L-2-oxothiazolidine-4-carboxylate: an agent that modulates lipopolysaccharide-induced peritonitis in rats

L-2-Oxothiazolidine-4-carboxylate (OTZ), a cysteine precursor, is a substrate for intracellular glutathione synthesis. As shown previously, OTZ prevents free-radical induced cellular damage during in vitro simulation of peritoneal dialysis. In the present study, we examined the effect of adding OTZ to peritoneal dialysis solution on peritoneal function and structure during lipopolysaccharide (LPS)-induced peritonitis in rats. In addition, we studied the effects of pretreatment with OTZ (given orally) on the effects of LPS-induced peritonitis in rats.

Peritonitis was induced in rats by adding LPS (5 microg/mL) to the dialysis fluid. For acute experiments, rats were exposed to a single infusion of dialysis solution containing LPS or to LPS plus 5 mmol/L OTZ; peritoneal cell counts and permeability were determined after 4 hours. Alternatively, rats were pretreated with OTZ added to the drinking water (0.1%) for 10 days prior to infusion of LPS. For chronic experiments, peritoneal dialysis was performed over a 3-week period in rats with implanted peritoneal catheters. On days 8, 9, and 10 of the experiment, the rats were infused intraperitoneally with solution containing LPS (5 micro/mL), or LPS plus 5 mmol/L OTZ, to induce acute peritonitis. At the end of dialysis (10 days after the episodes of peritonitis), peritoneal function was assessed using a peritoneal equilibration test (PET), and peritoneal biopsies were taken to assess effects on peritoneal morphology.

In the acute experiments, exposure to LPS led to increased peritoneal cell counts (+61% vs control, p < 0.05) and enhanced permeability of the peritoneum, leading to a loss in ultrafiltration (-63%, p < 0.0005). The glutathione concentration in peritoneal leukocytes also decreased during acute peritonitis (-31%, p < 0.05). During LPS-induced peritonitis, OTZ prevented the increase in dialysate cell count and the decrease in cellular glutathione content. Simultaneous administration of OTZ did not prevent the increased peritoneal permeability induced by LPS. However, in rats pretreated with OTZ, LPS-induced permeability to protein was significantly lower than in the nontreated animals (0.049 +/- 0.011 vs 0.087 +/- 0.034, p < 0.05). In the chronic experiments, LPS-induced peritonitis did not lead to any functional differences in peritoneal transport at the end of 3 weeks of dialysis. However, LPS-induced peritonitis led to increased thickness of the peritoneum and neovascularization within peritoneal interstitium compared to peritonitis-free animals. In contrast to the LPS-treated animals, the peritoneum of the rats exposed to LPS in the presence of OTZ was of a thickness similar to that in the control rats.

Supplementation of dialysis fluid with OTZ prevented changes in cellular glutathione levels and dialysate cell counts during acute peritonitis in rats. During chronic dialysis in rats exposed to intermittent peritonitis episodes, OTZ prevented increased thickening and neovascularization of the peritoneum. Our results suggest this may help to protect the peritoneal membrane during episodes of peritonitis.