Phytosterols Have Limited Direct Effect on Hepatocyte Transporter Expression but Synergize with Endotoxin to Enhance Kupffer Cell Inflammatory Response

Phytosterols, non‐nutritive components of soybean oil‐based lipid emulsions (SO), have been implicated in the development of parenteral nutrition associated liver disease (PNALD). Phytosterols may drive the pathogenesis of PNALD through a two‐hit mechanism: suppression of hepatic bile clearance through downregulation of the bile salt export pump (BSEP) and increased hepatic inflammation. Inflammation can further suppress BSEP and potentially the ATP‐binding cassette transporters ABCG5/8, the hepatic phytosterol clearance transporter, creating a feed‐forward loop leading to further hepatic injury. Two nuclear hormone receptors, Farnesoid X Receptor (FXR) and Liver X Receptor (LXR) regulate bile acid metabolism and have been shown to suppress the inflammatory response. The aim of our study was to first, determine if the hepatic transport dysfunction and inflammatory response is hepatocyte independent or requires activation of the resident macrophages, Kupffer cells; second, determine if ligand‐mediated activation of FXR and LXR can restore inflammation‐induced suppression of transporter function. Preterm piglets were administered parenteral nutrition for 10 d containing SO lipid emulsion. On day 10, piglets were given an 8‐h infusion of saline or LPS (10 μg*kg −1 *h −1 ). In a separate experiment, primary hepatocytes and Kupffer cells were isolated from neonatal piglets. Cells were treated with media supplemented with 1% SO with or without the addition of a phytosterol mixture containing β‐sitosterol, stigmasterol, and campesterol. After incubation for 24 h, cells were additionally treated with FXR ligand Obeticholic acid (OCA), or LXR ligand GW3694 in the presence or absence of 50 ng/mL LPS or 10 ng/mL IL‐1β for 24 h. In piglets, administration of LPS lead to a significant suppression of BSEP and ABCG5/8 expression compared to saline infused piglets. In cell culture, administration of IL‐1β, but not LPS or phytosterols, led to suppression of both BSEP and ABCG5/8. In hepatocytes co‐treated with IL‐1β and OCA or GW3694, only BSEP expression was rescued. In Kupffer cells, phytosterols alone failed to activate expression of cytokines, however, when treated with both LPS and phytosterols increased cytokine expression significantly more than with LPS alone. From this study, we conclude inflammation can suppress the transporters for bile acid and phytosterol clearance. Our in vitro data shows that Kupffer cells are susceptible to enhanced activation of cytokine expression by phytosterols when cells are primed with LPS. These results suggest that phytosterols may contribute to the progression of liver disease through inflammation. Support or Funding Information American Society of Parenteral and Enteral Nutrition Rhoads Research Foundation, National Institute of Health Grant DK‐094616