Concurrent measures of protein kinase C and phosphoinositides in lithium-treated bipolar patients and healthy individuals: a preliminary study

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Non-canonical pathways in the pathophysiology and therapeutics of bipolar disorder

Bipolar disorder (BD) is characterized by extreme mood swings ranging from manic/hypomanic to depressive episodes. The severity, duration, and frequency of these episodes can vary widely between individuals, significantly impacting quality of life. Individuals with BD spend almost half their lives experiencing mood symptoms, especially depression, as well as associated clinical dimensions such as anhedonia, fatigue, suicidality, anxiety, and neurovegetative symptoms. Persistent mood symptoms have been associated with premature mortality, accelerated aging, and elevated prevalence of treatment-resistant depression. Recent efforts have expanded our understanding of the neurobiology of BD and the downstream targets that may help track clinical outcomes and drug development. However, as a polygenic disorder, the neurobiology of BD is complex and involves biological changes in several organelles and downstream targets (pre-, post-, and extra-synaptic), including mitochondrial dysfunction, oxidative stress, altered monoaminergic and glutamatergic systems, lower neurotrophic factor levels, and changes in immune-inflammatory systems. The field has thus moved toward identifying more precise neurobiological targets that, in turn, may help develop personalized approaches and more reliable biomarkers for treatment prediction. Diverse pharmacological and non-pharmacological approaches targeting neurobiological pathways other than neurotransmission have also been tested in mood disorders. This article reviews different neurobiological targets and pathophysiological findings in non-canonical pathways in BD that may offer opportunities to support drug development and identify new, clinically relevant biological mechanisms. These include: neuroinflammation; mitochondrial function; calcium channels; oxidative stress; the glycogen synthase kinase-3 (GSK3) pathway; protein kinase C (PKC); brain-derived neurotrophic factor (BDNF); histone deacetylase (HDAC); and the purinergic signaling pathway.

Phosphatidylinositol 4,5-bisphosphate (PIP2) facilitates norepinephrine transporter dimerization and modulates substrate efflux

The plasmalemmal norepinephrine transporter (NET) regulates cardiovascular sympathetic activity by clearing extracellular norepinephrine in the synaptic cleft. Here, we investigate the subunit stoichiometry and function of NET using single-molecule fluorescence microscopy and flux assays. In particular, we show the effect of phosphatidylinositol 4,5-bisphosphate (PIP2) on NET oligomerization and efflux. NET forms monomers (~60%) and dimers (~40%) at the plasma membrane. PIP2 depletion results in a decrease in the average oligomeric state and decreases NET-mediated substrate efflux while not affecting substrate uptake. Mutation of the putative PIP2 binding residues R121, K334, and R440 to alanines does not affect NET dimerization but results in decreased substrate efflux that is not altered upon PIP2 depletion; this indicates that PIP2 interactions with these residues affect NET-mediated efflux. A dysregulation of norepinephrine and PIP2 signaling have both been implicated in neuropsychiatric and cardiovascular diseases. This study provides evidence that PIP2 directly regulates NET organization and function.

Neuromolecular Etiology of Bipolar Disorder: Possible Therapeutic Targets of Mood Stabilizers

Bipolar disorder is a mental illness that causes extreme mood swings and has a chronic course. However, the mechanism by which mood episodes with completely opposite characteristics appear repeatedly, or a mixture of symptoms appears, in patients with bipolar disorder remains unknown. Therefore, mood stabilizers are indicated only for single mood episodes, such as manic episodes and depressive episodes, and no true mood-stabilizing drugs effective for treating both manic and depressive episodes currently exist. Therefore, in this review, therapeutic targets that facilitate the development of mood stabilizers were examined by reviewing the current understanding of the neuromolecular etiology of bipolar disorder.

Intracellular Signaling Cascades in Bipolar Disorder

Bipolar spectrum disorders carry a significant public health burden. Disproportionately high rates of suicide, incarceration, and comorbid medical conditions necessitate an extraordinary focus on understanding the intricacies of this disease. Elucidating granular, intracellular details seems to be a necessary preamble to advancing promising therapeutic opportunities. In this chapter, we review a wide range of intracellular mechanisms including mitochondrial energetics, calcium signaling, neuroinflammation, the microbiome, neurotransmitter metabolism, glycogen synthase kinase 3-beta (GSK3β), protein kinase C (PKC) and diacylglycerol (DAG), and neurotrophins (especially BDNF), as well as the glutamatergic, dopaminergic, purinergic, and neurohormonal systems. Owing to the relative lack of understanding and effective therapeutic options compared to the rest of the spectrum, special attention is paid in the chapter to the latest developments in bipolar depression. Likewise, from a therapeutic standpoint, special attention should be paid to the pervasive mechanistic actions of lithium as a means of amalgamating numerous, disparate cascades into a digestible cognitive topology.

Protein and mRNA expression of protein kinase C (PKC) in the postmortem brain of bipolar and schizophrenic subjects

Abnormalities of protein kinase C (PKC) have been implicated in the pathophysiology of bipolar (BP) illness. This is primarily based on studies of PKC in platelets of BP patients. Whether such abnormalities of PKC activity and isoforms exist in the brain is unclear. We have therefore determined PKC activity, protein and mRNA expression of PKC isoforms in the prefrontal cortex (PFC), cingulate cortex (CING) and temporal cortex (TEMP) from BP (n = 19), schizophrenic (SZ) (n = 20) and normal control (NC) (n = 25) subjects. The brain samples were obtained from the Harvard Brain Bank, and the subjects were diagnosed according to DSM-IV criteria. Protein levels were determined using Western blot technique and mRNA levels were determined using real-time PCR (qPCR) method. We found that there was a significant decrease in the PKC activity in the cytosol and membrane fractions of PFC and TEMP obtained from BP subjects but not from SZ subjects. When we compared the expression of PKC isozymes, we found that the protein and mRNA expression of several isozymes was significantly decreased in the PFC (i.e., PKCα, PKCβI, PKCβII and PKCε) and TEMP (i.e., PKCα, PKCβI, PKCβII, PKCε and PKCγ) of BP subjects, but not in the CING. Overall, there was no difference in the mRNA or protein expression of PKC isozymes between SZ and NC subjects in any of the three brain areas we studied. Our results show that there is a region-specific decrease of certain PKC isozymes in the membrane and cytosol fractions of BP but not SZ subjects.

Significance of protein kinase C in the neuropsychotoxicity induced by methamphetamine-like psychostimulants

The abuse of methamphetamine (MA), an amphetamine (AMPH)-type stimulant, has been demonstrated to be associated with various neuropsychotoxicity, including memory impairment, psychiatric morbidity, and dopaminergic toxicity. Compelling evidence from preclinical studies has indicated that protein kinase C (PKC), a large family of serine/threonine protein kinases, plays an important role in MA-induced neuropsychotoxicity. PKC-mediated N-terminal phosphorylation of dopamine transporter has been identified as one of the prerequisites for MA-induced synaptic dopamine release. Consistently, it has been shown that PKC is involved in MA (or AMPH)-induced memory impairment and mania-like behaviors as well as MA drug dependence. Direct or indirect regulation of factors related to neuronal plasticity seemed to be critical for these actions of PKC. In addition, PKC-mediated mitochondrial dysfunction, oxidative stress or impaired antioxidant defense system has been suggested to play a role in psychiatric and cognitive disturbance induced by MA (or AMPH). In MA-induced dopaminergic toxicity, particularly PKCδ has been shown to trigger oxidative stress, mitochondrial dysfunction, pro-apoptotic changes, and neuroinflammation. Importantly, PKCδ may be a key mediator in the positive feedback loop composed of these detrimental events to potentiate MA-induced dopaminergic toxicity. This review outlines the role of PKC and its individual isozymes in MA-induced neuropsychotoxicity. Better understanding on the molecular mechanism of PKCs might provide a great insight for the development of potential therapeutic or preventive candidates for MA (or AMPH)-associated neuropsychotoxicity.

Role of Protein Kinase C in Bipolar Disorder: A Review of the Current Literature

Bipolar disorder (BD) is a major health problem. It causes significant morbidity and imposes a burden on the society. Available treatments help a substantial proportion of patients but are not beneficial for an estimated 40-50%. Thus, there is a great need to further our understanding the pathophysiology of BD to identify new therapeutic avenues. The preponderance of evidence pointed towards a role of protein kinase C (PKC) in BD. We reviewed the literature pertinent to the role of PKC in BD. We present recent advances from preclinical and clinical studies that further support the role of PKC. Moreover, we discuss the role of PKC on synaptogenesis and neuroplasticity in the context of BD. The recent development of animal models of BD, such as stimulant-treated and paradoxical sleep deprivation, and the ability to intervene pharmacologically provide further insights into the involvement of PKC in BD. In addition, the effect of PKC inhibitors, such as tamoxifen, in the resolution of manic symptoms in patients with BD further points in that direction. Furthermore, a wide variety of growth factors influence neurotransmission through several molecular pathways that involve downstream effects of PKC. Our current understanding identifies the PKC pathway as a potential therapeutic avenue for BD.

Serum phosphatidylinositol as a biomarker for bipolar disorder liability

OBJECTIVES

Individuals with bipolar disorder (BPD) exhibit alterations in their phospholipid levels. It is unclear whether these alterations are a secondary consequence of illness state, or if phospholipids and illness risk overlap genetically. If the latter were true, then phospholipids might provide key insights into the pathophysiology of the illness. Therefore, we rank-ordered phospholipid classes by their genetic overlap with BPD risk in order to establish which class might be most informative in terms of increasing our understanding of illness pathophysiology.

METHODS

Analyses were conducted in a sample of 558 individuals, unselected for BPD, from 38 extended pedigrees (average family size=14.79, range=2-82). We calculated a coefficient of relatedness for all family members of nine individuals with BPD in the sample (N=185); this coefficient was set to be zero in unrelated individuals (N=373). Then, under an endophenotype ranking value (ERV) approach, this scalar index was tested against 13 serum-based phospholipid concentrations in order to rank-order lipid classes by their respective overlap with BPD risk.

RESULTS

The phosphatidylinositol class was significantly heritable (h² =0.26, P=6.71 × 10^-05 ). It was the top-ranked class, and was significantly associated with BPD risk after correction for multiple testing (β=-1.18, P=2.10 × 10^-03 , ERV=0.49).

CONCLUSIONS

We identified a peripheral biomarker, serum-based phosphatidylinositol, which exhibits a significant association with BPD risk. Therefore, given that phosphatidylinositol and BPD risk share partially common etiology, it seems that this lipid class warrants further investigation, not only in terms of treatment, but also as a promising diagnostic and risk marker.

DGKH genetic risk variant influences gene expression in bipolar affective disorder

BACKGROUND

DGKH is a replicated risk gene of bipolar disorder (BD). However, the pathophysiological role of the coded protein, diacylglycerol kinase eta, remains elusive.

METHODS

In this proof-of-concept study we isolated mRNA from peripheral blood and fibroblasts of heterozygote DGKH risk variants carriers (risk haplotype rs994856/rs9525580/rs9525584 GAT) with bipolar disorder and non-risk variant carriers with and without bipolar disorder. Gene expression of DGKH1, DGKH2, INPP5E, PI4K2B, PIK4CA, PLCG2, PRKCA, PRKCD, PRKCE and PRKCH was analysed by qRT PCR.

RESULTS

DGKH1 expression was increased in peripheral blood of risk variant carriers (p=0.027). In fibroblast cells, PRKCD expression was significantly increased in DGKH GAT carriers (p=0.037). Patients with a current depressive episode had lower PRKCD levels and lithium treatment was associated with increased PRKCA expression (p=0.005, and p=0.033).

LIMITATIONS

No homozygote risk variant carriers and no healthy risk variant carriers were included due to their infrequency. Bipolar patients carrying the GAT haplotype were older with marginal significance, as age had also an influence on DGKH expression levels but not on PRKCD levels, replication with better age-matched samples and also bigger samples are needed.

CONCLUSIONS

The results add evidence for the role of fibroblast cells and peripheral blood as useful tools in the functional characterisation of risk gene variants. Also a combination of genotyping and peripheral gene expression analysis could proof useful in the search of biomarkers for endophenotypes. Furthermore, we could confirm the role of the inositol-1,4,5-triphosphate second messenger pathway and protein kinase C in the pathogenesis of BD.

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.

Signal transduction pathways in the pathophysiology of bipolar disorder

Signal transduction pathways and genes associated with cellular life and death have received much attention in bipolar disorder (BPD) and provide scientists with molecular targets for understanding the biological basis of BPD. In this chapter, we describe the signal transduction pathways involved in the molecular biology of BPD and the indications for the mechanisms of disease and treatment. We discuss the BPD literature with respect to the disease itself and the effects of mood stabilizer treatment on cellular receptors, including G-protein-coupled receptors, glutamate receptors, and tyrosine receptor kinase. We also discuss the intracellular alterations observed in BPD to second messenger systems, such as cyclic adenosine monophosphate (cAMP), protein kinase A, phosphoinositide pathways, glycogen synthase kinase-3, protein kinase B, Wnt, and arachidonic acid. We describe how receptor activation and modulation of second messengers occurs, and how transcription factors are activated and altered in this disease (e.g., the transcription factors ?-catenin, cAMP response element binding protein, heat shock transcription factor-1, and activator protein-1). Abnormalities in intracellular signal transduction pathways could generate a functional discrepancy in numerous neurotransmitter systems, which may explain the varied clinical symptoms observed in BPD. The influence of mood stabilizers on transcription factors may be important in connecting the regulation of gene expression to neuroplasticity and cellular resilience.

Evidence for rare and common genetic risk variants for schizophrenia at protein kinase C, alpha

We earlier reported a genome-wide significant linkage to schizophrenia at chromosome 17 that was identified in a single pedigree (C702) consisting of six affected, male siblings with DSM-IV schizophrenia and prominent mood symptoms. In this study, we adopted several approaches in an attempt to map the putative disease locus. First, mapping the source of linkage to chromosome 17 in pedigree C702. We refined the linkage region in family C702 to a 21-marker segment spanning 11.7 Mb at 17q23-q24 by genotyping a total of 50 microsatellites across chromosome 17 in the pedigree. Analysis of data from 1028 single nucleotide polymorphisms (SNPs) across the refined linkage region identified a single region of homozygosity present in pedigree C702 but not in 2938 UK controls. This spanned ~432 kb of the gene encoding protein kinase C, alpha (PRKCA), the encoded protein of which has been implicated in the pathogenesis of psychiatric disorders. Analysis of pedigree C702 by oligonucleotide-array comparative genome hybridization excluded the possibility that this region of homozygosity was because of a deletion. Mutation screening of PRKCA identified a rare, four-marker haplotype (C-HAP) in the 3' untranslated region of the gene, which was present in the homozygous state in all six affected members of pedigree C702. No other homozygotes were observed in genotype data for a total of 6597 unrelated Europeans (case N=1755, control N=3580 and parents of probands N=1262). Second, association analysis of C702 alleles at PRKCA. The low-frequency haplotype (C-HAP) showed a trend for association in a study of unrelated schizophrenia cases and controls from the UK (661 cases, 2824 controls, P=0.078 and odd ratio (OR)=1.9) and significant evidence for association when the sample was expanded to include cases with bipolar (N=710) and schizoaffective disorder (N=50) (psychosis sample: 1421 cases, 2824 controls, P=0.037 and OR=1.9). Given that all the affected members of C702 are male, we also undertook sex-specific analyses. This revealed that the association was strongest in males for both schizophrenia (446 male cases, 1421 male controls, P=0.008 and OR=3.9) and in the broader psychosis group (730 male cases, 1421 male controls, P=0.008 and OR=3.6). Analysis of C-HAP in follow-up samples from Ireland and Bulgaria revealed no evidence for association in either the whole sample or in males alone, and meta-analysis of all male psychosis samples yielded no significant evidence of association (969 male cases, 1939 male controls, 311 male probands P=0.304 and OR=1.4). Third, association mapping of the pedigree C702 linkage region. Independent of pedigree C702, genotype data from the Affymetrix 500k GeneChip set were available for 476 patients with schizophrenia and 2938 controls from the United Kingdom. SNPs in PRKCA showed evidence for association with schizophrenia that achieved gene-wide significance (P=0.027). Moreover, the same SNP was the most significantly associated marker out of the 1028 SNPs genotyped across the linkage region (rs873417, allelic P=0.0004). Follow-up genotyping in samples from Ireland, Bulgaria and Germany did not show consistent replication, but meta-analysis of all samples (4116 cases and 6491 controls) remained nominally significant (meta-analysis P=0.026, OR=1.1). We conclude that, although we have obtained convergent lines of evidence implicating both rare and common schizophrenia risk variants at PRKCA, none of these is individually compelling. However, the evidence across all approaches suggests that further study of this locus is warranted.

Protein kinase C inhibitors: rationale for use and potential in the treatment of bipolar disorder

Bipolar disorder is one of the most severely debilitating of all medical illnesses. For a large number of patients, outcomes are quite poor. The illness results in tremendous suffering for patients and their families and commonly impairs functioning and workplace productivity. Risks of increased morbidity and mortality, unfortunately, are frequent occurrences as well. Until recently, little has been known about the specific molecular and cellular underpinnings of bipolar disorder. Such knowledge is crucial for the prospect of developing specific targeted therapies that are more effective and that have a more rapid onset of action than currently available treatments. Exciting recent data suggest that regulation of certain signalling pathways may be involved in the aetiology of bipolar disorder and that these pathways may be profitably targeted to treat the disorder. In particular, mania is associated with overactive protein kinase C (PKC) intracellular signalling, and recent genome-wide association studies of bipolar disorder have implicated an enzyme that reduces the activation of PKC. Importantly, the current mainstays in the treatment of mania, lithium (a monovalent cation) and valproate (a small fatty acid) indirectly inhibit PKC. In addition, recent clinical studies with the relatively selective PKC inhibitor tamoxifen add support to the relevance of the PKC target in bipolar disorder. Overall, a growing body of work both on a preclinical and clinical level indicates that PKC signalling may play an important role in the pathophysiology and treatment of bipolar disorder. The development of CNS-penetrant PKC inhibitors may have considerable benefit for this devastating illness.

Mechanisms of action of the mood stabilizer valproate: a focus on GSK-3 inhibition

Valproate is the most widely prescribed antiepileptic drug worldwide, and it is also used in the treatment of bipolar affective disorder, migraine headache and cancer. However, the therapeutic mechanism of action of valproate in these illness states is not understood. This article reviews the pharmacological effects of valproate that may explain its therapeutic efficacy. It focuses on the hypothesis that inhibition of glycogen synthase kinase-3 by valproate is a crucial therapeutic mechanism of this drug in the treatment of bipolar affective disorder. Other cellular pathways and signaling molecules that are targets of valproate (such as inositol de novo biosynthesis, histone deacetylase, protein kinase C, γ-aminobutyric acid, the extracellular signal-regulated kinase pathway and others) are also discussed.

Decreased protein kinase C (PKC) in platelets of pediatric bipolar patients: effect of treatment with mood stabilizing drugs

Pediatric bipolar disorder (PBD) is a major public health concern, however, its neurobiology is poorly understood. We, therefore, studied the role of protein kinase C (PKC) in the pathophysiology of bipolar illness. We determined PKC activity and immunolabeling of various PKC isozymes (i.e., PKC alpha, PKC betaI, PKC betaII, and PKC delta) in the cytosol and membrane fractions of platelets obtained from PBD patients and normal control subjects. PKC activity and PKC isozymes were also determined after 8 weeks of pharmacotherapy of PBD patients (n=16) with mood stabilizers. PKC activity and the protein expression of PKC betaI and betaII, but not PKC alpha or PKC delta, were significantly decreased in both membrane as well as cytosol fractions of platelets obtained from medication-free PBD patients compared with normal control subjects. Eight weeks of pharmacotherapy resulted in significantly increased PKC activity but no significant changes in any of the PKC isozymes in PBD patients. These results indicate that decreases of specific PKC isozymes and decreased PKC activity may be associated with the pathophysiology of PBD and that pharmacotherapy with mood stabilizing drugs results in an increase and normalization of PKC activity along with improvement in clinical symptoms.

Modulation of phosphoinositide-protein kinase C signal transduction by omega-3 fatty acids: implications for the pathophysiology and treatment of recurrent neuropsychiatric illness

The phosphoinositide (PI)-protein kinase C (PKC) signal transduction pathway is initiated by pre- and postsynaptic Galphaq-coupled receptors, and regulates several clinically relevant neurochemical events, including neurotransmitter release efficacy, monoamine receptor function and trafficking, monoamine transporter function and trafficking, axonal myelination, and gene expression. Mounting evidence for PI-PKC signaling hyperactivity in the peripheral (platelets) and central (premortem and postmortem brain) tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, coupled with evidence that PI-PKC signal transduction is down-regulated in rat brain following chronic, but not acute, treatment with antipsychotic, mood-stabilizer, and antidepressant medications, suggest that PI-PKC hyperactivity is central to an underlying pathophysiology. Evidence that membrane omega-3 fatty acids act as endogenous antagonists of the PI-PKC signal transduction pathway, coupled with evidence that omega-3 fatty acid deficiency is observed in peripheral and central tissues of patients with schizophrenia, bipolar disorder, and major depressive disorder, support the hypothesis that omega-3 fatty acid deficiency may contribute to elevated PI-PKC activity in these illnesses. The data reviewed in this paper outline a potential molecular mechanism by which omega-3 fatty acids could contribute to the pathophysiology and treatment of recurrent neuropsychiatric illness.

Effects of mood stabilizers on hippocampus BDNF levels in an animal model of mania

There is an emerging body of data suggesting that mood disorders are associated with decreased brain-derived neurotrophic factor (BDNF). The present study aims to investigate the effects of the mood stabilizers lithium (Li) and valproate (VPT) in an animal model of bipolar disorder. In the first experiment (acute treatment), rats were administered D-amphetamine (AMPH) or saline for 14 days, and then between day 8 and 14, rats were treated with either Li, VPT or saline. In the second experiment (maintenance treatment), rats were pretreated with Li, VPT or saline, and then between day 8 and 14, rats were administered AMPH or saline. In both experiments, locomotor activity was measured using the open-field test and BDNF levels were measured in rat hippocampus by sandwich-ELISA. Li and VPT reversed AMPH-induced behavioral effects in the open-field test in both experiments. In the first experiment, Li increased BDNF levels in rat hippocampus. In the second experiment, AMPH decreased BDNF levels and Li and VPT increased BDNF levels in rat hippocampus. Our results suggest that the present model fulfills adequate face, construct and predictive validity as an animal model of mania.

Decrease in the AP-2 DNA-binding activity and in the protein expression of AP-2 alpha and AP-2 beta in frontal cortex of rats treated with lithium for 6 weeks

Lithium chloride (LiCl), when fed to rats for 6 weeks, has been reported to decrease brain mRNA, protein, and activity levels of arachidonic acid (AA)-selective cytosolic phospholipase A2 (cPLA2), without affecting secretory sPLA2 or Ca2+-independent iPLA2. We investigated whether transcription factors known to regulate cPLA2 gene expression are modulated by chronic lithium treatment. Male Fischer-344 rats were fed a LiCl-containing diet for 6 weeks to produce a therapeutically relevant brain lithium concentration. Control animals were fed a LiCl-free diet. Using a gelshift assay, we found that LiCl significantly decreased activating protein 2 (AP-2)-binding activity, and protein levels of the AP-2 alpha and AP-2 beta but not of the AP-2 gamma subunits in the frontal cortex. Activating protein 1 (AP-1)-binding activity was increased, whereas glucocorticoid response element, polyoma enhancer activator 3, and nuclear factor kappa B DNA-binding activities were not changed significantly. Since both cPLA2 and AP-2 can be activated by protein kinase C (PKC), we examined the frontal cortex protein levels of PKC alpha and PKC epsilon, as well as AA-dependent PKC activity. The protein levels of PKC alpha and PKC epsilon were decreased significantly, as was AA-dependent PKC activity, in the lithium-treated compared to control rats. Our results suggest that the reported decrease in brain gene expression of cPLA2 by chronic lithium may be mediated by reduced AP-2 transcriptional activity, and that decreased expression of PKC alpha and PKC epsilon contributes to lowering the AP-2 activity.

A proton magnetic resonance spectroscopy investigation of the dorsolateral prefrontal cortex in acute mania

BACKGROUND

Several neurochemical abnormalities have been reported in bipolar disorder (BD), but the exact mechanisms that underlie its pathophysiology remain to be elucidated. Proton magnetic resonance spectroscopy (1HMRS) allows in vivo measurements of certain neurometabolites in the human brain. 1HMRS was used to investigate the dorsolateral prefrontal cortex (DLPFC) in bipolar subjects during a manic or mixed phase. N-acetyl-L-aspartate (NAA), choline-containing molecules (Cho), creatine plus phosphocreatine (Cr) and myoinositol (Ino) were measured.

METHOD

Ten bipolar patients (nine manic, one mixed), diagnosed by a semi-structured clinical interview (SCID), and ten age- and gender-matched healthy volunteers were studied. Absolute neurometabolites levels were measured from two 8 cm3 voxels placed in left and right DLPFC using a short TE 1HMRS method at 1.5 T. T1- and T2-weighted anatomical magnetic resonance imaging was performed to exclude any neuroanatomical abnormality.

RESULTS

No significant differences were found for NAA, Cho, Cr, Ino, NAA/Cr, Cho/Cr or Ino/Cr between patients and controls. Manic/mixed patients had significantly higher left-to-right myoinositol ratios in DLPFC (p = 0.044).

CONCLUSIONS

Increased left-to-right myoinositol ratios in the DLPFC in bipolar patients during acute mania may represent a dysfunction in the phosphoinositide-signaling pathway. Longitudinal studies with larger samples of unmedicated patients assessing pre- and post-treatment times will be required for further clarification of the time course of these abnormalities and the relationship with treatment effects.

[Neuropatological and neurochemical abnormalities in bipolar disorder]

OBJECTIVES

Postmortem, pharmacological, neuroimaging, and animal model studies have demonstrated a possible association of intracellular signaling mechanisms in the pathophysiology of bipolar disorder. The objective of this paper is to review the findings in neuropathology and cellular biochemistry.

METHODS

We performed a MEDLINE research, between 1980-2003, using bipolar disorder, signaling, second messengers, and postmortem as keywords, and cross-references.

RESULTS

Neuropathological studies reported a decrease in neuronal and glial cells, mainly in the prefrontal cortex of bipolar patients. Neurochemical studies reported dysfunction in cAMP, phosphoinositide, Wnt/GSK-3b, and intracellular Ca++ pathways in these patients.

CONCLUSION

The neuropathological and neurochemical abnormalities demonstrated in BD may be related to the pathophysiology of this disorder and the effects of mood stabilizers. However, further studies are needed to clarify the role of the intracellular signaling cascade in the pathogenesis of this disorder.

Fisiopatologia do transtorno afetivo bipolar: o que mudou nos últimos 10 anos?

Apesar dos crescentes esforços para o entendimento da neurobiologia do transtorno afetivo bipolar (TAB), sua exata fisiopatologia permanece indeterminada. Inicialmente, a pesquisa estava voltada para o estudo das aminas biogênicas, devido aos efeitos dos diversos agentes psicofarmacológicos. Mais recentemente, evidências apontam que disfunções nos sistemas de sinalização intracelular e de expressão gênica podem estar associadas ao TAB. Estas alterações podem estar associadas a interrupções nos circuitos reguladores do humor, como sistema límbico, estriado e córtex pré-frontal, sendo que os efeitos neuroprotetores do uso crônico dos estabilizadores de humor podem reverter este processo patológico. Este artigo tem como objetivo trazer uma atualização dos achados recentes sobre a neuroquímica do TAB.

Predicting response to lithium in mood disorders: role of genetic polymorphisms

Lithium is considered to be the first choice mood stabilizer in recurrent mood disorders. Its widespread and large-scale use is the result of its proven efficacy. In spite of this fact, patients have been observed to show a variable response to lithium treatment: in some cases it is completely effective in preventing manic or depressive relapses, while in other cases it appears to show no influence on the disease course. The possible definition of a genetic liability profile for adverse effects and efficacy will be of great help, as lithium therapy needs at least 6 months to be effective in stabilizing mood disorders. During the last few years, a number of groups have reported possible liability genes. Lithium long-term prophylactic efficacy has been associated with serotonin transporter protein, tryptophan hydroxylase and inositol polyphosphate 1-phosphatase variants. A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even if some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified. Although the available data may not currently allow a meaningful prediction of lithium response, future research is aimed at the development of individualized treament of mood disorders, including the possibility of 'pharmacological genetic counseling'.

The effect of lithium on expression of genes for inositol biosynthetic enzymes in mouse hippocampus; a comparison with the yeast model

In the de novo synthesis of inositol, the conversion of D-glucose-6-phosphate to L-myo-inositol-1-phosphate (MIP) is catalyzed by MIP synthase. Little is known about mammalian MIP synthase and nothing is known about its regulation. The second step in inositol biosynthesis is the conversion of MIP to inositol by inositol-monophosphatase (IMPase), a common step to inositol production via the de novo pathway and its recycling from inositol phosphates. Because lithium inhibits IMPase both in yeast and in mammals, and the drug upregulates yeast MIP synthase (INO1) and downregulates IMPase (INM1), the present study was undertaken to determine whether chronic in vivo therapeutic lithium concentrations affect MIP synthase and IMPase expression in mouse frontal cortex and hippocampus. Mice were treated with food containing LiCl (2.5 g/kg) for 10 days. RNA was purified from the brain areas and mRNA amplified using RT-PCR. Expression of MIP synthase and IMPA1 (one of the genes coding for IMPase) but not IMPA2 was upregulated in mouse hippocampus. None of the genes were affected in the frontal cortex. In yeast, when inositol is limiting, the heterodimeric transcriptional activator Ino2p/Ino4p derepresses expression of INO1 by binding to the upstream activation sequence UAS(INO). Using the TFSEARCH program, we found that the promoter of the virtual human MIP synthase gene contains upstream stimulating factor (USF) elements with a similar core binding sequence. The fact that lithium treatment upregulates both MIP synthase and IMPA1 mRNA levels in mouse hippocampus may reflect a compensatory response of both genes to inositol depletion.

Congenitally learned helpless rats show abnormalities in intracellular signaling

BACKGROUND

Affective disorders and the drugs used to treat them lead to changes in intracellular signaling. We used a genetic animal model to investigate to what extent changes in intracellular signal transduction confer a vulnerability to mood or anxiety disorders.

METHODS

Levels of gene expression in a selectively bred strain of rats with a high vulnerability to develop congenitally learned helplessness (cLH), a strain highly resistant to the same behavior (cNLH) and outbred Sprague-Dawley (SD) control animals were compared using quantitative reverse transcription polymerase chain reaction.

RESULTS

Congenitally learned helpless animals had a 24%-30% reduced expression of the cyclic adenosine monophosphate response element binding protein messenger ribonucleic acid (mRNA) in the hippocampus and a 40%-41% increased level of the antiapoptotic protein bcl-2 mRNA in the prefrontal cortex compared to cNLH and SD rats. Other significant changes included changes in the expression levels of the alpha catalytic subunit of protein kinase A, glycogen synthase kinase 3beta, and protein kinase C epsilon.

CONCLUSIONS

Congenitally learned helpless animals show evidence of altered signal transduction and regulation of apoptosis compared to cNLH and SD control animals.

Lithium modulates expression of TRH receptors and TRH-related peptides in rat brain

Lithium is an established mood stabilizer and neuroprotective agent frequently used in the treatment of bipolar disorder and as an adjuvant in drug-resistant unipolar depression. The mechanisms underlying both the therapeutic efficacy of lithium and the exacerbation of symptoms following rapid withdrawal are not understood. From previous studies showing antidepressant and neuroprotective activities of thyrotropin releasing hormone (TRH) and TRH-related neuropeptides we hypothesized that lithium may have substantial effects on the expression and secretion of these peptides and/or their receptors in various rat brain regions involved in the regulation of mood. Chronic lithium effect on TRH receptor binding studies: The effect of 1 and 2 weeks of dietary lithium on [(3)H]3-Me-His-TRH binding to plasma membranes of nucleus accumbens, amygdala and pituitary of young adult male Wistar and the endogenously 'depressed' Wistar Kyoto (WKY) rats was measured by the method of Burt and Taylor [Burt, D.R., Taylor, R.L., Endocrinology 106 (1980) 1416-1423]. Acute, chronic and withdrawal effect of lithium on TRH and TRH-like peptide levels in young, adult male Sprague-Dawley rats: Rats were divided into four lithium treatment groups. Control animals received a standard laboratory rodent chow. The acute group received a single i.p. injection of 1.5 milli-equivalents of LiCl 2 h prior to killing. The chronic and withdrawal groups received standard rodent chow containing 1.7 g/kg LiCl for 2 weeks. Withdrawal rats were returned to standard chow 48 h prior to killing while the chronic animals continued on the LiCl diet. TRH, TRH-Gly (pGlu-His-Pro-Gly, a TRH precursor), EEP (pGlu-Glu-Pro-NH(2), a TRH-like peptide with antidepressant activity) and Ps4 (a prepro-TRH-derived TRH-enhancing decapeptide) immunoreactivity (IR) were measured in 13 brain regions. The remaining samples were pooled and fractionated by high-pressure liquid chromatography followed by EEP radioimmunoassay. Chronic lithium treatment increased [(3)H]3Me-TRH binding in the nucleus accumbens and amygdala about two-fold in both Wistar and WKY rats but no change was observed in pituitary binding. The most widespread changes in TRH and TRH-related peptide levels were observed in the withdrawal group compared to the controls. The direction of change for the total IR was consistent for all TRH-IR and TRH-related peptide-IR within a given tissue. For example, withdrawal increased all peptide levels in the pyriform cortex and striatum but decreased these levels in the anterior cingulate and lateral cerebellum. Both acute injection and chronic treatment with LiCl decreased TRH and TRH-related peptide levels in the entorhinal cortex. Acute injection and withdrawal both increased EEP-IR in striatum by more than two-fold. The acute effects are most likely due to changes in the release of these peptides since 2 h is not sufficient time for alterations in peptide biosynthesis. Chronic treatment increased levels of pGlu-Phe-Pro-NH(2) levels in hippocampus, pGlu-Leu-Pro-NH(2), and peak '2' in septum by more than four-fold. The present results are consistent with a component role for TRH and related peptides in the mood-altering effects of lithium administration and withdrawal frequently observed during treatment for depression and bipolar disorder.

Molecular basis of lithium action: integration of lithium-responsive signaling and gene expression networks

The clinical efficacy of lithium in the prophylaxis of recurrent affective episodes in bipolar disorder is characterized by a lag in onset and remains for weeks to months after discontinuation. Thus, the long-term therapeutic effect of lithium likely requires reprogramming of gene expression. Protein kinase C and glycogen synthase kinase-3 signal transduction pathways are perturbed by chronic lithium at therapeutically relevant concentrations and have been implicated in modulating synaptic function in nerve terminals. These signaling pathways offer an opportunity to model critical signals for altering gene expression programs that underlie adaptive responses of neurons to long-term lithium exposure. While the precise physiological events critical for the clinical efficacy of lithium remain unknown, we propose that linking lithium-responsive genes as a regulatory network will provide a strategy to identify signature gene expression patterns that distinguish between therapeutic and nontherapeutic actions of lithium.

The evolution of antiepileptic drugs for mood stabilization and their main mechanisms of action

Although much progress has been made in successfully treating bipolar disorder, there is increasing awareness of the limitations of traditional treatment regimes, such as lithium or antipsychotics and the possible beneficial use of antiepileptic drugs. After the first generation of antiepileptic drugs such as phenytoin and clonazepam, the second generation is comprised of the frequently-used substances carbamazepine/oxcarbazepine and valproate. Lamotrigine, gabapentin, tiagabine, levetiracetam, zonisamide and topiramate will represent the third generation 5 years from now. Drugs such as retigabine might represent the next generation. However, the efficacy of antiepileptic drugs investigated in the treatment of bipolar disorder differs and most promising effects are seen in combination therapy with mood stabilizers. The authors review the main mechanisms of action of these drugs which may, in turn, improve our understanding of the pathophysiology of bipolar disorder.

The neurobiology of bipolar disorder: focus on signal transduction pathways and the regulation of gene expression

OBJECTIVE

This article presents an overview of signal transduction pathways and reviews the research undertaken to study these systems in clinically relevant samples from patients with bipolar disorder (BD).

METHOD

We reviewed the published findings from studies of postmortem brain tissue and blood samples from patients with BD.

RESULTS

Although the exact biochemical abnormalities have yet to be identified, the presented findings strongly suggest that BD may be due, at least in part, to abnormalities in signal transduction mechanisms. In particular, altered levels or function, or both, of G-protein alpha subunits and effector molecules such as protein kinase A (PKA) and protein kinase C (PKC) have consistently been associated with BD both in peripheral cells and in postmortem brain tissue, while more recent studies implicate disruption in novel second-messenger cascades, such as the ERK/MAPK pathway.

CONCLUSIONS

Despite the difficulties inherent in biochemical studies of clinically relevant tissue samples, numerous investigations have illuminated the signal transduction mechanisms in patients with BD. These studies also suggest that BD may be due to the interaction of many abnormalities. In this context, novel techniques enabling the study of gene expression promise to assist in untangling these complex interactions, through visualizing the end result of these changes at the level of gene transcription.

Lithium long-term treatment in mood disorders: clinical and genetic predictors

Lithium is the most widely used long-term treatment for recurrent mood disorders. Despite its proven efficacy, patients show a variable response, ranging from complete efficacy to no influence at all. This paper reviews possible predictors of response focusing on molecular genetic studies. The functional polymorphism in the upstream regulatory region of the serotonin transporter gene (5-HTTLPR) has been associated with lithium long-term efficacy in two independent studies, marginal associations have been reported for tryptophan hydroxylase and inositol polyphosphate 1-phosphatase (INPP1). A number of other candidate genes and anonymous markers did not yield positive associations. Therefore, even though some positive results have been reported, no unequivocal susceptibility gene for lithium efficacy has been identified.

Transcriptional down-regulation of MARCKS gene expression in immortalized hippocampal cells by lithium

The gene (Macs) for the mouse myristoylated alanine-rich C kinase substrate (MARCKS) encodes a prominent substrate for protein kinase C that has been implicated in processes requiring signal dependent changes in actin-membrane plasticity and cytoskeletal restructuring. We have previously demonstrated that MARCKS protein is significantly down-regulated in rat hippocampus and in an immortalized hippocampal cell line (HN33.dw) following long-term exposure to lithium at clinically relevant concentrations (1 mM). Our current studies have examined transcriptional and post-transcriptional events that may underlie the lithium-induced down-regulation of MARCKS protein in the cultured hippocampal cell model system. MARCKS mRNA and protein expression were found to be concomitantly down-regulated following exposure of the HN33.dw cells to chronic lithium. Whereas the stability of MARCKS mRNA remained unchanged in the presence of lithium, nuclear run-off assay indicated that the transcription of nascent MARCKS mRNA was significantly reduced (approximately 50%) in the cells that had been treated with lithium for 7 days. Transient transfection of HN33.dw cells with a mouse cloned Macs promoter (993-bp) showed that the Macs promoter activity was attenuated to the same extent after chronic (7-10 days), but not subacute (24 h), lithium exposure. The inhibition of the Macs promoter was found to be dependent upon the presence of a 280-bp promoter region between -993-bp and -713-bp relative to the translation start site, suggesting that this region is a potential lithium-responsive region of Macs promoter (LRR). Mutant promoter lacking the LRR not only did not respond to chronic lithium exposure but also had significantly reduced promoter activity, suggesting that chronic lithium exposure represses the transcriptional activity of activator(s) bound to the promoter. Taken together, our data indicate that transcriptional inhibition of the Macs gene underlies the lithium-induced down-regulation of MARCKS expression in the immortalized hippocampal cells.

Emerging therapeutic targets in bipolar mood disorder

Bipolar mood disorder is a chronic, severe and life-threatening psychiatric illness, whose underlying pathophysiology is still obscure. Lithium is the mainstay of treatment for this illness, with robust acute antimanic and long-term prophylactic effects. Over the past decade, valproate has been another medication shown to have possibly similar mood-stabilising properties to lithium, in double-blind controlled trials. Nonetheless, among patients suffering from bipolar disorder, a substantial percentage appears to respond poorly to currently available pharmacological therapies, including lithium, valproate, carbamazepine and other newer compounds, clearly demonstrating that there is a substantial need for improved therapeutic agents. Very significant effort has been made in the past several years to elucidate the cellular mechanisms by which lithium and valproate produce their therapeutic effects. The available evidence points to a modulatory action of these compounds over multiple neural biochemical pathways and most investigations have found relevant actions of mood stabilisers on intracellular signal transduction mechanisms. Moreover, it has been shown in recent years that lithium and valproate lead to long-term changes in neural plasticity, with eventual neurotrophic and neuroprotective effects. Although these actions are not fully understood, stimulation of transcription factors and effects on gene expression are potentially involved. The search for the mechanisms of action of well-established mood-stabilisers has helped to reveal promising molecular targets to test novel therapeutic approaches. This review will examine the current investigations on the diverse biochemical and molecular pathways regulated by either lithium or valproate and highlight the potential cellular targets for the development of novel mood stabilisers.