Aminoguanidine inhibits aortic hydrogen peroxide production, VSMC NOX activity and hypercontractility in diabetic mice

Abstract

Background: Dysfunctionally uncoupled endothelial nitric oxide synthase (eNOS) is involved in producing reactive oxygen species (ROS) in the diabetic endothelium. The present study investigated whether anti-diabetes drug Aminoguanidine (AG) has any effect on eNOS function and vascular oxidant stress.

Methods and results: Blood glucose levels were increased to 452.0 +/- 15.1 mg/dl in STZ-treated male C57BL/6J mice (148.4 +/- 3.2 mg/dl in untreated controls). Aortic productions of NO* and O(2)*- were measured specifically and sensitively using electron spin resonance. Diabetic mice had a marked increase in aortic O(2)*- production. Aortic hydrogen peroxide (H(2)O(2)) production was also increased in diabetic aortas and significantly attenuated by AG. AG however had only a marginal effect in reducing aortic O(2)*- production, which corresponded to a minimal effect in improving aortic nitric oxide (NO*) bioavailability. The endothelium-dependent vasodilatation however was modestly but significantly improved by AG, likely consequent to AG-induced reduction in hyper-contractility. NAD(P)H oxidase (NOX)-dependent O(2)*- production was completely attenuated by AG in endothelium-denuded diabetic aortas.

Conclusion: In summary, despite that AG is not an effective eNOS recoupling agent presumably consequent to its ineffectiveness in preventing endothelial NOX activation, it is inhibitory of aortic H(2)O(2) production, VSMC NOX activity, and hypercontractility in diabetes.

Figure 1

Effects of AG on aortic superoxide (O₂^•-) production. A: Representative spectra for aortic O₂^•- detected by ESR. Freshly isolated aortic segments (~3 mm) were incubated with spin trapping solution and then analyzed using ESR. B: Grouped data of aortic O₂^•- production expressed as nmol/L per min per mg wet weight. Data are presented as mean ± SEM, n = 6-8.

Figure 2

Effects of AG on aortic hydrogen peroxide (H₂O₂) production. Total aortic H₂O₂ production by Amplex Red Assay. Data are presented as mean ± SEM, n = 8.

Figure 3

Effects of AG on aortic nitric oxide (NO^•) bioavailability in diabetes. A: Representative ESR spectra for NO^•; B: Grouped data of bioavailable NO^•. Data are presented as mean ± SEM, n = 6.

Figure 4

Effects of AG on vascular reactivity. A: AG partially restored endothelium-dependent vasorelaxation. B: AG diminished diabetes induced aortic hypercontractility. Data are presented as mean ± SEM, n = 6.

Figure 5

Effects of AG on NOX-sensitive superoxide (O₂^•-) production. A: NSC23766-sensitive O₂^•- production from intact aortas B: NSC23766-sensitive O₂^•- production from endothelium denuded aortas. Data are presented as mean ± SEM, n = 6.