Objective: To analyse whether an HIV-1 envelope protein might play a role in damaging the blood-brain barrier as a fundamental step in the early invasion of the central nervous system by HIV-1.
Design: Analysis of permeability of rat brain endothelium cultures to albumin, to assess the functional integrity of the vascular component of the blood-brain barrier.
Methods: Rat brain endothelium cultures prepared by cerebral microvessels were exposed to recombinant gp120IIIB on microporous membranes and passage of biotin-labelled albumin was analysed. Scanning electron microscopy was used to analyse cell culture morphology. Some cultures were preincubated with N-nitro-L-arginine methyl ester (L-NAME), a selective inhibitor of nitric oxide synthase, or with spantide, a selective substance P antagonist.
Results: HIV-1 gp120 increased the permeability of rat brain endothelial cells to albumin in a dose-dependent manner. Scanning electron microscopy revealed profound gp120-induced alterations in cell morphology accounting for the increased permeability to macromolecules. These alterations were neutralized by anti-gp120 monoclonal antibody but not by isotype control antibody or L-NAME. By contrast, spantide and anti-substance P polyclonal antibody completely blocked the gp120-induced increase in albumin permeability. Control cultures exposed to measles virus nucleoprotein showed an increase in permeability that was not blocked by spantide. Brain endothelial cells, exposed to gp120, displayed cell surface immunoreactivity for substance P, suggesting that substance P is secreted by brain endothelium in response to gp120 stimulation and binds to brain endothelial cells through a receptor-mediated mechanism.
Conclusions: These findings suggest a role for substance P in the gp120-induced increase in permeability of brain endothelium.