TRANSCRIPTION OF THE MURINE INOS GENE IS INHIBITED BY DOCOSAHEXAENOICACID, A MAJOR CONSTITUENT OF FETAL AND NEONATAL SERA AS WELL AS FISH OILS

Macrophage activation is deficient in the fetus and neonate when the s erum concentrations of docosahexaenoic acid (DHA) are 150 mu M, or 10- 50-fold higher than in the adult. We now show that DHA inhibits produc tion of nitric oxide (NO) by macrophages stimulated in vitro by IFN ga mma plus LPS, or by IFN gamma plus TNF alpha. The half-maximal inhibit ory activity of DHA was similar to 25 mu M. There were strict biochemi cal requirements of the fatty acid for inhibition. Polyenoic fatty aci ds with 22 carbons were more inhibitory than those with 20 carbons. Am ong 22 carbon fatty acids, those with a greater number of double bonds and a double bond in the n-3 position were more inhibitory. DHA was t he most inhibitory of the polyenoic acids we tested. Inducible nitric oxide synthase (iNOS) is the enzyme responsible for the production of NO by macrophages. NO production is initiated after new iNOS enzyme is synthesized following transcription of the iNOS gene. In macrophages stimulated by IFN gamma plus LPS, DHA inhibited accumulation of iNOS m RNA, as measured by Northern blotting, and iNOS transcription, as meas ured by nuclear run-on assays. We transfected RAW 264.7 macrophages wi th a construct containing the iNOS promoter fused to the chloramphenic ol acetyl transferase gene. DHA inhibited activation of this promoter by IFN gamma plus LPS. By inhibiting iNOS transcription in the fetus a nd neonate, DHA may contribute to their increased susceptibility to in fection.