Hepatic steatosis (i.e. lipid accumulation) and steatohepatitis have been related to diverse etiologic factors, including alcohol, obesity, environmental pollutants. However, no study has so far analyzed how these different factors might interplay regarding the progression of liver diseases. The impact of the co-exposure to the environmental carcinogen benzo[a]pyrene (B[a]P) and the lifestyle-related hepatotoxicant ethanol, was thus tested onin vitromodels of steatosis (human HepaRG cell line; hybrid human/rat WIF-B9 cell line), and on anin vivomodel (obese zebrafish larvae). Steatosis was induced prior to chronic treatments (14, 5 or 7 days for HepaRG, WIF-B9 or zebrafish, respectively). Toxicity and inflammation were analyzed in all models; the impact of steatosis and ethanol towards B[a]P metabolism was studied in HepaRG cells. Cytotoxicity and expression of inflammation markers upon co-exposure were increased in all steatotic models, compared to non steatotic counterparts. A change of B[a]P metabolism with a decrease in detoxification was detected in HepaRG cells under these conditions. A prior steatosis therefore enhanced the toxicity of B[a]P/ethanol co-exposurein vitroandin vivo; such a co-exposure might favor the appearance of a steatohepatitis-like state, with the development of inflammation. These deleterious effects could be partly explained by B[a]P metabolism alterations.

Aryl hydrocarbons (AHs), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo(a)pyrene (BP), are environmental contaminants promoting the development of atherosclerosis-related cardiovascular diseases. In order to identify molecular mechanisms involved in these effects, we have analysed AH-mediated regulation of the lipid trafficking Niemann–Pick type C1 protein (NPC1) and its contribution to AH-induced macrophage lipid accumulation. Exposure of primary human macrophages to TCDD and BP decreased NPC1 mRNA expression in a time-dependent manner. NPC1 protein expression and NPC1-related acid sphingomyelinase activity were reduced in parallel. NPC1 was also similarly down-regulated in mice exposed to BP. Moreover, TCDD and BP were demonstrated to trigger lipid accumulation in human macrophages, as assessed by Oil Red O and Nile Red staining and cholesterol determination. Such lipid loading occurred at least partly in endosomal/lysosomal compartments as demonstrated by immunolabelling of lipid vesicles by the lysosome-associated membrane protein 1. These cellular phenotypic effects were found to be similar to those triggered by knock-down of NPC1 expression using siRNAs and were counteracted by NPC1 overexpression, thus supporting the contribution of NPC1 to AH-mediated lipid accumulation in macrophages. Finally, both NPC1 down-expression and lipid accumulation in response to TCDD were found to be abolished through knock-down of the AH receptor (AHR), a ligand-activated transcription factor mediating many effects of AHs. Our data have shown that contaminants such as TCDD and BP repress NPC1 expression in macrophages in an AHR-dependent manner, which likely contributes to macrophage lipid accumulation caused by these environmental chemicals. Thus, NPC1 appears to be a new molecular target regulated by environmental AHs and putatively involved in their deleterious cardiovascular effects.