Aptamer-based proteomic profiling for prognostication in pulmonary arterial hypertension
Authors: Evangelos Giannitsis, Matthias Mueller-Hennessen, Hugo A Katus
Journal: The Lancet Respiratory Medicine (2017)

Despite the advances in risk assessment and therapy that have improved morbidity and mortality, pulmonary arterial hypertension still remains a devastating disease with high mortality.1Galiè N Humbert M Vachiery JL et al.2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: the Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT).Eur Heart J. 2016; 37: 67-119Crossref PubMed Scopus (3989) Google Scholar Therefore, precise prognostic stratification of patients with severe pulmonary arterial hypertension is of paramount importance. Most prognostic markers recommended by the European Society of Cardiology (ESC) and the European Respiratory Society (ERS) guidelines1Galiè N Humbert M Vachiery JL et al.2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: the Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT).Eur Heart J. 2016; 37: 67-119Crossref PubMed Scopus (3989) Google Scholar are related to right ventricular function and cardiac output, including various indices of exercise tolerance, mean right atrial pressure, and cardiac index. Biomarkers provide a tremendous opportunity to personalise medicine and can be used for early detection of disease, provide diagnostic and prognostic information. Although the list of biomarkers is constantly growing,2Warwick G Thomas PS Yates DH Biomarkers in pulmonary hypertension.Eur Respir J. 2008; 32: 503-512Crossref PubMed Scopus (114) Google Scholar, 3Zelniker T Uhlmann L Spaich S et al.Novel biomarkers for risk stratification in pulmonary arterial hypertension.ERJ Open Res. 2015; 1: 00008-02015Crossref PubMed Scopus (13) Google Scholar ESC and ERS guidelines recommend only a small number of biomarkers, including brain natriuretic peptide (BNP) or NT-proBNP, for basic and cardiac troponin (cTn) for extended laboratory workup.1Galiè N Humbert M Vachiery JL et al.2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: the Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT).Eur Heart J. 2016; 37: 67-119Crossref PubMed Scopus (3989) Google Scholar In the Article by Christopher J Rhodes and colleagues,4Rhodes CJ Wharton J Ghataorhe P et al.Plasma proteome analysis in pulmonary arterial hypertension patients: an observational cohort study.Lancet Respir Med. 2017; (published online June 14)http://dx.doi.org/10.1016/S2213-2600(17)30161-3Summary Full Text Full Text PDF PubMed Scopus (69) Google Scholar a high-throughput proteomic assay was evaluated for the screening of prognostically relevant proteins in patients with pulmonary arterial hypertension. This technology is based on single-stranded oligonucleotides, so-called aptamers, that bind a specific structural epitope on the surface of its target protein with high affinity via a unique three-dimensional folded structure.5SOMAmer Reagent Specificity Technical White Paper SM-500–102015 http://info.somalogic.com/hubfs/January_2016/SSM-002-Rev-3-SOMAscan-Technical-White-Paper.pdf (accessed April 19, 2017).Google Scholar The commercially available SOMAscan assay (Somalogic Inc, Boulder, CO, USA) used in this study screened 1129 target proteins in a large discovery cohort. Nine proteins that represent different components of the underlying pathological mechanisms of pulmonary arterial hypertension, including myocardial stress, inflammation, pulmonary vascular cellular dysfunction and structural dysregulation, iron status, and coagulation, were identified and validated in independent cohorts. In direct comparison, the panel was found to be independent of NT-proBNP and to add significant prognostic information to clinical assessment, as summarised in the prognostic risk equation derived from the REVEAL registry.6Benza RL Miller DP Gomberg-Maitland M et al.Predicting survival in pulmonary arterial hypertension: insights from the Registry to Evaluate Early and Long-Term Pulmonary Arterial Hypertension Disease Management (REVEAL).Circulation. 2010; 122: 164-172Crossref PubMed Scopus (1181) Google Scholar The authors have to be congratulated for their enormous efforts to screen and validate their finding on a protein panel discovered by a novel proteomics technology. The findings raise expectations that novel proteomics-based technologies will ultimately find their way into routine clinical practice because protein biomarkers can be helpful for early detection of disease, diagnosis, differential diagnosis, prognosis, and allow monitoring of disease and guidance of targeted therapy. Although the study findings are promising, several unexplained findings require further investigations. The final protein panel did not contain biomarkers that have been identified in earlier studies, such as TWEAK, proANP, GDF-15, soluble fms-like tyrosine kinase 1, placental growth factor, or galectin-3.2Warwick G Thomas PS Yates DH Biomarkers in pulmonary hypertension.Eur Respir J. 2008; 32: 503-512Crossref PubMed Scopus (114) Google Scholar, 3Zelniker T Uhlmann L Spaich S et al.Novel biomarkers for risk stratification in pulmonary arterial hypertension.ERJ Open Res. 2015; 1: 00008-02015Crossref PubMed Scopus (13) Google Scholar For unknown reasons, neither cTnT nor cTnI were among the prognostically relevant SOMAmers, which is unfortunate since cTn concentrations above the 99th percentile of a healthy reference value have been reported in 26%7Schuuring MJ van Riel AC Vis JC et al.High-sensitivity troponin T is associated with poor outcome in adults with pulmonary arterial hypertension due to congenital heart disease.Congenit Heart Dis. 2013; 8: 520-526Crossref PubMed Scopus (28) Google Scholar to 27·3%8Filusch A Giannitsis E Katus HA Meyer FJ High-sensitive troponin T: a novel biomarker for prognosis and disease severity in patients with pulmonary arterial hypertension.Clin Sci (Lond). 2010; 119: 207-213Crossref PubMed Scopus (79) Google Scholar of patients with pulmonary arterial hypertension, particularly when high-sensitivity cTn assays were used. Elevated concentrations of cTn have been consistently reported to correlate with functional parameters, including the 6-min walk test, and provide excellent prognostic information independent of other functional parameters, with area under the curve values for prediction of death between 0·78 in one study3Zelniker T Uhlmann L Spaich S et al.Novel biomarkers for risk stratification in pulmonary arterial hypertension.ERJ Open Res. 2015; 1: 00008-02015Crossref PubMed Scopus (13) Google Scholar and >0·9 in another.8Filusch A Giannitsis E Katus HA Meyer FJ High-sensitive troponin T: a novel biomarker for prognosis and disease severity in patients with pulmonary arterial hypertension.Clin Sci (Lond). 2010; 119: 207-213Crossref PubMed Scopus (79) Google Scholar The reasons for the inability to detect cTnI or cTnT are unclear but might involve issues potentially related to analytical sensitivity or binding specificity. Regarding sensitivity, a study9Ngo D Sinha S Shen D et al.Aptamer-based proteomic profiling reveals novel candidate biomarkers and pathways in cardiovascular disease.Circulation. 2016; 134: 270-285Crossref PubMed Scopus (129) Google Scholar using the same SOMAscan assay in 23 patients with spontaneous ST-segment elevation myocardial infarction and in 30 patients with myocardial infarction following alcohol septal ablation for the treatment of symptomatic hypertrophic cardiomyopathy reported detection of low cTnI concentrations, in the range of 10 pg/mL, with an acceptable imprecision. Regarding specificity, it should be remembered that cTnI represents a particularly difficult target protein for aptamer binding because it is prone to degradation, fragmentation, and conformational change resulting into impaired recovery due to loss of the epitope or as a consequence of reduced binding affinity to the aptamer.10Katrukha AG Bereznikova AV Filatov VL et al.Degradation of cardiac troponin I: implication for reliable immunodetection.Clin Chem. 1998; 44: 2433-2440Crossref PubMed Scopus (206) Google Scholar Aptamers might not be available for all previously reported prognostically relevant proteins or peptides, or their measurement might be confounded by cross-reactivity because of related or unrelated proteins with similar or lower binding affinity.5SOMAmer Reagent Specificity Technical White Paper SM-500–102015 http://info.somalogic.com/hubfs/January_2016/SSM-002-Rev-3-SOMAscan-Technical-White-Paper.pdf (accessed April 19, 2017).Google Scholar Additionally, there are imperfections with the method. Validation cohorts in this study were small, and survival has improved considerably rendering a statistically powered sample size unlikely in such a rare disease as pulmonary arterial hypertension. To become accepted in clinical use, the use of aptamer-based proteomics, and particularly this new protein panel, should be consistently shown in larger, prospective studies, and the prognostic role of the new protein panel should not only be tested against NT-proBNP but also against cTn measured quantitatively with a high-sensitivity assay. The REVEAL registry launched a prognostic equation that was derived in 2716 patients with pulmonary arterial hypertension with WHO Group I.6Benza RL Miller DP Gomberg-Maitland M et al.Predicting survival in pulmonary arterial hypertension: insights from the Registry to Evaluate Early and Long-Term Pulmonary Arterial Hypertension Disease Management (REVEAL).Circulation. 2010; 122: 164-172Crossref PubMed Scopus (1181) Google Scholar However, this equation has only been validated internally by a bootstrapping technique and has never undergone an external validation in an independent cohort. Until such a validation has been accomplished, preference of this equation over the individual risk indicators recommended by ESC and ERS guidelines1Galiè N Humbert M Vachiery JL et al.2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension: the Joint Task Force for the Diagnosis and Treatment of Pulmonary Hypertension of the European Society of Cardiology (ESC) and the European Respiratory Society (ERS): endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC), International Society for Heart and Lung Transplantation (ISHLT).Eur Heart J. 2016; 37: 67-119Crossref PubMed Scopus (3989) Google Scholar is not warranted. Although the current findings are encouraging, future studies are needed to corroborate the role of this novel modified aptamer-based proteomic technology into routine clinical practice. EG reports personal fees from AstraZeneca and Daiichi Sankyo, and grants and personal fees from Roche Diagnostic and Bayer Vita, outside of the submitted work. MMH reports grants, personal fees, and non-financial support from Roche Diagnostics, grants and non-financial support from BRAHMS Thermo Fisher and Metanomics Health, and non-financial support from Bayer Vital, outside of the submitted work. HAK reports personal fees from AstraZeneca, Roche Diagnostics, and Daiichi Sankyo, outside of the submitted work. Plasma proteome analysis in patients with pulmonary arterial hypertension: an observational cohort studyA combination of nine circulating proteins identifies patients with pulmonary arterial hypertension with a high risk of mortality, independent of existing clinical assessments, and might have a use in clinical management and the evaluation of new therapies. Full-Text PDF Open Access