Inhibition of ACOX1 enhances the therapeutic efficacy of obeticholic acid in treating non-alcoholic fatty liver disease and mitigates its lipotoxicity.

Background and aims: High-dose Obeticholic acid exhibits promise for non-alcoholic fatty liver disease (NAFLD) treatment but can induce lipotoxicity. Our study sought to understand this mechanism and propose a solution. Approach and Results: In a non-alcoholic fatty liver disease (NAFLD) model induced by a high-fat diet in FXR-/- mice, we pinpointed that FXR regulated the expression of ACOX1 through RNA-Seq analysis. In the livers of FXR-/- mice, both ACOX1 mRNA and protein expression notably decreased. In both HL-7702 and HEP-G2 cells, the silencing of FXR through shRNA plasmids decreased ACOX1 expression, while FXR activation with GW4064 increased it. These effects were reversible with the ACOX1-specific inhibitor, 10,12-Tricosadiynoic acid. In the NAFLD model of FXR-/- mice, The activation of ACOX1 is correlated with elevated serum LDL, triglycerides, and aggravated hepatic steatosis. However, the combination of 10,12-Tricosadiynoic acid with low-dose obeticholic acid effectively treated hepatic steatosis, reducing LDL levels in the NAFLD model of wild-type mice. This combination therapy demonstrated efficacy comparable to high-dose obeticholic acid alone. Notably, the combined drug regimen treats hepatic steatosis by inhibiting the IL-1ß and α-SMA pathways in NAFLD. Conclusion: Combining ACOX1-specific inhibitors with low-dose obeticholic acid effectively treats high-fat diet-induced hepatic steatosis and reduces serum LDL. This approach enhances the therapeutic effects of obeticholic acid and mitigates its lipotoxicity by inhibiting the IL-1ß and α-SMA pathways.

Research progress on the mechanism of cholesterol-25-hydroxylase in intestinal immunity.

Inflammatory bowel disease (IBD), a general term encompassing Crohn's disease (CD) and ulcerative colitis (UC), and other conditions, is a chronic and relapsing autoimmune disease that can occur in any part of the digestive tract. While the cause of IBD remains unclear, it is acknowledged that the disease has much to do with the dysregulation of intestinal immunity. In the intestinal immune regulatory system, Cholesterol-25-hydroxylase (CH25H) plays an important role in regulating the function of immune cells and lipid metabolism through catalyzing the oxidation of cholesterol into 25-hydroxycholesterol (25-HC). Specifically, CH25H focuses its mechanism of regulating the inflammatory response, signal transduction and cell migration on various types of immune cells by binding to relevant receptors, and the mechanism of regulating lipid metabolism and immune cell function via the transcription factor Sterol Regulator-Binding Protein. Based on this foundation, this article will review the function of CH25H in intestinal immunity, aiming to provide evidence for supporting the discovery of early diagnostic and treatment targets for IBD.

Obeticholic Acid Induces Hepatoxicity Via FXR in the NAFLD Mice.

Objective: Obeticholic acid (OCA), a potent farnesoid X receptor (FXR) agonist, is a promising drug for nonalcoholic fatty liver disease (NAFLD); however, it can cause liver injury, especially at high doses. Here, we investigated the role of FXR in the high-dose OCA-induced hepatoxicity in the condition of the NAFLD mouse model. Methods: Wild-type (WT) mice and FXR-/- mice were administered with over-dose OCA (0.40%) and high-dose OCA (0.16%), in a high-fat diet. RNA-seq on liver samples of mice fed with high-dose OCA was performed to dig out the prominent biological events contributing to hepatic fibrosis. Results: Over-dose OCA induced liver injury and shortened survival in WT mice, but not FXR-/- mice. High-dose OCA caused hepatic stellate cell activation and liver fibrosis in the presence of FXR. Furthermore, high-dose OCA induced cholesterol accumulation in livers via the upregulation of genes involved in cholesterol acquisition and downregulation of genes regulating cholesterol degradation in liver, leading to the production of interleukin -1ß and an FXR-mediated inflammatory response. Conclusion: The high-dose OCA induced FXR-dependent hepatic injury via cholesterol accumulation and interleukin -1ß pathway in the NAFLD mice.

Obeticholic acid inhibits hepatic fatty acid uptake independent of FXR in mouse.

OBJECTIVE: Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, is believed to alleviate nonalcoholic fatty liver disease (NAFLD) by decreasing hepatic lipogenesis in an FXR-dependent manner. Here, we revealed a novel mechanism by which OCA improves NAFLD by affecting hepatic long-chain fatty acids (LCFAs) uptake. METHODS: Stably transfected HEK-293 cells expressing fatty acid transport protein 5 (FATP5) were established to examine fatty acid uptake; FXR-/-, human (h) FATP5, and FXR-/-/hFATP5 mouse models were incorporated to explore the effects of OCA on FATP5 ex vivo and in vivo. RESULTS: OCA inhibited hFATP5 (IC50 =0.07 µM) more than murine (m) FATP5 (IC50 =1.04 µM) as measured by LCFAs uptake in FATP5 expressing HEK-293. OCA also inhibited LCFA uptake in primary hepatocytes from hFATP5 mice, FXR-/-/hFATP5 mice more than that from FXR-/- mice, ex vivo. Moreover, OCA inhibited LCFAs uptake by livers in hFATP5 mice and FXR-/-/hFATP5 mice, but not in FXR-/- mice, in vivo. Long-term administration of 0.04% OCA markedly reduced hepatic triglyceride (TG) accumulation in hFATP5 mice and FXR-/-/hFATP5 mice by 63% and 53%, respectively, but not in FXR-/- mice. CONCLUSIONS: OCA ameliorated high-fat diet-induced NAFLD independent of FXR by inhibiting hepatic hFATP5-mediated LCFAs uptake. This suggests that the therapeutic effects of OCA on NAFLD in vivo are mediated by a novel, hFATP5 dependent mechanism.