The latest issue of Rejuvenation Research is online. You'll find a few more esoteric items on calorie restriction biochemistry, but one paper on methionine restriction is more accessible and interesting. By way of a reminder, recall that there's a fairly good argument for the beneficial effects of calorie restriction to largely stem from lowering the intake of methionine, one of the eight essential amino acids in your diet.

On Methionine Restriction, Suppression of Mitochondrial Dysfunction and Aging

Rats and mice, when subjected to methionine restriction (MetR), may live longer with beneficial changes to their mitochondria. Most explanations of these observations have centered on MetR somehow suppressing the effects of oxygen free radicals.

It is suggested here that MetR's effects on protein metabolism should also be considered when attempting to explain its apparent anti-aging actions. Methionine is the initiating amino acid in mRNA translation. It is proposed that MetR decreases the protein biosynthesis rate due to methionine limitation, which correspondingly decreases generation of ribosomal-mediated error proteins, which then lowers the total abnormal protein load that cellular proteases and chaperone proteins (mitochondrial and cytoplasmic) must deal with.

That's an interesting thought. All cells carry some amount of damaged and malformed proteins as a result of errors in normal operation. The more abnormal proteins, the worse the cell performs - it makes sense that slowing the rate of operation also slows the rate of damage. You can read a little more about that in the context of bacterial reproduction, cell divison, and aging back a way in the Fight Aging! archives. The question is whether this is significant compared to the effects of mitochondrial generation of damaging free radicals.

The other paper that caught my attention is a nice demonstration that the benefits of calorie restriction don't necessarily have anything to do with insulin-like growth factor 1, IGF-1. For those who have been following research into IGF-1 metabolism and aging, a field with at least as much interest as investigations into mitochondria and aging, that might be a counterintuitive result.

Effect of Every Other Day Feeding on Mitochondrial Free Radical Production and Oxidative Stress in Mouse Liver

It is known that dietary restriction (DR) increases maximum longevity in rodents, but the mechanisms involved remain unknown. Among the possible mechanisms, several lines of evidence support the idea that decreases in mitochondrial oxidative stress and in insulin signaling are involved but it is not known if they are interconnected.

It has been reported that when C57BL/6 mice are maintained on an every other day (EOD) feeding their overall food intake is only slightly decreased and plasma insulin-like growth factor (IGF)-1 is even somewhat increased. In spite of this, their maximum longevity is increased, analogously to what occurs in classic DR. Thus, this model dissociates the increase in longevity from the decrease in IGF-1 observed in classic DR.

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These results support the possibility that EOD DR increases maximum life span at least in part through decreases in mitochondrial oxidative stress which are independent from insulin/IGF-1-like signaling.

As I said yesterday, metabolism is a complicated affair.

Posted by Reason at July 3, 2008 5:27 PM | TrackBack (0)