Madeline, L. | bioRxiv Science

bioRxiv2020

Characterization of chondroitinase-induced lumbar intervertebral disc degeneration in a sheep model intended for assessing biomaterials

Intervertebral disc (IVD) degeneration (IVDD) leads to structural and functional changes. Biomaterials for restoring IVD function and promoting regeneration are currently being investigated; however, such approaches require validation using animal models that recapitulate clinical, biochemical, and biomechanical hallmarks of the human pathology. Herein, we comprehensively characterized a sheep model of chondroitinase-ABC (C-ABC) induced IVDD. Briefly, C-ABC (1U) was injected into the L1/2, L2/3, and L3/4 IVDs. Degeneration was assessed via longitudinal magnetic resonance (MR) and radiographic imaging. Additionally, kinematic, biochemical, and histological analyses were performed on explanted functional spinal units (FSUs). At 17-weeks, C-ABC treated IVDs demonstrated significant reductions in MR index (p=0.030) and disc height (p=0.009) compared to pre-operative values. Additionally, C-ABC treated IVDs exhibited significantly increased creep displacement (p=0.004) and axial range of motion (p=0.007) concomitant with significant decreases in tensile (p=0.034) and torsional (p=0.021) stiffnesses and long-term viscoelastic properties (p=0.016). C-ABC treated IVDs also exhibited a significant decrease in NP glycosaminoglycan: hydroxyproline ratio (p=0.002) and changes in microarchitecture, particularly in the NP and endplates, compared to uninjured IVDs. Taken together, this study demonstrated that intradiscal injection of C-ABC induces significant degeneration in sheep lumbar IVDs and its potential for use in evaluating biomaterials for IVD repair. Statement of SignificanceSelecting the appropriate model for assessing biomaterials to repair and/or support regeneration of the intervertebral disc (IVD) has been controversial, leading to the use of many methods of simulating IVD degeneration (IVDD) in multiple species. Many of these models lack thorough characterization of their fidelity to human IVDD, which could hinder the translation of novel biomaterials and therapies due to unknown confounding factors. Herein, further investigation of one such model was performed using the matrix-degrading enzyme chondroitinase-ABC to induce degeneration in sheep lumbar IVDs. Degenerative changes were quantified using outcome measures relevant to human IVDD, and this dosage and method induces an aggressive degeneration environment that could be used to assess biomaterials that mimic the structure and function of the entire composite IVD. These findings may aid investigators in their selection of an appropriate animal model for preclinical testing of biomaterials and other therapeutics.

bioengineering↗

bioRxiv2018

A pilot investigation of chemonucleolysis-induced intervertebral disc degeneration in the ovine lumbar spine

Intervertebral disc (IVD) degeneration (IVDD) initiates in the nucleus pulposus (NP) and is marked by elevated levels of pro-inflammatory cytokines and matrix-degrading proteases, leading to structural and functional disruption. IVDD therapeutics are currently being investigated; however, such approaches require validation using large animal models that recapitulate clinical, biochemical, and biomechanical hallmarks of the human pathology. Others have previously utilized intradiscal administration of chondroitinase-ABC (C-ABC) to initiate IVDD in the NP of sheep lumbar IVDs. While these studies examined changes in IVD height, hydration, and tissue micro-architecture, changes in biochemical content and mechanical properties were not assessed. Thus, the objective herein was to comprehensively characterize this ovine model IVDD for salient features reported in human degenerate IVDs by evaluating biochemical, biomechanical, and histological changes. Briefly, C-ABC (1U) was administered via intradiscal injection into the L1/2, L2/3, and L3/4 IVDs, and degeneration was assessed at 6- and 10-weeks via longitudinal magnetic resonance (MR) imaging. After 6 weeks, degenerative samples showed significant reductions in IVD heights (p=0.048) and MR imaging index (p=0.048), which worsened at 10 weeks. Post-mortem degenerate and controls IVDs were evaluated for differences in interleukin-1{beta} concentration, axial and torsional functional spinal unit kinematics, and histological microarchitecture. Degenerate IVDs demonstrated significantly elevated concentrations of interleukin-1{beta} (p=0.002). Additionally, degenerative samples showed increased creep displacement (p=0.022) and compressive stiffnesss (p=0.007) concurrent with decreased long-term elastic (p=0.007) and viscous dampening coefficients (p=0.002). Histological analysis of degenerative IVDs showed changes in microarchitecture, including derangement of the nucleus pulposus and annulus fibrosus tissue as well as cartilaginous end-plate irregularities. This pilot study demonstrated that intradiscal injection of 1U C-ABC induces significant and progressive degeneration of sheep lumbar IVDs over the time course investigated. The changes observed in this pilots study small sample size resemble the hallmarks of moderate to severe IVD degeneration observed in humans. Further study is warranted on a larger sample size to further validate these findings.

bioengineering↗