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Ricin Toxicity

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Last Update: July 11, 2019.

Introduction

Ricin is a naturally occurring carbohydrate-binding protein produced in the seeds of Ricinus communis, the castor oil plant. It is toxic when inhaled, ingested, or injected. As few as five to ten micrograms per kilogram can be lethal.

Etiology

Ricin is a lectin (carbohydrate-binding protein) produced in the endosperm of the seeds of the castor oil plant. Ingestion of as few as two castor oil plant seeds has been shown to be toxic, although patients have survived ingesting as many as 30. Ricin is also toxic by inhalation or injection, and as little as five to ten micrograms per kilogram by inhalation can be lethal. Ricin was developed as a biological weapon by both the United States and the Soviet Union. The castor oil plant grows in the wild in tropical climates. Approximately two million tons of castor seeds are produced yearly around the globe. Castor seeds can be crushed to extract castor oil, which has industrial applications in lubricants, dyes, preservatives, and pharmaceuticals. The waste mash of castor seeds after the oil extraction process is approximately 5% ricin by weight. This waste can be detoxified and used as a fertilizer or as a supplement in animal feed. [1] [2]

Epidemiology

If a group was targeted as part of a ricin attack, the presentation of some patients with a history of being at a particular place at the same time and complaining of similar symptoms consistent with the route of exposure would likely be the first epidemiologic red flag. Sudden onset of respiratory distress among several people in one place would evidence of aerosol exposure. Nausea, vomiting, and gastrointestinal hemorrhage would common in an ingestion exposure. [1]

Pathophysiology

Ricin is a globular glycoprotein that is composed of different protein chains connected by a disulfide bond. It is classified as a Type II ribosome-inactivating protein (RIP). The ricin toxin A chain inactivates ribosomes by hydrolyzing the N-glycosidic bond of an adenosine residue in the 28 S ribosomal RNA of eukaryotic cells; this inhibits protein synthesis by blocking the binding of elongation factors. This inhibition of protein synthesis by the ricin toxin A chain is a mechanism of ricin toxicity. The ricin toxin B chain binds to carbohydrates on the surface of eukaryotic cells and facilitates entry of the toxin into the cell. Ricin can enter the cell by numerous mechanisms including both receptor-mediated and adsorptive-mediated endocytosis. After endocytosis, ricin is transferred by vesicular transport from early endosomes to the trans-Golgi network, then undergoes retrograde vesicular transport through the Golgi apparatus. Ricin has been shown to be transported from the Golgi apparatus to the endoplasmic reticulum by the chaperone protein calreticulin. Once ricin reaches the endoplasmic reticulum, the disulfide bond between the A chain and the B chain is reduced by protein disulfide isomerase. The A chain then undergoes partial unfolding, after which it crosses the endoplasmic reticulum membrane via the Sec61p translocon. The unfolded A chain avoids ubiquitination because of its low lysine content, thus enabling the A chain to evade degradation by proteasomes and refold into its biologically active conformation, after which it resumes catalytic activity. [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

Toxicokinetics

Ricin toxin A chain can inactivate approximately 1500 ribosomes per minute. There are reports that a single molecule of ricin reaching the cytosol can be lethal to a cell. The lethal oral dose by ingestion in humans is estimated to be one to twenty milligrams per kilogram. As little as five to ten micrograms per kilogram by inhalation can be lethal. [21] [22] [23] [7] [8] [9] [10] [15] 

History and Physical

Symptoms of ricin ingestion include nausea, vomiting, diarrhea, hematemesis, and melena. Necrosis of the spleen, liver, and kidneys may occur. Inhalation exposure symptoms include a cough, wheezing, dyspnea, sore throat, and congestion. Exposed patients may go on to develop pulmonary edema and pneumonia. Symptoms of injection exposure include erythema, induration, blisters, capillary leak syndrome, and localized necrosis surrounding the injection site. These symptoms may progress to seizures, shock, organ failure, pulmonary edema, and respiratory failure. Symptoms may begin within a few hours if ingested; however, symptoms may start almost immediately or may not be apparent for several hours in cases of ingestion or inhalation. [4]

Evaluation

Laboratory testing for ricin includes liquid chromatography-mass spectrometry and immunoassays. Laboratory studies may show leukocytosis, electrolyte abnormalities, liver failure, renal failure, and coagulopathy. Chest radiography may be normal or may show pulmonary edema or pneumonia in people with inhalational exposure. [24] [25] [26] [27] [28] [29] [30]

Treatment / Management

All symptomatic patients with suspected ricin exposure should be admitted. The treatment of ricin toxicity is supportive and includes management of shock, correction of electrolyte abnormalities, respiratory support, and treatment of seizures. Patients exposed to ricin by inhalation may require airway management and positive-pressure ventilation. Activated charcoal can be given to patients who have ingested ricin if vomiting has not yet occurred and the patient's airway has been secured. Gastric lavage can be used if the patient ingested ricin within the past hour. Electrolytes, coagulation studies, renal function, and liver function should be monitored; coagulopathies and electrolyte abnormalities should be corrected. There is no ricin antidote available for humans. [31] [32] [33] [34]

Pearls and Other Issues

Ricin was used in the assassination of Bulgarian dissident Georgi Markov in London in 1978; a pellet containing ricin was found in his leg during an autopsy. A Bulgarian defector, Vladimir Kostov, survived a similar assassination attempt in Paris involving the injection of a pellet containing ricin under his skin ten days prior. In August 1981, double-agent Boris Korczak survived being shot by an air gun with a pellet containing ricin while at a grocery store in Virginia. In 2003, ricin was detected in a facility that handled mail for the White House. However, no one was harmed. In April 2013, envelopes addressed to President Barack Obama, Mississippi Senator Roger Wicker, and Lee County, Mississippi Judge Sadie Holland tested positive for ricin; Tupelo, Mississippi, resident Everett Dutschke was arrested later that month and plead guilty in May 2014. In May 2013, actress Shannon Richardson mailed letters containing ricin to President Barack Obama, New York City Mayor Michael Bloomberg, and Mark Glaze, who at that time was executive director of Mayors Against Illegal Guns. All suspected cases of ricin exposure should be reported to poison control and the health department. Ricin is included on the United States Department of Health and Human Services Select Agents and Toxins List under 42 CFR 73.3. [35] [36] [34]

Enhancing Healthcare Team Outcomes

Recent use of ricin demonstrates how incidents involving ricin will quickly become international news. Once a patient has been poisoned with ricin, healthcare providers will be responsible for communicating not only numerous colleagues and staff but also with public health officials, law enforcement agencies, members of the media, and elected officials. In attacks involving numerous numbers of casualties or high-profile targets such as elected officials, the marshaling of resources to respond will almost certainly reach the national level. (Level V)

Important interprofessional communication points early in the care of the patient among physicians, nurses, and pharmacists will include adequate decontamination of the patient and appropriate precautions for first responders and hospital staff to avoid additional casualties. Training and education prior to such an event will be more effective than just-in-time training after an event has occurred when emotions run high and resources may run low. In large-scale events, it will be essential for healthcare staff to have a clear understanding of their available resources as well as the anticipated demands on those resources, and continuously communicating with government officials to access medical supply stockpiles and resources for the capacity to treat large numbers of patients will be vital. (Level V)

Questions

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