The antimanic-like effect of tamoxifen: Behavioural comparison with other PKC-inhibiting and antiestrogenic drugs

Efficacy and safety of endoxifen in bipolar disorder: A systematic review

BACKGROUND

Endoxifen, a protein kinase C inhibitor and selective estrogen receptor modulator, primarily used in breast cancer treatment, has recently emerged as a potential therapeutic option for managing manic episodes associated with bipolar disorder (BD). This review aims to assess the existing evidence base for endoxifen in BD treatment and evaluate the strengths and limitations of current research findings.

METHODS

A systematic search was conducted on Medline, Embase, and Web of Science databases. We included studies published in English that used endoxifen in BD, alongside any relevant studies identified through manual searching and conference papers with full-text availability. Information pertaining to dose, duration, clinical effects, and safety profiles was extracted from the included studies. The Cochrane Risk of Bias 2 tool was used to assess the risk of bias in clinical trials.

RESULTS

The final review included seven case reports (including two conference presentations), two clinical trials, and one prospective study. Most studies administered endoxifen 8 mg and reported an improvement in manic symptoms. Several case reports included patients with comorbid substance use, and most patients received mood stabilizers concurrently. Few reports lacked any structured outcome measures. The clinical trials used divalproex 1000 mg as an active comparator, which was deemed sub-therapeutic. Despite being multicentric, the first trial lacked data on center-wise recruitment, and certain methodological concerns were observed across the included trials. There were no serious adverse effects noted, except for a significant elevation in lipid profile within a 3-week period. Limited data were available regarding endoxifen efficacy and safety in mixed episodes, depressive episodes, and maintenance treatment.

CONCLUSION

There is a paucity of research on the efficacy and safety of endoxifen in BD. While existing evidence suggests short-term efficacy in manic episodes, significant limitations were identified in most of the included studies. Further research is imperative to establish the efficacy and safety of endoxifen in BD before considering its recommendation as a viable treatment option.

A cumulative Bayesian network meta-analysis on the comparative efficacy of pharmacotherapies for mania over the last 40 years

RATIONALE

Mania (or manic episodes) is a common symptom of bipolar disorder and is frequently accompanied by hyperactivity and delusions; given the cost and resources available, there is a paucity of evidence for direct comparison of different drugs.

OBJECTIVES

We aimed to provide evidence-based recommendations on the efficacy of overall currently used pharmacological treatments for patients with acute bipolar mania.

METHOD

We conducted a systematic review and network meta-analysis (NMA) using a Bayesian network frame. We searched the primary literature databases without language restrictions until Dec 18, 2021, for reports of randomized controlled trials (RCTs) of suspected antimanic drugs used as monotherapy for patients with acute bipolar mania, with the primary outcomes being efficacy (mean difference (MD), standardized mean difference (SMD) in the change of mania score).

RESULTS

Eighty-seven studies were included in which 18,724 manic participants (mean age = 34.6 years, with 50.36% males) were allocated at random to one of 25 active medication drug therapies or placebo, resulting in 87 direct comparisons on 192 data points. Tamoxifen (- 22·00 [- 26·00 to - 18·00]) had the best efficacy over the placebo. Meanwhile, risperidone (- 6·60 [- 8·40 to - 4·90]) was substantially more effective than placebo in treating acute mania. Carbamazepine, haloperidol, ziprasidone, cariprazine, olanzapine, quetiapine, aripiprazole, lithium, paliperidone, asenapine, and divalproex were noticeably more effective than placebo.

CONCLUSIONS

Overall, tamoxifen appears to be the most effective of the currently known pharmaceutical therapy available to treat acute mania or manic episodes; however, this conclusion is restricted by the scale of RCTs conducted, and risperidone was found to be the most effective medication among antipsychotics. Carbamazepine, haloperidol, ziprasidone, cariprazine, olanzapine, quetiapine, aripiprazole, lithium, paliperidone, asenapine, and divalproex were noticeably effective in treating acute mania or manic episodes.

Effects of tamoxifen alone and in combination with risperidone on hyperlocomotion, hippocampal structure and bone in ketamine-induced model of psychosis in rats

Background and aim of the work

Protein kinase C activation with subsequent increase in oxidative stress (OXS) and reduction in brain derived neurotrophic factor (BDNF) are implicated in the pathophysiology of psychotic disorders and in osteoporosis. Accordingly PKC inhibitors such as tamoxifen could be a novel approach to psychotic illness and may reduce progression of osteoporosis. Since current antipsychotics such as risperidone have inconsistent effects on OXS and BDNF, combination with tamoxifen could be beneficial. Accordingly in this work, tamoxifen was used to investigate the impact of changes in OXS and BDNF on behavioral, hippocampus structural changes in a ketamine induced model of psychosis in rats. The impact of tamoxifen on the antipsychotic effects of risperidone and on its bone damaging effects was also determined.

Ketamine was chosen, because it is a valid model of psychosis. Hippocampus was chosen, since hippocampal overactivity is known to correlate with the severity of symptoms in psychosis. Hippocampal overactivity contributes to hyperdopaminergic state in ventral tegmental area and increase in DA release in nucleus accumbens, these are responsible for positive symptoms of schizophrenia and hyperlocomotion in rodents. Hyperlocomotion is considered a corelate of positive symptoms of psychotic illness in rodents and is considered primary outcome to assess manic-like behavior.

Methods

Rats were divided into seven groups (ten rats each (1) non-ketamine control and (2) ketamine treated groups (a ketamine control, b risperidone/ketamine, c tamoxifen/ketamine, d Risp/Tamox/ketamine risperidone, tamoxifen/risperidone) to test if TAM exhibited behavioral changes or potentiated those of risperidone); (e clomiphene/ketamine and f clomiphene/risperidone/ketamine) to verify that estrogen receptor modulators do not exhibit behavioral changes or potentiates those of risperidone. In addition, thus, the effects of tamoxifen are not due to estrogen effects but rather due to protein kinase c inhibition. Drugs were given for 4 weeks and ketamine was given daily in the last week. Effects of drugs on ketamine-induced hyperlocomotion (open field test) and hippocampus and bone biochemical (MDA, GSH, BDNF) and histological changes (Nissel granules, GFAP positive astrocytes in hippocampus were determined).

Electron microscopy scanning of the femur bone was done. Histomorphometric parameters measuring the: 1. Trabecular bone thickness and 2. The trabecular bone volume percentage.

Results

Tamoxifen reduced hyperlocomotion, and improved hippocampus structure in ketamine-treated rats, by reducing OXS (reduced malondialdehyde and increased glutathione) and increasing BDNF. These effects might be related to (PKC) inhibition, rather than estrogen modulation, since the anti-estrogenic drug clomiphene had no effect on hyperlocomotion. Tamoxifen enhanced the beneficial effects of risperidone on hippocampal OXS and BDNF, augmenting its effectiveness on hyperlocomotion and hippocampal structure. It also reduced risperidone-induced OXS and the associated bone damage.

Conclusions

PKC inhibitors, particularly tamoxifen, might be potential adjuncts to antipsychotics, by reducing OXS and increasing BDNF increasing their effectiveness while reducing their bone damaging effects.

Prescribing Tamoxifen in Patients With Mood Disorders: A Systematic Review of Potential Antimanic Versus Depressive Effects

PURPOSE/BACKGROUND

Tamoxifen is a selective estrogen receptor modulator widely used for treatment and prevention of estrogenic receptor-positive breast cancer. Tamoxifen is an object of growing interest in psychopharmacology as an antimanic drug, because it inhibits the protein kinase C, a molecular target of bipolar disorder. Consistently, the potential depressive effect of tamoxifen has been repeatedly reported.

METHODS/PROCEDURES

This article systematically reviews studies examining tamoxifen impact on mood, exploring either its potential therapeutic use as antimanic agent or its potential depressive effect.

FINDINGS

Eight studies explored tamoxifen antimanic properties, all, but one, reported a rapid and efficacious antimanic action. As to the depressive effect, 9 cohort studies emerged among which 4 pointed out an increased risk of depression. Seven case reports described the onset or exacerbation of depressive episodes besides 1 case series study reported a high rate of depressive symptoms. In addition, 1 case report study described a tamoxifen-induced manic episode.

IMPLICATIONS/CONCLUSIONS

The present review highlights tamoxifen treatment as a possible trigger of mood symptoms onset or exacerbation in vulnerable patients. Accordingly, patients with a history of mood disorders may require a close clinical surveillance during tamoxifen use. At the same time, the use of tamoxifen as an antimanic agent in psychiatric settings requires caution, as available evidence came from small-sample studies with short observation time. More studies are needed to define how long-term tamoxifen use may affect the course of bipolar disorder.

Measuring mania-like elevated mood through amphetamine-induced 50-kHz ultrasonic vocalizations in rats

Rats emit 50-kHz ultrasonic vocalizations (USV) in appetitive situations, reflecting a positive affective state. Particularly high rates of 50-kHz USV are elicited by the psychostimulant d-amphetamine. Exaggerated 50-kHz USV emission evoked by d-amphetamine is modulated by dopamine, noradrenaline and 5-hydroxytyrptamine receptor ligands and inhibited by the mood stabilizer lithium, the gold standard anti-manic drug for treating bipolar disorder. This indicates that exaggerated 50-kHz USV emission can serve as a reliable and valid measure for assessing mania-like elevated mood in rats with sufficient translational power for gaining a better understanding of relevant pathophysiological mechanisms and the identification of new therapeutic targets. The improved capacity to study the effects of anti-manic pharmacological interventions on a broader range of behaviours by including exaggerated 50-kHz USV emission as preclinical outcome measure complementary to locomotor hyperactivity will refine rodent models for mania.

Effects of tamoxifen and glutamate and glutamine levels in brain regions in repeated sleep deprivation-induced mania model in mice

Protein kinase C inhibitor tamoxifen reduces symptoms of acute mania in bipolar patients and mania-like behaviors in animals. Memory impairment and altered levels of glutamate and glutamate/glutamine ratio have been reported in mania. Tamoxifen suppresses glutamate release which plays an important role in memory. The present study evaluated whether tamoxifen's activity participates in its antimanic efficacy in repeated sleep deprivation mania model. Mice were divided into control and 24-h sleep-deprived groups and were treated with vehicle or 1 mg/kg tamoxifen twice daily for 8 days. Sleep deprivation was repeated three times at intervals of 2 days. Square crossing and rearing were recorded as measures of locomotor activity. Memory and risk taking behavior were evaluated using novel object recognition and staircase tests, respectively. Glutamate and glutamine levels were measured in the frontal cortex and hippocampus. Behavioral tests were conducted 24 h after the second or immediately after the third sleep deprivations. Sleep deprivation increased locomotor activity and risk taking. Glutamate and glutamine levels and glutamate/glutamine ratio in the frontal cortex and hippocampus were unaffected. Locomotor hyperactivity was prevented by tamoxifen treatment. No change in the recognition index suggested lack of memory impairment in the model. These findings confirm the relevance of repeated sleep deprivation as a mania model and tamoxifen as an antimanic agent. However, future research is needed to further address lack of memory impairment in the model and lack of glutamatergic influence on the model and antimanic effect of tamoxifen.

Suicidality and Illness Course Worsening in a Male Patient with Bipolar Disorder during Tamoxifen Treatment for ER+/HER2+ Breast Cancer

PURPOSE

Tamoxifen is a selective estrogenic receptor modulator (SERM) drug. In addition to its common use in breast cancer ER+, Tamoxifen has been object of growing interest in psychiatry as antimanic drug. At the same time, clinical concerns about Tamoxifen's depressogenic effect have been repeatedly raised even without reaching univocal conclusions. We discuss the case of a 45-year-old-male with a diagnosis of Bipolar Disorder type II, treated with Tamoxifen as relapse prevention treatment after surgery for a ER+/HER2+ breast cancer. The patient required two psychiatric admissions in a few-month time span since he showed a progressive worsening of both depressive and anxiety symptoms, with the onset of delusional ideas of hopelessness and failure up to suicidal thoughts. The clinical picture showed poor response to treatment trials based on various associations of mood-stabilising, antidepressants, and antipsychotic drugs. During the second hospitalization, after a multidisciplinary evaluation, the oncologists agreed on Tamoxifen discontinuation upon the severity of the psychiatric condition. The patient underwent a close oncological and psychiatric follow-up during the following 12 months.

METHODS

Psychiatric assessments included the Montgomery-Asberg Depression Rating Scale (MADRS), the Hamilton Depression Scale (HAM-D), the Columbia Suicide Severity Rating Scale (C-SSRS), and the Quality of Life Enjoyment and Satisfaction Questionnaire Short Form (Q-LES-Q-SF). All questionnaires were administered at the time of the second hospitalization and in a one-year follow-up.

RESULTS

Suicidal ideation fully remitted and depressive symptoms markedly and rapidly improved in the aftermath of Tamoxifen discontinuation. The symptomatological improvement remained stable across one-year follow-up.

CONCLUSIONS

Male patients with a mood disorder history constitute a high-risk group as to Tamoxifen psychiatric side effects. The onset or worsening of depressive symptoms or suicidality should be carefully addressed and promptly treated, and clinicians should be encouraged to consider the possibility of discontinue or reduce Tamoxifen therapy after a multidisciplinary evaluation.

Neuropsychiatric effects of tamoxifen: Challenges and opportunities

Epidemiological, clinical, and basic research over the past thirty years have described the benefits of estrogen on cognition, mood, and brain health. Less is known about tamoxifen, a selective estrogen receptor modifier (SERM) commonly used in breast cancer which is able to cross the blood-brain barrier. In this article, we review the basic pharmacology of tamoxifenas well as its effects on cognition and mood. The literature reveals an overall impairing effect of tamoxifen on cognition in breast cancer patients, hinting at central antiestrogen activity. On the other hand, tamoxifen demonstrates promising effects in psychiatric disorders, like bipolar disorder, where its therapeutic action may be independent of interaction with estrogen receptors. Understanding the neuropsychiatric properties of SERMs like tamoxifen can guide future research to ameliorate unwanted side-effects and provide novel options for difficult to treat disorders.

Lithium and Tamoxifen Modulate Behavior and Protein Kinase C Activity in the Animal Model of Mania Induced by Ouabain

BACKGROUND

The intracerebroventricular injection of ouabain, a specific inhibitor of the Na+/K+-adenosine-triphosphatase (Na+/K+-ATPase) enzyme, induces hyperactivity in rats in a putative animal model of mania. Several evidences have suggested that the protein kinase C signaling pathway is involved in bipolar disorder. In addition, it is known that protein kinase C inhibitors, such as lithium and tamoxifen, are effective in treating acute mania.

METHODS

In the present study, we investigated the effects of lithium and tamoxifen on the protein kinase C signaling pathway in the frontal cortex and hippocampus of rats submitted to the animal model of mania induced by ouabain. We showed that ouabain induced hyperlocomotion in the rats.

RESULTS

Ouabain increased the protein kinase C activity and the protein kinase C and MARCKS phosphorylation in frontal cortex and hippocampus of rats. Lithium and tamoxifen reversed the behavioral and protein kinase C pathway changes induced by ouabain. These findings indicate that the Na+/K+-ATPase inhibition can lead to protein kinase C alteration.

CONCLUSIONS

The present study showed that lithium and tamoxifen modulate changes in the behavior and protein kinase C signalling pathway alterations induced by ouabain, underlining the need for more studies of protein kinase C as a possible target for treatment of bipolar disorder.

Quercetin reduces manic-like behavior and brain oxidative stress induced by paradoxical sleep deprivation in mice

Quercetin is a known antioxidant and protein kinase C (PKC) inhibitor. Previous studies have shown that mania involves oxidative stress and an increase in PKC activity. We hypothesized that quercetin affects manic symptoms. In the present study, manic-like behavior (hyperlocomotion) and oxidative stress were induced by 24h paradoxical sleep deprivation (PSD) in male Swiss mice. Both 10 and 40mg/kg quercetin prevented PSD-induced hyperlocomotion. Quercetin reversed the PSD-induced decrease in glutathione (GSH) levels in the prefrontal cortex (PFC) and striatum. Quercetin also reversed the PSD-induced increase in lipid peroxidation (LPO) in the PFC, hippocampus, and striatum. Pearson's correlation analysis revealed a negative correlation between locomotor activity and GSH in the PFC in sleep-deprived mice and a positive correlation between locomotor activity and LPO in the PFC and striatum in sleep-deprived mice. These results suggest that quercetin exerts an antimanic-like effect at doses that do not impair spontaneous locomotor activity, and the antioxidant action of quercetin might contribute to its antimanic-like effects.

Design and synthesis of triarylacrylonitrile analogues of tamoxifen with improved binding selectivity to protein kinase C

The clinical selective estrogen receptor modulator tamoxifen is also a modest inhibitor of protein kinase C, a target implicated in several untreatable brain diseases such as amphetamine abuse. This inhibition and tamoxifen's ability to cross the blood brain barrier make it an attractive scaffold to conduct further SAR studies toward uncovering effective therapies for such diseases. Utilizing the known compound 6a as a starting template and guided by computational tools to derive physicochemical properties known to be important for CNS permeable drugs, the design and synthesis of a small series of novel triarylacrylonitrile analogues have been carried out providing compounds with enhanced potency and selectivity for PKC over the estrogen receptor relative to tamoxifen. Shortened synthetic routes compared to classical procedures have been developed for analogues incorporating a β-phenyl ring, which involve installing dialkylaminoalkoxy side chains first off the α and/or α' rings of a precursor benzophenone and then condensing the resultant ketones with phenylacetonitrile anion. A second novel, efficient and versatile route utilizing Suzuki chemistry has also been developed, which will allow for the introduction of a wide range of β-aryl or β-heteroaryl moieties and side-chain substituents onto the acrylonitrile core. For analogues possessing a single side chain off the α- or α'-ring, novel 2D NMR experiments have been carried out that allow for unambiguous assignment of E- and Z-stereochemistry. From the SAR analysis, one compound, 6c, shows markedly increased potency and selectivity for inhibiting PKC with an IC₅₀ of 80nM for inhibition of PKC protein substrate and >10μM for binding to the estrogen receptor α (tamoxifen IC₅₀=20μM and 222nM, respectively). The data on 6c provide support for further exploration of PKC as a druggable target for the treatment of amphetamine abuse.

Tamoxifen and amphetamine abuse: Are there therapeutic possibilities?

Although best known as a selective estrogen receptor modulator (SERM), tamoxifen is a drug with a wide range of activities. Tamoxifen has demonstrated some efficacy has a therapeutic for bipolar mania and is believed to exert these effects through inhibition of protein kinase C (PKC). As the symptoms of amphetamine treatment in rodents are believed to mimic the symptoms of a manic episode, many of the preclinical studies for this indication have demonstrated that tamoxifen inhibits amphetamine action. The amphetamine-induced increase in extracellular dopamine which gives rise to the 'manic' effects is due to interaction of amphetamine with the dopamine transporter. We and others have demonstrated that PKC reduces amphetamine-induced reverse transport through the dopamine transporter. In this review, we will outline the actions of tamoxifen as a SERM and further detail another known action of tamoxifen-inhibition of PKC. We will summarize the literature showing how tamoxifen affects amphetamine action. Finally, we will present our hypothesis that tamoxifen, or an analog, could be used therapeutically to reduce amphetamine abuse in addition to treating mania.

Antimanic-like effects of (R)-(-)-carvone and (S)-(+)-carvone in mice

Carvone is a monoterpene that is present in spearmint (Mentha spicata) and caraway (Carum carvi) essential oils and has been shown to have anticonvulsant effects, likely through the blockade of voltage-gated sodium channels, and anxiolytic-like effects. Considering that some anticonvulsants that blocked voltage-gated sodium channels (e.g., sodium valproate and carbamazepine) exert clinical antimanic effects, the aim of the present study was to evaluate (R)-(-)-carvone and (S)-(+)-carvone in animal models of mania (i.e., hyperlocomotion induced by methylphenidate and sleep deprivation). Mice that were treated with methylphenidate (5mg/kg) or sleep-deprived for 24h using a multiple-platform protocol exhibited an increase in locomotor activity in an automated activity box. This effect was blocked by pretreatment with acute (R)-(-)-carvone (50-100mg/kg), (S)-(+)-carvone (50-100mg/kg), and lithium (100mg/kg, positive control). These doses did not alter spontaneous locomotor activity in the methylphenidate-induced experiments while (S)-(+)-carvone decreased spontaneous locomotor activity in sleep deprivation experiment, indicating a sedative effect. Chronic 21-day treatment with (R)-(-)-carvone (100mg/kg), (S)-(+)-carvone (100mg/kg), and lithium also prevented methylphenidate-induced hyperactivity. The present results suggest that carvone may have an antimanic-like effect.

PKC in rat dorsal raphe nucleus plays a key role in sleep-wake regulation

Studies suggest a tight relationship between protein kinase C (PKC) and circadian clock. However, the role of PKC in sleep-wake regulation remains unclear. The present study was conducted to investigate the role of PKC signaling in sleep-wake regulation in the rat. Our results showed that the phosphorylation level of PKC in dorsal raphe nucleus (DRN) was decreased after 6h sleep deprivation, while no alterations were found in ventrolateral preoptic nucleus (VLPO) or locus coeruleus (LC). Microinjection of a pan-PKC inhibitor, chelerythrine chloride (CHEL, 5 or 10nmol), into DRN of freely moving rats promoted non rapid eye movement sleep (NREMS) without influences on rapid eye movement sleep (REMS). Especially, CHEL application at 5nmol increased light sleep (LS) time while CHEL application at 10nmol increased slow wave sleep (SWS) time and percentage. On the other hand, microinjection of CaCl2 into DRN not only increased the phosphorylation level of PKC, but also reduced NREMS time, especially SWS time and percentage. While CHEL abolished the inhibitory effect of CaCl2 on NREMS and SWS. These data provide the first direct evidence that inhibition of intracellular PKC signaling in DRN could increase NREMS time including SWS time and percentage, while activation of PKC could suppress NREMS and reduce SWS time and percentage. These novel findings further our understanding of the basic cellular and molecular mechanisms of sleep-wake regulation.

Protein kinase C inhibition rescues manic-like behaviors and hippocampal cell proliferation deficits in the sleep deprivation model of mania

BACKGROUND

Recent studies revealed that bipolar disorder may be associated with deficits of neuroplasticity. Additionally, accumulating evidence has implicated alterations of the intracellular signaling molecule protein kinase C (PKC) in mania.

METHODS

Using sleep deprivation (SD) as an animal model of mania, this study aimed to examine the possible relationship between PKC and neuroplasticity in mania. Rats were subjected to SD for 72 h and tested behaviorally. In parallel, SD-induced changes in hippocampal cell proliferation were evaluated with bromodeoxyuridine (BrdU) labeling. We then examined the effects of the mood stabilizer lithium, the antipsychotic agent aripiprazole, and the PKC inhibitors chelerythrine and tamoxifen on both behavioral and cell proliferation impairments induced by SD. The antidepressant fluoxetine was used as a negative control.

RESULTS

We found that SD triggered the manic-like behaviors such as hyperlocomotion and increased sleep latency, and reduced hippocampal cell proliferation. These alterations were counteracted by an acute administration of lithium and aripiprazole but not of fluoxetine, and only a single administration of aripiprazole increased cell proliferation on its own. Importantly, SD rats exhibited increased levels of phosphorylated synaptosomal-associated protein 25 (SNAP-25) in the hippocampus and prefrontal cortex, suggesting PKC overactivity. Moreover, PKC inhibitors attenuated manic-like behaviors and rescued cell proliferation deficits induced by SD.

CONCLUSIONS

Our findings confirm the relevance of SD as a model of mania, and provide evidence that antimanic agents are also able to prevent SD-induced decrease of hippocampal cell proliferation. Furthermore, they emphasize the therapeutic potential of PKC inhibitors, as revealed by their antimanic-like and pro-proliferative properties.

Amphetamine-induced appetitive 50-kHz calls in rats: a marker of affect in mania?

RATIONALE

Animal models aimed to mimic mania have in common the lack of genuine affective parameters. Although rodent amphetamine-induced hyperlocomotion is a frequently used behavioral model of mania, locomotor activity is a rather unspecific target for developing new pharmacological therapies, and does not necessarily constitute a cardinal symptom in bipolar disorder (BD). Hence, alternative behavioral markers sensitive to stimulants are required.

OBJECTIVES

Since D-amphetamine induces appetitive 50-kHz ultrasonic vocalizations (USV) in rats, we asked whether established or potential antimanic drugs would inhibit this effect, thereby possibly complementing traditional analysis of locomotor activity.

METHODS

Amphetamine-treated rats (2.5 mg/kg) were systemically administered with the antimanic drugs lithium (100 mg/kg) and tamoxifen (1 mg/kg). Since protein kinase C (PKC) activity has been implicated in the pathophysiology of bipolar disorder and the biochemical effects of mood stabilizers, the new PKC inhibitor myricitrin (10, 30 mg/kg) was also evaluated.

RESULTS

We demonstrate for the first time that drugs with known or potential antimanic activity were effective in reversing amphetamine-induced appetitive 50-kHz calls. Treatments particularly normalized amphetamine-induced increases of frequency-modulated calls, a subtype presumably indicative of positive affect in the rat.

CONCLUSIONS

Our findings suggest that amphetamine-induced 50-kHz calls might constitute a marker for communicating affect that provides a useful model of exaggerated euphoric mood and pressured speech. The antimanic-like effects of the PKC inhibitors tamoxifen and myricitrin support the predictive and etiological validity of both drugs in this model and highlight the role of PKC signaling as a promising target to treat mania and psychosis-related disorders.

Expression and regulation of prostate apoptosis response-4 (Par-4) in human glioma stem cells in drug-induced apoptosis

Gliomas are the most common and aggressive of brain tumors in adults. Cancer stem cells (CSC) contribute to chemoresistance in many solid tumors including gliomas. The function of prostate apoptosis response-4 (Par-4) as a pro-apoptotic protein is well documented in many cancers; however, its role in CSC remains obscure. In this study, we aimed to explore the role of Par-4 in drug-induced cytotoxicity using human glioma stem cell line--HNGC-2 and primary culture (G1) derived from high grade glioma. We show that among the panel of drugs- lomustine, carmustine, UCN-01, oxaliplatin, temozolomide and tamoxifen (TAM) screened, only TAM induced cell death and up-regulated Par-4 levels significantly. TAM-induced apoptosis was confirmed by PARP cleavage, Annexin V and propidium iodide staining and caspase-3 activity. Knock down of Par-4 by siRNA inhibited cell death by TAM, suggesting the role of Par-4 in induction of apoptosis. We also demonstrate that the mechanism involves break down of mitochondrial membrane potential, down regulation of Bcl-2 and reduced activation of Akt and ERK 42/44. Secretory Par-4 and GRP-78 were significantly expressed in HNGC-2 cells on exposure to TAM and specific antibodies to these molecules inhibited cell death suggesting that extrinsic Par-4 is important in TAM-induced apoptosis. Interestingly, TAM decreased the expression of neural stem cell markers--Nestin, Bmi1, Vimentin, Sox2, and Musashi in HNGC-2 cell line and G1 cells implicating its potential as a stemness inhibiting drug. Based on these data and our findings that enhanced levels of Par-4 sensitize the resistant glioma stem cells to drug-induced apoptosis, we propose that Par-4 may be explored for evaluating anti-tumor agents in CSC.

Tamoxifen use for the management of mania: a review of current preclinical evidence

RATIONALE

Preliminary data on the efficacy of tamoxifen in reducing manic symptoms of bipolar disorder (BD) suggest that this agent may be a potential treatment for the management of this psychiatric disorder. However, the antimanic properties of tamoxifen have not been fully elucidated, hampering the development and/or use of mood-stabilising drugs that may share its same therapeutic mechanisms of action. Notably, we may gain a greater understanding of the neurobiological and therapeutic properties of tamoxifen by using suitable animal models of mania.

OBJECTIVES

Here, we review the preclinical studies that have evaluated the effects of tamoxifen to provide an overview of the current progress in our understanding of its antimanic actions, highlighting the critical role of protein kinase C (PKC) as a therapeutic target for the treatment of BD.

CONCLUSIONS

To date, this field has struggled to make significant progress, and the organisation of an explicit battery of tests is a valuable tool for assessing a number of prominent facets of BD, which may provide a greater understanding of the entire scope of this disease.

Protein kinase C regulates mood-related behaviors and adult hippocampal cell proliferation in rats

The neurobiological mechanisms underlying the pathophysiology and therapeutics of bipolar disorder are still unknown. In recent years, protein kinase C (PKC) has emerged as a potential key player in mania. To further investigate the role of this signaling system in mood regulation, we examined the effects of PKC modulators in behavioral tests modeling several facets of bipolar disorder and in adult hippocampal cell proliferation in rats. Our results showed that a single injection of the PKC inhibitors tamoxifen (80 mg/kg, i.p.) and chelerythrine (3 mg/kg, s.c.) attenuated amphetamine-induced hyperlocomotion and decreased risk-taking behavior, supporting the efficacy of PKC blockade in acute mania. Moreover, chronic exposure to tamoxifen (10 mg/kg/day, i.p., for 14 days) or chelerythrine (0.3 mg/kg/day, s.c., for 14 days) caused depressive-like behavior in the forced swim test, and resulted in a reduction of cell proliferation in the dentate gyrus of the hippocampus. Finally, we showed that, contrary to the PKC inhibitors, the PKC activator phorbol 12-myristate 13-acetate (PMA) enhanced risk-taking behavior and induced an antidepressant-like effect. Taken together, these findings support the involvement of PKC in regulating opposite facets of bipolar disorder, and emphasize a major role for PKC in this disease.

Lithium and tamoxifen modulate cellular plasticity cascades in animal model of mania

Lithium (Li) is the main mood stabilizer and acts on multiple biochemical targets, leading to neuronal plasticity. Several clinical studies have shown that tamoxifen (TMX) - a protein kinase C (PKC) inhibitor - has been effective in treating acute mania. The present study aims to evaluate the effects of TMX on biochemical targets of Li, such as glycogen synthase kinase-3β (GSK-3β), PKC, PKA, CREB, BDNF and NGF, in the brain of rats subjected to an animal model of mania induced by d-amphetamine (d-AMPH). Wistar rats were treated with d-AMPH (2mg/kg, once a day) or saline (Sal; NaCl 0.9%, w/v), Li (47.5 mg/kg, intraperitoneally (i.p.), twice a day) or TMX (1 mg/kg i.p., twice a day) or Sal in protocols of reversion and prevention treatment. Locomotor behavior was assessed using the open-field task, and protein levels were measured by immunoblot. Li and TMX reversed and prevented d-AMPH-induced hyperactivity. Western blot showed that d-AMPH significantly increased GSK-3 and PKC levels, and decreased pGSK-3, PKA, NGF, BDNF and CREB levels in the structures analyzed. Li and TMX were able to prevent and reverse these changes induced by d-AMPH in most structures evaluated. The present study demonstrated that the PKC inhibitor modulates the alterations in the behavior, neurotrophic and apoptosis pathway induced by d-AMPH, reinforcing the need for more studies of PKC as a possible target for treatment of bipolar disorder.

Myricitrin, a nitric oxide and protein kinase C inhibitor, exerts antipsychotic-like effects in animal models

Myricitrin is a nitric oxide (NO) and protein kinase C (PKC) inhibitor that has central nervous system activity, including anxiolytic-like action. Nitric oxide inhibitors blocked the behavioral effects of apomorphine, suggesting an antipsychotic-like effect. Furthermore, PKC inhibition reduced psychotic symptoms in acute mania patients and blocked amphetamine-induced hyperlocomotion, suggesting a potential antipsychotic-like effect. The present study evaluated the effects of myricitrin in animal models that assess antipsychotic-like effects (apomorphine-induced stereotypy and climbing and the paw test) and extrapyramidal side effects (catalepsy test and paw test). Olanzapine was used as a positive control. 7-Nitroindazole (7-NI), a NOS inhibitor, and l-arginine, a NO precursor, were used to evaluate nitrergic modulation, and tamoxifen was used to test the effect of PKC inhibition. In mice, myricitrin dose-dependently and olanzapine blocked the stereotypy and climbing induced by apomorphine at doses that did not induce catalepsy. 7-Nitroindazole also blocked apomorphine-induced stereotypy and climbing, which were reversed by l-arginine pretreatment. l-arginine only attenuated the effects of myricitrin on apomorphine's effects. Tamoxifen also blocked apomorphine-induced stereotypy and climbing. In the paw test in rats, myricitrin and olanzapine increased hindlimb retraction time at doses that did not affect forelimb reaction time, whereas haloperidol affected both parameters at the same dose. Myricitrin did not induce catalepsy in the bar test. Tamoxifen did not affect hindlimb retraction time or forelimb retraction time, whereas 7-NI significantly increased hindlimb reaction time. Thus, myricitrin exhibited an antipsychotic-like profile at doses that did not induce catalepsy, and this effect may be related to nitrergic action.

Magnesium sulfate and sodium valproate block methylphenidate-induced hyperlocomotion, an animal model of mania

Magnesium sulfate (MgSO4) is used to treat and prevent eclamptic seizures, and several anticonvulsant drugs (e.g., sodium valproate) are clinically effective antimanic drugs. Psychostimulant-induced hyperlocomotion has been proposed as an animal model for the study of antimanic drugs. The present study evaluated the effects of MgSO4 and sodium valproate (as a positive control) on hyperlocomotion induced by methylphenidate in mice. Acute MgSO4 (300-400 mg/kg), but not sodium valproate (100-300 mg/kg), prevented the increase in locomotor activity induced by methylphenidate (5.0 mg/kg). In contrast, repeated treatment (14 days) with valproate (300 mg/kg), but not MgSO4 (400 mg/kg), blocked methylphenidate-induced hyperlocomotion. Thus, acute MgSO4 exerted antimanic-like effects in this animal model.

Successful combined therapy with tamoxifen and lithium in a paradoxical sleep deprivation-induced mania model

BACKGROUND

Previous studies have suggested that manic states and sleep deprivation could contribute to the pathophysiology of bipolar disorder (BD) through protein kinase C (PKC) signaling abnormalities. Moreover, adjunctive therapy has become a standard strategy in the management of BD patients who respond poorly to current pharmacological treatments.

AIM

Thus, the aim of this study was to investigate the possible involvement of PKC inhibition by tamoxifen both separately or in combination with lithium, in paradoxical sleep deprivation (PSD)-induced hyperactivity, one facet of mania-like behavior.

MATERIALS & METHODS

Adult male C57BL/6J mice were randomly distributed (n = 7/group) in 24-h PSD or control groups and injected intraperitoneally (i.p.) with vehicle, lithium (50, 100, or 150 mg/kg) or tamoxifen (0.5, 1.0, or 2.0 mg/kg - experiment 1). In a second experiment, mice were injected i.p. with vehicle or a combination of subeffective doses of lithium and tamoxifen. Animals were subjected to a protocol based on repetitive PSD conditions, followed by assessment of locomotion activity in the open-field task.

RESULTS

PSD significantly increased locomotor activity in both experiments. These behavioral changes were prevented by a treatment with lithium or tamoxifen, or a combined treatment with both lithium and tamoxifen.

DISCUSSION

Therefore, our findings suggest that lithium and tamoxifen exert reversal effects against PSD-induced hyperactivity in mice.

CONCLUSION

Furthermore, tamoxifen as an adjunct to lithium therapy provides support for an alternative treatment of individuals who either do not respond adequately or cannot tolerate the adverse effects associated with therapeutic doses of lithium.

Electroconvulsive seizure increases phosphorylation of PKC substrates, including GAP-43, MARCKS, and neurogranin, in rat brain

Protein kinase C (PKC) has been suggested as a molecular target related to the pathogenetic and therapeutic mechanisms of mood disorders in which electroconvulsive seizure (ECS) is effective. However, the reports concerning the effects of ECS on PKC are anecdotal and need further clarification. In this study, we examined the effects of ECS treatment on the phosphorylation of PKC substrates, including GAP-43, MARCKS, and neurogranin. Immunoblot using anti-p-PKC substrate antibodies revealed that a single ECS treatment induced temporal changes in the phosphorylation level of PKC substrates in rat brain, reflecting the effects on PKC activity. Phosphorylation of GAP-43 and MARCKS, representative PKC substrates related to synaptic remodeling, increased from 5 to 30 min, after a transient decrease at 0 min immediately after ECS, and returned to basal levels at 60 min in rat frontal cortex, hippocampus, and cerebellum. Phosphorylation of neurogranin, another PKC substrate, showed a similar pattern of temporal changes in the frontal cortex and hippocampus. Immunohistochemical analysis revealed that p-GAP-43 and p-MARCKS were densely stained throughout the neuronal cells of the prefrontal cortex and hippocampus, and the Purkinje cells of cerebellum, after ECS treatment. Brief and transient activation of PKC may be translated into long-term biochemical changes, resulting in synaptic plasticity. Taken together, the acute effects of ECS on PKC activity, which could be an underpinning of long-term biochemical changes induced by ECS, may contribute to understand the molecular mechanism of ECS.