Biomedical subjects

Alexandra Aicher

Publications and source records attributed to Alexandra Aicher.

26 records · Page 2Linked to original sources

PubMed2003

Erythropoietin is a potent physiologic stimulus for endothelial progenitor cell mobilization.

Increasing evidence suggests that postnatal neovascularization involves the recruitment of circulating endothelial progenitor cells (EPCs). Hematopoietic and endothelial cell lineages share common progenitors. Cytokines formerly thought to be specific for the hematopoietic system have only recently been shown to affect several functions in endothelial cells. Accordingly, we investigated the stimulatory potential of erythropoietin (Epo) on EPC mobilization and neovascularization. The bone marrow of Epo-treated mice showed a significant increase in number and proliferation of stem and progenitor cells as well as in colony-forming units. The number of isolated EPCs and CD34+/flk-1+ precursor cells was significantly increased in spleen and peripheral blood of Epo-treated mice compared with phosphate-buffered saline-treated mice. In in vivo models of postnatal neovascularization, Epo significantly increased inflammation- and ischemia-induced neovascularization. The physiologic relevance of these findings was investigated in patients with coronary heart disease. In a multivariate regression model, serum levels of Epo and vascular endothelial growth factor were significantly associated with the number of stem and progenitor cells in the bone marrow as well as with the number and function of circulating EPCs. In conclusion, the present study suggests that Epo stimulates postnatal neovascularization at least in part by enhancing EPC mobilization from the bone marrow. Epo appears to physiologically regulate EPC mobilization in patients with ischemic heart disease. Thus, Epo serum levels may help in identifying patients with impaired EPC recruitment capacity.

Animals↗

PubMed2003

Assessment of the tissue distribution of transplanted human endothelial progenitor cells by radioactive labeling.

BACKGROUND: Transplantation of endothelial progenitor cells (EPCs) improves vascularization and left ventricular function after experimental myocardial ischemia. However, tissue distribution of transplanted EPCs has not yet been monitored in living animals. Therefore, we tested whether radioactive labeling allows us to detect injected EPCs. METHODS AND RESULTS: Human EPCs were isolated from peripheral blood, characterized by expression of endothelial marker proteins, and radioactively labeled with [111In]indium oxine. EPCs (106) were injected in athymic nude rats 24 hours after myocardial infarction (n=8) or sham operation (n=8). Scintigraphic images were acquired after 1, 24, 48, and 96 hours after EPC injection. Animals were then killed, and specific radioactivity was measured in different tissues. At 24 to 96 hours after intravenous injection of EPCs, approximately 70% of the radioactivity was localized in the spleen and liver, with only approximately 1% of the radioactivity identified in the heart of sham-operated animals. After myocardial infarction, the heart-to-muscle radioactivity ratio increased significantly, from 1.02+/-0.19 in sham-operated animals to 2.03+/-0.37 after intravenous administration of EPCs. Injection of EPCs into the left ventricular cavity increased this ratio profoundly, from 2.69+/-1.54 in sham-operated animals to 4.70+/-1.55 (P<0.05) in rats with myocardial infarction. Immunostaining of cryosections from infarcted hearts confirmed that EPCs homed predominantly to the infarct border zone. CONCLUSIONS: Although only a small proportion of radiolabeled EPCs are detected in nonischemic myocardium, myocardial infarction increases homing of transplanted EPCs in vivo profoundly. Radiolabeling might eventually provide an useful tool for monitoring the fate of transplanted progenitor cells and for clinical cell therapy.

Animals↗

PubMed2003

HMG-CoA reductase inhibitors reduce senescence and increase proliferation of endothelial progenitor cells via regulation of cell cycle regulatory genes.

Endothelial progenitor cells (EPCs) play an important role in postnatal neovascularization of ischemic tissue. Ex vivo expansion of EPCs might be useful for potential clinical cell therapy of myocardial ischemia. However, cultivation of primary cells leads to cellular aging (senescence), thereby severely limiting the proliferative capacity. Therefore, we investigated whether statins might be able to prevent senescence of EPCs. EPCs were isolated from peripheral blood and characterized. After ex vivo cultivation, EPCs became senescent as determined by acidic beta-galactosidase staining. Atorvastatin or mevastatin dose-dependently inhibited the onset of EPC senescence in culture. Moreover, atorvastatin increased proliferation of EPCs as assessed by BrdU incorporation and colony-forming capacity. Whereas geranylgeranylpyrophosphate or farnesylpyrophosphate reduced the senescence inhibitory effect of atorvastatin, NO synthase inhibition, antioxidants, or Rho kinase inhibitors had no effect. To get further insights into the underlying downstream effects of statins, we measured telomerase activity and determined the expression of various cell cycle regulatory genes by using a microarray assay. Whereas telomerase activity did not change, atorvastatin modulated expression of cell cycle genes including upregulation of cyclins and downregulation of the cell cycle inhibitor p27Kip1. Taken together, statins inhibited senescence of EPCs independent of NO, reactive oxygen species, and Rho kinase, but dependent on geranylgeranylpyrophosphate. Atorvastatin-mediated prevention of EPC senescence appears to be mediated by the regulation of various cell cycle proteins. The inhibition of EPC senescence and induction of EPC proliferation by statins in vitro may importantly improve the functional activity of EPCs for potential cell therapy.

Atorvastatin↗

PubMed2003

Transdifferentiation of blood-derived human adult endothelial progenitor cells into functionally active cardiomyocytes.

BACKGROUND: Further to promoting angiogenesis, cell therapy may be an approach for cardiac regeneration. Recent studies suggest that progenitor cells can transdifferentiate into other lineages. However, the transdifferentiation potential of endothelial progenitor cells (EPCs) is unknown. METHODS AND RESULTS: EPCs were obtained from peripheral blood mononuclear cells of healthy adults or coronary artery disease (CAD) patients by cultivating with endothelial cell medium and growth factors. After 3 days, >95% of adherent cells were functionally and phenotypically EPCs. Diacetylated LDL-labeled EPCs were then cocultivated with rat cardiomyocytes for 6 days, resulting in significant increases of EPC cell length and size to a cardiomyocyte-like morphology. Biochemically, 9.94+/-1.39% and 5.04+/-1.09% of EPCs from healthy adults (n=15) or CAD patients (n=14, P<0.01 versus healthy adults), respectively, expressed alpha-sarcomeric actinin as measured by flow cytometry. Immunocytochemistry showed that human EPCs expressed alpha-sarcomeric actinin, cardiac troponin I (both with partial sarcomeric organization), atrial natriuretic peptide, and myocyte enhancer factor 2. Fluo 4 imaging demonstrated calcium transients synchronized with adjacent rat cardiomyocytes in transdifferentiated human EPCs. Single-cell microinjection of Lucifer yellow and calcein-AM labeling of cardiomyocytes demonstrated gap junctional communication between 51+/-7% of EPCs (16 hours after labeling, n=4) and cardiomyocytes. EPC transdifferentiation into cardiomyocytes was not observed with conditioned medium but in coculture with paraformaldehyde-fixed cardiomyocytes. CONCLUSIONS: EPCs from healthy volunteers and CAD patients can transdifferentiate in vitro into functionally active cardiomyocytes when cocultivated with rat cardiomyocytes. Cell-to-cell contact but not cellular fusion mediates EPC transdifferentiation. The therapeutic use of autologous EPCs may aid cardiomyocyte regeneration in patients with ischemic heart disease.

Adult↗

PubMed2003

Nicotine strongly activates dendritic cell-mediated adaptive immunity: potential role for progression of atherosclerotic lesions.

BACKGROUND: Antigen-presenting cells (APCs) such as monocytes and dendritic cells (DCs) stimulate T-cell proliferation and activation in the course of adaptive immunity. This cellular interaction plays a role in the growth of atherosclerotic plaques. Nicotine has been shown to increase the growth of atherosclerotic lesions. Therefore, we investigated whether nicotine can stimulate APCs and their T cell-stimulatory capacity using human monocyte-derived DCs and murine bone marrow-derived DCs as APCs. METHODS AND RESULTS: Nicotine dose-dependently (10(-8) to 10(-4) mol/L) induced DC expression of costimulatory molecules (ie, CD86, CD40), MHC class II, and adhesion molecules (ie, LFA-1, CD54). Moreover, nicotine induced a 7.0-fold increase in secretion of the proinflammatory T(H)1 cytokine interleukin-12 by human DCs. These effects were abrogated by the nicotinic receptor antagonist alpha-bungarotoxin and mecamylamine, respectively. The effects of nicotine were mediated in part by the phosphorylation of the PI3 kinase downstream target Akt and the mitogen-activated kinases ERK and p38 MAPK. Nicotine-stimulated APCs had a greater capacity to stimulate T-cell proliferation and cytokine secretion, as documented by mixed lymphocyte reactions and ovalbumin-specific assays with ovalbumin-transgenic DO10.11 mice. In a murine model of atherosclerosis, nicotine significantly enhanced the recruitment of DCs to atherosclerotic lesions in vivo. CONCLUSIONS: Nicotine activates DCs and augments their capacity to stimulate T-cell proliferation and cytokine secretion. These effects of nicotine may contribute to its influence on the progression of atherosclerotic lesions.

Animals↗

PubMed2002

Transplantation of Progenitor Cells and Regeneration Enhancement in Acute Myocardial Infarction (TOPCARE-AMI).

BACKGROUND: Experimental studies suggest that transplantation of blood-derived or bone marrow-derived progenitor cells beneficially affects postinfarction remodeling. The safety and feasibility of autologous progenitor cell transplantation in patients with ischemic heart disease is unknown. METHODS AND RESULTS: We randomly allocated 20 patients with reperfused acute myocardial infarction (AMI) to receive intracoronary infusion of either bone marrow-derived (n=9) or circulating blood-derived progenitor cells (n=11) into the infarct artery 4.3+/-1.5 days after AMI. Transplantation of progenitor cells was associated with a significant increase in global left ventricular ejection fraction from 51.6+/-9.6% to 60.1+/-8.6% (P=0.003), improved regional wall motion in the infarct zone (-1.5+/-0.2 to -0.5+/-0.7 SD/chord; P<0.001), and profoundly reduced end-systolic left ventricular volumes (56.1+/-20 mL to 42.2+/-15.1 mL; P=0.01) at 4-month follow-up. In contrast, in a nonrandomized matched reference group, left ventricular ejection fraction only slightly increased from 51+/-10% to 53.5+/-7.9%, and end-systolic volumes remained unchanged. Echocardiography revealed a profound enhancement of regional contractile function (wall motion score index 1.4+/-0.2 at baseline versus 1.19+/-0.2 at follow-up; P<0.001). At 4 months, coronary blood flow reserve was significantly (P<0.001) increased in the infarct artery. Quantitative F-18-fluorodeoxyglucose-positron emission tomography analysis revealed a significant (P<0.01) increase in myocardial viability in the infarct zone. There were no differences for any measured parameter between blood-derived or bone marrow-derived progenitor cells. No signs of an inflammatory response or malignant arrhythmias were observed. CONCLUSIONS: In patients with AMI, intracoronary infusion of autologous progenitor cells appears to be feasible and safe and may beneficially affect postinfarction remodeling processes.

Cells, Cultured↗

PubMed2002

CD40 ligand inhibits endothelial cell migration by increasing production of endothelial reactive oxygen species.

BACKGROUND: The CD40/CD40 ligand system is involved in atherogenesis. Activated T lymphocytes and platelets, which express high amounts of CD40 ligand (CD40L) on their surface, contribute significantly to plaque instability with ensuing thrombus formation, leading to acute coronary syndromes. Because reendothelialization may play a pivotal role for plaque stabilization, we investigated a potential role of CD40L on endothelial cell (EC) migration. METHODS AND RESULTS: Stimulation of ECs with recombinant CD40L prevented vascular endothelial growth factor (VEGF)-induced EC migration, as determined by a "scratched wound assay." In addition, activated T lymphocytes and platelets significantly inhibited VEGF-induced EC migration and tube formation in vitro. Because the activation of endothelial nitric oxide (NO) synthase and the release of NO are required for EC migration and angiogenesis, we analyzed the effect of NO. Coincubation with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) did not reverse the inhibitory effect of CD40L on VEGF-induced EC migration and tube formation. In addition, EC migration induced by SNAP was completely inhibited by CD40L. CD40L, however, induced the production of reactive oxygen species and reduced endothelial NO bioavailability. This reactive oxygen species-dependent effect of CD40L stimulation was reversed with vitamin C or N-acetylcysteine. CONCLUSIONS: The activation of the CD40 receptor inhibits EC migration by increasing reactive oxygen species. The blockade of EC migration by CD40L may critically affect endothelial regeneration after plaque erosion and thereby may contribute to the increased risk for development of acute coronary events in patients with high circulating levels of CD40L.

Antioxidants↗

PubMed2002

A novel angiogenic pathway mediated by non-neuronal nicotinic acetylcholine receptors.

We have recently reported that nicotine has angiogenic effects, which appear to be mediated through non-neuronal nicotinic acetylcholine receptors (nAChRs). Here, we describe the endogenous cholinergic pathway for angiogenesis. In an in vitro angiogenesis model, increasing concentrations of the nonselective nAChR antagonist mecamylamine completely and reversibly inhibited endothelial network formation. Although several nAChR isoforms are expressed on endothelial cells (ECs), a similar inhibition was only obtained with the selective alpha7-nAChR antagonist alpha-bungarotoxin, whereas other selective antagonists did not result in significant inhibition of network formation. alpha7-nAChR was upregulated during proliferation, by hypoxia in vitro, and by ischemia in vivo. The nAChR-induced network formation was partially dependent on VEGF, was completely dependent on the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, and finally resulted in NF-kappaB activation. In vivo, pharmacological inhibition of nAChR as well as genetic disruption of alpha7-nAChR expression significantly inhibited inflammatory angiogenesis and reduced ischemia-induced angiogenesis and tumor growth. Our results suggest that nAChRs may play an important role in physiological and pathological angiogenesis. To our knowledge, this is the first description of a cholinergic angiogenic pathway, and it suggests a novel avenue for therapeutic modulation of angiogenesis.

Animals↗