Endothelin-1 in the rat bile duct ligation model of hepatopulmonary syndrome: correlation with pulmonary dysfunction

[Hepatopulmonary syndrome]

The hepatopulmonary syndrome (HPS) is one of the lung diseases associated with cirrhosis and portal hypertension. It should be discussed for any dyspnea in cirrhotic patients. HPS is a pulmonary vascular disease characterized by intrapulmonary vascular dilatations (IPVD). The pathogenesis is complex and seems to rely on communications between the portal and pulmonary circulations. The diagnosis is based on a triad of liver disease and portal hypertension, evidence of IPVDs, and impaired gas exchange (alveolar-arterial oxygen difference [A-aO2]≥15mmHg). HPS impairs prognosis (23% survival at 5years) and patients' quality of life. Liver transplantation (LT) allows regression of IPDVD in almost 100% of cases, normalization of gas exchange and improves survival with a 5-year post-LT survival between 76 and 87%. It is the only curative treatment, indicated in patients with severe HPS, defined by an arterial partial pressure of oxygen (PaO2) below 60mmHg. When LT is not indicated or feasible, long-term oxygen therapy may be proposed as a palliative treatment. A better understanding of the pathophysiological mechanisms is needed to improve the therapeutic possibilities in a near future.

The pan-liver network theory: From traditional chinese medicine to western medicine

In traditional Chinese medicine (TCM), the liver is the "general organ" that is responsible for governing/maintaining the free flow of qi over the entire body and storing blood. According to the classic five elements theory, zang-xiang theory, yin-yang theory, meridians and collaterals theory, and the five-viscera correlation theory, the liver has essential relationships with many extrahepatic organs or tissues, such as the mother-child relationships between the liver and the heart, and the yin-yang and exterior-interior relationships between the liver and the gallbladder. The influences of the liver to the extrahepatic organs or tissues have been well-established when treating the extrahepatic diseases from the perspective of modulating the liver by using the ancient classic prescriptions of TCM and the acupuncture and moxibustion. In modern medicine, as the largest solid organ in the human body, the liver has the typical functions of filtration and storage of blood; metabolism of carbohydrates, fats, proteins, hormones, and foreign chemicals; formation of bile; storage of vitamins and iron; and formation of coagulation factors. The liver also has essential endocrine function, and acts as an immunological organ due to containing the resident immune cells. In the perspective of modern human anatomy, physiology, and pathophysiology, the liver has the organ interactions with the extrahepatic organs or tissues, for example, the gut, pancreas, adipose, skeletal muscle, heart, lung, kidney, brain, spleen, eyes, skin, bone, and sexual organs, through the circulation (including hemodynamics, redox signals, hepatokines, metabolites, and the translocation of microbiota or its products, such as endotoxins), the neural signals, or other forms of pathogenic factors, under normal or diseases status. The organ interactions centered on the liver not only influence the homeostasis of these indicated organs or tissues, but also contribute to the pathogenesis of cardiometabolic diseases (including obesity, type 2 diabetes mellitus, metabolic [dysfunction]-associated fatty liver diseases, and cardio-cerebrovascular diseases), pulmonary diseases, hyperuricemia and gout, chronic kidney disease, and male and female sexual dysfunction. Therefore, based on TCM and modern medicine, the liver has the bidirectional interaction with the extrahepatic organ or tissue, and this established bidirectional interaction system may further interact with another one or more extrahepatic organs/tissues, thus depicting a complex "pan-hepatic network" model. The pan-hepatic network acts as one of the essential mechanisms of homeostasis and the pathogenesis of diseases.

Hepatopulmonary syndrome is associated with low sphingosine-1-phosphate levels and can be ameliorated by the functional agonist fingolimod

BACKGROUND & AIMS

Hepatopulmonary syndrome (HPS) is characterised by a defect in arterial oxygenation induced by pulmonary vascular dilatation in patients with liver disease. Fingolimod, a sphingosine-1-phosphate (S1P) receptor modulator, suppresses vasodilation by reducing nitric oxide (NO) production. We investigated the role of S1P in patients with HPS and the role of fingolimod as a therapeutic option in an experimental model of HPS.

METHODS

Patients with cirrhosis with HPS (n = 44) and without HPS (n = 89) and 25 healthy controls were studied. Plasma levels of S1P, NO, and markers of systemic inflammation were studied. In a murine model of common bile duct ligation (CBDL), variations in pulmonary vasculature, arterial oxygenation, liver fibrosis, and inflammation were estimated before and after administration of S1P and fingolimod.

RESULTS

Log of plasma S1P levels was significantly lower in patients with HPS than in those without HPS (3.1 ± 1.4 vs. 4.6 ± 0.2; p <0.001) and more so in severe intrapulmonary shunting than in mild and moderate intrapulmonary shunting (p <0.001). Plasma tumour necrosis factor-α (76.5 [30.3-91.6] vs. 52.9 [25.2-82.8]; p = 0.02) and NO (152.9 ± 41.2 vs. 79.2 ± 29.2; p = 0.001) levels were higher in patients with HPS than in those without HPS. An increase in Th17 (p <0.001) and T regulatory cells (p <0.001) was observed; the latter inversely correlated with plasma S1P levels. In the CBDL HPS model, fingolimod restored pulmonary vascular injury by increasing the arterial blood gas exchange and reducing systemic and pulmonary inflammation, resulting in improved survival (p = 0.02). Compared with vehicle treatment, fingolimod reduced portal pressure (p <0.05) and hepatic fibrosis and improved hepatocyte proliferation. It also induced apoptotic death in hepatic stellate cells and reduced collagen formation.

CONCLUSIONS

Plasma S1P levels are low in patients with HPS and even more so in severe cases. Fingolimod, by improving pulmonary vascular tone and oxygenation, improves survival in a murine CBDL HPS model.

IMPACT AND IMPLICATIONS

A low level of plasma sphingosine-1-phosphate (S1P) is associated with severe pulmonary vascular shunting, and hence, it can serve as a marker of disease severity in patients with hepatopulmonary syndrome (HPS). Fingolimod, a functional agonist of S1P, reduces hepatic inflammation, improves vascular tone, and thus retards the progression of fibrosis in a preclinical animal model of HPS. Fingolimod is being proposed as a potential novel therapy for management of patients with HPS.

Vascular Extracellular Vesicles Indicate Severe Hepatopulmonary Syndrome in Cirrhosis

Background: Hepatopulmonary syndrome (HPS) is a pulmonary vasculature complication in the setting of liver disease that is characterized by pathological vasodilation resulting in arterial oxygenation defects. We investigated the role of extracellular vesicles (EV) in cirrhosis patients with HPS, as well as the functional effect of EV administration in a common bile duct ligation (CBDL) HPS mouse model. Methods: A total of 113 cirrhosis patients were studied: 42 (Gr. A) with HPS and 71 (Gr. B) without HPS, as well as 22 healthy controls. Plasma levels of EV associated with endothelial cells, epithelial cells, and hepatocytes were measured. The cytokine cargoes were estimated using ELISA. The effect of EV administered intranasally in the CBDL mouse model was investigated for its functional effect in vascular remodeling and inflammation. Results: We found endothelial cells (EC) associated EV (EC-EV) were elevated in cirrhosis patients with and without HPS (p < 0.001) than controls. EC-EV levels were higher in HPS patients (p = 0.004) than in those without HPS. The epithelial cell EVs were significantly high in cirrhosis patients than controls (p < 0.001) but no changes found in patients with HPS than without. There was a progressive increase in EC-EV levels from mild to severe intrapulmonary shunting in HPS patients (p = 0.02 mild vs. severe), and we were able to predict severe HPS with an AUROC of 0.85; p < 0.001. An inverse correlation of EC-EVs was found with hemoglobin (r = −0.24; p = 0.031) and PaO2 (r = 0.690; p = 0.01) and a direct correlation with MELD (r = 0.32; p = 0.014). Further, both TNF-α (p = 0.001) and IL-1β (p = 0.021) as cargo levels were significantly elevated inside the EVs of HPS patients than without HPS. Interestingly, upon administration of intranasal EVs, there was a significant decrease in Evans blue accumulation and lung wet–dry ratio (p = 0.042; 0.038). A significant reduction was also noticed in inflammation and cholestasis. Conclusion: High levels of plasma EC-EV levels were found in patients with HPS with elevated pro-inflammatory cytokine cargoes. EC-EVs were indicative of severe HPS condition. In the CBDL HPS model, we were able to prove the beneficial effects of improving vascular tone, inflammation, and liver pathogenesis.

Hepatopulmonary Syndrome and Portopulmonary Hypertension: Pulmonary Vascular Complications of Liver Disease

Pulmonary vascular disease is a frequent complication of chronic liver disease and portal hypertension, affecting up to 30% of patients. There are two distinct pulmonary vascular complications of liver disease: hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH). HPS affects 25% of patients with chronic liver disease and is characterized by intrapulmonary vasodilatation and abnormal arterial oxygenation. HPS negatively impacts quality of life and is associated with a 2-fold increased risk of death compared to controls with liver disease without HPS. Angiogenesis, endothelin-1 mediated endothelial dysfunction, monocyte influx, and alveolar type 2 cell dysfunction seem to play important roles in disease pathogenesis but there are currently no effective medical therapies. Fortunately, HPS resolves following liver transplant (LT) with improvements in hypoxemia. POPH is a subtype of pulmonary arterial hypertension (PAH) characterized by an elevated mean pulmonary arterial pressure and pulmonary vascular resistance in the setting of normal left-sided filling pressures. POPH affects 5% to 6% of patients with chronic liver disease. Although the pathogenesis has not been fully elucidated, endothelial dysfunction, inflammation, and estrogen signaling have been identified as key pathways involved in disease pathogenesis. POPH is typically treated with PAH targeted therapy and may also improve with liver transplantation in selected patients. This article highlights what is currently known regarding the diagnosis, management, pathobiology, and outcomes of HPS and POPH. Ongoing research is needed to improve understanding of the pathophysiology and outcomes of these distinct and often misunderstood pulmonary vascular complications of liver disease. © 2021 American Physiological Society. Compr Physiol 11:1-22, 2021.

A Role for Alveolar Exhaled Nitric Oxide Measurement in the Diagnosis of Hepatopulmonary Syndrome

GOALS

The authors sought to characterize predominantly alveolar exhaled nitric oxide (eNO) in hepatopulmonary syndrome (HPS) compared with non-HPS, changes after liver transplantation, and diagnostic properties.

BACKGROUND

HPS is defined by liver disease, intrapulmonary vascular dilatations (IPVDs), and hypoxemia. Rat models and small human studies suggest that NO overproduction may cause IPVDs.

STUDY

A retrospective review of the Canadian HPS Database (2007 to 2017) and prospective eNO measurement (main outcome) in healthy controls (measurement expiratory flow, 200 mL/s). HPS was defined as: (1) liver disease; (2) contrast echocardiography consistent with IPVDs; and (3) partial pressure of arterial oxygen <70 mm Hg with alveolar-arterial gradient >20 mm Hg; subclinical HPS as criteria (1) and (2) only; and no HPS as criterion (1) only. Current smokers and subjects with asthma or pulmonary hypertension were excluded. A linear mixed effects model was used to compare eNO between groups and before and after transplantation.

RESULTS

eNO was 10.4±0.7 ppb in HPS (n=26); 8.3±0.6 ppb in subclinical HPS (n=38); 7.1±1.0 ppb in no HPS (n=15); and 5.6±0.7 ppb in controls (n=30) (P<0.001). eNO decreased from 10.9±0.8 ppb preliver to 6.3±0.8 ppb postliver transplant (n=6 HPS, 6 subclinical HPS) (P<0.001). eNO <6 ppb was 84.4% (73.1% to 92.2%) sensitive and ≥12 ppb was 78.1% (69.4% to 85.3%) specific for HPS (vs. subclinical HPS).

CONCLUSIONS

HPS subjects have higher alveolar eNO than non-HPS subjects, levels normalize with liver transplantation. Applying eNO cutoff values may aid in HPS diagnosis.

Hepatoprotective effect of ultrasonicated ginseng berry extract on a rat mild bile duct ligation model

Background

The Panax ginseng berry extract (GBE) is well known to have an antidiabetic effect. The aim of this study is to evaluate and investigate the protective effect of ultrasonication-processed P. ginseng berry extract (UGBE) compared with GBE on liver fibrosis induced by mild bile duct ligation (MBDL) model in rats. After ultrasonication process, the composition ratio of ginsenoside in GBE was changed. The component ratio of ginsenosides Rh1, Rh4, Rg2, Rg3, Rk1, Rk3, and F4 in the extract was elevated.

Methods

In this study, the protective effect of the newly developed UGBE was evaluated on hepatotoxicity and neuronal damage in MBDL model. Silymarin (150 mg/kg) was used for positive control. UGBE (100 mg/kg, 250 mg/kg, 500 mg/kg), GBE (250 mg/kg), and silymarin (150 mg/kg) were orally administered for 6 weeks after MBDL surgery.

Results

The MBDL surgery induced severe hepatotoxicity that leads to liver inflammation in rats. Also, the serum ammonia level was increased by MBDL surgery. However, the liver dysfunction of MBDL surgery–operated rats was attenuated by UGBE treatment via myeloid differentiation factor 88-dependent Toll-like receptor 4 signaling pathways.

Conclusion

UGBE has a protective effect on liver fibrosis induced by MBDL in rats through inhibition of the TLR4 signaling pathway in liver.

Potential Clinical Targets in Hepatopulmonary Syndrome: Lessons From Experimental Models

Hepatopulmonary syndrome (HPS) is a relatively common and potentially severe pulmonary complication of cirrhosis with increased risk of mortality. In experimental models, a complex interaction between pulmonary endothelial cells, monocytes, and the respiratory epithelium, which produces chemokines, cytokines, and angiogenic growth factors, causes alterations in the alveolar microvasculature, resulting in impaired oxygenation. Model systems are critical for evaluating mechanisms and for preclinical testing in HPS, due to the challenges of evaluating the lung in the setting of advanced liver disease in humans. This review provides an overview of current knowledge and recent findings in the rodent common bile duct ligation model of HPS, which recapitulates many features of human disease. We focus on the concepts of endothelial derangement, monocyte infiltration, angiogenesis, and alveolar type II cell dysfunction as main contributors and potential targets for therapy.

Placental growth factor inhibition targets pulmonary angiogenesis and represents a therapy for hepatopulmonary syndrome in mice

Hepatopulmonary syndrome (HPS) is a severe complication of cirrhosis with increased risk of mortality. Pulmonary microvascular alterations are key features of HPS; but underlying mechanisms are incompletely understood, and studies on HPS are limited to rats. Placental growth factor (PlGF), a proangiogenic molecule that is selectively involved in pathological angiogenesis, may play an important role in HPS development; however, its role has never been investigated. In this study, we validated an HPS model by common bile duct ligation (CBDL) in mice, investigated the kinetic changes in pulmonary angiogenesis and inflammation during HPS development, and provide evidence for a novel therapeutic strategy by targeting pathological angiogenesis. Mice with CBDL developed hypoxemia and intrapulmonary shunting on a background of liver fibrosis. Pulmonary alterations included increased levels of proangiogenic and inflammatory markers, which was confirmed in serum of human HPS patients. Increased PlGF production in HPS mice originated from alveolar type II cells and lung macrophages, as demonstrated by immunofluorescent staining. Dysfunctional vessel formation in CBDL mice was visualized by microscopy on vascular corrosion casts. Both prophylactic and therapeutic anti-PlGF (αPlGF) antibody treatment impeded HPS development, as demonstrated by significantly less intrapulmonary shunting and improved gas exchange. αPlGF treatment decreased endothelial cell dysfunction in vivo and in vitro and was accompanied by reduced pulmonary inflammation. Importantly, αPlGF therapy did not affect liver alterations, supporting αPlGF's ability to directly target the pulmonary compartment.

CONCLUSION

CBDL in mice induces HPS, which is mediated by PlGF production; αPlGF treatment improves experimental HPS by counteracting pulmonary angiogenesis and might be an attractive therapeutic strategy for human HPS. (Hepatology 2017).

Hepatopulmonary Syndrome: Oxidative Stress and Physical Exercise

Hepatopulmonary syndrome (HPS) may be defined by hepatic disease, gas exchange abnormalities that may lead to hypoxaemia, and the presence of pulmonary vascular dilations. The balance between the many substances involved in vasodilation and vasoconstriction is regulated by the liver; thus, liver damage may generate systemic changes throughout the body. The pulmonary tissue may be damaged by reactive oxygen species or nitric oxide. Dyspnoea is the most frequent pulmonary symptom, caused by tissue damage, and may become worse when an individual exercises. In experimental research the surgical model of bile duct ligation is the optimal model to simulate the typical lung alterations present in HPS, which results in an increase in oxidative stress in hepatic and pulmonary tissues. In liver injury, the muscular system may also be damaged, for example sarcopenia may seriously aggravate cirrhosis and is associated with cirrhotic patient mortality. Muscular changes can be explained by the actions of myostatin and insulin-like growth factor and the increase in body levels of ammonia. As a result of impaired cardiopulmonary and muscular conditions, HPS patients may exhibit a low exercise tolerance, low muscle strength, and low functionality. Liver disease can contribute to HPS oxidative stress and is one of the main factors responsible for the reduction of gas exchange. Physical exercise can be performed as a way of modifying this pathophysiological state. Studies that have investigated physical exercise as a therapy for cirrhosis suggest that this approach may be beneficial for cirrhotic patients, primarily with regard to muscular and cardiorespiratory injuries.

Is the Hepatic Factor a miRNA that Maintains the Integrity of Pulmonary Microvasculature by Inhibiting the Vascular Endothelial Growth Factor?

Background:

The “hepatic factor,” a molecule or group of molecules present in the hepatic venous blood, essential for the prevention of the development of pulmonary arteriovenous malfor-mations (PAVMs) and right-to-left shunting has been a conceptual enigma in the understanding of many related conditions.

Methods:

Patients with various forms of liver diseases including acute hepatic failure, and others with normal hepatic function like hereditary hemorrhagic telangiectasia (HHT), inflammatory and parasitic disorders, cardiogenic hepatopulmonary syndrome (cHPS) and skin disorders like Dyskeratosis con-genita are all known to cause PAVMs. Over a period of the last two decades our understanding of the pathogenesis of PAVMs has changed, but the mechanisms are still not clearly understood. The pres-ence of PAVMs once considered a contraindication for liver transplantation is now a cure for PAVMs in patients with HPS.

Results:

In this article the molecular mechanisms and the underlying pathogenesis of PAVMs are dis-cussed and the role of microRNA (miRNA) in its pathogenesis is favorably argued. Identifying and preventing or treating the underlying mechanisms will significantly influence the management of a large group of patients who at present cannot be effectively treated with a very poor prognosis. Progressive polycythemia, desaturation, stroke, and infection are serious complications of PAVMs.

Conclusion:

The clinical data and current understanding leads to the possible role of miRNA, which inhibits Vascular Endothelial Growth Factor (VEGF) synthesis as a pathogenic mechanism for the development of PAVMs.

Intrapulmonary vascular dilatations are common in portopulmonary hypertension and may be associated with decreased survival

Hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH) are pulmonary vascular complications of portal hypertension with divergent clinicopathologic features and management. The presence of intrapulmonary vascular dilatations (IPVDs), detected by agitated saline contrast-enhanced transthoracic echocardiography (cTTE), is an essential feature of HPS but is not typically characteristic of POPH. Although IPVDs have been reported rarely in POPH, the prevalence and significance of this finding have not been systematically studied. We conducted a retrospective chart review of 80 consecutive patients diagnosed with POPH from January 1, 2002 to June 30, 2014 with documentation of cTTE findings, pulmonary hemodynamics, oxygenation, and survival. A total of 34 of the 80 patients (42%) underwent cTTE during initial diagnosis of POPH. IPVDs were detected in 20/34 patients (59%); intracardiac shunting was detected in 9/34 patients (26%; 4 also had IPVDs); and 9 patients (26%) had negative cTTE with no evidence of IPVD or intracardiac shunting. Patients with IPVD had decreased survival as compared to those without IPVD (P = 0.003), a trend that persisted after exclusion of liver transplant recipients (P =  0.07). The IPVD group had a trend toward higher Model for End-Stage Liver Disease score with and without incorporating sodium (MELD or MELD-Na; P = 0.05 for both). The right ventricular index of myocardial performance (RIMP) was lower in the IPVD group (median, 0.4 versus 0.6; P = 0.006). Patients with moderate or large IPVDs (n = 6) had worse oxygenation parameters (partial pressure of arterial oxygen, diffusing capacity of the lung for carbon monoxide, and alveolar-arterial oxygen gradient) as compared to the rest of the cohort. Unexpectedly, IPVDs were frequently documented in POPH and associated with decreased survival. To further understand this observation, we recommend screening for IVPD in all patients with POPH.

Hepatopulmonary syndrome: the anaesthetic considerations

Hepatopulmonary syndrome (HPS) is a pulmonary complication observed in patients with chronic liver disease and/or portal hypertension, attributable to an intrapulmonary vascular dilatation that induces severe hypoxaemia. Considering the favourable long-term survival of HPS patients as well as the reversal of the syndrome with a functional liver graft, HPS is now an indication for orthotopic liver transplantation (OLT). Consequently, blood gas analysis and imaging techniques should be performed when cirrhotic patients present with shortness of breath as well as when OLT candidates are placed on the transplant waiting list. If the arterial partial pressure of oxygen (PaO2) is more than 10.7 kPa when breathing room air, HPS can be excluded and no other investigation is needed. When the PaO2 when breathing room air is 10.7 kPa or less, contrast-enhanced echocardiography should be performed to exclude pulmonary vascular dilatation. Lung function tests may also help detect additional pulmonary diseases that can contribute to impaired oxygenation. When contrast-enhanced echocardiography is negative, HPS is excluded and no follow-up is needed. When contrast-enhanced echocardiography is positive and PaO2 less than 8 kPa, patients should obtain a severity score that provides them with a reasonable probability of being transplanted within 3 months. In mild-to-moderate HPS (PaO2 8 to 10.6 kPa), periodic follow-up is recommended every 3 months to detect any further deterioration in PaO2. Although no intraoperative deaths have been directly attributed to HPS, oxygenation may worsen immediately following OLT due to volume overload and postoperative infections. Mechanical ventilation is often prolonged with an extended stay in the ICU. A high postoperative mortality (mostly within 6 months) is observed in this group of patients in comparison to non-HPS patients. However, the recovery of an adequate PaO2 within 12 months after OLT explains the similar outcome of HPS and non-HPS patients following OLT over a longer time period.

Hepatopulmonary syndrome

The hepatopulmonary syndrome (HPS) is a pulmonary complication of cirrhosis and/or portal hypertension whereby patients develop hypoxemia as a result of alterations in pulmonary microvascular tone and architecture. HPS occurs in up to 30% of patients with cirrhosis. Although the degree of hypoxemia does not reliably correlate with the severity of liver disease, patients with HPS have a higher mortality than do patients with cirrhosis without the disorder. There has been progress into defining the mechanisms that lead to hypoxemia in HPS, but to date there are no therapeutic options for HPS aside from liver transplantation.

Hepatopulmonary syndrome

PURPOSE OF REVIEW

To discuss the advances in the understanding of the pathophysiology of experimental and human hepatopulmonary syndrome (HPS) and in the management of HPS, particularly regarding liver transplantation.

RECENT FINDINGS

Advances have been made in defining the pathophysiology of HPS in experimental models as well as in human disease, including the role of endothelin-1, pulmonary monocytes, and angiogenesis. Additionally, the implications of the presence of HPS as it relates to prioritizing patients for liver transplantation and posttransplant outcomes will also be reviewed.

SUMMARY

Mechanisms of disease continue to be defined in HPS, providing potential targets for pharmacologic intervention. Outcomes after liver transplantation are also becoming clearer, including the management of HPS with severe hypoxemia.

Cirrhosis and hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) is characterized as a triad: liver disease, intrapulmonary vascular dilatation and arterial hypoxemia. HPS is reported to be present in 4% to 32% of adult patients with end-stage liver disease and in 9%-20% of children. The pathogenesis of HPS has not been clearly identified. Portal hypertension causes impairment in the perfusion of the bowel and increases the enteral translocation of Gram (-) bacteria and endotoxins. This stimulates the release of vasoactive mediators, such as tumor necrosis factor-alpha, heme oxygenase-derived carbon monoxide and nitric oxide. Genetic alterations have not been associated with this syndrome yet; however, cytokines and chemokines have been suggested to play a role. Recently, it was reported that cumulated monocytes lead to the activation of vascular endothelial growth factor-dependent signaling pathways and pulmonary angiogenesis, which plays an important role in HPS pathogenesis. At present, the most effective and only radical treatment is a liver transplant (LT). Cirrhotic patients who are on the waiting list for an LT have a shorter survival period if they develop HPS. Therefore, it is suggested that all cirrhotic cases should be followed closely for HPS and they should have priority in the waiting list.

The role of receptor tyrosine kinase activation in cholangiocytes and pulmonary vascular endothelium in experimental hepatopulmonary syndrome

Pulmonary vascular dilation and angiogenesis underlie experimental hepatopulmonary syndrome (HPS) induced by common bile duct ligation (CBDL) and may respond to receptor tyrosine kinase (RTK) inhibition. Vascular endothelial growth factor-A (VEGF-A) expression occurs in proliferating cholangiocytes and pulmonary intravascular monocytes after CBDL, the latter contributing to angiogenesis. CBDL cholangiocytes also produce endothelin-1 (ET-1), which triggers lung vascular endothelin B receptor-mediated endothelial nitric oxide synthase (eNOS) activation and pulmonary intravascular monocyte accumulation. However, whether RTK pathway activation directly regulates cholangiocyte and pulmonary microvascular alterations in experimental HPS is not defined. We assessed RTK pathway activation in cholangiocytes and lung after CBDL and the effects of the type II RTK inhibitor sorafenib in experimental HPS. Cholangiocyte VEGF-A expression and ERK activation accompanied proliferation and increased hepatic and circulating ET-1 levels after CBDL. Sorafenib decreased each of these events and led to a reduction in lung eNOS activation and intravascular monocyte accumulation. Lung monocyte VEGF-A expression and microvascular Akt and ERK activation were also found in vivo after CBDL, and VEGF-A activated Akt and ERK and angiogenesis in rat pulmonary microvascular endothelial cells in vitro. Sorafenib inhibited VEGF-A-mediated signaling and angiogenesis in vivo and in vitro and improved arterial gas exchange and intrapulmonary shunting. RTK activation in experimental HPS upregulates cholangiocyte proliferation and ET-1 production, leading to pulmonary microvascular eNOS activation, intravascular monocyte accumulation, and VEGF-A-mediated angiogenic signaling pathways. These findings identify a novel mechanism in cholangiocytes through which RTK inhibition ameliorates experimental HPS.

Pharmacological treatment for hepatopulmonary syndrome

AIM

Hepatopulmonary syndrome is a pulmonary dysfunction in the context of liver cirrhosis characterized by arterial deoxygenation. Affected patients have increased morbidity and mortality, and many of them expire before undergoing liver transplantation. Therefore, finding medical therapy as a bridge to transplantation or as a final treatment is necessary. In this study, we aimed to review the current literature about pharmacological options available for treatment of hepatopulmonary syndrome.

METHODS

A PubMED and Scopus search was conducted in January 2013 on the English literature published in any time period to find human and animal studies reporting pharmacological therapy of hepatopulmonary syndrome.

RESULTS

Out of 451 studies, 29 relevant articles were included. The number of patients, type, dose, duration, and mechanism of drugs in these studies was extracted and summarized separately. Most of pharmacologic agents act through inhibition of nitric oxide synthase and reduction in nitric oxide production, inactivation of endothelin-1, and treatment of bacterial translocation and pulmonary angiogenesis.

CONCLUSION

Several drugs have been applied for the treatment of HPS with conflicting results. However, no large randomized trial has been conducted probably due to low number of patients. Multicentered clinical trials are necessary to investigate these drugs.

Heme oxygenase/carbon monoxide pathway inhibition plays a role in ameliorating fibrosis following splenectomy

Splenectomy is a recognized therapy for liver cirrhosis with splenomegaly, since it decreases free iron concentration that accompanies the destruction of red blood cells. Heme oxygenase (HO)-1 and its by-products, iron and carbon monoxide (CO), play crucial roles in hepatic fibrosis. The aim of the present study was to determine whether splenectomy in cirrhotic rats induced by bile duct ligation (BDL), through the HO/CO pathway, could slow down the development of liver fibrosis. Male Sprague-Dawley rats were divided randomly into the sham, BDL, splenectomy, Fe, zinc protoporphyrin (Znpp) and cobalt protoporphyrin (Copp) treatment groups, for inhibiting and inducing HO-1 expression. The level of HO-1 was detected by western blot analysis and reverse transcription-polymerase chain reaction. Serum carboxyhemoglobin (COHb), iron and portal vein pressure (PVP) were also quantified. Liver iron was measured by atomic absorption spectrometry with acetylene-air flame atomization. HO-1 and α-smooth muscle actin (α-SMA) were localized by immunohistochemistry. Liver and spleen iron were visualized by Perls' Prussian blue staining. Hepatic fibrosis was assessed using hematoxylin and eosin (H&E) staining. Enzyme-linked immunosorbent assay (ELISA) was used to detect serum transforming growth factor-β1 (TGF-β1). The results showed that liver, spleen and serum levels of HO-1, COHb and iron were greatly enhanced in the BDL group compared with the sham group; they were reduced following splenectomy and Znpp treatment, but were elevated in the Copp and Fe groups. Hydroxyproline, TGF-β1, α-SMA, PVP and malonaldehyde levels were lower in the splenectomy and Znpp groups compared to BDL, while higher levels were observed in the Copp and Fe-treated groups. Our study shows that splenectomy reduces iron and CO levels in part by reducing HO-1 expression, and it decreases portal pressure and slightly decreases hepatic fibroproliferation.

Sorafenib treatment improves hepatopulmonary syndrome in rats with biliary cirrhosis

HPS (hepatopulmonary syndrome) is characterized by oxygen desaturation in patients with chronic liver disease. The initiation of HPS comes from abnormal pulmonary vasodilatation and/or angiogenesis. In the present study, we evaluated anti-angiogenesis therapy using sorafenib in experimental HPS animals. HPS was induced by CBDL (common bile duct ligation) in rats. A 2-week 10 mg·(kg of body weight)-1·day-1 treatment regimen of sorafenib or distilled water (control) was initiated 2 weeks after the surgical procedure. Haemodynamics, liver biochemistry, plasma VEGF (vascular endothelial growth factor) measurements and blood gas analysis of the CBDL rats were performed. The livers of the CBDL rats were dissected for histopathology examination, and the lungs were examined by immunohistochemical staining, real-time PCR and Western blot analysis. In another two parallel groups, intrapulmonary shunts were determined. The AaPO2 (alveolar-arterial O2 gradient) and plasma VEGF levels were reduced after sorafenib treatment [AaPO2, 7.2±3.4 mmHg in sorafenib-treated rats compared with 15.3±4.2 mmHg in controls (P=0.004); VEGF, 45.3±2.7 pg/ml in sorafenib-treated rats compared with 54.4±7.7 pg/ml in controls (P=0.021)]. Sorafenib attenuated pulmonary VEGF mRNA and VEGF, VEGFR-2 (VEGF receptor 2), phospho-VEGFR-2 and Akt protein expression. In addition, sorafenib significantly attenuated intrapulmonary angiogenesis and decreased the degree of intrapulmonary shunting by 33.7% (11.2±5.7% in sorafenib-treated rats compared with 16.9±5.9% in controls; P=0.003). Our findings suggest that sorafenib attenuates intrapulmonary shunting and decreases the AaPO2 in CBDL rats, implicating the improvement of HPS in this experimental animal model. The beneficial effect may be attributed to the reduction in intrapulmonary angiogenesis through inhibition of the VEGF/VEGFR-2/Akt pathway.

Hepatopulmonary syndrome: update on recent advances in pathophysiology, investigation, and treatment

Hepatopulmonary syndrome (HPS) is an important cause of dyspnea and hypoxia in the setting of liver disease, occurring in 10-30% of patients with cirrhosis. It is due to vasodilation and angiogenesis in the pulmonary vascular bed, which leads to ventilation-perfusion mismatching, diffusion limitation to oxygen exchange, and arteriovenous shunting. There is evidence, primarily from animal studies, that vasodilation is mediated by a number of endogenous vasoactive molecules, including endothelin-1 and nitric oxide (NO). In experimental HPS, liver injury stimulates release of endothelin-1 and results in increased expression of ET(B) receptors on pulmonary endothelial cells, leading to upregulation of endothelial NO synthase (eNOS) and subsequent increased production of NO, which causes vasodilation. In addition, increased phagocytosis of bacterial endotoxin in the lung not only promotes stimulation of inducible NO synthase, which increases NO production, but also contributes to intrapulmonary accumulation of monocytes, which may stimulate angiogenesis via vascular endothelial growth factor pathway. Despite these insights into the pathogenesis of experimental HPS, there is no established medical therapy, and liver transplantation remains the main treatment for symptomatic HPS, although selected patients may benefit from other surgical or radiological interventions. In this review, we focus on recent advances in our understanding of the pathophysiology of HPS, and discuss current approaches to the investigation and treatment of this condition.

Hepatopulmonary syndrome: update on pathogenesis and clinical features

Hepatopulmonary syndrome (HPS) is a serious vascular complication of liver disease that occurs in 5-32% of patients with cirrhosis. The presence of HPS markedly increases mortality. No effective medical therapies are currently available and liver transplantation is the only established treatment option for HPS. The definition and diagnosis of HPS are established by the presence of a triad of liver disease with intrapulmonary vascular dilation that causes abnormal arterial gas exchange. Experimental biliary cirrhosis induced by common bile duct ligation in the rat reproduces the pulmonary vascular and gas exchange abnormalities of human HPS and serves as a pertinent animal model. Pulmonary microvascular dilation and angiogenesis are two central pathogenic features that drive abnormal pulmonary gas exchange in experimental HPS, and thus might underlie HPS in humans. Defining the mechanisms involved in the microvascular alterations of HPS has the potential to lead to effective medical therapies. This Review focuses on the current understanding of the pathogenesis, clinical features and management of HPS.

Evaluation of different therapeutic approaches for spontaneous bacterial peritonitis

BACKGROUND AND STUDY AIMS

Spontaneous bacterial peritonitis (SBP) is a significant cause of mortality in cirrhosis. Reducing toxic burden of infected ascitic fluid through paracentesis needs further studies as adjunctive therapy of SBP. We aimed to evaluate different therapies for SBP.

PATIENTS AND METHODS

Thirty-six cirrhotic ascitic patients with SBP were examined and classified according to treatment modality (5-7 days) into: Group A received cefotaxime, group B received cefotaxime and albumin 1.5 g/kg body weight within 6h of SBP being diagnosed and 1g/kg body weight on day 3, group C received cefotaxime and paracentesis with volume dependent albumin infusion. Control group of 12 cirrhotic ascitic patients free from SBP were included. Routine laboratory tests, ascitic fluid analysis for leucocytes and culture were done, inflammatory mediators such as nitric oxide and tumour necrosis factor alpha were measured in serum and ascitic fluid. Duplex-Doppler assessment of portal flow volume and renal resistive index, Echocardiography to measure end diastolic and end systolic volumes, stroke volume and cardiac output were done. Tests were carried out before and after therapy.

RESULTS

Treatment response was assessed by, cardiac haemodynamics, portal and renal flow and NO and TNF. All studied parameters; laboratory, cardiac, Doppler exhibited a significant improvement in group B in contrast to the other groups as demonstrated by post therapy reduction of (blood and ascitic fluid WBCs & PNLS, serum and ascitic NO & TNF and renal resistive index), elevation of (serum albumin and portal flow volume) and improvement of cardiac haemodynamic.

CONCLUSION

Treatment of spontaneous bacterial peritonitis by cefotaxime and body weight based albumin infusion gave most favourable results compared to other regimens. Postulation of removing toxic burden through paracentesis has not been confirmed.

Effects of caffeic acid phenethyl ester (CAPE) on hepatopulmonary syndrome

The aim of this study was to investigate the effects of caffeic acid phenethyl ester (CAPE) on inflammatory and related histopathological changes in the lung and liver in experimental hepatopulmonary syndrome (HPS) model. Forty Sprague Dawley rats were used in this study. The animals were divided into four groups of ten rats each. Group 1 and 2 was subjected the common bile duct (CBD) but not ligated, Group 3; (cirrhosis + saline): the CBD was ligated and was given intraperitoneal saline infusion treatment during 5 weeks. Group 4; (cirrhosis + CAPE): the CBD was ligated and was given intraperitoneal CAPE infusion treatment during 5 weeks. A 5-week waiting period was observed for the development of cirrhosis and the rats' lungs and liver were taken for histopathological examination. The induction of HPS resulted in a significant increase in serum bilurubin, AST, ALT, and NO levels, and decrease PO2 and O2 saturation. The use of CAPE significant decrease these parameters. Histopathological examination revealed less congestion, portal inflammation, and nodular formations of the liver, and less congestion, emphysematous and inflammatory changes and smallest perialviolar vascular diameters, in the lung in the cirrhosis + CAPE groups than in the other groups. CAPE treatment may be a potential approach for the treatment of hepatopulmonary syndrome in the future.

Elevated levels of endothelin-1 in hepatic venous blood are associated with intrapulmonary vasodilatation in humans

BACKGROUND

Hepatopulmonary syndrome is a pulmonary vascular complication of cirrhosis in which intrapulmonary vasodilatation (IPV) results in hypoxemia. Endothelin-1 (ET-1), produced by proliferating cholangiocytes, has been identified as a mediator of IPV in an animal model of HPS, but the pathophysiology of IPV in humans has not been defined.

AIM

The purpose of this study was to assess whether cirrhosis with IPV, which often leads to HPS, is associated with increased hepatic venous ET-1 blood levels.

METHODS

We performed a prospective cohort pilot study of 40 patients with liver disease undergoing transjugular liver biopsy from November 1, 2008 to September 1, 2009. Patients were categorized according to absence (-) or presence (+) of IPV as determined by bubble-contrasted echocardiography. Hepatic venous blood was assayed for ET-1 by ELISA. The percent volume of cholangiocytes in the liver biopsy specimen was determined by morphometric analysis, as a measure of bile duct proliferation.

RESULTS

Nine subjects were excluded, due to absence of cirrhosis (6) and patent foramen ovale (3). Of the remaining 31 subjects, IPV was present in 18 (58%). Median hepatic venous ET-1 was higher with IPV+ than IPV- at levels of 9.1 pg/mL (range 7.5-11.7) versus 2.1 pg/mL (1.3-5.6), respectively (P = 0.004). ET-1 levels correlated positively with cholangiocyte percent volume (r = 0.72, P < 0.001) but not with measures of liver dysfunction (bilirubin, INR, MELD score, or hepatic venous pressure gradient).

CONCLUSION

In human cirrhosis, increased hepatic venous ET-1 is associated with IPV and increased hepatic cholangiocyte volume.

Effect of heme oxygenase-1 on renal function in rats with liver cirrhosis

AIM: To investigate the role of heme oxygenase-1 (HO-1) in pathogenesis of experimental hepatorenal syndrome (HRS).

METHODS: Rats were divided into liver cirrhotic group, zinc protoporphyrin IX (ZnPP) treatment group, cobalt protoporphyrin (CoPP) treatment group and sham group. Biliary cirrhosis was established by bile duct ligation in the first three groups. Rats in the ZnPP and CoPP treatment groups received intraperitoneal injection of ZnPP and CoPP, respectively, 24 h before sample collection. Expression of HO-1 mRNA in kidney was detected by reverse-transcription polymerase chain reaction, while protein expression was determined by immunohistochemical analysis. Hematoxylin and eosin staining was performed to observe liver cirrhosis and renal structure. Renal artery blood flow, mean arterial pressure and portal vein pressure, 24 h total urinary volume, serum and urine sodium concentrations, and creatinine clearance rate (Ccr) were also measured.

RESULTS: The HO-1 mRNA and protein expression levels in kidney, 24 h total urinary volume, renal artery blood flow, serum and urine sodium concentration and Ccr were lower in cirrhotic group than in sham group (P < 0.05). However, they were significantly lower in ZnPP treatment group than in cirrhotic group and significantly higher in CoPP treatment group than in cirrhotic group (P < 0.05).

CONCLUSION: Low HO-1 expression level in kidney is an important factor for experimental HRS.

Hepatopulmonary syndrome: an update

Hepatopulmonary syndrome (HPS) is a clinical threesome composed of liver disease, intrapulmonary vascular dilatation (IPVD) and arterial gas abnormalities. Its occurrence has been described in up to 32% of cirrhotic candidates for liver transplantation. It also affects non-cirrhotic patients with portal hypertension. Its pathogenesis is not well defined, but an association of factors such as imbalance in the endothelin receptor response, pulmonary microvascular remodeling and genetic predisposition is thought to lead to IPVD. Diagnosis is based on imaging methods that identify these dilatations, such as contrast echocardiography or perfusion scintigraphy with 99mTc, as well as analysis of arterial gases to identify elevated alveolar-arterial differences in O2 or hypoxemia. There is no effective pharmacological treatment and complete resolution only occurs through liver transplantation. The importance of diagnosing HPS lies in prioritizing transplant candidates, since presence of HPS is associated with worse prognosis. The aim of this paper was to review the pathogenetic theories and current diagnostic criteria regarding HPS, and to critically analyze the prioritization of patients with HPS on the liver transplant waiting list. Searches were carried out in the Medline (Medical Literature Analysis and Retrieval System Online) via PubMed, Cochrane Library and Lilacs (Literatura Latino-Americana e do Caribe em Ciências da Saúde) databases for articles published between January 2002 and December 2007 involving adults and written either in English or in Portuguese, using the term hepatopulmonary syndrome. The studies of greatest relevance were included in the review, along with text books and articles cited in references that were obtained through the review.

Attenuation of experimental hepatopulmonary syndrome in endothelin B receptor-deficient rats

Experimental hepatopulmonary syndrome (HPS) after common bile duct ligation (CBDL) in rat is accompanied by increased lung vascular endothelial endothelin B (ETB) receptor expression and increased circulating levels of endothelin-1 (ET-1). The onset of HPS is hypothesized to be triggered by ET-1/ETB receptor activation of endothelial nitric oxide synthase (eNOS)-derived NO production in the pulmonary endothelium. However, whether functional pulmonary vascular ETB receptors are required for the development of experimental HPS is not defined. We evaluated the effects of vascular ETB receptor deficiency on the development of experimental HPS. The molecular and physiological alterations of HPS were compared in 2-wk CBDL wild-type and ETB receptor-deficient (transgenic sl/sl) rats. Relative to wild-type rats, basal hepatic and plasma ET-1 levels were elevated in sl/sl controls although, unlike wild-type animals circulating ET-1 levels, did not increase further after CBDL in sl/sl animals. In contrast to wild-type animals, ETB receptor-deficient rats did not develop increased Akt and eNOS expression and activation and did not develop gas exchange abnormalities of HPS after CBDL. There was a similar degree of pulmonary intravascular monocyte accumulation in both 2-wk CBDL sl/sl and wild-type animals. In conclusion, ETB receptor deficiency inhibits lung Akt/eNOS activation and prevents the onset of experimental HPS after CBDL. This effect is independent of inhibition of pulmonary intravascular monocyte accumulation. These results demonstrate that ET-1/ETB receptor signaling plays a key role in the initiation of experimental HPS.

Pulmonary manifestations of liver diseases

Respiratory problems are common in patients with chronic liver diseases. The most common causes are disorders that are not related to liver diseases such as asthma and COPD. In addition certain liver diseases that are associated with specific pulmonary abnormalities, and conditions associated with end stage liver disease like tense ascites and intercostal muscular wasting are considered. Finally two unique disorders characterizing by vascular abnormalities independent of cardiorespiratory disorder-the hepatopulmonary syndrome (HPS) and portopulmonary hypertension (POPH) are observed. These disorders have different pathogenesis, different clinical pictures, treatment and prognosis. This article reviews the epidemiology, pathophysiology, clinical features, evaluation and current therapy of these two disorders.

Pulmonary angiogenesis in a rat model of hepatopulmonary syndrome

BACKGROUND & AIMS

Hepatopulmonary syndrome (HPS), defined as intrapulmonary vasodilation, occurs in 10%-30% of cirrhotics and increases mortality. In a rat model of HPS induced by common bile duct ligation (CBDL), but not thioacetamide (TAA)-induced nonbiliary cirrhosis, lung capillary density increases, monocytes accumulate in the microvasculature, and signaling factors in the angiogenesis pathway (Akt and endothelial nitric oxide synthase [eNOS]) are activated. Pentoxifylline (PTX) directly decreases lung endothelial Akt and eNOS activation, blocks intravascular monocyte accumulation, and improves experimental HPS; we evaluated whether pulmonary angiogenesis develops in this model.

METHODS

TAA- and PTX-treated animals were evaluated following CBDL. Lung angiogenesis was assessed by quantifying factor VIII-positive microvessels and levels of von Willebrand factor (vWf), vascular endothelial cadherin (VE-cadherin), and proliferating cell nuclear antigen (PCNA). Angiogenic factors including phospho-Akt, phospho-eNOS, vascular endothelial growth factor (VEGF)-A, and phospho-VEGF receptor-2 (p-VEGFR-2) were compared and monocyte accumulation was assessed.

RESULTS

Following CBDL, but not TAA exposure, rats developed HPS that was temporally correlated with increased numbers of lung microvessel; increased levels of vWf, VE-cadherin and PCNA; and activation of Akt and eNOS. Angiogenesis was accompanied by increased pulmonary VEGF-A and p-VEGFR-2 levels, with VEGF-A staining in accumulated intravascular monocytes and alveolar endothelial cells. Following CBDL, PTX-treated rats had reduced numbers of microvessels, reduced lung monocyte accumulation, downregulation of pulmonary angiogenic factors, and reduced symptoms of HPS.

CONCLUSIONS

A specific increase in pulmonary angiogenesis occurs as experimental HPS develops, accompanied by activation of VEGF-A-associated angiogenic pathways. PTX decreases the angiogenesis, reduces the symptoms of HPS, and downregulates VEGF-A mediated pathways.

Liver transplantation for pulmonary vascular complications of pediatric end-stage liver disease

PURPOSE

Hepatopulmonary syndrome (HPS) and portopulmonary hypertension (PPH) are poorly understood pulmonary complications of end-stage liver disease (ESLD). We present a case series of children with HPS and PPH.

METHODS

After institutional review board approval, query of our medical database identified children 0 to 18 years of age with ESLD diagnosed with HPS or PPH. Data were collected via chart review.

RESULTS

We identified 7 children with either HPS (n = 5) or PPH (n = 2). Patients with HPS presented with progressive dyspnea over a mean of 7 months (range, 4-12 months) at a mean of 13 years (range, 5-17 years) of age. Pulmonary shunting by albumin perfusion scan averaged 41% (range, 20%-66%) with an initial mean resting SpO(2) of 88% (range, 84%-94%) and mean SpO(2) during exertion of 79% (range, 60%-89%). Four patients required supplemental O(2) and, upon United Network for Organ Sharing (UNOS) appeal, received pediatric model for ESLD (or Child-Pugh) score exceptions, enabling them to undergo orthotopic liver transplant (OLT) within 1-2 months. The fifth patient was initially rejected by the UNOS regional review board, but 6 months of worsening hypoxemia led to OLT 2 months after successful UNOS appeal. All patients with HPS undergoing OLT experienced complete resolution of hypoxemia within 8 months. Both children with PPH were treated with intravenous epoprostenol, which lowered or stabilized mean pulmonary artery pressure and bridged them to OLT within 7 months of listing. Overall, there were no pulmonary complications; however, 1 patient with PPH expired shortly after OLT. The remaining patients are alive at a median follow-up of 27 months (range, 6-96 months).

CONCLUSION

Hepatopulmonary syndrome and PPH are uncommon complications of ESLD in children. Epoprostenol can bridge PPH patients to OLT. OLT leads to rapid resolution of HPS and PPH and currently represents the only successful treatment for these children.

Roles of vascular mediators in the pathogenesis of hepatopulmonary syndrome in rats

AIM: To explore the roles of endothelin-1 (ET-1), nitric oxide (NO) and calcitonin gene-related peptide (CGRP) in the pathogenesis of hepatopulmonary syndrome (HPS) in rats.

METHODS: Thirty-two male Wistar rats were randomly and averagely divided into 4 groups: sham operation group, common bile duct ligation (CBDL) 3-wk group, CBDL 4-wk group and CBDL 5-wk group. HPS model was induced by CBDL. Liver function and pathological changes of liver and lung were observed. The concentrations of ET-1 and CGRP in plasma, liver and lung tissues were detected by radioimmunoassay (RIA) and the NO content in serum, liver and lung tissues was measured with nitrate reductase method.

RESULTS: During the pathogenesis of HPS, liver was damaged with inflammation and fibrous hyperplasia. Fibrosis caused the formation of false lobules. Lung structural alterations such as alveolar capillary dilation and angiogenesis, thickened alveolar septa and decreased alveolar capacity were observed. The levels of ET-1, NO and CGRP in plasma, liver and lung tissues were gradually increased from the 3rd to 5th wk after CBDL, which were positively correlated with alanine aminotransferase level (plasma, ET-1: r = 0.9889, P = 0.0111; NO: r = 0.9935, P = 0065; CGRP: r = 0.9714, P = 0.0286; liver tissue: r = 0.9969, P = 0.0035; r = 0.9993, P = 0.0070; r = 0.9507, P = 0.0493; lung tissue: r = 0.9939, P = 0.0061; r = 0.9991, P = 0.0009; r = 0.9557, P = 0.0443).

CONCLUSION: The levels of ET-1, NO and CGRP in plasma, liver and lung are increased markedly during the process of HPS formation, suggesting that vascular mediators such as ET-1, NO and CGRP may play important roles in the pathogenesis of HPS.

Increased sinusoidal resistance is responsible for the basal state and endothelin-induced venoconstriction in perfused cirrhotic rat liver

The localization of increased intrahepatic vascular resistance and the segmental vascular responsiveness to endothelin-1 are not well known in liver cirrhosis. We determined the segmental vascular resistances and their response to endothelin-1 of isolated portally perfused bile duct ligation (BDL)-induced cirrhotic rat livers. The portal occlusion pressure (Ppo) and the hepatic venous occlusion pressure (Phvo) were obtained by analyzing the profiles of the portal (Ppv) and hepatic venous (Phv) pressures during the double occlusion maneuver of simultaneous occlusions of the inflow and outflow perfusion lines. From the pressure gradients among Ppv, Ppo, Phvo, and Phv, the portal-hepatic venous resistance was assigned to three segments of the portal [Rpv = (Ppv - Ppo)/blood flow (Q)], sinusoidal [Rsinus = (Ppo - Phvo)/Q] and hepatic venous [Rhv = (Phvo - Phv)/Q] resistances. Rsinus, but not Rpv or Rhv, was significantly greater in BDL livers than in sham livers. Endothelin-1 (0.1-1 nM) increased Rpv and Rsinus to a similar magnitude, but not Rhv, in both sham and BDL. At 3 nM, the responsiveness of Rpv was smaller in BDL than in sham, but that of Rsinus were similar between in BDL and sham. In conclusion, increased sinusoidal resistance accounts for increased intrahepatic resistance of BDL-induced liver cirrhosis. Endothelin-1 contracts portal veins and sinusoids, but not hepatic veins, in both sham and cirrhotic livers. Sinusoidal contractility to endothelin-1 is not impaired in cirrhotic livers.

Intestinal endotoxemia plays a central role in development of hepatopulmonary syndrome in a cirrhotic rat model induced by multiple pathogenic factors

AIM: To characterize the correlation between severity of hepatopulmonary syndrome (HPS) and degree of hepatic dysfunction, and to explore how intestinal endotoxemia (IETM) affects the development of HPS in cirrhotic rats.

METHODS: Male Wister rats were fed with a diet containing maize flour, lard, cholesterol, and alcohol and injected subcutaneously with CCl₄ oil solution every two days for 8 wk to induce typical cirrhosis and development of HPS. The animals were also given a nitric oxide (NO) production inhibitor, N^ω-nitro-L-arginine methyl ester (L-NAME) intraperitoneally, and an iNOS inhibitor, aminoguanidine hydrochloride (AG) via gavage daily from the end of the 4th wk to the end of the 6th or 8th wk, or a HO-1 inhibitor, zinc protoporphyrin (ZnPP) intraperitoneally 12 h prior to killing. Blood, liver and lung tissues were sampled.

RESULTS: Histological deterioration of the lung paralleled to that of the liver in the cirrhotic rats. The number of pulmonary capillaries was progressively increased from 6.1 ± 1.1 (count/filed) at the 4th wk to 14.5 ± 2.4 (count/filed) at the 8th wk in the cirrhotic rats. Increased pulmonary capillaries were associated with increased blood levels of lipopolysaccharide (LPS) (0.31 ± 0.08 EU/mL vs control 0.09 ± 0.03 EU/mL), alanine transferase (ALT, 219.1 ± 17.4 U/L vs control 5.9 ± 2.2 U/L) and portal vein pressure. Compared with normal control animals, the number of total cells in bronchoalveolar lavage fluid (BALF) of the cirrhotic rats at the 8th wk was not changed, but the number of macrophages and the ratio of macrophages to total cells were increased by nearly 2-fold, protein expression of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) started to increase significantly at the 4th wk, and reached its peak at the 8th wk in the lung of cirrhotic rats. The increase of iNOS expression appeared to be quicker than that of eNOS. NO₂^-/NO₃^- was also increased, which was correlated to the increase of iNOS (r = 0.7699, P < 0.0001) and eNOS (r = 0.5829, P < 0.002). mRNA expression of eNOS and iNOS was highly consistent with their protein expression.

CONCLUSION: Progression and severity of HPS as indicated by both increased pulmonary capillaries and histological changes are closely associated with LPS levels and progression of hepatic dysfunction as indicated by increased levels of ALT and portal vein pressure. Intestinal endotoxemia plays a central role in the development of HPS in the cirrhotic rat model by inducing NO and/or CO.

Opposite regulation of endothelial NO synthase by HSP90 and caveolin in liver and lungs of rats with hepatopulmonary syndrome

The hepatopulmonary syndrome is a complication of cirrhosis that associates an overproduction of nitric oxide (NO) in lungs and a NO defect in the liver. Because endothelial NO synthase (eNOS) is regulated by caveolin that decreases and heat shock protein 90 (HSP90) that increases NO production, we hypothesized that an opposite regulation of eNOS by caveolin and HSP90 might explain the opposite NO production in both organs. Cirrhosis was induced by a chronic bile duct ligation (CBDL) performed 15, 30, and 60 days before sample collection and pharmacological tests. eNOS, caveolin, and HSP90 expression were measured in hepatic and lung tissues. Pharmacological tests to assess NO released by shear stress and by acetylcholine were performed in livers (n = 28) and lungs (n = 28) isolated from normal and CBDL rats. In lungs from CBDL rats, indirect evidence of high NO production induced by shear stress was associated with a high binding of HSP90 and a low binding of caveolin to eNOS. Opposite results were observed in livers from CBDL rats. Our study shows an opposite posttranslational regulation of eNOS by HSP90 and caveolin in lungs and liver from rats with CBDL. Such opposite posttranslational regulation of eNOS by regulatory proteins may explain in part the pulmonary overproduction of NO and the hepatic NO defect in rats with hepatopulmonary syndrome.

Pentoxifylline attenuation of experimental hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) following rat common bile duct ligation results from pulmonary molecular changes that may be influenced by circulating TNF-alpha and increased vascular shear stress, through activation of NF-kappaB or Akt. Increased pulmonary microvascular endothelin B (ET(B)) receptor and endothelial nitric oxide synthase (eNOS) levels contribute to nitric oxide production and the development of experimental HPS. Pentoxifylline (PTX), a phosphodiesterase and nonspecific TNF-alpha inhibitor, ameliorates experimental HPS when begun before hepatic injury. However, how PTX influences the molecular events associated with initiation of experimental HPS after liver injury is established is unknown. We assessed the effects of PTX on the molecular and physiological features of HPS in vivo and on shear stress or TNF-alpha-mediated events in rat pulmonary microvascular endothelial cells in vitro. PTX significantly improved HPS without altering portal or systemic hemodynamics and downregulated pulmonary ET(B) receptor levels and eNOS expression and activation. These changes were associated with a reduction in circulating TNF levels and NF-kappaB activation and complete inhibition of Akt activation. In rat pulmonary microvascular endothelial cells, PTX inhibited shear stress-induced ET(B) receptor and eNOS expression and eNOS activation. These effects were also associated with inhibition of Akt activation and were reproduced by wortmanin. In contrast, TNF-alpha had no effects on endothelial ET(B) and eNOS alterations in vitro. PTX has direct effects in the pulmonary microvasculature, likely mediated through Akt inhibition, that ameliorate experimental HPS.

Effects of nebulized N(G)-nitro-L-arginine methyl ester in patients with hepatopulmonary syndrome

Enhanced pulmonary production of nitric oxide (NO) has been implicated in the pathogenesis of hepatopulmonary syndrome (HPS). NO inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) in both animals and humans with HPS has improved arterial hypoxemia. We assessed the role of enhanced NO production in the pathobiology of arterial deoxygenation in HPS and the potential therapeutic efficacy of selective pulmonary NO inhibition. We investigated the effects of nebulized L-NAME (162.0 mg) at 30 and 120 minutes on all intrapulmonary and extrapulmonary factors governing pulmonary gas exchange in 10 patients with HPS (60 +/- 7 [SD] yr; alveolar-arterial oxygen gradient, range 19-76 mm Hg; arterial oxygen tension, range 37-89 mm Hg). Nebulized L-NAME maximally decreased exhaled NO (by -55%; P < .001), mixed venous nitrite/nitrate (by -12%; P = .02), and cardiac output (by -11%; P = .002) while increased systemic vascular resistance (by 11%; P = .008) and pulmonary vascular resistance (by 25%; P = .03). In contrast, ventilation-perfusion mismatching, intrapulmonary shunt and, in turn, arterial deoxygenation remained unchanged. In conclusion, gas exchange disturbances in HPS may be related to pulmonary vascular remodeling rather than to an ongoing vasodilator effect of enhanced NO production.

The diagnosis and treatment of hepatopulmonary syndrome

Few prognostic indicators and outcomes reported for patients who have hepatopulmonary syndrome can be consistently reproduced between institutions. The lack of practice recommendations based upon consistent and predictable outcomes creates uncertainty for physicians trying to make the best patient choices. With the scarcity of donor organs, these issues are of particular importance when transplantation in considered as a treatment option. Much uncertainty arises from the basic tasks of making an accurate diagnosis in patients who have symptoms suggestive of hepatopulmonary syndrome. This article focuses on problems that underlie diagnostic accuracy and uses this information to appraise critically outcomes literature.

The pulmonary involvement in portal hypertension: portopulmonary hypertension and hepatopulmonary syndrome

Pulmonary abnormalities are common in patients with advanced chronic liver disease. Two distinct syndromes strictly related to the presence of portal hypertension, but clearly different from a pathophysiologic point of view, have been identified. Portopulmonary hypertension, characterized by an increased pulmonary arterial pressure, is due to a progressive arteriolar vasoconstriction induced by excess local production of vasoconstrictor substances. Hepatopulmonary syndrome results from intrapulmonary microvascular dilation caused by an inadequate synthesis or metabolism of putative pulmonary vasoactive substances leading to a functional vasodilation of the pulmonary vasculature, ultimately leading to hypoxemia. Controversies on pathogenesis imply different tentative therapeutic approaches for the medical management of these conditions. The development of portopulmonary hypertension or the hepatopulmonary syndrome has important clinical and prognostic implications facing the impact of new therapeutic strategies for the management of the main complications of advanced liver diseases on cardiopulmonary function.

[Common bile duct ligation as a model of hepatopulmonary syndrome and oxidative stress]

BACKGROUND

The hepatopulmonary syndrome is characterized by hepatic dysfunction and presence of dilated pulmonary vessels, with alterations in air diffusion that can be demonstrated in the experimental model of common bile duct ligation.

AIM

To evaluate the oxidative stress in pulmonary tissue of cirrhotic rats with common bile duct ligation.

MATERIAL/METHODS

We used 12 male Wistar rats weighing between 200-300 g divided in two groups: control (Co = 6) and cirrhotic (Ci = 6). We evaluated aminotransferases, arterial gasometry, lipoperoxidation and chemoluminescence), and antioxidant enzymatic activity with superoxide dismutase. The tissues analyzed for hepatopulmonary syndrome were cirrhotic liver and lung.

RESULTS

The animals with common bile duct ligation showed alterations in the following aminotransferases: aspartate aminotransferase, Co = 105.3 +/- 43/Ci = 500.5 +/- 90.3, alanine aminotransferase, Co = 78.75 +/- 37.7/Ci = 162.75 +/- 35.4, and alkaline phosphatase, Co = 160 +/- 20.45/Ci = 373 +/- 45.44. The lipoperoxidation and the antioxidant response had significant differences between the groups when evaluated in lung (lipoperoxidation) Co = 0.87 +/- 0.3/Ci = 2.01 +/- 0.9, chemoluminescence Co = 16008.41 +/- 1171.45/Ci = 20250.36 +/- 827.82 superoxide dismutase Co = 6.66 +/- 1.34/Ci = 16.06 +/- 2.67.

CONCLUSIONS

Our results suggest that in this experimental model of cirrhosis using common bile duct ligation, there is an increase in lipoperoxidation in pulmonary tissue as well as an increase in superoxide dismutase's antioxidant activity, suggesting a pulmonary injury caused by secondary biliary cirrhosis.

Recent advances in hepatopulmonary syndrome

Hepatopulmonary syndrome is defined as the clinical triad of advanced liver disease, arterial deoxygenation and intrapulmonary vascular dilatation. Its pathogenesis is not completely understood. Excessive pulmonary nitric oxide production seems to be one of the factors that contribute to the intrapulmonary vascular dilatation. Other mediators such as endothelin-1 and the heme oxygenase-1/carbon monoxide system have recently been found to be important contributors. The major clinical manifestations are arterial hypoxemia, clubbed fingers and spider nevi. Orthodeoxia is the characteristic clinical feature. Contrast-enhanced echocardiography is the preferred screening test. 99mTechnetium macroaggregated albumin (Tc-99m MAA) lung perfusion scan can further specify the diagnosis of hepatopulmonary syndrome and quantify the magnitude of shunting. No clearly effective medical treatments have been found. Although liver transplantation seems feasible to reverse this situation, it is associated with increased postoperative morbidity and mortality. A preoperative arterial oxygen tension of 50 mmHg or less and Tc-99m MAA shunt fractions of 20% or more are strong predictors of postoperative mortality that can be used to stratify patients with better outcome.

Hepatopulmonary syndrome

The hepatopulmonary syndrome is an increasingly important vascular complication of cirrhosis where microvascular dilatation impairs arterial oxygenation in the setting of liver disease. This syndrome is identified in as many as 20% of patients evaluated for liver transplantation and results in increased mortality. No clearly effective medical therapies are available, and liver transplantation is the only established treatment. Pathophysiologic insights obtained from experimental models may lead to the development of novel and effective medical treatments.

Hemodynamic features of advanced cirrhosis due to chronic bile duct ligation

AIM

The aim of the present study was to compare the hemodynamic features of portal hypertension in rats with early cirrhosis with those of rats with advanced cirrhosis following common bile duct ligation (CBDL).

METHODS

A total of 53 male Sprague-Dawley rats were used. Hemodynamics were evaluated under conscious and unrestrained conditions 4 weeks and 8 weeks after CBDL, and 4 weeks after a sham operation. Arterial pressure and portal pressure were measured directly via catheters placed in the right femoral artery and main portal vein, respectively. The cardiac index and organ (splanchninc organs, brain, kidneys and lungs) blood flow were determined by the reference sample method using (141)Ce-labeled microspheres (15 mum in diameter). Arterial levels of endothelin-1 and nitrate/nitrite, as well as liver function variables, were also determined.

RESULTS

Portal pressure was significantly higher 8 weeks after CBDL (15.8+/-2.1, n=8) than 4 weeks after CBDL (13.9+/-2.1 mmHg, n=12, p<0.05), and the hyperdynamic circulation of the early period was attenuated (p<0.05). Although hepatic artery blood flow 4 and 8 weeks after CBDL was higher than that after sham operation (p<0.05), portal territory blood flow was not increased. There was a significant positive correlation between portal pressure and portal territory blood flow 8 weeks after CBDL (r=0.822, n=8, p=0.012). In rats with anemia 4 weeks after CBDL, the hemoglobin concentration was negatively correlated with portal territory blood flow (r=-0.597, n=12, p=0.040).

CONCLUSION

Portal pressure was higher 8 weeks after CBDL than 4 weeks after CBDL and increased with portal territory blood flow, suggesting that portal hypertension is maintained by a mechanism consistent with the forward flow theory. Anemia might exacerbate the hyperdynamic systemic circulation 4 weeks after CBDL.

Correlation between pulmonary endothelin receptors and alveolar-arterial oxygen gradient in rats with hepatopulmonary syndrome

The correlation between pulmonary endothelin receptors and alveolar-arterial oxygen gradient (A-aDO2) in rats with hepatopulmonary syndrome was investigated. Animals were divided into 2 groups: Sham-operated (Sham) group and common bile duct ligation (CBDL) group. Arterial blood gas was evaluated by a blood gas analyzer. The concentrations of ET-1 in blood and lung tissue sample were evaluated by radioimmunoassay. The distribution and expression of two kinds of subtype receptor of ET-1, ETRA and ETRB were examined by in situ hybridization. The results showed that the level of A-aDO2 was higher in CBDL group than that in Sham group (P < 0.05). The levels of plasma and pulmonary ET-1 in CBDL group were both higher than in Sham group (P < 0.05). There was no significant difference in average A of ETRA between two groups by imaging analysis (0.21 +/- 0.06 vs 0.22 +/- 0.08, P > 0.05), while that of ETRB was higher in CBDL group than in Sham group (0.58 +/- 0.16 vs 0.28 +/- 0.07, P < 0.05). The expression of ETRB in lung was positively correlated with A-aDO2 (P < 0.05). It was concluded that the widened A-aDO2 may be related with enhancement of the expression of ETRB in lung.

Hepatopulmonary syndrome induced by common bile duct ligation in a rabbit model: correlation between pulmonary vascular dilatation on thin-section CT and angiography and serum nitrite concentration or endothelial nitric oxide synthase (eNOS)1 expression

OBJECTIVE

To investigate the correlation between radiologic vascular dilatation and serum nitrite concentration and eNOS expression in the endothelial cell and pneumocyte in a rabbit model of hepatopulmonary syndrome induced by common bile duct ligation (CBDL).

MATERIALS AND METHODS

Thin-section CT scans of the lung and pulmonary angiography were obtained 3 weeks after CBDL (n = 6), or a sham operation (n = 4), and intrapulmonary vasodilatation was assessed. The diameter and tortuosity of peripheral vessels in the right lower lobe by thin-section CT and angiography at the same level of the right lower lobe in all subjects were correlated to serum nitrite concentration and eNOS (endothelial nitric oxide synthase) expression as determined by immunostaining.

RESULTS

The diameters of pulmonary vessels on thin-section CT were well correlated with nitrite concentrations in serum (r = 0.92, p < 0.001). Dilated pulmonary vessels were significantly correlated with an increased eNOS expression (r = 0.94, p < 0.0001), and the severity of pulmonary vessel tortuosity was found to be well correlated with serum nitrite concentration (r = 0.90, p < 0.001).

CONCLUSION

The peripheral pulmonary vasculature in hepatopulmonary syndrome induced by CBLD was dilated on thin-section CT and on angiographs. Our findings suggest that peripheral pulmonary vascular dilatations are correlated with serum nitrite concentrations and pulmonary eNOS expression.

The Incidence of self-prescribed oral complementary and alternative medicine use by patients with gastrointestinal diseases

GOALS

To assess the incidence of oral complementary and alternative medicine (CAM) usage by gastroenterology patients at a single university center and compare against controls.

BACKGROUND

The public awareness and usage of CAM have increased. The use of CAM has been described in patients with functional bowel disorders; however, their role in patients with gastrointestinal disease is less clear.

STUDY

Patients attending luminal gastroenterology clinics and customers at local supermarkets completed a 30-point, structured questionnaire assessing their use of CAM.

RESULTS

A total of 1,409 subjects were recruited. The incidence of CAM use was 49.5% for inflammatory bowel disease, 50.9% for irritable bowel syndrome, 20% for general gastrointestinal diseases, and 27% for controls. Pearson's chi(2) tests showed that patients with inflammatory bowel disease (IBD) or irritable bowel syndrome were more likely to use CAM than controls (P < 0.001). Binary logistic regression analysis showed that females were more likely to take CAM than men (P < 0.05).

CONCLUSIONS

The percentage of CAM users among patients with IBD is similar to those with a functional diagnosis. Increasing numbers of IBD patients are using CAM in addition to conventional therapy. Awareness of this may prevent adverse CAM and conventional drug interactions.

Experimental study on the role of endotoxin in the development of hepatopulmonary syndrome

AIM: To evaluate the role of intestinal endotoxemia in the genesis of hepatopulmonary syndrome.

METHODS: A rat model of cirrhosis was prepared with the method of compound factors. At the end of the eighth week, rats with cirrhosis were treated with 300 μg LPS/100 g body weight, and 1 g/rat of glycine about four h prior to LPS. After three h of LPS treatment, blood and tissues were collected for various measurements. Kupffer cells were isolated from male Wistar rats and cultured, and divided into five groups. Supernatant was harvested at 3 h after treatment with LPS for measurement of tumor necrosis factor-alpha (TNF-α).

RESULTS: Our results showed that in rats with cirrhosis, slowed and deepened breath with occasional pause was. PaO₂, PaCO₂ and standard bicarbonate (SB) in arterial blood were decreased. Arterial O₂ and actual bicarbonate (AB) were markedly decreased. There was a close correlation between decreased O₂ and endotoxin. Metabolic acidosis accompanying respiratory alkalosis was the primary type of acid-base imbalance. The alveolar-arterial oxygen gradient was sharply widened. Massive accumulation of giant macrophages in the alveolar spaces and its wall and widened alveolar wall architecture were observed. The number of bacterial translocations in mesenteric lymph nodes increased. The ratio of TC99M-MAA brain-over-lung radioactivity rose. Endotoxin, and TNF-α, endothelin-1 (ET-1), nitric oxide (NO) in plasma and ET-1, carbon monoxide (CO) in lung homogenates increased. After administration of a given dosage of LPS in rats with cirrhosis, various pathological parameters worsened. Plasma level of endotoxin was related to TNF-α, ET-1, NO in plasma and ET-1, NO, CO in lung homogenates. TNF-α level was related to ET-1 and NO in plasma and lung homogenates and CO in lung homogenate as well. The level of TNF-α increased after infusion of LPS into culture supernatant of Kupffer cells in vitro. However, TNF-α significantly decreased after pretreatment with glycine, PD98059 and SB212850. Glycine could antagonize the effect of LPS in vivo and in vitro.

CONCLUSION: Intestinal endotoxemia accompanying by cirrhosis may be an important mechanism in the development of hepatopulmonary syndrome in rats. Overproduction of TNF-α due to endotoxin stimulation of Kupffer cells via mitogen-activated protein kinase (MAPK) signal transduction pathway may be a major mechanism mediating the pathologic alterations of hepatopulmonary syndrome.

Use of a mixed endothelin receptor antagonist in portopulmonary hypertension: a safe and effective therapy?

BACKGROUND & AIMS

Portopulmonary hypertension (PPHTN), a severe complication of portal hypertension is observed in 3%-6% of patients evaluated for liver transplantation. Endothelin-1, a potent vasoconstrictor, is likely to play a role in the pathogenesis of primary pulmonary hypertension, and, in 2 recent trials, the dual endothelin receptor antagonist bosentan has shown beneficial effects in this disease. A role for endothelins in the development of both pulmonary hypertension and cirrhosis has been suggested. We therefore hypothesized that endothelin receptor blockade may be beneficial in the treatment of PPHTN.

METHODS

We report a case of a 42-year-old patient with PPHTN and alcoholic cirrhosis treated with the mixed endothelin receptor antagonist bosentan.

RESULTS

The patient rapidly improved from NYHA IV to stage II, experienced a remarkable improvement of 6-minute walking distance from 0 to 590 m within 6 months, and resumed working full-time as a locksmith after 7 months of treatment. Improvement of cardiovascular parameters included a reduction of pulmonary vascular resistance by 60%, a decrease of mean pulmonary artery pressure (mPAP) from 55 to 44 mm Hg at 9 months, and a decline of plasma B-type natriuretic peptide (BNP) from 339 pg/mL to 19 pg/mL after 1 year. There were no adverse events except for a transient decrease in systemic blood pressure.

CONCLUSIONS

To our knowledge, this is the first report of a patient with PPHTN treated with an endothelin receptor antagonist. The marked and sustained improvement supports the undertaking of controlled studies of the safety and efficacy of bosentan in PPHTN.