In vivo and in vitro evidence for the glycoxidation of low density lipoprotein in human atherosclerotic plaques

Although there have been suggestions that the glycation and oxidation of lo w density lipoprotein (LDL) might increase its atherogenic potential, littl e is known about the presence of glycoxidative LDL in human atherosclerotic lesions. We developed specific antibodies against different immunological epitopes of AGE structures, including N-epsilon-(carboxymethyl)lysine-prote in adduct (CML), a glycoxidation product, and structure(s) other than CML ( nonCML), and a monoclonal antibody against oxidized phosphatidylcholine (ox PC), as an epitope of oxidized LDL. Immunohistochemical analysis demonstrat ed that the CML- and oxPC-epitopes were accumulated mainly in macrophage-de rived foam cells in atherosclerotic lesions, including fatty streaks and at herosclerotic plaques. On the other hand, the nonCML-epitope and apolipopro tein B were localized mainly in extracellular matrices of atherosclerotic l esions. The CML- and oxPC-epitopes were characterized by a model antigen-ge nerating system using the copper ion-induced peroxidation and/or glucose-in duced glycation of LDL. The glycoxidation of LDL caused the formation of CM L-epitope with increasing concentrations of copper ion and glucose. It was also formed to some extent in LDL incubated with high concentrations (500 m M) of glucose. However, no CML-epitope was observed in oxidized LDL induced by copper ion alone. On the other hand, the formation of oxPC-epitope in L DL was dependent on copper ion-induced peroxidation, but independent of glu cose-induced glycation. The addition of chelators, ethylenediaminetetraacet ic acid and diethylenetriaminepentaacetic acid, reduced the increase in ele ctrophoretic mobility and TEARS caused by the peroxidation and glycoxidatio n of LDL, but had no effects on the formation of fructosamine caused by the glycation and glycoxidation of LDL. Chelators as well as aminoguanidine pr otected the formation of CML-epitope in glycated or glycoxidative LDL. Alth ough the formation of oxPC-epitope was completely inhibited by the addition of chelators, it was partially protected by aminoguanidine. These in vitro results suggest that the glycoxidative modification of LDL may occur in th e arterial intima, and may contribute to the development of human atheroscl erotic lesions. (C) 2000Elsevier Science Ireland Ltd. All rights reserved.