The use of Ricin, Abrin or Modeccin in the context of criminal or terrorist attacks poses a significant threat. In sensory these toxins are unremarkable and have a delayed toxic effect. After metabolism they are no longer detectable in the body. When it is suspected, an investigation should be made retrospectively to the environment of the injured persons. Food, objects or the environment has to be analyzed for the presence of the toxins.
Origin and availability of the toxins
The most important toxin of this group is ricin, which is found in the seeds of the castor oil plant. The castor oil plant is native to northeast Africa and has meanwhile spread all over the world. It is intensively used for castor oil production. Global castor seed production is around one million tons per year. Leading producing countries are India, China and Brazil. Castor oil is used, among other things, to produce tensides for cosmetics and special lubricating oils.
The ricin content of the seed is about 1%. The seed weighs about 300 mg and consists of a thin brown shell and a soft white pip. That white mass has a neutral smell and a slightly nutty taste. The castor oil production process generates large quantities of a ricin-containing oil cake which contents about 3 % of ricin. The toxin in the oil-cake can be inactivated by heating and is used, for example, as a fertilizer.
A similar toxin is abrin, which is found in the seeds of rosary pea, a very common tropical and subtropical legume. Rosary peas are not used for alimentary or technical purposes; due to their bright red colour they are often found in necklaces. The abrin level of peas is about 0.08%, one pea weighs about 100 mg.
In southern Africa, there are plants that also contain a very similar toxin, which is named here modeccin. Modeccin toxin is found in the tuber of Adenia spp. It is found in rocky places in Africa in the dry savanna. The modeccin level of tubers is about 0.05%.
All three toxins can be extracted and purified from plants with weak aqueous acids. Detailed preparation instructions can be found in the internet.
Toxicity of ricin, abrin and modeccin
Ricin, abrin and modeccin are nearly identical, consisting of two chains connected by a single disulfide bond. Chain A is an enzyme (N-glycoside hydrolase) and chain B is a galactose specific lectin, which mediates entry of the A-B protein complex into the cytosol. The effect of ricin is the enzymatic depurination of Adenosine at position 4324 in the Sarcin-Ricin-Loop of the eukaryotic rRNA 28S. This loop is important in binding elongation factor eEF-2 during protein synthesis.
Upon oral ingestion, the toxins are stable against peptidase digestion, but only a small quantity is absorbed unchanged by the gastrointestinal tract. Symptoms mainly include the following: nausea, vomiting, diarrhea, tachycardia, hypotension and seizures, destruction of red blood cells. Human lethal doses are about 2 to 8 chewed seeds, 0.03 to 20 mg/kg of ricin or 1 mg/kg of abrin.
Injection or exposure to inhalable dusts is associated with a markedly higher toxicity, i.e. 3 to 10 µg/kg of ricin and about 0.04 µg/kg of abrin. The estimated subcutaneous LD 50 for modeccin is 4 mg/kg.
Determination in food, water, environmental samples and biological samples.
Determination of these toxins in samples needs sample preparation. Thisusually includes degreasing, neutralization and extraction with PBS buffer.
Lateral Flow Assay (LFA of miprolab, Göttingen, Germany)
One way to rapidly detect ricin as an unchanged peptide is the lateral flow assay (LFA) which is similar to the generally known pregnancy test. The aqueous sample solution is applied to the sample pad from where it migrates across a test strip. In the presence of ricin, a red line will appear at line “T”. When the test was performed correctly it still appears at “C” another red line
Due to its similarity to ricin, abrin and modeccin, are also detected by this test. The test could be quantitatively evaluated against an external calibration through densitometry. The measured quantity is the ratio of the height of the toxin band to the height of the control band.The limit of determination in water or aqueous extract is 50 µg/l.
In our laboratory, the ELISA test kit of Tetracore® is used. This is a so-called sandwich ELISA in which two different antibodies may be used. Thus, the tertiary structure of A-and B-chain of ricin is also examined. The limit of determination in water or aqueous extract is 5µg/l.
Determination of enzyme activity of the N-glycoside hydrolase
If the A chain of the toxin is still active, it splits off adenine from the sarcin-ricin loop. Alternatively a short-chain DNA ( GCGCGAGAGCGC „GAGA-Loop“) can be used as a substrate. The cleaved adenine can be determined by HPLC.
The detection limit of this method in water is 0.2 mg/l.
Determination of ricinine
Unpurified extracts from castor bean contain the specific alkaloid ricinine. It can be determined by gas chromatography-mass spectrometry. This is also the only way to detect a castor bean poisoning in blood serum, since ricinine is not metabolized rapidly.
For poisoning with ricin and the other toxins there are no specific treatment options. The following general treatment options are possible:
- Rapid external decontamination
- Symptomatic treatment
- Treatment with lactulose syrup or lactose in milk
The toxicological background to this is:
Ricin binds specifically to galactose compounds and is then no longer taken up by the cells. Lactose and lactulose containing galactose can therefore be used in a poisoning trial basis. This is the result of in vitro experiments in our lab.
This article is co-authored by LTC Dr. Martin Weber and Dr. Holger Schulz, Zentrales Institut des Sanitätsdienstes der Bundeswehr München, Außenstelle Munster, Laborgruppe Chemie der Gifte/ Kampfstoffanalytik, Humboldtstr. 1, D-29633 Munster, e-mail: [email protected], Tel. +49 (0)5192-136481. The laboratory is accredited for the determination of ricin, abrin and modeccin with the above methods according to ISO 17025 by the German Accreditation Body Berlin (DAkkS). On demand, we investigate your suspicion samples with these accredited methods. Literature can be requested from the authors.