roussin-s-black-salt and Glioma

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-mu3-thioxotetraferrate (1-)) resulted in a rapid and dose-dependent (50-250 microM) 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 microM) could be prevented by either haemoglobin (100 microM), methylene blue (200 microM), or by photon-induced inactivation of RBS. In contrast, the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (250 microM) caused no inhibition in the decline in resistance of RBS-exposed cultures. Addition of 8-bromo-guanosine-cyclic monophosphate (500 microM) 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 microM). 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.

Topics: Animals; Blood-Brain Barrier; Electric Impedance; Endothelium, Vascular; Glioma; Humans; Intercellular Junctions; Iron Chelating Agents; Iron Compounds; Nitric Oxide; Nitroso Compounds; Rats; Vasodilator Agents

Nitric oxide may regulate cellular respiration by competition with oxygen at mitochondrial cytochrome oxidase. Using an astrocyte-derived cell line, we have compared the mechanism of action of the nitric oxide-generating compound Roussin's black salt with that of sodium nitroprusside on cellular oxygen consumption. Intense light exposure induced the release of large quantities of nitric oxide from both of the donor compounds. However, in room light only Roussin's black salt generated low levels of the radical. Simultaneous measurement of oxygen consumption and of nitric oxide production demonstrated that sodium nitroprusside only had inhibitory actions when exposed to intense light (nitric oxide release), whereas Roussin's black salt had inhibitory actions in room light. Extracellular haemoglobin did not prevent the inhibition of respiration rate induced by Roussin's black salt even though stimulation of nitric oxide release on light exposure was markedly reduced. Preincubation of cells with Roussin's black salt and subsequent measurement of levels of light-liberated nitric oxide demonstrated that the compound was rapidly internalised. The uptake of sodium nitroprusside was minimal. These data suggest that, in contrast to sodium nitroprusside, the cellular internalisation of Roussin's black salt allows site-directed nitric oxide release and very effective inhibition of cellular respiration.

Topics: Animals; Cell Respiration; Energy Metabolism; Glioma; Hemoglobins; Iron Chelating Agents; Iron Compounds; L-Lactate Dehydrogenase; Nitric Oxide; Nitroprusside; Nitroso Compounds; Oxygen; Rats; Tumor Cells, Cultured; Vasodilator Agents

Topics: Animals; Glioma; Iron Chelating Agents; Iron Compounds; Nitric Oxide; Nitroprusside; Nitroso Compounds; Oxygen Consumption; Rats; Tumor Cells, Cultured