Parasiticidal effects of peroxynitrite on ovine liver flukes in vitro

Peroxynitrite (ONOO-) is a cytotoxic anion, produced by interaction between nitric oxide and superoxide in vivo in some inflammatory cells. This study investigated its effects on Fasciola hepatica and Dicrocoelium dendriticum isolated from ovine livers and kept in bile at room temperature. Peroxynit rite was synthesized using a quenched flow reactor and assayed spectrophoto metrically. It was applied at different concentrations (10(-3.5) to 10(-2.3 ) M) to the flukes kept in bile. The viability of the peroxynitrite-treated flukes was compared with a control group (n = 5-7 per group). Control F. h epatica and D. dendriticum lived for 226 +/- 11 and 208 +/- 14 min; respect ively. Life times were decreased by peroxynitrite at all concentrations use d (P < 0.001). At the highest concentration of peroxynitrite, F. hepatica a nd D, dendriticum lived only for 6.1 +/- 0.4 and 4.1 +/- 4.1 +/- 0.2 min, r espectively. Correlation between peroxynitrite concentration and parasite v iability was significant in the case of F. hepatica (r = -0.842; P = 0.0035 ). A single application of peroxynitrite can decrease the life span of ovin e liver flukes. A failure in the activation of hepatic macrophages in infec ted animals may lead to a decreased production of free radicals and, thus, peroxynitrite. Such a failure is likely to deprive the body of a defence to ol against multicellular parasites.