Limb remote ischemic post-conditioning reduces brain reperfusion injury by reversing eNOS uncoupling.

Limb remote ischemic postconditioning (LRIP) can reduce ischemia-reperfusion injury (IRI), but its mechanisms are still unclear. We hypothesize that LRIP reduces IRI by reversing eNOS uncoupling. Focal ischemia was induced in Sprague-Dawley rats by middle cerebral artery occlusion for 2 h followed by a 24 h reperfusion. Before this surgery, folic acid (FA) was administered to the drug treatment group by gavage for 11 days. After a 24 h reperfusion, behavioural testing, vascular function, NO concentration and superoxide dismutase activity in the serum were determined. In addition, the infarct size of the brain was also detected. The mRNA of eNOS, nNOS, GTP cyclohydrolase I (GTPCH), P22phox and xanthine oxidase (XO) in the ischemic region were detected by RT-PCR, and nitrotyrosine (Tyr-NO2) was detected using Western blot analysis. The results showed that LRIP, FA and FA+LRIP all could improve behavioural score, and increase NO–mediated endothelium-dependent vasomotor responses, reduce infarction of rats subjected to IRI. Western blot and RT-PCR analyses showed that the Tyr-NO2 levels and the mRNA expression of NADPH oxidase catalytic subunit P22phox and XO were up-regulated in the ischemic brain, which was significantly inhibited by LRIP, FA and FA+LRIP. The mRNA expression of the rate-limiting enzyme in BH4 synthesis, GTPCH, was down-regulated in the ischemic brain, which could be significantly augmented by LRIP and FA+LRIP. It can be concluded that IRI induces eNOS uncoupling in the cerebral ischemic region and LRIP partially reverses the eNOS uncoupling induced by IRI.

Research progress on endothelial nitric oxide synthase uncoupling / 中国药理学通报

Endothelial dysfunction in various vascular diseases is associated with reduced nitric oxide(NO) bioavailability.It has been clearly demonstrated that endothelial nitric oxide synthase(eNOS) uncoupling plays a key role in above vascular pathological status.eNOS uncoupling is characterized by eNOS generating super oxide rather than NO which may resulted from the increased oxidative stress,lack of eNOS protein cofactor tetrahydrobiopterin(BH4),or supplement shortage of eNOS substrate L-arginine.Accumulating evidences suggest that reversal of eNOS uncoupling by ether reduction of oxidative stress or promotion the bioavailability of BH4 and L-arginine may serve as a novel therapeutic strategy for endothelial dysfunction and cardiovascular diseases,such as hypertension,diabetes,and atherosclerosis.