Non-enzymatic glycation increases the failure risk of annulus fibrosus by predisposing the extrafibrillar matrix to greater stresses

Growing clinical evidence suggests a correlation between diabetes and more frequent and severe interver-tebral 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., crosslink-ing) 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 experimen-tal 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 & SIM;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 ef-fect 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 relation-ships with disease progression in fiber-reinforced soft tissues, which is essential for developing effective therapeutic measures.Statement of significanceIncreasing 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 gly-cation 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 me-chanical properties with glycation are achieved at the risk of exposing the extrafibrillar matrix to in-creased stresses under physiologic deformations, which may increase tissue mechanical failure or trig-ger 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.& COPY; 2023 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

Growing clinical evidence suggests a correlation between diabetes and more frequent and severe intervertebral disc failure. This study used a combined experimental-computational approach to evaluate the effect of advanced glycation end-products (AGEs) on annulus fibrosus (AF) tensile mechanics. The results showed that AGEs increase AF bulk tensile mechanical properties at the risk of tissue mechanical failure or catabolic remodeling. Computational results indicate that crosslinks along the fiber direction account for the increased tissue stiffness with glycation.