Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 9, 1997
Publication Date: N/A
Interpretive Summary: The stomach worm, Haemonchus contortus is an economically important parasite of grazing animals. The adult parasites are blood feeding and inflict significant pathology on the host. As part of a continuing study of enzymes involved in key processes within parasitic nematodes, the present study focuses on mechanisms involved in utilization of blood proteins by the adult parasite. These mechanism may prove to be useful target for development of novel controls. The ability of adult parasites to uptake and digest a the blood protein, albumin, during culture was determine. The results demonstrate that adult parasites take up and digest labeled albumin. However the parasites also secret an enzyme, a cysteine protease, which plays a significant role in digestion of albumin outside the parasite. The extracorporeal digestion is prevented by pretreatment of culture media with enzyme inhibitors. The results also indicate that another enzyme class, an aspartic protease, may also be involved in digestion of albumin.
To further characterize the digestion of blood proteins by Haemonchus. contortus adults, the uptake and degradation of albumin were investigated. Parasites were cultured in 1.0 ml of media in 24- well plates, and 1 mg/ml fluorescein isothiocyanate (FITC) labeled albumin was added to each well and incubated at 37 C for periods from 0 to 4 hrs. Fluorescence was detected rapidly in parasites after incubation in FITC-albumin. More than 50% of the FITC-albumin taken up by adult H. contortus was degraded as measured by an increase in TCA-soluble fluorescence within the parasite. In the presence of the specific cysteine protease inhibitor E-64, both the uptake and degradation of FITC-albumin within the parasite was reduced by 85%. Coincubation of parasites with E-64 and the aspartic protease inhibitor, pepstatin, significantly reduced the degradation of FITC-albumin suggesting a role for an aspartic protease in the intestinal digestion of albumin. Degradation of FITC-albumin in the media after a 4-hr incubation with H. contortus was blocked completely by cysteine protease inhibitors. The degradation of FITC-albumin by isolated H. contortus intestines was inhibited by 0.1 mM E-64. These results together suggest that there is rapid extracorporeal digestion of FITC- albumin mediated by the secreted cysteine proteases, and this degradation produces relatively high concentrations of low molecular weight FITC-labeled fragments that are rapidly taken up by the parasite.