Reactive oxygen metabolites in piglet cryptosporidiosis

Piglet cryptosporidiosis is characterized by intestinal villous damage and malabsorption, and by reduced NaCl absorption in response to prostaglandins (PGs), which act directly on the epithelium and indirectly through enteric nerves. We hypothesized that phagocyte-derived reactive oxygen metabolite (ROM) production contributed to PG synthesis and altered transport in inflamed ileum. Ileal mucosa from control and infected piglets was analyzed for villous height, PGE2, catalase (an endogenous antioxidant), and malondialdehyde (MDA, a by-product of lipid peroxidation) from d 2-8 after infection. The response of control ileal mucosa to exogenous ROM and infected mucosa to antioxidant treatment was also studied in tissues mounted in Ussing chambers. Increased levels of MDA on d 2 preceded increased PGE2 on d 3-4, which correlated with the acute diarrheal phase; however the most severe villous atrophy (d 8) correlated with the highest levels of catalase and MDA but low levels of PGE2. Control mucosa responded to H2O2 with indomethacin- and tetrodotoxin-sensitive transient increases in short circuit current (Isc), which were accompanied by increased tissue production of 6-keto-PGF1a, the stable metabolite of PGI2; however, no increased PGE2 production was detectable. A stable analog of PGI2, carbacyclin, mimicked the transient Isc response to H2O2; however, several antioxidants failed to alter the abnormal Isc of infected tissue. These results suggest that there is evidence of increased ROM production in cryptosporidial infection and that intestinal PG synthesis and inhibited NaCl absorption may be mediated partially by ROM in this model. Additional, cooperative factors, such as PGE2 production, however, are likely needed to induce the alterations in ion transport seen in this infection.