Aconitine

Aconitine
Names
IUPAC name
(1α,3α,6α,14α,16β)-8-(acetyloxy)-20-ethyl-3,13,15-trihydroxy-1,6,16-trimethoxy-4-(methoxymethyl)aconitan-14-yl benzoate
Other names
Acetylbenzoylaconine
Identifiers
302-27-2 YesY
ChEBI CHEBI:2430 YesY
ChEMBL ChEMBL507036 N
ChemSpider 214292 YesY
2617
Jmol interactive 3D Image
Image
PubChem 245005
UNII X8YN71D5WC YesY
Properties
C34H47NO11
Molar mass 645.73708
Appearance solid
Melting point 203 to 204 °C (397 to 399 °F; 476 to 477 K)
H2O: 0.3 mg/mL

ethanol: 35 mg/mL

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Aconitine is a toxin produced by the Aconitum plant, also known as devil’s helmet or monkshood. Monkshood is notorious for its toxic properties. In China, aconitine is also used in small doses as an analgesic .

Uses

Aconitine was previously used as an antipyretic and analgesic and still has some limited application in herbal medicine although the narrow therapeutic index makes calculating appropriate dosage difficult.[1]

Structure and reactivity

Aconitine belongs to the family of aconitum alkaloids and is barely soluble in water,[2] [3] but very soluble in organic solvents such as chloroform or diethyl ether. Aconitine is also soluble in mixtures of alcohol and water if the concentration of alcohol is high enough. Aconitine is very toxic due to several reactive groups. The nitrogen in one of the six-membered ring structure can easily form salts and ions. This turns the molecule into a structure with high binding affinity for polar and lipophilic structures (such as cell membranes and receptors) and makes it possible for the molecule to pass the blood-brain barrier.[4] The acetoxyl group at the c8 position can readily be replaced by a methoxy group, by heating aconitine in methanol, to produce a 8-deacetyl-8-o-methyl derivatives.[5] If aconitine is heated in its dry state, it undergoes a pyrolysis to form pyroaconitine((1α,3α,6α,14α,16β)-20-Ethyl-3,13-dihydroxy-1,6,16-trimethoxy-4-(methoxymethyl)-15-oxoaconitan-14-yl benzoate) with the chemical formula C32H43NO9.[6][7]

Synthesis

Aconitine is synthesized by the monkshood plant via the terpenoid biosynthesis pathway (MEP chloroplast pathway).

Mechanism of action

Aconitine can interact with the voltage-dependent sodium-ion channels, which are proteins in the cell membranes of excitable tissues, such as cardiac and skeletal muscles and neurons. These proteins are highly selective for sodium-ions. They open very fast to depolarize the cell membrane potential, causing the upstroke of an action potential. Normally, the sodium channels close very rapidly, but the depolarization of the membrane potential causes the opening (activation) of potassium channels and potassium-efflux, which results in repolarization of the membrane potential.

Aconitine binds to the receptor at the neurotoxin binding site 2 on the alpha-subunit of the channel protein.[8] This binding results in a sodium-ion channel that stays open longer. Aconitine suppresses the conformational change in the sodium-ion channel from the active state to the inactive state. The membrane stays depolarized due to the constant sodium-influx (which is 10-1000 fold greater than the potassium efflux). As a result, the membrane cannot be repolarized. The binding of aconitine to the channel also leads to the channel to change conformation from the inactive state to the active state at a more negative voltage.[9] In neurons, aconitine increases the permeability of the membrane for sodium-ions, resulting in a huge sodium-influx in the axon terminal. As a result, the membrane depolarizes rapidly. Due to the strong depolarization, the permeability of the membrane for potassium-ions increases fast, resulting in a potassium-reflux to release the positive charge out of the cell. Not only the permeability for potassium-ions but also the permeability for calcium-ions increases as a result of the depolarization of the membrane. A calcium-influx takes place. The increase of the calcium concentration in the cell stimulates the release of the neurotransmitter acetylcholine into the synaptic cleft. Acetylcholine binds to acetylcholine receptors at the postsynaptic membrane to open the sodium-channels there, generating a new action potential. Research with mouse nerve-hemidiaphragm muscle preparation indicate that at low concentrations (<0,1 microM) aconitine increases the electrically evoked acetylcholine release causing an induced muscle tension.[10] Action potentials are generated more often at this concentration. At higher concentration (0.3–3 microM) aconitine decreases the electrically evoked acetylcholine release, resulting in a decrease in muscle tension. At high concentration (0.3–3 microM), the sodium-ion channels are constantly activated, transmission of action potentials is suppressed, leading to non-excitable target cells or paralysis.

Metabolism

Aconitine is metabolized by cytochrome P450 isozymes (CYPs). There has been research in 2011 in China to investigate in-depth the CYPs involved in aconitine metabolism in human liver microsomes.[11] It has been estimated that more than 90 percent of currently available human drug metabolism can be attributed to eight main enzymes (CYP 1A2, 2C9, 2C8, 2C19, 2D6, 2E1, 3A4, 3A5).[12] The researchers used recombinants of these eight different CYPs and incubated it with aconitine. To initiate the metabolism pathway the presence of NADPH was needed. Six CYP-mediated metabolites (M1–M6) were found by liquid-chromatography, these six metabolites were characterized by mass-spectrometry. The six metabolites and the involved enzymes are summarized in the following table:

Metabolite Name Involved CYPs
M1 O-Demethyl-aconitine CYP3A4, CYP3A5, CYP2D6, CYP2C8
M2 16-O-Demethyl-aconitine CYP3A4, CYP3A5, CYP2D6, CYP2C9
M3 N-deethyl-aconitine CYP3A4, CYP3A5, CYP2D6, CYP2C9
M4 O-didemethyl-aconitine CYP3A5, CYP2D6
M5 3-Dehydrogen-aconitine CYP3A4, CYP3A5
M6 Hydroxyl-aconitine CYP3A5, CYP2D6

Selective inhibitors were used to determine the involved CYPs in the aconitine metabolism. The results indicate that aconitine was mainly metabolized by CYP3A4, 3A5 and 2D6. CYP2C8 and 2C9 had a minor role to the aconitine metabolism, whereas CYP1A2, 2E1 and 2C19 did not produce any aconitine metabolites at all. The proposed metabolic pathways of aconitine in human liver microsomes and the CYPs involved to it are summarized in the table above.

Toxicity

The toxic effects of aconitine have been tested in a variety of animals, including mammals (dog, cat, guinea pig, mouse, rat and rabbit), frogs and pigeons. Depending on the route of exposure, the observed toxic effects were: local anesthetic effect, diarrhea, convulsions, arrhythmias or death.[13] According to a review of different reports of aconite poisoning in humans the following clinical features were observed:[1]

Progression of symptoms: the first symptoms of aconitine poisoning appear approximately 20 minutes to 2 hours after oral intake and include paraesthesia, sweating and nausea. This leads to severe vomiting, colicky diarrhea, intense pain and then paralysis of the skeletal muscles. Following the onset of life-threatening arrhythmia, including ventricular tachycardia and ventricular fibrillation, death finally occurs as a result of respiratory paralysis or cardiac arrest.[14]

LD50 values for mice are 1 mg/kg orally, 0.100 mg/kg intravenously, 0.270 mg/kg intraperitoneally and 0.270 mg/kg subcutaneously. The lowest published lethal dose (LDLo) for mice is 1 mg/kg orally and 0.100 mg/kg intraperitoneally. The lowest published toxic dose (TDLo) for mice is 0.0549 mg/kg subcutaneously. LD50 value for rats is 0.064 mg/kg intraveneously. The LDLo for rats is 0.040 mg/kg intravenously and 0.250 mg/kg intraperitoneally. The TDLo for rats is 0.040 mg/kg parenterally. For an overview of more test animal results (LD50, LDLo and TDLo) see the following table.[13]

Species Observed Type of Test Route of Exposure Dose Data (mg/kg) Toxic Effects
Human LDLo Oral 0.028 Behavioral: excitement

Gastrointestinal: hypermotility, diarrhea Gastrointestinal: other changes

Human LDLo Oral 0.029 Details of toxic effects not reported other than lethal dose value
Cat LD50 Intravenous 0.080 Behavioral: convulsions or effect on seizure threshold
Cat LDLo Subcutaneous 0.100 Details of toxic effects not reported other than lethal dose value
Guinea pig LD50 Intravenous 0.060 Behavioral: convulsions or effect on seizure threshold
Guinea pig LDLo Subcutaneous 0.050 Details of toxic effects not reported other than lethal dose value
Guinea pig LDLo Intravenous 0.025 Cardiac: arrhythmias (including changes in conduction)
Mouse LD50 Intraperitoneal 0.270 Details of toxic effects not reported other than lethal dose value
Mouse LD50 Intravenous 0.100 Sense Organs and Special Senses (Eye): lacrimation

Behavioral: convulsions or effect on seizure threshold Lungs, Thorax, or Respiration: dyspnea

Mouse LD50 Oral 1 Details of toxic effects not reported other than lethal dose value
Mouse LD50 Subcutaneous 0.270 Details of toxic effects not reported other than lethal dose value
Mouse LDLo Intraperitoneal 0.100 Details of toxic effects not reported other than lethal dose value
Mouse LDLo Oral 1 Behavioral: convulsions or effect on seizure threshold

Cardiac: arrhythmias (including changes in conduction) Gastrointestinal: hypermotility, diarrhea

Mouse TDLo Subcutaneous 0.0549 Peripheral Nerve and Sensation: local anesthetic

Behavioral: analgesia

Rabbit LDLo Subcutaneous 0.131 Details of toxic effects not reported other than lethal dose value
Rat LD50 Intravenous 0.080 Behavioral: convulsions or effect on seizure threshold
Rat LD50 Intravenous 0.064 Details of toxic effects not reported other than lethal dose value
Rat LDLo Intraperitoneal 0.250 Cardiac: other changes

Lungs, Thorax, or Respiration: dyspnea

Rat LDLo Intravenous 0.040 Cardiac: arrhythmias (including changes in conduction)
Rat TDLo Parenteral 0.040 Cardiac: arrhythmias (including changes in conduction)
Frog LDLo Subcutaneous 0.586 Details of toxic effects not reported other than lethal dose value
Pigeon LDLo Subcutaneous 0.066 Details of toxic effects not reported other than lethal dose value

For humans the lowest published oral lethal dose of 28 μg/kg was reported in 1969.

Diagnosis and treatment

For the analysis of the Aconitum alkaloids in biological specimens such as blood, serum and urine, several GC-MS methods have been described. These employ a variety of extraction procedures followed by derivatisation to their trimethylsilyl derivatives. New sensitive HPLC-MS methods have been developed as well, usually preceded by SPE purification of the sample.[14] The antiarrhythmic drug lidocaine has been reported to be an effective treatment of aconitine poisoning of a patient. Considering the fact that aconitine acts as an agonist of the sodium channel receptor, antiarrhythmic agents which block the sodium-channel (Vaughan-Williams' classification I) might be the first choice for the therapy of aconitine induced arrhythmias.[15] Animal experiments have shown that the mortality of aconitine is lowered by tetrodotoxin. The toxic effects of aconitine were attenuated by tetrodotoxin, probably due to their mutual antagonistic effect on excitable membranes.[16] Also Paeoniflorin seems to have a detoxifying effect on the acute toxicity of aconitine in test animals. This may result from alternations of pharmacokinetic behavior of aconitine in the animals due to the pharmacokinetic interaction between aconitine and paeoniflorin.[17] In addition in emergencies to assist someone after calling 911 one can wash the stomach using either tannic acid or powdered charcoal. Heart stimulants such as strong coffee or caffeine may also help.[18]

Famous poisonings

During the Indian Rebellion of 1857, a British detachment were the subject of attempted poisoning with aconitine by the Indian regimental chefs. The plot was thwarted by John Nicholson who, having detected the plot, interrupted the British officers just as they were about to consume the poisoned meal. The chefs refused to taste their own preparation, whereupon it was force fed to a monkey who "expired on the spot". The chefs were hanged.

Aconitine was the poison used by George Henry Lamson in 1881 to murder his brother-in-law in order to secure an inheritance. Lamson had learned about aconitine as a medical student from professor Robert Christison, who had taught that it was undetectable—but forensic science had improved since Lamson's student days.[19][20][21]

Aconitine was also made famous by its use in Oscar Wilde's 1891 story "Lord Arthur Savile's Crime". Aconite also plays a prominent role in James Joyce's Ulysses, in which the protagonist Leopold Bloom's father used pastilles of the chemical to commit suicide.

In 1953 aconitine was used by a Soviet biochemist and poison developer Grigory Mairanovsky in experiments with prisoners in the secret NKVD laboratory in Moscow. He admitted killing around 10 people using the poison.[22]

In 2004 Canadian actor Andre Noble died from aconitine poisoning. He accidentally ate some monkshood while he was on a hike with his aunt in Newfoundland.

In 2009 Lakhvir Singh of Feltham, west London, used aconitine to poison the food of her ex-lover (who died as a result of the poisoning) and his current fiancée. Singh received a life sentence for the murder.[23]

See also

References

  1. 1 2 Chan TY (2009). "Aconite poisoning". Clinical Toxicology 47 (4): 279–285. doi:10.1080/15563650902904407. PMID 19514874.
  2. ↑ [http://www.sigmaaldrich.com/catalog/product/si gma/a8001?lang=en "Aconitine"] Check |url= value (help). Sigma Aldrich. line feed character in |url= at position 47 (help)
  3. ↑ "Aconitine sc-202441 Material Safety Data Sheet" (pdf). Santa Cruz Biotechnology.
  4. ↑ Dewick PM (2002). Medicinal Natural Products. A Biosynthetic Approach (2nd ed.). Wiley. ISBN 0-471-49640-5.
  5. ↑ Desai HK, Joshi BS, Ross SA, Pelletier SW (1989). "Methanolysis of the C-8 Acetoxyl Group in Aconitine-Type Alkaloids: A Partial Synthesis of Hokbusine A". Journal of Natural Products 52 (4): 720–725. doi:10.1021/np50064a009.
  6. ↑ Pelletier SW, Mody NV (1979). "Chapter 1 The Structure and Synthesis of C19-Diterpenoid Alkaloids". In Manske RH, Rodrigo R. The Alkaloids: Chemistry and Physiology 17. p. 4. doi:10.1016/S1876-0813(08)60296-1.
  7. ↑ "Pyroaconitine ChemSpider ID: 10211301". Chemspider.
  8. ↑ Gutser UT, Friese J, Heubach JF, Matthiesen T, Selve N, Wilffert B, Gleitz J (1998). "Mode of antinociceptive and toxic action of alkaloids of Aconitum species". Naunyn Schmiedeberg's Archive of Pharmacology 357 (1): 39–48. PMID 9459571.
  9. ↑ Benoit E (1998). "Comptes Rendus des Séances de la Société de Biologie et de ses Filiales" [Mechanism of action of neurotoxins acting on the inactivation of voltage-gated sodium channels] (in French) 192 (3): 409–436. PMID 9759381.
  10. ↑ Okazaki M, Kimura I, Kimura M (1994). "Aconitine-induced increase and decrease of acetylcholine release in the mouse phrenic nerve-hemidiaphragm muscle preparation" (pdf). Japanese Journal of Pharmacology 66 (4): 421–426. doi:10.1254/jjp.66.421. PMID 7723217.
  11. ↑ Tang L, Ye L, Ly C, Zheng Z, Gong Y, Liu Z (2011). "Involvement of CYP3A4/5 and CYP2D6 in the metabolism of aconitine using human liver microsomes and recombinant CYP450 enzymes". Toxicology Letters 202 (1): 47–54. doi:10.1016/j.toxlet.2011.01.019. PMID 21277363.
  12. ↑ Bertilsson L, Lou YQ, Du YL, Liu Y, Kuang TY, Liao XM, Wang KY, Reviriego J, Iselius L, Sjöqvist F (1992). "Pronounced differences between native Chinese and Swedish populations in the polymorphic hydroxylations of debrisoquin and S-mephenytoin". Clinical Pharmacology and Therapeutic 51 (4): 388–397. PMID 1345344.
  13. 1 2 "RTECS". Oct 2011.
  14. 1 2 Beike J, Frommherz L, Wood M, Brinkmann B, Köhler H (2004). "Determination of aconitine in body fluids by LC-MS-MS". International Journal of Legal Medicine 118 (5): 289–293. doi:10.1007/s00414-004-0463-2. PMID 15674996.
  15. ↑ Tsukada K, Akizuki S, Matsuoka Y, Irimajiri S (1992). "A case of aconitine poisoning accompanied by bidirectional ventricular tachycardia treated with lidocaine". Kokyu To Junkan (in Japanese) 40 (10): 1003–1006. PMID 1439251.
  16. ↑ Ohno Y, Chiba S, Uchigasaki S, Uchima E, Nagamori H, Mizugaki M, Ohyama Y, Kimura K, Suzuki Y (1992). "The influence of tetrodotoxin on the toxic effects of aconitine in vivo" (pdf). Tohoku Journal of Experimental Medicine 167 (2): 155–158. doi:10.1620/tjem.167.155. PMID 1475787.
  17. ↑ Fan YF, Xie Y, Liu L, Ho HM, Wong YF, Liu ZQ, Zhou H (2011). "Paeoniflorin reduced acute toxicity of aconitine in rats is associated with the pharmacokinetic alteration of aconitine". Journal of Ethnopharmacology 141 (2): 701–708. doi:10.1016/j.jep.2011.09.005. PMID 21930193.
  18. ↑ Sax N. Irving. Dangerous Properties of Industrial Materials Fifth Edition New York: Van Nostrand Reinhold Company Inc. , ISBN 0-442-27373-8 Library of Congress Catalog Card Number 78-20812
  19. ↑ Macinnis, Peter (2006). It's True! You Eat Poison Every Day. Allen & Unwin. pp. 80–81. ISBN 9781741146264.
  20. ↑ Macinnis, P. (2005). Poisons: From Hemlock to Botox and the Killer Bean of Calabar. Arcade Publishing. pp. 25–26. ISBN 1-55970-761-5.
  21. ↑ Parry, L. A.; Wright, W. H. (2000). Some Famous Medical Trials. Beard Books. p. 103. ISBN 1-58798-031-2.
  22. ↑ Лаборатория Икс [Laboratory X]. Novaya Gazeta (in Russian). 2010-05-06. Retrieved 2013-04-08.
  23. ↑ "Poisoning in west London in 2009". BBC TV News. 2010-02-10.

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