Date of Award:

5-1997

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Mark C. Healey

Committee

Mark C. Healey

Committee

Shiguang Yang

Committee

Stanley D. Allen

Committee

Bill B. Barnett

Committee

Reed P. Warren

Abstract

The human serine protease inhibitor (serpin) alpha-1-antitrypsin (AAT) was studied for potential interaction with components of the protozoan parasite Cryptosporidium parvum. A homogenate prepared from C. parvum oocysts was incubated with purified human AAT, and complexes formed between the serpin and components of the homogenate were detected using an enzyme-linked immunosorbent assay (ELISA). Serpin:parasite infections were effectively blocked by preincubating AAT with a cognate target enzyme, porcine pancreatic elastase, prior to performing the ELISA on the homogenate. Incubation of a mixture of C. parvum oocysts and sporozoites with AAT demonstrated preferential fluorescence labeling of the sporozoite surface membrane by indirect immunofluorescence assay. Localization of serpin complexes on sporozoites was confirmed by immunogold electron microscopy.

AAT was evaluated for in vitro anticryptosporidial activity in a bovine fallopian tube epithelial (BFTE) cell culture system using both oocysts and filter purified sporozoites as inocula. Serial dilutions of AAT were mixed with oocysts (or sporozoites) and used to inoculate BFTE cell monolayers. Inoculted cells were maintained at 37ºC/5% CO2 and collected at 24-,48-,72-, and 96-hr post-inoculation intervals. The addition of AAT and other select protease inhibitors (i.e.,antipain, aprotinin, leupeptin, soybean trypsin inhibitor, and phenylmethylsulfonyl floride) significantly inhibited parasite infection (P <0.01) in a concentration- and time-dependent manner when bleach-decontaminated oocysts were used in the inoculum.

The anticryptosporidial activity of AAT is postulated to be linked to an antagonistic effect on oocyst excystation and, putatively, the forced expenditure of bioenergetic reserves prior to host cell invasion. This postulate was supported by the observations that serpin activity had no statistically significant effect on reducing established in vitro infections (i.e., 24 hr post-inoculation prior to addition of AAT) and did not inhibit infection of BFTE cells when inoculted with sporozoite preparations. The combined application of AAT and the aminoglycoside paromomycin demonstrated a synergistic anticryptosporidial effect on in vitro infection and suggested the basis for a multi-agent therapeutic protocol in preventing cryptosporidosis. These studies collectively demonstrated an inticryptosporidial potential for serine protease inhibitors, in particular for AAT, and suggest an alternative approach to conventional therapeutic strategies.

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