Circulating endothelial cells in refractory pulmonary hypertension in children: markers of treatment efficacy and clinical worsening

Levels of Plasma Endothelin-1, Circulating Endothelial Cells, Endothelial Progenitor Cells, and Cytokines after Cardiopulmonary Bypass in Children with Congenital Heart Disease: Role of Endothelin-1 Regulation

Congenital heart disease (CHD) can be complicated by pulmonary arterial hypertension (PAH). Cardiopulmonary bypass (CPB) for corrective surgery may cause endothelial dysfunction, involving endothelin-1 (ET-1), circulating endothelial cells (CECs), and endothelial progenitor cells (EPCs). These markers can gauge disease severity, but their levels in children's peripheral blood still lack consensus for prognostic value. The aim of our study was to investigate changes in ET-1, cytokines, and the absolute numbers (Ɲ) of CECs and EPCs in children 24 h before and 48 h after CPB surgery to identify high-risk patients of complications. A cohort of 56 children was included: 41 cases with CHD-PAH (22 with high pulmonary flow and 19 with low pulmonary flow) and 15 control cases. We observed that Ɲ-CECs increased in both CHD groups and that Ɲ-EPCs decreased in the immediate post-surgical period, and there was a strong negative correlation between ET-1 and CEC before surgery, along with significant changes in ET-1, IL8, IL6, and CEC levels. Our findings support the understanding of endothelial cell precursors' role in endogenous repair and contribute to knowledge about endothelial dysfunction in CHD.

Pulmonary arterial hypertension in children with congenital heart disease: a deeper look into the role of endothelial progenitor cells and circulating endothelial cells to assess disease severity

Endothelial progenitor cells and circulating endothelial cells have been proposed as useful markers of severity and disease progression in certain vascular diseases, including pulmonary arterial hypertension. Our study focused on evaluating the levels of circulating endothelial progenitor cells and circulating endothelial cells in patients with congenital left-to-right shunts and pulmonary hypertension undergoing definitive repair. Endothelial progenitor cells (identified by simultaneous co-expression of CD45dim, CD34 + and KDR2 + surface antibodies) and circulating endothelial cells (identified by simultaneous co-expression of inherent antibodies CD45-, CD31+, CD146 + and CD105+) were prospectively measured in seventy-four children (including children with Down syndrome), median age six years (2.75-10), with clinically significant left-to-right shunts undergoing transcatheter or surgical repair and compared to thirty healthy controls. Endothelial progenitor cells and, particularly, circulating endothelial cells were significantly higher in children with heart disease and pulmonary arterial hypertension when compared to controls. Endothelial progenitor cells showed significant correlation with pulmonary vascular resistance index when measured both systemically (r = 0.259; p = 0.026) and in the superior vena cava (r = 0.302; p = 0.009). Children with Down syndrome showed a stronger correlation between systemic cellularity and pulmonary vascular resistance index (r = 0.829; p = 0.002). Endothelial progenitor cells were reduced along their transit through the lung, whereas circulating endothelial cells did not suffer any modification across the pulmonary circulation. In children with yet to be repaired left-to-right shunts, endothelial progenitor cells and circulating endothelial cell counts are increased compared to healthy subjects.

Are circulating endothelial cells the next target for transcriptome-level pathway analysis in ARDS?

Acute respiratory distress syndrome (ARDS) has had no mortality-improving pharmacological intervention despite 50 years of high-caliber research due to its heterogeneity (Huppert LA, Matthay MA, Ware LB. Semin Respir Crit Care Med 40: 31-39, 2019). For the field to advance, better definitions for ARDS subgroups that more uniformly respond to therapies are needed (Bos LDJ, Scicluna BP, Ong DSY, Cremer O, van der Poll T, Schultz MJ. Am J Respir Crit Care Med 200: 42-50, 2019; Dickson RP, Schultz MJ, T van der P, Schouten LR, Falkowski NR, Luth JE, Sjoding MW, Brown CA, Chanderraj R, Huffnagle GB, Bos LDJ, Biomarker Analysis in Septic ICU Patients (BASIC) Consortium. Am J Respir Crit Care Med 201: 555-563, 2020; Sinha P, Calfee CS. Am J Respir Crit Care Med 200: 4-6, 2019; Calfee CS, Delucchi K, Parsons PE, Thompson BT, Ware LB, Matthay MA, NHLBI ARDS Network. Lancet Respir Med 2: 611-620, 2014; Hendrickson CM, Matthay MA. Pulm Circ 8: 1-12, 2018). A plethora of high-quality clinical research has uncovered the next generation of soluble biomarkers that provide the predictive enrichment necessary for trial recruitment; however, plasma-soluble markers do not specify the damaged organ of origin nor do they provide insight into disease mechanisms. In this perspective, we make the case for querying the transcriptome of circulating endothelial cells (CECs), which when shed from vessels after inflammatory insult, become heralds of site-specific inflammatory damage. We review the application of CEC quantification to multiple disease phenotypes (including myocardial infarction, vasculitides, cancer, and ARDS), in each case supporting the association of CEC number with disease severity. We also argue for the utility of single-cell RNA transcriptomics to the understanding of cell-specific contributions to disease pathophysiology and its potential to uncover novel insight on signals contributing to CEC shedding in ARDS.

Ex Vivo Modeling of the PC (Protein C) Pathway Using Endothelial Cells and Plasma: A Personalized Approach

BACKGROUND

The endothelial cell-dependent PC (protein C) pathway is critically involved in the regulation of coagulation, anti-inflammatory, and cytoprotective signaling. Its reactivity shows high interindividual variability, and it contributes to prothrombotic disorders, such as the FVL (factor V Leiden) mutation.

METHODS

Endothelial colony-forming cells (ECFCs) were isolated from heparinized peripheral blood from healthy individuals and FVL carriers. Confluent monolayers of ECFCs were overlaid with plasma, and thrombin formation was initiated by addition of tissue factor (1 pmol/L). Subsequently, thrombin and APC (activated PC) formation rates were measured over time using oligonucleotide-based enzyme capture assays. To induce downregulation of TM (thrombomodulin) expression, ECFCs were stimulated with IL-1β (interleukin 1β). In vivo APC response rates were monitored in study participants after infusion of low-dose rFVIIa (recombinant activated factor VII).

RESULTS

The median peak APC concentration was 1.12 nmol/L in experiments with IL-1β stimulated ECFCs and 3.66 nmol/L without IL-1β. Although thrombin formation rates were comparable, APC formation rates were significantly higher in FVL carriers (n=6) compared to noncarriers (n=5) as evidenced by a higher ratio between the area under the curve of APC generation to the area under the curve of thrombin generation (median 0.090 versus 0.031, P=0.017). These ex vivo results were correlated with an increased APC response to rFVIIa-induced thrombin formation in FVL carriers in vivo.

CONCLUSIONS

Patient-specific ex vivo modeling of the PC pathway was achieved using blood-derived ECFCs. The correlation between in and ex vivo APC response rates confirms that the autologous PC model accurately depicts the in vivo situation.

Human Endothelial Colony-Forming Cells

Endothelial colony-forming cells (ECFCs) are progenitor cells that can give rise to colonies of highly proliferative vascular endothelial cells (ECs) with clonal expansion and in vivo blood vessel-forming potential. More than two decades ago, the identification of ECFCs in human peripheral blood created tremendous opportunities as having a clinically accessible source of autologous ECs could facilitate meaningful therapies with the potential to impact multiple vascular diseases. Nevertheless, until recently, the field of endothelial progenitor cells has been plagued with ambiguities and controversies, and reaching a consensus on the definition of ECFCs has not been straightforward. Moreover, although the basic phenotypical and functional characteristics of cultured ECFCs are now well established, some fundamental questions such as the origin of ECFCs and their physiological roles in health and disease remain incompletely understood. Here, I highlight some critical studies that have shaped our current understanding of ECFCs in humans. Insights into the biological attributes of ECFCs are essential for facilitating the clinical translation of their therapeutic potential.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Non-Invasive Assessment of Endothelial Dysfunction in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is characterised by an increased pressure in the pulmonary arterial circulation, resulting in the elevation of pulmonary vascular resistance. Pulmonary endothelial dysfunction and inflammation, triggered by shear stress and hypoxia, constitute the hallmarks of pulmonary vasculopathy by promoting endothelial and smooth muscle cells proliferation, vasoconstriction, and thrombosis. While research was predominantly focused on pulmonary vasculature, the investigation of peripheral endothelial damage in different vascular beds has attracted the interest over the last years. As a result, effective non-invasive methods that can assess the endothelial function and the architectural integrity have been utilized for the evaluation of pulmonary and peripheral vasculature. Non-invasive plethysmography, pulmonary flow reserve, nailfold videocapillaroscopy, near-infrared spectroscopy, and imaging techniques such as magnetic resonance angiography and perfusion imaging coupled by a number of biomarkers can be used for the assessment of peripheral vascular function in PAH individuals. In this review, we summarise and critically approach the current evidence of more systemic derangement of vascular function in PAH defined by novel, non-invasive methods employed for functional and morphological assessment of endothelium and microcirculation.

Endothelial characteristics in healthy endothelial colony forming cells; generating a robust and valid ex vivo model for vascular disease

BACKGROUND

Endothelial colony forming cells (ECFCs) derived from peripheral blood can be used to analyze the pathophysiology of vascular diseases ex vivo. However, heterogeneity is observed between ECFC clones and this variability needs to be understood and standardized for ECFCs to be used as a cell model for applications in vascular studies.

OBJECTIVE

Determine reference characteristics of healthy control ECFCs to generate a valid ex vivo model for vascular disease.

METHODS

Putative ECFCs (n = 47) derived from 21 individual healthy subjects were studied for cell morphology and specific cell characteristics. Clones were analyzed for the production and secretion of von Willebrand factor (VWF), cell proliferation, and the expression of endothelial cell markers.

RESULTS

Based on morphology, clones were categorized into three groups. Group 1 consisted of clones with classic endothelial cell morphology, whereas groups 2 and 3 contained less condensed cells with increasing cell sizes. All clones had comparable endothelial cell surface expression profiles, with low levels of non-endothelial markers. However, a decrease in CD31 and a group-related increase in CD309 and CD45 expression, combined with a decrease in cell proliferation and VWF production and secretion, was observed in clones in group 3 and to a lesser extent in group 2.

CONCLUSIONS

We observed group-related variations in endothelial cell characteristics when clones lacked the classic endothelial cell morphology. Despite this variation, clones in all groups expressed endothelial cell surface markers. Provided that clones with similar characteristics are compared, we believe ECFCs are a valid ex vivo model to study vascular disease.

Curative anticoagulation prevents endothelial lesion in COVID-19 patients

BACKGROUND

Coronavirus disease-2019 (COVID-19) has been associated with cardiovascular complications and coagulation disorders.

OBJECTIVES

To explore the coagulopathy and endothelial dysfunction in COVID-19 patients.

METHODS

The study analyzed clinical and biological profiles of patients with suspected COVID-19 infection at admission, including hemostasis tests and quantification of circulating endothelial cells (CECs).

RESULTS

Among 96 consecutive COVID-19-suspected patients fulfilling criteria for hospitalization, 66 were tested positive for SARS-CoV-2. COVID-19-positive patients were more likely to present with fever (P = .02), cough (P = .03), and pneumonia at computed tomography (CT) scan (P = .002) at admission. Prevalence of D-dimer >500 ng/mL was higher in COVID-19-positive patients (74.2% versus 43.3%; P = .007). No sign of disseminated intravascular coagulation were identified. Adding D-dimers >500 ng/mL to gender and pneumonia at CT scan in receiver operating characteristic curve analysis significantly increased area under the curve for COVID-19 diagnosis. COVID-19-positive patients had significantly more CECs at admission (P = .008) than COVID-19-negative ones. COVID-19-positive patients treated with curative anticoagulant prior to admission had fewer CECs (P = .02) than those without. Interestingly, patients treated with curative anticoagulation and angiotensin-converting-enzyme inhibitors or angiotensin receptor blockers had even fewer CECs (P = .007).

CONCLUSION

Curative anticoagulation could prevent COVID-19-associated coagulopathy and endothelial lesion.

Respiratory mechanics and gas exchanges in the early course of COVID-19 ARDS: a hypothesis-generating study

Rationale

COVID-19 ARDS could differ from typical forms of the syndrome.

Objective

Pulmonary microvascular injury and thrombosis are increasingly reported as constitutive features of COVID-19 respiratory failure. Our aim was to study pulmonary mechanics and gas exchanges in COVID-2019 ARDS patients studied early after initiating protective invasive mechanical ventilation, seeking after corresponding pathophysiological and biological characteristics.

Methods

Between March 22 and March 30, 2020 respiratory mechanics, gas exchanges, circulating endothelial cells (CEC) as markers of endothelial damage, and D-dimers were studied in 22 moderate-to-severe COVID-19 ARDS patients, 1 [1–4] day after intubation (median [IQR]).

Measurements and main results

Thirteen moderate and 9 severe COVID-19 ARDS patients were studied after initiation of high PEEP protective mechanical ventilation. We observed moderately decreased respiratory system compliance: 39.5 [33.1–44.7] mL/cmH₂O and end-expiratory lung volume: 2100 [1721–2434] mL. Gas exchanges were characterized by hypercapnia 55 [44–62] mmHg, high physiological dead-space (V_D/V_T): 75 [69–85.5] % and ventilatory ratio (VR): 2.9 [2.2–3.4]. V_D/V_T and VR were significantly correlated: r² = 0.24, p = 0.014. No pulmonary embolism was suspected at the time of measurements. CECs and D-dimers were elevated as compared to normal values: 24 [12–46] cells per mL and 1483 [999–2217] ng/mL, respectively.

Conclusions

We observed early in the course of COVID-19 ARDS high V_D/V_T in association with biological markers of endothelial damage and thrombosis. High V_D/V_T can be explained by high PEEP settings and added instrumental dead space, with a possible associated role of COVID-19-triggered pulmonary microvascular endothelial damage and microthrombotic process.

Loss of cavin1 and expression of p-caveolin-1 in pulmonary hypertension: Possible role in neointima formation

BACKGROUND

Pulmonary hypertension (PH) is a progressive disease with a high morbidity and mortality rate; and neointima formation leads to the irreversibility of the disease. We have previously reported that in rats, monocrotaline (MCT) injection leads to progressive disruption of endothelial cells (EC), and endothelial caveolin-1 (cav-1) loss, accompanied by the activation of pro-proliferative pathways leading to PH. Four weeks post-MCT, extensive endothelial cav-1 loss is associated with increased cav-1 expression in smooth muscle cells (SMC). Exposing the MCT-treated rats to hypoxia hastens the disease process; and at 4 wk, neointimal lesions and occlusion of the small arteries are observed.

AIM

To identify the alterations that occur during the progression of PH that lead to neointima formation.

METHODS

Male Sprague-Dawley rats (150-175 g) were divided in 4 groups (n = 6-8 per group): controls (C); MCT (M, a single sc injection 40 mg/kg); Hypoxia (H, hypobaric hypoxia); MCT + hypoxia (M+H, MCT-injected rats subjected to hypobaric hypoxia starting on day1). Four weeks later, right ventricular systolic pressure (RVSP), right ventricular hypertrophy (RVH), lung histology, and cav-1 localization using immunofluorescence technique were analyzed. In addition, the expression of cav-1, tyrosine 14 phosphorylated cav-1 (p-cav-1), caveolin-2 (cav-2), cavin-1, vascular endothelial cadherin (VE-Cad) and p-ERK1/2 in the lungs were examined, and the results were compared with the controls.

RESULTS

Significant PH and right ventricular hypertrophy were present in M and H groups [RVSP, mmHg, M 54±5*, H 45±2*, vs C 20±1, P < 0.05; RVH, RV/LV ratio M 0.57±0.02*, H 0.50±0.03*, vs C 0.23±0.007, P < 0.05]; with a further increase in M+H group [RVSP 69±9 mmHg, RV/LV 0.59±0.01 P < 0.05 vs M and H]. All experimental groups revealed medial hypertrophy; but only M+H group exhibited small occluded arteries and neointimal lesions. Immunofluorescence studies revealed endothelial cav-1 loss and increased cav-1 expression in SMC in M group; however, the total cav-1 level in the lungs remained low. In the M+H group, significant endothelial cav-1 loss was associated with increasing expression of cav-1 in SMC; resulting in near normalization of cav-1 levels in the lungs [cav-1, expressed as % control, C 100±0, M 22±4*, H 96±7, M+H 77±6, * = P < 0.05 vs C]. The expression of p-cav-1 was observed in M and M+H groups [M 314±4%, M+H 255±22% P < 0.05 vs C]. Significant loss of cav-2 [% control, C 100±0, M 15±1.4*, H 97±7, M+H 15±2*; M and M+H vs C, * = P < 0.05], cavin-1 [% control, C 100±0, M 20±3*, H 117±7, M+H 20±4*; M and M+H vs C, P < 0.05] and VE-Cad [% control, C 100±0, M 17±4*, H 96±9, M+H 8±3*; M and M+H vs C, P < 0.05] was present in M and M+H groups, confirming extensive disruption of EC. Hypoxia alone did not alter the expression of cav-1 or cav-1 related proteins. Expression of p-ERK1/2 was increased in all 3 PH groups [%control, C 100±0, M 284±23*, H 254±25*, M+H 270±17*; * = P < 0.05 vs C].

CONCLUSION

Both cavin-1 loss and p-cav-1 expression are known to facilitate cell migration; thus, these alterations may in part play a role in neointima formation in PH.

CD34+ Hematopoietic Stem Cell Count Is Predictive of Vascular Event Occurrence in Children with Sickle Cell Disease

BACKGROUND/OBJECTIVES

Sickle cell disease (SCD) complications mostly result from vascular dysfunction, concerning systemic microvasculature and cerebral large vessels. The aim of this cohort study was to identify potential circulating biomarkers predictive for further vascular event occurrence in pediatric SCD.

METHODS

We consecutively enrolled 108 children with SCD at steady state, aged 3-18 years old (median 9.8 years). Hematology, coagulation, hemolysis, endothelial, platelet and vascular activation parameters were recorded at inclusion. Neurovascular and systemic vascular events were prospectively recorded during a mean follow-up period of 27 months.

RESULTS

Patients at steady state displayed significantly higher hemolysis and platelet activation markers, higher leukocyte, CD34+ hematopoietic stem cell and microvesicle counts, and a pro-coagulant profile compared to controls matched for age and ethnicity. Circulating endothelial cell or nucleosome level did not differ. During the follow-up period, 36 patients had at least one neurovascular (n = 12) or systemic vascular event (n = 25). In a multivariate model, high CD34+ cell count was the best predictor for the occurrence of a vascular event (OR 1.2 for 1000 cell/mL increase, 95% CI [1.049-1.4], p = 0.013, sensitivity 53%, specificity 84% for a threshold of 8675 cells/mL).

CONCLUSION

CD34+ cell count at steady state is a promising biomarker of further vascular event in children with SCD.

Circulating endothelial cells as biomarker for cardiovascular diseases

BACKGROUND

Endothelial dysfunction is involved in several cardiovascular diseases. Elevated levels of circulating endothelial cells (CECs) and low levels of endothelial progenitor cells (EPCs) have been described in different cardiovascular conditions, suggesting their potential use as diagnostic biomarkers for endothelial dysfunction. Compared to typical peripheral blood leukocyte subsets, CECs and EPCs occur at very low frequency. The reliable identification and characterization of CECs and EPCs is a prerequisite for their clinical use, however, a validated method to this purpose is still missing but a key for rare cell events.

OBJECTIVES

To establish a validated flow cytometric procedure in order to quantify CECs and EPCs in human whole blood.

METHODS

In the establishment phase, the assay sensitivity, robustness, and the sample storage conditions were optimized as prerequisite for clinical use. In a second phase, CECs and EPCs were analyzed in heart failure with preserved (HFpEF) and reduced (HFrEF) ejection fraction, in arterial hypertension (aHT), and in diabetic nephropathy (DN) in comparison to age-matched healthy controls.

RESULTS

The quantification procedure for CECs and EPCs showed high sensitivity and reproducibility. CEC values resulted significantly increased in patients with DN and HFpEF in comparison to healthy controls. CEC quantification showed a diagnostic sensitivity of 90% and a sensitivity of 68.0%, 70.4%, and 66.7% for DN, HFpEF, and aHT, respectively.

CONCLUSION

A robust and precise assay to quantify CECs and EPCs in pre-clinical and clinical studies has been established. CEC counts resulted to be a good diagnostic biomarker for DN and HFpEF.

Treprostinil treatment decreases circulating platelet microvesicles and their procoagulant activity in pediatric pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) results from pulmonary vascular disease and may eventually lead to right heart failure and death. Vasodilator therapy has greatly improved PAH prognosis. Circulating microvesicles are considered as surrogate markers of endothelial and hematopoietic cell activation.

AIM

Thus, our purpose was to determine if MVs are upregulated in pediatric PAH such as reported in adult patients, and to analyze the impact of vasodilator therapies on MV count and function.

PATIENTS

Population study consisted of 26 patients of median age 6.09 years, with Congenital Heart Disease (CHD) and elevated pulmonary vascular resistance (CHD-PAH) or idiopathic PAH (iPAH).

RESULTS

Compared to healthy controls, all circulating MV subpopulations were found higher in untreated PAH patients. No significant differences of annexin-V+ total MV, endothelial, or leukocyte derived-MV counts were found between untreated patients and those receiving oral vasodilator therapies. Conversely, platelet MVs were significantly lower in the group treated with SC-treprostinil compared with both untreated PAH and oral therapy groups (P = 0.01), and exhibited a significant decrease of phospholipid procoagulant activity. Control samples treated in vitro with treprostinil at therapeutic concentrations showed as expected a significant decrease of platelet aggregation but also a reduced spontaneous MV generation.

CONCLUSION

Our results suggest that treprostinil, besides vasodilation, might exert its beneficial effect through an inhibition of platelet activation, resulting in a decreased number and procoagulant activity of circulating MVs.

Vasculogenic Stem and Progenitor Cells in Human: Future Cell Therapy Product or Liquid Biopsy for Vascular Disease

New blood vessel formation in adults was considered to result exclusively from sprouting of preexisting endothelial cells, a process referred to angiogenesis. Vasculogenesis, the formation of new blood vessels from endothelial progenitor cells, was thought to occur only during embryonic life. Discovery of adult endothelial progenitor cells (EPCs) in 1997 opened the door for cell therapy in vascular disease. Endothelial progenitor cells contribute to vascular repair and are now well established as postnatal vasculogenic cells in humans. It is now admitted that endothelial colony-forming cells (ECFCs) are the vasculogenic subtype. ECFCs could be used as a cell therapy product and also as a liquid biopsy in several vascular diseases or as vector for gene therapy. However, despite a huge interest in these cells, their tissue and molecular origin is still unclear. We recently proposed that endothelial progenitor could come from very small embryonic-like stem cells (VSELs) isolated in human from CD133 positive cells. VSELs are small dormant stem cells related to migratory primordial germ cells. They have been described in bone marrow and other organs. This chapter discusses the reported findings from in vitro data and also preclinical studies that aimed to explore stem cells at the origin of vasculogenesis in human and then explore the potential use of ECFCs to promote newly formed vessels or serve as liquid biopsy to understand vascular pathophysiology and in particular pulmonary disease and haemostasis disorders.

Assessment of reversibility in pulmonary arterial hypertension and congenital heart disease

Pulmonary arterial hypertension (PAH) in congenital heart disease (CHD) can be reversed by early shunt closure, but this potential is lost beyond a certain point of no return. Therefore, it is crucial to accurately assess the reversibility of this progressive pulmonary arteriopathy in an early stage. Reversibility assessment is currently based on a combination of clinical symptoms and haemodynamic variables such as pulmonary vascular resistance. These measures, however, are of limited predictive value and leave many patients in the grey zone. This review provides a concise overview of the mechanisms involved in flow-dependent progression of PAH in CHD and evaluates existing and future alternatives to more directly investigate the stage of the pulmonary arteriopathy. Structural quantification of the pulmonary arterial tree using fractal branching algorithms, functional imaging with intravascular ultrasound, nuclear imaging, putative new blood biomarkers, genetic testing and the potential for transcriptomic analysis of circulating endothelial cells and educated platelets are being reviewed.

Recellularization of Decellularized Venous Grafts Using Peripheral Blood: A Critical Evaluation

Vascular disease is a major cause of death worldwide, and the growing need for replacement vessels is not fully met by autologous grafts or completely synthetic alternatives. Tissue engineering has emerged as a compelling strategy for the creation of blood vessels for reconstructive surgeries. One promising method to obtain a suitable vessel scaffold is decellularization of donor vascular tissue followed by recellularization with autologous cells. To prevent thrombosis of vascular grafts, a confluent and functional autologous endothelium is required, and researchers are still looking for the optimal cell source and recellularization procedure. Recellularization of a decellularized scaffold with only a small volume of whole blood was recently put forward as a feasible option. Here we show that, in contrast to the published results, this method fails to re-endothelialize decellularized veins. Only occasional nucleated cells were seen on the luminal surface of the scaffolds. Instead, we saw fibrin threads, platelets and scattered erythrocytes. Molecular remnants of the endothelial cells were still attached to the scaffold, which explains in part why earlier results were misinterpreted. Decellularized vascular tissues may still be the best scaffolds available for vascular tissue engineering. However, for the establishment of an adequate autologous endothelial lining, methods other than exposure to autologous whole blood need to be developed.

Update on novel targets and potential treatment avenues in pulmonary hypertension

Pulmonary hypertension (PH) is a condition marked by a combination of constriction and remodeling within the pulmonary vasculature. It remains a disease without a cure, as current treatments were developed with a focus on vasodilatory properties but do not reverse the remodeling component. Numerous recent advances have been made in the understanding of cellular processes that drive pathologic remodeling in each layer of the vessel wall as well as the accompanying maladaptive changes in the right ventricle. In particular, the past few years have yielded much improved insight into the pathways that contribute to altered metabolism, mitochondrial function, and reactive oxygen species signaling and how these pathways promote the proproliferative, promigratory, and antiapoptotic phenotype of the vasculature during PH. Additionally, there have been significant advances in numerous other pathways linked to PH pathogenesis, such as sex hormones and perivascular inflammation. Novel insights into cellular pathology have suggested new avenues for the development of both biomarkers and therapies that will hopefully bring us closer to the elusive goal: a therapy leading to reversal of disease.

Decreased circulating thrombomodulin is improved by tadalafil therapy in hypoxemic patients with advanced pulmonary arterial hypertension

INTRODUCTION

Advanced pulmonary arterial hypertension (PAH) in patients with congenital cardiac communications and right-to-left shunting (Eisenmenger syndrome - PAH-ES) is associated with hypoxemia and decreased circulating levels of thrombomodulin (TM), probably reflecting decreased endothelial TM production. The combination of these two factors has been shown to induce fibrin deposition, with increased risk of thrombosis, a well known complication in this syndrome.

PATIENTS AND METHODS

We tested the hypothesis that vasodilator therapy with the phosphodiesterase-5 inhibitor tadalafil, an approved drug for management of PAH could improve endothelial dysfunction markers, in particular plasma TM, in addition to improving the physical capacity (expected effect of pulmonary vasodilatation) in PAH-ES patients. This was a prospective observational study of treatment-naïve patients subjected to specific PAH therapy. Fifteen patients aged 12 to 51years (median 30years) were treated for 6months with a single daily dose of 40mg oral tadalafil. The physical capacity (distance walked during the 6-min walk test - 6MWD), systemic oxygen saturation and laboratory parameters were measured at baseline, and 90days and 180days of treatment.

RESULTS

Plasma TM, which was decreased at baseline compared to controls (p<0.001) increased at 90 and 180days (p=0.003), and this was directly related (r=0.57, p=0.026) to improvement of oxygen saturation (p=0.008). Heightened baseline tissue-type plasminogen activator decreased during treatment (p=0.010), while heightened von Willebrand factor antigen remained unchanged. The 6MWD improved significantly (p<0.001).

CONCLUSION

Tadalafil therapy improved circulating TM and tissue-type plasminogen activator, in addition to improving the physical capacity and oxygen saturation in PAH-ES patients.

Genetic testing and blood biomarkers in paediatric pulmonary hypertension. Expert consensus statement on the diagnosis and treatment of paediatric pulmonary hypertension. The European Paediatric Pulmonary Vascular Disease Network, endorsed by ISHLT and DGPK

Childhood-onset pulmonary arterial hypertension (PAH) is considered complex and multifactorial, with relatively poor estimates of the natural history of the disease. Strategies allowing earlier detection, establishment of disease aetiology together with more accurate and sensitive biomarkers could enable better estimates of prognosis and individualise therapeutic strategies. Evidence is accumulating that genetic defects play an important role in the pathogenesis of idiopathic and hereditary forms of PAH. Altogether nine genes have been reported so far to be associated with childhood onset PAH suggesting that comprehensive multigene diagnostics can be useful in the assessment. Identification of disease-causing mutations allows estimates of prognosis and forms the most effective way for risk stratification in the family. In addition to genetic determinants the analysis of blood biomarkers are increasingly used in clinical practice to evaluate disease severity and treatment responses. As in genetic diagnostics, a multiplex approach can be helpful, as a single biomarker for PAH is unlikely to meet all requirements. This consensus statement reviews the current evidence for the use of genetic diagnostics and use of blood biomarkers in the assessment of paediatric patients with PAH.

Reproducibility of circulating endothelial cell enumeration and activation in children and adolescents

INTRODUCTION

We examined the reproducibility of circulating endothelial cells (CEC) enumeration and activation among youth.

MATERIALS AND METHODS

CECs from 151 youth were measured at baseline and 1 week follow-up. Enumeration of CEC in fresh whole blood was determined by direct assessment of buffy coat smears (CD146+ nucleated cells) and activated CEC (%VCAM-1 expression) was determined after immunomagnetic enrichment and co-staining of nuclei, plus positivity for P1H12 and VCAM-1.

RESULTS

No statistically significant difference in CEC enumeration (1.2 ± 2.5 vs 1.3 ± 2.2 CEC/milliliter of whole blood, p = 0.745) or activated CEC (57.1 ± 24.4 vs 58.0 ± 21.3 %VCAM-1, p = 0.592) between baseline and 1 week follow-up.

CONCLUSION

On a cohort basis, CEC enumeration and activation are reproducible in youth. Relatively high individual biological variability may limit its clinical utility.

Biomarkers for pediatric pulmonary arterial hypertension: challenges and recommendations

Pediatric pulmonary arterial hypertension (PAH) is an uncommon disease that can occur in neonates, infants, and children, and is associated with high morbidity and mortality. Despite advances in treatment strategies over the last two decades, the underlying structural and functional changes to the pulmonary arterial circulation are progressive and lead eventually to right heart failure. The management of PAH in children is complex due not only to the developmental aspects but also because most evidence-based practices derive from adult PAH studies. As such, the pediatric clinician would be greatly aided by specific characteristics (biomarkers) objectively measured in children with PAH to determine appropriate clinical management. This review highlights the current state of biomarkers in pediatric PAH and looks forward to potential biomarkers, and makes several recommendations for their use and interpretation.

Treprostinil indirectly regulates endothelial colony forming cell angiogenic properties by increasing VEGF-A produced by mesenchymal stem cells

Pulmonary vasodilators and prostacyclin therapy in particular, have markedly improved the outcome of patients with pulmonary hypertension (PH). Endothelial dysfunction is a key feature of PH, and we previously reported that treprostinil therapy increases number and proliferative potential of endothelial colony forming cells (ECFC) isolated from PH patients' blood. In the present study, the objective was to determine how treprostinil contributes to the proangiogenic functions of ECFC. We examined the effect of treprostinil on ECFC obtained from cord blood in terms of colony numbers, proliferative and clonogenic properties in vitro, as well as in vivo vasculogenic properties. Surprisingly, treprostinil inhibited viability of cultured ECFC but did not modify their clonogenic properties or the endothelial differentiation potential from cord blood stem cells. Treprostinil treatment significantly increased the vessel-forming ability of ECFC combined with mesenchymal stem cells (MSC) in Matrigel implanted in nude mice. In vitro, ECFC proliferation was stimulated by conditioned media from treprostinil-pretreated MSC, and this effect was inhibited either by the use of VEGF-A blocking antibodies or siRNA VEGF-A in MSC. Silencing VEGF-A gene in MSC also blocked the pro-angiogenic effect of treprostinil in vivo. In conclusion, increased VEGF-A produced by MSC can account for the increased vessel formation observed during treprostinil treatment. The clinical relevance of these data was confirmed by the high level of VEGF-A detected in plasma from patients with paediatric PH who had been treated with treprostinil. Moreover, our results suggest that VEGF-A level in patients could be a surrogate biomarker of treprostinil efficacy.

Impact of Conditional miRNA126 Overexpression on Apoptosis-Resistant Endothelial Cell Production

The activation of endothelial cells is essential to repair damage caused by atherosclerosis via endothelial cell proliferation and migration. Overexpression of VEGF (vascular endothelial growth factor) and the downstream gene, B-cell lymphoma-2 (BCL-2) could result in apoptosis-resistant endothelial cells, which are responsible for aggravated hyperplasia and instable plaques generation. Previous studies have shown that miRNA126 could regulate the expression of VEGF. Here, we verified the existence of a miRNA126 binding site in VEGF's 3'UTR. Additionally, VEGF regulated BCL-2 expression via AP1 (Activator Protein 1) binding site in BCL-2's promoter. Next, we established an apoptosis-resistant endothelial cell line and constructed a lentiviral vector to express miRNA126 under the control of the BCL-2 promoter to investigate whether conditional expression of miRNA126 could modulate VEGF and BCL-2 expression in apoptosis-resistant endothelial cells. This lentiviral system specifically expressed miRNA126 in cells with high BCL-2 levels, downregulated VEGF expression, inhibited MAPK pathway activation and downregulated BCL-2 expression via suppression of AP1, and as a whole, reduced apoptosis-resistant endothelial cells, while the effects of miRNA126 on normal endothelial cells were relatively small. Our results demonstrate that conditional miRNA126 overexpression under the control of the downstream BCL-2 promoter provides a flexible regulatory strategy for reducing the apoptosis-resistant endothelial cells without having a significant impact on normal endothelial cells.

[Pulmonary hypertension associated with congenital heart disease and Eisenmenger syndrome]

Pulmonary arterial hypertension is a common complication of congenital heart disease (CHD). Congenital cardiopathies are the most frequent congenital malformations. The prevalence in our country remains unknown, based on birthrate, it is calculated that 12,000 to 16,000 infants in our country have some cardiac malformation. In patients with an uncorrected left-to-right shunt, increased pulmonary pressure leads to vascular remodeling and endothelial dysfunction secondary to an imbalance in vasoactive mediators which promotes vasoconstriction, inflammation, thrombosis, cell proliferation, impaired apotosis and fibrosis. The progressive rise in pulmonary vascular resistance and increased pressures in the right heart provocated reversal of the shunt may arise with the development of Eisenmenger' syndrome the most advanced form de Pulmonary arterial hypertension associated with congenital heart disease. The prevalence of Pulmonary arterial hypertension associated with CHD has fallen in developed countries in recent years that is not yet achieved in developing countries therefore diagnosed late as lack of hospital infrastructure and human resources for the care of patients with CHD. With the development of targeted medical treatments for pulmonary arterial hypertension, the concept of a combined medical and interventional/surgical approach for patients with Pulmonary arterial hypertension associated with CHD is a reality. We need to know the pathophysiological factors involved as well as a careful evaluation to determine the best therapeutic strategy.

Endothelial progenitor cells and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by lung endothelial cell dysfunction and vascular remodelling. A number of studies now suggest that endothelial progenitor cells (EPCs) may induce neovascularisation and could be a promising approach for cell based therapy for PAH. On the contrary EPCs may contribute to pulmonary vascular remodelling, particularly in end-stage pulmonary disease. This review article will provide a brief summary of the relationship between PAH and EPCs, the application of the EPCs to PAH and highlight the potential clinical application of the EPCs cell therapy to PAH.

Biomarkers for pediatric pulmonary arterial hypertension - a call to collaborate

Therapeutic approaches in pediatric pulmonary arterial hypertension (PAH) are based primarily on clinician experience, in contrast to the evidence-based approach in adults with pulmonary hypertension. There is a clear and present need for non-invasive and objective biomarkers to guide the accurate diagnosis, treatment, and prognosis of this disease in children. The multifaceted spectrum of disease, clinical presentation, and association with other diseases makes this a formidable challenge. However, as more progress is being made in the understanding and management of adult PAH, the potential to apply this knowledge to children has never been greater. This review explores the state of the art with regard to non-invasive biomarkers in PAH, with an eye toward those adult PAH biomarkers potentially suitable for application in pediatric PAH.

Assessment of operability of patients with pulmonary arterial hypertension associated with congenital heart disease

Pulmonary arterial hypertension (PAH) is a common complication of congenital heart disease, and is now predominantly among patients with uncorrected left-to-right shunts. A growing population is characterized by persistent or recurrent PAH after surgical or interventional correction of left-to-right shunts; the latter having a worse prognosis than other forms of PAH associated with congenital heart disease. New treatments for PAH have been shown to be effective in improving PAH exercise capacity and hemodynamics, raising the hope for making previously inoperable congenital heart defects operable and shifting the framework for the assessment of operability. This review focuses on current methods for assessing operability in PAH associated with congenital heart disease, and the possibility of "treat-and-repair" vs. "repair-and-treat" strategies for patients with inoperable or borderline PAH.