Glucose tolerance is negatively associated with circulating progenitor cell levels

Procalcific phenotypic drift of circulating progenitor cells in type 2 diabetes with coronary artery disease

Diabetes mellitus (DM) alters circulating progenitor cells relevant for the pathophysiology of coronary artery disease (CAD). While endothelial progenitor cells (EPCs) are reduced, there is no data on procalcific polarization of circulating progenitors, which may contribute to vascular calcification in these patients. In a cohort of 107 subjects with and without DM and CAD, we analyzed the pro-calcific versus endothelial differentiation status of circulating CD34+ progenitor cells. Endothelial commitment was determined by expression of VEGFR-2 (KDR) and pro-calcific polarization by expression of osteocalcin (OC) and bone alkaline phosphatase (BAP). We found that DM patients had significantly higher expression of OC and BAP on circulating CD34+ cells than control subjects, especially in the presence of CAD. In patients with DM and CAD, the ratio of OC/KDR, BAP/KDR, and OC+BAP/KDR was about 3-fold increased than in other groups. EPCs cultured from DM patients with CAD occasionally formed structures highly suggestive of calcified nodules, and the expression of osteogenic markers by EPCs from control subjects was significantly increased in response to the toll-like receptor agonist LPS. In conclusion, circulating progenitor cells of diabetic patients show a phenotypic drift toward a pro-calcific phenotype that may be driven by inflammatory signals.

Amelioration of glucose control mobilizes circulating pericyte progenitor cells in type 2 diabetic patients with microangiopathy

Chronic diabetic complications result from an imbalance between vascular damage and regeneration. Several circulating lineage-committed progenitor cells have been implicated, but no data are available on pericyte progenitor cells (PPCs). Based on the evidence that PPCs increase in cancer patients after chemotherapy, we explored whether circulating PPC levels are affected by glucose control in type 2 diabetic patients, in relation to the presence of chronic complications. We enumerated peripheral blood PPCs as Syto16+CD45−CD31−CD140b+ events by flow cytometry at baseline and after 3 and 6 months of glucose control by means of add-on basal insulin therapy on top of oral agents in 38 poorly controlled type 2 diabetic patients. We found that, in patients with microangiopathy (n = 23), the level of circulating PPCs increased about 2 fold after 3 months and then returned to baseline at 6 months. In patients without microangiopathy (control group, n = 15), PPCs remained fairly stable during the whole study period. No relationship was found between change in PPCs and macroangiopathy (either peripheral, coronary, or cerebrovascular). We conclude that glucose control transiently mobilizes PPCs diabetic patients with microangiopathy. Increase in PPCs may represent a vasoregenerative event or may be a consequence of ameliorated glucose control on microvascular lesions.

Glucose-induced increase in circulating progenitor cells is blunted in polycystic amenorrhoeic subjects

BACKGROUND

Glucose-induced kinetics of bone marrow-derived stem cells in healthy females is presently unknown. The objectives of this study were to determine whether circulating levels of CD133(+), CD34(+) and CD133(+)CD34(+) cells increase in response to glucose load in healthy females and whether the kinetics is altered in amenorrhoeic women. The other objective of the work was to compare the endothelial differentiation potential of peripheral blood-derived endothelial progenitor cells (EPCs) from healthy versus amenorrhoeic women.

METHODS

In this case-control study, 44 amenorrhoeic subjects and 36 age-matched females with no menstrual disturbance were recruited at Apollo Hospitals, a Tertiary health care center in Chennai, India. Circulating bone marrow-derived stem cells were measured by two color direct flow cytometry. Cultured progenitor cells were characterized at Day 7 and 14 for expression of endothelial markers and production of nitric oxide (NO) via immunofluoroscence.

RESULTS

The amenorrhoeic subjects were insulin resistant with homeostatic model of assessment of insulin resistance values of 3.33 ± 0.3 versus 1.75 ± 0.148 observed for controls (P< 0.0001). Among the amenorrhoeic subjects, 38 subjects had polycystic ovaries with no signs of hyperandrogenism. Fasting levels of CD133(+), CD34(+) and CD133(+)CD34(+) cells were reduced in amenorrhoeic subjects (P< 0.001). There was a 1.5 to 2-fold increase in the circulating levels of these cells in response to 75 g oral glucose challenge at 1 and 2 h post-load conditions in controls, which was significantly blunted for CD133(+) (P< 0.001) and CD133(+)CD34(+) (P< 0.001) cells in amenorrhoeic subjects. A positive correlation was observed between estrogen and fasting CD133(+) (r= 0.205, P= 0.070), CD34(+) (r= 0.249, P= 0.027) and CD133(+)CD34(+) (r= 0.217, P= 0.055) cell counts. Additionally, fasting counts for CD34(+) and CD133(+)CD34(+) cells positively correlated with FSH and inversely correlated with LH and C-peptide in the polycystic group. Cultured cells from polycystic subjects exhibited reduced adherence to fibronectin and expressed lower levels of endothelial nitric-oxide synthase and NO.

CONCLUSIONS

Oral glucose-induced increase in circulating numbers of CD133(+) and CD133(+)CD34(+) cells and endothelial differentiation potential of peripheral blood-derived EPCs is attenuated in insulin resistant amenorrhoeic subjects.

Prior endurance exercise prevents postprandial lipaemia-induced increases in reactive oxygen species in circulating CD31+ cells

We hypothesized that prior exercise would prevent postprandial lipaemia (PPL)-induced increases in intracellular reactive oxygen species (ROS) in three distinct circulating angiogenic cell (CAC) subpopulations. CD34(+), CD31(+)/CD14(-)/CD34(-), and CD31(+)/CD14(+)/CD34(-) CACs were isolated from blood samples obtained from 10 healthy men before and 4 h after ingesting a high fat meal with or without ∼50 min of prior endurance exercise. Significant PPL-induced increases in ROS production in both sets of CD31(+) cells were abolished by prior exercise. Experimental ex vivo inhibition of NADPH oxidase activity and mitochondrial ROS production indicated that mitochondria were the primary source of PPL-induced oxidative stress. The attenuated increases in ROS with prior exercise were associated with increased antioxidant gene expression in CD31(+)/CD14(-)/CD34(-) cells and reduced intracellular lipid uptake in CD31(+)/CD14(+)/CD34(-) cells. These findings were associated with systemic cardiovascular benefits of exercise, as serum triglyceride, oxidized low density lipoprotein-cholesterol, and plasma endothelial microparticle concentrations were lower in the prior exercise trial than the control trial. In conclusion, prior exercise completely prevents PPL-induced increases in ROS in CD31(+)/CD14(-)/CD34(-) and CD31(+)/CD14(+)/CD34(-) cells. The mechanisms underlying the effects of exercise on CAC function appear to vary among specific CAC types.

Circulating endothelial progenitor cells in women with gestational alterations of glucose tolerance

Endothelial progenitor cells (EPCs) play a role in angiogenesis during pregnancy. The aim of this study was to evaluate circulating EPCs in pregnant women with gestational alterations of glucose tolerance. Glucose tolerance, insulin sensitivity and β-cell function were derived from oral glucose tolerance tests in 23 women with normal glucose tolerance (NGT), 18 with gestational impaired glucose tolerance (GIGT) and 24 with gestational diabetes mellitus (GDM). Circulating cells expressing CD34 in combination with CD133, kinase insert domain receptor (KDR) or both were quantified by flow cytometry. Women with GIGT and GDM had lower CD34(+)KDR(+) and CD34(+)CD133( +)KDR(+) cells at 27±3.2 weeks' gestation compared with NGT (ANOVA p<0.02 for both). CD34(+)KDR(+) and CD34(+)CD133(+)KDR(+) cells were inversely correlated with the area-under-the-glucose-curve (p<0.005, for both) and positively to insulin secretion-sensitivity index (p<0.05, for both). Alterations of glucose tolerance during pregnancy are associated with a decrease in EPCs. Hyperglycaemia might exert a direct effect on depletion of EPCs.

Circulating endothelial progenitor cells and cellular membrane microparticles in db/db diabetic mouse: possible implications in cerebral ischemic damage

For determining the implications of circulating endothelial progenitor cells (cEPCs) and cellular membrane microparticles (MPs) in diabetic stroke, levels of EPCs, EPC-MPs, and endothelium-derived MPs (EMPs) and their correlations with blood glucose concentration, cerebral microvascular density (cMVD), and ischemic damage were investigated in type 2 diabetic db/db and db/+ (wild-type control) mice. Therapeutic efficacy of EPC infusion (preincubated with MPs) was also explored. Ischemic stroke was induced by middle cerebral artery occlusion (MCAO) surgery. Ischemic damage and cMVD were determined using histological analyses. The levels of cEPCs and MPs were determined using flow cytometric analyses. EPC generation and functions were evaluated by in vitro cell cultures. Results showed the following. 1) In db/db mice, the basal level of cEPCs was less and cMVDs were lower, but the levels of circulating EPC-MPs and EMPs were more; 2) MCAO induced a larger infarct volume and less of an increase in cEPCs in db/db mice; 3) the level of cEPCs correlated with blood glucose concentration (negatively), cMVD (positively), and ischemic damage (negatively), but the levels of EPC-MPs and EMPs correlated inversely with those parameters; 4) EPCs were reduced and dysfunctional in db/db mice, and preincubation with db/db MPs impaired EPC functions; and 5) infusion of EPCs preincubated with db/+ MPs increased the level of cEPCs and reduced ischemic damage, and these beneficial effects were reduced or lost in EPCs preincubated with db/db MPs. These data suggest that reduced cEPCs, impaired EPC generation/function, and increased production of MPs might be the mechanisms responsible for increased ischemic damage seen in db/db mice.

Reduced circulating endothelial progenitor cell number in healthy young adult hyperinsulinemic men

BACKGROUND AND AIMS

The number of Endothelial Progenitor Cells (EPCs) is considered a novel marker of cardiovascular (CV) disease. It is not clear which are the main determinants of EPC number in apparently healthy subjects in the absence of overt clinical CV or metabolic abnormalities. We evaluated the main clinical determinants of EPC levels in a population of healthy subjects with normal glucose tolerance.

METHODS AND RESULTS

EPC number was determined in 122 healthy subjects (73M/49F;36.6 ± 8yrs). Blood samples were collected to test biochemical variables. OGTT was performed and insulin resistance/compensatory hyperinsulinemia was defined according to fasting plasma insulin (FPI) levels. EPCs were identified as cells co-expressing CD133/CD34/KDR antigens by flow-cytometry. CD133(+)/KDR(+) count inversely correlated with BMI (rho=-0.18;p < 0.05), waist circumference (-0.2;<0.05), diastolic (-0.23;<0.01) and systolic blood pressure (-0.21;<0.05), uric acid (-0.24;<0.005), PAI-1 (-0.197; <0.05) and FPI (-0.2;<0.05) and directly correlated with HDL cholesterol (0.182;<0.05). CD34(+)/CD133(+)/KDR(+) count inversely correlated with uric acid (-0.28;<0.005) and FPI (-0.2;<0.05). EPC number was lower in males (p < 0.05) and gender was the only independent predictor of EPC count (p < 0.05). By dividing the population in four subgroups based on gender and insulin resistance, CD133(+)/KDR(+) levels were lower in insulin resistant compared to insulin sensitive males (p < 0.05) with no differences in females.

CONCLUSION

The male gender is an independent predictor of low EPC levels in healthy subjects. This might contribute to explaining the higher CV risk in males compared to pre-menopausal age-matched females. In this study a reduced EPC number seems to be associated with insulin resistance in male subjects.

Effects of acute and chronic endurance exercise on intracellular nitric oxide and superoxide in circulating CD34⁺ and CD34⁻ cells

We investigated the influence of acute and chronic endurance exercise on levels of intracellular nitric oxide (NO), superoxide (O₂·⁻), and expression of genes regulating the balance between these free radicals in CD34⁺ and CD34⁻ peripheral blood mononuclear cells (PBMCs; isolated by immunomagnetic cell separation). Blood samples were obtained from age- and body mass index (BMI)-matched endurance-trained (n = 10) and sedentary (n = 10) men before and after 30 min of exercise at 75% maximal oxygen uptake (·VO(₂max)). Baseline levels of intracellular NO (measured by DAF-FM diacetate) and O₂·⁻ (measured by dihydroethidium) were 26% (P < 0.05) and 10% (P < 0.05) higher, respectively, in CD34⁺ PBMCs from the sedentary group compared with the endurance-trained group. CD34⁺ PBMCs from the sedentary group at baseline had twofold greater inducible nitric oxide synthase (iNOS) mRNA and 50% lower endothelial NOS (eNOS) mRNA levels compared with the trained group (P < 0.05). The baseline group difference in O₂·⁻ was eliminated by acute exercise. Experiments with apocynin indicated that the training-related difference in O₂·⁻ levels was explained by increased NADPH oxidase activity in the sedentary state. mRNA levels of additional angiogenic and antioxidant genes were consistent with a more angiogenic profile in CD34⁺ cells of trained subjects. CD34⁻ PBMCs, examined for exploratory purposes, also displayed a more angiogenic mRNA profile in trained subjects, with vascular endothelial growth factor (VEGF) and eNOS being more highly expressed in trained subjects. Overall, our data suggest an association between the sedentary state and increased nitro-oxidative stress in CD34⁺ cells.

Cell-based therapies for diabetic complications

In recent years, accumulating experimental evidence supports the notion that diabetic patients may greatly benefit from cell-based therapies, which include the use of adult stem and/or progenitor cells. In particular, mesenchymal stem cells and the circulating pool of endothelial progenitor cells have so far been the most studied populations of cells proposed for the treatment of vascular complications affecting diabetic patients. We review the evidence supporting their use in this setting, the therapeutic benefits that these cells have shown so far as well as the challenges that cell-based therapies in diabetic complications put out.

Clinical science review article: understanding the implications of diabetes on the vascular system

Patients with diabetes comprise an extremely complex subset of patients for the vascular surgeon. Often, they have numerous comorbidities that can further complicate matters. The diabetic environment is highly complex and the interplay of various diseases makes this an extremely challenging condition to manage. Knowing the mechanisms by which diabetes inflicts adverse microscopic changes in the vasculature allows the clinician to anticipate problems and minimize the heightened risks observed in diabetic patients undergoing surgery. In this review, we will illustrate how diabetes affects the vasculature and how the molecular and cellular derangements that occur in diabetic environments lead to these pathophysiologic consequences.

Cellular and molecular mechanisms of vascular injury in diabetes--part II: cellular mechanisms and therapeutic targets

Although the mechanisms by which insulin-resistance and hyperglycemia lead to cardiovascular disease are still incompletely understood, all mechanisms apparently converge on the vessel wall and the endothelium as a common disease target. Endothelial cells play a crucial role in vascular homeostasis, providing a functional barrier and modulating several signals involved in vasomotion, as well as antiplatelet, anti-inflammatory, anti-proliferative, and anti-oxidant properties of the vessel wall. Endothelial cell dysfunction occurs early in diabetes and insulin resistance states. Since atherosclerosis may result from an imbalance between the magnitude of vascular injury and the capacity of repair, a role has been recently postulated for a defective mobilization of vascular progenitors, including endothelial progenitor cells, in the pathogenesis of vascular disease. Here we summarize the evidence for such an occurrence. We also here highlight how new insights into pathways of vascular damage in diabetes may indicate new targets for preventive and treatment strategies.

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.

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.

Blood glucose control and coronary heart disease

Epidemiologic data support the hypothesis of a direct and independent relationship between hyperglycemia and cardiovascular disease. The lack of a clear-cut threshold value in diabetic patients, and the persistence of the relationship in nondiabetic population as well, suggest that glycemia is a continuous variable, similarly to other cardiovascular risk factors. Moreover, increased plasma glucose levels contribute to cardiovascular risk by activating multiple atherogenic mechanisms. In spite of evident plausibility for hyperglycemia as a cardiovascular risk factor per se, intervention data remain controversial. Results of recent large-scale intervention trials, such as ACCORD, ADVANCE, and VADT, seem to undermine the concept that tight glycemic control confers some protection against cardiovascular disease in patients with type 2 diabetes, while maintenance of near-normal glycemic control from earlier stage of the disease and during acute coronary events seems to be more beneficial. However, individualized therapies remain the cornerstone of strategies aimed to reduce cardiovascular risk associated to hyperglycemia.

Bone marrow and circulating stem/progenitor cells for regenerative cardiovascular therapy

Cardiovascular disease is the leading cause of death and disability in the Western world. In addition to the advancement of current therapeutic approaches to reduce the associated morbidity and mortality, regenerative medicine and cell-based therapy have been areas of continuous investigation. Circulating and bone-marrow-derived stem or endothelial progenitor cells are an attractive source for regenerative therapy in the cardiovascular field. In this review, we highlight the advantages and limitations of this approach with a focus on key observations from animal studies and clinical trials.

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.

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.

The promise of cell-based therapies for diabetic complications: challenges and solutions

The discovery of endothelial progenitor cells (EPCs) in human peripheral blood advanced the field of cell-based therapeutics for many pathological conditions. Despite the lack of agreement about the existence and characteristics of EPCs, autologous EPC populations represent a novel treatment option for complications requiring therapeutic revascularization and vascular repair. Patients with diabetic complications represent a population of patients that may benefit from cellular therapy yet their broadly dysfunctional cells may limit the feasibility of this approach. Diabetic EPCs have decreased migratory prowess and reduced proliferative capacity and an altered cytokine/growth factor secretory profile that can accelerate deleterious repair mechanisms rather than support proper vascular repair. Furthermore, the diabetic environment poses additional challenges for the autologous transplantation of cells. The present review is focused on correcting diabetic EPC dysfunction and the challenges involved in the application of cell-based therapies for treatment of diabetic vascular complications. In addition, ex vivo and in vivo functional manipulation(s) of EPCs to overcome these hurdles are discussed.

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.

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.

Effects of insulin resistance on endothelial progenitor cells and vascular repair

Insulin resistance, a key feature of obesity, the metabolic syndrome and Type 2 diabetes mellitus, results in an array of metabolic and vascular phenomena which ultimately promote the development of atherosclerosis. Endothelial dysfunction is intricately related to insulin resistance through the parallel stimulatory effects of insulin on glucose disposal in metabolic tissues and NO production in the endothelium. Perturbations characteristic of insulin resistance, including dyslipidaemia, inflammation and oxidative stress, may jeopardize the structural or functional integrity of the endothelium. Recent evidence suggests that endothelial damage is mitigated by endogenous reparative processes which mediate endothelial regeneration. EPCs (endothelial progenitor cells) are circulating cells which have been identified as mediators of endothelial repair. Several of the abnormalities associated with insulin resistance, including reduced NO bioavailability, increased production of ROS (reactive oxygen species) and down-regulation of intracellular signalling pathways, have the potential to disrupt EPC function. Improvement in the number and function of EPCs may contribute to the protective actions of evidence-based therapies to reduce cardiometabolic risk. In the present article, we review the putative effects of insulin resistance on EPCs, discuss the underlying mechanisms and highlight potential therapeutic manoeuvres which could improve vascular repair in individuals with insulin resistance.

Circulating endothelial progenitor cells, endothelial function, carotid intima-media thickness and circulating markers of endothelial dysfunction in people with type 1 diabetes without macrovascular disease or microalbuminuria

AIMS/HYPOTHESIS

Type 1 diabetes is associated with premature arterial disease. Bone-marrow derived, circulating endothelial progenitor cells (EPCs) are believed to contribute to endothelial repair. The hypothesis tested was that circulating EPCs are reduced in young people with type 1 diabetes without vascular injury and that this is associated with impaired endothelial function and increased carotid intima-media thickness (CIMT).

METHODS

We compared 74 people with type 1 diabetes with 80 healthy controls. CD34, CD133, vascular endothelial (VE) growth factor receptor-2 (VEGFR-2) and VE-cadherin antibodies were used to quantify EPCs and progenitor cell subtypes using flow-cytometry. Ultrasound assessment of endothelial function by brachial artery flow-mediated dilatation (FMD) and CIMT was made. Circulating endothelial markers, inflammatory markers and plasma plasminogen activator inhibitor-1 (PAI-1) levels were measured.

RESULTS

CD34+VE-cadherin+, CD133+VE-cadherin+ and CD133+VEGFR-2+ EPC counts were significantly lower in people with diabetes (46-69%; p = 0.004-0.043). In people with type 1 diabetes, FMD was reduced by 45% (p < 0.001) and CIMT increased by 25% (p < 0.001), these being correlated (r = -0.25, p = 0.033). There was a significant relationship between FMD and CD34+VE-cadherin+ (r = 0.39, p = 0.001), CD133+VEGFR-2+ (r = 0.25, p = 0.037) and CD34+ (r = 0.34, p = 0.003) counts. Circulating high-sensitivity C-reactive protein, PAI-1, interleukin-6 and E-selectin were significantly higher in the diabetes group (p < 0.001 to p = 0.049), the last two of these correlating with FMD (r = -0.27, p = 0.028 and r = -0.24, p = 0.048, respectively).

CONCLUSIONS/INTERPRETATION

These findings suggest that abnormalities of endothelial function in addition to pro-inflammatory and pro-thrombotic states are already common in people with type 1 diabetes before development of clinically evident arterial damage. Low EPC counts confirm risk of macrovascular complications and may account for impaired endothelial function and predict future cardiovascular events.

Molecular and clinical aspects of endothelial dysfunction in diabetes

Diabetic patients have an increased risk for cardiovascular complications with respect to the general population. Micro- and macrovascular complications such as nephropathy, retinopathy, atherosclerosis, and coronary artery disease are usually preceded by endothelial dysfunction, a condition characterized by impaired vasorelaxation resulting from reduced bioavailability of the endothelial mediator nitric oxide (NO). Nitric oxide is among endothelial mediators released by endothelial cells in response to insulin stimulation. Therefore, metabolic abnormalities such as insulin resistance, dyslipidemia, compensatory hyperinsulinemia and overt hyperglycemia may all contribute to impaired NO bioavailability and abnormal vasodilatation in diabetic patients. Each of these alterations may trigger endothelial dysfunction by multiple intracellular mechanisms including accelerated formation of advanced glycolysis end products, activation of protein kinase C, increased pro-inflammatory signaling, and impaired sensitivity of the PI 3-kinase signaling pathways. This review outlines the most important mechanisms by which insulin takes part in physiological regulation of endothelial function. Abnormal insulin signaling in endothelium under diabetic conditions and patho-physiological consequences on cardiovascular homeostasis will also be discussed.

Stem cell mobilisation for myocardial repair

BACKGROUND

The idea that autologous bone marrow derived stem cells (BMCs) can transdifferentiate into cardiomyocytes or vascular cells has been challenged in several scientific reports.

OBJECTIVE/METHODS

This review summarises conditions for stem cell mobilisation, their use for therapeutic approaches to prevent ischaemic cardiomyopathy after acute myocardial infarction and current clinical trials. Mechanisms for mobilisation and homing of BMCs are discussed.

RESULTS/CONCLUSIONS

The improvement in cardiac function after migration of autologous BMCs to the heart can be explained by their paracrine effects, inducing angiogenesis and preventing ischaemic myocardium from apoptosis. These effects may explain why the number of circulating BMCs is directly correlated with cardiovascular risk and life expectancy. Exercise and hormones are physiological stimuli for the mobilisation of BMCs, whereas cardiovascular risk factors severely reduce their number and functions. Current cardiovascular medications increase the amounts of autologous BMCs.