Nitric oxide-induced perturbations in a cell culture model of the blood-brain barrier

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Abstract
The actions of an intracellular nitric oxide generator compound on the properties of a co-culture model of the blood-brain barrier are described. Addition of the iron-sulphur cluster nitrosyl Roussin's black salt (RBS, heptanitrosyl-tri-μ3-thioxotetraferrate (1−)) resulted in a rapid and dose-dependent (50–250 μM) decline in the electrical resistance displayed by co-cultures of vascular endothelial cells and C6 glioma cells. The breach in barrier integrity elicited by RBS (250 μM) could be prevented by either haemoglobin (100 μM), methylene blue (200 μM), or by photon-induced inactivation of RBS. In contrast, the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (250 μM) caused no inhibition in the decline in resistance of RBS-exposed cultures. Addition of 8-bromo-guanosine-cyclic monophosphate (500 μM) did not mimic the actions of RBS. Exposure to intense light of co-cultures manifesting a high transcellular electrical resistance resulted in a reduction in tissue resistance which could be prevented by the presence of haemoglobin (100 μM). We conclude that nitric oxide liberated from RBS results in a reversible diminution in the integrity of the endothelial cell barrier in the co-culture system, and we suggest that light-sensitive endogenous nitric oxide generator compounds may be present in intact cells. Possible roles of nitric oxide in blood-brain-barrier function are considered.

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