Ricin

Overview

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Ricin

"Ricin is protein toxin found in castor beans which are obtained from the plant _Ricinus communis_ and it is a residual product obtained during the production of castor oil has applications as a purgative, an engine lubricant, and as a component of brake and hydraulic fluid. Ricin can be in the form of a powder, a mist, or a pellet.

 

Manufacture of Ricin

One million tons of castor beans are used every year for producing the oil. The waste mash obtain from the oil production process can have as much as 5 percent ricin by weight and it is easily and inexpensively isolated via a simple process in a low technology setting using materials easily obtainable.

 

Structure And Biochemistry Of Ricin

The tertiary structure of ricin was shown to be a globular, glycosylated heterodimer of approximately 60-65 kDA. Ricin toxin A chain (RTA) and ricin toxin B chain (RTB) are of similar molecular weight, approximately 32 kDA and 34 kDA respectively.

*Ricin A Chain is an N-glycoside hydrolase composed of 267 amino acids. It has three structural domains with approximately 50% of the polypeptide arranged into alpha-helices and beta-sheets. The three domains form a pronounced cleft that is the active site of RTA.

*Ricin B Chain is a lectin composed of 262 amino acids that is able to bind terminal galactose residues on cell surfaces. RTB form a bilobal, structure lacking alpha-helices or beta-sheets where individual lobes contain three subdomains. At least one of these three subdomains in each homologous lobe possesses a sugar-binding pocket that gives RTB its functional character.

 


Mode of action

Ribosome Inactivation

Ricin works by getting inside the cells of a person’s body and preventing the cells from making the proteins they need. Without the proteins, cells die, and eventually the whole body can shut down and die.

Study of the N-glycosidase activity of ricin was pioneered by Endo and Tsurugi who showed that RTA cleaves a glycosidic bond within the large rRNA of the 60S subunit of eukaryotic ribosomes. They subsequently showed RTA specifically and irreversibly hydrolyses the N-glycosidic bond of the adenine residue at position 4324 (A4324) within the 28S rRNA, but leaves the phosphodiester backbone of the RNA intact. The ricin targets A4324 that is contained in a highly conserved sequence of 12 nucleotides universally found in eukaryotic ribosomes. The sequence, 5’-AGUACGAGAGGA-3’, termed the sarcin-ricin loop, is important in binding elongation factors during protein synthesis. The depurination event rapidly and completely inactivates the ribosome, resulting in toxicity from inhibited protein synthesis. A single RTA molecule in the cytosol is capable of depurinating approximately 1500 ribosomes per minute.


Potential medicinal use

Ricins may have therapeutic use in the treatment of cancer, as a so-called "magic bullet" to specifically target and destroy cancer cells: Ricin could be linked to a monoclonal antibody to target malignant cells recognized by the antibody. Modification of ricin is believed to be possible to lessen its toxicity to humans, but not to the cancer cells. A promising approach is also to use the non-toxic B subunit as a vehicle for delivering antigens into cells thus greatly increasing their immunogenicity. Use of ricin as an adjuvant has potential implications for developing mucosal vaccines.

Use as a chemical/biological warfare agent

Ricin as a weapon: Ricin can be used as a weapon by—

 

*Releasing it into the air (as a powder or mist) and having people breathe it in (inhalation);

*Putting it into food or water (as a powder or mist) and having people eat or drink it (ingestion); or

*Injecting it into people’s bodies (for example, by using a syringe).

 

As a weapon of bioterrorism, ricin would most likely be dispersed as an aerosol although contamination of food and water supplies is also feasible. The major reason it is dangerous is that there is no specific antidote, and that it is very easy to obtain (the castor bean plant is a common ornamental, and can be grown at home without any special care). There have been several reported incidents where ricin has been involved with infanticide where small children have been tricked into eating castor beans because of their striking resemblance to chocolate covered coffee beans. Ricin is actually several orders of magnitude less toxic than botulinum or tetanus toxin, but those are more difficult to obtain.


How likely is someone to die from ricin poisoning?

The seriousness of poisoning caused by ricin depends on the purity of the ricin used, the amount of ricin a person comes into contact with, the length of time that a person is exposed and the way a person comes into contact with it. If ricin is injected or inhaled (breathed in), as little as 500 micrograms of ricin – an amount that would fit on the head of a pin – could be enough to kill an adult. A greater amount would likely be needed to kill someone if the ricin was put in food or drink.

 

Treatment for ricin poisoning

 

Prevention of illness after contact: First, leave the area where the ricin was released and move to fresh air.

o        Remove clothing.

*Quickly take off clothing that may have ricin on it. If possible, any clothing that has to be pulled over the head should be cut off the body instead so the ricin does not get near the eyes, mouth or nose. If helping other people remove their clothing, try to avoid touching any areas that may have ricin on them, and remove the clothing as fast as possible.

o        Wash affected areas.

*As quickly as possible, wash any ricin from the skin with lots of soap and water.

*If the eyes are burning or vision is blurred, rinse the eyes with plain water for 10 to 15 minutes.

*If contact lenses are worn, remove them and put them with the clothing. Do not put the contacts back in. If eyeglasses are worn, wash them with soap and water. Eyeglasses can be put back on after they are washed.

o        Discard contaminated items.

*Place the clothing and any other contaminated items that may have come into contact with ricin inside a plastic bag. Avoid touching them by wearing rubber gloves, turning the bag inside out and using it to pick up the clothing, or putting the clothing in the bag using tongs, tool handles, sticks or similar objects. Anything that touches the contaminated clothing should also be placed in the bag.

*Seal the bag, and then seal that bag inside another plastic bag.

*Contact the local county health department right away. The health department or emergency personnel will arrange for further disposal. Do not handle the plastic bags yourself.

If someone has ingested ricin, do not make the person vomit and do not give fluids to drink.

 

Treatment of illness: There is no specific treatment for ricin poisoning. After poisoning, it is important to get the ricin  out of the body as quickly as possible. Supportive care in a hospital is the standard treatment.

 

Medical care could include helping victims , giving them intravenous fluids, giving them medications to treat conditions such low blood pressure, flushing their stomachs with activated charcoal (a substance that binds with the poison in the stomach) or washing their eyes with water.  Acetaminophen for fever, and cough suppressants may make the patient more comfortable. Hydration is important. For those with pulmonary intoxification, respiratory support may be necessary. Standard management techniques for oral poisoning should be used if the toxin is ingested.

There is no vaccine for ricin poisoning.

 

Rapid diagnostic assay

 

Nasal or throat swabs and respiratory secretions may be collected for toxin assay. Blood for serum may be collected. Toxin assays and measurement of antibody response can be performed on serum. ELISA's are available for the detection of ricin. If ricin is  use as a weapon, clustering of patients with similar symptoms may be the first and only clue.


Symptoms of ricin poisoning

The major symptoms of ricin poisoning depend on the way someone comes into contact with it and the dose received. Many organs may be affected in severe cases.

*Inhalation (breathing it in): Breathing in ricin may cause difficulty breathing, fever, cough, nausea and tightness in the chest. Heavy sweating and fluid build-up in the lungs may follow. This would make breathing even more difficult, and the skin may turn blue from lack of oxygen flowing through the body. Low blood pressure and lung failure may occur, leading to death.

*Ingestion (eating or drinking it): Eating or drinking ricin may cause vomiting, bad stomach pain, cramping and bloody diarrhea. Severe dehydration may be the result, followed by low blood pressure. The person may experience hallucinations, seizures and bloody urine. Within a few days, the person’s liver, spleen and kidneys could stop working, and the person could die.

*Injection (via a syringe): Injecting ricin into a person may cause flu-like symptoms including nausea, vomiting and lack of energy. There may be pain and swelling by the spot of the injection. An injection of a small amount of ricin will cause the death of cells or tissue and stomach bleeding. It also will cause many of the body’s organs to shut down.

*Skin and eye contact : Ricin in powder or mist form can cause redness and pain to the skin and the eyes.


Detected ricin incidents

1978 assassination of Georgi Markov

On 7 September 1978 the Bulgarian dissident Georgi Markov was stabbed in the leg in public on Waterloo Bridge in the middle of London by a man using a weapon built into an umbrella. The weapon embedded a small pellet in Markov's leg which contained ricin. Markov died four days later

 

2003 envelope in South Carolina

 

In 2003, a package and letter sealed in a "ricin-contaminated" envelope was intercepted in Greenville, South Carolina, at a United States Postal Service processing center.

 

2006 home in Richmond, Virginia

 

In January 2006, ricin was found in a home in suburban Richmond, Virginia in the form of mashed castor beans. Although the suspect, Chetanand Sewraz, was allegedly isolating the toxin to kill his estranged wife, and not for some form of bioterrorism.

 

2008 hotel room in Las Vegas, Nevada

 

In February 2008, a man who stayed in a Las Vegas, Nevada motel room where ricin was found was taken to hospital in critical condition. The man, Roger Von Bergendorff, was hospitalized on February 14; however, the ricin was not found until February 27 when a relative retrieved his luggage because the motel had not been paid for two weeks several vials of ricin were found, police reported.

Ricin biosynthesis

Ricin and RCA are synthesized in the endosperm cells of maturing seeds, and are stored in an organelle called the "protein body", a vacuolar compartment. When the mature seed germinates, the toxins are destroyed by hydrolysis within a few days.

Ricin begins synthesis as a prepropolypeptide that contains both A and B chains. The signal sequence of the Nh3-terminus targets the nascent chain to the endoplasmic reticulum (ER) and is then cleaved off. As the proricin polypeptide elongates it is N-glycosylated within the lumen of the ER. Protein disulfide isomerases catalyze disulfide bond formation as the proricin molecule folds itself. Proricin undergoes further oligosaccharide modifications within the Golgi complex and then is transported within vesicles to the protein bodies.

Ricin is not catalytically active until it is proteolytically cleaved by an endopeptidase within the protein bodies. This splits the polypeptide into the A chain and the B chain still linked by a single disulfide bond. Since ricin is inactive until then, the plant avoids poisoning its own ribosomes in case some proricin accidentally passes into the cytosol during synthesis and transport.

In 1978, ricin was used to assassinate Georgi Markov in 1978, a Bulgarian journalist who spoke out against the Bulgarian government. He was stabbed with the point of an umbrella while waiting at a bus stop near Waterloo Station in London. They found a perforated metallic pellet embedded in his leg that had presumably contained the ricin toxin. Castor beans are used as an ingredient in some animal feeds after the oil has been extracted or inactivated by heating for 20 minutes at 140oC. Attempts to use castor beans in feed for livestock involve different methods of inactivating ricin while maintaining nutritional value. Some studies have shown that even after such heat treatment, toxicity remains. For example, it was lethal to mallard ducks given the feed. "The toxicity of the meal could be due to either a heat stable or growth inhibiting factor or due to minute residues of ricin"(Okoye et al.)

A study with sheep showed that autoclaved castor-bean-meal can be incorporated to 10% of sheep rations without any ill effect.

Poisoning of livestock usually occurs by accidental incorporation of castor beans in their feed. Horses are particularly vulnerable.

Reference

 

(Most of the contents are derived from works in Wikipedia: Ricin -- Ed.)


http://www.biology-online.org/articles/ricin.html