Inhaled iloprost reverses vascular remodeling in chronic experimental pulmonary hypertension

Current Management and Future Directions for Pulmonary Arterial Hypertension Associated with Congenital Heart Disease

Current management of patients with congenital heart disease has increased their survival into adulthood. This is accompanied by potential cardiac complications, including pulmonary hypertension associated with congenital heart disease (PAH-CHD). PAH-CHD constitutes a challenging subgroup of pulmonary hypertension and requires expert management to improve quality of life and prognosis. Novel agents have shown a significant improvement in morbidity and mortality in patients with pulmonary arterial hypertension. However, the long-term effects of these medications on PAH-CHD patients remain somewhat uncertain, necessitating treatment plans largely founded on the clinical experience of the healthcare providers. The aim of this review is to summarize the current evidence and future perspectives regarding treatment strategies for PAH-CHD to help better guide management of this complex disease.

Inhaled Iloprost Induces Long‐term Beneficial Hemodynamic Changes in Patients with Pulmonary Arterial Hypertension Receiving Combination Therapy

Inhaled iloprost is an established treatment for pulmonary arterial hypertension (PAH). However, the long‐term hemodynamic changes that inhaled iloprost induces are unclear. Here, we retrospectively enrolled 18 patients with PAH who received inhaled iloprost as add‐on to oral combination therapy from December 2016 to January 2021 at our institute in Japan. We then examined the changes in hemodynamic parameters induced by iloprost in these patients during right heart catheterization (RHC). To examine the long‐term effects of iloprost, we repeated the RHC examination at follow‐up (median time to follow‐up, 8.5 months). During both catheterization procedures, iloprost was administered by using an I‐neb AAD system (Philips NV). In a comparison of pre‐inhalation values at the first and follow‐up RHCs, inhaled iloprost significantly improved mean pulmonary artery pressure (mPAP; 39.9 ± 7.8 to 32.5 ± 7.2 mmHg, p = 0.016) and pulmonary vascular resistance (PVR; 588.5 ± 191.7 to 464.4 ± 188.5 dyn s cm⁻⁵, p = 0.047). During the follow‐up RHC, in a comparison of the pre‐inhalation and best recorded values out to 30 min after the end of iloprost inhalation, iloprost significantly decreased mPAP (32.5 ± 7.2 to 30.0 ± 6.6 mmHg, p = 0.007) and PVR (457.8 ± 181.4 to 386.2 ± 142.8 dyn s cm⁻⁵, p = 0.025) and significantly increased cardiac output (4.19 ± 0.91 to 4.64 ± 1.01 L/min, p = 0.035). Iloprost may have not only acute vasodilation effects but also long‐term hemodynamic benefits in PAH patients receiving combination therapy.

Treprostinil palmitil inhibits the hemodynamic and histopathological changes in the pulmonary vasculature and heart in an animal model of pulmonary arterial hypertension

Treprostinil palmitil (TP) is a long-acting inhaled pulmonary vasodilator prodrug of treprostinil (TRE). In this study, TP was delivered by inhalation (treprostinil palmitil inhalation suspension, TPIS) in a rat Sugen 5416 (Su)/hypoxia (Hx) model of pulmonary arterial hypertension (PAH) to evaluate its effects on hemodynamics, pulmonary vascular remodeling, and cardiac performance and histopathology. Male Sprague-Dawley rats received Su (20 mg/kg, s.c), three weeks of Hx (10% O2) and 5 or 10 weeks of normoxia (Nx). TPIS was given during the 5-10 week Nx period after the Su/Hx challenge. Su/Hx increased the mean pulmonary arterial blood pressure (mPAP) and right heart size (Fulton index), reduced cardiac output (CO), stroke volume (SV) and heart rate (HR), and increased the thickness and muscularization of the pulmonary arteries along with obliteration of small pulmonary vessels. In both the 8- and 13-week experiments, TPIS at inhaled doses ranging from 39.6 to 134.1 μg/kg, QD, dose-dependently improved pulmonary vascular hemodynamics, reduced the increase in right heart size, enhanced cardiac performance, and attenuated most of the histological changes induced by the Su/Hx challenge. The PDE5 inhibitor sildenafil, administered at an oral dose of 50 mg/kg, BID for 10 weeks, was not as effective as TPIS. These results in Su/Hx challenged rats demonstrate that inhaled TPIS may have superior effects to oral sildenafil. We speculate that the improvement of the pathobiology in this PAH model induced by TPIS involves effects on pulmonary vascular remodeling due to the local effects of TRE in the lungs.

Plasma matrix metalloproteinase 2 is associated with severity and mortality in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life‐threatening disease characterized by vasoconstriction and remodeling of the pulmonary vessels. Risk stratification in PAH could potentially be improved by including novel biomarkers related to PAH pathobiology. We aimed to investigate the relationship between extracellular matrix (ECM)‐related proteins, survival, and European Society of Cardiology and European Respiratory Society (ESC/ERS) risk stratification scores in patients with PAH. Plasma samples and hemodynamics were collected from PAH patients during right heart catheterizations at diagnosis (n = 48) and early follow‐up, after treatment initiation (n = 33). Plasma levels of 14 ECM‐related proteins, with altered levels in PAH compared to healthy controls, were analyzed with proximity extension assays, and related to hemodynamics, transplant‐free survival time, and ESC/ERS risk score. Glypican‐1 levels were higher before versus after treatment initiation (p = 0.048). PAH patients with high plasma levels of matrix metalloproteinase (MMP) ‐2, MMP‐7, MMP‐9, MMP‐12, perlecan, and tissue inhibitor of metalloproteinase 4 (TIMP‐4) at baseline, had worse transplant‐free survival (p < 0.03) than patients with low levels. Hazard ratio (95% confidence interval) was for MMP‐2 1.126 (1.011–1.255), perlecan 1.0099 (1.0004–1.0196), and TIMP‐4 1.037 (1.003–1.071) in age and sex‐adjusted Cox‐regression model. MMP‐2 correlated with ESC/ERS risk scores (r_s = 0.34, p = 0.019), mean right atrial pressure (r_s = 0.44, p = 0.002), NT‐proBNP (r_s = 0.49, p ≤ 0.001), and six‐minute walking distance (r_s = −0.34, p = 0.02). The present study indicates that high levels of MMP‐2, perlecan, and TIMP‐4 are associated with poor survival in PAH. High plasma MMP‐2, correlated with poor prognosis in PAH. Further validation in larger studies is needed to better determine this association.

Galectin-3 Promotes ROS, Inflammation, and Vascular Fibrosis in Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive vascular disease arising from the narrowing of pulmonary arteries (PA) resulting in high pulmonary arterial blood pressure and ultimately right ventricular (RV) failure. A defining characteristic of PAH is the excessive remodeling of PA that includes increased proliferation, inflammation, and fibrosis. There is no cure for PAH nor interventions that effectively impede or reverse PA remodeling, and research over the past several decades has sought to identify novel molecular mechanisms of therapeutic benefit. Galectin-3 (Gal-3; Mac-2) is a carbohydrate-binding lectin that is remarkable for its chimeric structure, comprised of an N-terminal oligomerization domain and a C-terminal carbohydrate-recognition domain. Gal-3 is a regulator of changes in cell behavior that contribute to aberrant PA remodeling including cell proliferation, inflammation, and fibrosis, but its role in PAH is poorly understood. Herein, we summarize the recent literature on the role of Gal-3 in the development of PAH and provide experimental evidence supporting the ability of Gal-3 to influence reactive oxygen species (ROS) production, NOX enzyme expression, inflammation, and fibrosis, which contributes to PA remodeling. Finally, we address the clinical significance of Gal-3 as a target in the development of therapeutic agents as a treatment for PAH.

Factors Associated with Ineffectiveness of Sildenafil Treatment in Patients with End-Stage Heart Failure and Elevated Pulmonary Vascular Resistance

Introduction: Elevated pulmonary vascular resistance (PVR) unresponsive to vasodilator treatment is a marker of heart failure (HF) severity, and an important predictor of poor results of heart transplantation (HT). Objective: We sought to analyze factors associated with ineffectiveness of sildenafil treatment in end-stage HF patients with elevated PVR with particular emphasis placed on tenascin-C (TNC) serum concentrations. Patients and Methods: The study is an analysis of 132 end-stage HF patients referred for HT evaluation in the Cardiology Department between 2015 and 2018. TNC was measured by sandwich enzyme-linked immunosorbent assay (Human TNC, SunRedBio Technology, Shanghai, China). The endpoint was PVR > 3 Wood units after the six-month sildenafil therapy. Results: The median age was 58 years, and 90.2% were men. PVR >3 Wood units after 6 months of sildenafil treatment were found in 36.6% patients. The multivariable logistic regression analysis confirmed that TNC (OR = 1.004 (1.002–1.006), p = 0.0003), fibrinogen (OR= 1.019 (1.005–1.033), p = 0.085), creatinine (OR =1.025 (1.004–1.047), p = 0.0223) and right ventricular end-diastolic dimension (RVEDd) (OR = 1.279 (1.074–1.525), p = 0.0059) were independently associated with resistance to sildenafil treatment. Area under the ROC curves indicated an acceptable power of TNC (0.9680 (0.9444–0.9916)), fibrinogen (0.8187 (0.7456–0.8917)) and RVEDd (0.7577 (0.6723–0.8431)), as well as poor strength of creatinine (0.6025 (0.4981–0.7070)) for ineffectiveness of sildenafil treatment. Conclusions: Higher concentrations of TNC, fibrinogen and creatinine, as well as a larger RVEDd are independently associated with the ineffectiveness of sildenafil treatment. TNC has the strongest predictive power, sensitivity and specificity for evaluation of resistance to sildenafil treatment.

MicroRNA-483 amelioration of experimental pulmonary hypertension

Endothelial dysfunction is critically involved in the pathogenesis of pulmonary arterial hypertension (PAH) and that exogenously administered microRNA may be of therapeutic benefit. Lower levels of miR-483 were found in serum from patients with idiopathic pulmonary arterial hypertension (IPAH), particularly those with more severe disease. RNA-seq and bioinformatics analyses showed that miR-483 targets several PAH-related genes, including transforming growth factor-β (TGF-β), TGF-β receptor 2 (TGFBR2), β-catenin, connective tissue growth factor (CTGF), interleukin-1β (IL-1β), and endothelin-1 (ET-1). Overexpression of miR-483 in ECs inhibited inflammatory and fibrogenic responses, revealed by the decreased expression of TGF-β, TGFBR2, β-catenin, CTGF, IL-1β, and ET-1. In contrast, inhibition of miR-483 increased these genes in ECs. Rats with EC-specific miR-483 overexpression exhibited ameliorated pulmonary hypertension (PH) and reduced right ventricular hypertrophy on challenge with monocrotaline (MCT) or Sugen + hypoxia. A reversal effect was observed in rats that received MCT with inhaled lentivirus overexpressing miR-483. These results indicate that PAH is associated with a reduced level of miR-483 and that miR-483 might reduce experimental PH by inhibition of multiple adverse responses.

Effects of iloprost on experimental ischemia and reperfusion injury in rat ovary

We investigated the protective effect of iloprost against ischemia/reperfusion (I/R) injury in rat ovary. We used 32 female Sprague-Dawley rats randomly allocated to four experimental groups: sham, ischemia, I/R and I/R + iloprost. Ovarian torsion was established in all rats except the sham group. The torsion group was exposed to ischemia for 3 h. The detorsion group was exposed to 3 h ischemia applied + 3 h reperfusion. The detorsion + iloprost group was exposed to ischemia for 3 h + reperfusion for 3 h + intravenous (IV) iloprost infusion for 60 min starting at the beginning of reperfusion. Ovaries were removed and prepared for histopathological evaluation. Reduced glutathione (GSH) and malondialdehyde (MDA) were measured in the blood. The total histopathological injury score and MDA level of the ischemia group were significantly higher than for the sham group. Ovarian injury score and MDA level following I/R increased compared to the ischemia group. Iloprost administration reduced the total injury score and MDA level. The GSH level was higher in the I/R + iloprost group than in the I/R group. We concluded that IV iloprost administration reduces I/R injury in rat ovarian tissue.

Galectin-3: A Harbinger of Reactive Oxygen Species, Fibrosis, and Inflammation in Pulmonary Arterial Hypertension

Significance: Pulmonary arterial hypertension (PAH) is a progressive disease arising from the narrowing of pulmonary arteries (PAs) resulting in high pulmonary arterial blood pressure and ultimately right ventricle (RV) failure. A defining characteristic of PAH is the excessive and unrelenting inward remodeling of PAs that includes increased proliferation, inflammation, and fibrosis. Critical Issues: There is no cure for PAH nor interventions that effectively arrest or reverse PA remodeling, and intensive research over the past several decades has sought to identify novel molecular mechanisms of therapeutic value. Recent Advances: Galectin-3 (Gal-3) is a carbohydrate-binding lectin remarkable for its chimeric structure, composed of an N-terminal oligomerization domain and a C-terminal carbohydrate-recognition domain. Gal-3 has been identified as a regulator of numerous changes in cell behavior that contributes to aberrant PA remodeling, including cell proliferation, inflammation, and fibrosis, but its role in PAH has remained poorly understood until recently. In contrast, pathological roles for Gal-3 have been proposed in cancer and inflammatory and fibroproliferative disorders, such as pulmonary vascular and cardiac fibrosis. Herein, we summarize the recent literature on the role of Gal-3 in the development of PAH. We provide experimental evidence supporting the ability of Gal-3 to influence reactive oxygen species production, NADPH oxidase enzyme expression, and redox signaling, which have been shown to contribute to both vascular remodeling and increased pulmonary arterial pressure. Future Directions: While several preclinical studies suggest that Gal-3 promotes hypertensive pulmonary vascular remodeling, the clinical significance of Gal-3 in human PAH remains to be established. Antioxid. Redox Signal. 00, 000-000.

The Role of G Protein-Coupled Receptors in the Right Ventricle in Pulmonary Hypertension

Pressure overload of the right ventricle (RV) in pulmonary arterial hypertension (PAH) leads to RV remodeling and failure, an important determinant of outcome in patients with PAH. Several G protein-coupled receptors (GPCRs) are differentially regulated in the RV myocardium, contributing to the pathogenesis of RV adverse remodeling and dysfunction. Many pharmacological agents that target GPCRs have been demonstrated to result in beneficial effects on left ventricular (LV) failure, such as beta-adrenergic receptor and angiotensin receptor antagonists. However, the role of such drugs on RV remodeling and performance is not known at this time. Moreover, many of these same receptors are also expressed in the pulmonary vasculature, which could result in complex effects in PAH. This manuscript reviews the role of GPCRs in the RV remodeling and dysfunction and discusses activating and blocking GPCR signaling to potentially attenuate remodeling while promoting improvements of RV function in PAH.

Efficacy of treprostinil in the SU5416-hypoxia model of severe pulmonary arterial hypertension: haemodynamic benefits are not associated with improvements in arterial remodelling

BACKGROUND AND PURPOSE

Pulmonary arterial hypertension (PAH) is a life-threatening disease that leads to progressive pulmonary hypertension, right heart failure and death. Parenteral prostaglandins (PGs), including treprostinil, a prostacyclin analogue, represent the most effective medical treatment for severe PAH. We investigated the effect of treprostinil on established severe PAH and underlying mechanisms using the rat SU5416 (SU, a VEGF receptor-2 inhibitor)-chronic hypoxia (Hx) model of PAH.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were injected with SU (20 mg·kg^-1 , s.c.) followed by 3 weeks of Hx (10% O₂ ) to induce severe PAH. Four weeks post-SU injection, baseline right ventricular (RV) systolic pressure (RVSP) was measured, and the rats were randomized to receive vehicle or treprostinil treatment (Trep-100: 100 ng·kg^-1 ·min^-1 or Trep-810: 810 ng·kg^-1 ·min^-1 ). Following 3 weeks of treatment, haemodynamic and echocardiographic assessments were performed, and tissue samples were collected for protein expression and histological analysis.

KEY RESULTS

At week 7, no difference in RVSP or RV hypertrophy was observed between vehicle and Trep-100; however, Trep-810 significantly reduced RVSP and RV hypertrophy. Trep-810 treatment significantly improved cardiac structure and function. Further, a short-term infusion of treprostinil in rats with established PAH at 4 weeks post-SU produced an acute, dose-dependent reduction in RVSP consistent with a vasodilator effect. However, chronic Trep-810 treatment did not alter media wall thickness, degree of vascular occlusion or total vessel count in the lungs.

CONCLUSIONS AND IMPLICATIONS

Treprostinil exerts therapeutic benefits in PAH through decreased vascular resistance and improved cardiac structure and function; however, treprostinil treatment does not have direct impact vascular remodelling.

TGF-β and BMPR2 Signaling in PAH: Two Black Sheep in One Family

Knowledge pertaining to the involvement of transforming growth factor β (TGF-β) and bone morphogenetic protein (BMP) signaling in pulmonary arterial hypertension (PAH) is continuously increasing. There is a growing understanding of the function of individual components involved in the pathway, but a clear synthesis of how these interact in PAH is currently lacking. Most of the focus has been on signaling downstream of BMPR2, but it is imperative to include the role of TGF-β signaling in PAH. This review gives a state of the art overview of disturbed signaling through the receptors of the TGF-β family with respect to vascular remodeling and cardiac effects as observed in PAH. Recent (pre)-clinical studies in which these two pathways were targeted will be discussed with an extended view on cardiovascular research fields outside of PAH, indicating novel future perspectives.

The Role of Neutrophils and Neutrophil Elastase in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe vasculopathy characterized by the presence of fibrotic lesions in the arterial wall and the loss of small distal pulmonary arteries. The vasculopathy is accompanied by perivascular inflammation and increased protease levels, with neutrophil elastase notably implicated in aberrant vascular remodeling. However, the source of elevated elastase levels in PAH remains unclear. A major source of neutrophil elastase is the neutrophil, an understudied cell population in PAH. The principal function of neutrophils is to destroy invading pathogens by means of phagocytosis and NET formation, but proteases, chemokines, and cytokines implicated in PAH can be released by and/or prime and activate neutrophils. This review focuses on the contribution of inflammation to the development and progression of the disease, highlighting studies implicating neutrophils, neutrophil elastase, and other neutrophil proteases in PAH. The roles of cytokines, chemokines, and neutrophil elastase in the disease are discussed and we describe new insight into the role neutrophils potentially play in the pathogenesis of PAH.

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.

Increased Serum Levels of Fetal Tenascin-C Variants in Patients with Pulmonary Hypertension: Novel Biomarkers Reflecting Vascular Remodeling and Right Ventricular Dysfunction?

Pulmonary vascular remodeling is a pathophysiological feature that common to all classes of pulmonary hypertension (PH) and right ventricular dysfunction, which is the major prognosis-limiting factor. Vascular, as well as cardiac tissue remodeling are associated with a re-expression of fetal variants of cellular adhesion proteins, including tenascin-C (Tn-C). We analyzed circulating levels of the fetal Tn-C splicing variants B⁺ and C⁺ Tn-C in serum of PH patients to evaluate their potential as novel biomarkers reflecting vascular remodeling and right ventricular dysfunction. Serum concentrations of B⁺ and C⁺ Tn-C were determined in 80 PH patients and were compared to 40 healthy controls by enzyme-linked immunosorbent assay. Clinical, laboratory, echocardiographic, and functional data were correlated with Tn-C levels. Serum concentrations of both Tn-C variants were significantly elevated in patients with PH (p < 0.05). Significant correlations could be observed between Tn-C and echocardiographic parameters, including systolic pulmonary artery pressure (B⁺ Tn-C: r = 0.31, p < 0.001, C⁺ Tn-C: r = 0.26, p = 0.006) and right atrial area (B⁺ Tn-C: r = 0.46, p < 0.001, C⁺ Tn-C: r = 0.49, p < 0.001), and laboratory values like BNP (B⁺ Tn-C: r = 0.45, p < 0.001, C⁺ Tn-C: r = 0.42, p < 0.001). An inverse correlation was observed between Tn-C variants and 6-minute walk distance as a functional parameter (B⁺ Tn-C: r = -0.54, p < 0.001, C⁺ Tn-C: r = -0.43, p < 0.001). In a multivariate analysis, B⁺ Tn-C, but not C⁺ Tn-C, was found to be an independent predictor of pulmonary hypertension. Both fetal Tn-C variants may represent novel biomarkers that are capable of estimating both pulmonary vascular remodeling and right ventricular load. The potential beneficial impact of Tn-C variants for risk stratification in patients with PH needs further investigation.

Plasma MMP2/TIMP4 Ratio at Follow-up Assessment Predicts Disease Progression of Idiopathic Pulmonary Arterial Hypertension

PURPOSE

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) are of particular interest in the remodeling processes of pulmonary hypertension. The aim of this study was to investigate MMP/TIMP ratios of selected biomarkers (MMP2, MMP9, TIMP1, TIMP4) at follow-up examination (V2) and their prognostic value in patients with idiopathic pulmonary arterial hypertension (iPAH).

METHODS

Blood samples were taken from iPAH patients during right heart catheterization at diagnosis (V1, from 2003 to 2012) and first follow-up examination (V2). MMP2, MMP9, TIMP1, and TIMP4 plasma levels at V2 were determined by ELISA. Coincident with sample collection hemodynamic, laboratory, and clinical parameters were acquired. Additionally, death and clinical worsening (CW) events were listed until July 2015.

RESULTS

MMP2/TIMP1 and MMP9/TIMP1 did not correlate with hemodynamic and clinical parameters. MMP2/TIMP4 showed a good correlation with mean pulmonary arterial pressure (mPAP), pulmonary vascular resistance, estimated glomerular filtration rate (eGFR), and tricuspid annular plain systolic excursion (TAPSE). MMP9/TIMP4 shows good correlation with mPAP and eGFR. MMP2/TIMP4 showed significant results in the receiver operating characteristics analysis predicting death (AUC = 0.922; p = 0.005) and CW event (AUC = 0.818; p = 0.026). Patients above the cut-off values had a significantly higher probability to die or experience CW, respectively, estimated by log-rank test (p = 0.010 for death; p = 0.032 for CW).

CONCLUSIONS

MMP2/TIMP4 ratio was detected as a marker of disease severity and right ventricular function as well as a predictor for survival and time to clinical worsening and therefore might help for guidance of disease progression in iPAH patients at V2.

Augmentation of the effects of vasoactive intestinal peptide aerosol on pulmonary hypertension via coapplication of a neutral endopeptidase 24.11 inhibitor

A deficiency of the pulmonary vasodilative vasoactive intestinal peptide (VIP) has been suggested to be involved in the pathophysiology of pulmonary hypertension (PH). Supplementation of VIP as an aerosol is hampered by the fact that it is rapidly inactivated by neutral endopeptidases (NEP) located on the lung surface. Coapplication of thiorphan, an NEP 24.11 inhibitor, could augment the biological effects of inhaled VIP alone. A stable pulmonary vasoconstriction with a threefold increase of pulmonary artery pressure was established by application the thromboxane mimetic U46619 in the isolated rabbit lung model. VIP and thiorphan were either applied intravascularly or as an aerosol. VIP caused a significant pulmonary vasodilation either during intravascular application or inhalation. These effects were of short duration. Thiorphan application had no effects on pulmonary vasoconstriction per se but significantly augmented the effects of VIP aerosol. Thiorphan, not only augmented the maximum hemodynamic effects of VIP aerosol, but also led to a significant prolongation of these effects. VIP causes pulmonary vasodilation in a model of acute experimental PH. The hemodynamic effects of VIP aerosol can be significantly augmented via coapplication of an NEP inhibitor.

Glycyrrhizin, inhibitor of high mobility group box-1, attenuates monocrotaline-induced pulmonary hypertension and vascular remodeling in rats

BACKGROUND

High mobility group box-1 (HMGB1), a proinflammatory cytokine, plays a pivotal role in tissue remodeling and angiogenesis, both of which are crucial for the pathogenesis of pulmonary arterial hypertension. In this study, we explored the relationship between HMGB1 and pulmonary hypertension and whether glycyrrhizin, an inhibitor of HMGB1, attenuates disease progression in an animal model of pulmonary hypertension induced by monocrotaline sodium (MCT).

METHODS

After inducing pulmonary hypertension through a single subcutaneous injection of MCT (60 mg/kg) to Sprague-Dawley rats, we administered daily intraperitoneal injections of either glycyrrhizin (GLY, 50 mg/kg), an inhibitor of HMGB1, or saline (control) for either 4 or 6 weeks.

RESULTS

Expression levels of HMGB1 in serum increased from the second week after MCT injection and remained elevated throughout the experiment periods. Lung tissue levels of HMGB1 assessed by immunohistochemical staining at 4 weeks after MCT injection also increased. Chronic inhibition of HMGB1 by GLY treatment reduced the MCT-induced increase in right ventricular (RV) systolic pressure, RV hypertrophy (ratio of RV to [left ventricle + septum]), and pulmonary inflammation. MCT-induced muscularization of the pulmonary artery was also attenuated in the GLY-treated group. As assessed 6 weeks after MCT injection, the GLY-treated group exhibited increased survival (90% [18 of 20]) when compared with the control group (60% [12 of 20]; p =0.0027).

CONCLUSIONS

Glycyrrhizin, an inhibitor of HMGB1, attenuates pulmonary hypertension progression and pulmonary vascular remodeling in the MCT-induced pulmonary hypertension rat model. Further studies are needed to confirm the potential of HMGB1 as a novel therapeutic target for pulmonary hypertension.

PDGF and TGF-β promote tenascin-C expression in subepithelial myofibroblasts and contribute to intestinal mucosal protection in mice

BACKGROUND AND PURPOSE

Tenascin-C (TnC) is a multi-domain extracellular matrix glycoprotein that is expressed at a high level during embryogenesis but is almost absent during normal postnatal life. This multi-domain complex molecule is reported to associate with both pro-inflammatory and anti-inflammatory signalling cascades. In this study, we examined how TnC modulated intestinal inflammation.

EXPERIMENTAL APPROACH

TnC pathophysiology was evaluated in cultures of rat intestinal subepithelial myofibroblasts (ISEMF) and intestinal epithelial cells. Wild-type and TnC(-/-) mice were treated with dextran sodium sulfate (DSS) to induce colitis.

KEY RESULTS

DSS-induced colitis in mice markedly increased TnC in the damaged mucosal areas and up-regulated mRNA for TnC, pro-inflammatory cytokines and growth factors (PDGF-B and TGF-β1). In addition, 2,4,6-trinitrobenzene sulfonic acid-induced colitis and SAMP1/Yit mice, a model of spontaneous Crohn's disease, also exhibited increased mucosal TnC in colon and ilea respectively. PDGF receptor-α (PDGFRα) positive ISEMF were the primary TnC-producing cells in colon tissues. Accordingly, ISEMF collected from the rat colon constitutively expressed both TnC and PDGFRα. PDGF-BB and TGF-β1 up-regulated both TnC mRNA and protein levels in ISEMF. Knock-down of TnC gene increased susceptibility to DSS-induced colitis, compared with TnC(+/+) littermates. TnC(-/-) mice showed marked abrasion of intestinal mucosal barrier and increased inflammatory scores. Moreover, TnC accelerated both trans-well migration and wound healing in epithelial cells.

CONCLUSIONS AND IMPLICATIONS

The pharmacological profiles of PDGF-BB and TGF-β in colitis tissues and ISEMF suggest that increased TnC production during inflammation contributed to epithelial cell migration, remodelling and protection of intestinal barriers.

Increased levels of plasma CXC-Chemokine Ligand 10, 12 and 16 are associated with right ventricular function in patients with idiopathic pulmonary arterial hypertension

OBJECTIVE

To investigate plasma levels of CXC-Chemokine Ligand 10 (CXCL10), CXC-Chemokine Ligand 12 (CXCL12) and CXC-Chemokine Ligand 16 (CXCL16) in patients with idiopathic pulmonary arterial hypertension (IPAH).

METHODS

Plasma levels of biomarkers were measured by enzyme-linked immunosorbent assay in 61 patients with IPAH and 20 healthy volunteers.

RESULTS

Plasma CXCL10, CXCL12 and CXCL16 concentrations were increased significantly in IPAH patients compared with controls, and significantly correlated with N-terminal pro-brain natriuretic peptide, tricuspid annulus plane systolic excursion and right ventricular ejection fraction.

CONCLUSIONS

Increased levels of CXCL10, CXCL12 and CXCL16 are associated with right ventricular dysfunction in patients with IPAH.

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.

Increased expression of hypoxia-inducible factor-1α in proliferating neointimal lesions in a rat model of pulmonary arterial hypertension

INTRODUCTION

The role of hypoxia-inducible factor-1α (HIF-1α) in pulmonary vascular remodeling is still undetermined. The objective of this study is to investigate the expression of HIF-1α and its role in proliferating neointimal lesions in a rat model of pulmonary arterial hypertension induced by monocrotaline (MCT) administration after left pneumonectomy.

METHODS

The rats were subjected to MCT (60 mg/kg, subcutaneously) 7 days after left pneumonectomy or sham surgery; controls with vehicle treatment after left pneumonectomy or sham surgery were also studied. On day 35, hemodynamic parameters of the rats were measured. The right lower lobes of the lungs were fixed for morphometric analysis. The expression of proliferating cell nuclear antigen and survivin was detected with Western blot. The expressions of HIF-1α and hexokinase-2 (HK-2) were detected with Western blot and immunohistochemistry assay.

RESULTS

The rats treated with MCT after pneumonectomy developed severe pulmonary arterial hypertension and marked medial thickening on day 35. The neointimal lesions in pulmonary arterioles were observed only in MCT-treated pneumonectomized rats. The severely injured pulmonary arterioles (intimal proliferation causing greater than 50% luminal occlusion) accounted for 40% of all the measured arterioles in rats treated by MCT after pneumonectomy. The intriguing finding showed that HIF-1α was predominantly expressed in neointimal lesion areas, paralleled with the increased expression of HK-2 in MCT-treated pneumonectomized rats, which was not observed in rats undergoing MCT treatment alone.

CONCLUSIONS

The activation of HIF-1α/HK-2 axis is probably the key mediator responsible for the neointimal lesion formation in MCT-treated pneumonectomized rats.

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.

Effects of inhaled iloprost on congenital heart disease with Eisenmenger syndrome

Identification of the pathophysiology associated with Eisenmenger syndrome has led to the evaluation of targeted therapies. Iloprost is one such targeted therapy used for patients with Eisenmenger syndrome. This study aimed to assess the efficacy and safety of iloprost used for patients with Eisenmenger syndrome. In this study, 12 patients with Eisenmenger syndrome (mean age, 33.2 ± 12.1 years; 75% female) started receiving iloprost 10 μg/dose administered six times a day. Of the 12 patients, 9 were classified as New York Heart Association (NYHA) functional class 3, and three were categorized as functional class 4. Changes in 6-min walk distance, NYHA functional class, oxygen saturation at resting, and results after the 6-min walk test were checked, as well as changes in right ventricle diameter and pulmonary arterial pressure shown by echocardiography. The distance during a 6-min walk increased from 255.8 ± 120.4 to 349.4 ± 134.7 m (p = 0.013), and 10 patients improved their NYHA functional class by one grade (p = 0.007). The mean resting oxygen saturation (SpO(2)) increased from 80.6 ± 14.2 to 84.9 ± 13.0% (p = 0.040), and after the 6-min walk test, it increased from 63.8 ± 22.9 to 68.8 ± 21.5% (p = 0.007). The mean right ventricle diameter during the diastolic phase changed from 53.7 ± 4.8 to 51.4 ± 3.9 mm (p = 0.068), and the mean pulmonary arterial pressure changed from 62.8 ± 13.7 to 58.9 ± 11.7 mmHg (p = 0.059). Neither death nor critical adverse effects occurred for any patients. Mild headache and dyspnea were common reports during the iloprost treatments. No patients stopped the therapy due to these adverse effects. Iloprost is well tolerated and appears to be beneficial in the management of patients with Eisenmenger syndrome.

Phosphodiesterase 4 inhibition attenuates persistent heart and lung injury by neonatal hyperoxia in rats

Phosphodiesterase (PDE) 4 inhibitors are potent anti-inflammatory drugs with antihypertensive properties, and their therapeutic role in bronchopulmonary dysplasia (BPD) is still controversial. We studied the role of PDE4 inhibition with piclamilast on normal lung development and its therapeutic value on pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) in neonatal rats with hyperoxia-induced lung injury, a valuable model for premature infants with severe BPD. The cardiopulmonary effects of piclamilast treatment (5 mg·kg(-1)·day(-1)) were investigated in two models of experimental BPD: 1) daily treatment during continuous exposure to hyperoxia for 10 days; and 2) late treatment and injury-recovery in which pups were exposed to hyperoxia or room air for 9 days, followed by 9 or 42 days of recovery in room air combined with treatment started on day 6 of oxygen exposure until day 18. Prophylactic piclamilast treatment reduced pulmonary fibrin deposition, septum thickness, arteriolar wall thickness, arteriolar vascular smooth muscle cell proliferation and RVH, and prolonged survival. In the late treatment and injury-recovery model, hyperoxia caused persistent aberrant alveolar and vascular development, PH, and RVH. Treatment with piclamilast in both models reduced arteriolar wall thickness, attenuated RVH, and improved right ventricular function in the injury recovery model, but did not restore alveolarization or angiogenesis. Treatment with piclamilast did not show adverse cardiopulmonary effects in room air controls in both models. In conclusion, PDE4 inhibition attenuated and partially reversed PH and RVH, but did not advance alveolar development in neonatal rats with hyperoxic lung injury or affect normal lung and heart development.

Microsomal prostaglandin e2 synthase-1 modulates the response to vascular injury

BACKGROUND

Microsomal (m) prostaglandin (PG) E₂ synthase (S)-1 catalyzes the formation of PGE₂ from PGH₂, a cyclooxygenase product that is derived from arachidonic acid. Previous studies in mice suggest that targeting mPGES-1 may be less likely to cause hypertension or thrombosis than cyclooxygenase-2-selective inhibition or deletion in vivo. Indeed, deletion of mPGES-1 retards atherogenesis and angiotensin II-induced aortic aneurysm formation. The role of mPGES-1 in the response to vascular injury is unknown.

METHODS AND RESULTS

Mice were subjected to wire injury of the femoral artery. Both neointimal area and vascular stenosis were significantly reduced 4 weeks after injury in mPGES-1 knockout mice compared with wild-type controls (65.6 ± 5.7 versus 37.7 ± 5.1 × 10³ pixel area and 70.5 ± 13.4% versus 47.7 ± 17.4%, respectively; P < 0.01). Induction of tenascin-C, a proproliferative and promigratory extracellular matrix protein, after injury was attenuated in the knockouts. Consistent with in vivo rediversion of PG biosynthesis, mPGES-1-deleted vascular smooth muscle cells generated less PGE₂ but more PGI₂ and expressed reduced tenascin-C compared with wild-type cells. Both suppression of PGE₂ and augmentation of PGI₂ attenuate tenascin-C expression and vascular smooth muscle cell proliferation and migration in vitro.

CONCLUSIONS

Deletion of mPGES-1 in mice attenuates neointimal hyperplasia after vascular injury, in part by regulating tenascin-C expression. This raises for consideration the therapeutic potential of mPGES-1 inhibitors as adjuvant therapy for percutaneous coronary intervention.

Smooth muscle proliferation and role of the prostacyclin (IP) receptor in idiopathic pulmonary arterial hypertension

RATIONALE

Prostacyclin analogs, used to treat idiopathic pulmonary arterial hypertension (IPAH), are assumed to work through prostacyclin (IP) receptors linked to cyclic AMP (cAMP) generation, although the potential to signal through peroxisome proliferator-activated receptor-γ (PPARγ) exists.

OBJECTIVES

IP receptor and PPARγ expression may be depressed in IPAH. We wished to determine if pathways remain functional and if analogs continue to inhibit smooth muscle proliferation.

METHODS

We used Western blotting to determine IP receptor expression in peripheral pulmonary arterial smooth muscle cells (PASMCs) from normal and IPAH lungs and immunohistochemistry to evaluate IP receptor and PPARγ expression in distal arteries.

MEASUREMENTS AND MAIN RESULTS

Cell proliferation and cAMP assays assessed analog responses in human and mouse PASMCs and HEK-293 cells. Proliferative rates of IPAH cells were greater than normal human PASMCs. IP receptor protein levels were lower in PASMCs from patients with IPAH, but treprostinil reduced replication and treprostinil-induced cAMP elevation appeared normal. Responses to prostacyclin analogs were largely dependent on the IP receptor and cAMP in normal PASMCs, although in IP(-/-) receptor cells analogs inhibited growth in a cAMP-independent, PPARγ-dependent manner. In IPAH cells, antiproliferative responses to analogs were insensitive to IP receptor or adenylyl cyclase antagonists but were potentiated by a PPARγ agonist and inhibited (∼ 60%) by the PPARγ antagonist GW9662. This coincided with increased PPARγ expression in the medial layer of acinar arteries.

CONCLUSIONS

The antiproliferative effects of prostacyclin analogs are preserved in IPAH despite IP receptor down-regulation and abnormal coupling. PPARγ may represent a previously unrecognized pathway by which these agents inhibit smooth muscle proliferation.

Circulating biomarkers of tissue remodelling in pulmonary hypertension

OBJECTIVE

Besides persisting high pulmonary arterial pressure and increased pulmonary vascular resistance, remodelling of pulmonary tissues and subsequently the right heart are the key pathomechanisms of pulmonary hypertension (PH). Extracellular matrix maintenance in this context plays a central role.

METHODS

We tested the hypothesis that plasma concentration of matrix metalloproteinase (MMP)-2, tissue inhibitor of matrix metalloproteinases (TIMP)-4 and tenascin C (TNC) might be useful as biomarkers for assessing the severity of PH. Therefore, the concentrations of MMP-2, TIMP-4, TNC and N-terminal b-type natriuretic peptide (NT-proBNP) of 36 PH patients were compared with those of 44 age- and gender-matched healthy volunteers. Additionally, lung function, 6-min walk distance and right heart function were assessed.

RESULTS

In PH patients, significantly elevated plasma levels of MMP-2, TIMP-4, TNC and NT-proBNP were detected. In particular, TIMP-4 was significantly increased in patients with higher NYHA classification, and in patients with severe right ventricular hypertrophy.

CONCLUSION

Monitoring of plasma TIMP-4 and to a lesser extent of MMP-2 and TNC levels in PH patients might help to assess the beneficial effects of PH pharmacotherapy on tissue remodelling.

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.

Novel approaches to treat experimental pulmonary arterial hypertension: a review

Background. Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy, RV failure, and ultimately death. Current treatments can improve symptoms and reduce severity of the hemodynamic disorder but gradual deterioration in their condition often necessitates a lung transplant. Methods and Results. In experimental models of PAH, particularly the model of monocrotaline-induced pulmonary hypertension, efficacious treatment options tested so far include a spectrum of pharmacologic agents with actions such as anti-mitogenic, proendothelial function, proangiogenic, antiinflammatory and antioxidative. Emerging trends in PAH treatment are gene and cell therapy and their combination, like (progenitor) cells enriched with eNOS or VEGF gene. More animal data should be collected to investigate optimal cell type, in vitro cell transduction, route of administration, and number of cells to inject. Several recently discovered and experimentally tested interventions bear potential for therapeutic purposes in humans or have been shown already to be effective in PAH patients leading to improved life expectation and better quality of life. Conclusion. Since many patients remain symptomatic despite therapy, we should encourage research in animal models of PAH and implement promising treatments in homogeneous groups of PAH patients.

Review of inhaled iloprost for the control of pulmonary artery hypertension in children

In the pediatric population, pulmonary hypertension may present as an acute event in the setting of lung or cardiac pathology or as a chronic disease, mainly as idiopathic pulmonary hypertension or associated with congenital heart disease. Recently, new pharmacologic approaches have demonstrated significant efficacy in the management of adults with pulmonary arterial hypertension; these include intravenous epoprostenol, prostacyclin analogs, endothelin receptor antagonists and phosphodiesterase type 5 inhibitors. The same treatment strategies are currently used in children. There are only few reports of the use of inhaled iloprost in pediatrics, only one of which reported the use of chronic inhaled iloprost in a significant number of children. This report showed that 1) the acute pulmonary vasodilator response to inhaled iloprost is equivalent to that of inhaled nitric oxide; 2) acute inhalation of iloprost can induce bronchoconstriction 3) the addition of inhaled iloprost can reduce the need for intravenous prostanoid therapy in some patients; 4) most children tolerated the combination of inhaled iloprost and endothelin receptor antagonist or phosphodiesterase inhibitors; 5) Several patients had clinical deterioration during chronic inhaled iloprost therapy and required rescue therapy with intravenous prostanoids. In this review we will discuss the role of inhaled iloprost in acute and chronic pulmonary hypertension in children.

Characterization of a murine model of monocrotaline pyrrole-induced acute lung injury

Background

New animal models of chronic pulmonary hypertension in mice are needed. The injection of monocrotaline is an established model of pulmonary hypertension in rats. The aim of this study was to establish a murine model of pulmonary hypertension by injection of the active metabolite, monocrotaline pyrrole.

Methods

Survival studies, computed tomographic scanning, histology, bronchoalveolar lavage were performed, and arterial blood gases and hemodynamics were measured in animals which received an intravenous injection of different doses of monocrotaline pyrrole.

Results

Monocrotaline pyrrole induced pulmonary hypertension in Sprague Dawley rats. When injected into mice, monocrotaline pyrrole induced dose-dependant mortality in C57Bl6/N and BALB/c mice (dose range 6–15 mg/kg bodyweight). At a dose of 10 mg/kg bodyweight, mice developed a typical early-phase acute lung injury, characterized by lung edema, neutrophil influx, hypoxemia and reduced lung compliance. In the late phase, monocrotaline pyrrole injection resulted in limited lung fibrosis and no obvious pulmonary hypertension.

Conclusion

Monocrotaline and monocrotaline pyrrole pneumotoxicity substantially differs between the animal species.

Effects of inhaled iloprost on right ventricular contractility, right ventriculo-vascular coupling and ventricular interdependence: a randomized placebo-controlled trial in an experimental model of acute pulmonary hypertension

Introduction

Prostacyclin inhalation is increasingly used to treat acute pulmonary hypertension and right ventricular failure, although its pharmacodynamic properties remain controversial. Prostacyclins not only affect vasomotor tone but may also have cAMP-mediated positive inotropic effects and modulate autonomic nervous system tone. We studied the role of these different mechanisms in the overall haemodynamic effects produced by iloprost inhalation in an experimental model of acute pulmonary hypertension.

Methods

In this prospective, randomized, placebo-controlled animal study, twenty-six pigs (mean weight 35 ± 2 kg) were instrumented with biventricular conductance catheters, a pulmonary artery flow probe and a high-fidelity pulmonary artery pressure catheter. The effects of inhaled iloprost (50 μg) were studied in the following groups: animals with acute hypoxia-induced pulmonary hypertension, and healthy animals with and without blockade of the autonomic nervous system.

Results

During pulmonary hypertension, inhalation of iloprost resulted in a 51% increase in cardiac output compared with placebo (5.6 ± 0.7 versus 3.7 ± 0.8 l/minute; P = 0.0013), a selective reduction in right ventricular afterload (effective pulmonary arterial elastance: 0.6 ± 0.3 versus 1.2 ± 0.5 mmHg/ml; P = 0.0005) and a significant increase in left ventricular end-diastolic volume (91 ± 12 versus 70 ± 20 ml; P = 0.006). Interestingly, right ventricular contractility was reduced after iloprost-treatment (slope of preload recruitable stroke work: 2.2 ± 0.5 versus 3.4 ± 0.8 mWatt·s/ml; P = 0.0002), whereas ventriculo-vascular coupling remained essentially preserved (ratio of right ventricular end-systolic elastance to effective pulmonary arterial elastance: 0.97 ± 0.33 versus 1.03 ± 0.15). In healthy animals, inhaled iloprost had only minimal haemodynamic effects and produced no direct effects on myocardial contractility, even after pharmacological blockade of the autonomic nervous system.

Conclusions

In animals with acute pulmonary hypertension, inhaled iloprost improved global haemodynamics primarily via selective pulmonary vasodilatation and restoration of left ventricular preload. The reduction in right ventricular afterload is associated with a paradoxical decrease in right ventricular contractility. Our data suggest that this reflects an indirect mechanism by which ventriculo-vascular coupling is maintained at the lowest possible energetic cost. We found no evidence for a direct negative inotropic effect of iloprost.

Role of the prostanoid EP4 receptor in iloprost-mediated vasodilatation in pulmonary hypertension

RATIONALE

Iloprost is effective for the treatment of pulmonary hypertension. It acts through elevation of cAMP by binding to the prostacyclin receptor (IP receptor). However, there is evidence that patients with severe pulmonary hypertension have decreased expression of the IP receptor in the remodeled pulmonary arterial smooth muscle.

OBJECTIVES

We hypothesized that prostanoid receptors other than the IP receptor are involved in signal transduction by iloprost.

METHODS

Immunoblotting was used to detect the IP and prostanoid EP4 receptor in lung tissue from patients with idiopathic pulmonary arterial hypertension, and immunohistochemistry was used to detect these receptors in lung sections from rats treated with monocrotaline (MCT28d). Protein and mRNA were isolated from pulmonary arterial smooth muscle cells (PASMCs) from control and MCT28d rats treated with AH6809 (an EP2 receptor antagonist) and AH23848 (an EP4 receptor antagonist) in combination with iloprost. Intracellular cAMP was also assessed in these tissues.

MEASUREMENTS AND MAIN RESULTS

IP receptor expression was reduced in idiopathic pulmonary arterial hypertension patient lung samples and MCT28d rat lungs compared with the controls. Reverse transcriptase-polymerase chain reaction and immunoblotting of MCT28d rat PASMC extracts revealed scant expression of the IP receptor but stable expression of EP4 receptor, compared with controls. Iloprost-induced elevation in intracellular cAMP in PASMCs was dose-dependently reduced by AH23848, but not by AH6809.

CONCLUSIONS

Iloprost mediates vasodilatory functions via the EP4 receptor in the case of low IP receptor expression associated with pulmonary arterial hypertension. This is a previously unrecognized mechanism for iloprost, and illustrates that the EP4 receptor may be a novel therapeutic approach for the treatment of pulmonary arterial hypertension.

Inhaled iloprost to control pulmonary artery hypertension in patients undergoing mitral valve surgery: a prospective, randomized-controlled trial

BACKGROUND

Pulmonary hypertension (PHT) is common in patients undergoing mitral valve surgery and is an independent risk factor for the development of acute right ventricular (RV) failure. Inhaled iloprost was shown to improve RV function and decrease RV afterload in patients with primary PHT. However, no randomized-controlled trials on the intraoperative use of iloprost in cardiac surgical patients are available. We therefore compared the effects of inhaled iloprost vs. intravenous standard therapy in cardiac surgical patients with chronic PHT.

METHODS

Twenty patients with chronic PHT undergoing mitral valve repair were randomized to receive inhaled iloprost (25 microg) or intravenous nitroglycerine. Iloprost was administered during weaning from cardiopulmonary bypass (CPB). Systemic and pulmonary haemodynamics were assessed with pulmonary artery catheterization and transoesophageal echocardiography. Milrinone and/or inhaled nitric oxide were available as rescue medication in case of failure to wean from CPB.

RESULTS

Inhaled iloprost selectively decreased the pulmonary vascular resistance index after weaning from CPB (208 +/- 108 vs. 422 +/- 62 dyn.s/cm(5)/m(2), P<0.05), increased the RV-ejection fraction (29 +/- 3% vs. 22 +/- 5%, P<0.05), improved the stroke volume index (27 +/- 7 vs. 18 +/- 6 ml/m(2), P<0.05) and reduced the transpulmonary gradient (10 +/- 4 vs. 16 +/- 3 mmHg, P<0.05). In all patients receiving inhaled iloprost, weaning from CPB was successful during the first attempt. In contrast, three patients in the control group required re-institution of CPB and had to be weaned from CPB using rescue medication.

CONCLUSIONS

In patients with pre-existing PHT undergoing mitral valve surgery, inhaled iloprost is superior to intravenous nitrogylycerine by acting as a selective pulmonary vasodilator, reducing RV afterload and moderately improving RV-pump performance.

Hypoxia-induced pulmonary hypertension: Different impact of iloprost, sildenafil, and nitric oxide

OBJECTIVES

Chronic alveolar hypoxia induces pulmonary hypertension, evident from elevated pulmonary artery pressure (PAP), pulmonary vascular resistance, right ventricular hypertrophy (RVH), and increased muscularization of the pulmonary vasculature. Additionally, the vasoconstrictor response to acute hypoxia (HPV) may be reduced in the remodeled vasculature. However, no direct comparison of different treatments on the various parameters characterizing pulmonary hypertension has been performed yet. Against this background, we compared the effects of inhaled NO, infused iloprost, a stable prostacyclin analogue, and oral sildenafil, a phosphodiesterase 5 inhibitor, on hypoxia-induced pulmonary hypertension.

METHODS

Exposure of rabbits to chronic hypoxia (FiO(2)=0.10) for 42 days. Treatment with infused iloprost, oral sildenafil, and inhaled nitric oxide.

RESULTS

We quantified PAP, pulmonary vascular resistance, RVH, vascular remodeling, vasoreactivity, and the strength of HPV. Chronic hypoxia resulted in an increase in (a) the right ventricle/(left ventricle+septum) ratio from 0.26+/-0.01 to 0.44+/-0.01, (b) PAP, and (c) the degree of muscularization from 14.0+/-4.0% to 43.5+/-5.3%. Treatment with iloprost and sildenafil, but not with NO, prevented the increase in muscularization. In contrast, RVH was strongly inhibited by sildenafil, whereas NO had some minor, and iloprost had no effect. Only iloprost reduced PAP compared to NO and sildenafil. The downregulation of HPV was abrogated only by NO.

CONCLUSION

We demonstrated (a) that the parameters characterizing hypoxia-induced pulmonary hypertension are not functionally linked, (b) that the downregulation of HPV under chronic hypoxia can be prevented by inhaled NO but not by sildenafil and iloprost, and (c) that iloprost is particularly effective in preventing vascular remodeling and sildenafil in preventing RVH.

Vasoconstrictor effect of endothelin-1 on hypertensive pulmonary arterial smooth muscle involves Rho-kinase and protein kinase C

Although one of the common characteristics of pulmonary hypertension is abnormal sustained vasoconstriction, the signaling pathways that mediate this heightened pulmonary vascular response are still not well defined. Protein kinase C (PKC) and Rho-kinase are regulators of smooth muscle contraction induced by G protein-coupled receptor agonists including endothelin-1 (ET-1), which has been implicated as a signaling pathway in pulmonary hypertension. Toward this end, it was hypothesized that both Rho-kinase and PKC mediate the pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle, and therefore, the purpose of this study was to determine the role of PKC and Rho-kinase signaling in ET-1-induced vasoconstriction in both normotensive (Sprague-Dawley) and hypertensive (Fawn-Hooded) rat pulmonary arterial smooth muscle. Results indicate that ET-1 caused greater vasoconstriction in hypertensive pulmonary arteries compared with the normal vessels, and treatment with the PKC antagonists chelerythrine, rottlerin, and Gö 6983 inhibited the vasoconstrictor response to ET-1 in the hypertensive vessels. In addition, the specific Rho-kinase inhibitor Y-27632 significantly attenuated the effect of ET-1 in both normotensive and hypertensive phenotypes, with greater inhibition occurring in the hypertensive arteries. Furthermore, Western blot analysis revealed that ET-1 increased RhoA expression in both normotensive and hypertensive pulmonary arteries, with expression being greater in the hypertensive state. These results suggest that both PKC and Rho/Rho-kinase mediate the heightened pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle.

Modèles animaux d’hypertension artérielle pulmonaire

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare syndrome of fatigue and dyspnoea, caused by increased pulmonary vascular resistance and right heart failure without an identifiable pulmonary or cardiac cause. Despite important recent advances in treatment the condition remains incurable.

BACKGROUND

Experimental animal models of PAH rely on hypoxic or monocrotaline injected rodents, the creation of left to right shunts in lambs or piglets, ligation of the ductus arteriosus in newborn lambs, genetically manipulated rodents and tissue culture. Hypoxic pulmonary hypertension is usually only moderate and limited to medial hypertrophy with varying degrees of adventitial change, but may progress to extensive remodelling in some species. Monocrotaline induced pulmonary hypertension is severe with prominent medial hypertrophy, inflammatory adventitial remodelling and, initially, pulmonary oedema and endothelial apoptosis. Pulmonary hypertension induced by shunting remains the most realistic model of PAH but causes only moderate increase in vascular resistance due to medial hypertrophy. Pulmonary hypertension of the newborn is severe but largely vasospastic, with predominant medial hypertrophy. An increasing number of genetically manipulated rodents are becoming available for the investigation of specific signalling pathways.

VIEWPOINT

While none of the models has yet reproduced PAH each allows investigation of a specific hypothesis. Recent progress has resulted from genetic manipulation and molecular and cellular approaches.

CONCLUSIONS

Animal models of PAH share basic biological abnormalities which, together with the study of lung tissue from patients with severe disease should lead to better understanding of the pathology and therapeutic innovation.

Treprostinil in advanced experimental pulmonary hypertension: beneficial outcome without reversed pulmonary vascular remodeling

INTRODUCTION

Beneficial effects of treprostinil, a stable prostacyclin analogue, were demonstrated in patients with pulmonary arterial hypertension (PAH). Although regression of pulmonary vascular remodeling has been suggested as therapeutic mechanism, its mode of action remains unknown.

METHODS

Flow-associated PAH was created in rats by injection of monocrotaline (60 mg/kg) combined with an abdominal aortocaval shunt. Subsequently, rats were treated with subcutaneous treprostinil (50 ng/kg/min, treated; n = 8) or saline (untreated; n = 9). A control group underwent sham-surgery (n = 8). Animals were sacrificed at symptoms of cardiac failure, together with their matched controls.

RESULTS

Dyspnea and weight loss determined the moment of sacrifice in 8/9 untreated animals (89%) versus in one of eight treated animals (13%; log-rank test survival curves; P = 0.02). Mean pulmonary arterial pressure increased in the model (42 +/- 2 mm Hg in untreated vs. 18 +/- 1 in controls; P < 0.01) and decreased by 8 mm Hg after therapy (34 +/- 3 mm Hg, P = 0.04 vs. untreated). No effects of treatment on right ventricular hypertrophy could be demonstrated. Quantitative morphometry of pre- and intra-acinar pulmonary arteries revealed no effects of treatment on vessel histopathology.

CONCLUSIONS

Treprostinil treatment improved clinical course and ameliorated symptoms of heart failure in a model of advanced PAH. However, beneficial effects were not associated with reversed structural remodelling of the pulmonary vasculature.

Iloprost-Containing Liposomes for Aerosol Application in Pulmonary Arterial Hypertension: Formulation Aspects and Stability

PURPOSE

Pulmonary arterial hypertension (PAH) is a severe and progressive disease. The prostacyclin analogue iloprost is effective against PAH, but requires six to nine inhalations per day. The feasibility of liposomes to provide a sustained release formulation to reduce inhalation frequency is evaluated from a technological point of view.

METHODS

Liposomal formulations consisting of di-palmitoyl-phosphatidyl-choline (DPPC), cholesterol (CH) and polyethyleneglycol-di-palmitoyl-phosphatidyl-ethanolamine (DPPE-PEG) were prepared. Their physico-chemical properties were investigated using dynamic light scattering, atomic force microscopy and differential scanning calorimetry. Stability of liposomes during aerosolization using three different nebulizers (air-jet, ultrasonic and vibrating mesh) was investigated with respect to drug loading and liposome size, pre- and post-nebulization.

RESULTS

The phospholipid composition affected the diameters of liposomes only slightly in the range of 200-400 nm. The highest iloprost loading (12 microg/ml) and sufficient liposome stability (70% drug encapsulation post-nebulization) was observed for the DPPC/CH (70:30 molar ratio) liposomes. The formulation's stability was confirmed by the relatively high phase transition temperature (53 degrees C) and unchanged particle sizes. The incorporation of DPPE-PEG in the liposomes (DPPC/CH/DPPE-PEG, 50:45:5 molar ratio) resulted in decreased stability (20-50% drug encapsulation post-nebulization) and a phase transition temperature of 35 degrees C. The vibrating mesh nebulizer offered a number of significant advantages over the other nebulizers, including the production of small aerosol droplets, high output, and the lowest deleterious physical influence upon all investigated liposomes.

CONCLUSION

Iloprost-loaded liposomes containing DPPC and CH components yield formulations which are well suited to aerosolization by the vibrating mesh nebulizer. The investigation of sustained release effects for the treatment of PAH in ex vivo and in vivo models is under way.

How valid are animal models to evaluate treatments for pulmonary hypertension?

Various animal models of pulmonary hypertension (PH) exist, among which injection of monocrotaline (MCT) and exposure to hypoxia are used most frequently. These animal models have not only been used to characterize the pathophysiology of PH and its sequelae such as right ventricular hypertrophy and failure, but also to test novel therapeutic strategies. This manuscript summarizes the available treatment studies in animal models of PH, and compares the findings to those obtained in patients with PH. The analysis shows that all approaches which have proven successful in patients, most notably prostacyclin and its analogs and endothelin receptor antagonists, are also effective in various animal models. However, the opposite it not always true. Therefore, promising results in animals have to be interpreted carefully until confirmed in clinical studies.

Phosphodiesterase type 4 expression and anti-proliferative effects in human pulmonary artery smooth muscle cells

Background

Pulmonary arterial hypertension is a proliferative vascular disease, characterized by aberrant regulation of smooth muscle cell proliferation and apoptosis in distal pulmonary arteries. Prostacyclin (PGI₂) analogues have anti-proliferative effects on distal human pulmonary artery smooth muscle cells (PASMCs), which are dependent on intracellular cAMP stimulation. We therefore sought to investigate the involvement of the main cAMP-specific enzymes, phosphodiesterase type 4 (PDE4), responsible for cAMP hydrolysis.

Methods

Distal human PASMCs were derived from pulmonary arteries by explant culture (n = 14, passage 3–12). Responses to platelet-derived growth factor-BB (5–10 ng/ml), serum, PGI₂ analogues (cicaprost, iloprost) and PDE4 inhibitors (roflumilast, rolipram, cilomilast) were determined by measuring cAMP phosphodiesterase activity, intracellular cAMP levels, DNA synthesis, apoptosis (as measured by DNA fragmentation and nuclear condensation) and matrix metalloproteinase-2 and -9 (MMP-2, MMP-9) production.

Results

Expression of all four PDE4A-D genes was detected in PASMC isolates. PDE4 contributed to the main proportion (35.9 ± 2.3%, n = 5) of cAMP-specific hydrolytic activity demonstrated in PASMCs, compared to PDE3 (21.5 ± 2.5%), PDE2 (15.8 ± 3.4%) or PDE1 activity (14.5 ± 4.2%). Intracellular cAMP levels were increased by PGI₂ analogues and further elevated in cells co-treated with roflumilast, rolipram and cilomilast. DNA synthesis was attenuated by 1 μM roflumilast (49 ± 6% inhibition), rolipram (37 ± 6%) and cilomilast (30 ± 4%) and, in the presence of 5 nM cicaprost, these compounds exhibited EC₅₀ values of 4.4 (2.6–6.1) nM (Mean and 95% confidence interval), 59 (36–83) nM and 97 (66–130) nM respectively. Roflumilast attenuated cell proliferation and gelatinase (MMP-2 and MMP-9) production and promoted the anti-proliferative effects of PGI₂ analogues. The cAMP activators iloprost and forskolin also induced apoptosis, whereas roflumilast had no significant effect.

Conclusion

PDE4 enzymes are expressed in distal human PASMCs and the effects of cAMP-stimulating agents on DNA synthesis, proliferation and MMP production is dependent, at least in part, on PDE4 activity. PDE4 inhibition may provide greater control of cAMP-mediated anti-proliferative effects in human PASMCs and therefore could prove useful as an additional therapy for pulmonary arterial hypertension.

Activation of soluble guanylate cyclase reverses experimental pulmonary hypertension and vascular remodeling

BACKGROUND

Severe pulmonary hypertension is a disabling disease with high mortality, characterized by pulmonary vascular remodeling and right heart hypertrophy. Using wild-type and homozygous endothelial nitric oxide synthase (NOS3(-/-)) knockout mice with pulmonary hypertension induced by chronic hypoxia and rats with monocrotaline-induced pulmonary hypertension, we examined whether the soluble guanylate cyclase (sGC) stimulator Bay41-2272 or the sGC activator Bay58-2667 could reverse pulmonary vascular remodeling.

METHODS AND RESULTS

Both Bay41-2272 and Bay58-2667 dose-dependently inhibited the pressor response of acute hypoxia in the isolated perfused lung system. When wild-type (NOS3(+/+)) or NOS3(-/-) mice were housed under 10% oxygen conditions for 21 or 35 days, both strains developed pulmonary hypertension, right heart hypertrophy, and pulmonary vascular remodeling, demonstrated by an increase in fully muscularized peripheral pulmonary arteries. Treatment of wild-type mice with the activator of sGC, Bay58-2667 (10 mg/kg per day), or the stimulator of sGC, Bay41-2272 (10 mg/kg per day), after full establishment of pulmonary hypertension from day 21 to day 35 significantly reduced pulmonary hypertension, right ventricular hypertrophy, and structural remodeling of the lung vasculature. In contrast, only minor efficacy of chronic sGC activator therapies was noted in NOS3(-/-) mice. In monocrotaline-injected rats with established severe pulmonary hypertension, both compounds significantly reversed hemodynamic and structural changes.

CONCLUSIONS

Activation of sGC reverses hemodynamic and structural changes associated with monocrotaline- and chronic hypoxia-induced experimental pulmonary hypertension. This effect is partially dependent on endogenous nitric oxide generated by NOS3.