Dexamethasone Inhibits Inducible Nitric-Oxide Synthase Expression and Nitric Oxide Production by Destabilizing mRNA in Lipopolysaccharide-Treated Macrophages

Abstract

Nitric oxide (NO) production through the inducible nitric-oxide synthase (iNOS) pathway is increased in inflammatory diseases and leads to cellular injury. Anti-inflammatory steroids inhibit the expression of various inflammatory genes, including iNOS. In the present study, we investigated the mechanism how dexamethasone decreased NO production in murine J774 macrophages. Dexamethasone (0.1-10 M) inhibited the production of NO and iNOS protein in a dose-dependent manner in cells stimulated with lipopolysaccharides (LPS). In contrast, in cells treated with a combination of LPS and interferon-␥ (IFN-␥), dexamethasone did not reduce iNOS expression and NO formation. Dissociated glucocorticoid RU24858 inhibited iNOS expression and NO production to levels comparable with that of dexamethasone, suggesting that the reduced iNOS expression by dexamethasone is not a GRE-mediated event. In further studies, the effect of dexamethasone on iNOS mRNA levels was tested by actinomycin assay. The half-life of iNOS mRNA after LPS treatment was 5 h 40 min, and dexamethasone reduced it to 3 h. The increased degradation of iNOS mRNA was reversed by a protein synthesis inhibitor cycloheximide. iNOS mRNA was more stabile in cells treated with a combination of LPS plus IFN-␥ (half-life ϭ 8 h 20 min), and dexamethasone had a minor effect in these conditions. In conclusion, dexamethasone decreases iNOS-dependent NO production by destabilizing iNOS mRNA in LPS-treated cells by a mechanism that requires de novo protein synthesis. Also, decreased iNOS mRNA and protein expression and NO formation by dexamethasone was not found in cells treated with a combination of LPS plus IFN-␥, suggesting that the effect of dexamethasone is stimulus-dependent.

Anti-inflammatory functions of glucocorticoid-induced genes

“…Targets of such regulation include COX-2 (Chivers et al, 2006;Lasa et al, 2001;Newton et al, 1998;Ristimaki et al, 1996), TNF (Han et al, 1990;Kontoyiannis et al, 1999;Swantek et al, 1997), vascular endothelial growth factor (Gille et al, 2001), interferon β (Peppel et al, 1991), colony stimulating factor 2 (CSF2) (Bergmann et al, 2004;Tobler et al, 1992;Tran et al, 2005), IL-5 (Staples et al, 2003), IL-6 (Amano et al, 1993;Tobler et al, 1992), IL-1α and -1β (Amano et al, 1993;Lee et al, 1988), inducible nitric oxide synthase (Korhonen et al, 2002) and several chemokines (Berkman et al, 1995;Brach et al, 1992;Chang et al, 2001;Chaudhary and Avioli, 1996;Chivers et al, 2006;Mukaida et al, 1991;Poon et al, 1999;Stellato et al, 1999;Tobler et al, 1992). The majority of these mRNAs have in common the presence of adenylate/uridylate-rich elements (AREs) in their 3' untranslated regions (UTRs).…”

The rigid steroid 21-hydroxy-6,19-epoxyprogesterone (21OH-6,19OP) is a dissociated glucocorticoid receptor modulator potentially useful as a novel coadjuvant in breast cancer chemotherapy

“…This compound, similar to the full GR agonist DEX and other dissociated GCs [38,[41][42][43][44] has been demonstrated to inhibit the LPS/IFN-γ mediated NO formation in a concentrationdependent manner and to repress NOS-2 and COX-2 gene expression in macrophages. 21OH-6,19OP also inhibits TNF-α-induced COX-2 and IL-8 expression in human lung cancer A549 cells.…”

A Patient with Erythema Nodosus Leprosum and Chagas Cardiopathy: Challenges in Patient Management and Review of the Literature

“…26 In addition, corticosteroids also interfere with microbicidal mechanisms of macrophages, either by inhibiting the release of toxic molecules such as nitric oxide, or by altering the Th-1/ Th-2 balance. 27 Glucocorticoids inhibit the release of IL-12 by macrophages, resulting in the deficiency of interferon-γ production and macrophage activation. At the same time, they increase IL-4 production and a shift toward Th-2 responses.…”