UC San Diego

We previously established that probucol decreases basal expression of VCAM-1 in the aorta of WHHL rabbits and inhibits the up-regulation of VCAM-1 expression that normally accompanies atherogenesis. To determine whether this effect is shared by other antioxidants in vivo, we now investigated whether a structurally unrelated antioxidant, vitamin E, also inhibits arterial VCAM-1 expression and whether the degree of VCAM-1 inhibition correlates with the reduction of atherosclerosis or the antioxidant protection of LDL. Atherogenesis and VCAM-1 mRNA and protein were determined in four groups of NZW rabbits (n = 6;-8) fed 0.5% cholesterol alone or supplemented with 0.1% vitamin E, a low dose (0.04;-0.075%) of probucol yielding the same degree of antioxidant protection of plasma LDL as vitamin E, or a high dose (0.5%) of probucol, and in normocholesterolemic rabbits. After 81 days, extensive atherosclerosis and a greater than 4-fold up-regulation of VCAM-1 mRNA was seen in rabbits on high cholesterol diet, mostly in the intima. Treatment with vitamin E, high-dose probucol, and low-dose probucol significantly decreased VCAM-1 mRNA by 49.0, 74.9, and 57. 5%, respectively, and reduced atherosclerosis in adjacent segments of the thoracic aorta to a similar degree as reported by previous studies. Immunocytochemistry confirmed that lesions of antioxidant-treated animals also contained less VCAM-1 protein. Neither the degree of VCAM-1 inhibition nor the extent of atherosclerosis correlated with the degree of antioxidant protection of plasma LDL.In summary, treatment with structurally unrelated antioxidants conveyed different degrees of antioxidant protection to plasma LDL but significantly reduced VCAM-1 expression in vivo and inhibited atherogenesis. This is consistent with the assumption that antiatherogenic effects of antioxidants may in part be mediated by interference with oxidation-dependent intracellular signaling.