Plasma Oxylipins Levels in Nonalcoholic Fatty Liver Disease

Activation of innate immunity by gut-derived immunogens such as lipopolysaccharides (LPS) may play an important role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Whether NAFLD-associated lipid disturbances and polyunsaturated fatty acid (PUFA) metabolism in particular contribute to heightened innate immunity, remains to be determined.

To determine if oxylipins, metabolic products of PUFA metabolism, enhance innate immune reactivity alone and/or following exposure to LPS.

Plasma and peripheral blood mononuclear cells (PBMC) were collected from 35 NAFLD patients and 8 healthy controls. Oxylipin levels were documented by HPLC-MS/MS, cytokines (IL-1, IL-6, IL-10, and TNF-α) by ELISA, and chemokine receptors (CCR1 and CCR2) by flow cytometry.

Mean plasma levels of four pro-inflammatory oxylipins (Tetranor 12-HETE, 20-HETE, 8-HETrE, and 7-HDoHE) were significantly elevated in NAFLD patients compared to healthy controls. However, the levels did not correlate with the severity of liver injury as reflected by serum aminotransferases, ck18M30, and Fib-4 determinations. In vitro, 20-HETE (0.01-100 nM), the plasma oxylipin with the most significantly elevated plasma levels, did not alter NAFLD or control PBMC cytokine release or enhance the increases in cytokine release following 24 h of LPS exposure. Similarly, 20-HETE alone did not alter PBMC CCR1 or CCR2 expression or LPS-induced downregulation of these receptors.

Pro-inflammatory oxylipin levels are increased in NAFLD, but these metabolites do not appear to drive short-term direct or LPS-induced increases in PBMC cytokine release or chemotaxis.