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

Co-exposure to cadmium and microplastics promotes liver fibrosis through the hemichannels -ATP-P2X7 pathway

Microplastics (MPs) and cadmium (Cd) are important environmental pollutants, that damage the liver. However, the effect and mechanism of combined Cd and MPs exposure on liver fibrosis are still largely unknown. In this study investigated, Cd + MPs exposure increased superoxide anion production and promoted extracellular ATP release compared with exposure to Cd or MPs individually. Cd + MPs increased inflammatory cell infiltration, activated the P2X7-NLRP3 signaling pathway, and promoted inflammatory factor release. Cd + MPs aggravated Cd- or MPs-induced liver fibrosis and induced liver inflammation. In AML12/HSC-T6 cell in vitro poisoning model, exposure of AML12 cells to Cd + MPs increased the opening of connexin hemichannels and promoted extracellular ATP release. Treatment of HSC-T6 cells with the supernatant of AML12 cells exposed to Cd + MPs significantly promoted HSC-T6 cell activation. Treatment of HSC-T6 cells with different concentrations of ATP produced similar results. TAT-Gap19TFA, an inhibitor of connexin hemichannels, significantly inhibited the ATP release and activation of Cd + MPs-treated HSC-T6 cells. Finally, the expression of the ATP receptor P2X7 was silenced in HSC-T6 cells, which significantly inhibited their activation. In conclusion, exposure to Cd + MPs promoted liver fibrosis through the ATP-P2X7 pathway and synergistically affected liver inflammation and fibrosis.

Natural Sulfur-Containing Compounds: An Alternative Therapeutic Strategy against Liver Fibrosis

Liver fibrosis is a pathophysiologic process involving the accumulation of extracellular matrix proteins as collagen deposition. Advanced liver fibrosis can evolve in cirrhosis, portal hypertension and often requires liver transplantation. At the cellular level, hepatic fibrosis involves the activation of hepatic stellate cells and their transdifferentiation into myofibroblasts. Numerous pro-fibrogenic mediators including the transforming growth factor-β1, the platelet-derived growth factor, endothelin-1, toll-like receptor 4, and reactive oxygen species are key players in this process. Knowledge of the cellular and molecular mechanisms underlying hepatic fibrosis development need to be extended to find novel therapeutic strategies. Antifibrotic therapies aim to inhibit the accumulation of fibrogenic cells and/or prevent the deposition of extracellular matrix proteins. Natural products from terrestrial and marine sources, including sulfur-containing compounds, exhibit promising activities for the treatment of fibrotic pathology. Although many therapeutic interventions are effective in experimental models of liver fibrosis, their efficacy and safety in humans are largely unknown. This review aims to provide a reference collection on experimentally tested natural anti-fibrotic compounds, with particular attention on sulfur-containing molecules. Their chemical structure, sources, mode of action, molecular targets, and pharmacological activity in the treatment of liver disease will be discussed.

The expression of ETAR in liver cirrhosis and liver cancer

BACKGROUND

To investigate the expression of endothelin receptors in liver diseases and discuss its role in the process of liver cirrhosis and liver cancer.

RESEARCH DESIGN AND METHODS

We examined the expressions of ETAR, ETBR and α-SMA in tissue samples using western blotting analysis. Furthermore, immunofluorescence was used to locate ETAR expression in hepatic stellate cells (HSCs) and hepatic sinusoidal endothelial cells (HSECs), we calculated the percentage of positive cells and then analyzed its relation with clinical indexes.

RESULTS

According to the western blotting analysis, the expression of ETAR was high in hepatic hemangioma and liver cancer tissues and ETBR was highly expressed in cirrhosis tissues. The immunofluorescence results demonstrated that the expression of ETAR was elevated in hepatic hemangioma and liver cancer tissues. Moreover, ETAR expression was found in both HSCs and HSECs. Finally, the statistical analysis revealed that the number of positive ETAR cells was correlated with the clinical index platelets (PLT), alanine transaminase (ALT) and diameter of portal vein.

CONCLUSION

Endothelin receptors express differently in liver cirrhosis and liver cancer tissues and play a role in hepatic diseases by affecting HSCs and HSECs.

The profibrotic role of endothelin-1: is the door still open for the treatment of fibrotic diseases?

The endothelin (ET) system consists of two G-protein-coupled receptors (ETA and ETB), three peptide ligands (ET-1, ET-2 and ET-3), and two activating peptidases (endothelin-converting enzyme-, ECE-1 and ECE-2). While initially described as a vasoregulatory factor, shown to influence several cardiovascular diseases, from hypertension to heart failure, ET-1, the predominant form in most cells and tissues, has expanded its pathophysiological relevance by recent evidences implicating this factor in the regulation of fibrosis. In this article, we review the current knowledge of the role of ET-1 in the development of fibrosis, with particular focus on the regulation of its biosynthesis and the molecular mechanisms involved in its profibrotic actions. We summarize also the contribution of ET-1 to fibrotic disorders in several organs and tissues. The development and availability of specific ET receptor antagonists have greatly stimulated a number of clinical trials in these pathologies that unfortunately have so far given negative or inconclusive results. This review finally discusses the circumstances underlying these disappointing results, as well as provides basic and clinical researchers with arguments to keep exploring the complex physiology of ET-1 and its therapeutic potential in the process of fibrosis.

Embryonic hepatocyte transplantation for hepatic cirrhosis: Efficacy and mechanism of action

AIM: To investigate the efficacy and mechanism of action of allogeneic embryonic hepatocyte transplantation for the treatment of hepatic cirrhosis.

METHODS: Rat embryonic hepatocytes were characterized by examining cell markers. Wistar rats with CCl₄-induced cirrhosis were randomly divided into two groups: a model group receiving continuous CCl₄, and a cell transplantation group receiving continuous CCl₄ and transplanted with embryonic fluorescent-labeled hepatocytes. In addition, a normal control group was composed of healthy rats. All rats were sacrificed after 2 wk following the initiation of the cell transplant. Ultrasound, pathological analyses and serum biochemical tests were used to evaluate the efficacy of embryonic hepatocyte transplantation. To analyze the recovery status of cirrhotic hepatocytes and the signaling pathways influenced by embryonic hepatocyte transplantation, real-time polymerase chain reaction was performed to examine the mRNA expression of stellate activation-associated protein (STAP), c-myb, α smooth muscle actin (α-SMA) and endothelin-1 (ET-1). Western blotting and immunohistochemistry were employed to detect α-SMA and ET-1 protein expression in hepatic tissues.

RESULTS: Gross morphological, ultrasound and histopathological examinations, serum biochemical tests and radioimmunoassays demonstrated that hepatic cirrhosis was successfully established in the Wistar rats. Stem cell factor receptor (c-kit), hepatocyte growth factor receptor (c-Met), Nestin, α fetal protein, albumin and cytokeratin19 markers were observed in the rat embryonic hepatocytes. Following embryonic hepatocyte transplantation, there was a significant reversal in the gross appearance, ultrasound findings, histopathological properties, and serum biochemical parameters of the rat liver. In addition, after the activation of hepatic stellate cells and STAP signaling, α-SMA, c-myb and ET-1 mRNA levels became significantly lower than in the untreated cirrhotic group (P < 0.05). These levels, however, were not statistically different from those of the normal healthy group. Immunohistochemical staining and Western blot analyses revealed that α-SMA and ET-1 protein expression levels in the transplantation group were significantly lower than in the untreated cirrhotic group, but being not statistically different from the normal group.

CONCLUSION: Transplantation of embryonic hepatocytes in rats has therapeutic effects on cirrhosis. The described treatment may significantly reduce the expression of STAP and ET-1.

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

Endothelin-1 mediated regulation of extracellular matrix collagens in cells of human lamina cribrosa

Endothelin-1 (ET-1), a potent vaso-active peptide, mediates extracellular matrix regulation resulting in an increase in collagen deposition in various cell types and tissues and has been proposed to play a key role in glaucoma pathology. The role of ET-1 in the regulation of extracellular matrix collagens at the level of optic nerve head is not known. In this study we have examined the role of ET-1 in extracellular matrix collagen regulation in primary cultures of human lamina cribrosa cells. Our hypothesis is that ET-1 increases remodeling of the ECM of cells of the lamina cribrosa. Such actions could contribute to the development of optic neuropathy. QPCR analysis revealed that ET-1 mediated an increase in mRNA levels of collagen type I alpha1 and collagen type VI alpha1 chains at all doses of ET-1 with a significant increase at 1nM and 10nM concentration in LC cells. A dose-dependent increase in collagen type I and type VI protein deposition and secretion was also observed by Western blot in response to ET-1 and was significant at 10nM and 100nM concentrations of ET-1. ET-1 increased the [3H] proline uptake in LC cells suggesting that ET-1 contributed to an increase in total collagen synthesis in LC cells. ET-1-mediated increase in collagen type I, type VI and total collagen synthesis was significantly blocked by the ET(A) receptor antagonist, BQ610, as well as with the ET(B) receptor antagonist, BQ788, suggesting the involvement of both receptor subtypes in ET-1 mediated collagen synthesis in LC cells. These results suggest that ET-1 regulates extracellular matrix collagen synthesis in LC cells and may contribute to ECM remodeling at the level of LC of POAG subjects who have elevated plasma and aqueous humor levels of endothelin-1.

Effects of liver fibrosis on verapamil pharmacokinetics in rats

1. Liver fibrosis is the compensatory state of cirrhosis. In the long asymptomatic period, it is imperative to select a proper dosing regimen for drugs that are applicable to hepatic fibrosis owing to altered pharmacokinetics and bioavailability. The present study was designed to observe the changes in verapamil pharmacokinetics in rats with early liver fibrosis with respect to alterations in cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp). 2. A rat liver fibrosis model was successfully established using several inducers, including a high-fat diet, alcohol and carbon tetrachloride. After rats received a single intravenous or oral dose of verapamil (5 mg/kg), the plasma concentrations of verapamil were determined at scheduled time-points using HPLC. The activity of hepatic and small intestinal microsomal erythromycin N-demethylase (a marker for CYP3A) and the expression of small intestinal cyp3a and multidrug resistance (mdr) mRNA were compared between normal rats and rats with liver fibrosis. 3. The results showed that when verapamil was administered intravenously, the area under the curve (AUC), elimination half-life (T((1/2)(K10))) and mean residence time (MRT) increased significantly, whereas clearance (Cl) decreased, in rats with liver fibrosis compared with normal rats. After oral administration of verapamil, the AUC, (T((1/2)(K10))) and maximum concentration (C(max)) increased, Cl decreased and the absorption half-life (T((1/2)(K01))) and time to peak concentration (T(max)) were unchanged compared with normal rats. The oral bioavailability of verapamil was 32.9% in normal rats and 34.4% in rats with liver fibrosis. Furthermore, decreased CYP3A activity in the liver was accompanied by upregulated cyp3a9/18 and unchanged mdr mRNA in the small intestine compared with normal rats. Expression of cyp3a9/18 and mdr mRNA in the intestine was significantly inhibited by verapamil. 4. The results suggest that the lowered Cl and increased AUC of verapamil after intravenous and oral administration in rats with liver fibrosis were due to downregulation of CYP3A in the liver. The absorption rate of verapamil in rats with liver fibrosis was unchanged because mdr was unchanged and cyp3a was inhibited in the intestine by verapamil itself. There was no notable difference in oral bioavailability between normal rats and rats with liver fibrosis.

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.

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.

Dynamic expression of extracellular signal-regulated kinase in rat liver tissue during hepatic fibrogenesis

AIM: To investigate whether extracellular signal-regulated kinase 1 (ERK₁) is activated and associated with hepatic stellate cell (HSC) proliferation in fibrotic rat liver tissue.

METHODS: Rat hepatic fibrosis was induced by bile duct ligation (BDL). Histopathological changes were evaluated by hematoxylin and eosin staining, and Masson’s trichrome method. ERK₁ mRNA in rat liver tissue was determined by reverse transcription-polymerase chain reaction, while the distribution of ERK₁ was assessed by immunohistochemistry. ERK₁ protein was detected by Western blotting analysis. The number of activated HSCs was quantified after alpha smooth muscle actin (α-SMA) staining.

RESULTS: With the development of hepatic fibrosis, the positive staining cells of α-SMA increased obviously, and mainly resided in the portal ducts. Fiber septa and perisinuses were accompanied with proliferating bile ducts. The positive staining areas of the rat livers in model groups 1-4 wk after ligation of common bile duct (12.88% ± 2.63%, 22.65% ± 2.16%, 27.45% ± 1.86%, 35.25% ± 2.34%, respectively) were significantly larger than those in the control group (5.88% ± 1.46%, P < 0.01). With the development of hepatic fibrosis, the positive cells of ERK₁ increased a lot, and were mainly distributed in portal ducts, fiber septa around the bile ducts, vascular endothelial cells and perisinusoidal cells. Western blotting analysis displayed that the expression of ERK₁ and ERK₂ protein was up-regulated during the model course, and its level was the highest 4 wk after operation, being 3.9-fold and 7.2-fold higher in fibrotic rat liver than in controls. ERK₁ mRNA was expressed in normal rat livers as well, which was up-regulated two days after BDL and reached the highest 4 wk after BDL. The expression of ERK₁ was positively correlated with α-SMA expression (r = 0.958，P < 0.05).

CONCLUSION: The expression of ERK₁ protein and mRNA is greatly increased in fibrotic rat liver tissues, which may play a key role in HSC proliferation and hepatic fibrogenesis.

Peroxisome proliferator-activated receptor gamma overexpression inhibits pro-fibrogenic activities of immortalised rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) play a key role in the development of pancreatic fibrosis, a constant feature of chronic pancreatitis and pancreatic cancer. In response to pro-fibrogenic mediators, PSCs undergo an activation process that involves proliferation, enhanced production of extracellular matrix proteins and a phenotypic transition towards myofibroblasts. Ligands of the peroxisome proliferator-activated receptor gamma (PPARgamma), such as thiazolidinediones, are potent inhibitors of stellate cell activation and fibrogenesis in pancreas and liver. The effects of PPARgamma ligands, however, are at least in part mediated through PPARgamma-independent pathways. Here, we have chosen a different approach to study regulatory functions of PPARgamma in PSCs. Using immortalised rat PSCs, we have established a model of tetracycline (tet)-regulated PPARgamma overexpression. Induction of PPARgamma expression strongly inhibited proliferation and enhanced the rate of apoptotic cell death. Furthermore, PPARgamma-overexpressing cells synthesised less collagen than controls. To monitor effects of PPARgamma on PSC gene expression, we employed Affymetrix microarray technology. Using stringent selection criteria, we identified 21 up- and 19 down-regulated genes in PPARgamma-overexpressing cells. Most of the corresponding gene products are either involved in lipid metabolism, play a role in signal transduction, or are secreted molecules that regulate cell growth and differentiation. In conclusion, our data suggest an active role of PPARgamma in the induction of a quiescent PSC phenotype. PPARgamma-regulated genes in PSCs may serve as novel targets for the development of antifibrotic therapies.