Mechanistic insights into the neurotoxicity of Isothiazolinone biocides in human neuronal cells

Isothiazolinones (ITs) are biocides with various biological properties and are hence used across different industries. They are commonly found in consumer products, disinfectants, and household cleaners. Although effective, ITs have been reported to exhibit neurotoxic effects in mouse- and rat-derived cells. However, the neurotoxicity of ITs in humans remains underexplored. In this study, we compared the neurotoxicity of four commonly used ITs-1,2-benzisothiazol-3(2H)-one (BIT), 2-methyl-4-isothiazolin-3-one (MIT), 2-n-octyl-4-isothiazolin-3-one (OIT), and 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT)-in human-derived neuronal cells. The viability of cells exposed to these ITs decreased the most with DCOIT, followed by OIT, BIT, and MIT, respectively. The ITs induced changes in neurite outgrowth and the expression of neurodevelopmental genes at concentrations considered noncytotoxic. RNA-sequencing revealed the regulation of the expression of genes associated with neurodevelopmental processes; ANXA2 and SYTL5 were upregulated following treatment with all four ITs, indicating their potential as biomarkers for IT-induced neurotoxicity. A Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated an association between all the tested ITs and neurodegenerative diseases. BIT caused the most pronounced changes in neurodevelopmental gene expression, with the highest potential for neurotoxicity. These findings provide insights into the potential neurotoxicity of ITs and highlight the need for revised safety assessments and regulatory strategies to address the risks associated with human exposure.