Exercise and nitrite prevent and Nω-nitrol-L-arginine methyl ester reproduces imbalance in the nuclear factor-κB/NADPH oxidase 2 and nuclear factor erythroid 2-related factor 2/NADPH oxidase 4/endothelial nitric oxide synthase systems in diabetes.

Abstract

Diabetes-induced vasculopathies are linked to inflammation mediated by mutually inhibitory nuclear factor-kappaB (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2). NF-κB is activated by superoxide (O2 ˙-)- producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase homologues, including NADPH oxidase 2 (Nox2), and vice versa, with NF-κB inducing Nox2. Nrf2 is activated by H2O2-producing Nox4 and nitric oxide (NO), but also induces NADPH oxidase 4 (Nox4) and endothelial nitric oxide synthase (eNOS). The NF-κB/Nox2 system is upregulated and Nrf2/Nox4/eNOS is downregulated in diabetes. We hypothesized that this vascular-deleterious imbalance results from the reduced vascular NO signaling, and so may be prevented by exercise training and sodium nitrite (interventions known to replenish vascular NO), and be reproduced by nitric oxide synthase (NOS) inhibition. Streptozotocin diabetic rats were examined on days 4, 10, 49 and 84 of diabetes. From day 4 onwards, plasma nitrite was reduced while NF-κB nuclear accumulation in the heart and kidneys gradually increased, while Nrf2 decreased. In parallel, the cardiac expression of signatures of the NF-κB (inducible nitric oxide synthase (iNOS), vascular cell adhesion molecule-1 (VCAM-1), NADPH oxidase 2 Nox2) increased and of the Nrf2 (Nox4, eNOS, heme-oxygenase-1 (HO-1)) decreased. Exercise training and dietary nitrite prevented this phenotype in the 49-day diabetes model. 7-day treatment of non-diabetic rats with NOS inhibitor of Nω-nitro-L-arginine methyl ester (L-NAME) recapitulated the NF-κB/Nox2 and Nrf2/Nox4/eNOS imbalance, as seen in diabetic rats. Nitrite failed to prevent the changes induced by L-NAME. The coherence of changes in NF-κB, Nox2, Nrf2, Nox4 and eNOS under the various settings of this study aimed at modifying the vascular NO leads us to propose that NF-κB/Nox2 and Nrf2/Nox4/eNOS are two crosstalking functional subsystems of one larger regulatory network, with NOS-derived NO ensuring the balance between these subsystems, and thus preventing vascular oxidative stress, endothelial dysfunction and inflammation.