Role of Ginsenoside Rd in Inhibiting 26S Proteasome Activity

Abstract

Drugs targeting 26S proteasome as antitumor agents are considered to be important for cancer therapy. Although the active components are yet to be identified, for more than 1000 years, the low-toxicity Panax ginseng has been used in traditional herbal medicine for either treating or preventing cancer. Ginsenosides Rb1, Rb2, Rc, Rd, Re, Rf, and Rg1 are distinct components that can be isolated from P. ginseng C.A. Meyer. In this study 26S proteasome was purified from pig red blood cells, and the activity of the seven isolated ginsenosides was analyzed by proteolysis assay. It was found that ginsenoside Rd inhibited 52.9% the chymotrypsin-like activity of 26S proteasome with an IC(50) value of 107.5 microM when Suc-LLVY-AMC was used as a substrate. Ginsenoside Rd displayed a mixed type inhibition of 26S proteasome when analyzed by Lineweaver-Burk plots of the inhibition kinetics. Unlike ginsenoside Rd, the other ginsenosides showed low inhibitory effect of the chymotrypsin-like activity of 26S proteasome. Seven ginsenosides did not inhibit the trypsin-like and caspase-like activities of 26S when Ac-RLR-AMC or Z-LLE-AMC was used as substrate. These results suggest that ginsenoside Rd is a potential drug for cancer prevention due to its specific 26S proteasome inhibitory effect and known low toxicity. Furthermore, both 3-O-Glc(2)-Glc and 20-O-beta-Glc positions of the ginsenoside may play a role in the inhibitory property of the chymotrypsin-like activity in 26S proteasome.

Inhibition of Human 20S Proteasome by Ginsenosides from Panax ginseng

“…Ginsenoside Rd induces apoptosis of cancer cells through downregulating Bcl-2 expression, up-regulating Bax expression, and activating the caspase-3 pathway. 25 Our study and a previous study 20 strongly suggest that ginsenoside Rd is a potent anticancer agent with mild side effects by inducing apoptosis through down-regulating the chymotrypsin acitivity of proteasomes. In addition, ginsenoside Rg3, Rg5, Rk1 also showed potent inhibitory activities although they were not as potent as Rd.…”

“…20 In our study, ginsenoside Rd showed more dramatic inhibitory activity on 20S proteasome from human erythrocyte with its IC50 at 33.5 µM than 26S proteasome from pigs' RBC, almost three times more effective. This result could be interpreted by two possibilities, one as that proteasomes from human erythrocyte might be more severely inhibited by Rd than those from pigs' RBC, or the other as that 20S proteasome itself might be more severely repressed by Rd than 26S proteasome.…”

“…20 The ginsenosides Rb1, Rb2, Rc, Rd, Re, Rf, and Rg1 efficacy in that study were evaluated on the 26S proteasome purified from the pig red blood cells (RBC). In this study, we used the 20S proteasome purified from human erythrocytes as our target and evaluated the efficacy of ginsenosides Rd, Re, Rf, Rg1, Rg2, Rg3, Rg5, Rh1, Rh2, and Rk1.…”

“…considering that ginsenosides seem to inhibit only chymotrypsin-like activity of proteasome in the previous study. 20 To investigate the proteasome inhibitory activity of ginsenosides, commercially available 20S proteasome purified from human erythrocytes was used in this study. All ginsenosides were isolated using high-speed counter current chromatography as well as preparative HPLC.…”

Chemoprevention of Lung Squamous Cell Carcinoma by Ginseng

“…Rb2, Rb3, Rc, and Re are all ginsenosides more commonly prevalent in white ginseng compared with red ginseng, and with high abundance in mountain ginseng (34) as well as in Chinese medicine Panax ginseng C. A. Meyer (35). Rd was previously found as a potential drug for cancer prevention due to its specific 26S proteasome inhibitory effect (36), and Rb2 was reported to be able to inhibit tumor angiogenesis and metastasis in a mouse melanoma model (37). Other than direct inhibition on various aspects of tumorigenesis of these ginsenosides, their metabolites also exhibit antitumor effect, such as the bacterial metabolit of Rb1 was found to be able to significantly inhibit lung carcinoma metastasis in vivo (38).…”