Oral noribogaine shows high brain uptake and anti-withdrawal effects not associated with place preference in rodents

This study investigated the effects of noribogaine, the principal metabolite of the drug ibogaine, on substance-related disorders. In the first experiment, mice chronically treated with morphine were subjected to naloxone-precipitated withdrawal two hours after oral administration of noribogaine. Oral noribogaine dose dependently decreased the global opiate withdrawal score by up to 88% of vehicle control with an ED50 of 13 mg/kg. In the second experiment, blood and brain levels of noribogaine showed a high brain penetration and a brain/blood ratio of 7±1 across all doses tested. In a third experiment, rats given oral noribogaine up to 100 mg/kg were tested for abuse liability using a standard biased conditioned place paradigm. Noribogaine-treated rats did not display place preference, suggesting that noribogaine is not perceived as a hedonic stimulus in rodents. Retrospective review of published studies assessing the efficacy of ibogaine on morphine withdrawal shows that the most likely cause of the discrepancies in the literature is the different routes of administration and time of testing following ibogaine administration. These results suggest that the metabolite noribogaine rather than the parent compound mediates the effects of ibogaine on blocking naloxone-precipitated withdrawal. Noribogaine may hold promise as a non-addicting alternative to standard opiate replacement therapies to transition patients to opiate abstinence

Safety, tolerability, pharmacokinetics, and subjective effects of 50, 75, and 100 μg LSD in healthy participants within a novel intervention paradigm: A proof-of-concept study

Background: Classic psychedelics hold promise as therapeutics for psychiatric disorders, but require scalable intervention protocols. This proof-of-concept study evaluated the safety, tolerability, pharmacokinetics, and subjective effects of 50, 75, and 100 μg lysergic acid diethylamide (LSD) in healthy adults within a novel intervention paradigm. Methods: Up to three participants were administered LSD on the same day in separate rooms, each with a single attendant, after 1 day of preparation. An open-label design and a double-blind placebo-controlled design were used. Results: Ninety-one percent of participants completed the study. Thirty-two adults (mean age = 28.8 years) received 50 (n = 3), 75 (n = 7), 100 (n = 3) LSD, 50 μg followed by 75 μg LSD (n = 9) 1 week apart, or placebo followed by a 75 μg LSD (n = 10) 1 week apart. There were no serious adverse events. Twenty-eight percent of participants experienced at least one expected mild adverse event, with one expected moderate adverse event. The maximum blood plasma levels occurred between 1.2 and 2 h post-administration, with an apparent half-life between 2.8 and 4.3 h. LSD largely induced greater subjective effects versus placebo. Conclusion: In the current novel intervention paradigm, 50, 75, and 100 μg LSD are tolerable with favourable safety profiles in healthy adults, only mild adverse events during the day of drug administration, and mystical-type subjective experiences. Future studies are needed to evaluate safety, tolerability, subjective effects, and cost-effectiveness in clinical populations

DUAL MODULATION OF NK2 TACHYKININ RECEPTOR SIGNALLING PATHWAYS BY AN ALLOSTERIC COMPOUND.Running Title: Dual allosteric modulation of NK2R

International audienceWhen stimulated by its natural agonist, neurokinin A, the tachykinin NK2 receptor undergoes stabilization in two active states that mediate distinct intracellular responses, a phospholipase C-mediated calcium response and an adenylyl cyclase-mediated cAMP production. Here, we show that the new compound LPI 805 modulates not only binding of agonists, but also differentially affects calcium and cAMP responses in opposite ways. LPI 805 has no biological activity by itself. It accelerates dissociation kinetics of bound neurokinin A by altering the equilibrium between the two active states of the NK2 receptor. In co-application with agonists, LPI 805 potentiates calcium responses and simultaneously decreases, or even abolishes, cAMP-dependent responses of NK2 receptors. LPI 805 thus behaves as an allosteric modulator that exhibits dual positive/negative response regulation of the NK2 tachykinin receptor. These data not only strengthen to the notion of multiple active, and interconvertible conformations of G protein-coupled receptors, but also opens new ways to design pharmacological agents able to selectively modulate a subset of intracellular responses linked to members of this important receptor family

Allosteric Functional Switch of Neurokinin A-Mediated Signaling at the Neurokinin NK2 Receptor: Structural Exploration

International audienceThe neurokinin NK2 receptor is known to pre-exist in equilibrium between at least three states: resting-inactive, calcium-triggering, and cAMP-producing. Its endogeneous ligand, NKA, mainly induces the calcium response. Using a FRET-based assay, we have previously discovered an allosteric modulator of the NK2 receptor that has the unique ability to discriminate among the two signaling pathways: calcium-signaling is not affected while cAMP signaling is significantly decreased. A series of compounds have been prepared and studied in order to better understand the structural determinants of this allosteric functional switch of a GPCR. Most of them display the same allosteric profile, with smooth pharmacomodulation. One compound however exhibits significantly improved modulatory properties of NKA induced signaling when compared to the original modulator

Noribogaine is a G-protein biased κ-opioid receptor agonist

Noribogaine is the long-lived human metabolite of the anti-addictive substance ibogaine. Noribogaine efficaciously reaches the brain with concentrations up to 20 μM after acute therapeutic dose of 40 mg/kg ibogaine in animals. Noribogaine displays atypical opioid-like components in vivo, anti-addictive effects and potent modulatory properties of the tolerance to opiates for which the mode of action remained uncharacterized thus far. Our binding experiments and computational simulations indicate that noribogaine may bind to the orthosteric morphinan binding site of the opioid receptors. Functional activities of noribogaine at G-protein and non G-protein pathways of the mu and kappa opioid receptors were characterized. Noribogaine was a weak mu antagonist with a functional inhibition constants (Ke) of 20 μM at the G-protein and β-arrestin signaling pathways. Conversely, noribogaine was a G-protein biased kappa agonist 75% as efficacious as dynorphin A at stimulating GDP-GTP exchange (EC50 = 9 μM) but only 12% as efficacious at recruiting β-arrestin, which could contribute to the lack of dysphoric effects of noribogaine. In turn, noribogaine functionally inhibited dynorphin-induced kappa β-arrestin recruitment and was more potent than its G-protein agonistic activity with an IC50 of 1 μM. This biased agonist/antagonist pharmacology is unique to noribogaine in comparison to various other ligands including ibogaine, 18-MC, nalmefene, and 6′-GNTI. We predict noribogaine to promote certain analgesic effects as well as anti-addictive effects at effective concentrations >1 μM in the brain. Because elevated levels of dynorphins are commonly observed and correlated with anxiety, dysphoric effects, and decreased dopaminergic tone, a therapeutically relevant functional inhibition bias to endogenously released dynorphins by noribogaine might be worthy of consideration for treating anxiety and substance related disorders. •The anti-addictive drug noribogaine was functionally characterized at the opioid receptors.•Noribogaine is a G-protein biased kappa opioid agonist.•Noribogaine is also a mu antagonist and a beta-arrestin biased kappa antagonist.•The unique pharmacological profile of noribogaine may explain its atypical effects on the opioid system in vivo

G Protein-Coupled Receptor Heteromerization: A Role in Allosteric Modulation of Ligand BindingS⃞

It is becoming increasingly recognized that G protein-coupled receptors physically interact. These interactions may provide a mechanism for allosteric modulation of receptor function. In this study, we examined this possibility by using an established model system of a receptor heteromer consisting of μ and δ opioid receptors. We examined the effect of a number of μ receptor ligands on the binding equilibrium and association and dissociation kinetics of a radiolabeled δ receptor agonist, [3H]deltorphin II. We also examined the effect of δ receptor ligands on the binding equilibrium and association and dissociation kinetics of a radiolabeled μ receptor agonist, [3H][d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin ([3H]DAMGO). We show that μ receptor ligands are capable of allosterically enhancing δ receptor radioligand binding and vice versa. Thus, there is strong positive cooperativity between the two receptor units with remarkable consequences for ligand pharmacology. We find that the data can be simulated by adapting an allosteric receptor model previously developed for small molecules, suggesting that the ligand-occupied protomers function as allosteric modulators of the partner receptor's activity