Ginsenosides, ingredients of the root of Panax ginseng, are not substrates but inhibitors of sodium-glucose transporter 1.
Recent pharmacokinetic studies have revealed that ginsenosides, the major ingredients of ginseng (the roots of Panax ginseng), are present in the plasma collected from subjects receiving ginseng, and speculated that ginsenosides might be actively transported via glucose transporters. We evaluated whether ginsenosides Rb1and Rg1, and their metabolites from enteric bacteria act as substrates of sodium-glucose cotransporter (SGLT) 1, the major glucose transporter expressed on the apical side of intestinal epithelial cells. First, we evaluated the competing effects of ginseng extract and ginsenosides on the uptake of [14C]methyl-glucose, a substrate of SGLT1, by SGLT1-overexpressing HEK293 cells. A boiling water extract of ginseng inhibited SGLT1 in a concentration-dependent manner with an IC50value of 0.85 mg/ml. By activity-guided fractionation, we determined that the fraction containing ginsenosides displayed an inhibitory effect on SGLT1. Of the ginsenosides evaluated, protopanaxatriol-type ginsenosides were not found to inhibit SGLT1, whereas protopanaxadiol-type ginsenosides, including ginsenosides Rd, Rg3, Rh2, F2and compound K, exhibited significant inhibitory effects on SGLT1, with ginsenoside F2having the highest activity with an IC50value of 23.0 µM. Next, we measured the uptake of ginsenoside F2and compound K into Caco-2 cells, a cell line frequently used to evaluate the intestinal absorption of drugs. The uptake of ginsenoside F2and compound K into Caco-2 cells was not competitively inhibited by glucose. Furthermore, the uptake of ginsenoside F2and compound K into SGLT1-overexpressing HEK293 cells was not significantly higher than into mock cells. Ginsenoside F2and compound K did not appear to be substrates of SGLT1, although these compounds could inhibit SGLT1. Ginsenosides might be absorbed by passive diffusion through the intestinal membrane or actively transported via unknown transporters other than SGLT1.
Department of Pharmacognosy, Graduate School of Pharmaceutical Sciences, Nagoya City University, Tanabe-Dori 3-1, Mizuho-ku, Nagoya, 467-8603, Japan.
Shengli
S
Gao
Tsumura Research Laboratories, Kampo Scientific Strategies Division, Tsumura & Co., 3586 Yoshiwara, Ami-machi, Inashiki-gun, Ibaraki, 300-1192, Japan.
Hirotaka
H
Kushida
Department of Pharmacognosy, Graduate School of Pharmaceutical Sciences, Nagoya City University, Tanabe-Dori 3-1, Mizuho-ku, Nagoya, 467-8603, Japan. makino@phar.nagoya-cu.ac.jp.
Toshiaki
T
Makino
D036145:Ginsenosides / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D005894:Panax / Q000737:chemistry*; D018517:Plant Roots / Q000737:chemistry*; D051269:Sodium-Glucose Transporter 1 / Q000378:metabolism*
D036145:Ginsenosides; D051269:Sodium-Glucose Transporter 1
Diabetes; Ginsenosides; Glucose transporter; Panax ginseng; SGLT1