Amanita muscaria: chemistry, biology, toxicology, and ethnomycology

This review (2003) examines the chemical, biological, and toxicological properties of the alkaloids contained in Amanita Muscaria (Fly Agaric) alongside the sociocultural context of its etymology. The principal substrates ibotenic acid and muscimol exert their psychotropic effects through stimulation of inhibitory glutamatergic and GABAergic neurotransmission.

Abstract

“The fly agaric is a remarkable mushroom in many respects; these are its bearing, history, chemical components and the poisoning that it provokes when consumed. The ‘pantherina’ poisoning syndrome is characterized by central nervous system dysfunction. The main species responsible are Amanita muscaria and A. pantherina (Amanitaceae) ; however, some other species of the genus have been suspected for similar actions. Ibotenic acid and muscimol are the active components, and probably, some other substances detected in the latter species participate in the psychotropic effects. The use of the mushroom started in ancient times and is connected with mysticism. Current knowledge on the chemistry, toxicology, and biology relating to this mushroom is reviewed, together with distinctive features concerning this unique species.”

Authors: Didier Michelot & Leda Maria Melendez-Howell

Summary

INTRODUCTION

The fly agaric and the panther mushroom are the species mainly involved in the pantherina-muscaria poisoning syndrome. The poisoning is usually minor and is characterized by central nervous system dysfunctions.

THE SUSPICIOUS SPECIES

Detailed mycological data have already been published on Amanita muscaria and A. pantherina, which can be mistaken for the edible Amanita rubescens and A. spissa. They grow in deciduous woods, especially beech and birch, and also coniferous ones.

A. smithiana contains large amounts of chlorocrotylglycine and amino-2-hexadien-4,5-oic acid, both derivatives of glycine. These substances may have an enzyme inhibitor activity.

Characteristics of poisoning and symptomatology

Chronosymptomatology of poisoning is variable amongst subjects, depending on the rituals, experimental and accidental poisonings, and the socio-cultural context and environment of the participant.

The pantherina-muscaria syndrome is atropine-like and has a short latency like the Coprinus syndrome. In most cases recovery is virtually complete after 24 h without noticeable after-effects.

Symptoms include confusion, dizziness, tiredness, visual and auditory aesthesia, space distortion, and unawareness of time. A deep sleep ends the poisoning, which lasts generally 8 h.

Subsequent gastrointestinal disorders with vomiting are not characteristic of the syndrome, and no damage to organs has been reported. Regular consumption of the mushroom would probably be harmful, even though most human poisoning cases do not report any after-effects.

Treatment

The appropriate treatment for ibotenic acid poisoning is symptomatic: vomiting, stomach washout, or the administration of activated charcoal and purging, preferably in an intensive care emergency unit. Physostigmine, a cholinesterase inhibitor, has been recommended as it counteracts the effects of poisoning by atropine and related antimuscarinic drugs.

Legal status and enforcement

About 12 species of mushrooms are consumed for recreational purpose, but Amanita muscaria is rarely used. In Europe, interest in this type of drug is lower than in North America, where laws prohibit its use.

CHEMICAL PRODUCTS

The fly agaric presented a challenge to chemists, biochemists, and biologists, who discovered many new substances and a common molecular architecture linking most of the structures.

The true toxins

Although the chemical constituents of this mushroom have been thoroughly investigated, a few details remain unclear. These concerns the relationships between the physicochemical properties of the active components and the mode of consumption.

The active principles of the species of concern are muscimol and ibotenic acid, isoxazole derivatives, and are only reported in A. muscaria and A. pantherina subspecies.

Ibotenic acid, a-amino-3-hydroxy-5-isoxazoloacetic acid, is colourless, readily soluble in cold water, and is the main component of muscimol, the substance responsible for the main symptoms.

Muscimol, isolated from A. muscaria, is colourless and readily soluble in cold water. It has a structure similar to ‘agarin’.

Muscazone, a lactame isomer of muscimol, exhibits minor pharmacological activities in comparison with the previous substances. It is also known to induce effects on the central nervous system, but with a longer latency period.

Several syntheses of ibotenic acid and muscimol have been developed via different routes, and thio-derivatives and even more potent inhibitors of GABA uptake have been prepared.

Amanita muscaria contains (x)-R-4-hydroxy-pyrrolidone-(2) 4, a compound that is closely related to ibotenic acid and muscimol. This compound gives information on the biogenesis of these compounds.

Stizolobic 6 and stilozobinic acids 7, found in Stizolobium hasjoo, have been found in A. pantherina, and both have been shown to have excitatory effects in the rat spinal cord.

Muscarine was long considered as the active principle in Amanita muscaria, but it is not responsible for the poisoning syndrome. Small amounts of muscarine occur in Amanita muscaria, but they are not enough to induce any muscarinic syndrome without excessive consumption.

Muscarine 8, epi-muscarine 9 and allo-muscarine 10 have been detected in A. pantherina, and epiallo-muscarine 11 has not been detected in detectable amounts. Chemical syntheses of these compounds have been performed.

Two additional active components, (2R),(1R)-2-amino-3-(1,2-dicarboxy-ethylthio) propanoic acid 12 and (2R),(1S)-2-amino-3-(1,2-dicarboxy-ethylthio) propanoic acid 13, have been reported in A. pantherina.

The occurrence of tropan alkaloids, atropine, hyoscyamine, scopolamine, and bufotenine in A. muscaria was confirmed, while the occurrence of amatoxins and phallotoxins were initially discounted. However, highly sensitive detection methods demonstrated traces of amatoxins and phallotoxins.

Pigments

Amanita muscaria has prompted investigations in several research groups, and the main pigment, muscarufin 14, has been elucidated. Muscaflavin 15, a yellow pigment, has also been elucidated, and its structure has been confirmed by synthesis.

Different compounds, called muscaaurins, are responsible for the red-orange colour of the caps of several Amanita species, including A. caesarea. Ibotenic and stizolobic acids are essentially elements added to the whole structure of muscaaurins.

Miscellaneous

Mushrooms can accumulate high levels of metals. A. muscaria can accumulate 200 ppm vanadium, 17.8 ppm selenium, 33.3 ppm lead, 61.3 ppm mercury, and 7.5 ppm nickel.

A lectin (APL) was isolated from A. pantherina and a b-(1p6) branched (1p3)-beta-D-glucan (AM-ASN) was isolated from A. muscaria. AM-ASN exhibited antitumour activity against Sarcoma 180 in mice.

Toxin detection, content, and occurrence

Several techniques were used to determine the active components in fungi, including bioassays on rats, paper chromatography, and gas chromatography. Muscarine was identified in Mexican fly agarics by cellulose column chromatography and identification as muscarinetetrachloroaurate.

Isoxazole derivatives have been explored in various Amanita species by two-dimensional paper chromatography, high performance thin layer chromatography on silica gel, and HPTLC. The amounts of muscarine detected in the samples were very low, and were lower than 0.0005% for A. muscaria and A. pantherina.

A very sensitive analysis of muscimol and ibotenic acid can be performed using an automated amino acid analyser equipped with a microbore column.

HPLC was developed for A. muscaria content analysis. Ibotenic acid and muscimol were assayed on two columns connected in series, and the amount of ibotenic acid was estimated at 100 ppm f.w. and that of muscimol at 3 ppm. An ion-interaction HPLC method was used to detect muscimol and ibotenic acid in A. muscaria. The amounts of both compounds were higher in caps than in stems, and ibotenic acid was not detected in A. mappa.

The ‘ insecticidal ’ effect

A large number of publications traditionally refer to the insecticidal properties of Amanita muscaria. However, quantitative experiments showed that diptera were weakly sensitive to any toxic action by contact or ingestion, and a putative use of Amanita muscaria components for house fly control has been discussed.

In vivo action of ibotenic related toxins

There are a few veterinary reports of accidental cat poisonings, with symptoms lasting up to 4 h.

30 min after peritoneal injection of aqueous extracts of Amanita muscaria, A. pantherina and A. rubrovolvata into male rats, biochemical changes develop, but the values return to normal within 6 h.

After administration of a short-acting narcotic, muscimol broadens mouse pupils, induces sedation, hypnosis, muscle twitching and catalepsy, and produces electroencephalogram (EEG) alterations that are different from those provoked by hallucinogenic substances such as LSD or mescaline.

The low pH gastric fluid hydrolyses ibotenic acid into muscimol, which is then eliminated via the systemic circulation. The remnant of the active component in the urine accounts for the tradition of drinking the urine of shamans.

Ibotenic acid, the key component of A. muscaria and A. pantherina, enters the central nervous system via the systemic circulation and induces a transient change in GABA receptor sensitivity and lesions in the basal forebrain. This results in a significant and prolonged learning and memory deficit.

Biochemical mode of action of ibotenic related toxins

Ibotenic acid and muscimol are the substances responsible for the psychotropic action of Amanita muscaria. These substances are members of a distinctive class of alkaloids, the excitatory amino acids.

Ibotenic acid and muscimol are derivatives of glutamic acid and GABA, which act like neurotransmitters in the mammalian central nervous system. However, ibotenic acid and muscimol cross the blood – brain barrier, causing brain disorders.

Ibotenic acid, a synthetic analogue of L-glutamate, acts on inhibitory glutamate receptors (IGluRs), a class of ion channel proteins equivalent to glycine and GABA receptors. It produces an increase of serotonin and dopamine in the brain of mice and rats.

Fig. 15. Chemical structure of tiagabine.

Muscimol, a toxin from A. muscaria, binds with the gamma-aminobutyrate receptor and inhibits neuronal and glial GABA uptake and a substrate for the GABA-metabolizing enzyme: GABA transaminase. This toxin is also marketed as a therapeutic agent for the treatment of epilepsy, Gabatril1.

Distinctive features of Amanita muscaria

The fly agaric mushroom is the most widely used pictogram for wild mushrooms, and is used in illustrations of tales for children, strip cartoons, Christmas tree decorations, pastries, and even tattoos. It is used by shamans, sorcerers, and witches in different ethnic groups to escape the human condition.

A. muscaria is associated with various symbols in northern and southern Asian cultures, as well as in Germanic tradition. Some publications even argue that Christianity originates from a cult of A. muscaria, but other religious and secular biblical scholars discredit this.

Two attitudes coexist in world cultures towards mushrooms consumption: myco-phobic and mycophilic. Some groups are mycophobic, while others are mycophilic, and educated people are careful about mushrooms, while those of less developed cultures tend to consume them more readily.

The name of the mushroom

The designation of the species as ‘fly agaric’, ‘bug agaric’, is surprisingly equivalent all over the world. However, experiments show that flies exposed to the juice of the mushroom do not die, but rather become intoxicated.

In ancient times, ‘fly’ was associated with madness or supernatural possession. In the Middle Ages, flies were believed to cause mental illness.

Bosch’s painting 1510 ‘Paradise and Hell’ shows a crowd of hideous insects flying from heaven, and the same artist’s ‘The garden of earthly delight’ 1504 shows a mushroom that can induce divine or evil states of possession similar to those that flies were supposed to produce in human brains.

The fly agaric tree is associated with rituals and beliefs, and is said to swallow the pool of water of life and nourish the ‘sacred mushroom’.

Paintings, frescos, and archaeological data

Historical documents suggest that the psychotropic properties of some mushrooms have been known from ancient times and that consumption has occurred in all continents.

The American surgeon general Puharich (1959) investigated the mycology, biology, physiology, ethnology, etymology, and comparative linguistics of A. muscaria and its psychotropic properties, and tried to prove there were cults in ancient Egypt similar to those in eastern Siberia.

CONCLUSION

Amanita muscaria and A. pantherina do not induce any critical organ damage, but severe neuron and even brain lesions could be anticipated in cases of recurrent consumption.

A. muscaria has contributed to the progress of chemistry and pharmacology, but is not yet subject to legislation. It has a low psychotropic action, but still a toxic one.