Inhibition of endothelial nitric oxide generation by low-density lipoprotein is partially prevented by l-arginine and l-ascorbate

Abstract

We evaluated, in endothelial cells, the relative effectiveness of l-arginine and l-ascorbate in preventing the decrease in nitric oxide (NO) production in response to native low-density lipoprotein (LDL) from healthy subjects (nLDL), oxidized LDL (oxLDL, formed by nLDL oxidation) or native LDL from type 2 diabetic patients (dLDL). Human umbilical vein endothelial cells (HUVEC) were exposed to nLDL, dLDL or oxLDL (100 mg protein/L), in the absence or presence of l-arginine 10 −4 mol/L and/or l-ascorbate 10 −4 mol/L; NO synthase (NOS) activity and cyclic guanosine-3′,5′-monophosphate (cGMP) were measured by the conversion of l-[ 3 H ]arginine to l-[ 3 H ]citrulline and by radioimmunoassay, respectively. Both l-arginine and l-ascorbate increased cGMP in HUVEC co-incubated with any LDL species, although to lower levels than found in the absence of LDL. l-Ascorbate did not affect NOS activity, whereas l-arginine increased it, both in the absence and presence of all LDL species. The effects of combined l-arginine and l-ascorbate on NOS activity and cGMP were no greater than those of l-arginine alone. Our results suggest that l-arginine or l-ascorbate can ameliorate, but not normalize, NO production in this situation, and that combining l-arginine with l-ascorbate is unlikely to produce additional benefit as compared with l-arginine alone.