Fundamental Toxicological Sciences

2018 - Vol. 5 No. 1

2018 - Vol. 5

Assessment of bladder DNA damage due to 2-acetylaminofluorene, diuron, and terephthalic acid by the rat comet assay Vol.5, No.1, p.63-69
Takahiro Kyoya , Rika Iwamoto , Yuko Shimamura , Megumi Terada , Shuichi Masuda
Released: March 20, 2018
Abstract Full Text PDF[801K]

Chemicals that induce tumors in the urinary bladder in long-term toxicity tests often induce hyperplasia, a pre-cancerous lesion in subacute toxicity tests. Determining whether or not the mechanism by which hyperplasia induced in the urinary bladder is due to genotoxicity at an early stage is important for the extrapolation of carcinogenicity to humans. An in vivo comet assay is suitable for shortterm evaluation of urinary bladder genotoxicity. 2-Acetylaminofluorene (2-AAF), diuron, and terephthalic acid (TPA) are known to induce tumors in rat bladder by different mechanisms in long-term toxicity tests, but so far there are no reports on the bladder comet assay for the evaluation of these compounds in short-term toxicity tests. Here, a comet assay in rat urinary bladder for short-term evaluation was assessed by using rat strains in which hyperplasia induction has been reported for diuron and TPA, both of which induce hyperplasia in subacute toxicity tests, and rat strains in which tumors have been observed in longterm toxicity tests of 2-AAF. Regarding the respective DNA damaging properties of these compounds, the result was positive for 2-AAF, a typical genotoxic urinary bladder carcinogen, but negative for diuron and TPA, which induce hyperplasia through the chemical action of metabolites and through physical cytotoxicity due to urinary crystals, respectively. Thus, the comet assay of rat urinary bladder as a short term in vivo genotoxicity test is considered to be a useful and convenient method for the short-term evaluation of the genotoxicity of compounds which induce hyperplasia in the urinary bladder.

Scanning electron microscopic analysis of the bladder epithelium in terephthalic acid administered rats: a case in acute toxicity study Vol.5, No.1, p.57-62
Takahiro Kyoya , Megumi Terada
Released: March 09, 2018
Abstract Full Text PDF[3M]

Terephthalic acid (TPA) was observed to have induced tumors due to the physical cytotoxicity of urinary calculi in the urinary bladders of rats. In the acute toxicity study, the extrapolation to humans was evaluated hastily by observation of the urinary crystals and cytotoxicity on the bladder epithelium. We examined whether it was possible to observe urine crystals and corresponding alterations on the epithelium in the urinary bladders in the acute toxicity study of TPA. TPA at a dose level of 2,000 mg/kg body weight, were administered twice by oral gavage at a 21-hr interval and the bladder mucosal epithelium was observed at 3, 6 and 9 hr after the second administration using scanning electron microscope (SEM). As a result, micro crystals were observed in the bladder surface at 6 and 9 hr after the second administration, and small raised ridges on the bladder surface, which were considered to be the effects of cytotoxicity, were observed at 9 hr after the second administration. However, these were not observed in rats administered only 0.5% sodium carboxymethyl cellulose solution, which is a vehicle of TPA. In this study, in cases where the substances induce crystals in urine in a short period, it was suggested that the urinary crystals and the alterations on bladder epithelium could be detected using SEM in acute toxicity study.

Original Article
Abundant migration of midazolam and 1’-hydroxymidazolam into the fetal brain following midazolam administration to pregnant mice in the second trimester Vol.5, No.1, p.49-56
Satoshi Kitaoka , Jo Hatogai , Nanako Niikura , Miho Hirata , Nanako Fukasawa , Satoru Miyazaki , Naoto Yamaguchi , Shohei Harada , Masanaho Sasatsu , Kiyoshi Sugiyama , Wataru Ochiai
Released: March 07, 2018
Abstract Full Text PDF[513K]

Midazolam is used in pregnancy post the second trimester for the treatment of convulsive seizures or as an anesthetic during cesarean section. However, its safety has not been validated. If the migration and accumulation of midazolam into the fetal brain can be clarified, the extent of damage to the fetal brain can be predicted. Therefore, we investigated the migration of midazolam and its active metabolite 1′-hydroxymidazolam into the fetal brain. Midazolam was administered intravenously to pregnant mice in the second trimester (E14.5), and the migration of midazolam and 1′-hydroxymidazolam to the maternal brain and plasma as well as the fetal brain were analyzed over time. Fetal brain levels of midazolam and 1′-hydroxymidazolam were high at 44.7% and 44.5% of that in the maternal brain. Furthermore, both mothers and fetuses expressed 1:1 brain ratios of midazolam and 1′-hydroxymidazolam. In both mothers and fetuses, migration of midazolam into the brain was higher than the migration of 1′-hydroxymidazolam. In this study, approximately half of midazolam and 1′-hydroxymidazolam in the maternal brain was transferred to the fetal brain. During the second trimester, neural stem cells in the fetal brain differentiate into neurons and glial cells and higher brain functions are developed. In the present study, we observed increased migration of midazolam and 1′-hydroxymidazolam into the fetal brain during this period. Therefore, damage to neuronal development may still be observed in the fetus even with post-second trimester midazolam use.

Original Article
Subacute toxicity evaluation of KMRC011, a Toll-like receptor-5 agonist administered by intramuscular injection to rats Vol.5, No.1, p.33-48
Min-Sung Kang , Min-Seok Kim , Sung-Hwan Kim , Doin Jeon , Hyeon-Young Kim , Kwang-Hyun Lim , Su-Cheol Han , Kyuhong Lee , Woo-Jong Lee , Chi-Min Choi , Hong-Soo Lee , Jong-Choon Kim
Released: March 07, 2018
Abstract Full Text PDF[3M]

The present study investigated the potential subacute toxicity of KMRC011, a Tolllike receptor-5 agonist, by a 4-week repeated intramuscular injection in Sprague-Dawley rats. The test article was administered once daily by intramuscular injection to rats at doses of 0, 0.06, 0.13, and 0.25 mg/kg/day for 4 weeks. At the end of the treatment period, 10 rats/sex/group were sacrificed. The study was continued for the remaining 5 rats/sex in the vehicle control and high dose groups without treatment for 2 weeks (recovery period). During the test period, clinical signs, mortality, body weight, food consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weight, and histopathology were examined. Hematological investigations revealed a decrease in the hemoglobin, hematocrit, and mean corpuscular hemoglobin values and an increase in the absolute and relative reticulocyte counts. Histopathological evaluation indicated an increase in the incidence of inflammatory cell infiltration in the cecum, lymphocytes infiltration in the duodenum, and hemopoiesis in the femoro-tibial joint/marrow and sternum/marrow in male and female rats. These changes decreased or were no longer observed after the 2-week recovery period, indicating these were reversible changes. Otherwise, no adverse effects were observed in any treatment group. Based on these results, the no-observed-adverse-effect level was considered to be greater than 0.25 mg/kg/day in the rats

Original Article
Comparison of stabilities of nitrenium ions and in vitro and in vivo genotoxic potential, between four aniline derivatives Vol.5, No.1, p.21-32
Hidekazu Suzuki , Takuya Ninoseki , Ayumi Hayashi , Yasunori Hase , Takuya Matsui , Masaru Naito , Shoichiro Sugai
Released: February 21, 2018
Abstract Full Text PDF[255K]

Stabilities of nitrenium ions estimated by in silico analyses and in vitro and in vivo genotoxicity were compared for four aniline derivatives, 2-chloro-4-methylaniline (2C4MA), 4-chloro-2-methylaniline (4C2MA), 2-chloro-4,5-difluoroaniline (2C4,5DFA) and 4-trifluoromethylaniline (4TFMA). The AM1 values as an index of stability of the nitrenium ions of 2C4MA, 4C2MA, 2C4,5DFA and 4TFMA were -5.38, -4.67, 8.36 and 16.6 kcal/mol, respectively, indicating that the potential of mutagenicity is high for 2C4MA and 4C2MA and low for 2C4,5DFA and 4-TFMA. The specific mutagenicity determined in Ames tests with S9 mix for 2C4MA and 4C2MA was 4,067 and 12,500 revertants/mg/plate, respectively. The specific mutagenicity could not be determined for 2C4,5DFA because the results of the Ames tests were equivocal. Among the four aniline derivatives, only 4TFMA showed positive results with and without S9 mix in the Ames tests and the specific mutagenicity of 4TFMA were 1,590 and 1,910 revertants/mg/plate for TA100 with and without S9 mix, respectively. These results indicated that the mutagenic potential is high for 2C4MA and 4C2MA and is low for 2C4,5DFA and 4TFMA. In vivo genotoxicity is positive for 2C4MA, 4C2MA and 2C4,5DFA and is negative for 4TFMA. The results of in silico analyses and in vitro and in vivo genotoxicity tests were consistent for aniline derivatives with strong mutagenicity (2C4MA and 4C2MA) but were not for those with weak mutagenicity (2C4,5DFA and 4TFMA). Careful assessment for the risk of carcinogenicity is necessary for aniline derivatives with weak mutagenicity by combining in silico analyses and in vitro and in vivo genotoxicity tests.

Original Article
Increased hepatic triglyceride level induced by a glucokinase activator in mice Vol.5, No.1, p.13-20
Junichi Namekawa , Mari Yasui , Atsuko Katayanagi , Mitsuyuki Shirai , Fumitoshi Asai
Released: February 06, 2018
Abstract Full Text PDF[1M]

Glucokinase (GK) is an enzyme that catalyzes the phosphorylation of glucose to glucose-6-phosphate, and plays an important role in maintaining glucose homeostasis by regulating secretion of insulin from pancreatic β-cells and glucose metabolism in the liver. Recently, GK activators are expected as a novel therapeutic agent for Type 2 diabetes mellitus (T2DM). However, the increase in plasma triglyceride (TG) levels is one of the major issues for the development of GK activators. In this study, we evaluated the effects of the GK activator GKA50 on the plasma and hepatic TG in mice. Male CD-1 mice received a single oral dose of vehicle or GKA50 (15, 30, or 60 mg/kg), and plasma glucose and insulin levels were measured. Next, CD-1 mice received oral doses of vehicle or GKA50 (20 or 60 mg/kg) once daily for 4 days, and clinical signs, body weight, food consumption, blood chemistry, and hepatic TG were evaluated. In the single oral dose study, dose-dependent decrease in plasma glucose levels and increase in plasma insulin levels were observed. In the 4-day repeated dose study, there were no treatment-related changes in clinical signs, body weight, food consumption, or plasma TG levels. In the 60 mg/kg group, a significant increase in the hepatic TG level was observed. Additionally, the detailed analysis of TG species composition revealed marked increases in TGs mainly composed of 18:1 fatty acids. This study revealed that GKA50 enhanced insulin secretion and hepatic glucose utilization, and increased hepatic TGs, which were mainly composed of 18:1 fatty acids.

Original Article
A 28-day repeated oral-dose toxicity study of insecticide synergist N-(2-ethylhexyl)-1-isopropyl-4-methylbicyclo[2.2.2] oct-5-ene-2,3-dicarboximide in rats Vol.5, No.1, p.1-11
Mariko Matsumoto , Masatoshi Furukawa , Katsumi Kobayashi , Takako Iso , Toshime Igarashi , Takashi Yamada , Akihiko Hirose
Released: January 19, 2018
Abstract Full Text PDF[254K]

N-(2-Ethylhexyl)-1-isopropyl-4-methylbicyclo[2.2.2]oct-5-ene-2,3-dicarboximide (Synepirin 500; CAS: 13358-11-7) is used as a synergist, a chemical that makes pesticide ingredients more effective. People can be exposed to Synepirin 500 by using insecticides containing this chemical or from residues in food. The Japanese government chose this chemical as a target substance in its existing chemical testing program. Crl:CD(SD) rats were administered 0, 40, 200, and 1000 mg/kg/day Synepirin 500 by gavage for 28 days, followed by a 14 day recovery period. Diarrhea or soft feces were observed in both sexes at 1000 mg/kg/day. Absolute and/or relative liver weights significantly increased at ≥ 40 mg/kg/day in females and at ≥ 200 mg/kg/day in males. Absolute and/or relative thyroid weights significantly increased in both sexes at 1000 mg/kg/day. These changes were still significant at the end of the recovery period in females. Significantly prolonged prothrombin time and activated partial thromboplastin time were observed in males receiving ≥ 40 mg/kg/day. Histopathological changes in the liver and thyroid were observed in both sexes at 1000 mg/kg/day. On the basis of the effects on the liver, the level of the lowest observed adverse effect from repeated doses of Synepirin 500 was judged to be 40 mg/kg/day for rats.