Endogenous opioids modulate the growth of the biliary tree in the course of cholestasis

Current Perspectives of Neuroendocrine Regulation in Liver Fibrosis

Liver fibrosis is a complicated process that involves different cell types and pathological factors. The excessive accumulation of extracellular matrix (ECM) and the formation of fibrotic scar disrupt the tissue homeostasis of the liver, eventually leading to cirrhosis and even liver failure. Myofibroblasts derived from hepatic stellate cells (HSCs) contribute to the development of liver fibrosis by producing ECM in the area of injuries. It has been reported that the secretion of the neuroendocrine hormone in chronic liver injury is different from a healthy liver. Activated HSCs and cholangiocytes express specific receptors in response to these neuropeptides released from the neuroendocrine system and other neuroendocrine cells. Neuroendocrine hormones and their receptors form a complicated network that regulates hepatic inflammation, which controls the progression of liver fibrosis. This review summarizes neuroendocrine regulation in liver fibrosis from three aspects. The first part describes the mechanisms of liver fibrosis. The second part presents the neuroendocrine sources and neuroendocrine compartments in the liver. The third section discusses the effects of various neuroendocrine factors, such as substance P (SP), melatonin, as well as α-calcitonin gene-related peptide (α-CGRP), on liver fibrosis and the potential therapeutic interventions for liver fibrosis.

Opioid receptors signaling network

Opioid receptors belong to the class A G-protein-coupled receptors and are activated by alkaloid opiates such as morphine, and endogenous ligands such as endorphins and enkephalins. Opioid receptors are widely distributed in the human body and are involved in numerous physiological processes through three major classical opioid receptor subtypes; the mu, delta and kappa along with a lesser characterized subtype, opioid receptor-like (ORL1). Opioids are the most potent analgesics and have been extensively used as a therapeutic drug for the treatment of pain and related disorders. Chronic administration of clinically used opioids is associated with adverse effects such as drug tolerance, addiction and constipation. Several investigations attempted to identify the molecular signaling networks associated with endogenous as well as synthetic opiates, however, there is a paucity of a cumulative depiction of these signaling events. Here, we report a systemic collection of downstream molecules pertaining to four subtypes of opioid receptors (MOR, KOR, DOR and ORL1) in the form of a signaling pathway map. We manually curated reactions induced by the activation of opioid receptors from the literature into five categories- molecular association, activation/inhibition, catalysis, transport, and gene regulation. This led to a dataset of 180 molecules, which is collectively represented in the opioid receptor signaling network following NetPath criteria. We believe that the public availability of an opioid receptor signaling pathway map can accelerate biomedical research in this area because of its high therapeutic significance. The opioid receptors signaling pathway map is uploaded to a freely available web resource, WikiPathways enabling ease of access ( https://www.wikipathways.org/index.php/Pathway:WP5093 ).

Novel lncRNA-HZ04 promotes BPDE-induced human trophoblast cell apoptosis and miscarriage by upregulating IP3 R1 /CaMKII/SGCB pathway by competitively binding with miR-hz04

Normal pregnancy is essential for human reproduction. However, BaP (benzo(a)pyrene) and its metabolite BPDE (benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide) could cause dysfunctions of human trophoblast cells and might further induce miscarriage. Yet, the underlying mechanisms remain largely unknown. Herein, we identified a novel upregulated lnc-HZ04 and a novel downregulated miR-hz04 in villous tissues of unexplained recurrent miscarriage (RM) relative to those in healthy control tissues and also in BPDE-treated human trophoblast cells. Lnc-HZ04 directly and specifically bound with miR-hz04, diminished the reduction effects of miR-hz04 on IP₃ R₁ mRNA expression level and on IP₃ R₁ mRNA stability, and then activated the Ca²⁺ -mediated IP₃ R₁ /p-CaMKII/SGCB pathway, which further promoted trophoblast cell apoptosis. The miR-hz04 target site on lnc-HZ04 played crucial roles in these regulations. In normal trophoblast, relatively less lnc-HZ04 and more miR-hz04 suppressed this apoptosis pathway and gave normal pregnancy. After exposure to BPDE or in RM tissues, p53 was upregulated, which might promote p53-mediated lnc-HZ04 transcription. Relatively more lnc-HZ04 and less miR-hz04 activated this apoptosis pathway and might further induce miscarriage. BaP could also induce mice miscarriage by upregulating its corresponding murine apoptosis pathway. Therefore, BPDE-induced apoptosis of human trophoblast cells was associated with the occurrence of miscarriage. This work discovered the regulation roles of lnc-HZ04 and miR-hz04 and provided scientific and clinical understanding of the occurrence of unexplained miscarriage.

Coordinated Targeting of Galanin Receptors on Cholangiocytes and Hepatic Stellate Cells Ameliorates Liver Fibrosis in Multidrug Resistance Protein 2 Knockout Mice

Galanin (Gal) is a peptide with a role in neuroendocrine regulation of the liver. In this study, we assessed the role of Gal and its receptors, Gal receptor 1 (GalR1) and Gal receptor 2 (GalR2), in cholangiocyte proliferation and liver fibrosis in multidrug resistance protein 2 knockout (Mdr2KO) mice as a model of chronic hepatic cholestasis. The distribution of Gal, GalR1, and GalR2 in specific liver cell types was assessed by laser-capture microdissection and confocal microscopy. Galanin immunoreactivity was detected in cholangiocytes, hepatic stellate cells (HSCs), and hepatocytes. Cholangiocytes expressed GalR1, whereas HSCs and hepatocytes expressed GalR2. Strategies were used to either stimulate or block GalR1 and GalR2 in FVB/N (wild-type) and Mdr2KO mice and measure biliary hyperplasia and hepatic fibrosis by quantitative PCR and immunostaining of specific markers. Galanin treatment increased cholangiocyte proliferation and fibrogenesis in both FVB/N and Mdr2KO mice. Suppression of GalR1, GalR2, or both receptors in Mdr2KO mice resulted in reduced bile duct mass and hepatic fibrosis. In vitro knockdown of GalR1 in cholangiocytes reduced α-smooth muscle actin expression in LX-2 cells treated with cholangiocyte-conditioned media. A GalR2 antagonist inhibited HSC activation when Gal was administered directly to LX-2 cells, but not via cholangiocyte-conditioned media. These data demonstrate that Gal contributes not only to cholangiocyte proliferation but also to liver fibrogenesis via the coordinate activation of GalR1 in cholangiocytes and GalR2 in HSCs.

microRNA-874 suppresses tumor proliferation and metastasis in hepatocellular carcinoma by targeting the DOR/EGFR/ERK pathway

The δ opioid receptor (DOR) is involved in the regulation of malignant transformation and tumor progression of hepatocellular carcinoma (HCC). However, regulation of the DOR in HCC remains poorly defined. We found that miR-874 was identified as a negative regulator of the DOR, which is a direct and functional target of miR-874 via its 3' untranslated region (UTR). Moreover, miR-874 was downregulated in HCC and its expression was inversely correlated with DOR expression. Downregulation of miR-874 was also associated with larger tumor size, more vascular invasion, a poor TNM stage, poor tumor differentiation, and inferior patient outcomes. Functionally, overexpression of miR-874 in the HCC cell line SK-hep-1 inhibited cell growth, migration, in vitro invasion, and in vivo tumorigenicity. Furthermore, miR-874 overexpression suppressed the DOR, resulting in a downregulated epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK) phosphorylation. The EGFR activator-epidermal growth factor (EGF)-can rescue the proliferation and migration suppression induced by miR-874 overexpression, and the rescue effects of the EGF were blocked by an ERK inhibitor. Our study results suggest that miRNA-874 is a negative regulator of the DOR that can suppress tumor proliferation and metastasis in HCC by targeting the DOR/EGFR/ERK pathway, which may be a potential target for HCC treatment.

Biology of Cholangiocytes: From Bench to Bedside

Cholangiocytes, the lining epithelial cells in bile ducts, are an important subset of liver cells. They are activated by endogenous and exogenous stimuli and are involved in the modification of bile volume and composition. They are also involved in damaging and repairing the liver. Cholangiocytes have many functions including bile production. They are also involved in transport processes that regulate the volume and composition of bile. Cholangiocytes undergo proliferation and cell death under a variety of conditions. Cholangiocytes have functional and morphological heterogenecity. The immunobiology of cholangiocytes is important, particularly for understanding biliary disease. Secretion of different proinflammatory mediators, cytokines, and chemokines suggests the major role that cholangiocytes play in inflammatory reactions. Furthermore, paracrine secretion of growth factors and peptides mediates extensive cross-talk with other liver cells, including hepatocytes, stellate cells, stem cells, subepithelial myofibroblasts, endothelial cells, and inflammatory cells. Cholangiopathy refers to a category of chronic liver diseases whose primary disease target is the cholangiocyte. Cholangiopathy usually results in end-stage liver disease requiring liver transplant. We summarize the biology of cholangiocytes and redefine the concept of cholangiopathy. We also discuss the recent progress that has been made in understanding the pathogenesis of cholangiopathy and how such progress has influenced therapy.

Expert consensus document: Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies with features of biliary tract differentiation. CCA is the second most common primary liver tumour and the incidence is increasing worldwide. CCA has high mortality owing to its aggressiveness, late diagnosis and refractory nature. In May 2015, the "European Network for the Study of Cholangiocarcinoma" (ENS-CCA: www.enscca.org or www.cholangiocarcinoma.eu) was created to promote and boost international research collaboration on the study of CCA at basic, translational and clinical level. In this Consensus Statement, we aim to provide valuable information on classifications, pathological features, risk factors, cells of origin, genetic and epigenetic modifications and current therapies available for this cancer. Moreover, future directions on basic and clinical investigations and plans for the ENS-CCA are highlighted.

DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ Operate in Parallel to Each Other in PLCγ1-Driven Cell Proliferation and Migration of Human Gastric Adenocarcinoma Cells, through Akt/mTOR/S6 Pathway

Phosphoinositide specific phospholipase Cγ (PLCγ) activates diacylglycerol (DAG)/protein kinase C (PKC) and inositol 1,4,5-trisphosphate (IP3)/Ca²⁺/calmodulin-dependent protein kinase II (CaMK II) axes to regulate import events in some cancer cells, including gastric adenocarcinoma cells. However, whether DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ axes are simultaneously involved in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells and the underlying mechanism are not elucidated. Here, we investigated the role of DAG/PKCδ or CaMK IIβ in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells, using the BGC-823 cell line. The results indicated that the inhibition of PKCδ and CaMK IIβ could block cell proliferation and migration of BGC-823 cells as well as the effect of inhibiting PLCγ1, including the decrease of cell viability, the increase of apoptotic index, the down-regulation of matrix metalloproteinase (MMP) 9 expression level, and the decrease of cell migration rate. Both DAG/PKCδ and CaMK IIβ triggered protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/S6 pathway to regulate protein synthesis. The data indicate that DAG/PKCδ and IP3/Ca²⁺/CaMK IIβ operate in parallel to each other in PLCγ1-driven cell proliferation and migration of human gastric adenocarcinoma cells through Akt/mTOR/S6 pathway, with important implication for validating PLCγ1 as a molecular biomarker in early gastric cancer diagnosis and disease surveillance.

Activated δ‑opioid receptors inhibit hydrogen peroxide‑induced apoptosis in liver cancer cells through the PKC/ERK signaling pathway

Apoptotic liver cancer cells have important roles in liver tumorigenesis and liver cancer progression. Recent studies have shown that δ‑opioid receptors are highly expressed in human liver and liver cancer cells. The present study aimed to investigate the role of activated δ‑opioid receptors on human liver cancer cell apoptosis and its interrelation with the mitochondria and the protein kinase C/extracellular‑signal‑regulated kinase (PKC/ERK) signaling pathway. H2O2 was used to induce apoptosis in human liver cancer cells. During apoptosis, mitochondrial transmembrane potentials were observed to decrease, cytochrome c expression was found to increase and B cell lymphoma 2 (Bcl‑2) expression decreased. These findings suggested that H2O2‑induced apoptosis was mediated through the mitochondrial pathway. Of note, activated δ‑opioid receptors were observed to inhibit H2O2‑induced apoptosis in human liver cancer cells. Following δ‑opioid receptor activation, the number of apoptotic liver cancer cells decreased, mitochondrial transmembrane potentials were restored, cytoplasmic cytochrome c and Bcl‑2‑associated X protein expression decreased and Bcl‑2 expression increased. These data suggested that δ‑opioid receptor activation inhibited mitochondria‑mediated apoptosis. In addition, activation of δ‑opioid receptors was observed to increase the expression of PKC and ERK in human liver cancer cells. Furthermore, upon inhibition of the PKC/ERK signaling pathway, the protective effect associated with the δ‑opioid receptor on liver cancer cell apoptosis was inhibited, which was not associated with the status of δ‑opioid receptor activation. These findings suggested that the PKC/ERK signaling pathway has an important role in δ‑opioid receptor‑mediated inhibition of apoptosis in human liver cancer cells.

Upregulation of the δ opioid receptor in liver cancer promotes liver cancer progression both in vitro and in vivo

The δ opioid receptor (DOR), is the first cloned G protein-coupled receptor. Many recent studies on DOR functions have determined that the DOR is involved in the regulation of malignant transformation and tumor progression in multiple cancers. However, it is still unclear if the DOR is involved in the regulation of malignant transformation and tumor progression in hepatocellular carcinoma (HCC). The purpose of our study was to investigate the expression of the DOR in HCC and to determine its effect on progression to further understand the influence of the DOR on the biological characteristics of HCC. Higher expression of DOR was observed in liver tumor tissue/cells compared to normal liver tissue/cells. When DOR gene expression was silenced or inhibited, the proliferation of HCC cells was inhibited, and tumor cells underwent apoptosis, the cell cycle was arrested and tumor cell invasion and migration were significantly decreased. Nude mice inoculated with cells stably expressing low levels of DOR displayed reduced tumor formation rates and reduced tumor growth. In conclusion, DOR is highly expressed in HCC and is involved in HCC progression, suggesting that DOR is a potential target for HCC treatment.

Recent advances in the morphological and functional heterogeneity of the biliary epithelium

This review focuses on the recent advances related to the heterogeneity of different-sized bile ducts with regard to the morphological and phenotypical characteristics, and the differential secretory, apoptotic and proliferative responses of small and large cholangiocytes to gastrointestinal hormones/peptides, neuropeptides and toxins. We describe several in vivo and in vitro models used for evaluating biliary heterogeneity. Subsequently, we discuss the heterogeneous proliferative and apoptotic responses of small and large cholangiocytes to liver injury and the mechanisms regulating the differentiation of small into large (more differentiated) cholangiocytes. Following a discussion on the heterogeneity of stem/progenitor cells in the biliary epithelium, we outline the heterogeneity of bile ducts in human cholangiopathies. After a summary section, we discuss the future perspectives that will further advance the field of the functional heterogeneity of the biliary epithelium.

Autocrine regulation of biliary pathology by activated cholangiocytes

The bile duct system of the liver is lined by epithelial cells (i.e., cholangiocytes) that respond to a large number of neuroendocrine factors through alterations in their proliferative activities and the subsequent modification of the microenvironment. As such, activation of biliary proliferation compensates for the loss of cholangiocytes due to apoptosis and slows the progression of toxic injury and cholestasis. Over the course of the last three decades, much progress has been made in identifying the factors that trigger the biliary epithelium to remodel and grow. Because a large number of autocrine factors have recently been identified as relevant clinical targets, a compiled review of their contributions and function in cholestatic liver diseases would be beneficial. In this context, it is important to define the specific processes triggered by autocrine factors that promote cholangiocytes to proliferate, activate neighboring cells, and ultimately lead to extracellular matrix deposition. In this review, we discuss the role of each of the known autocrine factors with particular emphasis on proliferation and fibrogenesis. Because many of these molecules interact with one another throughout the progression of liver fibrosis, a model speculating their involvement in the progression of cholestatic liver disease is also presented.

Regulation of biliary proliferation by neuroendocrine factors: implications for the pathogenesis of cholestatic liver diseases

The proliferation of cholangiocytes occurs during the progression of cholestatic liver diseases and is critical for the maintenance and/or restoration of biliary mass during bile duct damage. The ability of cholangiocytes to proliferate is important in many different human pathologic conditions. Recent studies have brought to light the concept that proliferating cholangiocytes serve as a unique neuroendocrine compartment in the liver. During extrahepatic cholestasis and other pathologic conditions that trigger ductular reaction, proliferating cholangiocytes acquire a neuroendocrine phenotype. Cholangiocytes have the capacity to secrete and respond to a variety of hormones, neuropeptides, and neurotransmitters, regulating their surrounding cell functions and proliferative activity. In this review, we discuss the regulation of cholangiocyte growth by neuroendocrine factors in animal models of cholestasis and liver injury, which includes a discussion of the acquisition of neuroendocrine phenotypes by proliferating cholangiocytes and how this relates to cholangiopathies. We also review what is currently known about the neuroendocrine phenotypes of cholangiocytes in human cholestatic liver diseases (ie, cholangiopathies) that are characterized by ductular reaction.

Opioid-like compound exerts anti-fibrotic activity via decreased hepatic stellate cell activation and inflammation

Hepatic fibrosis is characterized by excess type I collagen deposition and exacerbated inflammatory response. Naltrexone, an opioid receptor antagonist used for treating alcohol abuse, attenuates hepatocellular injury in fibrotic animal models, which can be accompanied by deleterious side effects. Additionally, opioid neurotransmission is upregulated in patients with inflammatory liver disease. Several derivatives of Naltrexone, Nalmefene (Nal) and JKB-119, exert immunomodulatory activity; however, unlike Nal, JKB-119 does not show significant opioid receptor antagonism. To delineate the potential hepatoprotective effects of these compounds, we investigated if JKB-119 and Nal could modulate activation of hepatic stellate cells (HSCs), primary effector cells that secrete type I collagen and inflammatory mediators during liver injury. Our results demonstrated that Nal or JKB-119 treatment decreased smooth muscle α-actin, a marker of HSC activation, mRNA and protein expression. Despite decreased collagen mRNA expression, both compounds increased intracellular collagen protein expression; however, inhibition of collagen secretion was observed. To address a possible mechanism for suppressed collagen secretion or retention of intracellular collagen, endoplasmic (ER) protein expression and matrix metalloproteinase (MMP) activity were examined. While no change in ER protein expression (Grp78, PDI, Hsp47) was observed, MMP13 mRNA expression was dramatically increased. In an acute LPS inflammatory injury animal model, JKB-119 treatment decreased liver injury (ALT), plasma TNFα and PMN liver infiltration. Overall, these results suggest that JKB-119 can directly inhibit HSC activation attributed to anti-inflammatory activity and may, therefore, attenuate inflammation associated with HSC activation and liver disease.

Recent advances in the regulation of cholangiocarcinoma growth

Cholangiocarcinomas arise after the neoplastic transformation of the cholangiocytes that line the intra- and extrahepatic biliary epithelium. Symptoms usually do not present until late in the course of the disease, at which time they are relatively resistant to chemotherapeutic agents and as such are difficult to treat and display a poor prognosis. Because of the relative rarity of this disease, the overall volume of research into the molecular pathophysiology associated with this disease is small compared with other more prevalent tumors. However, the incidence of this devastating cancer is on the rise and renewed efforts to understand the pathogenesis of cholangiocarcinoma is needed to design novel therapeutic strategies to combat this disease. This review summarizes the recent advances into our knowledge and understanding of cholangiocarcinoma and highlights potential novel therapeutic strategies that may prove useful to treat this deadly disease.

Clinical implications of novel aspects of biliary pathophysiology

Cholangiocytes are the epithelial cells that line the biliary tree; they are the target of chronic diseases termed cholangiopathies, which represent a daily challenge for clinicians, since definitive medical treatments are not available yet. It is generally accepted that the progression of injury in the course of cholangiopathies, and promotion and progression of cholangiocarcinoma are at least in part due to the failure of the cholangiocytes' mechanisms of adaptation to injury. Recently, several studies on the pathophysiology of the biliary epithelium have shed some light on the mechanisms that govern cholangiocyte response to injury. These studies provide novel information to help interpret some of the clinical aspects of cholangiopathies and cholangiocarcinoma; the purpose of this review is thus to describe some of these novel findings, focusing on their significance from a clinical perspective.

Mechanisms of Biliary Damage

Bile duct damage is present in virtually all cholangiopathies, which share the biliary epithelial cells (i.e. cholangiocytes) as a common pathogenic target. Cholangiocyte cell death largely occurs through the process of apoptosis. In this review, we will summarize the mechanisms through which biliary damage occurs in a variety of animal and in vitro models, such as extrahepatic cholestasis induced by bile duct ligation (BDL), cytotoxin- and hepatotoxin-induced liver injury, and biliary atresia. Although we have increased our knowledge of the factors that regulate cholangiocyte cell death mechanisms during cholangiopathies, especially in experimental models, there is still a lack of effective treatment modalities for these biliary disorders. However, future studies will hopefully provide for new therapeutic modalities for the prevention or restoration of biliary mass and function lost during the progression of cholangiopathies.

Human cholangiocarcinoma development is associated with dysregulation of opioidergic modulation of cholangiocyte growth

BACKGROUND/AIMS

Incidence of cholangiocarcinoma is increasing worldwide, yet remaining highly aggressive and with poor prognosis. The mechanisms that drive cholangiocyte transition towards malignant phenotype are obscure. Cholangiocyte benign proliferation is subjected to a self-limiting mechanism based on the autocrine release of endogenous opioid peptides. Despite the presence of both, ligands interact with delta opioid receptor (OR), but not with microOR, with the consequent inhibition of cell growth. We aimed to verify whether cholangiocarcinoma growth is associated with failure of opioidergic regulation of growth control.

METHODS

We evaluated the effects of OR selective agonists on cholangiocarcinoma cell proliferation, migration and apoptosis. Intracellular signals were also characterised.

RESULTS

Activation of microOR, but not deltaOR, increases cholangiocarcinoma cell growth. Such an effect is mediated by ERK1/2, PI3K and Ca(2+)-CamKIIalpha cascades, but not by cAMP/PKA and PKCalpha. microOR activation also enhances cholangiocarcinoma cell migration and reduces death by apoptosis. The anti-apoptotic effect of microOR was PI3K dependent.

CONCLUSIONS

Our data indicate that cholangiocarcinoma growth is associated with altered opioidergic regulation of cholangiocyte biology, thus opening new scenarios for future surveillance or early diagnostic strategies for cholangiocarcinoma.

Control of cholangiocyte adaptive responses by visceral hormones and neuropeptides

Cholangiocytes, the epithelial cells lining the biliary tree, are the target cells in several liver diseases, termed cholangiopathies. Cholangiopathies are a challenge for clinicians and an enigma for scientists, as the pathogenetic mechanisms by which they develop, and the therapeutic tools for these diseases are still undefined. Several studies demonstrate that many visceral hormones, neuropeptides, and neurotransmitters modulate the adaptive changes of cholangiocytes to chronic cholestatic injury. The aim of this review is to present the recent findings that contributed to clarify the role of visceral hormones and neuropeptides in the regulation of the pathophysiology of cholestasis. These studies helped to shed light on some aspects of cholangiocyte pathophysiology, revealing novel perspectives for the clinical managements of cholangiopathies.

Leptin enhances cholangiocarcinoma cell growth

Cholangiocarcinoma is a strongly aggressive malignancy with a very poor prognosis. Effective therapeutic strategies are lacking because molecular mechanisms regulating cholangiocarcinoma cell growth are unknown. Furthermore, experimental in vivo animal models useful to study the pathophysiologic mechanisms of malignant cholangiocytes are lacking. Leptin, the hormone regulating caloric homeostasis, which is increased in obese patients, stimulates the growth of several cancers, such as hepatocellular carcinoma. The aim of this study was to define if leptin stimulates cholangiocarcinoma growth. We determined the expression of leptin receptors in normal and malignant human cholangiocytes. Effects on intrahepatic cholangiocarcinoma (HuH-28) cell proliferation, migration, and apoptosis of the in vitro exposure to leptin, together with the intracellular pathways, were then studied. Moreover, cholangiocarcinoma was experimentally induced in obese fa/fa Zucker rats, a genetically established animal species with faulty leptin receptors, and in their littermates by chronic feeding with thioacetamide, a potent carcinogen. After 24 weeks, the effect of leptin on cholangiocarcinoma development and growth was assessed. Normal and malignant human cholangiocytes express leptin receptors. Leptin increased the proliferation and the metastatic potential of cholangiocarcinoma cells in vitro through a signal transducers and activators of transcription 3-dependent activation of extracellular signal-regulated kinase 1/2. Leptin increased the growth and migration, and was antiapoptotic for cholangiocarcinoma cells. Moreover, the loss of leptin function reduced the development and the growth of cholangiocarcinoma. The experimental carcinogenesis model induced by thioacetamide administration is a valid and reproducible method to study cholangiocarcinoma pathobiology. Modulation of the leptin-mediated signal could be considered a valid tool for the prevention and treatment of cholangiocarcinoma.

Hepatic fibrogenesis in response to chronic liver injury: novel insights on the role of cell-to-cell interaction and transition

Hepatic fibrosis represents the wound-healing response process of the liver to chronic injury, independently from aetiology. Advanced liver fibrosis results in cirrhosis that can lead to liver failure, portal hypertension and hepatocellular carcinoma. Currently, no effective therapies are available for hepatic fibrosis. After the definition of hepatic stellate cells (HSCs) as the main liver extracellular matrix-producing cells in the 1980s, the subsequent decade was dedicated to determine the role of specific cytokines and growth factors. Fibrotic progression of chronic liver diseases can be nowadays considered as a dynamic and highly integrated process of cellular response to chronic liver injury. The present review is dedicated to the novel mechanisms of cellular response to chronic liver injury leading to hepatic myofibroblasts' activation. The understanding of the cellular and molecular pathways regulating their function is crucial to counteract therapeutically the organ dysfunction caused by myofibroblasts' activation.

Small mouse cholangiocytes proliferate in response to H1 histamine receptor stimulation by activation of the IP3/CaMK I/CREB pathway

Cholangiopathies are characterized by the heterogeneous proliferation of different-sized cholangiocytes. Large cholangiocytes proliferate by a cAMP-dependent mechanism. The function of small cholangiocytes may depend on the activation of inositol trisphosphate (IP(3))/Ca(2+)-dependent signaling pathways; however, data supporting this speculation are lacking. Four histamine receptors exist (HRH1, HRH2, HRH3, and HRH4). In several cells: 1) activation of HRH1 increases intracellular Ca(2+) concentration levels; and 2) increased [Ca(2+)](i) levels are coupled with calmodulin-dependent stimulation of calmodulin-dependent protein kinase (CaMK) and activation of cAMP-response element binding protein (CREB). HRH1 agonists modulate small cholangiocyte proliferation by activation of IP(3)/Ca(2+)-dependent CaMK/CREB. We evaluated HRH1 expression in cholangiocytes. Small and large cholangiocytes were stimulated with histamine trifluoromethyl toluidide (HTMT dimaleate; HRH1 agonist) for 24-48 h with/without terfenadine, BAPTA/AM, or W7 before measuring proliferation. Expression of CaMK I, II, and IV was evaluated in small and large cholangiocytes. We measured IP(3), Ca(2+) and cAMP levels, phosphorylation of CaMK I, and activation of CREB (in the absence/presence of W7) in small cholangiocytes treated with HTMT dimaleate. CaMK I knockdown was performed in small cholangiocytes stimulated with HTMT dimaleate before measurement of proliferation and CREB activity. Small and large cholangiocytes express HRH1, CaMK I, and CaMK II. Small (but not large) cholangiocytes proliferate in response to HTMT dimaleate and are blocked by terfenadine (HRH1 antagonist), BAPTA/AM, and W7. In small cholangiocytes, HTMT dimaleate increased IP(3)/Ca(2+) levels, CaMK I phosphorylation, and CREB activity. Gene knockdown of CaMK I ablated the effects of HTMT dimaleate on small cholangiocyte proliferation and CREB activation. The IP(3)/Ca(2+)/CaMK I/CREB pathway is important in the regulation of small cholangiocyte function.

Wound healing and local neuroendocrine regulation in the injured liver

The hepatic wound-healing response is a complex process involving many different cell types and factors. It leads to the formation of excessive matrix and a fibrotic scar, which ultimately disrupts proper functioning of the liver and establishes cirrhosis. Activated hepatic myofibroblasts, which are derived from cells such as hepatic stellate cells (HSCs), play a key role in this process. Upon chronic liver injury, there is an upregulation in the local neuroendocrine system and it has recently been demonstrated that activated HSCs express specific receptors and respond to different components of this system. Neuroendocrine factors and their receptors participate in a complex network that modulates liver inflammation and wound healing, and controls the development and progression of liver fibrosis. The first part of this review provides an overview of the molecular mechanisms governing hepatic wound healing. In the second section, we explore important components of the hepatic neuroendocrine system and their recently highlighted roles in HSC biology and hepatic fibrogenesis. We discuss the therapeutic interventions that are being developed for use in antifibrotic therapy.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Lack of hepatocellular CD10 along bile canaliculi is physiologic in early childhood and persistent in Alagille syndrome

Many tissues, including hepatobiliary cells, express neutral endopeptidase (CD10), encoded by MME. Serum neutral endopeptidase activity (NEA) has been recommended as a marker of cholestasis in adults but not in children with Alagille syndrome (AGS). We investigated ontogenic and disease-related differences in the expression of CD10. CD10 was found on canalicular surfaces of hepatocytes throughout the lobule in 16 adults and in 31 children aged > or =24 months, with and without cholestasis, but not in 39 children aged <24 months, with and without cholestasis. Ten AGS children aged 2 months to 6 years lacked any canalicular CD10 expression. Cholangiocyte apices and/or intrasinusoidal granulocytes marked for CD10 in all subjects. Liver membrane fractions from a child with cholestasis aged <24 months and from 2 AGS patients aged >24 months contained reduced levels of CD10. In contrast, AGS children and all controls expressed CD10 similarly on granulocytes. MME mRNA was found in the liver of children aged <24 months and of adults, all with cholestasis, and of AGS patients. Granulocyte MME mRNA levels were similar among all study subjects; however, liver MME mRNA levels were 6- to 140-fold less than in normal adults in all cholestatic subjects, including AGS children. Methylation of the MME promoter was not detected in the liver of AGS children. In conclusion, hepatocytes in early childhood physiologically lack immunohistochemically detectable CD10. Reduced MME mRNA in AGS is not due to MME promoter methylation. Liver CD10 in childhood appears to undergo reduced synthesis or rapid degradation, which persists in AGS. Absence of CD10 expression thus may limit NEA as a marker of cholestasis in young patients and in AGS.

Liver derived endogenous opioids may interfere with the therapeutic effect of interferon in chronic hepatitis C

A substantial number of patients with chronic hepatitis C does not respond to treatment with interferon and ribavirin, the approved drugs to treat this viral infection. In vitro studies have shown that morphine, which exerts its effects by binding to opioid receptors, enhances the expression of hepatitis C RNA in hepatitis C-replicon containing liver cells, and that it interferes with the antiviral effect of interferon on the hepatitis C virus. Met-enkephalin, one of the endogenous opioid peptides, can bind to the same receptors to which morphine binds, triggering similar receptor-mediated effects. The liver in cholestasis can express Met-enkephalin immunoreactivity (MEIR). MEIR can also be detected in the liver of some patients with chronic hepatitis C. This finding suggests that Met-enkephalin is produced by or that it accumulates in the liver of patients with this viral hepatitis. Analogous to the effect of morphine on the hepatitis C-replicon containing liver cells, we hypothesize that Met-enkephalin enhances the replication of the hepatitis C virus in liver cells, and that it interferes with the antiviral effect of interferon, contributing to the lack of efficacy of this medication in the treatment of this viral infection in some patients. If this hypothesis is correct, the study of opiate antagonists in combination with antiviral therapy in patients with hepatitis C expressing MEIR in their livers merits consideration.

Glucagon-like peptide-1 and its receptor agonist exendin-4 modulate cholangiocyte adaptive response to cholestasis

BACKGROUND & AIMS

Cholangiopathies are characterized by progressive dysregulation of the balance between proliferation and death of cholangiocytes. In the course of cholestasis, cholangiocytes undergo a neuroendocrine transdifferentiation and their biology is regulated by neuroendocrine hormones. Glucagon-like peptide-1 (GLP-1), secreted by neuroendocrine cells, sustains beta-cell survival in experimental diabetes and induces the neuroendocrine transdifferentiation of pancreatic ductal cells. GLP-1 receptor (GLP-1R) selective agonist exendin-4 is used in humans as a novel therapeutic tool for diabetes. The aim of this study was to define if GLP-1 modulates cholangiocyte biologic response to cholestasis.

METHODS

Expression of GLP-1R in cholangiocytes was determined. Effects on cholangiocyte proliferation of the in vitro and in vivo exposure to GLP-1 or exendin-4, together with the intracellular signals, were then studied. Synthesis of GLP-1 by cholangiocytes and the effects of GLP-1R blockage on their growth were also determined.

RESULTS

Cholangiocytes express the GLP-1 receptor, which is up-regulated in the course of cholestasis. GLP-1 and exendin-4 increase cholangiocyte growth both in vitro and in vivo. The GLP-1R signal is mediated by the phosphatidyl-inositol-3-kinase, cAMP/Protein Kinase A, and Ca(2+)-CamKIIalpha but not by the ERK1/2 and PKCalpha pathways. Proliferating cholangiocytes synthesize GLP-1: neutralization of its action by GLP-1R antagonist blunts cholangiocyte response to cholestasis.

CONCLUSIONS

GLP-1 is required for the cholangiocyte adaptive response to cholestasis. Cholangiocytes are susceptible to the activation of GLP-1R and respond with increased proliferation and functional activity. Exendin-4 availability for employment in humans and these data may open novel perspectives for the medical treatment of cholangiopathies.

Proliferating cholangiocytes: a neuroendocrine compartment in the diseased liver

In the last 15 years, the intrahepatic biliary tree has become the object of extensive studies, which highlighted the extraordinary biologic properties of cholangiocytes involved in bile formation, proliferation, injury repair, fibrosis, angiogenesis, and regulation of blood flow. Proliferation is a "typical" property of cholangiocytes and is key as a mechanism of repair responsible for maintaining the integrity of the biliary tree. Cholangiocyte proliferation occurs virtually in all pathologic conditions of liver injury where it is associated with inflammation, regeneration, and repair, thus conditioning the evolution of liver damage. Interestingly, proliferating cholangiocytes acquire the phenotype of neuroendocrine cells, and secrete different cytokines, growth factors, neuropeptides, and hormones, which represent potential mechanisms for cross talk with other liver cells. Many studies suggest the generation of a neuroendocrine compartment in the injured liver, mostly constituted by cells with cholangiocyte features, which functionally conditions the progression of liver disease. These insights on cholangiocyte pathophysiology will provide new potential strategies for the management of chronic liver diseases. The purpose of this review is to summarize the recent findings on the mechanisms regulating cholangiocyte proliferation and the significance of the neuroendocrine regulation of cholangiocyte biology.