L-arginine does not improve endothelial function in patients with metabolic syndrome

Objective: To evaluate whether L-Arginine may improve the endothelial dysfunction in patients with metabolic syndrome (MS). Methods: in a randomized double blind study, 38 subjects with MS received either L-Arginine (6.64 g/die, group A, n=19) or placebo (group B, n=19) for 6 weeks. At baseline and at the end of the study flow mediated dilatation (FMD), systolic and diastolic blood pressure, visceral obesity, lipids, blood glucose, insuline, L-arginine, total NOx and symmetric and asymmetric dimethylarginine (SDMA and ADMA) were measured. Results: At baseline groups A and B differed just for waist circumference (100±7 vs. 107±12 cm; p<0.05). After treatment, beside the expected increases in L-arginine (from 83±17 to 97±26 µM; p=0.002) and L-arginine/ADMA ratio (from 215±40 to 243±53; p=0.002) no change was detected in group A. An increase of total cholesterol (from 173±47 to 184±44 mg/dL, p=0.027), LDL (from 95±26 to 109±34 mg/dL, p=0.012), HDL (from 44±7 to 46±8 mg/dL, p=0.003) and ADMA (from 0.39±0.07 to 0.42±0.09 µM, p=0.005) was observed in the placebo group. After data adjustment for possible confounders (age, pack-years and change in ADMA, arginine, blood glucose and pharmacological treatments) FMD significantly increased from 0.35±2.83 to 0.43±2.94 % (p=0.03) in the L-arginine treated group but not in the placebo group. The group A difference in FMD, however, lost its statistical significance after adjustment of the analysis also for Brachial artery diameter measured at rest. Conclusion: the oral supply of L-Arginine does not improve the endothelial function in patients with MS. Funding: Italian ministry of health (ricerca finalizzata).