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 quite 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. That's a red flag. 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.


Conclusions
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.

References

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.
http://onlinelibrary.wiley.com/doi/10.1111/acel.12170/full

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