Rabbit Notochordal Cells Modulate the Expression of Inflammatory Mediators by Human Annulus Fibrosus Cells Cocultured With Activated Macrophage-Like THP-1 Cells

Abstract

Study Design. We evaluated the influence of rabbit notochordal cells on the expression of inflammatory mediators by human annulus fibrosus (AF) cells cocultured with macrophage-like cells. Objective. To identify the protective effect of rabbit notochordal cells on AF during in vitro inflammation. Summary of Background Data. Discogenic pain, which is an important cause of intractable lower back pain, is associated with macrophage-mediated inflammation in the AF. Although rabbit notochordal cells prevent intervertebral disc degeneration, their effects on human AF inflammation remain unknown. Methods. Human AF pellets were cocultured for 48 hours with notochordal cell clusters from adult New Zealand White rabbits and phorbol myristate acetate (PMA)-stimulated human macrophage-like THP-1 cells. Conditioned media (CM) from the cocultures were assayed by enzyme-linked immunosorbent assay. The expression of inflammatory mediators in the AF pellets was evaluated by real-time reverse-transcription polymerase chain reaction. Results. The levels of mRNA for interleukin (IL)-6, IL-8, and inducible nitric oxide synthase (iNOS) in the AF pellets cocultured with notochordal cells and macrophages (hAF[rNC-M]) were significantly lower than those in the AF pellets cultured with macrophages alone (hAF[M]) (P < 0.05). The levels of IL-6 and IL-8 proteins in the CM of hAF(rNC-M) were significantly lower than those in the CM of hAF(M) (P < 0.05). Coculturing with notochordal cells significantly decreased the levels of mRNA for IL-6, IL-8, and iNOS in the macrophage-exposed AF pellets (P < 0.05). After 1 ng/mL IL-1 beta stimulation, the levels of IL-6 and IL-8 mRNA and the level of IL-8 protein production were significantly decreased in the AF pellets with notochordal cells compared with naive AF pellets (P < 0.05). Conclusion. In an in vitro coculture system, rabbit notochordal cells reduced the levels of main inflammatory mediators and gene expression in the human AF during inflammation. Therefore, rabbit notochordal cells may constitute an important protective tool against symptomatic disc development.