Leucine in age-associated sarcopenia
Year: 2006
Type: article
Abstract: A progressive loss of muscle mass has been well described in both humans and rodents during ageing. This loss of proteins results from an imbalance between protein synthesis and degradation rates. Although some authors have shown a decrease of myofibrillar protein synthesis rates in human volunteers, this imbalance is not clearly apparent when basal rates of protein turnover are measured. A decrease in muscle protein synthesis stimulation has nevertheless been detected in ageing rats during the postprandial period, suggesting that the ‘ meal signal’ is altered during ageing. Many results now suggest that aged muscle is less sensitive to the stimulatory effect of amino acids at physiological concentrations, but is still able to respond if the increase in aminoacidaemia is sufficiently large. Indeed, amino acids play an important role in regulating muscle protein turnover both in vitro and in vivo. Of amino acids, leucine seems to play the key role in regulating the metabolic function. It inhibits proteolysis and stimulates muscle protein synthesis independently of insulin. Leucine has been shown to act as a mediator, by modulating specifically the activities of intracellular kinases linked to the translation of proteins such as phosphatidylinositol 3_ kinase and mammalian target of rapamycin – 70 kDa ribosomal protein S6 (p70S6K) kinases. We recently demonstrated in vitro that protein synthesis in ageing rat muscles becomes resistant to the stimulatory effect of leucine in its physiological concentration range. Protein synthesis was however stimulated normally when the leucine concentration was increased well above its postprandial level. We also studied the effect of meal leucine supplementation on in vivo protein synthesis in adult and ageing rats. Leucine supplementation had no additional effect on muscle protein synthesis in adults but totally restored its stimulation in ageing rats. Whether chronic oral leucine supplementation would be beneficial for maintaining muscle protein mass in elderly humans remains to be studied.
DOI: 10.4267/2042/47849
Language: English
Subfield: Nutrition and Dietetics
Field: Nursing
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2092080825