Biotransformation of three hexabromocyclododecane diastereoisomers in HepG2 cells and their cellular metabolomics

In this study, human hepatoma cells (HepG2) were exposed to three concentrations (0.05, 1 and 10 mg/L) of individual hexabromocyclododecane (HBCD) diastereoisomers (α-, β- and γ-HBCD) for 24 h to investigate their cytotoxicity, biotransformation, bioisomerization, and induced metabolic disturbances. All isomers showed cytotoxicity, as indicated by dose-dependent decreases cell viability (γ-HBCD > β-HBCD > α-HBCD) and significant GSH depletion (β-HBCD > α-HBCD > γ-HBCD). While their cellular apparent uptake rates were similar, β-HBCD had a higher biotransformation rate than α- and γ-HBCD. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) identified putative pentabromocyclododecene (PBCDe) as the main metabolite, with varying levels among isomers. Bioisomerization (β/γ-HBCD to α-HBCD; β-HBCD to γ-HBCD) and reductive debromination were the major metabolic pathways. Metabolomic analysis revealed HBCD disrupted multiple metabolic pathways (e.g., choline, glycerophospholipid, fatty acid, purine metabolism), with distinct effects observed across different diastereoisomers.