Objective: To find clinically the most suitable tissue-engineered replacement for nucleus pulposus which should be able to prevent, or at least delay, the process of intervertebral disc degeneration, as well as narrowing of the intervertebral disc space after surgery of disc herniation.
Methods: We chose to transplant chondrocytes derived from elastic cartilage in site of previously evacuated nucleus pulposus from the lumbar intervertebral discs of New Zeeland White Rabbits. Elastic cartilage cells of the rabbit ear have been used as an easily accessible and quality source of chondrocytes. A small piece of ear cartilage has been sampled and disintegrated. Free chondrocytes have been isolated and labeled with a fluorescent marker before transplantation procedure in order to trace them after implantation. Both cultured chondrocytes and chondrocytes harvested after isolation have been used as a transplant. Prior to implantation these cells have been divided into two groups – the first group as a cell suspension and the second group as a cellular construct on plasma-thrombin gel as a carrier. Animals were sacrificed in groups: after two weeks, one month and three months, with their lumbar intervertebral discs removed. In control group only nucleus was removed and then replaced either with suspension or carrier without cells. Survival of transplanted cells in the intervertebral disc space and their extracellular matrix synthesis has both been evaluated by fluorescent microscopy, histological and gene expression analysis. Radiological analysis has been used to test the efficiency in preventing the narrowing of intervertebral space after evacuation of nucleus pulposus.
Results: By using labeled transplanted cells we were able to trace their viability with fluorescent microscope up to one month. Thereby we have proven the transplanted cells are able to survive in the environment of the rabbit’s intervertebral disc. In addition, they are able to produce basic structural molecules of extra cellular matrix, histological similar to native nucleus pulposus, in contrast with control group where only remnants of carrier and scar tissue were found. However, the gene expression studies have shown that the cells of the new-formed tissue express less tissue-specific extra cellular matrix genes, e.g. aggrecan, collagen II, then cells in the native tissue. Radiological analysis has not shown any significant differences between the two groups in prevention of intervertebral space narrowing following the discectomy.
Conclusion: Cell therapy has much to offer in the development of tissue-engineered replacements used in clinical orthopedics. results and techniques of this research may turn out to be useful in clinical practice, but further examinations are needed especially on the field of annular closure, before any clinical investigation.
