Background: Degeneration of the intervertebral disc is associated with back pain. Cell transplantation to enhance disc regeneration is an attractive concept and clinical trials using autologous disc cells have begun. However, the capacity of the disc, which is poorly supplied by blood vessels, to support viable cells is currently unclear. In this study, we have assessed cell seeding densities and nutrition required to optimise nucleus pulposus (NP) cell survival and proliferation.

Methods: NP cells were cultured in alginate beads at cell seeding densities 1.25×105 – 1.0×106 cells/ml, either in 10% or 20% serum (vol/vol) ± glucose for 8 days. Cell proliferation was measured by immunopositivity for a proliferation marker, the Ki67 antigen. Cell viability was assessed by DAPI staining.

Results: NP cells grown in 10% serum with glucose proliferated and formed cell clusters at low cell seeding densities; however, this proliferative response was significantly decreased at the higher cell seeding densities. Increasing serum from 10% to 20% markedly increased the size of cell clusters that formed. Interestingly, cells grown in 20% serum but without glucose produced the largest cell clusters, some containing > 40 cells. However, DAPI staining revealed that many cells forming these clusters were dieing via apoptosis.

Conclusion: The manipulation of cells in culture, prior to transplantation into degenerate discs, may be key to optimising cell-mediated tissue regeneration. This study has shown that the number of cells transplanted and the level of nutrition available in the degenerate disc microenvironment may directly influence cell proliferation and survival potential and therefore their regenerative capability.