OBJECTIVETo study the effects of L-arginine (L-Arg) on human colon carcinoma cell line LS174 through NO pathway and the mechanism.

METHODSLS174 cells were cultured in the presence of L-Arg at different concentrations for different time. MTT assay was employed to evaluate the cell proliferation, and the cell morphological changes were observed by optical and electron microscopy. The apoptosis of L-Arg-treated cells was observed by the Annexin V/PI staining. The expression levels of VEGF, COX-2, p53, bcl-2 and bax in the cells were determined using Western blotting and immunocytochemical staining.

RESULTSL-Arg promoted the growth of LS174 cells at a low concentration (0.125 mmol/L) and inhibited the cell growth at higher concentrations (0.5, 2, 8, and 32 mmol/L). Under electron microscope, ultrastructual changes in the cytoplasm and nuclei of LS174 cells were observed 48 h after exposure to L-Arg. Some of the cells showed morphological changes characteristic of cell apoptosis such as cell size reduction, condensation and margination of the nuclear chromatin. Low concentration of L-Arg resulted in a cell apoptosis rate of 2.29%, as compared with the rate of 2.84% in the control group; at higher concentrations, L-Arg caused significantly increased cell apoptosis rates to 26.88%, 28.95%, 63.36%, and 84.51%, respectively. In cells treated with a low concentration of L-Arg, the expressions of VEGF and COX-2 were increased as compared with those in the control cells; higher concentrations of L-Arg obviously decreased the expressions of p53 and bcl-2 and increased the expression of bax.

CONCLUSIONLow-concentration L-Arg can promote the growth of LS174 cells probably by up-regulating VEGF and COX-2 protein under the influence of NO, the metabolite of L-Arg. The inhibitory effect of high concentrations of L-Arg is probably mediated by inducing cell apoptosis via NO. The mechanism of L-Arg- induced cell apoptosis may be related to the up-regulation of bax protein and the down-regulation of p53 and bcl-2 proteins.