Common phenolic metabolites of flavonoids, but not their unmetabolized precursors, reduce the secretion of vascular cellular adhesion molecules by human endothelial cells

Warner, Emily F, Zhang, Qingzhi, Raheem, K Saki, O'Hagan, David, O'Connell, Maria A and Kay, Colin D (2016) Common phenolic metabolites of flavonoids, but not their unmetabolized precursors, reduce the secretion of vascular cellular adhesion molecules by human endothelial cells. Journal of Nutrition, 146 (3). pp. 465-473. ISSN 0022-3166

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Abstract

BACKGROUND: Flavonoids have been implicated in the prevention of cardiovascular disease; however, their mechanisms of action have yet to be elucidated, possibly because most previous in vitro studies have used supraphysiological concentrations of unmetabolized flavonoids, overlooking their more bioavailable phenolic metabolites. OBJECTIVE: We aimed to explore the effects of phenolic metabolites and their precursor flavonoids at physiologically achievable concentrations, in isolation and combination, on soluble vascular cellular adhesion molecule-1 (sVCAM-1). METHOD: Fourteen phenolic acid metabolites and 6 flavonoids were screened at 1 μM for their relative effects on sVCAM-1 secretion by human umbilical vein endothelial cells stimulated with tumor necrosis factor alpha (TNF-α). The active metabolites were further studied for their response at different concentrations (0.01 μM-100 μM), structure-activity relationships, and effect on vascular cellular adhesion molecule (VCAM)-1 mRNA expression. In addition, the additive activity of the metabolites and flavonoids was investigated by screening 25 unique mixtures at cumulative equimolar concentrations of 1 μM. RESULTS: Of the 20 compounds screened at 1 μM, inhibition of sVCAM-1 secretion was elicited by 4 phenolic metabolites, of which protocatechuic acid (PCA) was the most active (-17.2%, P = 0.05). Investigations into their responses at different concentrations showed that PCA significantly reduced sVCAM-1 15.2-36.5% between 1 and 100 μM, protocatechuic acid-3-sulfate and isovanillic acid reduced sVCAM-1 levels 12.2-54.7% between 10 and 100 μM, and protocatechuic acid-4-sulfate and isovanillic acid-3-glucuronide reduced sVCAM-1 secretion 27.6% and 42.8%, respectively, only at 100 μM. PCA demonstrated the strongest protein response and was therefore explored for its effect on VCAM-1 mRNA, where 78.4% inhibition was observed only after treatment with 100 μM PCA. Mixtures of the metabolites showed no activity toward sVCAM-1, suggesting no additive activity at 1 μM. CONCLUSIONS: The present findings suggest that metabolism of flavonoids increases their vascular efficacy, resulting in a diversity of structures of varying bioactivity in human endothelial cells.

Item Type: Article
Additional Information: This is an open access article distributed under the CC-BY license (http://creativecommons.org/licenses/by/3.0/).
Uncontrolled Keywords: polyphenol,vcam-1,metabolism,endothelial,inflammation,phase ii conjugate
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
Faculty of Science > School of Pharmacy
Depositing User: Pure Connector
Date Deposited: 02 Mar 2016 13:00
Last Modified: 22 Apr 2020 01:08
URI: https://ueaeprints.uea.ac.uk/id/eprint/57357
DOI: 10.3945/jn.115.217943

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