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

AbstractIntervertebral 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 L3/4IVDs. 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.