The FXR agonist 6ECDCA reduces hepatic steatosis and oxidative stress induced by ethanol and low-protein diet in mice

Farnesoid X Receptor Agonists: A Promising Therapeutic Strategy for Gastrointestinal Diseases

Farnesoid X receptor (FXR) agonists have emerged as a promising therapeutic strategy for the management of various gastrointestinal (GI) diseases, including primary biliary cholangitis, nonalcoholic fatty liver disease, inflammatory bowel disease, alcohol-related liver disease, and primary sclerosing cholangitis. In this review, we discuss the mechanisms of action of FXR agonists, including their metabolic and immunomodulatory effects, and provide an overview of the clinical evidence supporting their use in the treatment of GI diseases. We also highlight the safety, adverse effects, and potential drug interactions associated with FXR agonists. While these agents have demonstrated efficacy in improving liver function, reducing hepatic steatosis, and improving histological endpoints in primary biliary cholangitis and nonalcoholic fatty liver disease, further research is needed to determine their long-term safety and effectiveness in other GI diseases, such as inflammatory bowel disease, alcohol-related liver disease, and primary sclerosing cholangitis. Additionally, the development of next-generation FXR agonists with improved potency and reduced side effects could further enhance their therapeutic potential.

Cellular senescence in liver diseases: From mechanisms to therapies

Cellular senescence is an irreversible state of cell cycle arrest, characterized by a gradual decline in cell proliferation, differentiation, and biological functions. Cellular senescence is double-edged for that it can provoke organ repair and regeneration in physiological conditions but contribute to organ and tissue dysfunction and prime multiple chronic diseases in pathological conditions. The liver has a strong regenerative capacity, where cellular senescence and regeneration are closely involved. Herein, this review firstly introduces the morphological manifestations of senescent cells, the major regulators (p53, p21, and p16), and the core pathophysiologic mechanisms underlying senescence process, and then specifically generalizes the role and interventions of cellular senescence in multiple liver diseases, including alcoholic liver disease, nonalcoholic fatty liver disease, liver fibrosis, and hepatocellular carcinoma. In conclusion, this review focuses on interpreting the importance of cellular senescence in liver diseases and summarizes potential senescence-related regulatory targets, aiming to provide new insights for further researches on cellular senescence regulation and therapeutic developments for liver diseases.

Farnesoid X Receptor (FXR) Regulates mTORC1 Signaling and Autophagy by Inhibiting SESN2 Expression

SCOPE

The mechanistic target of rapamycin complex 1 (mTORC1), as a link between nutrients and autophagy, senses many nutrients in the microenvironment. A growing body of recent literature describes the function of bile acids (BAs) as versatile signaling molecules, while it remains largely unclear whether mTORC1 can sense BAs and the mechanism has not been studied.

METHODS AND RESULTS

After treating LO2 cells with indicated concentration of chenodeoxycholic acid (CDCA) and farnesoid X receptor (FXR) inhibitor/activator for 6 h, it finds that CDCA and FXR significantly accelerate mTORC1 activation. The results of immunofluorescence indicate that CDCA and FXR inhibit cellular autophagy through activating mTORC1 pathway. In particular, these findings show that CDCA and FXR promote the lysosomal translocation and activation of mTORC1 in an amino acid-sensitive manner. Mechanistically, the transcriptomics data indicate that SESN2 is a checkpoint for mTORC1 lysosome translocation and activation induced by FXR, and knockdown SESN2 with siRNA suppresses the regulation of FXR on autophagy.

CONCLUSION

These results indicate that FXR-induced decrease in SESN2 expression and activation of the mTORC1 pathway can control autophagy and be explored as potential therapeutic targets for enterohepatic and metabolic disorders.

Altered ethanol metabolism and increased oxidative stress enhance alcohol-associated liver injury in farnesoid X receptor-deficient mice

BACKGROUND & AIMS

Pharmacological activation of farnesoid X receptor (FXR) ameliorates liver injury, steatosis and inflammation in mouse models of alcoholic liver disease (ALD), but the underlying mechanisms of the protective effect of FXR against ALD remain unclear.

METHODS

To investigate the role of FXR in ALD, we used the NIAAA model of chronic plus binge ethanol feeding in FXR-deficient knockout (FXR KO) mice.

RESULTS

Ethanol-mediated liver injury and steatosis were increased in FXR KO mice, while both WT and FXR KO mice consumed the same amount of alcohol. Ethanol feeding induced liver inflammation and neutrophil infiltration that were further increased in FXR KO mice. In addition, collagen accumulation and expression of profibrotic genes were markedly elevated in the liver of alcohol-fed FXR KO compared to wild-type mice, suggesting that ethanol-induced liver fibrosis is enhanced in the absence of FXR. Surprisingly, FXR KO mice showed reduced blood alcohol levels post-binge, while CYP2E1 and ALDH1A1 were upregulated compared to WT mice, suggesting that alcohol metabolism is altered in FXR KO mice. Notably, exacerbated liver injury in FXR KO mice was associated with increased oxidative stress. ALDH1A1 activity was upregulated in FXR-deficient mouse primary hepatocytes, contributing to reactive oxygen species (ROS) generation, in vitro. Finally, using an ALDH1A1 inhibitor, we showed that ALDH1A1 activity is a key contributor to alcohol-induced ROS generation in FXR-deficient hepatocytes, in vitro.

CONCLUSION

ALD pathogenesis in FXR KO mice correlates with altered ethanol metabolism and increased oxidative stress, providing new insights into the protective function of FXR in ALD.

New insights into the bile acid-based regulatory mechanisms and therapeutic perspectives in alcohol-related liver disease

Cholestasis is a key causative factor in alcohol-related liver disease (ALD) and variable degrees of cholestasis occur in all stages of ALD. However, the pathogenetic mechanisms and biomarkers associated with cholestasis are not well characterized. Cholestatic disease is marked by the disruption of bile acids (BA) transport and homeostasis. Consequently, in both human and experimental ALD, the disease shows a direct correlation with an imbalance in BA equilibrium, which in turn may also affect the severity of the disease. Modulation of BA metabolism or signaling pathways is increasingly considered as a potential therapeutic strategy for ALD in humans. In this paper, we highlight the key advances made in the past two decades in characterizing the molecular regulatory mechanisms of BA synthesis, enterohepatic circulation, and BA homeostasis. We summarize recent insights into the nature of the linkage between BA dysregulation and ALD, including the abnormal expression of genes involved in BA metabolism, abnormal changes in receptors that regulate BA metabolism, and disturbance in the gut flora engaged in BA metabolism caused by alcohol consumption. Additionally, we provide novel perspectives on the changes in BAs in various stages of ALD. Finally, we propose potential pharmacological therapies for ALD targeting BA metabolism and signaling.

Oyster (Crassostrea gigas) Polysaccharide Ameliorates High-Fat-Diet-Induced Oxidative Stress and Inflammation in the Liver via the Bile Acid-FXR-AMPKα Pathway

Oyster polysaccharides (OPS) have a variety of biological activities. In this study, we aimed to investigate the potential mechanisms of OPS to ameliorate hepatic oxidative stress and inflammation in mice induced by a high-fat diet (HFD). The results showed that OPS reduced the HFD-induced increases in serum transaminase levels and alleviated hepatic oxidative stress and inflammation. Moreover, OPS regulated bile acid metabolism and increased bile acid content in the liver, serum, and feces. Serum bile acid profile results indicated that OPS reduced levels of chenodeoxycholic acid, deoxycholic acid, and lithocholic acid associated with high-affinity agonists of Farnesol X receptor (FXR). Western blot analysis showed that OPS accelerated bile acid metabolism by downregulating hepatic FXR expression and promoting its downstream CYP7A1, CYP27A1, and CYP8B1 protein expression. Meanwhile, OPS ameliorated oxidative stress and inflammation in the liver by modulating FXR-AMPKα-Nrf2/NF-κB signaling to reduce p-IκBα/IκBα, p-NF-κB p65/NF-κB p65, IL-1β, and TNF-α expression and increase p-Nrf2/Nrf2, HO-1, and NQO-1 expression. This study was the first to explore the possible mechanism of OPS in improving liver oxidative stress and inflammation from the perspective of bile acid metabolism, providing a theoretical basis for OPS as a new source of functional food.

Recent advances on FXR-targeting therapeutics

The bile acid receptor FXR has emerged as a bona fide drug target for chronic cholestatic and metabolic liver diseases, ahead of all non-alcoholic fatty liver disease (NAFLD). FXR is highly expressed in the liver and intestine and activation at both sites differentially contributes to its desired metabolic effects. Unrestricted FXR activation, however, also comes along with undesired effects such as a pro-atherogenic lipid profile, pruritus and hepatocellular toxicity under certain conditions. Several pre-clinical studies have confirmed the potency of FXR activation for cholestatic and metabolic liver diseases, but overall it remains still open whether selective activation of intestinal FXR is advantageous over pan-FXR activation and whether restricted or modulated FXR activation can limit some of the side effects. Even more, FXR antagonist also bear the potential as intestinal-selective drugs in NAFLD models. In this review we will discuss the molecular prerequisites for FXR activation, pan-FXR activation and intestinal FXR in/activation from a therapeutic point of view, different steroidal and non-steroidal FXR agonists, ways to restrict FXR activation and finally what we have learned from pre-clinical models and clinical trials with different FXR therapeutics.

Croton urucurana Baill. Ameliorates Metabolic Associated Fatty Liver Disease in Rats

Background: Metabolic associated fatty liver disease (MAFLD) affects a quarter of the worldwide population, but no drug therapies have yet been developed. Croton urucurana Baill. (Euphorbiaceae) is a medicinal species, that is, widely distributed in Brazil. It is used in popular medicine to treat gastrointestinal, cardiovascular, and endocrine system diseases. However, its hepatoprotective and lipid-lowering effects have not yet been scientifically investigated.

Aim of the study: The present study investigated the effects of an extract of C. urucurana in a rat model of MAFLD that was associated with multiple risk factors, including hypertension, smoking, and dyslipidemia.

Material and Methods: The phytochemical composition of C. urucurana was evaluated by liquid chromatography-mass spectrometry. Spontaneously hypertensive rats received a 0.5% cholesterol-enriched diet and were exposed to cigarette smoke (9 cigarettes/day for 10 weeks). During the last 5 weeks, the animals were orally treated with vehicle (negative control [C-] group), C. urucurana extract (30, 100, and 300 mg/kg), or simvastatin + enalapril (two standard reference drugs that are commonly used to treat dyslipidemia and hypertension, respectively). One group of rats that were not exposed to these risk factors was also evaluated (basal group). Blood was collected for the analysis of cholesterol, triglyceride, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels. The liver and feces were collected for lipid quantification. The liver was also processed for antioxidant and histopathological analysis.

Results: The main constituents of the C. urucurana extract were flavonoids, glycosides, and alkaloids. The model successfully induced MAFLD, reflected by increases in AST and ALT levels, and induced oxidative stress in the C- group. Treatment with the C. urucurana extract (300 mg/kg) and simvastatin + enalapril decreased plasma and hepatic lipid levels. In contrast to simvastatin + enalapril treatment, C. urucurana reduced AST and ALT levels. Massive lesions were observed in the liver in the C- group, which were reversed by treatment with the C. urucurana extract (300 mg/kg).

Conclusion:C. urucurana extract exerted promising hepatoprotective and lipid-lowering effects in a preclinical rat model of MAFLD.

Recent advances in nuclear receptors-mediated health benefits of blueberry

BACKGROUND

Blueberry is rich in bioactive substances and has anti-oxidant, anti-inflammatory, anti-obesity, anti-cancer, neuroprotective, and other activities. Blueberry has been shown to treat diseases by mediating the transcription of nuclear receptors. However, evidence for nuclear receptor-mediated health benefits of blueberry has not been systematically reviewed.

PURPOSE

This review aims to summarize the nuclear receptor-mediated health benefits of blueberry.

METHODS

This study reviews all relevant literature published in NCBI PubMed, Scopus, Web of Science, and Google Scholar by January 2022. The relevant literature was extracted from the databases with the following keyword combinations: "biological activities" OR "nuclear receptors" OR "phytochemicals" AND "blueberry" OR "Vaccinium corymbosum" as well as free-text words.

RESULTS

In vivo and in vitro experimental results and clinical evidence have demonstrated that blueberry has health-promoting effects. Supplementing blueberry is beneficial to the treatment of cancer, the alleviation of metabolic syndrome, and liver protection. Blueberry can regulate the transcription of PPARs, ERs, AR, GR, MR, LXRs, and FXR and mediate the expressions of Akt, CYP 1Al, p53, and Bcl-2.

CONCLUSION

Blueberry can be targeted to treat various diseases by mediating the transcription of nuclear receptors. Nevertheless, further human research is needed.

MEK1/2 inhibitors induce class I alcohol dehydrogenase (ADH1) expression by regulating farnesoid X receptor in hepatic cell lines and C57BL/6J mouse

BACKGROUND

Alcohol is mainly catabolized by class I alcohol dehydrogenase (ADH1) in liver. ADH deficiency can aggravate ethanol-induced tissue injury. Extracellular signal-regulated kinases 1/2 (ERK1/2) is involved in alcohol metabolism. However, the relationship between ERK1/2 and ADH1 remains unclear.

METHODS AND RESULTS

To inhibit ERK1/2, HepG2 and BNL cells were treated with mitogen-activated protein kinases 1/2 (MEK1/2) inhibitors (U0126 and PD98059), and C57BL/6J mice were fed U0126. After treatment, the protein and mRNA expression of ADH1 were determined by Western blot and quantitative real time-PCR. The activity of ADH1 promoter was detected using luciferase assay. The results showed MEK1/2 inhibitors significantly increased ADH1 protein expression by inducing its transcription activity. Then we demonstrated a farnesoid X receptor (FXR) response element (FXRE) in ADH1 promoter by ChIP assay. To test whether FXR mediates the induction of MEK1/2 inhibitors on ADH1, HepG2 cells were transfected with FXR siRNA or ADH1 promoters with FXRE mutation. We found both FXR siRNA and FXRE mutation in ADH1 promoter abolished MEK1/2 inhibitors-induced ADH1 expression, indicating the activation of MEK1/2 inhibitors on ADH1 depends on FXR.

CONCLUSIONS

Our findings revealed inhibition of ERK1/2 can significantly increase ADH1 expression, indicating MEK1/2 inhibitors may possess potential application in alcohol-related diseases.

The effect of Farnesoid X receptor agonist tropifexor on liver damage in rats with experimental obstructive jaundice

Purpose:

To investigate experimentally the effects of Tropifexor, a farnesoid X receptor agonist, on liver injury in rats with obstructive jaundice.

Methods:

Forty healthy Wistar albino female rats were divided randomly in selected groups. These groups were the sham group, control group, vehicle solution group, Ursodeoxycholic acid group and Tropifexor group. Experimental obstructive jaundice was created in all groups, except the sham one. In the blood samples obtained, aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT), total bilirubin and direct bilirubin levels were established and recorded. Additionally, liver malondialdehyde, myeloperoxidase and catalase enzyme activity in the tissue samples were studied. Histopathological analysis was also performed.

Results:

No statistical difference was found between the control group and the Tropifexor group when AST, ALT and ALP values were compared. However, it was found that the Tropifexor group had statistically significant decreases in the values of GGT, total bilirubin and direct bilirubin (p < 0.05). Additionally, Tropifexor decreased the median values of malondialdehyde and myeloperoxidase, but this difference was not statistically significant compared to the control group. Finally, the Tropifexor group was statistically significant in recurring histopathological liver damage indicators (p < 0.05).

Conclusions:

Tropifexor reduced liver damage due to obstructive jaundice.

Mitochondrial Dysfunction and Oxidative Stress in Liver Transplantation and Underlying Diseases: New Insights and Therapeutics

Mitochondria are essential organelles for cellular energy and metabolism. Like with any organ, the liver highly depends on the function of these cellular powerhouses. Hepatotoxic insults often lead to an impairment of mitochondrial activity and an increase in oxidative stress, thereby compromising the metabolic and synthetic functions. Mitochondria play a critical role in ATP synthesis and the production or scavenging of free radicals. Mitochondria orchestrate many cellular signaling pathways involved in the regulation of cell death, metabolism, cell division, and progenitor cell differentiation. Mitochondrial dysfunction and oxidative stress are closely associated with ischemia-reperfusion injury during organ transplantation and with different liver diseases, including cholestasis, steatosis, viral hepatitis, and drug-induced liver injury. To develop novel mitochondria-targeting therapies or interventions, a better understanding of mitochondrial dysfunction and oxidative stress in hepatic pathogenesis is very much needed. Therapies targeting mitochondria impairment and oxidative imbalance in liver diseases have been extensively studied in preclinical and clinical research. In this review, we provide an overview of how oxidative stress and mitochondrial dysfunction affect liver diseases and liver transplantation. Furthermore, we summarize recent developments of antioxidant and mitochondria-targeted interventions.

The critical role of FXR is associated with the regulation of autophagy and apoptosis in the progression of AKI to CKD

Autophagy is important for cells to break down and recycle cellular proteins, remove damaged organelles, and especially, for recovery from acute kidney injury (AKI). Despite research on the role and cellular mechanism of autophagy in AKI, the role of autophagy in the progression to chronic kidney disease (CKD) remains poorly understood. Here, using farnesoid X receptor (FXR) knockout (KO) mice, we determined whether FXR prevents the progression of AKI to CKD after renal ischemic-reperfusion (such as I/R) injury through the regulation of renal autophagy and apoptosis. FXR regulated genes that participate in renal autophagy under feeding and fasting conditions, such as hepatic autophagy, and the activation of FXR by agonists, such as GW4064 and INT-747, attenuated the increased autophagy and apoptosis of hypoxia-induced human renal proximal tubule epithelial (HK2) cells. The expression levels of autophagy-related and apoptosis-related proteins in FXR KO mice were increased compared with those in wild-type (WT) mice. We also showed that the increase in reactive oxidative species (ROS) in hypoxia-treated HK2 cells was attenuated by treatment with FXR agonist or by FXR overexpression, and that the level of ROS was elevated in FXR-deficient cells and mice. At 28 days after I/R injury, the autophagy levels were still elevated in FXR KO mice, and the expression levels of fibrosis-related proteins and ROS deposits were higher than those in WT mice. In conclusion, the regulation of renal autophagy and apoptosis by FXR may be a therapeutic target for the early stages of kidney damage, and the progression of AKI to CKD.

Obeticholic acid ameliorates hepatorenal syndrome in ascitic cirrhotic rats by down-regulating the renal 8-iso-PGF2α-activated COX-TXA2 pathway

BACKGROUNDS/AIMS

The present study explores the potential of chronic treatment with the Foresaid X receptor (FXR) agonist obeticholic acid (OCA), which inhibits oxidative stress-related pathogenesis, in ascitic cirrhotic rats with hepatorenal syndrome (HRS) developed 6 weeks after bile duct ligation (BDL).

METHODS

Systemic, splanchnic, and renal hemodynamics and pathogenic cascades were measured in ascitic BDL and sham rats receiving 2-weeks of either vehicle or OCA treatments (sham-OCA and BDL-OCA groups), and NRK-52E cells, rat kidney tubular epithelial cells.

RESULTS

Chronic OCA treatment significantly normalized portal hypertension, glomerular filtration rate, urine output, renal blood flow; decreased ascites, renal vascular resistance, serum creatinine, and the release of renal tubular damage markers, including urinary neutrophil gelatinase-associated lipocalin (uNGAL) and kidney injury moleculae-1 (uKim-1) in BDL-OCA rats. In the BDL group, inhibition of the renal oxidative stress (8-iso-PGF2α)-activated cyclooxygenase-thromboxane A2 [COX-TXA2] pathway, apoptosis, and tubular injury accompanied by a decrease in hyper-responsiveness to the vasoconstrictor 8-iso-PGF2α in perfused kidneys. In vitro experiments revealed that 8-iso-PGF2α induced oxidative stress, release of reactive oxygen species, and cell apoptosis, which were reversed by concomitant incubation with the FXR agonist.

CONCLUSIONS

Through the inhibition of renal 8-iso-PGF2α production and the down-regulation of the COX-TXA2 pathway, our study suggests that chronic OCA treatment can ameliorate the HRS in ascitic cirrhotic rats. Thus, OCA is an agent with antioxidative stress, antivasoconstrictive, antiapoptotic properties which benefit ascitic, cirrhotic rats with systemic, hepatic, and renal abnormalities.

Yangonin inhibits ethanol-induced hepatocyte senescence via miR-194/FXR axis

Chronic alcohol assumption has been recognized as a major cause of alcoholic liver disease (ALD), which ranges from alcoholic steatohepatitis to fibrosis and hepatocellular carcinoma. Alcoholic liver disease has become the leading cause of liver-related health problem in the world. Herewith, effective therapeutic strategy for alcoholic liver disease is necessary. Yangonin (Yan), a bioactive compound extract from Kava, has been reported to exert hepatoprotective effects via Farnesoid X receptor (FXR) activation. The present study aims to investigate whether Yan ameliorated the ethanol-stimulated liver injury and further to elucidate the mechanisms in vivo and in vitro. Yan improved cell viabilities via cell count kit-8 (CCK-8) methods and obviously reduced aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol (TC) and total triglyceride (TG) levels. We detected miR-194 levels in ethanol-induced LO₂ cells and male C57BL/6 mice by quantitative real-time PCR. Also, the effects of miR-194 on modulating cellular senescence via targeting FXR were further verified. The cellular senescence markers p16, p21, telomerase activity and senescence-related β-galactosidase (SA-β-gal) were evaluated by quantitative real-time PCR and Western blot. Also, LO₂ cells or liver tissues were stained with special primary antibodies and 4',6'-Diamidino-2-phenylindole (DAPI). The cell cycle was detected by flow cytometry. We observed that Yan significantly inhibited ethanol-induced cellular senescence via FXR activation (P < 0.05). Our results demonstrate that Yan significantly reduced the cellular markers p16, p21 and Hmga1 expression and inhibited the cell cycle arrest (P < 0.05). MiR-194 was upregulated in the alcoholic liver disease, which was significantly suppressed by Yan (P < 0.05). Moreover, miR-194 mimic inhibited FXR expression in vitro. In summary, these aggregated data demonstrate that Yan alleviates chronic ethanol-induced liver injury through inhibition of cellular senescence via regulating miR-194/FXR axis.

Enhanced alcoholic liver disease in mice with intestine-specific farnesoid X receptor deficiency

Alcoholic fatty liver disease (AFLD) is one of the major causes of liver morbidity and mortality worldwide. We have previously shown that whole-body, but not hepatocyte-specific, deficiency of farnesoid X receptor (FXR) in mice worsens AFLD, suggesting that extrahepatic FXR deficiency is critical for AFLD development. Intestinal FXR is critical in suppressing hepatic bile acid (BA) synthesis by inducing fibroblast growth factor 15 (FGF15) in mice and FGF19 in humans. We hypothesized that intestinal FXR is critical for reducing AFLD development in mice. To test this hypothesis, we compared the AFLD severity in wild type (WT) and intestine-specific Fxr knockout (FXR^Int-/-) mice following treatment with control or ethanol-containing diet. We found that FXR^Int-/- mice were more susceptible to ethanol-induced liver steatosis and inflammation, compared with WT mice. Ethanol treatment altered the expression of hepatic genes involved in lipid and BA homeostasis, and ethanol detoxification. Gut FXR deficiency increased intestinal permeability, likely due to reduced mucosal integrity, as revealed by decreased secretion of Mucin 2 protein and lower levels of E-cadherin protein. In summary, intestinal FXR may protect AFLD development by maintaining gut integrity.

Schaftoside alleviates HFD-induced hepatic lipid accumulation in mice via upregulating farnesoid X receptor

ETHNOPHARMACOLOGY RELEVANCE

The farnesoid X receptor (FXR) is a therapeutic target of for the treatment of non-alcoholic fatty liver disease (NAFLD) owing to its regulatory role in lipid homeostasis. Schaftoside (SS) is a bioactive compound of Herba Desmodii Styracifolii, which has traditionally been used to treat hepatitis and cholelithiasis. However, the potential hepatoprotective effect of SS against NAFLD and the underlying mechanisms remain unknown.

AIM OF THE STUDY

We investigated whether SS could improve NAFLD-induced liver injury by decreasing lipid accumulation via the activation of FXR signalling.

MATERIALS AND METHODS

In vivo, the effects of SS on high-fat diet (HFD)-induced lipid accumulation in the liver of mice were evaluated by serum biochemical parameters and histopathological analysis. In vitro, the intracellular triglyceride (TG) level and Oil Red O staining were used to evaluate the lipid removal ability of SS in Huh-7 cells or FXR knockout mouse primary hepatocytes (MPHs) induced by oleic acid (OA). Moreover, FXR/sterol regulatory element-binding protein 1 (SREBP1) mRNA and protein expression levels were detected.

RESULTS

SS reduced HFD-induced lipid accumulation in the liver, as indicated by decreased aspartate aminotransferase (AST), cholesterol (Ch), and TG levels in serum and TG levels in liver tissue, and subsequently resulting in attenuation of liver histopathological injury. Gene expression profiles demonstrated that SS dose-dependently prevented HFD-induced decrease of FXR expression and inversely inhibited SREBP1 expression in the nucleus. Furthermore, SS significantly suppressed excessive TG accumulation and decreased intracellular TG level in Huh-7 cells or MPHs via the upregulation of FXR and inhibition of SREBP1 expression in the nucleus.

CONCLUSION

Our results suggest that SS ameliorates HFD-induced NAFLD by the decrease of lipid accumulation via the control of FXR-SREBP1 signalling.

Promising therapeutic use of Baccharis trimera (less.) DC. as a natural hepatoprotective agent against hepatic lesions that are caused by multiple risk factors

ETHNOPHARMACOLOGICAL RELEVANCE

Baccharis trimera (Less.) DC is a perennial subshrub, popularly known as "carqueja," that belongs to the Asteraceae family. Ethnobotanical studies indicate that this species is used for the treatment of diabetes and digestive and liver diseases. However, studies that sought to validate its popular use were conducted using ethanolic extracts of the plant, which does not reflect the ethnomedicinal use of this species in humans.

AIM OF THE STUDY

Non-alcoholic fatty liver disease (NAFLD) is characterized by triglyceride accumulation in the liver that can progress to cirrhosis and hepatocellular carcinoma. Because of the severity of this disease, less toxic and more effective therapeutic agents need to be developed. B. trimera may be a promising therapeutic alternative, but its activity against multiple risk factors for liver disease (e.g., smoking, dyslipidemia, and diabetes mellitus) has not been studied. The present study investigated the effects of an ethnomedicinal form of a B. trimera preparation in a rat model of NAFLD that is associated with multiple risk factors.

MATERIAL AND METHODS

Phytochemical analysis of the ethanolic soluble fraction of B. trimera extract was performed using ultra-performance liquid chromatography coupled to high-resolution mass spectrometry. Streptozotocin was used to induce diabetes in male Wistar rats. The rats received a 0.5% cholesterol-enriched diet and were exposed to cigarette smoke (9 cigarettes/day, 5 days/week, for 4 weeks). In the last 2 weeks, the animals were orally treated with vehicle (negative control group), B. trimera extract (30, 100, and 300 mg/kg), or insulin + simvastatin. One group of rats that was not exposed to these risk factors was also evaluated. Blood was collected for glucose, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) analysis. The liver and feces were collected for lipid quantification. The liver was additionally processed for histopathological analysis.

RESULTS

The model successfully induced NAFLD and increased levels of glucose, AST, and ALT in the negative control group. Treatment with the B. trimera extract (30 and 100 mg/kg) and insulin + simvastatin decreased hepatic and fecal lipids. In contrast to insulin + simvastatin treatment, all three doses of B. trimera effectively reduced AST and ALT levels.

CONCLUSION

B. trimera may be promising as a hepatoprotective agent against hepatic lesions that are caused by multiple risk factors.

Preterm Lung Exhibits Distinct Spatiotemporal Proteome Expression at Initiation of Lung Injury

The development of regional lung injury in the preterm lung is not well understood. This study aimed to characterize time-dependent and regionally specific injury patterns associated with early ventilation of the preterm lung using a mass spectrometry-based proteomic approach. Preterm lambs delivered at 124-127 days gestation received 15 or 90 minutes of mechanical ventilation (positive end-expiratory pressure = 8 cm H₂O, Vt = 6-8 ml/kg) and were compared with unventilated control lambs. At study completion, lung tissue was taken from standardized nondependent and dependent regions, and assessed for lung injury via histology, quantitative PCR, and proteomic analysis using Orbitrap-mass spectrometry. Ingenuity pathway analysis software was used to identify temporal and region-specific enrichments in pathways and functions. Apoptotic cell numbers were ninefold higher in nondependent lung at 15 and 90 minutes compared with controls, whereas proliferative cells were increased fourfold in the dependent lung at 90 minutes. The relative gene expression of lung injury markers was increased at 90 minutes in nondependent lung and unchanged in gravity-dependent lung. Within the proteome, the number of differentially expressed proteins was fourfold higher in the nondependent lung than the dependent lung. The number of differential proteins increased over time in both lung regions. A total of 95% of enriched canonical pathways and 94% of enriched cellular and molecular functions were identified only in nondependent lung tissue from the 90-minute ventilation group. In conclusion, complex injury pathways are initiated within the preterm lung after 15 minutes of ventilation and amplified by continuing ventilation. Injury development is region specific, with greater alterations within the proteome of nondependent lung.

Farnesoid X receptor (FXR) activation induces the antioxidant protein metallothionein 1 expression in mouse liver

Farnesoid X receptor (FXR) is a metabolic nuclear receptor, which protects liver from many endogenous and exogenous injuries. Metallothioneins (MTs) belong to a low-molecular-weight protein family involved in metal homeostasis and the regulation of hepatic oxidative stress. In the present study, we aimed to investigate the effect of FXR on hepatic MT1 expression and the underlying mechanism. C57BL/6 mice or primary cultured mouse hepatocytes were treated with the synthetic FXR ligand GW4064 or natural ligand CDCA. RNA-Sequencing (RNA-seq) analysis was performed to identify gene expression profile in the livers of mice treated with GW4064. Real-time PCR and Western blot were applied to determine the expression of MT1 and other FXR target genes in the livers of mice and primary hepatocytes treated with GW4064 and CDCA. Cellular and subcellular locations of MT1 in the livers of mice treated with GW4064 were examined using immunohistochemistry assay. FXR small interfering RNAs (siRNA) was transfected to silence FXR. Luciferase reporter and chromatin immunoprecipitation (ChIP) assays were utilized to confirm the regulation of MT1 gene promoter activity by FXR. RNA-seq analysis revealed that GW4064 treatment significantly induced MT1 expression in mouse liver. Consistently, MT1 expression in the hepatocytes of mouse livers and cultured hepatocytes was upregulated by GW4064 as well as CDCA. In addition, adenovirus-mediated overexpression of FXR markedly increased, while siRNA-mediated FXR silencing significantly suppressed MT1 expression in cultured hepatocytes. Luciferase reporter and ChIP assays further confirmed that the MT1 gene was under the direct control of FXR. Collectively, our findings demonstrate that MT1 is a novel target gene of FXR and may contribute to antioxidative capacity of FXR in liver diseases.

Obeticholic Acid Ameliorates Valproic Acid-Induced Hepatic Steatosis and Oxidative Stress

Farnesoid X receptor (FXR), or NR1H4, protects the liver from insults of various etiologies. A role of FXR in drug-induced liver injury has also been hypothesized yet only marginally investigated. The aim of this study was to assess the effect of FXR activation on gene expression and phenotype of the liver of mice treated with valproic acid (VPA), or 2-propylpentanoic acid, a prototypical hepatotoxic drug. Obeticholic acid (OCA) was used to activate FXR both in mice and in human hepatocellular carcinoma (Huh-7) cells. Next-generation sequencing of mouse liver tissues was performed from control, VPA, and VPA + OCA-treated mice. Pathway analysis validation was performed using real-time reverse-transcription polymerase chain reaction, Western blotting, immunohistochemistry, and fluorometric assays. FXR activation induced antioxidative pathways, which was confirmed by a marked reduction in VPA-induced lipid peroxidation and endoplasmic reticulum stress. In vitro, VPA-induced oxidative stress was independent of lipid accumulation, stemmed from the cytoplasm, and was mitigated by OCA. In the liver of the mice treated with OCA, the levels of cytochrome P450 potentially involved in VPA metabolism were increased. The hepatic lipid-lowering effect observed in animals cotreated with VPA and OCA in comparison with that of animals treated with VPA was associated with regulation of the genes involved in the steatogenic nuclear receptor peroxisome proliferator-activated γ (PPARγ) pathway. In conclusion, pronounced antioxidant activity, repression of the PPARγ pathway, and higher expression of P450 enzymes involved in VPA metabolism may underlie the hepatoprotective of FXR activation during VPA treatment. SIGNIFICANCE STATEMENT: Valproic acid-induced oxidative stress occurs in absence of lipid accumulation and is not of mitochondrial origin. Valproic acid exposure induces the expression of the steatogenic nuclear receptor peroxisome proliferator-activated γ (PPARγ) and its downstream target genes. Constitutive activation of the farnesoid X receptor (FXR) reduces PPARγ hepatic expression and induces hepatic antioxidant activity. The variability in FXR expression level/activity, for instance in individuals carrying loss-of-function genetic variants of the FXR gene, could contribute to valproic acid pharmacokinetic and toxicokinetic profile.

FXR deficiency alters bile acid pool composition and exacerbates chronic alcohol induced liver injury

Recent studies have investigated the roles of FXR deficiency in the pathogenesis of alcoholic liver disease (ALD). However, the underlying molecular mechanisms remain unclear. In this study, FXR knockout (FXR^-/-) and wild-type (WT) mice were subjected to chronic-plus-binge alcohol feeding to study the effect of FXR deficiency on ALD development. The degree of liver injury was greater in FXR^-/- mice compared to WT mice. Ethanol feeding enhanced hepatic steatosis in FXR^-/- mice, accompanied by decreased mRNA levels of Pparα and Srebp-1c. The expression of Lcn2 was increased by ethanol treatment, despite unchanged expression of pro-inflammatory cytokines Tnfα, Il6 and Il-1β. Furthermore, ethanol treatment altered bile acid (BA) homeostasis to a greater extent in FXR^-/- mice, as well as serum and hepatic BA pool composition. The mRNA levels of hepatic Cyp7a1 and Shp, as well as intestinal Fgf15, were decreased in WT mice with ethanol feeding, which were further reduced in FXR^-/- mice. Levels of both primary and secondary BAs were markedly elevated in FXR^-/- mice, which were further increased after ethanol treatment. Moreover, hepatic MAPK signaling pathways were disturbed presumably by increased hepatic BA levels. In summary, FXR deficiency increased hepatic steatosis and altered BA pool composition, contributing to worsened liver toxicity.

Bile acid homeostasis and intestinal dysbiosis in alcoholic hepatitis

BACKGROUND

Intestinal microbiota plays an important role in bile acid homeostasis.

AIM

To study the structure of the intestinal microbiota and its function in bile acid homeostasis in alcoholic patients based on the severity of alcoholic liver disease.

METHODS

In this prospective study, we included four groups of active alcoholic patients (N = 108): two noncirrhotic, with (noCir_AH, n = 13) or without alcoholic hepatitis (noCir_noAH, n = 61), and two cirrhotic, with (Cir_sAH, n = 17) or without severe alcoholic hepatitis (Cir_noAH, n = 17). Plasma and faecal bile acid profiles and intestinal microbiota composition were assessed.

RESULTS

Plasma levels of total bile acids (84.6 vs 6.8 μmol/L, P < 0.001) and total ursodeoxycholic acid (1.3 vs 0.3 μmol/L, P = 0.03) were higher in cirrhosis with severe alcoholic hepatitis (Cir_sAH) than Cir_noAH, whereas total faecal (2.4 vs 11.3, P = 0.01) and secondary bile acids (0.7 vs 10.7, P < 0.01) levels were lower. Cir_sAH patients had a different microbiota than Cir_noAH patients: at the phyla level, the abundance of Actinobacteria (9 vs 1%, P = 0.01) was higher and that of Bacteroidetes was lower (25 vs 40%, P = 0.04). Moreover, the microbiota of Cir_sAH patients showed changes in the abundance of genes involved in 15 metabolic pathways, including upregulation of glutathione metabolism, and downregulation of biotin metabolism.

CONCLUSIONS

Patients with Cir_sAH show specific changes of the bile acid pool with a shift towards more hydrophobic and toxic species that may be responsible for the specific microbiota changes. Conversely, the microbiota may also alter the bile acid pool by transforming primary to secondary bile acids, leading to a vicious cycle.

FXR and TGR5 Agonists Ameliorate Liver Injury, Steatosis, and Inflammation After Binge or Prolonged Alcohol Feeding in Mice

Bile acids (BAs) activate various dedicated receptors, including the farnesoid X receptor (FXR) and the Takeda G protein‐coupled receptor 5 (TGR5). The FXR agonist obeticholic acid (OCA) is licensed for the treatment of primary biliary cholangitis and has shown promising results in NASH patients, whereas TGR5 agonists target inflammation and metabolism. We hypothesized that FXR and/or TGR5 agonists may be therapeutic in early alcoholic liver disease (ALD) in mice, in which hepatic inflammation plays a major role. OCA, INT‐777, and INT‐767 are BA derivatives with selective agonist properties for FXR, TGR5, or both, respectively. These compounds were tested in two mouse models (3‐day binge model and prolonged Lieber DeCarli diet for 12 days) of early ALD. Serum alanine aminotransferase and liver histology were used to assess liver injury, Oil Red O staining of liver sections to assess steatosis, and real‐time polymerase chain reaction to assess changes in gene expression. In the ethanol binge model, treatment with OCA and INT‐777 decreased hepatic macrovesicular steatosis and protected from ethanol‐induced liver injury. After prolonged ethanol administration, mice treated with OCA, INT‐767, or INT‐777 showed decreased hepatic steatosis, associated with reduced liver fatty acid synthase protein expression, and protection from liver injury. Treatment with BA receptor agonists in both models of ethanol administration modulated lipogenic gene expression, and decreased liver interleukin‐1β mRNA expression associated with increased ubiquitination of NLRP3 inflammasome through cyclic adenosine monophosphate–induced activation of protein kinase A. Conclusion: OCA, INT‐767, or INT‐777 administration is effective in reducing acute and chronic ethanol‐induced steatosis and inflammation in mice, with varying degrees of efficacy depending on the duration of ethanol administration, indicating that both FXR and TGR5 activation can protect from liver injury in ALD models.

FXR deletion in hepatocytes does not affect the severity of alcoholic liver disease in mice

Emerging evidence has shown that FXR activation ameliorates the development of alcoholic liver diseases (ALD) while whole-body deficiency of FXR in mice leads to more severe ALD. However, it's unknown whether the enhanced susceptibility to ALD development in FXR^-/- mice is due to deficiency of hepatic FXR or increased toxicity secondary to increased bile acid (BA) levels. Hepatocyte-specific FXR knockout mice (FXR^hep-/-) present similar BA levels compared to wild-type mice, and are therefore a useful model to study a direct role of hepatic FXR in ALD development. FXR^hep-/- mice were subject to an ALD model with chronic plus binge drinking of alcohol to determine the effects of hepatic FXR deficiency on ALD development. The FXR^hep-/- mice showed an altered expression of genes involved in BA and lipid homeostasis with alcohol treatment. Despite a slightly increased trend in hepatic lipid deposition and collagen accumulation in FXR^hep-/- mice, there were no significant differences in the severity of steatosis, inflammation, or fibrosis between WT and FXR^hep-/- mice. Therefore, these findings indicate that FXR deficiency in hepatocytes might only play a minor role in ALD development. Deficiency of FXR in other non-hepatic tissues and/or increased BA levels resultant from whole-body FXR deficiency might be responsible for more severe ALD development.

Farnesoid X receptor agonist obeticholic acid inhibits renal inflammation and oxidative stress during lipopolysaccharide-induced acute kidney injury

It is increasingly recognized that farnesoid X receptor (FXR) has anti-inflammatory and antioxidant activities. The present study investigated the effects of obeticholic acid (OCA), a novel synthetic FXR agonist, on renal inflammation and oxidative stress in a model of sepsis-induced acute kidney injury. All mice except controls were intraperitoneally injected with lipopolysaccharide (LPS, 2.0 mg/kg). In the OCA + LPS group, mice were orally pretreated with three doses of OCA (5 mg/kg) at 48, 24 and 1 h before LPS injection. Interestingly, OCA pretreatment alleviated LPS-induced renal dysfunction and pathological damage. Moreover, OCA pretreatment repressed renal inflammatory cytokines and chemokines during LPS-induced acute kidney injury. In addition, OCA blocked nuclear translocation of nuclear factor kappa B (NF-κB) p65 and p50 subunits in tubular epithelial cells of renal cortex. Additional experiment showed that OCA pretreatment attenuated LPS-induced renal glutathione depletion, lipid peroxidation and protein nitration. Moreover, OCA pretreatment inhibited the upregulation of renal NADPH oxidase and inos genes during LPS-induced acute kidney injury. In conclusion, OCA pretreatment protects against sepsis-induced acute kidney injury through inhibiting renal inflammation and oxidative stress. These results provide evidence for roles of FXR as an important regulator of inflammation and oxidative stress in the kidney.

Small heterodimer partner deficiency exacerbates binge drinking‑induced liver injury via modulation of natural killer T cell and neutrophil infiltration

Binge drinking among alcohol consumers is a common occurrence, and may result in the development of numerous diseases, including liver disorders. It has previously been reported that natural killer T (NKT) cells induce alcohol‑associated liver injury by promoting neutrophil infiltration. In the present study, the role of the orphan nuclear receptor small heterodimer partner (SHP), which is encoded by the NR0B2 gene, in acute binge drinking‑induced liver injury was investigated. SHP‑knockout (KO) and wild‑type (WT) control mice were intragastrically administered single doses of alcohol. The plasma concentrations of alanine aminotransferase and aspartate aminotransferase in SHP‑KO mice following alcohol treatment were significantly increased compared with WT mice. However, results of oil red O staining and 2',7'‑dichlorodihydrofluorescein diacetate staining indicated that levels of acute binge drinking‑associated hepatic lipid accumulation and oxidative stress were not significantly different between WT and SHP‑KO alcohol‑treated mice. Notably, tumor necrosis factor‑α mRNA expression in the liver of SHP‑KO mice was significantly increased following alcohol administration, compared with WT mice. Furthermore, the mRNA expression levels of C‑C motif chemokine ligand 2, C‑X‑C motif chemokine ligand 2 and interleukin‑4, which are all potent chemoattractants of NKT cells, as well as neutrophil expression levels, were significantly increased in the livers of SHP‑KO mice compared with WT mice following alcohol administration, as determined by reverse transcription‑quantitative polymerase chain reaction and flow cytometry. Enhanced infiltration of NKT cells, determined by flow cytometry, was also demonstrated in the livers of SHP‑KO mice following alcohol administration, compared with WT mice. The results of the present study indicate that SHP may be involved in liver‑associated protective mechanisms, with regards to the attenuation of damage caused by acute binge drinking, via regulation of NKT cell and neutrophil migration to the liver. The modulation of SHP may be a novel therapeutic strategy for the treatment of acute binge drinking‑induced liver injury.

Deficiency of cholesterol 7α-hydroxylase in bile acid synthesis exacerbates alcohol-induced liver injury in mice

Alcoholic fatty liver disease (AFLD) is a major risk factor for cirrhosis‐associated liver diseases. Studies demonstrate that alcohol increases serum bile acids in humans and rodents. AFLD has been linked to cholestasis, although the physiologic relevance of increased bile acids in AFLD and the underlying mechanism of increasing the bile acid pool by alcohol feeding are still unclear. In this study, we used mouse models either deficient of or overexpressing cholesterol 7α‐hydroxylase (Cyp7a1), the rate‐limiting and key regulatory enzyme in bile acid synthesis, to study the effect of alcohol drinking in liver metabolism and inflammation. Mice were challenged with chronic ethanol feeding (10 days) plus a binge dose of alcohol by oral gavage (5 g/kg body weight). Alcohol feeding reduced bile acid synthesis gene expression but increased the bile acid pool size, hepatic triglycerides and cholesterol, and inflammation and injury in wild‐type mice and aggravated liver inflammation and injury in Cyp7a1‐deficient mice. Interestingly, alcohol‐induced hepatic inflammation and injury were ameliorated in Cyp7a1 transgenic mice. Conclusion: Alcohol feeding alters hepatic bile acid and cholesterol metabolism to cause liver inflammation and injury, while maintenance of bile acid and cholesterol homeostasis protect against alcohol‐induced hepatic inflammation and injury. Our findings indicate that CYP7A1 plays a key role in protection against alcohol‐induced steatohepatitis. (Hepatology Communications 2018;2:99–112)

Farnesoid X receptor activation protects the kidney from ischemia-reperfusion damage

Farnesoid X receptor (FXR) activation has been reported to reduce inflammation and oxidative stress. Because both inflammation and oxidative stress are critical for tissue destruction during kidney ischemia reperfusion (I/R) injury, we investigated the protective role of FXR against kidney damage induced by I/R in mice. Mice undergoing renal I/R developed the typical features of acute kidney injury (AKI): increased creatinine, albuminuria, tubular necrosis and apoptosis. Inflammatory cytokine production and oxidative stress were also markedly increased. In mice pretreated with 6-ethyl-chenodeoxycholic acid (6-ECDCA), a selective FXR agonist, I/R induced changes were prevented and renal function and structure were improved. Moreover, FXR activation also effectively prevented the subsequent progression of AKI to chronic kidney disease (CKD) by ameliorating glomerulosclerosis and interstitial fibrosis and by suppressing fibrogenic gene expression. FXR mRNA levels were inversely correlated with the progression to CKD in mice and with the degree of interstitial fibrosis in human biopsies. In further experiments administering 6-ECDCA to renal proximal tubular cells cultured under hypoxia, the renoprotective effects of FXR activation were associated with inhibition of oxidative and ER stress and with increased antioxidant activity. In conclusion, FXR agonists may have a therapeutic role in conditions associated with ischemic kidney damage.

Targeting nuclear receptors for the treatment of fatty liver disease

Ligand-activated nuclear receptors, including peroxisome proliferator-activated receptor alpha (PPARα), pregnane X receptor, and constitutive androstane receptor, were first identified as key regulators of the responses against chemical toxicants. However, numerous studies using mouse disease models and human samples have revealed critical roles for these receptors and others, such as PPARβ/δ, PPARγ, farnesoid X receptor (FXR), and liver X receptor (LXR), in maintaining nutrient/energy homeostasis in part through modulation of the gut-liver-adipose axis. Recently, disorders associated with disrupted nutrient/energy homeostasis, e.g., obesity, metabolic syndrome, and non-alcoholic fatty liver disease (NAFLD), are increasing worldwide. Notably, in NAFLD, a progressive subtype exists, designated as non-alcoholic steatohepatitis (NASH) that is characterized by typical histological features resembling alcoholic steatohepatitis (ASH), and NASH/ASH are recognized as major causes of hepatitis virus-unrelated liver cirrhosis and hepatocellular carcinoma. Since hepatic steatosis is basically caused by an imbalance between fat/energy influx and utilization, abnormal signaling of these nuclear receptors contribute to the pathogenesis of fatty liver disease. Standard therapeutic interventions have not been fully established for fatty liver disease, but some new agents that activate or inhibit nuclear receptor signaling have shown promise as possible therapeutic targets. In this review, we summarize recent findings on the roles of nuclear receptors in fatty liver disease and discuss future perspectives to develop promising pharmacological strategies targeting nuclear receptors for NAFLD/NASH.

Farnesoid X Receptor Activation Promotes Hepatic Amino Acid Catabolism and Ammonium Clearance in Mice

BACKGROUND & AIMS

The nuclear receptor subfamily 1 group H member 4 (NR1H4 or farnesoid X receptor [FXR]) regulates bile acid synthesis, transport, and catabolism. FXR also regulates postprandial lipid and glucose metabolism. We performed quantitative proteomic analyses of liver tissues from mice to evaluate these functions and investigate whether FXR regulates amino acid metabolism.

METHODS

To study the role of FXR in mouse liver, we used mice with a disruption of Nr1h4 (FXR-knockout mice) and compared them with floxed control mice. Mice were gavaged with the FXR agonist obeticholic acid or vehicle for 11 days. Proteome analyses, as well as targeted metabolomics and chromatin immunoprecipitation, were performed on the livers of these mice. Primary rat hepatocytes were used to validate the role of FXR in amino acid catabolism by gene expression and metabolomics studies. Finally, control mice and mice with liver-specific disruption of Nr1h4 (liver FXR-knockout mice) were re-fed with a high-protein diet after 6 hours fasting and gavaged a ¹⁵NH₄Cl tracer. Gene expression and the metabolome were studied in the livers and plasma from these mice.

RESULTS

In livers of control mice and primary rat hepatocytes, activation of FXR with obeticholic acid increased expression of proteins that regulate amino acid degradation, ureagenesis, and glutamine synthesis. We found FXR to bind to regulatory sites of genes encoding these proteins in control livers. Liver tissues from FXR-knockout mice had reduced expression of urea cycle proteins, and accumulated precursors of ureagenesis, compared with control mice. In liver FXR-knockout mice on a high-protein diet, the plasma concentration of newly formed urea was significantly decreased compared with controls. In addition, liver FXR-knockout mice had reduced hepatic expression of enzymes that regulate ammonium detoxification compared with controls. In contrast, obeticholic acid increased expression of genes encoding enzymes involved in ureagenesis compared with vehicle in C57Bl/6 mice.

CONCLUSIONS

In livers of mice, FXR regulates amino acid catabolism and detoxification of ammonium via ureagenesis and glutamine synthesis. Failure of the urea cycle and hyperammonemia are common in patients with acute and chronic liver diseases; compounds that activate FXR might promote ammonium clearance in these patients.

Mechanism of Hepatocyte Apoptosis

Hepatocyte apoptosis plays important roles in both the removal of external microorganisms and the occurrence and development of liver diseases. Different conditions, such as virus infection, fatty liver disease, hepatic ischemia reperfusion, and drug-induced liver injury, are accompanied by hepatocyte apoptosis. This review summarizes recent research on the mechanism of hepatocyte apoptosis involving the classical extrinsic and intrinsic apoptotic pathways, endoplasmic reticulum stress, and oxidative stress-induced apoptosis. We emphasized the major causes of apoptosis according to the characteristics of different liver diseases. Several concerns regarding future research and clinical application are also raised.

Dihydroartemisinin protects against alcoholic liver injury through alleviating hepatocyte steatosis in a farnesoid X receptor-dependent manner

Alcoholic liver disease (ALD) is a common etiology of liver diseases, characterized by hepatic steatosis. We previously identified farnesoid X receptor (FXR) as a potential therapeutic target for ALD. Dihydroartemisinin (DHA) has been recently identified to possess potent pharmacological activities on liver diseases. This study was aimed to explore the impact of DHA on ALD and further elaborate the underlying mechanisms. Gain- or loss-of-function analyses of FXR were applied in both in vivo and in vitro studies. Results demonstrated that DHA rescued FXR expression and activity in alcoholic rat livers. DHA also reduced serodiagnostic markers of liver injury, including aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and lactate dehydrogenase. DHA improved alcohol-induced liver histological lesions, expression of inflammation genes, and inflammatory cell infiltration. In addition, DHA not only attenuated hyperlipidemia but also reduced hepatic steatosis through regulating lipogenesis and lipolysis genes. In vitro experiments further consolidated the concept that DHA ameliorated ethanol-caused hepatocyte injury and steatosis. Noteworthily, DHA effects were reinforced by FXR agonist obeticholic acid or FXR expression plasmids but abrogated by FXR antagonist Z-guggulsterone or FXR siRNA. In summary, DHA significantly improved alcoholic liver injury by inhibiting hepatic steatosis, which was dependent on its activation of FXR in hepatocytes.

Farnesoid X receptor as a regulator of fuel consumption and mitochondrial function

Maintenance of energy homeostasis is crucial for survival of organism. There exists a close link between energy metabolism and cell survival, which are coordinately regulated by common signaling pathways. Farnesoid X receptor (FXR) serves as a ligand-mediated transcription factor to regulate diverse genes involved in bile acid, lipid, and glucose metabolism, controlling cellular and systemic energy metabolism. Another important aspect on FXR biology is related to its beneficial effect on cell survival. FXR exerts antioxidative and cytoprotective effect, which is closely associated with the ability of FXR to regulate mitochondrial function. To maintain complex biological processes under homeostasis, FXR activity needs to be dynamically and tightly controlled by different signaling pathways and modifications. In this review, we discuss the role of FXR in the regulation of energy metabolism and cell survival, with the goal of understanding molecular basis for FXR regulation in physiological and pathological conditions. This information may be of assistance in understanding recent advancements of FXR research and strategies for the prevention and treatment of metabolic disorders.

The Role of Nuclear Receptors in the Pathophysiology, Natural Course, and Drug Treatment of NAFLD in Humans

Nonalcoholic fatty liver disease (NAFLD) describes steatosis, nonalcoholic steatohepatitis with or without fibrosis, and hepatocellular carcinoma, namely the entire alcohol-like spectrum of liver disease though observed in the nonalcoholic, dysmetabolic, individual free of competing causes of liver disease. NAFLD, which is a major public health issue, exhibits intrahepatic triglyceride storage giving rise to lipotoxicity. Nuclear receptors (NRs) are transcriptional factors which, activated by ligands, are master regulators of metabolism and also have intricate connections with circadian control accounting for cyclical patterns in the metabolic fate of nutrients. Several transcription factors, such as peroxisome proliferator-activated receptors, liver X receptors, farnesoid X receptors, and their molecular cascades, finely regulate energetic fluxes and metabolic pathways. Dysregulation of such pathways is heavily implicated in those metabolic derangements characterizing insulin resistance and metabolic syndrome and in the histogenesis of progressive NAFLD forms. We review the role of selected NRs in NAFLD pathogenesis. Secondly, we analyze the role of NRs in the natural history of human NAFLD. Next, we discuss the results observed in humans following administration of drug agonists or antagonists of the NRs pathogenically involved in NAFLD. Finally, general principles of treatment and lines of research in human NAFLD are briefly examined.

Soyasaponin Bb Protects Rat Hepatocytes from Alcohol-Induced Oxidative Stress by Inducing Heme Oxygenase-1

BACKGROUND

It has been known that oxidative stress induced by alcohol played a crucial role in the formation of alcoholic liver disease. Although the formation mechanisms underlying liver injury induced by alcohol still remained largely unknown, it has been considered that oxidative stress played a core role in the pathogenesis of hepatocyte damage.

OBJECTIVE

The aim of this study was to investigate the effects of soyasaponin Bb (Ss-Bb) on oxidative stress in alcohol-induced rat hepatocyte injury.

RESULTS

It has been shown that the administration of Ss-Bb could significantly restore antioxidant activity in BRL 3A cells. Moreover, the impaired liver function and morphology changes resulting from ethanol exposure were improved by Ss-Bb treatment. Treatment with a pharmacological inhibitor of haem oxygenase-1 (HO-1) indicated a critical role of HO-1 in mediating the protective role. Finally, we found that pretreatment with Ss-Bb to ethanol exposure cells increased the expression level of HO-1.

CONCLUSION

It was suggested that Ss-Bb may protect against alcohol-induced hepatocyte injury through ameliorating oxidative stress, and the induction of HO-1 was an important protective mechanism.

SUMMARY

Effects of soyasaponin Bb was investigated on oxidative stress in rat hepatocytesCell viability and antioxidant capacities were evaluated to determine the effectsThe expression level of HO-1 was measured to reveal the proptective mechanisms.

Molecular basis of alcoholic fatty liver disease: From incidence to treatment

Alcoholic liver diseases have complex and multiple pathogenic mechanisms but still no effective treatment. Steatosis or alcoholic fatty liver disease (AFLD) has a widespread incidence and is the first step in the progression to more severe stages of alcoholic liver disease, with concomitant increases in morbidity and mortality rates. The ways in which this progression occurs and why some individuals are susceptible are still unanswered scientific questions. Research with animal models and clinical evidence have shown that it is a multifactorial disease that involves interactions between lipid metabolism, inflammation, the immune response and oxidative stress. Each of these pathways provides a better understanding of the pathogenesis of AFLD and contributes to the development of therapeutic strategies. This review emphasizes the importance of research on alcoholic steatosis based on incidence data, key pathogenic mechanisms and therapeutic interventions, and discusses perspectives on the progression of this disease.

Leucine restores murine hepatic triglyceride accumulation induced by a low-protein diet by suppressing autophagy and excessive endoplasmic reticulum stress

Although it is known that a low-protein diet induces hepatic triglyceride (TG) accumulation in both rodents and humans, little is known about the underlying mechanism. In the present study, we modeled hepatic TG accumulation by inducing dietary protein deficiency in mice and aimed to determine whether certain amino acids could prevent low-protein diet-induced TG accumulation in the mouse liver. Mice fed a diet consisting of 3 % casein (3C diet) for 7 days showed hepatic TG accumulation with up-regulation of TG synthesis for the Acc gene and down-regulation of TG-rich lipoprotein secretion from hepatocytes for Mttp genes. Supplementing the 3 % casein diet with essential amino acids, branched-chain amino acids, or the single amino acid leucine rescued hepatic TG accumulation. In the livers of mice fed the 3 % casein diet, we observed a decrease in the levels of the autophagy substrate p62, an increase in the expression levels of the autophagy marker LC3-II, and an increase in the splicing of the endoplasmic reticulum (ER) stress-dependent Xbp1 gene. Leucine supplementation to the 3 % casein diet did not affect genes related to lipid metabolism, but inhibited the decrease in p62, the increase in LC3-II, and the increase in Xbp1 splicing levels in the liver. Our results suggest that ER stress responses and activated autophagy play critical roles in low-protein diet-induced hepatic TG accumulation in mice, and that leucine suppresses these two major protein degradation systems. This study contributes to understanding the mechanisms of hepatic disorders of lipid metabolism.

FXR agonists as therapeutic agents for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and a risk factor for both cardiovascular and hepatic related morbidity and mortality. The increasing prevalence of this disease requires novel therapeutic approaches to prevent disease progression. Farnesoid X receptors are bile acid receptors with roles in lipid, glucose, and energy homeostasis. Synthetic farnesoid X receptor (FXR) agonists have been developed to specifically target these receptors for therapeutic use in NAFLD patients. Here, we present a review of bile acid physiology and how agonism of FXR receptors has been examined in pre-clinical and clinical NAFLD. Early evidence suggests a potential role for synthetic FXR agonists in the management of NAFLD; however, additional studies are needed to clarify their effects on lipid and glucose parameters in humans.

Insulin resistance in clinical and experimental alcoholic liver disease

Alcoholic liver disease (ALD) is the number one cause of liver failure worldwide; its management costs billions of healthcare dollars annually. Since the advent of the obesity epidemic, insulin resistance (IR) and diabetes have become common clinical findings in patients with ALD; and the development of IR predicts the progression from simple steatosis to cirrhosis in ALD patients. Both clinical and experimental data implicate the impairment of several mediators of insulin signaling in ALD, and experimental data suggest that insulin-sensitizing therapies improve liver histology. This review explores the contribution of impaired insulin signaling in ALD and summarizes the current understanding of the synergistic relationship between alcohol and nutrient excess in promoting hepatic inflammation and disease.

Role of farnesoid X receptor and bile acids in alcoholic liver disease

Alcoholic liver disease (ALD) is one of the major causes of liver morbidity and mortality worldwide. Chronic alcohol consumption leads to development of liver pathogenesis encompassing steatosis, inflammation, fibrosis, cirrhosis, and in extreme cases, hepatocellular carcinoma. Moreover, ALD may also associate with cholestasis. Emerging evidence now suggests that farnesoid X receptor (FXR) and bile acids also play important roles in ALD. In this review, we discuss the effects of alcohol consumption on FXR, bile acids and gut microbiome as well as their impacts on ALD. Moreover, we summarize the findings on FXR, FoxO3a (forkhead box-containing protein class O3a) and PPARα (peroxisome proliferator-activated receptor alpha) in regulation of autophagy-related gene transcription program and liver injury in response to alcohol exposure.

Farnesoid X receptor: a master regulator of hepatic triglyceride and glucose homeostasis

Non-alcoholic fatty liver disease (NAFLD) is characterized by the aberrant accumulation of triglycerides in hepatocytes in the absence of significant alcohol consumption, viral infection or other specific causes of liver disease. NAFLD has become a burgeoning health problem both worldwide and in China, but its pathogenesis remains poorly understood. Farnesoid X receptor (FXR), a member of the nuclear receptor (NR) superfamily, has been demonstrated to be the primary sensor for endogenous bile acids, and play a crucial role in hepatic triglyceride homeostasis. Deciphering the synergistic contributions of FXR to triglyceride metabolism is critical for discovering therapeutic agents in the treatment of NAFLD and hypertriglyceridemia.

Farnesoid X receptor regulates forkhead Box O3a activation in ethanol-induced autophagy and hepatotoxicity

Alcoholic liver disease encompasses a wide spectrum of pathogenesis including steatosis, fibrosis, cirrhosis, and alcoholic steatohepatitis. Autophagy is a lysosomal degradation process that degrades cellular proteins and damaged/excess organelles, and serves as a protective mechanism in response to various stresses. Acute alcohol treatment induces autophagy via FoxO3a-mediated autophagy gene expression and protects against alcohol-induced steatosis and liver injury in mice. Farnesoid X Receptor (FXR) is a nuclear receptor that regulates cellular bile acid homeostasis. In the present study, wild type and FXR knockout (KO) mice were treated with acute ethanol for 16 h. We found that ethanol treated-FXR KO mice had exacerbated hepatotoxicity and steatosis compared to wild type mice. Furthermore, we found that ethanol treatment had decreased expression of various essential autophagy genes and several other FoxO3 target genes in FXR KO mice compared with wild type mice. Mechanistically, we did not find a direct interaction between FXR and FoxO3. Ethanol-treated FXR KO mice had increased Akt activation, increased phosphorylation of FoxO3 resulting in decreased FoxO3a nuclear retention and DNA binding. Furthermore, ethanol treatment induced hepatic mitochondrial spheroid formation in FXR KO mice but not in wild type mice, which may serve as a compensatory alternative pathway to remove ethanol-induced damaged mitochondria in FXR KO mice. These results suggest that lack of FXR impaired FoxO3a-mediated autophagy and in turn exacerbated alcohol-induced liver injury.

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FXR knockout mice are more susceptible to acute ethanol-induced steatosis and liver injury due to defective hepatic autophagy.

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FXR knockout mice had decreased FoxO3a activation and reduced expression of autophagy related genes in the liver after acute ethanol treatment.

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FXR knockout mice had increased mitochondrial spheroid formation after acute ethanol treatment.