Quercetin bioavailability is associated with inadequate plasma vitamin C status and greater plasma endotoxin in adults

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 mu mol/L), but no other antioxidants, were inversely correlated to the C-max and AUC(0) (to 24 h) of total quercetin (Q(total); sum of quercetin, isorhamnetin and tamarixetin; r = -0.52 to -0.53; P < 0.05). Plasma enclotoxin (0.13 +/- 0.01 EU/mL), a surrogate marker of intestinal permeability, was correlated to Q(total) C-max (r = 0.45; P < 0.05) and tended to be correlated to Q(total) AUC(0) (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. (C) 2014 Elsevier Inc. All rights reserved.