Reduced brain inositol in lithium-treated rats

Exploring Calbindin-IMPase fusion proteins structure and activity

Calbindin-D28k is a calcium binding protein that is highly expressed in the mammalian central nervous system. It has been reported that calbindin-D28k binds to and increases the activity of inositol Monophosphatase (IMPase). This is an enzyme that is involved in the homeostasis of the Inositol trisphosphate signalling cascade by catalysing the final dephosphorylation of inositol and has been implicated in the therapeutic mechanism of lithium treatment of bipolar disorder. Previously studies have shown that calbindin-D28k can increase IMPase activity by up to 250 hundred-fold. A preliminary in silico model was proposed for the interaction.

Here, we aimed at exploring the shape and properties of the calbindin-IMPase complex to gain new insights on this biologically important interaction. We created several fusion constructs of calbindin-D28k and IMPase, connected by flexible amino acid linkers of different lengths and orientations to fuse the termini of the two proteins together. The resulting fusion proteins have activities 200%–400% higher the isolated wild-type IMPase. The constructs were characterized by small angle X-ray scattering to gain information on the overall shape of the complexes and validate the previous model. The fusion proteins form a V-shaped, elongated and less compact complex as compared to the model. Our results shed new light into this protein-protein interaction.

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The interaction between calbindin-D28k and the enzyme IMPase is studies using fusion proteins.

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The fusion proteins have activities 200%–400% higher than wild-type IMPase.

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The calbindin-D28k and the enzyme IMPase fusion proteins have a V-shaped structure.

Modulation of Gq/PLC-Mediated Signaling by Acute Lithium Exposure

Although lithium has long been one of the most widely used pharmacological agents in psychiatry, its mechanisms of action at the cellular and molecular levels remain poorly understood. One of the targets of Li+ is the phosphoinositide pathway, but whereas the impact of Li+ on inositol lipid metabolism is well documented, information on physiological effects at the cellular level is lacking. We examined in two mammalian cell lines the effect of acute Li+ exposure on the mobilization of internal Ca2+ and phospholipase C (PLC)-dependent membrane conductances. We first corroborated by Western blots and immunofluorescence in HEK293 cells the presence of key signaling elements of a muscarinic PLC pathway (M1AchR, Gq, PLC-β1, and IP3Rs). Stimulation with carbachol evoked a dose-dependent mobilization of Ca, as determined with fluorescent indicators. This was due to release from internal stores and proved susceptible to the PLC antagonist U73122. Li+ exposure reproducibly potentiated the Ca response in a concentration-dependent manner extending to the low millimolar range. To broaden those observations to a neuronal context and probe potential Li modulation of electrical signaling, we next examined the cell line SHsy5y. We replicated the potentiating effects of Li on the mobilization of internal Ca, and, after characterizing the basic properties of the electrical response to cholinergic stimulation, we also demonstrated an equally robust upregulation of muscarinic membrane currents. Finally, by directly stimulating the signaling pathway at different links downstream of the receptor, the site of action of the observed Li effects could be narrowed down to the G protein and its interaction with PLC-β. These observations document a modulation of Gq/PLC/IP3-mediated signaling by acute exposure to lithium, reflected in distinct physiological changes in cellular responses.

De novo variation in bipolar disorder

Bipolar disorder (BD) is a common, highly heritable disorder that affects 1-2% of the world's population. To date, most genetic studies of BD have focused on common gene variation, and while robustly associated loci have been identified, a substantial proportion of the heritability remains missing and could be partially attributable to rare variation. In this study, we apply a de novo paradigm in BD to identify newly arisen variants that have yet to undergo natural selection and may represent highly pathogenic variants. We performed whole genome sequencing of 97 trios of Ashkenazi Jewish descent, selecting "simplex" families with no family history of BD and an early age of onset. We found a total of 6882 de novo variants (an average of 70.9 ± 12.9 S.D. variants per trio), including 107 variants within protein-coding genes. We combined our exonic variations with the results of 79 previously published BD trios, identifying 20 loss-of-function (LoF) and 77 missense damaging de novo variants in BD. These variants showed significant enrichment for constrained genes and for genes located to the postsynaptic density (PSD) (all Bonferroni corrected p < 0.05). Pathway analyses showed enrichment in several pathways, including "Phosphoinositides (PI) and their downstream targets" (Bonferroni p = 4.2 × 10-6), a pathway prominently featured in lithium's hypothesized mechanism of action. In addition, while we found overall evidence for transmission of common variant polygenic risk of BD in our full sample (pTDT p = 2.21 × 10-4), specific trios with LoF variants showed no evidence of polygenic transmission. In sum, our findings support the de novo paradigm as a contributor to the genetic architecture of BD and provide evidence that constrained genes, as well as genes within the PSD and PI pathway harbor rare variation associated with BD.

Lithium orotate: A superior option for lithium therapy?

Bipolar disorder (BD) poses a significant public health concern, with roughly one-quarter of sufferers attempting suicide. BD is characterized by manic and depressive mood cycles, the recurrence of which can be effectively curtailed through lithium therapy. Unfortunately, the most frequently employed lithium salt, lithium carbonate (Li₂ CO₃ ), is associated with a host of adverse health outcomes following chronic use: these unwanted effects range from relatively minor inconveniences (e.g., polydipsia and polyuria) to potentially major complications (e.g., hypothyroidism and/or renal impairment). As these undesirable effects can limit patient compliance, an alternative lithium compound with a lesser toxicity profile would dramatically improve treatment efficacy and outcomes. Lithium orotate (LiC₅ H₃ N₂ O₄ ; henceforth referred to as LiOr), a compound largely abandoned since the late 1970s, may represent such an alternative. LiOr is proposed to cross the blood-brain barrier and enter cells more readily than Li₂ CO₃ , which will theoretically allow for reduced dosage requirements and ameliorated toxicity concerns. This review addresses the controversial history of LiOr, complete with discussions of experimental and clinical efficacy, putative mechanisms of action, adverse effects, and its potential future in therapy.

Lithium toxicity and the kidney with special focus on nephrotic syndrome associated with the acute kidney injury: A case-based systematic analysis

Despite the progress made in treating bipolar and unipolar affective disorders, lithium carbonate is still a common drug in psychiatric practice. Lithium-related renal side effects include nephrogenic diabetes insipidus, chronic tubulointerstitial nephropathy, and acute kidney injury (AKI). Nephrotic syndrome (NS) is an uncommon but severe complication of lithium treatment. We present a 49-year-old female treated with lithium carbonate due to a recurrent depressive disorder who developed NS during this therapy. NS spontaneously remitted after the drug withdrawal. Since her lithium serum levels were within the recommended values, we performed a retrospective analysis of lithium-induced NS cases trying to determine causes predisposing to the NS development, underlying histopathology, and preservation or irreversible loss of kidney function. This analysis revealed that in lithium-induced NS with AKI, lithium serum level was the key determinant of AKI development (the β coefficient = 0.8499 with a confidence interval ranging from 0.7452 to 0.9546 and p value < 0.0001). In these cases, the underlying pathology was mainly minimal change disease (MCD), which was quickly reversible upon the drug withdrawal. The development of chronic kidney disease (CKD) seemed to be associated with lithium therapy duration. However, the multiple regression analysis for CKD as the dependent variable showed that the decisive factor was focal segmental glomerulosclerosis (FSGS) as the underlying pathology (the β coefficient = 0.7866 with a confidence interval ranging from 0.600 to 0.9704 and the p value < 0.0001). Thus, we conclude that in lithium-induced NS/AKI, serum lithium levels contribute to these complications, while FSGS lesions are responsible for CKD's disease progression.

A novel microduplication in INPP5A segregates with schizophrenia spectrum disorder in the family of a patient with both childhood onset schizophrenia and autism spectrum disorder

Childhood-Onset Schizophrenia (COS) is a very rare and severe psychiatric disorder defined by adult schizophrenia symptoms occurring before the age of 13. We report a microduplication in the 10q26.3 region including part of the Inositol Polyphosphate-5-Phosphatase A (INPP5A) gene that segregates with Schizophrenia Spectrum Disorders (SSDs) in the family of a female patient affected by both COS and Autism Spectrum Disorder (ASD). Phenotyping and genotyping (including CGH-array) were performed for mother, healthy sister, and affected child according to the GenAuDiss protocol (NCT02565524). The duplication size is 324 kb and is present in a patient with COS and in her mother with SSD, but not in the patient's healthy sister. INPP5A encodes a membrane-associated 43 kDa type I inositol 1,4,5-trisphosphate (InsP3) 5-phosphatase. This protein is found both in mouse and human brains and we found that its Drosophila homologue 5PtaseI is specifically expressed in the central nervous system. Hydrolyzed products from InsP3 5-phosphatases mobilize intracellular calcium, which is relevant for dendritic spine morphogenesis in neurons and altered in both schizophrenia and ASD. These may constitute arguments in favor of this gene alteration in the pathophysiology of COS.

A structural basis for lithium and substrate binding of an inositide phosphatase

Inositol polyphosphate 1-phosphatase (INPP1) is a prototype member of metal-dependent/lithium-inhibited phosphomonoesterase protein family defined by a conserved three-dimensional core structure. Enzymes within this family function in distinct pathways including inositide signaling, gluconeogenesis, and sulfur assimilation. Using structural and biochemical studies, we report the effect of substrate and lithium on a network of metal binding sites within the catalytic center of INPP1. We find that lithium preferentially occupies a key site involved in metal-activation only when substrate or product is added. Mutation of a conserved residue that selectively coordinates the putative lithium-binding site results in a dramatic 100-fold reduction in the inhibitory constant as compared with wild-type. Furthermore, we report the INPP1/inositol 1,4-bisphosphate complex which illuminates key features of the enzyme active site. Our results provide insights into a structural basis for uncompetitive lithium inhibition and substrate recognition and define a sequence motif for metal binding within this family of regulatory phosphatases.

A Short Historical Perspective of Methods in Inositol Phosphate Research

The multitudinous inositol phosphate family elicits a wide range of molecular effects that regulate countless biological responses. In this review, I provide a methodological viewpoint of the manner in which key advances in the field of inositol phosphate research were made. I also note some of the considerable challenges that still lie ahead.

Putative Mechanisms of Action and Clinical Use of Lithium in Children and Adolescents: A Critical Review

Background:

Lithium is a first-line treatment for bipolar disorder in adults, but its mechanism of action is still far from clear. Furthermore, evidences of its use in pediatric populations are sparse, not only for bipolar disorders, but also for other possible indications.

Objectives:

To provide a synthesis of published data on the possible mechanisms of action of lithium, as well as on its use in pediatric samples, including pharmacokinetics, efficacy, and safety data.

Methods:

Clinical trials in pediatric samples with at least one standardized measure of efficacy/effectiveness were included in this review. We considered: i) randomized and open label trials, ii) combination studies iii) augmentation studies iv) case series including at least 5 patients.

Results:

Different and non-alternative mechanisms of action can explain the clinical efficacy of lithium. Clinical studies in pediatric samples suggest that lithium is effective in managing manic symptoms/episodes of bipolar disorder, both in the acute phase and as maintenance strategy. Efficacy on depressive symptoms/phases of bipolar disorder is much less clear, while studies do not support its use in unipolar depression and severe mood dysregulation. Conversely, it may be effective on aggression in the context of conduct disorder. Other possible indications, with limited published evidence, are the acute attacks in Kleine-Levin syndrome, behavioral symptoms of X-fragile syndrome, and the management of clozapine- or chemotherapy- induced neutropenia. Generally, lithium resulted relatively safe.

Conclusions:

Lithium seems an effective and well-tolerated medication in pediatric bipolar disorder and aggression, while further evidences are needed for other clinical indications.

Crosstalk between Ras and inositol phosphate signaling revealed by lithium action on inositol monophosphatase in Schizophyllum commune

Mushroom forming basidiomycete Schizophyllum commune has been used as a tractable model organism to study fungal sexual development. Ras signaling activation via G-protein-coupled receptors (GPCRs) has been postulated to play a significant role in the mating and development of S. commune. In this study, a crosstalk between Ras signaling and inositol phosphate signaling by inositol monophosphatase (IMPase) is revealed. Constitutively active Ras1 leads to the repression of IMPase transcription and lithium action on IMPase activity is compensated by the induction of IMPase at transcriptome level. Astonishingly, in S. commune lithium induces a considerable shift to inositol phosphate metabolism leading to a massive increase in the level of higher phosphorylated inositol species up to the inositol pyrophosphates. The lithium induced metabolic changes are not observable in a constitutively active Ras1 mutant. In addition to that, proteome profile helps us to elucidate an overview of lithium action to the broad aspect of fungal metabolism and cellular signaling. Taken together, these findings imply a crosstalk between Ras and inositol phosphate signaling.

The Role of Pharmacogenomics in Bipolar Disorder: Moving Towards Precision Medicine

Bipolar disorder (BD) is a common and disabling psychiatric condition with a severe socioeconomic impact. BD is treated with mood stabilizers, among which lithium represents the first-line treatment. Lithium alone or in combination is effective in 60% of chronically treated patients, but response remains heterogenous and a large number of patients require a change in therapy after several weeks or months. Many studies have so far tried to identify molecular and genetic markers that could help us to predict response to mood stabilizers or the risk for adverse drug reactions. Pharmacogenetic studies in BD have been for the most part focused on lithium, but the complexity and variability of the response phenotype, together with the unclear mechanism of action of lithium, limited the power of these studies to identify robust biomarkers. Recent pharmacogenomic studies on lithium response have provided promising findings, suggesting that the integration of genome-wide investigations with deep phenotyping, in silico analyses and machine learning could lead us closer to personalized treatments for BD. Nevertheless, to date none of the genes suggested by pharmacogenetic studies on mood stabilizers have been included in any of the genetic tests approved by the Food and Drug Administration (FDA) for drug efficacy. On the other hand, genetic information has been included in drug labels to test for the safety of carbamazepine and valproate. In this review, we will outline available studies investigating the pharmacogenetics and pharmacogenomics of lithium and other mood stabilizers, with a specific focus on the limitations of these studies and potential strategies to overcome them. We will also discuss FDA-approved pharmacogenetic tests for treatments commonly used in the management of BD.

Ebselen has lithium-like effects on central 5-HT2A receptor function

BACKGROUND AND PURPOSE

Lithium's antidepressant action may be mediated by inhibition of inositol monophosphatase (IMPase), a key enzyme in G_q -protein coupled receptor signalling. Recently, the antioxidant agent ebselen was identified as an IMPase inhibitor. Here, we investigated both ebselen and lithium in models of the 5-HT_2A receptor, a G_q -protein coupled receptor involved in lithium's actions.

EXPERIMENTAL APPROACH

5-HT_2A receptor function was assessed in mice by measuring the behavioural (head-twitches, ear scratches) and molecular (cortical immediate early gene [IEG] mRNA; Arc, c-fos, Egr2) responses to 5-HT_2A receptor agonists. Ebselen and lithium were administered either acutely or repeatedly prior to assessment of 5-HT_2A receptor function. Because lithium and 5-HT_2A receptor antagonists augment the action of selective serotonin reuptake inhibitors (SSRIs), ebselen was tested for this activity by co-administration with the SSRI citalopram in microdialysis (extracellular 5-HT) experiments.

KEY RESULTS

Acute and repeated administration of ebselen inhibited behavioural and IEG responses to the 5-HT_2A receptor agonist DOI. Repeated lithium also inhibited DOI-evoked behavioural and IEG responses. In comparison, a selective IMPase inhibitor (L-690330) attenuated the behavioural response to DOI whereas glycogen synthase kinase inhibitor (AR-A014418) did not. Finally, ebselen enhanced the increase in extracellular 5-HT induced by citalopram, and also increased regional brain 5-HT synthesis.

CONCLUSIONS AND IMPLICATIONS

Our data demonstrated lithium-mimetic effects of ebselen in different experimental models of 5-HT_2A receptor function, probably mediated by IMPase inhibition. This evidence of lithium-like neuropharmacological effects of ebselen adds further support for the clinical testing of ebselen in mood disorders, including as an antidepressant augmenting agent.

Reconsidering Dietary Polyunsaturated Fatty Acids in Bipolar Disorder: A Translational Picture

Inflammation is an important mediator of pathophysiology in bipolar disorder. The omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acid (PUFA) metabolic pathways participate in several inflammatory processes and have been linked through epidemiologic and clinical studies to bipolar disorder and its response to treatment. We review the proposed role of PUFA metabolism in neuroinflammation, modulation of brain PUFA metabolism by antimanic medications in rodent models, and anti-inflammatory pharmacotherapy in bipolar disorder and in major depressive disorder (MDD). Although the convergence of findings between preclinical and postmortem clinical data is compelling, we investigate why human trials of PUFA as treatment are mixed. We view the biomarker and treatment study findings in light of the evidence for the hypothesis that arachidonic acid hypermetabolism contributes to bipolar disorder pathophysiology and propose that a combined high n-3 plus low n-6 diet should be tested as an adjunct to current medication in future trials.

Lithium Pharmacogenetics: Where Do We Stand?

Preclinical Research Bipolar disorder (BPD) is a chronic and disabling psychiatric disorder with a prevalence of 0.8-1.2% in the general population. Although lithium is considered the first-line treatment, a large percentage of patients do not respond sufficiently. Moreover, lithium can induce severe side effects and has poor tolerance and a narrow therapeutic index. The genetics of lithium response has been largely investigated, but findings have so far failed to identify reliable biomarkers to predict clinical response. This has been largely determined by the highly complex phenotipic and genetic architecture of lithium response. To this regard, collaborative initiatives hold the promise to provide robust and standardized methods to disantenagle this complexity, as well as the capacity to collect large samples of patietnts, a crucial requirement to study the genetics of complex phenotypes. The International Consortium on Lithium Genetics (ConLiGen) has recently published the largest study so far on lithium response reporting significant associations for two long noncoding RNAs (lncRNAs). This result provides relevant insights into the pharmacogenetics of lithium supporting the involvement of the noncoding portion of the genome in modulating clinical response. Although a vast body of research is engaged in dissecting the genetic bases of response to lithium, the several drawbacks of lithium therapy have also stimulated multiple efforts to identify new safer treatments. A drug repurposing approach identified ebselen as a potential lithium mimetic, as it shares with lithium the ability to inhibit inositol monophosphatase. Ebselen, an antioxidant glutathione peroxidase mimetic, represents a valid and promising example of new potential therapeutic interventions for BD, but the paucity of data warrant further investigation to elucidate its potential efficacy and safety in the management of BPD. Nevertheless, findings provided by the growing field of pharmacogenomic research will ultimately lead to the identification of new molecular targets and safer treatments for BPD. Drug Dev Res 77 : 368-373, 2016. © 2016 Wiley Periodicals, Inc.

Osmoregulatory inositol transporter SMIT1 modulates electrical activity by adjusting PI(4,5)P2 levels

Myo-inositol is an important cellular osmolyte in autoregulation of cell volume and fluid balance, particularly for mammalian brain and kidney cells. We find it also regulates excitability. Myo-inositol is the precursor of phosphoinositides, key signaling lipids including phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. However, whether myo-inositol accumulation during osmoregulation affects signaling and excitability has not been fully explored. We found that overexpression of the Na(+)/myo-inositol cotransporter (SMIT1) and myo-inositol supplementation enlarged intracellular PI(4,5)P2 pools, modulated several PI(4,5)P2-dependent ion channels including KCNQ2/3 channels, and attenuated the action potential firing of superior cervical ganglion neurons. Further experiments using the rapamycin-recruitable phosphatase Sac1 to hydrolyze PI(4)P and the P4M probe to visualize PI(4)P suggested that PI(4)P levels increased after myo-inositol supplementation with SMIT1 expression. Elevated relative levels of PIP and PIP2 were directly confirmed using mass spectrometry. Inositol trisphosphate production and release of calcium from intracellular stores also were augmented after myo-inositol supplementation. Finally, we found that treatment with a hypertonic solution mimicked the effect we observed with SMIT1 overexpression, whereas silencing tonicity-responsive enhancer binding protein prevented these effects. These results show that ion channel function and cellular excitability are under regulation by several "physiological" manipulations that alter the PI(4,5)P2 setpoint. We demonstrate a previously unrecognized linkage between extracellular osmotic changes and the electrical properties of excitable cells.

Inositol depletion, GSK3 inhibition and bipolar disorder

Valproic acid and lithium are widely used to treat bipolar disorder, a severe illness characterized by cycles of mania and depression. However, their efficacy is limited, and treatment is often accompanied by serious side effects. The therapeutic mechanisms of these drugs are not understood, hampering the development of more effective treatments. Among the plethora of biochemical effects of the drugs, those that are common to both may be more related to therapeutic efficacy. Two common outcomes include inositol depletion and GSK3 inhibition, which have been proposed to explain the efficacy of both valproic acid and lithium. Here, we discuss the inositol depletion and GSK3 inhibition hypotheses, and introduce a unified model suggesting that inositol depletion and GSK3 inhibition are inter-related.

Ion channel-transporter interactions

All living cells require membrane proteins that act as conduits for the regulated transport of ions, solutes and other small molecules across the cell membrane. Ion channels provide a pore that permits often rapid, highly selective and tightly regulated movement of ions down their electrochemical gradient. In contrast, active transporters can move moieties up their electrochemical gradient. The secondary active transporters (such as SLC superfamily solute transporters) achieve this by coupling uphill movement of the substrate to downhill movement of another ion, such as sodium. The primary active transporters (including H(+)/K(+)-ATPases and Na(+)/K(+)-ATPases) utilize ATP hydrolysis as an energy source to power uphill transport. It is well known that proteins in each of these classes work in concert with members of the other classes to ensure, for example, ion homeostasis, ion secretion and restoration of ion balance following action potentials. More recently, evidence is emerging of direct physical interaction between true ion channels, and some primary or secondary active transporters. Here, we review the first known members of this new class of macromolecular complexes that we term "chansporters", explore their biological roles and discuss the pathophysiological consequences of their disruption. We compare functional and/or physical interactions between the ubiquitous KCNQ1 potassium channel and various active transporters, and examine other newly discovered chansporter complexes that suggest we may be seeing the tip of the iceberg in a newly emerging signaling modality.

Effects of the potential lithium-mimetic, ebselen, on brain neurochemistry: a magnetic resonance spectroscopy study at 7 tesla

RATIONALE

Lithium is an effective treatment for bipolar disorder, but safety issues complicate its clinical use. The antioxidant drug, ebselen, may be a possible lithium-mimetic based on its ability to inhibit inositol monophosphatase (IMPase), an action which it shares with lithium.

OBJECTIVES

Our primary aim was to determine whether ebselen lowered levels of inositol in the human brain. We also assessed the effect of ebselen on other brain neurometabolites, including glutathione, glutamate, glutamine, and glutamate + glutamine (Glx)

METHODS

Twenty healthy volunteers were tested on two occasions receiving either ebselen (3600 mg over 24 h) or identical placebo in a double-blind, random-order, crossover design. Two hours after the final dose of ebselen/placebo, participants underwent proton magnetic resonance spectroscopy ((1)H MRS) at 7 tesla (T) with voxels placed in the anterior cingulate and occipital cortex. Neurometabolite levels were calculated using an unsuppressed water signal as a reference and corrected for individual cerebrospinal fluid content in the voxel.

RESULTS

Ebselen produced no effect on neurometabolite levels in the occipital cortex. In the anterior cingulate cortex, ebselen lowered concentrations of inositol (p = 0.028, Cohen's d = 0.60) as well as those of glutathione (p = 0.033, d = 0.58), glutamine (p = 0.024, d = 0.62), glutamate (p = 0.01, d = 0.73), and Glx (p = 0.001, d = 1.0).

CONCLUSIONS

The study suggests that ebselen produces a functional inhibition of IMPase in the human brain. The effect of ebselen to lower glutamate is consistent with its reported ability to inhibit the enzyme, glutaminase. Ebselen may have potential as a repurposed treatment for bipolar disorder.

Low unesterified:esterified eicosapentaenoic acid (EPA) plasma concentration ratio is associated with bipolar disorder episodes, and omega-3 plasma concentrations are altered by treatment

OBJECTIVES

Omega (n)-3 and n-6 polyunsaturated fatty acids (PUFAs) are molecular modulators of neurotransmission and inflammation. We hypothesized that plasma concentrations of n-3 PUFAs would be lower and those of n-6 PUFAs higher in subjects with bipolar disorder (BD) compared to healthy controls (HCs), and would correlate with symptom severity in subjects with BD, and that effective treatment would correlate with increased n-3 but lower n-6 PUFA levels. Additionally, we explored clinical correlations and group differences in plasma levels of saturated and monounsaturated fatty acids.

METHODS

This observational, parallel group study compared biomarkers between HCs (n = 31) and symptomatic subjects with BD (n = 27) when ill and after symptomatic recovery (follow-up). Plasma concentrations of five PUFAs [linoleic acid (LA), arachidonic acid (AA), alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA)], two saturated fatty acids (palmitic acid and stearic acid) and two monounsaturated fatty acids (palmitoleic acid and oleic acid) were measured in esterified (E) and unesterified (UE) forms. Calculated ratios included UE:E for the five PUFAs, ratios of n-3 PUFAs (DHA:ALA, EPA:ALA and EPA:DHA), and the ratio of n-6:n-3 AA:EPA. Comparisons of plasma fatty acid levels and ratios between BD and HC groups were made with Student t-tests, and between the BD group at baseline and follow-up using paired t-tests. Comparison of categorical variables was performed using chi-square tests. Pearson's r was used for bivariate correlations with clinical variables, including depressive and manic symptoms, current panic attacks, and psychosis.

RESULTS

UE EPA was lower in subjects with BD than in HCs, with a large effect size (Cohen's d = 0.86, p < 0.002); however, it was not statistically significant after correction for multiple comparisons. No statistically significant difference was seen in any plasma PUFA concentration between the BD and HC groups after Bonferroni correction for 40 comparisons, at p < 0.001. Neither depressive severity nor mania severity was correlated significantly with any PUFA concentration. Exploratory comparison showed lower UE:E EPA in the BD than the HC group (p < 0.0001). At follow-up in the BD group, UE, E DHA:ALA, and UE EPA:ALA were decreased (p < 0.002). Exploratory correlations of clinical variables revealed that mania severity and suicidality were positively correlated with UE:E EPA ratio, and that several plasma levels and ratios correlated with panic disorder and psychosis. Depressive severity was not correlated with any ratio. No plasma fatty acid level or ratio correlated with self-reported n-3 PUFA intake or use of medication by class.

CONCLUSIONS

A large effect size of reduced UE EPA, and a lower plasma UE:E concentration ratio of EPA in the symptomatic BD state may be important factors in vulnerability to a mood state. Altered n-3 PUFA ratios could indicate changes in PUFA metabolism concurrent with symptom improvement. Our findings are consistent with preclinical and postmortem data and suggest testing interventions that increase n-3 and decrease n-6 dietary PUFA intake.

Phosphatidylinositol-Phosphatidic Acid Exchange by Nir2 at ER-PM Contact Sites Maintains Phosphoinositide Signaling Competence

Sustained agonist-induced production of the second messengers InsP3 and diacylglycerol requires steady delivery of phosphatidylinositol (PtdIns) from its site of synthesis in the ER to the plasma membrane (PM) to maintain PtdIns(4,5)P2 levels. Similarly, phosphatidic acid (PtdOH), generated from diacylglycerol in the PM, has to reach the ER for PtdIns resynthesis. Here, we show that the Drosophila RdgB homolog, Nir2, a presumed PtdIns transfer protein, not only transfers PtdIns from the ER to the PM but also transfers PtdOH to the opposite direction at ER-PM contact sites. PtdOH delivery to the ER is impaired in Nir2-depleted cells, leading to limited PtdIns synthesis and ultimately to loss of signaling from phospholipase C-coupled receptors. These studies reveal a unique feature of Nir2, namely its ability to serve as a highly localized lipid exchanger that ensures that PtdIns synthesis is matched with PtdIns(4,5)P2 utilization so that cells maintain their signaling competence.

Inositol synthesis regulates the activation of GSK-3α in neuronal cells

The synthesis of inositol provides precursors of inositol lipids and inositol phosphates that are pivotal for cell signaling. Mood stabilizers lithium and valproic acid, used for treating bipolar disorder, cause cellular inositol depletion, which has been proposed as a therapeutic mechanism of action of both drugs. Despite the importance of inositol, the requirement for inositol synthesis in neuronal cells is not well understood. Here, we examined inositol effects on proliferation of SK-N-SH neuroblastoma cells. The essential role of inositol synthesis in proliferation is underscored by the findings that exogenous inositol was dispensable for proliferation, and inhibition of inositol synthesis decreased proliferation. Interestingly, the inhibition of inositol synthesis by knocking down INO1, which encodes inositol-3-phosphate synthase, the rate-limiting enzyme of inositol synthesis, led to the inactivation of GSK-3α by increasing the inhibitory phosphorylation of this kinase. Similarly, the mood stabilizer valproic acid effected transient decreases in intracellular inositol, leading to inactivation of GSK-3α. As GSK-3 inhibition has been proposed as a likely therapeutic mechanism of action, the finding that inhibition of inositol synthesis results in the inactivation of GSK-3α suggests a unifying hypothesis for mechanism of mood-stabilizing drugs. Inositol is an essential metabolite that serves as a precursor for inositol lipids and inositol phosphates. We report that inhibition of the rate-limiting enzyme of inositol synthesis leads to the inactivation of glycogen synthase kinase (GSK) 3α by increasing inhibitory phosphorylation of this kinase. These findings have implications for the therapeutic mechanisms of mood stabilizers and suggest that inositol synthesis and GSK 3α activity are intrinsically related.

Calcium signalling and psychiatric disease: bipolar disorder and schizophrenia

Neurons have highly developed Ca(2+) signalling systems responsible for regulating many neural functions such as the generation of brain rhythms, information processing and the changes in synaptic plasticity that underpins learning and memory. The signalling mechanisms that regulate neuronal excitability are particularly important for processes such as sensory perception, cognition and consciousness. The Ca(2+) signalling pathway is a key component of the mechanisms responsible for regulating neuronal excitability, information processing and cognition. Alterations in gene transcription are particularly important as they result in subtle alterations in the neuronal signalling mechanisms that have been implicated in many neural diseases. In particular, dysregulation of the Ca(2+) signalling pathway has been implicated in the development of some of the major psychiatric diseases such as bipolar disorder (BPD) and schizophrenia.

Molecular actions and clinical pharmacogenetics of lithium therapy

Mood disorders, including bipolar disorder and depression, are relatively common human diseases for which pharmacological treatment options are often not optimal. Among existing pharmacological agents and mood stabilizers used for the treatment of mood disorders, lithium has a unique clinical profile. Lithium has efficacy in the treatment of bipolar disorder generally, and in particular mania, while also being useful in the adjunct treatment of refractory depression. In addition to antimanic and adjunct antidepressant efficacy, lithium is also proven effective in the reduction of suicide and suicidal behaviors. However, only a subset of patients manifests beneficial responses to lithium therapy and the underlying genetic factors of response are not exactly known. Here we discuss preclinical research suggesting mechanisms likely to underlie lithium's therapeutic actions including direct targets inositol monophosphatase and glycogen synthase kinase-3 (GSK-3) among others, as well as indirect actions including modulation of neurotrophic and neurotransmitter systems and circadian function. We follow with a discussion of current knowledge related to the pharmacogenetic underpinnings of effective lithium therapy in patients within this context. Progress in elucidation of genetic factors that may be involved in human response to lithium pharmacology has been slow, and there is still limited conclusive evidence for the role of a particular genetic factor. However, the development of new approaches such as genome-wide association studies (GWAS), and increased use of genetic testing and improved identification of mood disorder patients sub-groups will lead to improved elucidation of relevant genetic factors in the future.

Plasma and Brain Pharmacokinetics of Previously Unexplored Lithium Salts

Despite its narrow therapeutic window, lithium is still regarded as the gold standard comparator and benchmark treatment for mania. Recent attempts to find new drugs with similar therapeutic activities have yielded new chemical entities. However, these potential new drugs have yet to match the many bioactivities attributable to lithium's efficacy for the treatment of neuropsychiatric diseases. Consequently, an intense effort for re-engineering lithium therapeutics using crystal engineering is currently underway. We sought to improve the likelihood of success of these endeavors by evaluating the pharmacokinetics of previously unexplored lithium salts with organic anions (lithium salicylate and lithium lactate). We report that these lithium salts exhibit profoundly different pharmacokinetics compared to the more common FDA approved salt, lithium carbonate, in rats. Remarkably, lithium salicylate produced elevated plasma and brain levels of lithium beyond 48 hours post-dose without the sharp peak that contributes to the toxicity problems of current lithium therapeutics. These findings could be important for the development of the next generation of lithium therapeutics.

Improving lithium therapeutics by crystal engineering of novel ionic cocrystals

Current United States Food and Drug Administration (FDA)-approved lithium salts are plagued with a narrow therapeutic window. Recent attempts to find alternative drugs have identified new chemical entities, but lithium's polypharmacological mechanisms for treating neuropsychiatric disorders are highly debated and are not yet matched. Thus, re-engineering current lithium solid forms in order to optimize performance represents a low cost and low risk approach to the desired therapeutic outcome. In this contribution, we employed a crystal engineering strategy to synthesize the first ionic cocrystals (ICCs) of lithium salts with organic anions. We are unaware of any previous studies that have assessed the biological efficacy of any ICCs, and encouragingly we found that the new speciation did not negatively affect established bioactivities of lithium. We also observed that lithium ICCs exhibit modulated pharmacokinetics compared to lithium carbonate. Indeed, the studies detailed herein represent an important advancement in a crystal engineering approach to a new generation of lithium therapeutics.

Second messenger/signal transduction pathways in major mood disorders: moving from membrane to mechanism of action, part II: bipolar disorder

In this second of two articles on second messenger/signal transduction cascades in major mood disorders, we will review the evidence in support of intracellular dysfunction and its rectification in the etiopathogenesis and treatment of bipolar disorder (BD). The importance of these cascades is highlighted by lithium's (the gold standard in BD psychopharmacology) ability to inhibit multiple critical loci in second messenger/signal transduction cascades including protein kinase C (involved in the IP3/PIP2 pathway) and GSK-3β (canonically identified in the Wnt/Fz/Dvl/GSK-3β cascade). As a result, and like major depressive disorder (MDD), more recent pathophysiological studies and rational therapeutic targets have been directed at these and other intracellular mediators. Even in the past decade, intracellular dysfunction in numerous neuroprotective/apoptotic cascades appears important in the pathophysiology and may be a future target for pharmacological interventions of BD.

Lithium: the pharmacodynamic actions of the amazing ion

Lithium has been used for the treatment of mood disorders for over 60 years, yet the exact mechanisms by which it exerts its therapeutic effects remain unclear. Two enzymatic chains or pathways emerge as targets for lithium: inositol monophosphatase within the phosphatidylinositol signalling pathway and the protein kinase glycogen synthase kinase 3. Lithium inhibits these enzymes through displacing the normal cofactor magnesium, a vital regulator of numerous signalling pathways. Here we provide an overview of evidence, supporting a role for the inhibition of glycogen synthase kinase 3 and inositol monophosphatase in the pharmacodynamic actions of lithium. We also explore how inhibition of these enzymes by lithium can lead to downstream effects of clinical relevance, both for mood disorders and neurodegenerative diseases. Establishing a better understanding of lithium's mechanisms of action may allow the development of more effective and more tolerable pharmacological agents for the treatment of a range of mental illnesses, and provide clearer insight into the pathophysiology of such disorders.

Treatment of trauma with lithium to forestall the development of posttraumatic stress disorder by pharmacological induction of a mild transient amnesia

Posttraumatic stress disorder (PTSD) is a severe anxiety disorder that develops after exposure to trauma. Symptoms include persistent reexperiencing, persistent avoidance, persistent numbing, and persistent hyperarousal. Subsequent to trauma exposure, the onset of symptoms of an acute stress reaction can typically develop over varying amounts of time from days to months. Current pharmacotherapies for PTSD are available after symptoms manifest, and primarily consist of selective serotonin reuptake inhibitor (SSRI) antidepressants. There are currently no FDA approved pharmacological interventions available for the treatment of acutely traumatized individuals to forestall the development of PTSD after trauma and prior to the onset of symptoms. A prominent model of PTSD developed by Roger Pitman attributes the pathogenesis of PTSD to over-consolidated traumatic memories that are mediated by endogenous stress hormones released with trauma and after trauma. The molecular processes of memory consolidation in neurons are mediated by intracellular signaling pathways. One secondary messenger signaling pathway with a putative role in long-term potentiation (LTP) is the inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) secondary messenger system. Lithium, a treatment for bipolar disorder, and a pharmacotherapy that is associated with inducing transient impairments in cognition, memory, and learning, is an inhibitor of inositol monophosphatase (IMP), an enzyme in the IP3 and DAG secondary messenger pathway. I am advancing the hypothesis that the administration of lithium for a brief interval to traumatized individuals at risk for PTSD within the time period after trauma and prior to the onset of symptoms could potentially forestall the development of PTSD by disrupting LTP. I am proposing that this treatment will reduce the incidence of PTSD and reduce the severity of symptoms in those who eventually develop PTSD.

Synaptic polarity depends on phosphatidylinositol signaling regulated by myo-inositol monophosphatase in Caenorhabditis elegans

Although neurons are highly polarized, how neuronal polarity is generated remains poorly understood. An evolutionarily conserved inositol-producing enzyme myo-inositol monophosphatase (IMPase) is essential for polarized localization of synaptic molecules in Caenorhabditis elegans and can be inhibited by lithium, a drug for bipolar disorder. The synaptic defect of IMPase mutants causes defects in sensory behaviors including thermotaxis. Here we show that the abnormalities of IMPase mutants can be suppressed by mutations in two enzymes, phospholipase Cβ or synaptojanin, which presumably reduce the level of membrane phosphatidylinositol 4,5-bisphosphate (PIP₂). We also found that mutations in phospholipase Cβ conferred resistance to lithium treatment. Our results suggest that reduction of PIP₂ on plasma membrane is a major cause of abnormal synaptic polarity in IMPase mutants and provide the first in vivo evidence that lithium impairs neuronal PIP₂ synthesis through inhibition of IMPase. We propose that the PIP₂ signaling regulated by IMPase plays a novel and fundamental role in the synaptic polarity.

Inhibitory effect of lithium on nucleotide hydrolysis and acetylcholinesterase activity in zebrafish (Danio rerio) brain

Lithium has been used as an effective antimanic drug in humans and it is well known for its effects on neuropsychiatric disorders and neuronal communication. ATP and adenosine are important signaling molecules, and most nerves release ATP as a fast co-transmitter together with classical neurotransmitters such as acetylcholine. In this study, we evaluated the in vitro and in vivo effects of lithium on acetylcholinesterase and ectonucleotidase activities in zebrafish brain. There was a significant inhibition of ADP hydrolysis after in vivo exposure to lithium at 5 and 10 mg/l (27.6% and 29% inhibition, respectively), whereas an inhibitory effect was observed for AMP hydrolysis only at 10 mg/l (30%). Lithium treatment in vivo also significantly decreased the acetylcholinesterase activity at 10 mg/l (21.9%). The mRNA transcript levels of the genes encoding for these enzymes were unchanged after exposure to 5 and 10 mg/l lithium chloride. In order to directly evaluate the action of lithium on enzyme activities, we tested the in vitro effect of lithium at concentrations ranging from 1 to 1000 μM. There were no significant changes in zebrafish brain ectonucleotidase and acetylcholinesterase activities at all concentrations tested in vitro. Our findings show that lithium treatment can alter ectonucleotidase and acetylcholinesterase activities, which may regulate extracellular nucleotide, nucleoside, and acetylcholine levels. These data suggest that cholinergic and purinergic signaling may be targets of the pharmacological effects induced by this compound.

Second-tier natural antidepressants: review and critique

The use of Complementary and Alternative Medicine (CAM) for physical and mental problems has increased significantly in the US over the past two decades, and depression is one of the leading indications for the use of CAM. This article reviews some of the lesser-known natural products with potential psychiatric applications that are starting to emerge with some scientific and clinical evidence and may constitute a next wave of natural antidepressants: Rhodiola rosea, chromium, 5-Hydroxytryptophan (5-HTP) and inositol. Background information, efficacy data, proposed mechanisms of action, recommended doses, side effects, and precautions are reviewed. We found some encouraging data for the use of these natural products in specific populations of depressed patients. R. rosea is an adaptogen plant that can be especially helpful in treating asthenic or lethargic depression, and may be combined with conventional antidepressants to alleviate some of their common side effects. Chromium has a beneficial effect on eating-related atypical symptoms of depression, and may be a valuable agent in treating atypical depression and seasonal affective disorder. Inositol may be useful in the treatment of bipolar depression when combined with mood stabilizers. Evidence for the clinical efficacy of 5-HTP is also promising but still preliminary. Although more well-designed and larger controlled studies are needed before any substantive conclusions can be drawn, the available evidence is compelling and these natural products deserve further investigation as a possibly significant addition to the antidepressant armamentarium.

Is prenatal myo-inositol deficiency a mechanism of CNS injury in galactosemia?

Classic Galactosemia due to galactose-1-phosphate uridyltransferase (GALT) deficiency is associated with apparent diet-independent complications including cognitive impairment, learning problems and speech defects. As both galactose-1-phosphate and galactitol may be elevated in cord blood erythrocytes and amniotic fluid despite a maternal lactose-free diet, endogenous production of galactose may be responsible for the elevated fetal galactose metabolites, as well as postnatal CNS complications. A prenatal deficiency of myo-inositol due to an accumulation of both galactose-1- phosphate and galactitol may play a role in the production of the postnatal CNS dysfunction. Two independent mechanisms may result in fetal myo-inositol deficiency: competitive inhibition of the inositol monophosphatase1 (IMPA1)-mediated hydrolysis of inositol monophosphate by high galactose-1- phosphate levels leading to a sequestration of cellular myo-inositol as inositol monophosphate and galactitol-induced reduction in SMIT1-mediated myo-inositol transport. The subsequent reduction of myo-inositol within fetal brain cells could lead to inositide deficiencies with resultant perturbations in calcium and protein kinase C signaling, the AKT/mTOR/ cell growth and development pathway, cell migration, insulin sensitivity, vescular trafficking, endocytosis and exocytosis, actin cytoskeletal remodeling, nuclear metabolism, mRNA export and nuclear pore complex regulation, phosphatidylinositol-anchored proteins, protein phosphorylation and/or endogenous iron "chelation". Using a knockout animal model we have shown that a marked deficiency of myo-inositol in utero is lethal but the phenotype can be rescued by supplementing the drinking water of the pregnant mouse. If myo-inositol deficiency is found to exist in the GALT-deficient fetal brain, then the use of myo-inositol to treat the fetus via oral supplementation of the pregnant female may warrant consideration.

Investigation of the H+–myo-inositol transporter (HMIT) as a neuronal regulator of phosphoinositide signalling

Phosphoinositide signalling regulates a series of important neuronal processes that are thought to be altered in mood disorders. Furthermore, mood-stabilizing drugs inhibit key enzymes that regulate phosphoinositide production and alter neuronal growth cone morphology in an inositol-reversible manner. Inositol is taken up by neurons from the extracellular fluid, presumably via membrane transporters; it can also be synthesized by the enzyme MIP-synthase (myo-inositol-1-phosphate synthase) and, in addition, it is generated by inositol phospholipid hydrolysis. The neuronal-specific HMIT (H+–myo-inositol transporter) represents a potential regulator of inositol signalling in neurons that warrants further investigation.

Quantitative determination of free glycerol and myo-inositol from plasma and tissue by high-performance liquid chromatography

A high-performance liquid chromatographic method that accurately measures glycerol and myo-inositol from plasma and tissue is described. The method incorporates a pre-column derivatization reaction using aqueous extracts with benzoyl chloride as a modifying agent. The benzoylated derivatives are isolated by HPLC using reversed-phase gradient chromatography and quantified via absorbance detection at 231 nm. The benzoylated derivatives of glycerol and myo-inositol are well resolved from other known carbohydrates, internal standard and other contaminants encountered within samples and during incubation. The benzoylation of these analytes reach a maximum between 3.5 and 6 h of incubation and are stable for at least 24 days at 4 degrees C. The limit of quantization (LOQ) of glycerol was equal to 2.5 nmol/ml plasma and 6.4 nmol/g tissue and the LOQ of myo-inositol was 1.8 nmol/ml plasma and 3.6 nmol/g tissue. Incubation of known standards and samples with benzoyl chloride at 40 degrees C for 4 h showed fully benzoylated products as determined by mass spectral analysis. Calibration curves were linear between 2.7 and 174 nmol for glycerol and 1.4-89 nmol for myo-inositol. Comparison of tissue and plasma concentrations of glycerol and myo-inositol found using this method are in good agreement with other reported values using other techniques.

Adenylate cyclase regulates elongation of mammalian primary cilia

The primary cilium is a non-motile microtubule-based structure that shares many similarities with the structures of flagella and motile cilia. It is well known that the length of flagella is under stringent control, but it is not known whether this is true for primary cilia. In this study, we found that the length of primary cilia in fibroblast-like synoviocytes, either in log phase culture or in quiescent state, was confined within a range. However, when lithium was added to the culture to a final concentration of 100 mM, primary cilia of synoviocytes grew beyond this range, elongating to a length that was on average approximately 3 times the length of untreated cilia. Lithium is a drug approved for treating bipolar disorder. We dissected the molecular targets of this drug, and observed that inhibition of adenylate cyclase III (ACIII) by specific inhibitors mimicked the effects of lithium on primary cilium elongation. Inhibition of GSK-3beta by four different inhibitors did not induce primary cilia elongation. ACIII was found in primary cilia of a variety of cell types, and lithium treatment of these cell types led to their cilium elongation. Further, we demonstrate that different cell types displayed distinct sensitivities to the lithium treatment. However, in all cases examined primary cilia elongated as a result of lithium treatment. In particular, two neuronal cell types, rat PC-12 adrenal medulla cells and human astrocytes, developed long primary cilia when lithium was used at or close to the therapeutic relevant concentration (1-2 mM). These results suggest that the length of primary cilia is controlled, at least in part, by the ACIII-cAMP signaling pathway.

The role of lithium in the treatment of bipolar disorder: convergent evidence for neurotrophic effects as a unifying hypothesis

Lithium has been and continues to be the mainstay of bipolar disorder (BD) pharmacotherapy for acute mood episodes, switch prevention, prophylactic treatment, and suicide prevention. Lithium is also the definitive proof-of-concept agent in BD, although it has recently been studied in other psychoses as well as diverse neurodegenerative disorders. Its neurotrophic effects can be viewed as a unifying model to explain several integrated aspects of the pathophysiology of mood disorders and putative therapeutics for those disorders. Enhancing neuroprotection (which directly involves neurotrophic effects) is a therapeutic strategy intended to slow or halt the progression of neuronal loss, thus producing long-term benefits by favorably influencing outcome and preventing either the onset of disease or clinical decline. The present article: (i) reviews what has been learned regarding lithium's neurotrophic effects since Cade's original studies with this compound; (ii) presents human data supporting the presence of cellular atrophy and death in BD as well as neurotrophic effects associated with lithium in human studies; (iii) describes key direct targets of lithium involved in these neurotrophic effects, including neurotrophins, glycogen synthase kinase 3 (GSK-3), and mitochondrial/endoplasmic reticulum key proteins; and (iv) discusses lithium's neurotrophic effects in models of apoptosis and excitotoxicity as well as its potential neurotrophic effects in models of neurological disorders. Taken together, the evidence reviewed here suggests that lithium's neurotrophic effects in BD are an example of an old molecule acting as a new proof-of-concept agent. Continued work to decipher lithium's molecular actions will likely lead to the development of not only improved therapeutics for BD, but to neurotrophic enhancers that could prove useful in the treatment of many other illnesses.

Lithium increases synapse formation between hippocampal neurons by depleting phosphoinositides

The mood-stabilizing effects of lithium are well documented, although its mechanism of action remains unknown. Increases in gray matter volume detected in patients with bipolar disorder who were treated with lithium suggest that changes in the number of synapses might underlie its therapeutic effects. We investigated the effects of lithium on the number of synaptic connections between hippocampal neurons in culture. Confocal imaging of neurons expressing postsynaptic density protein 95 fused to green fluorescent protein (PSD95-GFP) enabled visualization of synaptic sites. PSD95-GFP fluorescent puncta represented functional synapses, and lithium (4 h, 5 mM) increased their number by 150 +/- 12%. The increase was time- and concentration-dependent (EC(50) = 1.0 +/- 0.6 mM). Lithium induced a parallel increase in the presynaptic marker synaptophysin-GFP. Valproic acid, another mood stabilizer, also increased the number of fluorescent puncta at a clinically relevant concentration. Inhibition of postsynaptic glutamate receptors or presynaptic inhibition of neurotransmitter release significantly reduced lithium-induced synapse formation, indicating that glutamatergic synaptic transmission was required. Pretreatment with exogenous myo-inositol inhibited synapse formation, demonstrating that depletion of inositol was necessary to increase synaptic connections. In contrast, inhibition of glycogen synthase kinase 3beta did not mimic lithium-induced synapse formation. Pharmacological and lipid reconstitution experiments showed that new synapses formed as a result of depletion of phosphatidylinositol-4-phosphate rather than a build-up of polyphosphoinositides or changes in the activity of phospholipase C, protein kinase C, or phosphatidylinositol-3-kinase. Increased synaptic connections may underlie the mood-stabilizing effects of lithium in patients with bipolar disorder and could contribute to the convulsions produced by excessive doses of this drug.

Mode of action of mood stabilizers: is the arachidonic acid cascade a common target?

Bipolar disorder is a major medical, social and economic burden worldwide. However, the mechanisms of action of effective antibipolar disorder drugs remain elusive. In this paper, we review studies using a neuropharmacological approach in unanesthetized rats, combined with kinetic, biochemical and molecular biology techniques, showing that chronic administration of three Food and Drug Administration-approved mood stabilizers (lithium, valproate and carbamazepine) at therapeutically relevant doses, selectively target the brain arachidonic acid (AA) cascade. Whereas chronic lithium and carbamazepine decrease the binding activity of activator protein-2 and in turn the transcription, translation and activity of its AA-selective calcium-dependent phospholipase A(2) gene product, valproate appears to be a non-competitive inhibitor of long-chain acyl-CoA synthetase. The net overlapping effects of the three drugs are decreased turnover of AA but not of docosahexaenoic acid in rat brain phospholipids, and decreased brain cyclooxygenase-2 and prostaglandin E(2). Although these observations support the hypothesis proposed by Rapoport and colleagues that the AA cascade is a common target of mood stabilizers, this hypothesis is not necessarily exclusive of other targets. Targeting the AA cascade with drugs or diet may be a useful therapeutic approach in bipolar disorder, and examining the AA cascade in patients might help in better understanding the disease.

Acute dextro-amphetamine administration does not alter brain myo-inositol levels in humans and animals: MRS investigations at 3 and 18.8 T

The pathophysiological underpinnings of bipolar disorder are not fully understood. However, they may be due in part to changes in the phosphatidylinositol second messenger system (PI-cycle) generally, or changes in myo-inositol concentrations more specifically. Dextro-amphetamine has been used as a model for mania in several human studies as it causes similar subjective and physiological symptoms. We wanted to determine if dextro-amphetamine altered myo-inositol concentrations in vivo as it would clearly define a mechanism linking putative changes in the PI-cycle to the subjective psychological changes seen with dextro-amphetamine administration. Fifteen healthy human volunteers received a baseline scan, followed by second scan 75 min after receiving a 25 mg oral dose of dextro-amphetamine. Stimulated echo proton magnetic resonance spectroscopy (MRS) scans were preformed at 3.0 Tesla (T) in the dorsal medial prefrontal cortex (DMPFC). Metabolite data were adjusted for tissue composition and analyzed using LCModel. Twelve adult male rats were treated acutely with a 5-mg/kg intraperitoneal dose of dextro-amphetamine. After 1 h rats were decapitated and the brains were rapidly removed and frozen until dissection. Rat brains were dissected into frontal, temporal, and occipital cortical areas, as well as hippocampus. Tissue was analyzed using a Varian 18.8 T spectrometer. Metabolites were identified and quantified using Chenomx Profiler software. The main finding in the present study was that myo-inositol concentrations in the DMPFC of human volunteers and in the four rat brain regions were not altered by acute dextro-amphetamine. While it remains possible that the PI-cycle may be involved in the pathophysiology of bipolar disorder, it is not likely that the subjective and physiological of dextro-amphetamine are mediated, directly or indirectly, via alternations in myo-inositol concentrations.

Neurobiology of bipolar disorder

Bipolar disorder is one of the most severely debilitating of all medical illnesses. It can lead to significant suffering for patients and their families, limit functioning and workplace productivity, and with its risks of increased morbidity and mortality, it is increasingly recognized as a major public health problem. For a large number of patients, outcomes are poor. Patients with bipolar disorder generally experience high rates of relapse, a chronic recurrent course, lingering residual symptoms, functional impairment, psychosocial disability and diminished well-being. Despite this, little is known about the specific pathophysiology of bipolar disorder. A better understanding of the neurobiological underpinnings of this condition, informed by preclinical and clinical research, will be essential for the future development of specific targeted therapies that are more effective, achieve their effects more quickly and are better tolerated than currently available treatments. An abundance of research has implicated specific neuroendocrine, neurotransmitter and intracellular signaling systems in the pathophysiology and treatment of this illness. More recently, genetic association studies have identified numerous genes that confer vulnerability to the disorder, many of which are known to function in the signaling pathways previously identified as relevant to the etiology of the illness. In this article, we will review current knowledge regarding the neurotransmitter systems, signaling networks, neuroendocrine systems and genetics of bipolar disorder; all of these allow insight into the mechanism of illness and thus offer potential novel directions for the development of novel therapeutics.

IMPA1 is essential for embryonic development and lithium-like pilocarpine sensitivity

Lithium has been the standard pharmacological treatment for bipolar disorder over the last 50 years; however, the molecular targets through which lithium exerts its therapeutic effects are still not defined. We characterized the phenotype of mice with a dysfunctional IMPA1 gene (IMPA1-/-) to study the in vivo physiological functions of IMPA1, in general, and more specifically its potential role as a molecular target in mediating lithium-dependent physiological effects. Homozygote IMPA1-/- mice died in utero between days 9.5 and 10.5 post coitum (p.c.) demonstrating the importance of IMPA1 in early embryonic development. Intriguingly, the embryonic lethality could be reversed by myo-inositol supplementation via the pregnant mothers. In brains of adult IMPA1-/- mice, IMPase activity levels were found to be reduced (up to 65% in hippocampus); however, inositol levels were not found to be altered. Behavioral analysis of the IMPA1-/- mice indicated an increased motor activity in both the open-field test and the forced-swim test as well as a strongly increased sensitivity to pilocarpine-induced seizures, the latter supporting the idea that IMPA1 represents a physiologically relevant target for lithium. In conclusion the IMPA1-/- mouse represents a novel model to study inositol homeostasis, and indicates that genetic inactivation of IMPA1 can mimic some actions of lithium.

Calcium-sensing receptor antagonism or lithium treatment ameliorates aminoglycoside-induced cell death in renal epithelial cells

The aminoglycoside antibiotic gentamicin elicits proximal tubular toxicity and cell death. In calcium-sensing receptor (CaR)-transfected HEK-293 (CaR-HEK) cells and CaR-expressing proximal tubule-derived opossum kidney (OK) cells, chronic gentamicin treatment elicits dose-dependent, caspase-mediated apoptotic cell death. Here we investigated whether the renal cell toxicity of the CaR agonist gentamicin could be prevented by CaR antagonism or by lithium cotreatment which may interfere with receptor-mediated signalling. Chronic treatment of OK and CaR-HEK cells with low concentrations of gentamicin elicited cell death, an effect that was ameliorated by cotreatment with the CaR negative allosteric modulator (calcilytic) NPS-89636. This calcilytic also attenuated CaR agonist-induced ERK activation in these cells. In addition, 1 mM LiCl, equivalent to its therapeutic plasma concentration, also inhibited gentamicin-induced toxicity in both cell types. This protective effect of lithium was not due to the disruption of phosphatidylinositol-mediated gentamicin uptake as the cellular entry of Texas red-conjugated gentamicin into OK and CaR-HEK cells was unchanged by lithium treatment. However, the protective effect of lithium was mimicked by glycogen synthase 3beta inhibition. Together, these data implicate CaR activation and a lithium-inhibitable signalling pathway in the induction of cell death by gentamicin in renal epithelial cells in culture.