Claudia D. Fuchs

Inhibition of intestinal bile acid absorption improves cholestatic liver and bile duct injury in a mouse model of sclerosing cholangitis.

BACKGROUND AND AIMS Approximately 95% of bile acids (BAs) excreted into bile are reabsorbed in the gut and circulate back to the liver for further biliary secretion. Therefore, pharmacological inhibition of the ileal apical sodium-dependent BA transporter (ASBT/SLC10A2) may protect against BA-mediated cholestatic liver and bile duct injury. METHODS Eight week old Mdr2(-/-) (Abcb4(-/-)) mice (model of cholestatic liver injury and sclerosing cholangitis) received either a diet supplemented with A4250 (0.01% w/w) - a highly potent and selective ASBT inhibitor - or a chow diet. Liver injury was assessed biochemically and histologically after 4weeks of A4250 treatment. Expression profiles of genes involved in BA homeostasis, inflammation and fibrosis were assessed via RT-PCR from liver and ileum homogenates. Intestinal inflammation was assessed by RNA expression profiling and immunohistochemistry. Bile flow and composition, as well as biliary and fecal BA profiles were analyzed after 1week of ASBT inhibitor feeding. RESULTS A4250 improved sclerosing cholangitis in Mdr2(-/-) mice and significantly reduced serum alanine aminotransferase, alkaline phosphatase and BAs levels, hepatic expression of pro-inflammatory (Tnf-α, Vcam1, Mcp-1) and pro-fibrogenic (Col1a1, Col1a2) genes and bile duct proliferation (mRNA and immunohistochemistry for cytokeratin 19 (CK19)). Furthermore, A4250 significantly reduced bile flow and biliary BA output, which correlated with reduced Bsep transcription, while Ntcp and Cyp7a1 were induced. Importantly A4250 significantly reduced biliary BA secretion but preserved HCO3(-) and biliary phospholipid secretion resulting in an increased HCO3(-)/BA and PL/BA ratio. In addition, A4250 profoundly increased fecal BA excretion without causing diarrhea and altered BA pool composition, resulting in diminished concentrations of primary BAs tauro-β-muricholic acid and taurocholic acid. CONCLUSIONS Pharmacological ASBT inhibition attenuates cholestatic liver and bile duct injury by reducing biliary BA concentrations in mice.

Absence of adipose triglyceride lipase protects from hepatic endoplasmic reticulum stress in mice.

Nonalcoholic fatty liver disease (NAFLD) is characterized by triglyceride (TG) accumulation and endoplasmic reticulum (ER) stress. Because fatty acids (FAs) may trigger ER stress, we hypothesized that the absence of adipose triglyceride lipase (ATGL/PNPLA2)–the main enzyme for intracellular lipolysis, releasing FAs, and closest homolog to adiponutrin (PNPLA3) recently implicated in the pathogenesis of NAFLD–protects against hepatic ER stress. Wild‐type (WT) and ATGL knockout (KO) mice were challenged with tunicamycin (TM) to induce ER stress. Serum biochemistry, hepatic TG and FA profiles, liver histology, and gene expression for markers of hepatic lipid metabolism, ER stress, and inflammation were explored. Moreover, cell‐culture experiments were performed in Hepa1.6 cells after the knockdown of ATGL before FA and TM treatment. TM increased hepatic TG accumulation in ATGL KO, but not in WT, mice. Lipogenesis and β‐oxidation were repressed at the gene‐expression level (sterol regulatory element‐binding transcription factor 1c, fatty acid synthase, acetyl coenzyme A carboxylase 2, and carnitine palmitoyltransferase 1 alpha) in both WT and ATGL KO mice. Genes for very‐low‐density lipoprotein (VLDL) synthesis (microsomal triglyceride transfer protein and apolipoprotein B) were down‐regulated by TM in WT and even more in ATGL KO mice, which displayed strongly reduced serum VLDL cholesterol levels. Notably, ER stress markers glucose‐regulated protein, C/EBP homolog protein, spliced X‐box‐binding protein, endoplasmic‐reticulum–localized DnaJ homolog 4, and inflammatory markers Tnfα and iNos were induced exclusively in TM‐treated WT, but not ATGL KO, mice. Total hepatic FA profiling revealed a higher palmitic acid/oleic acid (PA/OA) ratio in WT mice, compared to ATGL KO mice, at baseline. Phosphoinositide‐3‐kinase inhibitor–known to be involved in FA‐derived ER stress and blocked by OA–was increased in TM‐treated WT mice only. In line with this, in vitro OA protected hepatocytes from TM‐induced ER stress. Conclusions: Lack of ATGL may protect from hepatic ER stress through alterations in FA composition. ATGL could constitute a new therapeutic strategy to target ER stress in NAFLD. (HEPATOLOGY 2012;56:270–280 )

New therapeutic concepts in bile acid transport and signaling for management of cholestasis

The identification of the key regulators of bile acid (BA) synthesis and transport within the enterohepatic circulation has revealed potential targets for pharmacological therapies of cholestatic liver diseases. Novel drug targets include the bile BA receptors, farnesoid X receptor and TGR5, the BA‐induced gut hormones, fibroblast growth factor 19 and glucagon‐like peptide 1, and the BA transport systems, apical sodium‐dependent bile acid transporter and Na+‐taurocholate cotransporting polypeptide, within the enterohepatic circulation. Moreover, BA derivatives undergoing cholehepatic shunting may allow improved targeting to the bile ducts. This review focuses on the pathophysiological basis, mechanisms of action, and clinical development of novel pharmacological strategies targeting BA transport and signaling in cholestatic liver diseases. (Hepatology 2017;65:1393‐1404).

Bile acid-mediated control of liver triglycerides.

Bile acids (BAs) are steroidal molecules generated in the liver by cholesterol oxidation. Beside their well-established role in lipid absorption and cholesterol homeostasis, they function as signaling molecules and activate dedicated BA receptors such as the farnesoid X receptor (FXR) and the G-protein coupled receptor TGR5. Through activation of downstream signaling pathways of these key receptors, BAs regulate not only their own synthesis and enterohepatic circulation, but also impact on hepatic lipid, glucose, and energy homeostasis. Therefore, BA-regulated signaling pathways have emerged as attractive targets for understanding the regulation of hepatic triglyceride metabolism in health and disease and treating fatty liver disease and associated metabolic disorders.

Nuclear Receptor Modulation for the Treatment of Nonalcoholic Fatty Liver Disease.

Nuclear receptors (NRs) are ligand-activated transcriptional regulators of several key metabolic processes including hepatic lipid and glucose metabolism, bile acid homeostasis, and energy expenditure as well as inflammation, fibrosis, and cellular proliferation in the liver. Dysregulation of these processes contributes to the pathogenesis and progression of nonalcoholic fatty liver disease (NAFLD). This places NRs at the forefront of novel therapeutic approaches for NAFLD. Some NRs are already pharmacologically targeted in metabolic disorders such as hyperlipidemia (peroxisomal proliferator-activated receptor α [PPARα], fibrates) and diabetes (PPARγ, glitazones) with potential applications for NAFLD. Other NRs with potential therapeutic implications are the vitamin D receptor (VDR) and xenobiotic sensors such as constitutive androstane receptor (CAR) and pregnane X receptor (PXR). Further new perspectives include combined ligands for NR isoforms such as PPARα/δ ligands. Other novel key players represent the nuclear bile acid receptor farnesoid X receptor (FXR; targeted by synthetic FXR ligands such as obeticholic acid) and RAR-related orphan receptor gamma two (RORγt). In this review the authors provide an overview of the preclinical and clinical evidence of current and future treatment strategies targeting NRs in metabolism, inflammation, and fibrogenesis of NAFLD.

Role of metabolic lipases and lipolytic metabolites in the pathogenesis of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is the most frequent chronic liver disease in Western countries, ranging from simple steatosis to steatohepatitis, cirrhosis, and hepatocellular cancer. Although the mechanisms underlying disease progression are incompletely understood, lipotoxic events in the liver resulting in inflammation and fibrosis appear to be central. Free fatty acids and their metabolites are potentially lipotoxic mediators triggering liver injury, suggesting a central role for metabolic lipases. These enzymes are major players in lipid partitioning between tissues and within cells, and provide ligands for nuclear receptors (NRs). We discuss the potential role of intracellular lipases and their lipolytic products in NAFLD. Because tissue-specific modulation of lipases is currently impossible, targeting NRs with ligands may open novel therapeutic perspectives.

24-nor-ursodeoxycholic acid ameliorates inflammatory response and liver fibrosis in a murine model of hepatic Schistosomiasis

Graphical abstract

Therapy of Primary Sclerosing Cholangitis - Today and Tomorrow

Primary sclerosing cholangitis (PSC) represents a fibro-obliterative bile duct disease with unpredictable individual clinical course that may progress to liver cirrhosis and malignancy. Due to our incomplete understanding of the etiology and pathogenesis of this disease, the therapeutic options are still rather limited. Bile acids play a key role in mediating cholangiocellular and hepatocellular injury in cholangiopathies such as PSC. Therefore, strategies targeting bile composition and homeostasis are valid approaches in PSC. Ursodeoxycholic acid (UDCA) is the paradigm therapeutic bile acid and its role in medical therapy of PSC is still under debate. Promising novel bile acid-based therapeutic options include 24-norursodeoxycholic acid (norUDCA), a side chain-shortened C23 homologue of UDCA, and bile acid receptor/farnesoid X receptor agonists (e.g. obeticholic acid). Other nuclear receptors such as fatty acid-activated peroxisome proliferator-activated receptors, vitamin D receptor and vitamin A receptors (retinoic acid receptor, retinoid X receptor) are also of potential interest and can be targeted by already available drugs. Furthermore, drugs targeting the gut-liver axis (e.g. intregrin blockers such as vedolizumab, antibiotics) appear promising, based on the close link of PSC to inflammatory bowel disease and the emerging relevance of the gut microbiome for the development of PSC. Finally, fibrosis represents a valid therapeutic target for anti-fibrotic drugs (e.g. simtuzumab) in PSC as paradigm fibro-obliterative disease. This review summarizes the current status and recent progress in the development of targeted therapeutic approaches based on increasing knowledge about the pathogenesis of this disease.

Metabolic preconditioning protects BSEP/ABCB11−/− mice against cholestatic liver injury

BACKGROUND & AIMS Cholestasis is characterized by intrahepatic accumulation of potentially cytotoxic bile acids (BAs) subsequently leading to liver injury with disruption of hepatocellular integrity, inflammation, fibrosis and ultimately liver cirrhosis. Bile salt export pump (BSEP/ABCB11) is the main canalicular BA transporter and therefore the rate limiting step for hepatobiliary BA excretion. In this study we aimed to investigate the role of BSEP/ABCB11 in the development of acquired cholestatic liver and bile duct injury. METHODS Wild-type (WT) and BSEP knockout (BSEP-/-) mice were subjected to common bile duct ligation (CBDL) or 3.5-diethoxycarbonyl-1.4-dihydrocollidine (DDC) feeding as models for cholestasis with biliary obstruction and bile duct injury. mRNA expression profile, serum biochemistry, liver histology, immunohistochemistry, hepatic hydroxyproline levels and BA composition as well as biliary pressure were assessed. RESULTS BSEP-/- mice were protected against acquired cholestatic liver injury induced by 7days of CBDL or 4weeks of DDC feeding, as reflected by unchanged serum levels of liver transaminases, alkaline phosphatase and BAs. Notably, BSEP-/- mice were also protected from cholestasis-induced hepatic inflammation and biliary fibrosis. In line with induced BA detoxification/hydroxylation pathways in BSEP-/- mice, polyhydroxylated BAs were increased 4-fold after CBDL and 6-fold after DDC feeding in comparison with cholestatic WT mice. Finally, following CBDL, biliary pressure in WT mice increased up to 47mmH2O but remained below 11mmH2O in BSEP-/- mice. CONCLUSION Metabolic preconditioning with subsequent changes in BA metabolism favors detoxification of potentially toxic BAs and thereby protects BSEP-/- mice from cholestatic liver and bile duct injury. LAY SUMMARY Reduced hepatobiliary bile acid transport due to loss of BSEP function leads to increased hydroxylation of bile acids in the liver. Metabolic preconditioning with a hydrophilic bile pool protects the BSEP-/- mice from acquired cholestatic liver disease.

Farnesoid X Receptor Agonists and Other Bile Acid Signaling Strategies for Treatment of Liver Disease

The intracellular nuclear receptor farnesoid X receptor (FXR) and the transmembrane G protein-coupled receptor 5 (TGR5) respond to bile acids (BAs) by activating transcriptional networks and/or signaling cascades. These cascades affect the expression of a great number of target genes relevant for BA, cholesterol, lipid and carbohydrate metabolism, as well as genes involved in inflammation, fibrosis and carcinogenesis. FXR activation in the liver tissue and beyond, such as the gut-liver axis, kidney and adipose tissue, plays a role in metabolic diseases. These BA receptors activators hold promise to become a new class of drugs to be used in the treatment of chronic liver disease, hepatocellular cancer and extrahepatic inflammatory and metabolic diseases. This review discusses the relevant BA receptors, the new drugs that target BA transport and signaling and their possible applications.