Pharmacological and neurochemical properties of 1,4-diazepines with two annelated heterocycles ('hetrazepines')

Designer Benzodiazepines' Activity on Opioid Receptors: A Docking Study

BACKGROUND

Previous studies have reported that benzodiazepines (BZDs) seem to enhance euphoric and reinforcing properties of opioids in opioid users so that a direct effect on opioid receptors has been postulated, together with a possible synergistic induction of severe side effects due to co use of BDZs and opioids. This is particularly worrisome given the appearance on the market of designer benzodiazepines (DBZDs), whose activity/toxicity profiles are scarcely known.

OBJECTIVES

This study aimed to evaluate, through computational studies, the binding affinity (or lack thereof) of 101 DBZDs identified online on the kappa, mu, and delta opioid receptors (K, M, DOR); and to assess whether their mechanism of action could include activation of the latter.

METHODS

MOE® was used for the computational studies. Pharmacophore mapping based on strong opioids agonist binders' 3D chemical features was used to filter the DBZDs. Resultant DBZDs were docked into the crystallised 3D active conformation of KOR (PDB6B73), DOR (PDB6PT3) and MOR (PDB5C1M). Co-crystallised ligands and four strong agonists were used as reference compounds. A score (S, Kcal/mol) representative of the predicted binding affinity, and a description of ligand interactions were obtained from MOE®.

RESULTS

The docking results, filtered for S < -8.0 and the interaction with the Asp residue, identified five DBZDs as putative binders of the three ORs : ciclotizolam, fluloprazolam, JQ1, Ro 48-6791, and Ro 48-8684.

CONCLUSION

It may be inferred that at least some DBZDs may have the potential to activate opioid receptors. This could mediate/increase their anxiolytic, analgesic, and addiction potentials, as well as worsen the side effects associated with opioid co-use.

1,4-Diazepines: A Review on Synthesis, Reactions and Biological Significance

Background:

1,4-Diazepines are two nitrogen containing seven membered heterocyclic compounds and associated with a wide range of biological activities. Due to its medicinal importance, scientists are actively involved in the synthesis, reactions and biological evaluation of 1,4-diazepines since number of decades.

Objective:

The primary purpose of this review is to discuss the synthetic schemes and reactivity of 1,4- diazepines. This article also describes biological aspects of 1,4-diazepine derivatives, that can be usefully exploited for the pharmaceutical sector.

Conclusion:

This review summarizes the abundant literature on synthetic routes, chemical reactions and biological attributes of 1,4-diazepine derivatives. We concluded that 1,4-diazepines have significant importance due to their biological activities like antipsychotic, anxiolytic, anthelmintic, anticonvulsant, antibacterial, antifungal and anticancer. 1,4-diazepine derivatives with significant biological activities could be explored for potential use in the pharmaceutical industries.

Effects of short-acting hypnotics on sleep latency in rats placed on grid suspended over water

The present study was performed to develop a new sleep disturbance model for evaluating hypnotic potencies by placing rats on a grid suspended over water up to 1 cm under the grid surface. When rats were placed on the grid, significant increases in sleep latency and amount of wakefulness were observed compared with those of rats placed on sawdust. However, the amounts of non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep of rats placed on the grid were significantly decreased compared with those of rats placed on sawdust. Four short-acting hypnotics (triazolam, zopiclone, brotizolam, lormetazepam) caused significant decreases in sleep latency, and the effects of hypnotics in rats placed on the grid were more potent than those in rats placed on sawdust. In conclusion, the present model can serve as a new sleep disturbance model and may also be useful for evaluating the sleep-inducing effects of short-acting hypnotics.

Control of motor seizures by brotizolam with maintenance of stable refractory periods for self-stimulation

In recent years, we have been pursuing our mapping investigations of the substrate for brain-stimulation reward in regions of the anterior hypothalamic and lateral preoptic areas. However, one problem is that stimulation of these sites often generates overt seizures so that their suppression via a pharmacological means would be very useful. The sedative-hypnotic benzodiazepine, brotizolam, is reportedly a long-lasting anticonvulsant. Hence, its effects on motor seizures elicited from stimulation of the lateral preoptic area were evaluated in the first experiment. Both tested doses (5.0 and 7.5 mg/kg) of the drug were shown to significantly decrease the number, and marginally, the severity of stimulation-induced seizures; furthermore, this effect was relatively long lasting, up to about 3 h. The higher dose of brotizolam did not alter the single-pulse thresholds for self-stimulation, a requirement for evaluations of poststimulation excitability, the purpose of the second experiment. Here, our interest was in documenting whether the membrane properties of the stimulated neurons, as assessed by refractory periods, were altered by brotizolam. No differences in the time course of recovery were observed; refractoriness began between 0.4 and 0.8 ms, and reached 50% recovery by 2.0 ms, which is consistent with the pattern of poststimulation excitability typically measured at these sites. Thus, in addition to its long-lasting suppression of motor seizures in rats, brotizolam does not alter the time course of recovery from refractoriness of the neurons that mediate brain-stimulation reward in the lateral preoptic area.

Pharmacological actions of Y-24180, a new specific antagonist of platelet activating factor (PAF): II. Interactions with PAF and benzodiazepine receptors

The inhibitory effect of Y-24180, 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H-t hieno [3,2-f][1,2,4]triazolo [4,3-a][1,4]diazepine, on platelet activating factor (PAF)-induced platelet aggregation and the specific binding of 3H-PAF to platelets was compared with other thienodiazepine derivatives, WEB 2086 and etizolam. Y-24180 inhibited PAF-induced rabbit platelet aggregation in vitro (IC50 3.84 nM), but had little effect on adenosine diphosphate- or arachidonic acid-induced aggregation. WEB 2086 and etizolam also showed an inhibitory effect of PAF-induced aggregation (IC50 values are 456 and 6730 nM, respectively). In PAF-induced human platelet aggregation, Y-24180 (IC50 0.84 nM) was more potent than WEB 2086 (IC50 4.21 nM) and etizolam (IC50 998 nM). Y-24180, WEB 2086 and etizolam displaced 3H-PAF binding from the washed-platelets of rabbits with an IC50 value of 3.50, 9.35 and 29.5 nM, respectively. In rabbits, pretreatment with Y-24180 and WEB 2086 antagonized PAF-induced platelet aggregation dose-dependently. The significant inhibitory effect of Y-24180 (1 mg/kg, p.o.) lasted 72 hr after a single dose oral administration. WEB 2086 (10 mg/kg, p.o.) also antagonized the ex vivo response induced by PAF 1 hr after administration, but no significant effect was observed 3 hr after administration. Y-24180 displaced 3H-diazepam binding from the synaptosomal membranes of rat cerebral cortex with a Ki value of 3.68 microM. The affinity of Y-24180 for benzodiazepine(BZP) receptors was lower than those of WEB 2086 and etizolam and was about 1000 times lower than that for PAF receptors in platelets.

Differences in pharmacological profiles of a new generation of benzodiazepine and non-benzodiazepine hypnotics

The hypnotics, quazepam (a benzodiazepine), brotizolam (a thienotriazolodiazepine), zopiclone (a cyclopyrrolone) and zolpidem (an imidazopyridine) have a common ability to bind to the benzodiazepine recognition site (omega receptor) within the GABAA receptor. For this reason we compared their pharmacological profiles in mice. All compounds shared anticonvulsant and central depressant effects. However, the sedative activity of zolpidem appeared at much lower doses than did the anticonvulsant and myorelaxant effects but the opposite was observed with the other hypnotics. In contrast to brotizolam, quazepam and zopiclone, zolpidem did not increase food intake in mice placed in a novel environment, indicating that this drug lacks disinhibitory activity. Moreover the efficacy of zolpidem at the GABAA receptor, as indicated by its activity against convulsions induced by the GABA synthesis inhibitor, isoniazid, was much greater than that of other hypnotics. These results suggest that the hypnoselective properties observed with zolpidem might be related to a high selectivity for the omega 1 recognition site of the GABAA receptor coupled with a very high intrinsic activity.

Relative efficacies of 1,4-diazepines on GABA-stimulated chloride influx in rat brain vesicles

The effects of 1,4-diazepines with two annelated heterocycles [brotizolam (WE 941), ciclotizolam (WE 973) and WE 1008] on gamma-aminobutyric acid (GABA)-stimulated chloride influx into rat brain membrane vesicles were examined. Brotizolam enhanced GABA (30 microM)-stimulated 36Cl- influx (146.1% of control), while ciclotizolam and WE 1008 showed only a small enhancement (119.3% and 119.1%, respectively) of GABA-stimulated 36Cl- uptake. Brotizolam resulted in a left shift of the GABA dose response curve at lower concentrations of GABA (10 microM), while at higher concentrations of GABA (1 mM), brotizolam caused a reduction of the maximal response. The enhancement of GABA-stimulated 36Cl- uptake by brotizolam (0.1 microM) was antagonized by Ro 15-1788. At higher concentration of GABA (300 microM), brotizolam inhibited GABA-stimulated 36Cl- uptake in a dose dependent manner and Ro15-1788 failed to antagonize this effect. These results suggest that 1) brotizolam produces an enhancement of GABA (30 microM)-stimulated chloride influx through the benzodiazepine receptor. 2) brotizolam inhibition of GABA (300 microM)-stimulated chloride influx involves an additional mechanism, and 3) the sedative-hypnotic action of brotizolam may be related to its high efficacy at the benzodiazepine/GABA-gated chloride channel.

Inhibition constants and GABA-shifts at 2 degrees C and 37 degrees C for a spectrum of ligands acting on the benzodiazepine receptors of guinea pig hippocampus

1. Dissociation constants and Hill coefficients were determined for 13 ligands inhibiting the binding of [3H]flunitrazepam to the benzodiazepine receptors of guinea pig hippocampus at 2 degrees C and 37 degrees C. 2. The ratio of I50 in the absence of gamma-aminobutyric acid (GABA) to that in the presence of 10(-5) M GABA (the GABA-shift) was found to vary from 0.4 to 2.5. 3. There was no correlation between the pharmacological activity of the ligand and the GABA-shift, or between the pharmacological activity and the magnitude of the increase in affinity of the ligand for the receptor as the temperature decreased from 37 degrees C to 2 degrees C. 4. A correlation was observed between the temperature-induced affinity change and the GABA-shift at 37 degrees C.

The potential pathophysiological role of platelet-activating factor in human diseases

Platelet-activating factor (PAF) is a new phospholipid mediator released from various cell types and tissues by the catalytic action of phospolipase A2 and acetyl transferase upon immunological and non-immunological stimuli. It activates the cells by binding to specific binding sites. PAF exhibits a broad range of biological and pharmacological activities including platelet and neutrophil aggregation, eosinophil chemotaxis, bronchoconstriction, hypotension, and acute renal failure. In addition, PAF is involved in acute graft rejection, endotoxin shock, and gastrointestinal ulceration. Furthermore, it closely mimics the pathology of bronchial asthma and is cabable of producing most of the phenomena seen in inflammation. So far several PAF antagonists have been described and shown to afford protection. In future, pharmacological studies using such antagonists will help to elucidate the pathophysiological role of PAF in human diseases.

Electrophysiology of benzodiazepine receptor ligands: multiple mechanisms and sites of action

Electrophysiology of BZR ligands has been reviewed from different points of view. A great effort was made to critically discuss the arguments for and against the temporarily leading hypothesis of the mechanism of action of BZR ligands, the GABA hypothesis. As has been discussed at length in the present article, an impressive body of electrophysiological and biochemical evidence suggests an enhancement of GABAergic inhibition in CNS as a mechanism of action of BZR agonists. Biochemical data even indicate a physical coupling between GABA recognition sites and BZR which, together with the effector site build-up by Cl- channels, form a supramolecular GABAA/BZR complex. By binding to a specific site on this complex, BZR agonists allosterically increase and BZR inverse agonists decrease the gating of GABA-linked Cl- channels, whereas BZR antagonists bind to the same site without an appreciable intrinsic activity and block the binding and action of both agonists as well as inverse agonists. While this model is supported by many electrophysiological experiments performed with BZR ligands in higher nanomolar and lower micromolar concentrations, it does not explain much controversial data from animal behavior and, more importantly, is not in line with electrophysiological effects obtained with low nanomolar BZ concentrations. The latter actions of BZR ligands in brain slices occur within a concentration range compatible with concentrations of BZ observed in CSF fluid, which would be expected to be found in the biophase (receptor level) during anxiolytic therapy in man. Enhanced K+ conductance seems to be a suitable candidate for this effect of BZR ligands. This direct action on neuronal membrane properties may underlie the many electrophysiological observations with extremely low systemic doses of BZR ligands in vivo which demonstrated a depressant effect on spontaneous neuronal firing in various CNS regions. Skeletomuscular spasticity and epilepsy are two neurological disorders, where both the enhanced GABAergic inhibition and increased K+ conductance may contribute to the therapeutic effect of BZR agonists, since electrophysiological and behavioral studies strongly support GABA-dependent as well as GABA-independent action of BZR ligands elicited by low to intermediate doses of BZ necessary to evoke anticonvulsant and muscle relaxant effects. Somewhat higher doses of BZR ligands, inducing sedation and sleep, lead perhaps to the only pharmacologically relevant CNS concentrations (ca. 1 microM) which might be due entirely to increased GABAergic inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypnotic activity of an imidazo-pyridine (zolpidem)

Effects of an imidazo-pyridine (zolpidem: 10, 20 and 30 mg) on overnight sleep and on performance the next day were studied in young adults and in middle aged individuals. The young adults were used particularly as an homogenous group to establish any possible adverse effects of the drug on sleep and on performance the next day, and the middle aged subjects with their less restful sleep were used to study efficacy. In the young adults zolpidem led to a marked increase in slow wave sleep with a reduction in stage 2 sleep. There were no significant changes in REM sleep, though there was a tendency for REM sleep to be delayed. In the middle aged there was a reduction in awake activity and drowsy sleep with an increase in stage 2 sleep. The latency to REM sleep was increased but the duration of REM sleep over the whole night was not reduced. Digit symbol substitution and a complex reaction time task were used to study performance, but there were no residual effects with zolpidem (9 h after ingestion). Zolpidem is likely to prove useful in the management of transient and short-term insomnia in healthy middle aged individuals when impaired performance the next day is to be avoided.