The press has recently reported on planned terrorist attacks using ricin or castor beans. This should remind us that even if the assassination of Georgi Markov in 1978 seems a long way off, this poison should still be considered a topical issue[1].
What are we talking about?
Although we have already devoted a full article to ricin, “Ricin: a toxin of war and terrorism (CBRNe) [1]“, it seems that attempts to use this toxic agent are once again being made: this is why we are going to review the properties of this toxic agent and follow developments in its treatment in humans.
Ricin: chemical or biological weapon?
Ricin is a chemical toxin derived from a living organism: should it therefore be classified as a chemical weapon or a biological weapon?
Biological agents are living micro-organisms that cause disease in humans, plants and animals. These living micro-organisms have the property of self-replication: the effect on the population can therefore be prolonged over time, after contamination, an outbreak during which living agents are transmitted from one individual to another can result in the inactivation of a large population.
As for toxins derived from biological agents, they are not self-replicating and are therefore closer to chemical agents, with the difference that their toxic power is much greater: the LD50 (50% lethal dose) is 0.001 microgrammes per kg for botulinum toxin, whereas it is only 15 microgrammes per kg of weight for VX. In the case of toxins such as ricin, we can therefore speak of non-infectious biological weapons.
From seed to ricin
The castor-oil plant (Ricinus communis L.) contains a powerful toxicant, particularly concentrated in the seeds: ricin. The seed is highly toxic and it is generally considered that one or two seeds chewed by a child or 8 seeds chewed by an adult can be fatal.
Ricin is not soluble in oil and will therefore not be extracted during the process of obtaining the oil: castor oil therefore represents no danger (provided the oil is perfectly purified). On the other hand, the residual cake from the oil extraction process is very rich in ricin, which can be easily isolated.
Because of its ease of preparation, wide availability and potential use as a bioterrorist agent, ricin is on the list of prohibited substances in List 1A of the Chemical Weapons Convention.
Uses of ricin
Georgi Markov was murdered in London on 11 September 1978 by a dart filled with a tiny ricin pellet fired from an umbrella. This is the famous story of the “Bulgarian umbrella”! Previously, other cases had been described: two deaths in Budapest/Hungary (Balázs 1933)[2], one death in Turkey (Abdülkadir-Lütfi and Taeger 1935)[3] and ten cases of schoolchildren who survived poisoning (Karszás and Papp 1960)[4].
Several other attempts have been made. In 2003, two letters containing ricin were sent to the White House and to Senator Bill Frist. In 2013, Everett Dutschke, a martial arts teacher, sent 3 letters that tested positive for ricin to Senator Roger Wicker, President Obama and Judge Sadie Holland. Since then, ricin has been classified as a class A biological weapon.
Between November 2003 and February 2004, the US Senate and the White House were the target of a ricin attack, sent by mail in the form of powder, without causing any casualties. The discovery of its presence led to the temporary closure of three congressional buildings.
The letters were signed by a certain “fallen angel”, calling for a change in the regulations governing the working hours of American truck drivers.
In 2016, a 23-year-old man attempted suicide by aborted parenteral administration of a castor seed extract, followed by ingestion of several of the same seeds.
The most recent cases are :
A terrorist plot in Cologne in 2018 was foiled when police arrested Sief Allah H. while he was making an explosive device containing ricin. He was arrested for breaching the War Weapons Control Act (Kriegswaffenkontrollgesetz)[5].
In January 2023, German anti-terrorist police searched a flat in the west of the country and arrested an Iranian national and his brother on charges of planning an attack. The 32-year-old man under investigation is suspected of planning an attack using cyanide and ricin, according to the Düsseldorf public prosecutor’s office.
An interesting review[6] can be found here
Structure and mode of action
Ricin is a glycoprotein made up of 2 A and B chains. The 2 chains are linked by a disulphide bridge. It has long been recognised that the isolated A and B chains are not toxic. The B chain, with lectin-like activity, is responsible for binding to galactose-containing receptors on the surface of eukaryotic cells, which is essential for the internalisation of the A chain by endocytosis. The A chain has N-glycosidase activity, which leads to irreversible depurination of adenine from 28S ribosomal RNA, thus putting an end to protein synthesis. This synergy between the A and B chains inactivates the ribosome, resulting in high cytotoxicity after oral or inhalation administration.
Symptoms
If ingested, the initial symptoms appear within 6 to 12 hours and affect the digestive system: nausea, vomiting and abdominal pain. Symptoms can progress rapidly (generally within 12 to 24 hours), leading to other complications such as severe dehydration and kidney and liver problems.
Inhalation is 1000 times more toxic than ingestion. The first symptoms may appear within 4 to 6 hours. Serious symptoms may appear up to 24 hours after exposure: breathing difficulties, shortness of breath, chest tightness and coughing. They are likely to progress rapidly (generally within 12 to 24 hours) with respiratory complications, pulmonary oedema (fluid in the lungs) and, eventually, respiratory failure. Ricin poisoning can cause death within 36 to 72 hours of exposure, depending on the form of exposure (inhalation, ingestion or injection) and the dose absorbed.
In the case of the Bulgarian umbrella Georgi Markov developed a high temperature and died within 4 days.
If you are caught in a ricin aerosol, you should avoid inhaling it and decontaminate your clothes to avoid self-contamination or cross-contamination.
Analytical detection
Basically, tests that can distinguish biologically active ricin from inactive ricin are essential for assessing both the lethality of a bioterrorist threat and the monitoring of decontamination procedures. Biological tests have limited selectivity and cannot distinguish ricin from related toxins (cholera and whooping cough).
Direct methods
Optimal assay design includes a rapid and efficient enrichment step, an A-chain activity checkpoint and a selectivity step to distinguish ricin from other bioactive toxins. A viable approach to sample enrichment would be to use sugar-conjugated materials that exploit the lectin-binding properties of ricin’s B chain (glycosphingolipids and synthetic sugars, for example). After sample enrichment, mass spectrometry can simultaneously identify ricin peptide fingerprints and in vitro RNA substrates that have been deadenylated by the ricin A chain. This test would detect the functional B chain required for cell penetration, confirm the activity of the A chain required for ribosome inactivation and selectively identify ricin as a harmful toxin.
Immunological tests, such as ELISA (Enzyme-Linked Immunosorbent Assay), can be used to specifically detect ricin in a sample.
Indirect methods
The alkaloid ricinine is also produced by this plant. It is present throughout the castor plant from the beginning of germination until the seeds ripen. Ricinine is commonly used to detect ricin poisoning because it is eliminated from the body in the urine and is easily identified by GC-MS or LC-MS.
Molecular methods
PCR can now be used to detect ricin DNA: using RT-PCR, the level of DNA can be quantified to give an indication of the level of contamination.
It is essential to note that ricin detection can differ depending on the type of sample (biological fluid, food, environment, etc.) and the means available. Laboratories specialising in the detection of dangerous biological agents are usually equipped to carry out these analyses.
New therapeutic approaches
There is currently no effective antidote, vaccine or other specific treatment for ricin poisoning or prevention. Research has been carried out to treat or prevent ricin poisoning using neutralising antibodies, but most anti-ricin antibodies have shown no neutralising activity or have only shown neutralising activity in vitro. Antibodies directed against epitopes close to the binding interface of the ricin A and B chains have better neutralising performance.
According to recent data, antibody cocktails composed of A and B chain antibodies show better neutralising activity at lower antibody doses than antibodies directed against a single chain.
In all cases, Inserm, in collaboration with other laboratories including IRBA, has developed a nebuliser that allows the active molecules to penetrate deep into ricin-infected lungs.
Symptomatically, patients infected by airborne ricin are placed on respiratory assistance and those who have consumed ricin undergo gastric lavage. Activated charcoal can also be administered to trap ricin that has not yet fixed.
Conclusion
Castor oil has been known since ancient times: castor oil seeds found in Egyptian tombs were used to extract oil for lighting.
Ricin can be used as part of a terrorist attack, which is why it is important to recognise the first clinical signs. However, aerosol toxicity, although far more effective than digestive toxicity, is not easy to apply. Actual cases of ricin poisoning currently only involve ingestion or injection.
References
1 Ricin: an ancient toxicant, but still an evergreen, Archives of Toxicology https://doi.org/10.1007/s00204-023-03472-w
2 [2] Balácz J (1933) Vergiftungs-Statistik aus Ungarn. Vergiftungsfälle (arch Toxicol) 4:A236–A270. https:// doi. org/ 10. 1007/ BF024 62717
3 [3] Abdülkadir-Lütfi, Taeger (1935) Tödliche Vergiftung durch Rizinussamen. Vergiftungsfälle (Arch Toxicol) 6:97–98. https://doi.org/10.1007/BF02454427 [4]
4 [5] Karzás T, Papp T (1960) Ricinussamen-Vergiftung von Schulkindern. Arch Toxicol 18:145–150. https://doi.org/10.1007/BF00577279
5 [6] Anonymous (2023) 2018 Cologne terrorist plot. Wikipedia. Last edited 27 Jan 2023. Accessed 3 Feb 2023. https://en.wikipedia.org/wiki/ 2018_Cologne_terrorist_plot
6 [7] https://jamanetwork.com/journals/jama/fullarticle/201818