Cytokine profiles in conditioned media from cultured human intervertebral disc tissue. Implications of their effect on bone marrow stem cell metabolism.

Background: Cytokines released from intervertebral discs cultured in vitro have not been profiled, and the effect of these cytokines on human bone marrow stem cells is yet to be studied.

Materials And Methods: Intervertebral discs from 14 patients who had undergone spinal fusion surgery were cultured separately in vitro. Conditioned media were collected after 48 and 96 h of culture in serum-free Minimum Essential Medium (MEM). Profiling of the cytokines was conducted using pooled media. Conditioned medium from each patient was also tested in human bone marrow stem cell culture, and incorporation of alkaline phosphatase and 3H-thymidine incorporation was evaluated.

Results: Of the 18 cytokines screened, 12 were found to be positive, but only eotaxin, IP-10, Rantes IL-6 and IL-8 seemed to be present at high levels. There was a close correlation between IL-6 and IL-8 levels in the medium (R = 0.90, p < 0.001). When the conditioned media were added to human bone marrow stem cell cultures, cellular proliferation was stimulated (p = 0.02), but alkaline phosphatase activity remained unchanged. Cellular proliferation correlated negatively with IL-6 levels (R = -0.44, p = 0.04).

Interpretation: Intervertebral discs secrete certain cytokines into the medium when cultured in vitro, and conditioned media from cultured intervertebral discs stimulate proliferation of bone marrow stem cells.