This vehicle-controlled rodent study (n=54) investigated the dose-dependent effects of noribogaine (10, 30, or 100mg/kg) on the uptake and anti-withdrawal symptoms of morphine. Results demonstrate the efficacy of noribogaine to reduce the somatic signs of morphine withdrawal up to 88% in mice two hours after oral administration and attenuates the negative signs of morphine withdrawal within substance-dependent mice, in a dose-dependent manner.
Abstract
“Introduction: This study investigated the effects of noribogaine, the principal metabolite of the drug ibogaine, on substance-related disorders.
Methods: 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.
Results: Noribogaine-treated rats did not display place preference, suggesting that noribogaine is not perceived as a hedonic stimulus in rodents.
Discussion: 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.”
Authors: Deborah C. Mash, Barbara Ameer, Delphine Prou, John F. Howes & Emeline L. Maillet
Summary
Introduction
Iboga roots have been used as a natural medicine and for ceremonial purposes in Equatorial Africa for centuries. Several decades later, the potential benefits of iboga in the treatment of addiction were highlighted.
Ibogaine was never approved as a medicine for the treatment of drug addiction in most Western countries, but clinical experience suggested that single large doses of ibogaine could promote drug cessation in dependent individuals.
Noribogaine, a metabolite of ibogaine, decreased the global opiate withdrawal score in mice chronically treated with morphine and did not induce place preference in rats given oral noribogaine up to 100 mg/kg. Noribogaine may hold promise as a non-addicting alternative to standard opiate replacement therapies.
Ibogaine is rapidly metabolized in rodents, but a long-acting metabolite, noribogaine, is formed following o-demethylation by first-pass metabolism. Noribogaine has a half-life of approximately 16 hours and can still be detected 24 hours after ibogaine ingestion.
Noribogaine’s known poly-pharmacology partially overlaps with ibogaine’s profile, but there are major differences, including a lack of affinity for N-Methyl-D-aspartate and sigma 2 receptors, and differential inhibitory potencies at nicotinic acetylcholine receptors subtypes.
Ibogaine has been shown to reduce opioid withdrawal symptoms in animal models, but the mechanisms of ibogaine’s blockade of opiate withdrawal in humans remain largely unstudied.
In a preclinical study, noribogaine was administered orally to mice to mimic the route of administration for human patients better. It was found that noribogaine reached brain concentrations high enough to target relevant receptors at doses directly correlated with in vivo efficacy.
- Naloxone-precipitated morphine withdrawal in mice
Morphine sulfate, naloxone, methylcellulose, Tween 80, and dextrose were dissolved in 0.9% saline, and noribogaine hydrochloride was prepared in 35% Tween 80 in 5% dextrose and stirred for at least 30 minutes. The mice tolerated noribogaine and did not evidence toxicity at these doses.
Fifty-two adult male Swiss Webster mice were purchased from Charles River Laboratories and were maintained on a 12-hour light/dark cycle. They were habituated to the testing room for at least one month prior to the experimental manipulations.
Morphine sulfate was injected subcutaneously three times daily in mice. Two hours after the last dose of morphine, mice received an intragastric dose of noribogaine, and two hours after that, they were injected with naloxone 3 mg/kg i.p. and immediately placed in transparent glass cylinders.
Data analysis was performed using GraphPad Prism v5, and a nonlinear regression dose – response model was fitted with an inhibitor model with a standard slope of 1. A modification of the Gellert and Holtzman (1978) global opiate withdrawal score was used to obtain a comprehensive index of the severity of somatic opiate withdrawal.
- CPP
Drugs were sourced as described in Methods for the morphine withdrawal study, and formulations of noribogaine in vehicle were evaluated for homogeneity and concentration.
Animals were used in the experiment: 32 experimentally naive CD® (Crl:CD® [SD]) male Sprague-Dawley rats were housed in standard cages with food and water ad libitum and kept on a 12-hour light/dark cycle.
Conditioning and pharmacologic treatment were performed in standard three-compartment straight alleyway CPP boxes on 32 animals. The preference of each animal was determined by the percentage of time the animal spent in either chamber 1 or 3.
Animals were randomized into four groups and given oral doses of noribogaine (10, 30, and 100 mg/ kg) or vehicle. They were then placed into conditioning chambers for two hours and tested for free choice on two occasions.
Statistical data analyses were performed on preference score for the CS+ side, and comparisons between intervals at each level of group were conducted using a Tukey adjustment.
- Whole blood and brain levels of noribogaine after oral administration in mice
Noribogaine base was obtained from Cerilliant (Sigma-Aldrich), and deuterated-noribogaine (d3-noribogaine) was obtained from Research Triangle Institute (Research Triangle Park, NC). All solvents were HPLC grade and were obtained from Sigma-Aldrich.
Male Swiss Webster mice received a single oral dose of noribogaine at four dosage levels. Blood and whole brain samples were collected two hours after dosing and stored at 80oC until analysis.
- LC-MS/MS for drug analysis
Noribogaine was determined by LC-MS/MS using a stable label IS, d3-noribogaine, and a mobile phase gradient. The elution conditions were initially 100% MP A for 30 seconds, then changed linearly to 85% MP B at two minutes, then stepped to 95% MP B for one minute.
Noribogaine and IS were characterized by their protonated species [M+H+] using an API 5500® triple quadropole mass spectrometer.
Calibration curves and quality control standards were prepared using Analyst® software (AB Sciex). A linear eight-point standard curve was used for measurement of unknown concentrations of noribogaine.
Intra-assay accuracy and precision were evaluated using replicates of QC samples. Calibration curves were bracketed by unknown samples, blank matrix samples, and QC samples.
Performance of the assay during sample analyses was good with accuracy and precision meeting acceptance criteria. Seven mouse-brain homogenate samples exhibited peaks above the highest point on the calibration curve.
Naloxone-precipitated morphine withdrawal
Oral noribogaine decreased jumping and paw tremors in mice, with a maximum decrease of 75% and 65% in comparison with vehicle-treated mice. Body tremors were inhibited by 50% after 10 mg/kg of noribogaine, and decreased by 80% at the highest dose of noribogaine tested (100 mg/kg).
Noribogaine dose dependently reduced signs of naloxone-precipitated morphine withdrawal in mice. The dose – response relationship was fitted using a sigmoidal equation and an apparent ED50 of 13.2 mg/kg was estimated.
Noribogaine whole blood concentrations and evidence of brain penetration
Noribogaine concentrations in blood increased linearly across the doses administered, while concentrations in the brain increased linearly, except for the highest dose level.
CPP
Noribogaine did not change preference scores in the rat up to 100 mg/kg. The mean CPP scores increased from 37.5 during the habituation phase to 45.2 during Test 1 and 45.7 during Test 2, but were not statistically significant.
Retrospective analysis of ibogaine efficacy in animal models of morphine withdrawal
We collected publications referring to the efficacy of ibogaine at inhibiting the somatic signs of antagonist-precipitated withdrawal in animal models. The effects of ibogaine administration were robust and reached statistical significance in studies where precipitation of withdrawal was performed 45 – 240 minutes after ibogaine administration.
Discussion
The present study demonstrated that noribogaine significantly reduces the somatic signs of morphine withdrawal in mice two hours after oral administration of the drug compared to vehicle. Noribogaine does not produce CPP in rats up to the 100 mg/kg dose, suggesting that it is not opiate substitution therapy.
Noribogaine has excellent brain penetration, with a mean brain-to-blood ratio close to 7 across all dose levels. Noribogaine has functional potencies at a series of central receptor targets, and the approximate ED50 for alleviating withdrawal signs following naloxone in mice is 13 mg/kg oral noribogaine.
A dose of 10 mg/kg in mice is equivalent to 0.8 mg/kg in humans, suggesting that brain levels are sufficient to modulate therapeutically relevant receptors of the central nervous system.
Noribogaine has been shown to have non-competitive antagonistic properties at the serotonin transporter, to be a biased agonist of the kappa opioid receptor, and to inhibit -arrestin2 signaling for both mu and kappa opioid receptors.
Noribogaine may have multi-target effects at several relevant targets, including the 5-containing ganglionic and the 7 nicotinic receptors, which may be beneficial for treating the constellation of symptoms associated with opiate withdrawal.
We observed that noribogaine had a trend to attenuate diarrhea, although there was no consistent dose-related effect on this measure. Noribogaine may have more central than peripheral nervous system effects.
Although some preclinical studies in animal models have shown that ibogaine can decrease morphine self-administration and reduce opioid withdrawal signs, others have reported that ibogaine was not effective. The effectiveness of ibogaine in reducing morphine withdrawal signs is likely due to pharmacokinetic parameters associated with route of administration.
Noribogaine failed to inhibit jumping in a precipitated morphine withdrawal paradigm in mice, but it reached high concentrations in the brain and dose dependently decreased withdrawal in morphine-dependent mice. This suggests that noribogaine may be effective for opiate detoxification in humans.