Scopolamine hydrobromide

Scopolamine hydrobromide is a high affinity (nM) muscarinic antagonist. 5-HT3 receptor-responses are reversibly inhibited by Scopolamine with an IC50 of 2.09 μM.

In Vitro:Application of Scopolamine to oocytes expressing 5-HT3 receptors does not elicit a response when applied alone, but causes a concentration-dependent inhibition of the response during a co-application of 2 μM 5-HT. The pIC50 value for Scopolamine is 5.68±0.05 (IC50=2.09 μM, n=6) with a Hill Slope of 1.06 ± 0.05. This gave a Kb of 3.23 μM. The same concentration-dependent effect is also seen when Scopolamine is applied during the 5-HT application. To further test for a competitive binding at the 5-HT3 receptor, the competition of unlabelled Scopolamine is measured with [3H]granisetron, an established high-affinity competitive antagonist at these receptors. Scopolamine displays concentration-dependent competition with 0.6 nM [3H]granisetron (~Kd), yielding an average pKi of 5.17±0.24 (Ki=6.76 μM, n=3)[1].

In Vivo:In the histopathology study, there is no significant change in the histology of the brain. However, it is observed that there is a reduction in density of cells in the hippocampus of the control mice pretreated with Scopolamine who received only distilled water[2]. Scopolamine administration alone significantly increases the activity of Acetylcholinesterase enzyme (AchE) (7.98±0.065; P<0.001) when compared to the normal group (3.06±0.296). The animals treated with Scopolamine report a significant increase (34.61±4.85; P<0.01) in levels of malondialdehyde (MDA) as compared to the normal group (12.82±2.86). The Scopolamine-treated group shows significant decrease in reduced glutathione (GSH) level (P<0.001; 0.1504±0.03) as compared to the normal group (0.3906±0.02). The Scopolamine-treated rats show a significant increase in the concentration ofβ amyloid (Aβ1-42) (P<0.001; 146.2±1.74) as compared to the normal group (43.21±3.46)[3].

References:
[1]. Lochner M, et al. The muscarinic antagonists Scopolamine and atropine are competitive antagonists at 5-HT3 receptors. Neuropharmacology. 2016 Sep;108:220-8. [2]. O ET, et al. COGNITIVE-ENHANCING PROPERTIES OF MORINDA LUCIDA (RUBIACEAE) AND PELTOPHORUM PTEROCARPUM (FABACEAE) IN SCOPOLAMINE-INDUCED AMNESIC MICE. Afr J Tradit Complement Altern Med. 2017 Mar 1;14(3):136-141. [3]. Pattanashetti LA, et al. Evaluation of neuroprotective effect of Quercetin with Donepezil in Scopolamine-induced amnesia in rats. Indian J Pharmacol. 2017 Jan-Feb;49(1):60-64.

Preparation of ion-activated in situ gel systems of scopolamine hydrobromide and evaluation of its antimotion sickness efficacy.[Pubmed:17376300]

Acta Pharmacol Sin. 2007 Apr;28(4):584-90.

AIM: To develop a novel, in situ gel system for nasal delivery of Scopolamine hydrobromide (SCOP) and study its efficacy on motion sickness. METHODS: SCOP in situ gels at 0.2%, 0.5%, and 1.0% gellan gum concentration (w/v) were prepared, respectively, and characterized in terms of viscosity, in vitro release, and nasal ciliotoxicity. Single photon emission computing tomography technique was used to evaluate the nasal residence time of gel containing (99m)Tc tracer. The antimotion sickness efficacy produced by the in situ gel formulation was investigated in rats and compared with those achieved after subcutaneous and oral administration. RESULTS: The viscosity of the gellan gum formulations either in solution or in gel increased with increasing concentrations of gellan gum. Its release in vitro was moderate in artificial nasal fluid. The micrographic results showed that in situ gels were safe, without nasal ciliotoxicity. In comparison with phosphate buffer saline, a prolonged radioactivity of (99m)Tc in the rabbit nasal cavity was observed after administration of the gellan gum formulation. Intranasal SCOP in situ gel at a dose of 100 microg/kg decreased symptoms of motion sickness significantly in comparison with subcutaneous and oral administration (P<0.01). CONCLUSION: SCOP nasal in situ gel is a safe and promising therapeutic alternative to existing medications for motion sickness.

A novel spray-dried nanoparticles-in-microparticles system for formulating scopolamine hydrobromide into orally disintegrating tablets.[Pubmed:21720502]

Int J Nanomedicine. 2011;6:897-904.

Scopolamine hydrobromide (SH)-loaded microparticles were prepared from a colloidal fluid containing ionotropic-gelated chitosan nanoparticles using a spray-drying method. The spray-dried microparticles were then formulated into orally disintegrating tablets (ODTs) using a wet granulation tablet formation process. A drug entrapment efficiency of about 90% (w/w) and loading capacity of 20% (w/w) were achieved for the microparticles, which ranged from 2 mum to 8 mum in diameter. Results of disintegration tests showed that the formulated ODTs could be completely dissolved within 45 seconds. Drug dissolution profiles suggested that SH is released more slowly from tablets made using the microencapsulation process compared with tablets containing SH that is free or in the form of nanoparticles. The time it took for 90% of the drug to be released increased significantly from 3 minutes for conventional ODTs to 90 minutes for ODTs with crosslinked microparticles. Compared with ODTs made with noncrosslinked microparticles, it was thus possible to achieve an even lower drug release rate using tablets with appropriate chitosan crosslinking. Results obtained indicate that the development of new ODTs designed with crosslinked microparticles might be a rational way to overcome the unwanted taste of conventional ODTs and the side effects related to SH's intrinsic characteristics.

Effects of scopolamine in comparison with apomorphine and phencyclidine on prepulse inhibition in rats.[Pubmed:10720641]

Eur J Pharmacol. 2000 Mar 10;391(1-2):105-12.

The potential involvement of the muscarinic cholinergic system in the underlying mechanisms of prepulse inhibition of the acoustic startle reflex was evaluated in male Sprague-Dawley rats under conditions of varying dose, prepulse intensity, and interstimulus interval. The effects of scopolamine on prepulse inhibition were also directly compared with the effects observed using apomorphine and phencyclidine under the same test parameters. Scopolamine (0. 03-1.0 mg/kg) produced a significant dose-dependent decrease in prepulse inhibition, but had no effect on startle amplitude over the dose range tested. Apomorphine (0.03-1.0 mg/kg) and phencyclidine (0. 1-5.6 mg/kg) produced significant dose-dependent decreases in prepulse inhibition and changes in startle amplitude. The scopolamine-induced decrease in prepulse inhibition varied with prepulse intensity in that the changes produced by scopolamine became smaller in magnitude as the prepulse intensity was increased from 9 to 30 dB above background. On the other hand, apomorphine and phencyclidine decreased prepulse inhibition to approximately the same magnitude across all prepulse intensities tested. The observed decreases in prepulse inhibition produced by scopolamine, apomorphine, and phencyclidine were also dependent on interstimulus interval duration. Scopolamine produced marked decreases in prepulse inhibition at the 100- and 300-ms interstimulus interval durations, but had little or no effect on prepulse inhibition at the 30- and 1000-ms interstimulus interval durations. In contrast, apomorphine decreased prepulse inhibition across all interstimulus interval durations while phencyclidine decreased prepulse inhibition across the 30- to 300-ms interstimulus interval durations. The present findings support the hypothesis that the muscarinic cholinergic system, like the dopaminergic and glutamatergic systems, is directly involved in the mechanisms of prepulse inhibition. However, these three neurotransmitter systems appear to modulate different aspects of prepulse inhibition.

Cerebral blood flow responses to somatosensory stimulation are unaffected by scopolamine in unanesthetized rat.[Pubmed:10411611]

J Pharmacol Exp Ther. 1999 Aug;290(2):929-34.

Studies with positron-emission tomography have indicated that muscarinic acetylcholine receptors may be involved in the mechanism of enhancement of cerebral blood flow (CBF) by neuronal functional activation. We examined the effects of muscarinic receptor blockade by scopolamine on the local CBF responses to vibrissal stimulation in the whisker-to-barrel cortex sensory pathway in unanesthetized rats. Local CBF was measured by the quantitative autoradiographic [(14)C]iodoantipyrine method. Scopolamine (0.4 or 0.8 mg/kg) was injected i.v. 30 min before measurement of local CBF; control rats received equivalent volumes of physiological saline. Vibrissae on the left side of the face were stroked continuously throughout the 1-min period of measurement of CBF. Local CBF was determined bilaterally in four structures of the pathway, i.e., spinal and principal sensory trigeminal nuclei, ventral posteromedial thalamic nucleus, and barrel field of the sensory cortex, as well as in four representative structures unrelated to the pathway. The higher dose of scopolamine raised baseline CBF in the two trigeminal nuclei, but neither dose diminished the percentage of increases in local CBF because of vibrissal stimulation in any of the stations of the pathway. These results do not support involvement of muscarinic receptors in the mechanism of enhancement of local CBF by functional neuronal activation, at least not in the whisker-barrel cortex sensory pathway in the unanesthetized rat.