TISSUEGENE-C INDUCES LONG-TERM ANALGESIC AND ANTI-INFLAMMATORY EFFECTS VIA M2 MACROPHAGE POLARIZATION IN A RAT MONOIODOACETATE-INDUCED MODEL OF DEGENERATIVE DISC DISEASE

초록

Purpose (the aim of the study): Degenerative disc disease (DDD) is a leading cause of low back pain, contributing to the growing burden of musculoskeletal disability and social costs globally. An effective therapy for painful DDD has yet to be established, despite ongoing exploration of various treatment modalities. TissueGene-C (TG-C) is a promising candidate for addressing DDD, representing a novel cell-based gene therapy that combines human allogeneic chondrocytes with irradiated GP2-293 cells genetically engineered to overexpress transforming growth factor-β1 (TGF-β1). This study aims to evaluate the analgesic effects and underlying mechanisms of TG-C treatment in a rat monoiodoacetate (MIA) model of DDD pain and inflammation. Methods: A rat DDD model was established by injecting 2 mg of MIA per disc level into both the lumbar 4/5 (L4/5) and 5/6 (L5/6) intervertebral discs (IVDs). Two weeks following MIA injection, TG-C was administered into the L4/5 and L5/6 IVDs. To evaluate the analgesic efficacy of TG-C, pain behavior testing was performed, including withdrawal threshold assessment in the hindpaws and dynamic weight-bearing (DWB) measurements. Neuronal excitability was investigated through calcium imaging of dorsal root ganglia (DRG) neurons and in vivo single nerve recording of autonomic afferent fibers innervating the lumbar discs. The expression of selected pro-inflammatory and anti-inflammatory cytokines was assessed at the gene level to elucidate the anti-inflammatory mechanism of TG-C. Additionally, immunohistochemistry was used to evaluate TG-C induced modulation of the macrophage markers CD86 and Arg-1 expression within disc tissue. Results: Intradiscal administration of TG-C significantly reduced pain behavior one week after treatment, and this analgesic effect persisted for eight weeks until the final measurement point. TRPV1 and TRPA1-dependent calcium influx was significantly reduced in primary cultured dorsal root ganglion (DRG) neurons two and four weeks following intradiscal TG-C administration. Additionally, intradiscal pressure-evoked neuronal firing was also significantly decreased at two, four, and eight weeks after TG-C administration. The TG-C treated group showed a significant increase in IL-10 and Arginase-1 gene expression compared to the vehicle group. Immunohistochemical analysis also revealed elevated levels of the M2 macrophage marker Arginase-1 and reduced levels of the M1 macrophage marker CD86 in coronal disc tissues four weeks post-treatment with TG-C. Conclusions: In this study, we demonstrated that a single intradiscal administration of TG-C resulted in long-lasting anti-inflammatory and analgesic effects. The significant reduction in both pain behavior and neuronal excitability following TG-C treatment provides compelling evidence for its effective pain-relieving properties. We propose that the analgesic efficacy of TG-C is largely driven by its anti-inflammatory action, as evidenced by elevated levels of M2 macrophage markers. This immunomodulatory mechanism of action highlights TG-C's potential as a promising therapeutic option for painful DDD. The anti-inflammatory mechanism observed aligns with our previous findings from nonclinical studies on knee osteoarthritis, reinforcing the concept that TG-C has potential as a versatile anti-inflammatory therapeutic platform.