Sunday, December 19, 2010

Leptin & AMPK Activation in Muscle - Did Scientists Investigate the Wrong Species?

Actually, this is something I have been reminding people of for years: Human beigns are no mice and although some people may be rats, genetically they are still very different. Usually I put this argument forward if anyone presents me with a study done on rodents that "shows" how bad dietary protein, especially from meat, is for you - thin of it: when was the last time you saw a mouse eating a cow? This time the issue is a little more sophisticated, though...

Australian scientists (Laker. 2010) have recently investigated the effect of leptin on AMP-activated protein kinase (AMPK) in muscle of sheep and (I do not know if to their, but maybe to some of the proclaimed experts surprise) they found that...
[...] leptin infusion reduced (P<0.05) food intake and body weight and it also increased plasma adrenaline concentration at 6 h and 7 days, suggesting increased sympathetic nerve activity. Despite this, and in contrast to rodent studies, central leptin infusion did not increase skeletal muscle AMPKα Thr172phosphorylation or ACCβ Ser221 phosphorylation.
With sheep being genetically closer to human beings than mice, this is an interesting finding and could possible lead into new insights into why leptin, once proclaimed as possible panacea for the obesity epidemic, does work on rodents, but has little positive effect on obese human beings. Hitherto, the most accepted theory is "leptin resistance", which, similar to insulin resistance, is supposed to prevent leptin from doing its magic. This study, however, suggests that there might be genetic issues involved, as well. As always, I will keep you posted...