title: Common Phenolic Metabolites of Flavonoids, but Not Their Unmetabolized Precursors, Reduce the Secretion of Vascular Cellular Adhesion Molecules by Human Endothelial Cells.
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).
  
  
  METHODS
  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.
authors: Department of Nutrition, Norwich Medical School, and.
authors: Emily F
authors: EF
authors: Warner
authors: School of Chemistry, University of St. Andrews, St. Andrews, United Kingdom; and.
authors: Qingzhi
authors: Q
authors: Zhang
authors: School of Chemistry, University of St. Andrews, St. Andrews, United Kingdom; and Department of Life Sciences, Faculty of Science and Technology, University of Westminster, London, United Kingdom.
authors: K Saki
authors: KS
authors: Raheem
authors: School of Chemistry, University of St. Andrews, St. Andrews, United Kingdom; and.
authors: David
authors: D
authors: O'Hagan
authors: School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich, United Kingdom;
authors: Maria A
authors: MA
authors: O'Connell
authors: Department of Nutrition, Norwich Medical School, and colin.kay@uea.ac.uk.
authors: Colin D
authors: CD
authors: Kay
mesh_terms: D005419:Flavonoids / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D062385:Hydroxybenzoates / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D005419:Flavonoids; D062385:Hydroxybenzoates; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1; C009091:protocatechuic acid; C017616:phenolic acid
keywords: VCAM-1; endothelial; inflammation; metabolism; phase II conjugate; polyphenol