Inflammation of the asthmatic airway is usually accompanied selleck products by increased vascular permeability and plasma exudation 1. Although other inflammatory mediators, including platelet-activating factor, can promote microvascular leakage 32, VEGF appears to be the critical mediator of vascular permeability in asthma 3, 16, 33, 34. The mechanism of VEGF-mediated induction of the vascular permeability seems to be the enhanced functional activity of vesiculo-vacuolar organelles 17, 33. VEGF can be produced by a wide variety of cells such as macrophages, neutrophils, eosinophils, and lymphocytes 3, 17, 33–35. Several studies

have shown that overproduction of VEGF causes an increase in vascular permeability, which results in leakage of plasma proteins, inflammatory mediators, and inflammatory

cells into the extravascular space thereby allowing migration of inflammatory cells into the airway 3, 33, 36. In addition, VEGF also plays a crucial role in adaptive Th2-mediated inflammation 17. Consistent with these observations, we have found that allergic airway disease of mice induced by OVA inhalation resulted in up-regulation of VEGF expression, increases in IL-4, IL-5, and IL-13 levels, and enhancement of vascular permeability. The increased VEGF, IL-4, IL-5, and IL-13 levels, vascular permeability, bronchial inflammation, and airway hyperresponsiveness were significantly reduced after administration of a VEGF receptor Thalidomide inhibitor, CBO-P11. This inhibitor is a cyclic peptide of selleck inhibitor 17 amino acids derived from VEGF residue 79–93 and thus blocks binding of VEGF to its receptor, thereby VEGF signaling is obstructed 37. In addition, our previous studies with a murine model of asthma have revealed that the VEGF receptor tyrosine kinase inhibitors SU5614 and SU1498 reduce asthmatic features such as the increase in Th2 cytokines, VEGF,

vascular permeability, inflammatory cells in airways, and airway hyperresponsiveness 3, 38, 39. Together, these findings suggest that VEGF is a key player in inducing and maintaining allergic airway disease. HIF-1α regulates VEGF expression, and activation of HIF-1α is controlled by a variety of inflammatory cytokines and growth factors as well as by cellular oxygen concentrations 7. Very recently, we have shown that increased expression of VEGF after OVA inhalation is decreased by administration of an HIF-1α inhibitor 9. In keeping with these observations, determination of HIF-1α protein levels in nuclear extracts in this study revealed that this protein is substantially increased in our current mouse model of OVA-induced allergic airway disease and tracheal epithelial cells isolated from OVA-treated mice, suggesting that HIF-1α is activated. The increased levels of HIF-1α were significantly reduced after administration of 2ME2 or transfection of siRNA targeting HIF-1α.