Glycoxidation in aortic collagen from STZ-induced diabetic rats and its relevance to vascular damage

Glycoxidation reactions lead to the formation of permanent, irreversible chemical modifications and cross-links in protein, such as the glycoxidation products carboxymethyllysine (CML) and pentosidine. It has been implicated that CML as well as Amadori products play a role in the formation of superoxidative products, such as H2O2 and advanced glycosylation endproducts in trapping LDL. Therefore, a possible relationship between glycoxidation and lipoperoxidation might exist because oxidized lipoprotein, which has been directly linked to atheroma formation, could be produced by the superoxidative products released from the pathway of CML formation. Using a CML-specific monoclonal antibody (6D12) and a specific antiserum against hexitol-lysine (HL), an Amadori product, we studied the relationship between glycoxidation and lipoperoxidation by determining the aortic CML contents with ELISA and the fluorescence levels of lipoperoxidation side products, malondialdehyde (MDA) and hydroxynonenal (HNE) from STZ-induced diabetic rats and age-matched control rats. The immunohistochemical and ultrastructural changes relevant to glycoxidation and lipoperoxidation were also studied. The CML content measured by ELISA in DM rats was significantly higher than that in the control rats at 28 weeks (n = 11, P < 0.01). The levels of MDA-linked and HNE-linked fluorescence in the DM rats increased in a similar way and were significantly higher than the levels in control rats at 28 weeks (n = 11, both P < 0.01 at 28 weeks). The CML contents correlated with the fluorescence levels of both MDA-linked (n = 19, r = 0.638, P < 0.01) and HNE-linked fluorescence (n = 19, r = 0.629, P < 0.01) only in the DM rats, but not in the control rats. Our immunohistochemical study thus demonstrated that CML was initially formed in the aortic media of diabetic rats in the 16th week of diabetes, localized primarily in the extracellular matrix surrounding the aortic smooth muscle cells after HL occurred early in the 2nd week of diabetes. Consequently, a significant increase in the extracellular matrix and decrease in the area of the SMCs were observed in the aortic media in the DM rats by a morphometrical study. The in vivo results of this study provided the first evidence that CML correlated with fluorescence levels of MDA and HNE, and thus suggested the existence of a close relationship between glycoxidation and lipoperoxidation in vivo. This information is thus considered to shed some new light on the etiology of atherogenesis in diabetes.