Chronic TBPH Exposure Drives the Transition from Steatosis to Hepatic Fibrosis via Lipid Droplet Dysregulation in Zebrafish.

Bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) is a widely used novel flame retardant and an emerging ubiquitous environmental contaminant. While acute exposure disrupts lipid signaling, the long-term consequences of TBPH exposure on the progression of metabolic dysfunction-associated steatotic liver disease (MASLD) remain poorly understood. This study aimed to elucidate the chronic hepatotoxic effects of TBPH and the underlying molecular mechanisms. Adult zebrafish were exposed to environmentally relevant concentrations of TBPH for 6 weeks. Hepatic damage was assessed using histological examination, biochemical assays, and integrated proteomic and transcriptomic profiling. In vitro assays using HepG2 cells were conducted to validate cellular mechanisms of lipid droplet (LD) dynamics. Chronic TBPH exposure induced severe macrovesicular steatosis and significant hepatic fibrosis in zebrafish. Transcriptional analysis revealed that TBPH activated both lipid synthesis and fatty acid oxidation. In vitro results confirmed that TBPH stimulated DGAT2-mediated triglyceride synthesis and promoted LD expansion via ER-LD co-localization. Proteomic analysis identified a microfibril-associated protein 4 (Mfap4) associated with extracellular matrix remodeling and fibrosis. These findings demonstrate that chronic TBPH exposure acts as a potent metabolic disruptor, driving a pathological cascade from steatosis to fibrosis. This study provides a comprehensive adverse outcome pathway for TBPH-induced hepatotoxicity, highlighting its potential role in the etiology of metabolic dysfunction-associated steatohepatitis.