Chronic lithium and sodium valproate both decrease the concentration of myo-inositol and increase the concentration of inositol monophosphates in rat brain

Human MIP synthase splice variants in bipolar disorder

OBJECTIVES

Alternative splicing allows the production of multiple gene products with different functions from a given sequence, affecting cellular function control. Tissue-specific splicing is most prevalent in the brain. We therefore investigate whether splice variants contribute to complex psychiatric disorders. A database search suggested that the myo-inositol-1-phosphate (MIP) synthase gene, possibly involved in pathophysiology of bipolar disorder, has splice variants.

METHODS

Human RNA was purified from lymphocytes and postmortem brain. MIP synthase alternative splice variants were amplified using reverse transcription-polymerase chain reaction.

RESULTS

The bioinformatics finding was confirmed in both tissues. No difference in lymphocyte MIP synthase mRNA splice-variant levels was found between bipolar patients and controls. However, patients with family history of a major psychiatric disorder had significantly higher levels of the variant lacking exons 3 and 4 versus patients with no family history and controls.

CONCLUSIONS

As alternative splicing may be a mechanism by which the approximately 30,000 genes are amplified in mammalian brain, further studies with other candidate genes for psychiatric disorders are needed.

Valproic acid activates notch-1 signaling and regulates the neuroendocrine phenotype in carcinoid cancer cells

Carcinoid tumors are neuroendocrine malignancies that frequently metastasize and secrete hormones that cause debilitating symptoms in patients. In this study we report the effects of valproic acid (VPA), a drug long used for the treatment of epilepsy, on the growth and neuroendocrine phenotype of human carcinoid cancer cells. VPA treatment of gastrointestinal and pulmonary carcinoid cells resulted in a dose-dependent inhibition of cancer cell growth. Western blot analysis revealed degradation of cyclin D1 and an increase in cyclin-dependent kinases p21 and p27 with VPA treatment. Flow cytometry confirmed that the mechanism of VPA-induced growth inhibition is G(1) phase cell cycle arrest. Furthermore, VPA suppressed expression of the neuroendocrine tumor marker chromogranin A. In addition to these effects, VPA also increased levels of full-length Notch-1 and the active Notch-1 intracellular domain. Luciferase reporter assays incorporating the centromere-binding factor 1 (CBF-1) binding site and the achaete-scute complex-like 1 (ASCL-1) promoter confirmed the functional activity of VPA-induced Notch-1. Transfection of Notch-1 small-interfering RNA into carcinoid tumor cells blocked the effects of VPA on Notch-1 activation, ASCL-1 suppression, p21 induction, and cell growth inhibition. VPA also suppressed growth of carcinoid tumors in vivo in a mouse tumor xenograft experiment. These findings confirm the important role of Notch-1 in regulating the growth and neuroendocrine phenotype of carcinoid tumor cells. On the basis of this study, a clinical trial of VPA for patients with advanced carcinoid cancer will be conducted. Disclosure of potential conflicts of interest is found at the end of this article.

Unlike lithium, anticonvulsants and antidepressants do not alter rat brain myo-inositol

Lithium is the first-line in bipolar disorder treatment. Lithium's clinical efficacy might be due to its inhibition of myo-inositol turnover in the phosphatidylinositol second messenger system. This study aimed to determine whether this action can extend to antidepressants and anticonvulsants also used to treat bipolar symptoms. Male rats were treated for 2 weeks with an intraperitoneal injection of phenelzine, fluoxetine, desipramine, carbamazepine, lamotrigine, sodium valproate or vehicle. Brains were dissected and myo-inositol concentrations were analyzed using high-field nuclear magnetic resonance spectroscopy at 18.8 T and quantified using Chenomx Profiler software. Brain regions assessed included the prefrontal, temporal and occipital cortical areas as well as the hippocampus. The main finding is that contrary to lithium, the anticonvulsants and antidepressants do not alter brain myo-inositol concentration. This suggests that these agents might work via a mechanism that is not centered on changes in myo-inositol concentration.

The pharmacogenetics of lithium response depends upon clinical co-morbidity

BACKGROUND

Based on results from randomized, controlled clinical trials, lithium monotherapy or lithium with the addition of an antipsychotic remains a first-line treatment option for both acute and long-term mood stabilization in bipolar mania. However, response to lithium is poor in bipolar patients who exhibit clinical characteristics such as rapid cycling and mixed manic states, suggesting that they may have a biologically and genetically distinct form of bipolar disorder. A test that could predict response to lithium based upon genetic factors would have significant clinical value.

METHODS

Eight clinical characteristics were assessed in 92 lithium responders and 92 nonresponders; all probands were from families recruited for linkage studies. Lithium response was rated retrospectively from a standardized interviews and medical records. Eight candidate genes were selected from those reported to be associated with susceptibility to illness, lithium response, or lithium mechanism of action. Sixty-seven single nucleotide polymorphisms (SNPs) were genotyped in these subjects and analyzed for association with the defined clinical characteristics.

RESULTS

Using q-value analysis for multiplicity correction, we found significant interactions between lithium response and SNPs (rs1387923 and rs1565445) in the gene encoding neurotrophic tyrosine kinase receptor type 2 (NTRK2) and suicidal ideation, and between SNP rs2064721 in the gene encoding inositol polyphosphate-1-phosphatase (INPP1) and post-traumatic stress disorder.

CONCLUSION

These data support the idea that response to lithium has a multi-genetic etiology dependent upon manifestations of other clinical co-diagnoses.

Specificity of mood stabilizer action on neuronal growth cones

OBJECTIVES

Lithium, valproic acid (VPA) and carbamazepine (CBZ) are commonly used mood stabilizers, but their therapeutic mechanism is unclear. These drugs all cause the same morphological effects on postnatal rat neuronal dorsal root ganglia (DRG) growth cones via an inositol-reversible mechanism. However, due to limitations in earlier analysis, the effects of combining drugs, drug specificity and inositol stereoisomer specificity are unknown. We devised an improved analytical method to address these issues.

METHODS

Dorsal root ganglia explants were cultured individually and incubated with combinations of psychotropic drugs and inositol stereoisomers. We recorded axonal growth cone morphology and calculated growth cone area per a modified method described by Williams et al. (Nature 2002; 417: 292-295). Statistically significant changes in area were calculated using non-parametric statistical testing.

RESULTS

(i) Lithium and VPA showed an additive effect on growth cone spreading. (ii) Among eight additional psychotropic drugs to those previously tested, only imipramine and chlorpromazine altered DRG growth cone morphology. As this effect was not reversed by myo-inositol, it arises from a different mechanism to the mood stabilizers lithium, VPA and CBZ. (iii) Myo-inositol, but not scyllo- or epi-inositol, causes a significant reversal of the lithium effect on the growth cones spreading, consistent with the inositol depletion hypothesis.

CONCLUSIONS

These results show that lithium, VPA and CBZ are unique in causing altered neuronal morphology via myo-inositol depletion.

The effect of sodium valproate on proton MRS visible neurochemical concentrations

The effect of the antiepileptic medication sodium valproate (VPA) on the concentrations of cerebral metabolites was studied longitudinally in ten patients with epilepsy using proton magnetic resonance spectroscopy (MRS). Myo-inositol was found to be lower while taking VPA, although no relationship between the change in metabolite concentration, VPA dose or seizure control was observed. MRS findings should be interpreted in the light of administered medications.

Neuroprotective effects of regulators of the glycogen synthase kinase-3beta signaling pathway in a transgenic model of Alzheimer's disease are associated with reduced amyloid precursor protein phosphorylation

The glycogen synthase kinase-3beta (GSK3beta) pathway plays an important role in mediating neuronal fate and synaptic plasticity. In Alzheimer's disease (AD), abnormal activation of this pathway might play an important role in neurodegeneration, and compounds such as lithium that modulate GSK3beta activity have been shown to reduce amyloid production and tau phosphorylation in amyloid precursor protein (APP) transgenic (tg) mice. However, it is unclear whether regulation of GSK3beta is neuroprotective in APP tg mice. In this context, the main objective of the present study was to determine whether pharmacological or genetic manipulations that block the GSK3beta pathway might ameliorate the neurodegenerative alterations in APP tg mice and to better understand the mechanisms involved. For this purpose, two sets of experiments were performed. First, tg mice expressing mutant human APP under the Thy1 promoter (hAPP tg) were treated with either lithium chloride or saline alone. Second, hAPP tg mice were crossed with GSK3beta tg mice, in which overexpression of this signaling molecule results in a dominant-negative (DN) effect with inhibition of activity. hAPP tg mice that were treated with lithium or that were crossed with DN-GSK3beta tg mice displayed improved performance in the water maze, preservation of the dendritic structure in the frontal cortex and hippocampus, and decreased tau phosphorylation. Moreover, reduced activation of GSK3beta was associated with decreased levels of APP phosphorylation that resulted in decreased amyloid-beta production. In conclusion, the present study showed that modulation of the GSK3beta signaling pathway might also have neuroprotective effects in tg mice by regulating APP maturation and processing and further supports the notion that GSK3beta might be a suitable target for the treatment of AD.

Intracellular signaling pathways pave roads to recovery for mood disorders

Mood disorders, including major depression and bipolar disorder, remain a major unmet medical need as current antidepressant and mood stabilizing therapies require chronic treatment for efficacy and are not effective in all patients. Multiple deficits, including cell atrophy and loss, have been observed in limbic and cortical brain regions of patients with mood disorders and in stressed animals. It is thought that antidepressant and mood stabilizing medications restore these deficits by reestablishing proper patterns of gene expression and function. In support of this hypothesis, numerous changes in gene expression and activity have been observed in limbic and cortical brain regions of mood disorder patients, and thymoleptic therapies have been shown to reciprocally regulate many of these changes. These findings have implicated four main signaling pathways in the pathophysiology and/or treatment of mood disorders, namely the cyclic-AMP, phosphoinositol, mitogen-activated protein kinase, and glycogen synthase kinase signaling cascades. Below we review this literature, and discuss potential targets for novel antidepressant and mood stabilizing drug design that are highlighted by these findings.

Lithium alters regional rat brain myo-inositol at 2 and 4 weeks: an ex-vivo magnetic resonance spectroscopy study at 18.8 T

Lithium has been the mainstay of treatment for bipolar disorder. Early studies suggest that lithium acts via inositol depletion. This study assesses the effect of 1, 2 and 4 weeks of lithium treatment on myo-inositol concentrations across several brain regions. Thirty-six Sprague-Dawley rats were treated for 2 weeks with an intraperitoneal injection of either 1 mmol/kg/day, twice daily lithium chloride (n=18) or placebo (2 ml/kg of saline) (n=18). The rats were separated into three groups: 1 week, 2 weeks and 4 weeks. Brains were dissected into prefrontal, temporal and occipital cortical areas, as well as hippocampus, and analyzed at 18.8 T. Myo-inositol was quantified using the Chenomx Profiler software. Lithium did not alter myo-inositol concentrations at 1 week. A significant reduction exists in myo-inositol concentrations in lithium-treated rats at 2 and 4 weeks, across all four brain regions. Studies suggest brain region-specific alterations in myo-inositol concentrations among bipolar patients. Our findings suggest that lithium-induced reduction of myo-inositol is more global.

SMIT1 haploinsufficiency causes brain inositol deficiency without affecting lithium-sensitive behavior

Two leading hypotheses to explain lithium action in bipolar disorder propose either inositol depletion or inhibition of GSK-3 as mechanisms of action. Behavioral effects of lithium are mimicked in Gsk-3beta+/- mice, but the contribution of inositol depletion to these behaviors has not been tested. According to the inositol depletion hypothesis, lithium-sensitive behavior is secondary to impaired phosphatidylinositol synthesis caused by inositol deficiency. By disrupting the sodium myo-inositol transporter1 gene, SMIT1, we show that depletion of brain myo-inositol in SMIT1+/- mice has no effect on lithium-sensitive behavior. These findings, taken together with our previous work showing that SMIT-/- mice have an even greater depletion of inositol in brain with no reduction in phosphatidylinositol levels, are difficult to reconcile with the current formulation of the inositol depletion hypothesis.

1H magnetic resonance spectroscopy at 3 T in cryptogenic and mesial temporal lobe epilepsy

The objectives of this work were to compare concentrations of N-acetylaspartate (NAA), glutamate (Glu), glutamine (Gln), Glx (=Glu + Gln), myo-inositol (mI), total creatine (Cre) and other metabolites in the temporal lobes of patients with mesial temporal lobe epilepsy (mTLE), cryptogenic TLE (cTLE), who show no abnormalities in high-resolution MRI, and healthy controls using single voxel (1)H MRS at 3 T. Twelve patients with mTLE, nine with cTLE and 22 controls were investigated using a short echo time STEAM protocol. Voxels were positioned bilaterally in the medial and lateral temporal lobes. Spectra were processed with LCModel. Significantly lower mean NAA were detected in mTLE patients (P < 0.001) and a trend towards lower NAA in cTLE patients compared to controls (P = 0.053). Glx was not different between groups. Estimates of Glu showed a different metabolic pattern in mTLE with elevated Glu in lateral compared with medial voxels on the ipsilateral side to seizure onset (P = 0.019). MI concentrations were significantly lower in cTLE (P < 0.001) and in mTLE patients (P = 0.005) compared with healthy controls. MI/Cre was significantly reduced in cTLE patients only (P = 0.004). The results confirm low NAA in mTLE and to a lesser extent in cTLE patients. MI and mI/Cre were identified as potential metabolic indicators of the epileptogenic area in cTLE.

Inositol deficiency diet and lithium effects

OBJECTIVES

A major hypothesis explaining the therapeutic effect of lithium (Li) in mania is depletion of inositol via inhibition of inositol monophosphatase. However, inositol is also present in the diet. Restriction of dietary inositol could theoretically enhance the effects of Li.

METHODS

We used dietary inositol restriction in animal studies and also devised a palatable diet for humans that is 90% free of inositol.

RESULTS

Dietary inositol restriction significantly augmented the inositol-reducing effect of Li in rat frontal cortex. Li reduced inositol levels by 4.7%, inositol-deficient diet by 5.1%, and Li plus inositol-deficient diet by 10.8%. However, feeding with the inositol-deficient diet did not enhance the behavioral effect of Li in the Li-pilocarpine seizure model. Fifteen patients participated in an open clinical study of the inositol-deficient diet: six rapid cycling bipolar patients responding inadequately to Li or valproate in different phases of illness; two Li-treated bipolar outpatients with residual symptomatology, and seven inpatient Li-treated bipolar patients in non-responding acute mania. The diet had a major effect in reducing the severity of affective disorder in 10 of the patients within the first 7-14 days of treatment.

CONCLUSION

These results suggest that dietary inositol restriction may be useful in some bipolar patients, but controlled replication is necessary.

Magnetisation transfer ratio of choline is reduced following epileptic seizures

The purpose of this study was to characterise the concentration and magnetisation transfer ratio (MTR) of brain metabolites following epileptic seizures. Magnetic resonance spectroscopy was performed in 10 patients with temporal or extra-temporal lobe epilepsy as soon as possible after a seizure, with a second interictal scan between 1 and 3 days after the postictal scan and 10 healthy controls were scanned twice. Voxels (26 +/- 2 mL) were placed in the frontal lobe in all patients and controls, on the side of seizure focus in the patient group. Spectra were obtained using a modified PRESS sequence (TE 30 ms, TR 3 s, with three hard pulses offset from the water frequency by 2,500 Hz for MT presaturation). Mean metabolite concentrations and median metabolite MTRs of N-acetylaspartate (NAA), creatine, choline (Cho), myo-inositol (Ins) and glutamate plus glutamine were compared between the first and second scans in each group. A significant decrease in the MTR of Cho was seen postictally in the patient group, but the metabolite concentrations showed no significant difference between interictal and postictal scans and in the control group there was no difference between the two scans. Inter-group comparison showed significantly reduced concentrations of NAA and Ins in the patients. Reduced MTR of Cho indicates a shift from a bound to a more mobile fraction. These changes might indicate membrane perturbation in areas of seizure spread.

Neuroprotective mechanisms of lithium in murine human immunodeficiency virus-1 encephalitis

Lithium (Li) has garnered considerable interest as a neuroprotective drug for a broad range of nervous system disorders. Its neuroprotective activities occur as a consequence of glycogen synthase kinase-3beta (GSK-3beta) inhibition leading to downstream blockade of beta-catenin and Tau phosphorylation. In the present study, we investigated Li-mediated neuroprotective mechanisms in laboratory and murine human immunodeficiency virus-1 (HIV-1) encephalitis (HIVE) models. In laboratory tests, Li protected neurons from neurotoxic secretions of HIV-1-infected monocyte-derived macrophages (MDMs). This neuroprotection was mediated, in part, through the phosphatidyl inositol 3-kinase/Akt and GSK-3beta pathways. To examine the effects of Li treatment in vivo, MDMs were injected into the basal ganglia of severe combined immunodeficient mice and then Li was administered (60 mg/kg/d). Seven days after MDM injection, mice were killed and CNS tissue was collected and subjected to immunocytochemical and Western blot assays for leukocyte and neural antigens, GSK-3beta, and key kinase substrates such as beta-catenin and Tau. Numbers of HIV-1 p24 antigen-positive MDMs were unaltered by Li treatment of HIVE mice. Similarly, the greatly increased extent of astrocyte and microglia activation in HIVE mice (10-fold and 16-fold, respectively, compared with unmanipulated controls) was also unaltered by Li. In contrast, Li restored HIVE-associated loss of microtubule-associated protein-2-positive neurites and synaptic density while reducing levels or activity of phospho-Tau Ser202, phospho-beta-catenin, and GSK-3beta. Electrophysiological recordings showed diminished long-term potentiation in hippocampal slices of HIVE mice that were restored by Li. Based on these data, the use of Li as an adjuvant for HIV-1-associated dementia is now being pursued.

Valproate attenuates dextroamphetamine-induced subjective changes more than lithium

Dextroamphetamine administration in healthy controls produces a range of subjective and physiological effects, which have been likened to those occurring during mania. However, it is uncertain if these can be attenuated by lithium since conflicting results have been reported. To date there have been no previous studies examining the effects of valproate on dextroamphetamine-induced mood and physiological changes. The current study was a double-blind, placebo-controlled, study in which volunteers received either 1000 mg sodium valproate (n=12), 900 mg lithium (n=9), or placebo (n=12) pre-treatment for 14 days. Subjective and physiological measures were then obtained prior to administration of a 25 mg dose of dextroamphetamine, and at two time points after administration. Differences in the response to dextroamphetamine were assessed between the three treatment groups. The results of this study show that pre-treatment with lithium only significantly attenuated dextroamphetamine-induced change in happiness, while valproate pre-treatment significantly attenuated the effects of dextroamphetamine on happiness, energy, alertness and on the diastolic blood pressure. These results suggest that lithium and valproate do not have the same mechanism of action on dextroamphetamine-induced changes, and this finding may relate to differences in their mechanism of action in mood disorders.

Genetic perturbation of glycolysis results in inhibition of de novo inositol biosynthesis

In a genetic screen for Saccharomyces cerevisiae mutants hypersensitive to the inositol-depleting drugs lithium and valproate, a loss of function allele of TPI1 was identified. The TPI1 gene encodes triose phosphate isomerase, which catalyzes the interconversion of dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate. A single mutation (N65K) in tpi1 completely abolished Tpi1p enzyme activity and led to a 30-fold increase in the intracellular DHAP concentration. The tpi1 mutant was unable to grow in the absence of inositol and exhibited the "inositol-less death" phenotype. Similarly, the pgk1 mutant, which accumulates DHAP as a result of defective conversion of 3-phosphoglyceroyl phosphate to 3-phosphoglycerate, exhibited inositol auxotrophy. DHAP as well as glyceraldehyde 3-phosphate and oxaloacetate inhibited activity of both yeast and human myo-inositol-3 phosphate synthase, the rate-limiting enzyme in de novo inositol biosynthesis. Implications for the pathology associated with TPI deficiency and responsiveness to inositol-depleting anti-bipolar drugs are discussed. This study is the first to establish a connection between perturbation of glycolysis and inhibition of de novo inositol biosynthesis.

Lithium citrate for Canavan disease

Current evidence suggests that the effects of lithium on metabolic and signaling pathways in the brain may vary depending on the specific clinical condition or disease model. For example, lithium increases levels of cerebral N-acetyl aspartate in patients with bipolar disorder but does not appear to affect N-acetyl aspartate levels in normal human subjects. Conversely, lithium significantly decreases whole-brain levels of N-acetyl aspartate in a rat genetic model of Canavan disease in which cerebral N-acetyl aspartate is chronically elevated. While N-acetyl aspartate is a commonly used surrogate marker for neuronal density and correlates with neuronal viability, grossly elevated whole-brain levels of N-acetyl aspartate in Canavan disease are associated with dysmyelination and mental retardation. This report describes the first clinical application of lithium in a human subject with Canavan disease. Spectroscopic and clinical changes were observed over the time period in which lithium was administered, which reversed during a 2-week wash-out period after withdrawal of lithium. This investigation reports decreased N-acetyl aspartate levels in the brain regions tested and magnetic resonance spectroscopic values that are more characteristic of normal development and myelination, suggesting that a larger, controlled trial of lithium may be warranted as supportive therapy for Canavan disease by decreasing abnormally elevated N-acetyl aspartate.

Mitochondrial dysfunction in bipolar disorder: evidence from magnetic resonance spectroscopy research

Magnetic resonance spectroscopy (MRS) affords a noninvasive window on in vivo brain chemistry and, as such, provides a unique opportunity to gain insight into the biochemical pathology of bipolar disorder. Studies utilizing proton ((1)H) MRS have identified changes in cerebral concentrations of N-acetyl aspartate, glutamate/glutamine, choline-containing compounds, myo-inositol, and lactate in bipolar subjects compared to normal controls, while studies using phosphorus ((31)P) MRS have examined additional alterations in levels of phosphocreatine, phosphomonoesters, and intracellular pH. We hypothesize that the majority of MRS findings in bipolar subjects can be fit into a more cohesive bioenergetic and neurochemical model of bipolar illness that is both novel and yet in concordance with findings from complementary methodological approaches. In this review, we propose a hypothesis of mitochondrial dysfunction in bipolar disorder that involves impaired oxidative phosphorylation, a resultant shift toward glycolytic energy production, a decrease in total energy production and/or substrate availability, and altered phospholipid metabolism.

A review of the possible relevance of inositol and the phosphatidylinositol second messenger system (PI-cycle) to psychiatric disorders--focus on magnetic resonance spectroscopy (MRS) studies

Myo-inositol is an important part of the phosphatidylinositol second messenger system (PI-cycle). Abnormalities in nerve cell myo-inositol levels and/or PI-cycle regulation has been suggested as being involved in the pathophysiology and/or treatment of many psychiatric disorders including bipolar disorder, major depressive disorder, panic disorder, obsessive-compulsive disorder, eating disorders and schizophrenia. This review examines the metabolism and biochemical importance of myo-inositol and the PI-cycle. It relates this to the current in vivo evidence for myo-inositol and PI-cycle involvement in these psychiatric disorders, particularly focusing upon the magnetic resonance spectroscopy (MRS) findings in patient studies to date. From this review it is concluded that while the evidence suggests probable relevance to the pathophysiology and/or treatment of bipolar disorder, there is much less support for a significant role for the PI-cycle or myo-inositol in any other psychiatric disorder. More definitive investigation is required before PI-cycle dysfunction can be considered specific to bipolar disorder.

Lithium and valproate attenuate dextroamphetamine-induced changes in brain activation

BACKGROUND

Previous studies have suggested that both lithium and valproate may decrease phosphoinositol second messenger system (PI-cycle) activity. There is also evidence that dextroamphetamine may increase PI cycle activity. It was previously demonstrated that dextroamphetamine administration in volunteers causes a region and task dependent decrease in brain activation in healthy volunteers. The current study assessed the effect of 14 days pretreatment with lithium and valproate on these dextroamphetamine-induced changes in regional brain activity in healthy volunteers.

METHODS

This was a double-blind, placebo-controlled, study in which volunteers received either 1000 mg sodium valproate (n = 12), 900 mg lithium (n = 9) or placebo (n = 12). Functional images were acquired using functional magnetic resonance imaging (fMRI) while subjects performed three cognitive tasks, a word generation paradigm, a spatial attention task and a working memory task. fMRI was carried out both before and after administration of dextroamphetamine (25 mg). Changes in the number of activated pixels and changes in the magnitude of the blood-oxygen-level-dependent (BOLD) signal after dextroamphetamine administration were then determined.

RESULTS

In keeping with previous findings dextroamphetamine administration decreased regional brain activation in all three tasks. Pretreatment with lithium attenuated changes in the word generation paradigm and the spatial attention task, while pretreatment with valproate attenuated the changes in the working memory task.

CONCLUSIONS

These results suggest that both lithium and valproate can significantly attenuate dextroamphetamine-induced changes in brain activity in a task dependent and region specific manner. This is the first human evidence to suggest that both lithium and valproate may have a similar effect on regional brain activation, conceivably via similar effects on PI-cycle activity.

Bipolar disorder and myo-inositol: a review of the magnetic resonance spectroscopy findings

OBJECTIVES

Myo-inositol is an important component of the phosphatidylinositol second messenger system (PI-cycle). Alterations in PI-cycle activity have been suggested to be involved in the pathophysiology and/or treatment of bipolar disorder. More specifically, lithium has been suggested to act primarily by lowering myo-inositol concentrations, the so-called inositol-depletion hypothesis. myo-Inositol concentrations can be measured in vivo with magnetic resonance spectroscopy (MRS).

METHODS

The current review primarily examines animal and human MRS studies that evaluated the role of myo-inositol in bipolar illness and treatment.

RESULTS

Studies have been carried out in patients who are manic, depressed, and euthymic, both on and off treatment. However, there are several limitations of these studies.

CONCLUSIONS

The preclinical and clinical MRS findings were generally supportive of the involvement of myo-inositol in bipolar disorder and its treatment. Overall, in bipolar patients who are manic or depressed there are abnormalities in brain myo-inositol concentrations, with changes in frontal and temporal lobes, as well as the cingulate gyrus and basal ganglia. These abnormalities are not seen in either euthymic patients or healthy controls, possibly due to a normalizing effect of treatment with either lithium or sodium valproate. There is also increasing evidence that sodium valproate may also act upon the PI-cycle. Nonetheless, it remains uncertain if these changes in myo-inositol concentration are primary or secondary. Findings regarding the specific inositol-depletion hypothesis are also generally supportive in acutely ill patients, although it is not yet possible to definitively confirm or refute this hypothesis based on the current MRS evidence.

Lithium and bipolar mood disorder: the inositol-depletion hypothesis revisited

Inositol, a simple six-carbon sugar, forms the basis of a number of important intracellular signaling molecules. Over the last 35 years, a series of biochemical and cell biological experiments have shown that lithium (Li(+)) reduces the cellular concentration of myo-inositol and as a consequence attenuates signaling within the cell. Based on these observations, inositol-depletion was proposed as a therapeutic mechanism in the treatment of bipolar mood disorder. Recent results have added significant new dimensions to the original hypothesis. However, despite a number of clinical studies, this hypothesis still remains to be either proven or refuted. In this review of our current knowledge, I will consider where the inositol-depletion hypothesis stands today and how it may be further investigated in the future.

Valproate decreases inositol biosynthesis

BACKGROUND

Lithium and valproate (VPA) are used for treating bipolar disorder. The mechanism of mood stabilization has not been elucidated, but the role of inositol has gained substantial support. Lithium inhibition of inositol monophosphatase, an enzyme required for inositol recycling and de novo synthesis, suggested the hypothesis that lithium depletes brain inositol and attenuates phosphoinositide signaling. Valproate also depletes inositol in yeast, Dictyostelium, and rat neurons. This raised the possibility that the effect is the result of myo-inositol-1-phosphate (MIP) synthase inhibition.

METHODS

Inositol was measured by gas chromatography. Human prefrontal cortex MIP synthase activity was assayed in crude homogenate. INO1 was assessed by Northern blotting. Growth cones morphology was evaluated in cultured rat neurons.

RESULTS

We found a 20% in vivo reduction of inositol in mouse frontal cortex after acute VPA administration. As hypothesized, inositol reduction resulted from decreased MIP synthase activity: .21-.28 mmol/LVPA reduced the activity by 50%. Among psychotropic drugs, the effect is specific to VPA. Accordingly, only VPA upregulates the yeast INO1 gene coding for MIP synthase. The VPA derivative N-methyl-2,2,3,3,-tetramethyl-cyclopropane carboxamide reduces MIP synthase activity and has an affect similar to that of VPA on rat neurons, whereas another VPA derivative, valpromide, poorly affects the activity and has no affect on neurons.

CONCLUSIONS

The rate-limiting step of inositol biosynthesis, catalyzed by MIP synthase, is inhibited by VPA; inositol depletion is a first event shown to be common to lithium and VPA.

Lithium and valproic acid treatment effects on brain chemistry in bipolar disorder

BACKGROUND

Prior work reported elevated gray matter (GM) lactate and Glx (glutamate + glutamine + GABA) concentrations in unmedicated patients with bipolar disorder (BP) compared with healthy controls (HC). This study examined whether lithium (Li) and valproic acid (VPA) treatment modulated these chemicals.

METHODS

A subset of previously reported BP patients were treated with Li (n = 12, 3.6 +/- 1.9 months) or VPA (n = 9, 1.4 +/- 1.7 months) and compared untreated HC subjects (n = 12, 2.9 +/- 2.4 months) using proton echo-planar spectroscopic imaging. Regression analyses (voxel gray/white composition by chemistry) were performed at each time point, and change scores computed. Metabolite relaxation and regions of interest (ROI) were also examined.

RESULTS

Across treatment, Li-treated BP subjects demonstrated GM Glx decreases (Li-HC, p =.08; Li-VPA p =.04) and GM myo-inositol increases (Li-HC p =.07; Li-VPA p =.12). Other measures were not significant. Serum Li levels were positively correlated with Glx decreases at the trend level.

CONCLUSIONS

Li treatment of BP was associated with specific GM Glx decreases and myo-inositol increases. Findings are discussed in the context of cellular mechanisms postulated to underlie Li and VPA therapeutic efficacy.

The neurobiology of antiepileptic drugs for the treatment of nonepileptic conditions

Antiepileptic drugs (AEDs) are commonly prescribed for nonepileptic conditions, including migraine headache, chronic neuropathic pain, mood disorders, schizophrenia and various neuromuscular syndromes. In many of these conditions, as in epilepsy, the drugs act by modifying the excitability of nerve (or muscle) through effects on voltage-gated sodium and calcium channels or by promoting inhibition mediated by gamma-aminobutyric acid (GABA) A receptors. In neuropathic pain, chronic nerve injury is associated with the redistribution and altered subunit compositions of sodium and calcium channels that predispose neurons in sensory pathways to fire spontaneously or at inappropriately high frequencies, often from ectopic sites. AEDs may counteract this abnormal activity by selectively affecting pain-specific firing; for example, many AEDs suppress high-frequency action potentials by blocking voltage-activated sodium channels in a use-dependent fashion. Alternatively, AEDs may specifically target pathological channels; for example, gabapentin is a ligand of alpha2delta voltage-activated calcium channel subunits that are overexpressed in sensory neurons after nerve injury. Emerging evidence suggests that effects on signaling pathways that regulate neuronal plasticity and survival may be a factor in the delayed clinical efficacy of AEDs in some neuropsychiatric conditions, including bipolar affective disorder.

Discriminative power of an assay for automated in vitro screening of teratogens

Screening for potential teratogenicity of 20 test compounds was performed using a computerised microscope workstation for determination of cytotoxicity, proliferation and morphology of fibroblastoid murine L929-cells. The test compounds, which were divided into four classes according to teratogenicity were: 5-bromo-2(')-deoxyuridine, 6-aminonicotinamide, acrylamide, boric acid, D-(+)-camphor, dimethadione, dimethyl phthalate, diphenhydramine, hydroxyurea, isobutyl-ethyl-valproic acid, lithium chloride, methyl mercury chloride, methotrexate, methoxyacetic acid, penicillin G, all-trans-retinoic acid, pentyl-4-yn-valproic acid, saccharin, salicylic acid and valproic acid. All compounds, with the exception of dimethadione inhibited proliferation in a linear dose-dependent manner, and there were statistically significant compound class-dependent differences between the IC(50)-values for the compounds (p<0.0374), the strongest teratogens being the most potent. Furthermore, the average efficacies (maximum relative change) for 10 parameters describing cell morphology exhibited statistically significant compound class-dependent differences (p<0.0001), the class I and II compounds exhibiting significantly lower efficacies than the class III and IV compounds (p<0.01). Thus, test compounds affected both the proliferation and morphology of L-cells in manner demonstrating a general relationship with the teratogenic potency of the compounds. However, the moderate teratogens dimethadione and lithium chloride only had minor effects on the morphology and proliferation of the cells whereas the non-teratogen diphenhydramine had effects on both proliferation and morphology comparable to the strong teratogens.

Brain choline concentrations may not be altered in euthymic bipolar disorder patients chronically treated with either lithium or sodium valproate

Background

It has been suggested that lithium increases choline concentrations, although previous human studies examining this possibility using ¹H magnetic resonance spectroscopy (¹H MRS) have had mixed results: some found increases while most found no differences.

Methods

The present study utilized ¹H MRS, in a 3 T scanner to examine the effects of both lithium and sodium valproate upon choline concentrations in treated euthymic bipolar patients utilizing two different methodologies. In the first part of the study healthy controls (n = 18) were compared with euthymic Bipolar Disorder patients (Type I and Type II) who were taking either lithium (n = 14) or sodium valproate (n = 11), and temporal lobe choline/creatine (Cho/Cr) ratios were determined. In the second part we examined a separate group of euthymic Bipolar Disorder Type I patients taking sodium valproate (n = 9) and compared these to controls (n = 11). Here we measured the absolute concentrations of choline in both temporal and frontal lobes.

Results

The results from the first part of the study showed that bipolar patients chronically treated with both lithium and sodium valproate had significantly reduced temporal lobe Cho/Cr ratios. In contrast, in the second part of the study, there were no effects of sodium valproate on either absolute choline concentrations or on Cho/Cr ratios in either temporal or frontal lobes.

Conclusions

These findings suggest that measuring Cho/Cr ratios may not accurately reflect brain choline concentrations. In addition, the results do not support previous suggestions that either lithium or valproate increases choline concentrations in bipolar patients.

Studies of myo-inositol and plasmalogen metabolism in rat brain

Plasmalogens are ether-linked phospholipids that are abundant in nervous tissues. Their biological role is unclear, but may involve membrane structure/function and antioxidant activities. This study further investigates a recent report that chronic administration of myo-inositol in rats increased brain phosphatidylethanolamine plasmalogen (PlsEtn). We examined the effects of myo-inositol administration on the incorporation of [2-(13)C]ethanolamine ([2-(13)C]Etn) into rat brain phospholipids using NMR spectroscopy. Rats received either acute myo-inositol (single dose) +/- [2-(13)C]Etn, or chronic myo-inositol (10-day treatment) + [2-(13)C]Etn. Controls received saline rather than myo-inositol. Acute myo-inositol produced a 68% increase in brain [myo-inositol] and an increase in the incorporation of [2-(13)C]Etn into phospholipids (P < .05). The PlsEtn/phosphatidylethanolamine ratio and the [PlsEtn] were increased by 27% and 30%, respectively. The PlsEtn content as a mole percentage of total phospholipids was elevated (P < or = .05). Acute administration of myo-inositol + ethanolamine illustrates a positive correlation between the brain [myo-inositol] and the biosynthesis of ethanolamine phospholipids, with preferential synthesis of PlsEtn.

Human 1-D-myo-Inositol-3-phosphate Synthase Is Functional in Yeast

We have cloned, sequenced, and expressed a human cDNA encoding 1-d-myo-inositol-3-phosphate (MIP) synthase (hINO1). The encoded 62-kDa human enzyme converted d-glucose 6-phosphate to 1-d-myo-inositol 3-phosphate, the rate-limiting step for de novo inositol biosynthesis. Activity of the recombinant human MIP synthase purified from Escherichia coli was optimal at pH 8.0 at 37 degrees C and exhibited K(m) values of 0.57 mm and 8 microm for glucose 6-phosphate and NAD(+), respectively. NH(4)(+) and K(+) were better activators than other cations tested (Na(+), Li(+), Mg(2+), Mn(2+)), and Zn(2+) strongly inhibited activity. Expression of the protein in the yeast ino1Delta mutant lacking MIP synthase (ino1Delta/hINO1) complemented the inositol auxotrophy of the mutant and led to inositol excretion. MIP synthase activity and intracellular inositol were decreased about 35 and 25%, respectively, when ino1Delta/hINO1 was grown in the presence of a therapeutically relevant concentration of the anti-bipolar drug valproate (0.6 mm). However, in vitro activity of purified MIP synthase was not inhibited by valproate at this concentration, suggesting that inhibition by the drug is indirect. Because inositol metabolism may play a key role in the etiology and treatment of bipolar illness, functional conservation of the key enzyme in inositol biosynthesis underscores the power of the yeast model in studies of this disorder.

Identification of abnormal neuronal metabolism outside the seizure focus in temporal lobe epilepsy

PURPOSE

The aim of this study was to identify metabolically abnormal extrahippocampal brain regions in patients with temporal lobe epilepsy with (TLE-MTS) and without (TLE-no) magnetic resonance imaging (MRI) evidence for mesial-temporal sclerosis (MTS) and to assess their value for focus lateralization by using multislice 1H magnetic resonance spectroscopic imaging (MRSI).

METHODS

MRSI in combination with tissue segmentation was performed on 14 TLE-MTS and seven TLE-no and 12 age-matched controls. In controls, N-acetylaspartate/(creatine + choline) [NAA/(Cr+Cho)] of all voxels of a given lobe was expressed as a function of white matter content to determine the 95% prediction interval for any additional voxel of a given tissue composition. Voxels with NAA/(Cr+Cho) below the lower limit of the 95% prediction interval were defined as "pathological" in patients and controls. Z-scores were used to identify regions with a higher percentage of pathological voxels than those in controls.

RESULTS

Reduced NAA/(Cr+Cho) was found in ipsilateral temporal and parietal lobes and bilaterally in insula and frontal lobes. Temporal abnormalities identified the epileptogenic focus in 70% in TLE-MTS and 83% of TLE-no. Extratemporal abnormalities identified the epileptogenic focus in 78% of TLE-MTS but in only 17% of TLE-no.

CONCLUSIONS

TLE is associated with extrahippocampal reductions of NAA/(Cr+Cho) in several lobes consistent with those brain areas involved in seizure spread. Temporal and extratemporal NAA/(Cr+Cho) reductions might be helpful for focus lateralization.

Localization of the mRNA encoding prolyl endopeptidase in the rat brain and pituitary

Prolyl endopeptidase (EC 3.4.21.26, PEP), a serine protease that hydrolyzes peptides at the carboxyl side of proline residues, is involved in the breakdown of several proline-containing neuropeptides and, thus, may contribute to the regulation of behavioral activities. In this study, the distribution of PEP mRNA was investigated in the central nervous system and pituitary of rat by means of quantitative reverse transcriptase-polymerase chain reaction analysis and in situ hybridization histochemistry. High densities of PEP transcripts were found in cerebellar Purkinje and granule cells, within most hypothalamic nuclei, in pyramidal neurons of the Ammon's horn, in granule cells of the dentate gyrus, and within the basolateral complex of the amygdala. Moderate levels of PEP mRNA were observed in layers 3-5 of the cerebral cortex, the anterior thalamic group, the septal region, the substantia nigra, the magnocellular neurons of the red nucleus, and the motor nuclei of the cranial nerves. Low concentrations of PEP mRNA were detected in the deep mesencephalic nuclei, the reticular formation, the pretectum, and the tectum. A high density of PEP mRNA was found in the intermediate and the anterior lobes of the pituitary, while the neural lobe was devoid of labeling. In several brain regions, the distribution pattern of PEP mRNA overlapped that of various neuropeptide receptors, suggesting that PEP is actually involved in the inactivation of regulatory neuropeptides.

Molecular targets of lithium action

Lithium is an effective drug for both the treatment and prophylaxis of bipolar disorder. However, the precise mechanism of lithium action is not yet well understood. Extensive research aiming to elucidate the molecular mechanisms underlying the therapeutic effects of lithium has revealed several possible targets. The behavioral and physiological manifestations of the illness are complex and are mediated by a network of interconnected neurotransmitter pathways. Thus, lithium's ability to modulate the release of serotonin at presynaptic sites and modulate receptor-mediated supersensitivity in the brain remains a relevant line of investigation. However, it is at the molecular level that some of the most exciting advances in the understanding of the long-term therapeutic action of lithium will continue in the coming years. The lithium cation possesses the selective ability, at clinically relevant concentrations, to alter the PI second-messenger system, potentially altering the activity and dynamic regulation of receptors that are coupled to this intracellular response. Subtypes of muscarinic receptors in the limbic system may represent particularly sensitive targets in this regard. Likewise, preclinical data have shown that lithium regulates arachidonic acid and the protein kinase C signaling cascades. It also indirectly regulates a number of factors involved in cell survival pathways, including cAMP response element binding protein, brain-derived neurotrophic factor, bcl-2 and mitogen-activated protein kinases, and may thus bring about delayed long-term beneficial effects via under-appreciated neurotrophic effects. Identification of the molecular targets for lithium in the brain could lead to the elucidation of the pathophysiology of bipolar disorder and the discovery of a new generation of mood stabilizers, which in turn may lead to improvements in the long-term outcome of this devastating illness (1).

Polymorphism screening of PIP5K2A: a candidate gene for chromosome 10p-linked psychiatric disorders

Lithium is a potent noncompetitive inhibitor of inositol monophosphatases, enzymes involved in phosphoinositide (PI) and inositol phosphate metabolism. A critical component of the PI pathway is phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)), which is hydrolyzed to second messengers and has a direct role in synaptic vesicle function. Interestingly, a number of genes involved in the synthesis and dephosphorylation of PtdIns(4,5)P(2) are found in regions of the genome previously mapped in bipolar disorder (BD) including 10p12, 21q22, and 22q11, among others. Some of these regions overlap with loci mapped in schizophrenia (SZ). One gene involved in PI metabolism that maps to a region of interest is 10p12-linked PIP5K2A, a member of the phosphatidylinositol 4-phosphate 5-kinase family. Polymorphism screening revealed the existence of an imperfect CT repeat polymorphism located near the exon 9-intron 9 splice donor site. A modest difference was found in the distribution of alleles from this highly polymorphic variant when bipolar and schizophrenic subjects were compared with controls; relatively rare short repeat variants were found more commonly in patients and homozygosity for a common long repeat variant was found more commonly in controls. These data suggest that the imperfect CT repeat in PIP5K2A intron 9 should be further investigated as a possible candidate allele for 10p12-linked psychiatric disorders.

Valproate disrupts regulation of inositol responsive genes and alters regulation of phospholipid biosynthesis

Valproate (VPA) is one of the two drugs approved by the Food and Drug Administration (FDA) for the treatment of bipolar disorder. The therapeutic mechanism of VPA has not been established. We have shown previously that growth of the yeast Saccharomyces cerevisiae in the presence of VPA causes a decrease in intracellular inositol and inositol-1-P, and a dramatic increase in expression of INO1, which encodes the rate limiting enzyme for de novo inositol biosynthesis. To understand the underlying mechanism of action of VPA, INO1, CHO1 and INO2 expression, intracellular inositol and phospholipid biosynthesis were studied as a function of acute and chronic exposure of growing cells to the drug. A decrease in intracellular inositol was apparent immediately after addition of VPA. Surprisingly, expression of genes that are usually derepressed during inositol depletion, including INO1, CHO1 and INO2 (that contain inositol-responsive UASINO sequences) decreased several fold during the first hour, after which expression began to increase. Incorporation of 32Pi into total phospholipids was significantly decreased. Pulse labelling of CDP-DG and PG, shown previously to increase during inositol depletion, increased within 30 min. However, pulse labelling of PS, which normally increases during inositol depletion, was decreased within 30 min. PS synthase activity in cell extracts decreased with time, although VPA did not directly inhibit PS synthase enzyme activity. Thus, in contrast to the effect of chronic VPA treatment, short-term exposure to VPA abrogated the normal response to inositol depletion of inositol responsive genes and led to aberrant synthesis of phospholipids.

Effects of chronic lithium and sodium valproate on concentrations of brain amino acids

The present study was designed to determine if the mood stabilizers, lithium and valproate, have common effects on concentrations of amino acid neurotransmitters which may be related to their mechanisms of action. Two separate groups of rats were administered therapeutic doses of lithium, sodium valproate, or saline for 2 weeks. Whole brain extracts were then examined using either high-field 1H NMR spectroscopy or HPLC. Both drugs decreased whole brain concentrations of aspartate, glutamate, and taurine while brain concentrations of gamma-aminobutyric acid (GABA) and alanine decreased following chronic sodium valproate administration but not following chronic lithium administration. These findings indicate that lithium and sodium valproate share common effects on the concentrations of certain amino acid neurotransmitters in whole brain which may be related to their mechanisms of action in bipolar disorder.

Search for a common mechanism of mood stabilizers

Manic-depression, or bipolar affective disorder, is a prevalent mental disorder with a global impact. Mood stabilizers have acute and long-term effects and at a minimum are prophylactic for manic or depressive poles without detriment to the other. Lithium has significant effects on mania and depression, but may be augmented or substituted by some antiepileptic drugs. The biochemical basis for mood stabilizer therapies or the molecular origins of bipolar disorder is unknown. One approach to this problem is to seek a common target of all mood stabilizers. Lithium directly inhibits two evolutionarily conserved signal transduction pathways. It both suppresses inositol signaling through depletion of intracellular inositol and inhibits glycogen synthase kinase-3 (GSK-3), a multifunctional protein kinase. A number of GSK-3 substrates are involved in neuronal function and organization, and therefore present plausible targets for therapy. Valproic acid (VPA) is an antiepileptic drug with mood-stabilizing properties. It may indirectly reduce GSK-3 activity, and can up-regulate gene expression through inhibition of histone deacetylase. These effects, however, are not conserved between different cell types. VPA also inhibits inositol signaling through an inositol-depletion mechanism. There is no evidence for GSK-3 inhibition by carbamazepine, a second antiepileptic mood stabilizer. In contrast, this drug alters neuronal morphology through an inositol-depletion mechanism as seen with lithium and VPA. Studies on the enzyme prolyl oligopeptidase and the sodium myo-inositol transporter support an inositol-depletion mechanism for mood stabilizer action. Despite these intriguing observations, it remains unclear how changes in inositol signaling underlie the origins of bipolar disorder.

[Neurobiological principles of bipolar affective disorders]

The neurobiology of bipolar affective illness can be described in a model with structural and functional components, which also address the role of stressors, coping mechanisms, and psychophysical disposition. More data exist on depressive than on manic patients or on patients switching from one clinical pole to the other. Structural and functional chronobiological alterations appear to play a major role in the pathophysiology of bipolar illness. From an anatomical view, neurobiological abnormalities are primarily confined to limbic-striatal-pallidal-thalamocortical circuits. The whole cascade of neural signaling is changed starting from neurotransmitters and neuromodulators to receptor-mediated intracellular signal transduction targeting nuclear gene expression. Transnosological factors such as suicidal tendency appear to essentially modulate those changes. Replicated data on decisive neurobiological differences between bipolar and unipolar affective disorders are currently not yet available.

Myoinositol abnormalities in temporal lobe epilepsy

PURPOSE

This study used magnetic resonance spectroscopy (MRS) to examine metabolite abnormalities in the temporal and frontal lobe of patients with temporal lobe epilepsy (TLE) of differing severity.

METHODS

We investigated myoinositol in TLE by using short-echo MRS in 34 TLE patients [26 late onset (LO-TLE), eight hippocampal sclerosis (HS-TLE)], and 16 controls. Single-voxel short-echo (35 ms) MR spectra of temporal and frontal lobes were acquired at 1.5 T and analyzed by using LCModel.

RESULTS

The temporal lobe ipsilateral to seizure origin in HS-TLE, but not LO-TLE, had reduced N-acetylaspartate (NA) and elevated myoinositol (MI; HS-TLE NA, 7.8 +/- 1.9 mM, control NA, 9.2 +/- 1.3 mM; p < 0.05; HS-TLE MI, 6.1 +/- 1.6 mM, control mI 4.9 +/- 0.8 mM, p< 0.05). Frontal lobe MI was low in both patient groups (LO-TLE, 4.3 +/- 0.8 mM; p < 0.05; HS-TLE, 3.6 +/-.05 mM; p < 0.001; controls, 4.8 +/- 0.5 mM). Ipsilateral frontal lobes had lower MI (3.8 +/- 0.7 mM; p < 0.01) than contralateral frontal lobes (4.3 +/- 0.8 mM; p < 0.05).

CONCLUSIONS

MI changes may distinguish between the seizure focus, where MI is increased, and areas of seizure spread where MI is decreased.

[Genes related to phospholipid metabolism as risk factors related to bipolar affective disorder]

The studies of genetic epidemiology provides consistent evidence of genetic factors having a major role on the risk for the bipolar affective disorder, although, vulnerability genes have not yet been identified in unequivocal form. The authors show that phospholipids play an important role in the cellular signalling processes, besides this, some studies with mood-stabilisers neurochemistry suggest that these drugs act in the phospholipase regulated signalling views. They conclude that analysis of gene variants that code enzymes of the phospholipids metabolism as potential susceptibility genes can extend the knowledge concerning the risk factors and the physiopatological mechanisms underling this mood disturbance.

Valproate attenuates hyperactive and perseverative behaviors in mutant mice with a dysregulated dopamine system

BACKGROUND

Dopamine transporter (DAT) knockdown (KD) mice, with approximately 90% loss of expression of the DAT, allow for the examination of the behavioral consequences of a chronically dysregulated dopamine system. The DAT KD mice have hyperdopaminergic tone, are hyperactive, and show impaired response inhibition in a number of paradigms. We hypothesized that the DAT KD mice would also display deficits in prepulse inhibition (PPI) and would be perseverative in their locomotor behavior.

METHODS

Basal levels of PPI and patterns of locomotor behavior were measured in two cohorts of DAT KD mice. In addition, measurements of locomotor behavior were recorded after pretreatment with 100 mg/kg valproate in both DAT KD and wildtype mice.

RESULTS

The DAT KD mice were hyperactive and displayed perseverative motor behavior but had normal levels of PPI. The clinically effective antimania drug valproate significantly attenuated the hyperactivity and perseverative locomotor behavior in the DAT KD mice and had no effect in control mice.

CONCLUSIONS

The DAT KD mice appear to provide a model of some aspects of manic behavior. With limited models of bipolar disorder, the DAT KD mice might provide a vehicle to screen for new psychiatric therapies to treat mania and its related symptoms.

Myo-inositol-1-phosphate (MIP) synthase: a possible new target for antibipolar drugs

Inositol metabolism is well characterized in yeast at a molecular level, and yeast is the only eukaryote in which genetic, molecular and functional genomic approaches to identify lithium. valproate and inositol targets may be combined readily. It has been shown that lithium inhibits yeast inositol monophosphatase (encoded by INM1 and INM2), and both valproate and lithium reduce intracellular inositol. Unlike lithium, valproate causes a decrease in intracellular inositol-1-phosphate as well. suggesting that myo-inositol-1-P (MIP) synthase is a site of valproate action in the yeast PI cycle. MIP synthase is the rate-limiting step in inositol biosynthesis and is highly regulated in response to inositol. Yeast genes that are affected by both lithium and valproate in the phosphoinositide pathways (INO1 increased over 10-fold, INO2 increased twofold and INM1 decreased about twofold) have been identified. It has also been reported previously that both lithium and inositol mildly up-regulate IMPA1 (encoding mammalian inositol monophosphatase) expression in human cells. These findings indicate that IMPA is regulated only mildly by lithium, and therefore may not be the major target in the inositol pathway. Given the substantial evidence for the role of inositol in the mechanism of action of lithium and valproate. the opposing and mild effects of lithium on the genes encoding inositol monophosphatase in yeast and human cells, but the powerful effect of lithium and valproate on INO1 in yeast, it is hypothesized that human hIANO1 is a factor in the psychopharmacology of mood stabilizers.

Frontal lobe differences in bipolar disorder as determined by proton MR spectroscopy

OBJECTIVES

Proton magnetic resonance spectroscopy (MRS) provides insight into neurochemical processes. Imaging and postmortem studies have implicated abnormalities of structure and function within the frontal lobe. Patients with bipolar disorder having a manic or mixed episode were hypothesized to demonstrate metabolic abnormalities within the frontal lobe.

METHODS

Seventeen patients with bipolar disorder type I (ages 16-35 years, mean 22 +/- 7.3 years) hospitalized for a manic (n = 9) or mixed (n = 8) episode and 21 healthy subjects (ages 16-35 years, mean 21.7 +/- 5.2 years) were evaluated with proton MRS. The gray matter medially and white matter laterally within the frontal lobe were sampled. Metabolite concentrations were calculated for each voxel, corrected for cerebral spinal fluid (CSF) contributions to the voxel, and compared between study populations.

RESULTS

Patients demonstrated with multivariate analyses of variance (MANOVA) a significant overall difference in gray matter metabolite concentrations compared with healthy subjects. The largest effect sizes for group differences were found with reductions of N-acetyl aspartate (NAA) and Choline (Cho) concentrations (f = 0.41 and 0.37, respectively). A significant group difference with MANOVA in white matter metabolite concentrations was also observed with the largest effect size at f = 0.44 for elevation of the composite amino acid (AA) concentration.

CONCLUSIONS

A reduction of NAA within the gray matter of patients suggests neuronal dysfunction. Altered phospholipid metabolism suggestive of a trend toward decreased volume is implicated with a reduction of Cho concentrations. Within white matter, composite concentrations of AAs were elevated in patients indicating altered neurotransmission.

Reduced extrahippocampal NAA in mesial temporal lobe epilepsy

PURPOSE

Structural and metabolic abnormalities in the hippocampal region in medial temporal lobe epilepsy (mTLE) are well described; less is known about extrahippocampal changes. This study was designed to characterize extrahippocampal metabolic abnormalities in mTLE with magnetic resonance spectroscopy in combination with tissue segmentation and volumetry of gray and white matter.

METHODS

Multislice magnetic resonance spectroscopic imaging (1H-MRSI) in combination with tissue segmentation was performed on 16 patients with mTLE and 12 age-matched healthy volunteers. The data were analyzed by using a regression-analysis model that estimated the metabolite concentrations in 100% cortical gray and 100% white matter in the frontal lobe and nonfrontal brain. The segmented image was used to calculate the fraction of gray and white matter in these regions.

RESULTS

mTLE had significantly lower N-acetyl aspartate (NAA) in ipsi- and contralateral frontal gray (p = 0.03) and in ipsi- and contralateral nonfrontal white matter (p = 0.008) compared with controls. Although there were no associated volumetric deficits in frontal gray and white matter, ipsilateral nonfrontal gray matter (p = 0.003) was significantly smaller than that in controls.

CONCLUSIONS

mTLE is associated with extrahippocampal metabolic abnormalities and volumetric deficits, but these do not necessarily affect the same regions.

Chronic treatment with both lithium and sodium valproate may normalize phosphoinositol cycle activity in bipolar patients

BACKGROUND

It has been proposed that lithium may be clinically effective due to its actions on the phosphoinositol second messenger system (PI-cycle). Studies have also suggested that untreated manic patients may have raised myo-inositol and phosphomonoester (PME) concentrations and also that unmedicated euthymic bipolar patients may have lowered PME concentrations. The objective of the present study was to test the hypothesis that chronic treatment with either lithium or sodium valproate in patients with bipolar mood disorder leads to a normalization in the activity of the PI-cycle.

METHODS

This study had two parts each with different MRS methodology. The first part compared healthy controls (n = 19) with euthymic bipolar patients who were taking either lithium (n = 16) or sodium valproate (n = 11) using both (1)H-MRS and (31)P-MRS. In the second part we examined a separate group of euthymic bipolar disorder patients taking sodium valproate (n = 9) and compared these with age and sex-matched healthy controls (n = 11) using (1)H-MRS.

RESULTS

Both studies showed that there were no differences in either myo-inositol or phosphomonoester (PME) concentrations between controls and patients taking either medication.

CONCLUSIONS

These findings examine two key components of the PI-cycle in treated euthymic bipolar (myo-inositol and PME concentrations). The results from this study are consistent with the suggestion that chronic treatment with either lithium or sodium valproate in bipolar patients may normalize PI-cycle functioning.