Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 1996
Publication Date: N/A
Interpretive Summary: The stomach worm Haemonchus contortus and related intestinal parasites of sheep and cattle cause significant economic losses through morbidity, mortality and cost of treatment. Current controls are restricted to the use of broad spectrum anthelmintics which may lead to drug resistance and also poses a risk of undesirable drug residues and environmental contamination. One strategy for the development of novel controls relies on an enhanced knowledge of enzymes that are critical to the parasites survival within the host. The present study develops a method to measure hemoglobin uptake by the parasite in vivo and examines the effect of specific enzyme inhibitors on the parasites ability to process hemoglobin. The results demonstrate the enzyme may not be involved in hemoglobin digestion but may play a key role in extracorporeal nutrient acquisition that can be exploited in development of novel controls.
Adult Haemonchus contortus, a blood feeding parasite, secrete and contain within their gut a cysteine protease which may play a role in digestion of blood proteins. To test this hypothesis, the incorporation of 3H-leucine- labeled hemoglobin (HGB) into parasite proteins was investigated. A cell lysate preparation containing 3H-leucine-labeled HBG was obtained from reticulocytes metabolically labeled, in vitro, with 3H-leucine and used as a substrate for H. contortus feeding. The protein synthesis inhibitor puromycin (200 g/ml), caused a 72% reduction in the incorporation of radioactivity suggesting the incorporation of hemoglobin by the parasite was dependent on protein synthesis. The specific cysteine protease inhibitor Z-phe-ala-FMK (PAF) had no effect on HBG incorporation at 0.1 mM. PAF (0.1mM) reduced by 50% the catabolism of HBG in the culture media suggesting an extracorporeal action by the enzyme. PAF (1.0 mM) caused a 78% reduction in HBG incorporation but also significantly decreased parasite viability indicating that the inhibition of HBG incorporation was not due to specific enzyme inhibition. The serine protease inhibitor 4- (2-aminoethyl)benzenesoulfonyl fluoride (AEBSF) caused a 40% reduction in HBG incorporation while the aspartic protease inhibitor pepstatin was without effect. The parasites also incorporated 3H-leucine from metabolically labeled erythrocytes. The incorporation was inhibited by 1.0 mM PAF and AEBSF in a manner similar to that for incorporation of isolated hemoglobin. Extracts or excretory/secretory products from adult parasites lacked hemolytic activity indicating an alternate method may be used to disrupt cells taken up by parasite during blood feeding. The results of this study do not support the hypothesis that the cysteine