Effect of dialysate composition on the apoptosis and proliferation of human peritoneal mesothelial cells and protein expression of Fas and c-Myc.

To investigate the effect of dialysate composition on apoptosis and proliferation of human peritoneal mesothelial cells (HPMCs) in vitro, HPMCs were cultured from human omental tissue. The cells were exposed for three days to culture medium containing: (1) 3.86% glucose, (2) 1.36% glucose, (3) 1.75 mmol/L Ca++, (4) 1.25 mmol/L Ca++, or (5) no additions (control). Apoptosis and proliferative cell nuclear antigen (PCNA) were measured by terminal deoxynucleotidyl transferase (TdT)-mediated in situ end-labelling and immunohistochemistry. Protein expression of Fas and of c-Myc were measured by flow cytometry. Apoptotic cells were significantly increased in the high glucose group compared to control (137 +/- 47 cells per field unit vs 63 +/- 30 cells per field unit, p < 0.01), but did not vary in the low glucose and low calcium groups versus control (76 +/- 25 cells per field unit and 77 +/- 31 cells per field unit, respectively, vs 63 +/- 30 cells per field unit, p > 0.05). Cells with positive expression of PCNA were increased in the high calcium group versus control (366 +/- 101 cells per field unit vs 186 +/- 76 cells per field unit, p < 0.01). However, the expression of PCNA was significantly more inhibited in the high glucose group than in the control group (158 +/- 52 cells per field unit vs 186 +/- 76 cells per field unit, p < 0.05). Expression of Fas was stimulated by high glucose (41% +/- 16% vs 25% +/- 8% in the control group, p < 0.05). High glucose and high calcium also up-regulated the expression of c-Myc, but only the high glucose group showed significant difference from control (39% +/- 10% vs 24% +/- 8%, p < 0.05). Our data suggest that: (1) Peritoneal dialysate could induce apoptosis of HPMCs in vitro, the degree of apoptosis depending on concentration of glucose. (2) High calcium stimulates PCNA expression by HPMCs and high glucose inhibits expression of PCNA. (3) Genes associated with apoptosis (Fas, c-Myc) might play an important role in triggering apoptosis of HPMCs.