Ethanol metabolism is not required for inhibition of LPS-stimulated transcription of inducible nitric oxide synthase

We examined the effect of inhibition of ethanol metabolism on ethanol-media ted suppression of Escherichia coli endotoxin (LPS-induced upregulation of transcription and release of inducible nitric oxide synthase (iNOS) and tum or necrosis factor alpha (TNF alpha) from rat alveolar macrophages (AM) in vivo. Ethanol (3.45 and 5.5 g/kg/IP) and t-butanol (3.7 g/kg, IP), given 30 min before intratracheal administration of LPS (1.0 mg/kg), inhibited the upregulation of iNOS mRNA and protein, determined by competitor equalized R T- PCR and Western immunoblot, respectively, but not TNF alpha mRNA in AM o btained 2 h after LPS administration by bronchoalveolar lavage (BAL). Howev er, ethanol and t-butanol inhibited LPS-stimulated nitrate and nitrite (RNI ) and TNF alpha protein in BAL fluid. Pretreatment of rats with 4-methylpyr azole (100 mg/kg, IP) 2 h before, or disulfiram 30 min before, administrati on of ethanol (3.45 g/kg, IP) failed to attenuate the inhibitory effect on iNOS mRNA or protein. t-Butyl hydroperoxide (100 mg/kg, IP) given to rats 3 0 min before administration of LPS enhanced LPS-mediated upregulation of iN OS mRNA and TNF alpha protein in AM and BAL fluid. The inhibitory effect of ethanol on iNOS mRNA was not mediated by an interaction with elevated leve ls of circulating corticosterone because pretreatment of rats with RU-38486 (100 mg/kg, IM), which inhibited prednisolone (50 mg/kg, IM), induced supp ression of LPS-stimulated iNOS mRNA, and failed to attenuate ethanol-mediat ed inhibition of LPS-stimulated iNOS mRNA in AM. We conclude that metabolis m of ethanol to acetaldehyde via alcohol dehydrogenase is not required for ethanol-mediated suppression of LPS-induced iNOS transcription and TNF alph a synthesis/release in AM. Moreover, an interaction of ethanol or acetaldeh yde with circulating corticosterone is not involved in ethanol-mediated att enuation of LPS-stimulated iNOS mRNA or protein or TNF alpha protein in the lung. Speculatively, because oxidation of t-butanol to t-butylhydroperoxid e results in activation, rather than inhibition, of iNOS and TNF-alpha, the reported ethanol-mediated enhancement of iNOS mRNA may result from the act ion of the hydroxyethyl radical. (C) 1999 Elsevier Science Inc. All rights reserved.