Changes in Energy Metabolism Induced by PFOS and Dietary Oxylipins

Perfluorooctanesulfonate (PFOS), an emerging environmental toxicant in addition to 9- hydroxyoctadecadienoic acid (9-HODE) and 9-hydroxyoctadecatrienoic acid (9-HOTrE), endogenously produced oxylipins from polyunsaturated fatty acids (PUFAs) by Cytochrome P450 2B6 (CYP2B6) have been recently associated with hepatic steatosis and peroxisome proliferator- activated receptor signaling by data produced from our laboratory and others. Given the importance of mitochondrial energy metabolism in the maintenance of lipid homeostasis, an array of extracellular flux assays was performed using HepG2 cells to test for the ability of these compounds to disrupt overall mitochondrial activity and respiration associated with fatty acid oxidation and glycolysis specifically. PFOS and 9-HOTrE increased spare respiratory capacity and various parameters of glycolysis including non-glycolytic acidification, while 9-HODE exhibited no effect on the mitochondria. 9-HOTrE also reduced HepG2 cells sensitivity to etomoxir, an inhibitor of CPT1A, indicating reduced basal fatty acid metabolism. All three compounds drastically increased triglyceride accumulation in HepG2 cells when supplemented with oleic acid, while the oxylipins additionally increased pyruvate concentrations, further associating these compounds and CYP2B6 with steatosis. 9-HODE perturbed gene expression of CD36, PPARg, FASN and FOXA2, providing mechanistic insight into the triglyceride accumulation observed and further implying PPAR signaling, while a lipogenic SREBF-FASN or FASN coupled with a decrease in fatty acid oxidation pathway appeared to be more sensitive to PFOS and 9-HOTrE treatment, respectively. This study revealed that all three compounds can induce triglyceride accumulation in HepG2 cells while providing putative mechanistic data that their effects occur through different pathways within hepatocytes