Antiremodeling effects of iloprost and the dual-selective phosphodiesterase 3/4 inhibitor tolafentrine in chronic experimental pulmonary hypertension

Pulmonary Hypertension-Associated Right Ventricular Cardiomyocyte Remodelling Reduces Treprostinil Function

(1) Pulmonary hypertension (PH)-associated right ventricular (RV) failure is linked to a reduction in pulmonary vasodilators. Treprostinil has shown effectiveness in PAH patients with cardiac decompensation, hinting at potential cardiac benefits. We investigated treprostinil's synergy with isoprenaline in RV and LV cardiomyocytes. We hypothesised that disease-related RV structural changes in cardiomyocytes would reduce contractile responses and cAMP/PKA signalling activity. (2) We induced PH in male Sprague Dawley rats using monocrotaline and isolated their ventricular cardiomyocytes. The effect of in vitro treprostinil and isoprenaline stimulation on contraction was assessed. FRET microscopy was used to study PKA activity associated with treprostinil stimulation in AKAR3-NES FRET-based biosensor-expressing cells. (3) RV cells exhibited maladaptive remodelling with hypertrophy, impaired contractility, and calcium transients compared to control and LV cardiomyocytes. Combining treprostinil and isoprenaline failed to enhance inotropy in PH RV cardiomyocytes. PH RV cardiomyocytes displayed an aberrant contractile behaviour, which the combination treatment could not rectify. Finally, we observed decreased PKA activity in treprostinil-treated PH RV cardiomyocytes. (4) PH-associated RV cardiomyocyte remodelling reduced treprostinil sensitivity, inotropic support, and impaired relaxation. Overall, this study highlights the complexity of RV dysfunction in advanced PH and suggests the need for alternative therapeutic strategies.

Perivascular inflammatory cells and their association with pulmonary arterial remodelling in dogs with pulmonary hypertension due to myxomatous mitral valve disease

Pulmonary hypertension (PH), an increase in pulmonary arterial pressure (PAP), may occur in dogs affected with myxomatous mitral valve disease (MMVD). Recent studies suggest that an accumulation of perivascular inflammatory cells may be involved with medial thickening which is a sign of the pulmonary artery remodelling in PH. The aim of this study was to characterise perivascular inflammatory cells in the surrounding pulmonary arteries of dogs with PH due to MMVD compared to MMVD dogs and healthy control dogs. Nineteen lung samples were collected from cadavers of small-breed dogs (control n = 5; MMVD n = 7; MMVD + PH n = 7). Toluidine blue stain and multiple IHC targeting α-SMA, vWF, CD20, CD68 and CD3 was performed to examine intimal and medial thickening, assess muscularisation of the small pulmonary arteries and characterise perivascular leucocytes. Medial thickening without intimal thickening of pulmonary arteries and muscularisation of normally non-muscularised small pulmonary arteries was observed in the MMVD and MMVD + PH groups compared with the control group. The perivascular numbers of B lymphocytes, T lymphocytes and macrophages was significantly increased in the MMVD + PH group compared with the MMVD and control groups. In contrast, the perivascular number of mast cells was significantly higher in the MMVD group compared with the MMVD + PH and control groups. This study suggested that pulmonary artery remodelling as medial thickening and muscularisation of the normally non-muscular small pulmonary arteries is accompanied by the accumulation of perivascular inflammatory cells.

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.

Inhibitory effects of RAGE-aptamer on development of monocrotaline-induced pulmonary arterial hypertension in rats

BACKGROUND

The receptor for advanced glycation end products (RAGE), a transmembrane receptor belonging to the immunoglobulin superfamily, is overexpressed in pulmonary artery smooth muscle cells (PASMCs) in patients with pulmonary arterial hypertension (PAH) and is implicated in the etiology of PAH. Recently, we reported that RAGE-aptamer, a short and single-stranded DNA directed against RAGE, inhibited an inappropriate increase in cultured PASMCs in PAH. The aim of this study was to determine the efficacy of RAGE-aptamer in monocrotaline-induced PAH in rats.

METHODS AND RESULTS

Rats were assigned to either an untreated control group, a group that received continuous subcutaneous administration of RAGE-aptamer immediately after monocrotaline injection, or a group that received control-aptamer immediately after monocrotaline injection. All rats survived 21 days after injection of monocrotaline and control-aptamer or RAGE-aptamer. Injection of monocrotaline with continuous subcutaneous delivery of control-aptamer resulted in higher right ventricular systolic pressure compared with controls. This increase was attenuated by continuous subcutaneous delivery of RAGE-aptamer. The proportion of small pulmonary arteries with full muscularization was greater in the monocrotaline and control-aptamer group than in the control group. Continuous subcutaneous delivery of RAGE-aptamer significantly reduced the percentage of small pulmonary arteries with full muscularization.

CONCLUSIONS

Continuous subcutaneous delivery of RAGE-aptamer suppresses development of monocrotaline-induced PAH in rats. Inhibition of RAGE ameliorates muscularization of small pulmonary arteries. Treatment with RAGE-aptamer might be a new therapeutic option for PAH.

Anatabine ameliorates intestinal inflammation and reduces the production of pro-inflammatory factors in a dextran sulfate sodium mouse model of colitis

Background

Inflammatory bowel disease (IBD) is the collective term for chronic immune-mediated diseases of unknown, multifactorial etiology, arising from the interplay between genetic and environmental factors and including two main disease manifestations: ulcerative colitis (UC) and Crohn’s disease. In the last few decades, naturally occurring alkaloids have gained interest because of their substantial anti-inflammatory effects in several animal models of disease. Studies on mouse models of IBD have demonstrated the anti-inflammatory action of the main tobacco alkaloid, nicotine. In addition, anatabine, a minor tobacco alkaloid also present in peppers, tomato, and eggplant presents anti-inflammatory properties in vivo and in vitro. In this study, we aimed to evaluate the anti-inflammatory properties of nicotine and anatabine in a dextran sulfate sodium (DSS) mouse model of UC.

Results

Oral administration of anatabine, but not nicotine, reduced the clinical symptoms of DSS-induced colitis. The result of gene expression analysis suggested that anatabine had a restorative effect on global DSS-induced gene expression profiles, while nicotine only had limited effects. Accordingly, MAP findings revealed that anatabine reduced the colonic abundance of DSS-associated cytokines and increased IL-10 abundance.

Conclusions

Our results support the amelioration of inflammatory effects by anatabine in the DSS mouse model of UC, and suggest that anatabine constitutes a promising therapeutic agent for IBD treatment.

Mechanobiological Feedback in Pulmonary Vascular Disease

Vascular stiffening in the pulmonary arterial bed is increasingly recognized as an early disease marker and contributor to right ventricular workload in pulmonary hypertension. Changes in pulmonary artery stiffness throughout the pulmonary vascular tree lead to physiologic alterations in pressure and flow characteristics that may contribute to disease progression. These findings have led to a greater focus on the potential contributions of extracellular matrix remodeling and mechanical signaling to pulmonary hypertension pathogenesis. Several recent studies have demonstrated that the cellular response to vascular stiffness includes upregulation of signaling pathways that precipitate further vascular remodeling, a process known as mechanobiological feedback. The extracellular matrix modifiers, mechanosensors, and mechanotransducers responsible for this process have become increasingly well-recognized. In this review, we discuss the impact of vascular stiffening on pulmonary hypertension morbidity and mortality, evidence in favor of mechanobiological feedback in pulmonary hypertension pathogenesis, and the major contributors to mechanical signaling in the pulmonary vasculature.

Fasudil and DETA NONOate, Loaded in a Peptide-Modified Liposomal Carrier, Slow PAH Progression upon Pulmonary Delivery

We investigated the feasibility of a combination therapy comprising fasudil, a Rho-kinase inhibitor, and DETA NONOate (diethylenetriamine NONOate, DN), a long-acting nitric oxide donor, both loaded in liposomes modified with a homing peptide, CAR (CARSKNKDC), in the treatment of pulmonary arterial hypertension (PAH). We first prepared and characterized unmodified and CAR-modified liposomes of fasudil and DN. Using individual drugs alone or a mixture of fasudil and DN as controls, we studied the efficacy of the two liposomal preparations in reducing mean pulmonary arterial pressure (mPAP) in monocrotaline (MCT) and SUGEN-hypoxia-induced PAH rats. We also conducted morphometric studies (degree of muscularization, arterial medial wall thickness, and collagen deposition) after treating the PAH rats with test and control formulations. When the rats were treated acutely and chronically, the reduction in mPAP was more pronounced in the liposomal formulation-treated rats than in plain drug-treated rats. CAR-modified liposomes were more selective in reducing mPAP than unmodified liposomes of the drugs. Both drugs, formulated in CAR-modified liposomes, reduced the degree of muscularization, medial arterial wall thickness, and collagen deposition more than the combination of plain drugs did. As seen with the in vivo data, CAR-modified liposomes of fasudil or DN increased the levels of the vasodilatory signaling molecule, cGMP, in the smooth muscle cells of PAH-afflicted human pulmonary arteries. Overall, fasudil and DN, formulated in liposomes, could be used as a combination therapy for a better management of PAH.

The role of Iloprost on bone edema and osteonecrosis: Safety and clinical results

INTRODUCTION

Iloprost is a commercially available prostaglandin I₂ (PGI₂) analogue that is shown to have antithrombotic, vasodilatative and antiproliferative effects. A number of clinical studies have shown that Iloprost can be effective in the management of bone marrow oedema and the treatment of avascular necrosis. The aim of this manuscript is to present our current understanding on the effect of Iloprost on the treatment of these conditions.

AREAS COVERED

The authors offer a comprehensive review of the existing literature on the experimental and clinical studies analysing the effect of Iloprost on bone, bone marrow oedema and avascular necrosis.

EXPERT OPINION

The available data from the clinical studies suggest that Iloprost has limited effect in advanced stages of avascular necrosis. However, literature suggests that Iloprost administration can be a viable option in the management of bone marrow oedema and early stages of osteonecrosis. Despite these promising results its effect on bone homeostasis needs further elucidation. Moreover, further data on its safety, dosage and efficiency through randomized multicenter studies are desirable in order to reach final conclusions.

Endothelial cell-related autophagic pathways in Sugen/hypoxia-exposed pulmonary arterial hypertensive rats

Pulmonary arterial hypertension (PAH) is characterized by progressive obstructive remodeling of pulmonary arteries. However, no reports have described the causative role of the autophagic pathway in pulmonary vascular endothelial cell (EC) alterations associated with PAH. This study investigated the time-dependent role of the autophagic pathway in pulmonary vascular ECs and pulmonary vascular EC kinesis in a severe PAH rat model (Sugen/hypoxia rat) and evaluated whether timely induction of the autophagic pathway by rapamycin improves PAH. Hemodynamic and histological examinations as well as flow cytometry of pulmonary vascular EC-related autophagic pathways and pulmonary vascular EC kinetics in lung cell suspensions were performed. The time-dependent and therapeutic effects of rapamycin on the autophagic pathway were also assessed. Sugen/hypoxia rats treated with the vascular endothelial growth factor receptor blocker SU5416 showed increased right ventricular systolic pressure (RVSP) and numbers of obstructive vessels due to increased pulmonary vascular remodeling. The expression of the autophagic marker LC3 in ECs also changed in a time-dependent manner, in parallel with proliferation and apoptotic markers as assessed by flow cytometry. These results suggest the presence of cross talk between pulmonary vascular remodeling and the autophagic pathway, especially in small vascular lesions. Moreover, treatment of Sugen/hypoxia rats with rapamycin after SU5416 injection activated the autophagic pathway and improved the balance between cell proliferation and apoptosis in pulmonary vascular ECs to reduce RVSP and pulmonary vascular remodeling. These results suggested that the autophagic pathway can suppress PAH progression and that rapamycin-dependent activation of the autophagic pathway could ameliorate PAH.

Prostacyclins have no direct inotropic effect on isolated atrial strips from the normal and pressure-overloaded human right heart

Prostacyclins are vasodilatory agents used in the treatment of pulmonary arterial hypertension. The direct effects of prostacyclins on right heart function are still not clarified. The aim of this study was to investigate the possible direct inotropic properties of clinical available prostacyclin mimetics in the normal and the pressure-overloaded human right atrium. Trabeculae from the right atrium were collected during surgery from chronic thromboembolic pulmonary hypertension (CTEPH) patients with pressure-overloaded right hearts, undergoing pulmonary thromboendarterectomy (n = 10) and from patients with normal right hearts operated by valve replacement or coronary bypass surgery (n = 9). The trabeculae were placed in an organ bath, continuously paced at 1 Hz. They were subjected to increasing concentrations of iloprost, treprostinil, epoprostenol, or MRE-269, followed by isoprenaline to elicit a reference inotropic response. The force of contraction was measured continuously. The expression of prostanoid receptors was explored through quantitative polymerase chain reaction (qPCR).

Iloprost, treprostinil, epoprostenol, or MRE-269 did not alter force of contraction in any of the trabeculae. Isoprenaline showed a direct inotropic response in both trabeculae from the pressure-overloaded right atrium and from the normal right atrium. Control experiments on ventricular trabeculae from the pig failed to show an inotropic response to the prostacyclin mimetics. qPCR demonstrated varying expression of the different prostanoid receptors in the human atrium. In conclusion, prostacyclin mimetics did not increase the force of contraction of human atrial trabeculae from the normal or the pressure-overloaded right heart. These data suggest that prostacyclin mimetics have no direct inotropic effects in the human right atrium.

Effects of chronic treprostinil treatment on experimental right heart hypertrophy and failure

BACKGROUND

Right heart function is an important predictor of morbidity and mortality in pulmonary arterial hypertension and many CHD. We investigated whether treatment with the prostacyclin analogue treprostinil could prevent pressure overload-induced right ventricular hypertrophy and failure.

METHODS

Male Wistar rats were randomised to severe pulmonary trunk banding with a 0.5-mm banding clip (n=41), moderate pulmonary trunk banding with a 0.6-mm banding clip (n=36), or sham procedure (n=10). The banded rats were randomised to 6 weeks of treatment with a moderate dose of treprostinil (300 ng/kg/minute), a high dose of treprostinil (900 ng/kg/minute), or vehicle.

RESULTS

Pulmonary trunk banding effectively induced hypertrophy, dilatation, and decreased right ventricular function. The severely banded animals presented with decompensated heart failure with extracardial manifestations. Treatment with treprostinil neither reduced right ventricular hypertrophy nor improved right ventricular function.

CONCLUSIONS

In the pulmonary trunk banding model of pressure overload-induced right ventricular hypertrophy and failure, moderate- and high-dose treatment with treprostinil did not improve right ventricular function neither in compensated nor in decompensated right heart failure.

Right Ventricular Pressure Overload and Pathophysiology of Growing Porcine Biomodel

The primary objective was to create a clinically relevant model of right ventricular hypertension and to study right ventricular myocardial pathophysiology in growing organism. The secondary objective was to analyse the effect of oral enoximone (phosphodiesterase inhibitor) therapy on right ventricular haemodynamic parameters and myocardial changes in biomodel of right ventricular hypertension. The study included a total of 12 piglets of 42 days of age. Under general anaesthesia, pulmonary artery banding (PAB) was performed surgically to constrict the main pulmonary artery to about 70-80 % of its original dimension. The study presented two groups of animals labelled C (control animals with PAB; n = 8) and E (animals with PAB and oral administration of enoximone; n = 4). Direct pressure and echocardiographic measurements were taken during operation (time-1), and again at 40 days after surgery (time-2). The animals were killed, and tissue samples from the heart chambers were collected for quantitative morphological assessment. Statistical analysis was performed on all acquired data. At time-2, the median weight of animals doubled and the median systolic pressure gradient across the PAB increased (46.59 ± 15.87 mmHg vs. 20.29 ± 5.76 mmHg; p < 0.001). Changes in haemodynamic parameters were compatible with right ventricular diastolic dysfunction in all the animals. Apoptosis, tissue proliferation and fibrosis were identified in all the myocardial tissue samples. Right ventricular pressure overload leads to increased apoptosis of cardiac myocytes, proliferation and myocardial fibrosis. Our study did not show evidence of haemodynamic benefit or myocardial protective effect of oral enoximone treatment.

Search for an animal model to investigate selective pulmonary vasodilation

Pulmonary arterial hypertension is a life-threatening disease with a poor prognosis. Oral treatment with vasodilators is often limited by systemic hypotension. Inhalation of vasodilators offers the opportunity for selective pulmonary vasodilation. Testing selective pulmonary vasodilation by inhaled nitric oxide or alternative substances in animal models requires an increased pulmonary vascular tone. The aim of this study was to identify animal models that are suitable for investigating selective pulmonary vasodilation. To do so, a haemodynamic stable pulmonary hypertension was initiated, with a 30 min duration deemed to be a sufficient time interval before and after a possible intervention. In anaesthetized and mechanically-ventilated Sprague-Dawley rats pulmonary hypertension was induced either by acute hypoxia due to reduction of the inspired oxygen fraction from 0.21 to 0.1 ( n = 6), a fixed infusion rate of the thromboxane analogue U46619 (240 ng/min; n = 6) or a monocrotaline injection (MCT; 60 mg/kg applied 23 days before the investigation; n = 7). The animals were instrumented to measure right ventricular and systemic arterial pressures. Acute hypoxia caused a short, and only transient, increase of pulmonary artery pressure as well as profound systemic hypotension which suggested haemodynamic instability. U46619 infusion induced variable changes in the pulmonary and systemic vascular tone without sufficient stabilization within 30 min. MCT provoked sustained pulmonary hypertension with normal systemic pressure values and inhalation of nitric oxide caused selective pulmonary vasodilation. In conclusion, out of the three examined rat animal models only MCT-induced pulmonary hypertension is a solid and reliable model for investigating selective pulmonary vasodilation.

Rosuvastatin intensifies the beneficial effects of rho-kinase inhibitor in reversal of monocrotaline-induced pulmonary hypertension

INTRODUCTION

It remains controversial whether statins have a beneficial effect on pulmonary arterial hypertension (PAH). This study is intended to evaluate whether statin, co-administered with Rho-kinase inhibitor, could enhance its efficacy. Although Rho-kinase inhibitors, including fasudil, have been reported to improve pulmonary hypertension in experimental and clinical studies, the combination of these agents has not been tested in the treatment of pulmonary hypertension (PH).

MATERIAL AND METHODS

The effects of such a regimen on hemodynamics, right ventricle hypertrophy, and Rho-associated protein kinase (ROCK) activity in experimental monocrotaline (MCT)-induced pulmonary hypertension were examined. Fourteen days after monocrotaline injection (60 mg/kg), male rats were treated orally for another 14 days with fasudil (15 mg/kg per day), or with a combination of fasudil + rosuvastatin (10 mg/kg per day).

RESULTS

The drug combination reversed the MCT-induced increase in right ventricle pressure (RVP) and reduced right ventricular hypertrophy (RV/LV + S ratio) more than Rho kinase inhibitor alone. The simultaneous administration of fasudil and rosuvastatin caused a further decrease of RhoA kinase activity in isolated lung tissues as compared to fasudil alone.

CONCLUSIONS

The results indicate that rosuvastatin intensifies the beneficial effects of Rho-kinase inhibitor on the Rho/Rho-kinase pathway and such a combination may represent an option for the treatment of pulmonary arterial hypertension.

Advancing knowledge of right ventricular pathophysiology in chronic pressure overload: Insights from experimental studies

The right ventricle (RV) has to face major changes in loading conditions due to cardiovascular diseases and pulmonary vascular disorders. Clinical experience supports evidence that the RV better compensates for volume than for pressure overload, and for chronic than for acute changes. For a long time, right ventricular (RV) pathophysiology has been restricted to patterns extrapolated from left heart studies. However, the two ventricles are anatomically, haemodynamically and functionally distinct. RV metabolic properties may also result in a different behaviour in response to pathological conditions compared with the left ventricle. In this review, current knowledge of RV pathophysiology is reported in the setting of chronic pressure overload, including recent experimental findings and emerging concepts. After a time-varying compensated period with preserved cardiac output despite overload conditions, RV failure finally occurs, leading to death. The underlying mechanisms involved in the transition from compensatory hypertrophy to maladaptive remodelling are not completely understood.

Absence of the inflammasome adaptor ASC reduces hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension is a serious condition that can lead to premature death. The mechanisms involved are incompletely understood although a role for the immune system has been suggested. Inflammasomes are part of the innate immune system and consist of the effector caspase-1 and a receptor, where nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) is the best characterized and interacts with the adaptor protein apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC). To investigate whether ASC and NLRP3 inflammasome components are involved in hypoxia-induced pulmonary hypertension, we utilized mice deficient in ASC and NLRP3. Active caspase-1, IL-18, and IL-1β, which are regulated by inflammasomes, were measured in lung homogenates in wild-type (WT), ASC(-/-), and NLRP3(-/-) mice, and phenotypical changes related to pulmonary hypertension and right ventricular remodeling were characterized after hypoxic exposure. Right ventricular systolic pressure (RVSP) of ASC(-/-) mice was significantly lower than in WT exposed to hypoxia (40.8 ± 1.5 mmHg vs. 55.8 ± 2.4 mmHg, P < 0.001), indicating a substantially reduced pulmonary hypertension in mice lacking ASC. Magnetic resonance imaging further supported these findings by demonstrating reduced right ventricular remodeling. RVSP of NLRP3(-/-) mice exposed to hypoxia was not significantly altered compared with WT hypoxia. Whereas hypoxia increased protein levels of caspase-1, IL-18, and IL-1β in WT and NLRP3(-/-) mice, this response was absent in ASC(-/-) mice. Moreover, ASC(-/-) mice displayed reduced muscularization and collagen deposition around arteries. In conclusion, hypoxia-induced elevated right ventricular pressure and remodeling were attenuated in mice lacking the inflammasome adaptor protein ASC, suggesting that inflammasomes play an important role in the pathogenesis of pulmonary hypertension.

A possible contribution of lipocalin-2 to the development of dermal fibrosis, pulmonary vascular involvement and renal dysfunction in systemic sclerosis

BACKGROUND

Lipocalin-2 is an adipocytokine implicated in apoptosis, innate immunity, angiogenesis, and the development of chronic kidney disease.

OBJECTIVES

To investigate the role of lipocalin-2 in systemic sclerosis (SSc).

MATERIALS AND METHODS

Serum lipocalin-2 levels were determined by enzyme-linked immunosorbent assay in 50 patients with SSc and 19 healthy subjects. Lipocalin-2 expression was evaluated in the skin of patients with SSc and bleomycin (BLM)-treated mice and in Fli1-deficient endothelial cells by reverse transcriptase-real time polymerase chain reaction, immunoblotting and/or immunohistochemistry.

RESULTS

Although serum lipocalin-2 levels were comparable between patients with SSc and healthy controls, the prevalence of scleroderma renal crisis was significantly higher in patients with SSc with elevated serum lipocalin-2 levels than in those with normal levels. Furthermore, serum lipocalin-2 levels inversely correlated with estimated glomerular filtration rate in patients with SSc with renal dysfunction. Among patients with SSc with normal renal function, serum lipocalin-2 levels positively correlated with skin score in patients with diffuse cutaneous SSc with disease duration of < 3 years and inversely correlated with estimated right ventricular systolic pressure in total patients with SSc. Importantly, in SSc lesional skin, lipocalin-2 expression was increased in dermal fibroblasts and endothelial cells. In BLM-treated mice, lipocalin-2 was highly expressed in dermal fibroblasts, but not in endothelial cells. On the other hand, the deficiency of transcription factor Fli1, which is implicated in SSc vasculopathy, induced lipocalin-2 expression in cultivated endothelial cells.

CONCLUSIONS

Lipocalin-2 may be involved in renal dysfunction and dermal fibrosis of SSc. Dysregulated matrix metalloproteinase-9/lipocalin-2-dependent angiogenesis due to Fli1 deficiency may contribute to the development of pulmonary arterial hypertension associated with SSc.

Cigarette Smoke-Induced Emphysema and Pulmonary Hypertension Can Be Prevented by Phosphodiesterase 4 and 5 Inhibition in Mice

Rationale

Chronic obstructive pulmonary disease (COPD) is a widespread disease, with no curative therapies available. Recent findings suggest a key role of NO and sGC-cGMP signaling for the pathogenesis of the disease. Previous data suggest a downregulation/inactivation of the cGMP producing soluble guanylate cyclase, and sGC stimulation prevented cigarette smoke-induced emphysema and pulmonary hypertension (PH) in mice. We thus aimed to investigate if the inhibition of the cGMP degrading phosphodiesterase (PDE)5 has similar effects. Results were compared to the effects of a PDE 4 inhibitor (cAMP elevating) and a combination of both.

Methods

C57BL6/J mice were chronically exposed to cigarette smoke and in parallel either treated with Tadalafil (PDE5 inhibitor), Piclamilast (PDE4 inhibitor) or both. Functional measurements (lung compliance, hemodynamics) and structural investigations (alveolar and vascular morphometry) as well as the heart ratio were determined after 6 months of tobacco smoke exposure. In addition, the number of alveolar macrophages in the respective lungs was counted.

Results

Preventive treatment with Tadalafil, Piclamilast or a combination of both almost completely prevented the development of emphysema, the increase in lung compliance, tidal volume, structural remodeling of the lung vasculature, right ventricular systolic pressure, and right ventricular hypertrophy induced by cigarette smoke exposure. Single, but not combination treatment prevented or reduced smoke-induced increase in alveolar macrophages.

Conclusion

Cigarette smoke-induced emphysema and PH could be prevented by inhibition of the phosphodiesterases 4 and 5 in mice.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

Phosphodiesterase inhibitors for the treatment of asthma and chronic obstructive pulmonary disease

Xanthines like theophylline have long been recognised as being effective drugs for the treatment of asthma and chronic obstructive pulmonary disease (COPD). They are of interest as they possess both anti-inflammatory and bronchodilator activity in the same molecule. Since the discovery of phosphodiesterases (PDEs) in the late 1950s, it has been suggested that xanthines work, in part, by acting as non-selective PDE inhibitors. However, it has also been suggested that the ability of xanthines to non-selectively inhibit PDEs contributes to their many unwanted side effects, thus limiting their use since the arrival of inhaled drugs with more favourable safety profiles. As our understanding of PDEs has improved over the last 30 years, and with the recognition that the distribution of different PDEs varies across different cell types, this family of enzymes has been widely investigated as targets for novel drugs. In particular, PDE3 in airway smooth muscle and PDE4 and PDE7 in inflammatory cells have been targeted to provide new bronchodilators and anti-inflammatory agents, respectively. This review discusses the progress made in this field over the last decade in the development of selective PDE inhibitors to treat COPD and asthma.

Prostacyclin suppresses twist expression in the presence of indomethacin in bone marrow-derived mesenchymal stromal cells

Background

Iloprost, a stable prostacyclin I₂ analogue, seems to have an osteoblast-protective potential, whereas indomethacin suppresses new bone formation. The aim of this study was to investigate human bone marrow stromal cell (BMSC) proliferation and differentiation towards the osteoblastic lineage by administration of indomethacin and/or iloprost.

Material/Methods

Human bone marrow cells were obtained from 3 different donors (A=26 yrs/m; B=25 yrs/f, C=35 yrs/m) via vacuum aspiration of the iliac crest followed by density gradient centrifugation and flow cytometry with defined antigens (CD105+/73+/45−/14−). The cells were seeded and incubated as follows: without additives (Group 0; donor A/B/C), with 10⁻⁷ M iloprost only (Group 0+ilo; A/B), with indomethacin only in concentrations of 10⁻⁶ M (Group 1, A), 10⁻⁵ M (Group 2, B), 10⁻⁴ M (Group 3, A/B), and together with 10⁻⁷ M iloprost (Groups 4–6, A/B/C). On Day 10 and 28, UV/Vis spectrometric and immunocytochemical assays (4 samples per group and donor) were performed to investigate cell proliferation (cell count measurement) and differentiation towards the osteoblastic lineage (CD34−, CD45−, CD105+, type 1 collagen (Col1), osteocalcin (OC), alkaline phosphatase (ALP), Runx2, Twist, specific ALP-activity).

Results

Indomethacin alone suppressed BMSC differentiation towards the osteoblastic lineage by downregulation of Runx2, Col1, and ALP. In combination with indomethacin, iloprost increased cell proliferation and differentiation and it completely suppressed Twist expression at Day 10 and 28. Iloprost alone did not promote cell proliferation, but moderately enhanced Runx2 and Twist expression. However, the proliferative effects and the specific ALP-activity varied donor-dependently.

Conclusions

Iloprost partially antagonized the suppressing effects of indomethacin on BMSC differentiation towards the osteoblast lineage. It enhanced the expression of Runx2 and, only in the presence of indomethacin, it completely suppressed Twist. Thus, in the treatment of avascular osteonecrosis or painful bone marrow edema, the undesirable effects of indomethacin might be counterbalanced by iloprost.

Iloprost improves ventricular function in the hypertrophic and functionally impaired right heart by direct stimulation

Right heart function is an important predictor of morbidity and mortality in patients suffering from pulmonary arterial hypertension and congenital heart diseases. We investigated whether the prostacyclin analog iloprost has a direct inotropic effect in the pressure-overloaded hypertrophic and dysfunctional right ventricle (RV). Rats were randomized to monocrotaline injection (60 mg/kg; [Formula: see text]), pulmonary trunk banding (PTB; [Formula: see text]), or a sham operation ([Formula: see text]). RV function was evaluated with magnetic resonance imaging, echocardiography, and invasive pressure measurements at baseline, after intravenous administration of placebo, iloprost 10 ng/kg/min, or iloprost 100 ng/kg/min (Ilo100). Infusion of Ilo100 induced a [Formula: see text] ([Formula: see text]) increase in stroke volume in the sham group and a [Formula: see text] ([Formula: see text]) increase in the PTB group. RV [Formula: see text] was elevated by [Formula: see text] ([Formula: see text]) in the sham group and by [Formula: see text] ([Formula: see text]) in the PTB group. An elevation in cardiac output of [Formula: see text] ([Formula: see text]) and an [Formula: see text] ([Formula: see text]) increase in RV systolic pressure were found in the PTB group. Iloprost caused a decrease in mean arterial blood pressure (MAP) in all groups of animals. An equal reduction in MAP induced by the arterial vasodilator nitroprusside did not improve any of the measured parameters of RV function. We conclude that iloprost has inotropic properties directly improving ventricular function in the hypertrophic and dysfunctional right heart of the rat.

Concurrent rho-kinase and tyrosine kinase platelet-derived growth factor inhibition in experimental pulmonary hypertension

BACKGROUND

We hypothesized that inhibition of Rho-kinase by fasudil, together with tyrosine kinase platelet-derived growth factor (PDGF) receptor inhibition by imatinib, results in greater pulmonary arterial hypertension (PAH) improvement.

METHODS

The effects of such regimens were investigated on hemodynamics, right ventricle hypertrophy, PDGF and ROCK in experimental monocrotaline (MCT)-induced pulmonary hypertension. Fourteen days after MCT injection, male rats were treated orally for another 14 days with imatinib, fasudil or their combination.

RESULTS

Concurrent imatinib and fasudil administration reversed an MCT-induced increase in right ventricular pressure more than either drug alone and decreased right ventricle hypertrophy (right ventricle weight to left ventricle plus septum weight ratio) significantly. The simultaneous administration of fasudil and imatinib caused a further decrease in plasma PDGF-BB levels compared to either drug alone.

CONCLUSIONS

Inhibition of Rho-kinase by fasudil in addition to tyrosine kinase PDGF inhibition by imatinib can result in further PAH improvement. Such outcome may result from additional impact of the Rho-kinase inhibitor on the decrease in PDGF-induced effects.

Dual PDE3/4 and PDE4 inhibitors: novel treatments for COPD and other inflammatory airway diseases

Selective phosphodiesterase (PDE) 4 and dual PDE3/4 inhibitors have attracted considerable interest as potential therapeutic agents for the treatment of respiratory diseases, largely by virtue of their anti-inflammatory (PDE4) and bifunctional bronchodilator/anti-inflammatory (PDE3/4) effects. Many of these agents have, however, failed in early development for various reasons, including dose-limiting side effects when administered orally and lack of sufficient activity when inhaled. Indeed, only one selective PDE4 inhibitor, the orally active roflumilast-n-oxide, has to date received marketing authorization. The majority of the compounds that have failed were, however, orally administered and non-selective for either PDE3 (A,B) or PDE4 (A,B,C,D) subtypes. Developing an inhaled dual PDE3/4 inhibitor that is rapidly cleared from the systemic circulation, potentially with subtype specificity, may represent one strategy to improve the therapeutic index and also exhibit enhanced efficacy versus inhibition of either PDE3 or PDE4 alone, given the potential positive interactions with regard to anti-inflammatory and bronchodilator effects that have been observed pre-clinically with dual inhibition of PDE3 and PDE4 compared with inhibition of either isozyme alone. This MiniReview will summarize recent clinical data obtained with PDE inhibitors and the potential for these drugs to treat COPD and other inflammatory airways diseases such as asthma and cystic fibrosis.

Iloprost for idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension is a rare but serious and life-threatening disease that leads to right heart failure and death within 2.8 years without specific treatment. This review focuses on the stable prostacyclin analog iloprost, its biologic action and pharmacology and, finally, on its clinical development, efficacy and safety in patients with idiopathic pulmonary arterial hypertension, which led to its approval for this indication. Furthermore, this review assesses the role of iloprost compared with other newly developed drugs, such as the endothelin receptor antagonist bosentan and the phosphodiesterase-5 inhibitor sildenafil, as well as other modes of application of prostacyclin and its analogs for the treatment of idiopathic pulmonary arterial hypertension. Based on the different modes of action of these substances, a combination of these treatments could be most promising for the future.

Evaluation of circulating proteins and hemodynamics towards predicting mortality in children with pulmonary arterial hypertension

BACKGROUND

Although many predictors have been evaluated, a set of strong independent prognostic mortality indicators has not been established in children with pediatric pulmonary arterial hypertension (PAH). The aim of this study was to identify a combination of clinical and molecular predictors of survival in PAH.

METHODS

This single-center, retrospective cohort study was performed from children with PAH between 2001 and 2008 at Children's Hospital Colorado. Blood samples from 83 patients (median age of 8.3 years-old) were obtained. We retrospectively analyzed 46 variables, which included 27 circulating proteins, 7 demographic variables and 12 hemodynamic and echocardiographic variables for establishing the best predictors of mortality. A data mining approach was utilized to evaluate predictor variables and to uncover complex data structures while performing variable selection in high dimensional problems.

RESULTS

Thirteen children (16%) died during follow-up (median; 3.1 years) and survival rates from time of sample collection at 1 year, 3 years and 5 years were 95%, 85% and 79%, respectively. A subset of potentially informative predictors were identified, the top four are listed here in order of importance: Tissue inhibitors of metalloproteinases-1 (TIMP-1), apolipoprotein-AI, RV/LV diastolic dimension ratio and age at diagnosis. In univariate analysis, TIMP-1 and apolipoprotein-AI had significant association with survival time (hazard ratio [95% confidence interval]: 1.25 [1.03, 1.51] and 0.70 [0.54-0.90], respectively). Patients grouped by TIMP-1 and apolipoprotein-AI values had significantly different survival risks (p<0.01).

CONCLUSION

Important predictors of mortality were identified from a large number of circulating proteins and clinical markers in this cohort. If confirmed in other populations, measurement of a subset of these predictors could aid in management of pediatric PAH by identifying patients at risk for death. These findings also further support a role for the clinical utility of measuring circulating proteins.

Reactive oxygen species in pulmonary vascular remodeling

The pathogenesis of pulmonary hypertension is a complex multifactorial process that involves the remodeling of pulmonary arteries. This remodeling process encompasses concentric medial thickening of small arterioles, neomuscularization of previously nonmuscular capillary-like vessels, and structural wall changes in larger pulmonary arteries. The pulmonary arterial muscularization is characterized by vascular smooth muscle cell hyperplasia and hypertrophy. In addition, in uncontrolled pulmonary hypertension, the clonal expansion of apoptosis-resistant endothelial cells leads to the formation of plexiform lesions. Based upon a large number of studies in animal models, the three major stimuli that drive the vascular remodeling process are inflammation, shear stress, and hypoxia. Although, the precise mechanisms by which these stimuli impair pulmonary vascular function and structure are unknown, reactive oxygen species (ROS)-mediated oxidative damage appears to play an important role. ROS are highly reactive due to their unpaired valence shell electron. Oxidative damage occurs when the production of ROS exceeds the quenching capacity of the antioxidant mechanisms of the cell. ROS can be produced from complexes in the cell membrane (nicotinamide adenine dinucleotide phosphate-oxidase), cellular organelles (peroxisomes and mitochondria), and in the cytoplasm (xanthine oxidase). Furthermore, low levels of tetrahydrobiopterin (BH4) and L-arginine the rate limiting cofactor and substrate for endothelial nitric oxide synthase (eNOS), can cause the uncoupling of eNOS, resulting in decreased NO production and increased ROS production. This review will focus on the ROS generation systems, scavenger antioxidants, and oxidative stress associated alterations in vascular remodeling in pulmonary hypertension.

Inhaled PLGA particles of prostaglandin E₁ ameliorate symptoms and progression of pulmonary hypertension at a reduced dosing frequency

This study sought to investigate the efficacy of a noninvasive and long acting polymeric particle based formulation of prostaglandin E1 (PGE1), a potent pulmonary vasodilator, in alleviating the signs of pulmonary hypertension (PH) and reversing the biochemical changes that occur in the diseased lungs. PH rats, developed by a single subcutaneous injection of monocrotaline (MCT), were treated with two types of polymeric particles of PGE1, porous and nonporous, and intratracheal or intravenous plain PGE1. For chronic studies, rats received either intratracheal porous poly(lactic-co-glycolic acid) (PLGA) particles, once- or thrice-a-day, or plain PGE1 thrice-a-day for 10 days administered intratracheally or intravenously. The influence of formulations on disease progression was studied by measuring the mean pulmonary arterial pressure (MPAP), evaluating right ventricular hypertrophy and assessing various molecular and cellular makers including the degree of muscularization, platelet aggregation, matrix metalloproteinase-2 (MMP-2), and proliferating cell nuclear antigen (PCNA). Both plain PGE1 and large porous particles of PGE1 reduced MPAP and right ventricular hypertrophy (RVH) in rats that received the treatments for 10 days. Polymeric porous particles of PGE1 produced the same effects at a reduced dosing frequency compared to plain PGE1 and caused minimal off-target effects on systemic hemodynamics. Microscopic and immunohistochemical studies revealed that porous particles of PGE1 also reduced the degree of muscularization, von Willebrand factor (vWF), and PCNA expression in the lungs of PH rats. Overall, our study suggests that PGE1 loaded inhalable particulate formulations improve PH symptoms and arrest the progression of disease at a reduced dosing frequency compared to plain PGE1.

The beneficial impact of fasudil and sildenafil on monocrotaline-induced pulmonary hypertension in rats: a hemodynamic and biochemical study

Pulmonary arterial hypertension (PAH) still cannot be cured effectively, hence the search for novel treatments continues. The effects of sildenafil (25 mg/kg body weight) and fasudil (30 mg/kg body weight) given alone or in combination, on normalization of right ventricular pressure (RVP), right ventricle mass, as well as the levels of several biomarkers (HDL-C, BNP, VEGF-A), were assessed in a rat model of monocrotaline (MCT)-induced PAH. MCT (60 mg/kg body weight) induced clear PAH in male Wistar rats. After 21 days, a significant decrease in RVP accompanied by a reduction of right ventricular hypertrophy - a significant decrease in the right ventricle/left ventricle plus septum ratio - as a result of sildenafil or fasudil administration was assessed. The administration of fasudil and sildenafil alone or in combination caused a significant decrease in plasma BNP level as compared to MCT-treated rats. Fasudil alone or with sildenafil, but not sildenafil alone, significantly increased HDL-C level as compared to MCT-treated rats. Fasudil and sildenafil given alone or in combination caused a significant increase in plasma VEGF-A level as compared to rats exposed to MCT.

Cardiomyocyte-specific overexpression of HEXIM1 prevents right ventricular hypertrophy in hypoxia-induced pulmonary hypertension in mice

Right ventricular hypertrophy (RVH) and right ventricular (RV) contractile dysfunction are major determinants of prognosis in pulmonary arterial hypertension (PAH) and PAH remains a severe disease. Recently, direct interruption of left ventricular hypertrophy has been suggested to decrease the risk of left-sided heart failure. Hexamethylene bis-acetamide inducible protein 1 (HEXIM1) is a negative regulator of positive transcription elongation factor b (P-TEFb), which activates RNA polymerase II (RNAPII)-dependent transcription and whose activation is strongly associated with left ventricular hypertrophy. We hypothesized that during the progression of PAH, increased P-TEFb activity might also play a role in RVH, and that HEXIM1 might have a preventive role against such process. We revealed that, in the mouse heart, HEXIM1 is highly expressed in the early postnatal period and its expression is gradually decreased, and that prostaglandin I(2), a therapeutic drug for PAH, increases HEXIM1 levels in cardiomyocytes. These results suggest that HEXIM1 might possess negative effect on cardiomyocyte growth and take part in cardiomyocyte regulation in RV. Using adenovirus-mediated gene delivery to cultured rat cardiomyocytes, we revealed that overexpression of HEXIM1 prevents endothelin-1-induced phosphorylation of RNAPII, cardiomyocyte hypertrophy, and mRNA expression of hypertrophic genes, whereas a HEXIM1 mutant lacking central basic region, which diminishes P-TEFb-suppressing activity, could not. Moreover, we created cardiomyocyte-specific HEXIM1 transgenic mice and revealed that HEXIM1 ameliorates RVH and prevents RV dilatation in hypoxia-induced PAH model. Taken together, these findings indicate that cardiomyocyte-specific overexpression of HEXIM1 inhibits progression to RVH under chronic hypoxia, most possibly via inhibition of P-TEFb-mediated enlargement of cardiomyocytes. We conclude that P-TEFb/HEXIM1-dependent transcriptional regulation may play a pathophysiological role in RVH and be a novel therapeutic target for mitigating RVH in PAH.

MAP kinase kinase kinase-2 (MEKK2) regulates hypertrophic remodeling of the right ventricle in hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) results in pressure overload of the right ventricle (RV) of the heart, initiating pathological RV remodeling and ultimately leading to right heart failure. Substantial research indicates that signaling through the MAPK superfamily mediates pathological cardiac remodeling. These considerations led us to test the hypothesis that the regulatory protein MAPKKK-2 (MEKK2) contributes to RV hypertrophy in hypoxia-induced PH. Transgenic mice with global knockout of MEKK2 (MEKK2(-/-) mice) and age-matched wild-type (WT) mice were exposed to chronic hypobaric hypoxia (10% O(2), 6 wk) and compared with animals under normoxia. Exposure to chronic hypoxia induced PH in WT and MEKK2(-/-) mice. In response to PH, WT mice showed RV hypertrophy, demonstrated as increased ratio of RV weight to body weight, increased RV wall thickness at diastole, and increased cardiac myocyte size compared with normoxic control animals. In contrast, each of these measures of RV hypertrophy seen in WT mice after chronic hypoxia was attenuated in MEKK2(-/-) mice. Furthermore, chronic hypoxia elicited altered programs of hypertrophic and inflammatory gene expression consistent with pathological RV remodeling in WT mice; MEKK2 deletion selectively inhibited inflammatory gene expression compared with WT mice. The actions of MEKK2 were mediated in part through regulation of the abundance and phosphorylation of its effector, ERK5. In conclusion, signaling by MEKK2 contributes to RV hypertrophy and altered myocardial inflammatory gene expression in response to hypoxia-induced PH. Therapies targeting MEKK2 may protect the myocardium from hypertrophy and pathological remodeling in human PH.

Assessment of the endothelial functions in monocrotaline-induced pulmonary hypertension

Pulmonary hypertension (PH) is a life-threatening disease that causes endothelial dysfunction in the pulmonary vascular bed. Systemic endothelial dysfunction has also been reported in PH. This study compared the systemic and pulmonary vascular responses and some blood biomarkers of endothelial function in monocrotaline (MCT)-induced PH of rats. It also investigated the effect of sildenafil and iloprost treatment. MCT application induced elevation in the right ventricular pressures of the rat heart that had been reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated pulmonary artery were decreased in the PH group and this failure was reversed by sildenafil and iloprost treatment. Acetylcholine-induced endothelium-dependent relaxations of the isolated thoracic aorta were similar in all groups. Serotonin-induced contractions of the pulmonary artery were augmented by PH. In the isolated aorta, serotonin-stimulated contraction was not different in the control and MCT groups, but sildenafil and iloprost treatment decreased serotonin responses. The nitric oxide (NO) level in systemic circulation was not significantly changed by PH. However, sildenafil and iloprost treatments caused a decrease in the plasma level of NO. Asymmetric dimethylarginine levels in plasma were significantly decreased after MCT application and were not recovered by sildenafil and iloprost treatment. Total antioxidant capacity and H2S level of plasma were similar in all groups. Results of this study showed that MCT-induced PH caused specific toxic effects on pulmonary vasculature without any functional effects on the aorta. In addition, it was also demonstrated that sildenafil and iloprost treatments were effective in the MCT-induced PH.

Benzenesulfonamide attenuates monocrotaline-induced pulmonary arterial hypertension in a rat model

In this study, we examined the effects of LASSBio-965 (N-[2-(3,4-dimethoxyphenyl) ethyl]-benzenesulfonamide), a compound designed as a simplified structure of a non-selective phosphodiesterase 4 inhibitor, on vascular smooth muscle in vitro as well as in a rat model of monocrotaline (MCT)-induced pulmonary arterial hypertension. LASSBio-965 (50 mg/kg) treatment caused a significant decrease in right systolic ventricular pressure (32.47 ± 3.09 mmHg) compared to the MCT-vehicle group (51.88 ± 3.23 mmHg; P<0.05) and in the ratio of right ventricular weight to left ventricular weight plus septum (0.42 ± 0.03 g compared to 0.59 ± 0.06 g, respectively; MCT-vehicle group; P<0.05). LASSBio-965 induced a concentration-dependent relaxation of rat aortic rings, which was decreased by mechanical removal of the endothelium. Milrinone, rolipram, and sildenafil reduced the maximum relaxation (100%) to 22.4 ± 5.8, 69.5 ± 5.6 and 80.1 ± 10.7%, respectively (P<0.05). Maximum relaxation responses of aortic and pulmonary artery rings were decreased in the MCT-vehicle group (54.80 ± 5.69 and 35.87 ± 4.78, respectively) compared to the control (91.51 ± 4.79 and 54.32 ± 2.39, respectively) but improved with LASSBio-965 treatment (50mg/kg; 88.43 ± 4.54 and 59.36 ± 4.83, respectively). These results indicate that LASSBio-965 can attenuate the pulmonary arterial hypertension in an animal model most likely through the nonselective inhibition of phosphodiesterases 3, 4, and 5.

The soluble guanylate cyclase stimulator riociguat ameliorates pulmonary hypertension induced by hypoxia and SU5416 in rats

BACKGROUND

The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signal-transduction pathway is impaired in many cardiovascular diseases, including pulmonary arterial hypertension (PAH). Riociguat (BAY 63-2521) is a stimulator of sGC that works both in synergy with and independently of NO to increase levels of cGMP. The aims of this study were to investigate the role of NO-sGC-cGMP signaling in a model of severe PAH and to evaluate the effects of sGC stimulation by riociguat and PDE5 inhibition by sildenafil on pulmonary hemodynamics and vascular remodeling in severe experimental PAH.

METHODS AND RESULTS

Severe angioproliferative PAH was induced in rats by combined exposure to the vascular endothelial growth factor receptor antagonist SU5416 and hypoxia (SUHx). Twenty-one days thereafter rats were randomized to receive either riociguat (10 mg/kg/day), sildenafil (50 mg/kg/day) or vehicle by oral gavage, for 14 days until the day of the terminal hemodynamic measurements. Administration of riociguat or sildenafil significantly decreased right ventricular systolic pressure (RVSP). Riociguat significantly decreased RV hypertrophy (RVH) (0.55 ± 0.02, p<0.05), increased cardiac output (60.8 ± .8 mL/minute, p<0.05) and decreased total pulmonary resistance (4.03 ± 0.3 mmHg min(-1) ml(-1) 100 g BW, p<0.05), compared with sildenafil and vehicle. Both compounds significantly decreased the RV collagen content and improved RV function, but the effects of riociguat on tricuspid annular plane systolic excursion and RV myocardial performance were significantly better than those of sildenafil (p<0.05). The proportion of occluded arteries was significantly lower in animals receiving riociguat than in those receiving vehicle (p<0.05); furthermore, the neointima/media ratio was significantly lower in those receiving riociguat than in those receiving sildenafil or vehicle (p<0.05).

CONCLUSION

Riociguat and sildenafil significantly reduced RVSP and RVH, and improved RV function compared with vehicle. Riociguat had a greater effect on hemodynamics and RVH than sildenafil.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

[Effect of nebulised iloprost combined with inhaled nitric oxide and oral sildenafil on lung transplant patients. Therapeutic efficacy in pulmonary hypertension during surgery]

OBJECTIVES

There is a high incidence of pulmonary hypertension during the lung transplant peri-operative period, and could lead to a haemodynamic deterioration that may require the need of extracorporeal circulation. Our aim was to study the haemodynamic effects on the pulmonary and systemic circulation of the combination of inhaled nitric oxide and iloprost and oral sildenafil in patients with severe pulmonary hypertension during lung transplant surgery.

PATIENTS AND METHODS

Seventeen patients received 10μg of nebulised iloprost during the peri-operative period of the lung transplant when their mean pulmonary pressure exceeded 50mmHg. AU the patients received 50mg of oral sildenafil 30min before anaesthetic induction, 20ppm of inhaled nitric oxide after tracheal intubation. The haemodynamic and respiratory variables were recorded at baseline (after anaesthetic induction), prior to the administering of iloprost, and at 5 and 30min after it was given.

RESULTS

The administering of iloprost significantly reduced the pulmonary arterial pressure and significantly increases the cardiac Índex and the right ventrícular ejection fractíon. There were no signíficant changes occurred in the systemic arterial pressure.

CONCLUSIONS

The triple combination significantly reduces the pulmonary pressures in the lung transplant peri-operative and should be considered when there is severe pulmonary hypertension during the surgery or during the immediate post-operative period of lung transplantation.

C-122, a novel antagonist of serotonin receptor 5-HT2B, prevents monocrotaline-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a chronic disease characterized by sustained elevation of pulmonary arterial pressure that leads to right ventricle failure and death. Pulmonary resistance arterioles in PAH undergo progressive narrowing and/or occlusion. Currently approved therapies for PAH are directed primarily at relief of symptoms by interfering with vasoconstrictive signals, but do not halt the microvascular cytoproliferative process. In this study we show that C-122 (2-amino-N-(2-{4-[3-(2-trifluoromethyl-phenothiazin-10-yl)-propyl]-piperazin-1-yl}-ethyl)-acetamide trihydrochloride, a novel antagonist of serotonin receptor 5-HT(2B) (Ki=5.2 nM, IC(50)=6.9 nM), when administered to rats for three weeks in daily oral 10mg/kg doses, prevents not only monocrotaline (MCT)-induced elevations in pressure in the pulmonary arterial circuit (19 ± 0.9 mmHg vs. 28 ± 2 mmHg in MCT-vehicle group, P<0.05) and hypertrophy of the right ventricle (right ventricular wt./body wt. ratio 0.52 ± 0.02 vs. 0.64 ± 0.04 in MCT-vehicle group, P<0.05), but also muscularization of pulmonary arterioles (23% vs. 56% fully muscularized in MCT-vehicle group, P<0.05), and perivascular fibrosis in the lung. C-122 is orally absorbed in the rat, and partitions strongly into multiple tissues, including heart and lung. C-122 has significant off-target antagonist activity for histamine H-1 and several dopamine receptors, but shows no evidence of crossing the blood-brain barrier after a single 10mg/kg oral dose in rats. We conclude that C-122 can prevent microvascular remodeling and associated elevated pressures in the rat MCT model for PAH, and offers promise as a new therapeutic entity to suppress vascular smooth muscle cell proliferation in PAH patients.

Ghrelin ameliorates hypoxia-induced pulmonary hypertension via phospho-GSK3 β/β-catenin signaling in neonatal rats

Effective treatment and/or prevention strategies for neonatal persistent pulmonary hypertension of the newborn (PPHN) have been an important topic in neonatal medicine. However, mechanisms of impaired pulmonary vascular structure in hypoxia-induced PPHN are poorly understood and consequently limit the development of effective treatment. In this study, we aimed to explore the molecular signaling cascades in the lungs of a PPHN animal model and used primary cultured rat pulmonary microvascular endothelial cells to analyze the physiological benefits of ghrelin during the pathogenesis of PPHN. Randomly selected newborn rats were exposed to hypoxia (10-12%) or room air and received daily s.c. injections of ghrelin (150 μg/kg) or saline. After 2 weeks, pulmonary hemodynamics and morphometry were assessed in the rats. Compared with the control, hypoxia increased pulmonary arterial pressure, right ventricle (RV) hypertrophy, and arteriolar wall thickness. Ghrelin treatment reduced both the magnitude of PH and the RV/(left ventricle+septum (Sep)) weight ratio. Ghrelin protected neonatal rats from hypoxia-induced PH via the upregulation of phosphorylation of glycogen synthase kinase 3β (p-GSK3β)/β-catenin signaling and associated with β-catenin translocation to the nucleus in the presence of growth hormone secretagogue receptor-1a. Our findings suggest that s.c. administration of ghrelin improved PH and attenuated pulmonary vascular remodeling after PPHN. These beneficial effects may be mediated by the regulation of p-GSK3β/β-catenin expression. We propose ghrelin as a novel potential therapeutic agent for PPHN.

New perspectives for the treatment of pulmonary hypertension

Pulmonary hypertension (PH) is a debilitating disease with a poor prognosis. Therapeutic options remain limited despite the introduction of prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors within the last 15 years; these interventions address predominantly the endothelial and vascular dysfunctionS associated with the condition, but simply delay progression of the disease rather than offer a cure. In an attempt to improve efficacy, emerging approaches have focused on targeting the pro-proliferative phenotype that underpins the pulmonary vascular remodelling in the lung and contributes to the impaired circulation and right heart failure. Many novel targets have been investigated and validated in animal models of PH, including modulation of guanylate cyclases, phosphodiesterases, tyrosine kinases, Rho kinase, bone morphogenetic proteins signalling, 5-HT, peroxisome proliferator activator receptors and ion channels. In addition, there is hope that combinations of such treatments, harnessing and optimizing vasodilator and anti-proliferative properties, will provide a further, possibly synergistic, increase in efficacy; therapies directed at the right heart may also offer an additional benefit. This overview highlights current therapeutic options, promising new therapies, and provides the rationale for a combination approach to treat the disease.

Phosphodiesterase 10A upregulation contributes to pulmonary vascular remodeling

Phosphodiesterases (PDEs) modulate the cellular proliferation involved in the pathophysiology of pulmonary hypertension (PH) by hydrolyzing cAMP and cGMP. The present study was designed to determine whether any of the recently identified PDEs (PDE7-PDE11) contribute to progressive pulmonary vascular remodeling in PH. All in vitro experiments were performed with lung tissue or pulmonary arterial smooth muscle cells (PASMCs) obtained from control rats or monocrotaline (MCT)-induced pulmonary hypertensive (MCT-PH) rats, and we examined the effects of the PDE10 inhibitor papaverine (Pap) and specific small interfering RNA (siRNA). In addition, papaverine was administrated to MCT-induced PH rats from day 21 to day 35 by continuous intravenous infusion to examine the in vivo effects of PDE10A inhibition. We found that PDE10A was predominantly present in the lung vasculature, and the mRNA, protein, and activity levels of PDE10A were all significantly increased in MCT PASMCs compared with control PASMCs. Papaverine and PDE10A siRNA induced an accumulation of intracellular cAMP, activated cAMP response element binding protein and attenuated PASMC proliferation. Intravenous infusion of papaverine in MCT-PH rats resulted in a 40%-50% attenuation of the effects on pulmonary hypertensive hemodynamic parameters and pulmonary vascular remodeling. The present study is the first to demonstrate a central role of PDE10A in progressive pulmonary vascular remodeling, and the results suggest a novel therapeutic approach for the treatment of PH.

cAMP phosphodiesterase inhibitors increases nitric oxide production by modulating dimethylarginine dimethylaminohydrolases

BACKGROUND

Pulmonary arterial hypertension is characterized by a progressive increase in pulmonary vascular resistance caused by endothelial dysfunction, inward vascular remodeling, and severe loss of precapillary pulmonary vessel cross-sectional area. Asymmetrical dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, and its metabolizing enzyme dimethylarginine dimethylaminohydrolase (DDAH) play important roles in endothelial dysfunction. We investigated whether combined phosphodiesterase (PDE) 3 and 4 inhibition ameliorates endothelial function by regulating the ADMA-DDAH axis.

METHODS AND RESULTS

We investigated the effects of the PDE3/4 inhibitor tolafentrine in vitro on endothelial cell survival, proliferation, and apoptosis. Effects of tolafentrine on the endothelial nitric oxide synthase/nitric oxide pathway, DDAH expression, DDAH promoter activity, and cytokine release from endothelial cells and their subsequent influence on DDAH expression were investigated. In monocrotaline-induced pulmonary arterial hypertension in rats, the effects of inhaled tolafentrine on DDAH expression and activity were investigated. Real-time-polymerase chain reaction, immunocytochemistry, and PDE activity assays suggested high expression of PDE3 and PDE4 isoforms in endothelial cells. Treatment of endothelial cells with PDE3/4 inhibitor significantly decreased ADMA-induced apoptosis via a cAMP/PKA-dependent pathway by induction of DDAH2. Chronic nebulization of PDE3/4 inhibitor significantly attenuated monocrotaline-induced hemodynamic, gas exchange abnormalities, vascular remodeling, and right heart hypertrophy. Interestingly, PDE3/4 inhibitor treatment reduced ADMA and elevated nitric oxide/cGMP levels. Mechanistically, this could be attributed to direct modulatory effects of cAMP on the promoter region of DDAH2, which was consequently found to be increased in expression and activity. Furthermore, PDE3/4 inhibitor suppressed apoptosis in endothelial cells and increased vascularization in the lung.

CONCLUSION

Combined inhibition of PDE3 and 4 regresses development of pulmonary hypertension and promotes endothelial regeneration by modulating the ADMA-DDAH axis.

Role of phosphodiesterases in adult-onset pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterized by increased mean pulmonary artery pressure (mPAP) due to vasoconstriction and structural changes in the small pulmonary arteries (PAs); proliferation of pulmonary artery smooth muscle cells (PASMCs) contributes to the remodeling. The abnormal pathophysiology in the pulmonary vasculature relates to decreased cyclic nucleotide levels in PASMCs. Phosphodiesterases (PDEs) catalyze the hydrolysis of cAMP and cGMP, thereby PDE inhibitors are effective in vasodilating the PA and decreasing PASMC proliferation. Experimental studies support the use of PDE3, PDE5, and PDE1 inhibitors in PAH. PDE5 inhibitors such as sildenafil are clinically approved to treat different forms of PAH and lower mPAP, increase functional capacity, and decrease right ventricular hypertrophy, without decreasing systemic arterial pressure. New evidence suggests that the combination of PDE inhibitors with other therapies for PAH may be beneficial in treating the disease. Furthermore, inhibiting PDEs in the heart and the inflammatory cells that infiltrate the PA may offer new targets to reduce right ventricular hypertrophy and inhibit inflammation that is associated with and contributes to the development of PAH. This chapter summarizes the advances in the area and the future of PDEs in PAH.

Regulation of cAMP by phosphodiesterases in erythrocytes

The erythrocyte, a cell responsible for carrying and delivering oxygen in the body, has often been regarded as simply a vehicle for the circulation of hemoglobin. However, it has become evident that this cell also participates in the regulation of vascular caliber in the microcirculation via release of the potent vasodilator, adenosine triphosphate (ATP). The regulated release of ATP from erythrocytes occurs via a defined signaling pathway and requires increases in cyclic 3',5'- adenosine monophosphate (cAMP). It is well recognized that cAMP is a critical second messenger in diverse signaling pathways. In all cells increases in cAMP are localized and regulated by the activity of phosphodiesterases (PDEs). In erythrocytes activation of either beta adrenergic receptors (beta(2)AR) or the prostacyclin receptor (IPR) results in increases in cAMP and ATP release. Receptor-mediated increases in cAMP are tightly regulated by distinct PDEs associated with each signaling pathway as shown by the finding that selective inhibitors of the PDEs localized to each pathway potentiate both increases in cAMP and ATP release. Here we review the profile of PDEs identified in erythrocytes, their association with specific signaling pathways and their role in the regulation of ATP release from these cells. Understanding the contribution of PDEs to the control of ATP release from erythrocytes identifies this cell as a potential target for the development of drugs for the treatment of vascular disease.

PRX-08066, a novel 5-hydroxytryptamine receptor 2B antagonist, reduces monocrotaline-induced pulmonary arterial hypertension and right ventricular hypertrophy in rats

Pulmonary arterial hypertension (PAH) is a life-threatening disease that results in right ventricular failure. 5-((4-(6-Chlorothieno[2,3-d]pyrimidin-4-ylamino)piperidin-1-yl)methyl)-2-fluorobenzonitrile monofumarate (PRX-08066) is a selective 5-hydroxytryptamine receptor 2B (5-HT2BR) antagonist that causes selective vasodilation of pulmonary arteries. In the current study, the effects of PRX-08066 were assessed by using the monocrotaline (MCT)-induced PAH rat model. Male rats received 40 mg/kg MCT or phosphate-buffered saline and were treated orally twice a day with vehicle or 50 or 100 mg/kg PRX-08066 for 5 weeks. Pulmonary and cardiac functions were evaluated by hemodynamics, heart weight, magnetic resonance imaging (MRI), pulmonary artery (PA) morphology, and histology. Cardiac MRI demonstrated that PRX-08066 (100 mg/kg) significantly (P < 0.05) improved right ventricular ejection fraction. PRX-08066 significantly reduced peak PA pressure at 50 and 100 mg/kg (P < 0.05 and < 0.01, respectively) compared with MCT control animals. PRX-08066 therapy also significantly reduced right ventricle (RV)/body weight and RV/left ventricle + septum (P < 0.01 and < 0.001, respectively) compared with MCT-treated animals. Morphometric assessment of pulmonary arterioles revealed a significant reduction in medial wall thickening and lumen occlusion associated with both doses of PRX-08066 (P < 0.01). The 5-HT2BR antagonist PRX-08066 significantly attenuated the elevation in PA pressure and RV hypertrophy and maintained cardiac function. Pulmonary vascular remodeling was also diminished compared with MCT control rats. PRX-08066 prevents the severity of PAH in the MCT rat model.