ABSTRACT To address potential mechanisms for oxidative
modification of lipids in vivo, we investigated the possibility
that phospholipids react directly with glucose to form advanced
glycosylation end products (AGEs) that then initiate lipid
oxidation. Phospholipid-linked AGEs formed readily in vitro,
mimicking the absorbance, fluorescence, and immunochemical
properties of AGEs that result from advanced glycosylation of
proteins. Oxidation of unsaturated fatty acid residues, as
assessed by reactive aldehyde formation, occurred at a rate that
paralleled the rate of lipid advanced glycosylation. Aminoguanidine,
an agent that prevents protein advanced glycosylation,
inhibited both lipid advanced glycosylation and oxidative
modification. Incubation of low density lipoprotein
(LDL) with glucose produced AGE moieties that were attached
to both the lipid and the apoprotein components. Oxidized LDL
formed concomitantly with AGE-modified LDL. Of signiflicance,
AGE ELISA analysis of LDL specimens isolated from
diabetic individuals revealed increased levels of both apoprotein-
and. lipid-linked AGEs when compared to specimens
obtained from normal, nondiabetic controls. Circulating levels
of oxidized LDL were elevated in diabetic patients and correlated
significantly with lipid AGE levels. These data support the
concept that AGE oxidation plays an important and perhaps
primary role in initiating lipid oxidation in vivo.