Spatial and Diurnal Variations in Sodium Content Within Intervertebral Disc Tissue

IF 3.9 3区医学 Q1 ORTHOPEDICS

JOR Spine Pub Date : 2025-08-05 DOI:10.1002/jsp2.70079

Jordin T. Marshall, Anthony D. Lutton, Mark W. Grinstaff, John W. Olesik, Benjamin A. Walter

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Abstract

Background

Daily cycles in tissue osmolarity within the intervertebral disc (IVD) are a biophysical signal that regulates cellular metabolism and arise from deformation of the charged and hydrated extracellular matrix (ECM). However, the magnitude of these osmotic cycles remains unclear due to spatial variations in ECM composition and fixed charge density (FCD) between the regions of the IVD and between the pericellular matrix (PCM) and surrounding ECM. This study aimed to (1) validate the use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to assess intra-tissue sodium content and (2) apply this method to assess temporal and spatial changes in intra-tissue sodium content during a diurnal loading cycle.

Methods

The FCD of nucleus pulposus (NP) tissue was modified via equilibrium dialysis, and intra-tissue sodium was assessed via inductively coupled plasma-optical emission spectroscopy (ICP-OES) and LA-ICP-MS. In addition, tissue was stained with a cationic iodine-based contrast agent, and iodine was assessed via LA-ICP-MS. Diurnal changes in sodium were measured via LA-ICP-MS and ICP-OES in bovine caudal motion segments loaded under simulated physiologic loading for 40 (n = 4) or 48 (n = 4) hours, representing end-of-day and end-of-night deformations, respectively.

Results

Intra-tissue sodium content assessed via LA-ICP-MS strongly correlated (r ≥ 0.95) with ICP-OES sodium content, theoretical FCD values, and LA-ICP-MS iodine content in equilibrated tissue. Diurnal sodium results demonstrate that at the macroscale the NP region possessed a greater sodium content than the annulus fibrosus (AF) and experienced greater diurnal changes (“end-of-day-NP” sodium [0.52 ± 0.18 mEq Na/g wet wt], “end of night-NP” sodium [0.34 ± 0.13 mEq Na/g wet wt]) than the AF which did not experience a diurnal change. At the microscale, average PCM sodium normalized to adjacent ECM sodium at the end-of-day (2.3 ± 0.96) was greater than at the end-of-night (1.5 ± 0.38), indicating cells embedded within their specialized PCM likely experience elevated osmotic fluctuations.

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椎间盘组织内钠含量的空间和日变化

椎间盘内组织渗透压（IVD）的每日循环是一种生物物理信号，它调节细胞代谢，产生于带电和水合的细胞外基质（ECM）的变形。然而，由于细胞外基质组成和固定电荷密度（FCD）在IVD区域之间以及细胞周基质（PCM）与周围细胞外基质之间的空间差异，这些渗透循环的大小仍不清楚。本研究旨在(1)验证激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）评估组织内钠含量的有效性；(2)应用该方法评估组织内钠含量在日加载周期内的时空变化。方法采用平衡透析法修饰髓核组织的FCD，采用电感耦合等离子体发射光谱（ICP-OES）和LA-ICP-MS测定组织内钠含量。此外，用阳离子碘造影剂对组织进行染色，并通过LA-ICP-MS评估碘含量。通过LA-ICP-MS和ICP-OES测量了在模拟生理负荷下加载40 （n = 4）或48 （n = 4）小时的牛尾端运动节段的钠的日变化，分别代表白天结束和晚上结束的变形。结果LA-ICP-MS测定的组织内钠含量与ICP-OES测定的组织内钠含量、理论FCD值和LA-ICP-MS测定的平衡组织内碘含量呈显著正相关（r≥0.95）。钠的日变化结果表明，在宏观尺度上，NP区比纤维环区（AF）具有更高的钠含量，并且比AF区有更大的日变化（“日末NP”钠[0.52±0.18 mEq Na/g wet wt]，“夜末NP”钠[0.34±0.13 mEq Na/g wet wt]），而AF区没有发生日变化。在微观尺度上，在白天结束时，平均PCM钠归一化到邻近ECM钠（2.3±0.96）大于在晚上结束时（1.5±0.38），表明嵌入其专门PCM的细胞可能经历了更高的渗透波动。

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