Hormonal and signaling role of branched-chain amino acids.

Amino acids (AAs), especially BCAAs, play pivotal roles in hormonal secretion and action as well as in intracellular signaling. There is emerging data showing that BCAAs regulate gene transcription and translation. Signaling proteins such as the mammalian target of rapamycin act as sensors of BCAAs, especially leucine, to modulate anabolic action. AAs stimulate protein synthesis and inhibit protein breakdown in skeletal muscle and liver. The specific role of BCAAs in regulating synthesis and breakdown of individual protein or proteins with common function or functions remains to be defined. Future studies should also focus on potential adverse effects of BCAAs on insulin sensitivity, renal function, and tumor growth. It also remains to be determined whether potential adverse effects of BCAA supplementation is similar in people of different age groups.