Technical notes on endothelial progenitor cells: ways to escape from the knowledge plateau

Molecular analysis of endothelial progenitor cell (EPC) subtypes reveals two distinct cell populations with different identities

Background

The term endothelial progenitor cells (EPCs) is currently used to refer to cell populations which are quite dissimilar in terms of biological properties. This study provides a detailed molecular fingerprint for two EPC subtypes: early EPCs (eEPCs) and outgrowth endothelial cells (OECs).

Methods

Human blood-derived eEPCs and OECs were characterised by using genome-wide transcriptional profiling, 2D protein electrophoresis, and electron microscopy. Comparative analysis at the transcript and protein level included monocytes and mature endothelial cells as reference cell types.

Results

Our data show that eEPCs and OECs have strikingly different gene expression signatures. Many highly expressed transcripts in eEPCs are haematopoietic specific (RUNX1, WAS, LYN) with links to immunity and inflammation (TLRs, CD14, HLAs), whereas many transcripts involved in vascular development and angiogenesis-related signalling pathways (Tie2, eNOS, Ephrins) are highly expressed in OECs. Comparative analysis with monocytes and mature endothelial cells clusters eEPCs with monocytes, while OECs segment with endothelial cells. Similarly, proteomic analysis revealed that 90% of spots identified by 2-D gel analysis are common between OECs and endothelial cells while eEPCs share 77% with monocytes. In line with the expression pattern of caveolins and cadherins identified by microarray analysis, ultrastructural evaluation highlighted the presence of caveolae and adherens junctions only in OECs.

Conclusions

This study provides evidence that eEPCs are haematopoietic cells with a molecular phenotype linked to monocytes; whereas OECs exhibit commitment to the endothelial lineage. These findings indicate that OECs might be an attractive cell candidate for inducing therapeutic angiogenesis, while eEPC should be used with caution because of their monocytic nature.

Time course and mechanisms of circulating progenitor cell reduction in the natural history of type 2 diabetes

OBJECTIVE

Reduction of bone marrow-derived circulating progenitor cells has been proposed as a novel mechanism of cardiovascular disease in type 2 diabetes. The present study was designed to describe the extent and potential mechanisms of progenitor cell reduction during the natural history of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We identified 425 individuals, divided into seven categories according to carbohydrate metabolism status (normal glucose tolerance [NGT], impaired fasting glucose, impaired glucose tolerance [IGT], and newly diagnosed type 2 diabetes) and diabetes duration (0-9, 10-19, and >or=20 years). These categories were examined as ideally describing the natural history of type 2 diabetes development and progression. We measured CD34+ and CD34+KDR+ progenitor cells by flow cytometry. We also evaluated progenitor cells in 20 coupled bone marrow and peripheral blood samples and examined progenitor cell apoptosis in 34 subjects.

RESULTS

In comparison to NGT, CD34+ cells were significantly reduced in IGT and had a first nadir in newly diagnosed type 2 diabetes and a second nadir after 20 years of diabetes. Statistical adjustment for possible confounders confirmed that CD34+ cell counts are deeply reduced at time of diagnosis, that they partially recover during the subsequent 0-19 years, and that they dip again after >or=20 years. A similar, but less consistent, trend was detected for CD34+KDR+ cells. Peripheral blood CD34+ cells were directly correlated with bone marrow CD34+ cells and inversely correlated with CD34+ cell apoptosis.

CONCLUSIONS

Circulating progenitor cell reduction marks the clinical onset of type 2 diabetes. Both defective mobilization and increased apoptosis may account for this phenomenon. While a partial recovery occurs during subsequent years, bone marrow reserve seems exhausted in the long term.

Comparison of endothelial progenitor cell function in type 2 diabetes with good and poor glycemic control

BACKGROUND

Endothelial progenitor cells (EPCs) play an important role in vascular repair and a decrease in the number of EPCs is observed in type 2 diabetes. However, there is no report on the change of EPCs after glycemic control. This study therefore aimed to investigate the EPC number and function in patients with good and poor glycemic control.

METHODS

The number of EPCs was studied using flow cytometry by co-expression of CD34 and VEGFR2. The EPCs were cultured and characterized by the expression of UEA-I, CD34, VEGFR2, vWF and Dil-Ac-LDL engulfment, as well as the ability to form capillary-like structures. An in vitro study on the effect of hyperglycemia on the proliferation and viability of the cultured EPCs was also performed.

RESULTS

The number of EPCs in type 2 diabetes was significantly decreased compared with healthy controls and there was an inverse correlation between the EPC numbers and plasma glucose, as well as HbA1C. The number and function of EPCs in patients with good glycemic control were recovered compared with those with poor glycemic control. When glucose was supplemented in the culture in vitro, there was a negative effect on the proliferation and viability of EPCs, in a dose-dependent manner, whereas the enhancement of apoptosis was observed.

CONCLUSION

There was EPC dysfunction in type 2 diabetes which might be improved by strict glycemic control. However, the circulating EPC number and proliferative function in patients with good glycemic control did not reach the level in healthy controls.

Unacylated ghrelin rescues endothelial progenitor cell function in individuals with type 2 diabetes

OBJECTIVE

Acylated ghrelin (AG) is a diabetogenic and orexigenic gastric polypeptide. These properties are not shared by the most abundant circulating form, which is unacylated (UAG). An altered UAG/AG profile together with an impairment of circulating endothelial progenitor cell (EPC) bioavailability were found in diabetes. Based on previous evidence for the beneficial cardiovascular effects of AG and UAG, we investigated their potential to revert diabetes-associated defects.

RESEARCH DESIGN AND METHODS

Healthy human subjects, individuals with type 2 diabetes, and ob/ob mice were AG or UAG infused. EPC mobilization in patients and mice was evaluated, and the underlying molecular mechanisms were investigated in bone marrow stromal cells. Recovered EPCs were also evaluated for the activity of senescence regulatory pathways and for NADPH oxidase activation by knocking down p47(phox) and Rac1. Finally, UAG modulation of human EPC vasculogenic potential was investigated in an in vivo mouse model.

RESULTS

Neither AG nor UAG had any effect in healthy subjects. However, systemic administration of UAG, but not AG, prevented diabetes-induced EPC damage by modulating the NADPH oxidase regulatory protein Rac1 and improved the vasculogenic potential both in individuals with type 2 diabetes and in ob/ob mice. In addition, unlike AG, UAG facilitated the recovery of bone marrow EPC mobilization. Crucial to EPC mobilization by UAG was the rescue of endothelial NO synthase (eNOS) phosphorylation by Akt, as UAG treatment was ineffective in eNOS knockout mice. Consistently, EPCs expressed specific UAG-binding sites, not recognized by AG.

CONCLUSIONS

These data provide the rationale for clinical applications of UAG in pathologic settings where AG fails.

Circulating vascular progenitor cells in patients with type 1 diabetes and microalbuminuria

OBJECTIVE

Patients with type 1 diabetes and microalbuminuria are at increased risk of cardiovascular disease (CVD). Abnormalities in vascular progenitor cells, which participate in vascular repair, may be implicated in this susceptibility.

RESEARCH DESIGN AND METHODS

We studied the number and function of vascular progenitor cells in 22 type 1 diabetic patients with history of microalbuminuria (MA(+)) and 22 type 1 diabetic patients without history of microalbuminuria (MA(-)), of similar age, diabetes duration, glycemic control, renal function, and no history of CVD.

RESULTS

MA(+) patients had lower circulating CD34(+) and CD34(+)/CD133(+) cell numbers compared with MA(-) patients (P < 0.006). In in vitro functional assays, MA(+) patients had a significantly lower number of colony-forming units and impaired vascular endothelial growth factor (VEGF)-A-mediated tube formation, when compared with MA(-) patients (P < 0.01).

CONCLUSIONS

In type 1 diabetic patients with microalbuminuria, a marker of microvascular injury and a risk factor for CVD, circulating vascular progenitor cell number is reduced and function is impaired.

Relationship between circulating progenitor cells, vascular function and oxidative stress with long-term training and short-term detraining in older men

Exercise may contribute to the maintenance of vascular function via enhanced liberation and action of bone-marrow-derived progenitor cells. Activity related changes in oxidative stress may also influence the number and function of these cells. In the present study, we sought to determine (i) whether adaptations in reactive hyperaemic FBF (forearm blood flow) response associated with long-term endurance exercise and short-term detraining were related to resting putative progenitor cell number and function, and (ii) whether oxidative stress affected these factors. Participants included men with a history of more than 30 years of moderate-to-high intensity exercise (HI group) and healthy low-active age- and BMI (body mass index)-matched control subjects (LO group). Vascular reactive hyperaemic FBF response, resting CD34+ and CD34+/VEGFR2+ (vascular endothelial growth factor receptor 2+] cell number, CFU-EC (colony forming unit-endothelial cell) count and CFU-EC senescence were evaluated. Oxidative stress measures included OxLDL (oxidized low-density lipoprotein) and TAC (total antioxidant capacity).These measures were assessed following 10 days of detraining in the HI group. The HI group had greater peak reactive hyperaemic FBF responses compared with the LO group, despite no difference in resting CD34+ cell number, CD34+/VEGFR2+ cell number, CFU-EC colonies or CFU-EC senescence. With detraining in the HI group, CD34+ cells declined 44 %, and the percentage change in CD34+/VEGFR2+ cells was positively correlated with the change in FBF response to reactive hyperaemia. The percentage change in CD34+/VEGFR2+ cells and the percentage change in EPC (endothelial progenitor cell) senescence with detraining were related to the percentage change in TAC. These results reveal that changes in reactive hyperaemic FBF are closely related to activity dependent dynamic changes in CD34+/VEGFR2+ cell number, which may be influenced by alterations in oxidative stress.

Selective estrogen receptor-alpha agonist provides widespread heart and vascular protection with enhanced endothelial progenitor cell mobilization in the absence of uterotrophic action

The beneficial effects of estrogens on the cardiovascular system are associated with adverse effects on reproductive tissues. On the basis of previous work indicating a major role for estrogen receptor (ER)-alpha in maintaining cardiovascular health, we evaluated the tissue selectivity of the ER alpha-selective agonist propyl pyrazole triol (PPT) compared with 17beta-estradiol (E2) in vivo. Four weeks postovariectomy, equimolar doses of PPT and E2 were administered to rats in subcutaneous implants for 5 d. Both treatments restored rapid vasorelaxation of aortic tissue to estrogenic agents and prevented coronary hyperresponsiveness to angiotensin II in isolated heart preparations. Accordingly, multiple endpoints of myocardial ischemia-reperfusion injury exacerbated by ovariectomy returned to baseline following treatment. These protective effects were linked to increased in vivo levels of endothelial progenitor cells (EPCs). Human EPC function was enhanced in vitro after PPT treatment. In sharp contrast to E2, PPT treatment had no effect on uterine weight and histomorphology except for vessel density, and failed to up-regulate classic estrogen target genes. Dissection of the effects on vascular reactivity and uterine morphology was also observed following increased exposure to PPT at a higher dose for longer time. These data provide the first in vivo evidence for tissue-specific ER alpha activation. By conferring cardiovascular protection dissected from unwanted uterotrophic effects, ER alpha-selective agonists may represent a potential safer alternative to natural hormones.

Transdifferentiation of bone marrow-derived endothelial progenitor cells into the smooth muscle cell lineage mediated by tansforming growth factor-beta1

OBJECTIVE

The aim of this study was to investigate the transdifferentiation of bone marrow (BM)-derived endothelial progenitor cells (EPCs) into the smooth muscle cell (SMC) lineage in vitro and in vivo.

METHODS AND RESULTS

EPCs were obtained from BM of rats and cultured on fibronectin-coated dishes for 15 days. Treatment of EPCs with transforming growth factor (TGF)-beta1 for 7 days changed morphology of EPCs, reduced the expression of endothelial markers in EPCs, induced the expression of SMC markers, and enhanced their proliferation. EPCs expressed TGF-beta receptor type II (TGF-beta RII) and TGF-beta1 induced the phosphorylation of Smad 2 in EPCs. TGF-beta1-induced transdifferentiation was specifically inhibited by neutralizing antibody against TGF-beta and gene silencing of TGF-beta RII. Local transplantation of autologous EPCs enhanced intimal hyperplasia of the balloon-injured artery on day 28. Transplanted EPCs were localized near the endothelial layer on day 14 but widely distributed within the hypertrophic neointima on day 28 differentiating toward SMC lineage. Neither expression of growth factors such as TGF-beta1 nor early inflammatory reactions within the denuded arteries were promoted by transplantation of EPCs.

CONCLUSIONS

TGF-beta1 induced the transdifferentiation of BM-derived EPCs toward SMC lineage mediated by TGF-beta RII. The augmentation of intimal hyperplasia by transplantation of EPCs was probably due to the transdifferentiation and proliferation of EPCs induced by TGF-beta1.

Optical characterization of colloidal CdSe quantum dots in endothelial progenitor cells

We have quantitatively analyzed the confocal spectra of colloidal quantum dots (QDs) in rat endothelial progenitor cells (EPCs) by using Leica TCS SP5 Confocal Microscopy System. Comparison of the confocal spectra of QDs located inside and outside EPCs revealed that the interaction between the QDs and EPCs effectively reduces the radius of the exciton confinement inside the QDs so that the excitonic energy increases and the QD fluorescence peak blueshifts. Furthermore, the EPC environment surrounding the QDs shields the QDs so that the excitation of the QDs inside the cells is relatively weak, whereas the QDs outside the cells can be highly excited. At high excitations, the occupation of the ground excitonic state in the QD outside the cells becomes saturated and high-energy states excited, resulting in a large relaxation energy and a broad fluorescence peak. This permits, in concept, to use QD biomarkers to monitor EPCs by characterizing QD fluorescence spectra.

Decreased number and impaired functionality of endothelial progenitor cells in subjects with metabolic syndrome: implications for increased cardiovascular risk

OBJECTIVE

Metabolic syndrome (MetS) is characterized by low-grade inflammation and confers an increased risk for cardiovascular disease. Endothelial progenitor cells (EPCs) are a measure of vascular health and are decreased in patients with various risk factors for cardiovascular disease (CVD). There is a paucity of data examining the EPC status especially in terms of their functionality in MetS subjects without diabetes or cardiovascular disease. We aimed to enumerate and functionally characterize EPCs in subjects with MetS in comparison to healthy controls.

METHODS

The study was performed at the University of California Davis Medical Center. Healthy controls (n=31) and MetS (n=46) subjects were included in the study. EPCs were enumerated in fasting blood by KDR/CD34 dual positivity. Functionality was assessed by the colony forming units (CFU) assay, migration and tubule formation.

RESULTS

Subjects with MetS had significantly decreased number of EPCs compared to control subjects. Furthermore, EPCs from MetS subjects depicted significantly impaired clonogenic capacity, i.e., decreased colony forming units, and impaired capacity to incorporate into tubular structures suggesting functional impairment of EPCs from MetS subjects.

CONCLUSIONS

We make the novel observation that MetS subjects without diabetes or CVD have decreased EPC number and impaired functionality as compared to control subjects. These findings could contribute to the increased CV risk in this population.

Reduced endothelial progenitor cells and brachial artery flow-mediated dilation as evidence of endothelial dysfunction in ocular hypertension and primary open-angle glaucoma

PURPOSE

This study aimed to assess vascular endothelial function in patients with ocular hypertension (OHT) or primary open-angle glaucoma (POAG) by measuring: (a) endothelium-dependent flow-mediated vasodilation (FMD) of the brachial artery, and (b) circulating endothelial progenitor cells, which are believed to support the integrity of the vascular endothelium.

METHODS

We enrolled 25 patients with OHT, 23 with POAG and 26 control subjects, all of whom were aged < 65 years and had no medical history of cardiovascular disease or cardiovascular risk factors. All subjects underwent a complete ophthalmological examination, biochemistry study, assessment of cardiovascular parameters, brachial artery ultrasound assessment of endothelium-dependent FMD, generic circulating progenitor cell (CPC) and circulating endothelial progenitor cell (EPC) count with the use of flow cytometry.

RESULTS

Flow-mediated vasodilation values differed significantly in OHT (4.5 +/- 1.1%; p = 0.021) and POAG (4.0 +/- 0.9%; p = 0.003) patients compared with controls (7.7 +/- 0.8%). The CD34(+) KDR(+) EPC count was markedly lower in OHT (28.0 +/- 5.0; p < 0.001) and POAG (24.3 +/- 3.4; p < 0.001) patients compared with controls (73.1 +/- 8.1). Neither FMD not EPCs differed significantly between OHT and POAG patients. No significant differences in CPC count or cardiovascular parameters were found among OHT or POAG patients and controls. The levels of CD34(+) KDR(+) EPCs were directly correlated (p = 0.043) with FMD, and inversely correlated (p = 0.032) with baseline intraocular pressure in OHT and POAG patients.

CONCLUSIONS

Both OHT and POAG patients without cardiovascular risk factors have previously unreported severely reduced circulating EPCs and reduced FMD, both of which are indicators of endothelial dysfunction and increased risk of cardiovascular events.

Reduction of both number and proliferative activity of human endothelial progenitor cells in obesity

OBJECTIVE

Circulating endothelial progenitor cells (EPCs), responsible for neoangiogenesis and vascular repair, negatively correlate with vascular dysfunction and atherosclerotic risk factors. Because obesity may have a crucial role in the development of endothelial dysfunction, this study evaluated the number and proliferative activity of circulating human EPCs in obese (body mass index (BMI)=48+/-9, n=45) compared with lean (23+/-2, n=45) volunteers.

METHODS

EPCs were quantified after isolation of peripheral blood mononuclear cells (PBMCs) using fluorescence-activated cell sorting analyses. In addition, plated PBMCs developed colony-forming units (CFUs) from which 'outgrowth' endothelial cells (OECs) sprouted and differentiated into mature endothelial cells. Growth rates were monitored by periodical microscopic evaluation. Cell-cycle protein expression was determined by western blot analyses.

RESULTS

BMI negatively correlated (P<0.01) with the number of CD34(+)/CD133(+)/KDR(+) (r=-0.442), CD34(+)/KDR(+) (r=-0.500) and CD133(+)/KDR(+) (r=-0.282) EPCs. Insulin, leptin, HbA(1c), high-sensitivity C-reactive protein and hypertension, as well as diminished high-density lipoprotein and apolipoprotein A1, were not only associated with obesity but also with significantly reduced EPC levels. Applying selective culture conditions, EPC-CFUs differentiated into OECs that proliferated more slowly when derived from obese compared with lean subjects (obese: 19.9+/-2.2% vs lean: 30.9+/-3.2% grown area per week, P<0.01). The reduced proliferation was reflected by decreased (P<0.05, n=24 for each group) expression of cell-cycle-promoting cyclins and E2F-1, by hypophosphorylation of retinoblastoma protein and by increased (P<0.05, n=24 for each group) expression of the cell-cycle inhibitor p21(WAF-1/Cip1).

CONCLUSIONS

Reduced numbers of EPCs along with their premature senescence, as shown in this study, could function as early contributors to the development and progression of vascular dysfunction in obesity.

Mechanisms and markers of vascular damage in ANCA-associated vasculitis

Much progress has been made in understanding the pathogenesis of anti-neutrophil cytoplasmic antibodies (ANCA)-associated small-vessel vasculitis and interaction between ANCA and micro-vascular endothelial cells are centre stage. The interactions of these key players culminate in respiratory burst of the neutrophil with release of radicals and proteases and subsequent endothelial cell and tissue damage. During the last decade, markers have become available to assess the extent and/or acuity of vascular damage in a clinical setting. First, circulating endothelial cells (CEC) have emerged as reliable surrogate markers of endothelial damage in vasculitis. More recently, endothelial microparticles have been used and appear to reflect damage and activation of the cells. Data on endothelial progenitor cells in vasculitis are sparse but intriguing while a genuine progenitor cell deficiency remains controversial. The severely damaged phenotype of CEC in vasculitis led to the hypothesis that such circulating apoptotic and/or necrotic debris may itself be a mediator of disease and first data from experimental studies have added proof to this assumption. Such effects may well contribute to a pro-inflammatory environment in ANCA-associated small-vessel vasculitis and in vascular disease in general. Here, we review mechanisms and markers of endothelial damage and repair in ANCA-associated vasculitis and put these findings into perspective.

Angiotensin II receptor antagonism with telmisartan increases number of endothelial progenitor cells in normotensive patients with coronary artery disease: a randomized, double-blind, placebo-controlled study

INTRODUCTION

Circulating endothelial progenitor cells (EPCs) provide an endogenous repair mechanism of the dysfunctional endothelium and therefore can play a crucial role in the pathophysiology of coronary artery disease (CAD). Angiotensin II receptor antagonism has been shown to be able to increase EPCs in hypertension but its effect in patients with CAD is unknown. Aim of this study was to evaluate whether telmisartan, an angiotensin II receptor antagonist, can modify the number of subpopulations of EPCs and may in turn affect the endothelial function of normotensive patients with CAD.

METHODS

In a prospective double-blind parallel group study, 40 normotensive patients with CAD were randomly treated with telmisartan (80 mg) or placebo for 4 weeks at time of coronary angiography. Measurements of EPCs and assessment of flow-mediated dilatation (FMD) of the brachial artery was performed before and after therapy.

RESULTS

Absolute number of EPCs was similar at baseline in the telmisartan and placebo groups. After 4 weeks treatment, CD34+/KDR+/CD45- cells increased significantly in the telmisartan group (from 0.010+/-0.003 to 0.014+/-0.004%, P=0.0001) but not in the placebo group (from 0.009+/-0.004 to 0.009+/-0.005%, NS). Similarly, CD133+/KDR+/CD45- cells raised significantly with telmisartan (from 0.003+/-0.002 to 0.006+/-0.002%, P=0.0001) but not with placebo (from 0.004+/-0.003 to 0.003+/-0.002%, NS). Also, CD14+/CD45+ cells increased significantly with telmisartan (from 0.005+/-0.002 to 0.008+/-0.002%, P=0.0001) and were unchanged with placebo (0.006+/-0.002 vs. 0.005+/-0.003%, NS). FMD improved significantly in patients who received telmisartan (10.4+/-3.9%, P=0.0015 vs. baseline) but did not change in the placebo group (5.9+/-2.8%; P=0.32 vs. baseline; telmisartan vs. placebo, P=0.002). A significant positive correlation was found in the telmisartan group between the improvement in FMD and the increase in CD34+/KDR+/CD45- cells and CD133+/KDR+/CD45- cells (r=0.55, P<0.01, and r=0.49, P<0.05, respectively).

CONCLUSION

Angiotensin II receptor antagonism with telmisartan increases the number of regenerative EPCs and improves endothelial function in normotensive patients with CAD. These novel effects are interrelated and can explain, at least in part, why telmisartan has beneficial cardiovascular effects independent of its blood pressure lowering action.

Role of endothelial progenitor cells in diabetes mellitus

Endothelial progenitor cells (EPCs) are bone marrow-derived cells involved in endothelial healing and angiogenesis. EPCs are considered an integrated component of the cardiovascular system, which promotes vascular health. Derangement of EPC biology in diabetes has been hailed as a novel concept in the pathogenesis of micro- and macro-vascular complications. Additionally, EPCs are considered to be disease biomarkers, as they provide an index of cardiovascular risk. The mechanisms leading to EPC dysfunction in diabetes may include defective mobilization from bone marrow to peripheral blood and reduced half-life. Hyperglycemia is considered the major determinant of microvascular complications, while other mechanisms concur to increase the risk of cardiovascular disease in diabetic patients. EPCs may represent a novel pathophysiological connection to understand development and progression of diabetic complications.

Evidence of dysfunction of endothelial progenitors in pulmonary arterial hypertension

RATIONALE

Severe pulmonary arterial hypertension (PAH) is characterized by the formation of plexiform lesions and concentric intimal fibrosis in small pulmonary arteries. The origin of cells contributing to these vascular lesions is uncertain. Endogenous endothelial progenitor cells are potential contributors to this process.

OBJECTIVES

To determine whether progenitors are involved in the pathobiology of PAH.

METHODS

We performed immunohistochemistry to determine the expression of progenitor cell markers (CD133 and c-Kit) and the major homing signal pathway stromal cell-derived factor-1 and its chemokine receptor (CXCR4) in lung tissue from patients with idiopathic PAH, familial PAH, and PAH associated with congenital heart disease. Two separate flow cytometric methods were employed to determine peripheral blood circulating numbers of angiogenic progenitors. Late-outgrowth progenitor cells were expanded ex vivo from the peripheral blood of patients with mutations in the gene encoding bone morphogenetic protein receptor type II (BMPRII), and functional assays of migration, proliferation, and angiogenesis were undertaken. measurements and main results: There was a striking up-regulation of progenitor cell markers in remodeled arteries from all patients with PAH, specifically in plexiform lesions. These lesions also displayed increased stromal cell-derived factor-1 expression. Circulating angiogenic progenitor numbers in patients with PAH were increased compared with control subjects and functional studies of late-outgrowth progenitor cells from patients with PAH with BMPRII mutations revealed a hyperproliferative phenotype with impaired ability to form vascular networks.

CONCLUSIONS

These findings provide evidence of the involvement of progenitor cells in the vascular remodeling associated with PAH. Dysfunction of circulating progenitors in PAH may contribute to this process.

Effects of androgens on endothelial progenitor cells in vitro and in vivo

The beneficial or detrimental effects of androgens on the cardiovascular system are debated. Endothelial progenitor cells are bone-marrow-derived cells involved in endothelial healing and angiogenesis, which promote cardiovascular health. Oestrogens are potent stimulators of endothelial progenitor cells, and previous findings have indicated that androgens may improve the biology of these cells as well. In the present study, we show that testosterone and its active metabolite dihydrotestosterone exert no effects on the expansion and function of late endothelial progenitors isolated from the peripheral blood of healthy human adult males, whereas they positively modulate early ‘monocytic’ endothelial progenitor cells. In parallel, we show that castration in rats is followed by a decrease in circulating endothelial progenitor cells, but that testosterone and dihydrotestosterone replacement fails to restore endothelial progenitor cells towards normal levels. This is associated with persistently low oestrogen levels after androgen replacement in castrated rats. In a sample of 62 healthy middle-aged men, we show that circulating endothelial progenitor cell levels are more directly associated with oestradiol, rather than with testosterone, concentrations. In conclusion, our results collectively demonstrate that androgens exert no direct effects on endothelial progenitor cell biology in vitro and in vivo.

Endothelial colony-forming cells from preterm infants are increased and more susceptible to hyperoxia

RATIONALE

Preterm birth and hyperoxic exposure increase the risk for bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by impaired vascular and alveolar growth. Endothelial progenitor cells, such as self-renewing highly proliferative endothelial colony-forming cells (ECFCs), may participate in vascular repair. The effect of hyperoxia on ECFC growth is unknown.

OBJECTIVES

We hypothesize that umbilical cord blood (CB) from premature infants contains more ECFCs with greater growth potential than term CB. However, preterm ECFCs may be more susceptible to hyperoxia.

METHODS

ECFC colonies were quantified by established methods and characterized by immunohistochemistry and flow cytometry. Growth kinetics were assessed in room air and hyperoxia (FI(O(2)) = 0.4).

MEASUREMENTS AND MAIN RESULTS

Preterm CB (28-35 wk gestation) yielded significantly more ECFC colonies than term CB. Importantly, we found that CD45(-)/CD34(+)/CD133(+)/VEGFR-2(+) cell number did not correlate with ECFC colony count. Preterm ECFCs demonstrated increased growth compared with term ECFCs. Hyperoxia impaired growth of preterm but not term ECFCs. Treatment with superoxide dismutase and catalase enhanced preterm ECFC growth during hyperoxia.

CONCLUSIONS

Preterm ECFCs appear in increased numbers and proliferate more rapidly but have an increased susceptibility to hyperoxia compared with term ECFCs. Antioxidants protect preterm ECFCs from hyperoxia.

Endothelial progenitor cell dysfunction in rheumatic disease

Rheumatic disease is characterized by inflammation and endothelial dysfunction, which contribute to accelerated atherosclerosis. Circulating endothelial progenitor cells (EPCs) can restore dysfunctional endothelium and thereby protect against atherosclerotic vascular disease. The number and function of EPCs are, however, affected in rheumatic diseases such as psoriatic arthritis, rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, and antineutrophil cytoplasmic autoantibody-associated vasculitis. rheumatic disease is often characterized by decreased numbers, and impaired function, of EPCs, although numbers of these cells might increase during the initial years of systemic sclerosis. Pioneering studies show that EPC dysfunction might be improved with pharmacological treatment. How best to restore EPC function, and whether achieving this aim can prevent long-term cardiovascular complications in rheumatic disease, remain to be established.

Circulating endothelial cells, microparticles and progenitors: key players towards the definition of vascular competence

The balance between lesion and regeneration of the endothelium is critical for the maintenance of vessel integrity. Exposure to cardiovascular risk factors (CRF) alters the regulatory functions of the endothelium that progresses from a quiescent state to activation, apoptosis and death. In the last 10 years, identification of circulating endothelial cells (CEC) and endothelial-derived microparticles (EMP) in the circulation has raised considerable interest as non-invasive markers of vascular dysfunction. Indeed, these endothelial-derived biomarkers were associated with most of the CRFs, were indicative of a poor clinical outcome in atherothrombotic disorders and correlated with established parameters of endothelial dysfunction. CEC and EMP also behave as potential pathogenic vectors able to accelerate endothelial dysfunction and promote disease progression. The endothelial response to injury has been enlarged by the discovery of a powerful physiological repair process based on the recruitment of circulating endothelial progenitor cells (EPC) from the bone marrow. Recent studies indicate that reduction of EPC number and function by CRF plays a critical role in the progression of cardiovascular diseases. This EPC-mediated repair to injury response can be integrated into a clinical endothelial phenotype defining the ‘vascular competence’ of each individual. In the future, provided that standardization of available methodologies could be achieved, multimarker strategies combining CEC, EMP and EPC levels as integrative markers of ‘vascular competence’ may offer new perspectives to assess vascular risk and to monitor treatment efficacy.

Circulating CD34+/KDR+ endothelial progenitor cells are reduced in chronic heart failure patients as a function of Type D personality

The aim of the present study was to assess whether EPC (endothelial progenitor cell) number/function might be an explanatory factor for the observed relationship between Type D personality (a joint tendency towards negative affectivity and social inhibition) and poor cardiovascular prognosis. We also assessed whether the effect of a single exercise bout on EPC number/function was affected by Type D personality. A total of 35 sedentary men with CHF (chronic heart failure; left ventricular ejection fraction <or=45%) underwent CPET (cardiopulmonary exercise testing) and personality assessment with the 14-item Type D scale. CD34+/KDR (kinase insert domain-containing receptor)+ cells were quantified by flow cytometry before and immediately after CPET. Migration of early EPC towards VEGF (vascular endothelial growth factor) and SDF-1alpha (stromal-cell-derived factor-1alpha) was investigated. Type D (n=10) and non-Type D (n=25) patients were comparable with regards to demographics, disease severity and Framingham risk factor score. Circulating EPC numbers were reduced by 54% in Type D compared with non-Type D patients (0.084+/-0.055 and 0.183+/-0.029% of lymphocytes respectively; P=0.006). Exercise led to a 60% increase in EPC in Type D patients, whereas the EPC number remained unchanged in the non-Type D group (P=0.049). Baseline migratory capacity was related to disease severity, but was not different between Type D and non-Type D patients. Exercise induced a highly significant enhancement of migratory capacity in both groups. In conclusion, reduced EPC numbers might explain the impaired cardiovascular outcome in Type D patients. The larger increase in circulating EPCs observed in these patients suggests that acute exercise elicits a more pronounced stimulus for endothelial repair.

Detection and characterization of circulating endothelial progenitor cells in normal rat blood

INTRODUCTION

There are currently few widely accepted noninvasive detection methods for drug-induced vascular damage. Circulating endothelial progenitor cell (EPC) enumeration in humans has recently gained attention as a potential biomarker of vascular injury/endothelial damage/dysfunction. The rat is commonly used in preclinical drug development toxicity testing and lacks consensus noninvasive methodologies for immunophenotypic identification of EPCs. Identification of immunophenotypic markers of EPCs in the rat would enable transfer of technologies used in human for potential development of biomarkers for vascular injury the rat. Therefore, the aim of this work was to develop methods to consistently identify a discreet population of EPCs from rat peripheral blood.

METHODS

EPCs were identified phenotypically from rat blood using cell culture, immunolabeling, fluorescence microscopy, and flow cytometry. EPCs isolated using immunolabeling coupled with magnetic separation and flow cytometric cell sorting were characterized genotypically using mRNA analysis.

RESULTS

A modified colony forming unit (CFU)-Hill assay confirmed existence of immature EPCs in peripheral blood. Extended in vitro culture resulted in a morphology and immunophenotype consistent with mature endothelial cells as noted by positive staining for CD31, von Willebrand factor, rat endothelial cell antigen, and negative staining for smooth muscle cell alpha-actin. The majority of the cells identified as LDL+/CD11b/c(-) did not stain positively for either vWF or CD31. EPC populations isolated using magnetic separation and cell sorting were consistently positive for PECAM1, EDN1, FLK1, VWF, ITGAD, CCR1, IP30, and MMP2 mRNA expression. Cells identified as EPCs express cell-surface and gene expression markers consistent with endothelial cells and endothelial progenitor cell populations.

DISCUSSION

Vascular trauma induces transient mobilization of EPCs in humans and their enumeration and characterization have been proposed as a surrogate biomarker for assessment of vascular injury. Potential exists for using rat circulating EPCs as a surrogate sampling population for biomarker development in drug-related injury in preclinical toxicity studies. A prerequisite to biomarker development is the ability to consistently identify a discreet population of EPCs from peripheral rat blood. This work describes novel methods for isolation and validation of phenotypically and genotypically consistent populations of rat EPCs from peripheral blood. These methods are well suited for potential future use in validation of enumeration and/or biomarker development methods in the rat.

Cell therapies for therapeutic angiogenesis: back to the bench

The discovery, over a decade ago, of endothelial progenitor cells that are able to participate in neovascularization of adult tissue has been greeted enthusiastically because of the potential for new cell-based therapies for therapeutic angiogenesis. Since that time, an ever-growing list of candidate cells has been proposed for cardiovascular regeneration. However, to date, pre-clinical and clinical studies evaluating the therapeutic potential of various cell therapies have reported conflicting results, generating controversy. Key issues within the field of cell therapy research include a lack of uniform cellular definitions, as well as inadequate functional characterization of the role of putative stem/progenitor cells in angiogenesis. Given the mixed results of initial clinical studies, there is now a scientific imperative to understand better the vascular biology of candidate cells in order to better translate cell therapy to the bedside. This review will provide a translationally relevant overview of the biology of candidate stem/progenitor cells for therapeutic angiogenesis.

Comparison of the effects of ramipril versus telmisartan on high-sensitivity C-reactive protein and endothelial progenitor cells after acute coronary syndrome

To compare the anti-inflammatory and endothelial progenitor cell mobilizing effects of ramipril and telmisartan in patients presenting with acute coronary syndrome (ACS), 42 patients with ACS were randomized after successful percutaneous coronary intervention to ramipril 5 mg/day (22 patients) or telmisartan 80 mg/day (20 patients). Peripheral blood samples were drawn at baseline and at 20 days to measure high-sensitivity C-reactive protein and to assess 4 populations of progenitor cells by flow cytometry, namely CD34+/KDR+, CD34+/CD133+, CD34+/CD133+/CD45-, and CD34+/KDR+/CD45- cells. High-sensitivity C-reactive protein levels, similar in the 2 groups at baseline, were significantly more decreased by telmisartan than by ramipril at follow up (p = 0.013 for time-by-drug interaction). The main effect for time was also significant (p <0.001). CD34+/KDR+ and CD34+/CD133+ cells were similar at baseline and did not change over time (p = 0.2 and p = 0.1, respectively). In contrast, for CD34+/KDR+/CD45- and CD34+/CD133+/CD45- cells, a significant increase with time was seen (p = 0.02 and p = 0.002, respectively) and no differential effect of either drug was seen. In conclusion, telmisartan shows a more potent anti-inflammatory effect than ramipril after an ACS. The 2 drugs do not show a differential effect on endothelial progenitor cell mobilization.

Circulating CD34+ Cell Count is Associated with Extent of Subclinical Atherosclerosis in Asymptomatic Amish Men, Independent of 10-Year Framingham Risk

Background:

Bone-marrow derived progenitor cells (PCs) may play a role in maintaining vascular health by actively repairing damaged endothelium. The purpose of this study in asymptomatic Old Order Amish men (n = 90) without hypertension or diabetes was to determine if PC count, as determined by CD34+ cell count in peripheral blood, was associated with 10-year risk of cardiovascular disease (CVD) and measures of subclinical atherosclerosis.

Methods and Results:

CD34+ cell count by fluorescence-activated cell sorting, coronary artery calcification (CAC) by electron beam computed tomography, and CVD risk factors were obtained. Carotid intimal-medial thickness (CIMT) also was obtained in a subset of 57 men. After adjusting for 10-year CVD risk, CD34+ cell count was significantly associated with CAC quantity (p = 0.03) and CIMT (p < 0.0001). A 1-unit increase in natural-log transformed CD34+ cell count was associated with an estimated 55.2% decrease (95% CI: −77.8% to −9.3%) in CAC quantity and an estimated 14.3% decrease (95% CI: −20.1% to −8.1%) in CIMT.

Conclusions:

Increased CD34+ cell count was associated with a decrease in extent of subclinical atherosclerosis in multiple arterial beds, independent of 10-year CVD risk. Further investigations of associations of CD34+ cell count with subclinical atherosclerosis in asymptomatic individuals could provide mechanistic insights into the atherosclerotic process.

Interleukin-1beta augments angiogenic responses of murine endothelial progenitor cells in vitro

Endothelial progenitor cells (EPCs) may provide novel opportunities for therapeutic angiogenesis after ischemic diseases. However, it is unclear how the angiogenic potential of EPCs might be affected by an inflammatory environment. We examine how the potent cytokine interleukin-1beta (IL-1beta) affects angiovasculogenic responses in EPCs in culture. Mononuclear cells isolated from mouse spleen were plated on fibronectin-coated wells and grown in EGM-2 MV media. Endothelial progenitor cells were phenotyped using multiple markers (UEA-Lectin, ac-LDL, CD133, CD34, vWillebrand Factor, Flk-1) and to identify the IL-1 Receptor-I. We quantified cell and colony counts and performed MTT (3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide) and Matrigel assays, in vitro, under control and IL-1beta (10 ng/mL) conditions. Endothelial progenitor cells exposed to IL-1beta increased in the number of cells and colonies compared with untreated cells, without any effect on cell metabolic integrity. Furthermore, IL-1beta treatment augmented EPC angiogenic function, significantly increasing the number of vessel-like structures in the Matrigel assay. An early phosphorylation of ERK1/2 occurred after IL-1beta stimulation, and this pathway was inhibited if IL-1 Receptor-I was blocked. Our results suggest that IL-1beta is a potent stimulator of in vitro angiogenesis through ERK signaling in mouse EPCs. Further studies are warranted to assess how interactions between proinflammatory environments and EPC responses may be leveraged to enhance therapeutic angiogenesis.

Low CD34+ cell count and metabolic syndrome synergistically increase the risk of adverse outcomes

OBJECTIVES

Metabolic syndrome (MetS) associates with endothelial dysfunction and a high risk of cardiovascular events and death. Circulating progenitor cells have been shown to contribute to endothelial homeostasis and repair . We aimed to test whether progenitor cell count is an independent event predictor and modifies cardiovascular risk associated with MetS.

METHODS

On the basis of the expression of CD34, CD133 and KDR, 6 phenotypes of progenitor cells were counted using flow cytometry in 214 subjects with and without MetS. We recorded classical risk factors and MetS components, cumulative risk estimates, and high-sensitive C-reactive protein. Subjects were followed-up for a median of 34 months to collect total events, cardiovascular events and all-cause mortality.

RESULTS

In the Cox proportional hazards regression analyses, we found that, unlike other phenotypes, reduced CD34+ cells predicted cardiovascular and total events and death, independently of all potential confounders. Remarkably, a low CD34+ cell count significantly increased the risk associated with MetS, as shown by synergy indexes.

CONCLUSION

The level of circulating CD34+ cells is a novel independent risk biomarker and modulates outcomes in the MetS, suggesting that generic progenitor cells have a role in disease development or progression over the long-term.

Endothelial progenitor cell therapy in atherosclerosis: a double-edged sword?

Atherosclerosis, an inflammatory process that selectively affects arteries, is highly prevalent in human. Thrombo-occlusive complications of atherosclerosis, including stroke and myocardial infarction, are becoming major causes of morbidity and mortality in the industrialized world. Atherosclerosis develops in response to local endothelial injuries. Endothelial dysfunction and cell loss are prominent features in atherosclerosis. Restoring the endothelial lining to normal is critical for slowing or reversing the progression of atherosclerosis. Increasing data suggest that endothelial progenitor cells (EPCs) play a significant role in reendothelialization of the injured blood vessels. This review focuses on the effects of EPC mobilization and transfusion in the condition of atherosclerosis. The aim of the review is to provide an update on the progress in this research field, highlight the role of EPCs in atherosclerosis and discuss the possible mechanisms and potential risks of progenitor cell-based therapy in atherosclerosis.

Aging and endothelial progenitor cell telomere length in healthy men

BACKGROUND

Telomere length declines with age in mature endothelial cells and is thought to contribute to endothelial dysfunction and atherogenesis. Bone marrow-derived circulating endothelial progenitor cells (EPCs) are critical to vascular health as they contribute to both reendothelialization and neovascularization. We tested the hypothesis that EPC telomere length decreases with age in healthy adult humans.

METHODS

Peripheral blood samples were collected from 40 healthy, non-obese, sedentary men: 12 young (age 21-34 years), 12 middle-aged (43-55 years) and 16 older (57-68 years). Putative EPCs were isolated from peripheral blood mononuclear cells and telomere length was determined using genomic DNA preparation and Southern hybridization techniques.

RESULTS

EPC telomere length (base pairs) was approximately 20% (p=0.01) lower in the older (8492+523 bp) compared to the middle-aged (10,565+572 bp) and young (10,205+501 bp) men. Of note, there was no difference in EPC telomere length between the middle-aged and young men.

CONCLUSIONS

These results demonstrate that EPC telomere length declines with age in healthy, sedentary men. Interestingly, telomere length was well preserved in the middle-aged compared to young men, suggesting that EPC telomere shortening occurs after the age of 55 years.

Endothelial progenitor cells and their potential therapeutic applications

Endothelial progenitor cells (EPCs) are derived from the bone marrow (BM) and peripheral blood (PB), contributing to tissue repair in various pathological conditions via the formation of new blood vessels, that is, neovascularization. EPCs can be mobilized into the circulation in response to growth factors and cytokines released following stimuli such as vascular trauma, wounding and cancer. EPCs are involved in vasculogenesis during embryogenesis, but are now recognized to have a significant bearing upon disease outcome through their contribution to neovascularization in a variety of pathological states in adulthood. EPCs exist in very small numbers, especially in circulating blood in adults where they only account for 0.01% of all cells. We discuss the contribution and potential therapeutic applications of EPCs in disease, also noting the prognostic value of PB EPC numbers, especially in heart disease and cancer.

Endothelial progenitor cell number and colony-forming capacity in overweight and obese adults

OBJECTIVE

To investigate whether adiposity influences endothelial progenitor cell (EPC) number and colony-forming capacity.

DESIGN

Cross-sectional study of normal weight, overweight and obese adult humans.

PARTICIPANTS

Sixty-seven sedentary adults (aged 45-65 years): 25 normal weight (body mass index (BMI) <or=25 kg/m(2); 12 males/13 females); 18 overweight (BMI=25-29.9 kg/m(2); 12 males/6 females); and 24 obese (BMI >or=30 kg/m(2); 18 males/6 females). All participants were non-smokers and free of overt cardiometabolic disease.

MEASUREMENTS

Peripheral blood samples were collected and circulating EPC number was assessed by flow cytometry. Putative EPCs were defined as CD45(-)/CD34(+)/VEGFR-2(+)/CD133(+) or CD45(-)/CD34(+) cells. EPC colony-forming capacity was measured in vitro using a colony-forming unit (CFU) assay.

RESULTS

Number of circulating putative EPCs (either CD45(-)/CD34(+)/VEGFR-2(+)/CD133(+) or CD45(-)/CD34(+) cells) was lower (P<0.05) in obese (0.0007+/-0.0001%; 0.050+/-0.006%) compared with overweight (0.0016+/-0.0004%; 0.089+/-0.019%) and normal weight (0.0015+/-0.0003%; 0.082+/-0.008%) adults. There were no differences in EPC number between the overweight and normal weight groups. EPC colony formation was significantly less in the obese (6+/-1) and overweight (4+/-1) compared with normal weight (9+/-2) adults.

CONCLUSION

These results indicate that: (1) the number of circulating EPCs is lower in obese compared with overweight and normal weight adults; and (2) EPC colony-forming capacity is blunted in overweight and obese adults compared with normal weight adults. Impairments in EPC number and function may contribute to adiposity-related cardiovascular risk.

Fluid shear stress induces arterial differentiation of endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized from bone marrow to peripheral blood and contribute to angiogenesis in tissues. In the process, EPCs are exposed to the shear stress generated by blood flow and tissue fluid flow. Our previous study showed that shear stress promotes differentiation of EPCs into mature endothelial cells. In this study, we investigated whether EPCs differentiate into arterial or venous endothelial cells in response to shear stress. When cultured EPCs derived from human peripheral blood were exposed to controlled levels of shear stress in a flow-loading device, the mRNA levels of the arterial endothelial cell markers ephrinB2, Notch1/3, Hey1/2, and activin receptor-like kinase 1 increased, but the mRNA levels of the venous endothelial cell markers EphB4 and neuropilin-2 decreased. Both the ephrinB2 increase and the EphB4 decrease were shear stress dependent rather than shear rate dependent. EphrinB2 protein was increased in shear-stressed EPCs, and the increase in ephrinB2 expression was due to activated transcription and not mRNA stabilization. Deletion analysis of the ephrinB2 promoter indicated that the cis-element (shear stress response element) is present within 106 bp 5' upstream from the transcription initiation site. This region contains the Sp1 consensus sequence, and a mutation in its sequence decreased the basal level of transcription and abolished shear stress-induced ephrinB2 transcription. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that shear stress markedly increased binding of Sp1 to its consensus sequence. These results indicate that shear stress induces differentiation of EPCs into arterial endothelial cells by increasing ephrinB2 expression in EPCs through Sp1 activation.

Endothelial progenitor cells and colony-forming units in rheumatoid arthritis: association with clinical characteristics

OBJECTIVE

To compare levels of a range of endothelial progenitor cells (EPCs) and endothelial colony-forming units (CFUs) in control participants and RA patients, in addition to verifying whether levels of EPCs or CFUs are associated with clinical characteristics in RA patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) from 36 RA patients and 30 control participants were analysed by flow cytometry for EPCs defined by the expression of CD34/CD133, CD34/CD117, CD34/CD31, CD34/KDR and CD34/CD133/KDR. Endothelial cell colonies derived from culture of PBMCs were also assessed by CFU assay.

RESULTS

No differences in levels of EPCs were observed in RA patients compared with controls. However, levels of EPCs were negatively associated with prognostic markers of poor disease status, but not cardiovascular (CV)-related risk factors. Furthermore, the majority of EPCs examined were negatively correlated with levels of RF. In contrast, CFU number was significantly reduced in RA patients compared with controls and was negatively associated with CV risk factors only.

CONCLUSION

These findings indicate that more informative than comparing changes in absolute levels of EPCs, the examination of their relationship with clinical characteristics of RA patients can reveal significant associations, which may provide important clinical insights.

VASCULAR INFLAMMATION AND ATHEROGENESIS ARE ACTIVATED VIA RECEPTORS FOR PAMPs AND SUPPRESSED BY REGULATORY T CELLS

Despite significant advances in identifying the risk factors and elucidating atherosclerotic pathology, atherosclerosis remains the leading cause of morbidity and mortality in industrialized society. These risk factors independently or synergistically lead to chronic vascular inflammation, which is an essential requirement for the progression of atherosclerosis in patients. However, the mechanisms underlying the pathogenic link between the risk factors and atherosclerotic inflammation remain poorly defined. Significant progress has been made in two major areas, which are determination of the roles of the receptors for pathogen-associated molecular patterns (PAMPs) in initiation of vascular inflammation and atherosclerosis, and characterization of the roles of regulatory T cells in suppression of vascular inflammation and atherosclerosis. In this review, we focus on three related issues: (1) examining the recent progress in endothelial cell pathology, inflammation and their roles in atherosclerosis; (2) analyzing the roles of the receptors for pathogen-associated molecular patterns (PAMPs) in initiation of vascular inflammation and atherosclerosis; and (3) analyzing the advances in our understanding of suppression of vascular inflammation and atherosclerosis by regulatory T cells. Continuous improvement of our understanding of the risk factors involved in initiation and promotion of artherogenesis, will lead to the development of novel therapeutics for ischemic stroke and cardiovascular diseases.