Ricin

Ricin is a highly toxic protein that is derived from the bean of the castor plant (Ricinus communis). The toxin causes cell death by inactivating ribosomes, which are responsible for protein synthesis. Ricin can be produced in a liquid, crystal or powdered forms and it can be inhaled, ingested, or injected. It causes fever, cough, weakness, abdominal pain, vomiting, diarrhea, dehydration, and death. There is no cure for ricin poisoning, and medical treatment is simply supportive.

Ricin comes from castor beans, which produce castor oil, a component of brake fluid and hydraulic fluid. One million tons of castor beans are processed each year and the resulting waste mash contains 5–10% ricin. The 66,000 Dalton protein can be purified from the mash using chromatography. Once purified, ricin is a very stable molecule, able to withstand changes in environmental conditions.

The protein composed of two hemaglutinins and two toxins (RCL III and RCL IV). The toxins are made up of an A polypeptide chain and a B polypeptide chain, which are joined by a disulfide bond. The general molecular structure of ricin is similar to other biologically produced toxins, such as botulinum, cholera, diptheria and tetanus.

The B portion of ricin binds to glycoproteins and glycolipids that terminate with galactose on the exterior of cell membranes. The toxin is then transported inside the cell by endocytosis. Once inside the cytosol of the cell, the A portion of the molecule binds to the 60S ribosome, stopping protein synthesis. A single molecule of ricin can kill a cell.

Ricin poisoning can occur by dermal (skin) exposure, aerosol inhalation, ingestion, or injections and the symptoms vary depending on the route of exposure. If ricin comes in contact with the skin, it is unlikely to be fatal, unless combined with a solvent such as dimethyl sulfoxide (DMSO). Aerosol inhalation can cause fever, chest tightness, cough, nausea, and joint pain within four to eight hours. Respiratory cell death can prelude respiratory failure. If ricin is ingested, it can cause severe lesions in the digestive system within two hours of exposure. It may cause abdominal pain, nausea, vomiting, and bloody diarrhea. Eventual complications include cell death in the liver, kidney, adrenal glands, and central nervous system. Injection of ricin causes local cell death in muscles, tissue, and lymph nodes. Ricin poisoning causes death generally within three to five days, although a victim may survive after the fifth day.

There is no cure for ricin poisoning, although a vaccine is currently under development. Treatment for dermal exposure includes decontamination using soap and water or a hypochlorite (bleach) solution, which deactivates Ricin. In case of aerosol inhalation, treatment is the administration of oxygen, intubation, and ventilation. Ingestion of ricin is treated with activated charcoal.

The most famous case involving ricin is the assassination of the Bulgarian dissident, Georgi Markov. In 1978, Markov was working in London as a British Broadcasting Company (BBC) correspondent. As he was walking across Waterloo Bridge, a man jabbed the tip of an umbrella into Markov's right thigh, murmured an apology and slipped away into the crowd. Markov died four days later. After the collapse of the Soviet Union, the new Bulgarian government admitted that their Secret Service had been responsible for the murder. The KGB produced the murder weapon: an umbrella modified to inject a 1.7 mm platinum pellet filled with ricin into Markov's leg.