Saturated fatty acid combined with lipopolysaccharide stimulates a strong inflammatory response in hepatocytes in vivo and in vitro

Abstract

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and consumption of high-fat diet (HFD) is a risk factor for NAFLD. The HFD not only increases intake of saturated fatty acid (SFA), but also induces metabolic endotoxemia, a HFD-associated increase in circulating lipopolysaccharide (LPS). Although it is known that SFA or LPS promotes hepatic inflammation, a hallmark of NAFLD, it remains unclear how SFA in combination with LPS stimulates host inflammatory response in hepatocytes. In this study, we performed both in vivo and in vitro experiments to investigate the effect of SFA in combination with LPS on proinflammatory gene expression in hepatocytes. Our animal study showed that feeding low-density lipoprotein-deficient mice HFD enriched with SFA and injection of low dose LPS cooperatively stimulated IL-6 expression in livers. To understand how SFA and LPS interact to promote IL-6 expression, our in vitro studies showed that palmitic acid (PA), a major SFA, and LPS exerted synergistic effect on the expression of IL-6 in hepatocytes. Furthermore, co-culture of hepatocytes with macrophages resulted in a greater IL-6 expression than culture of hepatocytes without macrophages in response to the combination of PA and LPS. Finally, we observed that LPS and PA increased ceramide production by cooperatively stimulating ceramide de novo synthesis, which played an essential role in the synergistic stimulation of proinflammatory gene expression by LPS and PA. Taken together, this study showed that SFA in combination with LPS stimulated a strong inflammatory response in hepatocytes in vivo and in vitro.

Candida Administration Worsens Cecal Ligation and Puncture-Induced Sepsis in Obese Mice Through Gut Dysbiosis Enhanced Systemic Inflammation, Impact of Pathogen-Associated Molecules From Gut Translocation and Saturated Fatty Acid

“…However, extracellular flux analysis in macrophages was not performed here due to well-known LPS-enhanced glycolysis ( 76 ). Our data support that saturated fatty acids, which are absorbed through portal vein ( 77 ), enhances LPS activity in hepatocytes and macrophages ( 53 , 54 ) and induced cytokine production ( 78 ). This suggests the inflammatory aggravating property of dietary saturated fatty acids on LPS + BG in sepsis with obesity.…”

“…Despite this limitation, LPS + BG altered cytokine responses and cell energy metabolism in hepatocytes enhanced by saturated fatty acid. This supports HFD-induced metabolic pro-inflammation ( 53 , 54 , 74 ). Saturated fatty acid alone did not alter cell energy metabolism of hepatocytes.…”

“…To provide mechanistic data for the previously described phenomena, we studied the interactions of LPS, BG, and PA on inflammation (53,54) and mitochondrial function in hepatocytes (HepG2) and macrophages (RAW264.7 cells) (31). As such, PA, a representative saturated fatty acid, induced lipid accumulation, mild cytokine production, and amplified cytokine responses in HepG2 cells after stimulation with LPS plus BG (LPS + BG; Figures 8A-E).…”

Role of Dietary Lipids in Modulating Inflammation through the Gut Microbiota

“…Though the above findings corroborate the impact of total fat content on liver inflammation, multiple complex inflammatory mechanisms remain at play and SFAs still pose a significant threat to hepatocyte homeostasis. Of note, Li et al investigated the hepatic inflammatory response of SFA in combination with LPS in male low-density lipoprotein receptor deficient (LDLR -/- ) mice and in vitro in a mechanistic approach to elucidate the synergistic effects of LPS and SFA [141]. Mice were fed an HFD with high or low PA content (HP-HFD and LP-HFD) for 20 weeks where half were subsequently injected with LPS during the last 12 weeks of the dietary intervention.…”

“…Results showed that the HP-HFD in combination with LPS enhanced F4/80 expression more than the HP-HFD or LPS alone in liver tissue. Likewise, IL-6 protein expression in hepatocytes and mononuclear cells increased the most with the HP-HFD and LPS than either alone as determined by immunohistochemistry; the combination of the LP-HFD and LPS did not increase IL-6 protein expression to the same degree and LPS alone had no effect [141]. In hepatocytes in vitro , LPS stimulated both IL-6 secretion and gene expression while PA alone had no effect.…”