Heterologous Expression of Human VEGF165 in Rat Brain: Dose-Dependent, Heterogeneous Effects on CBF in Relation to Vascular Density and Cross-Sectional Area

Abstract

Summary:Vascular endothelial growth factor (VEGF) induces increased vessel permeability and formation of abnormal vessels. To investigate cerebral blood flow (CBF) during local overexpression of VEGF recombinant adenoviruses carrying the human VEGF165 complementary DNA (2.3 to 23 · 10 8 pfu/mL) were injected stereotactically into the caudate nucleus of anesthetized rats. Saline and adenoviruses carrying the ␤-galactosidase gene served as controls. Eleven days later (1) size and density of vessels were assessed in hematoxylin-eosinstained sections, (2) vascular permeability was measured by intravenous Evans blue injections, and (3) local CBF (lCBF) was quantified using the iodo-[ 14 C]antipyrine technique. Dosedependent increases were found in (1) vessel density and size (only vessels >43 m could be quantified morphologically), (2) Evans blue extravasation and brain edema formation, and (3) lCBF (up to eightfold). At medium doses, hyperemic areas and smaller areas of decreased lCBF were found. In low flow areas, vascular cross-sectional areas were increased 223-fold and vessel density up to 10-fold. In high flow areas, these parameters were increased 32-fold and up to 15-fold, respectively. Adenovirus mediated VEGF overexpression results in (1) increased vessel size and density, (2) areas of increased and of decreased flow, and (3) more and smaller vessels in high flow than in low flow areas. These results indicate a diverging flow pattern of newly formed vessels.

Activation of the Central Histaminergic System is Involved in Hypoxia-Induced Stroke Tolerance in Adult Mice

“…Besides the direct vasodilation effect of histamine, VEGF may be another mechanism conferring increased CBF. Vascular endothelial growth factor is a regulator of CBF by inducing nitric oxide production or enhancing angiogenesis (Vogel et al, 2003;Zhang et al, 2000). It was interesting to find that SU1498 reversed the increased peripheral CBF induced by hypoxic preconditioning in WT mice, and histamine elevated VEGF expression in this study or in other reports (Ghosh et al, 2001(Ghosh et al, , 2002, suggesting that histamine release induced by hypoxic preconditioning might also improve peripheral CBF in ischemia partly through the VEGF/VEGFR2/Flk1 pathway.…”

Massive Inborn Angiogenesis in the Brain Scarcely Raises Cerebral Blood Flow

“…VEGF, the most potent angiogenic factor, induces the formation of abnormal vessels when administered solely to the adult organism; these newly formed vessels are leaky, thin walled, and have an increased diameter (Carmeliet, 2000;Lee et al, 2000;Pettersson et al, 2000;Vogel et al, 2003). In brain tissue, leakiness results in severe brain edema, which is lethal at high VEGF dosages (Vogel et al, 2003).…”

“…In brain tissue, leakiness results in severe brain edema, which is lethal at high VEGF dosages (Vogel et al, 2003). Transfection of the human VEGF 165 cDNA into brain tissue resulted in increased CBF in the transfected area but also in dramatically decreased blood flow in adjacent areas, showing that such abnormal vessels have limited functional properties (Vogel et al, 2003).…”

“…In brain tissue, leakiness results in severe brain edema, which is lethal at high VEGF dosages (Vogel et al, 2003). Transfection of the human VEGF 165 cDNA into brain tissue resulted in increased CBF in the transfected area but also in dramatically decreased blood flow in adjacent areas, showing that such abnormal vessels have limited functional properties (Vogel et al, 2003). In contrast, the mouse model presented here with morphologically normal capillaries and a tight blood-brain barrier despite sixfold higher VEGF 165 levels in the brain enabled us to elucidate the effect of increased capillary density independent of side effects such as abnormal vascular morphology or leakage.…”

Novel three-dimensional analysis tool for vascular trees indicates complete micro-networks, not single capillaries, as the angiogenic endpoint in mice overexpressing human VEGF165 in the brain

“…Increased VEGF expression leads to increased segment density of capillary network (Marti et al, 2000;Ment et al, 1997;Pettersson et al, 2000) and has been used to induce vessel growth in ischemic diseases (Hayashi et al, 1998;Isner et al, 1996a, b). However, locally elevated VEGF levels induced by injection or viral transfection resulted in formation of abnormal, leaky vessels (Carmeliet and Jain, 2000;Vogel et al, 2003), suggesting that additional cytokines are mandatory for the development of fully functional vessel networks. Since brainspecific overexpression of human VEGF 165 in mice led to growth of normal, functional vessels (Vogel et al, 2004) such additional factors seem to be activated in these animals.…”