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

Antonio T, Childers SR, Rothman RB, Dersch CM, King C, Kuehne M, Bornmann WG, Eshleman AJ, Janowsky A, Simon ER, Reith ME, Alper K - PLoS ONE (2013)

Bottom Line: 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.An MOR agonist action does not appear to account for the effect of these iboga alkaloids on opioid withdrawal.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, New York University School of Medicine, New York, New York, United States of America ; Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York, United States of America.

ABSTRACT

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.

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Antagonism of DAMGO (1 µM)-induced [35S]GTPγS binding in Sprague-Dawley rat thalamic membranes by ibogaine, noribogaine, and 18-MC (Reith lab).Degree of stimulation by drug alone, i.e., 1 µM DAMGO, 100 µM 18-MC, 100 µM noribogaine (NOR), or 100 µM ibogaine (IBO) is indicated by the symbols on the left. The colored curves represent the effect of increasing the concentration of the respective iboga alkaloids co-incubated with 1 µM DAMGO (5 independent experiments). Otherwise as in Figures 5 and 6.
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pone-0077262-g007: Antagonism of DAMGO (1 µM)-induced [35S]GTPγS binding in Sprague-Dawley rat thalamic membranes by ibogaine, noribogaine, and 18-MC (Reith lab).Degree of stimulation by drug alone, i.e., 1 µM DAMGO, 100 µM 18-MC, 100 µM noribogaine (NOR), or 100 µM ibogaine (IBO) is indicated by the symbols on the left. The colored curves represent the effect of increasing the concentration of the respective iboga alkaloids co-incubated with 1 µM DAMGO (5 independent experiments). Otherwise as in Figures 5 and 6.

Mentions: In thalamic membranes from Sprague-Dawley rats, DAMGO showed significant stimulation of [35S]GTPγS binding, with a maximal level of 214 ± 6% over basal, and an EC50 value of 238 ± 24 nM. In contrast, no significant stimulation was observed with concentrations up to up to 100 µM of ibogaine, noribogaine, or 18-MC (Figures 5, 6 and 7; Table 1). It is important to point out that the concentrations of noribogaine of 100 µM (Figures 6 and 7, Reith lab) or 30 µM (Figure 8, Childers lab) used in these separate experiments are far in excess of the EC50 of 324 nM reported previously by Pablo and Mash [43] for noribogaine in stimulating [35S]GTPγS binding in rat thalamic membranes. Concentrations of noribogaine that had no effect in this present study maximally stimulated [35S]GTPγS binding in rat thalamic membranes to a level observed with 10 µM DAMGO in the Pablo and Mash study. In a similar comparison regarding ibogaine, that study reported an approximate 20% stimulation by 100 µM ibogaine, whereas the results of this study indicated no stimulation (Figures 6 and 7; Table 1) (see below and Discussion).


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

Antonio T, Childers SR, Rothman RB, Dersch CM, King C, Kuehne M, Bornmann WG, Eshleman AJ, Janowsky A, Simon ER, Reith ME, Alper K - PLoS ONE (2013)

Antagonism of DAMGO (1 µM)-induced [35S]GTPγS binding in Sprague-Dawley rat thalamic membranes by ibogaine, noribogaine, and 18-MC (Reith lab).Degree of stimulation by drug alone, i.e., 1 µM DAMGO, 100 µM 18-MC, 100 µM noribogaine (NOR), or 100 µM ibogaine (IBO) is indicated by the symbols on the left. The colored curves represent the effect of increasing the concentration of the respective iboga alkaloids co-incubated with 1 µM DAMGO (5 independent experiments). Otherwise as in Figures 5 and 6.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3818563&req=5

pone-0077262-g007: Antagonism of DAMGO (1 µM)-induced [35S]GTPγS binding in Sprague-Dawley rat thalamic membranes by ibogaine, noribogaine, and 18-MC (Reith lab).Degree of stimulation by drug alone, i.e., 1 µM DAMGO, 100 µM 18-MC, 100 µM noribogaine (NOR), or 100 µM ibogaine (IBO) is indicated by the symbols on the left. The colored curves represent the effect of increasing the concentration of the respective iboga alkaloids co-incubated with 1 µM DAMGO (5 independent experiments). Otherwise as in Figures 5 and 6.
Mentions: In thalamic membranes from Sprague-Dawley rats, DAMGO showed significant stimulation of [35S]GTPγS binding, with a maximal level of 214 ± 6% over basal, and an EC50 value of 238 ± 24 nM. In contrast, no significant stimulation was observed with concentrations up to up to 100 µM of ibogaine, noribogaine, or 18-MC (Figures 5, 6 and 7; Table 1). It is important to point out that the concentrations of noribogaine of 100 µM (Figures 6 and 7, Reith lab) or 30 µM (Figure 8, Childers lab) used in these separate experiments are far in excess of the EC50 of 324 nM reported previously by Pablo and Mash [43] for noribogaine in stimulating [35S]GTPγS binding in rat thalamic membranes. Concentrations of noribogaine that had no effect in this present study maximally stimulated [35S]GTPγS binding in rat thalamic membranes to a level observed with 10 µM DAMGO in the Pablo and Mash study. In a similar comparison regarding ibogaine, that study reported an approximate 20% stimulation by 100 µM ibogaine, whereas the results of this study indicated no stimulation (Figures 6 and 7; Table 1) (see below and Discussion).

Bottom Line: 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.An MOR agonist action does not appear to account for the effect of these iboga alkaloids on opioid withdrawal.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, New York University School of Medicine, New York, New York, United States of America ; Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, New York, United States of America.

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus