Hepatic stellate cells and intrahepatic modulation of portal pressure

Hepatic alterations during the development and progression of cancer cachexia

Cancer-associated bodyweight loss (cachexia) is a hallmark of many cancers and is associated with decreased quality of life and increased mortality. Hepatic function can dramatically influence whole-body energy expenditure and may therefore significantly influence whole-body health during cancer progression. The purpose of this study was to examine alterations in markers of hepatic metabolism and physiology during cachexia progression. Male C57BL/6J mice were injected with 1 × 10⁶ Lewis Lung Carcinoma cells dissolved in 100 μL PBS and cancer was allowed to develop for 1, 2, 3, or 4 weeks. Control animals were injected with an equal volume of phosphate-buffered saline. Livers were analyzed for measures of metabolism, collagen deposition, protein turnover, and mitochondrial quality. Animals at 4 weeks had ∼30% larger livers compared with all other groups. Cancer progression was associated with altered regulators of fat metabolism. Additionally, longer duration of cancer development was associated with ∼3-fold increased regulators of collagen deposition as well as phenotypic collagen content, suggesting increased liver fibrosis. Mitochondrial quality control regulators appeared to be altered before any phenotypic alterations to collagen deposition. While induction of Akt was noted, downstream markers of protein synthesis were not altered. In conclusions, cancer cachexia progression is associated with hepatic pathologies, specifically liver fibrosis. Alterations to mitochondrial quality control mechanisms appear to precede this fibrotic phenotype, potentially suggesting mitochondrial mechanisms for the development of hepatic pathologies during the development and progression of cancer cachexia. Novelty Cachexia progression results in liver collagen deposition and fibrosis. Alterations in mitochondrial quality control may precede liver pathologies during cachexia.

Acute effects of endothelin receptor antagonists on hepatic hemodynamics of cirrhotic and noncirrhotic rats

Hepatic and circulating endothelin-1 (ET-1) are increased in patients with cirrhosis and in cirrhotic animals. However, the distinct roles of ET receptor subtypes ETA and ETB in cirrhosis and portal hypertension (PHT) have not been clearly elucidated. Thus, we studied the effects of selective ET-1 antagonists (ETA-ant or ETB-ant) and nonselective ET-1 antagonist (ETA/B-ant) on hepatic hemodynamics in cirrhotic rats. Liver fibrosis and PHT were induced by complete bile duct ligation (BDL) in rats. Two weeks after BDL or sham surgery, hemodynamic responses were measured during intraportal infusion of incremental doses of the following ET-ants: (i) BQ-123, (ii) BQ-788, and (iii) bosentan. After equilibration with vehicle, doses of ET-ants were infused for 30 min periods, and steady-state systemic and hepatic hemodynamics, portal venous pressure (PVP), and hepatic blood flow (HBF) were measured. BDL induced significant PHT and elevated concentrations of plasma ET-1 compared with sham. ETA-ant decreased PVP of cirrhotic rats but had no effect on sham, whereas ETB-ant increased PVP in sham but had no effect in BDL. Nonselective ETA/B-ant decreased PVP of BDL similarly to ETA-ant. Both ETA-ant and ETB-ant decreased local HBF, whereas a nonselective antagonist did not change HBF in sham; however no significant changes were observed in HBF of BDL rats with any of the antagonists. These findings suggest ETA activation contributes to PHT in cirrhotic rats, whereas ETB-mediated portal depressor effects are attenuated in cirrhotic rats compared with noncirrhotic rats.

Physiopathology of splanchnic vasodilation in portal hypertension

In liver cirrhosis, the circulatory hemodynamic alterations of portal hypertension significantly contribute to many of the clinical manifestations of the disease. In the physiopathology of this vascular alteration, mesenteric splanchnic vasodilation plays an essential role by initiating the hemodynamic process. Numerous studies performed in cirrhotic patients and animal models have shown that this splanchnic vasodilation is the result of an important increase in local and systemic vasodilators and the presence of a splanchnic vascular hyporesponsiveness to vasoconstrictors. Among the molecules and factors known to be potentially involved in this arterial vasodilation, nitric oxide seems to have a crucial role in the physiopathology of this vascular alteration. However, none of the wide variety of mediators can be described as solely responsible, since this phenomenon is multifactorial in origin. Moreover, angiogenesis and vascular remodeling processes also seem to play a role. Finally, the sympathetic nervous system is thought to be involved in the pathogenesis of the hyperdynamic circulation associated with portal hypertension, although the nature and extent of its role is not completely understood. In this review, we discuss the different mechanisms known to contribute to this complex phenomenon.

Endothelial markers in schistosomiasis patients with or without portal hypertension

PURPOSE

To evaluate the serum levels of von Willebrand factor (vWF), vascular endothelial growth factor (VEGF), endothelin-1 (ET-1), and endothelin-3 (ET-3) in patients with the isolated, inactive form of Schistosomiasis mansoni. Patients were classified into two groups: 10 patients without (SM group) and 18 with (PH group) portal hypertension.

RESULTS

Serum albumin, VEGF, and vWF levels did not differ between the two groups (P > 0.05). The prothrombin time (INR), number of platelets, spleen size, splenic vein diameter, and endothelin levels differentiated the PH group, which showed decreased ET-1 (SM = 22.4 +/- 2.4 pg/ml and PH = 16.4 +/- 1.5 pg/ml; P = 0.034) and increased ET-3 (SM = 2.1 +/- 0.1 ng/ml and PH = 3.2 +/- 0.1 ng/ml; P = 0.000) levels.

CONCLUSIONS

In patients with schistosomiasis and portal hypertension (presinusoidal type), the levels of VEGF and ET-1 differ from those reported in patients with cirrhosis.

Transforming growth factor-beta induces contraction of activated hepatic stellate cells

BACKGROUND/AIMS

Transforming growth factor-beta (TGF-beta) is a cytokine produced in abundance during liver injury. Recognizing the prominent roles that hepatic stellate cells (HSCs) and TGF-beta play in portal hypertension and fibrogenesis, respectively, we sought to evaluate the effect of TGF-beta on the contractility of activated HSCs.

METHODS

Spontaneous immortalized cell lines of HSC origin were used in this study. Cells were grown in three-dimensional collagen gel lattice, transferred to 60 mm dishes and exposed to varying concentrations of TGF-beta1 in serum-free medium at 37 degrees C for up to 120 h. The area of the floating gels was measured using a Fluor S-MultiImager (Biorad), the cellular smooth muscle-alpha actin (SMA) content quantified and PKC activation studies conducted.

RESULTS

TGF-beta1 induced a time- and dose-dependent decrease in lattice area up to 40% of control (P<0.05) that reflects the contraction of activated HSCs. This induced contraction was associated with increases in SMA content (3-fold, P<0.05) and PKC activation (5-fold, P<0.05) in these cells. Furthermore, pre-incubating with a PKC--specific inhibitor completely abrogated the TGF-beta-induced contraction.

CONCLUSIONS

TGF-beta induces contraction of activated HSCs via an increase in SMA content and a PKC--mediated pathway.

Expression of fibrillin-1 in focal nodular hyperplasia of the liver: a role in microcirculation adaptability

Introduction

It has been suggested that the elastic network plays an important role in the tissue response to mechanical stress. The components of the elastic network have been poorly studied in liver diseases. Therefore, in this work, the expression and distribution of fibrillin-1 and elastin were studied in hepatic focal nodular hyperplasia and compared with surrounding liver and hepatocellular adenoma.

Methods

Immunohistochemical studies for fibrillin-1 and elastin were performed on unfixed cryostat sections of focal nodular hyperplasia (22 cases), hepatocellular adenoma (15 cases) and surrounding liver (34 cases).

Results

Surrounding normal liver showed only a continuous, thin and regular immunostaining of fibrillin-1 in the space of Disse, whereas elastin was nearly absent. In focal nodular hyperplasia, fibrillin-1 was more strongly expressed in the perisinusoidal space, compared with surrounding liver; in contrast, in adenomas fibrillin-1 immunostaining was irregular and very low in perisinusoidal space, more intense in peliotic areas.

Conclusions

In focal nodular hyperplasia, the increased microfibrillar network containing fibrillin-1 in the space of Disse could reflect an adaptation of the sinusoidal wall to an increased arterial blood flow in sinusoids. In hepatocellular adenoma, the different patterns of fibrillin-1 could be related to the heterogeneity of the arterial vascularization and to the frequent necrotico-hemorrhagic changes. This study comparing the elastic network in two types of lesions with vascularization abnormalities and in the surrounding liver provides interesting new data for understanding the structural role of fibrillin-1 in the space of Disse.

Immunohistochemical localization of collagen type III and type IV, laminin, tenascin and alpha-smooth muscle actin (alphaSMA) in the human liver in peliosis

The expression of collagen types III and IV, laminin, tenascin, and hepatic stellate cells (HSCs) activation marker alphaSMA was evaluated immunohistochemically in the liver of three patients with non-bacilar peliosis. Peliosis was attributed to tuberculosis, endometriosis treated with anabolic androgenic steroids, and to pheochromocytoma. Ultrastructural examination of the lesions of the liver revealed cavities that were sometimes lined with sinusoidal endothelial cells or hepatocytic microvilli. In liver sinusoids around cavities, cystic dilatation of the space of Disse and an abundance of amorphous matrix were observed. At this location, HSCs were transformed into transitional cells or myofibroblasts. Extracellular matrix proteins (ECM) were increased in the dilated sinusoids around cavities perisinusoidally and in the wall of cavities themselves. AlphaSMA was also increased. Ultrastructural immunohistochemistry revealed strong intracellular deposits of collagen type IV, laminin, and alphaSMA in HSCs. Laminin immunoreactivity was also noted in the endocytic vesicles in the cytoplasm of a monocyte. These findings suggest that enhanced ECM accumulation and the transformation of HSCs into myofibroblasts constitute a secondary event in peliosis and an attempt of the liver to restrict and remove sinusoidal dilatation.

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.

In situ detection of reactive oxygen species and nitric oxide production in normal and pathological tissues: improvement by differential interference contrast

Reactive oxygen species (ROS), among which nitric oxide (NO) is currently included, play a plethora of (patho)physiological roles. Harman's free radical theory of aging put forth over 40 years ago received full support since then. A nitric oxide hypothesis of aging recently proposed by McCann, is very likely to be the object of widespread investigation in the near future. Therefore, the possibility of localizing at the (sub)cellular level under the light microscope the sites of ROS and NO production with simple and reliable methods appears as a powerful tool for analytic cytology and pathology. Various histochemical methods were developed for visualizing ROS production; a recently improved version to localize superoxide (and possibly also singlet oxygen), based on a DAB-Mn2+ -Co2+ reaction, appears very promising. Since the direct detection of NO is still very difficult, the action sites of NO are currently localized by the identification of NO synthase (NOS). The most widespread method to reveal the catalytic activity of NOS is that of demonstrating the fixation-resistant NADPH diaphorase activity with the tetrazolium salt method. We have improved this method by using a tetrazolium salt whose formazan particles are very thin and lipid insoluble (tetranitroblue tetrazolium, TNBT) and by including a tissue protectant, polyvinyl alcohol, in the incubation medium. Here significant examples of application of the DAB-Mn2+ -Co2+ technique for ROS and the TNBT-PVA method for NOS to normal liver and brain and to solid tumors are presented. We further document the usefulness of Nomarkis's differential interference contrast (DIC) to analyze wide tissue areas where ROS production or NOS activity is low or even nil. The improved version for NOS allowed for the first time to demonstrate NOS activity in liver fat-storing cells and in astrocyte-like cells in the brain.

Biological effects of C-type natriuretic peptide in human myofibroblastic hepatic stellate cells

During chronic liver diseases, hepatic stellate cells (HSC) acquire a myofibroblastic phenotype, proliferate, and synthetize fibrosis components. Myofibroblastic HSC (mHSC) also participate to the regulation of intrahepatic blood flow, because of their contractile properties. Here, we examined whether human mHSC express natriuretic peptide receptors (NPR). Only NPR-B mRNA was identified, which was functional as demonstrated in binding studies and by increased cGMP levels in response to C-type natriuretic peptide (CNP). CNP inhibited mHSC proliferation, an effect blocked by the protein kinase G inhibitor 8-(4 chlorophenylthio)-cGMP and by the NPR antagonist HS-142-1 and reproduced by analogs of cGMP. Growth inhibition was associated with a reduction of extracellular signal-regulated kinase and c-Jun N-terminal kinase and with a blockade of AP-1 DNA binding. CNP and cGMP analogs also blunted mHSC contraction elicited by thrombin, by suppressing calcium influx. The relaxing properties of CNP were mediated by a blockade of store-operated calcium channels, as demonstrated using a calcium-free/calcium readdition protocol. These results constitute the first evidence for a hepatic effect of CNP and identify mHSC as a target cell. Activation of NPR-B by CNP in human mHSC leads to inhibition of both growth and contraction. These data suggest that during chronic liver diseases, CNP may counteract both liver fibrogenesis and associated portal hypertension.

Quantitation of rat hepatic stellate cell contraction: stellate cells' contribution to sinusoidal resistance

Although it has been hypothesized that contraction of hepatic stellate cells (HSC) regulates blood flow by modulating sinusoidal resistance, neither HSC contraction nor relaxation has been directly quantitated. To test this hypothesis, a force transducer was employed to directly measure the magnitude and rate of contraction and relaxation by primary rat HSC (4.7 x 10(5) +/- 0.2 x 10(5) cells) cultured within a collagen gel. Serial exposures to 10% fetal bovine serum stimulated 81 +/- 14 and 82 +/- 10 dyn of contractile force, respectively. Subsequent stimulation with 2 nM endothelin-1 (ET-1) resulted in the development of 185 +/- 25 dyn of force. Contractions began within 10 s of ET-1 stimulation, and the half time of maximal force development was <5 min. Removal of agonist resulted in complete or nearly complete relaxation within 45 min. These results suggest that the magnitude and rate of HSC contraction and relaxation are capable of modulating blood flow via sinusoidal constriction.