INTRODUCTION: The newly developed chimera decoy oligodeoxynucleotide (CDODN) improves on the NF-κB decoy oligodeoxynucleotide (NDODN), with binding sequences for two transcription factors, NF-κB and STAT-6, which are associated with the gene expression of inflammatory cytokines. In this study, we hypothesized that CDODN would inhibit the inflammatory response of intervertebral disc (IVD) degeneration. First, the short-term (4 weeks) and long-term (12 weeks) effects of a CDODN injection in IVDs in the rabbit anular-puncture model were characterized. The recovered nucleus pulposus (NP) tissues from the 4-week group were transplanted on nude rat dorsal root ganglion (DRG) as a xenograft transplant to assess potency for pain generation; pain generation was assessed by behavioral testing.

METHODS:

Rabbit anular-puncture and injection of CDODN: Five-month-old female NZW rabbits (n=64) received anular-puncture in two non-consecutive lumbar IVDs (L2/3 and L4/5). Four weeks later, 10 ul of either phosphate-buffered saline (PBS), NDODN (100 ug in PBS), or CDODN (10 or 100 µg in PBS) was injected into the punctured IVDs. Rabbits were euthanized at eight weeks or 16 weeks after the initial anular-puncture.

Radiographic analysis of Disc Height Index: IVD height was expressed as disc height index (DHI) from lateral radiographs of the lumbar spine obtained at two-week intervals, up to 16 weeks, after the initial puncture. The average percent change in DHI of injected IVDs was calculated for each postoperative disc as a ratio to its preoperative DHI and then further normalized to the unpunctured L3/4 IVD (normalized %DHI).

Magnetic Resonance Imaging Analyses: The average degeneration of the injected IVDs were calculated by the Pfirrmann grade using T2 weighted sagittal images obtained from MRI examinations on post-sacrifice isolated spine segments.

Nude rat disc xenograft radiculopathy model: Degenerated NP tissue from the injected IVDs of the anular-punctured rabbits were placed on the L5 right DRGs of female nude rats (n=32) as xenografts to assess pain induction.

Mechanical allodynia: Mechanical allodynia was evaluated in nude rats using the 50% paw withdrawal threshold response to mechanical stimulation by Von Frey hair filaments for both hind paws.

RESULTS:

Radiographic analysis of normalized %DHI: (Fig 1): Two-way ANOVA analysis for normalized %DHI showed a significant difference between the CDODN and PBS group (p<0.05). At 16 weeks post-puncture, the NDODN 100 μg and CDODN 100 μg groups showed significantly higher normalized % DHI than the PBS group (p<0.05).

MRI Analyses: (Fig 2): The Pfirrmann scoring showed lower tendency (less degeneration) in the CDODN 10 and 100 μg groups compared to the PBS group (p=0.094, p=0.088. respectively).

Mechanical allodynia: (Fig 3): Rats transplanted with NDODN 100 μg, CDODN 10, and 100 μg-treated rabbit degenerated rabbit NPs exhibited reduced mechanical allodynia compared to rats transplanted with PBS-treated rabbit degenerated NPs (p<0.01).

DISCUSSION: A CDODN intradiscal injection showed a significant improvement in IVD height preservation and tendency to be different in MRI scoring and indicates that the suppression of both NF-κB and STAT 6 may attenuate disc degeneration. The decreased inflammation also corresponded with less pain generation in the nude rat radiculopathy model.