Autoimmunity Is a Significant Feature of Idiopathic Pulmonary Arterial Hypertension.

Rationale: Autoimmunity is believed to play a role in idiopathic pulmonary arterial hypertension (IPAH). It is not clear whether this is causative or a bystander of disease and if it carries any prognostic or treatment significance. Objectives: To study autoimmunity in IPAH using a large cross-sectional cohort. Methods: Assessment of the circulating immune cell phenotype was undertaken using flow cytometry, and the profile of serum immunoglobulins was generated using a standardized multiplex array of 19 clinically validated autoantibodies in 473 cases and 946 control subjects. Additional glutathione S-transferase fusion array and ELISA data were used to identify a serum autoantibody to BMPR2 (bone morphogenetic protein receptor type 2). Clustering analyses and clinical correlations were used to determine associations between immunogenicity and clinical outcomes. Measurements and Main Results: Flow cytometric immune profiling demonstrates that IPAH is associated with an altered humoral immune response in addition to raised IgG3. Multiplexed autoantibodies were significantly raised in IPAH, and clustering demonstrated three distinct clusters: "high autoantibody," "low autoantibody," and a small "intermediate" cluster exhibiting high concentrations of ribonucleic protein complex. The high-autoantibody cluster had worse hemodynamics but improved survival. A small subset of patients demonstrated immunoglobulin reactivity to BMPR2. Conclusions: This study establishes aberrant immune regulation and presence of autoantibodies as key features in the profile of a significant proportion of patients with IPAH and is associated with clinical outcomes.

Diagnostic test accuracy of artificial intelligence analysis of cross-sectional imaging in pulmonary hypertension: a systematic literature review.

OBJECTIVES: To undertake the first systematic review examining the performance of artificial intelligence (AI) applied to cross-sectional imaging for the diagnosis of acquired pulmonary arterial hypertension (PAH). METHODS: Searches of Medline, Embase and Web of Science were undertaken on 1 July 2020. Original publications studying AI applied to cross-sectional imaging for the diagnosis of acquired PAH in adults were identified through two-staged double-blinded review. Study quality was assessed using the Quality Assessment of Diagnostic Accuracy Studies and Checklist for Artificial Intelligence in Medicine frameworks. Narrative synthesis was undertaken following Synthesis Without Meta-Analysis guidelines. This review received no funding and was registered in the International Prospective Register of Systematic Reviews (ID:CRD42020196295). RESULTS: Searches returned 476 citations. Three retrospective observational studies, published between 2016 and 2020, were selected for data-extraction. Two methods applied to cardiac-MRI demonstrated high diagnostic accuracy, with the best model achieving AUC=0.90 (95% CI: 0.85-0.93), 89% sensitivity and 81% specificity. Stronger results were achieved using cardiac-MRI for classification of idiopathic PAH, achieving AUC=0.97 (95% CI: 0.89-1.0), 96% sensitivity and 87% specificity. One study reporting CT-based AI demonstrated lower accuracy, with 64.6% sensitivity and 97.0% specificity. CONCLUSIONS: Automated methods for identifying PAH on cardiac-MRI are emerging with high diagnostic accuracy. AI applied to cross-sectional imaging may provide non-invasive support to reduce diagnostic delay in PAH. This would be helped by stronger solutions in other modalities. ADVANCES IN KNOWLEDGE: There is a significant shortage of research in this important area. Early detection of PAH would be supported by further research advances on the promising emerging technologies identified.

Bayesian Inference Associates Rare KDR Variants with Specific Phenotypes in Pulmonary Arterial Hypertension.

Background - Approximately 25% of patients with pulmonary arterial hypertension (PAH) have been found to harbor rare mutations in disease-causing genes. To identify missing heritability in PAH we integrated deep phenotyping with whole-genome sequencing data using Bayesian statistics. Methods - We analyzed 13,037 participants enrolled in the NIHR BioResource - Rare Diseases (NBR) study, of which 1,148 were recruited to the PAH domain. To test for genetic associations between genes and selected phenotypes of pulmonary hypertension (PH), we used the Bayesian rare-variant association method BeviMed. Results - Heterozygous, high impact, likely loss-of-function variants in the Kinase Insert Domain Receptor (KDR) gene were strongly associated with significantly reduced transfer coefficient for carbon monoxide (KCO, posterior probability (PP)=0.989) and older age at diagnosis (PP=0.912). We also provide evidence for familial segregation of a rare nonsense KDR variant with these phenotypes. On computed tomographic imaging of the lungs, a range of parenchymal abnormalities were observed in the five patients harboring these predicted deleterious variants in KDR. Four additional PAH cases with rare likely loss-of-function variants in KDR were independently identified in the US PAH Biobank cohort with similar phenotypic characteristics. Conclusions - The Bayesian inference approach allowed us to independently validate KDR, which encodes for the Vascular Endothelial Growth Factor Receptor 2 (VEGFR2), as a novel PAH candidate gene. Furthermore, this approach specifically associated high impact likely loss-of-function variants in the genetically constrained gene with distinct phenotypes. These findings provide evidence for KDR being a clinically actionable PAH gene and further support the central role of the vascular endothelium in the pathobiology of PAH.

Characterization of GDF2 Mutations and Levels of BMP9 and BMP10 in Pulmonary Arterial Hypertension.

Rationale: Recently, rare heterozygous mutations in GDF2 were identified in patients with pulmonary arterial hypertension (PAH). GDF2 encodes the circulating BMP (bone morphogenetic protein) type 9, which is a ligand for the BMP2 receptor.Objectives: Here we determined the functional impact of GDF2 mutations and characterized plasma BMP9 and BMP10 levels in patients with idiopathic PAH.Methods: Missense BMP9 mutant proteins were expressed in vitro and the impact on BMP9 protein processing and secretion, endothelial signaling, and functional activity was assessed. Plasma BMP9 and BMP10 levels and activity were assayed in patients with PAH with GDF2 variants and in control subjects. Levels were also measured in a larger cohort of control subjects (n = 120) and patients with idiopathic PAH (n = 260).Measurements and Main Results: We identified a novel rare variation at the GDF2 and BMP10 loci, including copy number variation. In vitro, BMP9 missense proteins demonstrated impaired cellular processing and secretion. Patients with PAH who carried these mutations exhibited reduced plasma levels of BMP9 and reduced BMP activity. Unexpectedly, plasma BMP10 levels were also markedly reduced in these individuals. Although overall BMP9 and BMP10 levels did not differ between patients with PAH and control subjects, BMP10 levels were lower in PAH females. A subset of patients with PAH had markedly reduced plasma levels of BMP9 and BMP10 in the absence of GDF2 mutations.Conclusions: Our findings demonstrate that GDF2 mutations result in BMP9 loss of function and are likely causal. These mutations lead to reduced circulating levels of both BMP9 and BMP10. These findings support therapeutic strategies to enhance BMP9 or BMP10 signaling in PAH.

Traffic exposures, air pollution and outcomes in pulmonary arterial hypertension: a UK cohort study analysis.

While traffic and air pollution exposure is associated with increased mortality in numerous diseases, its association with disease severity and outcomes in pulmonary arterial hypertension (PAH) remains unknown.Exposure to particulate matter with a 50% cut-off aerodynamic diameter ≤2.5 µm (PM2.5), nitrogen dioxide (NO2) and indirect measures of traffic-related air pollution (distance to main road and length of roads within buffer zones surrounding residential addresses) were estimated for 301 patients with idiopathic/heritable PAH recruited in the UK National Cohort Study of Idiopathic and Heritable PAH. Associations with transplant-free survival and pulmonary haemodynamic severity at baseline were assessed, adjusting for confounding variables defined a prioriHigher estimated exposure to PM2.5 was associated with higher risk of death or lung transplant (unadjusted hazard ratio (HR) 2.68 (95% CI 1.11-6.47) per 3 µg·m-3; p=0.028). This association remained similar when adjusted for potential confounding variables (HR 4.38 (95% CI 1.44-13.36) per 3 µg·m-3; p=0.009). No associations were found between NO2 exposure or other traffic pollution indicators and transplant-free survival. Conversely, indirect measures of exposure to traffic-related air pollution within the 500-1000 m buffer zones correlated with the European Society of Cardiology/European Respiratory Society risk categories as well as pulmonary haemodynamics at baseline. This association was strongest for pulmonary vascular resistance.In idiopathic/heritable PAH, indirect measures of exposure to traffic-related air pollution were associated with disease severity at baseline, whereas higher PM2.5 exposure may independently predict shorter transplant-free survival.

Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a rare disorder with a poor prognosis. Deleterious variation within components of the transforming growth factor-ß pathway, particularly the bone morphogenetic protein type 2 receptor (BMPR2), underlies most heritable forms of PAH. To identify the missing heritability we perform whole-genome sequencing in 1038 PAH index cases and 6385 PAH-negative control subjects. Case-control analyses reveal significant overrepresentation of rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of a critical role for GDF2 in PAH. We demonstrate familial segregation of mutations in SOX17 and AQP1 with PAH. Mutations in GDF2, encoding a BMPR2 ligand, lead to reduced secretion from transfected cells. In addition, we identify pathogenic mutations in the majority of previously reported PAH genes, and provide evidence for further putative genes. Taken together these findings contribute new insights into the molecular basis of PAH and indicate unexplored pathways for therapeutic intervention.

Case Report: The risks associated with chronic theophylline therapy and measures designed to improve monitoring and management.

BACKGROUND: Symptoms of theophylline toxicity and factors that augment the risk of developing it are well documented in the literature. However these appear to be poorly considered in clinical practice. This case underlines the challenges in recognising and managing theophylline toxicity; moreover the requirement for improved application of knowledge of its pharmacokinetics to our practice. CASE PRESENTATION: In this case we observe how theophylline toxicity can be overlooked due to the presence of non-specific symptoms and lack of a structured system to mitigate error in detection, in both hospital medicine and general practice. Here, the initial theophylline concentration measurement was documented as 59.3 mg/l in a patient taking the medication long-term, with the previous concentration being recorded one year prior. Management consisted of suspension of theophylline along with best supportive care, however in the process other conditions were exacerbated and the patient ultimately died in hospital. Congestive cardiac failure, congestive liver disease and polypharmacy were factors isolated from this case that expedited the patients' development of theophylline toxicity. This was perpetuated by delay in diagnosis due to presentation with generalised symptoms including tachycardia, vomiting and neurological symptoms. CONCLUSIONS: Findings from this case necessitate a requirement for more stringent monitoring of theophylline when taken chronically in those who demonstrate risk factors for toxicity. This would aim to prevent accumulation of the drug, toxicity onset and subsequent acute presentation to hospital. Intervention, through charcoal haemoperfusion may provide a means of enhanced recovery to reduce sequelae of toxicity.

Endothelin ETA receptors predominate in chronic thromboembolic pulmonary hypertension.

AIMS: Endothelin-1 levels are raised in chronic thromboembolic pulmonary hypertension. Our aim in this study was to identify the presence of endothelin receptors in patients with CTEPH by analysing tissue removed at pulmonary endarterectomy. MAIN METHODS: Pulmonary endarterectomy tissue cross-sections were analysed using autoradiography with [(125)I]-ET-1 using ligands selective for ETA or ETB to determine sub-type distribution. The precise cellular localisation of ETA and ETB receptors was determined using selective antisera to both sub-types and compared with haematoxylin and eosin, Elastic Van Gieson and smooth muscle actin labelled sections. KEY FINDINGS: Two patterns of ET-1 binding were found. In sections with frequent recanalised channels, ET-1 bound to the smooth muscle cells surrounding the channels. In sections where there was less organised thrombus with no obvious re-canalisation, minimal ET-1 binding was observed. Some contractile type smooth muscle cells not associated with recanalised channels and diffusely spread throughout the PEA material were associated with ET receptor antibody binding on immunohistochemistry. There was a greater expression of the ETA receptor type in the specimens. SIGNIFICANCE: The presence of ET-1 receptors in the chronic thrombus in proximal CTEPH suggests ET-1 could act not only on the distal vasculopathy in the unobstructed vessels but may also stimulate smooth muscle cell proliferation within chronic clot. The abundance of ET receptors within the tissue provides evidence that the ET pathway is involved in the pathology of chronic thrombus reorganisation leading to CTEPH providing a rationale for the repurposing of ET receptor antagonists in the treatment of this condition.

Decreased time constant of the pulmonary circulation in chronic thromboembolic pulmonary hypertension.

This study analyzed the relationship between pulmonary vascular resistance (PVR) and pulmonary arterial compliance (Ca) in patients with idiopathic pulmonary arterial hypertension (IPAH) and proximal chronic thromboembolic pulmonary hypertension (CTEPH). It has recently been shown that the time constant of the pulmonary circulation (RC time constant), or PVR × Ca, remains unaltered in various forms and severities of pulmonary hypertension, with the exception of left heart failure. We reasoned that increased wave reflection in proximal CTEPH would be another cause of the decreased RC time constant. We conducted a retrospective analysis of invasive pulmonary hemodynamic measurements in IPAH (n = 78), proximal CTEPH (n = 91) before (pre) and after (post) pulmonary endarterectomy (PEA), and distal CTEPH (n = 53). Proximal CTEPH was defined by a postoperative mean pulmonary artery pressure (PAP) of ≤25 mmHg. Outcome measures were the RC time constant, PVR, Ca, and relationship between systolic and mean PAPs. The RC time constant for pre-PEA CTEPH was 0.49 ± 0.11 s compared with post-PEA-CTEPH (0.37 ± 0.11 s, P < 0.0001), IPAH (0.63 ± 0.14 s, P < 0.001), and distal CTEPH (0.55 ± 0.12 s, P < 0.05). A shorter RC time constant was associated with a disproportionate decrease in systolic PAP with respect to mean PAP. We concluded that the pulmonary RC time constant is decreased in proximal CTEPH compared with IPAH, pre- and post-PEA, which may be explained by increased wave reflection but also, importantly, by persistent structural changes after the removal of proximal obstructions. A reduced RC time constant in CTEPH is in accord with a wider pulse pressure and hence greater right ventricular work for a given mean PAP.