Donnerstag, 10. April 2014

ITP: Acarbose (ACA), 17-α-estradiol (EST), NDGA, Methylene Blue (MB)

Another paper from NIA's Interventions Testing Programme has been published a few months ago. Read it, it's free (1).
This study includes data from their "Cohort 5: [treatment started in] C2009"
 and preliminary data from "Cohort 6: C2010". As is obvious from the starting dates, a mouse lives up to about 1200 days. The authors claim that:
"Here, we report strong evidence for lifespan extension by ACA [acarbose], evidence for a possible effect of EST [17a-estrogen], and strong confirmatory evidence for benefits from NDGA."
Although, then they qualify their statement a little: "Surprisingly, each of these three agents extends lifespan either in males only or (for ACA) much more strongly in males than in females."

Later they also mention a problem that might invalidate a lot of their now-published data:
"One possible reason for the larger or exclusive effects of these compounds on males is the short lifespan of the male controls at two of the three sites (medians of 704, 807, and 924 days from male controls at UT, TJL, and UM, respectively, while female control medians are 864, 918, and 887, Table 1)."

However, a robust intervention must work in both genders. Must. No exceptions made. All validated life extension methods do, e.g. Rapamycin, Calorie Restriction (CR), Methionine Restriction (? maybe?), severe lack of GH (GHRHKO, GHRKO, Ames and Snell dwarfism). If it does not work in females, a mechanism must be shown and follow-up studies should alter the protocol so that it does work.
Remember, interventions solely reducing IGF-1 preferably extend LS in females (the opposite of what we see here). That's one of the reasons why these interventions are not considered established.

Acarbose (ACA) extended maximum lifespan by around 10% in both genders and also led to a similar decrease in weight. Max LS +11% in males, +9% in females. This is consistent with the effect being solely or mostly due to ("crypto-")CR, not glucose absorption kinetics or any other pharmacological effect. The data on median lifespan and weight-adjusted maximum LS is better to the compound:
"...we expected that ACA might produce some survival benefits, although not as much as produced by DR, because the weight reductions from ACA (Fig. 4) were much less than those seen in DR mice. In addition, as weight reductions (% body weight) due to ACA were greater in females [depending on time point, on the order of -20% vs -10%] than in males (Fig. 4), we hypothesized that lifespan effects would, similarly, be larger in females. The results were thus surprising: median lifespan was increased 22% in males and only 5% in females (Fig. 1)."

I maintain that crypto-CR is the most likely explanation until this is refuted by a pair-feeding study. I would not rule out some minor beneficial effect on top of crypto-CR, however.
The authors disagree with me or so it would seem at first glance: "...the lengthened survival for ACA-treated males vs. ACA-treated females cannot be explained by changes in body weight or seen simply as the effect of overall caloric restriction."
But this lengthended lifespan is a meagre 2% difference between +9% and +11%, when it comes to the all-important Maximum LS.

17-α-estradiol (EST) did not extend max LS, although, it had a similar effect to acarbose on weight. Again, this somewhat strengthens the ACA data: not all reductions of bodyweight seem to lead to Crypto-CR.
It is still beyond me why EST was chosen in the first place and for two cohorts, this being the first to publish data! Apparently "it might mimic, in male mice, the beneficial effects produced by estrogen in control females".
This is forgetting that mice as a species do not show a consistent sexual dimorphism in longevity (c.f. ref. 2). Their heterogenous cross (UM-HET3) does, but this could be quuite easily an idiosyncratic trait if it doesn't apply to the species as a whole.

NDGA does not look all that promising, but this is only an interim analysis. Its effects seem to be limited to changes in median/avg. lifespan of male mice. However, the effect of NDGA does not extend to females even at the same blood levels as in males. In the first NDGA study published the authors speculated that they'd have to increase the dose for the female mice so that they have the same blood-levels of the drug:
The blood level was indeed increased in females receiving 5000 ppm to a value similar to that in males receiving 2500 ppm NDGA (Fig. S5), but we saw no evidence for an increase in female lifespan with 70% of the survival curve complete...The high dose reduced female body weight about 14%, 22%, and 23% at 12, 18, and 24 months, respectively, while male weight was only reduced 3–6% (Fig. S6B); thus, the lack of effect of NDGA on female lifespan cannot be explained by concentration in the plasma or by effects on body weight. It is possible that NDGA produces beneficial effects in both sexes but produces harmful effects in females that prevent lifespan extension.

Interestingly, as stated abvoe, NDGA causes considerable weight-loss in females (-1x-2x%) but not males, which could be suggestive of toxicity, at least giving a plausible mechanism for the gender disparity.

Methylene Blue (MB) had a tiny positive effect of 6% on female max LS, but not on male LS. This is very little and could be a statistical fluke. I'd study other substances first before continiung with MB. We're desperate, but not that desperate.
Why was MB chosen in the first place? The rationale presented by the authors is not very convincing. It reads kind of like a supplement ad. We're desperate, I get it. But are we that desperate? Perhaps I'll do a follow-up post with better suggestions for treatments. And I'm not saying MB was a bad shot, just that there should be better substances.

Out of the 4 substances tested none merit any hype, but ACA and NDGA should be followed-up.

Pair-feeding of Acarbose, to match weights between control and intervention group, is the most important follow-up. We should investigate ACA as a CR-mimetic, but not so much on its own merits. We'll see if other interventions targetting glucose metabolism can be successful. Some time ago there were a few successes with AGE-restriction.
I am not sure ACA works as a CR-mimetic in humans as I did not find any documentation of "weight-loss" as a side-effect.

Finish the NDGA study and find out why it does not work in females. The compound remains unvalidated, but interesting. Spindler reported toxicity with high dose NDGA, so let's see how the NIA's highest doses look in the end. It must show maximum lifespan extension in both genders to be interesting from a biogerontologic perspective.

On a side-note, gender-related differences seem to be widespread in mice and their responses to "anti-aging" interventions. I am actually a little surprised, although, I shouldn't be.


1. Aging Cell. 2014 Apr;13(2):273-82. doi: 10.1111/acel.12170. Epub 2013 Nov 19.Acarbose, 17-α-estradiol, and nordihydroguaiaretic acid extend mouse lifespan preferentially in males. Harrison DE1, Strong R, Allison DB, Ames BN, Astle CM, Atamna H, Fernandez E, Flurkey K, Javors MA, Nadon NL, Nelson JF, Pletcher S,Simpkins JW, Smith D, Wilkinson JE, Miller RA.

2. Handbook of the Biology of Aging, Seventh Edition (Handbooks of Aging). Masoro and Austad.

Dienstag, 25. März 2014

Does reduced GH/IGF signalling extend lifespan? A possible answer.

Berryman et al. (Kopchick lab) recently published a paper (1) that I sort of disagree with. I'd like to take the opportunity to discuss a bigger issue: how can we know the true effects of GH-inihibtion, at least in mouse models? Isn't the data conflicting as Sonntag et al. have shown?

Let's start with a brief introduction to long-lived dwarf mice (1):
"[T]here appears to be a preferential accumulation of excess fat in the subcutaneous depots, which is thought to have metabolically beneficial effects in ... long-lived mice and that may contribute to their counterintuitive association between obesity and life span."
Then the authors say that:
"Not all mouse strains with reduced GH or IGF-1 action show improvements in life span. One example is GH receptor antagonist (GHA) transgenic mice, which were generated in our laboratory more than 20 years ago (22–24)...
The GHA expressed in these mice contains a lysine in place of glycine at position 119 (22–24) in the bGH protein. This single substitution results in the production of a protein that competes with endogenous GH for GHR [Growth Hormone Receptor] binding..."
However, I'd like to contest the claim that these mice do not show lifespan (LS) extension. I don't think their data is able to show one way or another.

Consider the problem of sample size and power. GHA mice weigh more than classical dwarf mice, e.g. GHR -/- mice, which is due to their incomplete inhibition of GH-signalling. Female GHA mice weigh up to 33% less than controls (ref. 1), males are even heavier. GHR -/- weigh closer to 60-70% less compared to controls! But this also implies that the effects on lifespan will be diminished in GHA mice, albeit non-zero. I think the IGF-1 data also highlights this striking difference:
"In the GHA mice, [serum IGF-1] levels were reduced to about 75–80% the level of controls (P 0.05). In the GHR [KO] mice, levels were reduced to about 20% the level of controls (P 0.0001)." (2)

Lorenzini et al. recently showed that subtle differences in LS due to modest changes in GH/IGF signalling may require n ~ 100 per group (3). In contrast: Coschigano et al."only" used n~50 per group. Normally, a very respectable sample size, but Lorenzinin and Co needed a larger sample size even though their mice have lower IGF1-levels, i.e. ~50% of controls.
In fact, in the study by Coschigano (2), numerically, the median, mean and maximum lifespan is higher in both genders.

Secondly, males show a smaller numerical improvement in lifespan (2):
Although there was a tendency for the GHA mice to live longer than their controls, especially for the females, this difference did not reach statistical significance for either gender.
First of all, this is consistent with other studies also showing a gender disparity. In addition, given their new data (1) it seems that some idiosyncratic side-effect of GH-antagonism or GH/gentoype interaction might be harming male mice.
"...male GHA mice had significantly lower body weights than WT males until 52 weeks, but thereafter, no statistical difference was observed. In contrast, female GHA mice had significantly lower body weights (ranging from 66% to 81% of female littermate controls) throughout the study...40% and 33% of the total body weight of male and female GHA mice, respectively, was attributed to fat by 68 weeks of age compared with 17% for both control males and females of the same age...  
male GHA mice became significantly more obese with advancing age...The mass of all adipose depots was higher in male GHA mice than their littermate controls at 82 weeks of age; however, there was only a significant increase in the mass of subcutaneous and retroperitoneal fat pads (p = 1.0 × 10−6 and p = .04, respectively) "
So either excess fat is harming them, or perhaps, GH antagonism is not maintained throughout the whole lifespan. However, I am not very satisfied with either explanation, since Berryman et al. also showed beneficial changes in male mice, i.e. increased adiponectin and subcutaneous adiposity with low-normal liver triacylglycerol content. There was also a slight uptick in late-life insulin levels and an increase of the leptin-adiponectin ratio which is more consistent with harmful effects.

Third, as much as I hate to say it, but their study (2) is not good enough, not rigorous enough. Their controls on the black 6 background have mean and median lifespans below 800d, while 900d would be expected. Maximum lifespans also appear to be well below the ~1200d expected from a healthy lab mouse.
Overall this weakens conclusions we can draw based on this study, though, it should not introduce much systematic bias. In fact, low LS is often seen as contributing to exaggerated lifespan effects. In particular, with interventions that offset some harmful aspect of questionable husbandry.

Fourth, GH-toxicity might be a real thing biasing low-IGF1 models, which often show compensatory increases in GH levels (5). I do wonder if the GHA-model (Kopchick lab) and the IGF1 hypomorphic mice also show these compensatory increases?
Increased GH-levels have been shown for the liver IGF1 deficient mice (5) and apparently for "Liver-specific GH receptor gene disrupted (LiGHRKO) mice" as well (6), also by Kopchick.

The solution
A meta-analysis  - not a narrative review, not a systematic review - could in principle overcome the issues I raised above, especially sample size and power. Husbandry effects and study quality could be considered as well.

Is the data too heterogenous for analysis? Perhaps, but I don't think so. Meta-analyses of the effects of dietary restriction have been performed, some even comparing different taxa (c.f. 4.a to d).

So far I'd side with the idea that almost all healthy, well-husbanded models of low GH/IGF1 signalling will show delayed aging if there's no frank toxicity. Let's not forgot that toxicity (extrinsic mortality) shouldn't be confused with intrinsic aging - which is what we'd like to study.


1. A Dwarf Mouse Model With Decreased GH/IGF-1 Activity That Does Not Experience Life-Span Extension: Potential Impact of Increased Adiposity, Leptin, and Insulin With Advancing Age. Berryman DE, Lubbers ER, Magon V, List EO, Kopchick JJ.J Gerontol A Biol Sci Med Sci. 2014 Feb;69(2):131-41. doi: 10.1093/gerona/glt069. Epub 2013 May 21

2. Coschigano KT, Holland AN, Riders ME, List EO, Flyvbjerg A, Kopchick JJ.
Deletion, but not antagonism, of the mouse growth hormone receptor results in severely decreased body weights, insulin, and insulin-like growth factor I levels and increased life span. Endocrinology. 2003; 144: 3799–3810.

3. J Gerontol A Biol Sci Med Sci. 2013 Jul 20. [Epub ahead of print]Mice Producing Reduced Levels of Insulin-Like Growth Factor Type 1 Display an Increase in Maximum, but not Mean, Life Span. Lorenzini A, Salmon AB, Lerner C, Torres C, Ikeno Y, Motch S, McCarter R, Sell C.

4.a. Aging Cell. 2013 Jun;12(3):410-4. doi: 10.1111/acel.12061. Epub 2013 Mar 27.Dietary restriction of rodents decreases aging rate without affecting initial mortality rate -- a meta-analysis. Simons MJ1, Koch W, Verhulst S.

4.b. Dietary restriction in rats and mice: a meta-analysis and review of the evidence for genotype-dependent effects on lifespan.Swindell WR.Ageing Res Rev. 2012 Apr;11(2):254-70. doi: 10.1016/j.arr.2011.12.006. Epub 2011 Dec 23. Review.

4.c. Mol Biosyst. 2012 Apr;8(4):1339-49. doi: 10.1039/c2mb05255e. Epub 2012 Feb 10.A meta-analysis of caloric restriction gene expression profiles to infer common signatures and regulatory mechanisms.Plank M1, Wuttke D, van Dam S, Clarke SA, de Magalhães JP.

4.d. Int J Cancer. 2003 Sep 20;106(5):766-70.Energy restriction and the risk of spontaneous mammary tumors in mice: a meta-analysis.Dirx MJ1, Zeegers MP, Dagnelie PC, van den Bogaard T, van den Brandt PA.

5. Reductions in serum IGF-1 during aging impair health span.Gong Z, Kennedy O, Sun H, Wu Y, Williams GA, Klein L, Cardoso L, Matheny RW Jr, Hubbard GB, Ikeno Y, Farrar RP, Schaffler MB, Adamo ML, Muzumdar RH, Yakar S.Aging Cell. 2013 Dec 17. doi: 10.1111/acel.12188. [Epub ahead of print]

6. Endocrinology. 2014 Feb 11:en20132086. [Epub ahead of print]Liver-specific GH receptor gene disrupted (LiGHRKO) mice have decreased endocrine IGF-1, increased local IGF-1 as well as altered body size, body composition and adipokine profiles.List EO1, Berryman DE, Funk K, Jara A, Kelder B, Wang F, Stout MB, Zhi X, Sun L, White TA, Lebrasseur NK, Pirtskhalava T, Tchkonia T, Jensen EA, Zhang W, Masternak MM, Kirkland JL, Miller RA, Bartke A, Kopchick JJ.

Montag, 30. Dezember 2013

Vicious Cycle Hypothesis of Mitochondrial Aging - Everything Old is New Again

There is little doubt that the classic vicious circle mitochondrial free radical "theory" of aging has been refuted. However, recent data shows that a different type of vicious circle may act on mitochondria (1) to promote organismal aging and drive sarcopenia.
Mitochondria in certain tissues are known to accumulate high levels of one and the same (= clonal) deletion. Several hypotheses have been postulated that can explain this accumulation - replication advantage, "survival of the slowest"and drift - but empirical evidence for these models has been lacking. Now the Aiken and McKenzie lab has considerably strengthened the replication advantage angle by showing a vicious circle that operates in vivo by promoting mitochondrial DNA replication. On the other hand, modeling by Kirkwood, Kowald and others (2, 3) further confirms that drift and size based replication advantage in and of themselves, and without any vicious feedback loops, operate too slowly to explain aging in short-lived species like mice.

Now, based on these three studies (1-3) we can propose a basic model for deletion accumulation that, as far as I can tell, is consistent with published data: Drift and replication advantage lead to an accumulation of OXPHOS-deficient, deletion-bearing mtDNAs until a critical threshold is reached. Then, the cell tries to compensate. Drift + Replication Advantage + Feedback Loop = fast accumulation of deletions. Aiken et al. call this feedback loop "non-adaptive program of mitochondrial biogenesis" or vicious cycle.

Two compensatory mechanisms could be maladaptive in this situation and a trigger of this vicious cycle:

Mittwoch, 11. Dezember 2013

"Vitamin D: chasing a myth?"

Hereby, I have to weaken my recommendation in favour of vitamin D supplementation, which is partly based on past analyses by Autier et al. (2) and a good risk/benefit ratio. Nowadays vitamin D still seems safe to supplement but useless.
However, the big weakness of recommendations for or against vitamin D is that the interventional studies on this topic are few and those that exist are weak. No matter how often you re-analyze garbage, the result won't improve. After so many years of research, we have not advanced much beyond the basic recommendation that vitamin D may benefit the elderly and there mainly women. Thus we absolutely have to wait for large studies to complete if we want to make strong recommendations, e.g. the VITAL and VIDAL studies.

Low serum concentrations of 25-hydroxyvitamin D (25[OH]D) have been associated with many non-skeletal disorders. However, whether low 25(OH)D is the cause or result of ill health is not known. We did a systematic search of prospective and intervention studies that assessed the effect of 25(OH)D concentrations on non-skeletal health outcomes in individuals aged 18 years or older. We identified 290 prospective cohort studies (279 on disease occurrence or mortality, and 11 on cancer characteristics or survival), and 172 randomised trials of major health outcomes and of physiological parameters related to disease risk or inflammatory status. Investigators of most prospective studies reported moderate to strong inverse associations between 25(OH)D concentrations and cardiovascular diseases, serum lipid concentrations, inflammation, glucose metabolism disorders, weight gain, infectious diseases, multiple sclerosis, mood disorders, declining cognitive function, impaired physical functioning, and all-cause mortality. High 25(OH)D concentrations were not associated with a lower risk of cancer, except colorectal cancer. Results from intervention studies did not show an effect of vitamin D supplementation on disease occurrence, including colorectal cancer. In 34 intervention studies including [only!] 2805 individuals with mean 25(OH)D concentration lower than 50 nmol/L at baseline supplementation with 50 μg per day or more did not show better results. Supplementation in elderly people (mainly women) with 20 μg vitamin D per day seemed to slightly reduce all-cause mortality. The discrepancy between observational and intervention studies suggests that low 25(OH)D is a marker of ill health. Inflammatory processes involved in disease occurrence and clinical course would reduce 25(OH)D, which would explain why low vitamin D status is reported in a wide range of disorders. In elderly people, restoration of vitamin D deficits due to ageing and lifestyle changes induced by ill health could explain why low-dose supplementation leads to slight gains in survival.

*1. Vitamin D status and ill health: a systematic review
Philippe Autier, Mathieu Boniol, Cécile Pizot, Patrick Mullie
The Lancet Diabetes & Endocrinology 1 January 2014 (Volume 2 Issue 1 Pages 76-89 DOI: 10.1016/S2213-8587(13)70165-7)

2. Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials.
Autier P, Gandini S.
Arch Intern Med. 2007 Sep 10;167(16):1730-7. Review.

*not read in full

Samstag, 16. November 2013

Coffee and all-cause mortality and morbidity

A few years ago I was reading a lot about coffee and noticed that recent studies were more and more suggestive of health benefits.
These days I still periodically check the literature, but rarely have the time to read the full text of papers. All in all, I do consider recent data to be consistent with beneficial effects at moderate intakes.

Here, I provide current abstracts and added comments.

Eur J Epidemiol. 2013 Jul;28(7):527-39. doi: 10.1007/s10654-013-9834-7. Epub 2013 Aug 11.
A meta-analysis of prospective studies of coffee consumption and mortality for all causes, cancers and cardiovascular diseases.
Malerba S, Turati F, Galeone C, Pelucchi C, Verga F, La Vecchia C, Tavani A.
Several prospective studies considered the relation between coffee consumption and mortality. Most studies, however, were underpowered to detect an association, since they included relatively few deaths. To obtain quantitative overall estimates, we combined all published data from prospective studies on the relation of coffee with mortality for all causes, all cancers, cardiovascular disease (CVD), coronary/ischemic heart disease (CHD/IHD) and stroke. A bibliography search, updated to January 2013, was carried out in PubMed and Embase to identify prospective observational studies providing quantitative estimates on mortality from all causes, cancer, CVD, CHD/IHD or stroke in relation to coffee consumption.
A systematic review and meta-analysis was conducted to estimate overall relative risks (RR) and 95 % confidence intervals (CI) using random-effects models.
The pooled RRs of all cause mortality for the study-specific highest versus low (≤1 cup/day) coffee drinking categories were 0.88 (95 % CI 0.84-0.93) based on all the 23 studies, and 0.87 (95 % CI 0.82-0.93) for the 19 smoking adjusting studies.
The combined RRs for CVD mortality were 0.89 (95 % CI 0.77-1.02, 17 smoking adjusting studies) for the highest versus low drinking and 0.98 (95 % CI 0.95-1.00, 16 studies) for the increment of 1 cup/day. Compared with low drinking, the RRs for the highest consumption of coffee were 0.95 (95 % CI 0.78-1.15, 12 smoking adjusting studies) for CHD/IHD, 0.95 (95 % CI 0.70-1.29, 6 studies) for stroke, and 1.03 (95 % CI 0.97-1.10, 10 studies) for all cancers.
This meta-analysis provides quantitative evidence that coffee intake is inversely related to all cause and, probably, CVD mortality.
Then I would like to highlight contradictory evidence, perhaps suggesting a non-linear dose-response(?), or more worryingly, something else.
In this case, the authors speculate that coffee may benefit the old while harming the young. Interestingly, a similar hypothesis about the effects of alcohol exists. This does not mean that young people cannot benefit from red wine or coffee, however. Presumably, the benefits on cardiovascular disease would accrue over time, because it is a chronic disease that begins ante- or perinatally (at around birth) and worsens throughout life.

Mayo Clin Proc. 2013 Oct;88(10):1066-74. doi: 10.1016/j.mayocp.2013.06.020. Epub 2013 Aug 15.
Association of coffee consumption with all-cause and cardiovascular disease mortality.
Liu J, Sui X, Lavie CJ, Hebert JR, Earnest CP, Zhang J, Blair SN.
During the 17-year median follow-up, 2512 deaths occurred (804 [32%] due to cardiovascular disease). In multivariate analyses, coffee intake was positively associated with all-cause mortality in men. Men who drank more than 28 cups of coffee per week had higher all-cause mortality (hazard ratio [HR], 1.21; 95% CI, 1.04-1.40). However, after stratification based on age, younger (<55 years old) men and women showed a significant association between high coffee consumption (>28 cups per week) and all-cause mortality after adjusting for potential confounders and fitness level (HR, 1.56; 95% CI, 1.30-1.87 for men; and HR, 2.13; 95% CI, 1.26-3.59 for women).
In this large cohort [n=43 727], a positive association between coffee consumption and all-cause mortality was observed in men and in men and women younger than 55 years. On the basis of these findings, it seems appropriate to suggest that younger people avoid heavy coffee consumption (ie, averaging >4 cups per day). However, this finding should be assessed in future studies of other populations.
And a verbal summary:
J Am Coll Cardiol. 2013 Sep 17;62(12):1043-51. doi: 10.1016/j.jacc.2013.06.035. Epub 2013 Jul 17.
Effects of habitual coffee consumption on cardiometabolic disease, cardiovascular health, and all-cause mortality.
O'Keefe JH, Bhatti SK, Patil HR, DiNicolantonio JJ, Lucan SC, Lavie CJ.
Coffee, after water, is the most widely consumed beverage in the United States, and is the principal source of caffeine intake among adults. The biological effects of coffee may be substantial and are not limited to the actions of caffeine. Coffee is a complex beverage containing hundreds of biologically active compounds, and the health effects of chronic coffee intake are wide ranging. 
From a cardiovascular (CV) standpoint, coffee consumption may reduce the risk of type 2 diabetes mellitus and hypertension, as well as other conditions associated with CV risk such as obesity and depression,
but it may adversely affect lipid profiles depending on [preparation technique]
Regardless, a growing body of data suggests that habitual coffee consumption is neutral to beneficial regarding the risks of a variety of adverse CV outcomes including coronary heart disease, congestive heart failure, arrhythmias, and stroke.
Moreover, large epidemiological studies suggest that regular coffee drinkers have reduced risks of mortality, both CV and all-cause.
The potential benefits also include protection against neurodegenerative diseases, improved asthma control, and lower risk of select gastrointestinal diseases.
A daily intake of ∼2 to 3 cups of coffee appears to be safe and is associated with neutral to beneficial effects for most of the studied health outcomes.
However, most of the data on coffee's health effects are based on observational data, with very few randomized, controlled studies, and association does not prove causation. Additionally, the possible advantages of regular coffee consumption have to be weighed against potential risks (which are mostly related to its high caffeine content) including anxiety, insomnia, tremulousness, and palpitations, as well as bone loss and possibly increased risk of fractures.
As alluded to a few things still need sorting out: contradictory studies, absence of RCTs, preparation technique, genotype effects, age-dependence of effects and risk-benefit dose-response.

Sonntag, 3. November 2013

Folic acid supplementation in primary prevention?

Increased cancer incidence could be a potential side-effect from supplementation, because folate is involved in purine and pyrimidine synthesis. What do controlled trials say?

Simply put: no risk, no benefit in recent analyses (1, 2). An earlier (now outdated?) meta-analysis suggested increased risk of cancer (3). Perhaps some time I can read the full papers:

"Our analyses suggest that cancer incidences were higher in the folic acid-supplemented groups than the non-folic acid-supplemented groups (relative risk=1.21 [95% confidence interval: 1.05-1.39]). Folic acid-supplementation trials should be performed with careful monitoring of cancer incidence" (3)

 Almost the same holds true for CVD (4). Folic acid's useless.

1. Lancet. 2013 Mar 23;381(9871):1029-36.
Effects of folic acid supplementation on overall and site-specific cancer incidence during the randomised trials: meta-analyses of data on 50,000 individuals.
Vollset et al.

Int J Cancer. 2013 Sep 1;133(5):1033-41. doi: 10.1002/ijc.28038. Epub 2013 Feb 15.
Folic acid supplementation and cancer risk: a meta-analysis of randomized controlled trials.
Qin X, Cui Y, Shen L, Sun N, Zhang Y, Li J, Xu X, Wang B, Xu X, Huo Y, Wang X.

3.  Cancer Epidemiol. 2012 Feb;36(1):78-81. doi: 10.1016/j.canep.2011.05.003. Epub 2011 Oct 21.
Meta-analysis of cancer risk in folic acid supplementation trials.
Baggott JE, Oster RA, Tamura T.

4. Eur J Intern Med. 2012 Dec;23(8):745-54. doi: 10.1016/j.ejim.2012.07.004. Epub 2012 Aug 11.
Efficacy of folic acid supplementation in cardiovascular disease prevention: an updated meta-analysis of randomized controlled trials.
Yang HT, Lee M, Hong KS, Ovbiagele B, Saver JL.

Sonntag, 20. Oktober 2013

Hypothesis Testing: Why I think Sonntag et al. are wrong

About one year ago Sonntag et al. published a superb review highlighting "progress and controversies" in the field of GH/IGF1 and aging (1). In this paper they are very critical of the whole hypothesis:
"These diverse results are incompatible with the concept that reductions in IGF-1 signaling increase life span in mammals as was reported in invertebrate models... 
Based on the current available studies, it appears that the definition of a conserved mechanism of aging requires clarification. If a “common” mechanism for increased life span does not relate to animals of different genders or more importantly to humans, it is difficult to conclude that it represents a conserved mechanism of aging. Importantly, the studies in humans on circulating GH and IGF-1 deficiency do not agree with the data from rodent models."
I believe instead they favor a model in which only early life exposure to low GH levels slows aging:
"In our opinion, it is plausible that the increase in life span observed in Ames and Snell dwarf animals as well as ghr knockout animals is the consequence of impairments in the developmental programming of key pathways... [NB: this would not explain why human patients with the same mutations fail to show a longevity phenotype. Emphasis mine.]"
So why do I think GH/IGF-1 matters, perhaps even throughout adulthood?
I do not want to delve into too much detail and I will try to keep this post short. Also note that my expertise lies outside of this field and I do not disagree that overall the issue is still controversial. However, I do consider the "optimistic" interpretation by e.g. Bartke et al. (2) to be more probable given my reading of the evidence.
"The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast....there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. "
What's wrong with the Sonntag paper?
Some of my criticisms are more general in nature, e.g. their reliance on prospective epidemiology to draw conclusions about aging, or the absence of a discussion of GHRHR -/- and PAPA -/- mice.

As far as I can see they left out a few other papers, although, these did not clearly favor the "optimistic" or "pessimistic" view.

Their choice of words also seems poor at times: "...the studies in humans on circulating GH and IGF-1 deficiency do not agree with the data from rodent models"
Really? Simply put, the epidemiology and human data they cite suggests that IGF-1 lowers cardiovascular disease (CVD) but increases cancer incidence. There is tentative data in GH-deficient animals showing exactly the same, i.e. evidence of CVDisease/damage despite an extended lifespan (Csiszar 2008, Reddy 2013 [3-5]). CVD and delayed aging are not mutually exclusive. If GH-deficiency promotes CVD it might be unsafe in humans even if it slows aging and independently of this effect. This does not mean the GH/IGF-1 pathway isn't conserved. It means that humans are highly susceptible to CVD at middle age.

What do more recent studies say?
Broadly speaking, recent studies support the relevance and conservation of the GH/IGF pathway in aging (6-8). Although, the gender-dependent effect of the IGF1R +/- mutations still cannot be explained to my satisfaction (6) and seems inconsistent with a highly conserved mechanism. On the other hand, I would like to highlight the paper by Lorenzini et al. (7) using a hypomorphic IGF-1 gene, because it has a very large sample size and their mice show acceptable maximum lifespans (around 1100d), albeit not mean LS (around 7xx d). The authors found an increase in the all important maximum but not mean lifespan.

EDIT: Zhang et al. 2012 produced life span extension using FGF-21 overexpression (PMID: 23066506 ), which further supports a conserved role of GH/IGF-signalling. Again, female mice benefit the most. I have no clue why.

Is there a biologic explanation for the inconsistent data regarding IGF-1?
Viewed from another angle, there might be a mechanistic explanation for the discrepancies in rodent studies noted by Sonntag:
Renna et al. (9) have shown that antagonizing the IGF-1 receptor inhibits autophagy by inhibiting mTORC2, PKCα/β, disrupting the actin cytoskeleton and endocytosis. The latter being important for autophagy.

What if experimental manipulation of IGF-1 used in aging studies (e.g. IGF1R +/-) also diminishes autophagy? We know that the most robust models of life extension (Snell, Ames and GHRKO) show both undetectable circulating IGF-1 and elevated autophagy. It is unclear why this is so. I do not know if autophagy studies in IGF1-deficient models have been carried out, but I have not looked very hard. This is an important direction for future research!

Finally, the authors almost suggest the experiment I'm going to suggest. Almost:

“…it is tempting to speculate that one may be able to achieve synergistic benefits by inhibiting the key effectors of the IGF-1R pathway, alongside pharmacological stimulation of the autophagic pathway.”
I hope I am one of the first to actually spell it out: it is possible that inhibiting mTOR[C1] and IGF-signalling will have synergistic effects on lifespan, e.g. using rapamycin + picropodophyllotoxin (PPP, an IGF1R inhibitor).

Conclusions and Hypotheses
(Hypothesis 0: GH/IGF-1 signalling is involved and conserved in mammalian aging up to humans.)
Hypothesis 1: Inhibition of autophagy through IGF-1 antagonism may explain inconsistent lifespan data seen in mouse studies of the GH/IGF-1 pathway.
Hypothesis 2: Autophagy stimulation + IGF1R antagonism will increase lifespan to a larger extent than either of them alone.

1. J Gerontol A Biol Sci Med Sci. 2012 Jun;67(6):587-98. doi: 10.1093/gerona/gls115. Epub 2012 Apr 20.
Diverse roles of growth hormone and insulin-like growth factor-1 in mammalian aging: progress and controversies.
Sonntag WE, Csiszar A, deCabo R, Ferrucci L, Ungvari Z.

2. Somatotropic signaling: trade-offs between growth, reproductive development, and longevity.
Bartke A, Sun LY, Longo V.
Physiol Rev. 2013 Apr;93(2):571-98. doi: 10.1152/physrev.00006.2012. Review.

3. J Gerontol A Biol Sci Med Sci. 2013 May 16. [Epub ahead of print]
Young Little Mice Express a Premature Cardiovascular Aging Phenotype.
Reddy AK, Hartley CJ, Pham TT, Darlington G, Entman ML, Taffet GE.

4. Am J Physiol Heart Circ Physiol. 2008 Nov;295(5):H1882-94. doi: 10.1152/ajpheart.412.2008. Epub 2008 Aug 29.
Endothelial function and vascular oxidative stress in long-lived GH/IGF-deficient Ames dwarf mice.
Csiszar A, Labinskyy N, Perez V, Recchia FA, Podlutsky A, Mukhopadhyay P, Losonczy G, Pacher P, Austad SN, Bartke A, Ungvari Z.

5. J Gerontol A Biol Sci Med Sci. 2012 Jun;67(6):553-64. doi: 10.1093/gerona/glr197. Epub 2011 Nov 10.
Growth hormone and IGF-1 deficiency exacerbate high-fat diet-induced endothelial impairment in obese Lewis dwarf rats: implications for vascular aging.
Bailey-Downs LC, Sosnowska D, Toth P, Mitschelen M, Gautam T, Henthorn JC, Ballabh P, Koller A, Farley JA, Sonntag WE, Csiszar A, Ungvari Z.

6. Aging Cell. 2013 Jul 30. doi: 10.1111/acel.12145. [Epub ahead of print]
Longevity effect of IGF-1R+/- mutation depends on genetic background-specific receptor activation.
Xu J, Gontier G, Chaker Z, Lacube P, Dupont J, Holzenberger M.

7. J Gerontol A Biol Sci Med Sci. 2013 Jul 20. [Epub ahead of print]
Mice Producing Reduced Levels of Insulin-Like Growth Factor Type 1 Display an Increase in Maximum, but not Mean, Life Span.
Lorenzini A, Salmon AB, Lerner C, Torres C, Ikeno Y, Motch S, McCarter R, Sell C.

8. Sasaki, T., et al. "Lifespan extension in the spontaneous dwarf rat and enhanced resistance to hyperoxia-induced mortality." Experimental gerontology (2013).

9. Hum Mol Genet. 2013 Jul 10. [Epub ahead of print]
IGF-1 receptor antagonism inhibits autophagy.
Renna M, Bento CF, Fleming A, Menzies FM, Siddiqi FH, Ravikumar B, Puri C, Garcia-Arencibia M, Sadiq O, Corrochano S, Carter S, Brown SD, Acevedo-Arozena A, Rubinsztein DC.