Chronic activation of FXR in transgenic mice caused perinatal toxicity and sensitized mice to cholesterol toxicity

Life cycle assessment of hepatotoxicity induced by cyhalofop-butyl in environmental concentrations on zebrafish in light of gut-liver axis

Cyhalofop-butyl (CB) poses a significant threat to aquatic organisms, but there is a discrepancy in evidence about hepatotoxicity after prolonged exposure to environmental levels. The aim of this study was to investigate long-term hepatotoxicity and its effects on the gut-liver axis through the exposure of zebrafish to environmental concentrations of CB (0.1,1,10 μg/L) throughout their life cycle. Zebrafish experienced abnormal obesity symptoms and organ index after a prolonged exposure of 120 days. The gut-liver axis was found to be damaged both morphologically and functionally through an analysis of histology, electron microscopy subcellular structure, and liver function. The disruption of the gut-liver axis inflammatory process by CB is suggested by the rise in inflammatory factors and the alteration of inflammatory genes. Furthermore, there was a noticeable alteration in the blood and gut-liver axis biochemical parameters as well as gene expression linked to lipid metabolism, which may led to an imbalance in the gut flora. In conclusion, the connection between the gut-liver axis, intestinal microbiota, and liver leads to the metabolic dysfunction of zebrafish exposed to long-term ambient concentrations of CB, and damaged immune system and liver lipid metabolism. This study gives another knowledge into the hepatotoxicity component of long haul openness to ecological centralization of CB, and might be useful to assess the potential natural and wellbeing dangers of aryloxyphenoxypropionate herbicides.

Gut microbiome and metabolic response in non-alcoholic fatty liver disease

Fatty liver disease (FLD) is one of the largest burdens to human health worldwide and is associated with gut microbiome and metabolite stability. Engineered liver tissues have shown promise in restoring liver functions in non-alcoholic FLD (NAFLD), hepatitis and cirrhosis. Fatty liver, largely noted in obesity and hepatic cancer, is highly fatal and has led to a global increase in death rates. It is associated with complex metabolic reprogramming too. A standard approach to therapy in the newly diagnosed setting includes surgery or identification of biomarkers/ metabolites for therapeutic purposes, which ultimately focus on improvement of liver health in patients. As such there are no standard procedures for patient care, but depending on the severity, systemic therapy with either genomic, proteomic or metabolomic profiling form potential options. Better comparisons and study of underlying mechanisms in gut microbiome-based metabolic functions in obesity are urgently required. Today, an emerging field, focusing on metabolomic approaches and metabolic phenotyping, involved in high-throughput identification of metabolome in obesity and gut disorders, is involved in biomarker and metabolite identification. There are supporting technologies and approaches in NAFLD that throw light on the metabolites and gut microbiome, and also on the understanding of the risk factors of obesity along with liver cancer metabolic reaction networks. We discuss the current state of NAFLD metabolites, gut micro-environmental changes, and the further challenges in digital metabolomics profiling. Innovative clinical trial designs, with biomarker-enrichment strategies that are required to improve the outcome of NAFLD in patients are also discussed.

Partial abrogation of FXR-KNG1 signaling by carboxyl-terminal truncated HBx-C30 in hepatitis B virus-associated hepatocellular carcinoma

Hepatitis B virus (HBV) X protein (HBx) is a key regulator of HBV-associated hepatocarcinogenesis. C-terminal-truncated HBx is frequently detected in hepatocellular carcinoma (HCC). The role of HBx, especially C-terminal-truncated HBx, in HCC pathogenesis has been controversial. To elucidate the biological role of C-terminal-truncated HBx underlying HBV-associated hepato-oncogenesis, we constructed a vector expressing HBx-C30 (deletion of 30 aa from the C terminus of HBx) and functionally analyzed its regulation on farnesoid X receptor (FXR) signaling, which is known to inhibit hepatocarcinogenesis. In the present study, we found full-length HBx and HBx C-terminal truncation coexist in HCC, and both full length HBx and HBx-C30 can activate FXR signaling. Moreover, HBx-C30 weakly coactivates FXR-KNG1 signaling compared to full-length HBx.

Hepatic Gluconeogenic Response to Single and Long-Term SGLT2 Inhibition in Lean/Obese Male Hepatic G6pc-Reporter Mice

Sodium-glucose cotransporter 2 inhibitor (SGLT2i) consistently reduces blood glucose levels in type 2 diabetes mellitus but increases hepatic gluconeogenic gene expression and glucose production, offsetting its glucose-lowering effect. This study aimed to elucidate the effect of SGLT2i on hepatic gluconeogenic response and its mechanism in both insulin-sensitive and insulin-resistant states. A hepatic mouse model was generated to show liver-specific expression of Gaussia luciferase (GLuc) driven by the gluconeogenic enzyme gene G6pc promoter. Hepatic gluconeogenic response was evaluated by measuring plasma GLuc activity. SGLT2i was given to lean and obese mice in single gavage administration or 4-week dietary administration with controlled feeding every 3 hours. In lean mice, single-dose SGLT2i increased plasma GLuc activity from 2 hours after administration, decreasing blood glucose and plasma insulin from 1 to 2 hours after administration. In obese mice, which had higher plasma GLuc activity than lean ones, SGLT2i did not further increase GLuc activity despite decreased blood glucose and plasma insulin. Hepatic Akt and GSK3β phosphorylation was attenuated by single-dose SGLT2i in lean mice in accordance with the plasma insulin decrease, but not in obese mice. Long-term SGLT2i administration, which increased plasma GLuc activity in lean mice, decreased it in obese mice from 3 weeks after initiation, with increased hepatic Akt and GSK3β phosphorylation. In conclusion, single SGLT2i administration increases hepatic gluconeogenic response in lean insulin-sensitive mice, but not in obese insulin-resistant mice. Long-term SGLT2i administration relieves obesity-induced upregulation of the hepatic gluconeogenic response by restoring impeded hepatic insulin signaling in obese insulin-resistant mice.

Chronic activation of FXR-induced liver growth with tissue-specific targeting Cyclin D1

The nuclear receptor (FXR) plays essential roles in maintaining bile acid and lipid homeostasis by regulating diverse target genes. And its agonists were promising agents for treating various liver diseases. Nevertheless, the potential side effect of chronic FXR activation by specific agonists is not fully understood. In this study, we investigated the mechanism of FXR agonist WAY-362450 induced liver enlargement during treating liver diseases. We demonstrated that chronic ingestion of WAY-362450 induced liver hypertrophy instead of hyperplasia in mouse. Global transcriptional pattern was also examined in mouse livers after treatment with WAY-362450 by RNA-seq assay. Through GO and KEGG enrichment analyses, we demonstrated that the expression of Cyclin D1 (Ccnd1) among the cell cycle-regulating genes was notably increased in WAY-362450-treated mouse liver. Activation of FXR-induced Ccnd1 expression in hepatocyte in a time-dependent manner in vivo and in vitro. Through bioinformatics analysis and ChIP assay, we identified FXR as a direct transcriptional activator of Ccnd1 through binding to a potential enhancer, which was specifically active in livers. We also found active histone acetylation was essential for Ccnd1 induction by FXR. Thus, our study indicated that activation of FXR-induced harmless liver hypertrophy with spatiotemporal modulation of Ccnd1. With a better understanding of the mechanism of tissue-specific gene regulation by FXR, it is beneficial for development and appropriate application of its specific agonist in preventing hepatic diseases.

Bile acid malabsorption is associated with diarrhea in acute phase of colitis

The enterohepatic circulation of bile acids (BAs) critically depends on BA transporters and enzymes, which can be affected by inflammatory bowel disease. Diarrhea in colitis is believed to result in part from BA malabsorption. The work aimed to investigate whether diarrhea in colitis was associated with the expression of BA transporters, enzymes, and nuclear receptors. RT-qPCR and Western blot techniques were used to evaluate the gene and protein levels of Cyp7a1, Asbt, SHP, FXR, Ostβ in a 2,4,6-trinitrobenzenesulfonic-acid-induced rat model of colitis. The total BAs (TBAs) levels were assayed using ELISA kits, and the individual BAs were measured by LC-MS/MS. Results showed that the fecal excretions of TBAs were significantly increased by 1.6-fold in acute stage of colitis. In ileum, Asbt was significantly decreased; however, there was a compensatory increase in Cyp7a1 level in liver. Moreover, FXR has a decreased tendency and the downstream target gene SHP was downregulated. Contrary to acute stage, molecular changes were completely reversible during the remission phase. Our results indicated that the expression of Asbt and Cyp7a1 were altered in acute colitis, which performed vital roles in maintaining BA homeostasis. Early medical manipulation of BA transporters and enzymes may help prevent diarrhea.

Fibroblast Growth Factor 15-Dependent and Bile Acid-Independent Promotion of Liver Regeneration in Mice

The role of intestine-derived factors in promoting liver regeneration after partial hepatectomy (PHx) are not entirely known, but bile acids (BAs) and fibroblast growth factor 15 (Fgf15) that is highly expressed in the mouse ileum could promote hepatocyte proliferation. Fgf15 strongly suppresses the synthesis of BAs, and emerging evidence indicates that Fgf15 is important for liver regeneration. The mechanisms by which Fgf15 promotes liver regeneration are unclear, but Fgf15 may do so indirectly by reducing BA levels and/or directly by promoting cell proliferation. However, it remains undetermined whether these two mechanisms are independent or integrated. In this study, we aimed to clarify these relationships by generating Fgf15 Tet-Off, transgenic mice (Fgf15 Tg) that had very low BA levels as a result from overexpressed Fgf15-mediated suppression of BA synthesis. Compared with wild-type mice, the Fgf15 Tg mice showed increased hepatocyte proliferation even without surgery, and a further induction of the genes in cell-cycle progression after PHx. Moreover, overexpression of Fgf15 by adeno-associated virus (AAV)-Fgf15 transduction or treatment with the recombinant Fgf15 protein led to increased cell proliferation in vivo. Furthermore, Fgf15 Tg mice exhibited an earlier and greater activation of mitogen-activated protein kinase, signal transducer and activator of transcription 3, and NF-κB signaling pathways in the priming stage, and a disruption of the hippo signaling pathway in the termination stage of liver regeneration. Conclusion: Direct in vivo evidence demonstrates that Fgf15 is critical in stimulating the phases of priming and termination of liver regeneration that are critical for cell survival and liver-size determination, independent of BA levels. (Hepatology 2018; 00:000-000).

Farnesoid X Receptor Agonist Treatment Alters Bile Acid Metabolism but Exacerbates Liver Damage in a Piglet Model of Short-Bowel Syndrome

BACKGROUND & AIMS

Options for the prevention of short-bowel syndrome-associated liver disease (SBS-ALDs) are limited and often ineffective. The farnesoid X receptor (FXR) is a newly emerging pharmaceutical target and FXR agonists have been shown to ameliorate cholestasis and metabolic disorders. The aim of this study was to assess the efficacy of obeticholic acid (OCA) treatment in preventing SBS-ALDs.

METHODS

Piglets underwent 75% small-bowel resection (SBS) or sham surgery (sham) and were assigned to either a daily dose of OCA (2.4 mg/kg/day) or were untreated. Clinical measures included weight gain and stool studies. Histologic features were assessed. Ultraperformance liquid chromatography tandem mass spectrometry was used to determine bile acid composition in end point bile and portal serum samples. Gene expression of key FXR targets was assessed in intestinal and hepatic tissues via quantitative polymerase chain reaction.

RESULTS

OCA-treated SBS piglets showed decreased stool fat and altered liver histology when compared with nontreated SBS piglets. OCA prevented SBS-associated taurine depletion, however, further analysis of bile and portal serum samples indicated that OCA did not prevent SBS-associated alterations in bile acid composition. The expression of FXR target genes involved in bile acid transport and synthesis increased within the liver of SBS piglets after OCA administration whereas, paradoxically, intestinal expression of FXR target genes were decreased by OCA administration.

CONCLUSIONS

Administration of OCA in SBS reduced fat malabsorption and altered bile acid composition, but did not prevent the development of SBS-ALDs. We postulate that extensive small resection impacts the ability of the remnant intestine to respond to FXR activation.

Intestinal Farnesoid X Receptor Signaling Modulates Metabolic Disease

Farnesoid X receptor (FXR) regulates the synthesis, transport and enterohepatic circulation of bile acids (BA) by modulating the expression of related genes in the liver and small intestine. The composition of the gut microbiota is correlated with metabolic diseases, notably obesity and non-alcoholic fatty acid disease (NAFLD). Recent studies revealed that bacterial metabolism of BA can modulate FXR signaling in the intestine by altering the composition and concentrations of FXR agonist and antagonist. FXR agonist enhances while FXR antagonist suppresses obesity, NAFLD and insulin resistance. The role of intestinal FXR in metabolic disease was firmly established by the analysis of mice lacking FXR that are metabolic resistant to HFD-induced metabolic disease. This is mediated by FXR modulating in part the expression of genes involved in ceramide synthesis in the small intestine. In ileum of obese mice due to the presence of endogenous FXR agonists produced in the liver, these genes are activated, while in mice with altered levels of specific gut bacteria, levels of an FXR antagonist, tauro-β-muricholic acid (T-β-MCA) increase and FXR signaling and ceramide synthesis are repressed. T-β-MCA, which is metabolized in wild-type mice, led to the discovery of glycine-β-muricholic acid (Gly-MCA) that is stable in the intestine and a potent inhibitor of FXR signaling. These studies reveal that ceramides produced in the ileum under the control of FXR, influence metabolic disease, and suggest that novel FXR antagonist such as Gly-MCA that specifically inhibit intestine FXR, could serve as potential drug for the treatment of metabolic disease.

An Intestinal Microbiota-Farnesoid X Receptor Axis Modulates Metabolic Disease

The gut microbiota is associated with metabolic diseases including obesity, insulin resistance, and nonalcoholic fatty liver disease, as shown by correlative studies and by transplant of microbiota from obese humans and mice into germ-free mice. Modification of the microbiota by treatment of high-fat diet (HFD)-fed mice with tempol or antibiotics resulted in decreased adverse metabolic phenotypes. This was owing to lower levels of the genera Lactobacillus and decreased bile salt hydrolase (BSH) activity. The decreased BSH resulted in increased levels of tauro-β-muricholic acid (MCA), a substrate of BSH and a potent farnesoid X receptor (FXR) antagonist. Mice lacking expression of FXR in the intestine were resistant to HFD-induced obesity, insulin resistance, and nonalcoholic fatty liver disease, thus confirming that intestinal FXR is involved in the potentiation of metabolic disease. A potent intestinal FXR antagonist, glycine-β-MCA (Gly-MCA), which is resistant to BSH, was developed, which, when administered to HFD-treated mice, mimics the effect of the altered microbiota on HFD-induced metabolic disease. Gly-MCA had similar effects on genetically obese leptin-deficient mice. The decrease in adverse metabolic phenotype by tempol, antibiotics, and Gly-MCA was caused by decreased serum ceramides. Mice lacking FXR in the intestine also have lower serum ceramide levels, and are resistant to HFD-induced metabolic disease, and this was reversed by injection of C16:0 ceramide. In mouse ileum, because of the presence of endogenous FXR agonists produced in the liver, FXR target genes involved in ceramide synthesis are activated and when Gly-MCA is administered they are repressed, which likely accounts for the decrease in serum ceramides. These studies show that ceramides produced in the ileum under control of FXR influence metabolic diseases.

Sevelamer Improves Steatohepatitis, Inhibits Liver and Intestinal Farnesoid X Receptor (FXR), and Reverses Innate Immune Dysregulation in a Mouse Model of Non-alcoholic Fatty Liver Disease

Bile acid sequestrants are synthetic polymers that bind bile acids in the gut and are used to treat dyslipidemia and hyperphosphatemia. Recently, these agents have been reported to lower blood glucose and increase insulin sensitivity by altering bile acid signaling pathways. In this study, we assessed the efficacy of sevelamer in treating mice with non-alcoholic fatty liver disease (NAFLD). We also analyzed how sevelamer alters inflammation and bile acid signaling in NAFLD livers. Mice were fed a low-fat or Western diet for 12 weeks followed by a diet-plus-sevelamer regimen for 2 or 12 weeks. At the end of treatment, disease severity was assessed, hepatic leukocyte populations were examined, and expression of genes involved in farnesoid X receptor (FXR) signaling in the liver and intestine was analyzed. Sevelamer treatment significantly reduced liver steatosis and lobular inflammation. Sevelamer-treated NAFLD livers had notably fewer pro-inflammatory infiltrating macrophages and a significantly greater fraction of alternatively activated Kupffer cells compared with controls. Expression of genes involved in FXR signaling in the liver and intestine was significantly altered in mice with NAFLD as well as in those treated with sevelamer. In a mouse model of NAFLD, sevelamer improved disease and counteracted innate immune cell dysregulation in the liver. This study also revealed a dysregulation of FXR signaling in the liver and intestine of NAFLD mice that was counteracted by sevelamer treatment.

Liver Cholesterol Overload Aggravates Obstructive Cholestasis by Inducing Oxidative Stress and Premature Death in Mice

Nonalcoholic steatohepatitis is one of the leading causes of liver disease. Dietary factors determine the clinical presentation of steatohepatitis and can influence the progression of related diseases. Cholesterol has emerged as a critical player in the disease and hence consumption of cholesterol-enriched diets can lead to a progressive form of the disease. The aim was to investigate the impact of liver cholesterol overload on the progression of the obstructive cholestasis in mice subjected to bile duct ligation surgery. Mice were fed with a high cholesterol diet for two days and then were subjected to surgery procedure; histological, biochemical, and molecular analyses were conducted to address the effect of cholesterol in liver damage. Mice under the diet were more susceptible to damage. Results show that cholesterol fed mice exhibited increased apoptosis and oxidative stress as well as reduction in cell proliferation. Mortality following surgery was higher in HC fed mice. Liver cholesterol impairs the repair of liver during obstructive cholestasis and aggravates the disease with early fatal consequences; these effects were strongly associated with oxidative stress.

Bile salts in control of lipid metabolism

PURPOSE OF REVIEW

The view on bile salts has evolved over the years from being regarded as simple detergents that aid intestinal absorption of fat-soluble nutrients to being important hormone-like integrators of metabolism. This review provides an update on the rapidly developing field of interactions between bile salts and lipid metabolism, with a particular emphasis on the underlying mechanisms.

RECENT FINDINGS

The nuclear receptor farnesoid X receptor (FXR) plays major roles in bile salt-mediated signaling pathways. The recent identification of novel FXR targets and factors involved in FXR signaling highlights the interactions of bile acids with lipid metabolism. Exciting data have been reported on the use of intestine-specific FXR agonists as well as antagonists. In addition, encouraging results for treatment of hepatic steatosis obtained with obeticholic acid in the FLINT trial underline the therapeutic potential of bile salt signaling and metabolism for the treatment of lipid disorders.

SUMMARY

Modulation of FXR activity appears to be a potent target, not only for improving bile salt homeostasis, but also to improve lipid metabolism. Depending on the metabolic context both, FXR agonists as well as antagonists, could prove to be of therapeutic benefit.