Abstract: 【Abstract】 Objective To investigate the influences of various concentrations of calcium on human peritoneal mesothelial cells (HPMCs) proliferation, damnification and interstitial fibrosis in vitro and in vivo. Methods HPMCs were cultured in the media containing calcium 0, 0.25, 0.75, 1.25, 1.75 or 2.25mmol/L for 12h or 48h. The proliferation of HPMCs was assessed by tetrazolium salt colorimetry assay (MTT assay), and the damage of HPMCs was evaluated by measuring LDH in the medium. Fibronectin (FN) in cytoplasm of HPMCs was determined by western blotting. For clinical observations, a self-controlled study was conducted in 47 patients on peritoneal dialysis using the dialysis fluid PD4 (1.25mmol/L calcium, Baxter) for 18.5±11.74 months. The patients were then treated with the dialysis fluid PD2 (1.75mmol/L calcium, other components are the same as PD4, Baxter) for 4 weeks without any other changes in their therapies. Patients were examined after the dialysis using PD2 fluid for 1, 2, 3 and 4 weeks. FN and LDH in peritoneal effluent were measured by enzyme linked immunosorbent assay (ELISA), and CA125 was detected by electrochemiluminescence assay (ECLA). We also assayed patients’ serum Ca, P, and intact parathyroid hormone (iPTH). Results Calcium in culture media correlated to the proliferation of HPMCs in concentration- and time- dependent manners, with the most promotion effect at 1.75mmol/L calcium. Calcium in culture media also correlated to the increase of LDH in peritoneal effluents in a time-dependent manner, with the least impact on LDH at 1.25mmol/L calcium (P＜0.05), and to the increase of FN in cells in concentration- and time-dependent manners. In peritoneal dialysis patients after switch to PD2 fluid, LDH in peritoneal effluents increased significantly in a time-dependent manner. In those after the switch for 4 weeks, LDH and FN reached to the highest values (P＜0.01), CA125 decreased to the lowest level (P＜0.01), serum calcium was higher than that of control group (P＜0.05), serum phosphorus was lower than that of control group (P＜0.05), and iPTH remained unchanged (P>0.05). Conclusions Our in vivo and in vitro studies demonstrate that higher calcium concentration in peritoneal dialysis fluid at 1.75mmol/L stimulates HPMCs proliferation, injures HPMCs, and up-regulates FN expression in HPMCs. Physiological calcium concentration in peritoneal dialysis fluid at 1.25mmol/L protects the peritoneum from fibrosis.

Key words: Human peritoneal mesothelial cell, Peritoneal dialysis, Fibrosis of peritoneu