Pharmacological screen for activities of 12-hydroxyibogamine: a primary metabolite of the indole alkaloid ibogaine

Noribogaine acute administration in rats promotes wakefulness and suppresses REM sleep

Ibogaine is a potent atypical psychedelic that has gained considerable attention due to its antiaddictive and antidepressant properties in preclinical and clinical studies. Previous research from our group showed that ibogaine suppresses sleep and produces an altered wakefulness state, which resembles natural REM sleep. However, after systemic administration, ibogaine is rapidly metabolized to noribogaine, which also shows antiaddictive effects but with a distinct pharmacological profile, making this drug a promising therapeutic candidate. Therefore, we still ignore whether the sleep/wake alterations depend on ibogaine or its principal metabolite noribogaine. To answer this question, we conducted polysomnographic recordings in rats following the administration of pure noribogaine. Our results show that noribogaine promotes wakefulness while reducing slow-wave sleep and blocking REM sleep, similar to our previous results reported for ibogaine administration. Thus, we shed new evidence on the mechanisms by which iboga alkaloids work in the brain.

5-HT2A Receptor Knockout Mice Show Sex-Dependent Differences following Acute Noribogaine Administration

Noribogaine (noribo) is the primary metabolite from ibogaine, an atypical psychedelic alkaloid isolated from the root bark of the African shrub Tabernanthe iboga. The main objective of this study was to test the hypothesis that molecular, electrophysiological, and behavioral responses of noribo are mediated by the 5-HT2A receptor (5-HT2AR) in mice. In that regard, we used male and female, 5-HT2AR knockout (KO) and wild type (WT) mice injected with a single noribo dose (10 or 40 mg/kg; i.p.). After 30 min., locomotor activity was recorded followed by mRNA measurements by qPCR (immediate early genes; IEG, glutamate receptors, and 5-HT2AR levels) and electrophysiology recordings of layer V pyramidal neurons from the medial prefrontal cortex. Noribo 40 decreased locomotion in male, but not female WT. Sex and genotype differences were observed for IEG and glutamate receptor expression. Expression of 5-HT2AR mRNA increased in the mPFC of WT mice following Noribo 10 (males) or Noribo 40 (females). Patch-clamp recordings showed that Noribo 40 reduced the NMDA-mediated postsynaptic current density in mPFC pyramidal neurons only in male WT mice, but no effects were found for either KO males or females. Our results highlight that noribo produces sexually dimorphic effects while the genetic removal of 5HT2AR blunted noribo-mediated responses to NMDA synaptic transmission.

Main targets of ibogaine and noribogaine associated with its putative anti-addictive effects: A mechanistic overview

BACKGROUND

There is a growing interest in studying ibogaine (IBO) as a potential treatment for substance use disorders (SUDs). However, its clinical use has been hindered for mainly two reasons: First, the lack of randomized, controlled studies informing about its safety and efficacy. And second, IBO's mechanisms of action remain obscure. It has been challenging to elucidate a predominant mechanism of action responsible for its anti-addictive effects.

OBJECTIVE

To describe the main targets of IBO and its main metabolite, noribogaine (NOR), in relation to their putative anti-addictive effects, reviewing the updated literature available.

METHODS

A comprehensive search involving MEDLINE and Google Scholar was undertaken, selecting papers published until July 2022. The inclusion criteria were both theoretical and experimental studies about the pharmacology of IBO. Additional publications were identified in the references of the initial papers.

RESULTS

IBO and its main metabolite, NOR, can modulate several targets associated with SUDs. Instead of identifying key targets, the action of IBO should be understood as a complex modulation of multiple receptor systems, leading to potential synergies. The elucidation of IBO's pharmacology could be enhanced through the application of methodologies rooted in the polypharmacology paradigm. Such approaches possess the capability to describe multifaceted patterns within multi-target drugs.

CONCLUSION

IBO displays complex effects through multiple targets. The information detailed here should guide future research on both mechanistic and therapeutic studies.

IUPHAR - invited review - Ibogaine - A legacy within the current renaissance of psychedelic therapy

Ibogaine is a powerful psychoactive substance that not only alters perception, mood and affect, but also stops addictive behaviors. Ibogaine has a very long history of ethnobotanical use in low doses to combat fatigue, hunger and thirst and, in high doses as a sacrament in African ritual contexts. In the 1960's, American and European self-help groups provided public testimonials that a single dose of ibogaine alleviated drug craving, opioid withdrawal symptoms, and prevented relapse for weeks, months and sometimes years. Ibogaine is rapidly demethylated by first-pass metabolism to a long-acting metabolite noribogaine. Ibogaine and its metabolite interact with two or more CNS targets simultaneously and both drugs have demonstrated predictive validity in animal models of addiction. Online forums endorse the benefits of ibogaine as an "addiction interrupter" and present-day estimates suggest that more than ten thousand people have sought treatment in countries where the drug is unregulated. Open label pilot studies of ibogaine-assisted drug detoxification have shown positive benefit in treating addiction. Ibogaine, granted regulatory approval for human testing in a Phase 1/2a clinical trial, joins the current landscape of psychedelic medicines in clinical development.

Three Naturally-Occurring Psychedelics and Their Significance in the Treatment of Mental Health Disorders

Classical psychedelics represent a family of psychoactive substances with structural similarities to serotonin and affinity for serotonin receptors. A growing number of studies have found that psychedelics can be effective in treating various psychiatric conditions, including post-traumatic stress disorder, major depressive disorder, anxiety, and substance use disorders. Mental health disorders are extremely prevalent in the general population constituting a major problem for the public health. There are a wide variety of interventions for mental health disorders, including pharmacological therapies and psychotherapies, however, treatment resistance still remains a particular challenge in this field, and relapse rates are also quite high. In recent years, psychedelics have become one of the promising new tools for the treatment of mental health disorders. In this review, we will discuss the three classic serotonergic naturally occurring psychedelics, psilocybin, ibogaine, and N, N-dimethyltryptamine, focusing on their pharmacological properties and clinical potential. The purpose of this article is to provide a focused review of the most relevant research into the therapeutic potential of these substances and their possible integration as alternative or adjuvant options to existing pharmacological and psychological therapies.

Drug Transporters ABCB1 (P-gp) and OATP, but not Drug-Metabolizing Enzyme CYP3A4, Affect the Pharmacokinetics of the Psychoactive Alkaloid Ibogaine and its Metabolites

The psychedelic alkaloid ibogaine is increasingly used as an oral treatment for substance use disorders, despite being unlicensed in most countries and having reported adverse events. Using wild-type and genetically modified mice, we investigated the impact of mouse (m)Abcb1a/1b and Abcg2 drug efflux transporters, human and mouse OATP drug uptake transporters, and the CYP3A drug-metabolizing complex on the pharmacokinetics of ibogaine and its main metabolites. Following oral ibogaine administration (10 mg/kg) to mice, we observed a rapid and extensive conversion of ibogaine to noribogaine (active metabolite) and noribogaine glucuronide. Mouse Abcb1a/1b, in combination with mAbcg2, modestly restricted the systemic exposure (plasma AUC) and peak plasma concentration (Cmax) of ibogaine. Accordingly, we found a ∼2-fold decrease in the relative recovery of ibogaine in the small intestine with fecal content in the absence of both transporters compared to the wild-type situation. Ibogaine presented good intrinsic brain penetration even in wild-type mice (brain-to-plasma ratio of 3.4). However, this was further increased by 1.5-fold in Abcb1a/1b;Abcg2−/− mice, but not in Abcg2−/− mice, revealing a stronger effect of mAbcb1a/1b in restricting ibogaine brain penetration. The studied human OATP transporters showed no major impact on ibogaine plasma and tissue disposition, but the mOatp1a/1b proteins modestly affected the plasma exposure of ibogaine metabolites and the tissue disposition of noribogaine glucuronide. No considerable role of mouse Cyp3a knockout or transgenic human CYP3A4 overexpression was observed in the pharmacokinetics of ibogaine and its metabolites. In summary, ABCB1, in combination with ABCG2, limits the oral availability of ibogaine, possibly by mediating its hepatobiliary and/or direct intestinal excretion. Moreover, ABCB1 restricts ibogaine brain penetration. Variation in ABCB1/ABCG2 activity due to genetic variation and/or pharmacologic inhibition might therefore affect ibogaine exposure in patients, but only to a limited extent. The insignificant impact of human CYP3A4 and OATP1B1/1B3 transporters may be clinically advantageous for ibogaine and noribogaine use, as it decreases the risks of undesirable drug interactions or interindividual variation related to CYP3A4 and/or OATP activity.

EEG Gamma Band Alterations and REM-like Traits Underpin the Acute Effect of the Atypical Psychedelic Ibogaine in the Rat

Ibogaine is a psychedelic alkaloid that has attracted large scientific interest because of its antiaddictive properties in observational studies in humans as well as in animal models. Its subjective effect has been described as intense, vivid dream-like experiences occurring while awake; hence, ibogaine is often referred to as an oneirogenic psychedelic. While this unique dream-like profile has been hypothesized to aid the antiaddictive effects, the electrophysiological signatures of this psychedelic state remain unknown. We previously showed in rats that ibogaine promotes a waking state with abnormal motor behavior along with a decrease in NREM and REM sleep. Here, we performed an in-depth analysis of the intracranial electroencephalogram during "ibogaine wakefulness". We found that ibogaine induces gamma oscillations that, despite having larger power than control levels, are less coherent and less complex. Further analysis revealed that this profile of gamma activity compares to that of natural REM sleep. Thus, our results provide novel biological evidence for the association between the psychedelic state and REM sleep, contributing to the understanding of the brain mechanisms associated with the oneirogenic psychedelic effect of ibogaine.

The iboga enigma: the chemistry and neuropharmacology of iboga alkaloids and related analogs

Covering: 2000 up to 2020 Few classes of natural products have inspired as many chemists and biologists as have the iboga alkaloids. This family of monoterpenoid indole alkaloids includes the anti-addictive compound ibogaine as well as catharanthine, a precursor to the chemotherapeutic vinblastine. Despite being known for over 120 years, these small molecules continue to challenge our assumptions about biosynthetic pathways, catalyze our creativity for constructing complex architectures, and embolden new approaches for treating mental illness. This review will cover recent advances in both the biosynthesis and chemical synthesis of iboga alkaloids as well as their use as next-generation neurotherapeutics. Whenever appropriate, we provide historical context for the discoveries of the past decade and indicate areas that have yet to be resolved. While significant progress regarding their chemistry and pharmacology has been made since the 1960s, it is clear that the iboga alkaloids will continue to stoke scientific innovation for years to come.

A Single Administration of the Atypical Psychedelic Ibogaine or Its Metabolite Noribogaine Induces an Antidepressant-Like Effect in Rats

Anecdotal reports and open-label case studies in humans indicated that the psychedelic alkaloid ibogaine exerts profound antiaddictive effects. Ample preclinical evidence demonstrated the efficacy of ibogaine, and its main metabolite, noribogaine, in substance-use-disorder rodent models. In contrast to addiction research, depression-relevant effects of ibogaine or noribogaine in rodents have not been previously examined. We have recently reported that the acute ibogaine administration induced a long-term increase of brain-derived neurotrophic factor mRNA levels in the rat prefrontal cortex, which led us to hypothesize that ibogaine may elicit antidepressant-like effects in rats. Accordingly, we characterized behavioral effects (dose- and time-dependence) induced by the acute ibogaine and noribogaine administration in rats using the forced swim test (FST, 20 and 40 mg/kg i.p., single injection for each dose). We also examined the correlation between plasma and brain concentrations of ibogaine and noribogaine and the elicited behavioral response. We found that ibogaine and noribogaine induced a dose- and time-dependent antidepressant-like effect without significant changes of animal locomotor activity. Noribogaine's FST effect was short-lived (30 min) and correlated with high brain concentrations (estimated >8 μM of free drug), while the ibogaine's antidepressant-like effect was significant at 3 h. At this time point, both ibogaine and noribogaine were present in rat brain at concentrations that cannot produce the same behavioral outcome on their own (ibogaine ∼0.5 μM, noribogaine ∼2.5 μM). Our data suggests a polypharmacological mechanism underpinning the antidepressant-like effects of ibogaine and noribogaine.

Human Serotonin Transporter Coding Variation Establishes Conformational Bias with Functional Consequences

The antidepressant-sensitive serotonin (5-HT) transporter (SERT) dictates rapid, high-affinity clearance of the neurotransmitter in both the brain and periphery. In a study of families with multiple individuals diagnosed with autism spectrum disorder (ASD), we previously identified several, rare, missense coding variants that impart elevated 5-HT transport activity, relative to wild-type SERT, upon heterologous expression as well as in ASD subject lymphoblasts. The most common of these variants, SERT Ala56, located in the transporter's cytosolic N-terminus, has been found to confer in transgenic mice hyperserotonemia, an ASD-associated biochemical trait, an elevated brain 5-HT clearance rate, and ASD-aligned behavioral changes. Hyperfunction of SERT Ala56 has been ascribed to a change in 5-HT KM, though the physical basis of this change has yet to be elucidated. Through assessments of fluorescence resonance energy transfer (FRET) between cytosolic N- and C-termini, sensitivity to methanethiosulfonates, and capacity for N-terminal tryptic digestion, we obtain evidence for mutation-induced conformational changes that support an open-outward 5-HT binding conformation in vitro and in vivo. Aspects of these findings were also evident with another naturally occurring C-terminal SERT coding variant identified in our ASD study, Asn605. We conclude that biased conformations of surface resident transporters that can impact transporter function and regulation are an unappreciated consequence of heritable and disease-associated SERT coding variation.

Ibogaine Administration Modifies GDNF and BDNF Expression in Brain Regions Involved in Mesocorticolimbic and Nigral Dopaminergic Circuits

Ibogaine is an atypical psychedelic alkaloid, which has been subject of research due to its reported ability to attenuate drug-seeking behavior. Recent work has suggested that ibogaine effects on alcohol self-administration in rats are related to the release of Glial cell Derived Neurotrophic Factor (GDNF) in the Ventral Tegmental Area (VTA), a mesencephalic region which hosts the soma of dopaminergic neurons. Although previous reports have shown ibogaine’s ability to induce GDNF expression in rat midbrain, there are no studies addressing its effect on the expression of GDNF and other neurotrophic factors (NFs) such as Brain Derived Neurotrophic Factor (BDNF) or Nerve Growth Factor (NGF) in distinct brain regions containing dopaminergic neurons. In this work, we examined the effect of ibogaine acute administration on the expression of these NFs in the VTA, Prefrontal Cortex (PFC), Nucleus Accumbens (NAcc) and the Substantia Nigra (SN). Rats were i.p. treated with ibogaine 20 mg/kg (I₂₀), 40 mg/kg (I₄₀) or vehicle, and NFs expression was analyzed after 3 and 24 h. At 24 h an increase of the expression of the NFs transcripts was observed in a site and dose dependent manner. Only for I₄₀, GDNF was selectively upregulated in the VTA and SN. Both doses elicited a large increase in the expression of BDNF transcripts in the NAcc, SN and PFC, while in the VTA a significant effect was found only for I₄₀. Finally, NGF mRNA was upregulated in all regions after I₄₀, while I₂₀ showed a selective upregulation in PFC and VTA. Regarding protein levels, an increase of GDNF was observed in the VTA only for I₄₀ but no significant increase for BDNF was found in all the studied areas. Interestingly, an increase of proBDNF was detected in the NAcc for both doses. These results show for the first time a selective increase of GDNF specifically in the VTA for I₄₀ but not for I₂₀ after 24 h of administration, which agrees with the effective dose found in previous self-administration studies in rodents. Further research is needed to understand the contribution of these changes to ibogaine’s ability to attenuate drug-seeking behavior.

Substrate and inhibitor binding to the serotonin transporter: Insights from computational, crystallographic, and functional studies

The serotonin transporter (SERT) belongs to the monoamine transporter family, which also includes the dopamine and norepinephrine transporters. SERT is essential for regulating serotonergic signaling by the reuptake of serotonin from the synaptic cleft back into the presynaptic neuron. Dysregulation of SERT has been implicated in several major psychiatric disorders such as major depressive disorder (MDD). MDD was among the top five leading causes of years lived with disease in 2016 and is characterized as a major global burden. Several drugs have been developed to target SERT for use in the treatment of MDD, and their respective binding modes and locations within SERT have been studied. The elucidation of the first structure of a bacterial SERT homologue in 2005 has accelerated crystallographic, computational, and functional studies to further elucidate drug binding and method of action in SERT. Herein, we aim to highlight and compare these studies with an emphasis on what the different experimental methods conclude on substrate and inhibitor binding modes, and the potential caveats of using the different types of studies are discussed. We focus this review on the binding of cognate substrate and drugs belonging to the different families of antidepressants, including tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and multimodal drugs, as well as illicit drugs such as cocaine, amphetamines, and ibogaine. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Ibogaine Detoxification Transitions Opioid and Cocaine Abusers Between Dependence and Abstinence: Clinical Observations and Treatment Outcomes

Ibogaine may be effective for transitioning opioid and cocaine dependent individuals to sobriety. American and European self-help groups provided public testimonials that ibogaine alleviated drug craving and opioid withdrawal symptoms after only a single dose administration. Preclinical studies in animal models of addiction have provided proof-of-concept evidence in support of these claims. However, the purported therapeutic benefits of ibogaine are based on anecdotal reports from a small series of case reports that used retrospective recruitment procedures. We reviewed clinical results from an open label case series (N = 191) of human volunteers seeking to detoxify from opioids or cocaine with medical monitoring during inpatient treatment. Whole blood was assayed to obtain pharmacokinetic measures to determine the metabolism and clearance of ibogaine. Clinical safety data and adverse events (AEs) were studied in male and female subjects. There were no significant adverse events following administration of ibogaine in a dose range that was shown to be effective for blocking opioid withdrawal symptoms in this study. We used multi-dimensional craving questionnaires during inpatient detoxification to test if ibogaine was effective in diminishing heroin and cocaine cravings. Participants also completed standardized questionnaires about their health and mood before and after ibogaine treatment, and at program discharge. One-month follow-up data were reviewed where available to determine if ibogaine's effects on drug craving would persist outside of an inpatient setting. We report here that ibogaine therapy administered in a safe dose range diminishes opioid withdrawal symptoms and reduces drug cravings. Pharmacological treatments for opioid dependence include detoxification, narcotic antagonists and long-term opioid maintenance therapy. Our results support product development of single oral dose administration of ibogaine for the treatment of opioid withdrawal during medically supervised detoxification to transition drug dependent individuals to abstinence.

Ibogaine Acute Administration in Rats Promotes Wakefulness, Long-Lasting REM Sleep Suppression, and a Distinctive Motor Profile

Ibogaine is a potent psychedelic alkaloid that has been the focus of intense research because of its intriguing anti-addictive properties. According to anecdotic reports, ibogaine has been originally classified as an oneirogenic psychedelic; i.e., induces a dream-like cognitive activity while awake. However, the effects of ibogaine administration on wakefulness (W) and sleep have not been thoroughly assessed. The main aim of our study was to characterize the acute effects of ibogaine administration on W and sleep. For this purpose, polysomnographic recordings on chronically prepared rats were performed in the light phase during 6 h. Animals were treated with ibogaine (20 and 40 mg/kg) or vehicle, immediately before the beginning of the recordings. Furthermore, in order to evaluate associated motor behaviors during the W period, a different group of animals was tested for 2 h after ibogaine treatment on an open field with video-tracking software. Compared to control, animals treated with ibogaine showed an increase in time spent in W. This effect was accompanied by a decrease in slow wave sleep (SWS) and rapid-eye movements (REM) sleep time. REM sleep latency was significantly increased in animals treated with the higher ibogaine dose. While the effects on W and SWS were observed during the first 2 h of recordings, the decrement in REM sleep time was observed throughout the recording time. Accordingly, ibogaine treatment with the lower dose promoted an increase on locomotion, while tremor and flat body posture were observed only with the higher dose in a time-dependent manner. In contrast, head shake response, a behavior which has been associated in rats with the 5HT_2A receptor activation by hallucinogens, was not modified. We conclude that ibogaine promotes a waking state that is accompanied by a robust and long-lasting REM sleep suppression. In addition, it produces a dose-dependent unusual motor profile along with other serotonin-related behaviors. Since ibogaine is metabolized to produce noribogaine, further experiments are needed to elucidate if the metabolite and/or the parent drug produced these effects.

Anxiolytic-like effects of noribogaine in zebrafish

Noribogaine is the main psychoactive metabolite of the hallucinogenic drug ibogaine, and is a particularly interesting compound potentially useful to treat dependence and various psychiatric disorders. Here, we report the effects of noribogaine on anxiety and locomotion in zebrafish (Danio rerio), a new promising model organism in neurobehavioral and psychopharmacological research. Adult zebrafish were subjected to the 5min novel tank test (NTT) following an acute, 20-min drug immersion in 1, 5 and 10mg/L noribogaine. Overall, noribogaine produced robust anxiolytic-like behavior in zebrafish (increasing the time spent and transitions to the top half compartment and reducing freezing bouts) without overt effects on fish locomotion. Taken together, these results indicate that noribogaine modulates the components of the acute stress response related to emotionality and anxiety behaviors, implicating this drug as a potentially useful non-sedative anxiolytic agent.

Ibogaine for treating drug dependence. What is a safe dose?

The indole alkaloid ibogaine, present in the root bark of the West African rain forest shrub Tabernanthe iboga, has been adopted in the West as a treatment for drug dependence. Treatment of patients requires large doses of the alkaloid to cause hallucinations, an alleged integral part of the patient's treatment regime. However, case reports and case series continue to describe evidences of ataxia, gastrointestinal distress, ventricular arrhythmias and sudden and unexplained deaths of patients undergoing treatment for drug dependence. High doses of ibogaine act on several classes of neurological receptors and transporters to achieve pharmacological responses associated with drug aversion; limited toxicology research suggests that intraperitoneal doses used to successfully treat rodents, for example, have also been shown to cause neuronal injury (purkinje cells) in the rat cerebellum. Limited research suggests lethality in rodents by the oral route can be achieved at approximately 263mg/kg body weight. To consider an appropriate and safe initial dose for humans, necessary safety factors need to be applied to the animal data; these would include factors such as intra- and inter-species variability and for susceptible people in a population (such as drug users). A calculated initial dose to treat patients could be approximated at 0.87mg/kg body weight, substantially lower than those presently being administered to treat drug users. Morbidities and mortalities will continue to occur unless practitioners reconsider doses being administered to their susceptible patients.

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.

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.

Noribogaine reduces nicotine self-administration in rats

Noribogaine, a polypharmacological drug with activities at opioid receptors, ionotropic nicotinic receptors, and serotonin reuptake transporters, has been investigated for treatment of substance abuse-related disorders. Smoking cessation has major benefits for both individuals and society, therefore the aim of this study was to evaluate the potential of noribogaine for use as a treatment for nicotine dependence. Adult male Sprague-Dawley rats were trained to self-administer nicotine intravenous. After initial food pellet training, followed by 26 sessions of nicotine self-administration training, the rats were administered noribogaine (12.5, 25 or 50 mg/kg orally), noribogaine vehicle, varenicline or saline using a within-subject design with a Latin square test schedule. Noribogaine dose-dependently decreased nicotine self-administration by up to 64% of saline-treated rats' levels and was equi-effective to 1.7 mg/kg intraperitoneal varenicline. Noribogaine was less efficient at reducing food pellets self-administration than at nicotine self-administration, inhibiting the nondrug reinforcing effects of palatable pellets by 23% at the highest dose. These results suggest that noribogaine dose-dependently attenuates drug-taking behavior for nicotine, attenuates the reinforcing effects of nicotine and is comparable to varenicline power in that regard. The findings from the present study hold promise for a new therapy to aid smoking cessation.

Effect of Iboga alkaloids on µ-opioid receptor-coupled G protein activation

OBJECTIVE

The iboga alkaloids are a class of small molecules defined structurally on the basis of a common ibogamine skeleton, some of which modify opioid withdrawal and drug self-administration in humans and preclinical models. These compounds may represent an innovative approach to neurobiological investigation and development of addiction pharmacotherapy. In particular, the use of the prototypic iboga alkaloid ibogaine for opioid detoxification in humans raises the question of whether its effect is mediated by an opioid agonist action, or if it represents alternative and possibly novel mechanism of action. The aim of this study was to independently replicate and extend evidence regarding the activation of μ-opioid receptor (MOR)-related G proteins by iboga alkaloids.

METHODS

Ibogaine, its major metabolite noribogaine, and 18-methoxycoronaridine (18-MC), a synthetic congener, were evaluated by agonist-stimulated guanosine-5´-O-(γ-thio)-triphosphate ([(35)S]GTPγS) binding in cells overexpressing the recombinant MOR, in rat thalamic membranes, and autoradiography in rat brain slices.

RESULTS AND SIGNIFICANCE

In rat thalamic membranes ibogaine, noribogaine and 18-MC were MOR antagonists with functional Ke values ranging from 3 uM (ibogaine) to 13 uM (noribogaine and 18MC). Noribogaine and 18-MC did not stimulate [(35)S]GTPγS binding in Chinese hamster ovary cells expressing human or rat MORs, and had only limited partial agonist effects in human embryonic kidney cells expressing mouse MORs. Ibogaine did not did not stimulate [(35)S]GTPγS binding in any MOR expressing cells. Noribogaine did not stimulate [(35)S]GTPγS binding in brain slices using autoradiography. An MOR agonist action does not appear to account for the effect of these iboga alkaloids on opioid withdrawal. Taken together with existing evidence that their mechanism of action also differs from that of other non-opioids with clinical effects on opioid tolerance and withdrawal, these findings suggest a novel mechanism of action, and further justify the search for alternative targets of iboga alkaloids.

Ibogaine and the inhibition of acetylcholinesterase

ETHNOPHARMACOLOGICAL RELEVANCE

Ibogaine is a psychoactive monoterpine indole alkaloid extracted from the root bark of Tabernanthe iboga Baill. that is used globally in medical and nonmedical settings to treat drug and alcohol addiction, and is of interest as an ethnopharmacological prototype for experimental investigation and pharmaceutical development. The question of whether ibogaine inhibits acetylcholinesterase (AChE) is of pharmacological and toxicological significance.

MATERIALS AND METHODS

AChE activity was evaluated utilizing reaction with Ellman's reagent with physostigmine as a control.

RESULTS

Ibogaine inhibited AChE with an IC(50) of 520±40 μM.

CONCLUSIONS

Ibogaine's inhibition of AChE is physiologically negligible, and does not appear to account for observations of functional effects in animals and humans that might otherwise suggest the possible involvement of pathways linked to muscarinic acetylcholine transmission.

Ibogaine, an anti-addictive drug: pharmacology and time to go further in development. A narrative review

Ibogaine is an indole alkaloid derived from the bark of the root of the African shrub Tabernanthe iboga. Psychoactive properties of ibogaine have been known for decades. More recently, based on experimental data from animals and anectodal reports in human, it has been found that this drug has anti-addictive effects. Several patents were published between 1969 and 1995. The pharmacology of ibogaine is quite complex, affecting many different neurotransmitter systems simultaneously. However, the pharmacological targets underlying the physiological and psychological actions of ibogaine are not completely understood. Ibogaine is rapidly metabolized in the body in noribogaine. The purpose of this article was to review data from the literature concerning physicochemical properties, bio-analytical methods, and pharmacology of ibogaine; this article will be focused on the use of this drug as anti-addictive agent.

Ibogaine, a noncompetitive inhibitor of serotonin transport, acts by stabilizing the cytoplasm-facing state of the transporter

Ibogaine, a hallucinogenic alkaloid with purported anti-addiction properties, inhibited serotonin transporter (SERT) noncompetitively by decreasing V(max) with little change in the K(m) for serotonin (5-HT). Ibogaine also inhibited binding to SERT of the cocaine analog 2beta-2-carbomethoxy-3-(4-[(125)I]iodophenyl)tropane. However, inhibition of binding was competitive, increasing the apparent K(D) without much change in B(max). Ibogaine increased the reactivity of cysteine residues positioned in the proposed cytoplasmic permeation pathway of SERT but not at nearby positions out of that pathway. In contrast, cysteines placed at positions in the extracellular permeation pathway reacted at slower rates in the presence of ibogaine. These results are consistent with the proposal that ibogaine binds to and stabilizes the state of SERT from which 5-HT dissociates to the cytoplasm, in contrast with cocaine, which stabilizes the state that binds extracellular 5-HT.

Medication Development of Ibogaine as a Pharmacotherapy for Drug Dependencea

The potential for deriving new psychotherapeutic medications from natural sources has led to renewed interest in rain forest plants as a source of lead compounds for the development of antiaddiction medications. Ibogaine is an indole alkaloid found in the roots of Tabernanthe iboga (Apocynaceae family), a rain forest shrub that is native to equatorial Africa. Ibogaine is used by indigenous peoples in low doses to combat fatigue, hunger and in higher doses as a sacrament in religious rituals. Members of American and European addict self-help groups have claimed that ibogaine promotes long-term drug abstinence from addictive substances, including psychostimulants and cocaine. Anecdotal reports attest that a single dose of ibogaine eliminates withdrawal symptoms and reduces drug cravings for extended periods of time. The purported antiaddictive properties of ibogaine require rigorous validation in humans. We have initiated a rising tolerance study using single administration to assess the safety of ibogaine for the treatment of cocaine dependency. The primary objectives of the study are to determine safety, pharmacokinetics and dose effects, and to identify relevant parameters of efficacy in cocaine-dependent patients. Pharmacokinetic and pharmacodynamic characteristics of ibogaine in humans are assessed by analyzing the concentration-time data of ibogaine and its desmethyl metabolite (noribogaine) from the Phase I trial, and by conducting in vitro experiments to elucidate the specific disposition processes involved in the metabolism of both parent drug and metabolite. The development of clinical safety studies of ibogaine in humans will help to determine whether there is a rationale for conducting efficacy trials in the future.

Complementary medicines in psychiatry: review of effectiveness and safety

BACKGROUND

The use of complementary medicines in those with mental health problems is well documented. However, their effectiveness is often not established and they may be less harmless than commonly assumed.

AIMS

To review the complementary medicines routinely encountered in psychiatric practice, their effectiveness, potential adverse effects and interactions.

METHOD

Electronic and manual literature search on the effectiveness and safety of psychotropic complementary medicines.

RESULTS

Potentially useful substances include ginkgo and hydergine as cognitive enhancers, passion flower and valerian as sedatives, St John's wort and s-adenosylmethionine as antidepressants, and selenium and folate to complement antidepressants. The evidence is less conclusive for the use of omega-3 fatty acids as augmentation treatment in schizophrenia, melatonin for tardive dyskinesia and 18-methoxycoronaridine, an ibogaine derivative, for the treatment of cocaine and heroin addiction.

CONCLUSIONS

Systematic clinical trials are needed to test promising substances. Meanwhile, those wishing to take psychotropic complementary medicines require appropriate advice.

Ibogaine attenuation of morphine withdrawal in mice: role of glutamate N-methyl-D-aspartate receptors

Ibogaine (IBO) is an alkaloid with putative antiaddictive properties, alleviating opiates dependence and withdrawal. The glutamate N-methyl-D-aspartate (NMDA) receptors have been implicated in the physiological basis of drug addiction; accordingly, IBO acts as a noncompetitive NMDA antagonist. The purpose of this study was to evaluate the effects of IBO on naloxone-induced withdrawal syndrome in morphine-dependent mice, focusing on the role of NMDA receptors. Jumping, a major behavioral expression of such withdrawal, was significantly (P<.01) inhibited by IBO (40 and 80 mg/kg, 64.2% and 96.9% inhibition, respectively) and MK-801 (0.15 and 0.30 mg/kg, 67.3% and 97.7%, respectively) given prior to naloxone. Coadministration of the lower doses of IBO (40 mg/kg) and MK-801 (0.15 mg/kg) results in 94.7% inhibition of jumping, comparable to the effects of higher doses of either IBO or MK-801. IBO and MK-801 also significantly inhibited NMDA-induced (99.0% and 71.0%, respectively) jumping when given 30 min (but not 24 h) prior to NMDA in nonaddictive mice. There were no significant differences in [3H]MK-801 binding to cortical membranes from naive animals, morphine-dependent animals, or morphine-dependent animals treated with IBO or MK-801. This study provides further evidence that IBO does have an inhibitory effect on opiate withdrawal symptoms and suggests that the complex process resulting in morphine withdrawal includes an IBO-sensitive functional and transitory alteration of NMDA receptor.

Ibogaine interferes with motivational and somatic effects of naloxone-precipitated withdrawal from acutely administered morphine

It has been reported that ibogaine interferes with somatic withdrawal reactions in rats chronically treated with morphine. The present experiments demonstrated that ibogaine also interferes with motivational withdrawal reactions and somatic withdrawal reactions in rats treated with morphine on only two occasions. On each of two conditioning trials, naloxone was administered 24 h following an injection of morphine. Four hours prior to each naloxone administration, rats were injected with either ibogaine or saline. In two experiments, ibogaine interfered with naloxone-precipitated withdrawal. In Experiment 1, ibogaine-treated rats displayed a weaker aversion to the withdrawal-paired chamber, and in Experiment 2, ibogaine-treated rats displayed fewer somatic withdrawal reactions than did saline treated rats.

Ibogaine alters synaptosomal and glial glutamate release and uptake

Ibogaine has aroused expectations as a potentially innovative medication for drug addiction. It has been proposed that antagonism of the NMDA receptor by ibogaine may be one of the mechanisms underlying its antiaddictive properties; glutamate has also been implicated in ibogaine-induced neurotoxicity. We here report the effects of ibogaine on [3H]glutamate release and uptake in cortical and cerebellar synaptosomes, as well as in cortical astrocyte cultures, from mice and rats. Ibogaine (2-1000 microM) had no effects on glutamate uptake or release by rat synaptosomes. However, ibogaine (500-1000 microM) significantly inhibited the glutamate uptake and stimulated the release of glutamate by cortical (but not cerebellar) synaptosomes of mice. In addition, ibogaine (1000 microM) nearly abolished glutamate uptake by cortical astrocyte cultures from rats and mice. The data provide direct evidence of glutamate involvement in ibogaine-induced neurotoxicity.

18-Methoxycoronaridine (18-MC) and ibogaine: comparison of antiaddictive efficacy, toxicity, and mechanisms of action

18-MC, a novel iboga alkaloid congener, is being developed as a potential treatment for multiple forms of drug abuse. Like ibogaine (40 mg/kg), 18-MC (40 mg/kg) decreases the intravenous self-administration of morphine and cocaine and the oral self-administration of ethanol and nicotine in rats; unlike ibogaine, 18-MC does not affect responding for a nondrug reinforcer (water). Both ibogaine and 18-MC ameliorate opioid withdrawal signs. Both ibogaine and 18-MC decrease extracellular levels of dopamine in the nucleus accumbens, but only ibogaine increases extracellular levels of serotonin in the nucleus accumbens. Both ibogaine and 18-MC block morphine-induced and nicotine-induced dopamine release in the nucleus accumbens; only ibogaine enhances cocaine-induced increases in accumbal dopamine. Both ibogaine and 18-MC enhance the locomotor and/or stereotypic effects of stimulants. Ibogaine attenuates, but 18-MC potentiates, the acute locomotor effects of morphine; both compounds attenuate morphine-induced locomotion in morphine-experienced rats. Ibogaine produces whole body tremors and, at high doses (> or = 100 mg/kg), cerebellar damage; 18-MC does not produce these effects. Ibogaine, but not 18-MC, decreases heart rate at high doses. While 18-MC and ibogaine have similar affinities for kappa opioid and possibly nicotinic receptors, 18-MC has much lower affinities than ibogaine for NMDA and sigma-2 receptors, sodium channels, and the 5-HT transporter. Both 18-MC and ibogaine are sequestered in fat and, like ibogaine, 18-MC probably has an active metabolite. The data suggest that 18-MC has a narrower spectrum of actions and will have a substantially greater therapeutic index than ibogaine.

Ibogaine: complex pharmacokinetics, concerns for safety, and preliminary efficacy measures

Ibogaine is an indole alkaloid found in the roots of Tabernanthe Iboga (Apocynaceae family), a rain forest shrub that is native to western Africa. Ibogaine is used by indigenous peoples in low doses to combat fatigue, hunger and thirst, and in higher doses as a sacrament in religious rituals. Members of American and European addict self-help groups have claimed that ibogaine promotes long-term drug abstinence from addictive substances, including psychostimulants and opiates. Anecdotal reports attest that a single dose of ibogaine eliminates opiate withdrawal symptoms and reduces drug craving for extended periods of time. The purported efficacy of ibogaine for the treatment of drug dependence may be due in part to an active metabolite. The majority of ibogaine biotransformation proceeds via CYP2D6, including the O-demethylation of ibogaine to 12-hydroxyibogamine (noribogaine). Blood concentration-time effect profiles of ibogaine and noribogaine obtained for individual subjects after single oral dose administrations demonstrate complex pharmacokinetic profiles. Ibogaine has shown preliminary efficacy for opiate detoxification and for short-term stabilization of drug-dependent persons as they prepare to enter substance abuse treatment. We report here that ibogaine significantly decreased craving for cocaine and heroin during inpatient detoxification. Self-reports of depressive symptoms were also significantly lower after ibogaine treatment and at 30 days after program discharge. Because ibogaine is cleared rapidly from the blood, the beneficial aftereffects of the drug on craving and depressed mood may be related to the effects of noribogaine on the central nervous system.

Noribogaine (12-hydroxyibogamine): a biologically active metabolite of the antiaddictive drug ibogaine

Ibogaine (IBO) is a plant-derived alkaloid that is being evaluated as a possible medication for substance use disorders. When administered peripherally to monkeys and humans, IBO is rapidly converted to an o-demethylated metabolite, 12-hydroxyibogamine (NORIBO). We have found in rats that peak blood levels of NORIBO can exceed those of the parent compound, and NORIBO persists in the bloodstream for at least 24 h. Surprisingly few studies have examined the in vivo biological activity of NORIBO. In the present series of experiments, we compared the effects of intravenous (i.v.) administration of IBO and NORIBO (1 and 10 mg/kg) on unconditioned behaviors, circulating stress hormones, and extracellular levels of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of male rats. IBO caused dose-related increases in tremors and forepaw treading, whereas NORIBO did not. Both IBO and NORIBO produced significant elevations in plasma corticosterone and prolactin, but IBO was more potent as a stimulator of corticosterone secretion. Neither drug affected extracellular DA levels in the nucleus accumbens. However, both IBO and NORIBO increased extracellular 5-HT levels, and NORIBO was more potent in this regard. The present data demonstrate that NORIBO is biologically active and undoubtedly contributes to the in vivo pharmacological profile of IBO in rats. Most importantly, NORIBO appears less likely to produce the adverse effects associated with IBO (i.e., tremors and stress-axis activation), suggesting that the metabolite may be a safer alternative for medication development.

Development of novel medications for drug addiction. The legacy of an African shrub

Ibogaine, one of several alkaloids found in the root bark of the African shrub Tabernanthe iboga, has been claimed to be effective in treating multiple forms of drug abuse. Problems associated with side effects of ibogaine have spawned a search for more effective and safer structural derivatives. 18-Methoxycoronaridine (18-MC), a novel iboga alkaloid congener, appears to have substantial potential for broad use as an anti-addictive therapy. Like ibogaine (40 mg/kg), 18-MC (40 mg/kg) decreases the intravenous self-administration of morphine and cocaine and the oral self-administration of ethanol and nicotine in rats; unlike ibogaine, 18-MC does not affect responding for a non-drug reinforcer (water). Ibogaine and 18-MC appear to reduce the reinforcing efficacies, rather than the potencies, of drugs of abuse. Both ibogaine and 18-MC decreases extracellular levels of dopamine in the nucleus accumbens while only ibogaine increases serotonin levels in this brain region. Both ibogaine and 18-MC block morphine-induced and nicotine-induced dopamine release in the accumbens; only ibogaine enhances cocaine-induced increases in dopamine levels. Ibogaine produces whole body tremors and, at high doses (at least 100 mg/kg), cerebellar damage; 18-MC does not produce these effects. Ibogaine, but not 18-MC, causes bradycardia at high doses. Ibogaine and its metabolite noribogaine have low microM affinities for kappa and mu opioid receptors, NMDA receptors, 5HT-3 receptors, sigma-2 sites, sodium channels and the serotonin transporter. 18-MC has low microM affinities at all three opioid receptors and at 5HT-3 receptors but much lower or no affinities for NMDA and sigma-2 receptors, sodium channels, and the 5HT transporter. Both 18-MC and ibogaine are sequestered in fat and, like ibogaine, 18-MC probably has an active metabolite. 18-MC also has (+) and (-) enantiomers, both of which are active. Considered together, all of the data indicate that 18-MC should be safer than ibogaine and at least as efficacious as an anti-addictive medication.

Long-lasting ibogaine protection against NMDA-induced convulsions in mice

Ibogaine, a putative antiaddictive drug, is remarkable in its apparent ability to downgrade withdrawal symptoms and drug craving for extended periods of time after a single dose. Ibogaine acts as a non-competitive NMDA receptor antagonist, while NMDA has been implicated in long lasting changes in neuronal function and in the physiological basis of drug addiction. The purpose of this study was to verify if persistent changes in NMDA receptors could be shown in vivo and in vitro after a single administration of ibogaine. The time course of ibogaine effects were examined on NMDA-induced seizures and [3H] MK-801 binding to cortical membranes in mice 30 min, 24, 48, and 72 h post treatment. Ibogaine (80 mg/kg, ip) was effective in inhibiting convulsions induced by NMDA at 24 and 72 hours post administration. Likewise, [3H] MK-801 binding was significantly decreased at 24 and 72 h post ibogaine. No significant differences from controls were found at 30 min or 48 h post ibogaine. This long lasting and complex pattern of modulation of NMDA receptors prompted by a single dose of ibogaine may be associated to its antiaddictive properties.

Comparative neurobiological effects of ibogaine and MK-801 in rats

Ibogaine is a plant-derived alkaloid with putative 'anti-addictive' properties. Although ibogaine binds to multiple targets in the brain, recent evidence suggests the drug acts as an N-methyl-D-aspartate (NMDA) antagonist similar to MK-801. The purpose of the present study was to compare neurochemical and neuroendocrine effects of ibogaine and MK-801 in vivo. Male rats received either i.p. saline, ibogaine (10 and 100 mg/kg), or MK-801 (0.1 and 1 mg/kg). Groups of rats (N=6-8/group) were decapitated 30 or 60 min after injection. Brains were harvested for analysis of dopamine (DA) and its metabolites, while trunk blood was collected for analysis of plasma corticosterone and prolactin. Ibogaine produced marked dose-dependent reductions in tissue DA with concurrent increases in the metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This profile of ibogaine-induced effects on DA metabolism was consistently observed in the cortex, striatum, olfactory tubercle, and hypothalamus. MK-801, on the other hand, did not reduce DA levels in any brain region but did cause modest region-specific elevations in DA metabolites. Ibogaine and MK-801 caused comparable elevations in circulating corticosterone, but only ibogaine increased prolactin. The present findings show that the effects of ibogaine on DA neurotransmission and neuroendocrine secretion are not fully mimicked by MK-801. Thus, the wide spectrum of in vivo actions of ibogaine can probably not be explained simply on the basis of antagonism at NMDA receptors.

The effects of ibogaine on dopamine and serotonin transport in rat brain synaptosomes

Ibogaine has been shown to affect biogenic amine levels in selected brain regions. Because of the involvement of these neurotransmitters in drug addiction, the effects of ibogaine on biogenic amine transport may contribute to the potential anti-addictive properties of ibogaine in vivo. With rat brain synaptosomes as our experimental system, we measured the effects of ibogaine on the uptake and release of dopamine (DA) and serotonin (5-HT). Ibogaine competitively blocked both DA and 5-HT uptake with IC50 values of 20 microM at 75 nM 3H-DA and 2.6 microM at 10 nM 3H-5-HT. Ibogaine had no effect on K+-induced release of 3H-DA from preloaded synaptosomes, but 20 microM and 50 microM ibogaine inhibited roughly 40% and 60%, respectively, of the K(+)-induced release of 3H-5-HT from preloaded synaptosomes. In the absence of a depolarizing stimulus, ibogaine evoked a small release of 3H-DA but not 3H-5-HT. These relatively low-potency effects of ibogaine on DA and 5-HT uptake in synaptosomes are consistent with the low binding affinity of ibogaine that has been previously reported for DA and 5-HT transporters. Our results show that if ibogaine modulates DA and 5-HT levels in the brain by directly blocking their uptake, then a concentration of ibogaine in the micromolar range is required. Furthermore, if the anti-addictive effects of ibogaine require this concentration, then ibogaine likely exerts these effects through a combination of neurotransmitter pathways, because binding affinities and functional potencies of ibogaine in the micromolar range have been reported for a variety of neuronal receptors and transporters.