Regenerative effects of notochordal cell matrix (NCM on degenerated canine intervertebral discs (IVDs) in vivo

Abstract

Introduction: Intervertebral disc (IVD) degeneration is a progressive condition, which is common in dogs and humans. Symptom-oriented treatments are available to alleviate the pain, but not to reverse degeneration of the IVD. IVD degeneration is diagnosed by using magnetic resonance imaging, whereby the disc height index (DHI) can be measured. Also, new sequences, New techniques like T1rho and T2 mapping are used to expose early degenerative changes in the IVD. Because only symptom-oriented treatments are available, the interest to resolve the degeneration has gained interest over the years. Cell therapies have potential regenerative effects, whereby mesenchymal stromal cells (MSCs) and notochordal cells (NCs) have shown to have anabolic and stimulatory effects on nucleus pulposus cells NPCs. It is difficult to identify the NC secreted factors with a notochordal cell conditioned medium (NCCM) and thereby a new approach is being researched, namely notochordal cell matrix (NCM). Positive results are found in vitro, but the long-term effects have not been determined yet in vivo. Thereby the aim of this study is to determine whether effects of NCM treatment are observed at MRI (T1, T2 mapping, DHI) and protein expression level (collagen type I, II, X, COX-2) and if MSC treatment can exert an additive effect. Materials and methods: Five Beagles were used in this study, whereby degeneration was induced in the IVDs six weeks before the start of the treatments. Different treatments were given at T= 0 months, including NCM, MSC and NCM+MSC treatment and a reinjection of NCM at T=3 months was given in one group (2x NCM). Also, a control group and a group with induction but without treatments were used. MRIs were made at T= 0 months, T=3 months and T=6 months and were analysed with T1rho mapping, T2 mapping and DHI. Furthermore, immunohistochemistry was performed with collagen type I, II and X staining and COX-2 staining. Results: The DHI increased between T0-T6 after 1x NCM, 2x NCM and NCM+MSC treatment in the induced IVDs compared with the control IVD. A decreased T2 relaxation between T0-T6 is found after every treatment compared with the control group. No significant effects were found between T0-T6 with T1rho mapping. Collagen type I and X are not deposited in the NPs of all the groups. Collagen type II is deposited in all groups and there are COX-2 positive cells detected in every group. Conclusion: NCM reinjection improved the DHI and induced healthy ECM production. However, NCM treatment does not show a regenerative effect at quantitative T1rho and T2 mapping. MSC treatment does not exert an additive effect.