The Journal of Toxicological Sciences
Online ISSN : 1880-3989
Print ISSN : 0388-1350
ISSN-L : 0388-1350
Volume 44 , Issue 7
Showing 1-6 articles out of 6 articles from the selected issue
Original Article
  • Kenta Watanabe, Tadashi Tsubouchi, Toru Yamada, Eiichi Hinoi, Izuru Mi ...
    2019 Volume 44 Issue 7 Pages 441-457
    Published: 2019
    Released: July 02, 2019
    JOURNALS FREE ACCESS FULL-TEXT HTML

    The objective of this study is to assess the response of telemetered common marmosets to multiple cardiac ion channel inhibitors and to clarify the usefulness of this animal model in evaluating the effects of drug candidates on electrocardiogram (ECG). Six multiple cardiac ion channel inhibitors (sotalol, astemizole, flecainide, quinidine, verapamil and terfenadine) were orally administered to telemetered common marmosets and changes in QTc, PR interval and QRS duration were evaluated. Drugs plasma levels were determined to compare the sensitivity in common marmosets to that in humans. QTc prolongation was observed in the marmosets dosed with sotalol, astemizole, flecainide, quinidine, verapamil and terfenadine. PR prolongation was noted after flecainide and verapamil administration, and QRS widening occurred following treatment with flecainide and quinidine. Drugs plasma levels associated with ECG changes in marmosets were similar to those in humans, except for verapamil-induced QTc prolongation. Verapamil-induced change is suggested due to body temperature decrease. These results indicate that telemetered common marmoset is a useful animal for evaluation of the ECG effects of multiple cardiac ion channel inhibitors and the influence of body temperature change should be considered in the assessment.

Original Article
  • Takafumi Yamaguchi, Minoru Maeda, Keiko Ogata, Jun Abe, Toru Utsumi, K ...
    2019 Volume 44 Issue 7 Pages 459-469
    Published: 2019
    Released: July 02, 2019
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    Phenobarbital (PB) and Di (2-ethylhexyl) phthalate (DEHP), an anti-epileptic drug and a plasticizer used in flexible polyvinylchloride formulations, respectively, are well-known typical hepatotoxicants. This study investigated the effects of PB (100 mg/kg/day) or DEHP (500 mg/kg/day) on the endocrine system in intact juvenile/peripubertal male rats exposed for 31 days beginning on postnatal day 23. Slight hormone level changes, histopathological changes in thyroid gland or induction of UDP-glucuronosyltransferase in liver were observed in both the PB and DEHP groups. One of the assumed mechanisms inducing thyroid effects is predictable to be secondary changes based on the enhancement in thyroid hormone metabolism via the induction of hepatic microsomal enzymes. No reproductive system-related changes in organ weights, histopathology, and sexual maturation were observed in both groups. Lower testosterone level was observed in the PB group. CYP2B and CYP3A, which are involved in testosterone metabolism, were induced in liver of the PB group. There was no change of 17β-hydroxysteroid dehydrogenase activity in testis of both groups. Lower testosterone level in the PB-treated male rats was attributed to an indirect, hepatotoxicity-associated effect on the reproductive system and not to direct effects on testis such as the antiandrogenic activity and the inhibition of steroidogenesis. These results did not indicate that PB or DEHP exposure affects the endocrine system directly.

Original Article
  • Takayuki Hoshi, Takashi Toyama, Youichi Shinozaki, Schuichi Koizumi, J ...
    2019 Volume 44 Issue 7 Pages 471-479
    Published: 2019
    Released: July 02, 2019
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    M1-microglia (neurotoxic microglia) regulate neuronal development and cell death and are involved in many pathologies in the brain. Although organotypic brain slice cultures are widely used to study the crosstalk between neurons and microglia, little is known about the properties of microglia in the mouse cerebral cortex slices. Here, we aimed to optimize the mouse cerebral slice cultures that reflect microglial functions and evaluate the effects of neurotoxic metals on M1-microglial activation. Most microglia in the cerebral slices prepared from postnatal day (P) 7 mice were similar to mature microglia in adult mice brains, but those in the slices prepared from P2 mice were immature, which is a conventional preparation condition. The degree of expression of M1-microglial markers (CD16 and CD32) and inflammatory cytokines (tumor necrosis factor-α and interleukin-1β) by lipopolysaccharide, a representative microglia activator, in the cerebral slices of P7 mice were higher than that in the slices of P2 mice. These results indicate that M1-microglial activation can be evaluated more accurately in the cerebral slices of P7 mice than in those of P2 mice. Therefore, we next examined the effects of various neurotoxic metals on M1-microglial activation using the cerebral slices of P7 mice and found that methylmercury stimulated the activation to M1-microglia, but arsenite, lead, and tributyltin did not induce such activation. Altogether, the optimized mouse cerebral slice cultures used in this study can be a helpful tool to study the influence of various chemicals on the central nervous system in the presence of functionally mature microglia.

Original Article
  • Qingrong Li, Hongmin Zhang, Jun Zou, Xiang Feng, Dan Feng
    2019 Volume 44 Issue 7 Pages 481-491
    Published: 2019
    Released: July 02, 2019
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    Bisphenol A (BPA), an environmental chemical to which humans are commonly exposed, has been shown to increase cholesterol level but the molecular mechanism is not clear. Since cholesterol biosynthesis plays an important role in elevating cholesterol level, the aim of the present study is to explore the effects of BPA on cholesterol biosynthesis in HepG2 cells and its possible mechanisms. HepG2 cells were treated with different concentrations of BPA for 24 hr, the total cholesterol level and the activity of 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) were measured using commercial enzymatic assay kits, and the mRNA and protein expression levels of sterol regulatory element binding protein-2(SREBP-2) and HMGCR were analyzed by qPCR, Western blotting and immunofluorescence, respectively. After treating HepG2 cells with different concentrations (0.1 nM~10 µM) of BPA for 24 hr, we found that BPA at the environmentally relevant concentrations of 1 nM and 10 nM significantly increased the total cholesterol content, the activity and expression of HMGCR in HepG2 cells, but at 100 nM, 1 µM and 10 µM doses, BPA had no stimulatory effect on cholesterol biosynthesis. The whole dose-response relationship follows non-monotonic dose responses, such as an inverted U-shape. Using human SREBP-2 small interfering RNA, we further discovered that the stimulatory effects of BPA on cholesterol biosynthesis and HMGCR expression could be prevented by blockade of the SREBP-2 pathway. This study provides important implications for understanding the potential lipotoxicity of BPA exposure, and it also indicates that low-dose BPA induces hepatic cholesterol biosynthesis through upregulating the SREBP-2/HMGCR signaling pathway.

Original Article
  • Lingling Chen, Li Zhou, Pengfei Yu, Fangfang Fang, Lei Jiang, Jian Fei ...
    2019 Volume 44 Issue 7 Pages 493-503
    Published: 2019
    Released: July 02, 2019
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    Methamphetamine (METH) is a potent and highly addictive central nervous system stimulant. The association between METH exposure and Alzheimer’s disease (AD) has gained more attention, but, the mechanisms behind METH-induced neuron-related adverse outcomes remain poorly understood. With the western blot assay, our results revealed that METH exposure significantly increased the expression of AD-associated pathological proteins, including the amyloid precursor protein (APP) and the phosphorylated tau protein (p-tau). Meanwhile, the insulin signaling was disturbed after the administration of METH, since the key insulin signaling proteins, such as p-AKT, p-GSK3α, p-GSK3β and p-ERK, were reduced. Additionally, the linking between the pathological proteins and the insulin signaling mediated by METH in the present work was verified by the treatment with the insulin signaling enhancer rosiglitazone, which was shown to improve the insulin signaling and decrease APP and p-tau expression. Thus, targeting insulin signaling may provide novel insights into potential therapeutic intervention for METH-mediated AD-like neurodegeneration.

Original Article
  • Nozomi Fujisawa, Chiharu Tohyama, Wataru Yoshioka
    2019 Volume 44 Issue 7 Pages 505-513
    Published: 2019
    Released: July 02, 2019
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    Dioxins are a group of structurally related chemicals that persist in the environment. Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener, is a suspected risk factor for cardiac diseases in humans. TCDD induces signs of cardiotoxicity in various animals. Mouse models of TCDD exposure suggest cardiotoxicity phenotypes develop differently depending on the timing and time-course of exposure. In order to clarify and characterize the TCDD-induced cardiotoxicity in the developing period, we utilized mouse pups exposed to TCDD. One day after delivery, groups of nursing C57BL/6J dams were orally administered TCDD at a dose of 0 (Control), 20 (TCDD-20), or 80 μg/kg (TCDD-80) body weight (BW). On postnatal days (PNDs) 7 and 21, pups’ hearts were examined by histological and gene expression analyses. The TCDD-80 group was found to have a left ventricular remodeling on PND 7, and to develop heart hypertrophy on PND 21. It was accompanied by fibrosis and increased expression of associated genes, such as those for atrial natriuretic peptide (ANP), β-myosin heavy chain (β-MHC), and endothelin-1 (ET-1). These results revealed that TCDD directly induces cardiotoxicity in the postnatal period represented by progressive hypertrophy in which ANP, β-MHC, and ET-1 have potentials to mediate the cardiac hypertrophy and heart failure.

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