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] With an IC50 value of 1μM, it can be regarded as an antagonist of the latter pathway.[13]
In 2024, a synthetic benzofuran analog (oxa-noribogaine) was reported that is devoid of the pro-arrhythmic side effect. It has analgesic effects as a potent (atypical) kappa-opioid receptor partial agonist and, opposed to standard KOR agonists, is characterized by the absence of pro-depressant effects. It induces a robust KOR-dependent increase in GDNF protein levels in the ventral tegmental area and medial prefrontal cortex. After a single dose or short-term treatment, oxa-noribogaine induces long-lasting suppression of opioid drug seeking in rodent relapse models. It also counteracts persistent opioid-induced hyperalgesia.[15]
Ibogaine is a psychoactive indole alkaloid obtained either by extraction from plants in the family Apocynaceae such as Tabernanthe iboga, Voacanga africana, and Tabernaemontana undulata or by semi-synthesis from the precursor compound voacangine, another plant alkaloid. The total synthesis of ibogaine was described in 1956. Structural elucidation by X-ray crystallography was completed in 1960.
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 proven 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.
Indole alkaloids are a class of alkaloids containing a structural moiety of indole; many indole alkaloids also include isoprene groups and are thus called terpene indole or secologanin tryptamine alkaloids. Containing more than 4100 known different compounds, it is one of the largest classes of alkaloids. Many of them possess significant physiological activity and some of them are used in medicine. The amino acid tryptophan is the biochemical precursor of indole alkaloids.
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 mitragynine present in the kratom leaf. 7-OH binds to opioid receptors like mitragynine, but research suggests that 7-OH binds with greater efficacy.
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.
Dezocine, sold under the brand name Dalgan, is an atypical opioid analgesic which is used in the treatment of pain. It is used by intravenous infusion and intramuscular injection.
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.
ICI-199,441 is a drug which acts as a potent and selective κ-opioid agonist, and has analgesic effects. It is a biased agonist of the KOR, and is one of relatively few KOR ligands that is G protein-biased rather than β-arrestin-biased.
(−)-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.
Mitragynine pseudoindoxyl is a rearrangement product of 7-hydroxymitragynine, an active metabolite of mitragynine.
6′-Guanidinonaltrindole (6′-GNTI) is a κ–δ-opioid receptor selective ligand used in scientific research.
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. 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.
PZM21 is an experimental opioid analgesic drug that is being researched for the treatment of pain. It is claimed to be a functionally selective μ-opioid receptor agonist which produces μ-opioid receptor mediated G protein signaling, with potency and efficacy similar to morphine, but with less β-arrestin 2 recruitment. However, recent reports highlight that this might be due to its low intrinsic efficacy, rather than functional selectivity or 'G protein bias' as initially reported. In tests on mice, PZM21 was slightly less potent than morphine or TRV130 as an analgesic, but also had significantly reduced adverse effects, with less constipation than morphine, and very little respiratory depression, even at high doses. This research was described as a compelling example of how modern high-throughput screening techniques can be used to discover new chemotypes with specific activity profiles, even at targets such as the μ-opioid receptor which have already been thoroughly investigated. More recent research has suggested however that at higher doses, PZM21 is capable of producing classic opioid side effects such as respiratory depression and development of tolerance and may have only limited functional selectivity.
Collybolide is a secondary metabolite of the Rhodocollybia maculata mushroom, a basidiomycete fungus that grows on rotting conifer wood. It was previously believed to be a potent and selective kappa-opioid receptor agonist. However, a total synthesis and independent biological assay determined that collybolide neither excites nor suppresses kappa-opioid receptor signaling. Collybolide is unlikely to be psychoactive, although it has been shown to inhibit L-type calcium channels in isolated rat aorta.
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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