The number of gene therapies in development continues to increase, as they represent a novel method to treat, and potentially cure, many diseases. Gene therapies can be conducted with an in vivo or ex vivo approach, to cause gene augmentation, gene suppression, or genomic editing. Adeno-associated viruses are commonly used to deliver gene therapies, but their use is associated with several manufacturing, nonclinical and clinical challenges. As these challenges emerge, regulatory agency expectations continue to evolve. Following administration of rAAV-based gene therapies, nonclinical toxicities may occur, which includes immunogenicity, hepatotoxicity, neurotoxicity, and the potential risks for insertional mutagenesis and subsequent tumorgenicity. The mechanism for these findings and translation into the clinical setting are unclear at this time but have influenced the nonclinical studies that regulatory agencies are increasingly requesting to support clinical trials and marketing authorizations. These evolving regulatory expectations and toxicities, as well as future nonclinical considerations, are discussed herein.
Excessive use of Ketamine (KET) has a neurotoxic effect on the brain. This study explored the effect of Transient Receptor Potential Vanilloid 4 (TRPV4) on KET-induced neurotoxicity in the hippocampus. We extracted and identified rat hippocampal neuronal cells. The hippocampal neurons were treated with different concentrations (0, 0.1, 1, 10, 100, 300 and 1000 μmol/L) of KET (6, 12 and 24 hr). Cell viability was detected by cell counting Kit-8 (CCK-8), and TRPV4 expression was detected by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) and western blot. After silencing TRPV4, we tested cell viability and apoptosis. The contents of superoxide dismutase (SOD), glutathione (GSH), malondialdehyde (MDA), and catalase (CAT) were detected by colorimetry, and the contents of TNF-α, IL-1β, IL-6 and reactive oxygen species (ROS) were detected by Enzyme-Linked ImmunoSorbent Assay (ELISA). Finally, the expression levels of apoptosis-related proteins Bcl-2, Bax and Cleaved caspase-3, and phosphorylated-p65 (p-65), p65, phosphorylated-IκBα (p-IκBα) and IκBα were detected by qRT-PCR and western blot. KET inhibited the viability of hippocampal neurons in a dose-dependent manner, and up-regulated TRPV4 expression. SiTRPV4 inhibits KET-induced decrease in cell viability and promotes apoptosis. SiTRPV4 reduced MDA and ROS content, increased SOD, GSH and CAT levels. The release of proinflammatory factors TNF-α, IL-1β and IL-6 was also inhibited by siTRPV4. In addition, siTRPV4 up-regulated KET-induced Bcl-2 expression in hippocampal neurons, down-regulated Bax and Cleaved caspase-3, and inhibited the activation of the inflammatory pathway. Silencing TRPV4 partially reverses the neurotoxic effects induced by KET through regulating apoptosis-related proteins and p65/IκBα pathway.
Epigenetic toxicity, a phenomenon in which chemicals exert epigenetic effects and produce toxicity, has been attracting attention in recent years due to advances in toxicology accompanying the development of life sciences. However, it has been difficult to identify epigenetic toxicants due to the lack of a simple experimental system to evaluate epigenetic toxicity. In this study, we developed a prototype of an in vitro reporter assay system for assessing the effects of chemicals on DNA methylation using two promoters showing different degrees of DNA methylation, Agouti IAP and Daz1 promoters, and a luciferase reporter. The system successfully detected DNA demethylating activity using 5-azacytidine, a chemical having DNA demethylation activity, as a positive control chemical, and demethylation of cytosine of CpG in the promoter was confirmed by pyrosequencing analysis. Next, in order to improve the detection sensitivity of the DNA demethylating activity of this system, we tried to increase the basal level of methylation of the Daz1 promoter by pre-methylase treatment of the reporter vectors. As a result, the detection sensitivity of the system was successfully improved in cells where the basal level of methylation was indeed increased by methylase treatment. Thus, the developed assay system here is effective for the simple evaluation of chemicals that affect DNA methylation.
Methylmercury (MeHg), an environmental electrophile, binds covalently to the cysteine residues of proteins in organs, altering protein function and causing cytotoxicity. MeHg has also been shown to alter the composition of gut microbes. The gut microbiota is a complex community, the disturbance of which has been linked to the development of certain diseases. However, the relationship between MeHg and gut bacteria remains poorly understood. In this study, we showed that MeHg binds covalently to gut bacterial proteins via cysteine residues. We examined the effects of MeHg on the growth of selected Lactobacillus species, namely, L. reuteri, L. gasseri, L. casei, and L. acidophilus, that are frequently either positively or negatively correlated with human diseases. The results revealed that MeHg inhibits the growth of Lactobacillus to varying degrees depending on the species. Furthermore, the growth of L. reuteri, which was inhibited by MeHg exposure, was restored by Na2S2 treatment. By comparing mice with and without gut microbiota colonization, we found that gut bacteria contribute to the production of reactive sulfur species such as hydrogen sulfide and hydrogen persulfide in the gut. We also discovered that the removal of gut bacteria accelerated accumulation of mercury in the cerebellum, liver, and lungs of mice subsequent to MeHg exposure. These results accordingly indicate that MeHg is captured and inactivated by the hydrogen sulfide and hydrogen persulfide produced by intestinal microbes, thereby providing evidence for the role played by gut microbiota in reducing MeHg toxicity.