Structured regularization is a mathematical technique which incorporates prior structural knowledge among variables into regression analysis to make a sparse estimation reflecting relationships among them. Abundance of structural information in biology, such as pathways formed by genes, transcripts, and proteins, especially suits well its application. Previously, we reported on the first application of latent group Lasso, a group-based regularization method, in toxicogenomics, with genes regulated by the same transcription factor treated as a group. We revealed that it achieved good predictive performances comparable to Lasso and allowed us to discuss mechanisms behind liver weight gain in rats based on selected groups. Latent group Lasso, however, does not lead to a sparse estimation, due to large group sizes in our analytical setting. In this study, we applied graph-based regularization methods, generalized fused Lasso and graph Lasso, for the same data, with regulatory networks formed by transcription factors and their downstream genes as a graph. These methods are expected to make a sparser estimation since they select variables based on edges. Comparisons showed that graph Lasso generated an accurate, biologically relevant and sparse model that could not have been possible with latent group Lasso and generalized fused Lasso.

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In recent years, human induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) and human embryonic stem cell-derived cardiomyocytes (hES-CMs) have been widely used to develop cardiotoxicity assessment systems. To accurately evaluate the arrhythmogenic potential of drugs, we tested three types of hiPS-CMs (iCell Cardiomyocytes, Cellartis hiPS-CM, and Cor.4U) and a type of hES-CMs (Cellartis Pure hES-CM) using impedance technology. All CMs were cultured as confluent monolayers and their beating activity was analyzed with an impedance-based real-time monitoring instrument, the xCELLigence RTCA Cardio System. Measurement of impedance provided information about the CM beating rate and impedance amplitude between negative and positive peaks. Although all CMs except iCell CMs showed similar beating rates, their amplitudes were different. In addition, the patterns of contraction and relaxation were notably different between iCell CMs and the other CMs. The hiPS-CMs and hES-CMs were treated with two arrhythmogenic drugs, sotalol and moxifloxacin, for 24 hr; the results showed that the drugs induced arrhythmic beating patterns on all CMs, although the response was varied. Thus, a more suitable type of CM remains to be found for optimal evaluation of the arrhythmogenic potential of drugs.

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∆⁹-Tetrahydrocannabinol (∆⁹-THC), an active ingredient of marijuana, evokes a number of biological effects including anti-cancer and anti-estrogenic actions. We and others have so far focused on and investigated the latter action. We recently reported that ∆⁹-THC up-regulates the expression of estrogen receptor β (ERβ, ESR2), resulting in the abrogation of 17β-estradiol (E2)-mediated ERα signaling (Takeda et al., Chem. Res. Toxicol., 26, 1073-1079, 2013). This finding may shed light on the possible endocrine-disrupting mechanism(s) employed by cannabinoids including ∆⁹-THC. Although previous studies have suggested that HU-210, a synthetic analog of ∆⁹-THC, evokes a set of endocrine alterations closely related to those of ∆⁹-THC, none have examined the effects of cannabinoids with a focus on the expression of ERβ, a “suppressive” molecule for ERα-mediated signaling. Thus, we herein determined whether HU-210 is also an endocrine modifier similar to ∆⁹-THC using ERα-positive MCF-7 cells in which the expression of ERβ is maintained at very low levels. The results of the present study revealed that HU-210, despite having a similar structure to ∆⁹-THC, did not modulate E2/ERα signaling or induce ERβ.

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To investigate the adaptive response of astrocytes to an environmental chemical, methylmercury (MeHg), we herein examined transcription factors activated in rat primary astrocytes treated with 10 μM MeHg for 6 hr using the Combo Protein/DNA Array. The activities of 38 transcription factors increased by 5-fold or greater in response to MeHg. The paired box family of transcription factors were strongly activated by MeHg exposure, which are considered to be activated downstream of NGF and BDNF upregulation induced by MeHg. Nrf-2 (an antioxidant response element) was also activated, which has been reported to act on MeHg detoxification.

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The in vivo nanotoxicity of nanoparticles is drawing increased attention as concerns grow over the biosafety of nanotechnology. TiO₂ nanoparticles are coated to decrease the potential of harmful effects due to their photoactivity. Rutile-type alumina-coated titanium dioxide nanoparticles (Al₂O₃-TiO₂-NPs) are frequently used in cosmetics to improve their dispersion stability. We herein discuss the effects of Al₂O₃-TiO₂-NPs exposure during pregnancy on mouse spermatogenesis. Pregnant mice were injected five times, once each with 0.1 mL of sequentially diluted concentrations of a Al₂O₃-TiO₂-NPs suspension (1, 10, 100 or 1,000 μg/mL) and received doses of 0.5, 5, 50 and 500 μg, respectively. Prior to injection, the size distribution of the Al₂O₃-TiO₂-NPs was analyzed by dynamic light scattering (DLS) measurement. The average diameter was increased in dose-dependent manner from an average of 153.8 nm to 654.6 nm. The offspring testes were examined at 12 weeks postpartum. The agglomerates in the testicular sections were small (< 200 nm). They were confirmed by the characteristic peaks of the Ti and Al elements on field emission-scanning electron microscope/energy dispersive X-ray spectroscopy (FE-SEM/EDS). Low cellular adhesion and degenerated Sertoli cells were observed in the seminiferous epithelium of all of the Al₂O₃-TiO₂-NP recipient groups by a histological analysis. The detrimental function of the Sertoli cells resulted in the formation of abnormal spermatozoa. The results suggested that Al₂O₃-TiO₂-NPs that transferred from the mother’s body affected spermatogenesis in the offspring.

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We have previously identified Akr1 as one factor in the reduction of methylmercury toxicity in yeast, and reported that Akr1’s palmitoyl transferase activity is necessary for reducing methylmercury toxicity. Palmitoylation transferases are highly conserved from yeast to humans. As such, we prepared SH-SY5Y neuroblastoma cells capable of overexpressing HIP14, a human homolog of Akr1, and investigated the cell’s sensitivity to methylmercury. Our results showed that, compared with the control, the cells were resistant to methylmercury. Thus, we believe the palmitoyl transferase activity of HIP14 in humans can play an important role in the reduction of methylmercury toxicity.

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According to International Conference on Harmonization guidelines, each drug in development for administration to women of child-bearing potential must be tested for possible developmental toxicities using at least two species (a rodent and non-rodent). With the high cost and slow pace of embryonic-fetal toxicity testing in mammals, both the zebrafish embryonic toxicity test (ZET) and mouse embryonic stem cell test (mEST) have been shown to be useful to assess developmental toxicity of various chemical compounds, including human pharmaceutical drugs, in a high-throughput manner. However, comparative study of the sensitivity and specificity of these methods using the same set of human pharmaceutical drugs is scarce. In this study, we assessed developmental toxicity tests of 39 chemical compounds, including human pharmaceutical drugs, in both the ZET and mEST. The accuracy, sensitivity, and specificity of the ZET were 69%, 59%, and 82%, respectively. The accuracy, sensitivity, and specificity of the mEST were 64%, 50%, and 82%, respectively. As a result, both the ZET and mEST showed acceptable accuracies compared with rat embryo-fetal toxicity study and Food and Drug Administration pregnancy categories. By comparing the results between the ZET and mEST, we identified different types of true positives and true negatives. Thus, complementary tests using both the ZET and mEST may better predict the developmental toxicity of human pharmaceuticals.

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