AGE Structures and their Biomedical Significance

蛋白质与葡萄糖的长期孵育通过Schiff碱和Amadori产物导致晚期糖基化终产物（AGE）的形成。从三个方面研究了AGE在体内的生物医学意义：（i）鉴定体内主要的AGE结构，（ii）及其在组织中的定位和（iii）AGE受体的结构和功能分析。(i)体内主要AGE结构的鉴定：甲基乙二醛，其通过甘油醛-3-磷酸的裂解由糖酵解和多元醇途径产生，与蛋白质反应形成AGE，如N^ε-（羧乙基）赖氨酸（CEL）。特别是，甲基乙二醛也产生了从美拉德反应的席夫碱的裂解，然后进一步AGE的形成的贡献。(ii)AGE在组织中的定位：N^ε-（羧甲基）赖氨酸（CML），一种主要的AGE结构，在肺巨噬细胞中的聚集已经被证实。 关于我们 提示AGE可能参与了家族性肌萎缩侧索硬化症发病过程。(iii)AGE受体的结构和功能分析：为了评价肝内皮细胞（LEC）中表达的AGE受体，我们还确定了LEC中高度表达的清道夫受体B类（如CD-36和SR-BI）是否作为AGE受体。CD-36过表达的CHO细胞表现出内吞摄取和随后的胞内降解AGE蛋白，表明原位产生的AGE配体被CD-36识别，这可能有助于糖尿病大血管并发症的发病机制。通过使用SR-BI过表达的CHO细胞（SR-BI-CHO），我们清楚地表明SR-BI也作为AGE受体参与AGE蛋白的内吞摄取。此外，AGE-蛋白不仅有效地抑制SR-BI介导的CE从HDL颗粒的选择性摄取，而且抑制HDL介导的胆固醇从SR-BI-CHO细胞的流出，表明AGE-配体在HDL介导的胆固醇体内逆向转运中起重要作用。少

Long-term incubation of proteins with glucose leads, through the Schiff base and Amadori product, to the formation of advanced glycation end products (AGE). The biomedical significance of AGE in vivo were studied from three lines of aspects ; (i) identification of major AGE-structures in vivo, (ii) and their localization in tissues and (iii) structural and functional analyses of AGE-receptors.(i) Identification of major AGE-structures in vivo : Methylglyoxal, which was generated from glycolysis and polyol pathways through the cleavage of gleceraldehyde-3-phosphate, reacted with protein to form the AGE such as N^ε-(carboxyethyl)lysine (CEL). Especially, methylglyoxal was also generated from the cleavage of Schiff base of the Maillard reaction, followed by contribution to further AGE formation.(ii) Localization of AGE in tissues : Accumulation of N^ε-(carboxymethyl)lysine (CML), one of the major AGE structures, has been identified in pulmonary macrophages in patients with pulmonary fibro … More sis and neuron in patient with familial amyotrophic lateral sclerosis, strongly suggesting that AGE may involve in the pathogenesis of these disease processes.(iii) Structural and functional analysis of AGE receptor : To evaluate the AGE-receptor expressed in liver endothelial cells (LEC), we also determined whether scavenger receptor class B such as CD-36 and SR-BI, highly expressed in LEC, serve as an AGE receptor. CD-36-overexpressed CHO cells showed endocytic uptake and subsequent intracellular degradation of AGE-proteins, suggesting that AGE-ligands generated in situ are recognized by CD36, which might contribute to the pathogenesis of diabetic macrovascular complications. By using SR-BI-overexpressed CHO cells (SR-BI-CHO), we clearly showed that SR-BI also serves as an AGE receptor involved in endocytic uptake of AGE-proteins. Furthermore, AGE-protein effectively inhibited not only SR-BI-mediated selective uptake of CE from HDL particles, but also HDL-mediated cholesterol efflux from SR-BI-CHO cells, indicating that AGE-ligands play a significant role in the HDL-mediated reverse cholesterol transport in vivo. Less