Diverse in vitro liver models reveal comprehensive biotransformation pathways of tetrabromobisphenol A

Tetrabromobisphenol A is a widely used brominated flame retardant. Its biotransformation in human liver has raised significant environmental and health concerns. This study investigated and compared the metabolism of TBBPA in three in vitro liver models-human liver microsome (HLM), human hepatoblastoma (HepG2) cell, and human normal hepatocyte (MIHA) cell systems. At the end of exposure, 92.4%, 13.6%, and 98.4% of TBBPA was metabolized in HLM, HepG2 cell, and MIHA cell systems, respectively. According to the nontarget analysis, a total of 21 metabolites of TBBPA, including 7 for HLM, 9 for HepG2 cell, and 16 for MIHA, were found. A novel metabolite TBBPA mono-β-d-glucopyranoside mono-β-d-glucuronide was identified for the first time. The metabolism degrees and metabolite types differed significantly across the three in vitro models, which might be related to the different expression and activity of enzymes. By combining these three in vitro models, complex transformation pathways were confirmed, including glucuronidation, deglucuronidation, sulfation, methylation, glycosylation, debromination, coupling elimination reaction, and substitution, contributing to a better understanding of the environmental fate and health risk assessment of TBBPA in the human body.