McNerny Erin M B, Gong Bo, Morris Michael D, Kohn David H
Department of Biomedical Engineering, College of Engineering and Medical School, University of Michigan, Ann Arbor, MI, USA.
J Bone Miner Res. 2015 Mar;30(3):455-64. doi: 10.1002/jbmr.2356.
Collagen cross-linking is altered in many diseases of bone, and enzymatic collagen cross-links are important to bone quality, as evidenced by losses of strength after lysyl oxidase inhibition (lathyrism). We hypothesized that cross-links also contribute directly to bone fracture toughness. A mouse model of lathyrism using subcutaneous injection of up to 500 mg/kg β-aminopropionitrile (BAPN) was developed and characterized (60 animals across 4 dosage groups). Three weeks of 150 or 350 mg/kg BAPN treatment in young, growing mice significantly reduced cortical bone fracture toughness, strength, and pyridinoline cross-link content. Ratios reflecting relative cross-link maturity were positive regressors of fracture toughness (HP/[DHLNL + HLNL] r(2) = 0.208, p < 0.05; [HP + LP]/[DHNL + HLNL] r(2) = 0.196, p < 0.1), whereas quantities of mature pyridinoline cross-links were significant positive regressors of tissue strength (lysyl pyridinoline r(2) = 0.159, p = 0.014; hydroxylysyl pyridinoline r(2) = 0.112, p < 0.05). Immature and pyrrole cross-links, which were not significantly reduced by BAPN, did not correlate with mechanical properties. The effect of BAPN treatment on mechanical properties was dose specific, with the greatest impact found at the intermediate (350 mg/kg) dose. Calcein labeling was used to define locations of new bone formation, allowing for the identification of regions of normally cross-linked (preexisting) and BAPN-treated (newly formed, cross-link-deficient) bone. Raman spectroscopy revealed spatial differences attributable to relative tissue age and effects of cross-link inhibition. Newly deposited tissues had lower mineral/matrix, carbonate/phosphate, and Amide I cross-link (matrix maturity) ratios compared with preexisting tissues. BAPN treatment did not affect mineral measures but significantly increased the cross-link (matrix maturity) ratio compared with newly formed control tissue. Our study reveals that spatially localized effects of short-term BAPN cross-link inhibition can alter the whole-bone collagen cross-link profile to a measureable degree, and this cross-link profile correlates with bone fracture toughness and strength. Thus, cross-link profile perturbations associated with bone disease may provide insight into bone mechanical quality and fracture risk.
在许多骨疾病中，胶原蛋白交联会发生改变，并且酶促胶原蛋白交联对骨质量很重要，如赖氨酰氧化酶抑制后强度降低（山黧豆中毒）所证明。我们假设交联也直接有助于提高骨骨折韧性。我们建立并表征了一种使用皮下注射高达500mg/kgβ-氨基丙腈（BAPN）的山黧豆中毒小鼠模型（4个剂量组共60只动物）。在年轻的生长小鼠中，给予150或350mg/kg BAPN治疗3周可显著降低皮质骨骨折韧性、强度和吡啶啉交联含量。反映相对交联成熟度的比率是骨折韧性的正回归因子（HP/[DHLNL + HLNL] r(2)=0.208，p<0.05；[HP + LP]/[DHNL + HLNL] r(2)=0.196，p<0.1），而成熟吡啶啉交联的量是组织强度的显著正回归因子（赖氨酰吡啶啉r(2)=0.159，p = 0.014；羟赖氨酰吡啶啉r(2)=0.112，p<0.05）。未被BAPN显著降低的不成熟和吡咯交联与力学性能无关。BAPN治疗对力学性能的影响具有剂量特异性，在中等剂量（350mg/kg）时影响最大。使用钙黄绿素标记来定义新骨形成的位置，从而能够识别正常交联（预先存在）和BAPN处理（新形成、交联缺陷）骨的区域。拉曼光谱揭示了归因于相对组织年龄和交联抑制作用的空间差异。与预先存在的组织相比，新沉积的组织具有较低的矿物质/基质、碳酸盐/磷酸盐和酰胺I交联（基质成熟度）比率。与新形成的对照组织相比，BAPN治疗不影响矿物质指标，但显著增加了交联（基质成熟度）比率。我们的研究表明，短期BAPN交联抑制的空间局部效应可在可测量的程度上改变全骨胶原蛋白交联谱，并且这种交联谱与骨骨折韧性和强度相关。因此，与骨疾病相关的交联谱扰动可能有助于深入了解骨力学质量和骨折风险。
