title: Quercetin bioavailability is associated with inadequate plasma vitamin C status and greater plasma endotoxin in adults.
abstract: OBJECTIVE
  Quercetin bioavailability exhibits high interindividual variation for reasons that remain unclear. We conducted a 24-h pharmacokinetic study to investigate whether individual differences in circulating antioxidants, oxidative stress and inflammation, and intestinal permeability affect quercetin bioavailability.
  
  
  METHODS
  Healthy adults (n = 9 M/7 F; 34.3 ± 4.5 y; 27.0 ± 1.7 kg/m(2)) ingested 1095 mg quercetin aglycone with a standardized meal. Plasma antioxidants, biomarkers of oxidative stress and inflammation, and endotoxin were measured at baseline (0 h), and quercetin and its methylated metabolites isorhamnetin and tamarixetin were measured at timed intervals for 24 h.
  
  
  RESULTS
  Plasma pharmacokinetics of quercetin, isorhamnetin and tamarixetin were highly variable between participants (CVinter = 37-96%). Plasma vitamin C concentrations (34.6 ± 2.5 μmol/L), but no other antioxidants, were inversely correlated to the Cmax and AUC0 to 24 h of total quercetin (Qtotal; sum of quercetin, isorhamnetin and tamarixetin; r = -0.52 to -0.53; P < 0.05). Plasma endotoxin (0.13 ± 0.01 EU/mL), a surrogate marker of intestinal permeability, was correlated to Qtotal Cmax (r = 0.45; P < 0.05) and tended to be correlated to Qtotal AUC0 to 24 h (r = 0.38; P = 0.07). Additionally, vitamin C was inversely related to C-reactive protein, myeloperoxidase, and endotoxin (r = -0.46 to -0.55; P < 0.05), whereas endotoxin was positively correlated to C-reactive protein (r = 0.73; P < 0.05).
  
  
  CONCLUSIONS
  These findings suggest that vitamin C status and plasma endotoxin may be associated with interindividual variations in quercetin bioavailability. Greater quercetin absorption and bioavailability may be associated with poor vitamin C status and increased intestinal permeability in healthy adults.
authors.affiliation: Human Nutrition Program, Department of Human Sciences, The Ohio State University, Columbus, Ohio, USA; Department of Nutritional Sciences, University of Connecticut, Storrs, Connecticut, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Human Nutrition Program, Department of Human Sciences, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Eunice
authors.initials: E
authors.lastname: Mah
authors.affiliation: Human Nutrition Program, Department of Human Sciences, The Ohio State University, Columbus, Ohio, USA; Department of Nutritional Sciences, University of Connecticut, Storrs, Connecticut, USA. Electronic address: Bruno.27@osu.edu.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Bruno
mesh_terms: D000328:Adult; D000975:Antioxidants / Q000378:metabolism* / Q000493:pharmacokinetics; D019540:Area Under Curve; D001205:Ascorbic Acid / Q000097:blood*; D001682:Biological Availability; D002097:C-Reactive Protein / Q000378:metabolism; D004187:Disaccharides / Q000493:pharmacokinetics; D004731:Endotoxins / Q000097:blood*; D005260:Female; D006801:Humans; D007249:Inflammation / Q000378:metabolism; D007408:Intestinal Absorption; D008297:Male; D018384:Oxidative Stress; D009195:Peroxidase / Q000097:blood; D011794:Quercetin / Q000031:analogs & derivatives / Q000493:pharmacokinetics*
chemical_list: D000975:Antioxidants; D004187:Disaccharides; D004731:Endotoxins; C047368:3-methylquercetin; C508967:tamarixetin; D002097:C-Reactive Protein; D011794:Quercetin; D009195:Peroxidase; D001205:Ascorbic Acid
keywords: Endotoxin; Interindividual variability; Pharmacokinetics; Quercetin; Vitamin C