Substance P antagonist blocks leakage and reduces activation of cytokine-stimulated rat brain endothelium

We recently demonstrated that substance P mediates increased permeability of brain endothelium exposed to HIV-1 gp120. To test whether substance P is involved in immune processes at the blood–brain barrier (BBB), we stimulated rat brain endothelial cultures prepared from cerebral microvessels with Interferon-γ (IFN-γ) and Tumor necrosis factor-α (TNF-α), two proinflammatory cytokines that alter the BBB and measured permeability to albumin and expression of adhesion molecule ICAM-1 and MHC class II antigen in the presence and absence of spantide, a powerful substance P antagonist. In a dose-dependent manner, spantide completely neutralized increased permeability induced by TNF-α and IFN-γ and expression of MHC class II molecule induced by IFN-γ and prevented associated cell morphological changes as revealed by scanning electron microscope. Spantide also reduced expression of ICAM-1 induced by TNF-α and IFN-γ by 35% and 30%, respectively. Substance P mRNA was found in unstimulated brain endothelial cells and was upregulated after stimulation with TNF-α and IFN-γ. These in vitro findings demonstrate that substance P plays a major pathogenetic role in damaging and activating the BBB vascular component in the presence of proinflammatory cytokines.