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

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.

Effect of High Glucose on Nitric Oxide Production in Culteured Rat Mesangial Cells / 대한신장학회잡지

Diabetic nephopathy is one of the leading causes of end-stage renal disease and characterized pathologically by the glomerular mesangial expansion and increased extracellular matrix(ECM) formation. Glomerular hyper-filtration and increased vascular permeability observed in the early stage of diabetic nephropathy have been proposed to play a significant pathophysiologic role in the eventual development of glomerulosclerosis of dia-betic nephropathy. Some studies have suggested that this glomerular hyperfiltration is mediated by increased nitric oxide(NO) production via the constitutive nitric oxide synthase(cNOS) pathway present in endothelial cells under the high glucose environment. However, the exact role of the inducible NOS(iNOS) pathway present in mesangial cells in the pathogenesis of diabetic neph-ropathy is not clearly established. The present study was carried out to examine whether NO production via the iNOS pathway is mo-dulated in cultured rat mesangial cells exposed to the high glucose environment and underlying mechanism of this modulation. For this purpose, the production of the stable metabolite of NO(nitrite), intracellular cyclic gu-anosine monophosphate(cGMP), iNOS mRNA expression and iNOS protein synthesis were examined under different glucose concentrations. Rat mesangial cells cultured in high glucose concen- tration(30mM D-glucose) increased significantly nitrit#e/ nitrate production and intracellular cGMP levels upon stimulation with lipopolysaccharide(LPS) plus interfer-on-r (IFN-r ) compared with control glucose concen- tration(5.6mM D-glucose). Mesangial iNOS mRNA expression and protein synthesis also increased signifi- cantly in response to high glucose. This enhanced iNOS mRNA expression induced by high glucose concentration was significantly suppressed by protein kinase C(PKC) inhibitor, calphostin C, and the aldose reductase inhibitor, 6-bromo-l, 3-dioxo-1H- benz[d, elisoquinoline-2(3H)-acetic acid. These results indicate that high glucose in combination with stimulation by LPS plus IFN- r enhances NO production from mesangial cells by the iNOS pathway, and that the activation of PKC and the polyol pathway may play a role in this enhancement.