Bilirubin Ameliorates Oleic and Palmitic Acid Accumulation in an In Vitro Model of MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a chronic progressive disorder characterized by an excess accumulation of lipids in the liver. The aim of this study was to examine the role of bilirubin (BR), the catabolic heme product and a putative peroxisome proliferator-activated receptor α (PPARα) agonist, in an in vitro model of MASLD. In our study, we used human hepatoblastoma HepG2 cells exposed to oleic (OA)/palmitic acid (PA) (2:1 ratio, 24 h) with subsequent treatment with BR or fenofibrate (FF, a clinically used PPARα agonist) at clinically relevant concentrations. A significant increase in total cellular lipid content after OA/PA treatment (p<0.05) was observed. When treated with BR and FF, intracellular concentrations of OA and PA decreased significantly (p<0.05). Changes in lipid content were attenuated by GW6471 (a PPARα antagonist) indicating the importance of PPARα pathway in a mechanism of action of BR and FF. Furthermore, we observed a significant increase in the gene expression of a pyruvate dehydrogenase kinase 4 after treatment with FF; FF also increased mitochondrial respiration. Collectively, our data indicate that both BR and FF reduce the accumulation of OA/PA in HepG2 cells exposed to these fatty acids, presumably by up-regulating fatty acid oxidation via PPARα pathway.