Neopterin as a Biomarker in Patients with Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension

Performance-based outcome measures for assessing physical capacity in patients with pulmonary embolism: A scoping review

INTRODUCTION

Up to 50 % of patients surviving a pulmonary embolism (PE) report persisting shortness of breath, reduced physical capacity and psychological distress. As the PE population is heterogeneous compared to other cardiovascular patient groups, outcome measures for assessing physical capacity traditionally used in cardiac populations may not be reliable for the PE population as a whole. This scoping review aims to 1) map performance-based outcome measures (PBOMs) used for assessing physical capacity in PE research, and 2) to report the psychometric properties of the identified PBOMs in a PE population.

METHODS

The review was conducted according to the Joanna Briggs Institute framework for scoping reviews and reported according to the PRISMA-Extension for Scoping Reviews guideline.

RESULTS

The systematic search of five databases identified 4585 studies, of which 243 studies met the inclusion criteria. Of these, 185 studies focused on a subgroup of patients with chronic thromboembolic pulmonary hypertension. Ten different PBOMs were identified in the included studies. The 6-minute walk test (6MWT) and cardiopulmonary exercise test (CPET) were the most commonly used, followed by the (Modified) Bruce protocol and Incremental Shuttle Walk test. No studies reported psychometric properties of any of the identified PBOMs in a PE population.

CONCLUSIONS

Publication of studies measuring physical capacity within PE populations has increased significantly over the past 5-10 years. Still, not one study was identified, reporting the validity, reliability, or responsiveness for any of the identified PBOMs in a PE population. This should be a priority for future research in the field.

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

Pterins are an inseparable part of living organisms. Pterins participate in metabolic reactions mostly as tetrahydropterins. Dihydropterins are usually intermediates of these reactions, whereas oxidized pterins can be biomarkers of diseases. In this review, we analyze the available data on the quantum chemistry of unconjugated pterins as well as their photonics. This gives a comprehensive overview about the electronic structure of pterins and offers some benefits for biomedicine applications: (1) one can affect the enzymatic reactions of aromatic amino acid hydroxylases, NO synthases, and alkylglycerol monooxygenase through UV irradiation of H₄pterins since UV provokes electron donor reactions of H₄pterins; (2) the emission properties of H₂pterins and oxidized pterins can be used in fluorescence diagnostics; (3) two-photon absorption (TPA) should be used in such pterin-related infrared therapy because single-photon absorption in the UV range is inefficient and scatters in vivo; (4) one can affect pathogen organisms through TPA excitation of H₄pterin cofactors, such as the molybdenum cofactor, leading to its detachment from proteins and subsequent oxidation; (5) metal nanostructures can be used for the UV-vis, fluorescence, and Raman spectroscopy detection of pterin biomarkers. Therefore, we investigated both the biochemistry and physical chemistry of pterins and suggested some potential prospects for pterin-related biomedicine.

Metabolomics-based mechanism exploration of pulmonary arterial hypertension pathogenesis: novel lessons from explanted human lungs

Pulmonary arterial hypertension has led to global health and social problems, but the pathogenic mechanism has not been fully elucidated. Dysregulated metabolism is closely associated with the pathogenesis of pulmonary arterial hypertension. Here, we investigated metabolic profile shifts to reveal the molecular mechanisms underlying pulmonary hypertension. Explanted lung tissues from 13 idiopathic pulmonary arterial hypertension patients, 5 pulmonary arterial hypertension associated with congenital heart disease patients, and 16 controls were collected for untargeted metabolomics analysis with liquid chromatography coupled with tandem mass spectrometry. The KEGG database and MetaboAnalyst 5.0 were used for pathway analysis. A Cox survival analysis model was applied to evaluate the predictive value of metabolites on prognosis. Protein expression levels in human and rat pulmonary arterial hypertension lungs and hypoxia-exposed human pulmonary artery smooth muscle cells were detected by Western blotting to study the molecular mechanisms. Significant differences in metabolites and metabolic pathways were identified among the pulmonary arterial hypertension subgroups and control tissues. The levels of spermine were positively correlated with the patients' cardiac output, and (2e)-2,5-dichloro-4-oxo-2-hexenedioic acid was positively correlated with the patients' serum creatinine levels. Patients with higher thymine levels had a better prognosis. Moreover, seven differential metabolites were associated with the AKT pathway. AKT pathway inactivation was confirmed in human and rat pulmonary hypertensive lungs and pulmonary artery smooth muscle cells exposed to hypoxia. Our findings provide the first metabolomics evidence for pulmonary arterial hypertension pathogenesis in human lungs and may contribute to the improvement in therapeutic strategies.

Circulating Blood-Based Biomarkers in Pulmonary Hypertension

Pulmonary hypertension (PH) is a serious hemodynamic condition, characterized by increased pulmonary vascular resistance (PVR), leading to right heart failure (HF) and death when not properly treated. The prognosis of PH depends on etiology, hemodynamic and biochemical parameters, as well as on response to specific treatment. Biomarkers appear to be useful noninvasive tools, providing information about the disease severity, treatment response, and prognosis. However, given the complexity of PH, it is impossible for a single biomarker to be adequate for the broad assessment of patients with different types of PH. The search for novel emerging biomarkers is still ongoing, resulting in a few potential biomarkers mirroring numerous pathophysiological courses. In this review, markers related to HF, myocardial remodeling, inflammation, hypoxia and tissue damage, and endothelial and pulmonary smooth muscle cell dysfunction are discussed in terms of diagnosis and prognosis. Extracellular vesicles and other markers with complex backgrounds are also reviewed. In conclusion, although many promising biomarkers have been identified and studied in recent years, there are still insufficient data on the application of multimarker strategies for monitoring and risk stratification in PH patients.

Physiology and Inflammation Driven Pathophysiology of Iron Homeostasis-Mechanistic Insights into Anemia of Inflammation and Its Treatment

Anemia is very common in patients with inflammatory disorders. Its prevalence is associated with severity of the underlying disease, and it negatively affects quality of life and cardio-vascular performance of patients. Anemia of inflammation (AI) is caused by disturbances of iron metabolism resulting in iron retention within macrophages, a reduced erythrocyte half-life, and cytokine mediated inhibition of erythropoietin function and erythroid progenitor cell differentiation. AI is mostly mild to moderate, normochromic and normocytic, and characterized by low circulating iron, but normal and increased levels of the storage protein ferritin and the iron hormone hepcidin. The primary therapeutic approach for AI is treatment of the underlying inflammatory disease which mostly results in normalization of hemoglobin levels over time unless other pathologies such as vitamin deficiencies, true iron deficiency on the basis of bleeding episodes, or renal insufficiency are present. If the underlying disease and/or anemia are not resolved, iron supplementation therapy and/or treatment with erythropoietin stimulating agents may be considered whereas blood transfusions are an emergency treatment for life-threatening anemia. New treatments with hepcidin-modifying strategies and stabilizers of hypoxia inducible factors emerge but their therapeutic efficacy for treatment of AI in ill patients needs to be evaluated in clinical trials.

Deficiency of Axl aggravates pulmonary arterial hypertension via BMPR2

Pulmonary arterial hypertension (PAH), is a fatal disease characterized by a pseudo-malignant phenotype. We investigated the expression and the role of the receptor tyrosine kinase Axl in experimental (i.e., monocrotaline and Su5416/hypoxia treated rats) and clinical PAH. In vitro Axl inhibition by R428 and Axl knock-down inhibited growth factor-driven proliferation and migration of non-PAH and PAH PASMCs. Conversely, Axl overexpression conferred a growth advantage. Axl declined in PAECs of PAH patients. Axl blockage inhibited BMP9 signaling and increased PAEC apoptosis, while BMP9 induced Axl phosphorylation. Gas6 induced SMAD1/5/8 phosphorylation and ID1/ID2 increase were blunted by BMP signaling obstruction. Axl association with BMPR2 was facilitated by Gas6/BMP9 stimulation and diminished by R428. In vivo R428 aggravated right ventricular hypertrophy and dysfunction, abrogated BMPR2 signaling, elevated pulmonary endothelial cell apoptosis and loss. Together, Axl is a key regulator of endothelial BMPR2 signaling and potential determinant of PAH.

Model of Chronic Thromboembolic Pulmonary Hypertension in Rats Caused by Repeated Intravenous Administration of Partially Biodegradable Sodium Alginate Microspheres

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare and life-threatening complication of pulmonary embolism. As existing animal models of CTEPH do not fully recapitulate complex disease pathophysiology, we report a new rat model for CTEPH evoked by repetitive embolization of the distal pulmonary artery branches with partially biodegradable alginate microspheres (MSs). MSs (180 ± 28 μm) were intravenously administered eight times at 4-day intervals; control animals received saline. The validity of the model was confirmed using transthoracic echocardiography, exercise testing, catheterization of the right ventricle, and histological examination of the lung and heart. The animals in the CTEPH group demonstrated a stable increase in right ventricular systolic pressure (RVSP) and decreased exercise tolerance. Histopathological examination revealed advanced medial hypertrophy in the small pulmonary arteries associated with fibrosis. The diameter of the main pulmonary artery was significantly larger in the CTEPH group than in the control group. Marinobufagenin and endothelin-1 serum levels were significantly elevated in rats with CTEPH. In conclusion, repetitive administration of alginate MSs in rats resulted in CTEPH development characterized by specific lung vasculature remodeling, reduced exercise tolerance, and a persistent rise in RVSP. The developed model can be used for pre-clinical testing of promising drug candidates.

Neopterin derivatives - a novel therapeutic target rather than biomarker for atherosclerosis and related diseases

This review provides an updated overview of the emerging roles of neopterin derivatives in atherosclerosis. Neopterin, a metabolite of guanosine triphosphate, is produced by interferon-γ-activated macrophages and is expressed at high levels in atheromatous plaques within the human carotid and coronary arteries as well as in the aorta. Plasma concentrations of neopterin are higher in patients with carotid, cerebral, and coronary artery diseases as well as aortic aneurysm. The concentration of neopterin is positively correlated with the severity of coronary artery disease. However, a prospective cohort study showed that neopterin contributes to protection against plaque formation in carotid arteries in patients with atherosclerosis. Moreover, using both in vitro and in vivo experiments, a recent study has shown the atheroprotective effects of neopterin. Neopterin suppresses the expression of monocyte chemotactic protein-1, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 in endothelial cells, and thereby suppresses the adhesion of monocytes to endothelial cells. It also suppresses the inflammatory phenotype of monocyte-derived macrophages. In addition, neopterin suppresses oxidized low-density lipoprotein-induced foam cell formation in macrophages and the migration and proliferation of vascular smooth muscle cells. Neopterin injection into apolipoprotein E-deficient (Apoe^-/-) mice suppresses the development of atherosclerotic lesions. A neopterin derivative tetrahydroneopterin (BH4), also known as a cofactor for nitric oxide (NO) synthases, suppresses atherosclerosis and vascular injury-induced neointimal hyperplasia in Apoe^-/- mice. BH4 administration improves endothelial dysfunction in patients with coronary artery disease. These findings suggest that neopterin production may increase to counteract the progression of atherosclerosis, as neopterin contributes to atheroprotection. Otherwise, the increased neopterin levels in atherosclerosis may reflect a compensatory mechanism associated with inducible NO synthase upregulation in macrophages to supply BH4 for high output NO production caused by decreased endothelial NO synthase in atherosclerosis. Therefore, neopterin derivatives are a novel therapeutic target for atherosclerosis and related diseases.

Sex differences of hemodynamics during acute vasoreactivity testing to predict the outcomes of chronic thromboembolic pulmonary hypertension

BACKGROUND

Acute vasoreactivity testing (AVT) which reflects the compliance of the pulmonary vascular bed has been proven to be of prognostic value. The purpose of the present study is to explore the sex differences of hemodynamics during the AVT and their impact on event-free survival in patients with chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

Eighty-six patients underwent a right heart catheterization and AVT at Shanghai Pulmonary Hospital from February 2009 to February 2018. Univariate and multiple stepwise regression analysis were performed to determine the predictors of independent event-free survival, and receiver operating characteristic curve was plotted to determine the cut-off value of independent parameters in CTEPH.

RESULTS

There were no significant differences in both demographics and hemodynamics between male and female patients with CTEPH. Except ΔPVR/PVR showed a significantly higher difference in female than male patients (P = 0.034). Male patients had higher mRAP of pre- and post-AVT than female patients in the event-free subgroup, while, female patients showed higher PVR of pre-AVT than male patients in the event subgroup (P < 0.05). The mRAP and SvO₂ were independent predictors of event-free survival in female patients both before and after the AVT, whereas ΔSvO₂ was an independent predictor of event-free survival in male patients.

CONCLUSION

Hemodynamics during the AVT varied between male and female patients with CTEPH. Both sexes displayed unique hemodynamic responses that were independently able to predict event-free survival. Therefore, better estimates of prognosis in CTEPH can be made when sex differences are also taken into consideration.

Prognostic Value of Oxidative Stress Markers in Patients with Pulmonary Arterial or Chronic Thromboembolic Pulmonary Hypertension

Oxidative stress is regarded to play a crucial role in the pathophysiology of pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH). This study evaluated the prognostic value of serum oxidative stress markers (malondialdehyde (MDA), total antioxidant capacity (TAC), catalase activity (CAT), and superoxide activity (SOD)) in patients with PAH and CTEPH (n = 45). During 13 months of follow-up (median 9 months), clinical deterioration occurred in 14 patients (including 2 deaths). On the Cox regression analysis, MDA, TAC, and CAT were associated with clinical deterioration (p = 0.0068, HR = 1.42, 95% CI: 1.10-1.82; p = 0.0038, HR = 0.033, 95% CI: 0.0032-0.33; and p = 0.046, HR = 0.20, 95% CI: 0.04-0.98, respectively). There was no significant difference in SOD (p = 0.53, HR = 0.97, 95% CI: 0.87-1.08). The cut-off value derived from ROC curve analysis was 3.79 μM (p = 0.0048, AUC = 0.76, 95% CI: 0.62-0.91) for MDA, 0.49 mM (p = 0.027, AUC = 0.71, 95% CI: 0.18-0.47) for TAC, and 1.34 U/L (p = 0.029, AUC = 0.71, 95% CI: 0.55-0.86) for CAT. MDA in the group with deterioration was higher (p = 0.0041), while TAC as well as CAT were lower (p = 0.027 and p = 0.028, respectively) when compared to stable patients. Survival without clinical deterioration was significantly longer in patients with lower MDA (p = 0.037, HR = 0.37, 95% CI: 0.12-1.14, log-rank), higher TAC (p = 0.0018, HR = 0.19, 95% CI: 0.06-0.60, log-rank), and higher CAT (p = 0.044, HR = 0.31 95% CI: 0.11-0.88, log-rank). Markers of oxidative stress such as MDA, TAC, and CAT were associated with adverse clinical outcomes in patients with PAH and inoperable or residual CTEPH.

Circulating biomarkers in chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a serious condition characterized with chronic organized thrombi that obstruct the pulmonary vessels, leading to pulmonary hypertension (PH) and ultimately right heart failure. Although CTEPH is the only form of PH that can be cured with surgical intervention, not all patients with CTEPH will be deemed operable. Some CTEPH patients still have a poor prognosis. Therefore, the determination of diagnostic and prognostic biomarkers of CTEPH is of great importance for the early intervention to improve prognosis of patients with CTEPH. Several markers related to multiple mechanisms of CTEPH have been recently identified as circulating diagnostic and prognostic biomarkers in these patients. However, the existing literature review of biomarkers of CTEPH is relatively sparse. In this article, we review recent advances in circulating biomarkers of CTEPH and describe future applications of these biomarkers in the management of CTEPH.