Kazuo YAMASAKI, Institute of Pharmaceutical Sciences, Faculty of Medicine, Hiroshima University, 734-8551 Hiroshima, Japan

Needless to say, Panax ginseng (Araliaceae) is one of the most important herbal medicines in Oriental traditional medicine. There are several other species in the same genus also used for medicine, such as P. japonicus, P. notoginseng, P. quinquefolium, etc.
Vietnamese ginseng is the new species of this genus found at highland of Central Vietnam in 1973, and was regarded as a new species as Panax vietnamensis Ha et Grushv (1985). This is the most southern distribution of this genus.
It is a secret medicine of the Sedang ethnic group as a miraculous, life-saving plant drug used for the treatment of many serious diseases and for enhancing body strength in long journeys in high mountains.
Chemical study on the constituents of the plants clarified 23 saponins including 14 new compounds. Some of them are common to Panax ginseng, such as protopanaxadiol and protopanaxatriol saponins but with higher contents in this species. In addition, extremely high yield of ocotillol saponins, i.e. majonoside-R2 (5.3% of the dried rhizome) were identified.
We have studied the pharmacological activity of this plant drug in two ways, 1. anti-stress effects and 2. anti-tumor promoting activities, both of which can be attributed to the main saponin, majonoside R2.

1. Vietnamese ginseng extract attenuated psychological stress-induced antinociception, produced the protective effect against psychological stress-induced gastric lesions, and restored the stress-induced decrease in pentobarbital sleep to the normal level. This action was not observed on Panax ginseng extract. Cumulative findings strongly indicate that majonoside-R2 plays an important role in this effect. The effects of Vietnamese ginseng extract and majonoside-R2 may be mediated by opioid and GABAA receptor mechanisms.

2. Vietnamese ginseng extract showed significant inhibitory activity on Epstein-Barr virus early antigen (EBV-EA) activation induced by TPA. This activity was concentrated to the saponin fraction and especially, major saponin, majonoside R2 exhibited the strongest activity. Flow cytometric study suggested that the activity is ascribable with influencing the cell cycle. The effect of majonoside R2 was confirmed with in vivo test. Two-stage carcinogenesis test of mouse skin tumor caused by DMBA as an initiator indicated the significant decrease of papilloma production prompted by TPA. Also, remarkable inhibitory effect of majonoside R2 on hepatic tumorigenesis initiated with DEN and promoted with phenobarbital was observed.