Endothelial dysfunction is a major risk factor for several of the vascular complications of diabetes, including
ischemic stroke.
Nitroxyl (HNO), the one electron reduced and protonated form of
nitric oxide (NO•), is resistant to scavenging by
superoxide, but the role of HNO in
diabetes mellitus associated endothelial dysfunction in the carotid artery remains unknown. Aim: To assess how diabetes affects the role of endogenous NO• and HNO in endothelium-dependent relaxation in rat isolated carotid arteries. Methods: Male Sprague Dawley rats were fed a high-fat-diet (HFD) for 2 weeks prior to administration of low dose
streptozotocin (STZ; 35 mg/kg i. p./day) for 2 days. The HFD was continued for a further 12 weeks.
Sham rats were fed standard chow and administered with
citrate vehicle. After 14 weeks total, rats were anesthetized and carotid arteries collected to assess responses to the endothelium-dependent
vasodilator,
acetylcholine (ACh) by myography. The combination of
calcium-activated potassium channel blockers,
TRAM-34 (1 μmol/L) and
apamin (1 μmol/L) was used to assess the contribution of endothelium-dependent hyperpolarization to relaxation. The corresponding contribution of NOS-derived
nitrogen oxide species to relaxation was assessed using the combination of the NO• synthase inhibitor,
L-NAME (200 μmol/L) and the
soluble guanylate cyclase inhibitor ODQ (10 μmol/L). Lastly,
L-cysteine (3 mmol/L), a selective HNO scavenger, and
hydroxocobalamin (HXC; 100 μmol/L), a NO• scavenger, were used to distinguish between NO• and HNO-mediated relaxation. Results: At study end, diabetic rats exhibited significantly retarded
body weight gain and elevated
blood glucose levels compared to
sham rats. The sensitivity and the maximal relaxation response to ACh was significantly impaired in carotid arteries from diabetic rats, indicating endothelial dysfunction. The vasorelaxation evoked by ACh was abolished by
L-NAME plus ODQ, but not affected by the
apamin plus
TRAM-34 combination, indicating that NOS-derived
nitrogen oxide species are the predominant endothelium-derived
vasodilators in
sham and diabetic rat carotid arteries. The maximum relaxation to ACh was significantly decreased by
L-cysteine in both
sham and diabetic rats, whereas HXC attenuated ACh-induced relaxation only in
sham rats, suggesting that diabetes impaired the contribution of NO•, whereas HNO-mediated vasorelaxation remained intact. Conclusion: Both NO• and HNO contribute to endothelium-dependent relaxation in carotid arteries. In diabetes, NO•-mediated relaxation is impaired, whereas HNO-mediated relaxation was preserved. The potential for preserved HNO activity under pathological conditions that are associated with oxidative stress indicates that HNO donors may represent a viable therapeutic approach to the treatment of vascular dysfunction.