Docosahexaenoic acid decreases IRF-1 mRNA and thus inhibits activation of both the IRF-E and NF kappa d response elements of the iNOS promoter

Background Nitric oxide produced by inducible nitric oxide synthase (iNOS) may be cytotoxic during cardiac, hepatic, and renal acute allograft rejecti on. Because the incidence of rejection is decreased by fish oils that conta in docosahexaenoic acid (DHA), we investigated the effects of DHA on iNOS. Using nuclear run-on assays and iNOS-promoter constructs, we previously sho wed that docosahexaenoic acid (DHA) inhibits activation of the iNOS gene by murine macrophages that had been stimulated in vitro by IFN gamma plus lip opolysaccharide, Methods, In our current investigation, our purpose has been to determine ho w DHA inhibits iNOS gene activation in murine macrophages, by using gel ret ardation and Northern blotting techniques. We studied the effects of DHA on the formation nuclear protein complexes that interact with the critical iN OS promoter's response elements for IRF-1 (IRF-E -923 to -913 bp) and NF-ka ppa B (NF kappa d -85 to -75 bp), Results, We now show that DHA inhibited increases of IRF-1 mRNA abundance i n response to IFN gamma plus lipopolysaccharide, As expected, we found that this prevented formation of the nuclear protein complex that binds to the IRF-E DNA response element. We also found that inhibition of IRF-1 inhibite d formation of the nuclear protein complex that binds to the NF kappa d DNA response element. Conclusions. DHA decreases the abundance of IRF-1 mRNA in stimulated cells. That, in turn, results in the decreased nuclear protein binding to the maj or iNOS promoter response elements (IRF-E and NF-kappa B), We found that th is occurred because IRE-I is a component of both the nuclear protein comple x that binds to IRF-E and the nuclear protein complex that binds to NF kapp a d.