Department of Mechanical Engineering, University of California, Berkeley, 2162 Etcheverry Hall, #1740, Berkeley, CA 94720-1740, USA.
Department of Mechanical Engineering, University of California, Berkeley, 5122 Etcheverry Hall, #1740, Berkeley, CA 94720-1740, USA; Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, USA.
Acta Biomater. 2023 Sep 15;168:223-234. doi: 10.1016/j.actbio.2023.07.003. Epub 2023 Jul 9.
Growing clinical evidence suggests a correlation between diabetes and more frequent and severe intervertebral disc failure, partially attributed to accelerated advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF) through non-enzymatic glycation. However, in vitro glycation (i.e., crosslinking) reportedly improved AF uniaxial tensile mechanical properties, contradicting clinical observations. Thus, this study used a combined experimental-computational approach to evaluate the effect of AGEs on anisotropic AF tensile mechanics, applying finite element models (FEMs) to complement experimental testing and examine difficult-to-measure subtissue-level mechanics. Methylglyoxal-based treatments were applied to induce three physiologically relevant AGE levels in vitro. Models incorporated crosslinks by adapting our previously validated structure-based FEM framework. Experimental results showed that a threefold increase in AGE content resulted in a ∼55% increase in AF circumferential-radial tensile modulus and failure stress and a 40% increase in radial failure stress. Failure strain was unaffected by non-enzymatic glycation. Adapted FEMs accurately predicted experimental AF mechanics with glycation. Model predictions showed that glycation increased stresses in the extrafibrillar matrix under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling, providing insight into the relationship between AGE accumulation and increased tissue failure. Our findings also added to the existing literature regarding crosslinking structures, indicating that AGEs had a greater effect along the fiber direction, while interlamellar radial crosslinks were improbable in the AF. In summary, the combined approach presented a powerful tool for examining multiscale structure-function relationships with disease progression in fiber-reinforced soft tissues, which is essential for developing effective therapeutic measures. STATEMENT OF SIGNIFICANCE: Increasing clinical evidence correlates diabetes with premature intervertebral disc failure, likely due to advanced glycation end-products (AGE) accumulation in the annulus fibrosus (AF). However, in vitro glycation reportedly increases AF tensile stiffness and toughness, contradicting clinical observations. Using a combined experimental-computational approach, our work shows that increases in AF bulk tensile mechanical properties with glycation are achieved at the risk of exposing the extrafibrillar matrix to increased stresses under physiologic deformations, which may increase tissue mechanical failure or trigger catabolic remodeling. Computational results indicate that crosslinks along the fiber direction account for 90% of the increased tissue stiffness with glycation, adding to the existing literature. These findings provide insight into the multiscale structure-function relationship between AGE accumulation and tissue failure.
越来越多的临床证据表明，糖尿病与更频繁和更严重的椎间盘失效之间存在关联，部分原因是由于非酶糖化导致在纤维环（AF）中加速积累的晚期糖基化终产物（AGE）。然而，据报道，体外糖化（即交联）改善了 AF 的单轴拉伸力学性能，这与临床观察结果相矛盾。因此，本研究采用了结合实验和计算的方法来评估 AGE 对各向异性 AF 拉伸力学的影响，应用有限元模型（FEM）来补充实验测试并研究难以测量的亚组织级力学。采用基于甲基乙二醛的处理方法在体外诱导三种生理相关的 AGE 水平。通过采用我们之前验证的基于结构的 FEM 框架，模型纳入了交联。实验结果表明，AGE 含量增加三倍会导致 AF 环向-放射状拉伸模量和失效应力增加约 55%，放射状失效应力增加 40%。非酶糖化对失效应变没有影响。经过糖化处理的适应性 FEM 可以准确预测实验 AF 力学。模型预测表明，在生理变形下，糖化会增加细胞外基质中的应力，这可能会增加组织力学失效或引发分解代谢重塑，从而深入了解 AGE 积累与组织失效增加之间的关系。我们的研究结果还补充了关于交联结构的现有文献，表明 AGE 对纤维方向的影响更大，而纤维环中的层间放射状交联不太可能发生。总之，该联合方法为研究纤维增强软组织的多尺度结构-功能关系提供了一种强大的工具，对于开发有效的治疗措施至关重要。
越来越多的临床证据表明，糖尿病与椎间盘早期失效有关，这可能是由于纤维环（AF）中晚期糖基化终产物（AGE）的积累所致。然而，据报道，体外糖化可提高 AF 的拉伸刚度和韧性，与临床观察结果相矛盾。本研究采用结合实验和计算的方法，证明了 AF 整体拉伸力学性能随糖化作用而增加，同时也增加了生理变形下细胞外基质中增加的应力，这可能会增加组织力学失效或引发分解代谢重塑。计算结果表明，纤维方向上的交联占糖化作用导致的组织刚度增加的 90%，这增加了现有文献的内容。这些发现为深入了解 AGE 积累与组织失效之间的多尺度结构-功能关系提供了依据。
