cDNA cloning and expression patterns of a peroxiredoxin, a catalase and a glutathione peroxidase from Haemonchus contortus
The toxicity of activated oxygen species towards adult Haemonchus contortus nematodes was examined in in vitro assays using ingestion of [3H]inulin to assess nematode viability. Both glucose/glucose oxidase (generation of hydrogen peroxide) and xanthine/xanthine oxidase (generation of superoxide anion) systems showed concentration-dependent toxicity to the nematodes. Both adult and larval Haemonchus contortus enzyme preparations showed significant catalase activities. Adult nematodes exposed to aminotriazole for 24 h showed catalase activities reduced to less than 20% of controls. Aminotriazole-treated nematodes exposed to a glucose/glucose oxidase system were significantly more susceptible to the toxic effects of the oxidant-generating system than controls (no aminotriazole pre-treatment). The concentration of glucose oxidase required to inhibit feeding by 50% was decreased 33-fold in aminotriazole-treated nematodes compared with controls. The effect of aminotriazole pre-treatment implicates hydrogen peroxide as a significant toxic agent in the glucose/glucose oxidase system. It is apparent that inhibition of Haemonchus contortus catalase increases the susceptibility of the parasite to the toxic effects of hydrogen peroxide, demonstrating a protective role for this enzyme. This suggests that catalase has the potential to play a significant role in the defence of this parasite against hydrogen peroxide produced as part of the respiratory burst of activated phagocytes within the host during its response to nematode infection.