Volume LXX, 2001, no. 1 vOJENSKÉ ZDRAVOTNICKÉ LISTY - SUPLEMENTUM 47 NATURAL CHOLINOTOXINS lJiří PATOČKA, 2Oıgzı BENEŠOVÁ lDepartment Of Toxicology, Purkyně Military Medical Academy, Hradec Králové 2Prague Psychiatric Center, Prague Summary Natural toxins represent interesting and recently very studied group of substances with great practical meaning. Especially toxins with targeting to cholinergic nervous system, which plays an important role in many physiological and behavioral functions in animals, represent meaningful group of neurotoxins with wide spectrum of clinical use. These Cholinotoxins are the aim of this paper. Natural toxins, biotoxins, are chemical agents motility of the ureters, the urinary bladder, the of biological origin, present in the bodies of many gallbladder, the billiary ducts, and stimulates exo- organisms. Venoms of toxic plants and animals are crine glands (25). Muscarine, furane derivative known and used for different purposes by native from mushroom Amanita muscaria, is pharmaco- civilizations in all continents. Biotoxins have evolved logically similar to pilocarpine on smooth muscle in organisms over many thousands of years to have and exocrine glands. Muscarine can cause a de- very often unique and interesting chemical struc- crease of blood pressure and slowing down the ture and no less interesting and specific pharma- heartbeat, gastro-intestinal irritation, vomiting, ab- cological effects. Toxins with specific affinity to dominal pain and diarrhoea, perspiration, saliva- the structure of nervous system are known as neuro- tion, lacrimation constriction of pupils and blurring toxins and some of them with the affinity to cho- of vision (9). Nicotine is alkaloid of leaves and stems linergic nervous system could be sign as Cholino- of the Nicotiana species. Its chemical structure is toxins and resumption of them is the theme of this derived from pyridine and pyrrolidine. Nicotine binds article. Cholinotoxins are pharmacologically inter- to nicotinic acetylcholine receptors and the drug has esting compounds which have been used scientific- a characteristic curare action on skeletal muscle cally to elucidate physiological mechanisms in (3). Anatoxin-a and homoanatoxin-a are strong cholinergic nervous system or as the starting point Cholinotoxins produced by the freshwater cyano- in the development of new therapeutic agents or phyte Anabaena flos-aquae. Structurally, both com- even as therapeutically applicable agents. All known pounds are similar to tropane alkaloids; both are natural Cholinotoxins can be divided into four prin— strong neurotoxins and potent depolarizing neuro- cipal groups: Acetylcholine receptor agonists, ace- muscular blocking agents, more potent than nico- tylcholine receptor antagonists, inhibitors of ace- tine (26). Epibatidine is an animal alkaloid from tylcholine releasing and cOmpounds with effect on Equadorian poison-dart frog Epipedobates tricolor, neuromuscular junction, and inhibitors of choline- very strong selective agonist of some types of nico- sterases (16). tinic acetylcholine receptors (18), likewise ana- Acetylcholine receptor agonists of natural ori- baseine, one of toxic compounds from the venom gin are some toxic plant alkaloids. Arecoline, main of North American ant Aphaenogaster rudis (14). alkaloid of Betel nut from Areca catechu, which is Numerous selective agonist of nicotinic acetylcho- used by various ethnic groups, including those line receptors are occur in venom of cone shell from India, South-East Asia and Africa, particular moluscs. There are short peptides, so-called cono— manner analogous to chewing tobacco. This tetra- toxins (11). hydropyridine derivative is pharmacologically cha- Acetylcholine receptor antagonists of natural racterized as a gangliomimetic compound which origin are known only as belladona alkaloids atro- stimulates the both muscarinic and nicotinic acetyl- pine and scopolamine from some Solanaceae. At- choline receptors (6). Pilocarpine from the leaves ropine is a competitive agonist of muscarinic ace- of Jaborandi bushes (Pilocarpus jaborandii), grow- tylcholine receptors, decreases bronchial and sali- ing in the rainforests of Brazil, is more than 120 -vary secretions, blocks the bradycardia associated years used for the treatment of glaucoma, due to with some drugs used in anesthesia and helps to reducing the intraoccular pressure. This alkaloid prevent bradycardia from excessive vagal stimula- causes bronchoconstriction and enhances tone and tion. Scopolamine produces inhibition of struc- 48 VOJENSKÉ ZDRAVOTNICKÉ LISTY _- SUPLEMENTUM Volume LXX, 2001, no. 1 tures innervated by postganglionic cholinergic nerves is structurally the most complex of any known and stimulation of the central nervous system fol- snake venom neurotoxin. It is composed from five lowed by depression. Other reversible and com- non—covalently linked subunits A, B, and C, and petitive antagonist with high affinity for neuronal two identical covalently linked D subunits. All nicotinic acetylcholine receptors is methyllycaco- subunits are necessary for maximum lethality (27). nitine, Clg-diterpenoid alkaloid from plants of the Erabutoxin is toxic protein from the sea snake Delphinium genus, Ranunculaceae (8). Cobratoxin, Laticauda Semifascı'ata and is composed from 83 let us say cobratoxins, are a family of toxic pep- amino acids cross-linked by four disulfide chains (5). tides isolated from the venom of the snake Naja Acetylcholinesterase inhibitors of natural ori- naja siamensis (Monocled cobra). Alpha-cobratoxin gin represent a numerous group of chemically very is composed from 71 amino acids cross-linked by different compounds. Some inhibitors of this very five disulfide chains. Cobratoxins produce periph- important neuronal enzyme are used as cognitive eral paralysis by blocking neuromuscular transmis- enhancers in the treatment of Alzheimer disease. sion. Physostigmine (eserine) is the best-known Sub- Acetylcholine releasing and neuromuscular stance of this type. It is an alkaloid from the junction inhibitors of natural origin are largely leguminous plant Physostigma venenosum known toxic peptides from venom of different snakes, as Calabar bean, remedy used in West Africa as an only best-known toxin of this type, botulotoxin, is “ordeal poison” in trials for witchcraft. Physostig- product of anaerobic microorganism. Botulinum mine as N-methylcarbamate is a strong pseudoirre- toxin (botulotoxin) is toxic protein from the C10:- versible inhibitor of acetylcholinesterase (AChE) tridium botulinum. There are seven antigenically and has been widely employed for various thera- distinct forms of botulinum neurotoxins: Types A, peutic purposes, including Alzheimer disease treat- B, C1, D, E, F, and G. Botulotoxins are disulfide— ment (22). This alkaloid has been also a model for —linked heterodimers of a light chain (L) and heavy preparation great many of modern therapeutics. chain (H). The L chain has the pharmacological ac- Galantamine is an alkaloid from snowdrop (Gal- tivity, while the H chain mediate channel forma- anthus woronowii, G. nivalis) and reversible in- tion and toxin binding, respectively. Botulotoxin hibitor of AChE (23), as well as alkaloid huperz- acts by inhibiting neurotransmitter release. It is ine A from the Chinese moss Huperzia serrata, the bind to peripheral neuronal synapses, internalized traditional Chinese herbal medicine called Qian and moved by retrograde transport up to the axon Ceng Ta (16). Anatoxin-a(s) is a neurotoxic alka- into the spinal cord where it can move between loid and as yet the only one organophosphate com- presynaptic and postsynaptic. neurons (7). Bunga- pound found in nature, product of fresh water blue- rotoxins represent a group of neurotoxic proteins -green alga Anabaena flOS-aquae (12). It is ire- from the venom of the banded of Formosan krait versible inhibitor of AChE, likewise onchidal, Bungarus multicinctus. Only beta- and gamma-bun? lipophilic acetate ester from molluscs Onchidella garotoxins act presynaptically causing acetylcholine binneyi, O. nigricans or 0. patelloides (1). Other release and depletion, while alpha-bungarotoxin natural inhibitors of AChE are pseudoazoantho- blocks nicotinic acetylcholine receptors (24). Cro- Xanthin and parazoanthoxanthin A Strongly fluo- toxin is the major toxin of the venom of the South rescent pigments occurring in zoanthids (20) and American rattlesnake, Crotalus durissus terrificus, evodiamine and dehydroevodiamine from the plant protein composed from two subunit: component B, Evodia rutaecarpa (14). Other Sort of antiacetyl- a basic and weakly toxic phospholipase A2, and cholinesterase compounds are for example terri- component A, an acidic non-toxic protein enhanc- trems, tremorgenic mycotoxins isolated from AS- ing the lethal potency of component B (2). Notexin pergillus terreus (10), arisugacins from some Pe- is presynaptic neurotoxin from the venom of Aus- nicı'llium (13) or interesting group of toxic 3-alkyl- tralian tiger snake Notechis scutatus scutatus. It is pyridinium polymers from the marine sponge a protein, which consists Of a Single chain Of 119 Raniera sarai (21). amino acids cross-linked by seven disulfide brid- Hitherto quite unique is the discovery of protein ges (4). Textilotoxin is presynaptic neurotoxin from with antiacetylcholinesterase activity. It is a family the venom of the Australian common brown snake, of peptides with 61 amino acid residues and four Pseudonaja textilis. It has the highest lethality and disulfide bridges, isolated from