Deadly plant series: *Riccinus communis* and the curious case of Georgi Markov

It was on the morning of September 7, 1978. Georgi Markov was at the bus stop waiting for the arrival of a vehicle that will convey him to the British Broadcasting Corporation complex where he earns his daily bread as a journalist and a broadcaster. At this time of the day, the bus stop on the south side of the Waterloo Bridge in London is usually packed with commuters trying to get to their various destinations for one appointment or the other. If he could have it his way, he would rather be at home and serve his country in any worthy capacity.

He has fled his home country a few years back when he saw that his life could be in danger as a dissident writer and a critic of the Bulgarian communist government. Despite studying chemical engineering and working as a chemical engineer and technical school teacher, he has grown to love literature. Hence, little wonder that he had a successful career as an acclaimed novelist, a playwright and a scriptwriter with the majority of his work been critical of the communist government. Hence, it came as a little surprise when he was labelled 'persona non grata' by the government. He first fled to Italy and then to Britain where he settled down as a political asylum seeker. Perhaps he would return to his home country one day, he thought.

A sharp, insect-bite like pain at the back of his right thigh jolted him back to life. Almost at the same time, a heavily built man with a foreign accent (later suspected to be a KGB agent) stooped to pick an umbrella beside him and mumbled 'sorry' before dashing to board an already waiting taxi at the other side of the street. Georgi Markov did not think much about the incident and continued with the activities of the day until he developed fever later on. He was admitted to the hospital in the evening and died three days after as a result of complications due to the sickness.

After series of investigations and coronary examination, he was purported to have died from a biological compound known as ricin which was shot in form of a pellet from an umbrella gun (picked by the built, accented man at the bus stop). How could something so minute have such a potent, deleterious effect?

Ricin

Ricin is a biological compound found in a plant known botanically as Ricinus communis. The compound which happens to be one of the most toxic and biologically poisonous substances in nature was first isolated from the seeds of the plant in the year 1888 by a German researcher Peter Hermann Stillmark.

^{Structure of ricin By AzaToth - CC BY 3.0, Link}

Ricin in purified form could be lethal in minute quantity if ingested, inhaled or injected into the human body. The purified form of the compound appears in form of a white powder and only a few grains of it is needed to cause mortality in an adult human. According to the European Food Safety Authority (EFSA), about 22 micrograms of the substance per kilogram body weight constitutes the mean lethal dose to human if it is injected or inhaled into the body. However, ingested forms have been reported to have less toxic effects due to the fact that some of the substance becomes inactivated within the stomach.

The purified form of ricin can be derived from the seeds of Ricinus communis or from the waste generated during the production of castor oil. The later has been reported to have a wide variety of medicinal as well as cosmetic uses. It has been repoted by several works of literature to have antimicrobial, anti-inflammatory as well as moisturising properties.

The bioactive compound derived its toxicity properties from its ability to inhibit protein synthesis as well as causes cell's death in the human body. It has actually been classified as a type 2 ribosome inactivation protein in some quarters. Few hours after entering the body system, ricin induces symptoms of poisoning as a result of rapid induction of apoptosis in the cells of the body. At sub-lethal doses, the biological compound has been found to be effective in selectively stimulating and programming the death of cancerous cells in the body. This particular ability opens up a new area of research of the compound as a potential candidate for the development of anticancer drugs.

Due to its toxicity to the body at a very low level of injection, ingestion or inhalation, and its relatively low cost of isolation, ricin has been considered in various quarters as a potential weapon in biological warfare. A host of countries such as United State and Britain have actually attempted to infuse ricin into bombs and artilleries that would disperse tiny pellets of the substance into the air during assaults. However, the idea was jetissioned due to the fact that the compound degrades under the effect of heat from the firing and explosion.

The plant itself: Ricinus communis

Ricinus communis is commonly known as castor oil or castor bean plant. It is a flowering, perennial shrub (grows to about 1.5 m) belonging to the Euphorbiaceae plant family. The plant is native to the Eastern Africa, Mediterranean Basin and India but usually grown as exotic ornamental species in several other countries.

^{By Tubifex - CC BY-SA 3.0, Link}

Phytochemical analysis of the tissues of castor oil plant showed the presence of bioactive compounds such as flavonoids, phenolic compounds, fatty acids, amino acids, terpenoids and a host of others. These substances are in addition to the ricin component. Different parts of the plant have been and are still been utilized in the treatment of a wide variety of ailments. According to Marwat and his co-researchers, the plant has demonstrated its effectiveness in the treatment of diseases/disorders such as arthritis, back and muscle aches, bilharziasis, chronic headache, constipation, expulsion of placenta during births, gallbladder related pains, menstrual cramps, rheumatism, insomnia and a lot of other diseases.

Barring any incident of mistaken ingestion, injection and inhalation of ricin, Ricinus communis plant and its product can be put to good or evil usage, depending on whose hand it falls.

Thank you all for reading.

References

aubg daily

jd crighton

britannica

phytojournal

wikipedia

researchgate