Sirt-1 as a novel therapeutic target for improving nitric oxide release in heterozygous and homozygous patients for mthfr mutations

Hyperhomocysteinemia is associated with increased risk of atherosclerosis, stroke, myocardial infarction, and possibly Alzheimer’s disease. The C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) is a polymorphism responsible for its decreased enzymatic activity leading to a mild to moderate increase in plasma homocysteine concentrations. Homocysteine accumulation on the vessel wall induces vascular dysfunction through mechanisms not yet known. In our experimental model, we have shown that endothelial dysfunction in MTHFR heterozygous mice is associated with both reduced phosphorylation of sirtuin-1 (Sirt-1) and decreased endothelial nitric oxide synthase (eNOS) dimer-to-monomer ratio, marker of enzymatic dysfunction and abnormalities in the production of nitric oxide (NO). Sirt-1 is an important modulator of NO production and resveratrol is one of its major activators. We evaluated the effect of both acute (25 microM) and chronic (10mg/Kg/die for 21 days) administration of resveratrol in heterozygous MTHFR mice and related controls. In both experimental conditions, resveratrol administration reduced endothelial dysfunction by increasing Sirt-1 phosphorylation and eNOS dimer/monomer ratio. Noteworthy, after Sirt-1 inhibition by EX527, resveratrol was no longer able to exert its endothelial protective action, suggesting Sirt-1 as a potential therapeutic target to reduce endothelial dysfunction during hyperhomocysteinemia. In order to translate the results obtained in experimental models, we have extended our study to platelets from heterozygous and homozygous patients for MTHFR mutations and healthy controls, evaluating the vascular effects of NO released by platelets. The treatment of platelets with resveratrol increased Sirt-1 and eNOS (in serine 1177) phosphorylation as well as NO-mediated vasodilation. This protective action of resveratrol was reverted by inhibiting Sirt-1. Our data demonstrate that Sirt-1 is responsible for decreased NO production in heterozygous and homozygous patients for MTHFR mutations suggesting Sirt-1 as a novel therapeutic target to reduce cerebro- and cardiovascular accidents in patients with hyperhomocysteinemia.