Proteolytic enzyme digestion caused by papain or trypsin injection can be used to simulate the condition of intervertebral disc (IVD) degeneration by degrading extracellular matrix and altering biomechanical properties. Tissue digestion by enzymes creates a cavity into which regeneration therapies can be implanted. The aim of this study was to develop a bovine organ culture model of disc degeneration using papain and to assess the influence of dynamic loading on matrix turnover and disc dimension.
Papain (65U/mL) or saline solution was injected into the centre of whole IVDs (n=9) isolated from three different bovine tails. Using a bioreactor system, physiological loading was applied to papain- (n=3) and saline-injected (n=3) samples for 2h daily on 7 consecutive days. Papain-injected samples (n=3) were cultured under free swelling conditions as unloaded control. Disc height was measured daily, matrix glycosaminoglycan content and gene expression levels of established IVD and catabolic matrix markers were analysed after the culturing period.
Injection of papain created a cavity, resulted in extracellular matrix disorganization and reduced tissue glycosaminoglycan content in the loaded and free swelling samples. Furthermore, daily dynamic loading induced a significant reduction in disc height and volume. Relative gene expression was downregulated for anabolic markers, while catabolic markers were upregulated.
The results suggest that the papain-induced degeneration model is suitable for implantation of regenerative therapeutic biomaterials and cells. Decrease in disc height, a hallmark of disc degeneration, was more pronounced in the dynamic loaded samples than in free swelling condition. In future work, the therapeutic efficacy of induced pluripotent stem cells (iPSCs) will be evaluated with this model.
This work is part of the iPSpine project, funded by the European Union’s Horizon 2020 Research and Innovation Programme (Grant No 825925).