Animal Models of Pulmonary Hypertension: Matching Disease Mechanisms to Etiology of the Human Disease

The Sugen/Hypoxia Rat Model for Pulmonary Hypertension and Right Heart Failure

Pulmonary hypertension (PH) is a devastating disease, characterized by complex remodeling of the pulmonary vasculature. PH is classified into five groups based on different etiology, pathology, as well as therapy and prognosis. Animal models are essential for the study of underlying mechanisms, pathophysiology, and preclinical testing of new therapies for PH. The complexity of the disease with different clinical entities dictates the necessity for more than one animal model to resemble PH, as a single model cannot imitate the broad spectrum of human PH.Here we describe a detailed protocol for creating a rat model of PH with right ventricular (RV) failure. Furthermore, we present how to characterize it hemodynamically by invasive measurements of RV and pulmonary arterial (PA) pressures. Animals subjected to this model display severe pulmonary vascular remodeling and RV dysfunction. In this model, rats undergo a single subcutaneous injection of Sugen (SU5416, a vascular endothelial growth factor inhibitor) and are immediately exposed to chronic hypoxia in a hypoxia chamber for 3-6 weeks. This Sugen/Hypoxia rat model resembles Group 1 PH.

CDN1163 alleviates SERCA2 dysfunction-induced pulmonary vascular remodeling by inhibiting the phenotypic transition of pulmonary artery smooth muscle cells

BACKGROUND AND PURPOSE

Substitution of Cys674 (C674) in the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) causes SERCA2 dysfunction which leads to activated inositol requiring enzyme 1 alpha (IRE1α) and spliced X-box binding protein 1 (XBP1s) pathway accelerating cell proliferation of pulmonary artery smooth muscle cells (PASMCs) followed by significant pulmonary vascular remodeling resembling human pulmonary hypertension. Based on this knowledge, we intend to investigate other potential mechanisms involved in SERCA2 dysfunction-induced pulmonary vascular remodeling.

EXPERIMENTAL APPROACH

Heterozygous SERCA2 C674S knock-in (SKI) mice of which half of cysteine in 674 was substituted by serine to mimic the partial irreversible oxidation of C674 were used. The lungs of SKI mice and their littermate wild-type mice were collected for PASMC culture, protein expression, and pulmonary vascular remodeling analysis.

RESULTS

SERCA2 dysfunction increased intracellular Ca2+ levels, which activated Ca2+-dependent calcineurin (CaN) and promoted the nuclear translocation and protein expression of the nuclear factor of activated T-lymphocytes 4 (NFAT4) in an IRE1α/XBP1s pathway-independent manner. In SKI PASMCs, the scavenge of intracellular Ca2+ by BAPTA-AM or inhibition of CaN by cyclosporin A can prevent PASMC phenotypic transition. CDN1163, a SERCA2 agonist, suppressed the activation of CaN/NFAT4 and IRE1α/XBP1s pathways, reversed the protein expression of PASMC phenotypic transition markers and cell cycle-related proteins, and inhibited cell proliferation and migration when given to SKI PASMCs. Furthermore, CDN1163 ameliorated pulmonary vascular remodeling in SKI mice.

CONCLUSIONS AND IMPLICATIONS

SERCA2 dysfunction promotes PASMC phenotypic transition and pulmonary vascular remodeling by multiple mechanisms, which could be improved by SERCA2 agonist CDN1163.

Bleomycin-induced lung injury: Revisiting an old tool to model group III PH associated with pulmonary fibrosis

Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation that often associates with other respiratory diseases (i.e., group III PH), leading to worsened symptoms and prognosis, notably when combined with interstitial lung diseases such as pulmonary fibrosis (PF). PH may lead to right ventricular (RV) failure, which accounts for a substantial part of the mortality in chronic lung disease patients. The disappointing results of pulmonary arterial hypertension (PAH)-related therapies in patients with PF emphasize the need to better understand the pathophysiologic mechanisms that drive PH development and progression in this specific setting. In this work, we validated an animal model of group III PH associated with PF (PH-PF), by using bleomycin (BM) intratracheal instillation and characterizing the nature of induced lung and vascular remodeling, including the influence on RV structure and function. To our knowledge, this is the first work describing this dose of BM in Sprague Dawley rats and the effects upon the heart and lungs, using different techniques such as echocardiography, heart catheterization, and histology. Our data shows the successful implementation of a rat model that mimics combined PF-PH, with most features seen in the equivalent human disease, such as lung and arterial remodeling, increased mPAP and RV dysfunction.

Farnesyl diphosphate synthase regulated endothelial proliferation and autophagy during rat pulmonary arterial hypertension induced by monocrotaline

Background

The proliferation ability and autophagy level of pulmonary artery endothelial cells (PAECs) play an important role in promoting the development of pulmonary artery hypertension (PAH), and there is still no effective treatment for PAH. Farnesyl diphosphate synthase (FDPS) is a key enzyme in the mevalonate pathway. The intermediate metabolites of this pathway are closely related to the activity of autophagy-associated small G proteins, including Ras-related C3 botulinum toxin substrate 1 (Rac1). Studies have shown that the mevalonate pathway affects the activation levels of different small G proteins, autophagy signaling pathways, vascular endothelial function, and so on. However, the exact relationship between them is still unclear in PAH.

Method

In vitro, western blotting and mRFP-GFP-LC3 puncta formation assays were used to observe the expression of FDPS and the level of autophagy in PAECs treated with monocrotaline pyrrole (MCTP). In addition, cell proliferation and migration assays were used to assess the effect of FDPS on endothelial function, and Rac1 activity assays were used to evaluate the effect of Rac1 activation on PAEC autophagy via the PI3K/AKT/mTOR signaling pathway. In vivo, the right heart catheterization method, hematoxylin and eosin (H&E) staining and western blotting were used to determine the effect of FDPS on PAEC autophagy and monocrotaline (MCT)-induced PAH.

Results

We show that the expression of FDPS is increased in the PAH module in vitro and in vivo, concomitant with the induction of autophagy and the activation of Rac1. Our data demonstrate that inhibition of FDPS ameliorates endothelial function and decreases MCT-induced autophagy levels. Mechanistically, we found that FDPS promotes autophagy, Rac1 activity and endothelial disfunction through the PI3K/AKT/mTOR signaling pathway.

Conclusion

Our study suggests that FDPS contributes to active small G protein-induced autophagy during MCT-induced PAH, which may serve as a potential therapeutic target against PAH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00511-7.

Signal Transduction during Metabolic and Inflammatory Reprogramming in Pulmonary Vascular Remodeling

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by (mal)adaptive remodeling of the pulmonary vasculature, which is associated with inflammation, fibrosis, thrombosis, and neovascularization. Vascular remodeling in PAH is associated with cellular metabolic and inflammatory reprogramming that induce profound endothelial and smooth muscle cell phenotypic changes. Multiple signaling pathways and regulatory loops act on metabolic and inflammatory mediators which influence cellular behavior and trigger pulmonary vascular remodeling in vivo. This review discusses the role of bioenergetic and inflammatory impairments in PAH development.

Plasticity and Enzymatic Degradation Coupled With Volumetric Growth in Pulmonary Hypertension Progression

Pulmonary hypertension (PH) is one of the least understood and highly elusive cardiovascular conditions associated with elevated pulmonary arterial pressure. Although the disease mechanisms are not completely understood, evidence has accumulated from human and animal studies that irreversible processes of pulmonary arterial wall damage, compensated by stress-mediated growth, play critical roles in eliciting the mechanisms of disease progression. The aim of this study is to develop a thermodynamic modeling structure of the pulmonary artery to consider coupled plastic-degradation-growth irreversible processes to investigate the mechanical roles of the dissipative phenomena in the disease progression. The proposed model performs a model parameter study of plastic deformation and degradation processes coupled with dissipative growth subjected to elevated pulmonary arterial pressure and computationally generates in silico simulations of PH progression using the clinical features of PH, found in human morphological and mechanical data. The results show that considering plastic deformation can provide a much better fitting of the ex vivo inflation tests than a widely used pure hyperelastic model in higher pressure conditions. In addition, the parameter sensitivity study illustrates that arterial damage and growth cause the increased stiffness, and the full simulation (combining elastic-plastic-degradation-growth models) reveals a key postpathological recovery process of compensating vessel damage by vascular adaptation by reducing the rate of vessel dilation and mediating vascular wall stress. Finally, the simulation results of luminal enlargement, arterial thickening, and arterial stiffness for an anisotropic growth are found to be close to the values from the literature.

Deficiency of Axl aggravates pulmonary arterial hypertension via BMPR2

Pulmonary arterial hypertension (PAH), is a fatal disease characterized by a pseudo-malignant phenotype. We investigated the expression and the role of the receptor tyrosine kinase Axl in experimental (i.e., monocrotaline and Su5416/hypoxia treated rats) and clinical PAH. In vitro Axl inhibition by R428 and Axl knock-down inhibited growth factor-driven proliferation and migration of non-PAH and PAH PASMCs. Conversely, Axl overexpression conferred a growth advantage. Axl declined in PAECs of PAH patients. Axl blockage inhibited BMP9 signaling and increased PAEC apoptosis, while BMP9 induced Axl phosphorylation. Gas6 induced SMAD1/5/8 phosphorylation and ID1/ID2 increase were blunted by BMP signaling obstruction. Axl association with BMPR2 was facilitated by Gas6/BMP9 stimulation and diminished by R428. In vivo R428 aggravated right ventricular hypertrophy and dysfunction, abrogated BMPR2 signaling, elevated pulmonary endothelial cell apoptosis and loss. Together, Axl is a key regulator of endothelial BMPR2 signaling and potential determinant of PAH.

Impact of human immunodeficiency virus on pulmonary vascular disease

With the advent of anti-retroviral therapy, non-AIDS-related comorbidities have increased in people living with HIV. Among these comorbidities, pulmonary hypertension (PH) is one of the most common causes of morbidity and mortality. Although chronic HIV-1 infection is independently associated with the development of pulmonary arterial hypertension, PH in people living with HIV may also be the outcome of various co-morbidities commonly observed in these individuals including chronic obstructive pulmonary disease, left heart disease and co-infections. In addition, the association of these co-morbidities and other risk factors, such as illicit drug use, can exacerbate the development of pulmonary vascular disease. This review will focus on these complex interactions contributing to PH development and exacerbation in HIV patients. We also examine the interactions of HIV proteins, including Nef, Tat, and gp120 in the pulmonary vasculature and how these proteins alter the endothelial and smooth muscle function by transforming them into susceptible PH phenotype. The review also discusses the available infectious and non-infectious animal models to study HIV-associated PAH, highlighting the advantages and disadvantages of each model, along with their ability to mimic the clinical manifestations of HIV-PAH.

AMPK and Pulmonary Hypertension: Crossroads Between Vasoconstriction and Vascular Remodeling

Pulmonary hypertension (PH) is a debilitating and life-threatening disease characterized by increased blood pressure within the pulmonary arteries. Adenosine monophosphate-activated protein kinase (AMPK) is a heterotrimeric serine-threonine kinase that contributes to the regulation of metabolic and redox signaling pathways. It has key roles in the regulation of cell survival and proliferation. The role of AMPK in PH is controversial because both inhibition and activation of AMPK are preventive against PH development. Some clinical studies found that metformin, the first-line antidiabetic drug and the canonical AMPK activator, has therapeutic efficacy during treatment of early-stage PH. Other study findings suggest the use of metformin is preferentially beneficial for treatment of PH associated with heart failure with preserved ejection fraction (PH-HFpEF). In this review, we discuss the "AMPK paradox" and highlight the differential effects of AMPK on pulmonary vasoconstriction and pulmonary vascular remodeling. We also review the effects of AMPK activators and inhibitors on rescue of preexisting PH in animals and include a discussion of gender differences in the response to metformin in PH.

Current Understanding of the Right Ventricle Structure and Function in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disease resulting in increased right ventricular (RV) afterload and RV remodeling. PAH results in altered RV structure and function at different scales from organ-level hemodynamics to tissue-level biomechanical properties, fiber-level architecture, and cardiomyocyte-level contractility. Biomechanical analysis of RV pathophysiology has drawn significant attention over the past years and recent work has found a close link between RV biomechanics and physiological function. Building upon previously developed techniques, biomechanical studies have employed multi-scale analysis frameworks to investigate the underlying mechanisms of RV remodeling in PAH and effects of potential therapeutic interventions on these mechanisms. In this review, we discuss the current understanding of RV structure and function in PAH, highlighting the findings from recent studies on the biomechanics of RV remodeling at organ, tissue, fiber, and cellular levels. Recent progress in understanding the underlying mechanisms of RV remodeling in PAH, and effects of potential therapeutics, will be highlighted from a biomechanical perspective. The clinical relevance of RV biomechanics in PAH will be discussed, followed by addressing the current knowledge gaps and providing suggested directions for future research.

Preventive treatment with ginsenoside Rb1 ameliorates monocrotaline-induced pulmonary arterial hypertension in rats and involves store-operated calcium entry inhibition

CONTEXT

Ginsenoside Rb1, the main active ingredient of ginseng, exhibits ex vivo depression of store-operated calcium entry (SOCE) and related vasoconstriction in pulmonary arteries derived from pulmonary hypertension (PH) rats. However, the in vivo effects of ginsenoside Rb1 on PH remain unclear.

OBJECTIVE

This study explored the possibility of using ginsenoside Rb1 as an in vivo preventive medication for type I PH, i.e., pulmonary arterial hypertension (PAH), and potential mechanisms involving SOCE.

MATERIALS AND METHODS

Male Sprague-Dawley rats (170-180 g) were randomly divided into Control, MCT, and MCT + Rb1 groups (n = 20). Control rats received only saline injection. Rats in the MCT + Rb1 and MCT groups were intraperitoneally administered single doses of 50 mg/kg monocrotaline (MCT) combined with 30 mg/kg/day ginsenoside Rb1 or equivalent volumes of saline for 21 consecutive days. Subsequently, comprehensive parameters related to SOCE, vascular tone, histological changes and hemodynamics were measured.

RESULTS

Ginsenoside Rb1 reduced MCT-induced STIM1, TRPC1, and TRPC4 expression by 35.00, 31.96, and 32.24%, respectively, at the protein level. SOCE-related calcium entry and pulmonary artery contraction decreased by 162.6 nM and 71.72%. The mean pulmonary artery pressure, right ventricle systolic pressure, and right ventricular mass index decreased by 19.5 mmHg, 21.6 mmHg, and 39.50%. The wall thickness/radius ratios decreased by 14.67 and 17.65%, and the lumen area/total area ratios increased by 18.55 and 15.60% in intrapulmonary vessels with 51-100 and 101-150 μm o.d.

CONCLUSION

Ginsenoside Rb1, a promising candidate for PH prevention, inhibited SOCE and related pulmonary vasoconstriction, and relieved MCT-induced PAH in rats.

Effects of macitentan and tadalafil monotherapy or their combination on the right ventricle and plasma metabolites in pulmonary hypertensive rats

Pulmonary arterial hypertension is a severe respiratory disease characterized by pulmonary artery remodeling. RV dysfunction and dysregulated circulating metabolomics are associated with adverse outcomes in pulmonary arterial hypertension. We investigated effects of tadalafil and macitentan alone or in combination on the RV and plasma metabolomics in SuHx and PAB models. For SuHx model, rats were injected with SU5416 and exposed to hypoxia for three weeks and then were returned to normoxia and treated with either tadalafil (10 mg/kg in chow) or macitentan (10 mg/kg in chow) or their combination (both 10 mg/kg in chow) for two weeks. For PAB model, rats were subjected to either sham or PAB surgery for three weeks and treated with above-mentioned drugs from week 1 to week 3. Following terminal echocardiographic and hemodynamic measurements, tissue samples were collected for metabolomic, histological and gene expression analysis. Both SuHx and PAB rats developed RV remodeling/dysfunction with severe and mild plasma metabolomic alterations, respectively. In SuHx rats, tadalafil and macitentan alone or in combination improved RV remodeling/function with the effects of macitentan and combination therapy being superior to tadalafil. All therapies similarly attenuated SuHx-induced changes in plasma metabolomics. In PAB rats, only macitentan improved RV remodeling/function, while only tadalafil attenuated PAB-induced changes in plasma metabolomics.

Perivascular Inflammation in Pulmonary Arterial Hypertension

Perivascular inflammation is a prominent pathologic feature in most animal models of pulmonary hypertension (PH) as well as in pulmonary arterial hypertension (PAH) patients. Accumulating evidence suggests a functional role of perivascular inflammation in the initiation and/or progression of PAH and pulmonary vascular remodeling. High levels of cytokines, chemokines, and inflammatory mediators can be detected in PAH patients and correlate with clinical outcome. Similarly, multiple immune cells, including neutrophils, macrophages, dendritic cells, mast cells, T lymphocytes, and B lymphocytes characteristically accumulate around pulmonary vessels in PAH. Concomitantly, vascular and parenchymal cells including endothelial cells, smooth muscle cells, and fibroblasts change their phenotype, resulting in altered sensitivity to inflammatory triggers and their enhanced capacity to stage inflammatory responses themselves, as well as the active secretion of cytokines and chemokines. The growing recognition of the interaction between inflammatory cells, vascular cells, and inflammatory mediators may provide important clues for the development of novel, safe, and effective immunotargeted therapies in PAH.

Pulmonary-arterial-hypertension (PAH)-on-a-chip: fabrication, validation and application

Currently used animal and cellular models for pulmonary arterial hypertension (PAH) only partially recapitulate its pathophysiology in humans and are thus inadequate in reproducing the hallmarks of the disease, inconsistent in portraying the sex-disparity, and unyielding to combinatorial study designs. Here we sought to deploy the ingenuity of microengineering in developing and validating a tissue chip model for human PAH. We designed and fabricated a microfluidic device to emulate the luminal, intimal, medial, adventitial, and perivascular layers of a pulmonary artery. By growing three types of pulmonary arterial cells (PACs)-endothelial, smooth muscle, and adventitial cells, we recreated the PAH pathophysiology on the device. Diseased (PAH) PACs, when grown on the chips, moved of out their designated layers and created phenomena similar to the major pathologies of human PAH: intimal thickening, muscularization, and arterial remodeling and show an endothelial to mesenchymal transition. Flow-induced stress caused control cells, grown on the chips, to undergo morphological changes and elicit arterial remodeling. Our data also suggest that the newly developed chips can be used to elucidate the sex disparity in PAH and to study the therapeutic efficacy of existing and investigational anti-PAH drugs. We believe this miniaturized device can be deployed for testing various prevailing and new hypotheses regarding the pathobiology and drug therapy in human PAH.

Effects of Different Types of Exercise Training on Pulmonary Arterial Hypertension: A Systematic Review

Pulmonary arterial hypertension (PAH) represents a chronic progressive disease characterized by high blood pressure in the pulmonary arteries leading to right heart failure. The disease has been a focus of medical research for many years due to its worse prognosis and limited treatment options. The aim of this study was to systematically assess the effects of different types of exercise interventions on PAH. Electronic databases were searched until July 2019. MEDLINE database was used as the predominant source for this paper. Studies with regards to chronic physical activity in adult PAH patients are compared on retrieving evidence on cellular, physiological, and psychological alterations in the PAH setting. Twenty human studies and 12 rat trials were identified. Amongst all studies, a total of 628 human subjects and 614 rats were examined. Regular physical activity affects the production of nitric oxygen and attenuates right ventricular hypertrophy. A combination of aerobic, anaerobic, and respiratory muscle training induces the strongest improvement in functional capacity indicated by an increase of 6 MWD and VO₂peak. In human studies, an increase of quality of life was found. Exercise training has an overall positive effect on the physiological and psychological components of PAH. Consequently, PAH patients should be encouraged to take part in regular exercise training programs.

Establishment of adult right ventricle failure in ovine using a graded, animal-specific pulmonary artery constriction model

BACKGROUND

Right ventricle failure (RVF) is associated with serious cardiac and pulmonary diseases that contribute significantly to the morbidity and mortality of patients. Currently, the mechanisms of RVF are not fully understood and it is partly due to the lack of large animal models in adult RVF. In this study, we aim to establish a model of RVF in adult ovine and examine the structure and function relations in the RV.

METHODS

RV pressure overload was induced in adult male sheep by revised pulmonary artery constriction (PAC). Briefly, an adjustable hydraulic occluder was placed around the main pulmonary artery trunk. Then, repeated saline injection was performed at weeks 0, 1, and 4, where the amount of saline was determined in an animal-specific manner. Healthy, age-matched male sheep were used as additional controls. Echocardiography was performed bi-weekly and on week 11 post-PAC, hemodynamic and biological measurements were obtained.

RESULTS

This PAC methodology resulted in a marked increase in RV systolic pressure and decreases in stroke volume and tricuspid annular plane systolic excursion, indicating signs of RVF. Significant increases in RV chamber size, wall thickness, and Fulton's index were observed. Cardiomyocyte hypertrophy and collagen accumulation (particularly type III collagen) were evident, and these structural changes were correlated with RV dysfunction.

CONCLUSION

In summary, the animal-specific, repeated PAC provided a robust approach to induce adult RVF, and this ovine model will offer a useful tool to study the progression and treatment of adult RVF that is translatable to human diseases.

Rats with a Human Mutation of NFU1 Develop Pulmonary Hypertension

NFU1 is a mitochondrial protein that is involved in the biosynthesis of iron-sulfur clusters, and its genetic modification is associated with disorders of mitochondrial energy metabolism. Patients with autosomal-recessive inheritance of the NFU1 mutation G208C have reduced activity of the respiratory chain Complex II and decreased levels of lipoic-acid-dependent enzymes, and develop pulmonary arterial hypertension (PAH) in ∼70% of cases. We investigated whether rats with a human mutation in NFU1 are also predisposed to PAH development. A point mutation in rat NFU1^G206C (human G208C) was introduced through CRISPR/Cas9 genome editing. Hemodynamic data, tissue samples, and fresh mitochondria were collected and analyzed. NFU1^G206C rats showed increased right ventricular pressure, right ventricular hypertrophy, and high levels of pulmonary artery remodeling. Computed tomography and angiography of the pulmonary vasculature indicated severe angioobliterative changes in NFU1^G206C rats. Importantly, the penetrance of the PAH phenotype was found to be more prevalent in females than in males, replicating the established sex difference among patients with PAH. Male and female homozygote rats exhibited decreased expression and activity of mitochondrial Complex II, and markedly decreased pyruvate dehydrogenase activity and lipoate binding. The limited development of PAH in males correlated with the preserved levels of oligomeric NFU1, increased expression of ISCU (an alternative branch of the iron-sulfur assembly system), and increased complex IV activity. Thus, the male sex has additional plasticity to overcome the iron-sulfur cluster deficiency. Our work describes a novel, humanized rat model of NFU1 deficiency that showed mitochondrial dysfunction similar to that observed in patients and developed PAH with the same sex dimorphism.

Quantitative 129Xe MRI detects early impairment of gas-exchange in a rat model of pulmonary hypertension

Hyperpolarized 129Xe magnetic resonance imaging (MRI) is capable of regional mapping of pulmonary gas-exchange and has found application in a wide range of pulmonary disorders in humans and animal model analogs. This study is the first application of 129Xe MRI to the monocrotaline rat model of pulmonary hypertension. Such models of preclinical pulmonary hypertension, a disease of the pulmonary vasculature that results in right heart failure and death, are usually assessed with invasive procedures such as right heart catheterization and histopathology. The work here adapted from protocols from clinical 129Xe MRI to enable preclinical imaging of rat models of pulmonary hypertension on a Bruker 7 T scanner. 129Xe spectroscopy and gas-exchange imaging showed reduced 129Xe uptake by red blood cells early in the progression of the disease, and at a later time point was accompanied by increased uptake by barrier tissues, edema, and ventilation defects-all of which are salient characteristics of the monocrotaline model. Imaging results were validated by H&E histology, which showed evidence of remodeling of arterioles. This proof-of-concept study has demonstrated that hyperpolarized 129Xe MRI has strong potential to be used to non-invasively monitor the progression of pulmonary hypertension in preclinical models and potentially to also assess response to therapy.

NTP42, a novel antagonist of the thromboxane receptor, attenuates experimentally induced pulmonary arterial hypertension

BACKGROUND

NTP42 is a novel antagonist of the thromboxane prostanoid receptor (TP), currently in development for the treatment of pulmonary arterial hypertension (PAH). PAH is a devastating disease with multiple pathophysiological hallmarks including excessive pulmonary vasoconstriction, vascular remodelling, inflammation, fibrosis, in situ thrombosis and right ventricular hypertrophy. Signalling through the TP, thromboxane (TX) A₂ is a potent vasoconstrictor and mediator of platelet aggregation. It is also a pro-mitogenic, pro-inflammatory and pro-fibrotic agent. Moreover, the TP also mediates the adverse actions of the isoprostane 8-iso-prostaglandin F_2α, a free-radical-derived product of arachidonic acid produced in abundance during oxidative injury. Mechanistically, TP antagonists should treat most of the hallmarks of PAH, including inhibiting the excessive vasoconstriction and pulmonary artery remodelling, in situ thrombosis, inflammation and fibrosis. This study aimed to investigate the efficacy of NTP42 in the monocrotaline (MCT)-induced PAH rat model, alongside current standard-of-care drugs.

METHODS

PAH was induced by subcutaneous injection of 60 mg/kg MCT in male Wistar-Kyoto rats. Animals were assigned into groups: 1. 'No MCT'; 2. 'MCT Only'; 3. MCT + NTP42 (0.25 mg/kg BID); 4. MCT + Sildenafil (50 mg/kg BID), and 5. MCT + Selexipag (1 mg/kg BID), where 28-day drug treatment was initiated within 24 h post-MCT.

RESULTS

From haemodynamic assessments, NTP42 reduced the MCT-induced PAH, including mean pulmonary arterial pressure (mPAP) and right systolic ventricular pressure (RSVP), being at least comparable to the standard-of-care drugs Sildenafil or Selexipag in bringing about these effects. Moreover, NTP42 was superior to Sildenafil and Selexipag in significantly reducing pulmonary vascular remodelling, inflammatory mast cell infiltration and fibrosis in MCT-treated animals.

CONCLUSIONS

These findings suggest that NTP42 and antagonism of the TP signalling pathway have a relevant role in alleviating the pathophysiology of PAH, representing a novel therapeutic target with marked benefits over existing standard-of-care therapies.

Primary pulmonary arterial hypertension: Protocol to assess comprehensively in the rat the response to pharmacologic treatments

The identification of new treatments for primary pulmonary arterial hypertension (PAH) is a critical unmet need since there is no a definitive cure for this disease yet. Due to the complexity of PAH, a wide set of methods are necessary to assess the response to a pharmacological intervention. Thus, a rigorous protocol is crucial when experimental studies are designed. In the present experimental protocol, a stepwise approach was followed in a monocrotaline-induced PAH model in the rat, moving from the dose finding study of treatment compounds to the recognition of the onset of disease manifestation, in order to identify when to start a curative treatment. A complete multidimensional evaluation of treatment effects represented the last step. The primary study endpoint was the change in right ventricular systolic pressure after 14 days of treatment; echocardiographic and biohumoral markers together with heart and pulmonary arterial morphometric parameters were considered as secondary efficacy and/or safety endpoints and for the evaluation of the biologic coherence in the different results.

Estradiol Metabolism: Crossroads in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a debilitating and progressive disease that predominantly develops in women. Over the past 15 years, cumulating evidence has pointed toward dysregulated metabolism of sex hormones in animal models and patients with PAH. 17β-estradiol (E2) is metabolized at positions C2, C4, and C16, which leads to the formation of metabolites with different biological/estrogenic activity. Since the first report that 2-methoxyestradiol, a major non-estrogenic metabolite of E2, attenuates the development and progression of experimental pulmonary hypertension (PH), it has become increasingly clear that E2, E2 precursors, and E2 metabolites exhibit both protective and detrimental effects in PH. Furthermore, both experimental and clinical data suggest that E2 has divergent effects in the pulmonary vasculature versus right ventricle (estrogen paradox in PAH). The estrogen paradox is of significant clinical relevance for understanding the development, progression, and prognosis of PAH. This review updates experimental and clinical findings and provides insights into: (1) the potential impacts that pathways of estradiol metabolism (EMet) may have in PAH; (2) the beneficial and adverse effects of estrogens and their precursors/metabolites in experimental PH and human PAH; (3) the co-morbidities and pathological conditions that may alter EMet and influence the development/progression of PAH; (4) the relevance of the intracrinology of sex hormones to vascular remodeling in PAH; and (5) the advantages/disadvantages of different approaches to modulate EMet in PAH. Finally, we propose the three-tier-estrogen effects in PAH concept, which may offer reconciliation of the opposing effects of E2 in PAH and may provide a better understanding of the complex mechanisms by which EMet affects the pulmonary circulation–right ventricular interaction in PAH.

Oxidation of PKGIα mediates an endogenous adaptation to pulmonary hypertension

Chronic hypoxia causes pulmonary hypertension (PH), vascular remodeling, right ventricular (RV) hypertrophy, and cardiac failure. Protein kinase G Iα (PKGIα) is susceptible to oxidation, forming an interprotein disulfide homodimer associated with kinase targeting involved in vasodilation. Here we report increased disulfide PKGIα in pulmonary arteries from mice with hypoxic PH or lungs from patients with pulmonary arterial hypertension. This oxidation is likely caused by oxidants derived from NADPH oxidase-4, superoxide dismutase 3, and cystathionine γ-lyase, enzymes that were concomitantly increased in these samples. Indeed, products that may arise from these enzymes, including hydrogen peroxide, glutathione disulfide, and protein-bound persulfides, were increased in the plasma of hypoxic mice. Furthermore, low-molecular-weight hydropersulfides, which can serve as "superreductants" were attenuated in hypoxic tissues, consistent with systemic oxidative stress and the oxidation of PKGIα observed. Inhibiting cystathionine γ-lyase resulted in decreased hypoxia-induced disulfide PKGIα and more severe PH phenotype in wild-type mice, but not in Cys42Ser PKGIα knock-in (KI) mice that are resistant to oxidation. In addition, KI mice also developed potentiated PH during hypoxia alone. Thus, oxidation of PKGIα is an adaptive mechanism that limits PH, a concept further supported by polysulfide treatment abrogating hypoxia-induced RV hypertrophy in wild-type, but not in the KI, mice. Unbiased transcriptomic analysis of hypoxic lungs before structural remodeling identified up-regulation of endothelial-to-mesenchymal transition pathways in the KI compared with wild-type mice. Thus, disulfide PKGIα is an intrinsic adaptive mechanism that attenuates PH progression not only by promoting vasodilation but also by limiting maladaptive growth and fibrosis signaling.

A novel cyclic biased agonist of the apelin receptor, MM07, is disease modifying in the rat monocrotaline model of pulmonary arterial hypertension

BACKGROUND AND PURPOSE

Apelin is an endogenous vasodilatory and inotropic peptide that is down-regulated in human pulmonary arterial hypertension, although the density of the apelin receptor is not significantly attenuated. We hypothesised that a G protein-biased apelin analogue MM07, which is more stable than the endogenous apelin peptide, may be beneficial in this condition with the advantage of reduced β-arrestin-mediated receptor internalisation with chronic use.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats received either monocrotaline to induce pulmonary arterial hypertension or saline and then daily i.p. injections of either MM07 or saline for 21 days. The extent of disease was assessed by right ventricular catheterisation, cardiac MRI, and histological analysis of the pulmonary vasculature. The effect of MM07 on signalling, proliferation, and apoptosis of human pulmonary artery endothelial cells was investigated.

KEY RESULTS

MM07 significantly reduced the elevation of right ventricular systolic pressure and hypertrophy induced by monocrotaline. Monocrotaline-induced changes in cardiac structure and function, including right ventricular end-systolic and end-diastolic volumes, ejection fraction, and left ventricular end-diastolic volume, were attenuated by MM07. MM07 also significantly reduced monocrotaline-induced muscularisation of small pulmonary blood vessels. MM07 stimulated endothelial NOS phosphorylation and expression, promoted proliferation, and attenuated apoptosis of human pulmonary arterial endothelial cells in vitro.

CONCLUSION AND IMPLICATIONS

Our findings suggest that chronic treatment with MM07 is beneficial in this animal model of pulmonary arterial hypertension by addressing disease aetiology. These data support the development of G protein-biased apelin receptor agonists with improved pharmacokinetic profiles for use in human disease.

Inhaled combination of sildenafil and rosiglitazone improves pulmonary hemodynamics, cardiac function, and arterial remodeling

Currently, dual- or triple-drug combinations comprising different vasodilators are the mainstay for the treatment of pulmonary arterial hypertension (PAH). However, the patient outcome continues to be disappointing because the existing combination therapy cannot restrain progression of the disease. Previously, we have shown that when given as a monotherapy, long-acting inhaled formulations of sildenafil (a phosphodiesterase-5 inhibitor) and rosiglitazone (a peroxisome proliferator receptor-γ agonist) ameliorate PAH in rats. Thus, with a goal to develop a new combination therapy, we prepared and characterized poly(lactic-co-glycolic acid) (PLGA)-based long-acting inhalable particles of sildenafil and rosiglitazone. We then assessed the efficacy of the combinations of sildenafil and rosiglitazone, given in plain forms or as PLGA particles, in reducing mean pulmonary arterial pressure (mPAP) and improving pulmonary arterial remodeling and right ventricular hypertrophy (RVH) in Sugen 5416 plus hypoxia-induced PAH rats. After intratracheal administration of the formulations, we catheterized the rats and measured mPAP, cardiac output, total pulmonary resistance, and RVH. We also conducted morphometric studies using lung tissue samples and assessed the degree of muscularization, the arterial medial wall thickening, and the extent of collagen deposition. Compared with the plain drugs, given via the pulmonary or oral route as a single or dual combination, PLGA particles of the drugs, although given at a longer dosing interval compared with the plain drugs, caused more pronounced reduction in mPAP without affecting mean systemic pressure, improved cardiac function, slowed down right heart remodeling, and reduced arterial muscularization. Overall, PLGA particles of sildenafil and rosiglitazone, given as an inhaled combination, could be a viable alternative to currently available vasodilator-based combination therapy for PAH.

Targeted HFpEF therapy based on matchmaking of human and animal models

The diversity in clinical phenotypes and poor understanding of the underlying pathophysiology of heart failure with preserved ejection fraction (HFpEF) is the main reason why no effective treatments have been found yet. Targeted, instead of one size fits all, treatment seems the only promising approach for treating HFpEF. To be able to design a targeted, phenotype-specific HFpEF treatment, the matrix relating clinical phenotypes and underlying pathophysiological mechanisms has to be clarified. This review discusses the opportunities for additional evaluation of the underlying pathophysiological processes, e.g., to evaluate biological phenotypes on top of clinical routine, to guide us toward a phenotype-specific HFpEF treatment. Moreover, a translational approach with matchmaking of animal models to biological HFpEF phenotypes will be a valuable step to test the effectiveness of novel, targeted interventions in HFpEF. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/personalized-medicine-in-hfpef/ .

BMPR2 mutations and endothelial dysfunction in pulmonary arterial hypertension (2017 Grover Conference Series)

Despite the discovery more than 15 years ago that patients with hereditary pulmonary arterial hypertension (HPAH) inherit BMP type 2 receptor ( BMPR2) mutations, it is still unclear how these mutations cause disease. In part, this is attributable to the rarity of HPAH and difficulty obtaining tissue samples from patients with early disease. However, in addition, limitations to the approaches used to study the effects of BMPR2 mutations on the pulmonary vasculature have restricted our ability to determine how individual mutations give rise to progressive pulmonary vascular pathology in HPAH. The importance of understanding the mechanisms by which BMPR2 mutations cause disease in patients with HPAH is underscored by evidence that there is reduced BMPR2 expression in patients with other, more common, non-hereditary form of PAH, and that restoration of BMPR2 expression reverses established disease in experimental models of pulmonary hypertension. In this paper, we focus on the effects on endothelial function. We discuss some of the controversies and challenges that have faced investigators exploring the role of BMPR2 mutations in HPAH, focusing specifically on the effects different BMPR2 mutation have on endothelial function, and whether there are qualitative differences between different BMPR2 mutations. We discuss evidence that BMPR2 signaling regulates a number of responses that may account for endothelial abnormalities in HPAH and summarize limitations of the models that are used to study these effects. Finally, we discuss evidence that BMPR2-dependent effects on endothelial metabolism provides a unifying explanation for the many of the BMPR2 mutation-dependent effects that have been described in patients with HPAH.

Echocardiographic validation of pulmonary hypertension due to heart failure with reduced ejection fraction in mice

Pulmonary hypertension (PH) associated with left heart diseases is the most prevalent cause of PH. The scarcity of studies exploring the pathophysiology and therapies of group II PH resides in the lack of validated small animal models with non-invasive determination of the presence and severity of PH. Heart failure (HF) was induced in mice by coronary artery ligation. Mice developed PH as evidenced by an elevated right ventricular (RV) systolic pressure and RV hypertrophy. Detailed non-invasive echocardiographic analysis on the left and right ventricles showed impaired left ventricular (LV) systolic and diastolic function. In addition, RV hypertrophy was confirmed by echo and accompanied by impaired function as well as increased pulmonary resistance. Correlation analysis validated the use of the LV wall-motion score index (WMSI) at a threshold value of ≥2.0 as a powerful and reliable indicator for the presence of PH and RV dysfunction. Echocardiography is an accurate non-invasive technique to diagnose PH in a HF mouse model. Moreover, an echocardiographic parameter of infarct size and LV function, the LV WMSI, reliably correlates with the presence of PH, RV hypertrophy and RV dysfunction and could be used to improve efficiency and design of pre-clinical studies.

Modeling Pulmonary Hypertension: A Pig Model of Postcapillary Pulmonary Hypertension

Pulmonary hypertension (PH) is a pathophysiological condition defined as an increase in mean pulmonary arterial pressure ≥25 mmHg at rest assessed by right heart catheterization.Based on hemodynamic criteria, precapillary PH is characterized by a mean pulmonary capillary wedge pressure ≤15 mmHg as opposed to the postcapillary PH by >15 mmHg. Postcapillary PH is one of the most common forms of PH, often caused by left ventricular dysfunction and heart failure.In this chapter, we describe protocols for creating a large animal model of postcapillary PH. It is induced by open chest surgery (lateral thoracotomy) to band the pulmonary veins. The model is characterized by low mortality, relatively easy surgical procedure with well reproducible results, and pulmonary and cardiac remodeling at the structural, functional, and molecular levels. The presence of right ventricular (RV) remodeling is of significant importance since right heart failure is the main cause of death in patients suffering from PH. One of the advantages of the model described in this chapter is that both adaptive and maladaptive forms of RV remodeling can be observed during the progression of the disease. This can help understand the progressive pathophysiology of RV failure in humans. Besides the description of the model, a detailed guidance of the RV functional assessment in pigs for both invasive (heart catheterization) and noninvasive (echocardiography) approaches is provided.

Involvement of endothelial progenitor cells in the formation of plexiform lesions in broiler chickens: possible role of local immune/inflammatory response

Plexiform lesions (PLs), which are often accompanied by perivascular infiltrates of mononuclear cells, represent the hallmark lesions of pulmonary arteries in humans suffering from severe pulmonary arterial hypertension (PAH). Endothelial progenitor cells (EPCs) have been recently implicated in the formation of PLs in human patients. PLs rarely develop in rodent animal models of PAH but can develop spontaneously in broiler chickens. The aim of the present study was to confirm the presence of EPCs in the PLs in broilers. The immune mechanisms involved in EPC dysfunction were also evaluated. Lungs were collected from commercial broilers at 1 to 4 weeks of age. The right/total ventricle ratios indicated normal pulmonary arterial pressures for all sampled birds. Immunohistochemistry was performed to determine the expressions of EPC markers (CD133 and VEGFR-2) and proangiogenic molecule hepatocyte growth factor (HGF) in the lung samples. An EPC/lymphocyte co-culture system was used to investigate the functional changes of EPCs under the challenge of immune cells. PLs with different cellular composition were detected in the lungs of broilers regardless of age, and they were commonly surrounded by moderate to dense perivascular mononuclear cell infiltrates. Immunohistochemical analyses revealed the presence of CD133⁺ and VEGFR-2⁺ cells in PLs. These structures also exhibited a strong expression of HGF. Lymphocyte co-culture enhanced EPC apoptosis and completely blocked HGF-stimulated EPC survival and in vitro tube formation. Taken together, this work provides evidence for the involvement of EPCs in the development of PLs in broilers. It is suggested that the local immune cell infiltrate might serve as a contributor to EPC dysfunction by inducing EPC death and limiting their response to angiogenic stimuli. Broiler chickens may be valuable for investigating reversibility of plexogenic arteriopathy using gene-modified inflammation-resistant EPCs.

Hypoxic pulmonary vasoconstriction and vascular contractility in monocrotaline-induced pulmonary arterial hypertensive rats

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by vascular remodeling of pulmonary arteries (PAs) and increased vascular resistance in the lung. Monocrotaline (MCT), a toxic alkaloid, is widely used for developing rat models of PAH caused by injury to pulmonary endothelial cells; however, characteristics of vascular functions in MCT-induced PAH vary and are not fully understood. Here, we investigated hypoxic pulmonary vasoconstriction (HPV) responses and effects of various vasoconstrictors with isolated/perfused lungs of MCT-induced PAH (PAH-MCT) rats. Using hematoxylin and eosin staining, we confirmed vascular remodeling (i.e., medial thickening of PA) and right ventricle hypertrophy in PAH-MCT rats. The basal pulmonary arterial pressure (PAP) and PAP increase by a raised flow rate (40 mL/min) were higher in the PAH-MCT than in the control rats. In addition, both high K⁺ (40 mM KCl)- and angiotensin II-induced PAP increases were higher in the PAH-MCT than in the control rats. Surprisingly, application of a nitric oxide synthase inhibitor, L-N^G-Nitroarginine methyl ester (L-NAME), induced a marked PAP increase in the PAH-MCT rats, suggesting that endothelial functions were recovered in the three-week PAH-MCT rats. In addition, the medial thickening of the PA was similar to that in chronic hypoxia-induced PAH (PAH-CH) rats. However, the HPV response (i.e., PAP increased by acute hypoxia) was not affected in the MCT rats, whereas HPV disappeared in the PAH-CH rats. These results showed that vascular contractility and HPV remain robust in the MCT-induced PAH rat model with vascular remodeling.

Applying Biotechnology and Bioengineering to Pediatric Lung Disease: Emerging Paradigms and Platforms

Pediatric lung diseases remain a costly worldwide health burden. For many children with end-stage lung disease, lung transplantation remains the only therapeutic option. Due to the limited number of lungs available for transplantation, alternatives to lung transplant are desperately needed. Recently, major improvements in tissue engineering have resulted in newer technology and methodology to develop viable bioengineered lungs. These include critical advances in lung cell biology, stem cell biology, lung extracellular matrix, microfabrication techniques, and orthotopic transplantation of bioartificial lungs. The goal of this short review is to engage the reader's interest with regard to these emerging concepts and to stimulate their interest to learn more. We review the existing state of the art of lung tissue engineering, and point to emerging paradigms and platforms in the field. Finally, we summarize the challenges and unmet needs that remain to be overcome.