The oxidative modification of low-density lipoprotein (LDL) hypothesis implies that antioxidants should be effective in suppressing atherosclerosis. This study is designed to test the potential of antioxidants to inhibit atherosclerotic plaque progression in balloon-denuded and irradiated hypercholesterolemic rabbits. Rabbits were fed with a 1% cholesterol diet supplemented with or without a mixture of antioxidants (vitamin E, vitamin C, selenium, zinc, copper, manganese, N-acetylcysteine, glutamine). At 7 days both iliac arteries were balloon denuded, and 4 weeks later, 1 iliac artery underwent endovascular irradiation (n=12), while the contralateral was sham treated (n=12). Four weeks after irradiation, animals were euthanized, and arteries were fixed and processed for histo- or immunohistochemistry for determining the plaque area, macrophage count, and oxidized LDL-positive areas. Plasma antioxidant levels were significantly higher in the animals fed with antioxidant diet. Plasma (thiobarbituric acid-reactive substances) and arterial tissue oxidized LDL (immunoreactive to specific oxidized LDL antibody) levels were significantly higher in the irradiated as compared with nonirradiated animals (0.69+/-0.09 and 31.05+/-4.21 versus 0.24+/-0.04 and 18.42+/-4.62, P<0.001 and 0.05), and antioxidants partially lowered the oxidized LDL levels (0.35+/-0.14 and 25.41+/-4.82, P<0.001 and 0.01). Plaque area in the irradiated animals was 175% greater than in nonirradiated animals (P<0.05). Antioxidant supplementation resulted in a 50% decrease in plaque area of both control and irradiated animals. Antioxidants reduced both the cholesterol-induced and radiation-enhanced circulating and tissue oxidized LDL levels, resulting in reduced plaque.