower intakes of protein. The lowest studied intake was 4E% of protein.

The authors believe that:
...the impact of CR plus PR on lifespan is a completely different phenomenon from PR alone. Hence, the effect of reducing food intake on lifespan in rodents acts only via the restriction of calorie intake. This conclusion is consistent with the fact that the morphological, physiological and behavioural responses of mice to CR with PR (between 0 and 40% restriction) are completely different to the responses of mice to PR alone over the equivalent range (20% down to 12% protein) ...
it is also clear that there is an independent impact of dietary protein reduction on lifespan, but it operates over a different range of restriction (50 to 85%: relative to a reference intake of 18–26% protein in the diet) than that over which CR is effective (10–65% relative to ad libitum intake), and has a much smaller impact. Hence, reducing protein levels by 80% (from 20% to 4%) increases median lifespan by about 15%, while reducing calories by half this amount (40%) increases median lifespan by on average twice as much (30%). 
The finding is a little surprising if I am reading it correctly, because PR seems to be exclusively beneficial under ad libitum conditions. This non-additivity is confusing: if CR and PR both led to a graded response via e.g. mTOR or IGF-1 reduction we would expect them to be additive. However, it is interesting to note that acute CR leads to a decrease in IGF-1 proportional to the reduction in calories (5), but protein restriction does not.

And a further caution against taking invertebrate studies too seriously:
...[there may be] a major methodological difference between studies on insects and rodents. In particular, rodents are generally provided with less food when on restriction, but insects are primarily manipulated by giving them food diluted with indigestible components, and hence, paradoxically, despite being called on ‘restriction’, they eat a greater mass of food.
A cautious conclusion: low/reduced protein is probably still beneficial as are other macros
First of all, there is evidence that reduced n3 fatty acid intake is relevant to CR in rodents, which was acknowledged by Speakman. Unfortunately, there was only study so far. Furthermore, the Situation in rodents is different from humans. In rodents CR leads to reduced IGF1 but in humans moderate protein restriction is absolutely essential for this reduction (cf Fontana work).

1. Speakman, J. R., Mitchell, S. E., & Mazidi, M. (2016). Calories or protein? The effect of dietary restriction on lifespan in rodents is explained by calories alone. Experimental Gerontology.

Kokkonen, G. C., & Barrows, C. H. (1988). The effect of dietary cellulose on life span and biochemical variables of male mice. Age, 11(1), 7-9.

Solon-Biet, S. M., McMahon, A. C., Ballard, J. W. O., Ruohonen, K., Wu, L. E., Cogger, V. C., ... & Gokarn, R. (2014). The ratio of macronutrients, not caloric intake, dictates cardiometabolic health, aging, and longevity in ad libitum-fed mice. Cell metabolism, 19(3), 418-430.
Anderson, R. L., Owens, J. W., & Timms, C. W. (1992). The toxicity of purified cellulose in studies with laboratory animals. Cancer letters, 63(2), 83-92.

Mitchell, S. E., Delville, C., Konstantopedos, P., Hurst, J., Derous, D., Green, C., ... & Lusseau, D. (2015). The effects of graded levels of calorie restriction: II. Impact of short term calorie and protein restriction on circulating hormone levels, glucose homeostasis and oxidative stress in male C57BL/6 mice. Oncotarget, 6(27), 23213-23237.

Montag, 11. Januar 2016

Cliffnotes: Molecular targets downstream of CR

A very brief list and not a comprehensive one follows. I focus on direct evidence from KO models and lifespan studies, because this is the most robust study design. I don't care for surrogate endpoints, with the exception of pathology. The most common study design can be summarized thusly: When you combine "Factor X" with CR, does this affect the magnitude of LS extension from CR? Where X is either a gain of function (e.g. other LS extension) or loss of function (usually KO) intervention.

A. Direct evidence
B. Indirect evidence
C. Speculative or parallel pathways

A. Direct evidence