Ghazwan Butrous

Intravenous Sildenafil Is a Potent Pulmonary Vasodilator in Children With Congenital Heart Disease

Background—Increased pulmonary vascular resistance (PVR) because of congenital heart disease (CHD) may be caused by a dysfunction in endogenous pulmonary endothelial nitric oxide (NO) production. In other forms of pulmonary vascular disease with increased PVR, an elevated activity of a phosphodiesterase type 5 (PDE-5), responsible for the degradation of cyclic guanidine monophosphate (cGMP), the second messenger of endothelially produced NO, has been demonstrated. This study compares the effects of inhaled NO before and after the specific inhibition of the PDE-5 by intravenous sildenafil (Viagra™) in pre- and postoperative children with increased PVR because of CHD. Methods and Results—12 children with congenital heart disease (age 0.2 to 15.7 years, median 2.4 years) and increased mean pulmonary arterial pressure, and 12 postoperative children (age 0.11 to 0.65 years, median 0.32 years) with increased PVR (8.3±1.0 Wood Units*m2) were studied during cardiac catheterization (“cath laboratory”), or within 2 hours after return from cardiac surgery (“post op”), respectively. All were sedated, tracheally intubated and paralyzed. During alveolar hyperoxygenation (FiO2=0.65), the effects of inhaled NO (20 ppm) were compared before and after the stepwise infusion of sildenafil (“cath laboratory”, 1 mg/kg; post op, 0.25 mg/kg). Intravenous sildenafil more effectively reduced PVR than NO (11.5% versus 4.3% in the “cath laboratory” patient group, P <0.05, and 25.8% versus 14.6% in the post op patient group, P =0.09. The increase in cGMP in response to NO was potentiated (2- to 2.4-fold) by PDE-5 inhibition. While the vasodilating effects of sildenafil showed pulmonary selectivity, its infusion was associated with increased intrapulmonary shunting in the postoperative patients (Qs/Qt=16.5±4.7% to 25.5±18.2%P =0.04). Conclusions—Intravenous sildenafil is as effective as inhaled NO as a pulmonary vasodilator in children with congenital heart disease. Although clinically insignificant in this study, increased intrapulmonary shunting with sildenafil may be disadvantageous in some patients after CHD surgery.

Pulmonary Vascular Disease in the Developing World

The prevalence, cause, and pathobiology of pulmonary vascular disease in the developing world are not known, but estimates put the prevalence at 20 to 25 million. A major contributor is infectious disease. The present review examines the association between infectious disease and other causes in the developing world and pulmonary vascular disease and the need for further research in this area. Schistosomiasis (Bilharzias)1 is the third-leading endemic parasitic disease in the world, following malaria and amebiasis. More than 300 million individuals are infected, and another 600 million are at risk of infection.2 The disease ranks higher in prevalence than HIV/AIDS. It is endemic in eastern South America, the Caribbean Islands, east Asia, and some parts of China and the Middle East, with sub-Saharan Africa being the most endemic area. It is a major public health problem that is closely correlated with socioeconomic conditions. Modern endeavors to develop and construct water schemes to meet local power and agricultural needs have increased the prevalence in many parts of the world.2,3 Few countries have eradicated the disease or undertaken successful and sustainable control programs despite the collaborative efforts of local governments, the World Health Organization, the World Bank, the United Nations, and philanthropic organizations. Schistosomiasis is caused by flatworms. There are many species of Schistosoma . S mansoni infects >120 million people in Africa and Brazil. The final target of this species is the intestinal and hepatic circulatory system. S hematobium is endemic in Africa, the Middle East, and east Asia. It targets the genitourinary circulatory system. S japonicum , which is endemic in China and southeast Asia, affects the intestinal and hepatic circulatory system. ### The Life Cycle of Schistosomiasis The worms live in the perivisceral veins of the intestine, liver, and genitourinary systems. Their eggs find their way into the urine and feces of …

Pulmonary Vascular Remodeling Correlates with Lung Eggs and Cytokines in Murine Schistosomiasis

RATIONALE Schistosomiasis is considered to be the most common worldwide cause of pulmonary hypertension. At present there is no well-characterized animal model to study the pathobiology of this important condition. OBJECTIVES To develop a mouse model of schistosomiasis, characterize the extent of pulmonary vascular remodeling, and determine the potential role of inflammatory cytokines. METHODS Mice (C57/Bl6) were infected transcutaneously with a high dose (approximately 75-100 cercariae) or a low dose (approximately 30 cercariae) of Schistosoma mansoni, and the development of lung and liver pathology was studied in the subacute (high-dose) and chronic (low-dose) settings. MEASUREMENTS AND MAIN RESULTS In the subacute setting, mice showed few eggs in the lungs and no evidence of pulmonary vascular remodeling. In contrast, chronically infected animals had a much greater lung egg burden and developed marked pulmonary vascular remodeling accompanied by perivascular inflammation from 12 weeks onwards. In addition, we observed the presence of plexiform-like lesions in these mice. Lung egg burden correlated with both liver egg burden and right ventricular (RV) index in the chronic group, although significant RV hypertrophy was lacking. Plasma Th1 and Th2 cytokines increased with time in the chronic group and correlated with the degree of pulmonary vascular remodeling. CONCLUSIONS This study provides evidence for extensive pulmonary vascular remodeling, despite the absence of RV hypertrophy, in a mouse model of schistosomiasis, including the formation of plexiform-like lesions. Inflammatory cytokines and lung egg burden may contribute to vascular lesion formation.

Role of Src Tyrosine Kinases in Experimental Pulmonary Hypertension

Objective—Pulmonary arterial hypertension is a progressive pulmonary vascular disorder with high morbidity and mortality. Compelling evidence suggests that receptor tyrosine kinases, such as platelet-derived growth factor (PDGF) are closely involved in the pathogenesis of pulmonary arterial hypertension. We investigated the effects of 2 novel PDGF inhibitors, nilotinib/AMN107 (Abl kinases/PDGF receptor inhibitor) and dasatinib/BMS-354825 (Abl kinases/PDGF receptor/Src inhibitor), on the proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) and on the hemodynamics and pulmonary vascular remodeling in experimental pulmonary hypertension, and determined the expression and regulation of Src family kinases. Methods and Results—Human PASMCs were stimulated by PDGF alone or multiple growth factors to induce proliferation and migration in vitro. Dasatinib (0.03 &mgr;mol/L), nilotinib (0.3 &mgr;mol/L), and imatinib (1 &mgr;mol/L) potently inhibited PDGF-induced signal transducer and activator of transcription 3 and Akt phosphorylation. All 3 inhibitors decreased PDGF-induced proliferation, cell cycle gene regulation, and migration. In contrast, only dasatinib inhibited multiple growth factor–induced PASMC proliferation, and this was associated with the inhibition of Src phosphorylation. Combination of specific Src inhibitors (phosphoprotein phosphatase 1, phosphoprotein phosphatase 2) with either imatinib or nilotinib reduced multiple growth factor–induced proliferation to a similar extent as dasatinib. Importantly, Src phosphorylation increased in pulmonary arterial hypertension PASMCs compared with control PASMCs. Finally, in vivo dasatinib (15 mg/kg per body weight) treatment caused a complete reversal of pulmonary vascular remodeling and achieved similar effectiveness as imatinib (100 mg/kg per body weight) in both monocrotaline- and hypoxia-induced pulmonary hypertension models. Conclusion—We suggest that dual inhibition of PDGF receptor and Src kinases potently inhibits mitogenic and motogenic responses to growth factors in PASMCs and pulmonary vascular remodeling in vivo so that dual inhibition may represent an alternative therapeutic approach for pulmonary arterial hypertension.

Schistosomiasis-Associated Pulmonary Hypertension : Pulmonary Vascular Disease: The Global Perspective

Inflammation is likely a critical underlying etiology in many forms of severe pulmonary hypertension (PH), and schistosomiasis-associated PH, one of the most common causes of PH worldwide, is likely driven by the host response to parasite antigens. More than 200 million people are infected with schistosomiasis, the third most common parasitic disease, and approximately 1% of those chronically infected develop PH. Acute cutaneous infection causes inflammation at the site of parasite penetration followed by a subacute immune complex-mediated hypersensitivity response as the parasite migrates through the lungs. Chronic schistosomiasis infection induces a granulomatous inflammation around ova deposited in the tissue. In particular, Schistosoma mansoni migrates to the portal venous system and causes preportal fibrosis in a subset of individuals and appears to be a prerequisite for PH. Portal hypertension facilitates shunting of ova from the portal system to the pulmonary arterial tree, resulting in localized periovular pulmonary granulomas. The pulmonary vascular remodeling is likely a direct consequence of the host inflammatory response, and portopulmonary hypertension may be a significant contributor. New specific therapies available for PH have not been widely tested in patients with schistosomiasis and often are unavailable for those infected in resource-poor areas of the world where schistosomiasis is endemic. Furthermore, the current PH therapies in general target vasodilation rather than vascular remodeling and inflammation. Further research is needed into the pathogenic mechanism by which this parasitic infection results in pulmonary vascular remodeling and PH, which also may be informative regarding the etiology of other types of PH.

Transforming Growth Factor-β Signaling Promotes Pulmonary Hypertension Caused by Schistosoma Mansoni

Background— The pathogenic mechanisms underlying pulmonary arterial hypertension resulting from schistosomiasis, one of the most common causes of pulmonary hypertension worldwide, remain unknown. We hypothesized that transforming growth factor-&bgr; (TGF-&bgr;) signaling as a consequence of Th2 inflammation is critical for the pathogenesis of this disease. Methods and Results— Mice sensitized and subsequently challenged with Schistosoma mansoni eggs developed pulmonary hypertension associated with an increase in right ventricular systolic pressure, thickening of the pulmonary artery media, and right ventricular hypertrophy. Rho-kinase–dependent vasoconstriction accounted for ≈60% of the increase in right ventricular systolic pressure. The pulmonary vascular remodeling and pulmonary hypertension were dependent on increased TGF-&bgr; signaling, as pharmacological blockade of the TGF-&bgr; ligand and receptor, and mice lacking Smad3 were significantly protected from Schistosoma-induced pulmonary hypertension. Blockade of TGF-&bgr; signaling also led to a decrease in interleukin-4 and interleukin-13 concentrations, which drive the Th2 responses characteristic of schistosomiasis lung pathology. Lungs of patients with schistosomiasis-associated pulmonary arterial hypertension have evidence of TGF-&bgr; signaling in their remodeled pulmonary arteries. Conclusion— Experimental S mansoni–induced pulmonary vascular disease relies on canonical TGF-&bgr; signaling.

Role of the Prostanoid EP4 Receptor in Iloprost-mediated Vasodilatation in Pulmonary Hypertension

RATIONALE Iloprost is effective for the treatment of pulmonary hypertension. It acts through elevation of cAMP by binding to the prostacyclin receptor (IP receptor). However, there is evidence that patients with severe pulmonary hypertension have decreased expression of the IP receptor in the remodeled pulmonary arterial smooth muscle. OBJECTIVES We hypothesized that prostanoid receptors other than the IP receptor are involved in signal transduction by iloprost. METHODS Immunoblotting was used to detect the IP and prostanoid EP4 receptor in lung tissue from patients with idiopathic pulmonary arterial hypertension, and immunohistochemistry was used to detect these receptors in lung sections from rats treated with monocrotaline (MCT28d). Protein and mRNA were isolated from pulmonary arterial smooth muscle cells (PASMCs) from control and MCT28d rats treated with AH6809 (an EP2 receptor antagonist) and AH23848 (an EP4 receptor antagonist) in combination with iloprost. Intracellular cAMP was also assessed in these tissues. MEASUREMENTS AND MAIN RESULTS IP receptor expression was reduced in idiopathic pulmonary arterial hypertension patient lung samples and MCT28d rat lungs compared with the controls. Reverse transcriptase-polymerase chain reaction and immunoblotting of MCT28d rat PASMC extracts revealed scant expression of the IP receptor but stable expression of EP4 receptor, compared with controls. Iloprost-induced elevation in intracellular cAMP in PASMCs was dose-dependently reduced by AH23848, but not by AH6809. CONCLUSIONS Iloprost mediates vasodilatory functions via the EP4 receptor in the case of low IP receptor expression associated with pulmonary arterial hypertension. This is a previously unrecognized mechanism for iloprost, and illustrates that the EP4 receptor may be a novel therapeutic approach for the treatment of pulmonary arterial hypertension.

Melatonin as a preventive and curative therapy against pulmonary hypertension.

Pulmonary hypertension (PH) is characterized by elevated pulmonary arterial pressure, which leads to right ventricular (RV) hypertrophy and failure. The pathophysiological mechanisms of PH remain unclear but oxidative stress is believed to contribute to RV dysfunction. Melatonin is a powerful antioxidant and is cardioprotective against ischemia–reperfusion injury and hypertension. Therefore, we hypothesized that a chronic treatment with melatonin, given as a curative or preventive therapy, may confer cardiovascular benefits in PH. PH was induced in Long Evans rats (n ≥ 6 per group), with a single subcutaneous injection of monocrotaline (MCT, 80 mg/kg). Melatonin was given daily in the drinking water, with the treatment starting either on the day of the injection of MCT (dose testing: melatonin 75 ng/L and 6 mg/kg), 14 days after the injection of MCT (curative treatment: 6 mg/kg), or 5 days before the injection (preventive treatment: 6 mg/kg). The development of PH was assessed by measuring RV hypertrophy, RV function, cardiac interstitial fibrosis, and plasma oxidative stress. Compared with controls, MCT‐treated rats displayed RV hypertrophy and dysfunction, increased interstitial fibrosis, and elevated plasma oxidative stress. A chronic melatonin treatment (75 ng/L or 6 mg/kg) reduced RV hypertrophy, improved RV function and reduced plasma oxidative stress. Curative and preventive treatment improved RV functional and plasma oxidative stress parameters and reduced cardiac interstitial fibrosis. Our data demonstrate that melatonin confers cardioprotection in this model of PH. As melatonin is an inexpensive and safe drug, we propose that clinical investigation of the effects of melatonin on RV function in patients with PH should be considered.

Praziquantel Reverses Pulmonary Hypertension and Vascular Remodeling in Murine Schistosomiasis

RATIONALE Schistosomiasis is the most common worldwide cause of pulmonary arterial hypertension. The anti-schistosome drug praziquantel has been shown to reverse the liver fibrosis associated with Schistosoma mansoni in mice. OBJECTIVES We sought to determine whether praziquantel reverses established pulmonary vascular remodeling and pulmonary hypertension in a mouse model of S. mansoni. METHODS Mice were infected percutaneously with S. mansoni. At 17 weeks after infection mice were either killed or received two doses of praziquantel or vehicle by oral gavage. Treated mice were studied at 25 weeks after infection. MEASUREMENTS AND MAIN RESULTS Vehicle-treated mice demonstrated significant increases in right ventricular systolic pressures (RVSP) and right ventricular hypertrophy (RVH) at 25 weeks, accompanied by pulmonary vascular remodeling. The degree of vascular remodeling correlated with proximity to granulomas. The elevation of RVSP and RVH at 25 weeks was dependent on the presence of eggs in the lung. Praziquantel eliminated the production of eggs in feces and led to clearance of eggs from the lung and to a lesser extent from liver. Praziquantel prevented the rise in RVSP and RVH seen in vehicle-treated mice and reversed established pulmonary vascular remodeling. Praziquantel significantly reduced lung mRNA expression of IL-13, IL-8, and IL-4, but did not reduce serum cytokine levels. CONCLUSIONS The development of pulmonary hypertension associated with S. mansoni infection can be prevented by praziquantel, and established vascular remodeling can be reversed. The mechanism involves clearance of lung eggs and reduced local expression of lung cytokines.

Protective role of IL-6 in vascular remodeling in Schistosoma pulmonary hypertension.

Schistosomiasis is one of the most common causes of pulmonary arterial hypertension worldwide, but the pathogenic mechanism by which the host inflammatory response contributes to vascular remodeling is unknown. We sought to identify signaling pathways that play protective or pathogenic roles in experimental Schistosoma-induced pulmonary vascular disease via whole-lung transcriptome analysis. Wild-type mice were experimentally exposed to Schistosoma mansoni ova by intraperitoneal sensitization followed by tail-vein augmentation, and the phenotype was assessed by right ventricular catheterization and tissue histology, as well as RNA and protein analysis. Whole-lung transcriptome analysis by microarray and RNA sequencing was performed, and RNA sequencing was analyzed according to two bioinformatics methods. Functional testing of the candidate IL-6 pathway was determined using IL-6 knockout mice and the signal transducers and activators of transcription protein-3 (STAT3) inhibitor S3I-201. Wild-type mice exposed to S. mansoni demonstrated increased right ventricular systolic pressure and thickness of the pulmonary vascular media. Whole-lung transcriptome analysis determined that the IL-6-STAT3-nuclear factor of activated T cells c2(NFATc2) pathway was up-regulated, as confirmed by PCR and the immunostaining of lung tissue from S. mansoni-exposed mice and patients who died of the disease. Mice lacking IL-6 or treated with S3I-201 developed pulmonary hypertension, associated with significant intima remodeling after exposure to S. mansoni. Whole-lung transcriptome analysis identified the up-regulation of the IL-6-STAT3-NFATc2 pathway, and IL-6 signaling was found to be protective against Schistosoma-induced intimal remodeling.