Mechanisms and significance of progenitor cell reduction in the metabolic syndrome

Low concentration of ethanol favors progenitor cell differentiation and neovascularization in high-fat diet-fed mice model

Endothelial progenitor cells (EPCs) and monocytic cells from bone marrow (BM) can be recruited to the injured endothelium and contribute to its regeneration. During metabolic diseases such as obesity and diabetes, progenitor cell function is impaired. Several studies have shown that moderate alcohol consumption prevents the development and progression of atherosclerosis in a variety of animal/mouse models and increases mobilization of progenitor cells. Along with these studies, we identify ethanol at low concentration as therapeutic tool to in vitro expand progenitor cells in order to obtain an adequate number of cells for their use in the treatment of cardiovascular diseases. We evaluated the effects of ethanol on the phenotype of BM-derived cells from mice fed with high-fat diet (HFD). HFD did not induce changes in weight of mice but induced metabolic alterations. HFD feeding increased the differentiation of monocytic progenitors but not EPCs. Whereas ethanol at 0.6% is able to increase monocytic progenitor differentiation, 1% ethanol diminished it. Furthermore, ethanol at 0.6% increased the ability of progenitor cells to promote in vivo angiogenesis as well as secretome of BM-derived cells from mice fed with HFD, but not in mice fed normal diet. In conclusion, ethanol at low concentration is able to increase angiogenic abilities of progenitor cells from animals with early metabolic alterations.

Circulating Endothelial Progenitor Cell Levels Predict Cardiovascular Events in End-Stage Renal Disease Patients on Maintenance Hemodialysis

BACKGROUND

The number of circulating endothelial progenitor cells (EPCs) has been identified as a surrogate biologic marker for vascular function and cumulative cardiovascular (CV) risk in the general population. Patients with end-stage renal disease (ESRD) on hemodialysis (HD) have markedly decreased EPC counts and function. We hypothesized that the number of circulating EPCs predicts death from all causes and CV events in patients with ESRD on HD.

METHODS

We quantified the EPCs in blood samples from 70 patients with ESRD on HD. Circulating EPCs were counted by flow cytometry as the number of CD45(low)CD34(+)VEGFR2(+) cells. Death from all causes and CV events served as outcome variables over a median follow-up period of 20 months.

RESULTS

It has been postulated that the number of circulating EPCs at baseline ranged from 1 to 350 cells/200 μl, with a mean of ± standard deviation (SD) of 26.0 ± 48.2 cells/200 μl. The median, lowest and highest tertiles of EPC counts were 11.0, 9.0, and 17.0 cells/200 μl, respectively. Patients with the lowest tertile EPC counts had significantly higher rates of CV events, but mortality was similar between the two groups. After adjusting for these risk factors, HbA1c and the lowest tertile EPC count remained as independent predictors of CV events. A cutoff value of 9.5 cells/200 μl maximized the power of the EPC count to predict future CV events as determined by ROC curve analysis.

CONCLUSIONS

Reduced circulating EPC counts independently predicted CV events in 70 patients with ESRD on maintenance HD. Circulating EPCs may play a role in vascular repair, thereby affecting the clinical course of CV events.

Elevated white blood cell count is associated with prevalence and development of the metabolic syndrome and its components in the general population

The metabolic syndrome (MS) is characterized by chronic inflammation. We aimed to determine the association of white blood cell (WBC) count with prevalence and development of the MS and its components in the general population. A cohort of 1,329 subjects from the local working population aged 41.3 ± 7.5 years and recruited since 2000-2008 was followed up for 4.0 ± 1.2 years. WBC count and MS components were determined at baseline and follow-up. To determine whether WBC predicted incident MS, we used a logistic regression analysis adjusted for demographics, baseline variables that define MS components, smoke, medications, and follow-up duration. Cross-sectionally in the whole population, WBC count increased in parallel with the number of MS components in the same individual, and the presence of each component was associated with higher WBC count. Baseline WBC count was significantly higher in subjects with prevalent MS. Among subjects without MS at baseline, those who developed MS had significantly higher WBC than those who did not develop MS at follow-up. Development of each MS component was associated with increased WBC count. WBC count remained significantly associated with MS development after correction for several potential confounders (OR for 1 SD increase in WBC 1.26; 95 % CI 1.01-1.58). In conclusion, elevated WBC is intimately linked to the prevalence and future development of the MS in a young population of working subjects.

A direct comparison of endothelial progenitor cell dysfunction in rat metabolic syndrome and diabetes

OBJECTIVES

Diabetes mellitus (DM) is associated with impairment of endothelial progenitor cells (EPCs), but the effects of metabolic syndrome (MS) on EPCs have been less well characterized. We hypothesized that in the presence of MS, the number and functionality of EPCs would be markedly reduced, and would be similar to DM.

METHODS

Mononuclear cells were isolated from the bone-marrow (BM) and peripheral blood of lean Zucker, obese Zucker, a model of MS, and Zucker diabetic fatty rats. Cultured BM-EPCs underwent in vitro functional testing and the ability of BM-EPCs to promote neovascularization in vivo was assessed in a model of hindlimb ischemia in athymic mice.

RESULTS

While circulating EPC numbers were similarly reduced in both MS and DM rats, BM-derived EPC numbers were less affected. In vitro testing of cultured BM-EPCs from obese Zucker demonstrated a marked reduction in EPC differentiation, a greater propensity to apoptosis, a reduced migratory response and matrigel tubule formation, similar to findings in Zucker diabetic fatty rats. When delivered to the ischemic hindlimb of athymic mice, the recovery of perfusion using both BM-EPCs from obese Zucker and Zucker diabetic fatty rats were diminished, as compared to lean Zuckers.

CONCLUSION

In the presence of the MS, BM-derived EPCs develop marked functional impairment, resulting in severely reduced angiogenic capacity in vivo. Similar to DM, EPC dysfunction may play a prominent role in the pathogenesis of vascular complications in the MS, and may potentially limit the use of BM-derived EPCs for therapeutic angiogenesis.

Critical reevaluation of endothelial progenitor cell phenotypes for therapeutic and diagnostic use

Diverse subsets of endothelial progenitor cells (EPCs) are used for the treatment of ischemic diseases in clinical trials, and circulating EPCs levels are considered as biomarkers for coronary and peripheral artery disease. However, despite significant steps forward in defining their potential for both therapeutic and diagnostic purposes, further progress has been mired by unresolved questions around the definition and the mechanism of action of EPCs. Diverse culturing methods and detection of various combinations of different surface antigens were used to enrich and identify EPCs. These attempts were particularly challenged by the close relationship and overlapping markers of the endothelial and hematopoietic lineages. This article will critically review the most commonly used protocols to define EPCs by culture assays or by fluorescence-activated cell sorter in the context of their therapeutic or diagnostic use. We also delineate new research avenues to move forward our knowledge on EPC biology.

Dysfunctional endothelial progenitor cells in metabolic syndrome

The metabolic syndrome (MetS) is highly prevalent and confers an increased risk of diabetes and cardiovascular disease. A key early event in atherosclerosis is endothelial dysfunction. Numerous groups have reported endothelial dysfunction in MetS. However, the measurement of endothelial function is far from optimum. There has been much interest recently in a subtype of progenitor cells, termed endothelial progenitor cells (EPCs), that can circulate, proliferate, and dfferentiate into mature endothelial cells. EPCs can be characterized by the assessment of surface markers, CD34 and vascular endothelial growth factor receptor-2, VEGFR-2 (KDR). The CD34(+)KDR(+) phenotype has been demonstrated to be an independent predictor of cardiovascular outcomes. MetS patients without diabetes or cardiovascular diseases have decreased EPC number and functionality as evidenced by decreased numbers of colony forming units, decreased adhesion and migration, and decreased tubule formation. Strategies that have been shown to upregulate and enhance EPC number and functionality include statins, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and peroxisome-proliferator-activating-receptor gamma agonists. Mechanisms by which they affect EPC number and functionality need to be studied. Thus, EPC number and/or functionality could emerge as novel cellular biomarkers of endothelial dysfunction and cardiovascular disease risk in MetS.

Endothelial progenitor cells as therapeutic agents in the microcirculation: an update

This review evaluates novel beneficial effects of circulating endothelial progenitor cells (EPCs) as shown by several preclinical studies and clinical trials carried out to test the safety and feasibility of using EPCs. There are 31 registered clinical trials (and many others still ongoing) and 19 published studies. EPCs originate in the bone marrow and migrate into the bloodstream where they undergo a differentiation program leading to major changes in their antigenic characteristics. EPCs lose typical progenitor markers and acquire endothelial markers, and two important receptors, (VEGFR and CXCR-4), which recruit circulating EPCs to damaged or ischemic microcirculatory (homing to damaged tissues) beds. Overall, therapeutic angiogenesis will likely change the face of regenerative medicine in the next decade with many patients worldwide predicted to benefit from these treatments.

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.

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.

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.

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.