Extension of the 4-week safety study for detecting immune system impairment appears not necessary: example of cyclosporin A in rats.

A 4-week study was conducted to shed light on the question of whether compounds impairing immune homeostasis may escape the standard safety testing. Wistar rats were orally treated with cyclosporin A at dosages of 0 (control: olive oil), 1, 5 or 25 mg/kg/day. Ten rats/sex/group (study segment 1) were not immunized while six other rats/sex/group (study segment 2) were immunized 4 days before killing to perform a plaque forming cell (PFC) assay. All rats were subjected to routine safety evaluations (OECD guideline 407) and determination of IgM and IgG serum levels. Other immune parameters were evaluated using cells from spleen and mesenteric lymph nodes (segment 1). Effects on safety parameters were similar for immunized and non-immunized rats. A slight decrease of body weight gain (males, 25 mg/kg) accompanied slight clinical chemical and histomorphologic evidence of renal tubulotoxicity. Changes in safety parameters indicative of immune system alterations were: increased thymic corticomedullary ratio (> or = 5 mg/kg) and 25 mg/kg) minimal lymphopenia, low thymus weight, thymic cortical lymphocytolysis and low lymphoid cellularity of spleen and lymph nodes. They were associated with (males at > or = 1 mg/kg) dose-related decreases of T-cell receptor+ and CD4+ cells and increases of CD8+ cells, and decreased PFC (> or = 5 mg/kg) and lymphoproliferative responses to mitogens and alloantigens (25 mg/kg). There were no changes in natural killer activity. The conventional assay identified the drug as a potential immunomodulator. Specific immune assays (phenotyping, PFC) improved the threshold of detection. These results did not support the incorporation of specific immune tests in the standard 4-week study protocol.

Functional, biochemical, and morphological hepatobiliary effects in rats chronically exposed to a steroidal antiandrogen.

Yellow-brown deposits in intrahepatic bile ducts and portal macrophages were observed for male, but not female, Sprague- Dawley rats fed zanoterone, a steroidal antiandrogen, for >=3 months. The lesion did not affect biliary canaliculi and was associated with changes of biliary epithelium, portal chronic inflammation, and bile duct proliferation. Deposit formation was assumed to be related to a gender-related anomaly in bile composition and/or flow. Therefore, the pathogenesis of the lesion was investigated in male, female, and orchiectomized rat. Hepatobiliary structure and function were evaluated after 3 months of treatment and 3 months of reversibility. Drug biliary disposition was evaluated at 3 months. Sulfobromophthalein clearance, bile flow, and plasma concentration and biliary excretion rate of cholesterol were increased at the end of the treatment phase without significant sex-related differences. These effects are consistent with the hepatic enzyme induction potential of the drug, were accompanied by perivenous hepatocellular hypertrophy and increased liver weights, and were no longer observed at the end of the recovery phase. Histomorphologic evidence of cholestasis was observed for most intact and orchiectomized males, the lesion being slightly less pronounced for the latter. Deposits were present at the end of the recovery phase, but were confined to macrophages in all but one case. The lesion differed from a protoporphyria, or precipitates of bile pigments, cholesterol, or proteins. The drug was extensively metabolized with major gender-related differences. Glucuronides of a 16- hydroxy- and another unidentified metabolite were the major metabolites found in bile of males, while a 15-hydroxy-glucuronide was the major metabolite for females. The concentration and biliary excretion of the 16-hydroxy- glucuronide markedly increased after chronic exposure. A possible explanation for pigment deposition in males is that the drug is converted to a metabolite(s) which is excreted at a rate beyond the solubilization potential of bile and, therefore, precipitates in bile ducts.