Fundamental Toxicological Sciences

2016 - Vol. 3 No. 6

2016 - Vol. 3

Original Article
Streptozotocin-induced diabetic state triggers glucose-dependent insulinotropic polypeptide (GIP) expression in the rat liver Vol.3, No.6, p.291-296
Yuka Kohda , Chiaki Minamigawa , Mikako Matsuo , Hitoshi Matsumura
Released: December 24, 2016
Abstract Full Text PDF[694K]

Streptozotocin (STZ), a toxic glucose analogue for pancreatic β cells, has been demonstrated as a treatment option for insulinoma. Glucose-dependent insulinotropic polypeptide (GIP), an incretin hormone, is secreted by K cells in the duodenum in response to food intake and acts on pancreatic β cells, leading to increased secretion of insulin. We previously reported that GIP gene expression in the liver is modified in a diabetic setting. However, the role of GIP in the liver has not been fully elucidated; we aimed to discover its effects on type 1 diabetes by focusing on GIP protein expression in a type 1 diabetes rat model following STZ administration. In this study, we assessed whether glucose and lipid metabolism affected GIP expression in the liver following STZ-induced diabetes. Diabetes was induced by intraperitoneal injection with 70 mg/kg STZ. We expected that blood glucose levels would be higher because of STZ treatment as a result of reduced insulin secretion in pancreatic β cells. Interestingly, GIP was expressed only in the liver of STZ-treated rats; however, blood glucose levels were not elevated. On the other hand, blood triglyceride and cholesterol levels were higher in STZ-treated rats with hepatic GIP protein expression than in control rats. These findings indicated that GIP protein expression in the liver possibly has hypoglycemic action, which may ameliorate the damage of pancreatic β cells induced by STZ treatment, rather than affect glycolipid metabolism.

Original Article
Sensitivity of MT-III null mice upon chronic exposure to cadmium Vol.3, No.6, p.285-289
Jin-Yong Lee , Maki Tokumoto , Yasuyuki Fujiwara , Gi-Wook Hwang , Moo-Yeol Lee , Masahiko Satoh
Released: December 21, 2016
Abstract Full Text PDF[892K]

Cadmium (Cd) is an environmental contaminant known to exert toxic effects on various tissues. Metallothionein (MT) acts as a protective protein with high affinity for Cd. However, among the four isoforms of MT, the physiologic function of MT-III in the liver of mice exposed to Cd chronically has not been determined. In the present study, we examined the susceptibility of MT-III null mice to hepatotoxicity by exposure to Cd for 67 weeks. Cd exposure reduced the body weight of wild-type mice but not MT-III null mice. MT-I/II null mice were also exposed to Cd; as expected, they died at 18 weeks of exposure. Long-term exposure to Cd exhibited mild hepatotoxicity to wild-type mice, and the effects of MT-III on hepatotoxicity were not extensive. Long-term exposure to Cd increased mRNA levels of MT-I and MT-II in the livers of wild-type mice and MT-III null mice. These results suggest that long-term exposure to Cd may contribute similar sensitivity to the livers of MT-III null mice as that of wild-type mice because expression of MT-I and MT-II was induced in the liver of both types of mice.

Cadmium-induced protein ubiquitination in UBA80 knockdown HK-2 cells Vol.3, No.6, p.281-284
Jin-Yong Lee , Maki Tokumoto , Gi-Wook Hwang , Masahiko Satoh
Released: November 26, 2016
Abstract Full Text PDF[634K]

Cadmium (Cd) is a toxic heavy metal that is particularly damaging to proximal tubular cells of the kidney. Cd-induced renal toxicity is associated with perturbation of the ubiquitin proteasome system. Our previous study demonstrated that Cd increased gene expression of ubiquitin-coding genes, UBB, UBC, and UBA80. Notably, knockdown of the polyubiquitin gene UBB by siRNA transfection significantly decreased ubiquitinated protein levels that had been increased by Cd treatment. The present study showed that in contrast to UBB, knockdown of the monoubiquitin gene UBA80 did not diminish the Cd-induced protein ubiquitination in HK-2 cells. Taken together, our results suggest that polyubiquitin rather than monoubiquitin is preferably engaged in Cd-induced accumulation of ubquitinated proteins in HK-2 cells.

DNA microarray analysis of fetal liver of C57BL/6J mice exposed to cadmium during gestation Vol.3, No.6, p.257-280
Hisaka Kurita , Hisamitsu Nagase , Maki Tokumoto , Jin-Yong Lee , Masahiko Satoh
Released: November 26, 2016
Abstract Full Text PDF[232K]

Cadmium (Cd) is a non-essential toxic metal widely distributed throughout the environment. Cd is reported to be toxic to the fetus, so we aimed to investigate changes in gene expression in the liver of fetal mice exposed to Cd during gestation. We exposed pregnant mice to Cd (5 mg/kg) and collected fetal livers to perform DNA microarray analysis. The expression of 1,669 genes was found to be increased more than 2.0-fold, while that of 194 genes was decreased less than 0.5-fold in fetal livers following Cd exposure during gestation. We categorized the Cd-changed genes in terms of cell cycle and cell proliferation, apoptosis, cell growth and differentiation, cellular defense, metabolism, transport, transcription, signal transduction, metal homeostasis, and ubiquitin proteasome system. These results provide useful information about fetal toxicity following gestational Cd exposure.

Original Article
Validation of retrospective evaluation method for false genotoxic chemicals with strong cytotoxicity: re-evaluation using in vitro micronucleus test Vol.3, No.6, p.251-256
Yurika Fujita , Yuichi Ito , Osamu Morita , Hiroshi Honda
Released: November 25, 2016
Abstract Full Text PDF[294K]

To reduce the false positives in in vitro mammalian genotoxicity tests for chromosomal damage, which is caused by severe cytotoxicity, OECD test guidelines have adopted new cytotoxicity indices, and we developed a retrospective evaluation workflow that can be used to identify false positives that are ultimately deemed negative when the new indices are used. Overall, 14 chemicals were estimated to have a negative result. The aim of the present study was to validate the strategy used for the identification of false positives via re-evaluation of these 14 chemicals using the in vitro micronucleus test to evaluate the clastogenicity and aneugenicity. As a result, 11 chemicals became negatives, whereas the other three chemicals remained positives. In particular, chemicals of high priority for re-evaluation are more likely to become negative. Therefore, we conclude that our developed strategy is useful to find false positives that have specifically shown chromosomal aberrations at doses inducing strong cytotoxicity. These chemicals can be correctly evaluated as negatives using the new cytotoxicity indices.

Safety assessment of probiotic bacteria, Bacillus coagulans strain SANK70258, in rats Vol.3, No.6, p.243-250
Yui Akagawa , Yasuyuki Ohnishi , Masatoshi Takaya , Yuko Watanabe
Released: October 19, 2016
Abstract Full Text PDF[283K]

Bacillus coagulans is a lactic acid, spore-forming gram-positive bacteria that has the potential of probiotic benefits. To evaluate the toxicological profiles of Bacillus coagulans strain SANK70258 (active element of LACRISTM-S), a 90-day oral gavage dose study was conducted in rats. The microbe was administered by oral gavage to 6-week old Crl:CD(SD) rats (10 males and 10 females/group) for 90 days at dose levels of 0, 500, 1000, and 2000 mg/kg/day. According to the results, no deaths occurred in either males or females, and no treatment-related changes were observed in any clinical sign including a detailed observation with functional observational battery (FOB), functional test, motor activity, body weight, food consumption, ophthalmoscopy, urinalysis, hematology, blood chemistry, organ weight, necropsy or histopathology. In conclusion, Bacillus coagulans strain SANK70258 had no subchronic toxicity in rats and the no-observed-adverse-effect-level (NOAEL) was judged to be greater than 2000 mg (about 1 × 1012 CFU)/kg/day. The microbe is harmless and can be used as a probiotic.