Protection of cells from oxidative insult could be attained by directly scavenging the reactive oxygen species or more significantly by stimulating the intracellular antioxidant defense through induction of antioxidant gene expression. It has been well documented that the transcriptional activation of Nrf2 in response to oxidative stress results in increased nuclear translocation and its binding to the antioxidant response elements (AREs) found in the promoters of genes, encoding antioxidant enzymes. Studies have demonstrated that Mitogen Activated Protein Kinase (MAPK) family is important in modulating ARE driven gene expression via Nrf2 activation. In the present study, we investigated which particular MAPK family member plays an important role in the regulation of chamomile-induced Nrf2-dependent ARE activity and ARE-driven antioxidant gene expression in mouse RAW 264.7 macrophage cells. We used aqueous chamomile extract (5, 10, 20 and 40µg/mL) obtained from dried flowers with and without MAPK pharmacological inhibitors to investigate their effect on Nrf2 activation. Pretreatment of macrophages with chamomile significantly induced the expression of antioxidant gene, heme oxygenase (HO)-1 mRNA and protein in concentration and time dependent manner. Chamomile exposure increased the nuclear Nrf2 levels which correlated with Nrf2 phosphorylation and its dissociation from Keap1 in both concentration and time dependent manner. Furthermore, chamomile treatment increased the phosphorylation of ERK1/2, but not other kinases, which might result in Nrf2 phosphorylation. Treatment of macrophages with 5µM U0126 (ERK1/2 inhibitor) was able to reduce chamomile-induced ERK phosphorylation, as well as Nrf2 phosphorylation, affecting the levels of HO-1. To confirm the role of Nrf2 in the induction of HO-1, knockdown of Nrf2 using siRNA in the macrophages resulted in significant inhibition of HO-1 expression. Furthermore, chamomile protected the cells against H2O2-induced oxidative stress and this protective effect was inhibited by U0126 and ZnPP (Zinc protoporphyrin-10µM), a HO-1 inhibitor. Taken together, these data suggest that chamomile augments cellular antioxidant defense capacity through induction of HO-1 via ERK-Nrf2-ARE signaling pathway, thereby protecting the cells from oxidative stress.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2594. doi:1538-7445.AM2012-2594