Biodegradable Microspheres and Hydrogel Drug Delivery System of Tumor Necrosis Factor (TNF) Inhibitor and Growth Differentiation Factor 5 (GDF5) Reduces Disk Inflammation in the Rabbit Model.

Study Design: Preclinical study.

Objective: Develop and test a drug delivery system (DDS) composed of anti-inflammatories and growth factors in the rabbit disk injury model.

Summary Of Background Data: Biological therapies that inhibit inflammation or enhance cell proliferation can alter intervertebral disk (IVD) homeostasis to favor regeneration. As biological molecules have short half-lives and one molecule may not cover multiple disease pathways, effective treatments may require a combination of growth factors and anti-inflammatory agents delivered in a sustained manner.

Materials And Methods: Biodegradable microspheres were generated separately to encapsulate tumor necrosis factor alpha (TNFα) inhibitors [etanercept (ETN)] or growth differentiation factor 5 (GDF5) and were embedded into a thermoresponsive hydrogel. Release kinetics and activity of ETN and GDF5 were measured in vitro . For in vivo testing, New Zealand White rabbits (n=12) underwent surgery for disk puncture and treatment with blank-DDS, ETN-DDS, or ETN+GDF5-DDS at levels L34, L45, and L56. Radiographic and magnetic resonance images of the spines were obtained. The IVDs were isolated for histologic and gene expression analyses.

Results: ETN and GDF5 were encapsulated into poly (L-lactide-co-glycolide) microspheres and had average initial bursts of 2.4±0.1 and 11.2±0.7 μg from DDS, respectively. In vitro studies confirmed that ETN-DDS inhibited TNFα-induced cytokine release and GDF5-DDS induced protein phosphorylation. In vivo studies showed that rabbit IVDs treated with ETN+GDF5-DDS had better histologic outcomes, higher levels of extracellular, and lower levels of inflammatory gene expression than IVDs treated with blank-DDS or ETN-DDS.

Conclusions: This pilot study demonstrated that DDS can be fabricated to deliver sustained and therapeutic dosages of ETN and GDF5. In addition, ETN+GDF5-DDS may have greater anti-inflammatory and regenerative effects than ETN-DDS alone. Thus, intradiscal injection of controlled release TNF-α inhibitors and growth factors may be a promising treatment to reduce disk inflammation and back pain.