Vascular smooth muscle cell signaling in cirrhosis and portal hypertension

Acute-on-chronic liver disease enhances phenylephrine-induced endothelial nitric oxide release in rat mesenteric resistance arteries through enhanced PKA, PI3K/AKT and cGMP signalling pathways

Acute-on-chronic liver disease is a clinical syndrome characterized by decompensated liver fibrosis, portal hypertension and splanchnic hyperdynamic circulation. We aimed to determine whether the alpha-1 agonist phenylephrine (Phe) facilitates endothelial nitric oxide (NO) release by mesenteric resistance arteries (MRA) in rats subjected to an experimental microsurgical obstructive liver cholestasis model (LC). Sham-operated (SO) and LC rats were maintained for eight postoperative weeks. Phe-induced vasoconstriction (in the presence/absence of the NO synthase –NOS- inhibitor L-NAME) and vasodilator response to NO donor DEA-NO were analysed. Phe-induced NO release was determined in the presence/absence of either H89 (protein kinase –PK- A inhibitor) or LY 294002 (PI3K inhibitor). PKA and PKG activities, alpha-1 adrenoceptor, endothelial NOS (eNOS), PI3K, AKT and soluble guanylate cyclase (sGC) subunit expressions, as well as eNOS and AKT phosphorylation, were determined. The results show that LC blunted Phe-induced vasoconstriction, and enhanced DEA-NO-induced vasodilation. L-NAME increased the Phe-induced contraction largely in LC animals. The Phe-induced NO release was greater in MRA from LC animals. Both H89 and LY 294002 reduced NO release in LC. Alpha-1 adrenoceptor, eNOS, PI3K and AKT expressions were unchanged, but sGC subunit expression, eNOS and AKT phosphorylation and the activities of PKA and PKG were higher in MRA from LC animals. In summary, these mechanisms may help maintaining splanchnic vasodilation and hypotension observed in decompensated LC.

Nitroglycerine effects on portal vein mechanics and oxidative stress in portal hypertension

AIM: Тo examine the effects of nitroglycerine on portal vein haemodynamics and oxidative stress in patients with portal hypertension.

METHODS: Thirty healthy controls and 39 patients with clinically verified portal hypertension and increased vascular resistance participated in the study. Liver diameters, portal diameters and portal flow velocities were recorded using color flow imaging/pulsed Doppler detection. Cross-section area, portal flow and index of vascular resistance were calculated. In collected blood samples, superoxide anion radical (O₂^-), hydrogen peroxide (H₂O₂), index of lipid peroxidation (measured as TBARS) and nitric oxide (NO) as a marker of endothelial response (measured as nitrite-NO₂^-) were determined. Time-dependent analysis was performed at basal state and in 10th and 15th min after nitroglycerine (sublingual 0.5 mg) administration.

RESULTS: Oxidative stress parameters changed significantly during the study. H₂O₂ decreased at the end of study, probably via O₂^- mediated disassembling in Haber Weiss and Fenton reaction; O₂^- increased significantly probably due to increased diameter and tension and decreased shear rate level. Consequently O₂^- and H₂O₂ degradation products, like hydroxyl radical, initiated lipid peroxidation. Increased blood flow was to some extent lower in patients than in controls due to double paradoxes, flow velocity decreased, shear rate decreased significantly indicating non Newtonian characteristics of portal blood flow.

CONCLUSION: This pilot study could be a starting point for further investigation and possible implementation of some antioxidants in the treatment of portal hypertension.

Hemodynamic changes in splanchnic blood vessels in portal hypertension

Portal hypertension (PHT) is associated with a hyperdynamic state characterized by a high cardiac output, increased total blood volume, and a decreased splanchnic vascular resistance. This splanchnic vasodilation is a result of an important increase in local and systemic vasodilators (nitric oxide, carbon monoxide, prostacyclin, endocannabinoids, and so on), the presence of a splanchnic vascular hyporesponsiveness toward vasoconstrictors, and the development of mesenteric angiogenesis. All these mechanisms will be discussed in this review. To decompress the portal circulation in PHT, portosystemic collaterals will develop. The presence of these portosystemic shunts are responsible for major complications of PHT, namely bleeding from gastrointestinal varices, encephalopathy, and sepsis. Until recently, it was accepted that the formation of collaterals was due to opening of preexisting vascular channels, however, recent data suggest also the role of vascular remodeling and angiogenesis. These points are also discussed in detail.

Vitamin E supplementation reverses renal altered vascular reactivity in chronic bile duct-ligated rats

An altered vascular reactivity is an important manifestation of the hemodynamic and renal dysfunction during liver cirrhosis. Oxidative stress-derived substances and nitric oxide (NO) have been shown to be involved in those alterations. In fact, both can affect vascular contractile function, directly or by influencing intracellular signaling pathways. Nevertheless, it is unknown whether oxidative stress contributes to the impaired systemic and renal vascular reactivity observed in cirrhosis. To test this, we evaluated the effect of vitamin E supplementation (5,000 IU/kg diet) on the vasoconstrictor and vasodilator responses of isolated perfused kidneys and aortic rings of rats with cirrhosis induced by bile duct ligation (BDL), and on the expression of renal and aortic phospho-extracellular regulated kinase 1/2 (p-ERK1/2). BDL induced a blunted renal vascular response to phenylephrine and ACh, while BDL aortic rings responded less to phenylephrine but normally to ACh. Cirrhotic rats had higher levels of oxidative stress-derived substances [measured as thiobarbituric acid-reactive substances (TBARS)] and NO (measured as urinary nitrite excretion) than controls. Vitamin E supplementation normalized the renal hyporesponse to phenylephrine and ACh in BDL, although failed to modify it in aortic rings. Furthermore, vitamin E decreased levels of TBARS, increased levels of NO, and normalized the increased kidney expression of p-ERK1/2 of the BDL rats. In conclusion, BDL rats showed a blunted vascular reactivity to phenylephrine and ACh, more pronounced in the kidney and reversed by vitamin E pretreatment, suggesting a role for oxidative stress in those abnormalities.

Molecular and structural basis of portal hypertension

Portal hypertension is a complication of diseases that obstruct portal blood flow, such as cirrhosis or portal vein thrombosis. In these diseases, increased vascular resistance to portal blood flow is the primary mechanism that increases portal pressure. In cirrhosis, increased intrahepatic vascular resistance is a result of both intrahepatic vasoconstriction and surrounding mechanical factors including collagen deposition and regenerative nodules. This article summarizes recent progress in the understanding of molecular mechanisms underlying the portal hypertension-associated arterial alterations in splanchnic systemic territories and those involved in the development of portal-systemic collateral circulation.

Functional status of beta-2-adrenoceptor in isolated membranes of mature erythrocytes from patients with cirrhosis and oesophageal varices

Propranolol is a widely used drug for prophylaxis of variceal bleeding in patients with cirrhosis, but not all patients show an adequate clinical response. This variability may be in relation to beta adrenoceptor activity, but no information is available in this setting. Thirty-nine patients with advanced cirrhosis and presence of oesophageal varices were sequentially included. We studied the function of beta-2-adrenoceptor in isolated membranes of mature erythrocytes obtained from patients by measuring cyclic AMP (cAMP) production before and after isoproterenol. Blood samples obtained from 11 healthy volunteers were used as control. Patients showed a six-fold increase in the mean basal cAMP production as compared to healthy volunteers. Isoproterenol produced a small, non-significantly and highly variable increase in the AC activity in patients compared with controls. cAMP values remain stable after three months of continuous treatment with oral beta-blockers in both groups. Patients without antecedent of variceal bleeding or with an active alcohol intake showed a significantly higher isoproterenol effect. In conclusion, beta-receptor function in human erythrocytes membranes is altered in patients with cirrhosis and oesophageal varices.

Impact of Nitric Oxide Synthase Inhibitor and Chloride Channel Antagonist on Mesenteric Vascular Conductance in Anesthetized Dahl Normotensive and Hypertensive Rats

The effects of nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) and chloride channel antagonist niflumic acid on vascular responsiveness to the effect of alpha1-adrenoceptor stimulation in the mesenteric bed of Dahl salt-resistant normotensive (SRN) and salt-sensitive hypertensive (SSH) rats were examined. Dahl salt-resistant and salt-sensitive rats were fed a high-salt diet (4% NaCl) for 7 weeks, and blood pressure, heart rate, and mesenteric blood flow were measured before and after treatment with L-NAME (0.3 mg/kg, IV) and/or niflumic acid (10 mg/kg, IV). Morphometry of the primary mesenteric blood vessel was also assessed. Administration of alpha1-adrenoceptor agonist cirazoline produced a dose-dependent increase in blood pressure, decrease in heart rate, mesenteric blood flow, and mesenteric vascular conductance in SRN and SSH rats. L-NAME significantly increased basal blood pressure and decreased basal mesenteric blood flow and vascular conductance in SRN but not in SSH rats. Niflumic acid attenuation of cirazoline-mediated decreases in mesenteric blood flow and vascular conductance was more pronounced in the SRN than SSH rats. This difference in the inhibitory actions of niflumic acid was absent following its concomitant administration with L-NAME. It seems that tonic release of nitric oxide modulates niflumic acid-sensitive chloride channels in vascular muscle. Blood vessels from SSH rats had significantly larger smooth muscle thickness and lumen diameter, but the ratio of the 2 were not different between the SRN and SSH. Our findings support the view that alterations in receptor-mediated signal transduction, rather than just changes in blood vessel architecture, are responsible for differences in behavior of blood vessels in salt-induced hypertensive rats.

Novel diacylglycerol kinase inhibitor selectively suppressed an U46619-induced enhancement of mouse portal vein contraction under high glucose conditions

1. Diacylglycerol kinase (DG kinase) is a key enzyme in vascular contraction; however, alterations of the regulatory mechanisms in vascular dysfunction are poorly understood. In this study, the effect of a novel DG kinase inhibitor, stemphone, on vascular contraction was investigated. 2. The conventional DG kinase inhibitor, 6-[2-(4-[(4-fluorophenyl)phenyl-methylene]-1-piperidinyl)ethyl]-7-methyl-5H-thiazolo [3,2-alpha] pyrimidine-5-one (R59022) (0.1-30 microm), inhibited thromboxane A(2) analogue 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha) (U46619)-induced sustained contractions in mouse aorta and porcine coronary artery in a dose-dependent manner. Treatment with stemphone did not affect contractions in these tissues. However, stemphone significantly inhibited (>0.3 microm) U46619-induced spontaneous phasic contraction in mouse portal vein. This inhibitory effect was not detected following R59022 treatment in portal vein. Therefore, stemphone demonstrated selectivity in terms of portal vein contraction. 3. Under high glucose (22.2 mm) conditions, U46619-induced contraction was enhanced in these three types of vascular tissue. Inhibitory effects of R59022 were attenuated under these conditions; however, effects of stemphone were observed. These results indicated that stemphone could inhibit portal vein contraction under high glucose conditions, for example, diabetes. These data suggested the possibility that DG kinase may be a target of hyperportal pressure. 4. Total mass of DG was enhanced under high glucose conditions. DG was derived from incorporated glucose via de novo synthesis in the absence of phospholipase C pathway mediation. This enhanced DG under high glucose conditions activated a calcium-independent protein kinase C (PKC). This PKC was associated with calcium-independent DG kinase activation. Treatment with stemphone also inhibited calcium-independent DG kinase. These signal transduction pathways were distinguishable from a DG-PKC pathway under normal glucose conditions. 5. The present investigation suggested that stemphone selectively inhibited overcontraction of portal vein induced by high glucose levels. This phenomenon was attributable to inhibition of calcium-independent DG kinase activation that occurred under high glucose conditions mediated by both DG synthesized from glucose and calcium-independent PKC activation.

Oxidative stress and vascular smooth muscle cell function in liver disease

Reactive oxygen species and reactive nitroxy species are now being recognized as regulatory molecules in signaling pathways influencing contractile and noncontractile functions of healthy vascular smooth muscle cells. In liver disease, oxidative stress is a systemic phenomenon, whose extent correlates with the severity of disease. A role for oxidative stress in the development of the hyperdynamic circulation in portal hypertension has been proposed. Evaluation of the limited available data indicates that it is premature to conclude that oxidative stress per se impacts on vascular smooth muscle cell function in liver disease.

Cirrhosis of the liver and receptor-mediated function in vascular smooth muscle

Altered regulation of receptors on the vascular smooth muscle has been proposed as one of the mechanisms that may account for the vascular abnormalities in patients with cirrhosis of the liver. Impaired contractility and down-regulation of contractile receptors have been demonstrated in cirrhotic patients and animal models, although interpretation of the literature is hampered by methodological variation and conflicting results. There is little evidence, however, that receptor down-regulation is the cause of contractile dysfunction in either patients or animal models. Receptor desensitisation may contribute to impaired contraction in human arteries, but further investigation is required to confirm this possibility.