Methylguanidine cytotoxicity on HK-2 cells and protective effect of antioxidants against MG-induced apoptosis in renal proximal tubular cells in vitro

Abstract

Methylguanidine (MG), a small molecule among guanidine compounds, is a product of protein catabolism. The concentration of MG in the serum of uremic patients is nearly 80 times of that in the serum of normal people. The present study was designed to explore the toxic effect of MG on renal proximal tubular cells as well as the protective effect of antioxidants PGE1 and probucol against MG-induced apoptosis in renal proximal tubular cells. HK-2 cells were used as the subject. The cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. N-Acetyl-3-d-glucosaminidase (NAG) activity, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity were determined. Cell apoptosis was determined by flow cytometry (light scatter and propidium iodide/annexin V-FTC fluorescence) and by nuclear staining with Hoechst 33258. Cells were exposed to MG (0.25, 0.5, or 1 mmol/L), MG (0.5 mmol/L) + PGE1 (2 μg/L), and MG (0.5 mmol/L) + probucol (20 μmol/L) respectively for 24 h. MG induced a significant dose-dependent loss of cell viability. Both PGE1 and probucol improved the viability of MG-treated HK-2 cells. Cells showed apoptotic morphology (deepened stain, karyopyknosis, and apoptotic body) when exposed to 0.5 mmol/L MG for 24 h, and the apoptosis ratio was increased compared with the control. The presence of PGE1 or probucol significantly lowered the apoptotic ratio. Moreover, PGE1 or probucol notably decreased the MDA content and increased the SOD activity compared with when the cells were treated with MG only. The results of the present study clearly demonstrate that MG could promote apoptosis of renal proximal tubular cells in vitro. Both PGE1 and probucol could protect renal proximal tubular cells from MG-induced apoptosis.