Methylmercury is a major environmental pollutant that exhibits neurotoxicity. We previously reported that proteolytic systems such as the ubiquitin–proteasome system (UPS) and autophagy are involved in methylmercury toxicity. It is known that the intercellular level of PTEN, a phosphatase involved in autophagy inhibition, is regulated by the UPS. In this study, we coincidentally found that the PTEN level was decreased by methylmercury in the lysate solubilized with RIPA buffer containing 0.1% sodium dodecyl sulfate (SDS). However, the decrease in PTEN level caused by methylmercury was scarcely observed in RIPA buffer containing 2% SDS. These results suggest that methylmercury lowers the solubility of PTEN protein. Moreover, phosphorylation of Akt, a protein kinase that is negatively controlled via PTEN, was accelerated in accordance with a decrease in PTEN protein solubility. This suggests that methylmercury may inhibit PTEN activity by decreasing its solubility. Moreover, PTEN overexpression confers resistance to methylmercury in SH-SY5Y neuroblastoma cells. These results suggest that PTEN is a novel factor involved in reducing methylmercury toxicity and that methylmercury inhibits PTEN activity by decreasing the solubility of PTEN protein, thereby increasing cytotoxicity.
Vancomycin (VCM), a glycopeptide antibiotic, is commonly applied to infectious diseases caused by Gram-positive bacteria, in particular including methicillin-resistant Staphylococcus aureus (MRSA). However, VCM treatment sometimes causes adverse side effects, such as nephropathy and deafness. Although both side effects have been implicated in inflammatory processes, the underlying mechanisms remain unknown. Here, we investigate the cellular responses induced by VCM, especially focusing on the inflammatory responses, and found that VCM promotes the gene expression of NOD-like receptor (NLR) and absent in melanoma 2 (AIM2)-like receptor (ALR) families that mediate release of pro-inflammatory cytokines, interleukin-1β (IL-1β) and IL-18, by forming the multiprotein complexes, called inflammasomes. Thus, our findings suggest that VCM promotes IL-1β- and IL-18-mediated inflammation through the upregulation of the components of inflammasomes, which provides insight into the VCM-induced inflammation-related side effects.
The nuclear receptor pregnane X receptor (PXR, NR1I2) regulates several liver functions such as xenobiotic metabolism, energy metabolism, inflammation or cell growth, which are associated with drug-drug interactions and some diseases. It is well known that there are large species differences between human PXR and mouse PXR (mPXR) ligands. Although mouse models are often used in biological research, the number of mPXR ligands are limited. In the present study, we have thus searched mPXR activators from 190 industrial chemicals and 161 agricultural chemicals by reporter assay system with a promoter region of PXR target gene, and mouse primary hepatocytes and mice were treated with the candidates to confirm mPXR activation. Thirty-eight chemicals were selected after reporter assay screening. Among them, seven chemicals were selected as potential mPXR activators since their treatment increased mRNA levels of Cyp3a11, a representative PXR target gene, in mouse primary hepatocytes. Finally, in in vivo experiments using mice, hepatic Cyp3a11 mRNA levels were induced by treatment with flusilazole and metconazole. These results suggest that these two chemicals function as mPXR activators in vitro and in vivo.
Several metal(loid) toxicants can trigger cytotoxicity by causing apoptosis. Our previous study demonstrated that cadmium induces apoptosis by suppressing expression of the apoptosis inhibitor, BIRC3 [Baculoviral inhibition of apoptosis (IAP) protein repeat containing 3], in human proximal tubular cells (HK-2 cells). BIRC3 is a member of the BIRC family, which consists of eight family members in human, and seven in mouse. The observed suppression of BIRC3 gene expression was mostly specific to cadmium and to HK-2 cells. In this study, we examined whether methylmercury, inorganic mercury, or arsenic may affect the gene expression of other BIRC family members in several different cultured cells. Methylmercury decreased the level of BIRC2 mRNA and increased the level of BIRC5 mRNA in human IMR-32 neuroblastoma cells. Methylmercury increased the mRNA levels of BIRC2, BIRC5, and BIRC8 and decreased the mRNA levels of BIRC6 in HK-2 cells. Inorganic mercury increased the mRNA levels of BIRC2 and BIRC5 in HK-2 cells. Finally, arsenic increased the levels of Birc1 and Birc7 and decreased the levels of Birc2, Birc4, Birc5, and Birc6 mRNA in mouse normal hepatic AML-12 cells. Taken together, these results indicate that each metal(loid) toxicant may regulate the gene expression of BIRC family members in different manners. Therefore, each BIRC family member may play distinct roles when various tissues are exposed to toxic heavy metals or metalloid toxicants.
We prepared virgin (Lig) and calcined lignin at 200–1000 °C (Lig200, Lig400, Lig600, Lig800, and Lig1000) and evaluated their adsorption capability for zinc ions from the water phase. The properties (morphology, specific surface area, pore volume, mean pore diameter, and functional groups) of adsorbents were characterized by scanning electron microscopy, specific surface area analysis, and FT-IR analysis. The specific surface area and pore volume of Lig800 was greater than those of the other adsorbents. In addition, -OH and -COOH groups were detected on Lig, Lig200, and Lig400, but those functional groups were not confirmed by calcination treatment over 600 °C. Amount of zinc ions adsorbed on Lig800 was greater than that on other adsorbents. We also evaluated the adsorption mechanism of zinc ions with adsorbents. The result showed that the amount of zinc ions adsorbed was related to ion-exchange with proton (correlation coefficient: 0.817) or physical property (mesopore volume; correlation coefficient: 0.867) for Lig, Lig200, and Lig400 or Lig600, Lig800, and Lig1000, respectively. These results indicate that the adsorption mechanism is changed with calcination treatment. Moreover, we elucidated the effect of temperature on the adsorption of zinc ions, and evaluated the adsorbent surface before and after zinc ion adsorption. We confirmed the zinc existed on the adsorbent surface after adsorption. Finally, as per the thermodynamic parameters, the negative value of ΔG indicates the spontaneous nature and feasibility of the zinc ion adsorption. These findings provide significant information that can be useful for removal of zinc ions from aqueous solution.