The Effects of Sustained Administration of Growth Factors on Traumatized Discs Using Adult Male Rats

INTRODUCTION The current modalities of treating symptomatic degenerative disc disease are either conservative non-surgical or surgical modalities. Non-surgical modalities include improving body posture and back muscle strengthening through physical therapy. Surgical treatment includes removal of the disc material and intervertebral fusion, or artificial disc replacement, which is still in experimental phases in the United States. However, none of these modalities is a true cure for the degenerative process. Ideally, the best treatment would be preventing the progression of degeneration. An understanding of the mechanisms involved in intervertebral disc disease is crucial to develop new methods to prevent disc degeneration. The goal of our research is to shed light on the biochemical aspect of disc degeneration and identification of growth factors that may slow or stop the degenerative process. It is important to determine the impact of the growth factors long-term on degenerated discs, and the appropriate timing of the delivery and therapeutic dose of growth factor that can lead to an effective treatment regimen. WE hypothesize that continuous sustained release of transforming growth factor beta (TGFβ) and insulin like growth factor-1 (IGF-1) alone and in combination will reverse the loss of cellularity associated with degenerating discs. METHODS Research Design: A degenerative disc adult male rat model was developed, and a drug delivery device was used to show the capability of TGF-β or IGF-1 to be used for slowing or reversing the decline of cellularity within the degenerating disc over time. Thirty adult male Sprague Dawley rats were divided into five equal groups (n=6). Group I naïve control, group II damaged disc alone, group III damaged disc + TGF carrier (2 pg/day), group IV damaged disc + IGF-1 carrier (2 pg/day), group V damaged disc + TGF-IGF-1 carrier (1 pg/day or each factor). All carriers delivered over a 2 week period, and the discs were harvest four weeks post-surgery. Fabrication of TCPL Microcrystals: Microcrystals of tricalciumphosphate powder were prepared using standard laboratory procedures (Benghuzzi et al., 1988, 1990, 2006). Surgical Defect and TCPL Implantation: A longitudinal right paramedian incision approximately one inch in length was made. The external oblique muscle was exposed. The lumbar spine was palpated through the external oblique muscles and blunt dissection was performed through the fibers of the external and internal oblique muscles. The bodies of the distal lumbar vertebrae were exposed. A 21-gauge needle was used to identify and induce trauma into the vertebrae. The targeted discs are L5-L-6 intervertebral disc (the rat has six lumbar vertebrae and are readily identified by the large transverse process that project ventrally and cranially). The disc was identified by palpating the first disc space proximal to the pelvic girdle. The disc space was easily identified and then punctured three times with the 21 gauge needle, and sham TCP or drug containing TCP was placed adjacent to the damaged disc. The disc space was easily identified and using a 45° ventral approach ensures that the spinal cord was not be involved. Light Microscopic Evaluation of Discs: Sections of bone were fixed in 10% neutral buffered formalin and decalcified using a standard decalcifying solution (VWR, Scientific) for 72 hours. Four spines were processed for cross section analysis and two spines were processed for transverse sections. Sections of 10 μm were obtained for each sample using a microtome (American Using Image Pro software, the transition zone area and the number of chondrocyte nuclei per area was determined (Figure 1) RESULTS Piercing the disc induced structural damage and accelerated degeneration of the annulus and nucleus without evidence of inflammation when compared with non-traumatized controls After four weeks, animals in group II (trauma only) showed evidence of disc degeneration with the largest decrease in cell number anterior to the site of trauma. Animals treated with growth factors increased cell numbers within the posterior lateral areas when compared with sham animals (Table 1). Disc heights of both the damaged and adjacent discs were measured and compared for each group and compared with control. There were no differences in the disc height in the adjacent disc height between the groups. The damaged disc height in the sham was significantly less than all other treatment groups and control (Figure 2). The growth factors either alone or in combination were able to maintain disc height comparable to control. However, the combination of TGF+IGF appeared to have cellularity similar to control undamaged disc (Figure 3). Table 1: Nuclei/area counts average of 4 different animals per group and 4 different views per slide. Groups Anterior Lateral Posterior Lateral Control 12.3 ± 0.84 12.0 ±0.75 13.0 ± 1.05 Sham 3.8 ± 0.62 5.8 ± 0.94 9.8 ± 0.99 TGF 7.5 ± 0.90 6.3 ± 0.60 9.6 ± 1.21 IGF 8.9 ± 1.06 8.7 ± 0.91 8.4 ± 0.94 TGF + IGF 9.6 ± 0.95 7.4 ± 0.62 9.9 ± 1.10