Three-day tetrahydrobiopterin therapy increases in vivo hepatic NOS activity and reduces portal pressure in CCl4 cirrhotic rats

BACKGROUND/AIMS

Tetrahydrobiopterin is an essential cofactor for NOS enzymes to synthesize NO. It has been suggested that reduced intrahepatic tetrahydrobiopterin decreases intrahepatic NO and contributes to increase hepatic vascular resistance and portal pressure in cirrhosis. The main aim of the study was to evaluate the effect of tetrahydrobiopterin supplementation in portal pressure in CCl4 cirrhotic rats.

METHODS

Cirrhotic rats received vehicle or tetrahydrobiopterin (10mg/kg/day i.p.) for 3 days. Hepatic and systemic hemodynamics and hepatic tetrahydrobiopterin, NOS activity and cGMP levels were measured. In addition, hepatic and systemic hemodynamics were evaluated in normal rats in which tetrahydrobiopterin deficiency was induced by administrating 2,4-diamino-6-hydroxy-pyrimidine (DAHP) for 8h.

RESULTS

In cirrhotic rats, tetrahydrobiopterin administration increased liver NOS activity and cGMP levels and markedly and significantly reduced portal pressure. Amelioration of portal hypertension was associated with a normalization of arterial pressure. In normal rats DAHP decreased hepatic tetrahydrobiopterin and NOS activity and increased hepatic vascular tone. These effects of DAHP administration were corrected by tetrahydrobiopterin supplementation.

CONCLUSIONS

The present study shows that tetrahydrobiopterin markedly reduces portal hypertension and improves systemic hemodynamics in cirrhotic rats. These data support the concept that tetrahydrobiopterin supplementation may represent a new therapeutic strategy for portal hypertension.

P-selectin mediates leukocyte rolling in concanavalin-A-induced hepatitis

Concanavalin-A (Con-A)-induced hepatitis is an experimental model of human autoimmune hepatitis characterized by leukocyte activation and infiltration of the liver. The aim of the present study was to evaluate the role of P-selectin on leukocyte-endothelial interactions within the hepatic microvasculature in response to Con-A.

METHODS

The study was performed in P-selectin-deficient mice and wild-type mice pretreated with anti-P-selectin blocking monoclonal antibody (mAb) or vehicle. After 2 h of Con-A (20 mg/kg i.v.) or PBS administration, leukocyte rolling and adhesion and the index of sinusoidal perfusion were evaluated using the intravital microscopy technique in the liver. Apoptosis was determined by flow cytometry analysis of caspase-3 activity assayed on freshly isolated hepatocytes.

RESULTS

Con-A induced a significant increase in leukocyte rolling, mainly located at the central venule (2.1+/-0.4 vs 0.6+/-0.2 cells/min in wild-type mice treated with vehicle) and less marked, but still significant, in portal venules. This was associated with a significant increase in leukocyte adhesion. In P-selectin-deficient mice treated with Con-A, leukocyte rolling in portal and central venules was markedly reduced. However, leukocyte adhesion was only partially attenuated. A few sinusoids were perfused in wild-type mice treated with Con-A (26%). The percentage of perfused sinusoids was significantly higher in P-selectin-deficient mice (45%; P<0.05 vs wild-type). Similar effects were noted after the simultaneous injection of Con-A and anti-P-selecting mAb in wild-type mice. After Con-A treatment, apoptosis was markedly reduced in isolated hepatocytes of P-selectin-deficent mice (37+/-7% vs 75+/-5% in wild type).

CONCLUSION

The results of this intravital microscopy study clearly demonstrate that P-selectin is involved in the initial leukocyte rolling that leads to the development of Con-A-induced liver injury.

Assessment of portal hypertension in humans

Patients suspected of having portal hypertension (either by clinical history, physical examination, or previous diagnosis) should undergo ultrasonography and upper gastrointestinal endoscopy. Ultrasonography, preferably using the duplex technique, can disclose the patency of the portal venous system, the presence of signs of portal hypertension (splenomegaly, portocollateral vessels, repermeabilization of the umbilical vein, and so forth) and provide additional information about liver, biliary, or pancreatic diseases that may be the cause of portal hypertension. Endoscopy can assess the presence and size of gastroesophageal varices, the appearance of the variceal wall, and the presence and severity of portal hypertensive gastropathy. Patients showing a patent portal vein should have hepatic vein catheterization to evaluate the presence of presinusoidal, sinusoidal, or postsinusoidal portal hypertension. Patients in whom presinusoidal portal hypertension is suspected (those having esophageal varices with an HVPG below 10 mm Hg) should have liver biopsy and percutaneous transhepatic measurement of portal pressure. In sinusoidal portal hypertension, the results of endoscopy and HVPG measurement are decisive for the therapeutic management of the patients. The authors' results indicate that, before starting prophylactic therapy with beta-blockers, all patients should undergo at least an hepatic vein catheterization to assess HVPG; it would be preferable to have a variceal pressure measurement also. These measurements must be repeated 3 to 4 weeks after the final dose of therapy has been reached to assess the risk of variceal bleeding or rebleeding.

Ischemia/reperfusion induces an increase in the hepatic portal vasoconstrictive response to endothelin-1

Microvascular impairment observed during reperfusion following ischemia (IR) is a major determinant of the development of liver injury. Previous studies have shown that hyper-responsiveness to endothelin-1 (ET-1) contributes to microvascular dysfunction following a primarily inflammatory stress induced by endotoxin. The present study investigates whether a similar hypercontractile response to ET-1 occurs in the hepatic portal system of IR rats. Pentobarbital-anesthetized Sprague-Dawley rats underwent liver ischemia of the left and medial lobes for 60 min (IR: n = 8) or a sham operation (n = 8). Six hours after reperfusion, the liver was isolated and perfused through the portal vein. Baseline portal pressure (Pp), portal flow (Qp), and sinusoidal diameter (Ds) were measured before and 3 and 10 min after adding ET-1 (1 nM). In baseline, IR livers had a significantly greater Pp, portal resistance, and Ds than sham. ET-1 significantly increased Pp and portal resistance and significantly decreased Qp and Ds in IR and sham rats. However, these effects were significantly greater in IR. The results of the present study demonstrate that IR increases the porto-hepatic contractile response to ET-1, which may further sensitize the portal circulation to elevated ET-1 and may be a prominent contributor to the development of microvascular impairment following IR.

Portal hypertension in acute liver failure

Twenty five patients with acute liver failure were measured for hepatic venous pressure gradient as an index of portal pressure during the course of a transjugular liver biopsy. Hepatic venous pressure gradient ranged from 4 to 24.5 mm Hg with a mean of 12.8 (5.3) mm Hg (normal values less than 5 mm Hg). All patients but one had increased portal pressure gradient. Portal hypertension correlated with the degree of architectural distortion of the liver, as suggested by a direct correlation between hepatic venous pressure gradient and the area of reticulin collapse, evaluated by means of a morphometric analysis on Sirius red stained liver slides (r = 0.43, p less than 0.05). Hepatic venous pressure gradient was significantly higher in patients with ascites (15.1 (5) mm Hg, n = 15) or renal failure (14.4 (5.3) mm Hg, n = 16) than in those without (9.3 (3.4) mm Hg and 10.1 (4) mm Hg, respectively; p less than 0.05). Portal hypertension was associated with systemic vasodilation and a hyperkinetic circulatory state, with decreased arterial pressure, and peripheral resistance and increased cardiac output.

Enhancement of portal pressure reduction by the association of isosorbide-5-mononitrate to propranolol administration in patients with cirrhosis

This study investigated whether oral doses of isosorbide-5-mononitrate, a preferential venous dilator that decreases portal pressure, could enhance the effects of propranolol on portal hypertension. Taking part in the study were 28 patients with cirrhosis and portal hypertension. Twenty patients (group 1) had hemodynamic measurements in baseline conditions after beta-blockade by intravenous administration of propranolol and after receiving oral doses of isosorbide-5-mononitrate. The remaining eight patients (group 2) were given oral isosorbide-5-mononitrate while receiving chronic propranolol therapy. In group 1, propranolol significantly reduced portal pressure (estimated as the gradient between wedged and free hepatic venous pressures) from 21.5 +/- 3.9 to 18.6 +/- 4.2 mm Hg (-13.7%, p less than 0.001), azygos blood flow (-38%, p less than 0.001), hepatic blood flow (-12.8%, p less than 0.05), cardiac output (-24.5%, p less than 0.001) and heart rate (-18.4%, p less than 0.001) without significant changes in mean arterial pressure. Addition of oral isosorbide-5-mononitrate caused a further and marked fall in portal pressure (to 15.7 +/- 3.1 mm Hg, p less than 0.001), without additional changes in azygos blood flow but with significant additional reductions in hepatic blood flow (-15.5%, p less than 0.05), cardiac output (-11.5%, p less than 0.001) and mean arterial pressure (-22%, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Portal hypertension

Portal hypertension is a frequent syndrome characterized by a chronic increase in portal venous pressure and by the formation of portal-systemic collaterals. Its main consequence is massive bleeding from ruptured esophageal and gastric varices. Bleeding is promoted by increased portal and variceal pressure, and is favored by dilatation of the varices. The evaluation of the portal hypertensive patient should include the assessment of portal vein patency by ultrasonography, endoscopic evaluation of the presence, size, and extent of esophageal varices, and hemodynamic studies with measurements of portal pressure and of portal-collateral blood flow. The preferred techniques are hepatic vein catheterization and measurement of azygos blood flow. Endoscopic measurements of variceal pressure and estimations of portal blood velocity by the Doppler technique have recently been introduced, but are still research procedures. Acute variceal hemorrhage should be treated under intensive care. Specific therapy to arrest variceal bleeding includes balloon tamponade, vasopressin, somatostatin, sclerotherapy, and emergency surgery. Treatment of portal hypertension is aimed at preventing variceal hemorrhage and bleeding-related deaths. Pharmacologic prophylaxis is based on the use of drugs that cause a sustained reduction in portal pressure; most studies have used propranolol. Surgery and endoscopic sclerotherapy can also be used to prevent rebleeding.