Submitted to: Free Radicals in Biology and Medicine
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2007
Publication Date: 1/2/2008
Citation: Guo, W., Wise, M.L., Collins, F.W., Meydani, M. 2008. Avenanthramides, polyphenols from oats, inhibit IL-1 beta-induced NF-kappaB activation in endothelial cells. Free Radicals in Biology and Medicine. 44:415-429. Interpretive Summary: Atherosclerosis, the formation of fatty deposits in the blood vessel walls, is one of the major causes of cardiovascular disease—diseases that affect the heart and blood vessel system. Chronic inflammation of the vessel walls is involved at every stage. Therefore, we need to lower lipid levels in order to lower fat, oils, wax levels in the bloodstream. Also, we need to prevent inflammation of vessel walls by using diet and drugs, which reduce the risk of this disease. Avenanthramide (Avn) is a special compound exclusively found in oats. We have shown it has anti-inflammatory properties. In this study we investigated its mechanism of action at molecular levels. We used a synthetically prepared form of avenanthramide called methyl ester avenanthramide-c. We found that this compound significantly decreased the production of substances that cause inflammation to the cells that cover the inside of the vessel walls. We also found that Avn inhibited the activity of special molecule within the cells called nuclear factor kappa B (NF-kappaB), which helps to produce these inflammation-causing compounds. In addition, Avn inhibited activity of an enzyme called proteasome and is known to cause degradation of NF-kappaB.. These observations suggest that the Avn of oats possess potential anti-inflammatory properties, which may have a beneficial effect in prevention of various cardiovascular diseases like atherosclerosis. Further, synthetically prepared variation of Avn appears to have health benefit potential against inflammatory disease.
Technical Abstract: The chronic inflammation of arterial walls is associated with the development of atherosclerosis. Earlier we reported that avenanthramide (Avn)s-enriched extract of oats (AvnsO) significantly suppressed interleukin (IL)-1beta-stimulated secretion of pro-inflammatory cytokines, such as IL-6, IL-8, and MCP-1, by human aortic endothelial cells (HAEC). The main objective of the current study was to determine if the mechanism of inhibitory effect of these polyphenols from oats on the expression of pro-inflammatory cytokines is mediated through modulation of nuclear factor kappaB (NF-kappaB) dependent transcription. Confluent HAEC monolayers were treated for 24h with AvnsO, and synthetically prepared Avn-c suppressed IL-beta-stimulated activation of NF-kappaB in a concentration dependent manner. CH3-Avn-c, a synthetically prepared methyl ester derivative of Avn-c with a high biological potency, significantly and dose-dependently decreased mRNA expression and secretion of IL-6, IL-8, and MCP-1 by HAEC as determined by real-time RT-PCR and ELISA, and it inhibited IL-1 beta'- and TNFalpha-stimulated NF-KB activation as determined by a NF-kappaB DNA binding assay and a NF-kappaB luciferase reporter assay. AvnsO and Avn-c as well as CH3-Avn-c also inhibited the NF-kappaB-dependent reporter gene expression activated by TNFR-associated factor 2 and 6 (TRAF2, TRAF6) and NFkappaB-inducing kinase (NIK). CH3-Avn-c also significantly and dose-dependently decreased the phosphorylation level of IkappaB kinase (IKK) and IkappaB, and prevented IkappaB degradation as measured by Western blotting. In addition, CH3-Avn-c markedly increased the overall levels of high mass ubiquitin-conjugated protein levels while it mildly inhibited proteasome activity. These observations suggest that Avns, unique polyphenols from oats, decrease the expression of endothelial pro-inflammatory cytokines at least in part through inhibition of NF-kappaB activation by inhibiting the phosphorylation of IKK and IkappaB, and by suppressing proteasome activity.