BACKGROUND: Glucose degradation products (GDP) are an important factor that contribute to bioincompatibility of peritoneal dialysis fluids. These substances are generated in the dialysis fluid during heat sterilization. Several approaches have been proposed to reduce the content or toxicity, or both, of GDP present in the dialysis fluid. We examined whether L-2-oxothiazolidine-4-carboxylic acid (OTZ), a precursor for glutathione synthesis, reduces the cytotoxicity of GDP in human peritoneal mesothelial cells. METHODS: Experiments were performed on primary mesothelial cell cultures. Free radical generation in these cells after exposure to acetaldehyde (ACT), glyoxal (GLYO) or methylglyoxal (M-GLYO) was detected with a fluorescent probe. Cell viability measurements were based on release of LDH from cell cytosol, and synthesis of IL-6 and proliferation after exposure to GDP. Effects of individual GDPs and of dialysis fluid free of GDP (GDP-free PDF) or containing GDP (GDP-high PDF) on cell viability were also studied in the presence of OTZ (1 mmol/l). RESULTS: All of the GDPs as well as the autoclaved dialysis fluid caused increased free radical generation. ACT increased LDH release from the cells by 374% (P < 0.001), and this effect was abolished by OTZ. All of the GDPs inhibited cell growth (ACT, 47%, P < 0.01; GLYO, 52%, P < 0.01; M-GLYO, 26%, P < 0.05) and this effect was reversed in presence of OTZ. ACT inhibited Il-6 synthesis in mesothelial cells by 74% P < 0.01 and this effect was prevented by OTZ. GDP-high PDF but not GDP-free PDF reduced synthesis of IL-6 in mesothelial cells by 40% (P < 0.01) an effect that was reversed by OTZ. Mesothelial cell growth was more strongly inhibited by GDP-high PDF (76%, P < 0.01) than by GDP-free PDF (31%, P < 0.05). OTZ improved growth of mesothelial cells in the presence of GDP-high PDF (+150%, P < 0.01) and in presence of GDP-low PDF (+38%, P < 0.05). OTZ prevented the cytotoxic effect of GDP-high PDF on mesothelial cells. CONCLUSIONS: The GDP-induced stimulation of free radicals in mesothelial cells in the present study may provide a possible mechanism of GDP cytotoxicity. Because OTZ reduced the toxic effects of GDP on mesothelial cells, this compound may improve biocompatibility of peritoneal dialysis fluids.