Annual Meeting of the Japanese Society of Toxicology

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The present study was designed to characterize the nephrotoxicity induced by the anti-neoplastic platinum complex nedaplatin (NDP) in rats of different ages in comparison with cisplatin (CDDP). A single dose of 15 mg/kg NDP or 7.5 mg/kg CDDP was administered intravenously to 8-, 11-, or 15-week-old male and female SD rats, which were then sacrificed after 10 days. Body weight decreases were observed for both drugs, in direct relation to age. CDDP treatment markedly increased urinary excretion of NAG, γ-GTP, LDH and protein with peaks on Day 4 and complete or partial recovery on Day 7; NDP increased NAG, LDH and protein excretion, but to a lesser extent, and these elevations were generally more marked for females. CDDP increased plasma creatinine and BUN in males and females of all age groups at necropsy. No apparent changes were seen following NDP treatment except in the 15-week-old rats. These results also show that NDP is less nephrotoxic than CDDP. CDDP-treated rats showed remarkable proximal tubular lesions in the renal cortex and corticomedullary region, and the papillary lesions were minor. On the other hand, the NDP-induced nephrotoxicity was morphologically characterized by hyaline droplet changes (electron microscopically, hyperplasia of lysosomes), necrosis or hyperplasia of the collecting duct epithelium in the renal papilla and the epithelium covering the papilla. Cortical lesions, indicated by slight tubular dilatation, were found only in the animals with papillary lesions. In summary, NDP is a promising second-generation platinum complex with reduced nephrotoxicity.

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Hydroxyurea(HU), a potent mammalian teratogen, affects proliferating embryonic cells and inhibits DNA synthesis. The teratogenic potential of HU has been well known in experimental animals for several decades. In this study, we investigated molecular mechanisms of HU-induced apoptosis in the telencephalon of the fetal brain by exposing pregnant mice to HU on day 13 of gestation. TUNEL-positive cells began to increase at 3 hr, peaked at 12 hr, and rapidly decreased at 24 hr. Although the changes of p53 mRNA expression was not observed by RT-PCR, p53-positive reaction was detected immunohistochemically in the nuclei of neuroepithelial cells from 1 hr to 6 hr, and p53-protein expression was simultaneously identified by Western blot analysis. The expression of p53-target genes mRNAs and proteins was detected. The expression of apotosis-related(fas, fasL, and bax) and cell cycle-related genes mRNAs(p21) was sifnificantly elevated, and the degree and sequence of these target genes expression were similar with those of fas, fasL, mdm2 and p21 proteins expression. Flow-cytometric analysis and Western blot analysis on cell cycle-related proteins suggested that neuroepithelial cells might be arrested at S checkpoint from 3 to 6 hr and at G2/M checkpoint at 12 hr, respectively. From the above-mentioned results, it is suggested that HU-induced apoptosis was considered to be mediated by p53 in the fetal brain.

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Etoposide (VP-16), a topoisomerase II inhibitor, is an anti-tumor agent which causes embryotoxicity, exencephaly, encephalocele, anophthalmia and major skeletal malformations of fetuses when administered to dams of rodents. We examined VP-16-induced histopathological changes in the brain of mouse fetuses. Pregnant mice were intraperitoneally treated with VP-16 (4 mg/kg) on 12th day of gestation (GD 12), and fetuses were collected from 1 to 48 hours after treatment (HAT). A moderate decrease of mitotic figures of neuroepithelial cells was observed in the telencephalic wall at 4 HAT. A moderate to marked increase of pyknotic neuroepithelial cells was detected in the brain of VP-16-treated fetuses, and being most prominent from 8 to 24 HAT. These pyknotic cells were also positively stained by TUNEL and cleaved caspase-3 immunostain. It was suggested that excessive neuronal apoptosis was induced in the brain of mouse fetuses treated with VP-16 on GD 12.

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Although CYP expression which is involved in drug metabolism has been suggested to be influenced by some physiological status, such as pregnancy and lactation, the details remain poorly known. In the present study, the alterations of CYPs expression during pregnancy and postpartum in the F344 rat liver were investigated by Western blot analysis and immunostain. Total nine anti-rat CYPs antibodies (CYP1A1, CYP2B1/2, CYP2C6, CYP2C12, CYP2D1, CYP2D4, CYP2E1, CYP3A1, and CYP4A1) were used. In comparison with age-matched non-pregnant control rats, there were significant decreases in hepatic levels of CYP2B2, CYP2C6 and CYP4A1 in mid-pregnancy (day 13) and CYP2B2, CYP2C6, CYP4A1, CYP1A1, CYP2B1 and CYP2E1 in late-pregnancy (day 19). By postpartum 28 day (PPD 28), however, the hepatic CYPs down-regulated during pregnancy reverted to the same level of control rats. The expression of CYP2C12, CYP2D1 and CYP3A1 remained unchanged even by pregnancy. CYP2D4 was not detectable in all the liver samples examined. The results of immunostain revealed that CYP1A1 was expressed in endothelial cells of both sinusoids and veins in the liver. The other CYPs were mainly expressed in centrilobular hepatocytes. There were no differences in the distribution and intensity of the expression of the CYPs between pregnant and non-pregnant rats. These results provide the possibility that pregnant and lactational animals are more susceptible to some toxic substrates which are metabolized by CYPs.

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