Fibroblast growth factor 15/19 (FGF15/19) protects from diet-induced hepatic steatosis: development of an FGF19-based chimeric molecule to promote fatty liver regeneration

FXR agonist GW4064 improves liver and intestinal pathology and alters bile acid metabolism in rats undergoing small intestinal resection

Mortality associated with liver disease has been observed in patients with short bowel syndrome (SBS); however, its mechanism remains unclear, but bile acid (BA) dysmetabolism has been proposed as a possible cause. The farnesoid X receptor (FXR) is the key regulator of BA synthesis. Here, we showed that, in a rat model of short bowel resection associated with liver disease (SBR-ALD), the BA composition of hepatic tissues reflected a larger proportion of primary and secondary unconjugated BAs, whereas that of the colon contents and serum showed an increased ratio of secondary unconjugated BAs. Both hepatic and intestinal regulation of BA synthesis was characterized by a blunted hepatic FXR activation response. The mRNA expression levels of cholesterol 7a-hydroxylase (CYP7A1), sterol 12a-hydroxylase (CYP8B1), and sterol 27 hydroxylase (CYP27A1), the key enzymes in BA synthesis, were upregulated. After intervention with the FXR agonist GW4064, both the liver histology and serum transaminase activity were improved, which demonstrated the attenuation of SBR-ALD. The BA compositions of hepatic tissue, the colon contents, and serum recovered and were closer to those of the sham group. The expression levels of hepatic FXR increased, and its target genes were activated. Consistent with this, the expression levels of CYP7A1, CYP8B1, and CYP27A1 were downregulated. Ileum tissue FXR and its target genes were slightly elevated. This study showed that the FXR agonist GW4064 could correct BA dysmetabolism to alleviate hepatotoxicity in SBR animals. GW4064 intervention resulted in a decrease in fecal bile excretion and elevated plasma/hepatic conjugated BA levels. GW4064 increased the reabsorption of conjugated BAs by inducing apical sodium-dependent bile salt transporter expression in the ileum. Concomitantly, FXR activation in the presence of GW4064 decreased BA production by repressing the expression of key synthetases, including CYP7A1, CYP8B1, and CYP27A1. These findings provide a clinical research direction for the prevention of liver disease in patients with SBS.NEW & NOTEWORTHY This study assessed the impact of treatment with GW4064, a farnesoid X receptor agonist, on the development of short bowel resection (SBR) associated with liver disease in a rat model of SBR. GW4064 was able to correct bile acid dysmetabolism and alleviate hepatotoxicity in SBR animals.

Obeticholic acid ameliorates dyslipidemia but not glucose tolerance in mouse model of gestational diabetes

Metabolism alters markedly with advancing gestation, characterized by progressive insulin resistance, dyslipidemia, and raised serum bile acids. The nuclear receptor farnesoid X receptor (FXR) has an integral role in bile acid homeostasis and modulates glucose and lipid metabolism. FXR is known to be functionally suppressed in pregnancy. The FXR agonist, obeticholic acid (OCA), improves insulin sensitivity in patients with type 2 diabetes with nonalcoholic fatty liver disease. We therefore hypothesized that OCA treatment during pregnancy could improve disease severity in a mouse model of gestational diabetes mellitus (GDM). C57BL/6J mice were fed a high-fat diet (HFD; 60% kcal from fat) for 4 wk before and throughout pregnancy to induce GDM. The impact of the diet supplemented with 0.03% OCA throughout pregnancy was studied. Pregnant HFD-fed mice displayed insulin resistance and dyslipidemia. OCA significantly reduced plasma cholesterol concentrations in nonpregnant and pregnant HFD-fed mice (by 22.4%, P < 0.05 and 36.4%, P < 0.001, respectively) and reduced the impact of pregnancy on insulin resistance but did not change glucose tolerance. In nonpregnant HFD-fed mice, OCA ameliorated weight gain, reduced mRNA expression of inflammatory markers in white adipose tissue, and reduced plasma glucagon-like peptide 1 concentrations (by 62.7%, P < 0.01). However, these effects were not evident in pregnant mice. OCA administration can normalize plasma cholesterol levels in a mouse model of GDM. However, the absence of several of the effects of OCA in pregnant mice indicates that the agonistic action of OCA is not sufficient to overcome many metabolic consequences of the pregnancy-associated reduction in FXR activity.

Gall bladder: The metabolic orchestrator

It is commonly held that the gall bladder (GB) is not indispensable for life. However, recent studies strongly suggest that GB removal can lead to the development of metabolic syndrome (MetS). With the recent recognition of the role of bile acids (BAs) in systemic metabolic regulation, it is worthwhile to re-examine the function of the GB, which can be regarded as the physiological "pacemaker" of BA flow. Thus, in the present study, we review the role of the GB in BA flow regulation, describe the epidemiologic evidence that associates cholecystectomy with various components of MetS, and discuss the possible mechanism behind these connections in order to demonstrate the pivotal role that GB plays in metabolic regulation.

Treatment of Experimental Autoimmune Encephalomyelitis by Sustained Delivery of Low-Dose IFN-α

Multiple sclerosis (MS) is a chronic autoimmune disease with no curative treatment. The immune regulatory properties of type I IFNs have led to the approval of IFN-β for the treatment of relapsing-remitting MS. However, there is still an unmet need to improve the tolerability and efficacy of this therapy. In this work, we evaluated the sustained delivery of IFN-α1, either alone or fused to apolipoprotein A-1 by means of an adeno-associated viral (AAV) system in the mouse model of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis. These in vivo experiments demonstrated the prophylactic and therapeutic efficacy of the AAV-IFN-α or AAV-IFN-α fused to apolipoprotein A-1 vectors in experimental autoimmune encephalomyelitis, even at low doses devoid of hematological or neurologic toxicity. The sustained delivery of such low-dose IFN-α resulted in immunomodulatory effects, consisting of proinflammatory monocyte and T regulatory cell expansion. Moreover, encephalitogenic T lymphocytes from IFN-α-treated mice re-exposed to the myelin oligodendrocyte glycoprotein peptide in vitro showed a reduced proliferative response and cytokine (IL-17A and IFN-γ) production, in addition to upregulation of immunosuppressive molecules, such as IL-10, IDO, or PD-1. In conclusion, the results of the present work support the potential of sustained delivery of low-dose IFN-α for the treatment of MS and likely other T cell-dependent chronic autoimmune disorders.

Bile Acid and Fibroblast Growth Factor 19 Regulation in Obese Diabetics, and Non-Alcoholic Fatty Liver Disease after Sleeve Gastrectomy

Background: Sleeve gastrectomy (SG) is an effective treatment for obesity and type 2 diabetes mellitus (T2DM), and non-alcoholic fatty liver disease (NAFLD); however, the mechanism is not completely understood. Bile acids and fibroblast growth factors (FGFs) are involved in the regulation of energy metabolism. Methods: We investigated the roles of total bile acid and FGF 19 in T2DM remission and NAFLD improvement in obese subjects undergoing SG. A total of 18 patients with obesity and T2DM undergoing laparoscopic SG were enrolled in this study. Serial plasma total bile acid and FGF 19 levels were measured, while the fatty liver index was calculated before and after surgery. Results: The FGF 19 level significantly increased, and the total bile acid level and fatty liver index decreased 1 year after surgery. The complete T2DM remission rate was 66.7% one year after surgery; the complete remitters had significantly lower FGF 19 levels and higher insulin levels than the non-complete remitters. The complete remitters also had significantly decreased total bile acid levels and increased FGF 19 levels 1 year after surgery compared with those before surgery. The fatty improvers had significantly decreased total bile acid levels and increased FGF 19 levels 1 year after surgery compared with those before surgery. Conclusion: The total bile acids level and fatty liver index decreased, and the FGF 19 levels increased 1 year after SG. Both T2DM complete remitters and NAFLD improvers showed significantly decreased total bile acid levels and increased FGF 19 levels 1 year after SG. Plasma total bile acids and FGF 19 might have roles in T2DM remission and NAFLD improvement. Low preoperative FGF 19 levels might be a predictor for NAFLD improvement after SG.

FGF19 sustains the high proliferative ability of keratinocytes in psoriasis through the regulation of Wnt/GSK-3β/β-catenin signalling via FGFR4

Accumulating evidence has shown that fibroblast growth factor 19 (FGF19) plays an important role in regulating cell proliferation. Psoriasis is characterized by the hyperproliferation of keratinocytes in skin lesions. However, whether FGF19 regulates the proliferation of keratinocytes in psoriasis remains unknown. In this study, we aimed to explore the potential relevance of FGF19 in psoriasis. We found that FGF19 was highly expressed in psoriatic skin from psoriasis patients, as well as keratinocytes that were stimulated with a cocktail of cytokines (M5), which is an in vitro model of psoriasis. Functional experiments demonstrated that FGF19 overexpression promoted the growth and proliferation of keratinocytes, while FGF19 knockdown showed opposite effect. Moreover, we found that FGF19 increased the phosphorylation of glycogen synthase kinase (GSK)-3β and promoted the expression of β-catenin and the activation of T cell factor 4 (TCF4) transcriptional activity. Notably, blocking Wnt/β-catenin signalling by silencing β-catenin partially reversed FGF19-mediated promotional effects on keratinocyte proliferation. In addition, FGFR4 inhibition significantly blocked the promotional effect of FGF19 on keratinocyte proliferation and GSK-3β/β-catenin/TCF4 signalling. Taken together, our results demonstrated that FGF19 contributes to sustaining the high proliferative ability of keratinocytes through promoting Wnt/GSK-3β/β-catenin signalling via FGFR4, highlighting the importance of FGF19 in the pathogenesis of psoriasis. Our study suggests that FGF19 may serve as a novel and potential therapeutic target for psoriasis.

Hepatocyte-specific loss of GPS2 in mice reduces non-alcoholic steatohepatitis via activation of PPARα

Obesity triggers the development of non-alcoholic fatty liver disease (NAFLD), which involves alterations of regulatory transcription networks and epigenomes in hepatocytes. Here we demonstrate that G protein pathway suppressor 2 (GPS2), a subunit of the nuclear receptor corepressor (NCOR) and histone deacetylase 3 (HDAC3) complex, has a central role in these alterations and accelerates the progression of NAFLD towards non-alcoholic steatohepatitis (NASH). Hepatocyte-specific Gps2 knockout in mice alleviates the development of diet-induced steatosis and fibrosis and causes activation of lipid catabolic genes. Integrative cistrome, epigenome and transcriptome analysis identifies the lipid-sensing peroxisome proliferator-activated receptor α (PPARα, NR1C1) as a direct GPS2 target. Liver gene expression data from human patients reveal that Gps2 expression positively correlates with a NASH/fibrosis gene signature. Collectively, our data suggest that the GPS2-PPARα partnership in hepatocytes coordinates the progression of NAFLD in mice and in humans and thus might be of therapeutic interest.

The Epidermal Growth Factor Receptor Ligand Amphiregulin Protects From Cholestatic Liver Injury and Regulates Bile Acids Synthesis

Intrahepatic accumulation of bile acids (BAs) causes hepatocellular injury. Upon liver damage, a potent protective response is mounted to restore the organ's function. Epidermal growth factor receptor (EGFR) signaling is essential for regeneration after most types of liver damage, including cholestatic injury. However, EGFR can be activated by a family of growth factors induced during liver injury and regeneration. We evaluated the role of the EGFR ligand, amphiregulin (AREG), during cholestatic liver injury and regulation of AREG expression by BAs. First, we demonstrated increased AREG levels in livers from patients with primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC). In two murine models of cholestatic liver injury, bile duct ligation (BDL) and alpha-naphthyl-isothiocyanate (ANIT) gavage, hepatic AREG expression was markedly up-regulated. Importantly, Areg^-/- mice showed aggravated liver injury after BDL and ANIT administration compared to Areg^+/+ mice. Recombinant AREG protected from ANIT and BDL-induced liver injury and reduced BA-triggered apoptosis in liver cells. Oral BA administration induced ileal and hepatic Areg expression, and, interestingly, cholestyramine feeding reduced postprandial Areg up-regulation in both tissues. Most interestingly, Areg^-/- mice displayed high hepatic cholesterol 7 α-hydroxylase (CYP7A1) expression, reduced serum cholesterol, and high BA levels. Postprandial repression of Cyp7a1 was impaired in Areg^-/- mice, and recombinant AREG down-regulated Cyp7a1 mRNA in hepatocytes. On the other hand, BAs promoted AREG gene expression and protein shedding in hepatocytes. This effect was mediated through the farnesoid X receptor (FXR), as demonstrated in Fxr^-/- mice, and involved EGFR transactivation. Finally, we show that hepatic EGFR expression is indirectly induced by BA-FXR through activation of suppressor of cytokine signaling-3 (SOC3). Conclusion: AREG-EGFR signaling protects from cholestatic injury and participates in the physiological regulation of BA synthesis.

Fibroblast Growth Factor 15/19: From Basic Functions to Therapeutic Perspectives

Discovered 20 years ago, fibroblast growth factor (FGF)19, and its mouse ortholog FGF15, were the first members of a new subfamily of FGFs able to act as hormones. During fetal life, FGF15/19 is involved in organogenesis, affecting the development of the ear, eye, heart, and brain. At adulthood, FGF15/19 is mainly produced by the ileum, acting on the liver to repress hepatic bile acid synthesis and promote postprandial nutrient partitioning. In rodents, pharmacologic doses of FGF19 induce the same antiobesity and antidiabetic actions as FGF21, with these metabolic effects being partly mediated by the brain. However, activation of hepatocyte proliferation by FGF19 has long been a challenge to its therapeutic use. Recently, genetic reengineering of the molecule has resolved this issue. Despite a global overlap in expression pattern and function, murine FGF15 and human FGF19 exhibit several differences in terms of regulation, molecular structure, signaling, and biological properties. As most of the knowledge originates from the use of FGF19 in murine models, differences between mice and humans in the biology of FGF15/19 have to be considered for a successful translation from bench to bedside. This review summarizes the basic knowledge concerning FGF15/19 in mice and humans, with a special focus on regulation of production, morphogenic properties, hepatocyte growth, bile acid homeostasis, as well as actions on glucose, lipid, and energy homeostasis. Moreover, implications and therapeutic perspectives concerning FGF19 in human diseases (including obesity, type 2 diabetes, hepatic steatosis, biliary disorders, and cancer) are also discussed.

The impact of steatosis on liver regeneration

Alcoholic and non-alcoholic fatty liver diseases are the leading causes of cirrhosis in Western countries. These chronic liver diseases share common pathological features ranging from steatosis to steatohepatitis. Fatty liver is associated with primary liver graft dysfunction, a higher incidence of complications/mortality after surgery, in correlation with impaired liver regeneration. Liver regeneration is a multistep process including a priming phase under the control of cytokines followed by a growth factor receptor activation phase leading to hepatocyte proliferation. This process ends when the initial liver mass is restored. Deficiency in epidermal growth factor receptor (EGFR) liver expression, reduced expression of Wee1 and Myt1 kinases, oxidative stress and alteration in hepatocyte macroautophagy have been identified as mechanisms involved in the defective regeneration of fatty livers. Besides the mechanisms, we will also discuss in this review various treatments that have been investigated in the reversal of the regeneration defect, for example, omega-3 fatty acids, pioglitazone, fibroblast growth factor (FGF)19-based chimeric molecule or growth hormone (GH). Since dysbiosis impedes liver regeneration, targeting microbiota could also be an interesting therapeutic approach.

FXR agonist obeticholic acid induces liver growth but exacerbates biliary injury in rats with obstructive cholestasis

Cholestasis impairs liver regeneration following partial liver resection (PHx). Bile acid receptor farnesoid X-receptor (FXR) is a key mediator of liver regeneration. The effects of FXR agonist obeticholic acid (OCA) on liver (re)growth were therefore studied in cholestatic rats. Animals underwent sham surgery or reversible bile duct ligation (rBDL). PHx with concurrent internal biliary drainage was performed 7 days after rBDL. Animals were untreated or received OCA (10 mg/kg/day) per oral gavage from rBDL until sacrifice. After 7 days of OCA treatment, dry liver weight increased in the rBDL + OCA group, indicating OCA-mediated liver growth. Enhanced proliferation in the rBDL + OCA group prior to PHx concurred with a rise in Ki67-positive hepatocytes, elevated hepatic Ccnd1 and Cdc25b expression, and an induction of intestinal fibroblast growth factor 15 expression. Liver regrowth after PHx was initially stagnant in the rBDL + OCA group, possibly due to hepatomegaly prior to PHx. OCA increased hepatobiliary injury markers during BDL, which was accompanied by upregulation of the bile salt export pump. There were no differences in histological liver injury. In conclusion, OCA induces liver growth in cholestatic rats prior to PHx but exacerbates biliary injury during cholestasis, likely by forced pumping of bile acids into an obstructed biliary tree.

Future Pharmacotherapy for Non-alcoholic Steatohepatitis (NASH): Review of Phase 2 and 3 Trials

Non-alcoholic steatohepatitis (NASH) results from inflammation and hepatocyte injury in the setting of hepatic steatosis. Non-alcoholic steatohepatitis increases the risk of progression to liver fibrosis and cirrhosis, and is the most rapidly growing etiology for liver failure and indication for liver transplantation in the USA. Weight loss and lifestyle modification remain the standard first-line treatment, as no USA Food and Drug Administration-approved pharmacotherapy currently exists. The past decade has seen an explosion of interest in drug development targeting pathologic pathways in non-alcoholic steatohepatitis, with numerous phase 2 and 3 trials currently in progress. Here, we concisely review the major targets and mechanisms of action by class, summarize results from completed pivotal phase 2 studies, and provide a detailed outline of key active studies with trial data for drugs in development, including obeticholic acid, elafibranor, cenicriviroc and selonsertib.

Differential receptor selectivity of the FGF15/FGF19 orthologues determines distinct metabolic activities in db/db mice

Fibroblast growth factors (FGF) 19, 21 and 23 are characterized by being endocrinely secreted and require co-receptor α-klotho or β-klotho (BKL) for binding and activation of the FGF receptors (FGFR). FGF15 is the rodent orthologue of human FGF19, but the two proteins share only 52% amino acid identity. Despite the physiological role of FGF21 and FGF19 being quite different, both lower blood glucose (BG) when administered to diabetic mice. The present study was designed to clarify why two human proteins with distinct physiological functions both lower BG in db/db mice and if the mouse orthologue FGF15 has similar effect to FGF19 and FGF21. Recombinant human FGF19, -21 and a mouse FGF15 variant (C110S) were expressed and purified from Escherichia coli While rhFGF19 (recombinant human fibroblast growth factor 19) and rhFGF21 (recombinant human fibroblast growth factor) bound FGFRs in complex with both human and mouse BKL, rmFGF15CS (recombinant mouse fibroblast growth factor 15 C110S) only bound the FGFRs when combined with mouse BKL. Recombinant hFGF21 and rhFGF19, but not rmFGF15CS, increased glucose uptake in mouse adipocytes, while rhFGF19 and rmFGF15CS potently decreased Cyp7a1 expression in rat hepatocytes. The lack of effect of rmFGF15CS on glucose uptake in adipocytes was associated with rmFGF15CS's inability to signal through the FGFR1c/mouse BKL complex. In db/db mice, only rhFGF19 and rhFGF21 decreased BG while rmFGF15CS and rhFGF19, but not rhFGF21, increased total cholesterol. These data demonstrate receptor- and species-specific differential activity of FGF15 and FGF19 which should be taken into consideration when FGF19 is used as a substitute for FGF15.

Up-regulation of FGF15/19 signaling promotes hepatocellular carcinoma in the background of fatty liver

BACKGROUND

Upregulated fibroblast growth factor 19 (FGF19) expression in human hepatocellular carcinoma (HCC) specimens is associated with tumor progression and poor prognosis. Nonalcoholic steatohepatitis (NASH) patients are at high risk for malignant transformation into HCC.

METHODS

A steatohepatitis-HCC model was established in male C57L/J mice treated with N-nitrosodiethylamine (DEN) and high-fat diet (HFD). A mouse HCC cell line (Hepa1-6) and a mouse hepatocyte line (FL83B) were used to elucidate the mechanism by free fatty acids (FFA) treatment. FGF15, the mouse orthologue of FGF19, and it receptor fibroblast growth factor receptor4 (FGFR4) as well as co-receptor β-klotho were studied. FGF19 signaling was also studied in human samples of HCC with steatohepatitis.

RESULTS

HCC incidence and tumor volume were significantly increased in the DEN+HFD group compared to that in the DEN+control diet (CD) group. Increased levels of FGF15/FGFR4/β-klotho, aberrant epithelial-mesenchymal transition (EMT) and Wnt/β-catenin signaling were detected in DEN+HFD mice. Blockage of the FGF15 signal can attenuate cell migration ability and aberrant EMT and Wnt/β-catenin signaling.

CONCLUSIONS

Up-regulated FGF15/FGFR4 signaling promoted the development of HCC by activation of EMT and Wnt/β-catenin signaling in the lipid metabolic disorder microenvironment. Further investigation of FGF19/FGFR4 signaling is important for potential early diagnosis and therapeutic targeting in HCC patients.

Foie gras and liver regeneration: a fat dilemma

The liver has a unique ability of regenerating after injuries or partial loss of its mass. The mechanisms responsible for liver regeneration - mostly occurring when the hepatic tissue is damaged or functionally compromised by metabolic stress - have been studied in considerable detail over the last few decades, because this phenomenon has both basic-biology and clinical relevance. More specifically, recent interest has been focusing on the widespread occurrence of abnormal nutritional habits in the Western world that result in an increased prevalence of non-alcoholic fatty liver disease (NAFLD). NAFLD is closely associated with insulin resistance and dyslipidemia, and it represents a major clinical challenge. The disease may progress to steatohepatitis with persistent inflammation and progressive liver damage, both of which will compromise regeneration under conditions of partial hepatectomy in surgical oncology or in liver transplantation procedures. Here, we analyze the impact of ER stress and SIRT1 in lipid metabolism and in fatty liver pathology, and their consequences on liver regeneration. Moreover, we discuss the fine interplay between ER stress and SIRT1 functioning when contextualized to liver regeneration. An improved understanding of the cellular and molecular intricacies contributing to liver regeneration could be of great clinical relevance in areas as diverse as obesity, metabolic syndrome and type 2 diabetes, as well as oncology and transplantation.

Fibroblast growth factors 19 and 21 in acute liver damage

Currently there are very few pharmacological options available to treat acute liver injury. Because its natural exposure to noxious stimuli the liver has developed a strong endogenous hepatoprotective capacity. Indeed, experimental evidence exposed a variety of endogenous hepatic and systemic responses naturally activated to protect the hepatic parenchyma and to foster liver regeneration, therefore preserving individual's survival. The fibroblast growth factor (FGF) family encompasses a range of polypeptides with important effects on cellular differentiation, growth survival and metabolic regulation in adult organisms. Among these FGFs, FGF19 and FGF21 are endocrine hormones that profoundly influence systemic metabolism but also exert important hepatoprotective activities. In this review, we revisit the biology of these factors and highlight their potential application for the clinical management of acute liver injury.

Endocrine Adiponectin-FGF15/19 Axis in Ethanol-Induced Inflammation and Alcoholic Liver Injury

Alcoholic liver disease (ALD) is the most prevalent form of liver disease, encompassing a spectrum of progressive pathological changes from steatosis to steatohepatitis to fibrosis/cirrhosis and hepatocellular carcinoma. Alcoholic steatosis/steatohepatitis is the initial stage of ALD and a major risk factor for advanced liver injuries. Adiponectin is a hormone secreted from adipocytes. Fibroblast growth factor (FGF) 15 (human homolog, FGF19) is an ileum-derived hormone. Adipocyte-derived adiponectin and gut-derived FGF15/19 regulate each other, share common signaling cascades, and exert similar beneficial functions. Emerging evidence has revealed that dysregulated adiponectin-FGF15/19 axis and impaired hepatic adiponectin-FGF15/19 signaling are associated with alcoholic liver damage in rodents and humans. More importantly, endocrine adiponectin-FGF15/19 signaling confers protection against ethanol-induced liver damage via fine tuning the adipose-intestine-liver crosstalk, leading to limited hepatic inflammatory responses, and ameliorated alcoholic liver injury. This review is focused on the recently discovered endocrine adiponectin-FGF15/19 axis that is emerging as an essential adipose-gut-liver coordinator involved in the development and progression of alcoholic steatohepatitis.

Gut as an emerging organ for the treatment of diabetes: focus on mechanism of action of bariatric and endoscopic interventions

Increasing worldwide prevalence of type 2 diabetes mellitus and its accompanying pathologies such as obesity, arterial hypertension and dyslipidemia represents one of the most important challenges of current medicine. Despite intensive efforts, high percentage of patients with type 2 diabetes does not achieve treatment goals and struggle with increasing body weight and poor glucose control. While novel classes of antidiabetic medications such as incretin-based therapies and gliflozins have some favorable characteristics compared to older antidiabetics, the only therapeutic option shown to substantially modify the progression of diabetes or to achieve its remission is bariatric surgery. Its efficacy in the treatment of diabetes is well established, but the exact underlying modes of action are still only partially described. They include restriction of food amount, enhanced passage of chymus into distal part of small intestine with subsequent modification of gastrointestinal hormones and bile acids secretion, neural mechanisms, changes in gut microbiota and many other possible mechanisms underscoring the importance of the gut in the regulation of glucose metabolism. In addition to bariatric surgery, less-invasive endoscopic methods based on the principles of bariatric surgery were introduced and showed promising results. This review highlights the role of the intestine in the regulation of glucose homeostasis focusing on the mechanisms of action of bariatric and especially endoscopic methods of the treatment of diabetes. A better understanding of these mechanisms may lead to less invasive endoscopic treatments of diabetes and obesity that may complement and widen current therapeutic options.

The ileal FGF15/19 to hepatic FGFR4 axis regulates liver regeneration after partial hepatectomy in mice

Fibroblast growth factor (FGF) has been considered to modulate liver regeneration (LR) after partial hepatectomy (PH) at the tissue level. Previous studies have demonstrated that FGF15 and FGF19 induce the activation of its receptor, FGF receptor 4 (FGFR4), which can promote hepatocellular carcinoma progression and regulate liver lipid metabolism. In this study, we aimed to explore the role of the ileal FGF15/19- hepatic FGFR4 axis in the LR after PH. Male C57BL/6 mice aged 8-12 weeks were partially hepatectomized and assessed for expression of ileal FGF15/19 to hepatic FGFR4 signaling. We used recombinant human FGF19 protein and a small interfering RNA (siRNA) of FGFR4 to regulate expression of the FGF15/19-FGFR4 axis in vitro and in vivo. The proliferation and cell cycle of hepatocytes, the expression levels of FGF15/19-FGFR4 downstream molecules, liver recovery, and lipid metabolism were assessed. We found that both ileal and serum FGF15 expression were upregulated and hepatic FGFR4 was activated after PH in mice. FGF15/19 promoted cell cycle progression, enhanced proliferation, and reduced hepatic lipid accumulation of hepatocytes both in vitro and in vivo. Furthermore, the proliferative effect and lipid regulatory properties of FGF15/19 were dependent on FGFR4 in hepatocytes. In addition, ileal FGF15/19-hepatic FGFR4 transduction during hepatocyte proliferation was regulated by extracellular regulated protein kinase (ERK) 1/2. In conclusion, the ileal FGF15/19 to hepatic FGFR4 axis is activated and promotes LR after PH in mice, supporting the potential of ileal FGF15/19 to hepatic FGFR4 axis-targeted therapy to enhance LR after PH.

Lipotoxicity and the gut-liver axis in NASH pathogenesis

The pathogenesis of non-alcoholic fatty liver disease, particularly the mechanisms whereby a minority of patients develop a more severe phenotype characterised by hepatocellular damage, inflammation, and fibrosis is still incompletely understood. Herein, we discuss two pivotal aspects of the pathogenesis of NASH. We first analyse the initial mechanisms responsible for hepatocellular damage and inflammation, which derive from the toxic effects of excess lipids. Accumulating data indicate that the total amount of triglycerides stored in hepatocytes is not the major determinant of lipotoxicity, and that specific lipid classes act as damaging agents on liver cells. In particular, the role of free fatty acids such as palmitic acid, cholesterol, lysophosphatidylcholine and ceramides has recently emerged. These lipotoxic agents affect the cell behaviour via multiple mechanisms, including activation of signalling cascades and death receptors, endoplasmic reticulum stress, modification of mitochondrial function, and oxidative stress. In the second part of this review, the cellular and molecular players involved in the cross-talk between the gut and the liver are considered. These include modifications to the microbiota, which provide signals through the intestine and bacterial products, as well as hormones produced in the bowel that affect metabolism at different levels including the liver. Finally, the activation of nuclear receptors by bile acids is analysed.

Pathogenesis of Nonalcoholic Steatohepatitis and Hormone-Based Therapeutic Approaches

Non-alcoholic fatty liver disease (NAFLD) is an emerging global health problem and a potential risk factor for type 2 diabetes, cardiovascular disease, and chronic kidney disease. Nonalcoholic steatohepatitis (NASH), an advanced form of NAFLD, is a predisposing factor for development of cirrhosis and hepatocellular carcinoma. The increasing prevalence of NASH emphasizes the need for novel therapeutic approaches. Although therapeutic drugs against NASH are not yet available, fundamental insights into the pathogenesis of NASH have been made during the past few decades. Multiple therapeutic strategies have been developed and are currently being explored in clinical trials or preclinical testing. The pathogenesis of NASH involves multiple intracellular/extracellular events in various cell types in the liver or crosstalk events between the liver and other organs. Here, we review current findings and knowledge regarding the pathogenesis of NASH, focusing on the most recent advances. We also highlight hormone-based therapeutic approaches for treatment of NASH.

The pathophysiology of human obstructive cholestasis is mimicked in cholestatic Gold Syrian hamsters

Obstructive cholestasis causes liver injury via accumulation of toxic bile acids (BAs). Therapeutic options for cholestatic liver disease are limited, partially because the available murine disease models lack translational value. Profiling of time-related changes following bile duct ligation (BDL) in Gold Syrian hamsters revealed a biochemical response similar to cholestatic patients in terms of BA pool composition, alterations in hepatocyte BA transport and signaling, suppression of BA production, and adapted BA metabolism. Hamsters tolerated cholestasis well for up to 28days and progressed relatively slowly to fibrotic liver injury. Hepatocellular necrosis was absent, which coincided with preserved intrahepatic energy levels and only mild oxidative stress. The histological response to cholestasis in hamsters was similar to the changes seen in 17 patients with prolonged obstructive cholestasis caused by cholangiocarcinoma. Hamsters moreover upregulated hepatic fibroblast growth factor 15 (Fgf15) expression in response to BDL, which is a cytoprotective adaptation to cholestasis that hitherto had only been documented in cholestatic human livers. Hamster models should therefore be added to the repertoire of animal models used to study the pathophysiology of cholestatic liver disease.

Engineered FGF19 eliminates bile acid toxicity and lipotoxicity leading to resolution of steatohepatitis and fibrosis in mice

Nonalcoholic fatty liver disease (NAFLD) is an increasingly prevalent chronic liver disease for which no approved therapies are available. Despite intensive research, the cellular mechanisms that mediate NAFLD pathogenesis and progression are poorly understood. Although obesity, diabetes, insulin resistance, and related metabolic syndrome, all consequences of a Western diet lifestyle, are well‐recognized risk factors for NAFLD development, dysregulated bile acid metabolism is emerging as a novel mechanism contributing to NAFLD pathogenesis. Notably, NAFLD patients exhibit a deficiency in fibroblast growth factor 19 (FGF19), an endocrine hormone in the gut–liver axis that controls de novo bile acid synthesis, lipogenesis, and energy homeostasis. Using a mouse model that reproduces the clinical progression of human NAFLD, including the development of simple steatosis, nonalcoholic steatohepatitis (NASH), and advanced “burnt‐out” NASH with hepatocellular carcinoma, we demonstrate that FGF19 as well as an engineered nontumorigenic FGF19 analogue, M70, ameliorate bile acid toxicity and lipotoxicity to restore liver health. Mass spectrometry‐based lipidomics analysis of livers from mice treated with FGF19 or M70 revealed significant reductions in the levels of toxic lipid species (i.e., diacylglycerols, ceramides and free cholesterol) and an increase in levels of unoxidized cardiolipins, an important component of the inner mitochondrial membrane. Furthermore, treatment with FGF19 or M70 rapidly and profoundly reduced levels of liver enzymes, resolved the histologic features of NASH, and enhanced insulin sensitivity, energy homeostasis, and lipid metabolism. Whereas FGF19 induced hepatocellular carcinoma formation following prolonged exposure in these mice, animals expressing M70 showed no evidence of liver tumorigenesis in this model. Conclusion: We have engineered an FGF19 hormone that is capable of regulating multiple pathways to deliver antisteatotic, anti‐inflammatory, and antifibrotic activities and that represents a potentially promising therapeutic for patients with NASH. (Hepatology Communications 2017;1:1024–1042)

Engineered fibroblast growth factor 19 protects from acetaminophen-induced liver injury and stimulates aged liver regeneration in mice

The liver displays a remarkable regenerative capacity triggered upon tissue injury or resection. However, liver regeneration can be overwhelmed by excessive parenchymal destruction or diminished by pre-existing conditions hampering repair. Fibroblast growth factor 19 (FGF19, rodent FGF15) is an enterokine that regulates liver bile acid and lipid metabolism, and stimulates hepatocellular protein synthesis and proliferation. FGF19/15 is also important for liver regeneration after partial hepatectomy (PH). Therefore recombinant FGF19 would be an ideal molecule to stimulate liver regeneration, but its applicability may be curtailed by its short half-life. We developed a chimaeric molecule termed Fibapo in which FGF19 is covalently coupled to apolipoprotein A-I. Fibapo retains FGF19 biological activities but has significantly increased half-life and hepatotropism. Here we evaluated the pro-regenerative activity of Fibapo in two clinically relevant models where liver regeneration may be impaired: acetaminophen (APAP) poisoning, and PH in aged mice. The only approved therapy for APAP intoxication is N-acetylcysteine (NAC) and no drugs are available to stimulate liver regeneration. We demonstrate that Fibapo reduced liver injury and boosted regeneration in APAP-intoxicated mice. Fibapo improved survival of APAP-poisoned mice when given at later time points, when NAC is ineffective. Mechanistically, Fibapo accelerated recovery of hepatic glutathione levels, potentiated cell growth-related pathways and increased functional liver mass. When Fibapo was administered to old mice prior to PH, liver regeneration was markedly increased. The exacerbated injury developing in these mice upon PH was attenuated, and the hepatic biosynthetic capacity was enhanced. Fibapo reversed metabolic and molecular alterations that impede regeneration in aged livers. It reduced liver steatosis and downregulated p21 and hepatocyte nuclear factor 4 α (Hnf4α) levels, whereas it stimulated Foxm1b gene expression. Together our findings indicate that FGF19 variants retaining the metabolic and growth-promoting effects of this enterokine may be valuable for the stimulation of liver regeneration.

Bile acids, FGF15/19 and liver regeneration: From mechanisms to clinical applications

The liver has an extraordinary regenerative capacity rapidly triggered upon injury or resection. This response is intrinsically adjusted in its initiation and termination, a property termed the "hepatostat". Several molecules have been involved in liver regeneration, and among them bile acids may play a central role. Intrahepatic levels of bile acids rapidly increase after resection. Through the activation of farnesoid X receptor (FXR), bile acids regulate their hepatic metabolism and also promote hepatocellular proliferation. FXR is also expressed in enterocytes, where bile acids stimulate the expression of fibroblast growth factor 15/19 (FGF15/19), which is released to the portal blood. Through the activation of FGFR4 on hepatocytes FGF15/19 regulates bile acids synthesis and finely tunes liver regeneration as part of the "hepatostat". Here we review the experimental evidences supporting the relevance of the FXR-FGF15/19-FGFR4 axis in liver regeneration and discuss potential therapeutic applications of FGF15/19 in the prevention of liver failure. This article is part of a Special Issue entitled: Cholangiocytes in Health and Disease edited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.