Verzijl N, DeGroot J, Oldehinkel E, Bank R A, Thorpe S R, Baynes J W, Bayliss M T, Bijlsma J W, Lafeber F P, Tekoppele J M
Gaubius Laboratory, Division of Vascular and Connective Tissue Research, TNO Prevention and Health, PO Box 2215, 2301 CE Leiden, The Netherlands.
Biochem J. 2000 Sep 1;350 Pt 2(Pt 2):381-7.
Non-enzymic modification of tissue proteins by reducing sugars, the so-called Maillard reaction, is a prominent feature of aging. In articular cartilage, relatively high levels of the advanced glycation end product (AGE) pentosidine accumulate with age. Higher pentosidine levels have been associated with a stiffer collagen network in cartilage. However, even in cartilage, pentosidine levels themselves represent <1 cross-link per 20 collagen molecules, and as such cannot be expected to contribute substantially to the increase in collagen network stiffness. In the present study, we investigated a broad range of Maillard reaction products in cartilage collagen in order to determine whether pentosidine serves as an adequate marker for AGE levels. Not only did the well-characterized AGEs pentosidine, N(epsilon)-(carboxymethyl)lysine, and N(epsilon)-(carboxyethyl)lysine increase with age in cartilage collagen (all P<0.0001), but also general measures of AGE cross-linking, such as browning and fluorescence (both P<0.0001), increased. The levels of these AGEs are all higher in cartilage collagen than in skin collagen. As a functional measure of glycation the digestibility of articular collagen by bacterial collagenase was investigated; digestibility decreased linearly with age, proportional to the extent of glycation. Furthermore, the arginine content and the sum of the hydroxylysine and lysine content of cartilage collagen decrease significantly with age (P<0.0001 and P<0. 01 respectively), possibly due to modification by the Maillard reaction. The observed relationship between glycation and amino acid modification has not been reported previously in vivo. Our present results indicate that extensive accumulation of a variety of Maillard reaction products occurs in cartilage collagen with age. Altogether our results support the hypothesis that glycation contributes to stiffer and more brittle cartilage with advancing age.
组织蛋白通过还原糖进行的非酶修饰，即所谓的美拉德反应，是衰老的一个显著特征。在关节软骨中，晚期糖基化终产物（AGE）戊糖苷的含量会随着年龄的增长而相对较高地累积。较高的戊糖苷水平与软骨中更僵硬的胶原网络有关。然而，即使在软骨中，戊糖苷水平本身也仅代表每20个胶原分子中不到1个交联键，因此预计其不会对胶原网络硬度的增加有显著贡献。在本研究中，我们调查了软骨胶原中广泛的美拉德反应产物，以确定戊糖苷是否可作为AGE水平的合适标志物。不仅特征明确的AGEs戊糖苷、N（ε）-（羧甲基）赖氨酸和N（ε）-（羧乙基）赖氨酸在软骨胶原中随年龄增加（所有P<0.0001），而且AGE交联的一般指标，如褐变和荧光（均P<0.0001）也增加。这些AGEs在软骨胶原中的水平均高于皮肤胶原。作为糖基化的功能指标，研究了细菌胶原酶对关节胶原的消化率；消化率随年龄呈线性下降，与糖基化程度成正比。此外，软骨胶原的精氨酸含量以及羟赖氨酸和赖氨酸含量之和随年龄显著下降（分别为P<0.0001和P<0.01），这可能是由于美拉德反应的修饰作用。这种糖基化与氨基酸修饰之间的关系此前尚未在体内报道过。我们目前的结果表明，随着年龄的增长，软骨胶原中会大量积累多种美拉德反应产物。总体而言，我们的结果支持了糖基化会导致软骨随着年龄增长而变硬变脆这一假说。
