Embelia (PROSEA)

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Plant Resources of South-East Asia
Introduction

List of species

Embelia Burm.f.

Protologue: Fl. indica: 62, t. 23 (1768).

Family: Myrsinaceae

Chromosome number: x= unknown

Major species

Embelia ribes Burm.f.

Origin and geographic distribution

Embelia comprises approximately 130 species and occurs in Africa, Asia including Malesia, the western Pacific and Australia. Most species are found in Asia. In Indo-China 11 species have been found, in Peninsular Malaysia 17, in Sumatra 6, in Java 6, in Borneo more than 15 and in New Guinea 10. However, no recent overview is available for the Malesian region.

Uses

Several Embelia species are well known for their anthelmintic and taeniafuge uses. The active principles primarily act as a purgative. E. ribes has been known since ancient times in Ayurvedic medicine under the Sanskrit name "vidanga". The dried fruit is considered anthelmintic, astringent, carminative, alterative and stimulant. In China, roots and leaves of E. laeta are used to treat dysentery, indigestion and eczema, while the fruits are used to treat anaemia, gum bleeding and anorexia. In eastern Africa, Embelia (e.g. E. schimperi Vatke) fruits either fresh or dried are a popular anthelmintic. The roots are used as a purgative and vermifuge. In Thailand, the roots of E. ribes are used as expectorant and in the treatment of internal inflammations. In Papua New Guinea, squeezed sap of Embelia stems and young leaves is drunk to treat malaria or as a general febrifuge. In East Kalimantan, the crushed fresh bark of E. ribes is used as a fish poison. In Java the young leaves, shoots and immature fruits of E. ribes are consumed cooked as a sour vegetable or condiment. E. philippinensis A. DC. is used in a similar way in the Philippines. The ripe sour-sweet fruits of both species are also eaten as a delicacy. The fruits of E. coriacea Wallich ex A. DC. are reported to be poisonous. When dissolved in alcohol, embelin (a major constituent of Embelia) can be used as a yellow dye for silk and wool.

Production and international trade

Although fruits of Embelia were traded from Malesia to Europe at the beginning of the 20th Century, at present no commercial trade is reported.

Properties

Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) is recognized as the main active principle of Embelia species. The fruits of E. ribes contain 2.5-3.1% embelin and about 1% of the sugar quercitol, those of E. tsjeriam-cottam about 1.6% embelin and no quercitol. The fruits of the African E. schimperi yield 4.8-7.5% embelin and about 1% quercitol. Embelin is also isolated from E. robusta. Embelin can be isolated as golden yellow needles, insoluble in water, but clearly soluble in ethanol, chloroform and benzene.

The best known pharmacological action of embelin is its effect on reproduction: male antifertility, anti-implantation and abortifacient activity has been shown in tests with various animals. Ethanolic (90%) extracts of E. ribes fruits administered orally to female rats at 250 mg/kg during early pregnancy showed 66% anti-implantation activity, and the abortifacient activity in late pregnancy was about 25%. A daily subcutaneous administration of embelin at a dose of 20 mg/kg body weight to male albino rats for 15 or 30 days inhibited the motility of epididymal sperm, fertility parameters (such as pregnancy attainment and litter size) and the activities of enzymes of glycolysis and energy metabolism. However, all changes were reversible, as seen after 15 and 30 days of recovery. Addition of embelin to epididymal sperm suspensions caused a dose and duration-dependent inhibition of spermatozoal motility and inhibited the activities of carbohydrate metabolism enzymes. Light and scanning electron microscopy showed that both in vitro and in vivo treatment with the substance causes profound morphological changes in spermatozoa such as decapitation of the spermatozoal head, discontinuity of the outer membranous sheath in the mid-piece and the tail region, and alteration in the shape of the cytoplasmic droplet in the tail. In another experiment, sixty 3-month-old pregnant mice were treated with a suspension of embelin (50 mg/kg body weight) in carboxymethylcellulose (CMC, 0.5 ml) from days 3 to 8, days 6 to 9 or days 10 to 16 of gestation. A control group was treated with distilled water and CMC (0.5 ml). In a second experiment, males and virgin females were treated with embelin (50 mg/kg body weight) for 15 and 30 days respectively. Treated males were than mated with untreated females, and treated females were mated with untreated males. A distilled water and CMC control was maintained during the experiment. Embelin treatment resulted in a significant increase in resorptions (maximum of 18.5% in females treated from days 3 to 8) and skeletal abnormalities (maximum of 26% in females treated from days 3 to 8). Furthermore, embelin treatment resulted in changes in the sex ratio of litters, with 132 females to 100 males occurring in females treated from days 3 to 8 compared with 96 females to 100 males in the distilled water control. Treatment with embelin prior to mating significantly increased the incidence of dead foetuses and increased the occurrence of physical and skeletal abnormalities and resorption. Histochemical and biochemical investigations of male rats, treated for 35 days with doses of 0.3-0.5 mg/kg body-weight (subcutaneously), revealed a picture of the testis with arrest of spermatogenesis, a marked diminution in the cell population and deformation of the seminiferous tubulus at all doses. Necrobiosis and nuclear degeneration of varying degrees were observed. The weight of testes, epididymis, vas deferens, seminal vesicle, coagulating gland, ventral prostate, dorso-lateral prostate, adrenal gland and levator and muscle were reduced considerably, just like the biochemical parameters in the tissues, such as glycogen in testis and fructose in seminal vesicle, prostate and coagulating glands. These observations may be due to a hormonal imbalance, caused by embelin; an anti-androgenic nature is suggested. A significant anti-oestrogenic and weak progestational activity was also found in female rats.

Oral administration of embelin (75 mg/kg body weight, daily for 15 and 30 days) to male rats caused a significant increase in the uptake of D-glucose, L-alanine, L-leucine and calcium in small intestine segments. Embelin also produced significant increases in intestinal brush border membrane-associated enzymes (invertase, lactase, maltase, alkaline phosphatase and leucine aminopeptidase) in both intestinal homogenates and partially purified brush border membrane preparations. Significant increases were also noted for microsomal glucose-6-phosphatase and cytosolic lactate dehydrogenase. Increases in brush border membrane-associated total lipids, phospholipids, cholesterol, triacylglycerol, unesterified fatty acids and ganglioside sialic acid were seen but there was little change in the cholesterol-phospholipid molar ratio. All changes returned to control or near control levels following withdrawal of the drug.

Embelin (isolated from the fruits of E. ribes) and administered to male albino rats with fibrosarcoma at doses of 50 or 100 mg/kg, orally, for 20 days, prolonged survival time and induced significant tumour regression. To evaluate the possible mode of action of embelin, the anti-oxidant status of the drug was studied. Embelin exhibited significant free radical scavenging properties. The biological defence system constituting the superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione was significantly enhanced, whereas lipid peroxidation was greatly restricted. In vivo studies in rats and mice indicated an analgesic effect of potassium embelate. It was found to be effective by oral, intramuscular, subcutaneous and intracerebro ventricular routes (doses ranged from 5-40 mg/kg), and the results compared well with morphine (a mainly μ receptor agonist) as reference. Potassium embelate acts centrally to produce analgesia (binding studies indicate that mixed μ and κ receptor sites may be involved), and its effect is not strongly antagonized by naloxone (a pure μ receptor antagonist), indicating that other central sites are also of importance. Furthermore, there is no precipitation of abstinence syndrome as observed with morphine. A toxicity evaluation which included subacute, chronic, reproductive testing and teratological investigations in laboratory animals (mice, rats and monkeys; doses 10-100 mg/kg per day, orally) did not indicate adverse effects, suggesting the compound is safe.

"Pestoban" is a mixture of 3 plant extracts, only 2 of which (Cedrus deodara Loud. and Azadirachta indica A.H.L. Juss. oils) show toxicity against the mollusc species Lymnaea acuminata and Indoplanorbis exustus. The third plant extract, that of E. ribes, is non-toxic, but when all three are mixed, the toxicity of the mixture is about 100 times more active than either of the two toxic components. The toxic effect against the snail Lymneae acuminata, an intermediate host for both Fasciola hepatica and F. gigantica is time- as well as dose-dependent. The molluscicidal activity is higher than synthetic molluscicides, and the dose levels used against the snail are safe for fish. "Ectozee" is a herbal preparation containing the same combination of plants, which is used against mites.

Application of a seed extract of E. ribes results in a high mortality of the nematodes Meloidogyne incognita and Rotylenchulus reniformis.

Adulterations and substitutes

Dried fruits of E. ribes and E. tsjeriam-cottam have been used as an adulterant of black pepper (Piper nigrum L.).

Description

Dioecious scandent shrubs or lianas up to 20 m long.
Leaves alternate, distichous or spirally arranged, simple, entire to serrate, glabrous, dotted with red-brown or black glandular dots or streaks, petioled.
Inflorescence axillary or terminal, fascicled or solitary, racemose or paniculate, sometimes subumbellate.
Flowers functionally unisexual, small, 4-5(-6)-merous; calyx deeply lobed, lobes imbricate; petals free or slightly connate at base, imbricate or contorted, usually papillate inside and glabrous outside; stamens and staminodes inserted towards the base of the petals, filaments short to rather long, anthers dorsifixed; ovary superior, in male flowers minute, in female flowers globose or ovoid, few-ovuled, style short, persistent, stigma broad, disciform.
Fruit a subglobose to ovoid drupe, usually drying black, 1-seeded.
Seedling with epigeal germination; cotyledons emergent, leafy with finely toothed margins, hypocotyl elongated.

Growth and development

The various Embelia species do not flower simultaneously, and fruit maturation takes several months. The juicy fruits are probably dispersed by birds.

Other botanical information

The closely related genus Grenacheria differs primarily in the connate petals. No recent taxonomical revision of the genus Embelia is available and the existing revision from the beginning of the 20th Century is based on a limited number of specimens. Numerous species have been described with a high degree of endemism, and this causes considerable taxonomic difficulties. The species are rather difficult to distinguish in the field. For example E. robusta and E. tsjeriam-cottam are often confused.

Ecology

Embelia can be found from sea-level up to 2000(-2800) m altitude. Some species prefer primary forest, but others are common along forest margins and in secondary forest.

Propagation and planting

Embelia can be propagated by seed or cuttings. Most species are common in secondary vegetation and not propagated or planted deliberately. Occasionally some Embelia are grown on a small scale in home gardens.

Harvesting

Embelia fruits are simply picked when ripe. Young shoots to be used as a vegetable are harvested shortly before use or sale. For collecting the roots, plants are uprooted.

Handling after harvest

Fruits of Embelia are either used fresh or dried for medicinal purposes. Sometimes the fruit pulp is removed by washing and threshing the fruits, and the seeds are dried and stored. Dried fruits and seeds guarantee a year-round supply in the market. Stems harvested to be used as a fish poison are simply bundled, and the bark is later pulverized at the spot to release the toxic agents.

Genetic resources and breeding

Some species like E. ribes and E. tsjeriam-cottam have a wide distribution, but most Embelia species have a very local occurrence. The latter species are theoretically more vulnerable to extinction.

Prospects

The application of embelin in herbal molluscicides and against mites appears promising. Other applications of embelin, e.g. as analgetic, antifertility or free radical scavenging agent deserve more attention.

Literature

Atal, C.K., Siddiqui, M.A., Zutshi, U., Amla, V., Johri, R.K., Rao, P.G. & Kour, S., 1984. Non-narcotic orally effective, centrally acting analgesic from an Ayurvedic drug. Journal of Ethnopharmacology 11: 309-317.
Chitra, M., Devi, C.S.S. & Sukumar, E.P., 1994. Protective action of embelin against lipid peroxidation on tumour bearing rats. Fitoterapia 65(4): 317-321.
Das, S.S. & Bhatia, B.B., 1994. Comparative therapeutic evaluation of Ectozee aerosol spray and Betnovate-N against mite causing canine dermatitis. Indian Journal of Indigenous Medicines 10(2): 9-10.
Gupta, S., Sanyal, S.N. & Kanwar, U., 1989. Antispermatogenic effect of embelin, a plant benzoquinone, on male albino rats in-vivo and in-vitro. Contraception 39(3): 307-320.
Gupta, S., Sanyal, S. & Kanwar, U., 1991. Effects of embelin, a male antifertility agent, on absorptive and digestive functions of rat intestine. Journal of Ethnopharmacology 33(3): 203-212.
Mez, C., 1902. Embelia. In: Engler, A. (Editor): Das Pflanzenreich [The plant kingdom]. Heft 9 (IV 236). Wilhelm Engelmann, Leipzig, Germany. pp. 295-332.
Singh, K., Singh, A. & Singh, D.K., 1995. Molluscicidal activity of different combinations of the plant products used in the molluscicide Pestoban. Biological Agriculture & Horticulture 12(3): 253-261.
Srinath, B.R., Vivekanandan, O.S., Shivakumar, K.R. & Rao, K.R.R., 1991. Foetotoxic and teratogenic effects of embelin - an abortifacient compound on mice. Current Research - University of Agricultural Sciences (Bangalore) 20(5): 91-93.
Varshney, M.D., Sharma, B.B. & Gupta, D.N., 1986. Antifertility screening of plants. Part II. Effect of ten indigenous plants on early and late pregnancy in albino rats. Comparative Physiology and Ecology 11(4): 183-189.
Zutshi, U., Johri, R.K. & Atal, C.K., 1989. Possible interaction of potassium embelate, a putative analgesic agent, with opiate receptors. Indian Journal of Experimental Biology 27(7): 656-657.

Selection of species

Authors

L.S.L. Chua & J.L.C.H. van Valkenburg