Circulating Angiopoietin-1 Is Not a Biomarker of Disease Severity or Prognosis in Pulmonary Hypertension

Cytokines as prognostic biomarkers in pulmonary arterial hypertension

BACKGROUND

Risk stratification and assessment of disease progression in patients with pulmonary arterial hypertension (PAH) are challenged by the lack of accurate disease-specific and prognostic biomarkers. To date, brain natriuretic peptide (BNP) and/or its N-terminal fragment (NT-proBNP) are the only markers for right ventricular dysfunction used in clinical practice, in association with echocardiographic and invasive haemodynamic variables to predict outcome in patients with PAH.

METHODS

This study was designed to identify an easily measurable biomarker panel in the serum of 80 well-phenotyped PAH patients with idiopathic, heritable or drug-induced PAH at baseline and at first follow-up. The prognostic value of identified cytokines of interest was secondly analysed in an external validation cohort of 125 PAH patients.

RESULTS

Among the 20 biomarkers studied with the multiplex Ella platform, we identified a three-biomarker panel composed of β-NGF, CXCL9 and TRAIL that were independently associated with prognosis both at the time of PAH diagnosis and at the first follow-up after initiation of PAH therapy. β-NGF and CXCL9 were predictors of death or transplantation, whereas high levels of TRAIL were associated with a better prognosis. Furthermore, the prognostic value of the three cytokines was more powerful for predicting survival than usual non-invasive variables (New York Heart Association Functional Class, 6-min walk distance and BNP/NT-proBNP). The results were validated in a fully independent external validation cohort.

CONCLUSION

The monitoring of β-NGF, CXCL9 and TRAIL levels in serum should be considered in the management and treatment of patients with PAH to objectively guide therapeutic options.

An Overview of Circulating Pulmonary Arterial Hypertension Biomarkers

Pulmonary arterial hypertension (PAH), also known as Group 1 Pulmonary Hypertension (PH), is a PH subset characterized by pulmonary vascular remodeling and pulmonary arterial obstruction. PAH has an estimated incidence of 15-50 people per million in the United States and Europe, and is associated with high mortality and morbidity, with patients' survival time after diagnosis being only 2.8 years. According to current guidelines, right heart catheterization is the gold standard for diagnostic and prognostic evaluation of PAH patients. However, this technique is highly invasive, so it is not used in routine clinical practice or patient follow-up. Thereby, it is essential to find new non-invasive strategies for evaluating disease progression. Biomarkers can be an effective solution for determining PAH patient prognosis and response to therapy, and aiding in diagnostic efforts, so long as their detection is non-invasive, easy, and objective. This review aims to clarify and describe some of the potential new candidates as circulating biomarkers of PAH.

Targeting the Angiopoietin/Tie Pathway: Prospects for Treatment of Retinal and Respiratory Disorders

Anti-angiogenic approaches have significantly advanced the treatment of vascular-related pathologies. The ephemeral outcome and known side effects of the current vascular endothelial growth factor (VEGF)-based anti-angiogenic treatments have intensified research on other growth factors. The angiopoietin/Tie (Ang/Tie) family has an established role in vascular physiology and regulates angiogenesis, vascular permeability, and inflammatory responses. The Ang/Tie family consists of angiopoietins 1-4, their receptors, tie1 and 2 and the vascular endothelial-protein tyrosine phosphatase (VE-PTP). Modulation of Tie2 activation has provided a promising outcome in preclinical models and has led to clinical trials of Ang/Tie-targeting drug candidates for retinal disorders. Although less is known about the role of Ang/Tie in pulmonary disorders, several studies have revealed great potential of the Ang/Tie family members as drug targets for pulmonary vascular disorders as well. In this review, we summarize the functions of the Ang/Tie pathway in retinal and pulmonary vascular physiology and relevant disorders and highlight promising drug candidates targeting this pathway currently being or expected to be under clinical evaluation for retinal and pulmonary vascular disorders.

Associations of Angiopoietins With Heart Failure Incidence and Severity

BACKGROUND

Angiopoietin-1 and 2 (Ang1, Ang2) are important mediators of angiogenesis. Angiopoietin levels are perturbed in cardiovascular disease, but it is unclear whether angiopoietin signaling is causative, an adaptive response, or merely epiphenomenon of disease activity.

METHODS AND RESULTS

In a cohort free of cardiovascular disease at baseline (Multi-Ethnic Study of Atherosclerosis [MESA]), relationships between angiopoietins, cardiac morphology, and subsequent incidence of heart failure or cardiovascular death were evaluated. In cohorts with pulmonary arterial hypertension or left heart disease, associations between angiopoietins, invasive hemodynamics, and adverse clinical outcomes were evaluated. In MESA, Ang2 was associated with a higher incidence of heart failure or cardiovascular death (hazard ratio 1.21 per standard deviation, P < .001). Ang2 was associated with increased right atrial pressure (pulmonary arterial hypertension cohort) and increased wedge pressure and right atrial pressure (left heart disease cohort). Elevated Ang2 was associated with mortality in the pulmonary arterial hypertension cohort.

CONCLUSIONS

Ang2 was associated with incident heart failure or death among adults without cardiovascular disease at baseline and with disease severity in individuals with existing heart failure. Our finding that Ang2 is increased before disease onset and that elevations reflect disease severity, suggests Ang2 may contribute to heart failure pathogenesis.

The Biological Bases of Group 2 Pulmonary Hypertension

Pulmonary hypertension (PH) is a potentially fatal condition with a prevalence of around 1% in the world population and most commonly caused by left heart disease (PH-LHD). Usually, in PH-LHD, the increase of pulmonary pressure is only conditioned by the retrograde transmission of the left atrial pressure. However, in some cases, the long-term retrograde pressure overload may trigger complex and irreversible biomechanical and biological changes in the pulmonary vasculature. This latter clinical entity, designated as combined pre- and post-capillary PH, is associated with very poor outcomes. The underlying mechanisms of this progression are poorly understood, and most of the current knowledge comes from the field of Group 1-PAH. Treatment is also an unsolved issue in patients with PH-LHD. Targeting the molecular pathways that regulate pulmonary hemodynamics and vascular remodeling has provided excellent results in other forms of PH but has a neutral or detrimental result in patients with PH-LHD. Therefore, a deep and comprehensive biological characterization of PH-LHD is essential to improve the diagnostic and prognostic evaluation of patients and, eventually, identify new therapeutic targets. Ongoing research is aimed at identify candidate genes, variants, non-coding RNAs, and other biomarkers with potential diagnostic and therapeutic implications. In this review, we discuss the state-of-the-art cellular, molecular, genetic, and epigenetic mechanisms potentially involved in PH-LHD. Signaling and effective pathways are particularly emphasized, as well as the current knowledge on -omic biomarkers. Our final aim is to provide readers with the biological foundations on which to ground both clinical and pre-clinical research in the field of PH-LHD.

Association between cytokines and functional, hemodynamic parameters, and clinical outcomes in pulmonary arterial hypertension

To assess the relationship of cytokines with functional and clinical outcomes in pulmonary arterial hypertension (PAH). Endothelial dysfunction and vascular inflammation are characteristic of PAH. We investigated whether markers of angiogenesis and inflammation associated with functional, hemodynamic parameters, and clinical outcomes in PAH. PAH patients (n = 206) were pooled from two clinical trials: TRUST-1 and FREEDOM-C2. Baseline and post-treatment cytokine levels were correlated to baseline clinical and hemodynamic parameters, were assessed in clinical subgroups, and were associated with clinical outcomes. In 206 patients (mean age = 48 years; 74% women) with WHO group-1 PAH, most cytokine levels were higher in those with 6-min walking distance (6MWD) < median (335 m) vs. those above median, including Ang-1 (11.9 ± 10.1 vs. 5.9 ± 6.0 ng/mL), Ang-2 (14.3 ± 11.8 vs. 12.2 ± 11.2 ng/mL), and MMP-9 (221 ± 262.3 vs. 119 ± 171 ng/mL). Baseline 6MWD inversely correlated with Ang-1 (r = −0.27, P < 0.0001), Ang-2 (r = −0.20, P = 0.004), and MMP-9 (r = −0.27, P < 0.0001). MMP-9 levels differed significantly by NYHA functional class (P = 0.001) suggesting an association between MMP-9 and subjective PAH severity. Mean Ang-2 levels were higher in those with baseline right atrial pressure (RAP) > 15 mmHg compared to those with RAP < 15 mmHg (23,841 vs. 11,020 pg/mL). Baseline RAP was associated with change in MMP-9 levels (r = −0.53, P = 0.03). Finally, baseline Ang-1, VEGF and MMP-9 levels were associated with risk of death and hospitalization at 16-week follow-up. Inflammatory cytokines and vascular angiogenesis markers are associated with baseline functional, hemodynamic parameters in PAH, and predict death and hospitalization. Larger prospective studies are needed to confirm the utility of cytokines in PAH.

Update on pulmonary arterial hypertension research: proceedings from a meeting of experts

BACKGROUND

While pulmonary arterial hypertension (PAH) remains a progressive, symptomatic condition characterized by increased pulmonary vascular resistance, ultimately leading to right heart failure, great strides have been made in its understanding and treatment over the past two decades.

REVIEW

Continued research in pre-clinical, clinical, and health economic areas of research, in addition to registry analyses and technology advances, is critical for understanding the pathophysiology of the disease and devising the best ways to monitor and manage patients. On December 3, 2016, the latest pre-clinical, clinical, health economic outcome, and registry data on PAH was presented in a symposium sponsored by Actelion. This paper reviews the published research and insight into upcoming research that was presented at this interactive meeting.