Benzodiazepine Binding Site Of GABAA Receptor Research Articles

A novel urea derivative anticonvulsant: In vivo biological evaluation, radioreceptor analysis of GABAA receptors and molecular docking studies of enantiomers

It has been experimentally established that the original new generation anticonvulsant Galodif, N-[(3-chlorophenyl)-(phenyl)methyl]urea, allosterically modulates GABAA receptor (GABAAR). Binding of [3H]flunitrazepam and [3H]Ro5-4864 to the benzodiazepine (BZD) site of GABAAR in the brain of Galodif-treated rats showes an increase in receptor affinity in Scatchard Plot for Ligand Receptor binding analysis. The results of molecular docking (Schrödinger program Glide) reveal that the enantiomers of Galodif are complementary to the BZD binding site of GABAAR; binding energy of R-Galodif is lower than that of S-Galodif (scoring GScore being –11.14 and –10.7 kcal mol–1, respectively); R-Galodif interacts with key amino acids at the α1γ2 interface: Tyr159, Tyr209, H101 Phe77 with high model fit – dG of insert: 7.41.

Investigation of the Mechanisms of Tramadol-Induced Seizures in Overdose in the Rat.

Tramadol overdose is frequently associated with the onset of seizures, usually considered as serotonin syndrome manifestations. Recently, the serotoninergic mechanism of tramadol-attributed seizures has been questioned. This study’s aim was to identify the mechanisms involved in tramadol-induced seizures in overdose in rats. The investigations included (1) the effects of specific pretreatments on tramadol-induced seizure onset and brain monoamine concentrations, (2) the interaction between tramadol and γ-aminobutyric acid (GABA)A receptors in vivo in the brain using positron emission tomography (PET) imaging and 11C-flumazenil. Diazepam abolished tramadol-induced seizures, in contrast to naloxone, cyproheptadine and fexofenadine pretreatments. Despite seizure abolishment, diazepam significantly enhanced tramadol-induced increase in the brain serotonin (p < 0.01), histamine (p < 0.01), dopamine (p < 0.05) and norepinephrine (p < 0.05). No displacement of 11C-flumazenil brain kinetics was observed following tramadol administration in contrast to diazepam, suggesting that the observed interaction was not related to a competitive mechanism between tramadol and flumazenil at the benzodiazepine-binding site. Our findings do not support the involvement of serotoninergic, histaminergic, dopaminergic, norepinephrine or opioidergic pathways in tramadol-induced seizures in overdose, but they strongly suggest a tramadol-induced allosteric change of the benzodiazepine-binding site of GABAA receptors. Management of tramadol-poisoned patients should take into account that tramadol-induced seizures are mainly related to a GABAergic pathway.

(415) Effect of the benzodiazepine clobazam in chronic low back pain and experimental pain modalities: a randomized placebo-controlled crossover study

GABAergic compounds enhance endogenous inhibitory control within the central nervous system and are therefore potentially useful in human pain conditions. Clobazam is an agonist at the benzodiazepine-binding site of GABA-A receptors. We investigated its effect on low back pain and experimental pain modalities in chronic low back pain. Forty-nine patients with chronic low back pain received a single oral dose of clobazam 20 mg and the active placebo tolterodine 1 mg in a double-blinded cross-over fashion. Pain intensity (0-10) (primary endpoint) was measured in the supine and sitting position. Nine experimental pain modalities of pressure, electrical and thermal pain, including conditioned pain modulation, were applied at body sites distant to the low back. All assessments were made during 2 hours after drug intake. Pain intensity in the supine position was significantly lower after clobazam compared to placebo (60 minutes: 2.9 vs. 3.5, p=0.008; 90 minutes: 2.7 vs. 3.3, p=0.024; 120 minutes: 2.4 vs. 3.1, p=0.005). Pain intensity in the sitting position was not significantly different between the groups. No effect on experimental pain tests was observed. The results are suggestive for an analgesic effect of clobazam in low back pain. The lack of effect in the sitting position suggests that GABAergic modulation may be less effective during mechanical strain of injured structures that may occur in the sitting position; the effect in the supine position suggests that GABAergic modulation is more effective at rest, when central sensitization processes may predominate over peripheral nociception. The lack of effect on experimental pain modalities suggests that GABAergic compounds may not be effective on non-sensitized neural pathways that are not functionally connected to the site of injury. The finding of the present study encourages pharmacologic research on GABAergic compounds that are devoid of tolerance and sedation. Funded by the Swiss National Science Foundation.

Analgesia and unwanted benzodiazepine effects in point-mutated mice expressing only one benzodiazepine-sensitive GABAA receptor subtype

Agonists at the benzodiazepine-binding site of GABAA receptors (BDZs) enhance synaptic inhibition through four subtypes (α1, α2, α3 and α5) of GABAA receptors (GABAAR). When applied to the spinal cord, they alleviate pathological pain; however, insufficient efficacy after systemic administration and undesired effects preclude their use in routine pain therapy. Previous work suggested that subtype-selective drugs might allow separating desired antihyperalgesia from unwanted effects, but the lack of selective agents has hitherto prevented systematic analyses. Here we use four lines of triple GABAAR point-mutated mice, which express only one benzodiazepine-sensitive GABAAR subtype at a time, to show that targeting only α2GABAARs achieves strong antihyperalgesia and reduced side effects (that is, no sedation, motor impairment and tolerance development). Additional pharmacokinetic and pharmacodynamic analyses in these mice explain why clinically relevant antihyperalgesia cannot be achieved with nonselective BDZs. These findings should foster the development of innovative subtype-selective BDZs for novel indications such as chronic pain.

Evaluation of Anti-Hyperalgesic and Analgesic Effects of Two Benzodiazepines in Human Experimental Pain: A Randomized Placebo-Controlled Study

Background and AimsCompounds that act on GABA-receptors produce anti-hyperalgesia in animal models, but little is known on their effects in humans. The aim of this study was to explore the potential usefulness of GABA-agonism for the control of pain in humans. Two agonists at the benzodiazepine-binding site of GABAA-receptors (clobazam and clonazepam) were studied using multiple experimental pain tests. Positive results would support further investigation of GABA agonism for the control of clinical pain.MethodsIn a randomized double-blind crossover design, 16 healthy male volunteers received clobazam 20 mg, clonazepam 1 mg and tolterodine 1 mg (active placebo). The area of static hyperalgesia after intradermal capsaicin injection was the primary endpoint. Secondary endpoints were: area of dynamic hyperalgesia, response to von Frey hair stimulation, pressure pain thresholds, conditioned pain modulation, cutaneous and intramuscular electrical pain thresholds (1, 5 and 20 repeated stimulation), and pain during cuff algometry.ResultsFor the primary endpoint, an increase in the area of static hyperalgesia was observed after administration of placebo (p<0.001), but not after clobazam and clonazepam. Results suggestive for an anti-hyperalgesic effect of the benzodiazepines were obtained with all three intramuscular pain models and with cuff algometry. No effect could be detected with the other pain models employed.ConclusionsCollectively, the results are suggestive for a possible anti-hyperalgesic effect of drugs acting at the GABAA-receptors in humans, particularly in models of secondary hyperalgesia and deep pain. The findings are not conclusive, but support further clinical research on pain modulation by GABAergic drugs. Because of the partial results, future research should focus on compounds acting selectively on subunits of the GABA complex, which may allow the achievement of higher receptor occupancy than unselective drugs. Our data also provide information on the most suitable experimental models for future investigation of GABAergic compounds.Trial RegistrationClinicalTrials.gov NCT01011036