Acute and chronic cyclooxygenase blockage in portal-hypertensive rats: influence in nitric oxide biosynthesis

Cirrhotic portal hypertension: From pathophysiology to novel therapeutics

Portal hypertension and bleeding from gastroesophageal varices is the major cause of morbidity and mortality in patients with cirrhosis. Portal hypertension is initiated by increased intrahepatic vascular resistance and a hyperdynamic circulatory state. The latter is characterized by a high cardiac output, increased total blood volume and splanchnic vasodilatation, resulting in increased mesenteric blood flow. Pharmacological manipulation of cirrhotic portal hypertension targets both the splanchnic and hepatic vascular beds. Drugs such as angiotensin converting enzyme inhibitors and angiotensin II type receptor 1 blockers, which target the components of the classical renin angiotensin system (RAS), are expected to reduce intrahepatic vascular tone by reducing extracellular matrix deposition and vasoactivity of contractile cells and thereby improve portal hypertension. However, these drugs have been shown to produce significant off-target effects such as systemic hypotension and renal failure. Therefore, the current pharmacological mainstay in clinical practice to prevent variceal bleeding and improving patient survival by reducing portal pressure is non-selective -blockers (NSBBs). These NSBBs work by reducing cardiac output and splanchnic vasodilatation but most patients do not achieve an optimal therapeutic response and a significant proportion of patients are unable to tolerate these drugs. Although statins, used alone or in combination with NSBBs, have been shown to improve portal pressure and overall mortality in cirrhotic patients, further randomized clinical trials are warranted involving larger patient populations with clear clinical end points. On the other hand, recent findings from studies that have investigated the potential use of the blockers of the components of the alternate RAS provided compelling evidence that could lead to the development of drugs targeting the splanchnic vascular bed to inhibit splanchnic vasodilatation in portal hypertension. This review outlines the mechanisms related to the pathogenesis of portal hypertension and attempts to provide an update on currently available therapeutic approaches in the management of portal hypertension with special emphasis on how the alternate RAS could be manipulated in our search for development of safe, specific and effective novel therapies to treat portal hypertension in cirrhosis.

Selective cyclooxygenase inhibition by SC-560 improves hepatopulmonary syndrome in cirrhotic rats

Objective

Hepatopulmonary syndrome (HPS) is characterized by hypoxia in patients with chronic liver disease. The mechanism of HPS includes pulmonary vasodilatation, inflammation, and angiogenesis. Prostaglandins synthesized by cyclooxygenases (COX) participate in vascular responsiveness, inflammation and angiogenesis, which can be modulated by COX inhibitors. We therefore evaluated the impact of COX inhibition in rats with common bile duct ligation (CBDL)-induced liver cirrhosis and HPS.

Methods

Cirrhotic rats were randomly allocated to receive non-selective COX inhibitor (indomethacin), selective COX-1 inhibitor (SC-560), or COX-2 inhibitor (celecoxib) for 14 days. After that, hemodynamic parameters, severity of hypoxia and intrapulmonary shunts, liver and renal biochemistry parameters, histological finding and protein expressions were evaluated.

Results

Non-selective COX inhibition by indomethacin improved hepatic fibrosis and pulmonary inflammation in cirrhotic rats with HPS. It also decreased mean arterial blood pressure, portal pressure, and alleviated hypoxia and intrapulmonary shunts. However, indomethacin increased mortality rate. In contrast, selective COX inhibitors neither affected hemodynamics nor increased mortality rate. Hypoxia was improved by SC-560 and celecoxib. In addition, SC-560 decreased intrapulmonary shunts, attenuated pulmonary inflammation and angiogenesis through down-regulating COX-, NFκB- and VEGF-mediated pathways.

Conclusion

Selective COX-1 inhibitor ameliorated HPS by mitigating hypoxia and intrapulmonary shunts, which are related to anti-inflammation and anti-angiogenesis.

Molecular Mechanisms Leading to Splanchnic Vasodilation in Liver Cirrhosis

In liver cirrhosis, portal hypertension is a consequence of enhanced intrahepatic vascular resistance and portal blood flow. Significant vasodilation in the arterial splanchnic district is crucial for an increase in portal flow. In this pathological condition, increased levels of circulating endogenous vasodilators, including nitric oxide, prostacyclin, carbon monoxide, epoxyeicosatrienoic acids, glucagon, endogenous cannabinoids, and adrenomedullin, and a decreased vascular response to vasoconstrictors are the main mechanisms underlying splanchnic vasodilation. In this review, the molecular pathways leading to splanchnic vasodilation will be discussed in detail.

Arachidonic acid metabolites and endothelial dysfunction of portal hypertension

Increased resistance to portal flow and increased portal inflow due to mesenteric vasodilatation represent the main factors causing portal hypertension in cirrhosis. Endothelial cell dysfunction, defined as an imbalance between the synthesis, release, and effect of endothelial mediators of vascular tone, inflammation, thrombosis, and angiogenesis, plays a major role in the increase of resistance in portal circulation, in the decrease in the mesenteric one, in the development of collateral circulation. Reduced response to vasodilators in liver sinusoids and increased response in the mesenteric arterioles, and, viceversa, increased response to vasoconstrictors in the portal-sinusoidal circulation and decreased response in the mesenteric arterioles are also relevant to the pathophysiology of portal hypertension. Arachidonic acid (AA) metabolites through the three pathways, cyclooxygenase (COX), lipoxygenase, and cytochrome P450 monooxygenase and epoxygenase, are involved in endothelial dysfunction of portal hypertension. Increased thromboxane-A2 production by liver sinusoidal endothelial cells (LSECs) via increased COX-1 activity/expression, increased leukotriens, increased epoxyeicosatrienoic acids (EETs) (dilators of the peripheral arterial circulation, but vasoconstrictors of the portal-sinusoidal circulation), represent a major component in the increased portal resistance, in the decreased portal response to vasodilators and in the hyper-response to vasoconstrictors. Increased prostacyclin (PGI2) via COX-1 and COX-2 overexpression, and increased EETs/heme-oxygenase-1/K channels/gap junctions (endothelial derived hyperpolarizing factor system) play a major role in mesenteric vasodilatation, hyporeactivity to vasoconstrictors, and hyper-response to vasodilators. EETs, mediators of liver regeneration after hepatectomy and of angiogenesis, may play a role in the development of regenerative nodules and collateral circulation, through stimulation of vascular endothelial growth factor (VEGF) inside the liver and in the portal circulation. Pharmacological manipulation of AA metabolites may be beneficial for cirrhotic portal hypertension.

Molecular pathophysiology of portal hypertension

Over the past two decades the advances in molecular cell biology have led to significant discoveries about the pathophysiology of portal hypertension (PHT). In particular, great progress has been made in the study of the molecular and cellular mechanisms that regulate the increased intrahepatic vascular resistance (IHVR) in cirrhosis. We now know that the increased IHVR is not irreversible, but that both the structural component caused by fibrosis and the active component caused by hepatic sinusoidal constriction can be, at least partially, reversed. Indeed, it is now apparent that the activation of perisinusoidal hepatic stellate cells, which is a key event mediating the augmented IHVR, is regulated by multiple signal transduction pathways that could be potential therapeutic targets for PHT treatment. Furthermore, the complexity of the molecular physiology of PHT can also be appreciated when one considers the complex signals capable of inducing vasodilatation and hyporesponsiveness to vasoconstrictors in the splanchnic vascular bed, with several vasoactive molecules, controlled at multiple levels, working together to mediate these circulatory abnormalities. Added to the complexity is the occurrence of pathological angiogenesis during the course of disease progression, with recent emphasis given to understanding its molecular machinery and regulation. Although much remains to be learned, with the current availability of reagents and new technologies and the exchange of concepts and data among investigators, our knowledge of the molecular basis of PHT will doubtless continue to grow, accelerating the transfer of knowledge generated by basic research to clinical practice. This will hopefully permit a better future for patients with PHT.

Prostacyclin decreases splanchnic vascular contractility in cirrhotic rats

BACKGROUND

Prostacyclin has been shown to increase portal hypertension, but the mechanism is unclear. This study aimed to investigate whether the overproduction of prostacyclin (PGI2) in cirrhosis participates in the splanchnic vascular hyporesponsiveness to vasoconstrictors in cirrhotic rats.

METHODS

Cirrhotic model was created by subcutaneous injection of 60% carbon tetrachloride (CCl4) corn oil solution combined with intermittent drinking of 5% alcohol, and age-matched rats served as controls. The isolated third-generation mesenteric arterioles were used to examine the contractile response to norepinephrine. The changes in vascular diameter were observed under a microscope imaging device. The plasma concentration of 6-ketone-prostaglandin F1alpha (6-keto-PGF1alpha, a stable metabolite of PGI2) was tested via enzyme immunoassays and the expression of cyclooxygenase (COX) in mesenteric arteries was detected by Western blotting.

RESULTS

In parallel with the increase of plasma 6-keto-PGF1alpha, the contractile response of arterioles from cirrhotic rats to norepinephrine was significantly impaired compared with that from controls. Inhibition of PGI2 or protein kinase A with indomethacin or Rp-adenosine 3', 5'-cyclic monophosphothioate (Rp-cAMPS) partially reversed the vascular hypo-contractile response to norepinephrine in arterioles from cirrhotic rats. Indomethacin significantly decreased the plasma 6-keto-PGF1alpha. Furthermore, indomethacin significantly attenuated the effect of Rp-cAMPS on arterioles from cirrhotic rats. COX-1 expression was up-regulated in mesenteric arteries from cirrhotic rats, whereas COX-2 was not detectable in the mesenteric arteries from both cirrhotic and control rats.

CONCLUSION

Enhanced COX-1 expression in cirrhotic rats resulted in elevated PGI2 production which partially contributed to the splanchnic vascular hyporesponsiveness to a vasoconstrictor via the protein kinase A pathway.

Splanchnic vasodilation and hyperdynamic circulatory syndrome in cirrhosis

Portal hypertension is a clinical syndrome which leads to several clinical complications, such as the formation and rupture of esophageal and/or gastric varices, ascites, hepatic encephalopathy and hepato-renal syndrome. In cirrhosis, the primary cause of the increase in portal pressure is the enhanced resistance to portal outflow. However, also an increase in splanchnic blood flow worsens and maintains portal hypertension. The vasodilatation of arterial splanchnic vessels and the opening of collateral circulation are the determinants of the increased splanchnic blood flow. Several vasoactive systems/substances, such as nitric oxide, cyclooxygenase-derivatives, carbon monoxide and endogenous cannabinoids are activated in portal hypertension and are responsible for the marked splanchnic vasodilatation. Moreover, an impaired reactivity to vasoconstrictor systems, such as the sympathetic nervous system, vasopressin, angiotensin II and endothelin-1, plays a role in this process. The opening of collateral circulation occurs through the reperfusion and dilatation of preexisting vessels, but also through the generation of new vessels. Splanchnic vasodilatation leads to the onset of the hyperdynamic circulatory syndrome, a syndrome which occurs in patients with portal hypertension and is characterized by increased cardiac output and heart rate, and decreased systemic vascular resistance with low arterial blood pressure. Understanding the pathophysiology of splanchnic vasodilatation and hyperdynamic circulatory syndrome is mandatory for the prevention and treatment of portal hypertension and its severe complications.

Nitric oxide and prostaglandin as mediators in the pathogenesis of hyperkinetic circulatory state in a model of endotoxemia-induced portal hypertension

AIMS

To evaluate the participation of nitric oxide (NO) and prostaglandin (PGI2) on hyperdynamic state in endotoxemia-induced portal hypertension (EIP) induced by chronic endotoxemia.

METHODS

The portal pressure (PP) and mean arterial pressure (MAP) were recorded, in vivo before and after administration of L-NAME (NOS inhibitor) and indomethacin (specific blocker of COX). The vasoactive responses to acetylcholine of thoracic rat aortic rings were studied in vitro before and after nitric oxide and cyclooxygenase blockade using multichannel organ bath. The mRNA expression for isoforms of (cyclooxygenase) COX and nitric oxide synthase (NOS) were analyzed using RT-PCR.

RESULTS

Administration of both L-NAME and indomethacin in EIP rabbits significantly reduced (p < 0.05) the PP and reversed the MAP to normal as compared to sham-operated (SO) rabbits. There was impaired vasodilatory response to acetylcholine in EIP rabbits. L-NAME caused a significant reduction in acetylcholine-induced vasorelaxation in SO rabbits than EIP due to preexisting hyperemia in EIP. Indomethacin partially restored vasoresponsiveness to acetylcholine in EIP group. The mRNA expression of eNOS (endothelial NOS) and COX-1 (constitutive COX) were significantly higher in SO than EIP rabbits. iNOS (inducible NOS) and COX-2 (inducible COX) mRNA expression was seen only in EIP rabbits.

CONCLUSIONS

A significant component of acetylcholine-mediated vasorelaxation in EIP model is modulated by eNOS. There was increased production of contractile prostaglandin in EIP rabbits. iNOS and COX-2 play an important role in the hemodynamic abnormalities of PHT. This novel model of PHT produced by chronic splanchnic endotoxemia in rabbit, mimics impaired vasodilation and vasoreactivity akin to other models of PHT.

Optimal management of hepatorenal syndrome in patients with cirrhosis

Hepatorenal syndrome (HRS) is a functional renal failure that often occurs in patients with cirrhosis and ascites. HRS develops as a consequence of a severe reduction of effective circulating volume due to both an extreme splanchnic arterial vasodilatation and a reduction of cardiac output. There are 2 different types of HRS. Type 1 HRS, which is often precipitated by a bacterial infection, especially spontaneous bacterial peritonitis, is characterized by a rapidly progressive impairment of renal function. Despite its functional origin, the prognosis of type 1 HRS is very poor. Type 2 HRS is characterized by a stable or slowly progressive renal failure so that its main clinical consequence is not acute renal failure but refractory ascites and its impact on prognosis is less negative. New treatments (vasoconstrictors plus albumin, transjugular portosystemic shunt, and molecular adsorbent recirculating system), which were introduced in the past 10 years, are effective in improving renal function in patients with HRS. Among these treatments vasoconstrictors plus albumin can also improve survival in patients with type 1 HRS. Thus, this therapeutic approach has changed the management of this severe complication in patients with advanced cirrhosis.

Atrophy of mesenteric sympathetic innervation may contribute to splanchnic vasodilation in rat portal hypertension

BACKGROUND AND AIMS

Portal hypertension is associated with downregulation of mRNA and proteins involved in adrenergic transmission in the superior mesenteric artery (SMA) in portal vein-ligated (PVL) and cirrhotic rats. We aimed to investigate whether SMA adrenergic dysfunction was accompanied by sympathetic nerve structural changes and whether it was extensive to resistance mesenteric arteries. We also attempted to localize the origin of mRNA of specific adrenergic genes.

METHODS AND RESULTS

In situ hybridization showed tyrosine hydroxylase (Th) mRNA expression in neuronal bodies of superior mesenteric ganglia and inside axonal fibres surrounding proximal SMA sections. Comparison of SMA by Th immunohistochemistry, both in PVL and bile duct-ligated (BDL) rats, demonstrated a significant decrease in the number of nervous structures (69% PVL; 62% BDL), total nervous area (70% PVL; 52% BDL) and Th-stained nervous area (89% PVL; 64% BDL) compared with sham rats. A strong correlation was detected between the Th-stained nervous area and the haemodynamic parameters, mainly with SMA resistance (r=0.9, P<0.001 for PVL and r=0.75, P=0.018 for BDL). Western blot analysis of Th, dopamine beta-hydroxylase and synaptosome-associated protein of 25 kDa indicated a significant inhibition in protein expression (35-58%) in mesenteric resistance arteries from both portal hypertension models compared with sham. By contrast, nervous structure analysis and protein expression in renal arteries showed no differences between sham and PVL rats.

CONCLUSION

Portal hypertension is associated with sympathetic nerve atrophy/regression in the mesenteric arterial vasculature that could contribute to the splanchnic vasodilation associated with portal hypertension.

Sorafenib attenuates the portal hypertensive syndrome in partial portal vein ligated rats

BACKGROUND/AIMS

Angiogenesis plays a key role in development of portal hypertension (PHT) and represents a potential therapeutic target. We aimed to evaluate the molecular effects of sorafenib, a multiple tyrosine kinase inhibitor, on splanchnic hemodynamics in rats with partial portal vein ligation (PPVL).

METHODS

The following four groups of rats were treated orally with sorafenib (10mg/kg per day; SORA group) or placebo (PLAC group) for 7 days, beginning at the day of PPVL or sham operation (SO): (1) PPVL-SORA, (2) PPVL-PLAC, (3) SO-SORA and (4) SO-PLAC. Measurements of mean arterial pressure (MAP), portal pressure (PP), and superior mesenterial artery blood flow (SMABF) were performed. Portosystemic collateral blood flow (PSCBF) was determined by radioactive microspheres. Splanchnic protein expression of CD31, alpha-smooth muscle actin (alphaSMA), phospho-extracellular signal-regulated kinase (pERK), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), tumor necrosis factor alpha (TNFalpha), and endothelial nitric oxide synthetase (eNOS) was assessed by Western blot. Gene expression was studied by angiogenesis-focused real-time reverse transcription polymerase chain reaction microarray.

RESULTS

PP, SMABF, and PSCBF were significantly higher in PPVL rats than in SO rats. MAP and heart rate were similar in all groups. Treatment with sorafenib resulted in a significant decrease of PP (p<0.001) and SMABF (p<0.05) in PPVL-SORA rats compared to PPVL-PLAC rats. PPVL-SORA rats had markedly less PSCBF than PPVL-PLAC rats (p<0.001). Superior mesenteric artery resistance (SMAR) was significantly lower in both PPVL groups compared to both SO groups, but PPVL-SORA rats showed significantly higher SMAR than PPVL-PLAC rats (p<0.05). The increased protein expression of CD31, alphaSMA, pERK, VEGF, PDGF, TNFalpha, and eNOS in rats with PHT was markedly decreased by sorafenib treatment. Sorafenib decreased mRNA levels of TNFalpha, VEGF receptor 2, VEGF receptor 1, transforming growth factor beta, cyclooxygenase 1, and expression of various genes that are involved in pathways of cellular proliferation, fibrogenesis, tissue remodeling, inflammation, and angiogenesis.

CONCLUSIONS

Treatment with sorafenib reduced PP, SMABF, and PSCBF in noncirrhotic rats with prehepatic PHT, without affecting systemic hemodynamics. Additional antiproliferative, anti-inflammatory, and antiangiogenic effects of sorafenib were identified.

Review: Vasoconstrictors for the treatment of portal hypertension

Vasoconstrictors have long been used in an attempt to mitigate the effects of portal hypertension. In this review, we discuss the current understanding of portal hypertension and the use of vasoconstrictors in the management of its sequlae, including variceal hemorrhage, hepatorenal syndrome, and paracentesis-induced circulatory dysfunction. Experimental and clinical evidence for the use of vasoconstrictors is considered, and several exciting recent developments are reviewed.

Apelin signaling modulates splanchnic angiogenesis and portosystemic collateral vessel formation in rats with portal hypertension

BACKGROUND/AIMS

Angiogenesis is a pathological hallmark of portal hypertension. Although VEGF is considered to be the most important proangiogenic factor in neoangiogenesis, this process requires the coordinated action of a variety of factors. Identification of novel molecules involved in angiogenesis is highly relevant, since they may represent potential new targets to suppress pathological neovascularization in angiogenesis-related diseases like portal hypertension. The apelin/APJ signaling pathway plays a crucial role in angiogenesis. Therefore, we determined whether the apelin system modulates angiogenesis-driven processes in portal hypertension.

METHODS

Partial portal vein-ligated rats were treated with the APJ antagonist F13A for seven days. Splanchnic neovascularization and expression of angiogenesis mediators (Western blotting) was determined. Portosystemic collateral formation (microspheres), and hemodynamic parameters (flowmetry) were also assessed.

RESULTS

Apelin and its receptor APJ were overexpressed in the splanchnic vasculature of portal hypertensive rats. F13A effectively decreased, by 52%, splanchnic neovascularization and expression of proangiogenic factors VEGF, PDGF and angiopoietin-2 in portal hypertensive rats. F13A also reduced, by 35%, the formation of portosystemic collateral vessels.

CONCLUSIONS

This study provides the first experimental evidence showing that the apelin/APJ system contributes to portosystemic collateralization and splanchnic neovascularization in portal hypertensive rats, presenting a potential novel therapeutic target for portal hypertension.

Role of cyclooxygenase isoforms in prostacyclin biosynthesis and murine prehepatic portal hypertension

Portal hypertension (PHT) is a common complication of liver cirrhosis and significantly increases morbidity and mortality. Abrogation of PHT using NSAIDs has demonstrated that prostacyclin (PGI(2)), a direct downstream metabolic product of cyclooxygenase (COX) activity, is an important mediator in the development of experimental and clinical PHT. However, the role of COX isoforms in PGI(2) biosynthesis and PHT is not fully understood. Prehepatic PHT was induced by portal vein ligation (PVL) in wild-type, COX-1(-/-), and COX-2(-/-) mice treated with and without COX-2 (NS398) or COX-1 (SC560) inhibitors. Hemodynamic measurements and PGI(2) biosynthesis were determined 1-7 days after PVL or sham surgery. Gene deletion or pharmacological inhibition of COX-1 or COX-2 attenuated but did not ameliorate PGI(2) biosynthesis after PVL or prevent PHT. In contrast, treatment of COX-1(-/-) mice with NS398 or COX-2(-/-) mice with SC560 restricted PGI(2) biosynthesis and abrogated the development of PHT following PVL. In conclusion, either COX-1 or COX-2 can mediate elevated PGI(2) biosynthesis and the development of experimental prehepatic PHT. Consequently, PGI(2) rather then COX-selective drugs are indicated in the treatment of PHT. Identification of additional target sites downstream of COX may benefit the >27,000 patients whom die annually from cirrhosis in the United States alone.

Pathogenesis and management of hepatorenal syndrome in patients with cirrhosis

Hepatorenal syndrome is a severe complication of advanced liver cirrhosis, in patients with ascites and marked circulatory dysfunction. It is clearly established that it has a functional nature, and that it is related to intense renal vasoconstriction. Despite its functional origin, the prognosis is very poor. In the present review, the most recent advances in diagnosis, pathophysiology, and treatment are discussed. Recent developments in pathophysiology are the basis of the new therapeutic strategies, which are currently under evaluation in randomised clinical trials.

Vascular actions of the prostacyclin receptor antagonist BAY 73-1449 in the portal hypertensive rat

We have investigated the actions of the postacyclin receptor antagonist BAY 73-1449 on shunt vessel development and shunt flow in the portal vein ligated portal hypertensive Wistar rat in vivo. BAY 73-1449 (0.1-1 mg/kg), given intravenously, did not significantly reduce mesenteric inflow, but significantly reduced splenic shunt vessel outflow, compared to the effects of vehicle, in anaesthetized portal vein ligated rats as measured by shunt vessel conductance. There were no differences between portal vein ligated animals treated, beginning just before portal vein ligation, with vehicle for 7 days and animals treated for 7 days with BAY 73-1449 (1-5 mg/kg, s.c.) in the degree of porto-systemic shunting, as measured by the radioactive microsphere technique in anaesthetized rats. Portal pressure was similar in animals treated with vehicle or BAY 73-1449. It is concluded that the prostacyclin receptor antagonist BAY 73-1449 can acutely reduce shunt vessel blood flow in portal hypertensive rats.

The somatostatin analogue octreotide inhibits angiogenesis in the earliest, but not in advanced, stages of portal hypertension in rats

Background: Angiogenesis is an important determinant of the pathophysiology of portal hypertension contributing to the formation of portosystemic collateral vessels and the hyperdynamic splanchnic circulation associated to this syndrome. Somatostatin and its analogues, like octreotide, have been shown to be powerful inhibitors of experimental angiogenesis. Aim: To determine whether octreotide has angioinhibitory effects in portal hypertensive rats. Methods: Partial portal vein-ligated (PPVL) rats were treated with octreotide or vehicle during 4 or 7 days. Splanchnic neovascularization and VEGF expression were determined by histological analysis and western blotting. Expression of the somatostatin receptor subtype 2 (SSTR2), which mediates the anti-angiogenic effects of octreotide, was also analyzed. Formation of portosystemic collaterals (radioactive microspheres) and hemodynamic parameters were also measured. Results: Octreotide treatment during 4 days markedly and significantly decreased splanchnic neovascularization, VEGF expression by 63% and portal pressure by 15%, whereas portosystemic collateralization and splanchnic blood flow were not modified. After 1 week of octreotide injection, portal pressure was reduced by 20%, but inhibition of angiogenesis escaped from octreotide therapy, a phenomenon that could be related to the finding that expression of SSTR2 receptor decreased progressively (up to 78% reduction) during the evolution of portal hypertension. Conclusion: This study provides the first experimental evidence showing that octreotide may be an effective anti-angiogenic therapy early after induction of portal hypertension, but not in advanced stages most likely due to SSTR2 down-regulation during the progression of portal hypertension in rats. These findings shed light on new mechanisms of action of octreotide in portal hypertension.

Chronic indomethacin treatment enhances the portal-systemic collateral vascular response to vasopressin in bile-duct ligated rats

BACKGROUND

Liver cirrhosis is often accompanied by portal-systemic collateral formation with hemorrhage and encephalopathy. Prostacyclin participates in hyperdynamic circulation and vascular hyporeactiveness to vasoconstrictors in cirrhosis. It has been shown that arginine vasopressin (AVP) induces direct collateral vasoconstriction in portal hypertensive rats, which is potentiated by indomethacin preincubation. However, the influence of chronic indomethacin administration in cirrhosis remains unexplored.

METHODS

This study was performed on male Sprague-Dawley rats with liver cirrhosis induced by common bile duct ligation. They received subcutaneous indomethacin (5 mg/kg/day) or distilled water (control) injection from the 36th to 42nd day after operation. On the 43rd day, systemic and portal hemodynamics were evaluated and the following experiments were performed with an in situ collateral perfusion model: in the first series, concentration-response curves to AVP (10(-10) to 10(-7) M) were obtained; in the second series, flow-pressure curves were plotted (Krebs solution, 6-18 mL/min), where the slope represents an index of collateral vascular resistance (the higher the resistance, the smaller the amount of shunting vessels, that is, the lower the degree of shunting).

RESULTS

The mean arterial pressure and portal pressure were similar between indomethacin and control groups (p > 0.05). Indomethacin elevated the collateral perfusion pressure to AVP (3 x 10(-9), 10(-8) M, p < 0.05) but did not influence the slope of the flow-pressure curve (p > 0.05).

CONCLUSION

In bile duct-ligated cirrhotic rats, indomethacin improves the portal-systemic collateral vascular responsiveness to AVP without alleviating the severity of shunting.

Vasoactive factors and hemodynamic mechanisms in the pathophysiology of portal hypertension in cirrhosis

Portal hypertension is primarily caused by the increase in resistance to portal outflow and secondly by an increase in splanchnic blood flow, which worsens and maintains the increased portal pressure. Increased portal inflow plays a role in the hyperdynamic circulatory syndrome, a characteristic feature of portal hypertensive patients. Almost all the known vasoactive systems/substances are activated in portal hypertension, but most authors stress the pathogenetic role of endothelial factors, such as COX-derivatives, nitric oxide, carbon monoxide. Endothelial dysfunction is differentially involved in different vascular beds and consists in alteration in response both to vasodilators and to vasoconstrictors. Understanding the pathogenesis of portal hypertension could be of great utility in preventing and curing the complications of portal hypertension, such as esophageal varices, hepatic encephalopathy, ascites.

Reversal of portal hypertension and hyperdynamic splanchnic circulation by combined vascular endothelial growth factor and platelet-derived growth factor blockade in rats

Vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) pathways are crucial to angiogenesis, a process that contributes significantly to the pathogenesis of portal hypertension. This study determined the effects of inhibition of VEGF and/or PDGF signaling on hyperdynamic splanchnic circulation and portosystemic collateralization in rats with completely established portal hypertension, thus mimicking the situation in patients. Portal vein-ligated rats were treated with rapamycin (VEGF signaling inhibitor), Gleevec (PDGF signaling inhibitor), or both simultaneously when portal hypertension was already fully developed. Hemodynamic studies were performed by transit-time flowmetry. The extent of portosystemic collaterals was measured by radioactive microspheres. The expression of angiogenesis mediators was determined by Western blotting and immunohistochemistry. Combined inhibition of VEGF and PDGF signaling significantly reduced splanchnic neovascularization (i.e., CD31 and VEGFR-2 expression) and pericyte coverage of neovessels (that is, alpha-smooth muscle actin and PDGFR-beta expression) and translated into hemodynamic effects as marked as a 40% decrease in portal pressure, a 30% decrease in superior mesenteric artery blood flow, and a 63% increase in superior mesenteric artery resistance, yielding a significant reversal of the hemodynamic changes provoked by portal hypertension in rats. Portosystemic collateralization was reduced as well.

CONCLUSIONS

Our results provide new insights into how angiogenesis regulates portal hypertension by demonstrating that the maintenance of increased portal pressure, hyperkinetic circulation, splanchnic neovascularization, and portosystemic collateralization is regulated by VEGF and PDGF in portal hypertensive rats. Importantly, these findings also suggest that an extended antiangiogenic strategy (that is, targeting VEGF/endothelium and PDGF/pericytes) may be a novel approach to the treatment of portal hypertension.

Evidence against a role for NADPH oxidase modulating hepatic vascular tone in cirrhosis

BACKGROUND & AIMS

Increased hepatic vascular resistance in cirrhosis is in part due to reduced nitric oxide (NO) bioavailability. This is related to insufficient NO synthesis from endothelial nitric oxide synthase and to enhanced NO scavenging by superoxide radicals (O(2)(-)). Nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase is an important source of O(2)(-) that increases vascular tone in different cardiovascular disorders. Thus, our aims were to study the molecular and biochemical state of NADPH-oxidase in cirrhotic livers and to investigate its possible role in modulating hepatic vascular tone in cirrhosis.

METHODS

NADPH-oxidase expression and enzymatic activity were determined in control (n = 8) and CCl(4)-cirrhotic (n = 8) rat livers. Additional control (n = 6) and CCl(4)-cirrhotic (n = 10) rats were treated with apocynin (a selective NADPH-oxidase inhibitor) or its vehicle. Mean arterial pressure, portal pressure, and superior mesenteric arterial blood flow were measured in vivo. Moreover, hepatic endothelial function was evaluated in isolated and perfused rat livers by dose-response curves to acetylcholine. In addition, in 6 control and 6 cirrhotic human livers NADPH-oxidase activity and expression were evaluated.

RESULTS

Rat cirrhotic livers had no increased NADPH-oxidase protein expression or activity in relation to control livers. NADPH-oxidase inhibition did not modify splanchnic or systemic hemodynamics in control or cirrhotic rats and did not improve the impaired endothelial-dependent vasodilatory response to acetylcholine of cirrhotic livers. Human cirrhotic livers also did not exhibit increased NADPH-oxidase expression or activity.

CONCLUSIONS

Our study shows that NADPH-oxidase activity is decreased in the cirrhotic livers and therefore cannot explain increased hepatic O(2)(-), endothelial dysfunction, and increased vascular tone in cirrhotic livers.

Nitroflurbiprofen, a nitric oxide-releasing cyclooxygenase inhibitor, improves cirrhotic portal hypertension in rats

BACKGROUND & AIMS

We studied whether administration of nitroflurbiprofen (HCT-1026), a cyclooxygenase inhibitor with nitric oxide (NO)-donating properties, modulates the increased intrahepatic vascular tone in portal hypertensive cirrhotic rats.

METHODS

In vivo hemodynamic measurements (n = 8/condition) and evaluation of the increased intrahepatic resistance by in situ perfusion (n = 5/condition) were performed in rats with thioacetamide-induced cirrhosis that received either nitroflurbiprofen (45 mg/kg), flurbiprofen (30 mg/kg, equimolar concentration to nitroflurbiprofen), or vehicle by intraperitoneal injection 24 hours and 1 hour prior to the measurements. Additionally, we evaluated the effect of acute administration of both drugs (250 micromol/L) on the intrahepatic vascular tone in the in situ perfused cirrhotic rat liver (endothelial dysfunction and hyperresponsiveness to methoxamine) and on hepatic stellate cell contraction in vitro. Typical systemic adverse effects of nonsteroidal anti-inflammatory drugs, such as gastrointestinal ulceration, renal insufficiency, and hepatotoxicity, were actively explored.

RESULTS

In vivo, nitroflurbiprofen and flurbiprofen equally decreased portal pressure (8 +/- 0.8 and 8.4 +/- 0.1 mm Hg, respectively, vs 11.8 +/- 0.6 mm Hg) and reduced the total intrahepatic vascular resistance. Systemic hypotension was not aggravated in the different treatment groups (P = .291). In the perfused cirrhotic liver, both drugs improved endothelial dysfunction and hyperresponsiveness. This was associated with a decreased hepatic thromboxane A(2)-production and an increased intrahepatic nitrate/nitrite level. In vitro, nitroflurbiprofen, more than flurbiprofen, decreased hepatic stellate cells contraction. Flurbiprofen-treated rats showed severe gastrointestinal ulcerations (bleeding in 3/8 rats) and nefrotoxicity, which was not observed in nitroflurbiprofen-treated cirrhotic rats.

CONCLUSIONS

Treatment with nitroflurbiprofen, an NO-releasing cyclooxygenase inhibitor, improves portal hypertension without major adverse effects in thioacetamide-induced cirrhotic rats by attenuating intrahepatic vascular resistance, endothelial dysfunction, and hepatic hyperreactivity to vasoconstrictors.

Chronic cyclooxygenase blockade enhances the vasopressin responsiveness in collaterals of portal hypertensive rats

OBJECTIVE

Collateral vascular responsiveness to vasoconstrictors may be crucial in the management of acute variceal bleeding. In an in situ perfusion model, arginine vasopressin (AVP) has been shown to cause a direct vasoconstrictive effect on portal-systemic collaterals and this effect is enhanced by preincubation of indomethacin (INDO). The purpose of this study was to investigate the effects of chronic INDO administration on the portal-systemic collateral responsiveness to AVP and the degree of portal-systemic shunting in portal hypertensive rats.

MATERIAL AND METHODS

Rats with partial portal vein ligation randomly received daily subcutaneous injections with INDO (5 mg/kg) or distilled water (control group) 2 days prior to until 7 days after ligation. Systemic and portal hemodynamics was evaluated on the 8th day. Using an in situ collateral perfusion model, AVP (10(-10)-10(-7) M) at a constant flow rate (20 ml/min) was applied. In another series, Krebs solution with different flow rates (5-30 ml/min) was used to obtain flow-pressure curves: the slopes represent collateral vascular resistances--the higher resistances indicate fewer collaterals.

RESULTS

Mean arterial pressure and portal pressure were not significantly different between the INDO-treated group and the control group (p>0.05). In the first series of experiments, INDO treatment increased the collateral perfusion pressure to AVP at 10(-8) M, 3x10(-8) M, and 10(-7) M (p<0.05). In the second series, INDO did not change collateral vascular resistance, which suggests that the degree of shunting was not altered.

CONCLUSIONS

Chronic INDO treatment improves the collateral vascular responsiveness to AVP without ameliorating portal-systemic shunting in portal hypertensive rats.

Lack of detrimental or therapeutic effects of cyclooxygenase inhibition in bile duct-ligated rats with hepatic encephalopathy

BACKGROUND

The pathogenetic mechanisms of hepatic encephalopathy (HE) are not fully understood. Cerebral blood flow regulated by cyclooxygenase (COX) may be involved in the development of HE. There are no comprehensive data concerning the effects of COX inhibition on HE in chronic liver disease.

METHODS

Male Sprague-Dawley rats weighing 240-270 g at the time of surgery were selected for experiments. Secondary biliary cirrhosis was induced by bile duct ligation (BDL). Those rats were then divided into two groups to receive i.p. injection of indomethacin (5 mg/kg per day) or distilled water for 7 days from day 36 to day 42 after BDL. The control group consisted of rats receiving a sham operation. Severity of encephalopathy was assessed by counts of motor activity. Plasma levels of tumor necrosis factor (TNF)-alpha and 6-keto-prostaglandin F(1alpha) (6-keto-PGF(1alpha)), and liver biochemistry tests were determined after treatment.

RESULTS

The motor activity in both groups of BDL rats were significantly lower than that of the control group (P < 0.001). As compared with the BDL rats treated with distilled water, BDL rats treated with indomethacin had significant lower levels of 6-keto-PGF(1alpha), but the motor activity, TNF-alpha levels and serum biochemistry tests were not significantly different between both BDL groups.

CONCLUSIONS

Chronic indomethacin administration did not have significantly detrimental or therapeutic effects on the severity of encephalopathy in BDL rats.

Heme oxygenase attenuates oxidative stress and inflammation, and increases VEGF expression in portal hypertensive rats

BACKGROUND/AIMS

The pathophysiological significance of heme oxygenase-1 up-regulation in portal hypertension is not completely understood. In this study, we determined the role of heme oxygenase-1 on oxidative stress, inflammation, angiogenesis, and splanchnic hemodynamics in rats with portal hypertension induced by partial portal vein ligation.

METHODS

Rats were treated with the heme oxygenase inhibitor SnMP or vehicle for 7 days. Then, oxidative stress was quantified by superoxide anion production, and inflammatory response was assessed by immunofluorescence. Expression of angiogenesis mediators was determined by western blotting, and the extent of portosystemic collaterals by radioactive microspheres. Hemodynamic studies were performed by flowmetry.

RESULTS

Oxidative stress was significantly increased in the mesentery of portal hypertensive rats, as compared with sham-operated controls. In portal hypertensive rats, chronic heme oxygenase inhibition (1) potentiated oxidative stress and inflammation, (2) significantly decreased VEGF expression, without modifying the extent of collaterals or the splanchnic neovascularization, and (3) significantly decreased superior mesenteric artery blood flow and portal pressure.

CONCLUSIONS

This study demonstrates that heme oxygenase plays an important (beneficial) role attenuating oxidative stress and inflammation, but it also plays a detrimental role in stimulating VEGF production, and contributing to the development of hyperdynamic splanchnic circulation in rats with portal hypertension.

A stable model of cirrhotic portal hypertension in the rat: thioacetamide revisited

BACKGROUND

Cirrhotic animal models are vital to investigate complications of chronic liver disease. We chronologically characterized the effect of thioacetamide, administrated orally and adapted weekly to weight changes, focusing on the optimal moment to obtain all typical features of portal hypertension and cirrhosis.

MATERIALS AND METHODS

Male Wistar rats, 200-250 g, were intoxicated for 6, 12 or 18 weeks (n = 8 per group), respectively, and compared with age-matched controls (n = 4 per group). An in-situ perfusion model was used to evaluate intrahepatic resistance and endothelial function. Splanchnic blood flow and portosystemic shunting were assessed by a perivascular flow probe.

RESULTS

Rats intoxicated for 6 or 12 weeks had no mortality and histologically showed hepatitis and advanced fibrosis, respectively. At 18 weeks, mortality was 16% (on a total of 56 animals) and only at that moment all animals showed homogenous macronodular cirrhosis with signs of high-grade hepatocellular dysplasia. Portal hypertension was present at 12 weeks (11 +/- 0.4 vs. 5.9 +/- 0.4 mmHg, P < 0.001), but was not associated with the hyperdynamic state until 18 weeks (12.1 +/- 0.8 vs. 5.6 +/- 0.5 mmHg, P < 0.001). At this latter time-point, we also observed increased intrahepatic resistance associated with endothelial dysfunction, hyperresponsiveness to vasoconstrictors, splanchnic hyperaemia and portosystemic shunting. These alterations were associated with increased systemic levels of nitrate/nitrite and thromboxane A(2).

CONCLUSION

Thioacetamide, adapted to weekly weight changes, leads to a homogenous, reproducible model of cirrhosis in the rat in 18 weeks, which is associated with all the typical characteristics of portal hypertension, including endothelial dysfunction.

Portal hypertension: from pathophysiology to clinical practice

Portal hypertension (PHT) is responsible for the more severe and often lethal complications of cirrhosis such as bleeding oesophageal varices, ascites, renal dysfunction and hepatic encephalopathy. Because of the combined impact of these complications, PHT remains the most important cause of morbidity and mortality in patients with cirrhosis. Over the years, it has become clear that a decrease in portal pressure is not only protective against the risk of variceal (re)bleeding but is also associated with a lower long-term risk of developing complications and an improved long-term survival. A milestone in therapy was the introduction of non-selective beta-blockers for the prevention of bleeding and rebleeding of gastro-esophageal varices. However, in practice, less than half the patients under beta-blockade are protected from these risks, supporting the overall demand for innovation and expansion of our therapeutic armamentarium. Recent advances in the knowledge of the pathophysiology of cirrhotic PHT have directed future therapy towards the increased intrahepatic vascular resistance, which, in part, is determined by an increased hepatic vascular tone. This increased vasculogenic component provides the rationale for the potential use of therapies aimed at increasing intrahepatic vasorelaxing capacity via gene therapy, liver-selective nitric oxide donors and statines on the one hand, and at antagonizing excessive intrahepatic vasoconstrictor force through the use of endothelin antagonists, angiotensin blockers, alpha(1) adrenergic antagonists or combined alpha(1)- and non-selective beta-blockers or somatostatin analogues on the other. The focus of this review is to give an update on the pathophysiology of PHT in order to elucidate these potential novel strategies subsequently.

Inhibition of VEGF receptor-2 decreases the development of hyperdynamic splanchnic circulation and portal-systemic collateral vessels in portal hypertensive rats

BACKGROUND/AIMS

Portal hypertension is characterized by the development of a hyperdynamic splanchnic circulation. To determine whether this process is angiogenesis-dependent, we assessed the effects of SU5416, a specific inhibitor of VEGF receptor-2, in portal hypertensive rats.

METHODS

Rats with portal hypertension induced by partial portal vein ligation were treated with SU5416 or vehicle during 5 days. Then, hemodynamic studies were performed using radioactive microspheres. Protein expressions of CD31, VEGF receptor-2 and VEGF were also determined by Western blotting.

RESULTS

Treatment of portal hypertensive rats with SU5416 resulted in a significant and marked decrease (by 44%) in portal venous inflow, and increases in splanchnic arteriolar resistance (by 68%) and portal venous resistance (by 93%). In addition, SU5416 administration significantly inhibited the formation of portal-systemic collateral vessels (52% inhibition), as well as the splanchnic CD31 and VEGF receptor-2 protein expressions in portal hypertensive rats, compared with those receiving vehicle.

CONCLUSIONS

This study demonstrates that the development of hyperdynamic splanchnic circulation and the formation of portal-systemic collateral vessels in portal hypertensive rats are angiogenesis-dependent processes that can be markedly inhibited by blockade of the VEGF signaling pathway. Therefore, modulation of angiogenesis may represent a potential target in the treatment of portal hypertension.

Role of heme oxygenase/carbon monoxide pathway on the vascular response to noradrenaline in portal hypertensive rats

1. Portal hypertension (PH), a major syndrome in cirrhosis, producing hyperdynamic splanchnic circulation and hyperaemia. In order to elucidate the contribution of heme oxygenase to the vascular hyporeactivity, we assessed the activity of heme oxygenase-1 (HO-1), measured the in vivo pressure response to noradrenaline (NA) and investigated the effects of blocking the carbon monoxide (CO) and nitric oxide (NO) pathways in a prehepatic model of PH in rats. 2. Portal hypertension was induced by partial portal vein ligation (PPVL). Noradrenaline was injected intravenously. Liver, spleen and mesentery homogenates were prepared for measurement of HO-1 activity and expression. Four groups of rats were used: (i) a sham group; (ii) a PPVL group; (iii) a sham group pretreated with Zn-protoporphyrin IX (ZnPPIX); and (iv) a PPVL group pretreated with ZnPPIX. Each group was studied before and after treatment with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). 3. For basal pressures and the pressure response to NA, inhibition of CO and NO pathways by ZnPPIX and L-NAME, respectively, produced an increase in mean arterial pressure (MAP) in sham-operated and in PH rats. Similarly, when both inhibitors were used together in either sham or PPVL rats, a greater increase in MAP was observed. 4. These results, together with the increased HO-1 activity and expression only in the PH group, have led us to suggest that the heme oxygenase/CO pathway is involved in the vascular response to NA in PH rats.

Effects of vasopressin on portal-systemic collaterals of cirrhotic rats

OBJECTIVE

Arginine vasopressin (AVP) exerts a constrictive effect on the portal-systemic collaterals of non-cirrhotic portal hypertensive rats, but its effect on cirrhotic rats is unknown. The aim of this study was to investigate the response of AVP and the modulatory roles of nitric oxide and prostaglandin on collaterals of common bile duct-ligated (BDL) cirrhotic rats.

MATERIAL AND METHODS

The collateral vascular responsiveness to graded concentrations of AVP (10(-10) - 3 x 10(-7) M) was tested by an in situ collateral perfusion system pretreated with Nomega-nitro-L-arginine (L-NNA, 100 microM), indomethacin (INDO, 10 microM), or both. The collateral responses to AVP with the pretreatment of a vasopressin V1 receptor antagonist d(CH2)5Tyr(Me) arginine vasopressin or a V2 receptor agonist 1-desamino-8-D-arginine vasopressin (DDAVP, 10(-10) - 3 x 10(-7) M) were also evaluated.

RESULTS

The perfusion pressure of collaterals was significantly increased by AVP, and this effect was inhibited by the addition of the V1 receptor antagonist. DDAVP had no effect on the collaterals. Incubation with L-NNA or L-NNA plus INDO, but not INDO alone, significantly potentiated the constrictive effects of AVP. The constrictive effect of AVP in the combination group was similar to that in the L-NNA alone group.

CONCLUSIONS

The results show that AVP produces a direct vasoconstrictive effect on the portal-systemic collaterals of BDL cirrhotic rats. The constrictive effect of AVP is mediated by the vasopressin V1, instead of V2, receptors. Nitric oxide may play a more important role than prostaglandin in modulating the collateral vascular response to AVP in BDL cirrhotic rats.

Effects of endothelin-1 on portal-systemic collaterals of common bile duct-ligated cirrhotic rats

BACKGROUND/AIMS

Endothelin-1 (ET-1) may induce intrahepatic vasoconstriction and consequently increase portal pressure. Endothelin-1 has been shown to exert a direct vasoconstrictive effect on the collateral vessels in partially portal vein-ligated rats with a high degree of portal-systemic shunting. This study investigated the collateral vascular responses to ET-1, the receptors in mediation and the regulation of ET-1 action by nitric oxide and prostaglandin in cirrhotic rats with a relatively low degree of portal-systemic shunting.

METHODS

The portal-systemic collaterals of common bile duct-ligated (BDL) cirrhotic rats were tested by in situ perfusion. The concentration-response curves of collaterals to graded concentrations of ET-1 (10(-10)-10(-7) m) with or without BQ-123 (ET(A) receptor antagonist, 2 x 10(-6) m), BQ-788 (ET(B) receptor antagonist, 10(-7) m) or both were recorded. In addition, the collateral responses to ET-1 with preincubation of N(omega)-nitro-L-arginine (NNA, 10(-4) M), indomethacin (INDO, 10(-5) M) or in combination were assessed.

RESULTS

Endothelin-1 significantly increased the perfusion pressures of portal-systemic collaterals. The ET-1-induced constrictive effects were inhibited by BQ-123 or BQ-123 plus BQ-788 but not by BQ-788 alone. The inhibitory effect was greater in the combination group. Pretreatment of NNA or NNA plus INDO equivalently enhanced the response of ET-1 while pretreatment of INDO alone exerted no effect.

CONCLUSION

Endothelin-1 has a direct vasoconstrictive effect on the collaterals of BDL cirrhotic rats, mainly mediated by ET(A) receptor. Endogenous nitric oxide may play an important role in modulating the effects of ET-1 in the portal-systemic collaterals of BDL cirrhotic rats.

[Role of cyclooxygenase-2 in the pathogenesis of chronic liver diseases]

Cyclooxygenase (COX) is a crucial enzyme in the biosynthesis of prostaglandins. There are two COX isoforms: COX-1 is constitutively expressed in a number of cell types and is involved in the homeostatic functions of prostaglandins, whereas COX-2 is inducible by a variety of proinflammatory stimuli, such as cytokines and lipopolysaccharide. In the liver, COX-2 and prostaglandins production has been implicated in hepatic regeneration, liver matrix remodeling and portal hypertension. In animal models of alcoholic-induced liver disease has been demonstrated its relation with necro-inflammatory activity. In viral hepatitis, hepatocellular COX-2 expression was observed and associated with fibrosis progression. More interestingly it has been the demonstration of COX-2 role in the development of hepatocellular carcinoma and cholangiocarcinoma, such in experimental models as in human samples. It has also been demonstrated that COX-2 was implicated in carcinogenesis through apoptosis inhibition and increased proliferation of human tumor cells. Experimental evidences show that selective pharmacologic inhibition of COX-2 could be useful in chemoprevention of primary liver tumors.

Anti-VEGF receptor-2 monoclonal antibody prevents portal-systemic collateral vessel formation in portal hypertensive mice

BACKGROUND & AIMS

Portal hypertension is a frequent syndrome that develops in patients with chronic liver diseases, which are one of the most common causes of death in adults worldwide. The most serious clinical consequences of portal hypertension are related to the development of portal-systemic collateral vessels. Those include hepatic encephalopathy and massive bleeding from ruptured gastroesophageal varices. The high relevance of these collateral vessels prompted us to investigate the mechanism underlying its formation in a murine model of portal hypertension.

METHODS

To determine whether the development of portal-systemic collateral vessels in portal hypertension is a vascular endothelial growth factor (VEGF)-dependent angiogenic process, we assessed the effects of a monoclonal antibody against VEGF receptor-2 on the formation of these collateral vessels in mice with portal hypertension induced by partial portal vein ligation. We also studied the effects of a selective and specific inhibitor of VEGF receptor-2 autophosphorylation in partial portal vein-ligated rats.

RESULTS

A significant and marked inhibition in the formation of portal-systemic collateral vessels was observed in both partial portal vein-ligated mice and rats treated with anti-VEGF receptor-2 monoclonal antibodies or with the inhibitor of VEGF receptor-2 autophosphorylation, respectively, compared with animals receiving control solutions.

CONCLUSIONS

Our present study shows that formation of collateral vessels is an angiogenesis-dependent process that can be markedly inhibited by blockade of the VEGF signaling pathway. These findings will make angiogenesis a focal point of research in portal hypertension and may lead to novel approaches for therapy of patients with chronic liver diseases.

Overexpression of inducible nitric oxide synthase in gastric mucosa of rats with portal hypertension: correlation with gastric mucosal damage

BACKGROUND

An increased biosynthesis of nitric oxide (NO) has been implicated in the hyperdynamic circulation and development of collaterals of portal hypertension (PHT) because of its potent vasodilatory effects. NO is synthesized from L-arginine by three different isozymes of nitric oxide synthase (nNOS, iNOS and eNOS). Thus, the expression of inducible NOS (iNOS) might account for NO overproduction in PHT. However, in previous investigations, the role of iNOS in the pathogenesis of PHT gastropathy remained controversial. Our current study was in both molecular and protein levels to determine whether the expression of iNOS is responsible for PHT gastropathy.

MATERIALS AND METHODS

PHT was induced experimentally by partial ligation of the portal vein. Fourteen days after partial ligation of the portal vein, the rats were randomly assigned to receive either vehicle or L-NAME (NOS inhibitor) at doses of 5 mg/kg/day, 10 mg/kg/day, or 25 mg/kg/day by gastric lavage twice a day for 1 week. Sham operated rats served as controls. Northern hybridization and in situ hybridization are used to compare the expression of gastric mucosa iNOS mRNA in the PHT rats and the controls. NO was measured by the Griess method after reduction of nitrate to nitrite with nitrate reductase. Immunohistochemical staining was carried out to detect the iNOS protein. In addition, the severity of gross gastric mucosal lesions was evaluated macroscopically by a gross ulcer index.

RESULTS

The iNOS expression at both mRNA and protein was prominently increased in PHT rats, accompanied with the enhanced NO production. The gastric mucosa iNOS mRNA and serum NO levels were significantly decreased after L-NAME administration (P < 0.05). However, the markedly reduced gastric mucosal damage in PHT rats was observed only at high does of L-NAME (25 mg/kg/day) administration.

CONCLUSION

PHT triggers overexpression of iNOS mRNA and proteins in rat gastric mucosa, but that this alone does not account for PHT gastropathy.

Eicosanoids in cirrhosis and portal hypertension

In the last decade, the knowledge of the pathogenesis of portal hypertension and cirrhosis has increased dramatically. In portal hypertension, almost all the known vasoactive systems/substances are activated or increased and the most recent studies have stressed the importance of the endothelial factors, in particular, prostaglandins. Prostaglandins are formed following the oxygenation of arachidonic acid by the cyclooxygenase (Cox) pathway. An important consideration in portal hypertension and cirrhosis in the periphery is the altered hemodynamic profile and its contributory role in controlling endothelial release of these vasoactive substances. Prostaglandins are released from the endothelium in response to both humoral and mechanical stimuli and can profoundly affect both intrahepatic and peripheral vascular resistance. Within the liver, intrahepatic resistance is altered due to a diminution in sinusoidal responsiveness to vasodilators and an increase in prostanoid vasoconstrictor responsiveness. This review will examine the contributory role of both hormonal and/or hemodynamic force-induced changes in prostaglandin production and signaling in cirrhosis and portal hypertension and the consequence of these changes on the structural and functional response of both the vasculature and the liver.

The role of nitric oxide synthase isoforms in extrahepatic portal hypertension: studies in gene-knockout mice

BACKGROUND & AIMS

Considerable debate exists concerning which isoform of nitric oxide synthase (NOS) is responsible for the increased production of NO in PHT. We used the portal vein ligation model of PHT in wild-type and eNOS- or iNOS-knockout mice to definitively determine the contribution of these isoforms in the development of PHT.

METHODS

The portal vein of wild-type mice, or those with targeted mutations in the nos2 gene (iNOS) or the nos3 gene (eNOS), was ligated and portal venous pressure (Ppv), abdominal aortic blood flow (Qao), and portosystemic shunt determined 2 weeks later.

RESULTS

In wild-type mice, as compared with sham-operated controls, portal vein ligation (PVL) resulted in a time-dependent increase in Ppv (7.72 +/- 0.37 vs 17.57 +/- 0.51 cmH(2)O, at 14 days) concomitant with a significant increase in Qao (0.12 +/- 0.003 vs 0.227 +/- 0.005 mL/min/g) and portosystemic shunt (0.47% +/- 0.01% vs 84.13% +/- 0.09% shunt). Likewise, PVL in iNOS-deficient mice resulted in similar increases in Ppv, Qao, and shunt development. In contrast, after PVL in eNOS-deficient animals, there was no significant change in Ppv (7.52 +/- 0.22 vs 8.07 +/- 0.4 cmH(2)0) or Qao (0.111 +/- 0.01 vs 0.14 +/-.023 mL/min/g). However, eNOS (-/-) mice did develop a substantial portosystemic shunt (0.33% +/- 0.005% vs 84.53% +/- 0.19% shunt), comparable to that seen in wild-type animals after PVL.

CONCLUSIONS

These data support a key role for eNOS, rather than iNOS, in the pathogenesis of PHT.

Endothelial COX-1 and -2 differentially affect reactivity of MVB in portal hypertensive rats

Expression of constitutive and inducible cyclooxygenase (COX-1 and COX-2, respectively) and the role of prostanoids were investigated in the aorta and mesenteric vascular bed (MVB) from the portal vein-ligated rat (PVL) as a model of portal hypertension. Functional experiments were carried out in MVB from PVL and sham-operated rats in the absence or presence of the nonselective COX inhibitor indomethacin or the selective inhibitors of COX-1 (SC-560) or COX-2 (NS-398). Western blots of COX-1 and COX-2 proteins were evaluated in aorta and MVB, and PGI(2) production by enzyme immunoassay of 6-keto-PGF(1alpha) was evaluated in the aorta. In the presence of functional endothelium, decreased contraction to norepinephrine (NE) and increased vasodilatation to ACh were observed in MVB from PVL. Exposure of MVB to indomethacin, SC-560, or NS-398 reversed the hyporeactivity to NE and the increased endothelial vasodilatation to ACh in PVL, with NS-398 being more potent than the other two inhibitors. Upregulation of COX-1 and COX-2 expressions was detected in aorta and MVB from PVL portal hypertensive rats, and increased production of 6-keto-PGF(1alpha) was observed in aorta from portal hypertensive rats. These results suggest that generation of endothelial vasodilator prostanoids, from COX-1 and COX-2 isoforms, accounts for the increased mesenteric blood flow in portal hypertension.

Total effective vascular compliance in patients with cirrhosis. Effects of propranolol

BACKGROUND

Total effective vascular compliance (TEVC), may be increased in cirrhosis. However, its significance is unclear.

AIMS

To investigate TEVC in patients with cirrhosis, and the effects of propranolol.

METHODS

Seven patients without liver disease and 44 cirrhotic patients were studied before and after double-blind administration of propranolol (n=33) or placebo (n=11).

MEASUREMENTS

TEVC (right atrial pressure response to rapid central volume expansion), hepatic venous pressure gradient (HVPG) and systemic hemodynamics.

RESULTS

TEVC (ml x mmHg(-1) x kg(-1)) was increased in cirrhotics (1.67 +/- 0.66 versus 1.33 +/- 0.32 in controls; P<0.05). TEVC was not modified by placebo, but was markedly reduced by propranolol (from 1.74 +/- 0.75 to 1.33 +/- 0.56; P<0.01). Propranolol decreased HVPG >10% in 20 patients ('responders': -20 +/- 9%) but <10% in 13 'non-responders'. TEVC was normalized by propranolol in HVPG 'responders' (from 1.76 +/- 0.88 to 1.21 +/- 0.51; P<0.01), but not in 'non-responders' (1.69 +/- 0.48 to 1.52 +/- 0.59; NS). Reduction of TEVC in responders was accompanied by increased free hepatic vein pressure (+21 +/- 20%, P=0.05; approximately 60% of the fall in HVPG), which was not observed in non-responders (+3 +/- 11%, NS).

CONCLUSIONS

TEVC is increased in cirrhosis. This abnormality is corrected by propranolol in patients exhibiting a >10% fall in HVPG, suggesting that changes in vascular compliance may influence the portal pressure response to propranolol.

Pathogenesis of portal hypertensive gastropathy: a clinical and experimental review

Portal hypertensive gastropathy (PHG) is recognized as a clinical entity in portal hypertension, but the pathogenesis of PHG is still unclear. Therefore, we reviewed the current state of knowledge concerning the portal hypertensive gastric mucosa and hypothesized the pathogenesis of PHG. Elevated portal pressure can induce changes of local hemodynamics, thus causing congestion in the upper stomach and gastric tissue damage. These changes may then activate cytokines and growth factors, such as tumor necrosis factor alpha, which are substances that activate endothelial constitutive nitric oxide synthase and endothelin 1 in the portal hypertensive gastric mucosa. Overexpressed nitric oxide synthase produces an excess of nitric oxide, which induces hyperdynamic circulation and peroxynitrite overproduction. The overproduction of peroxynitrite, together with endothelin overproduction may cause an increased susceptibility of gastric mucosa to damage. When combined with the characteristics of impaired mucosal defense and healing, these factors may together produce PHG in patients with portal hypertension.

Prostaglandin H synthase and vascular function

Prostaglandin H synthase (PGHS) is a rate-limiting enzyme in the production of prostaglandins and thromboxane, which are important regulators of vascular function. Under normal physiological conditions, PGHS-dependent vasodilators (such as prostacyclin) modulate vascular tone. However, PGHS-dependent vasoconstriction (mediated by thromboxane and/or its immediate precursor, PGH(2)) predominates in some vascular pathologies (eg, systemic hypertension, diabetes, cerebral ischemia, and aging). This review will discuss the role of PGHS-dependent modulation of vascular function in a number of vascular beds (systemic, pulmonary, cerebral, and uterine) with an emphasis on vascular pathophysiology. Moreover, the specific contributions of the different isoforms (PGHS-1 and PGHS-2) are discussed. Understanding the role of PGHS in vascular function is of particular importance because they are the targets of the commonly used nonsteroidal antiinflammatory drugs (NSAIDs), which include aspirin and ibuprofen. Importantly, with the advent of specific PGHS-2 inhibitors for treatment of conditions such as chronic inflammatory disease, it is an opportune time to review the data regarding PGHS-dependent modulation of vascular function.

New method of cardiac output measurement using ultrasound velocity dilution in rats

The aim of this study was to validate a new technique for the measurement of cardiac output (CO) based on ultrasound and dilution (COUD) in anesthetized rats. A transit time ultrasound (TTU) probe was placed around the rat carotid artery, and ultrasound velocity dilution curves were generated on intravenous injections of saline. CO by COUD were calculated from the dilution curves for normal and portal hypertensive rats in which CO was known to be increased. COUD was compared with the radiolabeled microsphere method and with direct aortic TTU flowmetry for baseline CO and drug-induced CO variations. CO in direct aortic TTU flowmetry was the ascending aorta blood flow measured directly by TTU probe (normal use of TTU flowmetry). The reproducibility of COUD within the same animal was also determined under baseline conditions. COUD detected the known CO increase in portal hypertensive rats compared with normal rats. CO values by COUD were correlated with those provided by microsphere technique or direct aortic TTU flowmetry (adjusted r = 0.76, P < 10(-4) and r = 0.79, P < 0.05, respectively). Baseline CO values and terlipressin-induced CO variations were detected by COUD and the other techniques. Intra- and interobserver agreements for COUD were excellent (intraclass r = 0.99 and 0.98, respectively). COUD was reproducible at least 10 times in 20 min. COUD is an accurate and reproducible method providing low-cost, repetitive CO measurements without open-chest surgery. It can be used in rats as an alternative to the microsphere method and to direct aortic flowmetry.

Laboratory assessment of hepatic hemodynamics

Although the study of hepatic circulation is complicated by the dual blood supply and complex anatomy of the liver, many distinct methods are available to facilitate its study. Before embarking on an investigation of hepatic hemodynamics, the investigator must be familiar with the available methods and their applications. All methods have their own attributes and limitations. No one method is superior to the others, but, depending on the aspect of hepatic hemodynamics to be investigated, a particular methodology may yield distinct advantages.

Adaptive vasodilatory response after octreotide treatment

Despite the suppression of glucagon release, an adaptive response aimed at maintaining vasodilatation after octreotide treatment may exist in portal hypertension. The present study was undertaken to evaluate the possible interaction between endothelium and non-endothelium-derived vasodilators after 1-wk octreotide administration in cirrhotic rats. Rats were allocated to receive either vehicle or octreotide (30 or 100 microg/kg every 12 h subcutaneously). Hemodynamic values, plasma glucagon levels, endothelium-related vasodilatory activities, and aortic endothelial nitric oxide synthase (eNOS) expression were determined after treatment. Octreotide administration decreased plasma glucagon and increased serum 6-keto-PGF(1 alpha) and NOx levels without affecting the hemodynamic values. In cirrhotic rats receiving octreotide, there was a blunt response to either L-NAME or indomethacin administration alone, but this blunt pressor response disappeared after simultaneous administration of the two drugs. Additionally, an increased aortic eNOS expression was observed in cirrhotic rats receiving 1-wk octreotide. It is concluded that 1-wk octreotide treatment did not correct the hemodynamic derangement in cirrhotic rats. The enhanced endothelium-related vasodilatory activity was noted after octreotide treatment that overcame the octreotide-induced hemodynamic effects in portal hypertension.

Increased heme oxygenase activity in splanchnic organs from portal hypertensive rats: role in modulating mesenteric vascular reactivity

BACKGROUND/AIMS

We have recently demonstrated that heme oxygenase-1 is upregulated in splanchnic organs of portal hypertensive rats. In the present study, we assessed whether heme oxygenase enzymatic activity is increased in splanchnic organs of portal hypertensive rats, and the relative contribution of heme oxygenase and nitric oxide synthase to the vascular hyporeactivity in portal hypertension.

METHODS

Heme oxygenase activity was measured in splanchnic organs of portal hypertensive and sham-operated rats. The effects of heme oxygenase and nitric oxide synthase inhibition on pressure responses to potassium chloride and methoxamine were assessed in perfused mesenteric vascular beds of portal hypertensive and sham-operated rats.

RESULTS

Heme oxygenase activity was increased in the mesentery, intestine, liver, and spleen of portal hypertensive rats. The hyporeactivity to potassium chloride in portal hypertensive rats was overcome after simultaneous inhibition of both heme oxygenase and nitric oxide synthase, but only partially attenuated after nitric oxide synthase inhibition alone. The hyporeactivity to methoxamine was completely reversed after nitric oxide synthase blockade.

CONCLUSIONS

These results demonstrate that heme oxygenase activity is increased in splanchnic organs of portal hypertensive rats. They also suggest that heme oxygenase contributes to the hyporeactivity to potassium chloride, but not to methoxamine, in portal hypertensive rats.

Endothelial dysfunction in cirrhosis and portal hypertension

Portal hypertension (PHT) is a common clinical syndrome associated with chronic liver diseases; it is characterized by a pathological increase in portal pressure. Pharmacotherapy for PHT is aimed at reducing both intrahepatic vascular tone and elevated splanchnic blood flow. Due to the altered hemodynamic profile in PHT, dramatic changes in mechanical forces, both pressure and flow, may play a pivotal role in controlling endothelial and vascular smooth muscle cell signaling, structure, and function in cirrhotics. Nitric oxide, prostacyclin, endothelial-derived contracting factors, and endothelial-derived hyperpolarizing factor are powerful vasoactive substances released from the endothelium in response to both humoral and mechanical stimuli that can profoundly affect both the function and structure of the underlying vascular smooth muscle. This review will examine the contributory role of hormonal- and mechanical force-induced changes in endothelial function and signaling and the consequence of these changes on the structural and functional response of the underlying vascular smooth muscle. It will focus on the pivotal role of hormonal and mechanical force-induced endothelial release of vasoactive substances in dictating the reactivity of the underlying vascular smooth muscle, i.e., whether hyporeactive or hyperreactive, and will examine the extent to which these substances may exert a protective and/or detrimental influence on the structure of the underlying vascular smooth muscle in both a normal hemodynamic environment and following hemodynamic perturbations typical of PHT and cirrhosis. Finally, it will discuss the intracellular processes that regulate the release/expression of these vasoactive substances and that control the transformation of this normally protective cell to one that may promote the development of vasculopathy in PHT.