Metabolic Disruption and Steatosis Induced by Drinking Water Disinfection Byproducts in HepG2 and HUH7 Cells

Disinfection byproducts (DBPs) are ubiquitous contaminants formed during drinking water treatment and are traditionally regulated based on cytotoxic and genotoxic endpoints. However, evidence suggests that DBPs may also act as metabolic disruptors interfering with hepatic metabolic pathways. This study investigates the early metabolic disruption and steatogenic effects of four regulated DBPs, bromoform (BR), bromodichloromethane (BDCM), monochloroacetic acid (MCA), and dichloroacetic acid (DCA), using the human hepatic cell models HepG2 (derived from hepatocellular carcinoma) and HUH7 (derived from hepatoblastoma). Cells were exposed to a broad concentration range (1 pM-100 µM) to capture both sub-cytotoxic and mechanistically informative responses at low, environmentally relevant levels. Effects on lipid and sterol metabolism were assessed through the transcriptional modulation of a panel of nuclear receptors (AHR, PXR, RXR, and LXR) and the sterol regulatory enzyme HMG-CoA reductase (HMGCR) as well as intracellular lipid accumulation; cytotoxicity and oxidative stress endpoints were concurrently evaluated. All DBPs tested induced significant, dose-dependent alterations in nuclear receptor signaling and also promoted lipid accumulation in the low-concentration range and without concurrent cytotoxicity; conversely, oxidative stress responses were limited or absent, and HMGCR emerged as a sensitive target, albeit with different patterns (upregulation by BR and MCA, and downregulation by BDCM and DCA). Relevant substance-specific aspects were also observed for other transcriptional targets, e.g., PXR upregulation was particularly evident for BR and BCDM while DCA downregulated the tested receptors. DBP-induced lipid accumulation was more pronounced in HUH7. Regulated DBPs can elicit early steatogenic and metabolic effects even at concentrations below current regulatory thresholds. The findings highlight that endocrine-metabolic disruption should be considered as a relevant endpoint in DBP risk assessment.