|Jmol-3D images||Image 1|
|Molar mass||196.20 g/mol|
|Melting point||212 °C|
|Main hazards||Highly toxic|
|LD50||0.03–0.5 mg/kg (human)|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)|
|(what is: / ?)|
Cantharidin, a type of terpenoid, is a chemical compound secreted by many species of blister beetle, and most notably by the Spanish fly, Lytta vesicatoria. The false blister beetles, cardinal beetles and soldier beetles also produce cantharidin. It is a poisonous substance, acting as a blister agent, and can cause severe chemical burns, but these same properties make it effective as a topical medication.
Cantharidin was first isolated in 1810 by Pierre Robiquet, a French chemist then living in Paris, from Lytta vesicatoria. Robiquet demonstrated that cantharidin was the actual principle responsible for the aggressively blistering properties of the coating of the eggs of that insect, and established that cantharidin had definite toxic properties comparable in degree to those of the most virulent poisons known in the 19th century, such as strychnine. It is an odorless and colorless solid at room temperature. It is secreted by the male blister beetle and given to the female as a copulatory gift during mating. Afterwards the female beetle will cover its eggs with it as a defense against predators. The complete mechanism of the biosynthesis of cantharidin is currently unknown.
The level of cantharidin in blister beetles can be quite variable: Among blister beetles of the genus Epicauta in Colorado, E. pennsylvanica contain approximately 0.2 mg, E. maculata contain 0.7 mg, and E. immaculata contain 4.8 mg per beetle; males also contain higher levels than females.
Medical risks for humans
As a blister agent, cantharidin has the potential to cause adverse effects when used medically; for this reason, it has been included in a list of "problem drugs" used by dermatologists and emergency personnel. However, when compounded properly and applied in the clinic topically by a medical provider familiar with its effects and uses, cantharidin can be safely and effectively used to treat some benign skin lesions like warts and molluscum.
When ingested by humans, the LD50 is around 0.5 mg/kg, with a dose of as little as 10 mg being potentially fatal. Ingesting cantharidin can initially cause severe damage to the lining of the gastrointestinal and urinary tract, and may also cause permanent renal damage. Symptoms of cantharidin poisoning include hematuria, abdominal pains, and rarely priapism.
The extreme toxicity of cantharidin makes any use as an aphrodisiac highly dangerous. As a result, it is illegal to sell (or use) cantharidin or preparations of spanish fly for this purpose in many countries.
Medical risks for animals
Horses are highly sensitive to cantharidin: the LD50 for horses is approximately 1 mg/kg of the horse's body weight. Horses may be accidentally poisoned when fed bales of fodder with blister beetles in them.
Mechanism of action
Cantharidin is absorbed by the lipid membranes of epidermal cells, causing the activation or release of serine proteases, enzymes that cleave (break) peptide bonds in proteins. This causes the disintegration of desmosomal plaques, cellular structures involved in cell-to-cell adhesion, leading to detachment of tonofilaments that hold cells together. The process leads to the loss of cellular connections (acantholysis) and ultimately blistering of the skin. Lesions heal without scarring.
Topical treatment with cantharidin appears to have some effect in an animal model of cutaneous leishmaniasis. In addition to topical medical applications, cantharidin and its analogues may have activity against cancer cells. Laboratory studies with cultured tumor cell lines suggest that this activity may relate to inhibition of protein phosphatase 2A.
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