The effect of niaprazine on the turnover of 5-hydroxytryptamine in the rat brain

The impact of piperazine and antipsychotic co-exposures and CB1 blockade on the effects elicited by AMB-FUBINACA, a synthetic cannabinoid, in mice

BACKGROUND & PURPOSE

The constant emergence and broad toxicological effects of synthetic cannabinoids create a discernible public health threat. The synthetic cannabinoid AMB-FUBINACA (AMB-FUB) is a potent agonist at the CB1 receptor and has been associated with numerous fatalities. Synthetic cannabinoids are commonly abused alongside other drugs and medications, including a "party pill" drug, para-fluorophenylpiperazine (pFPP), and the antipsychotic risperidone. This research aimed to investigate the mechanisms underpinning AMB-FUB toxicity and the impact of clinically relevant co-exposures in vivo.

EXPERIMENTAL APPROACH

Male and female C57Bl/6 mice received a single dose of AMB-FUB (3 or 6 mg kg-1), pFPP (10 or 20 mg kg-1) or vehicle intraperitoneally. Mice were co-exposed to AMB-FUB (3 mg kg-1) and pFPP (10 mg kg-1) or risperidone (0.5 mg kg-1) to investigate these drug combinations. To study receptor-dependency and potential rescue of AMB-FUB toxicity, rimonabant (3 mg kg-1) was administered both pre- and post-AMB-FUB. Adverse effects caused by drug administration, including hypothermia and convulsions, were recorded.

KEY RESULTS

AMB-FUB induced CB1-dependent hypothermia and convulsions in mice. The combination of AMB-FUB and pFPP significantly potentiated hypothermia, as did risperidone pre-treatment. Interestingly, risperidone provided significant protection from AMB-FUB-induced convulsions in female mice. Pre- and post-treatment with rimonabant was able to significantly attenuate both hypothermia and convulsions in mice administered AMB-FUB.

CONCLUSION & IMPLICATIONS

Factors such as dose, CB1 signalling, and substance co-exposure significantly contribute to the toxicity of AMB-FUBINACA. Mechanistic understanding of synthetic cannabinoid toxicity and fatality can help inform overdose treatment strategies and identify vulnerable populations of synthetic cannabinoid users.

The piperazine analogue para-fluorophenylpiperazine alters timing of the physiological effects of the synthetic cannabinoid receptor agonist AMB-FUBINACA, without changing its discriminative stimulus, signalling effects, or metabolism

AMB-FUBINACA is a synthetic cannabinoid receptor agonist (SCRA), which has been associated with substantial abuse and health harm since 2016 in many countries including New Zealand. A characteristic of AMB-FUBINACA use in New Zealand has included the observation that forensic samples (from autopsies) and drugs seized by police have often been found to contain para-fluorophenylpiperazine (pFPP), a relatively little-characterised piperazine analogue that has been suggested to act through 5HT1a serotonin receptors. In the current study, we aimed to characterise the interactions of these two agents in rat physiological endpoints using plethysmography and telemetry, and to examine whether pFPP altered the subjective effects of AMB-FUBINACA in mice trained to differentiate a cannabinoid (THC) from vehicle. Though pFPP did not alter the ability of AMB-FUBINACA to substitute for THC, it did appear to abate some of the physiological effects of AMB-FUBINACA in rats by delaying the onset of AMB-FUBINACA-mediated hypothermia and shortening duration of bradycardia. In HEK cells stably expressing the CB1 cannabinoid receptor, 5HT1a, or both CB1 and 5HT1a, cAMP signalling was recorded using a BRET biosensor (CAMYEL) to assess possible direct receptor interactions. Although low potency pFPP agonism at 5HT1a was confirmed, little evidence for signalling interactions was detected in these assays: additive or synergistic effects on potency or efficacy were not detected between pFPP and AMB-FUBINACA-mediated cAMP inhibition. Experiments utilising higher potency, classical 5HT1a ligands (agonist 8OH-DPAT and antagonist WAY100635) also failed to reveal evidence for mutual CB1/5HT1a interactions or cross-antagonism. Finally, the ability of pFPP to alter the metabolism of AMB-FUBINACA in rat and human liver microsomes into its primary carboxylic acid metabolite via carboxylesterase-1 was assessed by HPLC; no inhibition was detected. Overall, the effects we have observed do not suggest that increased harm/toxicity would result from the combination of pFPP and AMB-FUBINACA.

The crystal structures of salts of N-(4-fluoro-phen-yl)piperazine with four aromatic carb-oxy-lic acids and with picric acid

The structures are reported for five salts formed by reactions between N-(4-fluoro-phen-yl)piperazine and aromatic acids. In 4-(4-fluoro-phen-yl)piperazin-1-ium 2-fluoro-benzoate monohydrate, C10H14FN2 +·C7H4FO2 -·H2O, (I), the components are linked by a combination of N-H⋯O and O-H⋯O hydrogen bonds to form a chain of alternating R 4 6(12) and R 6 6(16) rings. The ionic components of 4-(4-fluoro-phen-yl)piperazin-1-ium 2-bromo-benzoate 0.353-hydrate, C10H14FN2 +·C7H4BrO2 -·0.353H2O, (II), are linked by N-H⋯O hydrogen bonds to form a centrosymmetric four-ion aggregate containing an R 4 4(12) motif, and these aggregates are linked into a mol-ecular ladder by a single C-H⋯π(arene) hydrogen bond. 4-(4-Fluoro-phen-yl)piperazin-1-ium 2-iodo-benzoate, C10H14FN2 +·C7H4IO2 -, (III), crystallizes with Z' = 2 in space group P : the four independent ions are linked by N-H⋯O hydrogen bonds to form a non-centrosymmetric aggregate again containing an R 4 4(12) motif, and aggregates of this type are linked into a ribbon by a combination of C-H⋯O and C-H⋯π(arene) hydrogen bonds. The anion in 4-(4-fluoro-phen-yl)piperazin-1-ium 2,4,6-tri-nitro-phenolate, C10H14FN2 +·C6H2N3O7 -, (IV), shows clear evidence of extensive electronic delocalization from the phenolate O atom into the adjacent ring. The ions are linked by a combination of two-centre N-H⋯O and three-centre N-H⋯(O)2 hydrogen bonds to form centrosymmetric four-ion aggregates containing three types of ring. The ions in 4-(4-fluoro-phen-yl)piperazin-1-ium 3,5-di-nitro-benzoate, C10H14FN2 +·C7H3N2O6 -, (V), are again linked by N-H⋯O hydrogen bonds to form centrosymmetric R 4 4(12) aggregates, which are themselves linked by a C-H⋯π(arene) hydrogen bond to form sheets, the stacking of which leads to the formation of narrow channels, containing disordered and/or mobile solvent entities. Comparisons are made with some related structures.

Three 4-(4-fluoro-phen-yl)piperazin-1-ium salts containing organic anions: supra-molecular assembly in one, two and three dimensions

Three salts containing the 4-(4-fluoro-phen-yl)piperazin-1-ium cation have been prepared and structurally characterized. In 4-(4-fluoro-phen-yl)piperazin-1-ium 2-hy-droxy-3,5-di-nitro-benzoate, C10H14FN2 +·C7H3N2O7 -, (I), the anion contains an intra-molecular O-H⋯O hydrogen bond, and it has a structure similar to that of the picrate ion. The cations and anions are linked into [001] chains of rings by a combination of two three-centre N-H⋯(O)2 hydrogen bonds. The anion in 4-(4-fluoro-phen-yl)piperazin-1-ium hydrogen oxalate, C10H14FN2 +·C2HO4 -, (II), is planar, and the cations and anions are linked into (100) sheets by multiple hydrogen bonds including two-centre N-H⋯O, three-centre N-H⋯(O)2, O-H⋯O, C-H⋯O and C-H⋯π(arene) types. In 4-(4-fluoro-phen-yl)piperazin-1-ium hydrogen (2R,3R)-tartrate monohydrate, C10H14FN2 +·C4H5O6 -·H2O, (III), the anion exhibits an approximate non-crystallographic twofold rotation symmetry with anti-periplanar carboxyl groups. A combination of eight hydrogen bonds, encompassing two- and three-centre N-H⋯O systems, O-H⋯O and C-H⋯π(arene) types, link the independent components into a three-dimensional framework. Comparisons are made with some related structures.

Metabolic interactions with piperazine-based ‘party pill’ drugs

Objectives

‘Party pills’ have found use worldwide as a substitute for amphetamine-derived designer drugs. Whilst some information exists about the metabolism of these drugs, there is little information about their ability to inhibit the metabolism of co-administered drugs. This study aimed to determine whether predictions can be made about global interactions between ‘party pills’ constituents and other drugs metabolised by the same cytochrome P450 (CYP) isoenzymes.

Methods

The inhibitory effects of seven benzyl and phenyl piperazines were measured in microsomal incubation assays of probe substrates for five major CYP isoenzymes. In addition, the metabolism of benzylpiperazine and trifluoromethylphenylpiperazine, the two most commonly used constituents of ‘party pills’, was investigated using human liver microsomes assays and known inhibitors of CYP isoenzymes.

Key findings

All piperazine analogues tested showed significant inhibitory activity against most, if not all, isoenzymes tested. The metabolism of benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP) involved CYP2D6, CYP1A2 and CYP3A4. Furthermore, BZP and TFMPP inhibited each other's metabolism.

Conclusions

Fluorophenylpiperazine, methoxyphenylpiperazine, chlorophenylpiperazine, methylbenzylpiperazine and methylenedioxybenzylpiperazine had significant inhibitory effects on CYP2D6, CYP1A2, CYP3A4, CYP2C19 and CYP2C9 isoenzymes but each piperazine had a different inhibitory profile. The metabolic interaction between BZP and TFMPP may have clinical implications, as these agents are often combined in ‘party pills’.

Treatment of alternating hemiplegia of childhood with aripiprazole

We report the pharmacological treatment of a case of alternating hemiplegia of childhood (AHC) in a 14-year-old female with an established diagnosis. Although the patient's symptoms are consistent with those of the condition, she did not respond to treatment with haloperidol, flunarizine, or propranolol. Treatment with aripiprazole resulted in a reduction in the frequency, duration, and severity of episodes of alternating hemiplegia, along with other therapeutic benefits. After treatment with aripiprazole was started, the patient was inadvertently given an inactive drug, resulting in a worsening of her hemiplegic episodes, which improved again on rechallenge. A comparison of the pharmacological actions of successful and unsuccessful treatments for AHC is made. Modulation of both dopamine and histamine systems together appears to be important in the treatment of AHC and further investigation of such pharmacotherapies is suggested.

The effect of niaprazine on some common sleep disorders in children. A double-blind clinical trial by means of continuous home-videorecorded sleep

A placebo-controlled double-blind clinical trial on the effect of niaprazine on children with some common sleep disorders was carried out. Niaprazine at a daily dosage of 1 mg/kg body weight or placebo at random was administered to a selected group of 36 children (aged from 6 months to 6 years) suffering from frequent nighttime waking or inability to fall asleep. The effect of niaprazine (or placebo) on sleep disorders was studied by means of continuous home-videorecorded sleep before and after the trial. A reliable positive effect of niaprazine on the sleep disorders considered was found. No adverse side effects were observed. We conclude that niaprazine seems to represent an effective and safe drug for the therapy of frequent nighttime waking and inability to fall asleep.

Molecular pharmacology of niaprazine

1. The pharmacological profile of niaprazine was investigated using in vitro ligand binding techniques. 2. Niaprazine exhibits a low affinity for the vesicular monoamine transporter and for D2, alpha 2, beta, H1 and muscarinic cholinergic receptors. Niaprazine, particularly the (+)stereoisomer, has a higher affinity for alpha 1 (Ki = 77 nM) and 5-HT2 (Ki = 25 nM) binding sites, but is poorly recognized by 5-HT1A and 5-HT1B binding sites (Ki sigma mciroM). In contrast, p-fluoro-phenylpiperazine, a major metabolite of niaprazine, exhibits a higher affinity for the 5-HT1 subclasses than for the 5HT2 class. 3. These results suggest that the pharmacological properties of niaprazine reflect both its non-reserpinic catecholamine depletor effect and its action on alpha 1 and 5-HT2 receptors. A role of p-fluoro-phenylpiperazine via 5-HT1 sites cannot be excluded.

Identification and quantitation of 1-arylpiperazines, metabolites resulting from side-chain cleavage of (4-substituted aryl-1-piperazinyl)alkyl heterocyclic derivatives in rat plasma and brain

Many drugs contain the arylpiperazine moiety in the side-chain of their molecules. A common metabolic pathway of such drugs is cleavage of the side-chain with the formation of 1-arylpiperazines. This has been verified by combined gas chromatography-mass spectrometry of biological samples from rats given orally a series of heterocyclic derivatives bearing a 4-aryl(phenyl, pyrimidinyl, pyridyl or thiazolyl)-1-piperazinylalkyl moiety (oxypertine, zolertine, millipertine, empiprazole, dapiprazole, antrafenine, piribedil, azaperone). A sensitive and selective electron-capture gas-liquid chromatographic procedure for 1-arylpiperazines in rat plasma and brain is described. The overall recovery from plasma and brain was 70-90%. The limit of detection for substituted (halogenated) phenylpiperazines was 10-25 ng/ml or ng/g and 25-100 ng/ml or ng/g for other derivatives. Preliminary data are reported on the time course of the production and elimination of 1-arylpiperazines after oral administration of representative compounds with the arylpiperazine moiety (oxypertine, azaperone and S-3608).