Angiogenesis is part of the natural defense mechanism in brain against hypoxia and ischemia. This proposal will address the hypothesis that steady state NMR imaging will detect changes in cerebral blood volume (CBV) induced by angiogenesis. Therapeutic angiogenesis is being investigated in myocardial ischemia and peripheral vascular disease, but the potential of stimulating angiogenesis to improve outcome in cerebral ischemia is unknown. Elucidating the time course of angiogenesis and regression will facilitate the study of angiogenic interventions. The time course of growth factor expression in this model is known, but this work will provide a link between molecular biological changes and morphological responses. A non-invasive, repeatable method for studying angiogenesis in brain will be developed and applied for making multiple measurements in the same animals. This is a steady state NMR imaging method using a serum based contrast agent (MION). By quantifying the relaxation rate R2 before and after infusion of monocrystalline iron-oxide nanoparticles (MION), we will obtain an index of cerebral microvascular volume. Adaptation to hypobaric hypoxia will increase microvessel density. We will validate the imaging method by showing that that the NMR measurements of CBV correlate with cerebral angiogenesis. CBV will then be measured in the same animals over a time course of angiogenesis and regression. Finally, a pilot study will determine if angiogenesis using adenoviral transfection of an oxygen-stable construct of HIF-la (the upregulation of which induces VEGF, a potent angiogenic stimulus) can be induced and detected with our technique.
