Akebia quinata

The lardizabalaceous family occurs in central (the Himalayas) to eastern Asia (Japan), and in Chile, and there are eight genera [Decaisnea (India, China), Sinofranchetia (China), Holboellia (E. Asia), Akebia (E. Asia), Parvatia (E. Himal.), Boquila (Chile), Stauntonia (E. Asia), and Lardizabala (Chile)]. About 38 species are recorded. The plants are woody vines or sometimes shrubs. Leaves are palmate or rarely pinnate alternate. Flowers are usually unisexual. Ovules are usually many, and fruit berrylike, dehiscing lengthwise. Some genera are cultivated in the United States, where Akebia is more common (Decaisnea, Lardizabala, Stauntonia, and rarely Sargentadoxa along the southern border of the United States). Futhermore, some few species are found in East Asia and three species in Japan, i.e., Akebia quinata Decne (Akebi in Japanese), A. triforiata Koidz (Mitubaakebi in Japanese), and Stauntonia hexaphylla Decne (Mube in Japanese). A. quinata is widely distributed in thickets in hills and mountains in Japan, Korea, and China. It is a glabrous climber with woody vines or sometimes shrubs, with plants reaching to more than 3 m high, whose flowers, usually unisexual, bloom pale purple in April-May. The ovules are usually many and the fruit is 5-8 cm long, oblong and is a fleshy follicle, bacciform, dehiscing lengthwise. It becomes dark purplish, and when mature in September-October, the seeds are black. Its air-dried stems are used as a crude drug (Mokutsu in Japanese) in Japan and China, for example as an antiphlogistic, diuretic, and analgesic. The drug is also prescribed in China as a diuretic and antiphlogistic to treat rheumatism, lumbago, hernia, dropsy, diabetes, amenorrhea, inflammation of the stomach and kidneys, breast trouble, headache, cold, and general debility. Another species, Akebia trifoliata, is occasionally used in China; further, a decoction of the stem and root of Stauntonia hexaphylla or the pericarp of the fruit is used as a diuretic in Japan and China.

The antiulcerogenic effect of the saponins of Akebia quinata has been examined by oral administration in rats. Its saponins showed an activity at 2000 mg/kg, p.o. (crude methanol extracts) and 500 mg/kg, p.o. (crude saponins). In screening tests using a model system of congestive edema in rats, the saponins showed antiedomatous and diuretic effects at 2000 mg/kg, p.o. (methanol extracts) on oral administration. Aqueous extract of stems of Akebia quinata is administered to rats fed a high fat diet containing 1.5% cholesterol and 1% cholelic acid in order to screen the hypocholesterolic activity of these crude drugs. Significant decreases in the serum TC, FC, and PL were observed in the high-fat groups on being given these crude drugs. TC in the liver showed no reduction in the groups administered Moktsu as compared with the fat-loaded control group. (TC = total cholesterol; FC = free cholesterol; CE = cholesterol ester). In this respect, the A. quinata plant is a very important crude drug in Japan.

These new 30-norolean type triterpenes from Akebia quinata callus tissue were not reported from the original plant source, which suggests biochemical differences between intact plants and the callus tissues derived from them. The result may make it possible to obtain new biologically active substances from plant tissue cultures as new sources of natural products.

For this purpose, plant tissue cultures must be developed for new phytochemical studies. Furthermore, the constituents of the callus tissues of A. quinata were deduced based on the degrees of oxidation that the speculative biogenesis of 30-norolean type triterpenes (ex. akebonoic acid) may proceed via the route of oxidation. In this respect, Akebia quinata tissue culture will provide one of the most useful experimental systems to study the biosynthesis of 30-noroleanan-type triterpenes. Studies of a more detailed speculative biogenetic pathway using callus tissues of S. hexaphylla was reported.

Medicinal and Aromatic Plants III (1991)