Fundamental Toxicological Sciences

2016 - Vol. 3 No. 1

2016 - Vol. 3

Fipronil, an insecticide, acts as an anti-estrogen via the concomitant down-regulation of ERα and PES1 Vol.3, No.1, p.33-37
Hiroyuki Okazaki , Eriko Kohro-Ikeda , Shuso Takeda , Hiroyuki Ishii , Erika Furuta , Saki Matsuo , Masaya Matsumoto , Masufumi Takiguchi , Hironori Aramaki
Released: February 23, 2016
Abstract Full Text PDF[295K]

Endocrine disruptors are ubiquitous in nature. Indeed, some pesticides are not only insect killers, they also function as “endocrine disruptors” in humans and animals; therefore, concern regarding the possible health risks of pesticides for humans is growing. However, few studies have investigated the adverse effects induced by pesticides. One study previously suggested that fipronil reduced the levels of 17β-estradiol (E2), a natural ligand for estrogen receptor α (ESR1, ERα), in female Wistar rat plasma. In the present study, we focused on three relatively novel insecticides: fipronil (a phenyl pyrazole), acetamiprid (a neonicotinoid), and imidacloprid (a neonicotinoid). The effects of these 3 insecticides on the expression of ERα as well as E2/ERα-mediated signaling were examined in an ERα-positive MCF-7 human breast cancer cell line. The results obtained showed that fipronil selectively down-regulated the expression of ERα, and its regulated gene, CDC2, and also that PES1, an upstream signaling molecule for the regulation of ERα, was suppressed by the insecticide. We discussed the potential of fipronil as an antiestrogen.

Quantitative analysis of the relationship between the LLNA:DAE method results and the LLNA EC3 values highlights the connection between the elicitation and induction phases during skin sensitization Vol.3, No.1, p.27-31
Kunihiko Yamashita , Shinsuke Shinoda , Saori Hagiwara , Hiroshi Itagaki
Released: February 03, 2016
Abstract Full Text PDF[232K]

We previously reported the skin sensitizing potential of 41 different chemicals using a modified local lymph node assay with an elicitation phase (LLNA:DAE). Of these, the measured skin sensitizing potential for 39 was consistent with the reported results from a murine local lymph node assay (LLNA). Furthermore, the increase in the weight of the left ear lymph node per 1% test dose of each chemical (as measured using the LLNA:DAE method) seemed to reflect the class of skin sensitization potency as evaluated by LLNA. However, this relationship has never been quantitatively investigated. In the present study, we sought to determine the connection between the results of the LLNA:DAE method, in terms of lymph node weight, and the skin sensitization potency as indicated by the EC3 value. We evaluated the concentration of each chemical needed to increase the weight of the left ear lymph node by 2 mg, 1 mg, 0.5 mg, and 0.25 mg during the elicitation phase using the LLNA:DAE method. These concentrations were then assessed in terms of how they directly compared to the LLNA EC3 value as well as how they matched the range of the EC3 value (under 1%, 1-10% and over 10%). Finally, clear quantitative relationships between the EC values at 1 mg and the EC3 values were observed using various statistical regression models. These results indicate that results obtained using the LLNA:DAE method can potentially be used to speculate the EC3 range found using LLNA method for these 29 kinds of skin sensitizers.

Original Article
A study on the influence of acotiamide hydrochloride hydrate on sex hormones, using a uterotrophic bioassay in rat Vol.3, No.1, p.19-25
Hiroyuki Kuroda , Takashi Yamaguchi , Toshiko Kinomoto , Shuji Ogawa , Hitoshi Naraoka , Kazuhiko Takamatsu , Yuji Oishi
Released: January 26, 2016
Abstract Full Text PDF[1M]

Acotiamide hydrochloride hydrate (acotiamide-HH) is the first approved drug in the world for the treatment of patients with functional dyspepsia in Japan. A statistically significant increase in the incidence of endometrial adenocarcinoma was found in a 104-week carcinogenicity study in rats, in a non-dose-dependent manner, and it was considered that further evaluation was required to clarify this issue. Therefore, we performed a uterotrophic bioassay using immature female rats, which is mentioned in the Organization for Economic Co-operation and Development (OECD) Guideline 440, to evaluate the effect of acotiamide-HH on estrogen, which is one of the most important mechanisms causing increase in the incidence of endometrial adenocarcinoma. The positive control substance selected was 17α-ethinyl estradiol (EE). While EE caused a dose-dependent increase in uterine weight, no increase in uterine weight, histopathological changes, or endometrial proliferation activity were observed in the acotiamide-HH treatment groups at doses of up to 1000 mg/kg. Based on this result, we concluded that acotiamide-HH has no potential risk to cause imbalance of the sex hormone environment in female rats.

Original Article
Hepatitis C virus core can induce lipid droplet formation in a yeast model system Vol.3, No.1, p.13-18
Shingo Iwasa , Naoko Satoh , Hayato Irokawa , Junichi Kikuchi , Jun Okawa , Masataka Nomoto , Gi-Wook Hwang , Akira Naganuma , Shusuke Kuge
Released: January 13, 2016
Abstract Full Text PDF[902K]

Chronic infection with the hepatitis C virus (HCV) frequently induces steatosis, which is characterized by the accumulation of lipid droplets (LDs) in hepatocytes. Steatosis is a significant risk factor for liver cancer. The HCV structural protein core is distributed on the surface of the endoplasmic reticulum (ER) and in LDs, thereby increasing LD levels. In this work, we attempt to elucidate the effect of the core protein on LD generation using yeast cells. We found that the core localized to the cytosolic surface of the ER in yeast and is able to increase LD levels when overexpressed from an inducible GAL1 promoter for 3 hr. The effect of the core was conserved among three different HCV serotypes: 1b, 2a and 3a. While the ER stress inducer tunicamycin both elicited an unfolded stress response (UPR) and increased LD levels, the core did not induce the UPR. The RNA viral genome changes rapidly due to its high mutation rate in order to replicate under a variety of circumstances. Our observations suggest a functional analogy between core function in hepatocytes and in yeast cells and thus might be applicable to the screening of small molecules that impair the core-ER interaction.

Single dose oral toxicity study of Picrorhiza kurroa rhizome extract in Wistar rats Vol.3, No.1, p.9-12
Acharya Bal Krishna , Hemanth Kumar Manikyam , Vinay K Sharma , Niti Sharma
Released: January 13, 2016
Abstract Full Text PDF[226K]

Picrorhiza kurroa is a well-known ayurvedic or herbal medicine which is used very commonly in the treatment of various diseases. Therefore, we studied the oral toxicity of Picrorhiza kurroa rhizome extract in rats. A single high dose of the extract at 2000 mg/kg body weight was tested on Wistar rats. Mortality/viability and clinical signs were recorded on test day 0 (prior to administration), 7, 14 and at death. All animals appeared normal from day one to throughout the experimental procedure. Picrorhiza kurroa rhizome extract is non-toxic to rats and helped in weight gain with LD50 > 2000 mg/kg body weight. Oral administration of Picrorhiza kurroa is not connected with any toxicologically significant effects and the data could provide satisfactory preclinical evidence of safety to launch a clinical trial on a standardized formulation of the plant extracts.

Physiological conditions in iPRECIO® -implanted rats Vol.3, No.1, p.1-8
Masaru Tsuboi , Yoshihide Ueda , Yasufumi Ota , Hiroshi Takehara , Takuya Aoshima , Fukutaro Mizuhashi
Released: January 09, 2016
Abstract Full Text PDF[471K]

Any devices used in toxicity studies should be validated. In the present study, the physiological conditions of rats implanted with a new micro-infusion pump, iPRECIO®, were examined to evaluate its availability for toxicity studies. Five or six animals/group of 6-week-old male CD(SD) rats received either sham surgery or the implantation surgery for either the iPRECIO® (iP) pump or a standard osmotic infusion pump (OSM) under the back skin. This was followed by 4 weeks (experiment I) or 13 weeks (experiment II) of observation. During the observation period, the iP- and OSM-animals received a continuous infusion of 2.0 or 2.5 μL/hr of saline via the external jugular vein. In experiment I, standard hematologic and blood chemical parameters used in toxicity studies were measured at weeks 1, 2, and 4. The iP-animals showed no abnormal changes in any parameters at any point when compared with the OSM-/SHAM-animals. In experiment II (only iP- and SHAM-animals), necropsy and histopathological examination were performed at weeks 1, 2, 4, and 13. The histopathological examination revealed foreign material-induced inflammatory changes in the dorsal subcutaneous tissue (implantation site) of the iP-animals, including the infiltration of polymorphonuclear or mononuclear cells, edema, granulation and fibrous capsule formation. However, the abnormalities were limited to the implantation site. These results suggest that the implantation of iPRECIO® exerted no significant impact on the physiological condition of the rats. Therefore, we concluded that iPRECIO® is applicable for toxicity studies.