Primary pulmonary hypertension. I. Clinical and hemodynamic study

Global, regional, and national burden of pulmonary arterial hypertension, 1990-2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND

Pulmonary arterial hypertension (PAH) is a vascular disease characterised by restricted flow and high pressure through the pulmonary arteries, leading to progressive right heart failure and death. This study reports the global burden of PAH, leveraging all available data and using methodology of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) to understand the epidemiology of this under-researched and morbid disease.

METHODS

Prior to the current effort, the burden of PAH was included in GBD as a non-specific contributor to "other cardiovascular and circulatory disease" burden. In this study, PAH was distinguished as its own cause of death and disability in GBD, producing comparable and consistent estimates of PAH burden. We used epidemiological and vital registry data to estimate the non-fatal and fatal burden of PAH in 204 countries and territories from 1990 to 2021 using standard GBD modelling approaches. We specifically focused on PAH (group 1 pulmonary hypertension), and did not include pulmonary hypertension groups 2-5.

FINDINGS

In 2021, there were an estimated 192 000 (95% uncertainty interval [UI] 155 000-236 000) prevalent cases of PAH globally. Of these, 119 000 (95 900-146 000) were in females (62%) and 73 100 (58 900-89 600) in males (38%). The age-standardised prevalence was 2·28 cases per 100 000 population (95% UI 1·85-2·80). Prevalence increased with age such that the highest prevalence was among individuals aged 75-79 years. In 2021, there were 22 000 deaths (18 200-25 400) attributed to PAH globally, with an age-standardised mortality rate of 0·27 deaths from PAH per 100 000 population (0·23-0·32). The burden of disease appears to be improving over time (38·2% improvement in age-standardised years of life lost [YLLs] in 2021 relative to 1990). YLLs attributed to PAH were similar to estimates for conditions such as chronic myeloid leukaemia, multiple sclerosis, and Crohn's disease.

INTERPRETATION

PAH is a rare but fatal disease that accounts for a considerable health-associated burden worldwide. PAH is disproportionally diagnosed among females and older adults.

FUNDING

Cardiovascular Medical Research and Education Fund and the Bill & Melinda Gates Foundation.

Lung Transplantation for Pulmonary Artery Hypertension

This manuscript discusses the role of lung transplantation in patients with pulmonary hypertension. The indications and timing for referral to a transplant unit and timing for wait-listing for lung transplantation are discussed. The type of transplantation—isolated (single or double) lung transplantation and situations when combined heart and double lung transplantation is indicated—will be elaborated. Escalation of medical therapy with the need and timing for bridging therapies such as extracorporeal membrane oxygenation until an appropriate organ becomes available will be discussed. Challenges in the postoperative period, specific to lung transplantation for pulmonary artery hypertension, will be reviewed. The outcomes following lung transplantation will also be considered in greater detail.

Acquired disorders of mitochondrial metabolism and dynamics in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an orphan disease of the cardiopulmonary unit that reflects an obstructive pulmonary vasculopathy and presents with hypertrophy, inflammation, fibrosis, and ultimately failure of the right ventricle (RVF). Despite treatment using pulmonary hypertension (PH)-targeted therapies, persistent functional impairment reduces the quality of life for people with PAH and death from RVF occurs in approximately 40% of patients within 5 years of diagnosis. PH-targeted therapeutics are primarily vasodilators and none, alone or in combination, are curative. This highlights a need to therapeutically explore molecular targets in other pathways that are involved in the pathogenesis of PAH. Several candidate pathways in PAH involve acquired mitochondrial dysfunction. These mitochondrial disorders include: 1) a shift in metabolism related to increased expression of pyruvate dehydrogenase kinase and pyruvate kinase, which together increase uncoupled glycolysis (Warburg metabolism); 2) disruption of oxygen-sensing related to increased expression of hypoxia-inducible factor 1α, resulting in a state of pseudohypoxia; 3) altered mitochondrial calcium homeostasis related to impaired function of the mitochondrial calcium uniporter complex, which elevates cytosolic calcium and reduces intramitochondrial calcium; and 4) abnormal mitochondrial dynamics related to increased expression of dynamin-related protein 1 and its binding partners, such as mitochondrial dynamics proteins of 49 kDa and 51 kDa, and depressed expression of mitofusin 2, resulting in increased mitotic fission. These acquired mitochondrial abnormalities increase proliferation and impair apoptosis in most pulmonary vascular cells (including endothelial cells, smooth muscle cells and fibroblasts). In the RV, Warburg metabolism and induction of glutaminolysis impairs bioenergetics and promotes hypokinesis, hypertrophy, and fibrosis. This review will explore our current knowledge of the causes and consequences of disordered mitochondrial function in PAH.

Simulation of Acute Pulmonary Hypertension in Beagle Dogs

Acoustic cardiography (AC) combined with heart sound (HS) recording and electrocardiogram (ECG) provides a noninvasive and inexpensive way to understand the electrical mechanical activity of the heart. Pulmonary artery stenosis can cause hemodynamic abnormalities that might lead to pulmonary hypertension (PH). In this paper, we examined the relationships between the acoustic characteristics of the AC and hemodynamic changes in a beagle dog model of PH.Four healthy beagle dogs were injected with the prostaglandin endoperoxide receptor agonist U-44069 to induce acute PH states. AC was employed to analyze the process of pre-PH, intra-PH, and post-PH. Right ventricular blood pressure (RVBP) was measured via right cardiac catheterization, an invasive method performed in parallel for comparative hemodynamic evaluation. As RVBP increased or decreased, the HS features changed accordingly during acute PH occurrence and development. Right ventricular systolic blood pressure (RVSBP) significantly correlated with the minimum of the first HS (S1) amplitude (correlation coefficient (CC) = -0.82), energy of the S1 (CC = 0.86), energy of the second HS (S2) (CC = 0.67), entropy of the S1 (CC = -0.94), and ratio of electromechanical systolic time (EMST) to the cardiac cycle time (CC = 0.81). The two techniques (AC [HSs and ECG] versus right cardiac catheterization [RVBP]) were significantly correlated. Especially, the diastolic filling time (DFT) had a significant relationship with the right ventricular diastolic time (RVDT) (CC = 0.97), perfusion time (PT) (CC = 0.96), and cardiac cycle time (RR) (CC = 0.96). The CCs between the RVDT and the max dp/dt to min dp/dt, the EMST and the Q to min dp/dt, and the electromechanical activation time and the Q to max dp/dt were 0.95, 0.99, and 0.86, respectively. Furthermore, the logistic regression model with different combinations was used to identify the effective features for monitoring hemodynamic and pathophysiologic conditions.AC provided significant insight into mechanical dysfunction in a rapid and noninvasive way that could be used for early screening of PH.

Lung transplantation for pulmonary hypertension

From its identification as a distinct disease entity, understanding and management of pulmonary hypertension has continuously evolved. Diagnostic and therapeutic interventions have greatly improved the prognostic implications of this devastating disease, previously rapidly and uniformly fatal to one chronically managed by multi-disciplinary teams. Improved diagnostic algorithms and active research into biochemical signatures of pulmonary hypertension (PH) have led to earlier diagnosis of PH. Medical therapy has moved from upfront use of continuous intravenous prostaglandins to administration of combinations of oral medications targeting multiple pathways underlying this disease process. In addition to improved medical therapies, recently introduced interventions such as pulmonary endarterectomy and pulmonary artery balloon angioplasty for chronic thromboembolic pulmonary hypertension (CTEPH) give patients an increasing array of treatment options. Despite these many advances, lung transplantation remains the definitive treatment for patients with disease refractory to or progressing on best medical therapy. As our understanding of medical therapy has advanced, so to have best practices for lung transplantation. Recipient selection and approach to organ transplantation techniques have continuously evolved. Mechanical circulatory support has become increasingly employed to bridge patients through lung transplantation in the immediate post transplantation recovery. In this review, we give a history of lung transplantation for PH, an overview of PH, discuss current best practices and look to the future for insights into the care of these patients.

Pulmonary Arterial Hypertension in Patients Infected with the Human Immunodeficiency Virus

It is important to recognize and treat human immunodeficiency virus-associated pulmonary arterial hypertension (HIV-PAH) because of the associated morbidity and mortality. With the introduction of antiretroviral therapies (ART), improved survival has changed the focus of treatment management from immunodeficiency-related opportunistic infections to chronic cardiovascular complications, including HIV-PAH. The 2018 6th World Symposium of Pulmonary Hypertension recommended a revised definition of PAH that might result in a greater number of patients with HIV-PAH; however, the implication of this change is not yet clear. Here, we review the current literature on the diagnosis, management, and outcomes of patients with HIV-PAH.

Advances in the management of pulmonary arterial hypertension

The management of pulmonary arterial hypertension (PAH) has significantly evolved over the last decades in the wake of more sensitive diagnostics and specialized clinical programs that can provide focused medical care. In the current era of PAH care, 1-year survival rates have increased to 86%–90% from 65% in the 1980s, and average long-term survival has increased to 6 years from 2.8 years. The heterogeneity in the etiology and disease course has opened doors to focusing research in phenotyping the disease and understanding the pathophysiology at a cellular and genetic level. This may eventually lead to precision medicine and the development of medications that may prevent or reverse pulmonary vascular remodeling. With more insight, clinical trial designs and primary end-points may change to identify the true survival benefit of pharmacotherapy. Identifying responders from non-responders to therapy may help provide individualized patient-centered care rather than an algorithm-based approach. The purpose of this review is to highlight the latest advances in screening, diagnosis, and management of PAH.

Sex Differences, Estrogen Metabolism and Signaling in the Development of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a complex and devastating disease with a poor long-term prognosis. While women are at increased risk for developing PAH, they exhibit superior right heart function and higher survival rates than men. Susceptibility to disease risk in PAH has been attributed, in part, to estrogen signaling. In contrast to potential pathological influences of estrogen in patients, studies of animal models reveal estrogen demonstrates protective effects in PAH. Consistent with this latter observation, an ovariectomy in female rats appears to aggravate the condition. This discrepancy between observations from patients and animal models is often called the "estrogen paradox." Further, the tissue-specific interactions between estrogen, its metabolites and receptors in PAH and right heart function remain complex; nonetheless, these relationships are essential to characterize to better understand PAH pathophysiology and to potentially develop novel therapeutic and curative targets. In this review, we explore estrogen-mediated mechanisms that may further explain this paradox by summarizing published literature related to: (1) the synthesis and catabolism of estrogen; (2) activity and functions of the various estrogen receptors; (3) the multiple modalities of estrogen signaling in cells; and (4) the role of estrogen and its diverse metabolites on the susceptibility to, and progression of, PAH as well as their impact on right heart function.

Insights from the Menstrual Cycle in Pulmonary Arterial Hypertension

Rationale: Sex hormones play a role in pulmonary arterial hypertension (PAH), but the menstrual cycle has never been studied.Objectives: We conducted a prospective observational study of eight women with stable PAH and 20 healthy controls over one cycle.Methods: Participants completed four study visits 1 week apart starting on the first day of menstruation. Relationships between sex hormones, hormone metabolites, and extracellular vesicle microRNA (miRNA) expression and clinical markers were compared with generalized linear mixed modeling.Results: Women with PAH had higher but less variable estradiol (E2) levels (P < 0.001) that tracked with 6-minute walk distance (P < 0.001), N-terminal prohormone of brain natriuretic peptide (P = 0.03) levels, and tricuspid annular plane systolic excursion (P < 0.01); the direction of these associations depended on menstrual phase. Dehydroepiandrosterone sulfate (DHEA-S) levels were lower in women with PAH (all visits, P < 0.001). In PAH, each 100-μg/dl increase in DHEA-S was associated with a 127-m increase in 6-minute walk distance (P < 0.001) and was moderated by the cardioprotective E2 metabolite 2-methoxyestrone (P < 0.001). As DHEA-S increased, N-terminal prohormone of brain natriuretic peptide levels decreased (P = 0.001). Expression of extracellular vesicle miRNAs-21, -29c, and -376a was higher in PAH, moderated by E2 and DHEA-S levels, and tracked with hormone-associated changes in clinical measures.Conclusions: Women with PAH have fluctuations in cardiopulmonary function during menstruation driven by E2 and DHEA-S. These hormones in turn influence transcription of extracellular vesicle miRNAs implicated in the pathobiology of pulmonary vascular disease and cancer.

Identifying Potential Mutations Responsible for Cases of Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive and devastating disease for which there is an escalating body of genetic and related pathophysiological information on disease pathobiology. Nevertheless, the success to date in identifying susceptibility genes, genetic variants and epigenetic processes has been limited due to PAH clinical multi-faceted variations. A number of germline gene candidates have been proposed but demonstrating consistently the association with PAH has been problematic, at least partly due to the reduced penetrance and variable expressivity. Although the data for bone morphogenetic protein receptor type 2 (BMPR2) and related genes remains undoubtedly the most extensive, recent advanced gene sequencing technologies have facilitated the discovery of further gene candidates with mutations among those with and without familial forms of PAH. An in depth understanding of the multitude of biologic variations associated with PAH may provide novel opportunities for therapeutic intervention in the coming years. This knowledge will irrevocably provide the opportunity for improved patient and family counseling as well as improved PAH diagnosis, risk assessment, and personalized treatment.

Sex Differences in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) occurs in women more than men whereas survival in men is worse than in women. In recent years, much research has been carried out to understand these sex differences in PAH. This article discusses clinical and preclinical studies that have investigated the influences of sex, serotonin, obesity, estrogen, estrogen synthesis, and estrogen metabolism on bone morphogenetic protein receptor type II signaling, the pulmonary circulation and right ventricle in both heritable and idiopathic pulmonary hypertension.

The Evolution in Nomenclature, Diagnosis, and Classification of Pulmonary Hypertension

The current description of pulmonary hypertension is a testament to the physicians and scientists who dedicated their lives to furthering understanding of the pulmonary circulation. This has spanned a millennium, from ancient Egyptian descriptions of human anatomy to the current molecular and hemodynamic phenotyping of pulmonary hypertension. The recent Sixth World Symposium on Pulmonary Hypertension is a direct result of these discoveries and reflects an evolution in a classification scheme that has spanned half a century. This provides a framework for future directions related to therapeutics and mechanisms of disease.

Contemporary Pharmacotherapeutic Approach in Pulmonary Arterial Hypertension

Since the 1973 World Symposium on Pulmonary Hypertension, advancements in the understanding of pathophysiology and pathobiology have led to a myriad of pharmacotherapies for the disease. This article journeys through the development of therapeutic approaches for pulmonary arterial hypertension.

Transplant Operative Considerations in Pulmonary Hypertension With Severe Right Heart Failure

Over the past several decades, the operation of choice for end-stage lung disease secondary to severe pulmonary hypertension (PH) has shifted from heart-lung transplantation (HLT) to bilateral lung transplantation (BLT). This change has maintained excellent long-term outcomes and is appropriate for the majority of patients presenting with end-stage disease in need of transplantation. However, a distinct subset of patients with severe PH have an excessive early mortality within 90 days of transplantation. Based on the different causes of this early mortality compared to BLT recipients with other indications, right heart failure and refractory primary graft dysfunction appear to play a significant role. It is therefore critical to identify this subset of patient during their evaluation for transplant. This distinction would allow specific patient referral for HLT, which may mitigate those causes of early mortality. Similarly, there is a subgroup of BLT recipients for severe PH that fail to recover right ventricular function, with suboptimal long-term functional status that is independent of early survival. Identification and referral for HLT of these patients may also be important. In this manuscript, we describe our institutional approach and consideration for the risks of early mortality from right heart failure and primary graft dysfunction, as well failure of right ventricular recovery long term. The described evaluation is used to ascertain those patients with severe PH who may benefit from an HLT over BLT.

Pulmonary hypertension: From an orphan disease to a global epidemic

[No abstract. Showing first paragraph of article]Pulmonary hypertension is a progressive disease characterized by an elevation of pulmonary artery pressure and pulmonary vascular resistance, leading to right ventricular failure and death. It remains a challenging chronic progressive disease, but the current interest and advent of medical therapy in the last 20 years has significantly changed the perception of medical community in this disease. Pulmonary hypertension is not a specific disease; the majority of cases present with other diseases and various pathological processes that affect the pulmonary vasculature, and consequently increase pulmonary pressure and vascular resistance.

Molecular genetic framework underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare, progressive disorder typified by occlusion of the pulmonary arterioles owing to endothelial dysfunction and uncontrolled proliferation of pulmonary artery smooth muscle cells and fibroblasts. Vascular occlusion can lead to increased pressure in the pulmonary arteries, often resulting in right ventricular failure with shortness of breath and syncope. Since the identification of BMPR2, which encodes a receptor in the transforming growth factor-β superfamily, the development of high-throughput sequencing approaches to identify novel causal genes has substantially advanced our understanding of the molecular genetics of PAH. In the past 6 years, additional pathways involved in PAH susceptibility have been described through the identification of deleterious genetic variants in potassium channels (KCNK3 and ABCC8) and transcription factors (TBX4 and SOX17), among others. Although familial PAH most often has an autosomal-dominant pattern of inheritance, cases of incomplete penetrance and evidence of genetic heterogeneity support a model of PAH as a Mendelian disorder with complex disease features. In this Review, we outline the latest advances in the detection of rare and common genetic variants underlying PAH susceptibility and disease progression. These findings have clinical implications for lung vascular function and can help to identify mechanistic pathways amenable to pharmacological intervention.

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.

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.

Gender Difference in Damage-Mediated Signaling Contributes to Pulmonary Arterial Hypertension

Aims: Pulmonary arterial hypertension (PAH) is a progressive lethal disease with a known gender dimorphism. Female patients are more susceptible to PAH, whereas male patients have a lower survival rate. Initial pulmonary vascular damage plays an important role in PAH pathogenesis. Therefore, this study aimed at investigating the role of gender in activation of apoptosis/necrosis-mediated signaling pathways in PAH. Results: The media collected from pulmonary artery endothelial cells (PAECs) that died by necrosis or apoptosis were used to treat naive PAECs. Necrotic cell death stimulated phosphorylation of toll-like receptor 4, accumulation of interleukin 1 beta, and expression of E-selectin in a redox-dependent manner; apoptosis did not induce any of these effects. In the animal model of severe PAH, the necrotic marker, high mobility group box 1 (HMGB1), was visualized in the pulmonary vascular wall of male but not female rats. This vascular necrosis was associated with male-specific redox changes in plasma, activation of the same inflammatory signaling pathway seen in response to necrosis in vitro, and an increased endothelial-leukocyte adhesion in small pulmonary arteries. In PAH patients, gender-specific changes in redox homeostasis correlated with the prognostic marker, B-type natriuretic peptide. Males had also shown elevated circulating levels of HMGB1 and pro-inflammatory changes. Innovation: This study discovered the role of gender in the initiation of damage-associated signaling in PAH and highlights the importance of the gender-specific approach in PAH therapy. Conclusion: In PAH, the necrotic cell death is augmented in male patients compared with female patients. Factors released from necrotic cells could alter redox homeostasis and stimulate inflammatory signaling pathways.

United States Pulmonary Hypertension Scientific Registry (USPHSR): rationale, design, and clinical implications

Diagnostic World Health Organization (WHO) Group 1 pulmonary arterial hypertension (PAH) and Diagnostic Group 1' pulmonary veno-occlusive disease (PVOD) and/or pulmonary capillary hemangiomatosis (PCH) are progressive and fatal disorders. Past registries provided important insights into these disorders, but did not include hormonal exposures or genomic data. The United States Pulmonary Hypertension Scientific Registry (USPHSR) will provide demographic, physiologic, anorexigen and hormone exposure, genomic, and survival data in the current therapeutic era for 499 patients diagnosed with PAH, PVOD, or PCH. The USPHSR also will explore the relationship between pharmacologic, non-pharmacologic, and dietary hormonal exposures and the increased risk for women to develop idiopathic or heritable PAH.

Thin Air, Thick Vessels: Historical and Current Perspectives on Hypoxic Pulmonary Hypertension

The association between pulmonary hypertension (PH) and hypoxia is well-established, with two key mechanistic processes, hypoxic pulmonary vasoconstriction and hypoxia-induced vascular remodeling, driving changes in pulmonary arterial pressure. In contrast to other forms of pulmonary hypertension, the vascular changes induced by hypoxia are reversible, both in humans returning to sea-level from high altitude and in animal models. This raises the intriguing possibility that the molecular drivers of these hypoxic processes could be targeted to modify pulmonary vascular remodeling in other contexts. In this review, we outline the history of research into PH and hypoxia, before discussing recent advances in our understanding of this relationship at the molecular level, focussing on the role of the oxygen-sensing transcription factors, hypoxia inducible factors (HIFs). Emerging links between HIF and vascular remodeling highlight the potential utility in inhibiting this pathway in pulmonary hypertension and raise possible risks of activating this pathway using HIF-stabilizing medications.

Genetic linkage analysis of a large family identifies FIGN as a candidate modulator of reduced penetrance in heritable pulmonary arterial hypertension

BACKGROUND

Mapping the genetic component of molecular mechanisms responsible for the reduced penetrance (RP) of rare disorders constitutes one of the most challenging problems in human genetics. Heritable pulmonary arterial hypertension (PAH) is one such disorder characterised by rare mutations mostly occurring in the bone morphogenetic protein receptor type 2 (BMPR2) gene and a wide heterogeneity of penetrance modifier mechanisms. Here, we analyse 32 genotyped individuals from a large Iberian family of 65 members, including 22 carriers of the pathogenic BMPR2 mutation c.1472G>A (p.Arg491Gln), 8 of them diagnosed with PAH by right-heart catheterisation, leading to an RP rate of 36.4%.

METHODS

We performed a linkage analysis on the genotyping data to search for genetic modifiers of penetrance. Using functional genomics data, we characterised the candidate region identified by linkage analysis. We also predicted the haplotype segregation within the family.

RESULTS

We identified a candidate chromosome region in 2q24.3, 38 Mb upstream from BMPR2, with significant linkage (LOD=4.09) under a PAH susceptibility model. This region contains common variants associated with vascular aetiology and shows functional evidence that the putative genetic modifier is located in the upstream distal promoter of the fidgetin (FIGN) gene.

CONCLUSION

Our results suggest that the genetic modifier acts through FIGN transcriptional regulation, whose expression variability would contribute to modulating heritable PAH. This finding may help to advance our understanding of RP in PAH across families sharing the p.Arg491Gln pathogenic mutation in BMPR2.

The Role of Sex in the Pathophysiology of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by increased pulmonary vascular resistance and pulmonary artery remodelling as result of increased vascular tone and vascular cell proliferation, respectively. Eventually, this leads to right heart failure. Heritable PAH is caused by a mutation in the bone morphogenetic protein receptor-II (BMPR-II). Female susceptibility to PAH has been known for some time, and most recent figures show a female-to-male ratio of 4:1. Variations in the female sex hormone estrogen and estrogen metabolism modify FPAH risk, and penetrance of the disease in BMPR-II mutation carriers is increased in females. Several lines of evidence point towards estrogen being pathogenic in the pulmonary circulation, and thus increasing the risk of females developing PAH. Recent studies have also suggested that estrogen metabolism may be crucial in the development and progression of PAH with studies indicating that downstream metabolites such as 16α-hydroxyestrone are upregulated in several forms of experimental pulmonary hypertension (PH) and can cause pulmonary artery smooth muscle cell proliferation and subsequent vascular remodelling. Conversely, other estrogen metabolites such as 2-methoxyestradiol have been shown to be protective in the context of PAH. Estrogen may also upregulate the signalling pathways of other key mediators of PAH such as serotonin.

Pulmonary Arterial Hypertension

This article provides an overview of pulmonary arterial hypertension (PAH), beginning with the initial pathologic recognition of pulmonary hypertension more than 100 years ago and progressing to the current diagnostic categorization of PAH. It reviews the epidemiology, pathophysiology, genetics, and modern treatment of PAH. The article discusses several important recent studies that have highlighted the importance of new management strategies, including serial risk assessment and combination pharmacotherapy.

Pulmonary Arterial Hypertension and the Sex Hormone Paradox

PURPOSE OF REVIEW

Prevalence and outcome differences between women and men with pulmonary arterial hypertension (PAH) raise questions about the role of sex hormones in disease pathobiology. This review will summarize the current understanding of sex and sex hormone pathways and their influence on heart-lung function in health and in disease.

RECENT FINDINGS

Female sex has been shown to be a risk factor for the development of PAH, but women have improved survival compared to men with PAH. These paradoxical observations are likely driven in part by complex sex hormone signaling and processing pathways and their interaction with the pulmonary vasculature and the right ventricle. These relationships may vary depending on an individual's underlying sex, age, and/or genetic substrate. The study of the connections between sex, sex hormones, the pulmonary circulation, and the right ventricle may improve our understanding of disease epidemiology and outcomes and lead to new treatment strategies for PAH.

Mitochondrial dysfunction and pulmonary hypertension: cause, effect, or both

Pulmonary hypertension describes a heterogeneous disease defined by increased pulmonary artery pressures, and progressive increase in pulmonary vascular resistance due to pathologic remodeling of the pulmonary vasculature involving pulmonary endothelial cells, pericytes, and smooth muscle cells. This process occurs under various conditions, and although these populations vary, the clinical manifestations are the same: progressive dyspnea, increases in right ventricular (RV) afterload and dysfunction, RV-pulmonary artery uncoupling, and right-sided heart failure with systemic circulatory collapse. The overall estimated 5-yr survival rate is 72% in highly functioning patients, and as low as 28% for those presenting with advanced symptoms. Metabolic theories have been suggested as underlying the pathogenesis of pulmonary hypertension with growing evidence of the role of mitochondrial dysfunction involving the major proteins of the electron transport chain, redox-related enzymes, regulators of the proton gradient and calcium homeostasis, regulators of apoptosis, and mitophagy. There remain more studies needed to characterize mitochondrial dysfunction leading to impaired vascular relaxation, increase proliferation, and failure of regulatory mechanisms. The effects on endothelial cells and resulting interactions with their microenvironment remain uncharted territory for future discovery. Additionally, on the basis of observations that the "plexigenic lesions" of pulmonary hypertension resemble the unregulated proliferation of tumor cells, similarities between cancer pathobiology and pulmonary hypertension have been drawn, suggesting interactions between mitochondria and angiogenesis. Recently, mitochondria targeting has become feasible, which may yield new therapeutic strategies. We present a state-of-the-art review of the role of mitochondria in both the pathobiology of pulmonary hypertension and potential therapeutic targets in pulmonary vascular processes.

Genetics of Pulmonary Arterial Hypertension

Tremendous progress has been made in understanding the genetics of pulmonary arterial hypertension (PAH) since its description in the 1950s as a primary disorder of the pulmonary vasculature. Heterozygous germline mutations in the gene coding bone morphogenetic receptor type 2 (BMPR2) are detectable in the majority of cases of heritable PAH, and in approximately 20% of cases of idiopathic pulmonary arterial hypertension (IPAH). However, recent advances in gene discovery methods have facilitated the discovery of additional genes with mutations among those with and without familial PAH. Heritable PAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, and female predominance. Biallelic germline mutations in the gene EIF2AK4 are now associated with pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis. Growing genetic knowledge enhances our capacity to pursue and provide genetic counseling, although the issue remains complex given that the majority of carriers of PAH-related mutations will never be diagnosed with the disease.

Anastrozole in Pulmonary Arterial Hypertension. A Randomized, Double-Blind, Placebo-controlled Trial

RATIONALE

The aromatase inhibitor anastrozole blocks the conversion of androgens to estrogen and blunts pulmonary hypertension in animals, but its efficacy in treating patients with pulmonary arterial hypertension (PAH) is unknown.

OBJECTIVES

We aimed to determine the safety and efficacy of anastrozole in PAH.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of anastrozole in patients with PAH who received background therapy at two centers.

MEASUREMENTS AND MAIN RESULTS

A total of 18 patients with PAH were randomized to anastrozole 1 mg or matching placebo in a 2:1 ratio. The two co-primary outcomes were percent change from baseline in 17β-estradiol levels (E2) and tricuspid annular plane systolic excursion (TAPSE) at 3 months. Anastrozole significantly reduced E2 levels compared with placebo (percent change: -40%; interquartile range [IQR], -61 to -26% vs. -4%; IQR, -14 to +4%; P = 0.003), but there was no difference in TAPSE. Anastrozole significantly increased the 6-minute-walk distance (median change = +26 m) compared with placebo (median change = -12 m) (median percent change: anastrozole group, 8%; IQR, 2 to 17% vs. placebo -2%; IQR, -7 to +1%; P = 0.042). Anastrozole had no effect on circulating biomarkers, functional class, or health-related quality of life. There was no difference in adverse events.

CONCLUSIONS

Anastrozole significantly reduced E2 levels in patients with PAH but had no effect on TAPSE. Anastrozole was safe, well tolerated, and improved 6-minute-walk distance in this small "proof-of-principle" study. Larger and longer phase II clinical trials of anastrozole may be warranted in patients with PAH. Clinical trial registered with www.clinicaltrials.gov (NCT 1545336).

Vasodilator responsiveness in idiopathic pulmonary arterial hypertension: identifying a distinct phenotype with distinct physiology and distinct prognosis

Within the cohort of patients suffering from idiopathic pulmonary arterial hypertension (IPAH) is a group that responds dramatically (VR-PAH) to an acute vasodilator challenge and that has excellent long-term hemodynamic improvement and prognosis on high dose calcium channel blockers compared with vasodilator non-responders (VN-PAH). For the purposes of diagnosing VR-PAH, there is to date no test to replace the acute vasodilator challenge. However, recent studies have identified markers that may aid in the identification of VR-PAH, including peripheral blood lymphocyte RNA expression levels of desmogelin-2 and Ras homolog gene family member Q, and plasma levels of provirus integration site for Moloney murine leukemia virus. Genome wide-array studies of peripheral blood DNA have demonstrated differences in disease specific genetic variants between VR-PAH and NR-PAH, with particular convergence on cytoskeletal function pathways and Wnt signaling pathways. These studies offer hope for future non-invasive identification of VR-PAH, and insights into pathogenesis that may lead to novel therapies. Examination of the degree of pulmonary microvascular perfusion in PAH has offered additional insights. During the acute vasodilator challenge, VR-PAH patients demonstrate true vasodilation with recruitment and increased perfusion of the capillary bed, while VN-PAH patients are unable to recruit vasculature. In the very few reports of lung histology, VR-PAH has more medial thickening in the precapillary arterioles, while VN-PAH has the classic histology of PAH, including intimal thickening. VR-PAH is a disorder with a phenotype distinct from VN-PAH and other types of PAH, and should be considered separately in the classification of PAH.

Emerging Metabolic Therapies in Pulmonary Arterial Hypertension

Pulmonary hypertension (PH) is an enigmatic vascular disorder characterized by pulmonary vascular remodeling and increased pulmonary vascular resistance, ultimately resulting in pressure overload, dysfunction, and failure of the right ventricle. Current medications for PH do not reverse or prevent disease progression, and current diagnostic strategies are suboptimal for detecting early-stage disease. Thus, there is a substantial need to develop new diagnostics and therapies that target the molecular origins of PH. Emerging investigations have defined metabolic aberrations as fundamental and early components of disease manifestation in both pulmonary vasculature and the right ventricle. As such, the elucidation of metabolic dysregulation in pulmonary hypertension allows for greater therapeutic insight into preventing, halting, or even reversing disease progression. This review will aim to discuss (1) the reprogramming and dysregulation of metabolic pathways in pulmonary hypertension; (2) the emerging therapeutic interventions targeting these metabolic pathways; and (3) further innovation needed to overcome barriers in the treatment of this devastating disease.

The Evolving Classification of Pulmonary Hypertension

CONTEXT

- An explosion of information on pulmonary hypertension has occurred during the past few decades. The perception of this disease has shifted from purely clinical to incorporate new knowledge of the underlying pathology. This transfer has occurred in light of advancements in pathophysiology, histology, and molecular medical diagnostics.

OBJECTIVES

- To update readers about the evolving understanding of the etiology and pathogenesis of pulmonary hypertension and to demonstrate how pathology has shaped the current classification.

DATA SOURCES

- Information presented at the 5 World Symposia on pulmonary hypertension held since 1973, with the last meeting occurring in 2013, was used in this review.

CONCLUSIONS

- Pulmonary hypertension represents a heterogeneous group of disorders that are differentiated based on differences in clinical, hemodynamic, and histopathologic features. Early concepts of pulmonary hypertension were largely influenced by pharmacotherapy, hemodynamic function, and clinical presentation of the disease. The initial nomenclature for pulmonary hypertension segregated the clinical classifications from pathologic subtypes. Major restructuring of this disease classification occurred between the first and second symposia, which was the first to unite clinical and pathologic information in the categorization scheme. Additional changes were introduced in subsequent meetings, particularly between the third and fourth World Symposia meetings, when additional pathophysiologic information was gained. Discoveries in molecular diagnostics significantly progressed the understanding of idiopathic pulmonary arterial hypertension. Continued advancements in imaging modalities, mechanistic pathogenicity, and molecular biomarkers will enable physicians to define pulmonary hypertension phenotypes based on the pathobiology and allow for treatment customization.

Regulation and function of miR-214 in pulmonary arterial hypertension

Dysregulation of microRNAs (miRNAs) can contribute to the etiology of diseases, including pulmonary arterial hypertension (PAH). Here we investigated a potential role for the miR-214 stem loop miRNA and the closely linked miR-199a miRNAs in PAH. All 4 miRNAs were upregulated in the lung and right ventricle (RV) in mice and rats exposed to the Sugen (SU) 5416 hypoxia model of PAH. Further, expression of the miRNAs was increased in pulmonary artery smooth muscle cells exposed to transforming growth factor β1 but not BMP4. We then examined miR-214(-/-) mice exposed to the SU 5416 hypoxia model of PAH or normoxic conditions and littermate controls. There were no changes in RV systolic pressure or remodeling observed between the miR-214(-/-) and wild-type hypoxic groups. However, we observed a significant increase in RV hypertrophy (RVH) in hypoxic miR-214(-/-) male mice compared with controls. Further, we identified that the validated miR-214 target phosphatase and tensin homolog was upregulated in miR-214(-/-) mice. Thus, miR-214 stem loop loss leads to elevated RVH and may contribute to the heart failure associated with PAH.

Clinical use of extended-release oral treprostinil in the treatment of pulmonary arterial hypertension

The development of parenteral prostacyclin therapy marked a dramatic breakthrough in the treatment of pulmonary arterial hypertension (PAH). Intravenous (IV) epoprostenol was the first PAH specific therapy and to date, remains the only treatment to demonstrate a mortality benefit. Because of the inherent complexities and risks of treating patients with continuous infusion IV therapy, there is great interest in the development of an oral prostacyclin analog that could mimic the benefits of IV therapy. Herein, we highlight the development of oral prostacyclin therapy, focusing on oral treprostinil, the only US Food and Drug Administration approved oral prostacyclin. Recent Phase III clinical trials have shown the drug to improve exercise tolerance in treatment-naïve PAH patients, but not patients on background oral therapy. Oral treprostinil appears to be most efficacious at higher doses, but its side effect profile and complexities with dosing complicate its use. While oral treprostinil’s current therapeutic role in PAH remains unclear, ongoing studies of this class of medication should help clarify their role in the treatment of PAH.

Epidemiology of pulmonary arterial hypertension

The epidemiology of pulmonary arterial hypertension (PAH) has changed over the last decade. Remarkable advances in understanding the pathobiology and clinical care required in PAH have resulted in improved quality of life and survival. Despite such important progress, the long-term rate of survival is still unacceptable. The epidemiology of PAH could not be easily generalized globally, due to the fact that nearly all of the present data has been gathered from Western, multicenter, prospective registries. There are potentially marked differences in PAH patients from Western and Eastern populations, and from developed and developing countries. Therefore, it is clear that more registry data will be needed to address novel questions emerging with improved knowledge of PAH.

The genetics of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease for which there is an ever-expanding body of genetic and related pathophysiological information on disease pathogenesis. Many germline gene mutations have now been described, including mutations in the gene coding bone morphogenic protein receptor type 2 (BMPR2) and related genes. Recent advanced gene-sequencing methods have facilitated the discovery of additional genes with mutations among those with and those without familial forms of PAH (CAV1, KCNK3, EIF2AK4). The reduced penetrance, variable expressivity, and female predominance of PAH suggest that genetic, genomic, and other factors modify disease expression. These multi-faceted variations are an active area of investigation in the field, including but not limited to common genetic variants and epigenetic processes, and may provide novel opportunities for pharmacological intervention in the near future. They also highlight the need for a systems-oriented multi-level approach to incorporate the multitude of biological variations now associated with PAH. Ultimately, an in-depth understanding of the genetic factors relevant to PAH provides the opportunity for improved patient and family counseling about this devastating disease.

Pharmacologic therapy for pulmonary arterial hypertension in adults: CHEST guideline and expert panel report

OBJECTIVE

Choices of pharmacologic therapies for pulmonary arterial hypertension (PAH) are ideally guided by high-level evidence. The objective of this guideline is to provide clinicians advice regarding pharmacologic therapy for adult patients with PAH as informed by available evidence.

METHODS

This guideline was based on systematic reviews of English language evidence published between 1990 and November 2013, identified using the MEDLINE and Cochrane Library databases. The strength of available evidence was graded using the Grades of Recommendations, Assessment, Development, and Evaluation methodology. Guideline recommendations, or consensus statements when available evidence was insufficient to support recommendations, were developed using a modified Delphi technique to achieve consensus.

RESULTS

Available evidence is limited in its ability to support high-level recommendations. Therefore, we drafted consensus statements to address many clinical questions regarding pharmacotherapy for patients with PAH. A total of 79 recommendations or consensus statements were adopted and graded.

CONCLUSIONS

Clinical decisions regarding pharmacotherapy for PAH should be guided by high-level recommendations when sufficient evidence is available. Absent higher level evidence, consensus statements based upon available information must be used. Further studies are needed to address the gaps in available knowledge regarding optimal pharmacotherapy for PAH.

Transient but not genetic loss of miR-451 is protective in the development of pulmonary arterial hypertension

MicroRNAs are small noncoding RNAs involved in the regulation of gene expression and have recently been implicated in the development of pulmonary arterial hypertension (PAH). Previous work has established that miR-451 is upregulated in rodent models of PAH. The role of miR-451 in the pulmonary circulation is unknown. We therefore sought to assess the involvement of miR-451 in the development of PAH. Silencing of miR-451 was performed in vivo using miR-451 knockout mice and an anti-miR targeting mature miR-451 in rats. Coupled with exposure to hypoxia, indices of PAH were assessed. The effect of modulating miR-451 on human pulmonary artery smooth muscle cell proliferation and migration was analyzed. We observed a reduction in systolic right ventricular pressure in hypoxic rats pretreated with anti-miR-451 compared with hypoxia alone ([Formula: see text] mmHg and [Formula: see text] mmHg, respectively; [Formula: see text]). In miR-451 knockout mice, compared with wild-type hypoxic mice, no significant differences were observed following exposure to chronic hypoxia. In vitro analysis demonstrated that overexpression of miR-451 in human pulmonary artery smooth muscle cells promoted migration under serum-free conditions. No effect on cellular proliferation was observed. In conclusion, transient inhibition of miR-451 attenuated the development of PAH in hypoxia-exposed rats. Genetic deletion of miR-451 had no beneficial effect on indices of PAH, potentially because of pathway redundancy compensating for the loss of miR-451.