The effects of Tabernaemontana divaricata root extract on amyloid beta-peptide 25-35 peptides induced cognitive deficits in mice

Leveraging hallmark Alzheimer's molecular targets using phytoconstituents: Current perspective and emerging trends

Alzheimer's disease (AD), a type of dementia, severely distresses different brain regions. Characterized by various neuropathologies, it interferes with cognitive functions and neuropsychiatrical controls. This progressive deterioration has negative impacts not only on an individual's daily activity but also on social and occupational life. The pharmacological approach has always remained in the limelight for the treatment of AD. However, this approach is condemned with several side effects. Henceforth, a change in treatment approach has become crucial. Plant-based natural products are garnering special attention due to lesser side effects associated with their use. The current review emphasizes the anti-AD properties of phytoconstituents, throws light on those under clinical trials, and compiles information on their specific mode of actions against AD-related different neuropathologies. The phytoconstituents alone or in combinations will surely help discover new potent drugs for the effective treatment of AD with lesser side effects than the currently available pharmacological treatment.

Major Bioactive Alkaloids and Biological Activities of Tabernaemontana Species (Apocynaceae)

Several species belonging to the genus Tabernaemontana have been well researched and utilized for their wide-ranging biological activities. A few of the most prominent species include Tabernaemontana divaricata, Tabernaemontana catharinensis, Tabernaemontana crassa, and Tabernaemontana elegans. These species and many others within the genus often display pharmacological importance, which is habitually related to their chemical constituents. The secondary metabolites within the genus have demonstrated huge medicinal potential for the treatment of infections, pain, injuries, and various diseases. Regardless of the indispensable reports and properties displayed by Tabernaemontana spp., there remains a wide variety of plants that are yet to be considered or examined. Thus, an additional inclusive study on species within this genus is essential. The current review aimed to extensively analyze, collate, and describe an updated report of the current literature related to the major alkaloidal components and biological activities of species within the genus Tabernaemontana.

Traditional Herbal Medicines Against CNS Disorders from Bangladesh

The majority of the population in Bangladesh uses traditional plant-based medicines to manage various ailments, including central nervous system (CNS) disorders. This review presents ethnobotanical information and relevant scientific studies on plants used in traditional healthcare for the management of various CNS disorders in Bangladesh. The information on the medicinal plants of Bangladesh effective against CNS disorders published in scientific journals, books, and reports was compiled from different electronic databases using specific key words. The present article provides comprehensive information on a total of 224 medicinal plant species belonging to 81 families used for the treatment of CNS disorders by the various peoples of Bangladesh. In total, we reviewed more than 290 relevant papers. In this study, leaves were found as the most often used plant organ, followed by roots, fruits, whole plants, barks, seeds, stems, rhizomes, and flowers. The Fabaceae family contributes the highest number of used species, followed by Rubiaceae, Lamiaceae, Cucurbitaceae, Vitaceae, Euphorbiaceae, Malvaceae, and Zingiberaceae. The most frequently used species (in decreasing order) are Asparagus racemosus, Centella asiatica, Stephania japonica, Aegle marmelos, Coccinia grandis, Tabernaemontana divaricata, Bacopa monnieri, Abroma augusta, and Scoparia dulcis. This review may serve as a starting point for a rational search for neuroactive natural products against CNS disorders within the Flora of Bangladesh.

Medicinal plants with acetylcholinesterase inhibitory activity

Alzheimer's disease, a progressive neurodegenerative disease, is characterised by hypofunction of acetylcholine (ACh) neurotransmitter in the distinct region of brain. Acetylcholinesterase (AChE) is an enzyme that metabolises the ACh at synaptic cleft resulting in Alzheimer's disease. Medicinal plants have been used to treat numerous ailments and improve human health from ancient time. A traditional system of medicine is long recognised for its effective management of neurological disorders. The present review confers the scope of some common medicinal plants with a special focus on AChE-mediated central nervous system complications especially Alzheimer's disease. Literature suggests that medicinal plants reduce neuronal dysfunctions by reducing AChE activity in different brain regions. In some instances, activation of AChE activity by medicinal plants also showed therapeutic potential. In conclusion, medicinal plants have a wide scope and possess therapeutic potential to efficiently manage neurological disorders associated with AChE dysregulation.

Ciproxifan improves cholinergic transmission, attenuates neuroinflammation and oxidative stress but does not reduce amyloid level in transgenic mice

AIM

The present study is aimed to investigate the ability of ciproxifan, a histamine H₃ receptor antagonist to inhibit β-amyloid (Aβ)-induced neurotoxicity in SK-N-SH cells and APP transgenic mouse model.

MATERIALS AND METHODS

In vitro studies was designed to evaluate the neuroprotective effects of ciproxifan in Aβ_25-35 - induced SK-N-SH cells. For the in vivo study, ciproxifan (1 and 3mg/kg, i.p.) was administrated to transgenic mice for 15days and behaviour was assessed using the radial arm maze (RAM). Brain tissues were collected to measure Aβ levels (Aβ_1-40 and Aβ_1-42), acetylcholine (ACh), acetylcholinesterase (AChE), nitric oxide (NO), lipid peroxidation (LPO), antioxidant activities, cyclooxygenases (COX) and cytokines (IL-1α, IL-1β and IL-6), while plasma was collected to measure TGF-1β.

RESULTS

The in vitro studies demonstrated neuroprotective effect of ciproxifan by increasing cell viability and inhibiting reactive oxygen species (ROS) in Aβ_25-35-induced SK-N-SH cells. Ciproxifan significantly improved the behavioural parameters in RAM. Ciproxifan however, did not alter the Aβ levels in APP transgenic mice. Ciproxifan increased ACh and showed anti-oxidant properties by reducing NO and LPO levels as well as enhancing antioxidant levels. The neuroinflammatory analysis showed that ciproxifan reduced both COX-1 and COX-2 activities, decreased the level of pro-inflammatory cytokines IL-1α, IL-1β and IL-6 and increased the level of anti-inflammatory cytokine TGF-1β.

CONCLUSION

This present study provides scientific evidence of the use of ciproxifan via antioxidant and cholinergic pathways in the management of AD.

Inhibitory effects of Tabernaemontana divaricata root extract on oxidative stress and neuronal loss induced by amyloid β25-35 peptide in mice

In Alzheimer's disease, there are numerous amyloid plaques, neurofibrillary tangles, and neuronal loss in several brain areas. Oxidative stress is involved in the mechanisms of Aβ-peptide induced neurotoxicity by the generation of free radical oxidative stress that may lead to neurodegeneration. Tabernaemontana divaricata has various medical properties in Thai folklore medicine including prevent forgetfulness or improve memory. The present study aimed to investigate the effects of T. divaricata root extract (TDE) on Aβ_25-35 peptides induced neuronal loss and oxidative stress in mice. Male ICR mice were administered with vehicle or TDE (250, 500, and 1000 mg/kg b.w., p.o.) for 28 consecutive days. Then, these mice were given a single intracerebroventricular (i.c.v.) injection of Aβ_25-35 or phosphate buffer saline (PBS) (10 μg/mouse). The novel object recognition (NOR) test was used to determine memory disturbance. In addition, the neuronal cells in the cerebral cortex and hippocampus were measured by using crystal violet staining and lipid peroxidation was determined by measuring the formation of thiobarbituric acid reactive substances. An i.c.v. injection of Aβ_25-35 peptides could significantly induce memory impairment, increase level of lipid peroxidation including the neuronal loss in CA3 of hippocampus. However, the mice pretreated with TDE could prevent the memory loss, neuronal loss and decrease lipid peroxidation. These results suggest the potential therapeutic value in dementia of TDE through its antioxidant property.

PROTECTIVE EFFECT OF IRIS GERMANICA L. IN Β-AMYLOID-INDUCED ANIMAL MODEL OF ALZHEIMER'S DISEASE

BACKGROUND

Alzheimer's disease (AD) is the most common cause of dementia that is an irretrievable chronic neurodegenerative disease. In the current study, we have examined the therapeutic effects of Iris germanica extract on Amyloid β (Aβ) induced memory impairment.

MATERIALS AND METHODS

Wistar rats were divided into five groups of 8 per each. Groups were as followed: control group which were normal rats without induction of AD, Aβ group which received Aβ (50 ng/side), iris 100 group which received Aβ + Iris (100 mg/kg), iris 200 group which received Aβ + Iris (200 mg/kg), and iris 400 group which received Aβ + Iris (400 mg/kg). AD was established by intrahippocampal injection of 50 ng/μl/side Aβ1-42. The day after surgery, animals in treatment groups received different doses of the aqueous extract of Iris by gavage for 30 days. Morris water maze test (MWM) was performed to assess the effects of I. germanica on learning and memory of rats with Aβ induced AD.

RESULTS

Data from MWM tests, including escape latency and traveled distance, demonstrated that I. germanica extract could markedly improve spatial memory in comparison to control. Moreover, the plant had a significantly better effect on the performance of AD rats in the probe test.

CONCLUSION

I. germanica extract can successfully reverse spatial learning dysfunction in an experimental model of AD. Further neuro psyco-pharmacological studies are mandatory to reveal the mechanism of action of this natural remedy in the management of AD symptoms.

Natural products against Alzheimer's disease: Pharmaco-therapeutics and biotechnological interventions

Alzheimer's disease (AD) is a severe, chronic and progressive neurodegenerative disease associated with memory and cognition impairment ultimately leading to death. It is the commonest reason of dementia in elderly populations mostly affecting beyond the age of 65. The pathogenesis is indicated by accumulation of the amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFT) in brain tissues and hyperphosphorylation of tau protein in neurons. The main cause is considered to be the formation of reactive oxygen species (ROS) due to oxidative stress. The current treatment provides only symptomatic relief by offering temporary palliative therapy which declines the rate of cognitive impairment associated with AD. Inhibition of the enzyme acetylcholinesterase (AChE) is considered as one of the major therapeutic strategies offering only symptomatic relief and moderate disease-modifying effect. Other non-cholinergic therapeutic approaches include antioxidant and vitamin therapy, stem cell therapy, hormonal therapy, use of antihypertensive or lipid-lowering medications and selective phosphodiesterase (PDE) inhibitors, inhibition of β-secretase and γ-secretase and Aβ aggregation, inhibition of tau hyperphosphorylation and intracellular NFT, use of nonsteroidal anti-inflammatory drugs (NSAIDs), transition metal chelators, insulin resistance drugs, etanercept, brain-derived neurotrophic factor (BDNF) etc. Medicinal plants have been reported for possible anti-AD activity in a number of preclinical and clinical trials. Ethnobotany, being popular in China and in the Far East and possibly less emphasized in Europe, plays a substantial role in the discovery of anti-AD agents from botanicals. Chinese Material Medica (CMM) involving Chinese medicinal plants has been used traditionally in China in the treatment of AD. Ayurveda has already provided numerous lead compounds in drug discovery and many of these are also undergoing clinical investigations. A number of medicinal plants either in their crude forms or as isolated compounds have exhibited to reduce the pathological features associated with AD. In this present review, an attempt has been made to elucidate the molecular mode of action of various plant extracts, phytochemicals and traditional herbal formulations investigated against AD as reported in various preclinical and clinical tests. Herbal synergism often found in polyherbal formulations were found effective to combat disease heterogeneity as found in complex pathogenesis of AD. Finally a note has been added to describe biotechnological improvement, genetic and genomic resources and mathematical and statistical techniques for empirical model building associated with anti-AD plant secondary metabolites and their source botanicals.

DL0410, a novel dual cholinesterase inhibitor, protects mouse brains against Aβ-induced neuronal damage via the Akt/JNK signaling pathway

AIM

1,1'-([1,1'-Biphenyl]-4,4'-diyl)bis(3-(piperidin-1-yl)propan-1-one)dihydrochloride (DL0410) is a novel synthetic dual acetylcholinesterase (AChE)/butyrocholinesterase (BuChE) inhibitor, which has shown a potential therapeutic effect on Alzheimer's disease (AD). In this study we examined whether DL0410 produced neuroprotective effects in an AD cellular model and an Aβ1-42-induced amnesia mouse model.

METHODS

The in vitro inhibitory activities against AChE and BuChE were estimated using Ellman's assay. Copper-induced toxicity in APPsw-SY5Y cells was used as AD cellular model, the cell viability was assessed using MTS assay, and cell apoptosis was evaluated based on mitochondrial membrane potential detection. Aβ1-42-induced amnesia mouse model was made in male mice by injecting aggregated Aβ1-42 (2 μg in 2 μL 0.1% DMSO) into the right cerebral ventricle. Before and after Aβ1-42 injection, the mice were orally administered DL0410 (1, 3, 9 mg·kg-1·d-1) or rivastigmine (2 mg·kg-1·d-1) for 3 and 11 d, respectively. Memory impairments were examined using Morris water maze (MWM) test and passive avoidance test. The expression levels of APP, CREB, BDNF, JNK and Akt in the mouse brains were measured with either immunohistochemistry or Western blotting.

RESULTS

DL0410 exhibited in vitro inhibitory abilities against AChE and BuChE with IC50 values of 0.286±0.004 and 3.962±0.099 μmol/L, respectively, which were comparable to those of donepezil and rivastigmine. In APPsw-SY5Y cells, pretreatment with DL0410 (1, 3, and 10 μmol/L) decreased the phosphorylation of JNK and increased the phosphorylation of Akt, markedly decreased copper-stimulated Aβ1-42 production, reversed the loss of mitochondrial membrane potential, and dose-dependently increased the cell viability. In Aβ1-42-treated mice, DL0410 administration significantly ameliorated learning and memory deficits in MWM test and passive avoidance test. Furthermore, DL0410 administration markedly decreased Aβ1-40/42 deposits in mouse cerebral cortices, and significantly up-regulated neurotrophic CREB/BDNF. Meanwhile, Akt/JNK signaling pathway may play a key role in the neuroprotective effect of DL0410.

CONCLUSION

DL0410 ameliorates cognitive deficit and exerts neuronal protection in AD models, implicating this compound as a candidate drug for the prevention and therapy of AD.

Yeast Model of Amyloid-β and Tau Aggregation in Alzheimer's Disease

The amyloid-β peptide (Aβ) and the phosphorylated protein tau have been widely implicated in Alzheimer's disease and are the focus of most research. Both agents have been extensively studied in mammalian cell culture and in animal studies, but new research is focusing on yeast models. Yeast are eukaryotes, just like us, and are amenable to effects and expression of Aβ and tau and appear able to 'report' with considerable relevance on the effects of these biomolecules. The use of yeast enables powerful new approaches to understanding how to overcome the effects of Aβ and tau, and such advances could lead to new therapies to prevent the progression of Alzheimer's disease.

Beneficial effect of diosgenin as a stimulator of NGF on the brain with neuronal damage induced by Aβ-42 accumulation and neurotoxicant injection

To investigate the beneficial effects of diosgenin (DG) on the multiple types of brain damage induced by Aβ-42 peptides and neurotoxicants, alterations in the specific aspects of brain functions were measured in trimethyltin (TMT)-injected transgenic 2576 (TG) mice that had been pretreated with DG for 21 days. Multiple types of damage were successfully induced by Aβ-42 accumulation and TMT injection into the brains of TG mice. However, DG treatment significantly reduced the number of Aβ-stained plaques and dead cells in the granule cells layer of the dentate gyrus. Significant suppression of acetylcholinesterase (AChE) activity and Bax/Bcl-2 expression was also observed in the DG treated TG mice (TG+DG group) when compared with those of the vehicle (VC) treated TG mice (TG+VC group). Additionally, the concentration of nerve growth factor (NGF) was dramatically enhanced in TG+DG group, although it was lower in the TG+VC group than the non-transgenic (nTG) group. Furthermore, the decreased phosphorylation of downstream members in the TrkA high affinity receptor signaling pathway in the TG+VC group was significantly recovered in the TG+DG group. A similar pattern was observed in p75^NTR expression and JNK phosphorylation in the NGF low affinity receptor signaling pathway. Moreover, superoxide dismutase (SOD) activity was enhanced in the TG+DG group, while the level of malondialdehyde (MDA), a marker of lipid peroxidation, was lower in the TG+DG group than the TG+VC group. These results suggest that DG could exert a wide range of beneficial activities for multiple types of brain damage through stimulation of NGF biosynthesis.

Valeriana amurensis improves Amyloid-beta 1-42 induced cognitive deficit by enhancing cerebral cholinergic function and protecting the brain neurons from apoptosis in mice

ETHNOPHAMACOLOGICAL RELEVANCE

Valeriana amurensis, a perennial medicinal herb, has been widely used as anxiolytic, antidepressant, antispasmodic, and sedative in traditional Chinese medicines (TCMs). Moreover, it has been used to treat dementia in Mongolia preparations. In our previous study, we reported that AD-effective fraction of Valeriana amurensis (AD-EFV) has protective effect on Aβ-induced toxicity in PC12 cells. Up to now, however, the therapeutic effect of Valeriana amurensis on Alzheimer disease (AD) has not been explored. This study was designed to determine whether the AD-EFV could improve the Amyloid-beta (Aβ)-induced cognitive deficit and to explore the mechanism of AD-EFV improves cognitive deficit in intact animals.

MATERIALS AND METHODS

The constituents of AD-EFV were isolated with silica gel, octadecyl silica gel (ODS) column chromatography (CC) and preparative HPLC. The structures of compounds were determined by detailed NMR and ESI-MS data analyses. AD mice model was established by injecting A(β1-42) (1 μL, 200 μmol) into the bilateral ventricle. Cognitive performance was evaluated by the Morris water maze (MWM) test. The level of cerebral acetylcholine (ACh), the activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) were investigated using Enzyme-linked immunoassay (ELISA) kits. Brain sections were processed and neuronal apoptosis in hippocampus were evaluated by Hematoxylin and Eosin (HE), Nissl, and Tunel stainings. The analyses of p-ERK/ERK and Bcl-2/Bax protein expression by western blot assay were used to explore the anti-neuronal apoptosis mechanism of AD-EFV.

RESULTS

Seventeen compounds (15 lignans and two iridoids) were isolated from AD-EFV. A significant improvement in cognitive function was observed in administrated AD-EFV AD model mice. AD-EFV increased the ACh level by enhancing the ChAT activity but has no effect on AChE activity in the cerebral cortex and hippocampus in mice. Moreover, the histological injury in hippocampus CA1 induced by A(β1-42) was inhibited following administration of the AD-EFV. As well as the expression ratios of Bcl-2 to Bax and p-ERK to ERK were increased significantly in the mice which were administrated AD-EFV.

CONCLUSION

These findings suggest that AD-EFV could ameliorate Aβ induced cognitive dysfunction through two underlying mechanisms: AD-EFV enhances the cerebral cholinergic function by increasing the secretion of ACh and enhancing the ChAT activity, and AD-EFV protects the brain neurons from Aβ induced apoptosis via activating the p-ERK and Bcl-2 signaling and suppressing the Bax pathways. Besides, the main constituents of AD-EFV are lignans which might be responsible for the AD-activity of Valeriana amurensis.

3'-R/S-hydroxyvoacamine, a potent acetylcholinesterase inhibitor from Tabernaemontana divaricata

Guided by the acetylcholinesterase inhibiting activity, the bisindole alkaloid 3'-R/S-hydroxyvoacamine was isolated from a stem extract of Tabernaemontana divaricata, a plant used in Thailand in traditional rejuvenation remedies for improving the memory. The structure of the alkaloid was elucidated by extensive use of NMR spectroscopy and the complete assignment of the (1)H and (13)C NMR spectra is reported. The alkaloid acted as a non-competitive inhibitor against AChE with an IC50 value of 7.00±1.99 μM. An HPLC method was developed for the quantitative analysis of the AChE inhibitor. It suggested that there was 12.4% (w/w) of 3'-R/S-hydroxyvoacamine in the alkaloid enriched fraction of T. divaricata stem.

Quercetin protects against the Aβ(25-35)-induced amnesic injury: involvement of inactivation of rage-mediated pathway and conservation of the NVU

Quercetin has demonstrated protective effects against Aβ-induced toxicity on both neurons and endothelial cells. However, whether or not quercetin has an effect on the neurovascular coupling is unclear. In the present study, we aim to investigate the anti-amnesic effects of quercetin and to explore the underlying mechanisms. Aβ(25-35) (10 nmol) was administrated to mice i.c.v. Quercetin was administrated orally for 8 days after injection. Learning and memory behaviors were evaluated by measuring spontaneous alternation in Morris Water Maze test and the step-through positive avoidance test. The regional cerebral blood flow was monitored before the Aβ(25-35) injection and on seven consecutive days after injection. Mice were sacrificed and cerebral cortices were isolated on the last day. The effects of quercetin on the neurovascular unit (NVU) integrity, microvascular function and cholinergic neuronal changes, and the modification of signaling pathways were tested. Our results demonstrate that quercetin treatment for Aβ(25-35)-induced amnesic mice improved the learning and memory capabilities and conferred robust neurovascular coupling protection, involving maintenance of the NVU integrity, reduction of neurovascular oxidation, modulation of microvascular function, improvement of cholinergic system, and regulation of neurovascular RAGE signaling pathway and ERK/CREB/BDNF pathway. In conclusion, in Aβ(25-35)-induced amnesic mice, optimal doses of quercetin administration were beneficial. Quercetin protected the NVU likely through reduction of oxidative damage, inactivation of RAGE-mediated pathway and preservation of cholinergic neurons, offering an alternative medication for Alzheimer's disease.

Pinocembrin protects against β-amyloid-induced toxicity in neurons through inhibiting receptor for advanced glycation end products (RAGE)-independent signaling pathways and regulating mitochondrion-mediated apoptosis

BACKGROUND

It is known that amyloid-β peptide (Aβ) plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). Interaction between Aβ and the receptor for advanced glycation end products (RAGE) has been implicated in neuronal degeneration associated with this disease. Pinocembrin, a flavonoid abundant in propolis, has been reported to possess numerous biological activities beneficial to health. Our previous studies have demonstrated that pinocembrin has neuroprotective effects on ischemic and vascular dementia in animal models. It has been approved by the State Food and Drug Administration of China for clinical use in stroke patients. Against this background, we investigated the effects of pinocembrin on cognitive function and neuronal protection against Aβ-induced toxicity and explored its potential mechanism.

METHODS

Mice received an intracerebroventricular fusion of Aβ25-35. Pinocembrin was administrated orally at 20 mg/kg/day and 40 mg/kg/day for 8 days. Behavioral performance, cerebral cortex neuropil ultrastructure, neuronal degeneration and RAGE expression were assessed. Further, a RAGE-overexpressing cell model and an AD cell model were used for investigating the mechanisms of pinocembrin. The mechanisms underlying the efficacy of pinocembrin were conducted on target action, mitochondrial function and potential signal transduction using fluorescence-based multiparametric technologies on a high-content analysis platform.

RESULTS

Our results showed that oral administration of pinocembrin improved cognitive function, preserved the ultrastructural neuropil and decreased neurodegeneration of the cerebral cortex in Aβ25-35-treated mice. Pinocembrin did not have a significant effect on inhibiting Aβ1-42 production and scavenging intracellular reactive oxygen species (ROS). However, pinocembrin significantly inhibited the upregulation of RAGE transcripts and protein expression both in vivo and in vitro, and also markedly depressed the activation of p38 mitogen-activated protein kinase (MAPK)-MAPKAP kinase-2 (MK2)-heat shock protein 27 (HSP27) and stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK)-c-Jun pathways and the downstream nuclear factor κB (NFκB) inflammatory response subsequent to Aβ-RAGE interaction. In addition, pinocembrin significantly alleviated mitochondrial dysfunction through improving mitochondrial membrane potential and inhibiting mitochondrial oxidative stress, and regulated mitochondrion-mediated apoptosis by restoration of B cell lymphoma 2 (Bcl-2) and cytochrome c and inactivation of caspase 3 and caspase 9.

CONCLUSIONS

Pinocembrin was shown to infer cognitive improvement and neuronal protection in AD models. The mechanisms of action of the compound were illustrated on RAGE-dependent transduction inhibition and mitochondrion protection. It appears to be a promising candidate for the prevention and therapy of AD.

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.