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Veratridine is a
steroidal alkaloid Steroidal alkaloids have organic ring backbones which feature nitrogen-based functional groups. More specifically, they are distinguished by their tetracyclic cyclopentanophenanthrene backbone that marks their close relationship with sterols. They ...
found in plants of the lily family, specifically the genera '' Veratrum'' and '' Schoenocaulon''. Upon absorption through the skin or mucous membranes, it acts as a
neurotoxin Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ...
by binding to and preventing the inactivation of voltage-gated sodium ion channels in heart, nerve, and skeletal muscle cell membranes. Veratridine increases nerve excitability and intracellular Ca2+ concentrations.


Isolation

Veratridine has been isolated from the seeds of ''Schoenocaulon officinale'' and from the
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow h ...
s of '' Veratrum album.'' Like the other steroidal alkaloids found in these plants and similar ones in the Melanthiaceae family, it is present as part of a glycosidal combination, bonded to carbohydrate moieties. Early isolation methods relied on formation of the
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insol ...
salt and then precipitation of the insoluble
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and man ...
form. Accounts of these efforts date back to 1878, but the first true purification of veratridine is the one carried out in 1953 by Kupchan et al. This, and later purification procedures, begin with veratrine, a mixture of the alkaloids present in the ''Veratrum'' plants, primarily containing cevadine and veratridine. The nitrate salt is formed by dissolving the veratrine in 1% sulfuric acid over ice and precipitating with sodium nitrate. After resuspending in water over ice, the solution is brought to pH 8.5 with aqueous NaOH and then pH 10 with aqueous ammonia, forming another precipitate which is extracted with ether and then with chloroform. The ether and chloroform fractions are combined and dried. The dried residue is dissolved in sulfuric acid and the sulfate salt of veratridine is precipitated by dropwise addition of a solution of ammonium sulfate. Finally, the free base form is generated with ammonium hydroxide. An even better isolation of veratridine from veratrine is achieved using high-performance liquid chromatography (HPLC); as commercially available veratridine may vary in purity, HPLC purification of veratrine is a preferred method for isolation of veratridine for biological studies.


Chemistry


Structure

Veratridine is a derivative, the 3-veratroate
ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glyceride ...
, of
veracevine Veracevine is an alkaloid that occurs in the seeds of '' Schoenocaulon officinale''. It is used as an insecticide in veterinary medicine. See also * Veratridine Veratridine is a steroidal alkaloid found in plants of the lily family, specific ...
, which belongs to the class of C-nor-D-homosteroidal alkaloids. The molecular structure and stereochemistry of this and related alkaloids were only established after decades of chemical investigations. The structure of veratridine has been confirmed by
NMR spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fi ...
and
X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. Veratridine displays an unusual
steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and ...
al backbone. In the typical four-ring nucleus with three six-membered rings and one five-membered ring (like the one in
cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell mem ...
), the five-membered ring is on the end. Veratridine, and other ''Veratrum'' alkaloids, have the five-membered ring between the second and third six-membered rings.


Solubility

Veratridine has a
pKa PKA may refer to: * Professionally known as: ** Pen name ** Stage persona * p''K''a, the symbol for the acid dissociation constant at logarithmic scale * Protein kinase A, a class of cAMP-dependent enzymes * Pi Kappa Alpha, the North-American ...
of 9.54. It is slightly soluble in
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again b ...
, soluble in
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
and
DMSO Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and ...
, and freely soluble in
chloroform Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various ...
. Solubility in water is pH-dependent; the
free base Free base (freebase, free-base) is the conjugate base (Deprotonation, deprotonated) form of an amine, as opposed to its conjugate acid (Protonation, protonated) form. The amine is often an alkaloid, such as nicotine, cocaine, morphine, and ephe ...
form is slightly soluble, but easily dissolves in 1 M HCl. Its
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insol ...
salt is slightly soluble in water. Its
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and man ...
salt is very
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substa ...
.


Mechanism of action and applications

Veratridine acts a neurotoxin by increasing nerve excitability. It binds to binding site 2 on the voltage-gated sodium channels (the same site bound by
batrachotoxin Batrachotoxin (BTX) is an extremely potent cardio- and neurotoxic steroidal alkaloid found in certain species of beetles, birds, and frogs. The name is from the Greek word grc, βάτραχος, bátrachos, frog, label=none. Structurally-related ...
,
aconitine Aconitine is an alkaloid toxin produced by various plant species belonging to the genus ''Aconitum'' (family Ranunculaceae), known also commonly by the names wolfsbane and monkshood. Monkshood is notorious for its toxic properties. Aconitine is ...
, and grayanotoxin), leading to persistent activation. Veratridine inhibits sodium channel inactivation by shifting the activation threshold toward a more negative potential. The resulting influx of Na+ also leads to the increase of intracellular Ca2+ concentrations, causing the overproduction of
reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () ...
responsible for neuronal damage. Veratridine is readily absorbed through the skin and mucous membranes and through ingestion. The tissues most affected are the heart, nerves, and skeletal muscles: main symptoms of veratridine toxicity include severe nausea,
bradycardia Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, ...
,
hypotension Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...
, difficulty breathing, salivation, and muscle weakness.{{Cite web, url=https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+4078, title=VERATRIDINE - National Library of Medicine HSDB Database, website=toxnet.nlm.nih.gov, access-date=2018-05-02 Treatment involves the administration of
activated charcoal "Activated" is a song by English singer Cher Lloyd. It was released on 22 July 2016 through Vixen Records. The song was made available to stream exclusively on '' Rolling Stone'' a day before to release (on 21 July 2016). Background In an inte ...
,
atropine Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given in ...
, and
benzodiazepine Benzodiazepines (BZD, BDZ, BZs), sometimes called "benzos", are a class of depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed to treat conditions such as anxiety disorders, ...
s (if the affected individual is seizing). Veratridine's ability to depolarize cells by affecting sodium channels lends it its applicability as a neuropharmacological tool for the study of electrical properties of nerve and muscle fibers. It has also been tested as a treatment for
myasthenia gravis Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness. The most commonly affected muscles are those of the eyes, face, and swallowing. It can result in double vision, dro ...
, in light of its potential to increase muscle responses to motor neuron stimulation. Furthermore, this compound has recently been reported to increase sperm progressive motility (although it does not produce hyperactivation by itself). It has the potential of enhancing protein tyrosine phosphorylation, which takes place during
capacitation Capacitation is the penultimate step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation. ''I ...
, and its effects are inhibited in the presence of
lidocaine Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, lidoc ...
and tetrodotoxin. Veratridine has not been reported to have any effect on the
acrosome reaction During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellular ...
on its own, but it is able to block the
progesterone Progesterone (P4) is an endogenous steroid and progestogen sex hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. It belongs to a group of steroid hormones called the progestogens and is the major ...
-induced acrosome reaction. Moreover, veratridine has the effect of turning the membrane potential to a more positive one and also modifies the effect of progesterone on a2+ and sperm membrane potential. The activation of Nav1.8 is a key point in Veratradine's mechanism of action and, consequently, this sodium ion channel coordinates the effects of this compound. Veratradine also activates additional Nav channels. These facts contribute to support the importance of these Veratradine-sensitive proteins in the regulation of mature sperm function, such as human sperm fertility acquisition regulating motility,
capacitation Capacitation is the penultimate step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation. ''I ...
and the progesterone-induced acrosome reaction.L. Candenas, F.M. Pinto, A. Cejudo-Román, C. González-Ravina, M. Fernández-Sánchez, N. Pérez-Hernández, et al. Veratridine-sensitive Na+ channels regulate human sperm fertilization capacity. Life Sci. 2018 Mar; 196:48-55.


References

Neurotoxins Steroidal alkaloids Ion channel toxins Non-protein ion channel toxins Benzoate esters Plant toxins Secondary alcohols Tertiary alcohols Sodium channel openers