Dynamics of dibutyryl cyclic AMP- and prostaglandin E2-mediated suppression of lipopolysaccharide-induced tumor necrosis factor alpha gene expression

Abstract

The regulation of lipopolysaccharide (LPS)-induced tumor necrosis factor alpha (TNF) production by prostaglandin E2 (PGE2), forskolin, and dibutyryl cyclic AMP (cAMP) was examined at the cellular and molecular levels. The above three agents could suppress LPS (100 ng/ml)-stimulated TNF production by immunologically activated murine macrophages (MΦs) in a dose-dependent manner. The concomitant addition of PGE2, dibutyryl cAMP, or forskolin to LPS-challenged MΦs resulted in 50% inhibition of TNF production at 10-7, 3 x 10-6, and 3 x 10-5 M, respectively. Interestingly, delaying the addition of PGE2 or dibutyryl cAMP by 1.5 h post-LPS stimulation was also effective in suppressing the production of TNF bioactivity, but only dibutyryl cAMP was effective when its addition was delayed by 3 h. Northern (RNA) blot analysis of mRNA isolated from LPS-challenged MΦs treated with PGE2 or dibutyryl cAMP corroborated the bioactivity data. The delayed addition of PGE2 or dibutyryl cAMP by 1.5 h post-LPS stimulation resulted in a suppression of TNF mRNA accumulation by 50 to 70%. These data support the concept that LPS is a potent stimulus for MΦ-derived TNF production and that this mediator is a very proximal signal in LPS-mediated disease states. Thus, therapeutic approaches that target the suppression of TNF in LPS-dependent disese states may be limited by the rapid expression of this mediator.