Preincubation of human synovial cells with IL-1 modulates prostaglandin E₂ release in response to bradykinin

Kinins are vasoactive peptides whose potent inflammatory and bone resorbing properties suggest a role for these autacoids in the pathogenesis of inflammatory arthritis. We used cultured human synovial cells as a model to evaluate the effects of bradykinin on articular tissue. In resting synovial cells, bradykinin was a relatively ineffective stimulus for PGE₂ production. However, after a period of preincubation with the cytokine, IL-1, which is itself a stimulus for PGE₂ production, synovial cells exhibited a further striking time- and dose-dependent response to bradykinin. Maximal release of PGE₂ was observed in response to 10^-7 to 10^-6 M bradykinin after first pretreating the cells for 24 h with 5 to 10 U/ml of IL-1. rIL-1α and IL-1β, as well as rTNF-α, induced a similar response to bradykinin in synovial cells, whereas recombinant IL-2 did not. The bradykinin analog, lysylbradykinin, was equipotent in inducing PGE₂ release from IL-1 pretreated synvovial cells, whereas des(Arg⁹) bradykinin, substance P, and neurokinins A and B were ineffective in this regard in both IL-1-pretreated and in resting cells. Synovial cells derived from patients with rheumatoid arthritis and osteoarthritis responded similarly to bradykinin. The synergistic response in PGE₂ production induced by IL-1 and bradykinin was significantly inhibited by pretreatment with 1 μM indomethacin or dexamethasone (96 and 94% inhibition, respectively). In addition, the response was abrogated by pretreatment with 10 μg/ml of cycloheximide or actinomycin D (81 and 97% inhibition, respectively). These data provide the first description of synergism of IL-1 with a noncytokine peptide in human synovial cells. The ability of IL-1 to increase the responsiveness of synovial tissues to bradykinin may play an important role in potentiating inflammatory responses within the joint.