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

We evaluated, in endothelial cells, the relative effectiveness of -arginine and -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 -arginine 10−4 mol/L and/or -ascorbate 10−4 mol/L; NO synthase (NOS) activity and cyclic guanosine-3′,5′-monophosphate (cGMP) were measured by the conversion of -[3H]arginine to -[3H]citrulline and by radioimmunoassay, respectively. Both -arginine and -ascorbate increased cGMP in HUVEC co-incubated with any LDL species, although to lower levels than found in the absence of LDL. -Ascorbate did not affect NOS activity, whereas -arginine increased it, both in the absence and presence of all LDL species. The effects of combined -arginine and -ascorbate on NOS activity and cGMP were no greater than those of -arginine alone. Our results suggest that -arginine or -ascorbate can ameliorate, but not normalize, NO production in this situation, and that combining -arginine with -ascorbate is unlikely to produce additional benefit as compared with -arginine alone.