In vitro and in vivo activation of rat hepatic stellate cells results in de novo expression of L-type voltage-operated calcium channels

Nimodipine ameliorates liver fibrosis via reshaping liver immune microenvironment in TAA-induced in mice

Nimodipine, a calcium antagonist, exert beneficial neurovascular protective effects in clinic. Recently, Calcium channel blockers (CCBs) was reported to protect against liver fibrosis in mice, while the exact effects of Nimodipine on liver injury and hepatic fibrosis remain unclear. In this study, we assessed the effect of nimodipine in Thioacetamide (TAA)-induced liver fibrosis mouse model. Then, the collagen deposition and liver inflammation were assessed by HE straining. Also, the frequency and phenotype of NK cells, CD4+T and CD8+T cells and MDSC in liver and spleen were analyzed using flow cytometry. Furthermore, activation and apoptosis of primary Hepatic stellate cells (HSCs) and HSC line LX2 were detected using α-SMA staining and TUNEL assay, respectively. We found that nimodipine administration significantly attenuated liver inflammation and fibrosis. And the increase of the numbers of hepatic NK and NKT cells, a reversed CD4+/CD8+T ratio, and reduced the numbers of MDSC were observed after nimodipine treatment. Furthermore, nimodipine administration significantly decreased α-SMA expression in liver tissues, and increased TUNEL staining adjacent to hepatic stellate cells. Nimodipine also reduced the proliferation of LX2, and significantly promoted high level of apoptosis in vitro. Moreover, nimodipine downregulated Bcl-2 and Bcl-xl, simultaneously increased expression of JNK, p-JNK, and Caspase-3. Together, nimodipine mediated suppression of growth and fibrogenesis of HSCs may warrant its potential use in the treatment of liver fibrosis.

Understanding the Potential Role of Nanotechnology in Liver Fibrosis: A Paradigm in Therapeutics

The liver is a vital organ that plays a crucial role in the physiological operation of the human body. The liver controls the body's detoxification processes as well as the storage and breakdown of red blood cells, plasma protein and hormone production, and red blood cell destruction; therefore, it is vulnerable to their harmful effects, making it more prone to illness. The most frequent complications of chronic liver conditions include cirrhosis, fatty liver, liver fibrosis, hepatitis, and illnesses brought on by alcohol and drugs. Hepatic fibrosis involves the activation of hepatic stellate cells to cause persistent liver damage through the accumulation of cytosolic matrix proteins. The purpose of this review is to educate a concise discussion of the epidemiology of chronic liver disease, the pathogenesis and pathophysiology of liver fibrosis, the symptoms of liver fibrosis progression and regression, the clinical evaluation of liver fibrosis and the research into nanotechnology-based synthetic and herbal treatments for the liver fibrosis is summarized in this article. The herbal remedies summarized in this review article include epigallocathechin-3-gallate, silymarin, oxymatrine, curcumin, tetrandrine, glycyrrhetinic acid, salvianolic acid, plumbagin, Scutellaria baicalnsis Georgi, astragalosides, hawthorn extract, and andrographolides.

In Vitro Liver Toxicity Testing of Chemicals: A Pragmatic Approach

The liver is among the most frequently targeted organs by noxious chemicals of diverse nature. Liver toxicity testing using laboratory animals not only raises serious ethical questions, but is also rather poorly predictive of human safety towards chemicals. Increasing attention is, therefore, being paid to the development of non-animal and human-based testing schemes, which rely to a great extent on in vitro methodology. The present paper proposes a rationalized tiered in vitro testing strategy to detect liver toxicity triggered by chemicals, in which the first tier is focused on assessing general cytotoxicity, while the second tier is aimed at identifying liver-specific toxicity as such. A state-of-the-art overview is provided of the most commonly used in vitro assays that can be used in both tiers. Advantages and disadvantages of each assay as well as overall practical considerations are discussed.

Deranged hepatocyte intracellular Ca2+ homeostasis and the progression of non-alcoholic fatty liver disease to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to non-alcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca²⁺ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca²⁺, and have provided evidence that altered Ca²⁺ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca²⁺ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca²⁺ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca²⁺ entry and SERCA2b, and activates Ca²⁺ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca²⁺ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca²⁺/calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca²⁺ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca²⁺ transporters, channels, and binding proteins as targets for pharmacological intervention.

Mechanical Stretch Increases Expression of CXCL1 in Liver Sinusoidal Endothelial Cells to Recruit Neutrophils, Generate Sinusoidal Microthombi, and Promote Portal Hypertension

BACKGROUND & AIMS

Mechanical forces contribute to portal hypertension (PHTN) and fibrogenesis. We investigated the mechanisms by which forces are transduced by liver sinusoidal endothelial cells (LSECs) into pressure and matrix changes.

METHODS

We isolated primary LSECs from mice and induced mechanical stretch with a Flexcell device, to recapitulate the pulsatile forces induced by congestion, and performed microarray and RNA-sequencing analyses to identify gene expression patterns associated with stretch. We also performed studies with C57BL/6 mice (controls), mice with deletion of neutrophil elastase (NE^-/-) or peptidyl arginine deiminase type IV (Pad4^-/-) (enzymes that formation of neutrophil extracellular traps [NETs]), and mice with LSEC-specific deletion of Notch1 (Notch1^iΔEC). We performed partial ligation of the suprahepatic inferior vena cava (pIVCL) to simulate congestive hepatopathy-induced portal hypertension in mice; some mice were given subcutaneous injections of sivelestat or underwent bile-duct ligation. Portal pressure was measured using a digital blood pressure analyzer and we performed intravital imaging of livers of mice.

RESULTS

Expression of the neutrophil chemoattractant CXCL1 was up-regulated in primary LSECs exposed to mechanical stretch, compared with unexposed cells. Intravital imaging of livers in control mice revealed sinusoidal complexes of neutrophils and platelets and formation of NETs after pIVCL. NE^-/- and Pad4^-/- mice had lower portal pressure and livers had less fibrin compared with control mice after pIVCL and bile-duct ligation; neutrophil recruitment into sinusoidal lumen of liver might increase portal pressure by promoting sinusoid microthrombi. RNA-sequencing of LSECs identified proteins in mechanosensitive signaling pathways that are altered in response to mechanical stretch, including integrins, Notch1, and calcium signaling pathways. Mechanical stretch of LSECs increased expression of CXCL1 via integrin-dependent activation of transcription factors regulated by Notch and its interaction with the mechanosensitive piezo calcium channel.

CONCLUSIONS

In studies of LSECs and knockout mice, we identified mechanosensitive angiocrine signals released by LSECs which promote PHTN by recruiting sinusoidal neutrophils and promoting formation of NETs and microthrombi. Strategies to target these pathways might be developed for treatment of PHTN. RNA-sequencing accession number: GSE119547.

The firing frequency of spontaneous action potentials and their corresponding evoked exocytosis are increased in chromaffin cells of CCl4 -induced cirrhotic rats with respect to control rats

High catecolamine plasma levels because of sympathetic nervous system over-activity contribute to cirrhosis progression. The aim of this study was to investigate whether chromaffin cells of the adrenal gland might potentiate the deleterious effect exerted by this over-activity. Electrophysiological patch-clamp and amperometric experiments with carbon-fibre electrodes were conducted in single chromaffin cells of control and CCl₄ -induced cirrhotic rats. The spontaneous action potential firing frequency was increased in chromaffin cells of cirrhotic rats with respect to control rats. The exocytosis evoked by that firing was also increased. However, exocytosis elicited by ACh did not vary between control and cirrhotic rats. Exocytosis triggered by depolarizing pulses was also unchanged. Amperometric recordings confirmed the lack of increased catecholamine charge released in cirrhosis after ACh or depolarization stimuli. However, the amperometric spikes exhibited faster kinetics of release. The overall Ca²⁺ entry through voltage-dependent Ca²⁺ channels (VDCC), or in particular through Cav1 channels, did not vary between chromaffin cells of control and cirrhotic rats. The inhibition of VDCC by methionine-enkephaline or ATP was not either altered, but it was increased by adrenaline in cells of cirrhotic rats. When a cocktail composed by the three neurotransmitters was tested in order to approach a situation closer to the physiological condition, the inhibition of VDCC was similar between both types of cells. In summary, chromaffin cells of the adrenal gland might contribute to exacerbate the sympathetic nervous system over-activity in cirrhosis because of an increased exocytosis elicited by an enhanced spontaneous electrical activity.

Loss of Prolyl-Hydroxylase 1 Protects against Biliary Fibrosis via Attenuated Activation of Hepatic Stellate Cells

Liver fibrosis, eventually progressing to cirrhosis necessitating liver transplantation, poses a significant clinical problem. Oxygen shortage (hypoxia) and hypoxia-inducible transcription factors (HIFs) have been acknowledged as important drivers of liver fibrosis. The significance of oxygen-sensing HIF prolyl-hydroxylase (PHD) enzymes in this context has, however, remained elusive. In this study, we demonstrate that loss of PHD1 (PHD1^-/-) attenuates the development of liver fibrosis in mice subjected to chronic bile duct injury, induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine. This effect was accompanied with reduced recruitment of inflammatory leukocytes and attenuated occurrence of profibrotic myofibroblasts in PHD1^-/- livers. Further analyses focused on the significance of PHD1 in the activation of hepatic stellate cells (HSCs), which represent the driving force in liver fibrosis. Primary HSCs isolated from PHD1^-/- mice displayed significantly attenuated myofibroblast differentiation and profibrogenic properties compared with HSCs isolated from wild-type mice. Consistently, the expression of various profibrogenic and promitogenic factors was reduced in PHD1^-/- HSCs, without alterations in HIF-1α protein levels. Of importance, PHD1 protein was expressed in HSCs within human livers, and PHD1 transcript expression was significantly increased with disease severity in hepatic tissue from patients with liver fibrosis. Collectively, these findings indicate that PHD1 deficiency protects against liver fibrosis and that these effects are partly due to attenuated activation of HSCs. PHD1 may represent a therapeutic target to alleviate liver fibrosis.

Calcium channel blockers ameliorate iron overload-associated hepatic fibrosis by altering iron transport and stellate cell apoptosis

Liver fibrosis is the principal cause of morbidity and mortality in patients with iron overload. Calcium channel blockers (CCBs) can antagonize divalent cation entry into renal and myocardial cells and inhibit fibrogenic gene expression. We investigated the potential of CCBs to resolve iron overload-associated hepatic fibrosis. Kunming mice were assigned to nine groups (n=8 per group): control, iron overload, deferoxamine, high and low dose verapamil, high and low dose nimodipine, and high and low dose diltiazem. Iron deposition and hepatic fibrosis were measured in mouse livers. Expression levels of molecules associated with transmembrane iron transport were determined by molecular biology approaches. In vitro HSC-T6 cells were randomized into nine groups (the same groups as the mice). Changes in proliferation, apoptosis, and metalloproteinase expression in cells were detected to assess the anti-fibrotic effects of CCBs during iron overload conditions. We found that CCBs reduced hepatic iron content, intracellular iron deposition, the number of hepatic fibrotic areas, collagen expression levels, and hydroxyproline content. CCBs rescued abnormal expression of α1C protein in L-type voltage-dependent calcium channel (LVDCC) and down-regulated divalent metal transporter-1 (DMT-1) expression in mouse livers. In iron-overloaded HSC-T6 cells, CCBs reduced iron deposition, inhibited proliferation, induced apoptosis, and elevated expression of matrix metalloproteinase-13 (MMP-13) and tissue inhibitor of metalloproteinase-1 (TIMP-1). CCBs are potential therapeutic agents that can be used to address hepatic fibrosis during iron overload. They resolve hepatic fibrosis probably correlated with regulating transmembrane iron transport and inhibiting HSC growth.

Inhibitory effects of relaxin on cardiac fibroblast-to-myofibroblast transition: an electrophysiological study

NEW FINDINGS

What is the central question of this study? Fibroblast-to-myofibroblast transition is a key mechanism in the reparative response to tissue damage, but myofibroblast persistence in the wound leads to fibrosis and organ failure. The role of relaxin as an antifibrotic agent capable of counteracting the acquisition of biophysical features of differentiated myofibroblasts deserves further investigation. What is the main finding and its importance? Electrophysiological analysis showed that relaxin, administered during profibrotic treatment, hyperpolarizes the membrane potential and attenuates delayed rectifier and inwardly rectifying K(+) currents, which usually increase in the transition to myofibroblasts. These findings provide further clues to the therapeutic potential of relaxin in fibrosis. The hormone relaxin (RLX) is produced by the heart and may be involved in endogenous mechanisms of cardiac protection against ischaemic injury and fibrosis. Recent findings in cultured cardiac stromal cells suggest that RLX can inhibit fibroblast-to-myofibroblast transition, thereby counteracting fibrosis. In order to explore its efficiency as an antifibrotic agent further, we designed the present study to investigate whether RLX may influence the electrophysiological events associated with differentiation of cardiac stromal cells to myofibroblasts. Primary cardiac proto-myofibroblasts and NIH/3T3 fibroblasts were induced to myofibroblasts by transforming growth factor-β1, and the electrophysiological features of both cell populations were investigated by whole-cell patch clamp. We demonstrated that proto-myofibroblasts and myofibroblasts express different membrane passive properties and K(+) currents. Here, we have shown, for the first time, that RLX (100 ng ml(-1) ) significantly reduced both voltage- and Ca(2+) -dependent delayed-rectifier and inward-rectifying K(+) currents that are typically increased in myofibroblasts compared with proto-myofibroblasts, suggesting that this hormone can antagonize the biophysical effects of transforming growth factor-β1 in inducing myofibroblast differentiation. These newly recognized effects of RLX on the electrical properties of cardiac stromal cell membrane correlate well with its well-known ability to suppress myofibroblast differentiation, further supporting the possibility that RLX may be used for the treatment of cardiac fibrosis.

K⁺-channel inhibition reduces portal perfusion pressure in fibrotic rats and fibrosis associated characteristics of hepatic stellate cells

BACKGROUND & AIMS

In liver fibrosis, activated hepatic stellate cells (HSC) secrete excess extracellular matrix, thus, represent key targets for antifibrotic treatment strategies. Intermediate-conductance Ca(2) (+) -activated K(+) -channels (KCa3.1) are expressed in non-excitable tissues affecting proliferation, migration and vascular resistance rendering KCa3.1 potential targets in liver fibrosis. So far, no information about KCa3.1 expression and their role in HSC exists. Aim was to quantify the KCa3.1 expression in HSC depending on HSC activation and investigation of antifibrotic properties of the specific KCa3.1 inhibitor TRAM-34 in vitro and in vivo.

METHODS

KCa3.1 expression and functionality were studied in TGF-β1-activated HSC by quantitative real time PCR, western-blot and patch-clamp analysis respectively. Effects of TRAM-34 on HSC proliferation, cell cycle and fibrosis-related gene expression were assessed by [(3) H]-thymidine incorporation, FACS-analysis and RT-PCR respectively. In vivo, vascular resistance and KCa3.1 gene and protein expression were determined in bile duct ligated rats by in situ liver perfusion, Taqman PCR and immunohistochemistry respectively.

RESULTS

Fibrotic tissues and TGF-β1-activated HSC exhibited higher KCa3.1-expressions than normal tissue and untreated cells. KCa3.1 inhibition with TRAM-34 reduced HSC proliferation by induction of cell cycle arrest and reduced TGF-β1-induced gene expression of collagen I, alpha-smooth muscle actin and TGF-β1 itself. Furthermore, TRAM-34 blocked TGF-β1-induced activation of TGF-β signalling in HSC. In vivo, TRAM-34 reduced the thromboxane agonist-induced portal perfusion pressure.

CONCLUSION

Inhibition of KCa3.1 with TRAM-34 downregulates fibrosis-associated gene expression in vitro, and reduces portal perfusion pressure in vivo. Thus, KCa3.1 may represent novel targets for the treatment of liver fibrosis.

The L-type voltage-gated calcium channel modulates microglial pro-inflammatory activity

Under pathological conditions, microglia, the resident CNS immune cells, become reactive and release pro-inflammatory cytokines and neurotoxic factors. We investigated whether this phenotypic switch includes changes in the expression of the L-type voltage-gated calcium channel (VGCC) in a rat model of N-methyl-D-aspartate-induced hippocampal neurodegeneration. Double immunohistochemistry and confocal microscopy evidenced that activated microglia express the L-type VGCC. We then analyzed whether BV2 microglia express functional L-type VGCC, and investigated the latter's role in microglial cytokine release and phagocytic capacity. Activated BV2 microglia express the CaV1.2 and CaV1.3 subunits of the L-type VGCC determined by reverse transcription-polymerase chain reaction, Western blot and immunocytochemistry. Depolarization with KCl induced a Ca2+ entry facilitated by Bay k8644 and partially blocked with nifedipine, which also reduced TNF-α and NO release by 40%. However, no nifedipine effect on BV2 microglia viability or phagocytic capacity was observed. Our results suggest that in CNS inflammatory processes, the L-type VGCC plays a specific role in the control of microglial secretory activity.

Myofibroblasts: trust your heart and let fate decide

Cardiac fibrosis is a substantial problem in managing multiple forms of heart disease. Fibrosis results from an unrestrained tissue repair process orchestrated predominantly by the myofibroblast. These are highly specialized cells characterized by their ability to secrete extracellular matrix (ECM) components and remodel tissue due to their contractile properties. This contractile activity of the myofibroblast is ascribed, in part, to the expression of smooth muscle α-actin (αSMA) and other tension-associated structural genes. Myofibroblasts are a newly generated cell type derived largely from residing mesenchymal cells in response to both mechanical and neurohumoral stimuli. Several cytokines, chemokines, and growth factors are induced in the injured heart, and in conjunction with elevated wall tension, specific signaling pathways and downstream effectors are mobilized to initiate myofibroblast differentiation. Here we will review the cell fates that contribute to the myofibroblast as well as nodal molecular signaling effectors that promote their differentiation and activity. We will discuss canonical versus non-canonical transforming growth factor-β (TGFβ), angiotensin II (AngII), endothelin-1 (ET-1), serum response factor (SRF), transient receptor potential (TRP) channels, mitogen-activated protein kinases (MAPKs) and mechanical signaling pathways that are required for myofibroblast transformation and fibrotic disease. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

Calcium receptors located in fibrotic septa: a new target to reduce portal pressure in liver cirrhosis

In rats with experimental liver cirrhosis, the kidney contains reduced amounts of membrane-bound CaRs (calcium-sensing receptors), and the specific stimulation of CaRs causes the generation of PGE2 (prostaglandin E2), renal vasodilation and increased natriuresis. CaR content and function in the liver of cirrhotic rats are unknown. To assess the activity of this Ca2+-dependent vasomotor system, we evaluated the effects of intravenous administration of PolyAg (poly-L-arginine), a selective CaR agonist, on hormonal status, portal haemodynamics, MAP (mean arterial pressure) in rats with liver cirrhosis induced by chronic CCl4 (carbon tetrachloride) administration. Two groups of eight control rats received intravenously 1 ml of 5% (w/v) glucose solution alone or containing 0.5 mg of PolyAg; two groups of ten cirrhotic rats were administered vehicle or PolyAg. Compared with controls, at baseline cirrhotic rats showed higher portal pressure (P<0.01), lower estimated functional liver plasma flow, measured as CICG (Indocyanine Green clearance) (P<0.03) and reduced hepatic protein content of CaRs (P<0.03), which were located mainly in sub-endothelial layers of portal venules and in myofibroblasts of fibrotic septa (immunohistochemistry and indirect immunofluorescence staining of liver sections). In cirrhotic animals, 0.5 mg of PolyAg decreased portal pressure (P<0.01) and increased CICG (P<0.05), without effects on arterial pressure and hormonal status. In conclusion, the present study provides evidence that in experimental cirrhosis agonists of liver CaRs elicit beneficial portal hypotensive effects by reducing intrahepatic resistance to portal flow. Moreover, these drugs are devoid of effects on systemic haemodynamics.

Azelnidipine is a calcium blocker that attenuates liver fibrosis and may increase antioxidant defence

BACKGROUND AND PURPOSE

Oxidative stress plays a critical role in liver fibrogenesis. Reactive oxygen species (ROS) stimulate hepatic stellate cells (HSCs), and ROS-mediated increases in calcium influx further increase ROS production. Azelnidipine is a calcium blocker that has been shown to have antioxidant effects in endothelial cells and cardiomyocytes. Therefore, we evaluated the anti-fibrotic and antioxidative effects of azelnidipine on liver fibrosis.

EXPERIMENTAL APPROACH

We used TGF-β1-activated LX-2 cells (a human HSC line) and mouse models of fibrosis induced by treatment with either carbon tetrachloride (CCl(4) ) or thioacetamide (TAA).

KEY RESULTS

Azelnidipine inhibited TGF-β1 and angiotensin II (Ang II)-activated α1(I) collagen mRNA expression in HSCs. Furthermore, TGF-β1- and Ang II-induced oxidative stress and TGF-β1-induced p38 and JNK phosphorylation were reduced in HSCs treated with azelnidipine. Azelnidipine significantly decreased inflammatory cell infiltration, pro-fibrotic gene expressions, HSC activation, lipid peroxidation, oxidative DNA damage and fibrosis in the livers of CCl(4) - or TAA-treated mice. Finally, azelnidipine prevented a decrease in the expression of some antioxidant enzymes and accelerated regression of liver fibrosis in CCl(4) -treated mice.

CONCLUSIONS AND IMPLICATIONS

Azelnidipine inhibited TGF-β1- and Ang II-induced HSC activation in vitro and attenuated CCl(4) - and TAA-induced liver fibrosis, and it accelerated regression of CCl(4) -induced liver fibrosis in mice. The anti-fibrotic mechanism of azelnidipine against CCl(4) -induced liver fibrosis in mice may have been due an increased level of antioxidant defence. As azelnidipine is widely used in clinical practice without serious adverse effects, it may provide an effective new strategy for anti-fibrotic therapy.

Improved antifibrotic effect of a combination of verapamil and silymarin in rat-induced liver fibrosis

BACKGROUND AND STUDY AIMS

Liver fibrosis progresses to cirrhosis in several settings, for example, severe acute alcoholic hepatitis, and hepatitis C virus (HCV) reinfection after liver transplantation. Cirrhosis produces hepatocellular dysfunction, which is also a risk factor for hepatocellular carcinoma. We studied verapamil as a prophylactic, therapeutic antifibrotic drug alone and in combination with silymarin in experimental rat's liver-induced fibrosis.

MATERIAL AND METHODS

Liver fibrosis was induced by intra-peritoneal injection of rats with pig serum 0.5ml twice weekly for 6 weeks, which resulted in score three fibrosis. Prophylactic verapamil alone and silymarin alone and a combination of both were administered at the same time of induction of liver fibrosis and continued for the duration of induction. Therapeutic verapamil was started on the last day of fibrosis induction and continued for 4 weeks. The extent of liver fibrosis was evaluated using Ishak's fibrosis score. Serum alanine aminotransferase (ALT) was measured for follow-up.

RESULTS

Compared to fibrotic model rats, prophylactic verapamil, silymarin and combined verapamil plus silymarin significantly resulted in lower serum ALT levels. Prophylactic use of verapamil and silymarin each alone revealed score 2 fibrosis with positive α-SMA immunostaining; while prophylactic treatment with combined verapamil plus silymarin revealed no fibrosis supported by negative α-SMA immunostaining. Verapamil treated fibrotic rat's liver revealed significant regression in liver fibrosis scores with positive α-SMA immunostaining.

CONCLUSIONS

Verapamil alone has a more significant prophylactic than therapeutic antifibrotic effect against induced liver fibrosis; it was more significant than silymarin. The combination of verapamil and silymarin, showed the best protection through their synergistic antifibrotic effect.

Switching-on of serotonergic calcium signaling in activated hepatic stellate cells

AIM

To investigate serotonergic Ca²+ signaling and the expression of 5-hydroxytryptamine (5-HT) receptors, as well as Ca²+ transporting proteins, in hepatic stellate cells (HSCs).

METHODS

The intracellular Ca²+ concentration [Ca²+](i) of isolated rat HSCs was measured with a fluorescence microscopic imaging system. Quantitative PCR was performed to determine the transcriptional levels of 5-HT receptors and endoplasmic reticulum (ER) proteins involved in Ca²+ storage and release in cultured rat HSCs.

RESULTS

Distinct from quiescent cells, activated HSCs exhibited [Ca²+](i) transients following treatment with 5-HT, which was abolished by U-73122, a phospholipase C inhibitor. Upregulation of 5-HT(2A) and 5-HT(2B) receptors, but not 5-HT₃, was prominent during trans-differentiation of HSCs. Pretreatment with ritanserin, a 5-HT₂ antagonist, inhibited [Ca²+](i) changes upon application of 5-HT. Expression of type 1 inositol-5'-triphosphate receptor and type 2 sarcoplasmic/endoplasmic reticulum Ca²+ ATPase were also increased during activation of HSCs and serve as the major isotypes for ER Ca²+ storage and release in activated HSCs. Ca²+ binding chaperone proteins of the ER, including calreticulin, calnexin and calsequestrin, were up-regulated following activation of HSCs.

CONCLUSION

The appearance of 5-HT-induced [Ca²+](i) response accompanied by upregulation of metabotropic 5-HT₂ receptors and Ca²+ transporting/chaperone ER proteins may participate in the activating process of HSCs.

Distinct roles for non-muscle myosin II isoforms in mouse hepatic stellate cells

BACKGROUND & AIMS

Upon liver injury, hepatic stellate cells (HSCs) undergo dramatic morphological and functional changes including migration and contraction. In the present study, we investigated the role of myosin II isoforms in the development of the contractile phenotype of mouse HSCs, which are considered therapeutic targets to decrease portal hypertension and fibrosis.

METHODS

We characterized the expression of myosin IIA and IIB in primary mouse HSCs and addressed their function by gene knock-down using isoform-specific siRNAs.

RESULTS

We found that myosin IIA and IIB are differentially expressed and localized and have clearly different functions in HSCs. Myosin IIA is mainly located in the subcortical area of quiescent HSCs and at α-SMA-containing stress fibres after activation, while myosin IIB is located in the cytoplasm and at the edge of protrusions of quiescent HSCs, at stress fibres of activated cells, and at the leading edge of lamellipodia. Knock-down of myosin IIA in HSCs influences cell size and shape, results in the disruption of stress fibres and in a decrease of focal adhesions, and inhibits contractility and intra-cellular Ca(2+) release but increases cell migration. Myosin IIB contributes to the extension of lamellipodia and cell spreading but has no direct role in stress fibres and focal adhesion formation, contraction, or intra-cellular Ca(2+) signalling.

CONCLUSIONS

In mouse HSCs, myosin IIA and IIB clearly fulfil distinct roles. Our results provide an insight into the contractile machinery of HSCs, that could be important in the search for new molecules to treat portal hypertension.

Synergistic antifibrotic effect of verapamil and interferon-gamma in rats: partially based on enhanced verapamil oral bioavailability

OBJECTIVE

The objective of this study was to investigate the synergistic antifibrotic effect of verapamil and interferon-gamma (IFN-gamma) on rat liver fibrosis and its potential pharmacokinetic-based mechanism.

METHODS

Rat liver fibrosis model was successfully established, and both the therapeutic effects and pharmacokinetic parameters of verapamil were evaluated after the administration of verapamil with or without IFN-gamma. The activities of cytochrome P450 3A (CYP3A) and the expression of multidrug resistance (Mdr) mRNA were measured in liver and small intestine.

RESULTS

The results showed the synergistic antifibrotic effect of verapamil and IFN-gamma in rat liver fibrosis, in terms of decreased serum L-alanine aminotransferase activity and liver hydroxyproline content and improved liver histopathology, when compared with rats treated with verapamil or IFN-gamma alone. Meanwhile, the area under the curve of verapamil increased significantly after single administration of verapamil and IFN-gamma and the concentration of verapamil in plasma increased, but the metabolite : parent ratio of verapamil decreased after consecutive administrations of verapamil and IFN-gamma. Furthermore, the activities of CYP3A in both the liver and the small intestine and the expression of Mdr in small intestine decreased in rats treated with verapamil and IFN-gamma.

CONCLUSION

All these results indicated that the combination of verapamil and IFN-gamma exerts a synergistic antifibrotic effect on rat liver fibrosis. The mechanism was partially based on the enhanced oral bioavailability of verapamil by increasing the intestinal absorption as well as reducing the first-pass metabolism, through inhibition of CYP3A activity and P-glycoprotein expression by IFN-gamma

[The role of activated hepatic stellate cells in liver fibrosis, portal hypertension and cancer angiogenesis]

Although hepatic stellate cells, which are liver specific pericytes, have been recognized within the vasculature of the sinusoid for more than one hundred years, the biology and function of these cells is unclear. Recent studies have highlighted the key role of stellate cells in a number of fundamental processes that include wound healing/fibrosis, vasoregulation, and vascular remodeling/angiogenesis. In the liver, these processes are particularly important in the development of cirrhosis, portal hypertension and cancer. This article highlights the recent advances in our understanding of the biology of hepatic stellate cells and discusses some of the recently-ascribed functions that are relevant to liver fibrosis, portal hypertension and cancer angiogenesis.

Stellate cell contraction: role, regulation, and potential therapeutic target

The contraction of hepatic stellate cells has been proposed to mediate fibrosis by regulating sinusoidal blood flow and extracellular matrix remodeling. Abundant data from diverse, yet complementary, experimental methods support a robust model for the regulation of contractile force generation by stellate cells. In this model, soluble factors associated with liver injury, including endothelin 1 and nitric oxide, are transduced primarily through Rho signaling pathways that promote the myosin II-powered generation of contractile force by stellate cells. The enhanced knowledge of the role and differential regulation of stellate cell contraction may facilitate the discovery of new and targeted strategies for the prevention and treatment of hepatic fibrosis.

Changes in inward rectifier K+ channels in hepatic stellate cells during primary culture

PURPOSE

This study examined the expression and function of inward rectifier K(+) channels in cultured rat hepatic stellate cells (HSC).

MATERIALS AND METHODS

The expression of inward rectifier K(+) channels was measured using real-time RT-PCR, and electrophysiological properties were determined using the gramicidin-perforated patch-clamp technique.

RESULTS

The dominant inward rectifier K(+) channel subtypes were K(ir)2.1 and K(ir)6.1. These dominant K(+) channel subtypes decreased significantly during the primary culture throughout activation process. HSC can be classified into two subgroups: one with an inward-rectifying K(+) current (type 1) and the other without (type 2). The inward current was blocked by Ba(2+) (100 microM) and enhanced by high K(+) (140 mM), more prominently in type 1 HSC. There was a correlation between the amplitude of the Ba(2+)-sensitive current and the membrane potential. In addition, Ba(2+) (300 microM) depolarized the membrane potential. After the culture period, the amplitude of the inward current decreased and the membrane potential became depolarized.

CONCLUSION

HSC express inward rectifier K(+) channels, which physiologically regulate membrane potential and decrease during the activation process. These results will potentially help determine properties of the inward rectifier K(+) channels in HSC as well as their roles in the activation process.

Regulation of sinusoidal perfusion in portal hypertension

Portal hypertension, a major complication of cirrhosis, is caused by both increased portal blood flow and augmented intrahepatic vascular resistance. Even though the latter is primarily caused by anatomical changes, it has become clear that dynamic factors contribute to the increased hepatic vascular resistance. The hepatic sinusoid is the narrowest vascular structure within the liver and is the principal site of blood flow regulation. The anatomical location of hepatic stellate cells, which embrace the sinusoids, provides a favorable arrangement for sinusoidal constriction, and for control of sinusoidal vascular tone and blood flow. Hepatic stellate cells possess the essential contractile apparatus for cell contraction and relaxation. Moreover, the mechanisms of stellate cell contraction are better understood, and many substances which influence contractility have been identified, providing a rationale and opportunity for targeting these cells in the treatment of portal hypertension in cirrhosis.

Mechanisms of hepatic fibrogenesis

Substantial improvements in the treatment of chronic liver disease have accelerated interest in uncovering the mechanisms underlying hepatic fibrosis and its resolution. Activation of resident hepatic stellate cells into proliferative, contractile, and fibrogenic cells in liver injury remains a dominant theme driving the field. However, several new areas of rapid progress in the past 5-10 years also have taken root, including: (1) identification of different fibrogenic populations apart from resident stellate cells, for example, portal fibroblasts, fibrocytes, and bone-marrow-derived cells, as well as cells derived from epithelial mesenchymal transition; (2) emergence of stellate cells as finely regulated determinants of hepatic inflammation and immunity; (3) elucidation of multiple pathways controlling gene expression during stellate cell activation including transcriptional, post-transcriptional, and epigenetic mechanisms; (4) recognition of disease-specific pathways of fibrogenesis; (5) re-emergence of hepatic macrophages as determinants of matrix degradation in fibrosis resolution and the importance of matrix cross-linking and scar maturation in determining reversibility; and (6) hints that hepatic stellate cells may contribute to hepatic stem cell behavior, cancer, and regeneration. Clinical and translational implications of these advances have become clear, and have begun to impact significantly on the management and outlook of patients with chronic liver disease.

Large-conductance calcium-activated potassium channels modulate vascular tone in experimental cirrhosis

BACKGROUND

Large-conductance calcium-activated potassium (BK(Ca)) channels regulate vascular tone in different vascular systems. Moreover, activated hepatic stellate cells (HSC) contain BK(Ca) channels. The aim of this study was to evaluate the role of BK(Ca) channels in the regulation of vascular tone in control (CT) and carbon tetrachloride-cirrhotic (CH) rat livers.

METHODS

Changes in intrahepatic vascular resistance were assessed by evaluating the portal perfusion pressure (PP) response to methoxamine (Mtx) in the presence of Iberiotoxin (Ibtx; a BK(Ca) channel blocker), NS1619 (a BK(Ca) channel opener), Ibtx plus the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine (L-NNA) or L-NNA alone. In addition, in CH livers, PP dose-response curves to the NO donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP), were performed after pre-incubation with Ibtx or its vehicle. BK(Ca) mRNA expression was assessed in liver homogenates, and BK(Ca) protein expression in HSC isolated from CT and CH livers.

RESULTS

In CH livers, Ibtx significantly increased baseline PP and exacerbated the PP response to Mtx. Conversely, NS1619 induced a mild nonsignificant decrease of baseline PP and attenuated the hyperresponse to Mtx. CH livers exhibited an upregulation of both mRNA and protein of the alpha-subunit of BK(Ca).

CONCLUSION

Large-conductance calcium-activated potassium channels are overexpressed in CH livers and might represent a compensatory mechanism modulating the increased hepatic vascular tone of cirrhosis.

Antagonizing TGF-beta induced liver fibrosis by a retinoic acid derivative through regulation of ROS and calcium influx

Transforming growth factor-beta1 (TGF-beta1) mediates the regulation of extracellular matrix via reactive oxygen species (ROS) and calcium influx, both are activators of hepatic stellate cells (HSC) which play a critical role in hepatic fibrogenesis. Hence one can use ROS assay as the main screening tool for molecules that might antagonize the process of liver fibrosis. A retinoic acid derivative isolated from the mycelium of Phellinus linteus that down-regulates ROS generation and calcium influx in HSC-T6 cells was thus obtained in our screening process. The retinoic acid derivative also reverses an early liver fibrosis, as assayed by liver contents of hydroxyproline, alpha-smooth muscle actin (alpha-SMA), and collagen 1A2, in an early liver fibrosis model we established previously where an inducible expression vector containing a TGF-beta gene was hydrodynamically transferred into a testing animal. Retinoic acid derivative thus acts both in vitro and in vivo to prevent liver fibrosis at an early phase.

Hemodynamics in the isolated cirrhotic liver

Increased intrahepatic resistance is the initial event to the increased portal pressure and development portal hypertension in cirrhosis. Narrowing of the sinusoids due to anatomic changes is the main component of the increased intrahepatic resistance. However, a dynamic component is also involved in the increased vascular tone in cirrhosis. The imbalance between the hyperresponsiveness and overproduction of vasoconstrictors (mainly endothelin-1 and cyclooxygenase-derived prostaglandins) and the hyporesponsiveness and impaired production of vasodilators [mainly nitric oxide (NO)] are the mechanisms responsible of the increased vascular tone in the sinusoidal/postsinusoidal area. In contrast, the vascular resistance in the hepatic artery, which is determined in the presinusoidal area, is decreased due to increased vasodilators (NO and adenosine). This suggests different availabilities of NO in the intrahepatic circulation with preserved production in the presinusoidal area and impaired production in the sinusoidal/postsinusoidal area.

Heterogeneous composition of voltage-dependent K(+) currents in hepatic stellate cells

PURPOSE

Hepatic stellate cells (HSC) are a type of pericyte with varying characteristics according to their location. However, the electrophysiological properties of HSC are not completely understood. Therefore, this study investigated the difference in the voltage-dependent K(+) currents in HSC.

MATERIALS AND METHODS

The voltage-dependent K(+) currents in rat HSC were evaluated using the whole cell configuration of the patch-clamp technique.

RESULTS

Four different types of voltage-dependent K(+) currents in HSC were identified based on the outward and inward K(+) currents. Type D had the dominant delayed rectifier K(+) current, and type A had the dominant transient outward K(+) current. Type I had an inwardly rectifying K(+) current, whereas the non-type I did not. TEA (5 mM) and 4-AP (2 mM) suppressed the outward K(+) currents differentially in type D and A. Changing the holding potential from -80 to -40 mV reduced the amplitude of the transient outward K(+) currents in type A. The inwardly rectifying K(+) currents either declined markedly or were sustained in type I during the hyperpolarizing step pulses from -120 to -150 mV.

CONCLUSION

There are four different configurations of voltage-dependent K(+) currents expressed in cultured HSC. These results are expected to provide information that will help determine the properties of the K(+) currents in HSC as well as the different type HSC populations.

Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

BACKGROUND

A transient induction of apoptosis accompanies the normalization of left ventricular mass index in spontaneously hypertensive rats (SHR) treated with dihydropyridine calcium-channel blockers. However, the cell type undergoing apoptosis in this model and the temporal correlation with onset cardiac remodeling remain undefined.

METHODS AND RESULTS

SHR were treated either with vehicle or amlodipine (20 mg/kg per day) for 4, 7, 10, 14 or 28 days. Amlodipine stably reduced systolic blood pressure by day 2 (-26 +/- 2%) and stably reduced the left ventricular concentration of atrial natriuretic peptide (ANP) mRNA by approximately 50% as early as day 4, suggesting the early reduction of cardiomyocyte stress. Left ventricular mass index was significantly reduced by day 7 (-4.6 +/- 1.5%), in coordination with reduced DNA content (-23 +/- 2%) and non-cardiomyocyte number (-17 +/- 4%). However, the cardiomyocyte cross-sectional area was reduced only starting from day 14. Caspase-3 cleavage was significantly increased at day 7 only. Ultimately, amlodipine for 28 days induced a slight increase in capillary density without affecting total cardiomyocyte number, while reducing the total number of non-cardiomyocytes down to levels seen in untreated normotensive Wistar-Kyoto rats. Bax to Bcl-2 protein ratios were increased from day 7 to day 28. In situ double labeling by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) method (apoptosis) combined with rhodamine-labeled lectin binding (endothelial cell marker) revealed a significant increase (> 3-fold) in TUNEL-positive, lectin-negative non-cardiomyocytes in the interstitium between days 7 and 14.

CONCLUSIONS

Left ventricular remodeling induced by amlodipine in SHR involves selective deletion of excess fibroblasts via apoptosis prior to cardiomyocyte mass reduction, but after attenuation of ANP gene expression.

Different profiles of Ca2+ responses to endothelin-1 and PDGF in liver myofibroblasts during the process of cell differentiation

BACKGROUND AND PURPOSE

Hepatic stellate cells play an important role in liver fibrosis but little is known about liver myofibroblasts located around the central vein and in the portal area. In this study, intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured to assess the response to endothelin-1 (ET-1), platelet derived growth factor (PDGF) and ATP in rat liver myofibroblasts.

EXPERIMENTAL APPROACH

Rat liver myofibroblasts were compared in 'quiescent' (cultured on Matrigel-coated dishes) and 'activated' (cultured on non-coated plastic dishes) conditions. [Ca(2+)](i) was measured with the fluorescent dye fura-2 and mRNA for ET-1, PDGF and their receptors by RT-PCR.

KEY RESULTS

ET-1 increased [Ca(2+)](i) in quiescent cells but not in activated cells, whereas PDGF-BB increased [Ca(2+)](i) in activated cells but not in quiescent cells. However, there was no difference between responses to ATP in quiescent or activated cells. ET-1 (in quiescent cells), PDGF-BB (in activated cells) and ATP (in both cells) all induced transient increases in [Ca(2+)](i) in the absence of extracellular Ca(2+) (with EGTA), indicating the involvement of Ca(2+) release from intracellular Ca(2+) stores. The sustained increase in [Ca(2+)](i) in the presence of external Ca(2+) in activated cells (ATP and PDGF) was significantly reduced by nicardipine, a L-type Ca(2+) channel blocker, but not in quiescent cells (ATP and ET-1).

CONCLUSIONS AND IMPLICATIONS

The different pharmacological profiles of [Ca(2+)](i)-response in quiescent and activated myofibroblasts suggest that ET-1 and PDGF contribute differently to myofibroblast activation during the process of liver fibrosis.

Both Ca2+ -dependent and -independent pathways are involved in rat hepatic stellate cell contraction and intrahepatic hyperresponsiveness to methoxamine

In chronic liver injury, hepatic stellate cells (HSCs) have been implicated as regulators of sinusoidal vascular tone. We studied the relative role of Ca(2+)-dependent and Ca(2+)-independent contraction pathways in rat HSCs and correlated these findings to in situ perfused cirrhotic rat livers. Contraction of primary rat HSCs was studied by a stress-relaxed collagen lattice model. Dose-response curves to the Ca(2+) ionophore A-23187 and to the calmodulin/myosin light chain kinase inhibitor W-7 served to study Ca(2+)-dependent pathways. Y-27632, staurosporin, and calyculin (inhibitors of Rho kinase, protein kinase C, and myosin light chain phosphatase, respectively) were used to investigate Ca(2+)-independent pathways. The actomyosin interaction, the common end target, was inhibited by 2,3-butanedione monoxime. Additionally, the effects of W-7, Y-27632, and staurosporin on intrahepatic vascular resistance were evaluated by in situ perfusion of normal and thioacetamide-treated cirrhotic rat livers stimulated with methoxamine (n = 25 each). In vitro, HSC contraction was shown to be actomyosin based with a regulating role for both Ca(2+)-dependent and -independent pathways. Although the former seem important, an important auxiliary role for the latter was illustrated through their involvement in the phenomenon of "Ca(2+) sensitization." In vivo, preincubation of cirrhotic livers with Y-27632 (10(-4) M) and staurosporin (25 nM), more than with W-7 (10(-4) M), significantly reduced the hyperresponsiveness to methoxamine (10(-4) M) by -66.8 +/- 1.3%, -52.4 +/- 2.7%, and -28.7 +/- 2.8%, respectively, whereas in normal livers this was significantly less: -43.1 +/- 4.2%, -40.2 +/- 4.2%, and -3.8 +/- 6.3%, respectively. Taken together, these results suggest that HSC contraction is based on both Ca(2+)-dependent and -independent pathways, which were shown to be upregulated in the perfused cirrhotic liver, with a predominance of Ca(2+)-independent pathways.

Protective effect of verapamil on multiple hepatotoxic factors-induced liver fibrosis in rats

The purpose of the present work was to investigate the effect of verapamil on liver fibrosis induced by multiple hepatotoxic factors in rats. Male Wistar rats were divided into a normal control group, a liver fibrosis model control group, and verapamil groups with different dosages. Multiple hepatotoxic factors including carbon tetrachloride (CCl(4)), ethanol and high cholesterol were used to make the animal model of liver fibrosis. The parameters of serum l-alanine aminotransferase (ALT), liver malondialdehyde and hydroxyproline contents were measured. Samples of the liver obtained by biopsy were subjected to histological and immunohistochemical studies for the expressions of alpha-smooth muscle actin (alpha-SMA) and transforming growth factor-beta(1) (TGF-beta(1)). Results showed that verapamil induced a dose-dependent decrease of serum ALT, liver malondialdehyde and hydroxyproline compared with liver fibrosis model control. Verapamil reduced hepatocyte degeneration and necrosis, and delayed the formation of liver fibrosis. The levels of expression of alpha-SMA and TGF-beta(1) in the hepatic tissue of three of the verapamil-treated groups were significantly less than those of the liver fibrosis model control group. The results showed that verapamil acts against the formation of liver fibrosis, the mechanism might be due to a protective effect for hepatocytes and through decreasing TGF-beta(1) to block the activation of hepatic stellate cells (HSCs) and collagen gene expression.

The role of voltage-gated calcium channels in pancreatic beta-cell physiology and pathophysiology

Voltage-gated calcium (CaV) channels are ubiquitously expressed in various cell types throughout the body. In principle, the molecular identity, biophysical profile, and pharmacological property of CaV channels are independent of the cell type where they reside, whereas these channels execute unique functions in different cell types, such as muscle contraction, neurotransmitter release, and hormone secretion. At least six CaValpha1 subunits, including CaV1.2, CaV1.3, CaV2.1, CaV2.2, CaV2.3, and CaV3.1, have been identified in pancreatic beta-cells. These pore-forming subunits complex with certain auxiliary subunits to conduct L-, P/Q-, N-, R-, and T-type CaV currents, respectively. beta-Cell CaV channels take center stage in insulin secretion and play an important role in beta-cell physiology and pathophysiology. CaV3 channels become expressed in diabetes-prone mouse beta-cells. Point mutation in the human CaV1.2 gene results in excessive insulin secretion. Trinucleotide expansion in the human CaV1.3 and CaV2.1 gene is revealed in a subgroup of patients with type 2 diabetes. beta-Cell CaV channels are regulated by a wide range of mechanisms, either shared by other cell types or specific to beta-cells, to always guarantee a satisfactory concentration of Ca2+. Inappropriate regulation of beta-cell CaV channels causes beta-cell dysfunction and even death manifested in both type 1 and type 2 diabetes. This review summarizes current knowledge of CaV channels in beta-cell physiology and pathophysiology.

Effects of radix salviae miltiorrhizae on endothelin-1-induced calcium changes in hepatic stellate cells

AIM: To investigate the effect of radix salviae miltiorrhizae (RSM) on the changes of [Ca²⁺]i induced by endothelin-1 (ET-1) in hepatic stellate cells (HSCs).

METHODS: After preparation of RSM cream, the effects of RSM on ET-1-induced changes of HSCs [Ca²⁺]i were observed by laser scanning confocal microscopy.

RESULTS: In normal buffer (including Ca²⁺, buffer A), the fluorescence intensity was enhanced accordingly with the increase of ET-1 concentration. The cumulative-response curve showed EC₅₀ was 1.1×10^-9 mol/L. After incubation of HSCs with ET-1 in buffer A and buffer B (absence of extracellular calcium, EGTA), the duration of calcium peak had significant difference (165.2 ± 10.1 s vs 91.0 ± 7.2 s, P < 0.01), while the value of calcium peak had no significant difference. The ET-1-induced duration of calcium wave decreased markedly in the cells pretreated with RSM in buffer A as compared with that in the ones treated by ET-1 alone (69.1 ± 12.5 s vs 165.2 ± 10.1 s, P < 0.01). The calcium peak value and duration of calcium wave had no significant changes between the cells pre-incubated with RSM in buffer B and A (P > 0.05). In the cells pre-incubated with RSM, KCl-induced elevation of [Ca²⁺]i was decreased, and the calcium peak value (78.0% ± 6.1% → 26.3% ± 1.2%, P < 0.01) and duration of calcium wave (70.8 ± 10.4 s → 15.9 ± 5.1 s, P < 0.01) were decreased significantly.

CONCLUSION: RSM inhibits ET-1-induced depletion of intracellular calcium, which has no correlations with the influx of extracellular calcium. RSM can also inhibit KCl-induced influx of calcium, indicating its characteristic of blocking voltage-operated Ca²⁺ channel.

Effect of verapamil on nitric oxide synthase in a portal vein-ligated rat model: Role of prostaglandin

AIM: To investigate the effects of verapamil on nitric oxide (NO) synthesis in a portal vein-ligated rat model.

METHODS: Systemic and splanchnic hemodynamics were measured by radiolabeled microspheres in portal hypertensive rats after acute administration of verapamil (2 mg/kg) on chronic treatment with N^w–nitro-L-arginine (NNA)(80 mg/kg) and/or indomethacin (2 mg/kg) .

RESULTS: Verapamil (2 mg/kg) caused a marked fall in both arterial pressure and cardiac output accompanied by an insignificant change in the portal pressure and no change in portal venous inflow. This result suggested that verapamil did not cause a reduction in portal vascular resistance of portal hypertensive rats, which was similar between N^w- nitro–L-arginine-treated and indomethacin-treated groups.

CONCLUSION: In portal hypertensive rats pretreated with NNA and/or indomethacin, acute verapamil administration can not reduce the portal pressure, suggesting that NO and prostaglandin play an important role in the pathogenesis of splanchnic arterial vasodilation in portal hypertension.

[Hepatic stellate cells: it's role in normal and pathological conditions]

Hepatic fibrosis is a dynamic and sophisticatedly regulated wound healing response to chronic hepatocellular injury. This fibrotic process results from the accumulation of extracellular matrix (ECM) including collagen, proteoglycan, and adhesive glycoproteins which are principally produced by hepatic stellate cells (HSC), a mesenchymal cell type located between parenchymal cell plates and sinusoidal endothelial cells in the space of Disse. In physiological conditions, quiescent HSCs play important roles in the regulation of retinoid homeostasis and ECM remodeling by producing ECM components as well as metalloproteases and its inhibitor. However during hepatic fibrogenesis, HSCs are known to be activated or "transdifferentiated" to myofibroblast-like cells which play a pivotal role in ECM remodeling and hepatic blood flow regulation. Activation of HSC is now well established as the key process involved in the development of hepatic fibrosis. Both basic morphology and functions of HSCs in normal conditions and its role in pathological fibrosis will be discussed in this review.

[Ca2+]i-independent contractile force generation by rat hepatic stellate cells in response to endothelin-1

The contractile force generated by hepatic stellate cells in response to endothelin-1 contributes to sinusoidal blood flow regulation and hepatic fibrosis. This study's aim was to directly test the widely held view that changes in cytosolic Ca2+ concentration ([Ca2+]i) mediate stellate cell force generation. Contractile force generation by primary cultures of rat hepatic stellate cells grown in three-dimensional collagen gels was directly and quantitatively measured using a force transducer. Stellate cell [Ca2+]i, myosin activation, and migration were quantified using standard techniques. [Ca2+]i was modulated using ionomycin, BAPTA, KCl, and removal of extracellular Ca2+. Removal of extracellular Ca2+ did not alter endothelin-1-stimulated force development or [Ca2+]i. Ionomycin, a Ca2+ ionophore, triggered an increase in [Ca2+]i that was three times greater than that stimulated by endothelin-1, but only induced 16% of the force and 38% of the myosin regulatory light chain (MLC) phosphorylation induced by endothelin-1. Physiological increases in [Ca2+]i induced by hyperkalemia had no effect on contractile force. Loading BAPTA, a Ca2+ chelator, in stellate cells completely blocked endothelin-1-induced increases in [Ca2+]i but had no effect on endothelin-1-stimulated force generation or MLC phosphorylation. In contrast, Y-27632, a selective rho-associated kinase inhibitor, inhibited endothelin-1-stimulated force generation by at least 70% and MLC phosphorylation by at least 80%. Taken together, these observations indicate that changes in [Ca2+]i are neither necessary nor sufficient for contractile force generation by rat stellate cells. Our results challenge the current model of contractile regulation in hepatic stellate cells and have important implications for our understanding of hepatic pathophysiology.

Effect of octreotide on regulation of intracellular free Ca2+ concentration of hepatic stellate cells in rats

AIM: To investigate the effect of octreotide on the regulation of intracellular free Ca²⁺ concentration ([Ca²⁺]i) and proliferation of hepatic stellate cells (HSCs) in rats.

METHODS: Fluorescence Ca²⁺ indicator Fura-2/AM was used to observe the [Ca²⁺]i of HSCs in normoxic and chronic hypoxic condition. The effects of octreotide on the proliferation of HSCs were assessed by MTT assay, and the levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were detected by radioimmunoassay.

RESULTS: The [Ca²⁺]i in hypoxic condition was markedly increased as compared with that in normoxic condition (293.2±12.4 nmol/L vs 137.7±7.8 nmol/L, P<0.01). In normoxic condition, the level of [Ca²⁺]i decreased sharply after 500, 800 and 1 000 mg/L octreotide treatment (92.52±2.52, 83.77±2.30 and 76.58±2.21 nmol/L, respectively, P<0.01); In hypoxic condition, 500, 800 and 1 000 mg/L octreotide caused significant reduction in [Ca²⁺]i(204.28±7.41, 174.08±4.77 and 156.75±6.59 nmol/L, respectively, P<0.01). MTT assay showed that 500, 800 and 1 000 mg/L octreotide reduced the value of optical density (A value) in normoxic (0.173±0.010, 0.138±0.009, 0.100±0.010, respectively) and hypoxic (0.443±0.027, 0.320±0.014, 0.230±0.014, respectively) condition. After exposure to hypoxic condition, the level of cAMP was not significantly different from that of cGMP (P>0.05). The contents of cAMP and cGMP markedly increased after 500, 800, and 1 000 μg/L octreotide treatment in normoxic (cAMP: 1.69±0.18, 1.99±0.27, 2.48±0.37 pmol/mg vs 1.10±0.32 pmol/mg, P<0.05 or P<0.01; cGMP: 1.08±0.24, 1.24±0.17, 1.31±0.29 pmol/mg vs 0.86±0.12 pmol/mg, P<0.05 or P<0.01) and hypoxic (cAMP: 1.87±0.30, 2.09±0.35, 2.24±0.15 pmol/mg vs 1.37±0.25 pmol/mg, P<0.05 or P<0.01; cGMP: 1.17±0.53, 1.38±0.29, 1.46±0.35 pmol/mg vs 0.89±0.20 pmol/mg, P<0.05 or P<0.01) condition as compared with those in the corresponding control groups.

CONCLUSION: Hypoxia can promote the proliferation of HSCs through the second messenger system, while octreotide antagonizes this action in a dose-dependant manner in both hypoxic and normoxic conditions. cAMP and cGMP play certain roles in the regulation of HSCs.

Genomic and functional characterization of stellate cells isolated from human cirrhotic livers

BACKGROUND/AIMS

Hepatic stellate cells (HSCs) are believed to participate in liver fibrogenesis and portal hypertension. Knowledge on human HSCs is based on studies using HSCs isolated from normal livers. We investigated the phenotypic, genomic and functional characteristics of HSCs from human cirrhotic livers.

METHODS

HSC were obtained from normal and cirrhotic human livers. Cells were characterized by immunocytochemistry and gene microarray analysis. Cell proliferation, Ca(2+) changes and cell contraction were assessed by 3H-thymidine incorporation and by using an epifluorescence microscope.

RESULTS

HSCs freshly isolated from human cirrhotic livers showed phenotypical features of myofibroblasts. These features were absent in HSCs freshly isolated from normal human livers and become prominent after prolonged culture. HSCs from cirrhotic human livers markedly express genes involved in fibrogensis, inflammation and apoptosis. HSCs from normal livers after prolonged culture preferntially expressed genes related to fibrogenesis and contractility. Agonists induced proliferation, Ca(2+) increase and cell contraction in HSCs isolated from human cirrhotic livers. Response to agonists was more marked in culture-activated HSCs and was not observed in HSCs freshly isolated from normal livers.

CONCLUSIONS

HSCs from human cirrhotic livers show fibrogenic and contractile features. However, the current model of HSCs activated in culture does not exactly reproduce the activated phenotype found in cirrhotic human livers.

K+ currents regulate the resting membrane potential, proliferation, and contractile responses in ventricular fibroblasts and myofibroblasts

Despite the important roles played by ventricular fibroblasts and myofibroblasts in the formation and maintenance of the extracellular matrix, neither the ionic basis for membrane potential nor the effect of modulating membrane potential on function has been analyzed in detail. In this study, whole cell patch-clamp experiments were done using ventricular fibroblasts and myofibroblasts. Time- and voltage-dependent outward K+ currents were recorded at depolarized potentials, and an inwardly rectifying K+ (Kir) current was recorded near the resting membrane potential (RMP) and at more hyperpolarized potentials. The apparent reversal potential of Kir currents shifted to more positive potentials as the external K+ concentration ([K+]o) was raised, and this Kir current was blocked by 100–300 μM Ba2+. RT-PCR measurements showed that mRNA for Kir2.1 was expressed. Accordingly, we conclude that Kir current is a primary determinant of RMP in both fibroblasts and myofibroblasts. Changes in [K+]o influenced fibroblast membrane potential as well as proliferation and contractile functions. Recordings made with a voltage-sensitive dye, DiBAC3(4), showed that 1.5 mM [K+]o resulted in a hyperpolarization, whereas 20 mM [K+]o produced a depolarization. Low [K+]o (1.5 mM) enhanced myofibroblast number relative to control (5.4 mM [K+]o). In contrast, 20 mM [K+]o resulted in a significant reduction in myofibroblast number. In separate assays, 20 mM [K+]o significantly enhanced contraction of collagen I gels seeded with myofibroblasts compared with control mechanical activity in 5.4 mM [K+]o. In combination, these results show that ventricular fibroblasts and myofibroblasts express a variety of K+ channel α-subunits and demonstrate that Kir current can modulate RMP and alter essential physiological functions.

The selective cyclooxygenase-2 inhibitor SC-236 reduces liver fibrosis by mechanisms involving non-parenchymal cell apoptosis and PPARgamma activation

The importance of inflammation in initiating the sequence of events that lead to liver fibrosis is increasingly recognized. In this study, we tested the effects of SC-236, a selective cyclooxygenase (COX)-2 inhibitor, in rats with carbon tetrachloride (CCl4)-induced liver fibrosis. Livers from CCl4-treated rats showed increased COX-2 expression and 15-deoxy-prostaglandin (PG)J2 (15d-PGJ2) formation, as well as decreased peroxisome proliferator-activated receptor (PPAR)gamma expression. In these animals, SC-236 reduced liver fibrosis as revealed by histological analysis and by a reduction in hepatic hydroxyproline levels, metalloproteinase-2 activity, and alpha-smooth muscle actin expression. Interestingly, SC-236 normalized 15d-PGJ2 levels and restored PPARgamma expression in the liver of CCl4-treated rats. In isolated hepatic stellate cells (HSCs)--the major player in liver fibrogenesis--and Kupffer cells--the cell type primarily responsible for increased hepatic COX-2-SC-236 exhibited remarkable pro-apoptotic and growth inhibitory properties. Of interest, SC-236 decreased HSC viability to a similar extent than the PPARgamma ligand rosiglitazone. Moreover, SC-236 significantly induced PPARgamma expression in HSCs and acted as a potent PPARgamma agonist in a luciferase-reporter trans-activation assay. These data indicate that, by mechanisms involving non-parenchymal cell apoptosis and PPARgamma activation, the selective COX-2 inhibitor SC-236 might have therapeutic potential for prevention of liver fibrosis.

Sinusoidal endothelial COX-1-derived prostanoids modulate the hepatic vascular tone of cirrhotic rat livers

CCl(4) cirrhotic rat liver exhibits a hyperresponse to the alpha(1)-adrenergic agonist methoxamine (Mtx) that is associated with enhanced thromboxane A(2) (TXA(2)) production and is abrogated by indomethacin. To further elucidate the molecular mechanisms involved in the hyperresponse to vasoconstrictors, portal perfusion pressure dose-response curves to Mtx were performed in CCl(4) cirrhotic rats livers after preincubation with vehicle, the cyclooxygenase (COX)-1 selective inhibitor SC-560, and the COX-2 selective inhibitor SC-236. TXA(2) production was determined in samples of the perfusate. COX-1 expression was analyzed and quantified in hepatocytes, Kupffer cells, sinusoidal endothelial cells (SEC), and hepatic stellate cells (HSC) isolated from control and cirrhotic rat livers by double-immunofluorescence staining, with specific markers for each population using flow cytometry or Western blot analysis. COX-1 protein levels were not significantly increased in cirrhotic livers, but COX-2 protein expression was increased. COX-1 inhibition, but not COX-2, significantly attenuated the response to Mtx and prevented the increased production of TXA(2). Cirrhotic livers showed an increased expression of COX-1 in SEC and reduced expression in HSC compared with control livers, whereas COX-1 was similarly distributed in Kupffer cells. Despite abundant hepatic COX-2 expression, the increased response to Mtx of cirrhotic livers is mainly dependent of COX-1. Upregulation of COX-1 in cirrhotic SEC may be responsible for the hyperesponse to Mtx.

Cellular mechanisms of direct-current electric field effects: galvanotaxis and metastatic disease

Endogenous direct-current electric fields (dcEFs) occur in vivo in the form of epithelial transcellular potentials or neuronal field potentials, and a variety of cells respond to dcEFs in vitro by directional movement. This is termed galvanotaxis. The passive influx of Ca2+ on the anodal side should increase the local intracellular Ca2+ concentration, whereas passive efflux and/or intracellular redistribution decrease the local intracellular Ca2+ concentration on the cathodal side. These changes could give rise to `push-pull' effects, causing net movement of cells towards the cathode. However, such effects would be complicated in cells that possess voltage-gated Ca2+ channels and/or intracellular Ca2+ stores. Moreover, voltage-gated Na+ channels, protein kinases, growth factors, surface charge and electrophoresis of proteins have been found to be involved in galvanotaxis. Galvanotactic mechanisms might operate in both the short term (seconds to minutes) and the long term (minutes to hours), and recent work has shown that they might be involved in metastatic disease. The galvanotactic responses of strongly metastatic prostate and breast cancer cells are much more prominent, and the cells move in the opposite direction compared with corresponding weakly metastatic cells. This could have important implications for the metastatic process and has clinical implications. Galvanotaxis could thus play a significant role in both cellular physiology and pathophysiology.

Skeletal myosin heavy chain function in cultured lung myofibroblasts

Myofibroblasts are unique contractile cells with both muscle and nonmuscle properties. Typically myofibroblasts are identified by the expression of alpha smooth muscle actin (ASMA); however some myofibroblasts also express sarcomeric proteins. In this study, we show that pulmonary myofibroblasts express three of the eight known sarcomeric myosin heavy chains (MyHCs) (IIa, IId, and embryonic) and that skeletal muscle myosin enzymatic activity is required for pulmonary myofibroblast contractility. Furthermore, inhibition of skeletal myosin activity and myofibroblast contraction results in a decrease in both ASMA and skeletal MyHC promoter activity and ASMA protein expression, suggesting a potential coupling of skeletal myosin activity and ASMA expression in myofibroblast differentiation. To understand the molecular mechanisms whereby skeletal muscle genes are regulated in myofibroblasts, we have found that members of the myogenic regulatory factor family of transcription factors and Ca(2+) - regulated pathways are involved in skeletal MyHC promoter activity. Interestingly, the regulation of skeletal myosin expression in myofibroblasts is distinct from that observed in muscle cells and suggests that cell context is important in its control.

Cysteinyl-leukotrienes and the liver

Leukotrienes are potent biological mediators implicated in an increasing number of disease processes. This review outlines the basic biology of leukotrienes and discusses recent developments in our understanding of the specific role of cysteinyl-leukotrienes (cLTs) in cholestasis, hepatic inflammation, portal hypertension, and the pathogenesis of the hepatorenal syndrome (HRS).

Pharmacological rationale for the use of somatostatin and analogues in portal hypertension

Somatostatin and its analogue octreotide have been used for two decades to treat oesophageal variceal haemorrhage. The drug was introduced because of its capacity to decrease portal venous pressure without major side effects. In clinical trials assessing the efficacy of somatostatin and long-acting analogues in arresting variceal haemorrhage, conflicting results have been obtained. Furthermore, in haemodynamic studies evaluating the effects of somatostatin and analogues in patients with cirrhosis, divergent effects were observed. The main reason for these differences is probably related to different affinities of the drugs for different somatostatin receptor subtypes. The effects of somatostatin and analogues are mediated via five different G-protein coupled receptors (somatostatin receptor subtypes 1-5), which regulate the activity of ion channels (Ca2+, K+, Na+ and Cl-) and enzymes (adenyl cyclase, phospholipase C, phospholipase A2, phosphoinositide 3-kinase and guanylate cyclase) responsible for the synthesis or degradation of intracellular second messengers including cyclic AMP, inositol 1,4,5-trisphosphate, diacylglycerol and cyclic GMP. Despite universal use of somatostatin, the cellular and biochemical mechanisms of its effects in portal hypertension are relatively poorly studied and remain incompletely understood. In this review, we summarize relevant signal transduction of somatostatin and analogues, the haemodynamic effects of the drugs and the possible mechanisms by which these effects are mediated.

Activated human hepatic stellate cells express the renin-angiotensin system and synthesize angiotensin II

BACKGROUND & AIMS

The renin-angiotensin system plays an important role in hepatic fibrogenesis. In other organs, myofibroblasts accumulated in damaged tissues generate angiotensin II, which promotes inflammation and extracellular matrix synthesis. It is unknown whether myofibroblastic hepatic stellate cells, the main hepatic fibrogenic cell type, express the renin-angiotensin system and synthesize angiotensin II. The aim of this study was to investigate whether quiescent and activated human hepatic stellate cells contain the components of the renin-angiotensin system and synthesize angiotensin II.

METHODS

Hepatic stellate cells were freshly isolated from normal human livers (quiescent hepatic stellate cells) and from human cirrhotic livers (in vivo activated hepatic stellate cells). Culture-activated hepatic stellate cells were used after a second passage of quiescent hepatic stellate cells. Angiotensinogen, renin, and angiotensin-converting enzyme were assessed by quantitative polymerase chain reaction. Angiotensin II production was assessed by enzyme-linked immunosorbent assay and immunohistochemistry.

RESULTS

Quiescent hepatic stellate cells barely express the renin-angiotensin system components--angiotensinogen, renin, and angiotensin-converting enzyme--and do not secrete angiotensin II. In contrast, both in vivo activated hepatic stellate cells and culture-activated hepatic stellate cells highly express active renin and angiotensin-converting enzyme and secrete angiotensin II to the culture media. Mature angiotensin II protein is also detected in the cytoplasm of in vivo activated and culture-activated hepatic stellate cells. Growth factors (platelet-derived growth factor and epidermal growth factor) and vasoconstrictor substances (endothelin-1 and thrombin) stimulate angiotensin II synthesis, whereas transforming growth factor-beta and proinflammatory cytokines have no effect. Vasodilator substances markedly attenuate the effect of endothelin-1.

CONCLUSIONS

After activation, human hepatic stellate cells express the components of the renin-angiotensin system and synthesize angiotensin II. These results suggest that locally generated angiotensin II could participate in tissue remodeling in the human liver.

Regulation of endothelin-A receptor sensitivity by cyclic adenosine monophosphate in rat hepatic stellate cells

Sensitization of the endothelin-A receptor (ET(A)) occurs during HSC transdifferentiation, but the underlying mechanisms remained unclear. Sensitization of ET(A) was studied in quiescent and activated hepatic stellate cells (HSC) at the levels of receptor phosphorylation, localization, endothelin (ET)-1-induced Ca(2+) signals, and cell contraction. The endothelin-1 (ET-1) concentrations required to obtain an ET(A)-mediated Ca(2+) signal in 50% of HSC cultured for 1 to 2 or 10 days were approximately 1.2 and 0.012 nmol/L, respectively. This transdifferentiation-dependent sensitization of ET(A) was accompanied by receptor translocation to the plasma membrane. Cyclic AMP rapidly desensitized ET(A) in activated HSC and shifted their ET-1 responsiveness from picomolar to nanomolar concentrations with respect to Ca(2+) signals and HSC contraction. ET(A) desensitization also occurred in response to prostaglandin E(2), adenosine, or ET(B) stimulation. Desensitization by cAMP in activated HSC was accompanied by an increased Ser/Thr phosphorylation of ET(A) and their rapid internalization. Quiescent HSC exhibited Ser/Thr phosphorylation of the ET(A) protein, which was not affected by cAMP. In conclusion, the ET(A) response in HSC is regulated by protein kinase A (PKA)-dependent receptor phosphorylation and internalization. This may explain the transdifferentiation-dependent sensitization of HSC towards ET-1 and its reversal by cAMP and ET(B) activation.

Human myofibroblastic hepatic stellate cells express Ca(2+)-activated K(+) channels that modulate the effects of endothelin-1 and nitric oxide

BACKGROUND/AIMS

High-conductance Ca(2+)-activated K(+) (BK(Ca)) channels modulate the effects of vasoactive factors in contractile cells. It is unknown whether hepatic stellate cells (HSCs) contain BK(Ca) channels and what their role in the regulation of HSCs contractility is.

METHODS

The presence of BK(Ca) channels in HSCs was assessed by the patch-clamp technique. The functional role of BK(Ca) channels was investigated by measuring intracellular calcium concentration ([Ca(2+)](i)) and cell contraction in individual cells after stimulation with endothelin-1 in the presence or absence of specific modulators of BK(Ca) channels.

RESULTS

BK(Ca) channels were detected by patch-clamp in most of the activated HSCs studied. Incubation of cells with iberiotoxin, a BK(Ca) channel blocker, increased both the sustained phase of [Ca(2+)](i) elicited by endothelin-1 and the number of cells undergoing contraction, while the use of NS1619, a BK(Ca) channel opener, induced opposite effects. Stimulation of HSCs with S-nitroso-N-acetyl-penicillamine (SNAP), a nitric oxide (NO)-donor, increased the opening of BK(Ca) channels and reduced the effects of endothelin-1. Conversely, iberiotoxin abolished the inhibitory effect of SNAP on endothelin-induced [Ca(2+)](i) increase and cell contraction.

CONCLUSIONS

Activated human HSCs contain BK(Ca) channels that modulate the contractile effect of endothelin-1 and mediate the inhibitory action of NO.