Inorganic Nitrite Supplementation Improves Endothelial Function With Aging

To determine the efficacy of inorganic nitrite supplementation on endothelial function in humans and mechanisms of action, we performed (1) a randomized, placebo-controlled, parallel-group clinical trial with sodium nitrite (80 mg/day, 12 weeks) in older adults (N=49, 68±1 year) and (2) reverse-translation experiments in young (6 months) and old (27 months) c57BL/6 mice. In the clinical trial, sodium nitrite increased plasma nitrite ( P <0.05) and was well tolerated. Brachial artery flow-mediated dilation (endothelial function) was increased 28% versus baseline after nitrite supplementation ( P <0.05) but unchanged with placebo. Nitrotyrosine, a marker of oxidative stress, was reduced by 45% versus baseline in biopsied endothelial cells after nitrite, but not placebo, treatment. Plasma from nitrite-treated, but not placebo-treated, subjects decreased whole-cell (CellROX) and mitochondria-specific (MitoSOX) reactive oxygen species in cultured human umbilical vein endothelial cells ( P <0.05). Old mice (old [27 months] control, n=9) had ≈30% lower ex vivo carotid artery endothelium-dependent dilation (EDD) versus young mice (young [6 months] control, n=9) due to reduced NO bioavailability ( P <0.05). Nitrite supplementation (drinking water, 50 mg/L, 8 weeks) restored EDD and NO bioavailability in old mice (n=10) to (6 months) control. Mitochondrial reactive oxygen species suppression of EDD was present in old control (increased EDD with a mitochondrial-targeted antioxidant, P <0.05) but not in young control or old mice supplemented with sodium nitrite. A mitochondrial reactive oxygen species inducer (rotenone) further impaired EDD in old control ( P <0.05); young control and old mice supplemented with sodium nitrite were protected. Markers of mitochondrial health were greater in aorta of old mice supplemented with sodium nitrite versus old control ( P <0.05). Inorganic nitrite supplementation improves endothelial function with aging by increasing NO, decreasing mitochondrial reactive oxygen species/oxidative stress, and increasing mitochondrial stress resistance. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT02393742.