Augmented S-nitrosylation contributes to impaired relaxation in angiotensin II hypertensive mouse aorta: role of thioredoxin reductase.

BACKGROUND: Vascular dysfunction, including reduced endothelium-dependent dilation, is a major characteristic of hypertension. We previously investigated that thioredoxin reductase (TrxR) inhibition impairs vasodilation via soluble guanylyl cyclase S-nitrosylation, but S-nitrosylation and TrxR function are not known in hypertension. We hypothesized that S-nitrosylation is associated with reduced vasodilation in hypertensive mice.
METHOD: Aortic rings from normotensive (sham) and angiotensin II (AngII)-induced hypertensive C57BL/6 mice were treated with a TrxR inhibitor, 1-chloro-2,4-dinitrobenzene (DNCB) for 30  min, and relaxation to acetylcholine (ACh) was measured in the rings following contraction with phenylephrine.
RESULTS: DCNB reduced relaxation to ACh compared with vehicle in sham aorta but not in AngII (sham-vehicle E(max) = 77 ± 2, sham-DNCB E(max) = 59 ± 4, P < 0.05). DNCB shifted the concentration-response relaxation to sodium nitroprusside (SNP) to the right in both sham and AngII aortic rings (sham-vehicle pD(2) = 8.8±0.1, sham-DNCB pD(2) = 8.4±0.1, *P < 0.05; AngII-vehicle pD(2) = 8.5±0.1, AngII-DNCB pD(2) = 8.3 ± 0.1, P < 0.05). As downstream signaling of nitric oxide, cyclic GMP level was reduced by DNCB during activation with SNP. The effect of DNCB to increase S-nitrosylation was confirmed by the biotin-switch method and western blot analysis, and total protein S-nitrosylation was increased in AngII aorta (1.5-fold) compared with sham. TrxR activity was inhibited in AngII aorta compared with sham.
CONCLUSION: We conclude that increased S-nitrosylation contributes to impaired relaxation in aorta from AngII-induced hypertensive mice. AngII treatment resulted in inactivation of TrxR and increased S-nitrosylation, indicating that TrxR and S-nitrosylation may provide a critical mechanism in hypertension associated with abnormal vascular reactivity.