Plexiform-like lesions and increased tissue factor expression in a rat model of severe pulmonary arterial hypertension

Pneumonectomy combined with SU5416 or monocrotaline pyrrole does not cause severe pulmonary hypertension in mice

In the field of pulmonary hypertension (PH), a well-established protocol to induce severe angioproliferation in rats (SuHx) involves combining the VEGF-R inhibitor Sugen 5416 (SU5416) with 3 wk of hypoxia (Hx). In addition, injecting monocrotaline (MCT) into rats can induce inflammation and shear stress in the pulmonary vasculature, leading to neointima-like remodeling. However, the SuHx protocol in mice is still controversial, with some studies suggesting it yields higher and reversible PH than Hx alone, possibly due to species-dependent hypoxic responses. To establish an alternative rodent model of PH, we hypothesized mice would be more sensitive to hemodynamic changes secondary to shear stress compared with Hx. We attempted to induce severe and irreversible PH in mice by combining SU5416 or monocrotaline pyrrole (MCTP) injection with pneumonectomy (PNx). However, our experiments showed SU5416 administered to mice at various time points after PNx did not result in severe PH. Similarly, mice injected with MCTP after PNx (MPNx) showed no difference in right ventricular systolic pressure or exacerbated pulmonary vascular remodeling compared with PNx alone. These findings collectively demonstrate that C57/B6 mice do not develop severe and persistent PH when PNx is combined with either SU5416 or MCTP.NEW & NOTEWORTHY We attempted to establish a mouse model of severe and irreversible pulmonary hypertension by substituting hypoxia with pulmonary overcirculation. To do so, we treated mice with either SU5416 or monocrotaline pyrrole after pneumonectomy and performed hemodynamic evaluations for PH. Despite this "two-hit" protocol, mice did not exhibit signs of severe pulmonary hypertension or exacerbated pulmonary vascular remodeling compared with PNx alone.

STAT3 phosphorylation at Tyr705 affects DRP1 (dynamin-related protein 1) controlled-mitochondrial fission during the development of apoptotic-resistance in pulmonary arterial endothelial cells

BACKGROUND

The apoptosis-resistant pulmonary arterial endothelial cells (PAECs) are known to be major players in the pulmonary remodeling of pulmonary arterial hypertension (PAH) and exhibit an abnormal metabolic profile with mitochondrial dysfunction. Mitochondrial fission has been shown to regulate the apoptosis of several cell types, but this is largely unexplored in the PAECs.

OBJECTIVE

The roles of mitochondrial fission control by Dynamin related protein-1 (DRP1) in the development of PAECs apoptosis suppression were investigated in present study and the potential mechanisms behind this were furtherly explored.

METHODS

The mitochondrial morphology was investigated in PAECs from PAH rats with the pulmonary plexiform lesions, and the relations of it with DRP1 expression and apoptosis were furtherly identified in apoptosis-resistant PAECs induced by hypoxia. PAECs were isolated from rats with severe PAH and from normal subjects, the apoptotic-resistant PAECs were induced by hypoxia. DRP1 gene knockdown was achieved via DRP1-siRNA, DRP1 and STAT3 phosphorylation were blocked using its inhibitors, respectively. Apoptosis was analyzed by flow cytometry, and mitochondrial morphology was investigated by transmission electron microscope and confocal microscopy.

RESULTS

The PAECs isolated from PAH rats with the pulmonary plexiform-like lesions and displayed lower apoptotic rate with increased DRP1 expression and mitochondrial fragmentation. In addition, similar observations were achieved in apoptosis-resistant PAECs induced by hypoxia. Targeting DRP1 using siRNA and pharmacologic blockade prevented the mitochondrial fission and subsequent apoptotic resistance in PAECs under hypoxia. Mechanistically, STAT3 phosphorylation at Tyr705 was shown to be activated in both PAH and hypoxia-treated PAECs, leading to the regulation of DRP1 expression. Of importance, targeting STAT3Tyr705 phosphorylation prevented DRP1 disruption on apoptosis in PAECs under hypoxia.

CONCLUSIONS

These data indicated that STAT3 phosphorylation at Tyr705 impacted DRP1-controlled mitochondrial fission during the development of apoptosis-resistance in PAECs, suggesting mitochondrial dynamics may represent a therapeutic target for PAH.

Dysregulated VEGF/VEGFR-2 Signaling and Plexogenic Lesions in the Embryonic Lungs of Chickens Predisposed to Pulmonary Arterial Hypertension

Plexiform lesions are a hallmark of pulmonary arterial hypertension (PAH) in humans and are proposed to stem from dysfunctional angioblasts. Broiler chickens (Gallus gallus) are highly susceptible to PAH, with plexiform-like lesions observed in newly hatched individuals. Here, we reported the emergence of plexiform-like lesions in the embryonic lungs of broiler chickens. Lung samples were collected from broiler chickens at embryonic day 20 (E20), hatch, and one-day-old, with PAH-resistant layer chickens as controls. Plexiform lesions consisting of CD133+/vascular endothelial growth factor receptor type-2 (VEGFR-2)+ angioblasts were exclusively observed in broiler embryos and sporadically in layer embryos. Distinct gene profiles of angiogenic factors were observed between the two strains, with impaired VEGF-A/VEGFR-2 signaling correlating with lesion development and reduced arteriogenesis. Pharmaceutical inhibition of VEGFR-2 resulted in enhanced lesion development in layer embryos. Moreover, broiler embryonic lungs displayed increased activation of HIF-1α and nuclear factor erythroid 2-related factor 2 (Nrf2), indicating a hypoxic state. Remarkably, we found a negative correlation between lung Nrf2 activation and VEGF-A and VEGFR-2 expression. In vitro studies indicated that Nrf2 overactivation restricted VEGF signaling in endothelial progenitor cells. The findings from broiler embryos suggest an association between plexiform lesion development and impaired VEGF system due to aberrant activation of Nrf2.

Pulmonary arterial hypertension and COVID-19: Piecing the puzzle

COVID-19 remains a health care concern despite the end of the pandemic. Patients with cardiovascular disease (CVD) are at a higher risk for developing severe COVID-19 complications. Studies investigating the COVID-19 clinical characteristics in pulmonary arterial hypertension (PAH) patients have reported discordant conclusions so far. In this review, we summarize the literature pertaining to the clinical presentation of COVID-19 in patients with PAH. In addition, we discuss common pathological aspects and disease mechanisms between PAH and COVID-19. We present an overview of the different types of PAH-approved therapy and their potential utilization as a treatment in the context of COVID-19. Moreover, we summarize the clinical trials that assessed the safety and efficiency of PAH-approved drugs in COVID-19 patients. Finally, we conclude with proposals for prospective research studies.

Acid ceramidase gene therapy ameliorates pulmonary arterial hypertension with right heart dysfunction

BACKGROUND

Up-regulation of ceramides in pulmonary hypertension (PH), contributing to perturbations in sphingolipid homeostasis and the transition of cells to a senescence state. We assessed the safety, feasibility, and efficiency of acid ceramidase gene transfer in a rodent PH model.

METHODS

A model of PH was established by the combination of left pneumonectomy and injection of Sugen toxin. Magnetic resonance imaging and right heart catheterization confirmed development of PH. Animals were subjected to intratracheal administration of synthetic adeno-associated viral vector (Anc80L65) carrying the acid ceramidase (Anc80L65.AC), an empty capsid vector, or saline. Therapeutic efficacy was evaluated 8 weeks after gene delivery.

RESULTS

Hemodynamic assessment 4 weeks after PH model the development demonstrated an increase in the mean pulmonary artery pressure to 30.4 ± 2.13 mmHg versus 10.4 ± 1.65 mmHg in sham (p < 0.001), which was consistent with the definition of PH. We documented a significant increase in pulmonary vascular resistance in the saline-treated (6.79 ± 0.85 mm Hg) and empty capsid (6.94 ± 0.47 mm Hg) groups, but not in animals receiving Anc80L65.AC (4.44 ± 0.71 mm Hg, p < 0.001). Morphometric analysis demonstrated an increase in medial wall thickness in control groups in comparison to those treated with acid ceramidase. After acid ceramidase gene delivery, a significant decrease of pro-inflammatory factors, interleukins, and senescence markers was observed.

CONCLUSION

Gene delivery of acid ceramidase provided tropism to pulmonary tissue and ameliorated vascular remodeling with right ventricular dysfunction in pulmonary hypertension.

Coagulation-independent effects of thrombin and Factor Xa: role of protease-activated receptors in pulmonary hypertension

AIMS

Pulmonary arterial hypertension (PAH) is a devastating disease with limited therapeutic options. Vascular remodelling of pulmonary arteries, characterized by increased proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs), is a hallmark of PAH. Here, we aimed to systematically characterize coagulation-independent effects of key coagulation proteases thrombin and Factor Xa (FXa) and their designated receptors, protease-activated receptor (PAR)-1 and -2, on PASMCs in vitro and experimental PAH in vivo.

METHODS AND RESULTS

In human and murine PASMCs, both thrombin and FXa were identified as potent mitogens, and chemoattractants. FXa mediated its responses via PAR-1 and PAR-2, whereas thrombin signalled through PAR-1. Extracellular-signal regulated kinases 1/2, protein kinase B (AKT), and sphingosine kinase 1 were identified as downstream mediators of PAR-1 and PAR-2. Inhibition of FXa or thrombin blunted cellular responses in vitro, but unexpectedly failed to protect against hypoxia-induced PAH in vivo. However, pharmacological inhibition as well as genetic deficiency of both PAR-1 and PAR-2 significantly reduced vascular muscularization of small pulmonary arteries, diminished right ventricular systolic pressure, and right ventricular hypertrophy upon chronic hypoxia compared to wild-type controls.

CONCLUSION

Our findings indicate a coagulation-independent pathogenic potential of thrombin and FXa for pulmonary vascular remodelling via acting through PAR-1 and PAR-2, respectively. While inhibition of single coagulation proteases was ineffective in preventing experimental PAH, our results propose a crucial role for PAR-1 and PAR-2 in its pathobiology, thus identifying PARs but not their dedicated activators FXa and thrombin as suitable targets for the treatment of PAH.

Inhaled seralutinib exhibits potent efficacy in models of pulmonary arterial hypertension

BACKGROUND

Signalling through platelet-derived growth factor receptor (PDGFR), colony-stimulating factor 1 receptor (CSF1R) and mast/stem cell growth factor receptor kit (c-KIT) plays a critical role in pulmonary arterial hypertension (PAH). We examined the preclinical efficacy of inhaled seralutinib, a unique small-molecule PDGFR/CSF1R/c-KIT kinase inhibitor in clinical development for PAH, in comparison to a proof-of-concept kinase inhibitor, imatinib.

METHODS

Seralutinib and imatinib potency and selectivity were compared. Inhaled seralutinib pharmacokinetics/pharmacodynamics were studied in healthy rats. Efficacy was evaluated in two rat models of PAH: SU5416/Hypoxia (SU5416/H) and monocrotaline pneumonectomy (MCTPN). Effects on inflammatory/cytokine signalling were examined. PDGFR, CSF1R and c-KIT immunohistochemistry in rat and human PAH lung samples and microRNA (miRNA) analysis in the SU5416/H model were performed.

RESULTS

Seralutinib potently inhibited PDGFRα/β, CSF1R and c-KIT. Inhaled seralutinib demonstrated dose-dependent inhibition of lung PDGFR and c-KIT signalling and increased bone morphogenetic protein receptor type 2 (BMPR2). Seralutinib improved cardiopulmonary haemodynamic parameters and reduced small pulmonary artery muscularisation and right ventricle hypertrophy in both models. In the SU5416/H model, seralutinib improved cardiopulmonary haemodynamic parameters, restored lung BMPR2 protein levels and decreased N-terminal pro-brain natriuretic peptide (NT-proBNP), more than imatinib. Quantitative immunohistochemistry in human lung PAH samples demonstrated increased PDGFR, CSF1R and c-KIT. miRNA analysis revealed candidates that could mediate seralutinib effects on BMPR2.

CONCLUSIONS

Inhaled seralutinib was an effective treatment of severe PAH in two animal models, with improved cardiopulmonary haemodynamic parameters, a reduction in NT-proBNP, reverse remodelling of pulmonary vascular pathology and improvement in inflammatory biomarkers. Seralutinib showed greater efficacy compared to imatinib in a preclinical study.

Urokinase-loaded cyclic RGD-decorated liposome targeted therapy for in-situ thrombus of pulmonary arteriole of pulmonary hypertension

Backgroud: In-situ thrombosis is a significant pathophysiological basis for the development of pulmonary hypertension (PH). However, thrombolytic therapy for in-situ thrombus in PH was often hampered by the apparent side effects and the low bioavailability of common thrombolytic medications. Nanoscale cyclic RGD (cRGD)-decorated liposomes have received much attention thanks to their thrombus-targeting and biodegradability properties. As a result, we synthesized urokinase-loaded cRGD-decorated liposome (UK-cRGD-Liposome) for therapy of in-situ thrombosis as an exploration of pulmonary hypertensive novel therapeutic approaches. Purpose: To evaluate the utilize of UK-cRGD-Liposome for targeted thrombolysis of in-situ thrombus in PH and to explore the potential mechanisms of in-situ thrombus involved in the development of PH. Methods: UK-cRGD-Liposome nanoscale drug delivery system was prepared using combined methods of thin-film hydration and sonication. Induced PH via subcutaneous injection of monocrotaline (MCT). Fibrin staining (modified MSB method) was applied to detect the number of vessels within-situ thrombi in PH. Echocardiography, hematoxylin-eosin (H & E) staining, and Masson's trichrome staining were used to analyze right ventricular (RV) function, pulmonary vascular remodeling, as well as RV remodeling. Results: The number of vessels with in-situ thrombi revealed that UK-cRGD-Liposome could actively target urokinase to in-situ thrombi and release its payload in a controlled manner in the in vivo environment, thereby enhancing the thrombolytic effect of urokinase. Pulmonary artery hemodynamics and echocardiography indicated a dramatical decrease in pulmonary artery pressure and a significant improvement in RV function post targeted thrombolytic therapy. Moreover, pulmonary vascular remodeling and RV remodeling were significantly restricted post targeted thrombolytic therapy. Conclusion: UK-cRGD-Liposome can restrict the progression of PH and improve RV function by targeting the dissolution of pulmonary hypertensive in-situ thrombi, which may provide promising therapeutic approaches for PH.

Nets, pulmonary arterial hypertension, and thrombo-inflammation

Pulmonary arterial hypertension (PAH) is a progressive and fatal vascular disease in which high blood pressure in the pulmonary artery and remodeling of the pulmonary vasculature ensues. This disorder is characterized by the presence of thrombotic lesions, resulting from chronic platelet, coagulation factors, and endothelium activation, which translate into platelet aggregation, vasoconstriction, and medial thickening. Neutrophil extracellular traps (NETs), a network of chromatin and cytoplasmatic enzymes (myeloperoxidase and neutrophil elastase) forming after neutrophil programmed cell death, were described in multiple cardiovascular diseases as thrombotic mediators, by creating a scaffold or by surface receptor interaction. In this review, we analyze the possible involvement of NETs in PAH, to enlighten future studies to explore this hypothesis. NETs may have a determining role in pulmonary hypertension through activation of platelets and endothelial cells. Simultaneously, NETosis may be induced by endothelial signaling and/or cell-cell interaction between platelets and primed neutrophils, creating a positive feedback loop. Confirming its role in the pathophysiology and prognosis of PAH may represent a new opportunity to explore new therapeutic options. KEY MESSAGES: Thrombosis and innate immunity are relevant axes in PAH. Patients with PAH display elevated levels of NETs. NETs could activate platelets/endothelium with proliferative and thrombotic effects. Activated platelets and endothelium could contribute to NETosis. NETs could open new therapy research avenues.

Experimental animal models of pulmonary hypertension: Development and challenges

Pulmonary hypertension (PH) is clinically divided into 5 major types, characterized by elevation in pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR), finally leading to right heart failure and death. The pathogenesis of this arteriopathy remains unclear, leaving it impossible to target pulmonary vascular remodeling and reverse the deterioration of right ventricular (RV) function. Different animal models have been designed to reflect the complex mechanistic origins and pathology of PH, roughly divided into 4 categories according to the modeling methods: non‐invasive models in vivo, invasive models in vivo, gene editing models, and multi‐means joint modeling. Though each model shares some molecular and pathological changes with different classes of human PH, in most cases the molecular etiology of human PH is poorly known. The appropriate use of classic and novel PH animal models is essential for the hunt of molecular targets to reverse severe phenotypes.

Endothelial upregulation of mechanosensitive channel Piezo1 in pulmonary hypertension

Piezo is a mechanosensitive cation channel responsible for stretch-mediated Ca2+ and Na+ influx in multiple types of cells. Little is known about the functional role of Piezo1 in the lung vasculature and its potential pathogenic role in pulmonary arterial hypertension (PAH). Pulmonary arterial endothelial cells (PAECs) are constantly under mechanic stretch and shear stress that are sufficient to activate Piezo channels. Here, we report that Piezo1 is significantly upregulated in PAECs from patients with idiopathic PAH and animals with experimental pulmonary hypertension (PH) compared with normal controls. Membrane stretch by decreasing extracellular osmotic pressure or by cyclic stretch (18% CS) increases Ca2+-dependent phosphorylation (p) of AKT and ERK, and subsequently upregulates expression of Notch ligands, Jagged1/2 (Jag-1 and Jag-2), and Delta like-4 (DLL4) in PAECs. siRNA-mediated downregulation of Piezo1 significantly inhibited the stretch-mediated pAKT increase and Jag-1 upregulation, whereas downregulation of AKT by siRNA markedly attenuated the stretch-mediated Jag-1 upregulation in human PAECs. Furthermore, the mRNA and protein expression level of Piezo1 in the isolated pulmonary artery, which mainly contains pulmonary arterial smooth muscle cells (PASMCs), from animals with severe PH was also significantly higher than that from control animals. Intraperitoneal injection of a Piezo1 channel blocker, GsMTx4, ameliorated experimental PH in mice. Taken together, our study suggests that membrane stretch-mediated Ca2+ influx through Piezo1 is an important trigger for pAKT-mediated upregulation of Jag-1 in PAECs. Upregulation of the mechanosensitive channel Piezo1 and the resultant increase in the Notch ligands (Jag-1/2 and DLL4) in PAECs may play a critical pathogenic role in the development of pulmonary vascular remodeling in PAH and PH.

Platelets, extracellular vesicles and coagulation in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare disease of the pulmonary vasculature, characterised pathologically by proliferation, remodelling and thrombosis in situ. Unfortunately, existing therapeutic interventions do not reverse these findings and the disease continues to result in significant morbidity and premature mortality. A number of haematological derangements have been described in pulmonary arterial hypertension which may provide insights into the pathobiology of the disease and opportunities to explore new therapeutic pathways. These include quantitative and qualitative platelet abnormalities, such as thrombocytopaenia, increased mean platelet volume and altered platelet bioenergetics. Furthermore, a hypercoagulable state and aberrant negative regulatory pathways can be observed, which could contribute to thrombosis in situ in distal pulmonary arteries and arterioles. Finally, there is increasing interest in the role of extracellular vesicle autocrine and paracrine signalling in pulmonary arterial hypertension, and their potential utility as biomarkers and novel therapeutic targets. This review focuses on the potential role of platelets, extracellular vesicles and coagulation pathways in the pathobiology of pulmonary arterial hypertension. We highlight important unanswered clinical questions and the implications of these observations for future research and pulmonary arterial hypertension-directed therapies.

Pulmonary hypertension after pneumonectomy: a preclinical model in rats and human pulmonary endothelial cells

OBJECTIVES

Pulmonary hypertension and heart disease contribute to the high morbidity rate following pneumonectomy (PN). The pathophysiology is still poorly understood. The objective was to investigate the consequences of PN on cardiopulmonary function in rats and to explore in vitro the involved mechanisms.

METHODS

Sixty Sprague-Dawley male rats randomly underwent either a right PN (PN group) or sham surgery. Ten rats per group were sacrificed on postoperative days 3, 7 and 28. Cardiopulmonary alterations were investigated by echocardiographic, haemodynamic and histological analyses. In vitro, the shear stress was reproduced using a Flexcell Tension™ cyclic stretch on cultured human pulmonary endothelial cells (P-ECs) to investigate the impact on pulmonary artery smooth muscle cell (PA-SMC) growth. Data are expressed as mean ± SD.

RESULTS

Mean pulmonary arterial pressure gradually increased in the PN group to reach 35 ± 7 mmHg on postoperative day 28 vs 18 ± 4 in sham (P = 0.001), likewise the proportion of muscularized distal pulmonary arteries, 83 ± 1% vs 5 ± 1%, respectively (P < 0.001), related to in situ PA-SMC proliferation. The right ventricle area and lateral wall thickness were doubled in the PN group on postoperative day 28. The left ventricle ejection fraction decreased on postoperative days 7 and 28 while the right ventricle function was maintained. In vitro, the human PA-SMC growth was significantly greater when seeded with stretched vs non-stretched P-EC media, highlighting the role of shear stress on the P-EC paracrine function.

CONCLUSIONS

Right PN led to pulmonary hypertension and proportional right heart remodelling in rats. The shear stress related to high blood flow alters the pulmonary endothelial paracrine control of SMC growth.

Rivaroxaban Attenuates Right Ventricular Remodeling in Rats with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive condition that frequently results in right ventricular (RV) remodeling. The objectives of this study are to investigate effects of rivaroxaban on RV remodeling in a rat model of PAH, created with Sugen5416 and chronic hypoxia, and the in vitro effects of rivaroxaban on human cardiac microvascular endothelial cells (HCMECs). To create the PAH model, male Sprague-Dawley rats were subcutaneously injected with Sugen5416 (20 mg/kg) and exposed to 2 weeks of hypoxia (10% O2), followed by 2 weeks of exposure to normoxia. The animals were then divided into 2 groups with or without administration of rivaroxaban (12 mg/kg/d) for a further 4 weeks. HCMECs were cultured under hypoxic conditions (37 °C, 1% O2, 5% CO2) with Sugen5416 and with or without rivaroxaban. In the model rats, RV systolic pressure and Fulton index increased by hypoxia with Sugen5416 were significantly decreased when treated with rivaroxaban. In HCMECs, hypoxia with Sugen5416 increased the expression of protease-activated receptor-2 (PAR-2) and the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor-kappa B (NF-κB), while treatment with rivaroxaban significantly suppressed the expression of these proteins. Rivaroxaban attenuated RV remodeling in a rat model of PAH by reducing ERK, JNK and NF-κB activation. Rivaroxaban has the possibility of providing additive effects on RV remodeling in patients with PAH.

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.

Endothelial Dysfunction in Pulmonary Hypertension: Cause or Consequence?

Pulmonary arterial hypertension (PAH) is a rare, complex, and progressive disease that is characterized by the abnormal remodeling of the pulmonary arteries that leads to right ventricular failure and death. Although our understanding of the causes for abnormal vascular remodeling in PAH is limited, accumulating evidence indicates that endothelial cell (EC) dysfunction is one of the first triggers initiating this process. EC dysfunction leads to the activation of several cellular signalling pathways in the endothelium, resulting in the uncontrolled proliferation of ECs, pulmonary artery smooth muscle cells, and fibroblasts, and eventually leads to vascular remodelling and the occlusion of the pulmonary blood vessels. Other factors that are related to EC dysfunction in PAH are an increase in endothelial to mesenchymal transition, inflammation, apoptosis, and thrombus formation. In this review, we outline the latest advances on the role of EC dysfunction in PAH and other forms of pulmonary hypertension. We also elaborate on the molecular signals that orchestrate EC dysfunction in PAH. Understanding the role and mechanisms of EC dysfunction will unravel the therapeutic potential of targeting this process in PAH.

SARS-CoV-2 Spike Protein and Lung Vascular Cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is causing the current pandemic of coronavirus disease 2019 (COVID-19), and COVID-19 vaccines focus on its spike protein. However, in addition to facilitating the membrane fusion and viral entry, the SARS-CoV-2 spike protein promotes cell growth signaling in human lung vascular cells, and patients who have died of COVID-19 have thickened pulmonary vascular walls, linking the spike protein to a fatal disease, pulmonary arterial hypertension (PAH). In addition to SARS-CoV spike proteins, gp120, the viral membrane fusion protein of human immunodeficiency virus (HIV), has been reported to promote cell signaling, and long-term surviving HIV-positive patients have a high incidence of developing PAH. This article describes the findings of the SARS-CoV-2 spike protein affecting lung vascular cells and explains how the spike protein possibly increases the incidence of PAH. Since the SARS-CoV-2 spike protein will be administered to millions of people as COVID-19 vaccines, it is critical to understand the biological effects of this protein on human cells to ensure that it does not promote long-term adverse health consequences.

Anticoagulation in Pulmonary Arterial Hypertension: Do We Know the Answer?

The shear stress and hypoxia in the pulmonary artery in patients with pulmonary arterial hypertension(PAH) causes endothelial dysfunction, smooth muscle proliferation and activation of thrombotic pathways leading to in situ thrombosis. Targeting the thrombotic pathways is a proposed mechanism to slow disease progression and improve survival. Over the years, the survival in patients with PAH has improved due to multiple factors with the increased use of anticoagulation as one of them. Both European Respiratory Society/European Society of Cardiology and American College of Cardiology/American Heart Association guidelines make grade II recommendations for using anticoagulation in PAH. The guidelines are based on weak observational studies with high risk of bias which have only studied warfarin as the choice of anticoagulation. In this article, we review the pathophysiology, rationale and the current literature investigating the role of anticoagulation in PAH.

Plexiform Lesions in an Experimental Model of Monocrotalin-Induced Pulmonary Arterial Hypertension

BACKGROUND

The monocrotaline (MCT)-induced pulmonary arterial hypertension model is one of the most reproduced today, presenting as a limitation the absence of plexiform lesions, typical manifestations of the severe disease in humans.

OBJECTIVE

To evaluate the severity of MCT-induced pulmonary arteriopathy by pathological findings of lung and heart tissue samples, clinical course and 37-day survival.

METHODS

Fifty male Wistar rats were divided into one of the four groups - control (CG) (n = 10) and three intervention (MCT) groups. The MCT groups received intraperitoneal injection (60 mg/kg) of MCT and remained exposed to the substance for 15 days (G15, n = 10), 30 days (G30, n = 10) and 37 days (G37, n = 20). At the end of each period, the animals were sacrificed, and pulmonary and cardiac tissues were collected for anatomopathological and morphometric analysis. The Kruskal-Wallis test was used, considering a level of significance of 5%.

RESULTS

In the lungs of MCT animals, lesions related to pulmonary arteriopathy were found, including muscularization of the arterioles, hypertrophy of the middle layer and concentric neointimal lesions. Complex lesions were observed in MCT groups, described as plexiform and plexiform-like lesions. Right ventricular hypertrophy was evidenced by increased thickness and diameter of the cardiomyocytes and a significant increase in the right ventricular wall thickness (p <0.0000).

CONCLUSION

The MCT model was able to generate moderate-severe pulmonary arteriopathy associated with secondary right ventricular hypertrophy. The 37-day survival rate was 50%. To our knowledge, this study was the first to note the presence of complex vascular lesions, similar to those observed in patients with severe pulmonary arterial hypertension, in an isolated MCT model. (Arq Bras Cardiol. 2020; 115(3):480-490).

Increased levels of platelet-derived microparticles in pulmonary hypertension

INTRODUCTION

Thrombosis and coagulation abnormalities are thought to be involved in disease progression of pulmonary hypertension. Platelet-derived microparticles (PDMP) are released from platelets following stimulation and have recently been demonstrated to play an important role in pathogenesis of various diseases. This study aimed to evaluate PDMP levels in patients with pulmonary hypertension.

MATERIALS AND METHODS

Our cross-sectional study enrolled a total of 113 participants including 73 patients with pulmonary hypertension and 40 participants to serve as a control group. PDMP levels were measured using a PDMP ELISA kit, which detects glycoproteins CD42a and CD42b. Clinical parameters, including exercise capacity and hemodynamic parameters, were collected, and the relationship to PDMP levels were evaluated.

RESULTS

PDMP levels were significantly higher in patients than in participants in the control group (23.2 ± 39.4 U/mL and 7.8 ± 3.6 U/mL, respectively, P < 0.05). PDMP levels in patients with chronic thromboembolic pulmonary hypertension were correlated with right atrial pressure and cardiac index. PDMP levels were higher in male patients with idiopathic pulmonary arterial hypertension. Furthermore, patients administered a higher dose of epoprostenol had a tendency for lower PDMP levels.

CONCLUSIONS

The data suggest that PDMP levels are increased in patients with pulmonary hypertension. Further study is needed to understand the mechanism and impact of PDMP on disease progression.

The changing face of pulmonary hypertension diagnosis: a historical perspective on the influence of diagnostics and biomarkers

Pulmonary hypertension is a complex, multifactorial disease that results in right heart failure and premature death. Since the initial reports of pulmonary hypertension in the late 1800s, the diagnosis of pulmonary hypertension has evolved with respect to its definition, screening tools, and diagnostic techniques. This historical perspective traces the earliest roots of pulmonary hypertension detection and diagnosis through to the current recommendations for classification. We highlight the diagnostic tools used in the past and present, and end with a focus on the future directions of early detection. Early detection of pulmonary hypertension and pulmonary arterial hypertension and the proper determination of etiology are vital for the early therapeutic intervention that can prolong life expectancy and improve quality of life. The search for a non-invasive screening tool for the identification and classification of pulmonary hypertension is ongoing, and we discuss the role of animal models of the disease in this search.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Combination therapy improves vascular volume in female rats with pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a female predominant disease in which progressive vascular remodeling and vasoconstriction result in right ventricular (RV) failure and death. Most PAH patients utilize multiple therapies. In contrast, the majority of preclinical therapeutic studies are performed in male rats with a single novel drug often markedly reversing disease in the model. We sought to differentiate single drug therapy from combination therapy in female rats with severe disease. One week after left pneumonectomy, we induced PH in young female Sprague-Dawley rats with an injection of monocrotaline (45 mg/kg). Female rats were then randomized to receive combination therapy (ambrisentan plus tadalafil), ambrisentan monotherapy, tadalafil monotherapy, or vehicle. We measured RV size and function on two serial echocardiograms during the development of disease. We measured RV systolic pressure (RVSP) invasively at day 28 after monocrotaline before analyzing the vascular volume with microcomputed tomography (microCT) of the right middle lobe. RVSP was significantly lower in female rats treated with combination therapy, and combination therapy resulted in increased small vessel volume density measured by microCT compared with untreated rats. Combination-treated rats had the smallest RV end-diastolic diameter on echocardiogram as compared with the other groups. In summary, we report a female model of pulmonary hypertension that can distinguish between one and two drug therapies; this model may facilitate better preclinical drug testing for novel compounds.

Hypercoagulability in Pulmonary Hypertension

Pulmonary hypertension (PH) is divided into varied pathophysiological and etiologic groupings, as classified by the World Health Organization (WHO). Pulmonary arterial hypertension (PAH), which falls under WHO group 1 PH, is a progressive and potentially fatal disease characterized by a vasoconstrictive, proliferative, and thrombotic phenotype, which leads to increased pulmonary artery pressure, right heart failure, and death. Pathologically, in situ thromboses are found in the small distal pulmonary arteries. Dysregulation of coagulation, platelet function, and endothelial cells may contribute to a prothrombotic state. There is mixed evidence for the use of anticoagulation or antiplatelet therapy in PAH patients.

Plexiform Arteriopathy in Rodent Models of Pulmonary Arterial Hypertension

As time progresses, our understanding of disease pathology is propelled forward by technological advancements. Much of the advancements that aid in understanding disease mechanics are based on animal studies. Unfortunately, animal models often fail to recapitulate the entirety of the human disease. This is especially true with animal models used to study pulmonary arterial hypertension (PAH), a disease with two distinct phases. The first phase is defined by nonspecific medial and adventitial thickening of the pulmonary artery and is commonly reproduced in animal models, including the classic models (ie, hypoxia-induced pulmonary hypertension and monocrotaline lung injury model). However, many animal models, including the classic models, fail to capture the progressive, or second, phase of PAH. This is a stage defined by plexogenic arteriopathy, resulting in obliteration and occlusion of the small- to mid-sized pulmonary vessels. Each of these two phases results in severe pulmonary hypertension that directly leads to right ventricular hypertrophy, decompensated right-sided heart failure, and death. Fortunately, newly developed animal models have begun to address the second, more severe, side of PAH and aid in our ability to develop new therapeutics. Moreover, p38 mitogen-activated protein kinase activation emerges as a central molecular mediator of plexiform lesions in both experimental models and human disease. Therefore, this review will focus on plexiform arteriopathy in experimental animal models of PAH.

The Left Pneumonectomy Combined with Monocrotaline or Sugen as a Model of Pulmonary Hypertension in Rats

In this protocol, we detail the correct procedural steps and necessary precautions to successfully perform a left pneumonectomy and induce PAH in rats with the additional administration of monocrotaline (MCT) or SU5416 (Sugen). We also compare these two models to other PAH models commonly used in research. In the last few years, the focus of animal PAH models has moved towards studying the mechanism of angioproliferation of plexiform lesions, in which the role of increased pulmonary blood flow is considered as an important trigger in the development of severe pulmonary vascular remodeling. One of the most promising rodent models of increased pulmonary flow is the unilateral left pneumonectomy combined with a "second hit" of MCT or Sugen. The removal of the left lung leads to increased and turbulent pulmonary blood flow and vascular remodeling. Currently, there is no detailed procedure of the pneumonectomy surgery in rats. This article details a step-by-step protocol of the pneumonectomy surgical procedure and post-operative care in male Sprague-Dawley rats. Briefly, the animal is anesthetized and the chest is opened. Once the left pulmonary artery, pulmonary vein, and bronchus are visualized, they are ligated and the left lung is removed. The chest then closed and the animal recovered. Blood is forced to circulate only on the right lung. This increased vascular pressure leads to a progressive remodeling and occlusion of small pulmonary arteries. The second hit of MCT or Sugen is used one week post-surgery to induce endothelial dysfunction. The combination of increased blood flow in the lung and endothelial dysfunction produces severe PAH. The primary limitation of this procedure is that it requires general surgical skills.

Magnolol ameliorates pneumonectomy and monocrotaline-induced pulmonary arterial hypertension in rats through inhibition of angiotensin II and endothelin-1 expression

BACKGROUND

Magnolol, a major bioactive component extracted from Magnolia officinalis, exerts several beneficial effects, such as anti-inflammatory and anti-hypertensive activities.

PURPOSE

In this study, we investigated whether magnolol has a protective effect on pneumonectomy and monocrotaline-induced pulmonary arterial hypertension (PAH) in rats.

DESIGN/METHODS

The alterations of right ventricular (RV) hypertrophy, pulmonary vascular remodeling, histopathological parameters, and related gene expression and signaling pathways in lungs by magnolol treatment were studied in the PAH rats.

RESULTS

Administration of magnolol greatly ameliorated the characteristic features of PAH, including increased pulmonary arterial pressure, RV hypertrophy, and pulmonary vascular remodeling. Moreover, magnolol inhibited angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II type 1 receptor (AT-1R) cascade, whereas upregulates ACE2 in the lungs of PAH rats. The overexpression of endothelin-1 (ET-1) and ET_A receptor occurred in the PAH rats was significantly attenuated by magnolol through inhibition of Akt/ERK1/2/GSK3β/β-catenin pathway. Compared with that of untreated PAH rats, higher expression of endothelial nitric oxide synthase, and lower expression of inducible nitric oxide synthase and O₂^- production in lungs were observed in magnolol-treated PAH rats.

CONCLUSION

We demonstrated that treatment with magnolol reduces the development of PAH induced by pneumonectomy and monocrotaline in rats, and suppressing Ang II and ET-1-mediated processes may contribute to its protective effects. These findings suggest that magnolol may be a potential agent for PAH therapy.

AOS ameliorates monocrotaline-induced pulmonary hypertension by restraining the activation of P-selectin/p38MAPK/NF-κB pathway in rats

Perivascular inflammation, vascular luminal area reduction and hemodynamics changes are important pathophysiologic bases of pulmonary hypertension (PH). In this study, PH was induced by an intraperitoneal single injection of monocrotaline (MCT, 60 mg/kg). Alginate oligosaccharides (AOS), one of the most famous marine drugs, provided protections in the perivascular inflammation, vascular luminal area reduction and hemodynamics changes of the PH rat induced by MCT. The downregulation of P-selectin plays an important role in the protective effects of AOS against MCT induced PH. The results showed that the treatment with AOS (5, 10, or 20 mg/kg) dose-dependently decreased the expression of P-selectin in serum, pulmonary tissue and pulmonary artery of MCT-induced pulmonary arterial hypertension rats. What's more, the study showed that the protective effects were mediated by the inhibition of p38MAPK/NF-κB pathway, which was caused by reducing the p-p38MAPK protein expression, IκBα degradation and nuclear transcription of NF-κB protein in the pulmonary artery of MCT-induced PH rats. These findings provided an alternative potent medicine for the prevention and therapy of PH.

Compensated right ventricular function of the onset of pulmonary hypertension in a rat model depends on chamber remodeling and contractile augmentation

Right-ventricular function is a good indicator of pulmonary arterial hypertension (PAH) prognosis; however, how the right ventricle (RV) adapts to the pressure overload is not well understood. Here, we aimed at characterizing the time course of RV early remodeling and discriminate the contribution of ventricular geometric remodeling and intrinsic changes in myocardial mechanical properties in a monocrotaline (MCT) animal model. In a longitudinal study of PAH, ventricular morphology and function were assessed weekly during the first four weeks after MCT exposure. Using invasive measurements of RV pressure and volume, heart performance was evaluated at end of systole and diastole to quantify contractility (end-systolic elastance) and chamber stiffness (end-diastolic elastance). To distinguish between morphological and intrinsic mechanisms, a computational model of the RV was developed and used to determine the level of prediction when accounting for wall masses and unloaded volume measurements changes. By four weeks, mean pulmonary arterial pressure and elastance rose significantly. RV pressures rose significantly after the second week accompanied by significant RV hypertrophy, but RV stroke volume and cardiac output were maintained. The model analysis suggested that, after two weeks, this compensation was only possible due to a significant increase in the intrinsic inotropy of RV myocardium. We conclude that this MCT-PAH rat is a model of RV compensation during the first month after treatment, where geometric remodeling on EDPVR and increased myocardial contractility on ESPVR are the major mechanisms by which stroke volume is preserved in the setting of elevated pulmonary arterial pressure. The mediators of this compensation might themselves promote longer-term adverse remodeling and decompensation in this animal model.

Right Ventricular-Pulmonary Vascular Interactions

Accurate and comprehensive evaluation of right ventricular (RV)-pulmonary vascular (PV) interactions is critical to the assessment of cardiopulmonary function, dysfunction, and failure. Here, we review methods of quantifying RV-PV interactions and experimental results from clinical trials as well as large- and small-animal models based on pressure-volume analysis. We conclude by outlining critical gaps in knowledge that should drive future studies.

Baicalein Ameliorates Pulmonary Arterial Hypertension Caused by Monocrotaline through Downregulation of ET-1 and ETAR in Pneumonectomized Rats

Baicalein (BE) extracted from Scutellaria baicalensis Georgi is able to alleviate various cardiovascular and inflammatory diseases. However, the effects of BE on pulmonary arterial hypertension (PAH) remain unknown. Therefore, the present study aimed to examine whether BE ameliorates pneumonectomy and monocrotaline-induced PAH in rats and further investigate the underlying molecular mechanisms. Administration of BE greatly attenuated the development of PAH as evidenced by an improvement of its characteristic features, including elevation of right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary vascular remodeling. Moreover, the increased protein expression of endothelin-1 (ET-1) and ETA receptor (ETAR), superoxide overproduction, and activation of Akt/ERK1/2/GSK3[Formula: see text]/[Formula: see text]-catenin pathway that occurred in the lungs of PAH rats were markedly reversed by BE treatment. Compared with the untreated PAH rats, higher expression of endothelial nitric oxide synthase (eNOS), but lower levels of inducible nitric oxide synthase and vWF were observed in BE-treated PAH rats. Collectively, treatment with BE remarkably attenuates the pathogenesis of PAH, and the protection of BE may be associated with suppressing Akt/Erk1/2/GSK3[Formula: see text]/[Formula: see text]-catenin/ET-1/ETAR signaling and preventing endothelial dysfunction. These results suggest that BE is a potential agent for treatment of PAH.

Features associated with pulmonary arterial hypertension in Chinese hospitalized systemic lupus erythematosus patients

Pulmonary arterial hypertension (PAH) is an increasingly recognized complication of systemic lupus erythematosus (SLE). This study aims to estimate the point prevalence of PAH and identify risk factors for PAH in a large cohort of hospitalized SLE patients. We have collected the medical records of patients hospitalized with SLE at the First Affiliated Hospital of Anhui Medical University and Anhui Provincial Hospital. Resting transthoracic echocardiography (TTE) was used to estimate pulmonary artery pressure (PAP) and PAH was defined as systolic PAP (PASP) > 30 mmHg. Patients with other connective tissue diseases, aPL syndrome, left heart disease, valvular heart disease, congenital heart disease, HIV, and portal hypertension were excluded because of diseases affecting the PAP. We assessed potential risk factors for PAH such as thrombogenic factors, SLE clinical manifestations, laboratory abnormalities and disease activity. Ninety-five were diagnosed with PAH of 1639 patients with SLE. The presence of high fibrinogen, serositis, and thrombocytopenia were significantly higher in patients with PAH than in those without PAH (all P < 0.05). Multivariate logistic regression found the associations between high fibrinogen (OR = 1.629), serositis (OR = 2.866), and thrombocytopenia (OR = 1.825) with PAH. The point prevalence of PAH was 5.8% in our cohort of patients with SLE. The significant association of high fibrinogen, serositis, and thrombocytopenia with PAH suggested that hypercoagulable state, organ damage, and hematological abnormality may all contribute to the development of PAH in SLE. This is important, as it is treatable.

Drug-induced pulmonary arterial hypertension: a primer for clinicians and scientists

Drug-induced pulmonary arterial hypertension (D-PAH) is a form of World Health Organization Group 1 pulmonary hypertension (PH) defined by severe small vessel loss and obstructive vasculopathy, which leads to progressive right heart failure and death. To date, 16 different compounds have been associated with D-PAH, including anorexigens, recreational stimulants, and more recently, several Food and Drug Administration-approved medications. Although the clinical manifestation, pathology, and hemodynamic profile of D-PAH are indistinguishable from other forms of pulmonary arterial hypertension, its clinical course can be unpredictable and to some degree dependent on removal of the offending agent. Because only a subset of individuals develop D-PAH, it is probable that genetic susceptibilities play a role in the pathogenesis, but the characterization of the genetic factors responsible for these susceptibilities remains rudimentary. Besides aggressive treatment with PH-specific therapies, the major challenge in the management of D-PAH remains the early identification of compounds capable of injuring the pulmonary circulation in susceptible individuals. The implementation of pharmacovigilance, precision medicine strategies, and global warning systems will help facilitate the identification of high-risk drugs and incentivize regulatory strategies to prevent further outbreaks of D-PAH. The goal for this review is to inform clinicians and scientists of the prevalence of D-PAH and to highlight the growing number of common drugs that have been associated with the disease.

Low dose monocrotaline causes a selective pulmonary vascular lesion in male and female pneumonectomized rats

Purpose/Aim: Low doses (30-80 mg/kg) of monocrotaline are commonly used to create experimental models of pulmonary hypertension in rats. At these doses, monocrotaline causes pulmonary endothelial apoptosis and acute lung injury which ultimately results in pulmonary vascular disease. Higher doses of monocrotaline (300 mg/kg) are known to create severe liver injury, but previous investigations with lower doses have not reported histology in other organs to determine whether the vascular injury with monocrotaline is pulmonary-selective or generalized.

MATERIALS AND METHODS

We therefore sought to determine whether monocrotaline caused extra-pulmonary injury at doses commonly used in pulmonary hypertension studies. We performed left pneumonectomy on young male and female rats before administering 50-60 mg/kg monocrotaline 7 days later. We monitored serum chemistry and urine dipsticks during the first 3 weeks while the animals developed pulmonary hypertension. After 3 weeks, we sacrificed animals and stained the lungs and highly vascular visceral organs (kidney, liver, and spleen) for elastin to evaluate the degree of vascular injury and remodeling.

RESULTS

We did not observe proteinuria or significant transaminitis over the 3 weeks following monocrotaline. As previously published, monocrotaline caused severe pulmonary vascular disease with neointimal lesions and medial hypertrophy. We did not identify significant large or small arterial damage in the kidneys, liver, or spleen. Two external veterinary pathologists did not identify histopathology in the kidneys, liver, or spleen of these rats.

CONCLUSIONS

We conclude that 50-60 mg/kg of monocrotaline causes a selective pulmonary vascular lesion and that male and female rats have little non-pulmonary damage over 3 weeks at these doses of monocrotaline.

The new frontiers of the targeted interventions in the pulmonary vasculature: precision and safety (2017 Grover Conference Series)

The pulmonary vasculature plays an important role in many lung pathologies, such as pulmonary arterial hypertension, primary graft dysfunction of lung transplant, and acute respiratory distress syndrome. Therapy for these diseases is quite limited, largely due to dose-limiting side effects of numerous drugs that have been trialed or approved. High doses of drugs targeting the pulmonary vasculature are needed due to the lack of specific affinity of therapeutic compounds to the vasculature. To overcome this problem, the field of targeted drug delivery aims to target drugs to the pulmonary endothelial cells, especially those in pathological regions. The field uses a variety of drug delivery systems (DDSs), ranging from nano-scale drug carriers, such as liposomes, to methods of conjugating drugs to affinity moieites, such as antibodies. These DDSs can deliver small molecule drugs, protein therapeutics, and imaging agents. Here we review targeted drug delivery to the pulmonary endothelium for the treatment of pulmonary diseases. Cautionary notes are made of the risk–benefit ratio and safety—parameters one should keep in mind when developing a translational therapeutic.

Preserved right ventricular integrity in a new telemetric rat model of severe pulmonary hypertension

Telemetric monitoring of hemodynamic parameters has become an established standard in experimental models of pulmonary arterial hypertension (PAH). To that purpose, a dedicated catheter is usually implanted through the right ventricular wall of study animals. Drawbacks of this standard technique are as follows: obtained pressures are from the right ventricle and therefore only surrogates for pulmonary arterial pressures, and furthermore, right ventricular myocardium is always damaged to a certain degree. To overcome shortcomings of standard hemodynamic assessment, we modified an established rat model, where severe PAH is induced by left-sided pneumonectomy plus monocrotaline injection. We describe here a novel telemetry catheter implantation technique, where the device is advanced into the pulmonary artery via the remaining stump and the transmitter is placed in a subcutaneous pocket. A total of 105 rats were operated with a median (range) implantation time of 50 (30-88) min and an excellent perioperative survival of 93%. After monocrotaline induction on day 7, animals developed severe PAH with mean ± SD pressures of 75.9 ± 18.6 (systolic), 55.0 ± 18.0 (mean), and 42.1 ± 21.3 mmHg (diastolic) after 4 wk. Postmortem, the animals showed severe right ventricular hypertrophy, and histological analysis confirmed excessive medial hypertrophy and intimal hyperplasia, both characteristic features of human PAH. Comparison of the new telemetric model with standard microtip catheterization did not show relevant measurement differences. We established the first experimental animal model for PAH with preserved right ventricular integrity that allows direct telemetric monitoring of real-time systolic, mean, and diastolic pressures in the main pulmonary artery of freely moving rats.

The role of mononuclear cell tissue factor and inflammatory cytokines in patients with chronic thromboembolic pulmonary hypertension

Thrombosis and inflammation are two major factors underlying chronic thromboembolic pulmonary hypertension (CTEPH). Tissue factor (TF), C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein 1 (MCP-1) may play critical roles in the process of CTEPH thrombosis and pulmonary vascular remodeling. Ten patients with a confirmed diagnosis of CTEPH, 20 patients with acute pulmonary thromboembolism and 15 patients with other types of pulmonary hypertension were enrolled in this study, along with 20 healthy subjects as the control group. The immunoturbidimetric method was used to determine the plasma content of CRP. The plasma levels of TNF-α, MCP-1, and TF antigen were measured by an enzyme-linked immunosorbent assay, and TF activity was measured by the chromogenic substrate method. Percoll density gradient centrifugation was used to separate peripheral blood mononuclear cells from plasma. The level of monocyte TF mRNA was examined by reverse transcriptase-polymerase chain reaction. The correlations between all indices described above were analyzed. In CTEPH patients, the expression of CRP, TNF-α, and MCP-1 was significantly higher than that in controls (P < 0.05). The levels of TF activity, TF antigen, and TF mRNA in monocyte cells were increased in CTEPH patients when compared with control subjects, but only the TF antigen and TF mRNA levels were significantly different (P < 0.05). In CTEPH patients, levels of CRP, MCP-1, and TNF-α significantly correlated with the level of TF antigen in plasma. TF gene expression was increased in patients with CTEPH, suggesting that blood-borne TF mainly comes from mononuclear cells. TF expression significantly correlated with levels of CRP, TNF-α and MCP-1. These factors may play an important role in the development of CTEPH via the inflammation–coagulation–thrombosis cycle.

Chronic hypoxia aggravates monocrotaline-induced pulmonary arterial hypertension: a rodent relevant model to the human severe form of the disease

Pulmonary arterial hypertension (PAH) is a severe form of pulmonary hypertension that combines multiple alterations of pulmonary arteries, including, in particular, thrombotic and plexiform lesions. Multiple-pathological-insult animal models, developed to more closely mimic this human severe PAH form, often require complex and/or long experimental procedures while not displaying the entire panel of characteristic lesions observed in the human disease. In this study, we further characterized a rat model of severe PAH generated by combining a single injection of monocrotaline with 4 weeks exposure to chronic hypoxia. This model displays increased pulmonary arterial pressure, right heart altered function and remodeling, pulmonary arterial inflammation, hyperresponsiveness and remodeling. In particular, severe pulmonary arteriopathy was observed, with thrombotic, neointimal and plexiform-like lesions similar to those observed in human severe PAH. This model, based on the combination of two conventional procedures, may therefore be valuable to further understand the pathophysiology of severe PAH and identify new potential therapeutic targets in this disease.

Challenges in the development of chronic pulmonary hypertension models in large animals

Pulmonary hypertension (PH) results in significant morbidity and mortality. Chronic PH animal models may advance the study of PH's mechanisms, evolution, and therapy. In this report, we describe the challenges and successes in developing three models of chronic PH in large animals: two models (one canine and one swine) utilized repeated infusions of ceramic microspheres into the pulmonary vascular bed, and the third model employed a surgical aorto-pulmonary shunt. In the canine model, seven dogs underwent microsphere infusions that resulted in progressive elevation of pulmonary arterial pressure over a few months. In this model, pulmonary endoarterial tissue was obtained for histology. In the aorto-pulmonary shunt swine model, 17 pigs developed systemic level pulmonary pressures after 2-3 months. In this model, pulmonary endoarterial tissue was sequentially obtained to assess for changes in gene and microRNA expression. In the swine microsphere infusion model, three pigs developed only a modest chronic increase in pulmonary arterial pressure, despite repeated infusions of microspheres (up to 40 in one animal). The main purpose of this model was for vasodilator testing, which was performed successfully immediately after acute microsphere infusions. Chronic PH in large animal models can be successfully created; however, a model's characteristics need to match the investigational goals.

A novel mouse model of high flow-induced pulmonary hypertension-surgically induced by right pulmonary artery ligation

BACKGROUND

This study sought to establish a new model of high-flow pulmonary hypertension (PH) in mice. This model may be useful for studies seeking to reduce the pulmonary vascular resistance and delay the development of PH caused by congenital heart disease.

MATERIALS AND METHODS

The right pulmonary artery was ligated via a right posterolateral thoracotomy. Pulmonary hemodynamics was evaluated by right heart catheterization immediately after ligation and at 2, 4, 8, and 12 wk postoperatively. The right ventricle (RV) and the left ventricle (LV) with septum (S) were weighed to calculate the RV/(LV + S) ratio as an index of right ventricular hypertrophy. Morphologic changes in the left lungs were analyzed, and percentages of muscularized pulmonary vessels were assessed by hematoxylin and eosin, elastica van Gieson and alpha-smooth muscle actin staining. All the study data were compared with data from a model of PH generated by hypoxic stimulation.

RESULTS

A pulmonary hypertensive state was successfully induced by 2 wk after surgery. However, the morphologic analysis demonstrated that pulmonary vascular muscularization, as evaluated using right ventricular systolic pressure and RV/(LV + S), was not significantly increased until 4 wk postoperatively. When mice from the new model and the hypoxic model were compared, no significant differences were observed in any of the evaluated indices.

CONCLUSIONS

High-flow PH can be induced within 4 wk after ligation of the right pulmonary artery, which is easily performed in mice. Such mice can be used as a model of high-flow PH.

Pneumonectomy combined with SU5416 induces severe pulmonary hypertension in rats

The SU5416 + hypoxia (SuHx) rat model is a commonly used model of severe pulmonary arterial hypertension. While it is known that exposure to hypoxia can be replaced by another type of hit (e.g., ovalbumin sensitization) it is unknown whether abnormal pulmonary blood flow (PBF), which has long been known to invoke pathological changes in the pulmonary vasculature, can replace the hypoxic exposure. Here we studied if a combination of SU5416 administration combined with pneumonectomy (PNx), to induce abnormal PBF in the contralateral lung, is sufficient to induce severe pulmonary arterial hypertension (PAH) in rats. Sprague Dawley rats were subjected to SuPNx protocol (SU5416 + combined with left pneumonectomy) or standard SuHx protocol, and comparisons between models were made at week 2 and 6 postinitiation. Both SuHx and SuPNx models displayed extensive obliterative vascular remodeling leading to an increased right ventricular systolic pressure at week 6 Similar inflammatory response in the lung vasculature of both models was observed alongside increased endothelial cell proliferation and apoptosis. This study describes the SuPNx model, which features severe PAH at 6 wk and could serve as an alternative to the SuHx model. Our study, together with previous studies on experimental models of pulmonary hypertension, shows that the typical histopathological findings of PAH, including obliterative lesions, inflammation, increased cell turnover, and ongoing apoptosis, represent a final common pathway of a disease that can evolve as a consequence of a variety of insults to the lung vasculature.

Reconciling paradigms of abnormal pulmonary blood flow and quasi-malignant cellular alterations in pulmonary arterial hypertension

In pulmonary arterial hypertension (PAH) structural and functional abnormalities of the small lung vessels interact and lead to a progressive increase in pulmonary vascular resistance and right heart failure. A current pathobiological concept characterizes PAH as a 'quasi-malignant' disease focusing on cancer-like alterations in endothelial cells (EC) and the importance of their acquired apoptosis-resistant, hyper-proliferative phenotype in the process of vascular remodeling. While changes in pulmonary blood flow (PBF) have been long-since recognized and linked to the development of PAH, little is known about a possible relationship between an altered PBF and the quasi-malignant cell phenotype in the pulmonary vascular wall. This review summarizes recognized and hypothetical effects of an abnormal PBF on the pulmonary vascular bed and links these to quasi-malignant changes found in the pulmonary endothelium. Here we describe that abnormal PBF does not only trigger a pulmonary vascular cell growth program, but may also maintain the cancer-like phenotype of the endothelium. Consequently, normalization of PBF and EC response to abnormal PBF may represent a treatment strategy in patients with established PAH.

Anti-Endothelin Receptor Type A Autoantibodies in Systemic Lupus Erythematosus-Associated Pulmonary Arterial Hypertension

OBJECTIVE

To investigate the role of autoantibodies against endothelin 1 receptor type A (ETRA) in patients with systemic lupus erythematosus (SLE)-associated pulmonary arterial hypertension (PAH) and to examine the possibility that the pathogenesis of this disease is mediated by these autoantibodies.

METHODS

ETRA autoantibodies in serum from patients with SLE-associated PAH and serum from controls (SLE patients without PAH) were detected via a human ETRA epitope peptide-based enzyme-linked immunosorbent assay. An exploratory cohort of patients with SLE-associated PAH (n = 76) and an independent validation cohort of patients with SLE-associated PAH confirmed by right-sided heart catheterization (RHC) (n = 82) were enrolled. The clinical relevance of ETRA autoantibodies in SLE-associated PAH was analyzed. The proliferation of vascular smooth muscle cells (SMCs) and the permeability of endothelial cells (ECs) were assessed in vitro in cells stimulated with polyclonal ETRA IgG autoantibodies. Expression of PAH-related markers, i.e., serotonin transporter, platelet-derived growth factor receptor β, vascular endothelial growth factor A, and platelet-derived growth factor B was measured by quantitative polymerase chain reaction. In addition, a suboptimal dose of monocrotaline was used to induce PAH in rats, and the effect of ETRA autoantibodies in vivo was determined using a right ventricular hypertrophy index, pulmonary angiography, and laboratory parameters.

RESULTS

ETRA autoantibodies occurred more frequently in SLE-associated PAH (41.5%) than in controls (17.1%). There was a significant correlation between ETRA autoantibody titers and pulmonary artery systolic pressure measured by echocardiography (r = 0.2978, P = 0.0038) or pulmonary artery systolic pressure measured by RHC (r = 0.2159, P = 0.0257) in SLE-associated PAH. ETRA autoantibodies could promote SMC proliferation, disrupt the endothelial barrier, and up-regulate expression of PAH-related markers, which could be blocked in the presence of an endothelin receptor antagonist. ETRA autoantibodies aggravated right ventricular hypertrophy and vascular remodeling in vivo.

CONCLUSION

We identified ETRA autoantibodies as a biomarker of mechanistic relevance in SLE. These autoantibodies may mediate PAH development in SLE.

Enhanced caveolin-1 expression in smooth muscle cells: Possible prelude to neointima formation

AIM: To study the genesis of neointima formation in pulmonary hypertension (PH), we investigated the role of caveolin-1 and related proteins.

METHODS: Male Sprague Dawley rats were given monocrotaline (M, 40 mg/kg) or subjected to hypobaric hypoxia (H) to induce PH. Another group was given M and subjected to H to accelerate the disease process (M + H). Right ventricular systolic pressure, right ventricular hypertrophy, lung histology for medial hypertrophy and the presence of neointimal lesions were examined at 2 and 4 wk. The expression of caveolin-1 and its regulatory protein peroxisome proliferator-activated receptor (PPAR) γ, caveolin-2, proliferative and anti-apoptotic factors (PY-STAT3, p-Erk, Bcl-xL), endothelial nitric oxide synthase (eNOS) and heat shock protein (HSP) 90 in the lungs were analyzed, and the results from M + H group were compared with the controls, M and H groups. Double immunofluorescence technique was used to identify the localization of caveolin-1 in pulmonary arteries in rat lungs and in human PH lung tissue.

RESULTS: In the M + H group, PH was more severe compared with M or H group. In the 4 wk M+H group, several arteries with reduced caveolin-1 expression in endothelial layer coupled with an increased expression in smooth muscle cells (SMC), exhibited neointimal lesions. Neointima was present only in the arteries exhibiting enhanced caveolin-1 expression in SMC. Lung tissue obtained from patients with PH also revealed neointimal lesions only in the arteries exhibiting endothelial caveolin-1 loss accompanied by an increased caveolin-1 expression in SMC. Reduction in eNOS and HSP90 expression was present in the M groups (2 and 4 wk), but not in the M + H groups. In both M groups and in the M + H group at 2 wk, endothelial caveolin-1 loss was accompanied by an increase in PPARγ expression. In the M + H group at 4 wk, increase in caveolin-1 expression was accompanied by a reduction in the PPARγ expression. In the H group, there was neither a loss of endothelial caveolin-1, eNOS or HSP90, nor an increase in SMC caveolin-1 expression; or any alteration in PPARγ expression. Proliferative pathways were activated in all experimental groups.

CONCLUSION: Enhanced caveolin-1 expression in SMC follows extensive endothelial caveolin-1 loss with subsequent neointima formation. Increased caveolin-1 expression in SMC, thus, may be a prelude to neointima formation.

Targeted delivery of genes to endothelial cells and cell- and gene-based therapy in pulmonary vascular diseases

Pulmonary arterial hypertension (PAH) is a devastating disease that, despite significant advances in medical therapies over the last several decades, continues to have an extremely poor prognosis. Gene therapy is a method to deliver therapeutic genes to replace defective or mutant genes or supplement existing cellular processes to modify disease. Over the last few decades, several viral and nonviral methods of gene therapy have been developed for preclinical PAH studies with varying degrees of efficacy. However, these gene delivery methods face challenges of immunogenicity, low transduction rates, and nonspecific targeting which have limited their translation to clinical studies. More recently, the emergence of regenerative approaches using stem and progenitor cells such as endothelial progenitor cells (EPCs) and mesenchymal stem cells (MSCs) have offered a new approach to gene therapy. Cell-based gene therapy is an approach that augments the therapeutic potential of EPCs and MSCs and may deliver on the promise of reversal of established PAH. These new regenerative approaches have shown tremendous potential in preclinical studies; however, large, rigorously designed clinical studies will be necessary to evaluate clinical efficacy and safety.

Tissue factor, protease activated receptors and pathologic heart remodelling

Tissue factor is the primary initiator of coagulation cascade and plays an essential role in haemostasis and thrombosis. In addition, tissue factor and coagulation proteases contribute to many cellular responses via activation of protease activated receptors. The heart is an organ with high levels of constitutive tissue factor expression. This review focuses on the role of tissue factor, coagulation proteases and protease activated receptors in heart haemostasis and the pathological heart remodelling associated with myocardial infarction, viral myocarditis and hypertension.