l-arginine infusion decreases plasma total homocysteine concentrations through increased nitric oxide production and decreased oxidative status in Type II diabetic patients

AIMS/HYPOTHESIS: Hyperhomocysteinaemia increases cardiovascular risk in Type II (non-insulin-dependent) diabetes mellitus by augmenting oxidative stress and reducing nitric oxide availability. In vitro, nitric oxide decreases homocysteine by its conversion to the vasodilative and antioxidant compound S-nitrosohomocysteine. We investigated whether or not changes in nitric oxide availability decrease homocysteine concentrations in vivo. METHODS: The study group consisted of 20 normotensive, normolipidaemic, non-atherosclerotic Type II diabetic patients in good metabolic control (16 men, 51.2+/-1.4 years) and 15 healthy subjects (12 men, 48.1+/-1.5 years). Circulating concentrations of homocysteine, nitrite+nitrate and sulphydryl groups, a marker of oxidative stress, were assessed at baseline and then 5', 10', 30' and 60' after the intravenous infusion of either L-arginine (3 g in 10 ml saline), the nitric oxide precursor, or vehicle according to a double-blind cross-over randomized protocol. RESULTS: At baseline diabetic patients showed lower plasma sulphydryl group concentrations (491.8+/-16.9 vs 551.3+/-21.0 micro mol/l, p<0.04) and nitrite+nitrate (21.4+/-0.8 vs 29.5+/-0.9 micro mol/l, p<0.0001) and higher total homocysteine concentrations (11.1+/-0.5 vs 8.3+/-0.6 micro mol/l, p<0.002) than the control subjects. After L-arginine infusion, blood pressure levels and total homocysteine concentrations ( p< or =0.05) decreased (peak at 5' and 30', respectively) whereas nitric oxide and sulphydryl group concentrations ( p< or =0.003) increased (peak at 10' and 30', respectively) in the patients and control subjects. CONCLUSION/INTERPRETATION: Acute L-arginine infusion in both Type II diabetic patients and healthy subjects decreases plasma total homocysteine concentrations, counteract oxidative stress and increases the availability of nitric oxide.