Caloric restriction improves endothelial dysfunction during vascular aging: Effects on nitric oxide synthase isoforms and oxidative stress in rat aorta

Aging is characterized by activation of inducible over endothelial nitric oxide synthase (iNOS and eNOS), impaired antioxidant activity and increased oxidative stress, which reduces nitric oxide bioavailability and causes endothelial dysfunction. Caloric restriction (CR) blunts oxidative stress. We investigated whether CR impacts endothelial dysfunction in aging and the underlying mechanisms. Aortas from young (YC, 6 months of age) and old (OC, 24 months of age) rats ad-libitum fed and from old rats caloric-restricted for 3-weeks (OR, 26%) were investigated. Endothelium-dependent vasorelaxation was impaired in OC, associated with reduced eNOS and increased iNOS expression (P < 0.05). Aortic nitrite was similar in OC and YC, but the contribution of calcium-independent NOS to total NOS activity was increased whereas that of calcium-dependent NOS was reduced (p ≤ 0.0003). Plasma thiobarbituric acid-reactive substances (TBARS) were elevated in OC as well as aortic nitrotyrosine (P < 0.05). Expression of manganese superoxide dismutase (MnSOD) and total SOD activity were impaired in OC (P < 0.05 vs. YC), whereas copper-zinc (CuZn) SOD expression was similar in OC and YC. CR restored endothelial dysfunction in old rats, reduced iNOS expression, total nitrite and calcium-independent NOS activity in aorta (P < 0.05) without changes in eNOS expression and calcium-dependent NOS activity. Sirtuin-1 expression did not differ among groups. Plasma TBARS and aortic nitrotyrosine were reduced (P < 0.05) in OR compared with OC. In OR CuZnSOD protein and SOD activity increased (P < 0.05) without changes in MnSOD expression. Short-term CR improves age-related endothelial dysfunction. Reversal of altered iNOS/eNOS ratio, reduced oxidative stress and increased SOD enzyme activity rather than enhanced NO production appear to be involved in this effect.

Research highlights
► Aging-associated endothelial dysfunction (EDD) is linked with cardiovascular disease.
► Oxidative stress and altered iNOS/eNOS ratio contribute to aging-associated EDD.
► Short-term caloric restriction initiated late in life reverses aging-associated EDD.
► This effect is linked with lower systemic and vascular oxidative stress.
► Decreased iNOS protein levels and activity are also implicated.