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Other names 6,7-Dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline | |
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3D model (JSmol) | |
ChEBI | |
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KEGG | |
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Properties | |
C10H13NO2 | |
Molar mass | 179.219 g·mol−1 |
Melting point | 147–149 °C (297–300 °F; 420–422 K) [1] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Salsolinol is a chemical compound derived from dopamine which plays a role in neurotransmission and is neurotoxic.
It has been linked to dopamine-related disorders including Parkinson's disease and alcohol use disorder. It is both synthesized in the human body and ingested in several common dietary sources. [2]
Salsolinol is a catechol isoquinoline which is a yellow solid at room temperature. [1] Salsolinol, as a chiral molecule, comes in two enantiomers: (R)-salsolinol and (S)-salsolinol. The two may have different biological effects.
The racemate can be synthesized via a Pictet-Spengler reaction. [3] A chemoenzymatic, enantioselective synthesis of the (R)-enantiomer has also been reported. [4] Salsolinol has been used as a starting material to prepare some tetrahydroisoquinoline-based prospective drugs. [5] [6]
Salsolinol is found in several edible plants, most prominently bananas and cocoa products as well as beer. [7] [8] [9] Other plants, including black cohosh, which is used in many herbal remedies, also contain salsolinol. [10]
Salsolinol is endogenously synthesized by multiple routes, although its origin in the human body remains controversial. There are two main routes for its production: one which is through a non-enantiospecific Pictet-Spengler reaction of dopamine and acetaldehyde, and one which is mediated by the enzyme salsolinol synthase. [11]
Salsolinol synthase exclusively produces the (R)-enantiomer of salsolinol.
It has been speculated that salsolinol may also arise from salsolinol-1-carboxylic acid, which is formed by the reaction of dopamine and pyruvic acid. This transformation would occur via a proposed enzymatic pathway that has not been elucidated yet. [11]
Salsolinol is metabolized by an N-methyltransferase enzyme into N-methyl-(R)-salsolinol. This can then be converted by an amine oxidase into 1,2-dimethyl-6,7-dihydroxyisoquinolinium (DMDHIQ+). It can also be methylated to form its 7-methoxy and 6-methoxy versions by the enzyme catechol-O-methyltransferase (COMT). [12] [11]
Salsolinol binds to several receptors associated with dopaminergic pathways. [2] [13] It may be an agonist of the μ-opioid receptor and of dopaminergic D1 and D3 receptors. [2]
Salsolinol itself also appears to be neurotoxic, the mechanism of which is not clear. Its metabolites, including N-methyl-(R)-salsolinol, also exhibit neurotoxic effects.
Salsolinol has been shown to be involved in the secretion of prolactin in the pituitary gland in lactating rats and lactating sheep. [14] [15] Administration of a solution of salsolinol was not shown to raise prolactin levels in human women. [16]
Salsolinol is detectable in the cerebrospinal fluid of Parkinson's disease (PD) patients and is involved in the pathogenesis of PD. [17] It is known to exercise inhibitory effects on tyrosine hydroxylase [18] and to be toxic to dopaminergic neurons. [19] A mechanism for the induction of Parkinson's by salsolinol is linked to its mediation of pyroptosis. [20]
The connection between salsolinol and alcohol intake remains controversial. An early hypothesis was that the synthesis of salsolinol in the human body was caused by ethanol consumption, because it was being made from dopamine and acetaldehyde (a metabolite of ethanol). Several studies in the 1970s and 80s would seem to corroborate this link. However, no consistent connection between ethanol intake and salsolinol levels were conclusively established. As of the 2020s, it is understood that the primary contributor to levels of salsolinol in blood plasma is dietary intake, not acute ethanol consumption. [21] Part of the challenge in studying this is that salsolinol also is produced endogenously, and in all cases its levels are very low, making it difficult to detect and quantify with precision. [22]
Further confounding the issue, there is evidence that salsolinol may be implicated in alcohol use disorder and may play a role in increasing cravings for ethanol. (R)-Salsolinol stereospecifically induces behavioral sensitization and leads to excessive alcohol intake in rats. [23]
Dopamine is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 80% of the catecholamine content in the brain. It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical, L-DOPA, which is synthesized in the brain and kidneys. Dopamine is also synthesized in plants and most animals. In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons to send signals to other nerve cells. Neurotransmitters are synthesized in specific regions of the brain, but affect many regions systemically. The brain includes several distinct dopamine pathways, one of which plays a major role in the motivational component of reward-motivated behavior. The anticipation of most types of rewards increases the level of dopamine in the brain, and many addictive drugs increase dopamine release or block its reuptake into neurons following release. Other brain dopamine pathways are involved in motor control and in controlling the release of various hormones. These pathways and cell groups form a dopamine system which is neuromodulatory.
Parkinsonism is a clinical syndrome characterized by tremor, bradykinesia, rigidity, and postural instability. These are the four motor symptoms found in Parkinson's disease (PD) – after which it is named – dementia with Lewy bodies (DLB), Parkinson's disease dementia (PDD), and many other conditions. This set of symptoms occurs in a wide range of conditions and may have many causes, including neurodegenerative conditions, drugs, toxins, metabolic diseases, and neurological conditions other than PD.
MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is an organic compound. It is classified as a tetrahydropyridine. It is of interest as a precursor to the neurotoxin MPP+, which causes permanent symptoms of Parkinson's disease by destroying dopaminergic neurons in the substantia nigra of the brain. It has been used to study disease models in various animals.
Dopaminergic pathways in the human brain are involved in both physiological and behavioral processes including movement, cognition, executive functions, reward, motivation, and neuroendocrine control. Each pathway is a set of projection neurons, consisting of individual dopaminergic neurons.
The Pictet–Spengler reaction is a chemical reaction in which a β-arylethylamine undergoes condensation with an aldehyde or ketone followed by ring closure. The reaction was first discovered in 1911 by Amé Pictet and Theodor Spengler. Traditionally, an acidic catalyst in protic solvent was employed with heating; however, the reaction has been shown to work in aprotic media in superior yields and sometimes without acid catalysis. The Pictet–Spengler reaction can be considered a special case of the Mannich reaction, which follows a similar reaction pathway. The driving force for this reaction is the electrophilicity of the iminium ion generated from the condensation of the aldehyde and amine under acid conditions. This explains the need for an acid catalyst in most cases, as the imine is not electrophilic enough for ring closure but the iminium ion is capable of undergoing the reaction.
Nomifensine (Merital, Alival) is a norepinephrine-dopamine reuptake inhibitor, i.e. a drug that increases the amount of synaptic norepinephrine and dopamine available to receptors by blocking the dopamine and norepinephrine reuptake transporters. This is a mechanism of action shared by some recreational drugs like cocaine and the medication tametraline (see DRI). Research showed that the (S)-isomer is responsible for activity.
A dopamine agonist(DA) is a compound that activates dopamine receptors. There are two families of dopamine receptors, D1-like and D2-like. They are all G protein-coupled receptors. D1- and D5-receptors belong to the D1-like family and the D2-like family includes D2, D3 and D4 receptors. Dopamine agonists are primarily used in the treatment of Parkinson's disease, and to a lesser extent, in hyperprolactinemia and restless legs syndrome. They are also used off-label in the treatment of clinical depression. The use of dopamine agonists is associated with impulse control disorders and dopamine agonist withdrawal syndrome (DAWS).
Aporphine is an alkaloid with the chemical formula C17H17N. It is the core chemical substructure of the aporphine alkaloids, a subclass of quinoline alkaloids. It can exist in either of two enantiomeric forms, (R)-aporphine and (S)-aporphine.
The nuclear receptor 4A2 (NR4A2) also known as nuclear receptor related 1 protein (NURR1) is a protein that in humans is encoded by the NR4A2 gene. NR4A2 is a member of the nuclear receptor family of intracellular transcription factors.
Dopamine receptor D2, also known as D2R, is a protein that, in humans, is encoded by the DRD2 gene. After work from Paul Greengard's lab had suggested that dopamine receptors were the site of action of antipsychotic drugs, several groups, including those of Solomon Snyder and Philip Seeman used a radiolabeled antipsychotic drug to identify what is now known as the dopamine D2 receptor. The dopamine D2 receptor is the main receptor for most antipsychotic drugs. The structure of DRD2 in complex with the atypical antipsychotic risperidone has been determined.
Tetrahydroisoquinoline (TIQ or THIQ) is an organic compound with the chemical formula C9H11N. Classified as a secondary amine, it is derived from isoquinoline by hydrogenation. It is a colorless viscous liquid that is miscible with most organic solvents. The tetrahydroisoquinoline skeleton is encountered in a number of bioactive compounds and drugs.
Oxidopamine, also known as 6-hydroxydopamine (6-OHDA) or 2,4,5-trihydroxyphenethylamine, is a neurotoxic synthetic organic compound used by researchers to selectively destroy dopaminergic and noradrenergic neurons in the brain.
GBR-12935 is a piperazine derivative which is a potent and selective dopamine reuptake inhibitor. It was originally developed in its 3H radiolabelled form for the purpose of mapping the distribution of dopaminergic neurons in the brain by selective labelling of dopamine transporter proteins. This has led to potential clinical uses in the diagnosis of Parkinson's disease, although selective radioligands such as Ioflupane (¹²³I) are now available for this application. GBR-12935 is now widely used in animal research into Parkinson's disease and the dopamine pathways in the brain.
Norsalsolinol is a chemical compound that is produced naturally in the body through metabolism of dopamine. It has been shown to be a selective dopaminergic neurotoxin, and has been suggested as a possible cause of neurodegenerative conditions such as Parkinson's disease and the brain damage associated with alcoholism, although evidence for a causal relationship is unclear.
JNJ-7925476 is a triple reuptake inhibitor antidepressant discovered by Johnson & Johnson, but never marketed.
OSU-6162 (PNU-96391) is a compound which acts as a partial agonist at both dopamine D2 receptors and 5-HT2A receptors. It acts as a dopamine stabilizer in a similar manner to the closely related drug pridopidine, and has antipsychotic, anti-addictive and anti-Parkinsonian effects in animal studies. Both enantiomers show similar activity but with different ratios of effects, with the (S) enantiomer (–)-OSU-6162 that is more commonly used in research, having higher binding affinity to D2 but is a weaker partial agonist at 5-HT2A, while the (R) enantiomer (+)-OSU-6162 has higher efficacy at 5-HT2A but lower D2 affinity.
Salsoline is a tetrahydroisoquinoline alkaloid found in some plants of the genus Salsola. Salsoline is the monomethylated metabolite of salsolinol which has been thought to contribute to Parkinson's disease. Also, this has been tied to the neuropathology of chronic alcoholism.
While researchers have found that moderate alcohol consumption in older adults is associated with better cognition and well-being than abstinence, excessive alcohol consumption is associated with widespread and significant brain lesions. Other data – including investigated brain-scans of 36,678 UK Biobank participants – suggest that even "light" or "moderate" consumption of alcohol by itself harms the brain, such as by reducing brain grey matter volume. This may imply that alternatives and generally aiming for lowest possible consumption could usually be the advisable approach.
A prolactin modulator is a drug which affects the hypothalamic–pituitary–prolactin axis by modulating the secretion of the pituitary hormone prolactin from the anterior pituitary gland. Prolactin inhibitors suppress and prolactin releasers induce the secretion of prolactin, respectively.
Mevidalen (developmental code name LY-3154207) is a dopaminergic drug which is under development for the treatment of Lewy body disease, including those with Parkinson's disease. It acts as a selective positive allosteric modulator (PAM) of the dopamine D1 receptor. The drug is orally active and crosses the blood–brain barrier. It is a tetrahydroisoquinoline and is a close analogue of DETQ, another D1 receptor PAM. Mevidalen has been found to have wakefulness-promoting effects in sleep-deprived humans. Side effects of mevidalen have been reported to include increased heart rate and blood pressure, insomnia, dizziness, nausea, vomiting, anxiety, nervousness, fatigue, headaches, palpitations, and contact dermatitis, as well as falls in those with dementia. As of March 2022, mevidalen is in phase 2 clinical trials for the treatment of Lewy body disease. Besides for movement disorders and dementia, D1 receptor PAMs like mevidalen might have value in the treatment of certain neuropsychiatric disorders, such as depression, excessive somnolence, and attention deficit hyperactivity disorder.