Probucol inhibits mononuclear cell adhesion to vascular endothelium in the cholesterol-fed rabbit

Mononuclear cells, isolated from the blood of hyperlipidaemic patients, are hyper-reactive and possess an increased propensity to adhere to vascular endothelial cells. Hyperlipidaemia is also associated with a dysfunctional endothelium, to which mononuclear cells stick with greater avidity. In order to assess the importance of lipid peroxidation and free-radical generation in these processes, we have investigated the effects of probucol on mononuclear cell adhesion to vascular endothelial cells in vivo and in vitro in the cholesterol-fed rabbit. New Zealand White rabbits were fed either: (i) control chow (n = 15), (ii) 2% cholesterol (n = 11), or (iii) 2% cholesterol with 1% probucol (n = 11). Mononuclear cell adherence to endothelium in the common carotid artery was assessed 5 weeks after the start of the experimental diet using the Hoechst 33342 staining technique. The 2% cholesterol diet caused a more than 6-fold increase in mean mononuclear cell adherence (P < 0.001). Concurrent probucol therapy abrogated the effects of cholesterol feeding, and in animals in this group, in vivo mononuclear cell adherence did not differ significantly from control animals. In vivo mononuclear cell adherence was directly related to serum cholesterol levels (r = 0.68, P < 0.0001) and inversely related to serum probucol concentrations (r = -0.63, P < 0.002). Concurrent probucol therapy also reduced the in vitro binding of mononuclear cells, isolated from hypercholesterolaemic animals, to endothelial cell monolayers (P < 0.01). These data suggest that the increased binding of mononuclear cells to vascular endothelium of cholesterol-fed rabbits may be a free radical mediated process that is inhibited by antioxidants.