Inseparably Tied

Abstract

See related article, pages 254–261 New blood vessel formation is required to increase blood supply to the myocardium or other tissues after critical ischemia. Capillary formation after ischemia can be achieved by the sprouting of preexisting vessels, a process named angiogenesis. However, in the last few years it has become evident that bone marrow–derived circulating endothelial progenitor cells (EPCs) can contribute to and amplify neovascularization. EPCs significantly contribute to adult vessel formation by physically incorporating and promoting vessel growth by paracrine mechanisms.1 Injected EPCs improve neovascularization of ischemic hind limbs and ischemic hearts in animal models (for review see reference 2). Moreover, initial clinical trials demonstrate that the infusion or injection of bone marrow–derived or circulating progenitor cells augment perfusion and increase the ejection fraction in patients with ischemic heart disease (for review see reference 3). To contribute to tissue repair, EPCs, and stem cells in general, have to be equipped with antioxidative defense systems to survive in necrotic and ischemic tissues. Interestingly, a high resistance to oxidative stress has been considered a characteristic feature of stem cells.4,5 Protection against oxidative stress by reactive oxygen species is accomplished by a complex defense system composed of several antioxidative enzymes that reduce the damaging effects of …