Ricin Lara Coleman & Krystel Cortez

Peter Hermann Stillmark (1860 – 1923) 1888 completed his doctoral thesis “Ueber Ricin, ein giftiges Ferment aus den Samen von Ricinus comm. L. und einigen anderen Euphorbiaceen” His doctoral thesis was presented at the University of Dorpat, (one of the oldest universities in czarist Russia). Stillmark succeeded in isolating a poisonous protein component, toxine, from castor beans which he named ricin.

Where does Ricin come from? Made from castor beans, Castor beans are processed throughout the world to make castor oil. Ricin is part of the waste "mash" produced when castor oil is made. Ricin is 6,000 X more powerful than cyanide Ricin can be found in many forms: powder, mist, pellet, or it can be dissolved in water or weak acid. Ricin is a stable substance. For example, it is not affected much by extreme conditions such as very hot or very cold temperatures. ***Ricin has some potential medical uses, such as bone marrow transplants and cancer treatment (to kill cancer cells).***

Castor Bean Seed Ricinus communis Castor bean seeds are highly poisonous and can cause death even when consumed in small quantities. The primary toxin the seeds contain is ricin, a lectin that inhibits protein synthesis in animal cells and leads to cell death.

Mechanism of Action (A-B Mechanism) Ricin is a glycoprotein lectin composed of 2 chains, linked by a disulfide bond B chain facilitates the entry of ricin into cytosol B chain: binds to galactose- containing glycoproteins and glycolipids expressed on the surface of cells: facilitates the entry of ricin into cytosol. A chain: inhibits protein synthesis A chain: inhibits protein synthesis by irreversibly inactivating eukaryotic ribosomes through removal of a single adenin residue from the 28S ribosomal RNA loop…prevents chain elongation of polypeptites and leads to cell death

Three Exposure Pathways Ingestion Injection Inhalation

Ingestion No literature reports of poisoning from ingesting purified ricin – All reports refer to castor bean ingestion Median lethal dose (LD 50 ) in mice is 30mg/kg, or approximately 1000-fold higher than by injection Lethal oral dose in humans ~1-20mg of ricin/kg of body weight (~8 beans!) Animal studies: ricin is absorbed within 2 hours by both lymphatic and blood vessels, accumulates mainly in the liver and spleen and ~20% - 45% is excreted unchanged in the feces up to 72 hours after ingestion

Ingestion symptoms Symptom onset within 4 – 6 hours but may be as late as 10 hours Initial symptoms nonspecific: colicky abdominal pain, vomiting, diarrhea, heartburn, and oropharyngeal pain Fluid losses lead to electrolyte imbalances, dehydration, hypotension and circulatory collapse Leukocytosis, elevated transaminases and creatinine kinase, hyperbilirubinemia, renal insufficiency and anemia

Injection Little published data on human exposure LD 50 in mice is ~5 – 10 μg/kg After injection in rodents, the majority of ricin excretion occurs in the urine over the first 24 hours with less than 2% recovered in feces

Injection symptoms Nonspecific signs: similar to sepsis (fever, headache, dizziness, nausea, anorexia, hypotension, abdominal pain) Can be delayed for as much as 10 – 12 hours, even with high doses Local tissue damage at site of injection Clinical course may progress to multisystem organ failure Lymph nodes, kidneys and intestines may also demonstrate necrosis, hemorrhage and edema

Inhalation Significantly influenced by particle size Particles of low micron-size can deposit deeper into the respiratory tract resulting in higher mortality Particles of increasingly larger diameter typically deposit higher in the airways and can be swept up by the mucociliary system and subsequently swallowed LD 50 in mice exposed to ricin of particle sizes less than 5μm is ~3 – 5 μg/kg

Inhalation symptoms Respiratory failure likely the primary cause of morbidity in humans Respiratory symptoms as soon as 4 – 6 hours – Delays in the onset of serious symptoms are considered possible up to 24 hours after exposure Airborne ricin exposure may also cause an allergic response leading to reactive airway inflammation, rhinitis and ocular irritation 1940’s: 8 people developed fever, nausea, cough, dyspnea, chest tightness, and arthralgias within 4 to 8 hours of presumed inhalational exposure to uncharacterized ricin- containing material

Immunizations Animal studies have demonstrated the possibility of protection against inhalational and parenteral ricin through passive (ricin- specific antibodies) or active immunization Passive: protection prior to exposure Active: adequate levels of ricin-neutralizing protective antibodies would be maintained

What clinicians should consider Gastrointestinal or respiratory tract illness, especially in the setting of progressively worsening symptoms and organ dysfunction may be ricin poisoning!

Ricin CDC categorizes ricin as a Category B agent (second highest in priority) – Moderately easy to disseminate, resulting in low mortality but moderate to high morbidity

Ricin Toxicity Examples The next few slides will demonstrate how ricin can be used in the form of bioterrorism…

October 2003 Two distinct incidences Oct. 15 th Oct. 15 th : a threatening letter was discovered at a US Postal facility in Greenville, South Carolina – Author(s) of a typewritten letter claimed that he or she was a fleet owner of a tanker company and demanded that the present laws regarding truck driver hours of service regulations remain unchanged. Inside the envelope was a metal vial which contained ricin. Oct 17 th Oct 17 th : a second letter was addressed to the White House and processed through a postal facility in Chattanooga, Tennessee. (letter on next slide) – It contained a similar threatening message and was directed at the US department of Transportation, threatening the lives of millions of people. A substance contained in the letter was identified as ricin

The Umbrella Assassination You may recall this event from class September 7 th 1978 – At the south end of Waterloo Bridge, Georgi Markov, a Bulgarian dissident working for the BBC, is approaching a bus stop. Crowds of office workers jostle him as they stream past, and he gazes absently mindedly across the Tiver Thames. Suddenly he feels a sharp pain o the back of his right thigh. Turning quickly he sees a man bending down to pick up a dropped umbrella. The man says he’s sorry in a strong foreign accent. A second later, a taxi pulls up, the man jumps inside and disappears. – Within 3 days, Georgi Markov is dead. Killed by ricin somehow injected into him by the umbrella Forensic scientists explain how they dug a miniature metal pellet made of platinum iridium out of Mardov’s thigh, which had been fired into his leg with a coating of ricin.

Umbrella Assassin This tiny watch bearing with two drilled-out cavities filled with the poison, ricin, was injected into Georgi Markov's leg by an umbrella adapted with a firing mechanism and silencer. Georgi Markov

Overview Ricin, discovered in the late 1800’s is a substance 6,000 X more powerful than cyanide. Though it is a very harmful toxin, it has some potential medical uses, such as bone marrow transplants and cancer treatments. Ricin is a lectin that inhibits protein synthesis in animal cells and leads to cell death. There are three main exposure pathways. Ricin has been used in the past as a weapon and has great potential to be used as a bioterrorist weapon in the future.

References Ricin Poisoning: A comprehensive review. JAMA, November 9, 2005 vol. 294, No. 18 CDC : Ricin letters: Umbrella assasin: and Pictures: – – – – – – gnition/ricin.gif gnition/ricin.gif –