Interaction between the tetracyclic antidepressant mianserin HCl and opioid receptors

Treatment-Resistant Depression (TRD): Is the Opioid System Involved?

About 30% of major depression disorder patients fail to achieve remission, hence being diagnosed with treatment-resistant major depression (TRD). Opium had been largely used effectively to treat depression for centuries, but when other medications were introduced, its use was discounted due to addiction and other hazards. In a series of previous studies, we evaluated the antinociceptive effects of eight antidepressant medications and their interaction with the opioid system. Mice were tested with a hotplate or tail-flick after being injected with different doses of mianserin, mirtazapine, trazodone, venlafaxine, reboxetine, moclobemide, fluoxetine, or fluvoxamine to determine the effect of each drug in eliciting antinociception. When naloxone inhibited the antinociceptive effect, we further examined the effect of the specific opioid antagonists of each antidepressant drug. Mianserin and mirtazapine (separately) induced dose-dependent antinociception, each one yielding a biphasic dose-response curve, and they were antagonized by naloxone. Trazodone and venlafaxine (separately) induced a dose-dependent antinociceptive effect, antagonized by naloxone. Reboxetine induced a weak antinociceptive effect with no significant opioid involvement, while moclobemide, fluoxetine, and fluvoxamine had no opioid-involved antinociceptive effects. Controlled clinical studies are needed to establish the efficacy of the augmentation of opiate antidepressants in persons with treatment-resistant depression and the optimal dosage of drugs prescribed.

Intoxication by 3-MeO-PCP and O-desmethyltramadol: an unusual NPS mix

Over the past few years, the new psychoactive substances' phenomenon has been continuously studied. Its dynamic context is characterized by a broad diversity of substances, including several groups, such as synthetic cathinones, synthetic opiates, and synthetic cannabinoids. However, and due both to this diversity and to the low number of detected cases, information on intoxication reports is always important, in order to understand their biological mechanisms. In this case, a male individual was found unresponsive, with some different powders and paraphernalia near him. After toxicological analysis to the powders, paraphernalia, and whole blood samples, five different compounds were identified. From these, two of them (3-MeO-PCP and o-desmethyltramadol) were identified and quantitated in the whole blood sample. The obtained results suggested that death was due to the presence and action of these two substances, in what may be considered an unusual mix of NPS. This case highlights the value of evaluating all the traces found in the scene investigation and the need of sending all the paraphernalia found for toxicological examination, together with all the possible information obtained on the scene, namely by relatives or witnesses. On the other hand, this case shows the significance of broad-spectrum analytical methods, in order to detect and identify, as specifically as possible, eventual substances present and used by victims.

Trazodone and mirtazapine: A possible opioid involvement in their use (at low dose) for sleep?

The efficacy of each antidepressant available has been found equal to that of amitriptyline in double-blind studies. However, a few of them are being prescribed (at under-therapeutic doses) for sleep, in non-depressed persons, when there are relative contraindications for sedative-hypnotics. Following previous studies regarding the antinociceptive mechanisms of various antidepressants, we suggest that the involvement of the opioid system in some of the antidepressants' mechanism of action may contribute to these medications' use for the induction and maintenance of sleep. The mostly prescribed antidepressants for sleep are trazodone (a weak, but specific inhibitor of the synaptosomal uptake of serotonin, that also binds to alpha-1 and alpha-2 adrenoreceptor sites) and mirtazapine (a postsynaptic drug which enhances noradrenergic and 5-HT1A-mediated serotonergic neurotransmission via antagonism of central alpha-2-auto- and hetero-adrenoreceptors). In our previous studies when ICR mice were tested with a hotplate analgesia meter, both trazodone and mirtazapine induced, a naloxone-reversible antinociceptive effect following i.p administration. Summing up the various interactions of trazodone and mirtazapine with opioid, noradrenergic and serotonergic agonists and antagonists, we found that the antinociceptive effect of trazodone is influenced by the opioid receptor subtypes mu and delta (and a clear 5-HT mechanism of antinociception), while the antinociceptive effect of mirtazapine is mainly influenced by kappa and mu opioid receptor subtype (combined with both serotonergic and noradrenergic receptors). This opioid profile of the two drugs may be one of the explanations to their efficacy in the treatment of insomnia, when sedatives (either benzodiazepines or the non-benzodiazepine "Z-compounds") cannot be prescribed.

Psychotropic Drugs for the Management of Chronic Pain and Itch

Clinical observations have shown that patients with chronic neuropathic pain or itch exhibit symptoms of increased anxiety, depression and cognitive impairment. Such patients need corrective therapy with antidepressants, antipsychotics or anticonvulsants. It is known that some psychotropic drugs are also effective for the treatment of neuropathic pain and pruritus syndromes due to interaction with the secondary molecular targets. Our own clinical studies have identified antipruritic and/or analgesic efficacy of the following compounds: tianeptine (atypical tricyclic antidepressant), citalopram (selective serotonin reuptake inhibitor), mianserin (tetracyclic antidepressant), carbamazepine (anticonvulsant), trazodone (serotonin antagonist and reuptake inhibitor), and chlorprothixene (antipsychotic). Venlafaxine (serotonin-norepinephrine reuptake inhibitor) is known to have an analgesic effect too. The mechanism of such effect of these drugs is not fully understood. Herein we review and correlate the literature data on analgesic/antipruritic activity with pharmacological profile of these compounds.

Opioid Receptors Contribute to Antinociceptive Effect of Tianeptine on Colorectal Distension-Induced Visceral Pain in Rats

Tianeptine is a clinically effective atypical antidepressant with distinct neurochemical properties. In this study, we aimed to investigate the contribution of opioid receptors in the antinociceptive effect of tianeptine on visceral pain in awake rats and to differentiate the subtype and the localization (central and/or peripheral) of these opioid receptors involved in this antinociception. Visceromotor response to noxious colorectal distension (CRD) was quantified with electromyographic recordings, obtained from previously implanted electrodes into the external oblique musculature of rats under anesthesia, before and after tianeptine administration. The opioid receptor antagonist naloxone hydrochloride (NLX) and peripherally restricted opioid receptor antagonist naloxone methiodide (NLXM) were administered intravenously 10 min before tianeptine (10 mg/kg, i.v.). The antinociceptive effect of tianeptine was abolished by NLX (1 and 2 mg/kg, i.v.), but was partially reduced by NLXM (1 and 2 mg/kg, i.v.). A µ-opioid receptor-selective dose (0.03 mg/kg, i.v.) of NLX, but not NLXM, significantly inhibited the antinociceptive effect of tianeptine. Our results suggest that antinociceptive effect of tianeptine on CRD-induced visceral nociception in rats involves the activation of both central and peripheral opioid receptors.

Antihyperalgesic and antiallodynic effects of mianserin on diabetic neuropathic pain: a study on mechanism of action

This study used various experimental pain methods to investigate the effects of subacute mianserin administration on diabetes-induced neuropathic pain in rats. The effect of mianserin on hyperalgesia occurring in connection with peripheral diabetic neuropathy was examined using the Randall-Selitto (mechanical nociceptive stimulus), Hargreaves (thermal nociceptive stimulus), and cold-plate (4°C, thermal nociceptive stimulus) tests. The dynamic plantar aesthesiometer, which measures the threshold values for mechanical stimuli, was used for allodynia studies. Thermal allodynia was evaluated with the warm-plate (38°C) test. At 30 and 45 mg/kg, mianserin effectively improved mechanical and thermal hyperalgesia occurring in connection with diabetic neuropathy. Subacute administration of mianserin also reduced diabetes-associated mechanical and thermal allodynia. The ability of mianserin to reduce diabetic neuropathic pain was comparable to that of pregabalin (10mg/kg). The antihyperalgesic and antiallodynic effects of mianserin were reversed with α-methyl-para-tyrosine methyl ester (AMPT, an inhibitor of catecholamine synthesis), phentolamine (a non-selective α-adrenoceptor antagonist), propranolol (a non-selective β-adrenoceptor antagonist), and naloxone (a non-selective opioid receptor antagonist) administrations. The same effects were not reversed, however, by para-chlorophenylalanine methyl ester (PCPA; an inhibitor of serotonin synthesis). These results suggest that the beneficial effect of mianserin on diabetic neuropathic pain is mediated through an increase in catecholamine levels in the synaptic cleft as well as through interactions with both subtypes of adrenoceptors and opioid receptors. Considering that mianserin exhibits simultaneous antidepressant and antinociceptive effects, this drug could provide a good alternative for treating the pain associated with diabetic neuropathy and the mood disorders caused directly by diabetes.

Changes in the basal membrane of dorsal root ganglia Schwann cells explain the biphasic pattern of the peripheral neuropathy in streptozotocin-induced diabetic rats

Peripheral neuropathy is one of the main complications of diabetes mellitus. The current study demonstrated the bimodal pattern of diabetic peripheral neuropathy found in the behavioral study of pain perception in parallel to the histopathological findings in dorsal root ganglia (DRGs) neurons and satellite Schwann cell basement membranes. A gradual decrease in heparan sulfate content, with a reciprocal increase in deposited laminin in the basement membranes of dorsal root ganglia Schwann cells, was shown in streptozotocin-treated rats. In addition, the characteristic biphasic pain profiles were demonstrated in diabetic rats, as shown by hypersensitivity at the third week and hyposensitivity at the tenth week post-streptozotocin injection, accompanied by a continuous decrease in the sciatic nerve conduction velocity. It appears that these basal membrane abnormalities in content of heparan sulfate and laminin, noticed in diabetic rats, may underline the primary damage in dorsal ganglion sensory neurons, simultaneously with the bimodal painful profile in diabetic peripheral neuropathy, simulating the scenario of filtration rate in diabetic kidney.

The atypical antidepressant mianserin exhibits agonist activity at κ-opioid receptors

BACKGROUND AND PURPOSE

Antidepressants are known to interact with the opioid system through mechanisms not completely understood. We previously reported that tricyclic antidepressants act as agonists at distinct opioid receptors. Here, we investigated the effect of the atypical antidepressant mianserin at cloned and native opioid receptors.

EXPERIMENTAL APPROACH

Effects of mianserin were examined in CHO cells transfected with human opioid receptors, C6 glioma cells and rat brain membranes by the use of radioligand binding and functional assays including the stimulation of [(35)S]GTPγS binding and MAPK phosphorylation.

KEY RESULTS

Mianserin displayed 12- and 18-fold higher affinity for κ- than µ- and δ-opioid receptors respectively. In [(35)S]GTPγS assays, mianserin selectively activated κ-opioid receptors. The agonist activity was antagonized by the selective κ-opioid blocker nor-binaltorphimine (nor-BNI). The mianserin analogue mirtazapine also displayed κ-opioid agonist activity. Mianserin and mirtazapine increased ERK1/2 phosphorylation in CHO cells expressing κ-opioid receptors and C6 cells, and these effects were antagonized by nor-BNI. In rat striatum and nucleus accumbens, mianserin stimulated [35S]GTPγS binding in a nor-BNI-sensitive manner with maximal effects lower than those of the full κ-opioid agonists (-)-U50,488 and dynorphin A. When combined, mianserin antagonized the effects of the full κ-opioid receptor agonists in [(35)S]GTPγS assays and reduced the stimulation of p38 MAPK and ERK1/2 phosphorylation by dynorphin A.

CONCLUSIONS AND IMPLICATIONS

In different cell systems, mianserin directly activates κ-opioid receptors, displaying partial agonist activity at brain receptors. Thus, this property appears to be a common feature of different classes of antidepressants.

Tricyclic antidepressants abuse, with or without benzodiazepines abuse, in former heroin addicts currently in methadone maintenance treatment (MMT)

BACKGROUND

To measure suspected abuse of the tricyclic antidepressant amitriptyline among methadone maintenance treatment (MMT) patients in Israel, we studied cross-sectionally, all our 303 patients (February, 2007).

METHODS

Tricyclics presence was screened in one of the random urine samples routinely taken for tests of other drugs. ASI questionnaire, variables from patients' records.

FINDINGS

48 (15.8%) patients were positive for amitriptyline. Logistic regression (multivariate analyses) found that the extent of being amitriptyline-positive was higher in benzodiazepine (BDZ) abusers (OR=11.6 95% CI 4.4-30.7), in subjects with positive antibody to hepatitis C (OR=2.2, 95% CI 1.02-4.9) and in patients treated with high-dose methadone (>150 mg/day) (OR=2.4, 95% CI 1.2-4.9). Amitriptyline was found in 12 (7.5%) of the "privileged" group of patients (stabilized patients who, based on their long-standing cessation of any type of street-drugs abuse and prolonged normative behavior in treatment are granted "take home" methadone doses) who, by definition, should not be abusing anything.

CONCLUSION

The high prevalence of amitriptyline abuse found in our patients, and its potential cardiac hazards when combined with BDZ abuse, emphasizes the importance of amitriptyline routine monitoring in order to decrease the potential risk associated with amitriptyline combined with methadone and BDZ, and to implement appropriate interventions.

The effect of mianserin add-on, on the intensity of opioid withdrawal symptoms during detoxification program--a randomized, double blind, placebo controlled, prospective study

BACKGROUND

Based on pre-clinical studies regarding the interaction of various antidepressant drugs with the opioid system, we designed a clinical study to be carried out in the 'in-patient detoxification unit' within a large community centre for treatment of drugs dependent people. We evaluated the effect of mianserin add-on, on the intensity of opioid withdrawal symptoms in opiate dependent subjects undergoing medication-supported physical detoxification and integrated psychosocial and psychotherapeutic intervention for the treatment of dependence.

METHODS

Mianserin (or placebo) was added to the routine medication protocol, during the 3-week in-patient phase of detoxification in a prospective, randomized, double blind, placebo controlled study. Mianserin (or placebo) was continued after discharge and patients were followed up for 3 months in order to evaluate relapse rates. Opiate withdrawal symptoms were assessed during the first 10 days, while depression and anxiety were assessed throughout the 3 months of study.

RESULTS

From day 2 onward, patients in the study group showed significantly lower withdrawal symptoms than the control group patients and reached this peak faster (study group 2.8 days, control group 3.2 days, p<0.001). However, drop out rates were higher in the study group throughout the study period and only 13% of the study group patients, compared to 30% of the control group patients reached the end point.

CONCLUSION

Though adding mianserin to the medication treatment during detoxification of opiate-dependent persons attenuated significantly both the intensity and the duration of withdrawal symptoms, the overall drop out rate was negatively influenced in the study group compared to the control group and fewer patients completed the study. Further study is needed in order to establish the origin of the paradox of higher drop out rates in the presence of attenuated intensity and duration of opiate withdrawal symptoms in the study group, and the clinical implications that should be drown.

The influence of electroconvulsive therapy on pain threshold and pain tolerance in major depression patients before, during and after treatment

Despite the findings that pain and depression are not always directly linked, enough evidence suggest that a complex relationship between pain and depression exists. Using an electronic pressure algometer placed on the sternum, the changes in pressure pain threshold (PPThr) and pressure pain tolerance (PPTol) were evaluated in 19 patients affected by refractory major depression without psychotic features, throughout a full course of electroconvulsive therapy (ECT) treatment. Measurements were done before the first treatment, after the 6th treatment and after the last treatment. After the 6th treatment, mean (+/- SD) PPThr increased significantly from 11.48 (+/- 4.81) kg/cm2 at baseline, to 13.7 (+/- 5.59) kg/cm2 (p=0.0076) while PPTol did not change significantly (from 18.46 (+/- 6.75)kg/cm2 to 17.4 (+/- 8.1)kg/cm2). At the end of the treatment course, mean (+/- SD) PPThr did not increase further significantly (15.06 (+/- 5.21)kg/cm2 (p=0.0234)) while PPTol increased significantly to 21.34 (+/- 7.8)kg/cm2 (p=0.0047). ECT's efficacy was measured with the 21-item Hamilton Rating Scale for Depression (21-HAM-D). Mean (+/- SD) 21-HAM-D scores decreased significantly from 30.9 (+/- 4.15) at baseline, to 10.47 (+/- 5.78) (p=0.0001) after the 6th treatment, with no further significant change at the end of the treatment course (9.94 +/- 3.07; p=0.0254). Both pain threshold and pain tolerance increased following the alleviation of the depressive disorder and a possible usefulness of ECT may be postulated for treating severe, chronic pain syndromes. However, a more significant conclusion is that the increase of the PPThr noted early during ECT treatment may serve as an early outcome possible detector of ECT efficacy in depressed patients.

The antinociceptive effect of mirtazapine in mice is mediated through serotonergic, noradrenergic and opioid mechanisms

The antinociceptive effects of the noradrenergic and specific serotonergic antidepressant (NaSSA) drug mirtazapine and its interaction with various opioid receptor subtypes were evaluated in mice with a hotplate analgesicmeter. Mirtazapine elicited an antinociceptive effect in a dose-dependent manner following doses from 1 to 7.5mg/kg. As the mirtazapine dose increased beyond 10mg/kg latencies returned to baseline, yielding a biphasic dose-response curve. The effect of opioid, adrenergic, and serotonergic receptor antagonists was examined as to their ability to block mirtazapine antinociception. Mirtazapine (at 10mg/kg)-induced antinociception was significantly inhibited by naloxone, nor-BNI, and naltrindole, but neither by beta-FNA nor by naloxonazine, implying the involvement of kappa(1)- and delta-opioid mechanisms. When adrenergic and serotonergic antagonists were used, both metergoline and yohimbine, decreased antinociception elicited by mirtazapine, implying a combined serotonergic and noradrenergic mechanism of antinociception. When mirtazapine was administered together with various agonists of the opioid receptor subtypes, it significantly potentiated antinociception mediated only by kappa(3)-opioid receptor subtypes. Summing up these results we conclude that the antinociceptive effect of mirtazapine is mainly influenced by the kappa(3)-opioid receptor subtype combined with both serotonergic and noradrenergic receptors. These results suggest a potential use of mirtazapine in the management of some pain syndromes, and raise questions regarding a possible indirect opioid-dependence induced by mirtazapine. However, further research is needed in order to establish both the exact clinical indications and the effective doses of mirtazapine when prescribed for pain.

The antinociceptive effect of trazodone in mice is mediated through both mu-opioid and serotonergic mechanisms

The antinociceptive effects of trazodone (a triazolopyridine derivative with antidepressant activity) and its interaction with various opioid, noradrenaline and serotonin receptor subtypes were evaluated. Mice were tested with a hotplate analgesia meter. Trazodone induced a dose-dependent antinociceptive effect following i.p. administration. The ED(50) for mice in the hotplate assay for trazodone was 24.8 mg/kg (9.8; 67.4; 95% CL). The effect of opioid, adrenergic and serotonergic receptor antagonists was examined as to their ability to block trazodone antinociception. Trazodone-induced antinociception was significantly inhibited by naloxone, beta-FNA and naloxonazine, but not by nor-BNI or naltrindole, implying involvement of mu1- and mu2-opioid mechanisms. When adrenergic and serotonergic antagonists were used, metergoline (p<0.05) but not phentolamine or yohimbine, decreased antinociception elicited by trazodone, implying a clear 5-HT mechanism of antinociception. When trazodone was administered together with various agonists of the opioid receptor subtypes, it significantly potentiated antinociception mediated by mu1- and mu2- opioid receptor subtypes. Summing up these results, we conclude that the antinociceptive effect of trazodone is mainly influenced by the mu1- +mu2-opioid receptor subtype combined with the serotonergic receptor. These results explain the diffuse clinical use of trazodone in the management of some pain syndromes, and in opioid- and alcohol-detoxification programs, but raise questions regarding a possible 'indirect' opioid-dependence induced by trazodone itself.

The antinociceptive effect of venlafaxine in mice is mediated through opioid and adrenergic mechanisms

The antinociceptive effects of the novel phentylethylamine antidepressant drug venlafaxine and its interaction with various opioid, noradrenaline and serotonin receptor subtypes were evaluated. When mice were tested with a hotplate analgesia meter, venlafaxine induced a dose-dependent antinociceptive effect following i.p. administration with an ED50 of 46.7 mg/kg (20.5; 146.5; 95% CL). Opioid, adrenergic and serotoninergic receptor antagonists were tested for their ability to block venlafaxine antinociception. Venlafaxine-induced antinociception was significantly inhibited by naloxone, nor-BNI and naltrindole but not by beta-FNA or naloxonazine, implying involvement of kappa1- and delta-opioid mechanisms. When adrenergic and serotoninergic antagonists were used, yohimbine (P < 0.005) but not phentolamine or metergoline, decreased antinociception elicited by venlafaxine, implying a clear alpha2- and a minor alpha1-adrenergic mechanism of antinociception. When venlafaxine was administered together with various agonists of the opioid and alpha2- receptor subtypes, it significantly potentiated antinociception mediated by kappa1- kappa3- and delta-opioid receptor subtypes. The alpha2-adrenergic agonist clonidine significantly potentiated venlafaxine-mediated antinociception. Summing up these results, we conclude that the antinociceptive effect of venlafaxine is mainly influenced by the kappa- and delta-opioid receptor subtypes combined with the alpha2-adrenergic receptor. These results suggest a potential use of venlafaxine in the management of some pain syndromes. However, further research is needed in order to establish both the exact clinical indications and the effective doses of venlafaxine when prescribed for pain.

The atypical neuroleptics clozapine and olanzapine differ regarding their antinociceptive mechanisms and potency

Using the mouse tail-flick assay, we evaluated the antinociceptive effect and the interaction with the opioid, adrenergic, and serotonergic systems of the two "atypical" neuroleptic agents clozapine and olanzapine. Clozapine induced a potent antinociceptive effect in a dose-dependent manner with ED50 of 8.7 mg/kg. This effect was antagonized by the nonselective opioid antagonist naloxone (p < 0.05), implying an opioid mechanism of action involved in clozapine-induced antinociception. Further evaluation demonstrated the involvement of micro1-, micro2-, kappa1- opioid receptor subtypes and of alpha2-adrenoreceptors in clozapine antinociception but not the serotonin receptors. Olanzapine induced a weak antinociceptive effect. The highest effect found was a 50% antinociception following an injection of 10 mg/kg. As the olanzapine dose increased beyond 10 mg/kg, latencies declined almost back to baseline. Yohimbine (an alpha2-adrenoreceptor antagonist) significantly reduced olanzapine's antinociceptive effect almost completely (to 10%; p < 0.05), while both naloxone and metergoline (a nonselective 5-HT receptor antagonist) reduced it only partially. These results indicate the possible involvement of the alpha2-adrenoreceptors in olanzapine antinociception and to a less extent the involvement of opioid and serotonergic receptors. Although both clozapine and olanzapine are dibenzodiazepines with similar "atypical" antipsychotic properties, it seems that they differ notably not only regarding their hematological side effects, but regarding their interaction with the opioid system as well.

The antinociceptive effect of moclobemide in mice is mediated by noradrenergic pathways

Moclobemide is an antidepressant which affects the monoaminergic neurotransmitter system through a reversible inhibition of monoamine oxidase (MAO), preferentially type A. We examined the antinociceptive effects of moclobemide alone and in conjunction with specific opioid, adrenergic and serotonergic antagonists, using the mouse-tail flick test. Intraperitoneal moclobemide produced a dose-dependent antinociceptive effect with an ED50 of 69.1 mg/kg. Tests with selective antagonists yielded positive results only for yohimbine (P < 0.001), implying a noradrenergic mechanism of action in the moclobemide antinociceptive effect. This was confirmed by the coadministration of moclobemide with inactive doses of prototype agonists of the opioid, adrenergic and serotonergic systems. Only clonidine, an alpha2 agonist, significantly shifted (8-fold) the dose response curve of moclobemide. We conclude that there is a selective involvement of the alpha2 adrenergic pathways in the moclobemide-induced antinociceptive effect and a lesser involvement (if any) of the opioid, serotonergic and alpha1 adrenergic mechanisms. More research is needed to establish a possible role for moclobemide in pain management.