Abstract-Circulating blood-derived vasculogenic cells improve neovascularization of ischemic tissue by a broad repertoire of potential therapeutic actions. Whereas initial studies documented that the cells incorporate and differentiate to cardiovascular cells, other studies suggested that short-time paracrine mechanisms mediate the beneficial effects. The question remains to what extent a physical incorporation is contributing to the beneficial effects of cell therapy. By using the inducible suicide gene thymidine kinase to deplete transplanted cells, we determined the contribution of physical incorporation in 3 animal models. After acute myocardial infarction, depletion of cells 14 days after infusion resulted in a reduction of capillary density and a substantial deterioration of heart function. Likewise, neovascularization of Matrigel plugs and ischemic limbs was significantly suppressed when infused cells were depleted 7 days after infusion. Key Words: progenitor cells Ⅲ neovascularization Ⅲ cell therapy C ell therapy is a promising option for treating ischemic diseases. Adult stem and progenitor cells from various sources have experimentally been shown to augment the functional recovery after ischemia. Clinical trials confirmed that autologous cell therapy using bone marrow-derived or circulating blood-derived progenitor cells is safe and provides beneficial effects 1-3 (see also recent metaanalysis 4 ). Endothelial progenitor cells (EPCs) were initially isolated from bone marrow or peripheral blood and were characterized by the expression of the hematopoietic stem cell marker CD34 or CD133 and endothelial markers such as vascular endothelial growth factor receptor 2 (KDR). 5,6 Isolated CD34 ϩ cells differentiate to endothelial cells in vitro and incorporate into newly formed vessels during angiogenesis in vivo. 5 These pioneering studies suggested that bone marrow-derived cells can participate in vascular repair. Indeed, a single hematopoietic stem cell was shown to give rise to both blood cells and vascular endothelium. [7][8][9] The contribution of circulating cells to the endothelium was further supported by sexmismatched heart transplantation in humans. 10,11 Other investigators used culture assays to enrich for EPC-yielding cells, which coexpress endothelial and myeloid marker ("early EPCs," proangiogenic cells), or to show a more mature endothelial cell phenotype on further culture and expansion ("late or outgrowing EPCs"). 12,13 Although the origin and the phenotype of the cultured EPCs is not entirely clear and may vary depending on the defined specific culture conditions, 14 the therapeutic potential and improved neovascularization mediated by the cultured cells has been documented extensively in ischemic models. 12,15,16 Progenitor cell-mediated improved neovascularization of ischemic tissue might be attributable to various therapeutic actions including a physical incorporation of the infused cells in the endothelium leading to the formation of new capillaries. 16 -18 Transplanted or infused hema...

Objective-Migratory capacity of endothelial progenitor cells (EPCs) and mature endothelial cells (ECs) is a key prerequisite for endothelial repair after denuding injury or endothelial damage. Methods and Results-We demonstrate that caffeine in physiologically relevant concentrations (50 to 100 mol/L) induces migration of human EPCs as well as mature ECs. In patients with coronary artery disease (CAD), caffeinated coffee increased caffeine serum concentration from 2 mol/L to 23 mol/L, coinciding with a significant increase in migratory activity of patient-derived EPCs. Decaffeinated coffee neither affected caffeine serum levels nor migratory capacity of EPCs. Treatment with caffeine for 7 to 10 days in a mouse-model improved endothelial repair after denudation of the carotid artery. The enhancement of reendothelialization by caffeine was significantly reduced in AMPK knockout mice compared to wild-type animals. Transplantation of wild-type and AMPK Ϫ/Ϫ bone marrow into wild-type mice revealed no difference in caffeine challenged reendothelialization. ECs which were depleted of mitochondrial DNA did not migrate when challenged with caffeine, suggesting a potential role for mitochondria in caffeine-dependent migration. Conclusion-These results provide evidence that caffeine enhances endothelial cell migration and reendothelialization in part through an AMPK-dependent mechanism, suggesting a beneficial role for caffeine in endothelial repair.