Chemistry and Cancer Preventing Activities of Ginseng Saponins and Some Related Triterpenoid Compounds

ABSTRACT

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 deglyco-sylation 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.