The Journal of Toxicological Sciences
Online ISSN : 1880-3989
Print ISSN : 0388-1350
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Letter
  • Norie Murayama, Hiroshi Yamazaki
    Volume 43 (2018) Issue 4 Pages 241-245
    Released: April 04, 2018
    JOURNALS FREE ACCESS FULL-TEXT HTML

    Hepatocyte-like cells differentiated from human induced pluripotent stem (iPS) cells are of great interest for applications in pharmacological research. For drug metabolism testing, commercially available hepatocytes derived from human iPS cells are generally recommended to be used 1 week after seeding on plates. In this study, however, after 3-4 weeks of culture according to the manufacturer’s instructions, human cytochrome P450 (P450) 2C9- and 2C19-dependent diclofenac 4′-hydroxylation and omeprazole 5-hydroxylation activities of the iPS-derived hepatocytes had significantly increased above the activities at 1 week and had reached levels similar to those in HepaRG cells, a human hepatocyte-like cell line. This increase in activities was associated with increasing P450 2C9 and 2C19 mRNA levels. Human P450 3A4-dependent midazolam 1′/4-hydroxylation activities in the iPS-derived hepatocytes were also enhanced after 3 weeks of culture, but the levels were low compared with those of HepaRG cells. These results indicate that the induction of mRNA of typical P450s in human iPS-derived hepatocyte-like cells occurred after 3 weeks of normal culture conditions. However, the induction levels varied considerably depending on the pregnane X receptor pathway and/or the P450 isoform. Our findings that the hepatic functions of human iPS-derived hepatocytes were enhanced by 3 weeks of simple culture could facilitate the use of these cells for drug metabolism and toxicity testing.

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Original Article
  • Akemi Toyoda, Hiroshi Itagaki
    Volume 43 (2018) Issue 4 Pages 247-256
    Released: April 04, 2018
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    Photoreactive compounds that may experience exposure to ultraviolet (UV) radiation can lead to the intracellular production of reactive oxygen species (ROS), which may cause phototoxic and photoallergenic responses. Here, we developed a novel in vitro photosafety assay and investigated whether it could be used to predict phototoxicity and photosensitivity by measuring changes in intracellular ROS production. THP-1 cells that had previously taken up 5-(and-6)-carboxy-2’,7’-difluorodihydrofluorescein diacetate (carboxy-H2DFFDA), a ROS-sensitive fluorescent reagent, were exposed to photoreactive substances such as phototoxic and photoallergenic materials and then subjected to with UV-A irradiation (5 J/cm2). The fluorescence intensity was subsequently measured using a flow cytometer, and the intracellular ROS production was calculated. A statistically significant increase in ROS following treatment with photoreactive substances was observed in cells irradiated with UV-A. In contrast, no significant increase was observed for non-photoreactive substances in comparison to the control solution. Next, to confirm the impact of intracellular ROS on the photosensitive response, changes in CD86 and CD54 expression were measured following quencher addition during the photo human cell line activation test (photo h-CLAT). The results confirmed the reduction of CD86 and CD54 expression in response to photoallergenic substances following quencher addition. Together, these findings suggest that intracellular ROS production is involved in photosensitizing reactions. Therefore, we suggest that the developed method utilizing intracellular ROS production as an index may be useful as a novel in vitro evaluation tool for photoreactive substances.

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Original Article
  • Yoichi Ohshima, Kazumi Iwata, Masakazu Ibi, Misaki Matsumoto, Masato K ...
    Volume 43 (2018) Issue 4 Pages 257-266
    Released: April 04, 2018
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    The increased ratio of longer amyloid-β (Aβ1-42)/shorter amyloid-β (Aβ1-40) peptides, generated from amyloid precursor protein (APP), is known to promote the development of Alzheimer’s disease (AD). To investigate the role of smoking in Aβ production, we determined the production of Aβ species in the presence of nicotine or methyl vinyl ketone (MVK), major components of cigarette smoke extracts, in Flp-In T-REx-293 (T-REx293) cells harboring a single copy of human APP. While treatment with nicotine or MVK did not affect the amount of APP, the levels of Aβ1-40 in the culture media were significantly increased. On the other hand, the levels of Aβ1-42 were unaltered by nicotine or MVK treatment. The Aβ1-42/Aβ1-40 ratio was therefore attenuated by cigarette smoke extracts. Similar results were obtained in T-REx293 cells harboring APP of Swedish- or London-type mutation linked to familial AD. T-REx293 cells expressed the nicotinic acetylcholine receptor (nAchR) and tubocurarine, an nAChR antagonist, completely blocked the effects of nicotine. Treatment with nicotine significantly elevated cellular levels of β-secretase that cleaves APP prior to Aβ generation. Taken together, a protective role of nicotine against AD pathology was suggested by enhanced extracellular Aβ1-40 production, which may suppress Aβ fibrillogenesis.

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Letter
  • Tasuku Nawaji, Naohiro Mizoguchi, Mika Ono, Takeshi Matuura, Masanori ...
    Volume 43 (2018) Issue 4 Pages 267-273
    Released: April 04, 2018
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    Developmental toxicity is an adverse developmental outcome, i.e., death, malformation, growth retardation, or functional deficiency. Recently, alternative methods of assessing developmental toxicity using zebrafish (Danio rerio) as a preliminary screening have attracted attention because of their low cost and high throughput. However, most toxicity evaluations have been based on a chemical concentration in an aqueous solution, and the chemical concentrations in embryos/larvae and their temporal behavior have in most cases been unclear, regardless of differences of chemical hydrophobicity. In the present study, we selected three teratogens with different hydrophobicities (caffeine, CA, log Kow -0.07; sodium valproate, VA, log Kow 0.26 (pH 7.4); and diethylstilbestrol, DES, log Kow 5.07), and we measured their concentrations in embryos/larvae exposed to these chemicals every 24 hr post-fertilization (hpf) until 144 hpf. Kinetic analysis based on a one-compartment fish model that yields first order kinetics for CA and VA revealed that concentrations of both CA and VA in embryos/larvae increased gradually and became saturated by around 100 hpf. In contrast, DES concentrations in embryos/larvae reached a maximum at 48 or 72 hpf and then decreased gradually. The present study suggests that the temporal pattern of chemical concentrations is a function of the hydrophobicity of the chemicals.

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Letter
  • Maki Tokumoto, Jin-Yong Lee, Akinori Shimada, Chiharu Tohyama, Masahik ...
    Volume 43 (2018) Issue 4 Pages 275-280
    Released: April 04, 2018
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    Inorganic mercury is a harmful heavy metal that causes severe kidney damage. Glutathione (GSH), a tripeptide comprising L-glutamic acid, glycine and L-cysteine, and metallothionein (MT), a cysteine-rich and metal-binding protein, are biologically important protective factors for renal toxicity by inorganic mercury. However, the relationship between GSH and MT for the prevention of renal toxicity by inorganic mercury is unknown. We examined the sensitivity of the mice depleted in GSH by treatment with L-Buthionine-SR-sulfoximine (L-BSO), and MT-I/II null mice genetically deleted for MT-I and MT-II, to inorganic mercury (HgCl2). Kidney damage was not induced in the wild-type mice treated with HgCl2 (30 µmol/kg). In the MT-I/II null mice, renal toxicity was induced by HgCl2 at a dose of 30 µmol/kg but not 1.0 µmol/kg. All GSH-depleted mice of both strains were dead following the injection of HgCl2 (30 µmol/kg). GSH-depleted wild-type mice treated with HgCl2 (1.0 µmol/kg) developed kidney damage similar to MT-I/II null mice treated with HgCl2 (30 µmol/kg). Moreover, renal toxicity induced by HgCl2 (1.0 µmol/kg) was more severe in GSH-depleted MT-I/II null mice compared with GSH-depleted wild-type mice. The present study found that GSH and MT-I/II play cooperatively an important role in the detoxification of severe kidney damage caused by inorganic mercury. In addition, GSH may act as a primary protective factor against inorganic mercury-induced acute renal toxicity, because GSH-depleted mice were more sensitive to inorganic mercury than MT-I/II null mice.

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Original Article
  • Xinhang Jiang, Xiaoying Wu, Feiyu Chen, Wei He, Xintong Chen, Linhua L ...
    Volume 43 (2018) Issue 4 Pages 281-289
    Released: April 04, 2018
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    Our aim was to demonstrate the significance of miRNA, lncRNA, and circRNA in the transformation of human bronchial epithelial cells induced by benzo(a)pyrene (BaP), and to investigate their regulatory networks. Hierarchical clustering, gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and network regulation analysis were used to analyze the high-throughput sequencing results of human bronchial epithelial cell line BEAS-2B and BaP-transformed BEAS-2B cells (BEAS-2B-T). 76,191,786 and 3,431differentially-expressed miRNA, lncRNA, mRNA and circRNA were detected, respectively; 43 miRNA, 48 lncRNA, 438 mRNA and 2,079 circRNA were up-regulated; 33 miRNA, 143 lncRNA, 348 mRNA and 1,352 circRNA were down-regulated. Through GO analysis, 257 biological process (BP) terms, 12 cell composition (CC) terms and 49 molecular function (MF) terms were found in differentially-expressed lncRNA; 143 BP terms, 32 CC terms, and 48 MF terms were found in differentially-expressed circRNA. Pathways of KEGG analysis of lncRNA and circRNA could be classified into the categories “human diseases” and “organism systems”. From miRNA-circRNA, circRNA-mRNA, and lncRNA-circRNA networks analysis, we found that mir-137, circ-RPS5, circ-ZNF292, circ-ERBB2IP, circ-SEMA3C, circ-IGF1R, circ-RTN4, APOC1, and CDKN2A may be of great significance for cell transformation. From the analysis of miRNA, lncRNA, mRNA, and circRNA networks, we found that PDGFRB, lncRNA RGMB-AS1, circ-ZNF292 are associated with miR-138-5p. Our study shows that miRNA, lncRNA, and circRNA have a significant regulatory role in the transformation of human bronchial epithelial cell induced by BaP.

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