Noribogaine has been determined to act as a biased agonist of the κ-opioid receptor (KOR).[13] It activates the G protein (GDP-GTP exchange) signaling pathway with 75% the efficacy of dynorphin A (EC50 = 9μM), but it is only 12% as efficacious at activating the β-arrestin pathway.[13] Moreover, due to its very low efficacy on the β-arrestin pathway, noribogaine blocked dynorphin A activation of the pathway (IC50 = 1μM) and hence functioned as an antagonist of it.[13]
The β-arrestin pathway is thought to be responsible for the dysphoric and aversive effects of KOR activation,[14] and its lack of activation by noribogaine may be the reason for the lack of dysphoric effects of the drug.[13] This biased agonist/antagonist action of noribogaine at the KOR is unique to it relative to other iboga alkaloids and related compounds such as ibogaine and 18-methoxycoronaridine (18-MC).[13] Moreover, it has been hypothesized that it may give noribogaine unique properties such that it may have the analgesic and antiaddictive effects of KOR agonists without the anxiogenic, dysphoric, or anhedonic effects that are typical of them.[13]
Dynorphins (Dyn) are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 (PC2), multiple active peptides are released: dynorphin A, dynorphin B, and α/β-neoendorphin. Depolarization of a neuron containing prodynorphin stimulates PC2 processing, which occurs within synaptic vesicles in the presynaptic terminal. Occasionally, prodynorphin is not fully processed, leading to the release of “big dynorphin.” “Big Dynorphin” is a 32-amino acid molecule consisting of both dynorphin A and dynorphin B.
Ibogaine is a naturally occurring psychoactive substance found in plants in the family Apocynaceae such as Tabernanthe iboga, Voacanga africana, and Tabernaemontana undulata. It is a psychedelic with dissociative properties.
Opioid peptides or opiate peptides are peptides that bind to opioid receptors in the brain; opiates and opioids mimic the effect of these peptides. Such peptides may be produced by the body itself, for example endorphins. The effects of these peptides vary, but they all resemble those of opiates. Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, control of food intake, and the rewarding effects of alcohol and nicotine.
18-Methoxycoronaridine, also known as zolunicant, is a derivative of ibogaine invented in 1996 by the research team around the pharmacologist Stanley D. Glick from the Albany Medical College and the chemists Upul K. Bandarage and Martin E. Kuehne from the University of Vermont. In animal studies it has proved to be effective at reducing self-administration of morphine, cocaine, methamphetamine, nicotine and sucrose. It has also been shown to produce anorectic effects in obese rats, most likely due to the same actions on the reward system which underlie its anti-addictive effects against drug addiction.
Voacangine is an alkaloid found predominantly in the root bark of the Voacanga africana tree, as well as in other plants such as Tabernanthe iboga, Tabernaemontana africana, Trachelospermum jasminoides, Tabernaemontana divaricata and Ervatamia yunnanensis. It is an iboga alkaloid which commonly serves as a precursor for the semi-synthesis of ibogaine. It has been demonstrated in animals to have similar anti-addictive properties to ibogaine itself. It also potentiates the effects of barbiturates. Under UV-A and UV-B light its crystals fluoresce blue-green, and it is soluble in ethanol.
The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP for its ligand ketazocine, is a G protein-coupled receptor that in humans is encoded by the OPRK1 gene. The KOR is coupled to the G protein Gi/G0 and is one of four related receptors that bind opioid-like compounds in the brain and are responsible for mediating the effects of these compounds. These effects include altering nociception, consciousness, motor control, and mood. Dysregulation of this receptor system has been implicated in alcohol and drug addiction.
Cyclazocine is a mixed opioid agonist/antagonist related to dezocine, pentazocine and phenazocine. This family of opioid drugs is called the benzomorphans or benzazocines. It is a KOR agonist and MOR partial agonist, and also has high affinity for the DOR.
The μ-opioid receptors (MOR) are a class of opioid receptors with a high affinity for enkephalins and beta-endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium and for which the receptor was named, with mu being the first letter of Morpheus, the compound's namesake in the original Greek. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels.
7-Hydroxymitragynine (7-OH) is a terpenoid indole alkaloid from the plant Mitragyna speciosa, commonly known as kratom. It was first described in 1994 and is a natural product derived from the mitragynine present in the kratom leaf. 7-OH binds to opioid receptors like mitragynine, but research suggests that 7-OH binds with greater potency.
Nalfurafine is an antipruritic that is marketed in Japan for the treatment of uremic pruritus in individuals with chronic kidney disease undergoing hemodialysis. It activates the κ-opioid receptor (KOR) and is potent, selective, and centrally active. It was the first selective KOR agonist approved for clinical use. It has also been dubiously referred to as the "first non-narcotic opioid drug" in history.
Coronaridine, also known as 18-carbomethoxyibogamine, is an alkaloid found in Tabernanthe iboga and related species, including Tabernaemontana divaricata for which it was named.
Ibogamine is an anti-convulsant, anti-addictive, CNS stimulant alkaloid found in Tabernanthe iboga and Crepe Jasmine. Basic research related to how addiction affects the brain has used this chemical.
Tabernanthine is an alkaloid found in Tabernanthe iboga.
(−)-2-Methoxyethyl-18-methoxycoronaridinate (ME-18-MC) is a second generation synthetic derivative of ibogaine developed by the research team led by the pharmacologist Stanley D. Glick from the Albany Medical College and the chemist Martin E. Kuehne from the University of Vermont. In animal studies it has shown similar efficacy to the related compound 18-methoxycoronaridine (18-MC) at reducing self-administration of morphine and methamphetamine but with higher potency by weight, showing anti-addictive effects at the equivalent of half the minimum effective dose of 18-MC. Similarly to 18-MC itself, ME-18-MC acts primarily as a selective α3β4 nicotinic acetylcholine antagonist, although it has a slightly stronger effect than 18-MC as an NMDA antagonist, and its effects on opioid receptors are weaker than those of 18-MC at all except the kappa opioid receptor, at which it has slightly higher affinity than 18-MC.
(−)-18-Methylaminocoronaridine (18-MAC) is a second generation synthetic derivative of ibogaine developed by the research team led by the pharmacologist Stanley D. Glick from the Albany Medical College and the chemist Martin E. Kuehne from the University of Vermont.
Mitragynine pseudoindoxyl is a rearrangement product of 7-hydroxymitragynine an active metabolite of mitragynine. It is an analgesic being more potent than morphine.
6′-Guanidinonaltrindole (6′-GNTI) is a κ–δ-opioid receptor selective ligand used in scientific research.
Buprenorphine/samidorphan is a combination formulation of buprenorphine and samidorphan which is under development as an add on to antidepressants in treatment-resistant depression (TRD).
RB-64 is a semi-synthetic derivative of salvinorin A. It is an irreversible agonist, with a reactive thiocyanate group that forms a bond to the κ-opioid receptor (KOR), resulting in very high potency. It is functionally selective, activating G proteins more potently than β-arrestin-2. RB-64 has a bias factor of up to 96 and is analgesic with fewer of the side-effects associated with unbiased KOR agonists. The analgesia is long-lasting. Compared with unbiased agonists, RB-64 evokes considerably less receptor internalization.
Iboga-type alkaloids are a set of monoterpene indole alkaloids comprising naturally occurring compounds found in Tabernanthe and Tabernaemontana, as well as synthetic structural analogs. Naturally occurring iboga-type alkaloids include ibogamine, ibogaine, tabernanthine, and other substituted ibogamines (see below). Many iboga-type alkaloids display biological activities such as cardiac toxicity and psychoactive effects, and some have been studied as potential treatments for drug addiction.
References
↑ Mash DC, Ameer B, Prou D, Howes JF, Maillet EL (2016). "Oral noribogaine shows high brain uptake and anti-withdrawal effects not associated with place preference in rodents". J. Psychopharmacol. (Oxford). 30 (7): 688–97. doi:10.1177/0269881116641331. PMID27044509. S2CID40776971.
↑ Baumann MH, Pablo J, Ali SF, Rothman RB, Mash DC (2001). "Comparative neuropharmacology of ibogaine and its O-desmethyl metabolite, noribogaine". The Alkaloids: Chemistry and Biology. 56: 79–113. doi:10.1016/S0099-9598(01)56009-5. PMID11705118.
↑ Pearl SM, Herrick-Davis K, Teitler M, Glick SD (March 1995). "Radioligand-binding study of noribogaine, a likely metabolite of ibogaine". Brain Research. 675 (1–2): 342–344. doi:10.1016/0006-8993(95)00123-8. PMID7796150. S2CID28001919.
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