Role of nitric oxide and superoxide in Giardia lamblia killing

Abstract

Giardia lamblia trophozoites were incubated for 2 h with activated murine macrophages, nitric oxide (NO) donors or a superoxide anion generator (20 mU/ml xanthine oxidase plus 1 mM xanthine). Activated macrophages were cytotoxic to Giardia trophozoites (~60% dead trophozoites). This effect was inhibited (>90%) by an NO synthase inhibitor (200 µM) and unaffected by superoxide dismutase (SOD, 300 U/ml). Giardia trophozoites were killed by the NO donors, S-nitroso-acetyl-penicillamine (SNAP) and sodium nitroprusside (SNP) in a dose-dependent manner (LD 50 300 and 50 µM, respectively). A dual NO-superoxide anion donor, 3-morpholino-sydnonimine hydrochloride (SIN-1), did not have a killing effect in concentrations up to 1 mM. However, when SOD (300 U/ml) was added simultaneously with SIN-1 to Giardia, a significant trophozoite-killing effect was observed (~35% dead trophozoites at 1 mM). The mixture of SNAP or SNP with superoxide anion, which yields peroxynitrite, abolished the trophozoite killing induced by NO donors. Authentic peroxynitrite only killed trophozoites at very high concentrations (3 mM). These results indicate that NO accounts for Giardia trophozoite killing and this effect is not mediated by peroxynitrite.

Nitric Oxide Production by Human Intestinal Epithelial Cells and Competition for Arginine as Potential Determinants of Host Defense Against the Lumen-Dwelling Pathogen Giardia lamblia

“…We found NO to be cytostatic, but not cytotoxic, for G. lamblia trophozoites, which is in contrast to a recent report that NO donors appeared to kill trophozoites in vitro (45). In that study the effects of NO donors were assessed in a minimal medium (buffered salt solution), which may have exaggerated the results, because such media do not support prolonged viability and growth of trophozoites even in the absence of NO donors.…”

The Reduction of Fusobacterium nucleatum in Mice Is Irrelevant to the Nitric Oxide Induced by iNOS

“…More recent studies have focused on the role of nitrogen radicals as the primary macrophage microbicidal mediator. Using a variety of experimental approaches, NO and its congeners have been shown to kill intracellular and extracellular pathogens as well as both gram-negative and -positive bacteria (1,3,5,12). In the present study, we investigated whether the NO derived from iNOS in PEC was able to kill Fn in vivo.…”

“…More recent studies have focused on the role of RNS as the primary macrophage microbicidal mediator. The killing of Leishmania major (1), Giardia lamblis (12) and Cryptococcus neoformans (34) by NO were reported. All of these organisms are susceptible to NO; however, the addition of superoxide to NO to yield peroxynitrite lowers the NO concentration and reduces the toxicity against these organisms.…”

Untitled

“…Nitric oxide formation has been encountered in many parasitic infections including Giardia [30,31]. It is considered as only part of an immunopathological series against infection [32].…”