Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 1999
Publication Date: N/A
Interpretive Summary: Flavonoids are widely distributed in plants, fruits and vegetables. Flavonoids have been proposed to have a variety of biological roles in humans. Genistein, an isoflavone, was reported to be an inhibitor of a glucose transporter,. However, the study used only two isoflavonoids (genistein and daidzein) to determine the inhibition of glucose uptake, and some conflicting data were published regarding the inhibition of glucose transport. To verify a biological role of flavonoids as a glucose inhibitor, more than ten flavonoids were tested (apigenin, quercetin, rutin, fisetin, myricetin, naringenin, naringein hesperetin, genistein, daidzein, catechin, and cyanidin). The data indicated clearly that some flavonoids in addition to genistein, inhibit glucose uptake. Also, the diversity of flavonoids made it possible to identify a moiety of flavonoid structure as a putative binding site for the transporter. This study indicated that some natural flavonoids could be used as alternative blockers of glucose uptake, and a moiety of flavonoid structure might be accountable for an inhibition of glucose uptake. The discovery of natural glucose blockers has been a topic of intensive study, since a gradual adsorption of glucose in the intestine was reported to have the beneficial effect on diabetic humans. This potential therapeutical effect of natural flavonoids were discussed in this paper. However, the beneficial effect of natural flavonoids in a diet has not been completely studied in humans. This study demands to perform the epidemiologic and pharmacokinetic studies of flavonoids to validate the in vitro effects, and evaluate the in vivo effects on humans, in the near future.
Technical Abstract: Flavonoids are a group of polyphenolic compounds ubiquitously found in plants, fruits, and vegetables. Broad ranges of the biological activities of flavonoids have been reported in vitro studies. We report that several natural flavonoids blocked glucose uptake in myelocytic U937 cells. Although there were some variations in the blocking activity of individual flavonoids, approximately half of the glucose uptake was blocked by flavonoids at the concentrations of 8-50 uM. The decreasing order of the blocking activity was fisetin > myricetin > quercetin = apigenin > genistein > cyanidin > daidzein = hesperetin > naringenin > catechin. Fisetin showed approximate 50 o/o inhibition of glucose uptake at a concentration of 8 uM. Simliar patterns of the inhibition were observed in lymphocytic Jurkat cells. Fisetin and quercetin inhibited glucose transport in a competitive manner. Ki values for fisetin and quercetin were proximately 9 and 12 uM, respectively. This study showed that some types of natural flavonoids block the glucose uptake in U937 cells and that natural flavonoids could be used as alternative blockers of glucose uptake, in vitro.