Evidence for 21-aminosteroid association with the hydrophobic domains of brain microvessel endothelial cells.

Studies were conducted to demonstrate 21-aminosteroid distribution into the hydrophobic or lipid domains of biological membranes, a presumed site at which these compounds inhibit lipid peroxidation. Bovine brain microvessel endothelial cells (BMECs) were labeled with diphenylhexatriene fluorophores and interactions with cell membranes characterized with fluorescence anisotropy and lifetimes. Two 21-aminosteroids (U-74500A and U74006F) were shown to preferentially alter the fluorescence anisotropy and lifetime parameters of the diphenylhexatriene probe distributing into membranes throughout the BMECs. Little or no effect of the compounds was observed on the fluorescence parameters of the probe localized on the surface of BMEC plasma membranes. By contrast, cholesterol used as a positive control substantially altered the fluorescence parameters of BMECs labeled with either diphenylhexatriene probe. Results suggest 21-aminosteroid-induced changes in the molecular packing order and drug: fluorescent probe interactions in membrane hydrophobic (or lipid) domains throughout the BMEC. Concentrations of 21-aminosteroids altering the fluorescence parameters of diphenylhexatriene labeled BMECs correspond to those concentrations of 21-aminosteroids effective in vitro in inhibition of lipid peroxidation.