Effects of Advanced Glycation Endproducts on Type 2 Diabetic and Fragility Fractures

摘要 骨折对影响生活质量的医疗保健成本有很大影响。临床上，骨折风险 可以通过双能X线吸收测定法（DXA）或骨折风险评估（FRAX）工具进行预测。因为 2型糖尿病（T2 D）患者表现出高骨矿物质密度（BMD），这两种工具都不能正确预测 骨折风险，导致糖尿病受试者脆性骨折显著增加。因此有 需要研究骨中胶原蛋白和其他有机成分的变化如何预测 糖尿病骨折Pentosidine（PEN），一种荧光晚期糖基化终产物（AGE），在 通过糖和蛋白质之间的反应而形成的骨脆性是骨脆性的唯一确定的标志。但 不能一致预测T2 D和脆性骨折。在这里，我们第一次在骨骼中展示了 存在羧甲基赖氨酸（CML），一种非荧光糖氧化AGE，并提出了一种技术， 测量它。我们发现它在骨骼中大量存在，并且与骨骼韧性的丧失高度相关。 我们证明，与其他AGEs相比，CML在T2 D人骨中上调>60%， 与年龄相匹配的对照组。然后，我们提供证据表明，CML促进形成和生长的 额外的羟基磷灰石（HA）晶体，类似于人类T2 D状况，并形成“分子连接” 骨的有机和无机成分（胶原-HA界面）之间的相互作用，损害骨质量。我们 总体假设是CML是T2 D骨折的“新的相关”生物标志物， 高血糖和氧化应激在骨中的作用，并解释了骨对高血糖和氧化应激的敏感性。 T2 D骨折。使用肥胖和非肥胖的T2 D小鼠模型，模拟因果关系和 人类T2 D对骨的影响，我们提供了T2 D增加AGEs的证据，CML解释了骨 脆弱同样，使用健康，衰老和身体成分（ABC）研究的数据，我们表明， 较高的血清CML水平与2型糖尿病患者临床骨折发生风险增加相关， 与BMD无关。因此，我们的总体目标是建立CML作为一个新的和相关的骨生物标志物 脆性，并确定它如何有助于T2 D的骨脆性。使用体外模型，离体人 尸体组织，肥胖和非肥胖T2 D的体内小鼠模型，以及来自健康中心的现有数据。 ABC研究，我们将追求以下目标：目标1：建立NEG条件，以增强CML的形成， 其他AGEs，并确定其降低骨中能量耗散的机制;目的2： 确定CML和其他AGEs对骨基质改变和能量耗散的贡献， 来自髋部骨折患者的人T2 D椎骨以及皮质骨和松质骨;以及目的3：慢性粒细胞白血病 作为T2 D骨脆性的生物标志物，并建立其与高血糖症和氧化应激的相关性。 我们的研究结果将为慢性粒细胞白血病和其他AGEs对慢性粒细胞白血病的机制和作用提供新的认识。 骨折导致新的战略，以预测，管理和减轻T2 D和脆性骨折。

Abstract Bone fractures contribute significantly to healthcare cost affecting the quality of life. Clinically, fracture risk can be predicted by dual x-ray absorptiometry (DXA) or the fracture risk assessment (FRAX) tool. Because type 2 diabetes (T2D) patients exhibit high bone mineral density (BMD), both tools fail to correctly predict fracture risk, leading to a significant increase of fragility fractures in diabetic subjects. Therefore, there is a need to investigate how modifications in collagen and other organic components in bone can predict diabetic fractures. Pentosidine (PEN), a fluorescent Advanced Glycation Endproduct (AGE) that forms in bone by reaction between sugars and proteins, is the only established marker of bone fragility. However, it does not consistently predict T2D and fragility fractures. Here, for the first time in bone, we demonstrate the presence of carboxymethyl-lysine (CML), a non-fluorescent glycoxidative AGE, and present a technique to measure it. We show that it forms in abundance in bone and is highly correlated to loss of bone toughness. We demonstrate that, in contrast to other AGEs, CML is upregulated >60% in T2D human bone compared to their age-matched controls. We then provide evidence that CML promotes formation and growth of additional hydroxyapatite (HA) crystals, similar to human T2D condition, and forms a ‘molecular link’ between the organic and inorganic components of bone (collagen-HA interface) impairing bone quality. Our overall hypothesis is that CML is a ‘new and relevant’ biomarker of T2D fracture that captures the effects of both hyperglycemia and oxidative stress in bone and explains the susceptibility of bone to fracture in T2D. Using an obese and a non-obese mouse model of T2D, that mimic both causality and impact of human T2D on bone, we provide evidence that T2D increases AGEs, with CML explaining bone fragility. Similarly, using data from the Health, Aging and Body Composition (ABC) study we show that higher serum CML levels are associated with increased risk of incident clinical fractures in T2D, independent of BMD. Thus, our overall goal is to establish CML as a new and relevant biomarker of bone fragility and determine how it contributes to bone fragility in T2D. Using in vitro models, ex vivo human cadaveric tissue, in vivo mouse models of obese and non-obese T2D, and existing data from the Health ABC study we will pursue there aims: Aim 1: Establish NEG conditions for enhanced formation of CML over other AGEs and determine the mechanism(s) by which it reduces energy dissipation in bone; Aim 2: Determine the contribution of CML and other AGEs to alterations in bone matrix and energy dissipation in human T2D vertebrae and cortical and cancellous bone from hip fracture patients; and Aim 3: Validate CML as a biomarker of T2D bone fragility and establish its association with hyperglycemia and oxidative stress. Our findings will provide a new understanding of the mechanism and the effects of CML and other AGEs on bone fractures leading to new strategies to predict, manage and mitigate T2D and fragility fractures.