The influence of human intervertebral disc tissue on the metabolism of osteoblast-like cells

Extensive studies have been performed to evaluate different factors that may affect on spinal interbody fusion, but the role of intervertebral disc tissue in the fusion process remains unclear. To study the influence of intervertebral disc tissue on osteoblast metabolism, we harvested disc tissue from patients who had undergone spinal surgery. The nucleus pulposus and annulus fibrosus were separately co-cultured with osteoblast-like cells SaOS-2 by means of culture inserts or organ culture. We assayed alkaline phosphoatase activity, H-3-thymidine incorporation into the DNA, and production of collagen type I, IL-1 beta, IL-6, IL-10, and TNP-alpha. Exposure of the nucleus pulposus (NP) to osteoblastlike cells revealed stimulation of alkaline phosphatase production, H-3-thymidine incorporation and collagen type I production. Exposure of the annulus fibrosus (AF) stimulated H-3-thymidine incorporation and collagen type I production, but did not affect ALP activity. IL-6 was detected after application of NP and AF. Interleukin IL-10, IL-1 beta and TNF-alpha were all below detection levels after application of disc tissue. Our findings show that frozen disc tissue stimulates the metabolism of osteoblast-like cells in vitro.