- Protologue: Fam. pl. 2: 327, 511 (1763).
- Family: Leguminosae
- Chromosome number: x= 10, 11, 12; A. fruticulosus: n= 12, 24, 2n= 22, A. precatorius: n= 11, 2n= 22
- Abrus fruticulosus Wight & Arn.,
- A. precatorius L.
- Indonesia, Malaysia, the Philippines: saga.
Origin and geographic distribution
There are 4-20 species in Abrus, the number depending on how a species is defined. The genus is distributed pantropically, with 2 species in South-East Asia including the whole of Malesia.
An extract of roots and leaves is used in traditional medicine to treat cough, hoarseness, digestive disorders such as gastralgia, and aphtha; it is also used as a diuretic. The seeds of A. precatorius have also played an important role in the treatment of conjunctivitis in various parts of the world. Macerating 3-5 seeds in 1 l water and applying drops of the liquid to the eye produces an inflammation of the conjunctiva, which used to be considered a cure for granular conjunctivitis. This practice has been abandoned because it appeared to be dangerous and uncontrollable. Although extremely toxic, the seeds have been used against malaria and dysentery, in conjunction with other drugs. In India, A. precatorius has a considerable reputation in the Ayurvedic, homeopathic, Unani and allopathic systems of medicine. The seed is one of the components of an oil applied to expel worms and against itching and skin diseases. It is also used to prepare an aphrodisiac and for a paste to remove piles, as an antidote when poisoned, and to treat glandular swellings and ulcers. It is used to induce abortion. Extracts from the seeds are used in Africa for the treatment of urinary schistosomiasis.
Leaves and roots have been used in various countries to sweeten foods. The leaves of A. fruticulosus are employed to sweeten traditional medicines used in central Thailand. The attractively coloured seeds of A. precatorius are often used as objects of art, ornaments or mascots; they are used as beads in rosaries and necklaces. They have also been used in soldering jewellery; when macerated in water they become mucous, and this sticky substance was mixed with solder to distribute it evenly and as a temporary cement prior to heating. In the Philippines, powdered seeds made into a paste have been used to poison darts and arrows. The stems have been used to tie together materials in harbour works. A. precatorius is often cultivated in Java as an ornamental.
Production and international trade
Although A. precatorius is sometimes cultivated for its medicinal uses or for the sweetening properties of the leaves, there are no statistics on production.
A. precatorius seeds are extremely poisonous. They contain a toxic lectin fraction, usually called abrin, which is a complex mixture of toxic abrins and relatively non-toxic Abrus agglutinins. There are several methods for isolating the different toxins and agglutinins. However, there are so many isomorphs of the toxins (glycoproteins) that a number of subfractions (e.g. abrins A, B, C, D or abrins a, b or abrins I, II, III - all with slightly different characteristics) can be isolated, depending on the procedure used. Very little information is available on relations between the toxins isolated by the different methods; a gross relationship has been established on the basis of subunit compositions and sepharose 4B binding. From this, it can be concluded that abrin III probably corresponds to abrin C, and abrin I might resemble abrin A.
Typically, 100 g of seed kernels yield approximately 120 mg of abrin I, 150 mg of abrin II and 240 mg of abrin III. All abrins are glycoproteins (Mr 63 000-67 000), composed of 2 polypeptide chains (A and B chains) linked through a single disulphide bond. The smaller A chain inhibits protein synthesis at nanomolar concentrations, and causes cell death. It is an N-glycosidase which inactivates eucaryotic ribosomes by cleaving the N-glycoside link of the residue at A4324 of 28S-rRNA. It does not directly affect protein synthesis under the same conditions. Because of its ribosome-inactivating properties, studies of its biological activity have mainly focused on its potential as an immunotoxin in cancer therapy. It has been shown to be more toxic to tumour cells than to normal cells, and to provide therapeutic protection against Ehrlich ascites tumour and fibrosarcoma in mice and Yoshida sarcoma in rats, and to have an inhibitory effect in mice with solid human tumours. The larger B chain of the abrins is a galactose-specific lectin that binds to galactose-containing receptors on the cell plasma membrane. Abrus agglutinin is a tetramer with Mr 134 900. It can be separated on DEAE-Sephacel into 2 fractions (APA-I, -II) that have several isomorphs. It is non-toxic to animal cells, but it is a potent haemagglutinator. When tested on mouse spleen cells, abrin was demonstrated to be a potent lymphocyte mitogen. Fresh preparations from the seeds of A. precatorius are extraordinarily toxic, but are not mitogenic. However, after being stored for several months at 4¬∞C it seems that such preparations are relatively non-toxic and are effective mitogens. The lectins from the seeds have blastogenic properties on human blood lymphocytes in vitro.
Abrin is one of the two most toxic substances of plant origin known (the other being ricin from the seeds of Ricinus communis L.). The LD50 value of abrin in mice is as low as 20 μ/kg (intra peritoneal) for the purified substance, and goats fed with a daily amount of 1 g/kg body weight of the seeds die within a few days. The symptoms are loss of appetite, bloody diarrhoea, dyspnoea, dehydration, loss of condition and recumbency caused by fatty change and necrosis of hepatocytes and renal convoluted tubules, pulmonary haemorrhage, oedema and emphysema, and erosions of the abomasal and intestinal epithelium. Intoxication of dogs resulted in death after 15-40 hours. When non-lethal doses of abrin were given to mice and dogs, the symptoms were reversible. The animals recovered, apparently completely, in 1-3 weeks. In addition to its toxic effect, the aqueous seed extract also has antigenic, abortive and teratogenic properties. Human poisoning is characterized by a latent period of several hours to days, followed by severe gastro-enteritis with erosion, necrosis of the liver, kidneys, spleen and lymphatic tract. After ingestion of seeds, for instance by children, immediate emesis is essential; less than one seed can be fatal when it is thoroughly masticated and the tough seed-coat has been damaged. Seeds swallowed whole with intact testa remain innocuous. The toxins are heat-stable to incubation at 60¬∞C for 30 minutes; at 80¬∞C, however, most of the toxicity is lost within 30 minutes.
Abrus seeds are also a rich source of alkaloids, among which abrin (N-methyl-L-tryptophan), hypaphorine, N,N-dimethyl tryptophan methylester, precatorine, choline and trigonelline. The insecticidal properties of seed extracts are attributed to the alkaloids (rotenoids), with hypaphorine being the most effective. The alkaloids reduce the fecundity of female mites and also deter feeding. The seeds contain an indole fraction that inhibits the growth of several plant species, e.g. of germinating lettuce. The active component of this fraction differs from the indole alkaloids abrine and hypaphorine, and has been determined as N,N-dimethyl tryptophan.
A methanol extract of the seeds furthermore showed a concentration-related inhibitory effect on the motility of human spermatozoa, and reduced sperm viability; this offers prospects for application as a human contraceptive. Seed extracts also fully inhibit germination of spores of the fungi Botrytis cinerea and Colletotrichum gloeosporioides. An almost 100% inhibition of tobacco mosaic virus was found on Capsicum pepper plants in vitro.
The roots and leaves of A. precatorius are known to contain constituents that have anti-inflammatory, anti-tumour, antitoxic, antitussive, anti-thrombotic and antibiotic properties. Phytochemical investigations of the herb and roots have revealed the presence of a series of isoflavanquinones: abruquinones A, B and C from the herb, and abruquinones A, B, D, E and F from the roots. Abruquinones A, B and D were found to exhibit remarkable inhibitory effects on platelet aggregation. The IC50 of abruquinones A and B for the inhibition of the platelet aggregation induced by arachidonic acid and collagen were less than 5μ/ml, whereas that of abruquinone D was less then 10μ/ml for the aggregation induced by arachidonic acid. Abruquinones A, B, D and F also showed strong anti-inflammatory and anti-allergic effects: superoxide formation was inhibited at a dose of less than 0.3 μ/ml, and the release of both β-glucuronidase and lysozyme from rat neutrophils and of both β-glucuronidase and histamine from mast cells were inhibited at a dose of less than 1 ŒºuŒ≥/ml. All these effects were measured in vitro.
The roots are also known to have antioestrogenic activity. Tests with laboratory animals (hamsters) infected with Schistosoma haematobium seemed to confirm the activity against urinary schistosomiasis. After oral application of a root extract of A. precatorius both the egg count and worm load were significantly reduced when compared to the controls.
The powdered drug from the leaves of A. fruticulosus used in Thailand is pale green and has a sweet taste. The sweet constituents of the leaves (of A. precatorius and A. fruticulosus) have been characterized as the cycloartane glycosides abrusosides A, B, C and D. Their aglucone, obtained by acid hydrolysis has been identified as abrusogenin. Abrusosides exhibit sweetness potencies in the range of 3-100 times greater than sugar (2% sucrose solution). In preliminary safety tests they were found to be non-toxic for rodents and were non-mutagenic. The yield of abrusosides A-D from A. fruticulosus leaves (0.33%) is slightly lower than from A. precatorius leaves (0.39%), but the concentration of abrusoside B, the sweetest compound, is higher in A. fruticulosus (0.08% versus 0.03% in A. precatorius).
The ethanol extract of the leaves has been found to inhibit acetylcholine-induced contractions of preparations of toad rectus abdominis and rat phrenic nerve-diaphragm muscle. The effects were concentration-dependent and reversible. Furthermore there were no effects on direct electrical stimulation of the rat diaphragm. Thus the ethanol extract is similar to d-tubocurarine with respect to its pattern of neuromuscular blockade. Leaves and roots have been reported to contain some abrin.
Adulterations and substitutes
As already mentioned, the toxicity of abrin is parallelled by ricin from Ricinus communis, which has similar properties. Other vegetable proteins with pharmacological potential that are broadly comparable with abrin are found in the Cucurbitaceae genera Luffa, Momordica and Trichosanthes. They also have abortifacient and antitumour properties.
The roots of true liquorice (Glycyrrhiza glabra L.) contain the sweetener glycyrrhizine, which is used worldwide on a much larger scale than the sweetening substances in Abrus leaves or roots. It has similar medicinal properties to the abrusosides (e.g. anti-inflammatory and antitussive properties) and is used to cure coughs, bronchitis and gastralgia.
- Woody subshrubs or lianas up to 6(-9) m long, stems often reaching 1.5 cm in diameter, often slender-branched.
- Leaves alternate, paripinnate with opposite leaflets, the rachis projecting beyond the last pair of leaflets; stipules small, usually persistent.
- Inflorescence axillary or terminal, pseudoracemose with the flowers in clusters on short reduced wart-like branchlets often arranged unilaterally on the rachis.
- Flowers sessile or subsessile, bisexual, 5-merous; calyx tube almost toothless or with 5 short teeth, the upper pair partly joined; corolla papilionaceous, much longer than the calyx, white, yellow, pink to dark purple, standard ovate-orbicular with a short claw and notched at the apex, wings oblong-falcate with long claws, keel longer than wings; stamens 9, filaments joined into a tube but free in upper part, staminal tube at the base adnate to the standard; ovary superior, subsessile, pubescent, 1-loculate, with numerous ovules, style curved, usually persistent, stigma capitate.
- Fruit an oblong to linear pod, flattened or inflated, beaked, pubescent, dehiscent, (1-)3-12-seeded, more or less septate between the seeds.
- Seeds subglobose, ovoid to ellipsoid, sometimes compressed, usually shiny. Seedling with epigeal germination; hypocotyl elongated.
Growth and development
The swollen wart-like branchlets of the inflorescence of A. precatorius are visited by ants.
Other botanical information
Abrus is usually considered to have an isolated position within the subfamily Papilionoideae and placed in a separate tribe Abreae. It is characterized by the combination of woody stems with a tendency to twine, paripinnate leaves, pseudoracemes and 9 stamens. Some taxonomists adhere to a wide species concept, resulting in the acceptance of only 4 species worldwide. Others prefer a more narrow species concept and accept up to 20 species. A. fruticulosus is an extremely polymorphic and widely distributed species, which is sometimes considered as a complex of several separate species.
Abrus occurs rather frequently in grasslands, cropped land (also as a weed), thickets, edges of rain forest and gallery forest, up to 1500 m altitude.
Propagation and planting
The seed weight of A. precatorius averages 150-410 mg. When untreated, the germination rate is about 40% in 18 days. After seeds have been soaked in concentrated H2SO4 for 3 hours at 30¬∞C the germination is about 85% in 10 days. Mechanical scarification results in a germination rate of 97%. Seed can be sown directly in the field or in a nursery. When sown directly in the field, 40 kg/ha is needed to obtain 40 000-50 000 plants. 2-3 seeds are planted per hole. Plants from seed sown in a nursery are planted into the field at 25 cm √ó 60 cm when 3-4 months old. Young plants should preferably be shaded by trees. In Indonesia, Gliricidia sepium (Jacq.) Kunth ex Walp. and Leucaena leucocephala (Lamk) de Wit are commonly used as shade trees. Propagation by cuttings is easy. A. precatorius can be raised in sole cropping or as a cover crop e.g. in rubber plantations in Peninsular Malaysia.
In vitro production of active compounds
Ribosome-inactivating proteins and agglutinins have been isolated from callus and cell suspension cultures established from seed explants of A. precatorius. Biosynthesis of these lectins is positively correlated with the growth of the cultures. The lectins can be purified from the culture, and their electrophoretic mobility and biological activity are comparable with those of the lectins purified from the seeds. The cultures can be maintained on revised Murashige and Skoog medium. The rotenoid content of leaves, stems and seeds is, however, greater than in tissue cultures. Small amounts of tephrosin and deguelin can be found in the tissue culture.
Farmyard manure can be given early at 10-15 t/ha. Plants 2-3 months old can be fertilized with 150 kg urea + 150 kg triplesuperphosphate + 50-100 kg KCl per ha. Experiments with planting A. precatorius without support gave a higher yield of leaves (14.5%) and facilitated harvesting.
Diseases and pests
The most serious disease of A. precatorius in Indonesia is Rhizoctonia solani, a fungus that causes stem rot. Witches broom disease caused by a mycoplasma-like organism has been reported on A. precatorius in Taiwan.
The first harvest can be obtained when A. precatorius plants are 6-8 months old. Plants are cut 25-30 cm above the ground; 4-6 harvests per year can be expected.
When harvested 4-6 times per year, a total of 4.7 t/ha of fresh leaves and twigs per year is obtained, which is equivalent to 0.6-1 t of dry leaves. Roots are harvested when plants are 30-36 months old, yielding 2.5-3.5 t of fresh roots per ha.
Genetic resources and breeding
Both Malesian Abrus species have large areas of distribution and often inhabit anthropogenic localities. They do not seem to be at risk of genetic erosion. In India, the populations of A. precatorius have been gradually depleted because of the extensive use in local medicine. No germplasm collections are known to exist, except in botanical gardens. In Indonesia, living plant material is available at the Research Institute for Spices and Medicinal Plants, Bogor and the Research Institute for Medicinal Plants at Tawangmangu.
Extensive research has been carried out on A. precatorius to elucidate the chemical composition, structure and properties of the seed constituents and to a lesser extent of those in the leaves and roots. It appears that certain constituents exhibit anti-cancer and anti-leukaemia effects. Moreover, they may influence fertility as well, whereas the toxic properties may be applicable as effective insecticide. In short, Abrus shows promise.
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R.H.M.J. Lemmens & F.J. Breteler