On the enigma of carnosine's anti-ageing actions.

Carnosine (beta-alanyl-L-histidine) has described as a forgotten and enigmatic dipeptide. Carnosine's enigma is particularly exemplified by its apparent anti-ageing actions; it suppresses cultured human fibroblast senescence and delays ageing in senescence-accelerated mice and Drosophila, but the mechanisms responsible remain uncertain. In addition to carnosine's well-documented anti-oxidant, anti-glycating, aldehyde-scavenging and toxic metal-ion chelating properties, its ability to influence the metabolism of altered polypeptides, whose accumulation characterises the senescent phenotype, should also be considered. When added to cultured cells, carnosine was found in a recent study to suppress phosphorylation of the translational initiation factor eIF4E resulting in decreased translation frequency of certain mRNA species. Mutations in the gene coding for eIF4E in nematodes extend organism lifespan, hence carnosine's anti-ageing effects may be a consequence of decreased error-protein synthesis which in turn lowers formation of protein carbonyls and increases protease availability for degradation of polypeptides altered postsynthetically. Other studies have revealed carnosine-induced upregulation of stress protein expression and nitric oxide synthesis, both of which may stimulate proteasomal elimination of altered proteins. Some anti-convulsants can enhance nematode longevity and suppress the effects of a protein repair defect in mice, and as carnosine exerts anti-convulsant effects in rodents, it is speculated that the dipeptide may participate in the repair of protein isoaspartyl groups. These new observations only add to the enigma of carnosine's real in vivo functions. More experimentation is clearly required.