Chemistry and cancer preventing activities of ginseng saponins and some related triterpenoid compounds

More than 25 dammarane-type tetracyclic triterpenoid saponins have been isolated from ginseng, the root and rhizome of Panax ginseng C.A. Meyer (Araliaceae). The genuine sapogenins of those saponins, 20(S)-protopanaxa-diol and -triol, were identified as 20(S) 12beta-hydroxy-and 20(S) 6alpha,12beta-dihydroxy-dammarenediol-II, respectively. There are two types of preparations from ginseng: white ginseng prepared by drying after peelling off and red ginseng prepared by steaming and drying. Some partly deglycosylated saponins such as ginsenoside Rh-1, Rh-2, and Rg-3 are obtained from red ginseng as artifacts produced during steaming. Several workers studied the metabolic transformation by human intestinal bacteria after oral administration of ginsenoside Rb-1 and Rb-2 and found that the stepwise deglycosylation yielded compound K and finally 20(S)-protopanaxadiol. Ginsenoside Rg-1 was converted into 20(S)-protopanaxatriol via ginsenoside Rh-1. Yun et al. in Korea conducted the epidemiological case-control studies of ginseng and suggested its cancer preventing activities. Kitagawa et al. demonstrated in vitro that ginsenosides, especially 20(R)-ginsenoside Rg-3, specifically inhibited cancer cell invasion and metastasis. Azuma et al. found that ginsenoside Rb-2 inhibited tumor angiogenesis, and Kikuchi et al. reported that ginsenoside Rh-2 inhibited the human ovarian cancer growth in nude mice. Recently, ginsenoside Rg-3 was produced as an anti-angiogenic anti-cancer drug in China. The aforementioned reports suggest that less glycosylated protopanaxadiol derivatives are effective in cancer prevention. Apart from Ginseng tetracyclic triterpenoid saponins, some oleanane-type pentacyclic triterpenoid compounds showed the anti-carcinogenic activity in the two-stage anti-cancer-promotion experiments in vitro and in vivo.