IMMUNOLOGICAL EVIDENCE FOR THE PRESENCE OF ADVANCED GLYCOSYLATION END-PRODUCTS IN ATHEROSCLEROTIC LESIONS OF EUGLYCEMIC RABBITS

Atherosclerosis is known to be accelerated in diabetic patients, but t he mechanisms of this acceleration are poorly understood. Nonenzymatic glycosylation of long-lived proteins results in the formation of adva nced glycosylation end products (AGEs), which are extensively cross-li nked and could contribute to atherogenesis. Oxidative modification of LDL is also an important process in atherogenesis. In vitro evidence s uggests that hyperglycemia may enhance lipid peroxidation, and convers ely, that increased lipid peroxidation may enhance AGE formation. If s uch interactions occur in vivo, we hypothesized that AGE should be fou nd in atherosclerotic lesions of euglycemic LDL receptor-deficient rab bits in areas rich in lipids and oxidized lipoproteins. To demonstrate the presence of AGEs, we developed antisera against a specific ''mode l'' compound of AGE, 2-furoyl-4(5)-(2-furanyl)-1H-imidazole (FFI) by u sing FFI-hexanoic acid (FFI-HA)-protein adducts as the antigen and aga inst AGEs in general by using AGE-albumin as the antigen. Antisera gen erated with FFI-HA-protein adducts recognized FFI-HA alone as well as FFI-protein adducts. Native proteins or proteins conjugated with aldeh ydes formed during lipid peroxidation in vitro were not recognized by these antisera. Immunocytochemistry with both FFI-specific and AGE-spe cific antisera revealed the presence of these epitopes in atherosclero tic lesions of euglycemic LDL receptor-deficient rabbits but not in no rmal aortic tissues. AGE epitopes within atherosclerotic lesions were predominantly found in similar locations as epitopes generated during modification of the lipoproteins by oxidation, consistent with the hyp othesized interactions between oxidation and glycosylation. Indirect e vidence in support of the in vivo presence of FFI-like structures was also obtained by the observation that both diabetic and euglycemic hum an subjects contained autoantibodies that recognize FFI-protein adduct s. Taken together, these data provide immunological evidence for the i n vivo presence of FFI-like structures and other AGE-protein adducts i n atherosclerotic lesions, even in euglycemic conditions.