A new experimental model of localized candidosis for the study of antifungal chemotherapy

Experimental murine mycotic mastitis: a sensitive and lenient model for studies of antifungal chemotherapy

The murine model of mycotic mastitis was used to study the efficacy of amphotericin B (AmB). Twenty-four BALB/cJ mice at the fifth day of lactation were anesthetized and inoculated through the teat canal (two glands) with 50 microl suspension containing 5.0 x 10(7) cfu ml(-1) Candida albicans blastospores. Mice were randomly divided into two groups: untreated controls and AmB treated. Animals were euthanized 3 and 6 days after infection and treatment (4 mg kg(-1) per day intraperitoneally). The fungal burden of the mammary gland was determined by quantitative cultures. The number of C. albicans cells recovered from mammary gland homogenates were significantly lower in the AmB treated animals (both 3 and 6 days post-infection) than in the untreated controls (P<0.007 and P<0.003, respectively). The mammary glands of all untreated control animals showed marked neutrophilic infiltration, severe necrosis, and presence of blastospores, hyphae and pseudohyphae. In contrast, 10 of 12 animals treated with AmB showed only a mild neutrophilic infiltration which was restricted to alveoli and excretory ducts. All extra-mammary organs were free of infection in both groups. The results demonstrate that the murine mycotic mastitis model is suitable for investigations of new antifungal compounds. In addition, this model is more lenient than the systemic candidiasis models.

Protective effect of human granulocyte colony stimulating factor (hG-CSF) on Candida infections in normal and immunosuppressed mice

Prophylactic treatment with human granulocyte colony stimulating factor (hG-CSF) affords significant protection against systemic infections caused by C. albicans in cyclophosphamide-treated but not in cortisone-treated mice. Localized candidosis in neutropenic mice does not respond to hG-CSF. Our data show that granulocytes play an important role in the immune defence against deep mycoses, but not against local infections. From our data it is reasonable to assume that prophylactic treatment with hG-CSF may augment the resistance of immunosuppressed patients to deep Candida infection, but it would be of little help against oral candidosis of HIV patients.

Antifungal combination therapy in localized candidosis

A mouse model of localized candidosis in air-filled subcutaneous cysts imitating thrush has been developed. We have now tested various antifungal combinations in this animal model. Flucytosine (5-FC) + amphotericin B (Amph B) showed the highest efficacy, a clear additive or even synergistic effect was seen. The combination of 5-FC + imidazole or triazole derivative was less efficacious, an additive effect was rare. The combination of 5-FC + Amph B was also tested against Candida albicans strains showing various degrees of 5-FC-resistance. A significant reduction in 5-FC-resistant mutants was seen after the treatment with the combination.

Biochemical mode of action and enantiomeric selectivity of SDZ 89-485, a new triazole antimycotic

SDZ 89-485, a new triazole antimycotic agent, potently inhibited ergosterol biosynthesis in cells of Candida. Trichophyton and Aspergillus. Biosynthesis was measured both by incorporation of radiolabelled acetate and also by methylation of the sterol side chain. Inhibition was accompanied by accumulation of radiolabel in 4,4-dimethylsterols and to a lesser extent in the 4-methylsterols, consistent with inhibition of lanosterol 14-demethylation. No other steps were affected. Ergosterol biosynthesis in the mycelial growth form of Candida albicans was about twice as sensitive to the drug as that in the yeast form. Inhibition by SDZ 89-485 was qualitatively and quantitatively similar to that shown by other systemically active azoles (ketoconazole, itraconazole, ICI 195,739) in Candida cells and cell-free preparations. Rat liver cell-free cholesterol biosynthesis was much less sensitive to inhibition by SDZ 89-485 than was the equivalent Candida system (selectivity ratio of about 300). In contrast to miconazole and econazole, SDZ 89-485 had no uncoupling effect on respiration in C. albicans cells. The structure of SDZ 89-485 contains an asymmetric centre, the drug being the (-)(R) enantiomer. The (+)(S) enantiomer 89-486, which is antifungally much less effective, was at least 10-fold less active than SDZ 89-485 as an ergosterol biosynthesis inhibitor in all test systems employed. The difference between the two enantiomers appears to reside in stereo-selectivity at the level of interaction with the demethylase enzyme.

Preclinical antimycotic activity of SDZ 89-485: a new orally and topically effective triazole

SDZ 89-485 is a new orally and topically active triazole antifungal with efficacy superior to reference compounds in most animal infection models used for preclinical comparison of antifungals. The compound inhibits mycelial transformation of Candida albicans in vitro at MIC50 concentrations of 0.006 and 0.00019 mg l-1 in MEM and NYP medium, respectively. In rodent models of vaginal candidosis SDZ 89-485 was significantly more active than reference compounds after various oral or topical treatment regimens, with ED50 values ranging from 0.09 to 0.79 mg kg-1 and 0.01% active ingredient, respectively. When administered orally, the efficacy of SDZ 89-485 was superior to, or as good as that of the reference compounds in several murine models of systemic candidosis, sporotrichosis and histoplasmosis. In murine aspergillosis, using the kidney as the target organ. SDZ 89-485 was as active as itraconazole. Guinea pig trichophytosis was more responsive to oral fluconazole and itraconazole than to oral SDZ 89-485.

An animal model for oropharyngeal, esophageal and gastric candidosis

Conventional mice inoculated with Candida albicans by the oral-intragastric route as infants (6-day-old) have previously been shown to develop gastrointestinal (GI) candidosis which persists for at least 30-60 days post-challenge without the use of compromising procedures. Histological preparations of the stomachs of these animals reveal hyphae which have crossed the mucin barrier and are associated with the stratified squamous epithelium of the gastric mucosa primarily in the region of the cardial-atrium fold. Host inflammatory cells are frequently observed adjacent to these filaments and yeast cells. In this study, groups of neonates were challenged oral-intragastrically with either C. albicans strain CA30, or strain CA87. The two strains showed marked differences in the numbers of cells associated with tissue of the tongue, esophagus and stomach of non-immunocompromised mice at 20 days post-inoculation. After immunocompromising treatment by intraperitoneal administration of cyclosphosphamide and cortisone acetate, both groups of mice showed extensive colonization and tissue invasion of the tongue, proximal and distal portions of the esophagus, and cardial-atrium fold of the stomach. C. albicans-containing abscesses were occasionally observed on the tongue of these animals. Histological preparations of the cardiac antrum, located at the junction of esophagus and stomach, frequently revealed concentrations of hyphae and yeast cells associated with the stratified squamous epithelium. We suggest that these non-immunocompromised and immunocompromised mice with persistent C. albicans infections of oropharyngeal, esophageal and gastric tissue, initiated by oral-intragastric challenge at infancy, simulates conditions in different groups of chronically infected humans, and serves as a useful model for testing the efficacy of anti-Candida drugs in clearance of candidosis from the alimentary canal.