Objective: Peroxisome proliferator-activated receptor gamma (PPAR gamma) 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 gamma in self-limiting episodes of acute gouty arthritis. To do this, we investigated PPAR gamma expression by monosodium urate monohydrate (MSU) crystal-stimulated monocytes, and we studied the effects of PPAR gamma ligands on crystal-induced acute inflammation.
Methods: PPAR gamma expression by MSU crystal-stimulated 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 gamma 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 gamma 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 gamma was functional, since a PPAR gamma ligand was able to up-regulate CD36 expression on monocytes. A natural ligand of PPAR gamma, 15-deoxy-Delta(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 gamma expression on monocytes by MSU crystals may contribute, at least in part, to the spontaneous resolution of acute attacks of gout.