Putative anticryptosporidial agents tested with an immunodeficient mouse model

Abstract

Lasalocid, sinefungin, and dehydroepiandrosterone were tested for anticryptosporidial activity with an immunodeficient mouse model at doses that have been reported effective when tested with immunosuppressed rodent models. Small but significant reductions in oocyst excretion were only observed under some conditions with lasalocid and dehydroepiandrosterone, but sinefungin had no elfect.Cryptosporidiosis is an enteric protozoan parasitic disease of animals and humans that is self-limiting in the immunocompetent host, but it may cause persistent diarrhea and severe malabsorption in the immunodeficient host (5, 17). Chronic cryptosporidiosis makes a contribution to the morbidity and mortality of a significant number of AIDS patients (10), with the result that finding effective anticryptosporidial chemotherapeutic agents has become a major priority. In spite of a number of promising preliminary clinical reports (1,12), no effective agent has been found (17).Several immunodeficient and immunosuppressed animal models have been employed to study the pathophysiology of the Cryptosporidium infection and to evaluate the efficacies of potential antiparasitic agents (3, 4, 8, 9, 11, 13-16, 18, 19). Steroid-immunosuppressed rats and mice have been extensively used in drug evaluation studies, and several agents have been found to be effective with such animal models (3,4,8,9,(13)(14)(15)(16). Such studies have been undertaken with short-term infections (3 weeks or less), with the agents often being administered a few hours before or after the inoculation of infecting oocysts or prior to the time of maximum oocyst excretion. The present study compares the anticryptosporidial effects of such agents by using a chronic immunodeficient mouse model rather than an immunosuppressed rodent model.Immunodeficient mouse model. Young adult intact or splenectomized male athymic nude mice were purchased from Harlan Sprague-Dawley Inc. (Indianapolis, Ind.). Cryptosporidium parvum, originally of calf origin, has been carried in a colony of these animals for over 2 years. Oocysts were isolated from the feces of infected mice (2) and administered per os. Oocyst excretion was monitored by collecting five fresh fecal pellets, macerating them in 2 ml of neutral formalin, and counting the number of oocysts visualized in a 10-,ul sample of this homogenate by a commercially available immunofluorescent assay (Meridian Diagnostics Inc., Cincinnati, Ohio). The following oocyst excretion score was developed: based on the oocyst counts of the 10-,ul samples, 0, no oocysts; 1, <10 oocysts; 2, 11 to 50 oocysts; 3, 51 to 100 oocysts; 4, >100 oocysts.When a histological study was performed with chronically (>3 months) infected nude mice, linear relationships were found between the oocyst excretion score (y) and the percentage of infected ileal villus cells (x1), described by the equation 755-7318. y = 0.76 + 0.092x1 (r = 0.888), and between the oocyst excretion score and the percentage of infected ileal crypt cells (x2), described by the equation y = 0.06...

Administration of lasalocid‐NA is preventive against cryptosporidiosis of newborn calves

“…These data suggested that, during the treatment period, lasalocid is preventive against cryptosporidiosis. The finding of a preventive effect of lasalocid supports a similar report on the administration of 120 mg/kg lasalocid to nude mice (Leitch and He 1994). Lasalocid was not protective after the dosing period; however, this finding that lasalocid prevents oocyst excretion in calves was found to be important because diarrhoea in newborn calves can lead to a serious loss of growth.…”

Reactive Nitrogen and Oxygen Species Ameliorate Experimental Cryptosporidiosis in the Neonatal BALB/c Mouse Model

“…At 4 days of age all animals in a litter were either administered 50,000 Cryptosporidium parvum oocysts in 50 l of water or 50 l of water by stomach tube. The C. parvum isolate was originally of bovine origin and has been maintained in nude mice for approximately 5 years (29). At appropriate times, pups were killed by cervical dislocation and weaned animals were killed with an intraperitoneal injection of pentobarbital (100 mg/kg of body weight).…”

“…C. parvum oocysts in 10 l of either colonic content or fecal homogenate were visualized by a commercial immunofluorescent assay (Meridian Diagnostics, Cincinnati, Ohio) and counted. The oocyst score was derived from this count (29,30) as follows: 1 indicated 1 to 9 oocysts, 2 indicated 10 to 49 oocysts, 3 indicated 50 to 99 oocysts, and 4 indicated Ն100 oocysts.…”

“…The majority of experimental cryptosporidiosis studies have used rodent models. Three such models are a steriod-immunosuppressed-mouse or -rat model (40,59); an immunodeficient-rodent model, most commonly the athymic nude mouse (22,29,34,35) or SCID mouse (28,34,35); and a neonatalmouse model (11,21,38,54). Differences have been reported among these models in terms of the responses of the Cryptosporidium infection to chemotherapeutic agents (29) and to manipulation of putative protective cytokines or mediators such as nitric oxide (NO) (28,30).…”

Assessment of drugs againstCryptosporidium parvumusing a simple in vitro screening method

“…Determination of an accurate MLC is particularly important when assessing anticryptosporidial agents due to the fact that C. parvum has proved to be refractory to treatment both in vitro and in vivo. The use of MLC rather than IC 50 as a more appropriate tool for assessing anticryptosporidial compounds is exemplified when reviewing in vivo drug trials which showed significant reductions in oocyst numbers excreted from treated animals yet oocyst numbers increased to those of controls when treatment ceased [9–12].…”