Of Rats, Birds and Man

Why do birds have a much longer maximum lifespan than mammals of similar metabolic rate? The difference may have to do with mitochondria. Oxygen radical production is significantly lower in the mitochondria of pigeons (maximum lifespan 35 years) than rats (maximum lifespan 4 years), despite similar oxygen consumption rates. Although all of the factors that might be influencing this difference are not known, recent research has identified a major difference in the lipid composition of mitochondria [Pamplona et al., 1996]. Rats have higher levels of longer and more unsaturated fatty acids (arachidonic and docosahexaenoic acids) than do pigeons. This same difference shows up in comparisons of rat and human mitochondria. It appears that human and pigeon mitochondria use more linoleic acid (18 carbons long with 2 double bonds) while rat mitochondria use more arachidonic acid (20 carbons, 4 double bonds) and docosahexaenoic acid (22 carbons, 6 double bonds). Less double bonds (less unsaturation) makes the phospholipids more resistant to peroxidation. And this, in turn, makes human and pigeon mitochondria less sensitive to oxygen radicals.

The consistency of this pattern suggests that the degree of saturation in mitochondrial phospholipids may be an important factor influencing mitochondrial aging rate. If saturation and chain length are readily influenced by dietary factors (fatty acid composition or nutrient intake), then this might prove to be a useful anti-aging intervention. ——SWF