Extended Duration of Torsional Loading Reduces the Survival of Nucleus Pulposus Cells in the Intact Disc

Abstract

Introduction

Previous studies on the influence of torsion and combined torsion-compression loading revealed a positive effect on the cell viability when a repetitive short-term torsion was applied at a physiological magnitude to intervertebral disc organ culture.¹ However, after an extended period (8 hours) of combined torsion-compression loading, substantial cell death was detected in the nucleus pulposus (NP).² In this follow-up study, we aimed to investigate the relationship, if any, between the duration of torsion applied to the intervertebral disc (IVD) and the level of NP cell viability.

Materials and Methods

Bovine caudal discs were harvested and cultured in a custom-built multiaxis dynamic loading bioreactor.² Torsion (± 2 degrees) was applied to the samples at a frequency of 0.2 Hz. Torsion was applied for durations of 0, 1, 4, and 8 h/d, repeated over 7 days. After the last day of loading, disc tissue was dissected for analysis of cell viability and gene expression.

Results

Disc NP cell viability remained above 85% after torsional loading for 0, 1, or 4 h/d. Viability was statistical significantly reduced to below 70% when torsion was applied for 8 h/d (p = 0.03) (Table 1). The daily duration of torsional loading did not affect the AF cell viability (> 80% for all loading durations). The trend of collagen 2 gene upregulation and matrix metalloproteases 13 downregulation with an increasing duration of torsion was observed in both NP and AF (Fig. 1).

Table 1

Cell viability of the disc after different duration of torsion

Cell viability	NP	AF
Note: Mean ± SD. N = 6.
ap < 0.05
0	87.17 ± 10.89	89.87 ± 7.34
1	91.24 ± 6.31a	92.05 ± 12.27
4	89.31 ± 12.35	81.38 ± 13.89
8	67.19 ± 16.07a	84.45 ± 13.96

Conclusion

We have demonstrated that an extended duration of torsion could inhibit the survival of NP cells within the IVD in organ culture.

Acknowledgments Funds from the Orthopedic Department of the Insel University Hospital of Bern and a private donation from Prof. Dr. Paul Heini, Spine Surgeon, Sonnenhof Clinic Bern were received to support this work.

Disclosure of Interest

None declared

References

Chan SC, Ferguson SJ, Wuertz K, Gantenbein-Ritter B. Biological response of the intervertebral disc to repetitive short-term cyclic torsion. Spine 2011;36(24):2021–2030

Chan SC, Walser J, Käppeli P, Shamsollahi MJ, Ferguson SJ, Gantenbein-Ritter B. Region specific response of intervertebral disc cells to complex dynamic loading: an organ culture study using a dynamic torsion-compression bioreactor. PLoS ONE 2013;8(8):e72489