β-Carotene stimulates chemotaxis of human endothelial progenitor cells

Β-carotene inhibits neuroblastoma tumorigenesis by regulating cell differentiation and cancer cell stemness

Neuroblastoma (NB) is the most common extracranial solid cancer in young children and malignant NB cells have been shown to possess cancer stem cell (CSC) characteristics. Thus, the successful elimination of CSCs represents a strategy for developing an effective preventive and chemotherapeutic agent. CSCs are characterized by differentiation and tumorigenicity. β-Carotene (BC) has been associated with many anticancer mechanisms, although the efficacy of BC on CSCs remains unclear. In the present study, the effects of BC on tumor cell differentiation and tumorigenicity was investigated using a xenograft model. Mice were pretreated with BC for 21 days, then received a subcutaneous injection of SK-N-BE(2)C cells. Both tumor incidence and tumor growth were significantly inhibited for mice that received BC supplementation compared to the control group. Treatment with BC has also been shown to induce tumor cell differentiation by up-regulating differentiation markers, such as vimentin, peripherin, and neurofilament. Conversely, BC treatment has been shown to significantly suppress tumor stemness by down-regulating CSC markers such as Oct 3/4 and DLK1. BC treatment also significantly down-regulated HIF1-α expression and its downstream target, vascular endothelial growth factor (VEGF). Taken together, these results suggest that BC is a potential chemotherapeutic reagent for the treatment of NB, and mediates this effect by regulating the differentiation and stemness of CSCs, respectively.

Connexin 43 and metabolic effect of fatty acids in stressed endothelial cells

Changes in the inner mitochondrial membrane potential (∆ψ) may lead either to apoptosis or to protective autophagy. Connexin 43 (Cx43), a gap junction protein, is suggested to affect mitochondrial membrane permeability. The aim of our study was to analyze Cx43 gene expression, Cx43 protein localization and mitochondrial function in the human endothelial cells stressed by dietary-free fatty acids (FFA) and TNFα. Human endothelial cells (HUVECs) were incubated with (10–30 uM) palmitic (PA), oleic (OA), eicosapentaenoic (EPA) or arachidonic (AA) acids for 24 h. TNFα (5 ng/ml) was added at the last 4 h of incubation. The Cx43 gene expression was analyzed by the quantitative real-time PCR. The Cx43 protein concentrations in whole cells and in the isolated mitochondria were measured. Changes in ∆ψ and Cx43 localization were analyzed by flow cytometry or fluorescence microscopy. Generated ATP was measured by a luminescence assay. TNFα, PA and OA significantly decreased ∆ψ, while AA (P = 0.047) and EPA (P = 0.004) increased ∆ψ value. Preincubation with EPA or AA partially prevented the TNFα-induced decrease of ∆ψ. Incubation with AA resulted in up-regulation of the Cx43 gene expression. AA or PA significantly increased Cx43 protein content; however, presence of TNFα in general aggravated the negative effect of FFA. Only EPA was found to increase ATP generation in HUVECs. The fatty acid-specific induction of changes in Cx43 expression and protein concentration as well as the normalization of ∆ψ and increase of ATP generation seem to be the separate, independent mechanisms of FFA-mediated modulatory effect in the human endothelial cells pathology.

The CpG island methylation regulated expression of endothelial proangiogenic genes in response to β-carotene and arachidonic acid

β-carotene (BC) and arachidonic acid (AA) were demonstrated to modulate carcinogenesis by influencing angiogenesis. DNA methylation is an epigenetic mechanism regulating gene expression. The aim of this study was to investigate whether BC and AA change DNA methylation and expression of the proangiogenic genes, which might help explain their impact on carcinogenesis. Human umbilical vein endothelial cells (HUVECs) and endothelial progenitors (EPCs) were incubated with BC or AA for 24 h. Based on microarray results, we selected 18 genes for DNA methylation analysis. CpG island methylation was quantified using the combined bisulphite restriction analysis method and methylation sensitive restriction enzymes. Relative gene expression was quantified using a quantitative real-time PCR (qRT-PCR) method. Incubation with AA significantly decreased methylation of the promoters of both KDR (P = 0.048) and Notch4 (P = 0.027) genes in HUVECs. In EPCs, BC increased methylation of the connexin 43 gene (P = 0.036). qRT-PCR showed that AA (P = 0.059) and BC (P = 0.044) upregulated the KDR gene expression in HUVECs. Connexin 43 gene expression was induced in the presence of 1 μM (P = 0.039) and 3 μM (P = 0.043) BC in EPCs. No significant changes in the Notch4 gene expression were found. The impact of BC and AA on carcinogenesis may be due, at least in part, to changes in expression of angiogenic genes and these transcriptional effects may be mediated by changes in methylation of CpG islands in the gene promoters. However more research is necessary to confirm this hypothesis.

Mediterranean diet reduces endothelial damage and improves the regenerative capacity of endothelium

BACKGROUND

Endothelial dysfunction is a fundamental step in the atherosclerotic disease process. Activation or injury of the endothelium leads to a variety of inflammatory disorders, including the release of microparticles. Endothelial progenitor cells may contribute to the maintenance of the endothelium by replacing injured mature endothelial cells.

OBJECTIVE

We studied the influence of dietary fat on the release of endothelial microparticles (EMPs) and endothelial progenitor cells (EPCs) in elderly subjects.

DESIGN

Twenty healthy, elderly subjects (10 men and 10 women) consumed 3 diets following a randomized crossover design, each for 4 wk: a saturated fatty acid diet; a low-fat, high-carbohydrate diet; and a Mediterranean diet (MedDiet) enriched in monounsaturated fatty acids. We investigated total microparticles, EMPs from activated endothelial cells (activated EMPs), EMPs from apoptotic endothelial cells (apoptotic EMPs), EPCs, oxidative stress variables, and ischemic reactive hyperemia (IRH).

RESULTS

The MedDiet led to lower total microparticle, activated EMP, and apoptotic EMP concentrations and higher EPC numbers than did the other diets (P < 0.001). We detected lower superoxide dismutase activity (P < 0.001), a higher plasma β-carotene concentration (P < 0.001), and lower urinary isoprostane and plasma nitrotyrosine concentrations after consumption of the MedDiet than after consumption of the other 2 diets (P < 0.05). Furthermore, the occurrence of IRH was higher after consumption of the MedDiet than after consumption of the other 2 diets (P < 0.05).

CONCLUSION

Consumption of the MedDiet induces a reduction in endothelial damage and dysfunction, which is associated with an improvement in the regenerative capacity of the endothelium, in comparison with 2 other diets.

Essential role of HDL on endothelial progenitor cell proliferation with PI3K/Akt/cyclin D1 as the signal pathway

High-density lipoprotein (HDL) is known as an important factor in vascular wall remodeling that also affects gene expression in cell proliferation and differentiation. In this article, the role of HDL on endothelial progenitor cell (EPC) proliferation, angiogenesis and the signal pathway involved was studied, particularly the influence of HDL in strengthening the promoting effect of EPCs on wound healing of the arterial wall in hypercholesterolemic rats. Mononuclear cells isolated from rat bone marrow displayed characteristics of EPCs after cultivation. The role of HDL on EPC function and the signal pathway involved were studied by Western blotting, in vitro migration and 'tube' formation. Re-endothelialization and the number of circulating EPCs were compared between normal rats, hypercholesterolemic rats and hypercholesterolemic rats with HDL treatment. Results showed that HDL participated in the healing process by promoting EPC proliferation, migration and 'tube' formation. HDL activates cyclin D1 via phosphatidylinositol 3-kinase (PI3K)/Akt stimulation. Inhibition of PI3K/Akt via pharmacological or small interfering RNA approaches significantly attenuated HDL-induced EPC migration, proliferation and 'tube' formation. Results of experiments in vivo showed that HDL increased the number of circulating EPCs and promoted re-endothelialization in wound healing. These findings demonstrate for the first time that PI3K/Akt-dependent cyclin D1 activation plays an essential role in HDL-induced EPC proliferation, migration and angiogenesis.

Angiogenesis in Balb/c mice under beta-carotene supplementation in diet

Angiogenesis is a process of new blood vessel formation from pre-existing ones. The most important steps in angiogenesis include detachment, proliferation, migration, homing and differentiation of vascular wall cells, which are mainly endothelial cells and their progenitors. The study focused on the effect of beta-carotene (BC) supplementation (12,000 mg/kg) in the diet on angiogenesis in Balb/c mice. Female Balb/c mice were fed for 5 weeks with two different diets: with BC or without BC supplementation. After 4 weeks of feeding, Balb/c mice were injected subcutaneously with two matrigel plugs with or without basic fibroblast growth factor (bFGF). Six days later, the animals were killed, and the matrigel plugs were used for immunohistochemical staining with CD31 antibody and for gene expression analysis. Microarray and Real-Time PCR data showed down-regulation of genes involved in proliferation and up-regulation of genes encoding inhibitors of apoptosis, proteins regulating cell adhesion, matrix-degrading enzymes and proteins involved in the VEGF pathway. The results of this study demonstrated that BC proangiogenic activity (with or without bFGF) in vivo seemed to be more significantly associated with cells' protection from apoptosis and their stimulation of chemotaxis/homing than cell proliferation.

Antioxidants increase number of progenitor endothelial cells through multiple gene expression pathways

To date, there is no report on the effect of antioxidants on endothelial progenitor cells (EPCs). This study shows that in vitro incubation of EPCs with vitamin C and E reverted the already well documented lowering effect of TNF-alpha on EPC number and increased p-p38 expression levels. In order to document major changes of gene expression levels and gain insight into signalling pathways, microarray analysis was performed and a significant variation of the expression of 5389 genes in EPCs following antioxidant treatment was detected. Also in vivo evidence is provided about the positive effect of antioxidant vitamins on EPCs, since vitamin C and E supplementation potentiated the physical training-induced increase of EPC number and VEGF levels. Together, these data indicate that antioxidant treatment ameliorates EPC number and causes major changes of gene expression within these cells in vitro. Furthermore, concomitant antioxidant supplementation and physical training in vivo raised the levels of circulating EPCs and serum VEGF more than physical training alone.

Progenitor cells and vascular disease

Vascular progenitor cells have been the focus of much attention in recent years; both from the point of view of their pathophysiological roles and their potential as therapeutic agents. However, there is as yet no definitive description of either endothelial or vascular smooth muscle progenitor cells. Cells with the ability to differentiate into mature endothelial and vascular smooth muscle reportedly reside within a number of different tissues, including bone marrow, spleen, cardiac muscle, skeletal muscle and adipose tissue. Within these niches, vascular progenitor cells remain quiescent, until mobilized in response to injury or disease. Once mobilized, these progenitor cells enter the circulation and migrate to sites of damage, where they contribute to the remodelling process. It is generally perceived that endothelial progenitors are reparative, acting to restore vascular homeostasis, while smooth muscle progenitors contribute to pathological changes. Indeed, the number of circulating endothelial progenitor cells inversely correlates with exposure to cardiovascular risk factors and numbers of animal models and human studies have demonstrated therapeutic roles for endothelial progenitor cells, which can be enhanced by manipulating them to overexpress vasculo-protective genes. It remains to be determined whether smooth muscle progenitor cells, which are less well studied than their endothelial counterparts, can likewise be manipulated to achieve therapeutic benefit. This review outlines our current understanding of endothelial and smooth muscle progenitor cell biology, their roles in vascular disease and their potential as therapeutic agents.