Mechanism of inhibitory action of ethanol on inducible nitric oxide synthesis in macrophages

Effects of ethanol in vitro on inducible nitric oxide (NO) production in RAW 264.7 macrophages were investigated. Adding ethanol (100-600 mM) to the incubation medium simultaneously with lipopolysaccharide (LPS) concentration-dependently inhibited LPS-induced NO production without being cytotoxic. This inhibitory effect of ethanol on NO production was almost abolished when ethanol was added to the medium 12 h after the start of incubation with LPS, implying that ethanol inhibits the induction of inducible NO synthase (iNOS). Both LPS-induced protein and mRNA expression of iNOS were inhibited by ethanol (100-600 mM) concentration-dependently. LPS-induced activation of signal transducer and activator of transcription-1 (STAT-1) was inhibited by ethanol (100-400 mM). On the other hand, LPS-induced translocation of nuclear factor-kappaB (NF-kappaB) was not affected significantly by 100-600 mM ethanol. When cells were exposed to ethanol for 72 h before LPS stimulation, the inhibitory effect of ethanol on subsequent NO production was significantly attenuated compared with that in control cells pretreated with vehicle for 72 h, suggesting the development of tolerance to the inhibitory action of ethanol. These results suggest that ethanol inhibits inducible NO production, probably by inhibiting STAT1 activation. Tolerance to this inhibitory action of ethanol is produced after chronic exposure.