Effects of an environmentally relevant mixture of organophosphate esters on the phenotype and function of HepG2 liver cells.

Organophosphate esters (OPEs), commonly used as flame retardants and plasticizers, are ubiquitous environmental contaminants, with high concentrations found in indoor house dust. Previously, we have reported that individual OPEs have adverse effects on HepG2 liver cells. However, real-world exposure involves mixtures of OPEs. In this study, we investigated the effects of an environmentally relevant mixture of OPEs, detected in Canadian house dust, on HepG2 cell phenotype and function. Using high-content imaging, we found that this mixture increased cytotoxicity and lipid droplet size, while lysosomes were the most effected endpoint. We used the DQ-BSA degradation assay to assess the function of lysosomes and confocal microscopy to confirm the status of lysosomal transcription factor EB (TFEB). We then tested lysosomal enzyme activities to determine potential downstream effects. OPE mixture induced concentration-dependent increases in the degradation capacity of lysosomes and elevated nuclear translocation of TFEB when compared to controls. Increased activities of downstream lysosomal acid lipase (LAL) and cathepsin B (CTSB) validated the activation of TFEB and its downstream effect of lysosome biogenesis. Together, these data demonstrate that exposure to an environmentally relevant OPE mixture adversely affects liver cell survival, phenotype, and lysosome functions, providing potential mechanistic insight into consequences of OPE exposure and increased risk of liver damage associated with disrupted lipid and lysosome homeostasis. This study also highlights the importance of evaluating real-world chemical exposures as mixtures rather than as individual compounds.