5-lipoxygenase inhibition reduces intrahepatic vascular resistance of cirrhotic rat livers: a possible role of cysteinyl-leukotrienes

Involvement of platelet-activating factor and leukotrienes in anaphylactic segmental venoconstriction in ovalbumin sensitized guinea pig livers

The hepatic anaphylactic venoconstriction is partly involved in anaphylactic hypotension, and is characterized by significant post-sinusoidal constriction and liver congestion in guinea pigs. We determined what chemical mediators are involved in anaphylaxis-induced segmental venoconstriction and liver congestion in perfused livers isolated from ovalbumin sensitized guinea pigs. Livers were perfused portally and recirculatingly at constant flow with diluted blood. The sinusoidal pressure was measured by the double occlusion pressure (Pdo), and was used to determine the pre-sinusoidal (Rpre) and post-sinusoidal (Rpost) resistances. An antigen injection increased both the portal vein pressure and Pdo, resulting in 4.1- and 2.3-fold increases in Rpre and Rpost, respectively. Hepatic congestion was observed as reflected by liver weight gain. Pretreatment with TCV-309 (10microM, platelet-activating factor (PAF) receptor antagonist) or ONO-1078 (100microM, human cysteinyl-leukotriene (Cys-LT) receptor 1 antagonist), but not indomethacin (10microM, cyclooxygenase inhibitor), ketanserin (10microM, serotonin receptor antagonist), or diphenhydramine (100microM, histamine H1 antagonist), significantly attenuated this anaphylactic hepatic venoconstriction. Anaphylaxis-induced increases in Rpre and Rpost were significantly inhibited by TCV-309 (by 48%) and ONO-1078 (by 36%), respectively. Combined TCV-309 and ONO-1078 pretreatment exerted additive inhibitory effects on anaphylactic hepatic venoconstriction. Anaphylactic hepatic weight gain was converted to weight loss when post-sinusoidal constriction was attenuated. It is concluded that anaphylaxis-induced pre-sinusoidal constriction is mainly caused by PAF and the post-sinusoidal constriction by Cys-LTs in guinea pig livers.

The management of portal hypertension

Portal hypertension is an almost unavoidable complication of cirrhosis, and it is responsible for the more lethal complications of this syndrome. Appearance of these complications represents the major cause of death and liver transplantation in patients who have cirrhosis. This article highlights treatment modalities in use for managing portal hypertension and those that may be available in the future.

Sinusoidal endothelial COX-1-derived prostanoids modulate the hepatic vascular tone of cirrhotic rat livers

CCl(4) cirrhotic rat liver exhibits a hyperresponse to the alpha(1)-adrenergic agonist methoxamine (Mtx) that is associated with enhanced thromboxane A(2) (TXA(2)) production and is abrogated by indomethacin. To further elucidate the molecular mechanisms involved in the hyperresponse to vasoconstrictors, portal perfusion pressure dose-response curves to Mtx were performed in CCl(4) cirrhotic rats livers after preincubation with vehicle, the cyclooxygenase (COX)-1 selective inhibitor SC-560, and the COX-2 selective inhibitor SC-236. TXA(2) production was determined in samples of the perfusate. COX-1 expression was analyzed and quantified in hepatocytes, Kupffer cells, sinusoidal endothelial cells (SEC), and hepatic stellate cells (HSC) isolated from control and cirrhotic rat livers by double-immunofluorescence staining, with specific markers for each population using flow cytometry or Western blot analysis. COX-1 protein levels were not significantly increased in cirrhotic livers, but COX-2 protein expression was increased. COX-1 inhibition, but not COX-2, significantly attenuated the response to Mtx and prevented the increased production of TXA(2). Cirrhotic livers showed an increased expression of COX-1 in SEC and reduced expression in HSC compared with control livers, whereas COX-1 was similarly distributed in Kupffer cells. Despite abundant hepatic COX-2 expression, the increased response to Mtx of cirrhotic livers is mainly dependent of COX-1. Upregulation of COX-1 in cirrhotic SEC may be responsible for the hyperesponse to Mtx.

Increased hepatic resistance: a new target in the pharmacologic therapy of portal hypertension

Increased resistance to portal blood flow is the primary factor in the pathophysiology of portal hypertension, and is mainly determined by the morphologic changes occurring in chronic liver diseases. This is aggravated by an increased hepatic vascular tone, which results from an insufficient hepatic bioavailability of nitric oxide (NO) and an increased production of circulating and local vasoconstrictors (angiotensin, endothelin, cysteinyl-leukotrienes, and thromboxane, among others). This dynamic and reversible component provides the rationale for the use of therapies aimed at decreasing portal pressure by reducing the vascular tone. Among them, systemic and liver-selective NO donors, statins, and gene therapy with adenovirus encoding NO synthases have been used to increase NO availability with promising results. Other attempts have been the blockade of the effect of vasoconstrictors, using anti alpha-adrenergic agents and renin-angiotensin system blockers. Some of these pharmacologic approaches have already been incorporated into clinical practice while others are still under investigation.

Portal hypertension: from bedside to bench

The initial factor leading to portal hypertension is an increase in hepatic resistance. Later, an increase in portal blood flow contributes to maintain and exacerbate portal hypertension despite the development of portosystemic collaterals. The critical step in the development and acceptance of these concepts, which proved crucial for the management of patients with portal hypertension, was the development of animal models. These allowed the full characterization of the profound hemodynamic abnormalities in the systemic and splanchnic circulation associated with portal hypertension, and the elucidation of the molecular mechanisms implicated in these disturbances. This review traces how seminal clinical observations in the 1950s raised meaningful questions that were subsequently answered at the bench, leading to our current understanding of the pathophysiology of portal hypertension and of the pathogenesis of severe complications of cirrhosis, such as variceal bleeding or ascites.

Variceal bleeding: pharmacological therapy

The complications of portal hypertension are totally prevented if hepatic venous pressure gradient is decreased below 12 mm Hg. Besides, if this target is not achieved, a 20% decrease in portal pressure from baseline levels offers an almost total protection from variceal bleeding. This sets the rationale for drug therapy to reduce portal pressure in portal hypertension. Pharmacological therapy to decrease portal pressure includes vasoconstrictors to decrease portal blood inflow, vasodilators to decrease hepatic resistance, and combination therapy. Oral agents, such as beta-adrenergic blockers and organic nitrates, are used for long-term prevention of variceal bleeding, while parenteral agents, such as somatostatin (and analogues) and terlipressin, are used for the treatment of acute variceal bleeding.

Contributory role of 5-lipoxygenase and its association with angiogenesis in the promotion of inflammation-associated colonic tumorigenesis by cigarette smoking

Our previous study shows that cigarette smoking can promote inflammation-associated adenoma formation in the mouse colon, but the underlying mechanism remains unknown. Several studies suggest that there is a link between 5-lipoxygenase (5-LOX) and carcinogenesis in humans and animals. In the present study, we aims to investigate whether the promoting action of cigarette smoke on inflammation-associated colon cancer formation is associated with 5-LOX activation in mice. Results showed that exposure to the mainstream smoke of unfiltered cigarettes enhanced the 5-LOX protein expression in the inflammation-associated colonic adenomas. It was accompanied with an up-regulation of matrix metalloproteinase-2 (MMP-2) and vascular endothelial growth factor (VEGF). Both are the key angiogenic factors for tumorigenesis. 5-LOX inhibitors decreased the incidence of colonic adenoma formation and reduced angiogenesis, MMP-2 activity and VEGF protein expression in the colons of these animals. Taken together, these results strongly suggest that cigarette smoke can induce 5-LOX expression which plays an important role in activation of MMP-2 and VEGF to induce angiogenic process and promotion of inflammation-associated adenoma formation in mice.

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Endoluminal therapies for gastroesophageal reflux disease

While medical therapy, particularly with proton pump inhibitors, is effective for the large majority of patients with reflux disease, there remains a subset of patients who are dissatisfied, due to cost, side effects of medications, or persistent symptoms such as regurgitation. For this population, surgical fundoplication has been, and remains, an appropriate option. A new class of endoluminal interventions, attempting to create a mechanical antireflux barrier, has emerged recently. Three such devices are currently approved and available, and a number of others are in various stages of evaluation. This article will review the approved technologies, as well as selected promising emerging ones. with particular emphasis on the scientific evidence available to date supporting their efficacy.

Simvastatin enhances hepatic nitric oxide production and decreases the hepatic vascular tone in patients with cirrhosis

BACKGROUND & AIMS

In cirrhosis, an insufficient release of nitric oxide contributes to increased hepatic resistance and portal pressure and enhances the postprandial increase in portal pressure. We hypothesized that simvastatin, which enhances Akt-dependent endothelial nitric oxide synthase phosphorylation, may increase hepatic nitric oxide release and decrease hepatic resistance in patients with cirrhosis and portal hypertension.

METHODS

In protocol 1, 13 patients had measurements of the hepatic venous pressure gradient, hepatic blood flow, mean arterial pressure, cardiac output, and nitric oxide products before and 30 and 60 minutes after 40 mg of simvastatin. In protocol 2, 17 patients were randomized to receive placebo or simvastatin (40 mg) 12 hours and 1 hour before the study. After baseline measurements of the hepatic venous pressure gradient, hepatic blood flow, and nitric oxide products, a standard liquid meal was given, and measurements were repeated at 15, 30, and 45 minutes.

RESULTS

In protocol 1, acute simvastatin did not modify the hepatic venous pressure gradient but increased the hepatic blood flow (21% +/- 13% at 30 minutes; P = 0.01) and decreased hepatic sinusoidal resistance by 14% +/- 11% (P = 0.04). Nitric oxide product levels significantly increased in hepatic venous blood (from 31.4 +/- 12.3 nmol. mL(-1) to 35.8 +/- 10.7 nmol. mL(-1); P = 0.04), but not in peripheral blood. Systemic hemodynamics were not modified. In protocol 2, simvastatin pretreatment significantly attenuated the postprandial increase in hepatic venous pressure gradient (mean peak increase, 10% +/- 9% vs. 21% +/- 6% in placebo; P = 0.01). Hepatic blood flow increased similarly in the 2 groups. Hepatic nitric oxide products increased in the simvastatin group but not in the placebo group.

CONCLUSIONS

Simvastatin administration increases the hepatosplanchnic output of nitric oxide products and decreases hepatic resistance in patients with cirrhosis.

Cyclooxygenase-1 inhibition corrects endothelial dysfunction in cirrhotic rat livers

BACKGROUND/AIMS

Cirrhotic livers exhibit endothelial dysfunction that contributes to the increased hepatic vascular resistance. The present study evaluates the role of cyclooxygenase (COX)-derived prostanoids, implicated in the pathogenesis of endothelial dysfunction in other settings, in the pathogenesis of endothelial dysfunction in cirrhotic livers.

METHODS

Endothelial dysfunction was evaluated by performing concentration-effect curves to acetylcholine after precontracting the liver with methoxamine in groups of control and CCl(4)-cirrhotic rat livers preincubated either with vehicle, indomethacin, the COX-1 selective inhibitor, SC-560, the COX-2 selective inhibitor, SC-236, the thromboxane A(2) receptor antagonist, SQ 29,548 or the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine. Thromboxane A(2) (TXA(2)) production was determined in samples of the perfusate.

RESULTS

Cirrhotic livers exhibited endothelial dysfunction, as shown by the significantly lower relaxation to acetylcholine than control livers, that was totally corrected by indomethacin. COX-1 inhibition and TXA(2) blockade, but not COX-2 inhibition, also corrected endothelial dysfunction. Acetylcholine significantly increased TXA(2) production in cirrhotic but not in control livers. Indomethacin and COX-1 inhibition, but not COX-2 or NO inhibition, prevented the increased production of TXA(2).

CONCLUSIONS

An increased production of TXA(2) is involved in the pathogenesis of endothelial dysfunction in cirrhotic rat livers. This is mainly mediated by COX-1, but not by COX-2.

Targeting enteric bacteria in treatment of inflammatory bowel diseases: why, how, and when

PURPOSE

This review discusses the role of bacterial adjuvants and antigens in induction and reactivation of chronic intestinal inflammation in susceptible hosts; discusses the results of recent therapeutic trials of antibiotics, probiotics, and prebiotics; and suggests future treatment strategies.

RECENT FINDINGS

Bacterial adjuvants, including peptidoglycan, lipopolysaccharide, and DNA (CpG) bind to membrane-bound toll-like receptors (TLR-2, 4, and 9. respectively) or cytoplasmic (NOD1 and NOD2) receptors (pattern recognition receptors) that activate nuclear factor-kappaB and transcription of many proinflammatory cytokines and adhesion, costimulatory, and major histocompatibility complex class II molecules. Experimental enterocolitis does not occur in a sterile (germ-free) environment and is prevented and treated by broad-spectrum antibiotics. Individual nonpathogenic intestinal bacterial species selectively induce experimental colitis, with host specificity. Crohn disease and ulcerative colitis patients exhibit pathogenic immune responses (loss of immunologic tolerance) to multiple normal enteric bacterial species and serologic responses to Mycobacterium paratuberculosis. Metronidazole and ciprofloxacin selectively treat colonic Crohn disease, but not ulcerative colitis or ileal Crohn disease, and may prevent recurrence of postoperative Crohn disease. Certain probiotic species decrease relapse of ulcerative colitis and chronic pouchitis and delay onset of pouchitis.

SUMMARY

Normal, nonpathogenic enteric bacteria induce and perpetuate chronic intestinal inflammation in genetically susceptible hosts with defective immunoregulation, bacterial clearance, or mucosal barrier function. Altering the composition and decreasing mucosal adherence/invasion of commensal bacteria with antibiotics, probiotics, and prebiotics can potentially prevent and treat Crohn disease, pouchitis, and possibly ulcerative colitis, but optimal treatments have not yet been identified.

Portal hypertension

Portal hypertension, the main complication of cirrhosis, is responsible for its most common complications: variceal hemorrhage, ascites, and portosystemic encephalopathy. Portal hypertension is the result of increased intrahepatic resistance and increased portal venous inflow. Vasodilatation (splanchnic and systemic) and the hyperdynamic circulation are hemodynamic abnormalities typical of cirrhosis and portal hypertension. Gastroesophageal varices result almost solely from portal hypertension, although the hyperdynamic circulation contributes to variceal growth and hemorrhage. Ascites results from sinusoidal hypertension and sodium retention, which, in turn, is secondary to vasodilatation and activation of neurohumoral systems. The hepatorenal syndrome represents the result of extreme vasodilatation, with an extreme decrease in effective blood volume that leads to maximal activation of vasoconstrictive systems, renal vasoconstriction, and renal failure. Spontaneous bacterial peritonitis is a potentially lethal infection of ascites that occurs in the absence of a local source of infection. Portosystemic encephalopathy is a consequence of both portal hypertension (shunting of blood through portosystemic collaterals) and hepatic insufficiency that result in the accumulation of neurotoxins in the brain. This review covers the recent advances in the pathophysiology and management of the complications of portal hypertension.

Cyclooxygenase-derived products modulate the increased intrahepatic resistance of cirrhotic rat livers

In cirrhotic livers, increased resistance to portal flow, in part due to an exaggerated response to vasoconstrictors, is the primary factor in the pathophysiology of portal hypertension. Our aim was to evaluate the response of the intrahepatic circulation of cirrhotic rat livers to the alpha(1)-adrenergic vasoconstrictor methoxamine and the mechanisms involved in its regulation. A portal perfusion pressure dose-response curve to methoxamine was performed in control and cirrhotic rat livers preincubated with vehicle, the nitric oxide synthase blocker N(G)-nitro-L-arginine (L-NNA), indomethacin cyclooxygenase (COX) inhibitor, L-NNA + indomethacin, or the thromboxane (TX) A(2) receptor blocker SQ 29,548. TXA(2) production, COX-1 and COX-2 mRNA expression, and immunostaining for TXA(2) synthase were evaluated. Cirrhotic livers exhibited a hyperresponse to methoxamine associated with overexpression of COX-2 and TXA(2) synthase as well as with increased production of TXA(2). The hyperresponse to methoxamine of cirrhotic livers disappeared by COX inhibition with indomethacin but not after NO inhibition. SQ 29,548 also corrected the hyperresponse of cirrhotic livers to methoxamine. In conclusion, COX-derived prostanoids, mainly TXA(2), play a major role in regulating the response of cirrhotic livers to methoxamine.

Nitric oxide and portal hypertension

In liver cirrhosis, an increase in hepatic resistance is the initial phenomenon leading to portal hypertension. This is primarily due to the structural distortion of the intrahepatic microcirculation caused by cirrhosis. However, similar to other vascular conditions, architectural changes in the liver are associated with a deficient nitric oxide (NO) production, which results in an increased vascular tone with a further increase in hepatic resistance and portal pressure. New therapeutic strategies are being developed to selectively provide the liver with NO, overcoming the deleterious effects of systemic vasodilators. On the other hand, a strikingly opposite process occurs in splanchnic arterial circulation, where NO production is increased. This results in splanchnic vasodilatation and subsequent increase in portal inflow, which contributes to portal hypertension. Systemic blockade of NO in portal hypertension attenuates the hyperdynamic circulation, but its effects increasing hepatic resistance may offset the benefit of reducing portal inflow, thus preventing an effective reduction of portal pressure. Moreover, it cannot be ruled out that NO blockade may have a deleterious action on cirrhosis progression, which raises caution about their use in patients with cirrhosis.

The Stretta procedure for the treatment of GERD: a registry of 558 patients

PURPOSE

To evaluate gastroesophageal reflux disease (GERD) symptoms, patient satisfaction, and antisecretory drug use in a large group of GERD patients treated with the Stretta procedure (endoluminal temperature-controlled radiofrequency energy for the treatment of GERD) at multiple centers since February 1999.

METHODS

All subjects provided informed consent. A health care provider from each institution administered a standardized GERD survey to patients who had undergone Stretta. Subjects provided (at baseline and follow-up) (1) GERD severity (none, mild, moderate, severe), (2) percentage of GERD symptom control, (3) satisfaction, and (4) antisecretory medication use. Outcomes were compared with the McNemar test, paired t test, and Wilcoxon signed rank test.

RESULTS

Surveys of 558 patients were evaluated (33 institutions, mean follow-up of 8 months). Most patients (76%) were dissatisfied with baseline antisecretory therapy for GERD. After treatment, onset of GERD relief was less than 2 months (68.7%) or 2 to 6 months (14.6%). The median drug requirement improved from proton pump inhibitors twice daily to antacids as needed (P < .0001). The percentage of patients with satisfactory GERD control (absent or mild) improved from 26.3% at baseline (on drugs) to 77.0% after Stretta (P < .0001). Median baseline symptom control on drugs was 50%, compared with 90% at follow-up (P < .0001). Baseline patient satisfaction on drugs was 23.2%, compared with 86.5% at follow-up (P < .0001). Subgroup analysis (<1 year vs. >1 year of follow-up) showed a superior effect on symptom control and drug use in those patients beyond 1 year of follow-up, supporting procedure durability.

CONCLUSIONS

The Stretta procedure results in significant GERD symptom control and patient satisfaction, superior to that derived from drug therapy in this study group. The treatment effect is durable beyond 1 year, and most patients were off all antisecretory drugs at follow-up. These results support the use of the Stretta procedure for patients with GERD, particularly those with inadequate control of symptoms on medical therapy.