Effect of the antioxidant probucol on transplant arteriosclerosis in aorta-allografted rabbits

The attenuation of atherogenesis by oral probucol treatment, demonstrated in several animal studies, has been attributed to the antioxidative property of probucol. It is thought that probucol, by inhibiting oxidation of low density lipoproteins (LDL) decreases the uptake of LDL into monocytes, and thereby reduces the development of foam cells and fatty streaks. Also, the neointimal proliferation seen after balloon injury has been attenuated by treatment with probucol. Since foam cells and neointimal proliferation are both important elements of transplant arteriosclerosis, we have investigated whether probucol might also retard the development of experimental transplant arteriosclerosis. The thoracic aorta from one rabbit was transplanted as a bypass graft onto the abdominal aorta of another rabbit. Nine rabbits were treated with 1 g probucol per day and seven animals were treated with vehicle. After a recovery period of 2 weeks, all rabbits were clamped at a human level of plasma cholesterol (6 to 7 mmol/l) for a period of 3 weeks. The amount of dietary cholesterol necessary for this clamping tended to be higher in probucol treated than in vehicle-treated rabbits. The distribution of plasma cholesterol between lipoprotein classes was similar in the two groups, except for the concentration of high density lipoproteins (HDL), which was significantly lowered by probucol. Probucol markedly decreased the susceptibility of LDL and intermediate density lipoprotein plus very low density lipoprotein (IDL + VLDL) particles to oxidation, as measured by the production of conjugated dienes when adding Cu2+. Despite this, the development of transplant arteriosclerosis as well as the number of macrophages in the neointima were not significantly different in the aortic allografts from the two groups. These results suggest that antioxidative agents do not retard the development of experimental transplant arteriosclerosis.