Ricin

I recently watched a Youtube video about natural poisons. One of poisons that they talked about was Ricin. I had heard of this poison before in a TV show or movie before so I decided to read more about it. This is what I found.

Ricin structure.

Ricin is known as a highly toxic lectin which is naturally occurring. lectins are one of many types of proteins that can bind to a cell's membrane. Ricin is produced by in the seeds of the castor plant. According to the CDC  "the LD50 by intravenous injection is about 5 µg/kg, whereas it is 20 mg/kg by intragasteric route.23,24 The ricin aerosol LD50 for NHP is estimated to be 10-15 µg/kg.17 The human lethal dose has not been established rigorously, but may be as low as 1-5 mg of ricin by injection 25 or by the aerosol route" This shows just how little Ricin is needed to kill a human.

Just some quick backstory on what median lethal dose is means. Median lethal dose its a means to measure how lethal a toxin is. It means that its dose required to kill half the members of a tested population after a specified test duration. LD50 is simply and abbreviation meaning lethal dose 50%. A lower LD50 number means more toxicity. This test was first done in 1927 by J.W. Trevan. The main way to find the LD50 is to simply test the substance on lab rats. The LD50 test can be some what unreliable as the variation is so great between different species' immune system and physiology.

Ricin has been around for some time. according to Globalsecruity.org "During World War I, the United States explored ricin as a potential offensive biological weapons toxin at the American University Experimental Station. Two methods of weaponizing ricin were explored: bullets and shrapnel coated with ricin toxins or a 'dust cloud' of toxin toxins inhaled into the lungs." Recently some terrorist groups have experimented with using ricin as a weapon and caused several incidents of the poisons being mailed to U.S. politicians. For example, A letter containing ricin was allegedly sent  to American President Barack Obama at the same time.

Ricin is extremely toxic if inhaled, injected, or ingested. It kills by slowing or stopping protein synthesis. This means that ricin prevents cells from assembling amino acids into proteins. A Cornell university resource goes much more in-depth about this. According to the Cornell university college of agriculture and life sciences "Ricin inhibits protein sythesis by specifically and irreversibly inactivating eukaryotic ribosomes." It goes on to say "These "ribosome-inactivating proteins" (RIPs) are typically N-glycosylated, 30 kDa monomers (Type 1 RIPs). However, in order to bind to the cell surface galactosides and enter the cytosol to reach ribosomes, they require a second monomer, a galactose-binding, 30 kDa lectin. The monomers are joined by a disulfide bridge to form the toxic heterodimers (Type 2 RIPs)." Here is a diagram showing the life cycle of ricin as it inter acts with the cells.

Sources:

http://emergency.cdc.gov/agent/ricin/qa.asp
http://www.cdc.gov/biosafety/publications/bmbl5/BMBL5_sect_VIII_g.pdf
http://www.globalsecurity.org/wmd/intro/bio_ricin.htm
http://www.ansci.cornell.edu/plants/toxicagents/ricin.html

http://www.theguardian.com/world/2013/jun/08/shannon-richardson-ricin-plot-husband