Biomarkers in pulmonary arterial hypertension

The Role of Biomarkers and Surrogate End Points in Drug Development for Neonatal Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rare disease in newborns, infants, and children. It is associated with significant morbidity and mortality, but has limited treatment options. Except for inhaled nitric oxide, which is approved for persistent pulmonary hypertension of the newborn (PPHN), no drug is approved for the treatment of newborns, infants, and children with PAH. The lack of developmentally appropriate pediatric efficacy end points and pediatric clinical trials contribute to this unmet medical need. The noninvasive biomarkers reported in the literature that can be used as potential surrogate end points to assess disease severity and treatment response in neonates, infants, and children with PAH are reviewed herein. In addition, the role of the US Food and Drug Administration in developing potential biomarkers as surrogate end points to facilitate drug development for the treatment of children with PPHN and PAH in children is reviewed herein.

Serum Caveolin-1 as a Novel Biomarker in Idiopathic Pulmonary Artery Hypertension

Pulmonary arterial hypertension (PAH) is a rare disease but with significant morbidity and high mortality. There is no specific way to diagnose PAH. Thus, an easy used with good sensitivity and specificity biomarker of PAH is highly desirable to aid in the screening, diagnosis, and follow-up. Caveolin-1 (Cav1) is the structural protein of caveolae and is highly expressed in type I pneumocytes. Lungs tissues from idiopathic PAH (IPAH) patients showed decreased expression of Cav1 in vascular endothelial cells. Therefore, we developed a direct sandwich immunoassay for the determination of Cav1 in IAPH patient's serum. The result disclosed serum Cav1 level was significantly lower in IPAH than control groups. Using serum Cav1, 17.17 pg/mL as a cutoff value, the sensitivity was 0.59 and the specificity was 1.0. There were two major findings in our results. First, serum Cav1 might be a novel biomarker in the diagnosis of IPAH with fare sensitivity and good specificity. Second, Cav1 might be used to make differential diagnosis between COPD-PH and IPAH group.

Treatment-related biomarkers in pulmonary hypertension

Significant advances in the treatment of pulmonary arterial hypertension (PAH) over the last two decades have led to the introduction of multiple classes of oral therapy, but the disease remains devastating for many patients. Disease progression, in spite of oral monotherapy, is a major problem, and alternative therapy, such as infusion of prostacyclins, is cumbersome and carries considerable potential morbidity. Use of combination oral therapy, including drugs from both the endothelin receptor antagonist and phosphodiesterase-5 inhibitor classes, has increased, and there is some evidence to support this approach. Given the multiple options now available in pulmonary hypertension (PH) therapy, biomarkers to guide treatment decisions could be helpful. Here, we review the evidence for and against the clinical use of molecular biomarkers relevant to PH pathogenesis, emphasizing assayable markers that may also inform more rational selection of agents that influence pathways targeted by treatment. We emphasize the interactive nature of changes in mediators and messengers, such as endothelin-1, prostacyclin, brain natriuretic peptide (which has demonstrated biomarker utility), nitric oxide derivatives, and cyclic guanosine monophosphate, which play important roles in processes central to progression of PAH, such as vascular remodeling, vasoconstriction, and maladaptive right ventricular changes, and are relevant to its therapy. Accordingly, we propose that the identification and use of a molecular biomarker panel that assays these molecules in parallel and serially might, if validated, better inform unique patient phenotypes, prognosis, and the rational selection and titration of combination oral and other therapy in individual patients with PH/PAH.

Pulmonary hypertension in patients with advanced heart failure is associated with increased levels of interleukin-6

CONTEXT

Inflammatory, endothelial and neurohormonal biomarkers are involved in heart failure (HF) and pulmonary hypertension (PH) pathogenesis.

OBJECTIVE

To study these biomarkers in PH due to advanced HF.

MATERIALS AND METHODS

Thirty adults with HF were included. Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), high-sensitivity C-reactive protein (hsCRP), endothelin-1 and N-terminal prohormone of brain natriuretic peptide (NT-proBNP) were measured in peripheral vein and pulmonary artery during right heart catheterisation.

RESULTS

IL-6, TNF-α, hsCRP and NT-proBNP correlated with pulmonary pressures independent of ventricular function, HF etiology and vascular bed. IL-6 was independent predictor of systolic pulmonary artery pressure (sPAP).

DISCUSSION AND CONCLUSION

Inflammatory biomarkers correlate to PH severity. IL-6 predicts sPAP in advanced HF.

Genomics and proteomics of pulmonary vascular disease

Study of RNA and proteins in cells of both normal and diseased tissues is providing researchers with new knowledge of disease pathologies. While still in its early stages, high-throughput expression analysis is improving our understanding of the pathogenesis of pulmonary arterial hypertension (PAH). While many studies have used microarray and proteomic analyses as "hypothesis-generating" tools, the technologies also have potential to identify and quantify biomarkers of disease. To date, many of the published studies have examined gene expression profiles of tissue biopsies, others have utilized cells from peripheral blood. Microarray technology has been employed successfully in the investigation of a diverse array of human diseases. The potential of high-throughput expression analysis to improve our understanding of the pathogenesis of PAH is highlighted in this review. Proteomic studies of PAH and pulmonary vascular diseases in general have been little utilized thus far. To date, such studies are few and no consistent biomarker has emerged from studies of either plasma or blood cells from idiopathic pulmonary arterial hypertension (IPAH) patients. The studies of both lung tissue and lymphocytes are perhaps more revealing and suggest that changes in the cytoskeletal machinery may play a role in the pathogenesis of idiopathic pulmonary arterial hypertension. The oncology literature has demonstrated the utility of gene microarray analysis to predict important outcomes such as response to therapy and survival. It is likely that in the near future, gene microarrays and proteomic analyses will also be employed in a pharmacogenomics approach in PAH, helping to identify the most appropriate therapies for individual patients.

Epigenetics: novel mechanism of pulmonary hypertension

INTRODUCTION

Epigenetics refers to changes in phenotype and gene expression that occur without alterations in DNA sequence. MicroRNAs are relatively recently discovered negative regulators of gene expression and act at the posttranscriptional level.

METHODS

This review summarizes epigenetic mechanisms of pulmonary hypertension, focusing on microRNAs related to pulmonary hypertension.

RESULTS

There are three major mechanisms of epigenetic regulation, including methylation of CpG islands, modification of histone proteins, and microRNAs. There may be an epigenetic component to pulmonary hypertension. These epigenetic abnormalities can be reversed therapeutically.

CONCLUSIONS

By better integrating network biology with evolving technologies in cell culture and in vivo experimentation, we will better understand epigenetic mechanisms of pulmonary hypertension and identify more diagnostic and therapeutic targets in pulmonary hypertension.

HbA1c in pulmonary arterial hypertension: a marker of prognostic relevance?

BACKGROUND

Patients with pulmonary arterial hypertension (PAH) exhibit impaired glucose metabolism and increased insulin resistance. The clinical consequences of these metabolic changes are not known.

METHODS

We assessed HbA1c levels in 115 patients newly diagnosed with PAH (79 females and 36 males; mean age 49.2 years; idiopathic n = 67, collagen vascular disease n = 16, congenital heart defect n = 19, pulmonary veno-occlusive disease n = 8, portopulmonary n = 5). No patients had diabetes or were receiving anti-diabetic medication or systemic steroids. After initiation of pulmonary vasoactive treatment, patients remained in long-term follow-up.

RESULTS

Initially, patients were in an advanced stage of disease (mean pulmonary arterial pressure 53 ± 18 mm Hg, cardiac index 2.3 ± 0.8 liters/min/m2) with a 6-minute-walk distance of 337 ± 123 meters, and in NYHA Functional Class 3.0 ± 0.7. The HbA1c was 5.73 ± 0.75%. A moderate but statistically significant positive correlation was observed between HbA1c levels and BNP (r(p) = 0.41, p = 0.014), but no correlation was found with hemodynamics or 6-minute-walk distance. The 5-year survival rate for the entire group was 68%. Kaplan-Meier analysis and multivariate Cox proportional hazard models correcting for demographic and clinical covariates revealed that patients with HbA1c < 5.7% had a significantly better 5-year survival compared with those having higher initial values (85.1% vs. 55.9%; log rank p = 0.002). HbA1c was a predictor of all-cause mortality with a hazard ratio of 2.23 (95% CI 1.06 to 4.70; p = 0.034) per 1-unit increase of HbA1c.

CONCLUSIONS

In patients with pulmonary arterial hypertension, the HbA1c level at time of diagnosis is an independent predictor of long-term prognosis.

The potential of biomarkers in pulmonary arterial hypertension

Effective management of patients with pulmonary arterial hypertension (PAH) requires comprehensive prognostic evaluation in order to determine optimal management strategies. Although a number of clinical and hemodynamic parameters linked to PAH prognosis have been identified, some are associated with significant limitations (eg, invasive techniques, subjective measures). There is a need for noninvasive and objective measures to be established that function as biomarkers for the diagnosis and assessment of disease prognosis, and that determine response to therapy in patients with PAH. Reflecting the highly complex etiology of the disease, a large number of potential biomarkers have been, and continue to be, investigated in PAH, including those reflecting right heart function, endothelial dysfunction, and markers of inflammation and second organ failure. However, it has become clear that scientifically interesting biomarkers may not necessarily be clinically useful. Of the range of biomarkers investigated in PAH to date, only brain natriuretic peptide and its N-terminal cleavage product have been included as prognostic parameters in treatment guidelines. It is unlikely that any single biomarker will provide all the relevant information required for an individual patient, and the potential for combining markers is currently of considerable interest. Future studies are required to determine the optimal combination of existing and emerging biomarkers in the clinical setting.

Clinical perspective: biomarkers in pulmonary arterial hypertension

Biomarkers are objectively measured characteristics used as indicators of disease in clinical practice and as surrogate endpoints in clinical trials. The six-minute walk test has been widely used as a trial endpoint in pulmonary arterial hypertension (PAH) to gain approval for targeted therapies. Other biomarkers have been studied to overcome certain limitations of the walk test. Potential clinical applications for biomarkers in PAH include screening, determination of prognosis, and monitoring response to therapy. Measurement of the B-type natriuretic peptides is currently recommended by guidelines, despite a lack of appropriate validation in the PAH population. Novel biomarkers based on recently discovered pathobiologic pathways have been identified, like CXC chemokine ligand 10, C-reactive protein, high-density lipoprotein cholesterol and growth-differentiation factor-15. Rigorous statistical, biologic and clinical validation should be necessary before any biomarker can be endorsed for widespread clinical use.

In search of markers of treatment failure and poor prognosis in IPAH - the value of mosaic lung attenuation pattern on thin-section CT scans

Despite the development of specific therapies for pulmonary arterial hypertension (PAH) some patients fail to respond to such treatment. One of the potential reasons for the unresponsiveness to targeted therapies may be the presence of fibrous occlusion of small pulmonary veins that accompanies pre-capillary arteriopathy. This type of pathologic change is called pulmonary veno-occlusive disease (PVOD). Underdiagnosed PVOD occurs probably in 5-10% of idiopathic pulmonary hypertension (IPAH) and in a substantial proportion of PAH related to connective tissue diseases (mainly in scleroderma). A definite diagnosis of PVOD requires histological examination of lung sample, but surgical lung biopsy in pulmonary hypertension is combined with high risk of bleeding. Thus major interest is focused on a non-invasive diagnostic approach enabling early recognition of PVOD and referral for lung transplantation. The present review is focused on the radiological features suggestive of PVOD-like vasculopathy in PAH.