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

Activation of BK Channels Prevents Hepatic Stellate Cell Activation and Liver Fibrosis Through the Suppression of TGFβ1/SMAD3 and JAK/STAT3 Profibrotic Signaling Pathways

Large-conductance and Ca²⁺-activated K⁺ (BK) channels are expressed in human hepatic stellate cells (HSCs), where they have roles in normal hepatic microcirculation, as well as in portal hypertension in liver cirrhosis through the regulation of contractility in activated HSCs. Nevertheless, whether BK channel activity exerts protective effects against aberrant HSC activation and hepatic fibrosis is unknown. Here, we report that BK channels are expressed in activated primary rat HSCs as well as in a human HSC line. Moreover, whole-cell K⁺ currents recorded from activated HSCs were markedly increased by exposure to rottlerin, a BK channel-specific activator, but were inhibited by treatment with the BK channel-specific inhibitor, paxilline, suggesting that BK channels are functional in activated HSCs. Overexpression but not downregulation of the BK channel pore-forming alpha subunit, KCNMA1, led to reduced migration and collagen expression in activated HSCs. Consistently, rottlerin treatment suppressed the fibrogenic cell function both in vitro and in CCl₄-induced liver fibrosis in vivo. Microarray and pathway analysis, combined with a luciferase reporter assay and western blotting, further showed that rottlerin treatment led to a significant downregulation of the profibrotic TGFβ1/SMAD3 and JAK/STAT3 signaling pathways, both in vitro and in vivo. Our findings not only link BK channel function to profibrotic signaling pathways, but also provide evidence that BK channel activation represents a promising therapeutic strategy for the treatment of liver fibrosis.

Ion Channels and Oxidative Stress as a Potential Link for the Diagnosis or Treatment of Liver Diseases

Oxidative stress results from a disturbed balance between oxidation and antioxidant systems. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) may be either harmful or beneficial to the cells. Ion channels are transmembrane proteins that participate in a large variety of cellular functions and have been implicated in the development of a variety of diseases. A significant amount of the available drugs in the market targets ion channels. These proteins have sulfhydryl groups of cysteine and methionine residues in their structure that can be targeted by ROS and RNS altering channel function including gating and conducting properties, as well as the corresponding signaling pathways associated. The regulation of ion channels by ROS has been suggested to be associated with some pathological conditions including liver diseases. This review focuses on understanding the role and the potential association of ion channels and oxidative stress in liver diseases including fibrosis, alcoholic liver disease, and cancer. The potential association between ion channels and oxidative stress conditions could be used to develop new treatments for major liver diseases.

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.

Transient receptor potential vanilloid 4 inhibits rat HSC-T6 apoptosis through induction of autophagy

Hepatic stellate cell (HSC) activation is a significant event in the development of liver fibrosis. Promoting the activated HSCs apoptosis contributes to the reversal of liver fibrosis. Autophagy is considered to be critical for many cellular and pathological processes including liver fibrosis. Transient receptor potential vanilloid 4 (TRPV4), another member of the transient receptor potential (TRP) channel, is proved to be a vital modulator in regulating HSC proliferation during liver fibrosis. However, the precise mechanism of TRPV4 on HSC apoptosis is still unclear. Here, we explored the role of TRPV4 in regulating HSC-T6 cell apoptosis. Our study detected that the expressions of TRPV4 mRNA and protein were dramatically increased in HSC-T6 in response to TGF-β1 stimulation by qRT-PCR and Western blot. Moreover, the HSC-T6 transfected with si-TRPV4 increased apoptosis and inhibited autophagy. In addition, the HSC-T6 treated with 4α-phorbol 12,13-didecanoate results in suppression of apoptosis and increase of autophagy. Furthermore, we indicated that TRPV4 induces autophagy by regulating AKT signaling pathway. In addition, we found that blockade of autophagy by chemical antagonists chloroquine (CQ) leads to increased apoptosis. Furthermore, blocking autophagy by CQ did not lead to a distinct change with or without TRPV4 over-expression. These results indicated that TRPV4 could inhibit HSCs apoptosis partially by regulating autophagy-dependent AKT signaling pathway activation.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

Understanding the mechanism of hepatic fibrosis and potential therapeutic approaches

Hepatic fibrosis (HF) is a progressive condition with serious clinical complications arising from abnormal proliferation and amassing of tough fibrous scar tissue. This defiance of collagen fibers becomes fatal due to ultimate failure of liver functions. Participation of various cell types, interlinked cellular events, and large number of mediator molecules make the fibrotic process enormously complex and dynamic. However, with better appreciation of underlying cellular and molecular mechanisms of fibrosis, the assumption that HF cannot be cured is gradually changing. Recent findings have underlined the therapeutic potential of a number of synthetic compounds as well as plant derivatives for cessation or even the reversal of the processes that transforms the liver into fibrotic tissue. It is expected that future inputs will provide a conceptual framework to develop more specific strategies that would facilitate the assessment of risk factors, shortlist early diagnosis biomarkers, and eventually guide development of effective therapeutic alternatives.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

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.

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.

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.

Hemodynamic and antifibrotic effects of a selective liver nitric oxide donor V-PYRRO/NO in bile duct ligated rats

AIM: To assess whether a liver specific nitric oxide (NO) donor (V-PYRRO/NO) would prevent the development of portal hypertension and liver fibrosis in rats with bile duct ligation (BDL).

METHODS: Treatment (placebo or V-PYRRO/NO 0.53 μmol/kg per hour) was administered i.v. to rats 2 d before BDL (D-2) and maintained until the day of hemodynamic measurement (D26). Intra-hepatic NO level was estimated by measuring liver cGMP level. Effects of V-PYRRO/NO on liver fibrosis and lipid peroxidation were also assessed.

RESULTS: Compared to placebo treatment, V-PYRRO/NO improved splanchnic hemodynamics in BDL rats: portal pressure was significantly reduced by 27% (P < 0.0001) and collateral circulation development was almost completely blocked (splenorenal shunt blood flow by 74%, P = 0.007). Moreover, V-PYRRO/NO significantly prevented liver fibrosis development in BDL rats (by 30% in hepatic hydroxyproline content and 31% in the area of fibrosis, P < 0.0001 respectively), this effect being probably due to a decrease in lipid peroxidation by 44% in the hepatic malondialdehyde level (P = 0.007). Interestingly, we observed a significant and expected increase in liver cGMP, without any systemic hemodynamic effects (mean arterial pressure, vascular systemic resistance and cardiac output) in both sham-operated and BDL rats treated with V-PYRRO/NO. This result is in accordance with studies on V-PYRRO/NO metabolism showing a specific release of NO in the liver.

CONCLUSION: Continuous administrations of V-PYRRO/NO in BDL rats improved liver fibrosis and splanchnic hemodynamics without any noxious systemic hemo-dynamic effects.

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.

Defects in cGMP-PKG pathway contribute to impaired NO-dependent responses in hepatic stellate cells upon activation

NO antagonizes hepatic stellate cell (HSC) contraction, although activated HSC in cirrhosis demonstrate impaired responses to NO. Decreased NO responses in activated HSC and mechanisms by which NO affects activated HSC remain incompletely understood. In normal rat HSC, the NO donor diethylamine NONOate (DEAN) significantly increased cGMP production and reduced serum-induced contraction by 25%. The guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) abolished 50% of DEAN effects, whereas the cGMP analog 8-bromoguanosine 3',5'-cyclic monophosphate (8-BrcGMP) reiterated half the observed DEAN response, suggesting both cGMP-dependent protein kinase G (PKG)-dependent and -independent mechanisms of NO-mediated antagonism of normal HSC contraction. However, NO donors did not increase cGMP production from in vivo activated HSC from bile duct-ligated rats and showed alterations in intracellular Ca(2+) accumulation suggesting defective cGMP-dependent effector pathways. The LX-2 cell line also demonstrated lack of cGMP generation in response to NO and a lack of effect of ODQ and 8-BrcGMP in modulating the NO response. However, cGMP-independent effects in response to NO were maintained in LX-2 and were associated with S-nitrosylation of proteins, an effect reiterated in primary HSC. Adenovirus-based overexpression of PKG significantly attenuated contraction of LX-2 by 25% in response to 8-BrcGMP. In summary, these studies demonstrate that NO affects HSC through cGMP-dependent and -independent pathways. The HSC activation process is associated with maintenance of cGMP-independent actions of NO but defects in cGMP-PKG-dependent NO signaling that are improved by PKG gene delivery in LX-2 cells. Activating targets downstream from NO-cGMP in activated HSC may represent a novel therapeutic target for portal hypertension.

[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.

Emerging drugs for idiopathic pulmonary fibrosis

Pulmonary fibrosis is often the end stage of chronic, persistent, low-level lung injury, either of known or unknown cause. The most severe form of pulmonary fibrosis is idiopathic pulmonary fibrosis (IPF), a disease process of unknown aetiology and one that often leads to respiratory failure and death. At present there are no proven or effective drug therapies for IPF. Recent advances in understanding of disease pathogenesis have focused attention on drug targeting of fibrogenic pathways, as opposed to traditional anti-inflammatory approaches. In this report, the present status of drug development of a number of emerging antifibrotic strategies and agents that may prove more effective in the therapy of this progressive, debilitating and fatal disease are reviewed.

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.

Idiopathic pulmonary fibrosis: emerging concepts on pharmacotherapy

Idiopathic pulmonary fibrosis (IPF) is a progressive, fibrosing disease of the distal air spaces of the lung of unknown aetiology. IPF is usually fatal with a median survival of < 3 years. There are currently no effective pharmacotherapeutic agents for the treatment of IPF. In this review, unifying concepts on the pathogenesis of IPF based on understanding of host responses to tissue injury are presented. These host responses involve tightly regulated and contextually orchestrated inflammatory and repair processes. Dysregulation of either of these processes can lead to pathological outcomes. Fibrosis results from an exaggerated or dysregulated repair process that proceeds 'uncontrolled' even after inflammatory responses have subsided. Disease heterogeneity may arise when inflammation and repair are in different (dys)regulatory phases, thus accounting for regional disparity. Usual interstitial pneumonia (UIP), the histopathological correlate of clinical IPF, represents a more fibrotic tissue reaction pattern and for which anti-inflammatory agents are ineffective. Emerging 'antifibrotic' drugs and strategies for UIP/IPF are discussed. The importance of accurately phenotyping a highly heterogeneous disease process that may require individualised and 'combined' therapies is emphasised.

Effects of endothelin-1 on hepatic stellate cell proliferation, collagen synthesis and secretion, intracellular free calcium concentration

AIM: To explore the effects of endothelin-1 (ET-1) on hepatic stellate cells (HSCs) DNA uptake, DNA synthesis, collagen synthesis and secretion, inward whole-cell calcium concentration ([Ca²⁺]_i) as well as the blocking effect of verapamil on ET-1-stimulated release of inward calcium (Ca²⁺) of HSC in vitro.

METHODS: Rat hepatic stellate cells (HSCs) were isolated and cultivated. ³H-TdR and ³H-proline incorporation used for testing DNA uptake and synthesis, collagen synthesis and secretion of HSCs cultured in vitro; Fluorescent calcium indicator Fura-2/AM was used to measure [Ca²⁺]_i inward HSCs.

RESULTS: ET-1 at the concentration of 5 × 10^-8 mol/L, caused significant increase both in HSC DNA synthesis (2247 ± 344 cpm, P < 0.05) and DNA uptake (P < 0.05) when compared with the control group. ET-1 could also increase collagen synthesis (P < 0.05 vs control group) and collagen secretion (P < 0.05 vs control group). Besides, inward HSC [Ca²⁺] _i reached a peak concentration (422 ± 98 mol/L, P < 0.001) at 2 min and then went down slowly to165 ± 51 mol/L (P < 0.01) at 25 min from resting state (39 ± 4 mol/L) after treated with ET-1. Verapamil (5 mol/L) blocked ET-1-activated [Ca²⁺]_i inward HSCs compared with control group (P < 0.05). Fura-2/AM loaded HSC was suspended in no Ca²⁺ buffer containing 1 mol/L EGTA, 5 min later, 10^-8 mol/L of ET-1 was added, [Ca²⁺]_i inward HSCs rose from resting state to peak 399 ± 123 mol/L, then began to come down by the time of 20 min. It could also raise [Ca²⁺]_i inward HSCs even without Ca²⁺ in extracellular fluid, and had a remarkable dose-effect relationship (P < 0.05). Meanwhile, verapamil could restrain the action of ET-1 (P < 0.05).

CONCLUSION: Actions of ET-1 on collagen metabolism of HSCs may depend on the transportation of inward whole-cell calcium.