Quercetin metabolites downregulate cyclooxygenase-2 transcription in human lymphocytes ex vivo but not in vivo

Sonia de Pascual-Teresa, Kelly L. Johnston, M. Susan DuPont, Karen A. O'Leary, Paul W. Needs, Linda M. Morgan, Mike N. Clifford, Yongping Bao, Gary Williamson

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Flavonoids have the potential to modulate inflammation by inhibition of cyclooxygenase-2 (COX-2) transcription. In this study, we compared the effect of the human flavonoid plasma metabolites (quercetin 3'-sulfate, quercetin 3-glucuronide and 3'-methylquercetin 3-glucuronide) on expression of COX-2 mRNA in human lymphocytes ex vivo using TaqMan real-time RT-PCR. We show that the flavonoid quercetin metabolites as detected in human plasma at physiologically significant concentrations inhibit COX-2 expression in human lymphocytes ex vivo. To examine the effect in vivo, we measured COX-2 mRNA levels in 8 subjects (5 men and 3 women) participating in a 3-way, single-blind, randomized crossover study after consumption of a single meal of white, low-quercetin onions, compared with yellow, high-quercetin onions. After consumption of high-quercetin onions, quercetin conjugates were detected in plasma (up to a maximum concentration of 4 micro mol/L at approximately 1 h). However, the expression of COX-2 mRNA in lymphocytes was unchanged by the consumption of high-quercetin onions compared with the low-quercetin group. The results show that a single high dose of the flavonoid quercetin from onions does not change COX-2 mRNA expression in human lymphocytes in vivo even though this change occurred in vitro and ex vivo.
Original languageEnglish
Pages (from-to)552-557
Number of pages6
JournalJournal of Nutrition
Issue number3
Publication statusPublished - Mar 2004


  • Base Sequence
  • Biotransformation
  • Cyclooxygenase 2
  • DNA Primers
  • Gene Expression Regulation, Enzymologic
  • Humans
  • Isoenzymes
  • Kinetics
  • Lymphocytes
  • Membrane Proteins
  • Onions
  • Prostaglandin-Endoperoxide Synthases
  • Quercetin
  • RNA, Messenger
  • Reverse Transcriptase Polymerase Chain Reaction
  • Time Factors
  • Transcription, Genetic

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