Fundamental Toxicological Sciences

2018 - Vol. 5 No. 6

2018 - Vol. 5

Toxicomics Report
Cyclin-dependent kinase inhibitor p21/Cip1 down-regulates the expression of proteasome activator PA28γ in normal hepatocyte-derived cells Vol.5, No.6, p.203-207
Tomofumi Fujino , Toshiyuki Oshima , Makio Hayakawa
Released: December 28, 2018
Abstract Full Text PDF[1M]

We previously reported that knockdown of the farnesoid X receptor (FXR), a bile acid-activated nuclear receptor, increases mRNA level of cyclin-dependent kinase inhibitor p21/Cip1 in normal hepatocyte-derived cell line Fa2N-4 and hepatocellular carcinoma cell line HepG2. Although p21/Cip1 protein levels of HepG2 cells are also increased by FXR knockdown, elevated levels of p21/Cip1 mRNA does not cause an increase in p21/Cip1 protein levels of Fa2N-4 cells, indicating post-transcriptional suppression of p21/Cip1 expression in Fa2N-4 cells. Given that degradation of p21/Cip1 by proteasomes is mediated by PA28γ, an activator of the 20S proteasome, we examined whether p21/Cip1 regulates the expression of PA28γ, a proteasome activator, in HepG2 and Fa2N-4 cells. In Fa2N-4 cells, ectopic expression of p21/Cip1 increased the mRNA and protein levels of PA28γ. PA28γ expression was down-regulated by knockdown of p21/Cip1. In contrast, in HepG2 cells, neither ectopic expression nor knockdown of p21/Cip1 affected the expression of PA28γ. Therefore, p21/Cip1 likely down-regulates its own expression in a post-transcriptional manner by stimulating the expression of the proteasome activator PA28γ in normal hepatocyte-derived cells, while hepatocellular carcinoma cells lack such feedback regulation of p21/Cip1 expression.

The temporal turning window for rat behavioral phenotypes by rotenone Vol.5, No.6, p.195-202
Masami Ishido
Released: December 28, 2018
Abstract Full Text PDF[13M]

Availability of animal models of human neuronal disease has been contributing to reveal their etiology. Particularly, dopaminergic neurodegeneration has been shown by exposure of rats to chemicals, such as rotenone, corresponding to the rat models of attention deficit hyperactivity disorder (ADHD) and Parkinson’s disease. A single chemical of rotenone causes two behavioral phenotypes, both of which are completely opposite; hyperactivity or hypoactivity. They were created by different timing of chemical exposure, neonatal periods or adulthood, suggesting that there would be a temporal turning point of two behavioral phenotypes. Therefore, we examine a turning point of these behavioral phenotypes by measuring the spontaneous motor activity of rotenone models. We estimate the turning window of both behavioral phenotypes would be around between three weeks and four weeks of age in the rat dopaminergic neurodegeneration. Gene set enrichment analysis extracts a cytokine network in both rat models.

Original Article
Study of metabolic activation of the UV-filter octyl methoxycinnamate for endocrine-disrupting activity Vol.5, No.6, p.185-193
Yoko Watanabe , Chihiro Emori , Naoto Uramaru , Nariaki Fujimoto , Shigeyuki Kitamura
Released: December 18, 2018
Abstract Full Text PDF[1M]

We examined whether octyl methoxycinnamate (OMC), a UV-filter, is metabolically activated by liver microsomes of rats and humans in respect to endocrine-disrupting action. OMC itself showed no agonistic activity towards estrogen receptor (ER) or aryl hydrocarbon receptor (AhR), and no antagonistic activity towards ER or androgen receptor (AR). The hydrolysis product, 4-methoxycinnamic acid (4-MCA), was also inactive in all the assays. In contrast, the desmethylated product, octyl hydroxycinnamate (OHC), exhibited agonistic activities towards ERα, ERβ and AhR. Importantly, when OMC was incubated with rat liver microsomes in the presence of NADPH, the major product was 4-MCA, and OHC was not formed at all. 4-MCA was also produced as the main metabolite of OMC by pooled human liver and small-intestinal microsomes. The OMC-hydrolyzing activity was higher in small-intestinal microsomes than in liver microsomes of both rats and humans, and was higher in humans than in rats. Therefore, OMC hydrolysis appears to be mainly catalyzed by small-intestinal carboxylesterase 2 isoforms, and partly by liver carboxylesterase 1 isoforms. We confirmed that OMC was hydrolyzed by human recombinant carboxylesterase isozymes, CES1b, CES1c and CES2. Our results indicate that OMC is not metabolically activated to OHC in humans, but is mainly hydrolyzed to inactive 4-MCA, suggesting that it is unlikely to pose a risk of human health in terms of endocrine-disrupting activity.

A zinc complex that suppresses the expression of a reactive sulfur species-producing enzyme, cystathionine γ-lyase, in cultured vascular endothelial cells Vol.5, No.6, p.181-184
Akane Takahashi , Musubu Takahashi , Tomoya Fujie , Takato Hara , Eiko Yoshida , Chika Yamamoto , Toshiyuki Kaji
Released: December 11, 2018
Abstract Full Text PDF[2M]

Persulfide species present in mammalian cells play important toxicological roles against oxidative stress and methylmercury. Cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS) are enzymes that produce persulfide species using cysteine as a substrate in the presence of vitamin B6. However, little is known about the regulatory mechanisms underlying the expression of these enzymes. In the present study, we searched for molecular probes from a library of 27 zinc complexes to analyze the mechanisms in vascular endothelial cells. We found dichloro(1,10-phenanthroline)zinc(II), termed Zn11, as a zinc complex that suppressed endothelial CSE expression without any change in CBS expression. This zinc complex can be used as molecular probes to analyze the regulation underlying endothelial CSE expression.