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Ricin is obtained from Ricinus communis, the castor oil plant. Castor beans are not true beans (not pulses). The plant belongs to the spurges (i.e. fam. Euphorbiaceae). This beautiful plant is sometimes used to decorate gardens. It is cultivated chiefly to harvest oil from the seeds: ricinus oil or castor oil. In temperate regions it is an annual plant with brownish red stalks and large palmate leaves with long stalks and 5-11 jagged lobes. The plant reaches a height of 75 cm to more than 3 metres. In the tropics it is perennial, and grows even taller. Most varieties are green, but some are red or purple. The flowers may be strikingly green, or a pronounced pink in the pigmented varieties. The female flowers are uppermost and after fertilisation by the wind form fruit clusters. Each fruit contains 3 greyish brown marbled seeds. The fruit cases sometimes open explosively, spreading the seeds over a wide area. On each seed there is a small protuberance. This makes them look rather like bloated male ticks. Linnaeus noted the similarity and named the plant after this (L. ricinus = tick, cf. Ixodes ricinus). The seeds are approximately 17 mm long and 8 mm broad. Present-day cultivars have seeds weighing approximately 3 g. The seed mantle accounts for approximately ¼ of the weight. Dry seeds contain approximately 50% oil. The seeds also contain a lipase, which can be used commercially. The present world production is more than one million tons of seed per year. The main producers are India, Brazil and China.
Even in ancient Egypt, more than 4,000 years ago, castor oil was used for lamps. Where does the name "castor" come from? Castor is the generic name for the North American beaver (Castor canadensis). It is also a bright star in the constellation Gemini. In the Greek legend Castor was one of the twin sons of Leda and one of the argonauts participating in the hunt for the golden fleece. However, the name castor has nothing to do with beavers, stars or Greek gods. In olden days the oil was confused with one coming from another plant: Vitex agnus-castus, which became bastardised to agno-casto and finally to castor. Due to its high viscosity, resistance to cold and insolubility in petrole, it is added to the oils used in engineering for lubrication, motors and hydraulics. There are multiple other uses: leather production, hair oil, cosmetics, transparent soaps, printing ink, linoleum, explosives, and for some special industrial oils, paints, varnishes and lacquers. Sulphonated oil is an additive in the printing of cotton with the aniline dye alizarin. Hydrogenated oil is used as a basis for wax, candles and crayons. The oil is the raw material for a certain kind of nylon. In the USA ricinus oil is seen as a strategic material, of which there has to be sufficient in the country at any one time (military value). In medicine the oil was used as a "miracle oil" with a strong laxative action. If the seeds are pressed cold to extract the oil, it contains no toxin. This is because the toxin is not fat soluble. Oil obtained via warm pressing can contain small amounts of poison. Cold pressed and otherwise untreated ricinus cakes are poisonous and must not be processed into animal food. Heating to 140°C destroyes the toxin, so that the meal cake after oil extraction can be used in animal fodder.
Several insects may feed on the plant. The plant protects itself by producing toxins. The seeds contain the highest concentration of poison. The most important component is the protein ricin. Other poisonous components are tricinin and ricinin. Ricin is synthesised in the endosperm of ripening seeds and is stored as inactive proricin in a cell organelle ("protein body").
[Endosperm is the polyploid food tissue of the seed.] In this way the plant allows its own ribosomes to function. Ricin becomes activated after proteolytic splitting into A and B components. The ricin A part binds to a specific adenine of 28S ribosomal RNA. It prevents further production of protein in the cell. Ricin kills aphids on the plant within 24 hours. Ricin is also active in humans and is deadly in minute amounts. This is illustrated by the strange story of the Bulgarian journalist Georgi Markov. In pure James Bond style he was murdered in 1978 near Waterloo station in London by sticking a very small ricin-containing platinum pellet into his leg with the tip of an umbrella. He died three days after the attack. In January 2003, ricin and a makeshift poison laboratory was found in a north London flat. Ricin can be used for terrorism. Early 2004, small amounts were found in a mailroom of the US senate. Investigations are under way.*
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Abrus precatorius (rosary bead) contains the very powerful poison abrin, a protein similar to ricin. The small seeds are a beautiful bright red with a black spot and are often used as beads. Swallowing just a few of the chewed seeds can be deadly. Small children should not be allowed to play with these "beads".
Abrus means gracefull and refers to the beautifull flowers. The term precatorius is derived from precor, which means "to pray" because the seeds are often used as ornamental beads in rosaries meant for prayers. The plant is commonly known as Ratti or Gunchi in India. Ancient Indian weights included terms as tola, masha and ratti. The ratti referred to a single ratti seed. This seed was the standard weight in the ancient Indian system of measurements, because the seed is fairly constant in weight; on avarage it weights about 105 mg. The seeds are about 100 times less poisonous when taken by mouth than when injected. Criminals can decorticate the seeds, removing their outer covering. The decorticated seeds are then powdered, mixed with spirit or water and made into a paste. Long thin needles can be formed from this paste and can be dried in the sun. When used to stab a person, enough poison is released to kill the victim.
The prevention of protein production can be used therapeutically. Ricin can be conjugated with antibodies, which are directed against neoplastic cells, for example. Using these immunotoxins it is possible to destroy T-cells from histocompatible donors in vitro during bone marrow transplantation. This reduces the risk of graft-versus-host disease. In autologous bone marrow transplantation, the patient’s own marrow is treated with anti-T-cell immunotoxins to destroy malignant T-cells in T-cell leukaemia and lymphomas. In basic research ricin is used to cause selective cell death e.g. after intracellular injection into axons. Cell death occurs after retroaxonal transport. It can be used therapeutically to destroy latent herpes simplex in the trigeminus ganglion. Ricin may be combined with lectins of varying specificities to unravel neuronal glycosylation patterns. It is also used in a model of neurodegenerative diseases.
It is important to know whether the ricin seeds have been chewed. If they have been swallowed whole, the hard seed coat will not let the poisonous protein through. For a child just 1-3 chewed seeds can be fatal. For an adult the fatal dose is estimated as 15-20 seeds. Among animals the horse is the most sensitive (0.1-0.2 mg/kg seed is fatal). Ricin is antigenically active and antitoxin is produced in the course of time.
Worldwide, one million tons of castor beans are processed annually in the production of castor oil. The waste is five percent ricin by weight. The toxin is also quite stable and extremely toxic by several routes of exposure, including the respiratory route.
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Clinical signs, symptoms and pathological manifestations in intoxicated victims depends on the route of exposure. When inhaled as a small particle aerosol, ricin produces symptoms within 8 hours. Respiratory distress, fever, cough, dyspnea, nausea, and chest tightness are followed by profuse sweating, the development of pulmonary oedema, cyanosis, hypotension, and finally respiratory failure and circulatory collapse. Time to death ranges from 36-72 hours, depending on the dose received. Ingestion of ricin causes gastrointestinal signs and gastrointestinal hemorrhage with necrosis of liver, spleen and kidneys. Intramuscular administration causes severe localized pain, muscle and regional lymph node necrosis, and moderate involvement of visceral organs. Transient leukocytosis appears to be a constant feature, whether intoxication is via injection or oral ingestion. Leukocyte counts are 2- to 5-fold higher than the normal value. If death has not occurred in 3-5 days, the victim usually recovers.
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No specific treatment exists and care is thus supportive. In cases of gastrointestinal exposure, gut decontamination via lavage, activated charcoal and cathartics is recommended. For intoxication via aerosol, supportive therapy to counteract acute pulmonary oedema and respiratory distress is indicated. Large amounts of volume replacement may be necessary. Intensive respiratory therapy, fluid and electrolyte replacement, anti-inflammatory agents and analgesics would likely be of benefit in treating aerosol-intoxicated humans.
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For decontamination of exposed surfaces, it is important to know that ricin may be inactivated with 0.5% hypochlorite soution ("bleach").
