Accumulating evidence implicates interleukin-8 (IL-8) as an essential mediator in neutrophil-mediated acute inflammation. Neutrophils have also been shown to have a crucial role in the pathogenesis of acute gouty arthritis. Thus, we investigate the pathophysiological role of IL-8 in an experimental model of acute gout, monosodium urate (MSU) crystal-induced arthritis in rabbits. The injection of MSU crystals into knee joints caused a marked swelling of joints. Concomitantly, the infiltration ofleukocytes, mostly neutrophils, was observed in synovial membrane and synovial fluids. The injection of MSU crystals also induced an elevation in synovial fluid IL-8 levels preceding neutrophil infiltration into synovial fluids, without an accompanying increase in plasma IL-8 levels. Immunoreactive IL-8 protein was detected in synovial lining cells at 12-24 h after the injection. IL-8 protein was also observed in infiltrated leukocytes in synovium as early as 3-24 h after the injection. Finally, the intraarticular injection of a neutralizing anti-IL-8 antibody significantly attenuated the crystal-induced joint swelling that occurred at 12 h, and neutrophil infiltration into arthritic joints at 12 and 24 h after the induction. These results provide evidence on the pathogenic roles of locally produced IL-8 in MSU crystal-induced gouty arthritis.
Objective. Peroxisome proliferator-activated receptor ␥ (PPAR␥) is a member of the nuclear hormone receptor superfamily and functions as a key regulator of lipid and glucose metabolism, atherosclerosis, and inflammatory responses. This study was undertaken to evaluate the biologic role of PPAR␥ in self-limiting episodes of acute gouty arthritis. To do this, we investigated PPAR␥ expression by monosodium urate monohydrate (MSU) crystal-stimulated monocytes, and we studied the effects of PPAR␥ ligands on crystal-induced acute inflammation.Methods. PPAR␥ expression by MSU crystalstimulated human peripheral blood mononuclear cells was determined by reverse transcription-polymerase chain reaction and immunostaining. Expression of CD36 on monocytes was detected by flow cytometric analysis. The effects of PPAR␥ ligands on in vitro crystal-induced cytokine production and on in vivo cellular infiltration during crystal-induced acute inflammation were also investigated.Results. MSU crystals rapidly and selectively induced PPAR␥ expression by monocytes. Gene expression was detected as early as 2 hours, and maximum expression was observed at 4 hours after stimulation. The induced PPAR␥ was functional, since a PPAR␥ ligand was able to up-regulate CD36 expression on monocytes. A natural ligand of PPAR␥, 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15deoxy-PGJ 2 ), significantly reduced the crystal-induced production of cytokines by monocytes. Indomethacin inhibited cytokine production only at high concentrations, and an antidiabetic thiazolidinedione (troglitazone) failed to exert significant effects. Administration of troglitazone and 15deoxy-PGJ 2 significantly prevented cellular accumulation in a mouse air-pouch model of MSU crystal-induced acute inflammation.Conclusion. Rapid induction of PPAR␥ expression on monocytes by MSU crystals may contribute, at least in part, to the spontaneous resolution of acute attacks of gout.
SUMMARY
To determine the roles of IL‐8 in inflammatory synovitis. examination was made of the results of continuously injecting human recombinant IL‐8 into the knee joints of New Zealand white rabbits. Recombinant human lL‐8 was infused continuously into the joint cavity at 75 ng/h for 14 days by a polypropylene catheter connected to a mini‐osmotic pump implanted in each rabbit. Infiltration of inflammatory cells into joint cavity and histopathological changes in synovial tissue were examined at 7 and 14 days following the start of infusion. The continuous infusion of IL‐8 for 14days led to severe arthritis characterized by apparent erythema and joint pain, the accumulation of leucocytes, infiltration of mononuclear cells in synovial tissue, and marked hypervascularization in the synovial lining layer. IL‐8 may be a factor which can contribute to the inflammatory process of chronic arthritis by mediating leucocyte recruitment and hypervascularization in inflamed joints.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.