bis-Eugenol Induces Heme Oxygenase 1 Expression and Activation of Nrf2 in RAW264.7 Cells.

Background/aim: Eugenol dimer (bis-eugenol), a representative ortho-bisphenol, has been reported to have potent antioxidant/anti-inflammatory activity. To clarify the antioxidant/anti-inflammatory mechanisms of bis-eugenol, we investigated its involvement in heme oxygenase-1 (HO-1) expression and anti-inflammatory activity.

Materials and methods: HO-1 expression in RAW264.7 cells was measured using real-time reverse transcription polymerase chain reaction analysis (RT-PCR) and western blot analysis. Expression of Escherichia coli lipopolysaccharide (LPS)-stimulated cyclooxygenase-2 (Cox2) and tumor necrosis factor-α (Tnfα) mRNA was measured using RT-PCR. Nuclear factor (NF)-erythroid 2-related factor 2 (Nrf2) activation was measured using an ELISA-based transcription factor assay.

Results: bis-Eugenol induced HO-1 expression in a dose-dependent manner, and tin-protoporphyrin IX (PPIX) suppressed this increase in terms of Ho-1 mRNA. LPS-stimulated expression of Cox2 and Tnfα mRNA was significantly suppressed by bis-eugenol, but not by eugenol. The inhibitory effect of bis-eugenol on LPS-stimulated Cox2 and Tnfα mRNA expression was not changed by the addition of PPIX, but an inhibitory effect was evident in the case of eugenol. bis-Eugenol activated Nrf2 and promoted its binding to the antioxidant response element (ARE).

Conclusion: bis-Eugenol is a potent HO-1 inducer and Nrf2 activator. The present findings offer interesting insights for re-evaluating the antioxidant/anti-inflammatory mechanisms of ortho-bisphenols.