Supplementation of dietary nitrate attenuated oxidative stress and endothelial dysfunction in diabetic vasculature through inhibition of NADPH oxidase.

ABSTRACT

The metabolic disorders in diabetes, which are usually accompanied by oxidative stress and impaired nitric oxide (NO) bioavailability, increase the risk of detrimental cardiovascular complications. Herein, we investigated the therapeutic potential of dietary nitrate, which is found in high content in green leafy vegetables, on vascular oxidative stress and endothelial dysfunction in diabetic mice induced by high-fat diet and streptozotocin injection. Dietary nitrate in drinking water fuelled a nitrate-nitrite-NO pathway, which inhibited vascular oxidative stress, endothelial dysfunction and many features of metabolic syndrome in diabetic mice. These beneficial effects of nitrate on diabetic mice were abolished by PTIO (NO scavenger) treatment and significantly prevented by febuxostat (xanthine oxidoreductase inhibitor), demonstrating the central importance of NO in bioactivation of nitrate. The favorable effects of nitrate were not further influenced by apocynin (NADPH oxidase inhibitor), suggesting NADPH oxidase as a possible target. In high glucose-incubated vascular endothelial cells, NO donor attenuated oxidative stress and endothelial dysfunction via the inhibition of NADPH oxidase, where a heme oxygenase-1 (HO-1)-dependent mechanism was demonstrated for the antioxidant abilities of NO. Altogether, boosting this nitrate-nitrite-NO signaling pathway resulted in the decreases of NADPH oxidase-derived oxidative stress, endothelial dysfunction and metabolic disorders in diabetic vasculature. These findings may have novel implications for the preventive strategy against diabetes-induced vascular dysfunction and associated complications.