A fatal case of amoxapine poisoning under the influence of chronic use of psychotropic drugs

Elucidation of Degradation Behavior of Tricyclic Antidepressant Amoxapine in Artificial Gastric Juice

The degradation behavior of eight tricyclic antidepressants (TCAs; amitriptyline, amoxapine (AMX), imipramine, clomipramine, desipramine, doxepin, dothiepin, and nortriptyline) in artificial gastric juice was investigated to estimate their pharmacokinetics in the stomach. As a result, among the eight TCAs, only AMX was degraded in artificial gastric juice. The degradation was a pseudo first-order reaction; activation energy (Ea) was 88.70 kJ/mol and activation entropy (ΔS) was -80.73 J/K·mol. On the other hand, the recovery experiment revealed that the degradation product did not revert to AMX and accordingly, this reaction was considered to be irreversible. In the AMX degradation experiment, peaks considered to be degradation products A (I) and B (II) were detected at retention times of around 3 min and 30 min in LC/UV measurements, respectively. Structural analysis revealed that compound (I) was [2-(2-aminophenoxy)-5-chlorophenyl]-piperazin-1-yl-methanone, a new compound, and compound (II) was 2-chlorodibenzo[b,f][1,4]oxazepin-11(10H)-one. As for the degradation behavior, it was estimated that AMX was degraded into (II) via (I), i.e., (II) was the final product. The results are expected to be useful in clinical chemistry and forensic science, including the estimation of drugs to be used at the time of judicial dissection and suspected drug addiction.

Enantioseparation of phenothiazines through capillary electrophoresis with solid phase extraction and polymer based stacking

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at nanomolar concentration levels. The method consists of hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of d,l-phenothiazines were baseline separated using a background electrolyte containing 0.9% PDDAC, 5 mM Hp-γ-CD, and 100 mM tris(hydroxymethyl)aminomethane (Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of d,l-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%.

Inhibition of human cytochrome P450 isoenzymes by a phenothiazine neuroleptic levomepromazine: An in vitro study

BACKGROUND

Inhibition of cytochrome P450 (CYP) isoenzymes is the most common cause of harmful drug-drug interactions. The present study was aimed at examining the inhibitory effect of the phenothiazine neuroleptic levomepromazine on main CYP isoenzymes in human liver.

METHODS

The experiment was performed in vitro using the human cDNA-expressed CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 (Supersomes). CYP isoenzyme activities were determined using the CYP-specific reactions: caffeine 3-N-demethylation (CYP1A2), diclofenac 4'-hydroxylation (CYP2C9), perazine N-demethylation (CYP2C19), bufuralol 1'-hydroxylation (CYP2D6) and testosterone 6β-hydroxylation (CYP3A4). The rates of the CYP-specific reactions were assessed in the absence and presence of levomepromazine (1-50 μM). The concentrations of CYP-specific substrates and their metabolites formed by CYP isoenzymes were measured by HPLC with UV or fluorimetric detection.

RESULTS

Levomepromazine potently inhibited CYP2D6 (K(i) = 6 μM) in a competitive manner. Moreover, the neuroleptic moderately diminished the activity of CYP1A2 (K(i) = 47 μM) and CYP3A4 (K(i) = 34 μM) via a mixed mechanism. On the other hand, levomepromazine did not affect the activities of CYP2C9 and CYP2C19.

CONCLUSION

The inhibition of CYP1A2, CYP2D6 and CYP3A4 by levomepromazine, demonstrated in vitro in the present study, should also be observed in vivo (especially the CYP2D6 inhibition by levomepromazine), since the calculated K(i) values are below or close to the presumed concentration range for levomepromazine in the liver in vivo. Therefore pharmacokinetic interactions involving levomepromazine and CYP2D6, CYP1A2 or CYP3A4 substrates are likely to occur in patients during co-administration of the above-mentioned substrates/drugs.

Amoxapine inhibits delayed outward rectifier K(+) currents in cerebellar granule cells via dopamine receptor and protein kinase A activation

BACKGROUND

Although tricyclic antidepressants amoxapine is proposed to target 5-HT and D2 receptors, very few studies have addressed the effect of amoxapine on molecular and cellular mechanisms via receptor pathways. In this study, we test the effect of amoxapine on rat cerebellar granule neurons (CGNs) to address this possibility.

METHODS

CGNs cell culture, whole-cell current recording using a patch-clamp technique, western blot and non-radioactive detection analysis of phosphorylated protein kinase A (PKA) were used.

RESULTS

Amoxapine inhibits delayed rectifier potassium (I(K)) current in a dose-dependent manner and modulates inactivation properties in CGNs. Those effects were not eliminated by preincubation with 5-HT or 5-HT receptor antagonists, but abolished by dopamine and D1/D5 receptor antagonists. Application of GTPγ-S and inhibitor of the Gs signalling cascade abolished the amoxapine-induced effect on I(K). The application of forskolin or dibutyryl-cAMP mimicked the inhibitory effect of amoxapine on I(K). Western blotting for phosphorylated PKA revealed that amoxapine significantly increased the intracellular levels of phosphorylated PKA, a marker of PKA activation.

CONCLUSION

Amoxapine inhibits I(K) currents in rat CGNs via cAMP/PKA-dependent pathways, as in mouse cortical neurons we reported earlier, but that involves D1-like receptors instead of 5-HT receptors.

Multiple mechanisms of hERG liability: K+ current inhibition, disruption of protein trafficking, and apoptosis induced by amoxapine

The antidepressant amoxapine has been linked to cases of QT prolongation, acute heart failure, and sudden death. Inhibition of cardiac hERG (Kv11.1) potassium channels causes prolonged repolarization and is implicated in apoptosis. Apoptosis in association with amoxapine has not yet been reported. This study was designed to investigate amoxapine effects on hERG currents, hERG protein trafficking, and hERG-associated apoptosis in order to elucidate molecular mechanisms underlying cardiac side effects of the drug. hERG channels were expressed in Xenopus laevis oocytes and HEK 293 cells, and potassium currents were recorded using patch clamp and two-electrode voltage clamp electrophysiology. Protein trafficking was evaluated in HEK 293 cells by Western blot analysis, and cell viability was assessed in HEK cells by immunocytochemistry and colorimetric MTT assay. Amoxapine caused acute hERG blockade in oocytes (IC(50) = 21.6 microM) and in HEK 293 cells (IC(50) = 5.1 microM). Mutation of residues Y652 and F656 attenuated hERG blockade, suggesting drug binding to a receptor inside the channel pore. Channels were mainly blocked in open and inactivated states, and voltage dependence was observed with reduced inhibition at positive potentials. Amoxapine block was reverse frequency-dependent and caused accelerated and leftward-shifted inactivation. Furthermore, amoxapine application resulted in chronic reduction of hERG trafficking into the cell surface membrane (IC(50) = 15.3 microM). Finally, the antidepressant drug triggered apoptosis in cells expressing hERG channels. We provide evidence for triple mechanisms of hERG liability associated with amoxapine: (1) direct hERG current inhibition, (2) disruption of hERG protein trafficking, and (3) induction of apoptosis. Further experiments are required to validate a specific pro-apoptotic effect mediated through blockade of hERG channels.

Amoxapine inhibits the delayed rectifier outward K+ current in mouse cortical neurons via cAMP/protein kinase A pathways

Ion channels are known to be modulated by antidepressant drugs, but the molecular mechanisms are not known. We have shown that the antidepressant drug amoxapine suppresses rectifier outward K(+) (I(K)) currents in mouse cortical neurons. At a concentration of 10 to 500 muM, amoxapine reversibly inhibited I(K) in a dose-dependent manner and modulated both steady-state activation and inactivation properties. The application of forskolin or dibutyryl cAMP mimicked the inhibitory effect of amoxapine on I(K) and abolished further inhibition by amoxapine. N-[2-(p-Bromocinnamylamino)ethyl]-5-iso-quinolinesulphonamide (H-89), a protein kinase A (PKA) inhibitor, augmented I(K) amplitudes and completely eliminated amoxapine inhibition of I(K). Amoxapine was also found to significantly increase intracellular cAMP levels. The effects of amoxapine on I(K) were abolished by preincubation with 5-hydroxytryptamine (5-HT) and the antagonists of 5-HT(2) receptor. Moreover, intracellular application of guanosine 5'-[gammathio]-triphosphate increased I(K) amplitudes and prevented amoxapine-induced inhibition. The selective Kv2.1 subunit blocker Jingzhaotoxin-III reduced I(K) amplitudes by 30% and also significantly abolished the inhibitory effect of amoxapine. Together these results suggest that amoxapine inhibits I(K) in mouse cortical neurons by cAMP/PKA-dependent pathway associated with the 5-HT receptor, and suggest that the Kv2.1 alpha-subunit may be the target for this inhibition.