Oenanthotoxin is atoxin extracted from hemlock water-dropwort (Oenanthe crocata) and other plants of the genusOenanthe. It is a central nervous system poison, and acts as anoncompetitive antagonist of theneurotransmittergamma-aminobutyric acid.[1] A case has been made for the presence of this toxin in localOenanthe species playing a causative role in euthanasia in ancient Sardinia.[2][3] It was crystallized in 1949 by Clarke and co-workers.[4] It is structurally closely related to the toxinscicutoxin[5] andcarotatoxin.[6][7] Oenanthotoxin is a C17 polyacetylene isomer of cicutoxin.
Oenanthotoxin concentration in plants is dependent on seasonal changes and geographical location, the most is present during late winter and early spring.[8] Contrary to most poisonous plants that contain bitter tastes or burning sensations, the water dropwort has a rather sweet and pleasant taste and odor.[9] Water dropwort is characterized by a yellow liquid that changes color due to air exposure.[1][9] The roots are the most toxic part, although the entire plant contains poisonous properties.[8][10]
The discovery and use of plants containing oenanthotoxin predatesSocrates andHomer and its first use as a poison is thought to have been implemented between 1800 BC and 800 BC in Pre-Roman Sardinia.[9][11] In Ancient Sardinia, it was considered to be a humane form of euthanasia. Elderly people who were unable to care for themselves were given water dropwort and dropped from a high rock to ensure death.[9][11] It is also believed that Socrates ingested the plant when executed.[12]
A common symptom of oenanthotoxin isrisus sardonicus, better known as the Sardonic Grin, coined by Homer in the 8th century BC, due to the victim's rigid smile after ingestion.
Although oenanthotoxin is a relatively well known poison, its mechanism of action is not entirely understood. However, there is evidence that its mechanism of action is similar to that ofcicutoxin.
Oenanthotoxin is part of a group of C17 conjugatedpolyacetylenes that act as noncompetitivegamma-aminobutyric acid (GABA) inhibitors in thecentral nervous system (CNS). GABA binds to the beta-domain of theGABAA receptor in the central nervous system and activates the receptor increasing chloride ion flow across the membrane and inhibiting the neuron.[1] When oenanthotoxin is introduced to the body, it non-competitively binds to the same beta-domain receptor as GABA and prevents normal inhibitory function. Binding to the same receptor, oenanthotoxin blocks the chloride channel, allowing excessive excitation to occur. This, blockingGABAergic responses, causes hyperactivity in the neurons, resulting in convulsions, and seizures.[9]
Oenanthotoxin is extremely dangerous and toxic (LD = 0.58 mg/kg for mice),[1] there have been numerous case studies documenting the common symptoms including: convulsions, seizures, nausea, diarrhea,tachycardia,mydriasis,rhabdomyolysis, renal failure, respiratory impairment, and cardiac dysrhythmias.[1][8][9]
Below is a comprehensive table listing the recorded symptoms caused by oenanthotoxin within each system in the bodyOenanthe crocata:[1]
