Anti-inflammatory actions of 15-deoxy-Δ^12,14-prostaglandin J₂ and troglitazone evidence for heat shock-dependent and-independent inhibition of cytokine-induced inducible nitric oxide synthase expression

In this study, the anti-inflammatory actions of the peroxisome proliferator-activated receptor (PPAR)-γ agonists 15-deoxy-Δ ^12,14- prostaglandin J₂ (15-d-Δ ^12,14-PGJ₂) and troglitazone have been examined. Treatment of RAW 264.7 cells and CD-1 mouse peritoneal macrophages with lipopolysaccharide (LPS) + interferon-γ (IFN-γ) results in inducible nitric oxide synthase (iNOS), inducible cyclooxygenase (COX-2) and interleukin-1 (IL-1) expression, increased production of nitric oxide, and the release of IL-1. In a concentration-dependent manner, 15-d-Δ ^12,14-PGJ₂ inhibits each of these proinflammatory actions of LPS + IFN-γ with half-maximal inhibition at -0.5 pg/ml and complete inhibition at 1-5 pg/ml. The inhibitory actions of 15-d-Δ ^12,14-PGJ₂ on LPS + IFN- γ-induced inflammatory events are not associated with the inhibition of iNOS enzymetic activity or macrophage cell death, but appear to result from an inhibition of iNOS and IL-1 transcription. In addition, the anti- inflammatory actions of 15-d-Δ ^12,14-PGJ₂ are not limited to peritoneal macrophages, as 15-d-Δ ^12,14-PGJ₂ prevents TNF-α + LPS- induced resident islet macrophage expression of IL-1β and β-cell expression of iNOS stimulated by the local release of IL-1 in rat islets. 15-d-Δ ^12,14-PGJ₂ appears to be -10-fold more effective at inhibiting resident islet macrophage activation (in response to TNF + LPS) than IL-l- induced nitrite production by β-cells. Two mechanisms appear to be associated with the anti-inflammatory actions of both 15-d-Δ ^12,14- PGJ₂ and troglitazone: 1) the direct inhibition of cytokine- and endotoxin- stimulated iNOS and IL-1 transcription; and 2) the inhibition of IL-1 signaling, an event associated with PPAR-γ agonist-induced activation of the heat shock response (as assayed by heat shock protein 70 expression). These findings indicate that the PPAR-γ agonists, troglitazone and the J series of prostaglandins, are potent anti-inflammatory agents that prevent cytokine- and endotoxin-stimulated activation of peripheral and resident tissue macrophages and cytokine-induced iNOS expression by β-cells by the inhibition of transcriptional activation and induction of the heat shock response.