SHIGELLA-DYSENTERIAE TYPE-1 TOXIN-INDUCED LIPID-PEROXIDATION IN ENTEROCYTES ISOLATED FROM RABBIT ILEUM

To evaluate the role of reactive oxygen species (ROS) in Shigella dyse nteriae I toxin (STx) mediated intestinal infection, the ligated rabbi t small intestinal loops were injected with STx. The enterocytes isola ted from STx treated rabbit ileal loops had a significantly higher lev el of lipid peroxidation as compared to enterocytes isolated from cont rol rabbit ileum. To study the role of second messengers in STx mediat ed intestinal damage, the in vivo and in vitro effects of modulators o f lipid peroxidation of enterocytes were used. The presence of Ca2+-io nophore A23187 enhanced the extent of lipid peroxidation in enterocyte s isolated from the control and STx treated rabbit ileum. However, 1-v erapamil only marginally decreased the lipid peroxidation level of ent erocytes isolated from STx treated rabbit ileum. The in vitro effect o f modulators was in agreement with in vivo studies. Dantrolene signifi cantly decreased the extent of lipid peroxidation of enterocytes isola ted from STx treated rabbit ileum. PMA significantly increased the lip id peroxidation level of enterocytes isolated from control ileum. Howe ver, PMA could not further enhance the lipid peroxidation level of ent erocytes isolated from STx treated rabbit ileum. The presence of H-7 s ignificantly decreased the extent of lipid peroxidation of enterocytes isolated from STx treated rabbit ileum. In vitro effect of PMA and H- 7 was in agreement with that of in vivo findings. The role of arachido nic acid metabolites, prostaglandins (PGs), in mediating STx induced l ipid peroxidation was also studied. The presence of indomethacin (a PG synthesis inhibitor) significantly decreased the lipid peroxidation i nduced by STx. These findings suggest that lipid peroxidation induced by STx is mediated through cytosolic calcium. The increase in (Ca2+)(i ) leads to activation of PKC. A significant decrease in the enterocyte levels of antioxidant enzymes superoxide dismutase, catalase and redu ced glutathione in STx treated rabbit ileum as compared to control was seen. A significant decrease in vitamin E levels was also observed. T his suggests that there is decreased endogenous intestinal protection against ROS in STx mediated intestinal infection which could contribut e to enterocyte membrane damage that ultimately leads to changes in me mbrane permeability and thus to fluid secretion.