Development of new solvents applicable to in vitro toxicity tests of insoluble substances

<p>[Background and Aim] From the point of view of sustainability, economic efficiency, and throughput, in vitro toxicity tests applicable to a wide range of test compounds and doses are growing in importance. In most of the cases, test substances are dissolved in water. However, safety assessment of some substances is difficult due to their insolubility. Dimethyl sulfoxide (DMSO), an organic solvent commonly used in toxicity tests, affects the cell cycle of living cells even at low concentrations (1-2%). Therefore, we decided to conduct a screening test to develop a new solvent with high biocompatibility and its safety evaluation. We focused on zwitterionic liquid (ZIL) for reports as a solvent to dissolve cellulose, which is insoluble in water and DMSO (Commun. Chem., 3, 163 (2020)), and conducted safety evaluation. [Methods] A screening test was conducted by dissolving food-related substances with low solubility in both water and DMSO in ZIL at concentrations of 0.1, 1, and 10% (w/w). The safety of candidate ZIL with potentially higher biocompatibility compared to DMSO was assessed by Ames test and hepatotoxicity test using human hepatoma-derived cell lines. [Results] ZIL with histidine-like structure, developed by Kuroda Laboratory, Kanazawa University, improved solubility of some food-related substances. This ZIL was negative in the Ames test and was less toxic than DMSO to hepatocytes. [Conclusion] We demonstrated that ZIL is advantageous as a new solvent for food-related substances from the viewpoint of solubility. Since it has no mutagenicity, it may be applied to in vitro genotoxicity tests. In addition, biocompatibility of ZIL was higher than that of DMSO, suggesting ZIL’s usefulness as a solvent for various tests using living cells.</p>