INTRODUCTION: Critical contributors to matrix turnover in the intervertebral disc include inflammation and mechanical stress. NF‐kB (nuclear factor kappa B) is a key transcription factor involved in the response of cells to both stimuli. It was hypothesized that NFkB inhibition would prevent the catabolic effects of inflammatory and mechanical stimulation.
METHODS: Annulus fibrosus cells isolated from New Zealand White rabbits were exposed to either inflammatory stimuli (1 ng/mL IL‐1 beta), NF‐kB inhibitor(ACHP), or tensile loading at 6% 0.1 Hz using the Flexercell® Tension Plus System, or a combination of stimuli. After 24 hours, cells were analyzed for gene expression by RTPCR, prostaglandin E2 (PGE2) production via ELISA, nuclear translocation of NF‐kB by immunofluorescence of p65, and total proteoglycan and total collagen synthesis via incorporation of 35S‐sulfate and 3H‐L‐proline.
RESULTS: Immunoflourescence staining demonstrated inhibition of NF‐kB nuclear translocation by ACHP in AF cells under IL‐1 induced inflammatory condition. Gene expression of iNOS, MMP‐3 and COX‐2 was decreased 67%, 86%, and 21% respectively by treatment with ACHP in cells exposed to IL‐1 beta. Minimal effects of NF‐kB inhibition on gene expression and total proteoglycan and collagen synthesis were noted in cells exposed to mechanical stretch alone. However, under conditions of combined inflammatory and mechanical stimulation, ACHP treatment nearly abolished expression of iNOS and MMP‐3, and decreased COX‐2 expression by 70%. In addition, PGE2, a major pro‐inflammatory prostaglandin product of COX‐2 biosynthesis, was decreased.
DISCUSSION: Inhibition of NF‐kB activation greatly limits cellular catabolic response under conditions of combined inflammatory and mechanical stress in annulus fibrosus cells, suggesting synergy between the two pathways. These data identify NFkB as a potential therapeutic target against the negative effects of inflammatory and mechanical stress.