Mitsuyoshi Moto

FYX-051, a Xanthine Oxidoreductase Inhibitor, Induces Nephropathy in Rats, but not in Monkeys

The present studies were performed to investigate the possible mechanism of marked species differences on nephropathy found in the long-term toxicity study of FYX-051, a xanthine oxidoreductase inhibitor. In the twenty-six-week dose toxicity study in the rat, in which FYX-051 was administered by oral gavage at 0.04, 0.2, and 1 mg/kg, xanthine-mediated nephropathy was seen only at 1 mg/kg, despite the presence of xanthine crystals in urine at 0.2 mg/kg and more; however, in the fifty-two-week dose toxicity study in the monkey, in which FYX-051 was administered by oral gavage at 30, 100, and 300 mg/kg, no toxicities were seen, even at 300 mg/kg. These outcomes showed there would be 1500-fold or more differences in the mode of intrarenal xanthine deposition between rats and monkeys. Thus we performed the mechanistic study, and the following outcomes were obtained. First, the amount of urinary purine metabolites was thirty-fold higher in rats than in monkeys. Second, urinary xanthine solubility was sixfold higher in monkeys than in rats. Third, exposure levels of FYX-051 were five-fold higher in rats than in monkeys. Therefore, the present study indicated that the combined effects of purine metabolism, urinary xanthine solubility, and toxicokinetics would contribute to species differences in nephropathy, that is, absence of xanthine-mediated nephropathy in monkeys even at the highest dose of FYX-051.

Carcinogenic susceptibility to N-bis(2-hydroxypropyl)nitrosamine (DHPN) in rasH2 mice.

To evaluate the susceptibility of rasH2 mice to N-bis(2-hydroxypropyl)nitrosamine (DHPN), a potent carcinogen targeting the lung, liver, thyroid, and kidney, male, 6-week old, rasH2 mice and wild-type littermates (non-Tg mice) were given DHPN in drinking water at 0, 20 or 200 ppm, and 0 or 200 ppm, respectively, for 26 weeks. The experiment using rasH2 mice given 200 ppm DHPN and non-Tg mice given 200 and 0 ppm DHPN was completed at 20 weeks, since mortality in these groups was remarkably increased due to hemangiosarcomas of the liver. Histologically, tumors developed in the lung and liver in both rasH2 and non-Tg mice treated with DHPN. In addition, proliferative lesions were observed in the forestomach, urethra, and excretory duct of salivary glands in rasH2 mice given 200 ppm DHPN. RT-PCR analysis showed no marked difference in expression of mRNAs for the transgene and the endogenous mouse ras gene between the whole lung tissue containing a neoplasm and normal lung tissue. Our results suggest that rasH2 mice are highly susceptible to DHPN, the target organs including the forestomach, salivary gland and urethra, which have not been found to develop tumors in previous long-term carcinogenicity studies of DHPN in rats and mice.

Study on toxicological aspects of crystal-mediated nephrotoxicity induced by FYX-051, a xanthine oxidoreductase inhibitor, in rats

To clarify the toxicological aspects of crystal-mediated nephrotoxicity, we performed analysis concerning the correlation between representative kidney-related parameters and renal histopathology, using the individual data obtained from the 4-week toxicity studies of FYX-051, a xanthine oxidoreductase inhibitor, by oral administration at 1 and 3 mg/kg to Sprague-Dawley (SD) rats and at 3 and 10 mg/kg to F344 rats. In SD rats, the correlation coefficient on histopathology between the right and left kidneys was 0.7826 and remained within a lower range of strong correlation (range: ±0.7 ∼ ±0.9). The correlation coefficient between body-weight gains, urinary volume, osmolarity, serum blood urea nitrogen (BUN), creatinine, and relative kidney weights and renal histopathology was −0.6648, 0.7896, −0.7751, 0.8195, 0.8479, and 0.8969, respectively, showing a strong correlation, except a moderate correlation in body-weight gains (range: ±0.4 ∼ ±0.7). In F344 rats, the correlation coefficient on histopathology between the right and left kidneys was 0.8637, remaining within an upper range of strong correlation. The correlation coefficient between the above parameters and renal histopathology was −0.8175, 0.8616, −0.9045, 0.9010, 0.8991, and 0.9524, respectively, showing an extremely strong correlation in urinary osmolarity, serum BUN, and relative kidney weights (range: ±0.9 ∼ ±1.0). Therefore, the present study suggests that FYX-051-induced nephrotoxicity may occur with more inconsistency in the degree of nephropathy between the right and left kidneys in SD rats than in F344 rats, which would explain the above outcomes.

Establishment of simultaneous treatment model with citrate for preventing nephropathy induced by FYX-051, a xanthine oxidoreductase inhibitor, in rats

As a precedent study for elucidating the mechanism of possible urinary bladder carcinogenesis due to xanthine crystals induced by FYX-051, a xanthine oxidoreductase inhibitor, we have determined the experimental conditions suitable for the 52-week simultaneous treatment with citrate in F344 rats. Simultaneous treatment with citrate and FYX-051 produced both increased urinary citrate excretion and suppression of urinary xanthine deposition at around 4 hours after a single dosing, but these effects disappeared 2 hours later, indicating a lack of the durability of citrate effects. Next, we carried out a 7-day simultaneous treatment study by two daily treatments, that is, FYX-051 (6 mg/kg) and citrate (2,000 mg/kg), followed by citrate-alone treatment, under the conditions of selected dosing intervals, the second dose of citrate, and dosing volume. As a result, the dosing interval of citrate was found to be optimal at 4 hours, but not at 3 or 5 hours, because this treatment completely inhibited intrarenal xanthine deposition. The dose of citrate for the second treatment and the dosing volume were found to be sufficient at 1,500 mg/kg and 10 mL/kg, respectively. Subsequently, a 4-week study by simultaneous treatment at 3 mg/kg of FYX-051 and citrate (2,000 mg/kg) + citrate (1,500 mg/kg), under the improved conditions, revealed that renal lesions could be drastically inhibited. Thus, the present study demonstrated that the interval of two citrate treatments is pivotal and indicated that the improved model would be useful for the mechanistic study of FYX-051-induced urinary bladder carcinogenesis because of an easier treatment method than our previous model.

A 26-Week Carcinogenicity Study of 2-Amino-3-Methylimidazo(4,5-f)Quinoline in rasH2 Mice

To evaluate the carcinogenic susceptibility of rasH2 mice to 2-amino-3-methylimidazo[4,5- f ]quinoline (IQ), 7-week-old rasH2 mice and their wild-type littermates (non-Tg mice) of both the sexes were fed a diet containing 0 or 300 ppm IQ for 26 weeks. Microscopical examinations revealed that the proliferative lesions of the forestomach, including squamous cell hyperplasias, papillomas, and carcinomas, were frequently encountered in male and female rasH2 mice fed with IQ. In non-Tg mice, no significant differences in the incidence of forestomach lesions were observed between the 0 ppm and 300 ppm groups. Histopathological changes such as periportal hepatocellular hypertrophy and oval cell proliferation in the liver were more apparent in female rasH2 and non-Tg mice than in males, and the incidence of hepatocellular altered foci significantly increased in female rasH2 mice in the 300 ppm group as compared to that in the 0 ppm group. These results suggest that the carcinogenic potential of IQ can be detected in rasH2 mice by a 26-week, short-term carcinogenicity test.