Dehydrodiisoeugenol, an isoeugenol dimer, inhibits lipopolysaccharide-stimulated nuclear factor kappa B activation and cyclooxygenase-2 expression in macrophages

o-Methoxyphenols such as eugenol and isoeugenol exhibit anti-oxidant and anti-inflammatory activities, but at higher concentrations act as oxidants and potent allergens. We recently demonstrated the eugenol dimer bis-eugenol to be an efficient inhibitor of lipopolysaccharide (LPS)-induced inflammatory cytokine expression in macrophages without cytotoxicity. This result suggested that dimer compound of o-methoxyphenols may possess anti-inflammatory activity. Thus, we further synthesized dehydrodiisoeugenol and α-diisoeugenol from isoeugenols, and investigated whether these dimers could inhibit LPS-stimulated nuclear factor kappa B (NF-κB) activation and cyclooxygenase (COX)-2 gene expression, both of which are closely involved in inflammation and mutagenesis. The expression of the COX-2 gene was strongly inhibited by dehydrodiisoeugenol in RAW264.7 murine macrophages stimulated with LPS. In contrast, isoeugenol and α-diisoeugenol did not inhibit it. Dehydrodiisoeugenol also significantly inhibited LPS-stimulated phosphorylation-dependent proteolysis of inhibitor κB-α and transcriptional activity of NF-κB in the cells. These findings suggest that dehydrodiisoeugenol acts as a potent anti-inflammatory agent.