Protective Vascular and Cardiac Effects of Inducible Nitric Oxide Synthase in Mice with Hyperhomocysteinemia

Abstract

Diet-induced hyperhomocysteinemia produces endothelial and cardiac dysfunction and promotes thrombosis through a mechanism proposed to involve oxidative stress. Inducible nitric oxide synthase (iNOS) is upregulated in hyperhomocysteinemia and can generate superoxide. We therefore tested the hypothesis that iNOS mediates the adverse oxidative, vascular, thrombotic, and cardiac effects of hyperhomocysteinemia. Mice deficient in iNOS (Nos2−/−) and their wild-type (Nos2+/+) littermates were fed a high methionine/low folate (HM/LF) diet to induce mild hyperhomocysteinemia, with a 2-fold increase in plasma total homocysteine (P<0.001 vs. control diet). Hyperhomocysteinemic Nos2+/+ mice exhibited endothelial dysfunction in cerebral arterioles, with impaired dilatation to acetylcholine but not nitroprusside, and enhanced susceptibility to carotid artery thrombosis, with shortened times to occlusion following photochemical injury (P<0.05 vs. control diet). Nos2−/− mice had decreased rather than increased dilatation responses to acetylcholine (P<0.05 vs. Nos2+/+ mice). Nos2−/− mice fed control diet also exhibited shortened times to thrombotic occlusion (P<0.05 vs. Nos2+/+ mice), and iNOS deficiency failed to protect from endothelial dysfunction or accelerated thrombosis in mice with hyperhomocysteinemia. Deficiency of iNOS did not alter myocardial infarct size in mice fed the control diet but significantly increased infarct size and cardiac superoxide production in mice fed the HM/LF diet (P<0.05 vs. Nos2+/+ mice). These findings suggest that endogenous iNOS protects from, rather than exacerbates, endothelial dysfunction, thrombosis, and hyperhomocysteinemia-associated myocardial ischemia-reperfusion injury. In the setting of mild hyperhomocysteinemia, iNOS functions to blunt cardiac oxidative stress rather than functioning as a source of superoxide.

Microvascular Dysfunction and Cognitive Impairment

“…Each of these genetic alterations results in hyperhomocysteinemia. Models using diets containing low folate and/or high methionine to induce hyperhomocysteinemia are also common (Table) (Dayal et al, 2014; Kamat et al, 2015; Kim et al, 2002). …”

High Methionine Diet Poses Cardiac Threat: A Molecular Insight

“…In hyperhomocysteinemic rats, there is upregulation of iNOS in the carotid and the coronary artery (Ungvari et al, ; Zhang et al, ; Celotto et al, ) and iNOS inhibitors mitigate the increased ROS production in the carotid and the coronary artery (Dayal et al, ). However, Dayal et al () have shown that in diet induced hyperhomocysteinemic mice, endogenous iNOS protects from endothelial dysfunction and myocardial ischemia‐reperfusion injury. The present findings suggest that upregulation of iNOS, with increased production of superoxide radicals; underline the mechanism of vascular dysfunction.…”

“…However, Dayal et al (2014) have shown that in diet induced hyperhomocysteinemic mice, endogenous iNOS protects from endothelial dysfunction and myocardial ischemia-reperfusion injury. The present findings suggest that upregulation of iNOS, with increased production of superoxide radicals; underline the mechanism of vascular dysfunction.…”

Homocysteine Exposure Impairs Myocardial Resistance to Ischaemia Reperfusion and Oxidative Stress

“…This is the first study to investigate the effects of perfusing normal isolated hearts with Hcy on cardiac functional parameters during ischaemia reperfusion. Previous studies of the effects of homocysteine during ischaemia reperfusion have either investigated transgenic mice [15], or have explored oxidant damage [16] or area at risk [17] in methionine fed animals. The results showed that exposure to 0.1mM Hcy prior to global normothermic ischaemia impaired recovery of LVDP (Fig.…”

“…Two studies have shown impaired functional recovery following ischaemia reperfusion in transgenic cystathionine beta synthase deficient mice and increased reperfusion damage [15] and oxidant damage in methionine fed rat hearts [16] and increased area at risk in methionine fed mice [17]. Therefore the aim of this study was to specifically investigate the effect of exposing whole hearts and isolated cardiomyocytes to the clinically relevant dose of 0.1 mM Hcy on functional performance during ischaemia reperfusion and on calcium homeostasis, morphology and viability, and contractile activity under normal conditions and during oxidative stress.…”