Cryptosporidium parvum metalloaminopeptidase inhibitors prevent in vitro excystation

Abstract

Cryptosporidium parvum arginine aminopeptidase (RAP) was studied during in vitro excystation. Specific RAP inhibitors were identified by using C. parvum extracts. Amastatin, a series of α-aminoboronic acids, and the chelating agents EDTA and 1.10-phenanthrolene, but not endoproteinase inhibitors, blocked enzymatic activity. RAP inhibitors found to be effective in soluble enzymatic assays were then studied for their effect on in vitro excystation. 1,10-Phenanthrolene, amastatin, and 11-boronorleucine (pinacol) inhibited excystation by 84, 57, and 61%, respectively, compared with solvent-treated control oocysts. Sporozoites remained viable within the oocyst an determined by propidium iodide and fluorescein diacetate dye uptake, suggesting that α-aminoboronic acids were not directly lethal to the parasite.