Abstract
It is speculated that some kinds of biochemical mediators, such as proinflammatory cytokines and prostaglandin E2 (PGE2), may play an important role in the pathogenesis of lumbar disc herniation. Though PGE2 seems to be one of the key factors of the pain induction in terms of radiculopathy, it is still elusive that the regulation of this synthesis at the site of lumbar disc herniation. Since cyclooxygenase-2 (COX-2), which is one of the isoforms of the prostaglandin synthase, is expressed in the many kinds of cells such as macrophage or synovial cell in the presence of proinflammatory cytokines, it seems to regulate this PGE2 synthesis in lumbar disc herniation as well as other inflammatory conditions. The purpose of this study is to clarify the role of COX-2 and proinflammatory cytokines in the pathomechanism of radiculopathy induced by lumbar disc herniation. Three herniated lumbar disc specimens were obtained from the patients who underwent surgery for certain radicular symptoms. They were examined immunohistologically using monorlonal or polyclonal antibodies against either human COX-2, interleukin-1 β (IL-1β) or tumor necrosis factor- α (TNF-α). The monolayer culture of the disc cells were prepared from the herniated lumbar disc of the same patients by collagenase digestion. In the 6-multiwell plates, 1.0 × 105 attached cells/cm2 were cultured in DMEM supplemented with 10% fetal calf serum in the presence of either 100 U/ml of IL-1β or TNF-α. After 6 hours, total cellular RNA was directly isolated from the cell monolayers using AGPC method for RT-PCR in order to detect the COX-2 and IL-1β mRNA expression. Both of COX-2 and proinflammatory cytokines, IL-1β and TNF-α, were detected in the cytosol of the disc chondrocytes as well as the inflammatory cells infiltrating around the herniated disc tissues histologically. By the RT-PCR, COX-2 mRNA was strongly expressed in the herniated lumbar disc-derived cells stimulated with both IL-1 β and TNF-α, while little COX-2 mRNA expression was detected in unstimulated cells. Furthermore, IL-1 β mRNA expression was also induced by 100 U/ml of IL-1β stimulation autocrinely. These results reveal that the cells in the lumbar disc express COX-2 paracrinely and release IL-1β autocrinely by the stimulation of proinflammatory cytokines. It is, therefore, suggested that proinflammatory cytokines play an important role in causing radiculopathy of lumbar disc herniation due to produce PGE2 by COX-2 induction and enhance IL-1β release autocrinely or paracrinely.
