Investigation of Avenanthramides, a Type of New Healthy Compounds in Oat
Avenanthramides are a group of N-cinnamolyanthranilic acids comprising anthranilic acid and cinnamic acid connected by an amide linkage with health-promoting properties mainly found in oat (Avena sativa L.). In this research, avenanthramide A, B and C (Avn-A, B and C), the three most abundant avenanthramides (Avns) in oat, were identified and quantified from oat varieties. Subsequently, in vitro antioxidant activities of oat extracts and Avn-A, B and C were evaluated, and Avn-C had the highest in vitro antioxidant activity among the three avenanthramides. To investigate the cytoprotective activity of Avns, normal human skin fibroblasts (2DD) were treated with Avn C followed by exposure to extracellular stress and its ability to reduce cellular damage was determined. Pre-treatment of cells with Avn-C reduced hydrogen peroxide (H2O2)-induced oxidative stress significantly as demonstrated by decreased intracellular free radical levels and antioxidant gene transcripts. Avn-C pre-treatment also resulted in decreased levels of gene transcripts encoding pro-inflammatory cytokines in response to H2O2 or tumor necrosis factor α (TNF-α) stimulation. This reduction in cytokine gene transcription occurred concomitantly with reduced phosphorylated nuclear factor-κB (NF-κB) p65, indicating reduced pro-inflammatory response. To better understand the mechanisms of actions, the impact of Avn-C on cellular signaling pathways was investigated on Avn C-treated 2DD cells without exposure to stress. Avn-C was found to induce heme oxygenase-1 (HO-1) expression through increased DNA-Nrf2 binding activity. Also, it reduced basal levels of pro-inflammatory cytokines through decreased DNA-NF-κB binding activity. Moreover, anti-proliferative effect of Avn C on 2DD cells was observed via mechanisms independent of autophagy activation. Collectively, our findings suggest that Avn-C protects normal human skin fibroblasts against oxidative stress and inflammatory response through Nrf2/HO-1 activation and NF-κB inhibition.