The Effects of Lactate and pH on Human Peritoneal Mesothelial Cell Biology

Kim, Young Min; Ha, Hun Joo; Yoo, Mi Ra; Lee, Hi Bahl

Abstract

Preservation of peritoneal membrane function is important in the success of long-term peritoneal dialysis (PD). During PD, human peritoneal mesothelial cells (HPMC) are continuously exposed to unphysiological peritoneal dialysis solution(PDS) charaterized by high glucose and lactate concentrations, low pH, and hyperosmolality. Since few studies have examined the effects of lactate and pH on HPMC biology, the present study investigated the effects of lactate and pH on the viability and proliferation of cultured HPMC and on the production of TGF-beta1, a fibrogenic cytokine, and fibronectin by cultured HPMC. HPMC were obtained from the omental tissue of pregnant women who were undergoing Cesarean section. Cells at confluence were utilized to determine the viability(LDH release), proliferation([3H]-thymidine incorporation), and the production of fibronectin and TGF-beta1(ELISA) after synchronizing the cell growth by incubating with serum free media for 24 hours. After exposure to the media containing lactate and pH, LDH release increased in dose- and time-dependent manner. Both 1.5% and 4.25% commercial PD solutions were cytotoxic and induced more than 80% LDH release within 24 hours. LDH release decreased with increasing dilution of commercial peritoneal dialysate, but there was no significant difference in LDH release between 1.5% and 4.25% PDS. LDH release increased in response to pH 5.5. Thymidine incorporation assay revealed that lactate and low pH significantly inhibited proliferation of HPMC. ELISA revealed that exposure of HPMC to lactate and low pH decreased fibronectin protein synthesis, when compared to cell exposed to bicarbonate containing M199 media. Our results clearly show that lactate and low pH lead to dose- and time-dependent cell death and reduce proliferation of cultured HPMC. Lactate and low pH per se appear to decrease fibronectin production by HPMC but may set a stage for other factors to promote progressive fibrosis during the healing stage in long-term PD.