Methylmercury selectively damages the central nervous system (CNS). The tumor necrosis factor (TNF) superfamily includes representative cytokines that participate in the inflammatory response as well as cell survival, and apoptosis. In this study, we found that administration of methylmercury selectively induced TNF-α expression in the brain of mice. Although the accumulated mercury concentration in the liver and kidneys was greater than in the brain, TNF-α expression was induced to a greater extent in brain. Thus, it is possible that there may exist a selective mechanism by which methylmercury induces TNF-α expression in the brain. We also found that TNF-α expression was induced by methylmercury in C17.2 cells (mouse neural stem cells) and NF-κB may participate as a transcription factor in that induction. Further, we showed that the addition of TNF-α antagonist (WP9QY) reduced the toxicity of methylmercury to C17.2 cells. In contrast, the addition of recombinant TNF-α to the culture medium decreased the cell viability. We suggest that TNF-α may play a part in the selective damage of the CNS by methylmercury. Furthermore, our results indicate that the higher TNF-α expression induced by methylmercury maybe the cause of cell death, as TNF-α binds to its receptor after being released extracellularly.

5-Aminolevulinic acid (5-ALA) is an amino acid derivative and a precursor of protoporphyrin IX (PpIX). The photophysical feature of PpIX is clinically used in photodynamic diagnosis (PDD) and photodynamic therapy (PDT). These clinical applications are potentially based on in vitro cell culture experiments. Thus, conducting a systematic review and meta-analysis of in vitro 5-ALA PDT experiments is meaningful and may provide opportunities to consider future perspectives in this field. We conducted a systematic literature search in PubMed to summarize the in vitro 5-ALA PDT experiments and calculated the effectiveness of 5-ALA PDT for several cancer cell types. In total, 412 articles were identified, and 77 were extracted based on our inclusion criteria. The calculated effectiveness of 5-ALA PDT was statistically analyzed, which revealed a tendency of cancer-classification-dependent sensitivity to 5-ALA PDT, and stomach cancer was significantly more sensitive to 5-ALA PDT compared with cancers of different origins. Based on our analysis, we suggest a standardized in vitro experimental protocol for 5-ALA PDT.

To elucidate the molecular mechanism involved in methylmercury-induced cerebellar disorder, we performed DNA microarray analysis of the cerebellum of methylmercury-treated mice. The expression levels of 21 genes were elevated 2-fold or higher in response to methylmercury, including many genes encoding proteins involved in inflammatory reactions associated with chemokines. The expression levels of 11 genes were reduced by half or more in response to methylmercury.

Methylmercury is an environmental pollutant that is toxic to the central nervous system; however, the molecular mechanisms underlying its toxicity remain unclear. Methylmercury increases expression of several chemokines in the cerebellum of mice treated with methylmercury. The present study analyzes the mechanism underlying methylmercury-induced chemokine expression using human 1321N1 astrocytes, and shows that methylmercury increases CCL2 expression in these cells. The transcription factor NF-κB is involved in the induction of chemokine expression. Methylmercury increased the level of the NF-κB p65 subunit in the nuclei of 1321N1 cells. The methylmercury-induced increase in CCL2 expression was significantly decreased by suppression of p65 expression by RNA interference. These results suggest that methylmercury induces chemokine expression through activation of NF-κB in human astrocytes.

Photodynamic therapy (PDT) using talaporfin sodium (TS) is tumor cell-selective less invasive therapy for the treatment of malignant glioma. We previously demonstrated that PDT using TS (TS-PDT) treatment exhibits anti-tumor activity against not only glioblastoma cells but also malignant meningioma cells. In general, various stress response proteins have been reported to affect the sensitivity determination for anticancer agents against tumor cells. However, the relationship between the therapeutic effect of TS-PDT and stress response systems in tumor cells is not adequately investigated. In this study, we investigated the gene expression of stress response proteins, including Sod1, Cat1, Gstp1, Gpx1, Nqo1, and Hmox1, in rat malignant meningioma KMY-J cells after treatment of TS-PDT. TS-PDT treatment significantly decreased the cell viability when compared with the no laser irradiation group. In morphological observation, TS at 25.6 µM treatment exhibited a significant cytotoxic effect after 12 hr of laser irradiation to KMY-J cells. After 3 and 6 hr of TS-PDT treatment, mRNA expression of heme oxygenase-1 (HO-1, encoded by Hmox1) was significantly increased by TS-PDT treatment. We also demonstrated that zinc protoporphyrin IX (ZnPPIX), a HO-1 inhibitor, significantly augmented the cytotoxic effect of TS-PDT treatment. These data suggest that HO-1 induction may contribute to a protective response against TS-PDT treatment in the malignant meningioma cells and may attenuate the therapeutic effect for TS-PDT treatment.