As mentioned above, Gly-AGEs evoked oxidative, inflammatory and thrombogenic reactions in ECs via the interaction with RAGE [
15-
20]. Furthermore, we have found that Gly-AGEs exist in human serum, and the levels are correlated with endothelial dysfunction and vascular inflammation, surrogate markers for atherosclerotic cardiovascular disease [
12,
13]. In addition, Gly-AGEs are immunologically distinct from other sugar-derived AGEs or structurally identified AGEs such as glucose-, glycolaldehyde-, fructose-, methylglyoxal-, glyoxal-modified AGEs, carboxymethyllysine-BSA, carboxyethyllysine-BSA, pyrraline-BSA, pentosidine-BSA, argpyrimidine-BSA, and 3-deoxyglucosone imidazolone-BSA [
12,
48]. These observations suggest that glyceraldehyde-related specific AGE structure in Gly-AGEs might play a role in vascular injury both
in vitro and
in vivo. Since GLAP mimicked the deleterious effects of Gly-AGEs on HUVECs, it is conceivable that GLAP is a cytotoxic AGE structure in Gly-AGEs. However, it remains unclear whether AGE-aptamer, which bound to Gly-AGEs, blocked the binding of Gly-AGEs to RAGE and resultantly inhibited the Gly-AGE-evoked oxidative and inflammatory reactions in cell culture and animal models [
24-
27,
30,
49], could also inhibit the harmful effects of GLAP on HUVECs. To address the issue, we investigated the effects of AGE-aptamer on GLAP-evoked oxidative stress generation, RAGE, MCP-1, ICAM-1, VCAM-1 and PAI-1 gene induction in HUVECs. In this study, we found that AGE- or GLAP-aptamer, but not Control-aptamer, bound to GLAP and subsequently prevented the interaction of GLAP with RAGE. Moreover, GLAP-evoked increase in ROS generation and up-regulation in RAGE, MCP-1, ICAM-1, VCAM-1 and PAI-1 mRNA levels were significantly blocked by the treatment with AGE- or GLAP-aptamer, but not Control-aptamer. The present findings suggest that GLAP is a target compound for AGE-aptamer and might be a main glyceraldehyde-related AGE structure in Gly-AGEs that interacted with RAGE and subsequently elicited oxidative, inflammatory and thrombogenic reactions in HUVECs. GLAP was only formed in glyceraldehyde-modified BSA, not in other sugar-modified one [
34], further supporting our speculation.
Plasma or tissue concentration levels of GLAP in diabetic animals or patients are about 3–4 μg/ml [
34,
35]. So, the concentration of GLAP (1–10 μg/ml) used here are comparable with those of the
in vivo-diabetic situation. We did not know how GLAP formation was accelerated under diabetic conditions. However, we, along with others, have previously shown that hyperglycemia-induced overproduction of superoxide by the mitochondrial electron transport chain activates the three major pathways, including increased AGE formation, and causes EC damage by inhibiting glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity [
50,
51]. Therefore, although glyceraldehyde, which could be derived from glucose metabolism, is not a major sugar
in vivo, glyceraldehyde and glyceraldehyde-3 phosphate could be increased under hyperglycemic and oxidative stress conditions via reduced activity of GAPDH, which might lead to promote the formation and accumulation of GLAP in diabetes.