The electron spin resonance (ESR)-based photosafety test (ESR-PT) is a non-animal prediction test for photosafety evaluations that can be used even for hydrophobic chemicals; the method is based on the detection of singlet oxygen generation using ESR spectroscopy and showing high accuracy for compounds with known photosafety information. During the process of extending the application data for ESR-PT, we found three false-negative chemicals: bithionol, fenticlor and cilnidipine. These chemicals did not show the characteristic triplet signal of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-hydroxy-TEMPO), which is used as a classifier for positive or negative chemicals; instead, bithionol and fenticlor induced an apparent single peak signal with a g-value of 2.0048, while cilnidipine produced a small, fragmented signal. Bithionol and fenticlor reportedly induce free radicals, and positive phototoxic or photoallergic evidence have been reported. Although the small, fragmented signal observed for cilnidipine was confirmed to be identical to that of a phenylnitroxy radical by the computer simulation, the significance of this chemical for photosafety considerations may be low because cilnidipine has quite a low incidence of phototoxic or photoallergic reactions in humans. Accordingly, the current ESR-PT protocol should be improved to detect free radical photoproducts generated from chemicals such as bithionol and fenticlor, thereby helping to reduce false negatives in ESR-PT.

Chronic exposure to cadmium (Cd) leads to an accumulation of Cd in the kidneys. Metallothionein (MT) is a low-molecular-weight protein having a high affinity for Cd. Cd bound to MT in serum is filtered through the glomeruli of kidney nephrons and reabsorbed by endocytosis into the proximal tubules from the luminal side. Accumulation of Cd in renal cells induces MT synthesis, leading to long-term deposition of Cd and the suppression of Cd toxicity. Recently, many studies have investigated the tissue distribution of metals using laser ablation ICP-MS (LA-ICP-MS). However, little information has been available regarding renal Cd distribution. Hence, we dually investigated the renal distribution of Cd by LA-ICP-MS and that of MT by immunohistochemistry to clarify the dose- and time-dependent changes in the distributions of Cd and MT in mice exposed to Cd from drinking water for 1, 2, and 4 months. Both Cd and MT exhibited characteristic heterogeneous distribution patterns in the renal cortex. The accumulation of Cd and MT near the surface of the cortex suggests a preferential accumulation of Cd in the surface nephrons. MT distribution was more pronounced in the proximal tubules than in the distal tubules, and there were clear differences in MT immunostaining even among the proximal tubules. The heterogeneous localization of MT may reflect the nephron-specific accumulation of Cd. Combining elemental imaging of Cd with immunostaining of MT proved a successful strategy to reveal the characteristic renal Cd distribution, especially in the early stages of Cd accumulation.

As a widespread environmental pollutant, benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE)-induced neurotoxicity has received increasing attention. Studies have shown that BPDE-induced neurodegeneration is due partly to neuronal apoptosis. Unlike apoptosis, ferroptosis is a non-apoptotic form of programmed cell death, but its specific role in the neurotoxicity of BPDE remains unclear. In this work, we investigated the ferroptosis in BPDE-induced cell death in human neuroblastoma cell line SH-SY5Y using a specific pharmacological inhibitor. Lipid peroxides, malondialdehyde production, glutathione / glutathione peroxidase activity, superoxide dismutase activity, and iron content were evaluated. Consistent with previous studies, our data showed that 0.5 μM BPDE poisoning for 24 hr could induce cell apoptosis and that cell survival could be improved by using apoptosis inhibitors. But with prolonged exposure time (72 hr) or increased exposure dose (1.0 μM), we have elucidated and validated that BPDE triggered ferroptosis in human SH-SY5Y cells. We also revealed that suppression of ferroptosis by specific inhibitors, ferrostatin-1 and deferoxamine, significantly rescued the phenotypes of ferroptosis induced by BPDE. BPDE downregulated Nrf2 and its target genes related to redox regulation, GPX4 and SLC7A11, but upregulated HO-1. Our results first demonstrated that BPDE caused cytotoxic effects on cell death via apoptosis and ferroptosis. Most notably, long-term environmental exposure to BPDE becomes a concern due to ferroptosis. Redox imbalance is controlled by the Nrf2, SLC7A11, and HO-1, through which lipid peroxides and ferrous ion accumulation cause ferroptosis after BPDE treatment. These findings highlight that targeting ferroptosis could serve as an effective protective strategy for neurotoxicity of BPDE.

Although human urinary aniline and 2,6-dimethylaniline were unexpectedly detected in biomonitoring data, little is known about the daily intake doses of aniline and 2,6-dimethylaniline in the living environment or their relation to tolerable daily intake (TDI) values in humans. In the current study, to evaluate the daily oral intake of aniline and 2,6-dimethylaniline in humans, forward and reverse dosimetry was carried out using simplified in silico physiologically based pharmacokinetic (PBPK) modeling established using in vivo experimental pharmacokinetic data. These data were from humanized-liver mice after single oral doses of 100 mg/kg aniline (previously determined) and 116 mg/kg 2,6-dimethylanine (currently investigated). The in vivo elimination rates of 2,6-dimethylaniline from plasma in humanized-liver mice were generally slow compared with those of aniline. Faster in vitro metabolic elimination rates of aniline mediated by liver 9000 × g supernatant fractions from rats than those from humans may suggest the existence of higher first-pass effects in rats than in humanized-liver mice. In silico aniline and 2,6-dimethylaniline concentration curves in human urine after virtual oral administrations were estimated by human PBPK models created with data from humanized-liver mice. Reverse dosimetry analysis using human PBPK models estimated the daily intake of aniline, based on reported human urinary concentrations in biomonitoring data, to be roughly similar to the aniline TDI level. These results suggest that forward and reverse dosimetry using simplified human PBPK models founded on data from humanized-liver mice can be used to evaluate possible higher than expected exposures of aniline and 2,6-dimethylaniline in humans.

Organobismuth compounds, i.e., organic–inorganic hybrid molecules composed of an organic structure and bismuth metal, have been reported to induce cytotoxicity in cancer cells; however, the target proteins associated with this cytotoxicity have not been elucidated. Herein, we investigated the inhibitory effect of five organobismuth compounds on human glyoxalase I (hGLO I), a promising target candidate for cancer therapy. Among these compounds, triphenylbismuth dichloride (Bi-05) exerted a strong inhibitory effect on hGLO I. Indeed, Bi-05 inhibited hGLO I in a dose-dependent manner with an IC₅₀ value of 0.18 µM. Bi-05 also induced cytotoxicity in human leukemia HL-60 cells and human lung cancer NCI-H522 cells, both of which exhibit high expression levels of GLO I. However, the hGLO I-inhibiting and cytotoxic effects of Bi-05 disappeared when the bismuth atom was replaced with an antimony or phosphorus atom. Bismuth(III) nitrate had little inhibitory effect on hGLO I activity and only slightly reduced the viability of cancer cells. In the culture medium of Bi-05–treated HL-60 cells, the concentration of the GLO I substrate methylglyoxal was markedly elevated. In addition, Bi-05 treatment more strongly inhibited human lung cancer NCI-H522 cell (exhibiting high GLO I expression) proliferation than human lung cancer NCI-H460 cell (exhibiting low GLO I expression) proliferation. Furthermore, the cytotoxicity of Bi-05 was significantly decreased by pre- and co-treatment with the methylglyoxal scavengers N-acetyl-L-cysteine and aminoguanidine. Overall, these results suggest that Bi-05 treatment leads to the accumulation of methylglyoxal via GLO I inhibition, resulting in cytotoxic effects in cancer cells.

Zinc (Zn) is one of the most essential trace elements in the body and an integral part of many enzyme systems. Zn deficiency is characterized by growth retardation, loss of appetite, and impaired immune function. In contrast, Zn overdoses can be associated with liver, kidney, and stomach damage. We focused on the “chronotoxicity,” or the relationship between injection time and severity of chemical toxicity. The aim of this study was to investigate the chronotoxicity of Zn and the in vivo factors involved. Seven-week-old male ICR mice were administered Zn at six different time points per day (zeitgeber time [ZT]: ZT2, ZT6, ZT10, ZT14, ZT18, and ZT22). Mortality was monitored for 7-days after administration. The mice were tolerant to Zn administered at ZT2 and ZT6, and were highly sensitive at ZT14 and ZT18. Furthermore, when mice were administered a non-lethal dose of Zn, the levels of hepatic injury indicators (AST and ALT) were much higher at ZT14 than at ZT2. To explore the mechanism of Zn-induced diurnal hepatotoxicity, we performed an in vitro experiment, focusing on the clock genes. We found that Zn downregulated the expression levels of several clock genes, neuronal PAS domain protein 2 (Npas2) and Peroid2 (Per2), in Hepa1-6 cells. Interestingly, overexpression of both Npas2 and Per2 restored Zn-induced toxicity in Hepa1-6 cells. Since NPAS2 and PER2 are known to modulate the hepatic injury induced by carbon tetrachrolide or acetaminophen, our results suggest that Zn-induced diurnal toxicity may be associated with modulation of Npas2 and Per2 gene expression.

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) and are associated with thyroid diseases. Our previous study reported that 2,3’,4,4’,5-Pentachlorobiphenyl (PCB118) could induce thyroid dysfunction and the rat thyroid tissues exhibit abnormal mitochondrial ultrastructure. However, the more specific effects of PCB118 on mitochondria and the relationship between mitochondria and thyroid dysfunction remain unclear. In this study, Wistar rats were injected with PCB118 intraperitoneally at 0, 10, 100, and 1000 μg/kg/d for 13 weeks and FRTL-5 rat thyroid cells were treated with PCB118 (0, 0.25, 2.5, and 25 nM) for 24 hr, which did not influence the general conditions of rats and FRTL-5 cells viability. The detection of serum levels of thyroid hormones (THs) and the expression of sodium/iodide symporter (NIS) protein demonstrated that thyroid function was impaired after PCB118 exposure. Transmission electron microscopy showed mitochondrial damage in the thyroids of PCB118-treated rats. Biological processes analysis revealed that differentially expressed mRNAs in thyroid tissues induced by PCB118 were enriched in reactive oxygen species (ROS) metabolic process, hydrogen peroxide metabolic process, and hydrogen peroxide catabolic process. Moreover, mRNA expression of mitochondrial respiratory chain genes NDUFB3, UQCRC2, COX17, ATP5I and ATP5E decreased in PCB118-treated groups. In vivo and in vitro data showed that ROS production increased significantly after PCB118 exposure, accompanied by increased levels of phospho-c-Jun N-terminal kinase (P-JNK). Taken together, these results suggest that PCB118 could damage mitochondria by increasing oxidative stress and PCB118-induced thyroid dysfunction may be related to ROS-dependent activation of the JNK pathway.