AGE Structures and their Biomedical Significance

蛋白质与葡萄糖的长期孵育通过席夫碱和Amadori产物导致晚期糖基化终产物(AGE)的形成。从三个方面研究了体内AGE的生物医学意义：(1)体内主要AGE结构的鉴定；(2)AGE受体在组织中的定位；(3)AGE受体的结构和功能分析。(1)体内主要AGE结构的鉴定：甲基乙二醛是糖酵解和多元醇途径的产物，通过裂解3-磷酸甘油醛与蛋白质反应生成AGE，如N，ε-(羧乙基)赖氨酸。特别是，美拉德反应中席夫碱的裂解也产生了甲基乙二醛，进而促进了AGE的进一步形成。(Ii)AGE在组织中的定位：在肺纤维化患者的肺巨噬细胞中发现了主要的AGE结构之一N-ε-(羧甲基)赖氨酸(CML)的积累家族性肌萎缩侧索硬化症患者有更多的SIS和神经元，强烈提示AGE可能参与了这些疾病的发病过程。(Iii)AGE受体的结构和功能分析：为了评估肝内皮细胞(LEC)中AGE受体的表达，我们还确定了在LEC中高表达的清道夫受体B类分子CD-36和SR-BI是否作为AGE受体。CD36高表达的CHO细胞内吞AGE蛋白，细胞内AGE蛋白降解，提示CD36可识别原位生成的AGE配体，这可能参与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受体参与内吞AGE蛋白的过程。此外，AGE-蛋白不仅能有效地抑制SR-BI介导的从高密度脂蛋白颗粒中选择性摄取CE，而且还能有效地抑制高密度脂蛋白介导的胆固醇从SR-BI-CHO细胞中流出，表明AGE-配体在体内高密度脂蛋白介导的胆固醇反向转运中起着重要作用。较少

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