Endothelial progenitor cells in the natural history of atherosclerosis

Endothelial progenitor cells functionally express inward rectifier potassium channels

Since the first isolation of endothelial progenitor cells (EPCs) from human peripheral blood in 1997, many researchers have conducted studies to understand the characteristics and therapeutic effects of EPCs in vascular disease models. Nevertheless, the electrophysiological properties of EPCs have yet to be clearly elucidated. The inward rectifier potassium channel (Kir) performs a major role in controlling the membrane potential and cellular events. Here, via the whole cell patch-clamp technique, we found inwardly rectifying currents in EPCs and that these currents were inhibited by Ba(2+) (100 μM) and Cs(+) (1 mM), known as Kir blockers, in a dose-dependent manner (Ba(2+), 91.2 ± 1.4% at -140 mV and Cs(+), 76.1 ± 6.9% at -140 mV, respectively). Next, using DiBAC(3), a fluorescence indicator of membrane potential, we verified that Ba(2+) induced an increase of fluorescence in EPCs (10 μM, 123 ± 2.8%), implying the depolarization of EPCs. At the mRNA and protein levels, we confirmed the existence of several Kir subtypes, including Kir2.x, 3.x, 4.x, and 6.x. In a functional experiment, we observed that, in the presence of Ba(2+), the number of tubes on Matrigel formed by EPCs was dose-dependently reduced (10 μM, 62.3 ± 6.5%). In addition, the proliferation of EPCs was increased in a dose-dependent fashion (10 μM, 157.9 ± 17.4%), and specific inhibition of Kir2.1 by small interfering RNA also increased the proliferation of EPCs (116.2 ± 2.5%). Our results demonstrate that EPCs express several types of Kir which may modulate the endothelial function and proliferation of EPCs.

Endothelial progenitor cells: novel biomarker and promising cell therapy for cardiovascular disease

Bone-marrow-derived EPCs (endothelial progenitor cells) play an integral role in the regulation and protection of the endothelium, as well as new vessel formation. Peripheral circulating EPC number and function are robust biomarkers of vascular risk for a multitude of diseases, particularly CVD (cardiovascular disease). Importantly, using EPCs as a biomarker is independent of both traditional and non-traditional risk factors (e.g. hypertension, hypercholesterolaemia and C-reactive protein), with infused ex vivo-expanded EPCs showing potential for improved endothelial function and either reducing the risk of events or enhancing recovery from ischaemia. However, as the number of existing cardiovascular risk factors is variable between patients, simple EPC counts do not adequately describe vascular disease risk in all clinical conditions and, as such, the risk of CVD remains. It is likely that this limitation is attributable to variation in the definition of EPCs, as well as a difference in the interaction between EPCs and other cells involved in vascular control such as pericytes, smooth muscle cells and macrophages. For EPCs to be used regularly in clinical practice, agreement on definitions of EPC subtypes is needed, and recognition that function of EPCs (rather than number) may be a better marker of vascular risk in certain CVD risk states. The present review focuses on the identification of measures to improve individual risk stratification and, further, to potentially individualize patient care to address specific EPC functional abnormalities. Herein, we describe that future therapeutic use of EPCs will probably rely on a combination of strategies, including optimization of the function of adjunct cell types to prime tissues for the effect of EPCs.

Glucose challenge increases circulating progenitor cells in Asian Indian male subjects with normal glucose tolerance which is compromised in subjects with pre-diabetes: A pilot study

BACKGROUND

Haematopoietic stem cells undergo mobilization from bone marrow to blood in response to physiological stimuli such as ischemia and tissue injury. The aim of study was to determine the kinetics of circulating CD34+ and CD133+CD34+ progenitor cells in response to 75 g glucose load in subjects with normal and impaired glucose metabolism.

METHODS

Asian Indian male subjects (n = 50) with no prior history of glucose imbalance were subjected to 2 hour oral glucose tolerance test (OGTT). 24 subjects had normal glucose tolerance (NGT), 17 subjects had impaired glucose tolerance (IGT) and 9 had impaired fasting glucose (IFG). The IGT and IFG subjects were grouped together as pre-diabetes group (n = 26). Progenitor cell counts in peripheral circulation at fasting and 2 hour post glucose challenge were measured using direct two-color flow cytometry.

RESULTS

The pre-diabetes group was more insulin resistant (p < 0.0001) as measured by homeostasis assessment model (HOMA-IR) compared to NGT group. A 2.5-fold increase in CD34+ cells (p = 0.003) and CD133+CD34+ (p = 0.019) cells was seen 2 hours post glucose challenge in the NGT group. This increase for both the cell types was attenuated in subjects with IGT. CD34+ cell counts in response to glucose challenge inversely correlated with neutrophil counts (ρ = -0.330, p = 0.019), while post load counts of CD133+CD34+ cells inversely correlated with serum creatinine (ρ = -0.312, p = 0.023).

CONCLUSION

There is a 2.5-fold increase in the circulating levels of haematopoietic stem cells in response to glucose challenge in healthy Asian Indian male subjects which is attenuated in subjects with pre-diabetes.

Accumulation of VEGFR-2+/CD133+ cells and decreased number and impaired functionality of CD34+/VEGFR-2+ cells in patients with SLE

OBJECTIVE

Inflammation and atherosclerosis are the major causes of cardiovascular disease (CVD) in SLE. Both traditional and disease-specific risk factors contribute to the formation of endothelial dysfunction. Endothelial progenitor cells (EPCs) have the ability to restore endothelial integrity. The aim of this study was to determine whether the number and function of EPCs are altered in SLE.

METHODS

Nineteen patients with SLE and 19 controls were analysed. VEGF receptor-2 (VEGFR-2)(+)/CD133(+) and CD34(+)/VEGFR-2(+) cells were quantified by flow cytometry. EPC differentiation was measured by DiI-acLDL/Lectin I staining. Furthermore, apoptosis, proliferation capacity, migration capacity and clonogenic ability of EPCs were determined.

RESULTS

VEGFR-2(+)/CD133(+) cells were enhanced in SLE [215 (37) vs 122 (11) cells/1 x 10(6) lymphocytes; P = 0.029], whereas the number [106 (13) vs 215 (27) cells/1 x 10(6) lymphocytes; P = 0.002] and the proliferation rate [96% (6%) vs 143% (19%); P = 0.008] of CD34(+)/VEGFR-2(+) cells were decreased compared with controls. Additionally, EPCs in SLE showed an increased apoptosis [7% (1.4%) vs 3% (0.4%); P = 0.004], an impaired differentiation [36 (5) vs 121 (20) cells/mm(2); P < 0.001] and a reduced migratory capacity [116% (4%) vs 139% (4%); P = 0.001].

CONCLUSIONS

Our results suggest that the mobilization of progenitor cells is unaffected in SLE, but the diminished number and the altered functionality of circulating CD34(+)/VEGFR-2(+) cells reduce the ability to repair vascular damage and thus may trigger the development of atherosclerosis in SLE.

Treatment of peripheral arterial disease using stem and progenitor cell therapy

Peripheral arterial disease (PAD) is a highly prevalent atherosclerotic syndrome associated with significant morbidity and mortality. PAD is most commonly caused by atherosclerosis obliterans (ASO) and thromboangiitis obliterans (TAO), and can lead to claudication and critical limb ischemia (CLI), often resulting in a need for major amputation and subsequent death. Standard treatment for such severe cases of PAD is surgical or endovascular revascularization. However, up to 30% of patients are not candidates for such interventions, due to high operative risk or unfavorable vascular involvement. Therefore, new strategies are needed to offer these patients a viable therapeutic option. Bone-marrow derived stem and progenitor cells have been identified as a potential new therapeutic option to induce angiogenesis. These findings prompted clinical researchers to explore the feasibility of cell therapies in patients with peripheral and coronary artery disease in several small trials. Clinical benefits were reported from these trials including improvement of ankle-brachial index (ABI), transcutaneous partial pressure of oxygen (TcO(2)), reduction of pain, and decreased need for amputation. Nonetheless, large randomized, placebo-controlled, double-blind studies are necessary and currently ongoing to provide stronger safety and efficacy data on cell therapy. Current literature is supportive of intramuscular bone marrow cell administration as a relatively safe, feasible, and possibly effective therapy for patients with PAD who are not subjects for conventional revascularization.

Reduced endothelial progenitor cells in children with hemodialysis but not predialysis chronic kidney disease

In adults with chronic kidney disease (CKD), reduced levels of vasculoprotective endothelial progenitor cells (EPCs) may contribute to their increased risk of cardiovascular disease. Children with CKD also show signs of cardiovascular disease. However, to our knowledge, there have been no studies on circulating EPC levels in pediatric patients with CKD. We investigated CD34+KDR+ EPC numbers by using flow cytometry in 15 children with predialysis CKD, 13 children on hemodialysis, and 18 age-matched healthy controls. Children on hemodialysis showed 47% reduced EPC levels compared with controls, whereas no significant difference was found for patients with predialysis CKD. Lower EPC levels were found in patients with higher levels of inflammatory marker high-sensitivity C-reactive protein. Our data show, for the first time, that children on hemodialysis have reduced CD34+KDR+ EPC levels, which potentially contributes to their increased cardiovascular risk. In children with predialysis CKD, a decline in renal function was not associated with reduced EPC levels, which may reflect a capacity for preservation of the endogenous repair system during relatively moderate disturbances of the systemic environment.

Mechanisms and significance of progenitor cell reduction in the metabolic syndrome

Bone marrow-derived progenitor cells are involved in the homeostasis of the cardiovascular system through differentiation into endothelium, smooth muscle, and cardiomyocytes. Alterations of these extremely plastic cells have been recognized as both markers of cardiovascular risk and pathophysiological links between risk factors and development of atherosclerosis. Metabolic syndrome, as a cluster of well-defined cardiovascular risk factors, represents a strong predictor of cardiovascular events and death. Moreover, components of the syndrome interact with one another and synergistically increase this risk. Here we describe all metabolic syndrome components as being characterized by alterations in circulating progenitor cells, especially endothelial cells. We also highlight how endothelial progenitors may mediate the interactions between cardiometabolic risk factors in a complex interplay and discuss potential implications for prevention and therapy.

Circulating progenitor cell count for cardiovascular risk stratification: a pooled analysis

Background

Circulating progenitor cells (CPC) contribute to the homeostasis of the vessel wall, and a reduced CPC count predicts cardiovascular morbidity and mortality. We tested the hypothesis that CPC count improves cardiovascular risk stratification and that this is modulated by low-grade inflammation.

Methodology/Principal Findings

We pooled data from 4 longitudinal studies, including a total of 1,057 patients having CPC determined and major adverse cardiovascular events (MACE) collected. We recorded cardiovascular risk factors and high-sensitive C-reactive protein (hsCRP) level. Risk estimates were derived from Cox proportional hazard analyses. CPC count and/or hsCRP level were added to a reference model including age, sex, cardiovascular risk factors, prevalent CVD, chronic renal failure (CRF) and medications. The sample was composed of high-risk individuals, as 76.3% had prevalent CVD and 31.6% had CRF. There were 331 (31.3%) incident MACE during an average 1.7±1.1 year follow-up time. CPC count was independently associated with incident MACE even after correction for hsCRP. According to C-statistics, models including CPC yielded a non-significant improvement in accuracy of MACE prediction. However, the integrated discrimination improvement index (IDI) showed better performance of models including CPC compared to the reference model and models including hsCRP in identifying MACE. CPC count also yielded significant net reclassification improvements (NRI) for CV death, non-fatal AMI and other CV events. The effect of CPC was independent of hsCRP, but there was a significant more-than-additive interaction between low CPC count and raised hsCRP level in predicting incident MACE.

Conclusions/Significance

In high risk individuals, a reduced CPC count helps identifying more patients at higher risk of MACE over the short term, especially in combination with a raised hsCRP level.

The oral dipeptidyl peptidase-4 inhibitor sitagliptin increases circulating endothelial progenitor cells in patients with type 2 diabetes: possible role of stromal-derived factor-1alpha

OBJECTIVE

Vasculoprotective endothelial progenitor cells (EPCs) are regulated by stromal-derived factor-1alpha (SDF-1alpha) and are reduced in type 2 diabetes. Because SDF-1alpha is a substrate of dipeptidyl-peptidase-4 (DPP-4), we investigated whether the DPP-4 inhibitor sitagliptin modulates EPC levels in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

This was a controlled, nonrandomized clinical trial comparing 4-week sitagliptin (n = 16) versus no additional treatment (n = 16) in addition to metformin and/or secretagogues in type 2 diabetic patients. We determined circulating EPC levels and plasma concentrations of SDF-1alpha, monocyte chemoattractant protein-1 (MCP-1), vascular endothelial growth factor (VEGF), and nitrites/nitrates.

RESULTS

There was no difference in clinical baseline data between the sitagliptin and control arms. After 4 weeks, as compared with control subjects, patients receiving sitagliptin showed a significant increase in EPCs and SDF-1alpha and a decrease in MCP-1.

CONCLUSIONS

Sitagliptin increases circulating EPCs in type 2 diabetic patients with concomitant upregulation of SDF-1alpha. This ancillary effect of DPP-4 inhibition might have potential favorable cardiovascular implications.

Potential manipulation of endothelial progenitor cells in diabetes and its complications

Diabetes mellitus increases cardiovascular risk through its negative impact on vascular endothelium. Although glucotoxicity and lipotoxicity account for endothelial cell damage, endothelial repair is also affected by diabetes. Endothelial progenitor cells (EPCs) are involved in the maintenance of endothelial homoeostasis and in the process of new vessel formation. For these reasons, EPCs are thought to have a protective impact within the cardiovascular system. In addition, EPCs appear to modulate the functioning of other organs, providing neurotropic signals and promoting repair of the glomerular endothelium. The exact mechanisms by which EPCs provide cardiovascular protection are unknown and the definition of EPCs is not standardized. Notwithstanding these limitations, the literature consistently indicates that EPCs are altered in type 1 and type 2 diabetes and in virtually all diabetic complications. Moreover, experimental models suggest that EPC-based therapies might help prevent or reverse the features of end-organ complications. This identifies EPCs as having a novel pathogenic role in diabetes and being a potential therapeutic target. Several ways of favourably modulating EPCs have been identified, including lifestyle intervention, commonly used medications and cell-based approaches. Herein, we provide a comprehensive overview of EPC pathophysiology and the potential for EPC modulation in diabetes.

Knockdown of stromal interaction molecule 1 attenuates hepatocyte growth factor-induced endothelial progenitor cell proliferation

Increased Ca(2+) entry through store-operated Ca(2+) channels (SOCCs) plays an essential role in the regulation of hepatocyte growth factor (HGF)-induced cell proliferation. Stromal interaction molecule 1 (STIM1) is thought to transmit endoplasmic reticulum (ER) Ca(2+) store depletion signals to the plasma membrane (PM), causing the opening of SOCCs in the PM. However, the relationship between HGF and STIM1 in endothelial progenitor cell (EPC) proliferation remains uncharacterized. The objective of this study was to evaluate the potential involvement of STIM1 in HGF-induced EPC proliferation. For this purpose, we used cultured rat bone marrow-derived EPCs and found that HGF-induced EPC proliferation at low concentrations. Store-operated Ca(2+) entry (SOCE) was elevated in HGF-treated EPCs, and the SOCC inhibitors 2-aminoethoxydiphenyl borate (2-APB) and BTP-2 inhibited the HGF-induced proliferation response. Moreover, STIM1 mRNA and protein expression levels were increased in response to HGF stimulation and knockdown of STMI1 decreased SOCE and prevented HGF-induced EPC proliferation. In conclusion, our data suggest that HGF-induced EPC proliferation is mediated partly via activation of STIM1.

HDL cholesterol is a strong determinant of endothelial progenitor cells in hypercholesterolemic subjects

Endothelial progenitor cells (EPC) can repair the endothelial layer and are considered a component of the cardiovascular system. EPC number and function may change under pathological conditions, including cardiovascular risk factors. The study was carried out to investigate circulating EPC number, in vitro function and relationship with LDL-C, HDL-C and endothelium-dependent vasodilatation in hypercholesterolemic subjects. Forty-one male and 39 female subjects, age>35 and<45, LDL cholesterol plasma level>130 mg/dl with normal (> or =50 mg/dl females and> or =40 mg/dl males) or low HDL-C, absence of any concomitant disorders and/or drug treatment, at their first diagnosis of hypercholesterolemia, were consecutively recruited in the Outpatient Service of the Medical Pathophysiology Department of Rome Sapienza University. In high LDL-C patients, circulating EPC number was decreased and EPC capability to migrate was impaired as well. This pattern was far less evident in the normal HDL-C subgroup. The endothelium-dependent vasodilatation (EDV) was significantly decreased according to the HDL-C decrease in male but not in female subjects. Univariate analysis showed a direct correlation between EPC number and EDV, and the association persisted after adjustment for sex, age and HDL-C, which were all significantly correlated to EDV, which may suggest a protective role of EPC on endothelium in vivo. Our study documented that, in hypercholesterolemic subjects, HDL-C is a strong determinant of EPC number and function, and EPC number decrease is an independent risk factor for endothelial dysfunction.

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.

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.

Is exercise training an effective therapy targeting endothelial dysfunction and vascular wall inflammation?

There is an increasing evidence that endothelial dysfunction and vascular wall inflammation are present in all stages of atherosclerosis. Atherosclerosis does not have to necessarily progress to an acute clinical event. Several therapeutic strategies exist, such as exercise training, which mitigates endothelial dysfunction and inflammation. Exercise training consistently improves the nitric oxide bioavailability, and the number of endothelial progenitor cells, and also diminishes the level of inflammatory markers, namely pro-inflammatory cytokines and C-reactive protein. However, the mechanisms by which exercise improves endothelial function in coronary artery disease patients are not fully clarified. Several mechanisms have been proposed to explain the positive effect of exercise on the disease progression. They include the decrease in cytokine production by the adipose tissue, skeletal muscles, endothelial cells, and blood mononuclear cells, and also, the increase in the bioavailability of nitric oxide, antioxidant defences, and regenerative capacity of endothelium. This study aims to provide a critical review of the literature linking exercise, inflammation, and endothelial dysfunction in coronary artery patients, and to discuss the potential mechanisms behind the exercise-training improvement of endothelial function and inflammatory status.

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.

Autologous stem cell therapy for peripheral arterial disease meta-analysis and systematic review of the literature

BACKGROUND

Peripheral arterial disease (PAD) is a common cause of disability and mortality. Up to one third of patients are not susceptible to traditional revascularization and may benefit from stem cell therapies.

OBJECTIVE

In this meta-analysis, we sought to determine whether autologous cell therapy is effective in the treatment of PAD.

METHODS

We searched the English literature in Medline, Excerpta Medica and the Cochrane database for trials of autologous cell therapy in patients with PAD published before 31 January 2009. We included controlled and non-controlled, randomized and non-randomized trials using autologous bone marrow or granulocyte colony stimulating factor (G-CSF) mobilized peripheral blood cells to treat PAD. We also collected data from trials of G-CSF monotherapy, as a control treatment.

RESULTS

In a meta-analysis of 37 trials, autologous cell therapy was effective in improving surrogate indexes of ischemia, subjective symptoms and hard endpoints (ulcer healing and amputation). On the contrary, G-CSF monotherapy was not associated with significant improvement in the same endpoints. Patients with thromboangiitis obliterans showed some larger benefits than patients with atherosclerotic PAD. The intramuscular route of administration and the use of bone marrow cells seemed somehow more effective than intrarterial administration and the use of mobilized peripheral blood cells. The procedures were well tolerated and generally safe.

CONCLUSION

This meta-analysis indicates that intramuscular autologous bone marrow cell therapy is a feasible, relatively safe and potentially effective therapeutic strategy for PAD patients, who are not candidate for traditional revascularization. Larger, placebo-controlled, randomized multicenter trials need to be planned and conducted to confirm these findings.

Long-term secondary prevention programs after cardiac rehabilitation for the reduction of future cardiovascular events: focus on regular physical activity

Cardiac rehabilitation/secondary prevention programs are recognized as integral to the comprehensive care of patients with coronary heart disease, and as such are recommended in most contemporary clinical practice guidelines. The interventions are aimed at reducing disability, optimizing cardiovascular risk reduction by drug therapy and promoting healthy behavior. Healthy lifestyle habits must be recognized as capable of substantially reducing the risk for cardiovascular events in patients with coronary heart disease. This review highlights the recommended components of cardiac rehabilitation/secondary prevention programs, with special emphasis on regular physical activity.

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.

The evolving role of C-reactive protein in atherothrombosis

BACKGROUND

Inflammation is pivotal in all phases of atherosclerosis. Among the numerous inflammatory biomarkers, the largest amount of published data supports a role for C-reactive protein (CRP) as a robust and independent risk marker in the prediction of primary and secondary adverse cardiovascular events. In addition to being a risk marker, there is much evidence indicating that CRP may indeed participate in atherogenesis.

CONTENT

In this review, we focus on the role of CRP in promoting atherothrombosis by discussing its effects on endothelial cells, endothelial progenitor cells, monocyte-macrophages, and smooth muscle cells.

CONCLUSIONS

CRP is clearly a risk marker for cardiovascular disease and is recommended for use in primary prevention. In addition, CRP appears also to contribute to atherogenesis. However, much further research is needed, especially in appropriate animal models, to confirm the possible role of CRP in promoting atherothrombosis.

Inflammation at the molecular interface of atherogenesis: an anthropological journey

Despite the multifactorial nature of atherosclerosis, substantial evidence has established inflammation as an often surreptitious, yet critical and unifying driving force which promotes disease progression. To this end, research has defined molecular networks initiated by cytokines, growth factors and other pro-inflammatory molecules which promote hallmarks of atherosclerosis such as endothelial dysfunction, macrophage infiltration, LDL oxidation, cell proliferation and thrombosis. Although commonly associated with risk factors such as dyslipidemia, diabetes and hypertension, the global etiology of atherosclerosis may be alternatively attributed to underlying anthropological pressures. The agricultural, industrial and technological revolutions produced alterations in dietary, social and economic factors which have collectively exaggerated the exposure of the human genome to environmental stimuli. Furthermore, advances in sanitation, nutrition, and medicine have increased the lifespan of humans, effectively prolonging blood vessel exposure to these factors. As a result, the vasculature has become conditioned to respond to injury with what is arguably an overzealous immunological response; thus setting the stage for the prevalence of cardiovascular disease, including atherosclerotic plaque development in Western populations. Evidence suggests that each of these alterations can be linked to specific mediators in the inflammatory process. Integration of these factors with an inflammation-based hypothesis of atherosclerosis has yet to be extrapolated to observations in the realms of basic and clinical sciences and is the focus of this review.

The metabolic syndrome, diabetes and lung dysfunction

Sleep-disordered breathing and sleep apnoea are conditions frequently associated with comorbidity, including obesity, diabetes, hypertension, insulin resistance (metabolic syndrome) and cardiovascular disease. The diabetic state (type 1 and type 2 diabetes) may be associated to diminished lung function and, in particular, decreased vital capacity, and the association between chronic obstructive pulmonary disease (COPD) and type 2 diabetes may be due to a shared inflammatory process. Also, the alteration in circulating endothelial progenitor cells found in respiratory disease, the metabolic syndrome and cardiovascular disease reflect a common condition of endothelial dysfunction.

Normal levels and function of endothelial progenitor cells in patients with psoriatic arthritis

Endothelial progenitor cells (EPCs) are a population of bone marrow derived cells which have been attributed with the ability to migrate into areas of tissue ischemia and to posses reparative qualities. EPCs have been shown to be decreased in level and function in various inflammatory disorders. Psoriasis and psoriatic arthritis are associated with an increase in cardiovascular morbidity. The aim of the study was to investigate the number of EPCs among patients suffering from psoriasis and psoriatic arthritis. Patients suffering from active psoriasis and psoriatic arthritis were recruited as well as healthy controls. Disease activity was assessed with the DAS-28, BASDAI and PASI scores. Peripheral blood mononuclear cells were isolated and EPC numbers evaluated by FACS analysis using the CD34/133 and CD34/KDR. No significant difference was found between numbers of EPCs between healthy controls, patients with psoriasis and psoriatic arthritis. A significant correlation was found between levels of VGEF and the BASDAI score. The results of the current study do not support a significant role for EPCs in the pathogenesis of psoriasis and psoriatic arthritis.

Endothelial progenitor cell research in stroke: a potential shift in pathophysiological and therapeutical concepts

BACKGROUND AND PURPOSE

Stroke is the leading cause of disability in the Western world; however, few therapies are at hand to decrease this burden.

SUMMARY OF REVIEW

Endothelial progenitor cells (EPCs) have been introduced in cardiovascular medicine as factotums. EPCs can repair damaged endothelium and attenuate the development and progression of atherosclerosis. Also, EPCs can form new vessels in ischemic areas and thus promote recovery after ischemic events. In stroke, however, EPC research is limited. In our overview, we provide background information on EPC use as a risk marker and as a potential therapeutic agent.

CONCLUSIONS

In our opinion, the lack of EPC studies in stroke should instigate vascular neurologists to participate in EPC research, as EPCs could also change pathophysiological concepts and improve clinical treatments in vascular neurology.

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

In the last 10 years an increasing interest has been devoted to the study of endothelial progenitor cells (EPCs), a subtype of immature cells involved in endothelial repair and neoangiogenesis. EPCs have been discovered as a novel integrated part of the cardiovascular system, which plays a comprehensive role in tissue homeostasis. Consistently, alterations and/or reduction of the circulating EPC pool have been associated with different manifestations of cardiovascular disorders and atherosclerosis. This is why, the extent of the EPC pool is now considered a mirror of vascular health, while EPC reduction has become a surrogate biomarker of cardiovascular risk and of the ongoing vascular damage. Unfortunately, the methods used to study EPCs still lack standardization, and this is significantly decelerating progress in the field. In this review, we focus on some aspects related to the two methods used to assess circulating EPCs: flow cytometry and cell culture. We uncover the many traps hidden in the choice of the right protocol, and suggest the best solutions on the basis of evidence and background theories.

Stem cells and scaffolds for vascularizing engineered tissue constructs

The clinical impact of tissue engineering depends upon our ability to direct cells to form tissues with characteristic structural and mechanical properties from the molecular level up to organized tissue. Induction and creation of functional vascular networks has been one of the main goals of tissue engineering either in vitro, for the transplantation of prevascularized constructs, or in vivo, for cellular organization within the implantation site. In most cases, tissue engineering attempts to recapitulate certain aspects of normal development in order to stimulate cell differentiation and functional tissue assembly. The induction of tissue growth generally involves the use of biodegradable and bioactive materials designed, ideally, to provide a mechanical, physical, and biochemical template for tissue regeneration. Human embryonic stem cells (hESCs), derived from the inner cell mass of a developing blastocyst, are capable of differentiating into all cell types of the body. Specifically, hESCs have the capability to differentiate and form blood vessels de novo in a process called vasculogenesis. Human ESC-derived endothelial progenitor cells (EPCs) and endothelial cells have substantial potential for microvessel formation, in vitro and in vivo. Human adult EPCs are being isolated to understand the fundamental biology of how these cells are regulated as a population and to explore whether these cells can be differentiated and reimplanted as a cellular therapy in order to arrest or even reverse damaged vasculature. This chapter focuses on advances made toward the generation and engineering of functional vascular tissue, focusing on both the scaffolds - the synthetic and biopolymer materials - and the cell sources - hESCs and hEPCs.

Glucose tolerance is negatively associated with circulating progenitor cell levels

AIMS/HYPOTHESIS

Circulating progenitor cells participate in cardiovascular homeostasis. Depletion of the pool of endothelial progenitor cells (EPCs) is associated with increased cardiovascular risk. Furthermore, EPCs are reduced in the presence of classical risk factors for atherosclerotic disease, including diabetes mellitus. This study was designed to evaluate progenitor cell levels in volunteers with different degrees of glucose tolerance.

METHODS

Cardiovascular parameters and the levels of circulating CD34(+) and CD34(+) kinase insert domain receptor (KDR)(+) cells were determined in 219 middle-aged individuals with no pre-diagnosed alterations in carbohydrate metabolism. Glucose tolerance was determined by fasting and 2 h post-challenge glucose levels, with IFG and IGT considered as pre-diabetic states.

RESULTS

CD34(+) and CD34(+)KDR(+) cells were significantly reduced in individuals who were found to have diabetes mellitus, and were negatively correlated with both fasting and post-challenge glucose in the whole population. While only CD34(+) cells, but not CD34(+)KDR(+) cells, were significantly reduced in pre-diabetic individuals, post-challenge glucose was an independent determinant of the levels of both CD34(+) and CD34(+)KDR(+) cells.

CONCLUSIONS/INTERPRETATION

Glucose tolerance was negatively associated with progenitor cell levels in middle-aged healthy individuals. Depletion of endothelial progenitors with increasing fasting and post-meal glucose may be one cause of the high incidence of cardiovascular damage in individuals with pre-diabetes.