l-Arginine stimulates proliferation and prevents endotoxin-induced death of intestinal cells

This study tested the hypothesis that l-arginine (Arg) may stimulate cell proliferation and prevent lipopolysaccharide (LPS)-induced death of intestinal cells. Intestinal porcine epithelial cells (IPEC-1) were cultured for 4 days in Arg-free Dulbecco's modified Eagle's-F12 Ham medium (DMEM-F12) containing 10, 100 or 350 mu M Arg and 0 or 20 ng/ml LPS. Cell numbers, protein concentrations, protein synthesis and degradation, as well as mammalian target of rapamycin (mTOR) and Toll-like receptor 4 (TLR4) signaling pathways were determined. Without LPS, IPEC-1 cells exhibited time- and Arg-dependent growth curves. LPS treatment increased cell death and reduced protein concentrations in IPEC-1 cells. Addition of 100 and 350 mu M Arg to culture medium dose-dependently attenuated LPS-induced cell death and reduction of protein concentrations, in comparison with the basal medium containing 10 mu M Arg. Furthermore, supplementation of 100 and 350 mu M Arg increased protein synthesis and reduced protein degradation in both control and LPS-treated IPEC-1 cells. Consistent with the data on cell growth and protein turnover, addition of 100 or 350 mu M Arg to culture medium increased relative protein levels for phosphorylated mTOR and phosphorylated ribosomal protein S6 kinase-1, while reducing the relative levels of TLR4 and phosphorylated levels of nuclear factor-kappa B in LPS-treated IPEC-1 cells. These results demonstrate a protective effect of Arg against LPS-induced enterocyte damage through mechanisms involving mTOR and TLR4 signaling pathways, as well as intracellular protein turnover.