Oral Amino Acid Administration Decreases Oxidative Stress and Improves Brachial Reactivity in Elderly Individuals

Abstract

Atherosclerosis is a major cause of death in elderly individuals. Endothelial dysfunction is recognized as a key early event in atherogenesis. In the present study, we evaluated the possible beneficial effect of amino acid administration on endothelial regulation in elderly subjects. A total of 25 healthy elderly subjects were administered essential amino acids (EAA) for 4 months. Before and after EAA administration, each subject underwent brachial reactivity investigation with and without an intra-arterial infusion of 4 micromol/min of N(G)-monomethyl-l-arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthase. At baseline, age correlated with free plasma insulin growth factor-1 IGF-1 (r = -0.48; P < .01), plasma Trolox equivalent antioxidant capacity (TEAC) (r = -0.40; P < .04), and thiobarbituric acid-reactive substances (TBARS) (r = 0.42, P < .04), and homeostasis model assessment (HOMA) index (r = 0.45, P < .03), as well as with changes in diameter (r = -0.49, P < .01) and flow (r = -0.43, P < .03). Administration of EAA was associated with a significant increase in plasma TEAC (P < .001) and decline in plasma TBARS (P < .001) and with improvement in changes in diameter (7.15 +/-1.10 v 8.98 +/-1.80, P < .001) and flow (5.6 +/-1.2 v 6.4 +/- 1.2, P < .03). These latter two associations were independent of changes in HOMA index (P < .04 for both correlations). The beneficial effects of EAA administration on brachial reactivity were partly attenuated by L-NMMA. Administration of EAA may improve brachial reactivity in elderly persons and may also protect against the development of atherosclerosis via the rise in plasma-free IGF-1 levels.