Arginine or citrulline associated with a statin stimulates nitric oxide production in bovine aortic endothelial cells

Abstract

Nitric oxide (NO) is an antiatherogenic vasodilator synthesized from arginine and, indirectly, from citrulline through argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL). Hypercholesterolemia-induced atherosclerosis is usually treated by statins, which decrease cholesterolemia and increase endothelial NO synthase (eNOS) activity. Therefore, a treatment associating a statin with arginine or citrulline could be more efficient than statin alone. The aim of this study was to optimize NO production in bovine aortic endothelial cells (BAEC) by a combination of simvastatin with arginine or citrulline and to identify the molecular mechanisms involved. NO production was measured after stimulation of BAEC in different conditions (simvastatin 0 to 10 μM associated with arginine or citrulline 0 to 5 mM) after 24-hour incubation. Intracellular levels of specific proteins were evaluated by Western-Blot analysis, and mRNA levels of eNOS, iNOS, caveolin-1, ASS and ASL were assessed by RT-PCR. Simvastatin co-administrated with arginine or citrulline increased NO production, but at simvastatin 10 μM, 1 mM arginine-induced NO production was significantly (P < 0.01) higher than 1 mM citrulline-induced NO production. Simvastatin induced an increase in eNOS mRNA expression and protein levels in the presence of arginine or citrulline. ASS and ASL mRNA levels were increased by simvastatin, whereas a high substrate concentration (1 mM) strongly decreased ASL mRNA levels. Combining statin with arginine or citrulline increased NO production in endothelial cells by increasing eNOS protein levels. These results form a strong rationale to evaluate the potential utilization of these in atherosclerosis prevention and treatment.