Circulating endothelial progenitor cells in HIV infection: A systematic review

Circulating endothelial and angiogenic cells predict hippocampal volume as a function of HIV status

Circulating endothelial cells (CECs) and myeloid angiogenic cells (MACs) have the capacity to stabilize human blood vessels in vivo. Evidence suggests that these cells are depleted in dementia and in persons living with HIV (PWH), who have a higher prevalence of dementia and other cognitive deficits associated with aging. However, the associations of CECs and MACs with MRI-based measures of aging brain health, such as hippocampal gray matter volume, have not been previously demonstrated. The present study examined differences in these associations in 51 postmenopausal women with and without HIV infection. Gray matter volume was quantified using MRI. CECs and MACs were enumerated using fluorescence-activated cell sorting. Analyses examined the association of these cell counts with left and right hippocampal gray matter volume while controlling for age and hypertension status. The main finding was an interaction suggesting that compared to controls, postmenopausal PWH with greater levels of CECs and MACs had significantly greater hippocampus GMV. Further research is necessary to examine potential underlying pathophysiological mechanisms in HIV infection linking morpho-functional circulatory reparative processes with more diminished hippocampal volume in postmenopausal women.

The Role of Inflammation and Immune Activation on Circulating Endothelial Progenitor Cells in Chronic HIV Infection

Endothelial inflammation and damage are the main drivers of cardiovascular risk/disease. Endothelial repair is mediated in part by recruitment of bone marrow endothelial progenitor/endothelial colony forming cells (EPC/ECFC). People with HIV (PWH) have increased cardiovascular risk and the impact of infection in endothelial repair is not well defined. The low frequencies and challenges to in vitro isolation and differentiation of EPC/ECFC from PBMCs had made it difficult to study their role in this context. We hypothesized that HIV driven inflammation induces phenotypic changes that reflects the impact of infection. To test this hypothesis, we evaluated expression of markers of trafficking, endothelial differentiation, and angiogenesis, and study their association with biomarkers of inflammation in a cohort of PWH. In addition, we investigated the relationship of circulating endothelial progenitors and angiogenic T cells, a T cell subset with angiogenic function. Using a flow cytometry approach, we identified two subsets of circulating progenitors LIN4^-CD45^-CD34⁺ and LIN4^-CD45^dimCD34⁺ in PWH. We found that the phenotype but not frequencies were associated with biomarkers of inflammation. In addition, the percentage of LIN4^-CD45^dimCD34⁺ was associated with serum levels of lipids. This data may provide a new tool to better address the impact of HIV infection in endothelial inflammation and repair.

Low Levels of Endothelial Progenitor Cells and Their Association with Systemic Inflammation and Monocyte Activation in Older HIV-Infected Men

Endothelial progenitor cells (EPCs) repair damaged vascular endothelium, and low circulating EPC levels have been associated with cardiovascular disease (CVD). CD34⁺/KDR⁺ EPCs are commonly reported in the literature and CD34⁺/CD133⁺/KDR⁺ EPCs are rare in circulation but highly specific for endothelial lineage. HIV-infected (HIV+) adults have chronic inflammation and increased CVD risk, but the relationship between CVD, vascular inflammation, and EPCs in HIV remains unclear. In a pilot study, EPCs were measured in 57 HIV+ men [≥50 years old, HIV-1 RNA <50 copies/ml on antiretroviral therapy (ART)] by real-time flow cytometry using cellular immaturity (CD34 and/or CD133) and endothelial commitment (KDR) markers. Fasting inflammatory biomarker levels were measured by ELISA. Median age was 57 years; CD4⁺ T lymphocyte count was 570 cells/mm³. Prevalent CVD risk factors included 16% diabetes, 28% hypertension, 53% dyslipidemia, and 33% smoking. Median (interquartile range) EPC values were CD34⁺/KDR⁺ 0.1 (0.0-0.9) cells/10⁵ peripheral blood mononuclear cells (PBMCs) and CD34⁺/CD133⁺/KDR⁺ 0.1 (0.0-0.9) cells/10⁵ PBMCs. We observed a high prevalence of undetectable CD34⁺/KDR⁺ (40%) and CD34⁺/CD133⁺/KDR⁺ EPCs (44%). Men with undetectable EPCs were more likely to have ≥2 CVD risk factors, lower interleukin-6 (IL-6), and higher sCD163 levels. In these older HIV+ men on suppressive ART, CD34⁺/KDR⁺ and CD34⁺/CD133⁺/KDR⁺ EPC levels were low and often undetectable. Undetectable EPC levels were associated with greater CVD risk factor burden, lower IL-6 (consistent with decreased EPC production stimulus), and higher sCD163 (consistent with monocyte activation and prior CVD associations) levels, suggesting a potential relationship between EPCs and atherosclerotic burden in this population.

Fluorescence detection, enumeration and characterization of single circulating cells in vivo: technology, applications and future prospects

There are many diseases and biological processes that involve circulating cells in the bloodstream, such as cancer metastasis, immunology, reproductive medicine, and stem cell therapies. This has driven significant interest in new technologies for the study of circulating cells in small animal research models and clinically. Most currently used methods require drawing and enriching blood samples from the body, but these suffer from a number of limitations. In contrast, 'in vivo flow cytometry' (IVFC) refers to set of technologies that allow study of cells directly in the bloodstream of the organism in vivo. In recent years the IVFC field has grown significantly and new techniques have been developed, including fluorescence microscopy, multi-photon, photo-acoustic, and diffuse fluorescence IVFC. In this paper we review recent technical advances in IVFC, with emphasis on instrumentation, contrast mechanisms, and detection sensitivity. We also describe key applications in biomedical research, including cancer research and immunology. Last, we discuss future directions for IVFC, as well as prospects for broader adoption by the biomedical research community and translation to humans clinically.

Circulating endothelial cells and their subsets: novel biomarkers for cancer

Angiogenesis contributes to the growth of solid tumors. Antiangiogenic agents are widely used in various cancers and considerable efforts have been made in the development of novel biomarkers that can predict the outcome of an anticancer treatment. Of those, circulating endothelial cells (CECs) and their subsets constitute a surrogate tool for monitoring disease activity. However, owing to the lack of standardization on the phenotypes and detection of CECs and their subsets, results have always been inconsistent and uninterpretable. In this review, we focus on the biological characteristics in terms of physiology, phenotypes and detection of CECs along with their subsets; review the current scenario of CEC enumeration as a surrogate biomarker in clinical oncology; and explore their future potential applications.

Telmisartan increases vascular reparative capacity in older HIV-infected adults: a pilot study

BACKGROUND

Endothelial progenitor cells (EPCs) are bone marrow-derived cells that contribute to vascular repair. EPCs may be reduced in HIV-infected (HIV+) persons, contributing to cardiovascular disease (CVD). Telmisartan is an angiotensin receptor blocker that increases EPCs in HIV-uninfected adults.

OBJECTIVE

To assess telmisartan's effects on EPC number and immunophenotype in older HIV + adults at risk for CVD.

METHODS

HIV + persons ≥50 years old with HIV-1 RNA < 50 copies/mL on suppressive antiretroviral therapy and ≥1 CVD risk factor participated in a prospective, open-label, pilot study of oral telmisartan 80 mg daily for 12 weeks. Using CD34 and CD133 as markers of early maturity and KDR as a marker of endothelial lineage commitment, EPCs were quantified via flow cytometry and defined as viable CD3^-/CD33^-/CD19^-/glycophorin^- cells of four immunophenotypes: CD133⁺/KDR⁺, CD34⁺/KDR⁺, CD34⁺/CD133⁺, or CD34⁺/KDR⁺/CD133⁺. The primary endpoint was a 12-week change in EPC subsets (NCT01578772).

RESULTS

Seventeen participants (88% men, median age 60 years and peripheral CD4⁺ T lymphocyte count 625 cells/mm³) enrolled and completed the study. After 6 and 12 weeks of telmisartan, frequencies of all EPC immunophenotypes were higher than baseline (all p < 0.10 except week 12 CD133⁺/KDR⁺ EPC, p = 0.13). Participants with lower baseline EPC levels had the largest gains. Additionally, the percentage of CD34⁺ cells with endothelial commitment (KDR⁺) increased.

CONCLUSIONS

Our data suggest that telmisartan use is associated with an increase in circulating EPCs in older HIV + individuals with CVD risk factors. Further controlled studies are needed to assess whether EPC increases translate to a reduction in CVD risk in this population.

Flow cytometric analysis of circulating endothelial cells and endothelial progenitors for clinical purposes in oncology: A critical evaluation

Malignant tumors are characterized by uncontrolled cell growth and metastatic spread, with a pivotal importance of the phenomenon of angiogenesis. For this reason, research has focused on the development of agents targeting the vascular component of the tumor microenvironment and regulating the angiogenic switch. As a result, the therapeutic inhibition of angiogenesis has become an important component of anticancer treatment, however, its utility is partly limited by the lack of an established methodology to assess its efficacy in vivo. Circulating endothelial cells (CECs), which are rare in healthy subjects and significantly increased in different tumor types, represent a promising tool for monitoring the tumor clinical outcome and the treatment response. A cell population circulating into the blood also able to form endothelial colonies in vitro and to promote vasculogenesis is represented by endothelial progenitor cells (EPCs). The number of both of these cell types is extremely low and they cannot be identified using a single marker, therefore, in absence of a definite consensus on their phenotype, require discrimination using combinations of antigens. Multiparameter flow cytometry (FCM) is ideal for rapid processing of high numbers of cells per second and is commonly utilized to quantify CECs and EPCs, however, remains technically challenging since there is as yet no standardized protocol for the identification and enumeration of these rare events. Methodology in studies on CECs and/or EPCs as clinical biomarkers in oncology is heterogeneous and data have been obtained from different studies leading to conflicting conclusions. The present review presented a critical review of the issues that limit the comparability of results of the most significant studies employing FCM for CEC and/or EPC detection in patients with cancer.

Brief report: Endothelial colony-forming cells and inflammatory monocytes in HIV

The relationships between HIV infection, monocyte activation, and endothelial colony-forming cells (ECFCs) are unknown. We compared ECFC, intermediate monocytes (CD14 CD16), and nonclassical monocytes (CD14 CD16) levels in HIV-infected participants virologically suppressed on antiretroviral therapy, HIV-infected treatment-naive participants, and HIV-uninfected healthy controls. ECFC levels were significantly higher in the HIV-infected virologically suppressed group compared with the uninfected controls. CD14 CD16 percentages (but not CD14 CD16 cells) were significantly higher in both HIV-infected groups vs. uninfected controls. In the HIV-infected groups, ECFCs and CD14 CD16 intermediate monocytes were significantly and inversely correlated. Lower availability of ECFCs may partly explain the relationship between greater intermediate monocytes and atherosclerosis in HIV.

Circulating endothelial cells and their subpopulations: role as predictive biomarkers in antiangiogenic therapy for colorectal cancer

Several anticancer therapies have been developed to block angiogenesis, a key mechanism in tumor growth and metastasis. The predominantly cytostatic action of these compounds makes an assessment of their clinical activities inadequate if based only on the reduction of the tumor dimensions, as this may not reflect their true biologic efficacy. Thus, it is crucial to identify biomarkers that permit the recognition of potentially responsive subjects and to spare toxicity in those who are unlikely to benefit from treatment. Circulating endothelial cells (CECs) have been recently indicated as potential surrogate biomarkers of angiogenesis in several types of cancer. The possibility of rapidly quantifying these cells represents a promising tool for monitoring the clinical outcome of tumors with the potential to assess response to various treatments. However, the identification and quantification of CECs is technically difficult and not well standardized. A variety of methods to detect CECs in patients with solid tumors have been used; these are based on different technical approaches, combinations of surface markers, sample handling, and staining protocols. With an expanding interest in the field of potential clinical applications for CECs in oncology, the development of standardized protocols for analysis is mandatory. The aim of this review was to critically summarize the available data concerning the clinical value of CECs and their subpopulations as biomarkers of antiangiogenic therapy in patients with metastatic colorectal cancer.

The effect of statins on circulating endothelial progenitor cells in humans: a systematic review

Numerous clinical trials have demonstrated early reductions in cardiovascular events occurring independently of the lipid-lowering effects of statins. These pleiotropic effects have been attributed to antiinflammatory properties, to atherosclerotic plaque stabilization, and more recently to mobilization of endothelial progenitor cells (EPCs). Our aim was to evaluate the evidence supporting statin-induced EPC mobilization in humans. We, therefore, performed a computerized literature search and systematic review of randomized trials to determine the effect of statin therapy and statin dosing on circulating EPC numbers. Our literature search identified 10 studies including 479 patients which met inclusion criteria with publication dates ranging from 2005 to 2011. Seven studies compared statin to nonstatin regimens whereas 3 studied low versus high-dose statin therapy. Reported increases in EPC number ranged from 25.8% to 223.5% with a median reported increase of 70.2% when compared to nonstatin regimens with 7 of 10 studies reporting significant increases. Considerable heterogeneity exists in regard to patient population, statin regimens, and the definition of an EPC within the identified studies. In conclusion, randomized studies in humans suggest that statin therapy mobilizes EPCs into the circulation. Larger randomized studies using uniform definitions are needed to definitively establish this effect.

The evolution of coronary stents: a brief review

Percutaneous coronary intervention is the most prevalent method for coronary artery revascularization. Initial interventions using balloon angioplasty had limited efficacy because coronary dissections, arterial recoil, and neointimal formation led to high rates of abrupt vessel closure and clinical restenosis. With the introduction of coronary stents, vascular dissections were stabilized and arterial recoil was eliminated, but neointimal accumulation remained problematic, resulting in the development of in-stent restenosis (ISR) in 20%-30% of cases. Drug-eluting stents (DESs) were developed to release antiproliferative agents at the site of arterial injury to attenuate neointimal formation. Although DESs have incrementally improved outcomes after percutaneous coronary intervention, delayed re-endothelialization and stent thrombosis remain important challenges. Herein we review the pathophysiology of ISR, stent thrombosis, and briefly summarize the clinical evidence behind first- and second-generation DESs. Moreover, we discuss advancements in our understanding of the pathogenesis of ISR and potential novel therapeutic strategies to improve clinical outcomes.