Prnp knockout mice disrupted PrPC-related genes have played an essential role to elucidate the relationship between PrPC, a normal host gene product, and PrPSc, a protease-resistant, infectious PrP; Prnp knockout mice developed by Büeler et al. (1992) were completely protected against scrapie disease when challenged with mouse prions. Furthere, varying expression levels in PrPC were revisited along with a varying susceptibility of mouse prions, when mouse Prnp genes were introduced into Prnpo/o mice. How these murine models for human prion-related disease would contribute to the presently ongoing TSE research?
5-Fluorouracil (5-FU) is a cytostatic anti-tumor drug which is known to have immunosuppressive activities. To assess the immunotoxic effects of 5-FU on fetal thymocyte populations and immune functions after birth, pregnant C57BL/6 mice were orally administered vehicle or 17 mg/kg/day of 5-FU during gestational days (GD) from 6 to 14. The fetal thymocyte populations were analyzed with flow cytometry (CD4/CD8 double staining), and immune functions (a mixed lymphocyte reaction, in vitro cytotoxic T-cell response, in vitro antibody-forming response) after birth were measured. Fetal thymus weight and thymocyte numbers were decreased by 5-FU administration. The decrease of the thymocytes was due mainly to the decrease of small CD4CD8 double positive (DP) thymocytes. The thymocyte numbers and populations recovered to the normal level 1 week after birth. The mixed lymphocyte response at the 6th week after birth tended to be slightly lower than the control levels, but the cytotoxic T-cell response and the antibody-forming response were the same as the control levels. These results suggest that immune functions might recover after birth, although maternal administration of 5-FU has a suppressive effect on fetal thymocyte maturation.
In the drug discovery process, effects to the human spermatogenesis must be fully evaluated before the first human trial. To estimate testicular toxicity, histopathological evaluation has been recommended in addition to the traditional mating procedure. However, it is laborious and time-consuming. Flow cytometric analysis (FCM) has also been applied to estimate testicular toxicity because of its speed, simplicity, and the objectivity of the data. Using cyclophosphamide (CP)- and ethinylestradiol (EE)-treated rat testis, we attempted to validate our dual-parameter, DNA ploidy and cell-size FCM, in a high-throughput toxicity study. Our results showed that CP damaged some spermatogonia and some early meiotic spermatocytes and EE caused severe decrease of spermatogenic cells except for spermatogonia as well as marked decrease of somatic cells, most probably Leydig cells. This is the first report discriminating between the changes of spermatogonia and that of somatic cells with FCM analysis. These results demonstrate that this method is a very useful and powerful tool to assess testicular toxicity, especially in high-throughput toxicological studies.
Ethanol extracts of seeds of Psoralea corylifolia are proposed as food additives for processed food preservation. An extract was administered by admixing into diet at concentrations of 0, 0.375, 0.75, 1.5 or 3.0% to 10 male and 10 female F344 rats each for 90 days to evaluate its toxicity. Body weight gain, food consumption and food conversion efficiency (body weight gain per food consumption) were lower in the extract-treated animals, except for the 0.375% males, as compared to the control animals. Absolute and/or relative testes weights in the 1.5 and 3.0% groups and those of ovaries in the 3.0% group were significantly (p<0.01) lower than in the control group. On histopathological examination, seminiferous tubular atrophy and Leydig cell atrophy in the testes, and epithelial cell atrophy in the seminal vesicles and prostate were observed in the 1.5 and 3.0% males. Decrease in the number of corpora lutea associated with frequent necrotic follicles in the ovaries in the 1.5 and 3.0% females and less frequent endometrial glands in the uterus in the 3.0% females were also detected. These results might suggest disruption of the hypothalamus-pituitary-gonadal axis in Psoralea corylifolia-treated rats as possible mechanisms underlying this gonadal toxicity.
The water-soluble azole, 4-[1-[(3-methylaminoacetoxymethyl-pyridin-2-yl)-methyl-carbamoyloxy]-ethyl]-1-[(2R,3R)-3-[4-(4-cyano-phenyl)-thiazol-2-yl]-2-(2,5-difluoro-phenyl)-2-hydroxy-butyl]-1H-[1,2,4]triazol-4-ium chloride hydrochloride (hereinafter referred to as WSA), is a new water-soluble triazole anti-fungal compound. WSA is rapidly converted into its active metabolite after administration by either the intravenous or oral route. The clinical effects of WSA are expected to be consistent whether it is administered by injection (intravenous) or orally. To evaluate and compare the toxicities of WSA via oral and intravenous administration, repeated toxicity studies of WSA were conducted in cynomolgus monkeys (oral dosage levels: 0, 10, 30 and 90 mg/kg/day over a 4-week period; intravenous infusion dosage levels: 0, 10, 30 and 60 mg/kg/day over a 2-week period). In addition, a 2-week oral toxicity study of the active metabolite of WSA was conducted with similar dosages (0, 10, 30 and 90 mg/kg/day). From the results obtained from the evaluation, hepatotoxicity (liver) and endocrinological toxicity (adrenals) were the major toxicities, a finding which is comparable to other previously tested azole compounds. In the 4-week oral toxicity study, the lethal dose of WSA was determined to be 90 mg/kg. However, no animal mortality was observed during the 2-week intravenous continuous infusion study. The toxicokinetics (TK) profile of WSA at 10 and 30 mg/kg dosages illustrated a rapid, dose-dependent conversion of WSA to its active metabolite, and the plasma levels of Cmax and AUC were well correlated to their toxicities. However, at high dosages (60 and 90 mg/kg), WSA demonstrated high exposure beyond the dose-proportional manner. Overall, the results obtained indicate that maintaining an effective concentration and a non-toxic dosage level would be manageable by utilizing an initial intravenous continuous infusion followed by oral administration.
The purpose of this study was to evaluate a telemetry system for examining the cardiovascular system in the conscious common marmoset. Parameters obtained were blood pressure, heart rate, respiratory rate, ECG, body temperature and locomotor activity, and these were continuously recorded on a data recorder via the telemetry system and then processed by a computerized system. Diurnal rhythms of blood pressure, heart rate, body temperature and locomotor activity were observed in this system. We studied the effects of astemizole (antihistamine) and nicardipine ( Ca2+ channel blocker) on cardiovascular parameters. Astemizole at 30 mg/kg (po) and at 1 to 3 mg/kg (iv), prolonged QT interval and induced ventricular extrasystole. Torsades de pointes occurred in one of three cases at 3 mg/kg (iv) and 30 mg/kg (po), while it did not affect the blood pressure, respiratory rate and body temperature. Nicardipine at 30 mg/kg (po) caused sustained hypotension and tachycardia. These results demonstrate the usefulness of the telemetry system using the common marmoset for evaluating the cardiovascular effects of drugs under physiological conditions.