Modulation of the Tryptophan Hydroxylase 1/Monoamine Oxidase-A/5-Hydroxytryptamine/5-Hydroxytryptamine Receptor 2A/2B/2C Axis Regulates Biliary Proliferation and Liver Fibrosis During Cholestasis

Expression of tryptophan hydroxylase in rat adrenal glands: Upregulation of TPH2 by chronic stress

It has been shown that chronic restraint stress (CRS) increases adrenal 5-HT levels and turnover through a mechanism that appears unrelated to tryptophan hydroxylase (TPH). In the present study we re-analyzed the effects of CRS (20 min/day) for 14 days relative to control (CTRL) conditions on TPH expression, distribution, and activity in rat adrenal glands. On day 15, adrenal glands were collected for TPH1 and TPH2 immunohistochemistry, Western blot, and RT-PCR; TPH activity was estimated by quantification of 5-hydroxytryptophan (5-HTP) and, indirectly, through measurement of 5-HT and 5-hydroxindolacetic acid (5-HIAA) levels and turnover (5-HIAA/5-HT ratio) by HPLC. TPH expression and activity in the dorsal raphe nucleus (DRN) were also determined for comparison. TPH1 and TPH2 immunostaining was observed in the adrenal medulla, and measurable levels of TPH1 and TPH2 protein and mRNA were detected in rat adrenal glands from CTRL animals. CRS exposure noticeably increased TPH2- but not THP1-immunostaining in the medulla and the outer adrenocortical areas of left (LAG) but not of right adrenal glands (RAG). In addition, CRS exposure increased TPH2 protein and mRNA levels in LAG; however, both measures decreased in DRN. Finally, CRS treatment produced an increase and a decrease of TPH activity and 5-HT turnover in LAG and DRN, respectively. Results indicate that TPH is indeed expressed in rat adrenal glands. Exposure to CRS upregulates TPH2 in LAG, while inducing downregulation of it in the DRN. Then, the increased levels of 5-HT in LAG from CRS-exposed animals likely results from TPH2-mediated synthesis.

Deletion of Tgm2 suppresses BMP-mediated hepatocyte-to-cholangiocyte metaplasia in ductular reaction

Transglutaminase 2 (Tgm2) plays an essential role in hepatic repair following prolonged toxic injury. During cholestatic liver injury, the intrahepatic cholangiocytes undergo dynamic tissue expansion and remodelling, referred to as ductular reaction (DR), which is crucial for liver regeneration. However, the molecular mechanisms governing the dynamics of active cells in DR are still largely unclear. Here, we generated Tgm2-knockout mice (Tgm2-/-) and Tgm2-CreERT2-Rosa26-mTmG flox/flox (Tgm2CreERT2-R26T/Gf/f) mice and performed a three-dimensional (3D) collagen gel culture of mouse hepatocytes to demonstrate how Tgm2 signalling is involved in DR to remodel intrahepatic cholangiocytes. Our results showed that the deletion of Tgm2 adversely affected the functionality and maturity of the proliferative cholangiocytes in DR, thus leading to more severe cholestasis during DDC-induced liver injury. Additionally, Tgm2 hepatocytes played a crucial role in the regulation of DR through metaplasia. We unveiled that Tgm2 regulated H3K4me3Q5ser via serotonin to promote BMP signalling activation to participate in DR. Besides, we revealed that the activation or inhibition of BMP signalling could promote or suppress the development and maturation of cholangiocytes in DDC-induced DR. Furthermore, our 3D collagen gel culture assay indicated that Tgm2 was vital for the development of cholangiocytes in vitro. Our results uncovered a considerable role of BMP signalling in controlling metaplasia of Tgm2 hepatocytes in DR and revealed the phenotypic plasticity of mature hepatocytes.

Akkermansia muciniphila improve cognitive dysfunction by regulating BDNF and serotonin pathway in gut-liver-brain axis

BACKRGROUND

Akkermansia muciniphila, a next-generation probiotic, is known as a cornerstone regulating the gut-organ axis in various diseases, but the underlying mechanism remains poorly understood. Here, we revealed the neuronal and antifibrotic effects of A. muciniphila on the gut-liver-brain axis in liver injury.

RESULTS

To investigate neurologic dysfunction and characteristic gut microbiotas, we performed a cirrhosis cohort (154 patients with or without hepatic encephalopathy) and a community cognition cohort (80 participants in one region for three years) and validated the existence of cognitive impairment in a 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced hepatic injury mouse model. The effects of the candidate strain on cognition were evaluated in animal models of liver injury. The expression of brain-derived neurotrophic factor (BDNF) and serotonin receptors was accessed in patients with fibrosis (100 patients) according to the fibrosis grade and hepatic venous pressure gradient. The proportion of A. muciniphila decreased in populations with hepatic encephalopathy and cognitive dysfunction. Tissue staining techniques confirmed gut-liver-brain damage in liver injury, with drastic expression of BDNF and serotonin in the gut and brain. The administration of A. muciniphila significantly reduced tissue damage and improved cognitive dysfunction and the expression of BDNF and serotonin. Isolated vagus nerve staining showed a recovery of serotonin expression without affecting the dopamine pathway. Conversely, in liver tissue, the inhibition of injury through the suppression of serotonin receptor (5-hydroxytryptamine 2A and 2B) expression was confirmed. The severity of liver injury was correlated with the abundance of serotonin, BDNF, and A. muciniphila.

CONCLUSIONS

A. muciniphila, a next-generation probiotic, is a therapeutic candidate for alleviating the symptoms of liver fibrosis and cognitive impairment.

Preclinical mitigation of 5-HT2B agonism-related cardiac valvulopathy revisited

Cardiac valvulopathy (Cardiac Valve Disease; CVD) associated with off-target activation of the 5-hydroxytryptamine (5-HT) 2B receptor has been well recognized, but is still poorly predicted during drug development. The regulatory guidance proposes the use of 5-HT2B binding data (i.e., Ki values) and free maximum therapeutic exposure (Cmax) to calculate safety margins as a threshold of detection (>10) for eliminating the risk of drug-induced cardiac valvulopathy. In this paper, we provide additional recommendations for preclinical prediction of CVD risk based on clinical pharmacodynamic and pharmacokinetic data obtained from drugs with or without 5-HT2B receptor activation. Our investigations showed that 5-HT2B agonist affinity of molecules tested in an in vitro 5-HT2B cell-based functional assay, placed in perspective to their sustained plasma exposure (AUCs) and not to their peak plasma exposure, Cmax (i.e., maximum therapeutic exposure) provide a solid basis for interpreting 5-HT2B data, for calculating safety margins and then, accurately differentiate drugs associated with a clinical risk of CVD from those which are not (despite having some agonist 5-HT2B activity). In addition, we discuss the risk of multi-organ fibrosis linked to 5-HT2B receptor activation, often underestimated, however well reported in FAERS for 5-HT2B agonists. We believe that our recommendations have the potential to mitigate the risk for the clinical development of CVD and fibrosis.

Ductular Reactions in Liver Injury, Regeneration, and Disease Progression-An Overview

Ductular reaction (DR) is a complex cellular response that occurs in the liver during chronic injuries. DR mainly consists of hyper-proliferative or reactive cholangiocytes and, to a lesser extent, de-differentiated hepatocytes and liver progenitors presenting a close spatial interaction with periportal mesenchyme and immune cells. The underlying pathology of DRs leads to extensive tissue remodeling in chronic liver diseases. DR initiates as a tissue-regeneration mechanism in the liver; however, its close association with progressive fibrosis and inflammation in many chronic liver diseases makes it a more complicated pathological response than a simple regenerative process. An in-depth understanding of the cellular physiology of DRs and their contribution to tissue repair, inflammation, and progressive fibrosis can help scientists develop cell-type specific targeted therapies to manage liver fibrosis and chronic liver diseases effectively.

Safety comparisons among monoamine oxidase inhibitors against Parkinson's disease using FDA adverse event reporting system

Monoamine oxidase B (MAO-B) inhibitors are used to control Parkinson's disease (PD). Selegiline, rasagiline, and safinamide are widely used as MAO-B inhibitors worldwide. Although these drugs inhibit MAO-B, there are pharmacological and chemical differences, such as the inhibitory activity, the non-dopaminergic properties in safinamide, and the amphetamine-like structure in selegiline. MAO-B inhibitors may differ in adverse events (AEs). However, differences in actual practical clinics are not fully investigated. A retrospective study was conducted using FAERS, the largest database of spontaneous adverse events. AE signals for MAO-B inhibitors, including selegiline, rasagiline, and safinamide, were detected using the reporting odds ratio method and compared. Hypocomplementemia, hepatic cyst, hepatic function abnormal, liver disorder and cholangitis were detected for selegiline as drug-specific signals. The amphetamine effect was not confirmed for any of the three MAO-B inhibitors. The tyramine reaction was detected as an AE signal only for rasagiline. Moreover, the REM sleep behavior disorder was not detected as an AE signal for safinamide, suggesting that non-dopaminergic effects might be beneficial. Considering the differences in AEs for MAO-B inhibitors will assist with the appropriate PD medication.

Evaluation of the serotonin pathway as a biomarker in cholangiocarcinoma

Background

Cholangiocarcinomas (CCAs) are rare and aggressive malignant tumors of the biliary tract. Serotonin (5HT) has tumor-promoting effects in CCA while inhibition of 5HT synthesis can decrease tumor growth.

Methods

In this retrospective study, we evaluated the expression of 5HT and tryptophane hydroxylase-1 (TPH-1) in tumor specimens from patients treated with cisplatin plus gemcitabine (CisGem). We included consecutive patients ≥18 years, with locally advanced unresectable, recurrent, or metastatic CCA who were treated with CisGem and had available archival tumor tissue for immunohistochemistry. Formalin-fixed paraffin (FFPE) sections were stained for 5HT and TPH-1. Specimens were evaluated for neuroendocrine features and tumor-infiltrating lymphocytes (TILs). Serum 5HT was measured.

Results

We identified 23 patients fulfilling the inclusion criteria. 5HT expression was absent in almost all tumors examined. TPH-1 expression was neither associated with stage or primary tumor location nor predictive of response to CisGem. There was a trend for improved overall survival (OS) in patients whose tumors had high TPH-1 expression. The examined tumor specimens had no neuroendocrine features. Most sections had no TILs. There was a trend for worse OS in patients with high serum 5HT concentration.

Conclusions

Tumor TPH-1 expression was not predictive of response to treatment. There was a trend for improved long-term outcomes in patients with high tumor TPH expression and lower serum 5HT concentration.

Generation and metabolomic characterization of functional ductal organoids with biliary tree networks in decellularized liver scaffolds

Developing functional ductal organoids (FDOs) is essential for liver regenerative medicine. We aimed to construct FDOs with biliary tree networks in rat decellularized liver scaffolds (DLSs) with primary cholangiocytes isolated from mouse bile ducts. The developed FDOs were dynamically characterized by functional assays and metabolomics for bioprocess clarification. FDOs were reconstructed in DLSs retaining native structure and bioactive factors with mouse primary cholangiocytes expressing enriched biomarkers. Morphological assessment showed that biliary tree-like structures gradually formed from day 3 to day 14. The cholangiocytes in FDOs maintained high viability and expressed 11 specific biomarkers. Basal-apical polarity was observed at day 14 with immunostaining for E-cadherin and acetylated α-tubulin. The rhodamine 123 transport assay and active collection of cholyl-lysyl-fluorescein exhibited the specific functions of bile secretion and transportation at day 14 compared to those in monolayer and hydrogel culture systems. The metabolomics analysis with 1075 peak pairs showed that serotonin, as a key molecule of the tryptophan metabolism pathway linked to biliary tree reconstruction, was specifically expressed in FDOs during the whole period of culture. Such FDOs with biliary tree networks and serotonin expression may be applied for disease modeling and drug screening, which paves the way for future clinical therapeutic applications.

Altered serotonin metabolism in Takeda G protein-coupled receptor 5 knockout mice protects against diet-induced hepatic fibrosis

Background and aims

Diet-induced obesity and metabolic syndrome can trigger the progression of fatty liver disease to non-alcoholic steatohepatitis and fibrosis, which is a major public health concern. Bile acids regulate metabolic homeostasis and inflammation in the liver and gut via the activation of nuclear farnesoid X receptor (Fxr) and the membrane receptor Takeda G protein-coupled receptor 5 (Tgr5). Tgr5 is highly expressed in the gut and skeletal muscle, and in cholangiocytes and Kupffer cells of the liver. Tgr5 is implicated in the mediation of liver and gut inflammation, as well as the maintenance of energy homeostasis. Here, we used a high fat, high fructose, and high sucrose (HFS) diet to determine how bile acid signaling through Tgr5 may regulate metabolism during the progression from fatty liver to non-alcoholic steatohepatitis and fibrosis.

Materials and methods

Female C57BL/6J control wild type (WT) and Tgr5 knockout (Tgr5 -/-) mice were fed HFS (high fat (40% kcal), high fructose, and 20% sucrose water) diet for 20 weeks. Metabolic phenotypes were characterized through examination of bile acid synthesis pathways, lipid and cholesterol metabolism pathways, and fibrosis and inflammation pathways.

Results

Tgr5 -/- mice were more glucose intolerant when fed HFS diet, despite gaining the same amount of weight as WT mice. Tgr5 -/- mice accumulated significantly more hepatic cholesterol and triglycerides on HFS diet compared to WT mice, and gene expression of lipogenic genes was significantly upregulated. Hepatic cholesterol 7alpha-hydroxylase (Cyp7a1) gene expression was consistently elevated in Tgr5 -/- mice, while oxysterol 7alpha-hydroxylase (Cyp7b1), sterol 27-hydroxylase (Cyp27a1), Fxr, and small heterodimer partner (Shp) were downregulated by HFS diet. Surprisingly, hepatic inflammation and fibrosis were also significantly reduced in Tgr5 -/- mice fed HFS diet, which may be due to altered serotonin signaling in the liver.

Conclusions

Tgr5 -/- mice may be protected from high fat, high sugar-induced hepatic inflammation and injury due to altered serotonin metabolism.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, "general chemicals," natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10-15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

A Molecular Logic Gate for Developing "AND" Logic Probes and the Application in Hepatopathy Differentiation

Accurate diagnosis and therapy are challenging because most diseases lack a single biomarker that distinguishes them from other disorders. A solution would enhance targeting accuracy by using AND-gated combinations of two disease-associated stimuli. Here, we report a novel "AND" molecular logic gate, enabling a double-controlled release of intact functional molecules. Benefiting from a significant difference in intramolecular cyclization rate, cargo release occurs notably faster with the presence of both stimuli. According to this finding, several AND logic probes have been developed that respond to a broad scope of stimuli and show remarkably improved signal-to-background contrast compared to those of monoresponsive probes. In addition, an AND logic probe that is responsive to monoamine oxidase (MAO) and leucine aminopeptidase (LAP) has been constructed for hepatopathy diagnosis. It works efficiently in living cells and mouse models. Of note, this probe can successfully differentiate cirrhotic from hepatitis B by testing the blood samples from patients.

Interactions between Tryptophan Metabolism, the Gut Microbiome and the Immune System as Potential Drivers of Non-Alcoholic Fatty Liver Disease (NAFLD) and Metabolic Diseases

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing and therefore is its burden of disease as NALFD is a risk factor for cirrhosis and is associated with other metabolic conditions such as type II diabetes, obesity, dyslipidaemia and atherosclerosis. Linking these cardiometabolic diseases is a state of low-grade inflammation, with higher cytokines and c-reactive protein levels found in individuals with NAFLD, obesity and type II diabetes. A possible therapeutic target to decrease this state of low-grade inflammation is the metabolism of the essential amino-acid tryptophan. Its three main metabolic pathways (kynurenine pathway, indole pathway and serotonin/melatonin pathway) result in metabolites such as kynurenic acid, xanturenic acid, indole-3-propionic acid and serotonin/melatonin. The kynurenine pathway is regulated by indoleamine 2,3-dioxygenase (IDO), an enzyme that is upregulated by pro-inflammatory molecules such as INF, IL-6 and LPS. Higher activity of IDO is associated with increased inflammation and fibrosis in NAFLD, as well with increased glucose levels, obesity and atherosclerosis. On the other hand, increased concentrations of the indole pathway metabolites, regulated by the gut microbiome, seem to result in more favorable outcomes. This narrative review summarizes the interactions between tryptophan metabolism, the gut microbiome and the immune system as potential drivers of cardiometabolic diseases in NAFLD.

Harmine suppresses collagen production in hepatic stellate cells by inhibiting DYRK1B

Liver fibrosis is a major consequence of chronic liver disease, where excess extracellular matrix is deposited, due caused by the activation of hepatic stellate cells (HSCs). The suppression of collagen production in HSCs is therefore regarded as a therapeutic target of liver fibrosis. The present study investigated effects of harmine, which is a β-carboline alkaloid and known as an inhibitor of dual-specificity tyrosine-regulated kinases (DYRKs), on the production of collagen in HSCs. LX-2 cells, a human HSC cell line, were treated with harmine (0-10 μM) for 48 h in the presence or absence of TGF-β1 (5 ng/ml). The expression of collagen type I α1 (COL1A1) and DYRK isoforms was investigated by Western blotting, quantitative RT-PCR, or immunofluorescence. The influence of knockdown of each DYRK isoform on the COL1A1 expression was further investigated. The expression of COL1A1 was markedly increased by treating with TGF-β1 for 48 h in LX-2 cells. Harmine (10 μM) significantly inhibited the increased expression of COL1A1. LX-2 cells expressed mRNAs of DYRK1A, DYRK1B, DYRK2, and DYRK4, although the expression of DYRK4 was much lower than the others. Knockdown of DYRK1B, but not DYRK1A or DYRK2, with siRNA significantly suppressed TGF-β1-induced increase in COL1A1 expression. These results suggest that harmine suppresses COL1A1 expression via inhibiting DYRK1B in HSCs and therefore might be effective for the treatment of liver fibrosis.

The regulative effect and repercussion of probiotics and prebiotics on osteoporosis: involvement of brain-gut-bone axis

Osteoporosis (OP) is a systemic disease characterized by decreased bone mass and degeneration of bone microstructure. In recent years, more and more researches have focused on the close relationship between gut microbiota (GM) and the occurrence and progression of OP, and the regulation of probiotics and prebiotics on bone metabolism has gradually become a research hotspot. Based on the influence of brain-gut-bone axis on bone metabolism, this review expounds the potential mechanisms of probiotics and prebiotics on OP from next perspectives: regulation of intestinal metabolites, regulation of intestinal epithelial barrier function, involvement of neuromodulation, involvement of immune regulation and involvement of endocrine regulation, so as to provide a novel and promising idea for the prevention and treatment of OP in the future.

Serotonin and systemic sclerosis. An emerging player in pathogenesis

OBJECTIVES

Systemic sclerosis (SSc) is a complex, autoimmune disease characterized by multiple organ fibrosis and vasculopathy. Experimental and clinical evidence indicates that serotonin is crucially involved in the fibrotic process and mediates vascular manifestations such as Raynaud's phenomenon (RP) or pulmonary arterial hypertension (PAH), all key features of SSc. In this review, we summarize the current knowledge on the potential contribution of serotonin in SSc pathogenesis and provide a rationale for further investigation of this molecule as a therapeutic target.

METHODS

Medline and Cochrane databases were searched from inception to April 2021 using the search terms (systemic sclerosis OR scleroderma OR Raynaud OR Pulmonary arterial hypertension) AND serotonin.

RESULTS

Serotonin, a key molecule in an array of central and peripheral functions, has a multifaceted role in regulating fibrosis and vasculopathy. Experimental data suggest that serotonin drives fibrosis in the skin and visceral organs, promotes platelet aggregation, induces vasoconstriction and increases pulmonary vascular resistance. Earlier human trials regarding drugs that inhibit serotonin signaling produced mixed results. However, recent advances in the understanding of the underlying molecular mechanisms could help identify novel therapeutics targeting the serotonin pathway and inform future clinical trials.

CONCLUSIONS

Serotonin may be a mediator in both fibrosis and vasculopathy. Further exploration of the potential role of serotonin in SSc is justified.

Hepatic stellate cell reprogramming via exosome-mediated CRISPR/dCas9-VP64 delivery

Hepatic stellate cells (HSCs) play a crucial role in the progression of liver fibrosis, which can be considered as the specific therapeutic target of anti-fibrotic treatment. Targeted induction of HSCs to hepatocytes via delivery of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (dCas9) system holds promise for hepatic fibrosis treatment. Our study here revealed that CRISPR/dCas9-VP64 system encapsulated in AML12 cell-derived exosomes could efficiently and successfully be delivered into the HSCs. In turn, the CRISPR/dCas9-VP64 system loaded in the exosomes can be efficiently released into the HSCs. As a proof-of-concept study, gRNA against hepatocyte nuclear factor 4α (HNF4α) together with the delivery of CRISPR/dCas9-VP64 system induced the HSCs to hepatocyte-like phenotype. In conclusion, our study here revealed that CRISPR/dCas9-VP64 system encapsulated in AML12 cell-derived exosomes could be functional in HSCs, emerging as a gene therapy strategy for hepatic fibrosis.

Modulation of serotonin in the gut-liver neural axis ameliorates the fatty and fibrotic changes in non-alcoholic fatty liver

The etiology of non-alcoholic fatty liver disease (NAFLD) consists of various factors, including neural signal pathways. However, the molecular mechanisms of the autonomic neural signals influencing NAFLD progression have not been elucidated. Therefore, we examined the involvement of the gut-liver neural axis in NAFLD development and tested the therapeutic effect of modulation of this axis in this study. To test the contribution of the gut-liver neural axis, we examined NAFLD progression with respect to body weight, hepatic steatosis, fibrosis, intestinal tight junction, microbiota and short-chain fatty acids in NAFLD models of choline-deficient defined L-amino-acid and high-fat diet-fed mice with or without blockades of autonomic nerves from the liver. Blockade of the neural signal from the liver to the gut in these NAFLD mice models ameliorated the progression of liver weight, hepatic steatosis and fibrosis by modulating serotonin expression in the small intestine. It was related to the severity of the liver pathology, the tight junction protein expression, microbiota diversity and short-chain fatty acids. These effects were reproduced by administrating serotonin antagonist, which ameliorated the NAFLD progression in the NAFLD mice models. Our study demonstrated that the gut-liver neural axis is involved in the etiologies of NAFLD progression and that serotonin expression through this signaling network is the key factor of this axis. Therefore, modulation of the gut-liver neural axis and serotonin antagonist ameliorates fatty and fibrotic changes in non-alcoholic fatty liver, and can be a potential therapeutic target of NAFLD.This article has an associated First Person interview with the first author of the paper.

Fluoxetine-induced hepatic lipid accumulation is linked to elevated serotonin production

Fluoxetine, a commonly prescribed selective serotonin reuptake inhibitor antidepressant, has been shown to increase hepatic lipid accumulation, a key factor in the development of nonalcoholic fatty liver disease. Interestingly, fluoxetine has also been reported to increase peripheral serotonin synthesis. As emerging evidence suggests that serotonin may be involved in the development of nonalcoholic fatty liver disease, we sought to determine if fluoxetine-induced hepatic lipid accumulation is mediated via altered serotonin production. Fluoxetine treatment increased lipid accumulation in association with increased mRNA expression of tryptophan hydroxylase 1 (Tph1, serotonin biosynthetic enzyme) and intracellular serotonin content. Serotonin alone had a similar effect to increase lipid accumulation. Moreover, blocking serotonin synthesis reversed the fluoxetine-induced increases in lipid accumulation. Collectively, these data suggest that fluoxetine-induced lipid accumulation can be mediated, in part, by elevated serotonin production. These results suggest a potential therapeutic target to ameliorate the adverse metabolic effects of fluoxetine exposure.

Depletion of serotonin relieves concanavalin A-induced liver fibrosis in mice by inhibiting inflammation, oxidative stress, and TGF-β1/Smads signaling pathway

Serotonin exerts important functions in several liver pathophysiological processes. In this study, we investigated the role of serotonin in concanavalin A (Con A)-induced liver fibrosis (LF) in mice and the underlying mechanisms. To establish the mouse model of LF, mice of wild-type (WT) and tryptophan hydroxylase 1 (Tph1) knockout (serotonin depletion) received Con A for 8 successive weeks. Degree of fibrosis was assessed by Sirius red staining, as well as the measurements of alpha smooth muscle actin (α- SMA), hydroxyproline (Hyp) and type I collagen in liver tissues. To elucidate the potential mechanisms, we assessed the effect of serotonin depletion on inflammatory, oxidative stress as well as TGF-β1/Smads signaling pathway. We found that serotonin depletion significantly inhibited collagen deposition as evaluated by less collagenous fiber in Sirus Red staining and reduced contents of Hyp and type I collagen. In addition, the absence of serotonin significantly inhibited the release of several inflammatory cytokines, including interleukin-6 (IL-6), interferon-gamma (IFN-γ), tumor necrosis-alpha (TNF-α), and transforming growth factor β1 (TGF-β1). Oxidative stress was also largely mitigated in LF mice with serotonin deficiency as manifested by the decreases of oxidative stress markers (malonaldehyde (MDA) and myeloperoxidase (MPO)), as well as the increases of antioxidant stress indicators (glutathione (GSH), and GSH-px, catalase (CAT), superoxide dismutase (SOD)) in liver tissues. Moreover, the lack of serotonin may provide an antifibrotic role by inhibiting the intrahepatic expressions of TGF-β1, phosphorylated-smad2 (p-smad2), and phosphorylated-smad3 (p-smad3). These results indicated that, serotonin depletion attenuates Con A-induced LF through the regulation of inflammatory response, oxidative stress injury, and TGF-β1/Smads signaling pathway.

Strategies Targeting the Innate Immune Response for the Treatment of Hepatitis C Virus-Associated Liver Fibrosis

Direct-acting antivirals eliminate hepatitis C virus (HCV) in more than 95% of treated individuals and may abolish liver injury, arrest fibrogenesis, and reverse fibrosis and cirrhosis. However, liver regeneration is usually a slow process that is less effective in the late stages of fibrosis. What is more, fibrogenesis may prevail in patients with advanced cirrhosis, where it can progress to liver failure and hepatocellular carcinoma. Therefore, the development of antifibrotic drugs that halt and reverse fibrosis progression is urgently needed. Fibrosis occurs due to the repair process of damaged hepatic tissue, which eventually leads to scarring. The innate immune response against HCV is essential in the initiation and progression of liver fibrosis. HCV-infected hepatocytes and liver macrophages secrete proinflammatory cytokines and chemokines that promote the activation and differentiation of hepatic stellate cells (HSCs) to myofibroblasts that produce extracellular matrix (ECM) components. Prolonged ECM production by myofibroblasts due to chronic inflammation is essential to the development of fibrosis. While no antifibrotic therapy is approved to date, several drugs are being tested in phase 2 and phase 3 trials with promising results. This review discusses current state-of-the-art knowledge on treatments targeting the innate immune system to revert chronic hepatitis C-associated liver fibrosis. Agents that cause liver damage may vary (alcohol, virus infection, etc.), but fibrosis progression shows common patterns among them, including chronic inflammation and immune dysregulation, hepatocyte injury, HSC activation, and excessive ECM deposition. Therefore, mechanisms underlying these processes are promising targets for general antifibrotic therapies.

Biliary damage and liver fibrosis are ameliorated in a novel mouse model lacking l-histidine decarboxylase/histamine signaling

Primary sclerosing cholangitis (PSC) is characterized by biliary damage and fibrosis. Multidrug resistance-2 gene knockout (Mdr2^-/-) mice and PSC patients have increased histamine (HA) levels (synthesized by l-histidine decarboxylase, HDC) and HA receptor (HR) expression. Cholestatic HDC^-/- mice display ameliorated biliary damage and hepatic fibrosis. The current study evaluated the effects of knockout of HDC^-/- in Mdr2^-/- mice (DKO) on biliary damage and hepatic fibrosis. WT, Mdr2^-/- mice, and homozygous DKO mice were used. Selected DKO mice were treated with HA. We evaluated liver damage along with HDC expression and HA serum levels. Changes in ductular reaction were evaluated along with liver fibrosis, inflammation and bile acid signaling pathways. The expression of H1HR/PKC-α/TGF-β1 and H2HR/pERK/VEGF-C was determined. In vitro, cholangiocyte lines were treated with HA with/without H1/H2 inhibitors before measuring: H1/H2HR, TGF-β1, and VEGF-C expression. Knockout of HDC ameliorates hepatic damage, ductular reaction, fibrosis, inflammation, bile acid signaling and H1HR/PKC-α/TGF-β1 and H2HR/pERK/VEGF-C signaling. Reactivation of the HDC/HA axis increased these parameters. In vitro, stimulation with HA increased HR expression and PKC-α, TGF-β1, and VEGF-C expression, which was reduced with HR inhibitors. Our data demonstrate the key role for the HDC/HA axis in the management of PSC progression.

Platelet C-Type Lectin-Like Receptor 2 Reduces Cholestatic Liver Injury in Mice

Cholestatic liver injury leads to liver dysfunction. The available evidence suggests that platelets can either promote or reduce liver injury and fibrosis. This study focused on the functions of the C-type lectin-like receptor 2 (CLEC-2), a new special platelet receptor that binds with podoplanin-activating platelets. The role of CLEC-2 and podoplanin in cholestatic liver injury was investigated. Mice were injected intraperitoneally with weekly doses of anti-CLEC-2 antibody (2A2B10) to achieve effective CLEC-2 inhibition in their platelets. Next, left and middle hepatic bile duct ligation (BDL) procedures were performed, and mice were euthanized 1 week later (2A2B10-BDL group). In addition, mice were prepared for control groups, and relevant histological and laboratory variables were compared among these groups. The inhibition of CLEC-2 resulted in increasing hepatocellular necrosis, hepatic inflammation, and liver fibrosis. In addition, podoplanin was strongly expressed in hepatic sinusoidal endothelial cells in BDL-treated mice. Moreover, in 2A2B10-BDL mice, total plasma bile acid levels were significantly increased. In summary, podoplanin is expressed on hepatic sinusoidal endothelial cells upon BDL. Platelets bind with podoplanin via CLEC-2 and become activated. As a result, the total bile acid pool is decreased. Therefore, the CLEC-2-podoplanin interaction promotes liver protection and inhibits liver fibrosis after cholestatic liver injury.

Cholangiocarcinoma: novel therapeutic targets

Introduction: Cholangiocarcinoma (CCA) is a liver cancer derived from the biliary tree with a less than 30% five-year survival rate. Early diagnosis of CCA is challenging and treatment options are limited. Some CCA patients have genetic mutations and several therapeutic drugs or antibodies have been introduced to target abnormally expressed proteins. However, CCA is heterogeneous and patients often present with drug resistance which is attributed to multiple mutations or other factors. Novel approaches and methodologies for CCA treatments are in demand.Area covered: This review summarizes current approaches for CCA treatments leading to the development of novel therapeutic drugs or tools for human CCA patients. A literature search was conducted in PubMed utilizing the combination of the searched term 'cholangiocarcinoma' with other keywords such as 'miRNA', 'FGFR', 'immunotherapy' or 'microenvironment'. Papers published within 2015-2019 were obtained for reading.Expert opinion: Preclinical studies have demonstrated promising therapeutic approaches that target various cells or pathways. Recent studies have revealed that hepatic cells coordinate to promote CCA tumor progression in the tumor microenvironment, which may be a new therapeutic target. Although further studies are required, novel therapeutic tools such as extracellular vesicles could be utilized to manage CCA and its microenvironment.

Amelioration of Large Bile Duct Damage by Histamine-2 Receptor Vivo-Morpholino Treatment

Histamine binds to one of the four G-protein-coupled receptors expressed by large cholangiocytes and increases large cholangiocyte proliferation via histamine-2 receptor (H2HR), which is increased in patients with primary sclerosing cholangitis (PSC). Ranitidine decreases liver damage in Mdr2^-/- (ATP binding cassette subfamily B member 4 null) mice. We targeted hepatic H2HR in Mdr2^-/- mice using vivo-morpholino. Wild-type and Mdr2^-/- mice were treated with mismatch or H2HR vivo-morpholino by tail vein injection for 1 week. Liver damage, mast cell (MC) activation, biliary H2HR, and histamine serum levels were studied. MC markers were determined by quantitative real-time PCR for chymase and c-kit. Intrahepatic biliary mass was detected by cytokeratin-19 and F4/80 to evaluate inflammation. Biliary senescence was determined by immunofluorescence and senescence-associated β-galactosidase staining. Hepatic fibrosis was evaluated by staining for desmin, Sirius Red/Fast Green, and vimentin. Immunofluorescence for transforming growth factor-β₁, vascular endothelial growth factor-A/C, and cAMP/ERK expression was performed. Transforming growth factor-β₁ and vascular endothelial growth factor-A secretion was measured in serum and/or cholangiocyte supernatant. Treatment with H2HR vivo-morpholino in Mdr2^-/--mice decreased hepatic damage; H2HR protein expression and MC presence or activation; large intrahepatic bile duct mass, inflammation and senescence; and fibrosis, angiogenesis, and cAMP/phospho-ERK expression. Inhibition of H2HR signaling ameliorates large ductal PSC-induced damage. The H2HR axis may be targeted in treating PSC.

Neuroendocrine Changes in Cholangiocarcinoma Growth

Cholangiocarcinoma (CCA) is a highly aggressive malignancy that emerges from the biliary tree. There are three major classes of CCA-intrahepatic, hilar (perihilar), or distal (extrahepatic)-according to the location of tumor development. Although CCA tumors are mainly derived from biliary epithelia (i.e., cholangiocytes), CCA can be originated from other cells, such as hepatic progenitor cells and hepatocytes. This heterogeneity of CCA may be responsible for poor survival rates of patients, limited effects of chemotherapy and radiotherapy, and the lack of treatment options and novel therapies. Previous studies have identified a number of neuroendocrine mediators, such as hormones, neuropeptides, and neurotransmitters, as well as corresponding receptors. The mediator/receptor signaling pathways play a vital role in cholangiocyte proliferation, as well as CCA progression and metastases. Agonists or antagonists for candidate pathways may lead to the development of novel therapies for CCA patients. However, effects of mediators may differ between healthy or cancerous cholangiocytes, or between different subtypes of receptors. This review summarizes current understandings of neuroendocrine mediators and their functional roles in CCA.

Significance of expression of lncRNA-ATB in serum of patients with cholestatic liver disease

BACKGROUND

Cholestatic liver disease (CSLD) refers to a collection of liver diseases that can cause cholestasis. The etiology of CSLD is complex, the pathogenesis needs to be elucidated, and there is still a lack of effective treatment. Over the past decade, there has been a deep understanding of many aspects of CSLD, which provides more effective means for its accurate diagnosis and treatment. However, many problems are still pending, and further research is urgently needed.

AIM

To observe the difference of serum lncRNA-ATB levels between patients with intrahepatic cholestasis and normal people, and to explore the correlation between the changes of serum lncRNA-ATB and disease condition and prognosis in patients with intrahepatic cholestasis.

METHODS

Seventy-five patients with intrahepatic cholestasis of different etiologies and 30 healthy controls were included. The expression of lncRNA-ATB in serum samples of the above subjects was detected by qRT-PCR. The levels of lncRNA-ATB between normal controls and patients with cholestasis and between patients with different degrees of cholestasis were analyzed. Linear correlation analysis was used to analyze the correlation between the changes of lncRNA-ATB and clinical biochemical indicators, and receiver operating characteristic curve analysis was performed to analyze the clinical significance of the changes of lncRNA-ATB in judging the condition of intrahepatic cholestasis.

RESULTS

Compared with the healthy control group, lncRNA-ATB increased significantly in the serum of patients with intrahepatic cholestasis (P < 0.05). There was no significant difference in the expression of lncRNA-ATB between patients with cholestatic liver disease caused by different etiologies and and between patients with different courses of cholestasis (P > 0.05). Serum lncRNA-ATB decreased with the aggravation of cholestasis (P < 0.001). There was a negative correlation between lncRNA-ATB and total bile acid (r = -0.627, P < 0.001). The area under the curve of lncRNA-ATB in the diagnosis of cholestasis liver disease was 0.856 (95%CI: 0.809-0.904, P < 0.001), with a sensitivity of 81.42% and specificity of 73.45%.

CONCLUSION

The level of lncRNA-ATB in serum of patients with intrahepatic cholestasis liver disease is significantly increased, and it decreases with the aggravation of cholestasis. The expression level of LncRNA-ATB is expected to be a biomarker for judging the condition and prognosis of patients with intrahepatic cholestasis.

Inhibition of serotonin synthesis: A novel therapeutic paradigm

The rate-limiting enzyme in serotonin synthesis is tryptophan hydroxylase (TPH). There are two independent serotonin systems in the body characterized by two isoforms of TPH, TPH1 and TPH2. While TPH2 synthesizes serotonin in the brain, TPH1 is expressed in the gut and in other peripheral tissues and supplies platelets in the circulation with serotonin. This duality of the serotonin system is enforced by the blood-brain barrier which is impermeable for serotonin. In the brain serotonin acts as neurotransmitter and is a main target for the treatment of psychiatric disorders. In the periphery it is released by platelets at the site of activation and elicits numerous physiological effects. TPH1 deficient mice were shown to be protected from diverse diseases including hemostatic, inflammatory, fibrotic, gastrointestinal, and metabolic disorders and therefore serotonin synthesis inhibition emerged as a reasonable therapeutic paradigm. Recently the first TPH inhibitor, telotristat ethyl, came on the market for the treatment of carcinoid syndrome. This review summarizes the state of development and the therapeutic opportunities of such compounds.