Reactive nitrogen and oxygen species ameliorate experimental cryptosporidiosis in the neonatal BALB/c mouse model

Four-day-old BALB/c mice were infected by the oral administration of 50,000 Cryptosporidium parvum oocysts, and the resulting infection was scored histologically and by counting colonic oocysts. Infection occurred in the ileum and proximal colon (but not duodenum and jejunum), peaked on days 14 to 18, and was cleared between days 24 and 30. Nitric oxide (NO) appeared to play a protective role in this model as evidenced by the facts that plasma nitrite and nitrate levels increased during the period of peak parasitosis; immunohistochemically detected inducible nitric oxide synthase (iNOS) was increased in the ileum and colon enterocytes of infected animals; the NOS inhibitor L-N-iminoethyl lysine or N-nitro-L-arginine methyl ester (L-NAME) decreased the elevated plasma nitrite and nitrate levels while exacerbating the infection and increasing oocyst shedding; administration of a NO donor, S-nitroso-N-penicillamine, reduced oocyst and infection scores; and neonatal iNOS knockout mice exhibited a slightly longer infection than control animals. The oral administration of oocysts to L-NAME-treated BALB/c mice, but not control animals, between 24 and 40 days old resulted in the fecal excretion of oocysts 1 week later. Administration of the antioxidant ascorbic acid also exacerbated the C. parvum infection, suggesting a protective role for reactive nitrogen and/or reactive oxygen compounds, while administration of the superoxide scavenger superoxide dismutase exacerbated the infection. Taken together these data suggest that both reactive nitrogen and reactive oxygen species play protective roles in experimental cryptosporidiosis.