Soy protein isolate reduces the oxidizability of LDL and the generation ofoxidized LDL autoantibodies in rabbits with diet-induced atherosclerosis

The incidence of atherosclerosis can be modified by diet, and plant-derived proteins have a beneficial effect, but the underlying mechanisms remain un clear. It has been suggested that oxidized LDL (oxLDL) and autoantibodies a gainst oxLDL are important in the development of atherosclerosis. We analyz ed these factors in rabbits fed a nonpurified diet supplemented with high c holesterol (10.0 g/kg) containing either 270.0 g/kg casein (CAS, n = 10) or 270.0 g/kg soy protein isolate (SPI, n = 10) for 2 mo, Plasma and purified serum LDL from rabbits were analyzed at d 0, 15, 30, 45 and 60 of treatmen t, and the size of atherosclerotic lesions was evaluated at d 60 of treatme nt. GAS-fed rabbits had significantly higher plasma cholesterol at d 15-45 and LDL cholesterol levels at d 15 and 30. Levels of trilinolein and phosph atidylcholine hydroperoxides were higher in the LDL fraction of rabbits fed GAS than in those fed SPI. Also, GAS-fed rabbits had higher levels of high ly oxidized LDL [monoclonal antibody (mAb) 24-reactive oxLDL] in plasma at d 60, whereas SPI-fed rabbits had higher levels of minimally oxidized LDL ( mAb 28-reactive oxLDL) at d 45, These results were consistent with the earl ier formation of anti-oxLDL antibodies and the presence of a larger area of atherosclerotic lesion in rabbits fed the CAS diet. These data indicate th e importance of both the type of dietary protein used in the induction of a therosclerosis and the relevance of immunologic mechanisms in addition to b iochemical and physiologic factors in the pathogenesis of atherosclerosis.