Hypoxia-induced Pulmonary Hypertension Model Research Articles

Galectin-3: A Potential Biomarker in Pulmonary Arterial Hypertension

Objectives: Pulmonary arterial hypertension (PAH) is a syndrome resulting from a restricted flow through the pulmonary arterial circulation, giving rise to increased pulmonary vascular resistance (PVR) and ultimately right heart failure. Previous reports have suggested that Galectin-3 (Gal-3) induced endothelial cell morphogenesis and regulated myofibroblast activation. The aim of this study was to determine the diagnostic utility of circulating Gal-3 as a potential biomarker of disease severity in PAH. Methods: Gal-3 was measured in plasma from 31 patients with PAH, diagnosed from the right heart catheterization as well as 18 healthy controls by ELISA. Chronic hypoxia-induced pulmonary hypertension models were established in Sprague-Dawley rats. Lung tissues were collected for histological analysis including Gal-3 lung qualitative localization by immunohistochemistry. Total mRNA was extracted from pulmonary arteries in rats and quantitative polymerase chain reaction was performed with total cellular mRNA to measure Gal-3 expression. Results: Plasma level of Gal-3 was significantly decreased in PAH patients compared with healthy controls (P

Mitofusin 2 Downregulation Triggers Pulmonary Artery Smooth Muscle Cell Proliferation and Apoptosis Imbalance in Rats With Hypoxic Pulmonary Hypertension Via the PI3K/Akt and Mitochondrial Apoptosis Pathways.

During hypoxia-induced pulmonary hypertension (HPH), pulmonary artery smooth muscle cells (PASMCs) proliferate as part of the characteristic pulmonary vascular remodeling. We investigated the expression of mitofusin 2(Mfn2) and its role in maintaining the balance between PASMC proliferation and apoptosis during hypoxia. In an experimental model of HPH, we exposed rats to hypoxia (10% ± 0.5% O2) or room air for 4 weeks. We found that Mfn2 messenger RNA and protein levels were reduced and that proliferating cell nuclear antigen protein expression was upregulated in HPH rat lung tissues. We also exposed primary cultured PASMCs from rat pulmonary arterioles to normoxia (21% O2/5% CO2) or hypoxia (2.5% O2/5% CO2) for 24 hours. We found that PASMC proliferation increased under hypoxic conditions and that more hypoxic cells than normoxic cells entered the S + G2/M phase. Additionally, phosphorylated Akt and proliferating cell nuclear antigen expression increased, whereas Mfn2 expression, cleaved caspase 9 expression, and the ratio of mitochondrial to cytosolic cytochrome C expression each decreased. These hypoxia-induced effects were reversed in PASMCs by Mfn2 overexpression and by phosphatidylinositide 3-kinases (PI3K) inhibition. Our results indicate that downregulation of Mfn2 in HPH may activate the PI3K/Akt pathway, thereby causing more cells to enter the S + G2/M phase of the cell cycle and inhibiting the mitochondrial apoptosis pathway.

MicroRNA-103/107 is involved in hypoxia-induced proliferation of pulmonary arterial smooth muscle cells by targeting HIF-1β

AimsActivation of hypoxia inducible factor-1 (HIF) is a hallmark in hypoxia-induced pulmonary hypertension (HPH). microRNAs play a significant role in regulating proliferation of pulmonary arterial smooth muscle cells (PASMCs) in pulmonary hypertension. Previous studies have shown that HIF-1β is a target of miR-103/107. In this present study, we aimed to investigate whether miR-103/107 regulate vascular remodeling in HPH via HIF-1β. Main methodsThe HPH model was built by hypoxia exposure in rats. Real-time PCR and Western blotting were used to determine the expression of miR-103/107 and HIF-1β. Proliferation of PASMCs was examined by 5-bromo-2′-deoxyuridine (BrdU) incorporation method. The functions of miR-103/107 on PASMCs proliferation, HIF-1α and HIF-1β expression were assessed by transfecting miR-103/107 mimics and inhibitors. Key findingsSignificant down-regulation of miR-103/107 was observed in remodeled intrapulmonary vascular in HPH rats and hypoxia-exposured PASMCs, whereas HIF-1α and HIF-1β expression were up-regulated. Hypoxia exposure induced significant proliferation of PASMCs, overexpression of miR-103/107 inhibited but miR-103/107 inhibitors exacerbated PASMCs proliferation. Gain-of-function and loss-of-function experiments showed that miR-103/107 expression was inversely correlated with HIF-1β level. No significant changes of HIF-1α expression were observed under miR-103/107 mimic treatment. SignificanceLoss of suppression on HIF-1β by miR-103/107 may contribute to excess proliferation of PASMCs and vascular remodeling in hypoxic pulmonary hypertension.

The potential of asiaticoside for TGF-β1/Smad signaling inhibition in prevention and progression of hypoxia-induced pulmonary hypertension.

Asiaticoside (AS) is a saponin monomer extracted from the medicinal plant Centella asiatica, which has a variety of biological effects. We intended to investigate the effects of asiaticoside on a hypoxia-induced pulmonary hypertension (HPH) rat model and examine the possible effects of asiaticoside on TGF-β1/Smad signaling in vivo and in vitro. The rat HPH model was established by hypoxic exposure and asiaticoside was administered for four weeks. Parameters including the mean pulmonary artery pressure (mPAP), the right ventricular hypertrophy (RVH) and the percentage of medial wall thickness were used to evaluate the development of HPH. TGF-β1, TGF-β receptor, Smad2/3 and phospho-Smad2/3 expressions were detected and the proliferation, migration and apoptosis of pulmonary arterial smooth muscle cells (PASMCs) adjusted by asiaticoside under the hypoxic condition were evaluated. Our data indicate that asiaticoside attenuated pulmonary hypertension, pulmonary vascular remodeling and RV hypertrophy in HPH rats, which was probably mediated by restraining the hypoxia-induced overactive TGF-β1/Smad2/3 signaling and inhibiting the proliferation by inducing apoptosis of the PASMCs. Given the preventative potential in animal models and in vitro, we propose asiaticoside as a promising protective treatment in HPH.

Inhaled Nitric Oxide Augments Left Ventricular Assist Device Capacity by Ameliorating Secondary Right Ventricular Failure.

Clinical right ventricular (RV) impairment can occur with left ventricular assist device (LVAD) use, thereby compromising the therapeutic effectiveness. The underlying mechanism of this RV failure may be related to induced abnormalities of septal wall motion, RV distension and ischemia, decreased LV filling, and aberrations of LVAD flow. Inhaled nitric oxide (NO), a potent pulmonary vasodilator, may reduce RV afterload, and thereby increase LV filling, LVAD flow, and cardiac output (CO). To investigate the mechanisms associated with LVAD-induced RV dysfunction and its treatment, we created a swine model of hypoxia-induced pulmonary hypertension and acute LVAD-induced RV failure and assessed the physiological effects of NO. Increased LVAD speed resulted in linear increases in LVAD flow until pulse pressure narrowed. Higher speeds induced flow instability, LV collapse, a precipitous fall of both LVAD flow and CO. Nitric oxide (20 ppm) treatment significantly increased the maximal achievable LVAD speed, LVAD flow, CO, and LV diameter. Nitric oxide resulted in decreased pulmonary vascular resistance and RV distension, increased RV ejection, promoted LV filling and improved LVAD performance. Inhaled NO may thus have broad utility for the management of biventricular disease managed by LVAD implantation through the effects of NO on LV and RV wall dynamics.

IGF-1 signaling in neonatal hypoxia-induced pulmonary hypertension: Role of epigenetic regulation

Pulmonary hypertension is a fatal disease characterized by a progressive increase in pulmonary artery pressure accompanied by pulmonary vascular remodeling and increased vasomotor tone. Although some biological pathways have been identified in neonatal hypoxia-induced pulmonary hypertension (PH), little is known regarding the role of growth factors in the pathogenesis of PH in neonates. In this study, using a model of hypoxia-induced PH in neonatal mice, we demonstrate that the growth factor insulin-like growth factor-1 (IGF-1), a potent activator of the AKT signaling pathway, is involved in neonatal PH. After exposure to hypoxia, IGF-1 signaling is activated in pulmonary endothelial and smooth muscle cells in vitro, and the IGF-1 downstream signal pAKTS473 is upregulated in lungs of neonatal mice. We found that IGF-1 regulates ET-1 expression in pulmonary endothelial cells and that IGF-1 expression is regulated by histone deacetylases (HDACs). In addition, there is a differential cytosine methylation site in the IGF-1 promoter region in response to neonatal hypoxia. Moreover, inhibition of HDACs with apicidin decreases neonatal hypoxia-induced global DNA methylation levels in lungs and specific cytosine methylation levels around the pulmonary IGF-1 promoter region. Finally, HDAC inhibition with apicidin reduces chronic hypoxia-induced activation of IGF-1/pAKT signaling in lungs and attenuates right ventricular hypertrophy and pulmonary vascular remodeling. Taken together, we conclude that IGF-1, which is epigenetically regulated, is involved in the pathogenesis of pulmonary hypertension in neonatal mice. This study implicates a novel HDAC/IGF-1 epigenetic pathway in the regulation of hypoxia-induced PH and warrants further study of the role of IGF-1 in neonatal pulmonary hypertensive disease.

The hypoxia-induced microRNA-130a controls pulmonary smooth muscle cell proliferation by directly targeting CDKN1A

Excessive proliferation of human pulmonary artery smooth muscle cells (HPASMC) is one of the major factors that trigger vascular remodeling in hypoxia-induced pulmonary hypertension. Several studies have implicated that hypoxia inhibits the tumor suppressor p21 (CDKN1A). However, the precise mechanism is unknown.The mouse model of hypoxia-induced PH and in vitro experiments were used to assess the impact of microRNAs (miRNAs) on the expression of CDKN1A. In these experiments, the miRNA family miR-130 was identified to regulate the expression of CDKN1A. Transfection of HPASMC with miR-130 decreased the expression of CDKN1A and, in turn, significantly increased smooth muscle proliferation. Conversely, inhibition of miR-130 by anti-miRs and seed blockers increased the expression of CDKN1A. Reporter gene analysis proved a direct miR-130–CDKN1A target interaction. Exposure of HPASMC to hypoxia was found to induce the expression of miR-130 with concomitant decrease of CDKN1A. These findings were confirmed in the mouse model of hypoxia-induced pulmonary hypertension showing that the use of seed blockers against miR-130 restored the expression of CDKN1A.These data suggest that miRNA family miR-130 plays an important role in the repression of CDKN1A by hypoxia. miR-130 enhances hypoxia-induced smooth muscle proliferation and might be involved in the development of right ventricular hypertrophy and vascular remodeling in pulmonary hypertension.

Effects of chrysin (5,7-dihydroxyflavone) on vascular remodeling in hypoxia-induced pulmonary hypertension in rats.

BackgroundChrysin (5,7-dihydroxyflavone) inhibits platelet-derived growth factor-induced vascular smooth muscle cell proliferation and arterial intima hyperplasia. This study aims to investigate the effects of chrysin on rat pulmonary vascular remodeling in hypoxia-induced pulmonary hypertension (PH).MethodsSprague–Dawley rats were continuously exposed to 10% O2 for 4 weeks to induce PH. The effect of chrysin (50 or 100 mg/kg/d, subcutaneous) on vascular remodeling was investigated in hypoxia-induced PH model. At the end of the experiments, the indexes for pulmonary vascular remodeling and right ventricle hypertrophy were measured by vascular medial wall thickness and the ratio of right ventricle to (left ventricle plus septum). The expressions of NOX4, collagen I, and collagen III were analyzed by immunohistochemistry, real-time PCR, or western blotting. The proliferation of cultured pulmonary artery smooth muscle cells (PASMCs) was determined by BrdU incorporation and flow cytometry. The levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were also determined by thiobarbituric acid reactive substances assay and 2′7′-dichlorofluorescein diacetate method.ResultsChrysin treatment for 4 weeks significantly attenuated pulmonary vascular remodeling and improved collagen accumulation and down-regulated collagen I and collagen III expressions, accompanied by downregulation of NOX4 expression in the pulmonary artery (P = 0.012 for 50 mg/kg/d, P < 0.001 for 100 mg/kg/d) and lung tissue (P = 0.026, P < 0.001). In vitro, chrysin (1, 10, and 100 μM) remarkably attenuated PASMC proliferation (P = 0.021 for 1 μM, P < 0.001 for 10 μM, and P < 0.001 for 100 μM), collagen I expression (P = 0.035, P < 0.001, and P < 0.001), and collagen III expression (P = 0.027, P < 0.001, and P < 0.001) induced by hypoxia, and these inhibitory effects of chrysin were accompanied by inhibition of NOX4 expression (P = 0.019, P < 0.001, and P < 0.001), ROS production (P = 0.038, P < 0.001, and P < 0.001), and MDA generation (P = 0.024, P < 0.001, and P < 0.001).ConclusionsThis study demonstrated that chrysin treatment in hypoxia-induced PH in rats reversed the hypoxia-induced (1) elevations of NOX4 expression, (2) productions of ROS and MDA, (3) proliferation of PASMC, and (4) accumulation of collagen.

Down-regulation of hypoxia-inducible factor-1 alpha and vascular endothelial growth factor by HEXIM1 attenuates myocardial angiogenesis in hypoxic mice

Pulmonary hypertension (PH) sustains elevation of pulmonary vascular resistance and ultimately leads to right ventricular (RV) hypertrophy and failure and death. Recently, proangiogenic factors hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) have been known to promote left ventricular myocardial angiogenesis and lead to cardiac hypertrophy, and this would be involved in RV hypertrophy of PH patients. Previously, we revealed that overexpression of HEXIM1 prevents endothelin-1-induced cardiomyocyte hypertrophy and hypertrophic genes expression, and that cardiomyocyte-specific HEXIM1 transgenic mice ameliorates RV hypertrophy in hypoxia-induced PH model. Given these results, here we analyzed the effect of HEXIM1 on the expression of HIF-1α and VEGF and on myocardial angiogenesis of RV in PH. We revealed that overexpression of HEXIM1 prevented hypoxia-induced expression of HIF-1α protein and its target genes including VEGF in the cultured cardiac myocytes and fibroblasts, and that cardiomyocyte-specific HEXIM1 transgenic mice repressed RV myocardial angiogenesis in hypoxia-induced PH model. Thus, we conclude that HEXIM1 could prevent RV hypertrophy, at least in part, via suppression of myocardial angiogenesis through down-regulation of HIF-1α and VEGF in the myocardium under hypoxic condition.

Fasudil reversed MCT-induced and chronic hypoxia-induced pulmonary hypertension by attenuating oxidative stress and inhibiting the expression of Trx1 and HIF-1α

Antioxidant therapy attenuates pulmonary hypertension (PH). In the present study, we tested the antioxidant effects of fasudil against PH in rats. Monocrotaline (MCT)-induced and chronic hypoxia-induced PH models of rats were established, and the haemodynamic and pathomorphologic results of three different doses of fasudil (10mg/kg, 30mg/kg, and 75mg/kg per day) were subsequently compared with those of bosentan (30mg/kg per day). Additionally, the protein expressions of thioredoxin-1 (Trx1) and hypoxia inducible factor-1α (HIF-1α), the content of superoxide dismutase (SOD), and the levels of hydrogen peroxide (H2O2), malonyldialdehyde (MDA), and hydroxy radical (OH) were investigated. Fasudil effectively reduced the right ventricular systolic pressure (RVSP) and alleviated right ventricle (RV) hypertrophy, as well as the histological changes in the pulmonary arterioles. Moreover, fasudil markedly lessened the expression of Trx1 and HIF-1α, up-regulated the concentration of SOD, and lowered the levels of H2O2, MDA, and OH. In conclusion, fasudil is a notably attractive potential therapy for PH.

High proliferative potential endothelial colony-forming cells contribute to hypoxia-induced pulmonary artery vasa vasorum neovascularization

Angiogenic expansion of the vasa vasorum (VV) is an important contributor to pulmonary vascular remodeling in the pathogenesis of pulmonary hypertension (PH). High proliferative potential endothelial progenitor-like cells have been described in vascular remodeling and angiogenesis in both systemic and pulmonary circulations. However, their role in hypoxia-induced pulmonary artery (PA) VV expansion in PH is not known. We hypothesized that profound PA VV neovascularization observed in a neonatal calf model of hypoxia-induced PH is due to increased numbers of subsets of high proliferative cells within the PA adventitial VV endothelial cells (VVEC). Using a single cell clonogenic assay, we found that high proliferative potential colony-forming cells (HPP-CFC) comprise a markedly higher percentage in VVEC populations isolated from the PA of hypoxic (VVEC-Hx) compared with control (VVEC-Co) calves. VVEC-Hx populations that comprised higher numbers of HPP-CFC also demonstrated markedly higher expression levels of CD31, CD105, and c-kit than VVEC-Co. In addition, significantly higher expression of CD31, CD105, and c-kit was observed in HPP-CFC vs. the VVEC of the control but not of hypoxic animals. HPP-CFC exhibited migratory and tube formation capabilities, two important attributes of angiogenic phenotype. Furthermore, HPP-CFC-Co and some HPP-CFC-Hx exhibited elevated telomerase activity, consistent with their high replicative potential, whereas a number of HPP-CFC-Hx exhibited impaired telomerase activity, suggestive of their senescence state. In conclusion, our data suggest that hypoxia-induced VV expansion involves an emergence of HPP-CFC populations of a distinct phenotype with increased angiogenic capabilities. These cells may serve as a potential target for regulating VVEC neovascularization.

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Brahma-related gene 1 (Brg1) epigenetically regulates CAM activation during hypoxic pulmonary hypertension

Establishment of an inflammatory milieu following elevated leukocyte adhesion to the vascular endothelium, which is mediated by transcriptional activation of cell adhesion molecules (CAMs), contributes to the pathogenesis of chronic hypoxia-induced pulmonary hypertension (HPH). The epigenetic switch that dictates CAM transactivation in response to hypoxia in endothelial cells leading up to HPH is not fully appreciated. We report here that brahma-related gene 1 (Brg1) and brahma (Brm), two catalytic components of the mammalian chromatin remodelling complex, were induced in cultured endothelial cells challenged with hypoxia in vitro as well as in pulmonary arteries in an animal model of HPH. Over-expression of Brg1/Brm enhanced, while the depletion of Brg1/Brm attenuated, CAM transactivation and adhesion of leukocytes. Endothelial-specific deletion of Brg1/Brm ameliorated vascular inflammation and HPH in mice. Chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that hypoxia up-regulated the occupancies of Brg1 and Brm on CAM promoters in a nuclear factor κB (NF-κB) -dependent manner. Finally, Brg1 and Brm activated CAM transcription by altering the chromatin structure surrounding the CAM promoters. Our data suggest that Brg1 provides the crucial epigenetic link to hypoxia-induced CAM induction and leukocyte adhesion that engenders endothelial malfunction and pathogenesis of HPH. As such, targeting Brg1 in endothelial cells may yield promising strategies in the intervention and/or prevention of HPH.

The Nuclear Factor Erythroid 2–Related Factor 2 Activator Oltipraz Attenuates Chronic Hypoxia–Induced Cardiopulmonary Alterations in Mice

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a key regulator that activates many antioxidant enzymes. Oxidative stress, which accumulates in diseased lungs associated with pulmonary hypertension (PH), is thought to be responsible for the progression of cardiopulmonary changes. To test whether Nrf2 activation would exert therapeutic efficacy against cardiopulmonary changes in a hypoxia-induced PH model, wild-type (WT) and Nrf2-deficient mice as well as Kelch-like ECH associating protein 1 (Keap1) (negative regulator of Nrf2) knockdown mutant mice were exposed to hypobaric hypoxia for 3 weeks. This chronic hypoxia exacerbated right ventricular systolic pressure, right ventricular hypertrophy (RVH), and pulmonary vascular remodeling in the WT mice. These pathological changes were associated with aberrant accumulation of Tenascin-C, a disease-indicative extracellular glycoprotein. Simultaneous administration of oltipraz, a potent Nrf2 activator, significantly attenuated RVH and pulmonary vascular remodeling and concomitantly ameliorated Tenascin-C accumulation in the hypoxic mice. Hypoxia-exposed Nrf2-deficient mice developed more pronounced RVH than WT mice, whereas hypoxia-exposed Keap1-knockdown mice showed less RVH and pulmonary vascular remodeling than WT mice, underscoring the beneficial potency of Nrf2 activity against PH. We also demonstrated that expression of the Nrf2-regulated antioxidant enzymes was decreased in a patient with chronic obstructive pulmonary disease associated with PH. The decreased antioxidant enzymes may underlie the pathogenesis of cardiopulmonary changes in the patient with chronic obstructive pulmonary disease and PH. The pharmacologically or genetically induced Nrf2 activity clearly decreased RVH and pulmonary vascular remodeling in the hypoxic PH model. The efficacy of oltipraz highlights a promising therapeutic potency of Nrf2 activators for the prevention of PH in patients with hypoxemic lung disease.

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Notch Signaling Change in Pulmonary Vascular Remodeling in Rats with Pulmonary Hypertension and Its Implication for Therapeutic Intervention

Pulmonary hypertension (PH) is a fatal disease that lacks an effective therapy. Notch signaling pathway plays a crucial role in the angiogenesis and vascular remodeling. However, its roles in vascular remodeling in PH have not been well studied. In the current study, using hypoxia-induced PH model in rat, we examined the expression of Notch and its downstream factors. Then, we used vessel strip culture system and γ-secretase inhibitor DAPT, a Notch signaling inhibitor to determine the effect of Notch signaling in vascular remodeling and its potential therapeutic value. Our results indicated that Notch 1–4 were detected in the lung tissue with variable levels in different cell types such as smooth muscle cells and endothelial cells of pulmonary artery, bronchia, and alveoli. In addition, following the PH induction, all of Notch1, Notch3, Notch4 receptor, and downstream factor, HERP1 in pulmonary arteries, mRNA expressions were increased with a peak at 1–2 weeks. Furthermore, the vessel wall thickness from rats with hypoxia treatment increased after cultured for 8 days, which could be decreased approximately 30% by DAPT, accompanied with significant increase of expression level of apoptotic factors (caspase-3 and Bax) and transformation of vascular smooth muscle cell (VSMC) phenotype from synthetic towards contractile. In conclusion, the current study suggested Notch pathway plays an important role in pulmonary vascular remodeling in PH and targeting Notch signaling pathway could be a valuable approach to design new therapy for PH.

Tadalafil in pulmonary hypertension: May be more than seen?

I read an interesting article about the superiority of tadalafil over tempol via its antioxidant capacity on acute hypoxia-induced pulmonary hypertension (PH) model. Rashid et al. investigated and compared the antioxidant capacity of specific phosphodiesterase type-5 (PDE5) inhibitor, tadalafil, with superoxide dismutase mimetic and an efficient free radical scavenging agent tempol in acute hypoxia-induced PH model. They demonstrated that tadalafil was superior to tempol in inhibiting hypoxia-induced rise in right ventricular systolic pressure (RVSP) without producing any fall in mean arterial pressure. Also, tadalafil was shown to partially prevent oxidative stress. In conclusion, Rashid et al. highlighted the superiority of tadalafil especially in the settings of chronic hypoxia-induced PH. Monocrotaline (MCT)-induced PH is the other widely accepted animal model in PH studies. MCT is a member of the pyrrolizidine alkaloid family of plant toxins, which induces a delayed, yet progressive vascular injury resulting in PH in rats, dogs and monkeys. It is recognized that the initial reaction to MCT-induced PH is injury to the endothelial cells that precedes media hypertrophy in small size pulmonary arteries, and leads to an increase in pulmonary artery disease. These alterations in morphology largely mimic the primary PH in humans. We have recently compared the effects of three commercially available PDE5 inhibitors: sildenafil, vardenafil and tadalafil in rat MCT-induced PH model. It has been briefly demonstrated that vardenafil was more effective than sildenafil and tadalafil in this model. Vardenafil relaxes pulmonary artery rings in pulmonary hypertensive group through nitric oxide (NO)-cyclic guanosine monophosphate (NO-cGMP)-independent pathway. Neither sildenafil nor tadalafil achieves to induce relaxation response in pulmonary artery rings when NO-cGMP pathway inhibitor (NO synthase inhibitor, L-NAME and soluble guanylyl cyclase inhibitor, ODQ) incubations were used. This superiority potentially results from the differences in the heterocyclic ring system of vardenafil. Biochemical potencies (affinities) of these compounds for PDE5 have been determined by half maximal inhibitory concentration (IC50) and dissociation rate (KD), respectively, were the following: sildenafil (3.7 + 1.4, 3.7 + 0.29 nM), tadalafil (1.8 + 0.40, 1.9 + 0.37 nM), vardenafil (0.091 + 0.031, 0.27 + 0.01 nM), and it has been clearly demonstrated that vardenafil was the most potent inhibitor of PDE-5 because of its slow dissociation rate. Although tadalafil has an advantage over sildenafil and vardenafil because of its longer duration of action, tadalafil did not significantly alter the time to exercise treadmill test-induced ischemia compared with placebo in subjects with coronary artery disease. It is well-known that PH and coronary artery disease share similar risk factors, including endothelial dysfunction, diminishing of NO production and increased oxidative stress. This study is also in agreement with the others demonstrating that tadalafil was less effective than sildenafil and vardenafil in reducing the infarct size. In other preparations such as rat aorta-penile arteries and rabbit isolated pulmonary artery–corpus cavernosum tissue, vardenafil was shown to be more potent than other PDE5 inhibitors in relaxing the vascular tissues and preparations. These discrepancies may be attributed to experimental model, protocols or preparations difference employed in these studies. Also, these studies demonstrated that vardenafil has some beneficial effects in addition to its PDE5 inhibitory activity (e.g. activation of some ion channels or blocking of calcium influx).

Hypoxia induces unique proliferative response in adventitial fibroblasts by activating PDGFβ receptor-JNK1 signalling

Pulmonary hypertension (PH) is a devastating condition for which no disease-modifying therapies exist. PH is recognized as proliferative disease of the pulmonary artery (PA). In the experimental newborn calf model of hypoxia-induced PH, adventitial fibroblasts in the PA wall exhibit a heightened replication index. Because elevated platelet-derived growth factor β receptor (PDGFβ-R) signalling is associated with PH, we tested the hypothesis that the activation of PDGFβ-R contributes to fibroblast proliferation and adventitial remodelling in PH. Newborn calves were exposed to either ambient air (P(B) = 640 mmHg) (Neo-C) or high altitude (P(B) = 445 mm Hg) (Neo-PH) for 2 weeks. PDGFβ-R phosphorylation was markedly elevated in PA adventitia of Neo-PH calves as well as in cultured PA fibroblasts isolated from Neo-PH animals. PDGFβ-R activation with PDGF-BB stimulated higher replication in Neo-PH cells compared with that of control fibroblasts. PDGF-BB-induced proliferation was dependent on reactive oxygen species generation and extracellular signal-regulated kinase1/2 activation in both cell populations; however, only Neo-PH cell division via PDGFβ-R activation displayed a unique dependence on c-Jun N-terminal kinase1 (JNK1) stimulation as the blockade of JNK1 with SP600125, a pharmacological antagonist of the JNK pathway, and JNK1-targeted siRNA selectively blunted Neo-PH cell proliferation. Our data strongly suggest that hypoxia-induced modified cells engage the PDGFβ-R-JNK1 axis to confer distinctively heightened proliferation and adventitial remodelling in PH.

Role of Src Tyrosine Kinases in Experimental Pulmonary Hypertension

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. Human PASMCs were stimulated by PDGF alone or multiple growth factors to induce proliferation and migration in vitro. Dasatinib (0.03 μmol/L), nilotinib (0.3 μmol/L), and imatinib (1 μmol/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. 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.

Vascular reverse remodeling in the mouse model of hypoxia-induced pulmonary hypertension - role of AMD-1

Vascular reverse remodeling in the mouse model of hypoxia-induced pulmonary hypertension - role of AMD-1