Royal jelly acid, 10-hydroxy-trans-2-decenoic acid (10H2DA), is a major lipid component of royal jelly, which is the exclusive diet of queen honeybees. Previously, we showed partial inhibition of lipopolysaccharide (LPS)-induced NF-κB activation by 10H2DA. In this study, the ability of 10H2DA to inhibit LPS-induced nitric oxide (NO) production was investigated. LPS-induced NO production and inducible NO synthase (iNOS) gene transcription were inhibited by 10H2DA. LPS-stimulated interferon (IFN)-β production, IFN regulatory factor-1 induction and IFN-stimulated response element activation, which are required for iNOS induction, were unaffected by 10H2DA. IFN-β-induced NO production, however, was significantly inhibited by 10H2DA. Furthermore, IFN-β-induced nuclear factor (NF)-κB activation and tumour necrosis factor (TNF)-α production were significantly inhibited by 10H2DA, and TNF-α-induced NF-κB activation was also inhibited by 10H2DA. These results and our previous study suggest that 10H2DA inhibits LPS- and IFN-β-induced NO production via inhibition of NF-κB activation induced by LPS or IFN-β.

To examine the role of the soxRS regulon in mutagenesis, we characterized the spontaneous mutations occurring in the endogenous tonB gene in the delta soxR strain and the SoxS overproducing strain of Escherichia coli. Neither the delta soxR strain nor the SoxS overproducing strain led to an enhancement or diminishment of the spontaneous mutation frequency. By DNA sequencing, we determined 50 spontaneous mutants from the delta soxR strains, and found that 36% were both base substitutions and IS insertions, 14% frameshifts and 10% deletions. Among the base substitutions, G:C-->T:A transversions and G:C-->A:T transitions predominated, followed by A:T-->T:A transversions. We determined 54 spontaneous mutants from the SoxS overproducing strains, and found that 37% were IS insertions, 31% base substitutions, 17% frameshifts, 9% deletions and 6% duplications. Among the base substitutions, G:C-->T:A transversions dominated, followed by A:T-->T:A transversions and G:C-->A:T transitions. These results were similar to those from the soxRS+ strains. Thus, it is suggested that the soxRS-regulated genes do not play a significant role in the defense against spontaneous mutagenesis.