Affordable Access

Extensive binding of the bioflavonoid quercetin to human plasma proteins.

Authors
  • Boulton, D W
  • Walle, U K
  • Walle, T
Type
Published Article
Journal
The Journal of pharmacy and pharmacology
Publication Date
Feb 01, 1998
Volume
50
Issue
2
Pages
243–249
Identifiers
PMID: 9530994
Source
Medline
License
Unknown

Abstract

Although the bioflavonoids, a large group of polyphenolic natural products, exert chemopreventive effects in cardiovascular disease and cancer, there is little information about the disposition of these dietary components in man. The objective of this study was to investigate the plasma-protein binding of the most abundant bioflavonoid, quercetin, using 14C-labelled quercetin. An ultracentrifugation assay (170,000 g for 16 h at 20 degrees C) was shown to sediment plasma proteins. Binding of quercetin to normal plasma was extensive (99.1+/-0.5%, mean +/- s.d., n = 5). The unbound fraction varied as much as 6-fold, 0.3-1.8%, between subjects. This high binding was independent of quercetin concentration over the range 1.5-15 microM (0.5-5 microg mL(-1)). Human serum albumin was the primary protein responsible for the binding of quercetin in plasma (99.4+/-0.1%). Binding by alpha1-acid glycoprotein (39.2+/-0.5%) and very-low-density lipoproteins (<0.5% of total quercetin) did not make substantial contributions to overall plasma binding. The equilibrium association constant for the binding of quercetin to serum albumin was 267+/-33 x 10(3) M(-1) (n = 15). Thermodynamic data for the binding of quercetin to serum albumin indicated spontaneous, endothermic association. Displacement studies suggested that in man the 'IIA' subdomain binding site of human serum albumin was the primary binding site for quercetin. Association of quercetin with erythrocytes was significantly (P < 0.001) reduced by plasma protein binding. These data indicate poor cellular availability of quercetin because of its extensive binding to plasma proteins.

Report this publication

Statistics

Seen <100 times