Notochordal Cell-Derived Therapies for Painful Disc Degeneration

Abstract

Degenerated human intervertebral discs (IVDs) are commonly associated with low back pain conditions including stenosis, herniation, and axial back pain. There are few minimally invasive treatments available to treat painful IVD degeneration and axial back pain. Painful IVD degeneration is associated with structural disruption, chronic inflammation, and neurovascular ingrowth deep into the IVD and all of these conditions must be addressed to promote function and inhibit painful conditions in the spine. During development of the spine, the notochord produces factors including chondroitin sulfate that are important for creating the IVD structure as well as for patterning the spine to inhibit ingrowth of dorsal root ganglia (DRGs) axons into the IVD. Our overall concept is that we can use concepts and factors important in the developing spine to develop therapeutic candidates for painful IVD degeneration. In this study, we focus on improved understanding of notochordal cells, their maturation, and the secreted factors they produce that can be used for therapeutic effect. We focus on three studies. Study 1 describes the effects of loading on the notochordal cell phenotype. Study 2 identifies cell culture models to screen therapies for discogenic pain and to investigate which factors in notochordal cell conditioned medium are capable of inhibiting neurite growth. Study 3 investigates the capacity of notochordal cell conditioned medium to inhibit the neovascularization that may be a predecessor to neurite growth into the IVD. We use a variety of cell culture models using nucleus pulposus tissue from porcine IVDs and neural and vascular endothelial cells from human and rodent sources. Study 1 indicated that hydrostatic loading can induce maturation of notochordal cells from large vacuolated to small chondrocytic cells. This maturation was accompanied by some shifts in the quantity and quality of secreted factors. Study 2 determined that notochordal cell conditioned medium is capable of inhibiting neurite growth in two neural cell types: human neuroblastoma cells (SH-SY5Ys) and rat DRGs. Results indicated that the effect was dose-specific, and that CS is a necessary protein causing this inhibition. Study 3 determined that notochordal cell conditioned medium can inhibit neovascularization using cell human umbilical vascular endothelial cells. Importantly, notochordal cell conditioned medium was not cytotoxic to neural or endothelial cells, suggesting this could be used safely for back pain even if leakage occurred in the area around the IVD. However, future in vivo testing is required for further characterization of safety and efficacy profiles. Together, we present a novel paradigm for designing therapeutic interventions derived from trophic agents from notochordal cells and for screening the efficacy of those therapies. We conclude that notochordal cells secrete factors with structure and symptom modifying potential, and these may be useful for developing therapeutic agents with the capacity to restore IVD function and preventing discogenic pain. Acknowledgments This work was funded by NIAMS/NIH Grants (R01 AR064157 R01, R01 AR057397) and Grant S-13-50P of the AO Research Fund of the AO Foundation (D.P.) and Orthopaedic Research and Education Foundation (S.K.C.). Disclosure of Interest None declared