Increased calcium absorption from synthetic stable amorphous calcium carbonate: double-blind randomized crossover clinical trial in postmenopausal women.

Calcium supplementation is a widely recognized strategy for achieving adequate calcium intake. We designed this blinded, randomized, crossover interventional trial to compare the bioavailability of a new stable synthetic amorphous calcium carbonate (ACC) with that of crystalline calcium carbonate (CCC) using the dual stable isotope technique. The study was conducted in the Unit of Clinical Nutrition, Tel Aviv Sourasky Medical Center, Israel. The study population included 15 early postmenopausal women aged 54.9 ± 2.8 (mean ± SD) years with no history of major medical illness or metabolic bone disorder, excess calcium intake, or vitamin D deficiency. Standardized breakfast was followed by randomly provided CCC or ACC capsules containing 192 mg elemental calcium labeled with 44Ca at intervals of at least 3 weeks. After swallowing the capsules, intravenous CaCl2 labeled with 42Ca on was administered on each occasion. Fractional calcium absorption (FCA) of ACC and CCC was calculated from the 24-hour urine collection following calcium administration. The results indicated that FCA of ACC was doubled (± 0.96 SD) on average compared to that of CCC (p < 0.02). The higher absorption of the synthetic stable ACC may serve as a more efficacious way of calcium supplementation.

Cholinergic-associated loss of hnRNP-A/B in Alzheimer's disease impairs cortical splicing and cognitive function in mice.

Genetic studies link inherited errors in RNA metabolism to familial neurodegenerative disease. Here, we report such errors and the underlying mechanism in sporadic Alzheimer's disease (AD). AD entorhinal cortices presented globally impaired exon exclusions and selective loss of the hnRNP A/B splicing factors. Supporting functional relevance, hnRNP A/B knockdown induced alternative splicing impairments and dendrite loss in primary neurons, and memory and electrocorticographic impairments in mice. Transgenic mice with disease-associated mutations in APP or Tau displayed no alterations in hnRNP A/B suggesting that its loss in AD is independent of Aß and Tau toxicity. However, cholinergic excitation increased hnRNP A/B levels while in vivo neurotoxin-mediated destruction of cholinergic neurons caused cortical AD-like decrease in hnRNP A/B and recapitulated the alternative splicing pattern of AD patients. Our findings present cholinergic-mediated hnRNP A/B loss and impaired RNA metabolism as important mechanisms involved in AD.

Lithium treatment attenuates muscarinic M(1) receptor dysfunction.

OBJECTIVE: Altered muscarinic acetylcholine receptor levels and receptor-coupled signaling processes have been reported in mood disorders. M(1) , one of five muscarinic receptor subtypes, couples to the phospholipase C/protein kinase C and extracellular signal-regulated kinase (ERK) pathways. Mood stabilizers regulate these pathways. MicroRNAs (miRNAs) are small noncoding RNAs that suppress translation in a sequence-selective manner. Lithium downregulates several miRNAs, including let-7b and let-7c. One predicted target of let-7b and let-7c is the M(1) receptor. We hypothesized that miRNAs regulate M(1) receptor translation, and that disrupted M(1) expression leads to aberrant behaviors and disrupted downstream signaling pathways that are rescued by lithium treatment. METHODS: The effects of miRNAs and chronic treatment with mood stabilizers on M(1) levels were tested in primary cultures and in rat frontal cortex. Effects of M(1) ablation and chronic treatment with mood stabilizers on several signaling cascades and M(1) -modulated behaviors were examined in wild-type and M(1) knockout mice. RESULTS: Let-7b, but not let-7c, negatively regulated M(1) levels. Chronic treatment with lithium, but not valproate, increased M(1) levels in the rat cortex. M(1) knockout mice exhibit ERK pathway deficits and behavioral hyperactivity; chronic treatment with lithium attenuated these deficits and hyperactivity. CONCLUSIONS: Lithium treatment can affect M(1) receptor function through intracellular signaling enhancement and, in situations without M(1) ablation, concomitant receptor upregulation via mechanisms involving miRNAs. Muscarinic dysfunction may contribute to mood disorders, while M(1) receptors and the downstream ERK pathway may serve as potential therapeutic targets for alleviating manic symptoms such as psychomotor hyperactivity.

The female urine sniffing test: a novel approach for assessing reward-seeking behavior in rodents.

BACKGROUND: Abnormal hedonic behavior is a key feature of many psychiatric disorders. Several paradigms measure reward-seeking behavior in rodents, but each has limitations. We describe a novel approach for monitoring reward-seeking behavior in rodents: sniffing of estrus female urine by male mice, along with number of ultrasonic vocalizations (USVs) emitted during the test. METHODS: The female urine sniffing test (FUST) was designed to monitor reward-seeking activity in rodents together with tests of helplessness and sweet solution preference. USVs and dopamine release from the nucleus accumbens (NAc) were recorded. Sniffing activity was measured in 1) manipulation-naive C57BL/6J and 129S1/SVImJ mice and Wistar-Kyoto rats; 2) stressed mice; 3) two groups of mice that underwent the learned helplessness paradigm-one untreated, and one treated with the SSRI citalopram; and 4) GluR6 knockout mice, known to display lithium-responsive, mania-related behaviors. RESULTS: Males from all three strains spent significantly longer sniffing female urine than sniffing water. Males emitted USVs and showed significantly elevated NAc dopamine levels while sniffing urine. Foot-shock stress significantly reduced female urine sniffing time. Compared with mice that did not undergo the LH paradigm, LH males spent less time sniffing female urine, and citalopram treatment alleviated this reduction. Compared with their wildtype littermates, GluR6KO males sniffed female urine longer and showed enhanced saccharin preference. CONCLUSIONS: In rodents, sniffing female urine is a preferred activity accompanied by biological changes previously linked to reward-seeking activities. The FUST is sensitive to behavioral and genetic manipulation and to relevant drug treatment.

Yeast bioassay for identification of inositol depleting compounds.

Bipolar affective disorder is a chronic, severe, debilitating illness affecting 1-2% of the population. Valproate, along with lithium and carbamazepine, are the only drugs for which long-term efficacy has been established. However, these drugs are ineffective for, and not well tolerated by, a large number of patients and are also associated with teratogenicity and reproductive defects. Therefore, there is a substantial need to develop more effective anti-bipolar drugs. We have previously shown that valproate, like lithium, decreases intracellular inositol, which supports the inositol depletion hypothesis. We employed inositol depletion in yeast as a screening tool to identify potential new anti-bipolar medications. We show here that hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, ethylhexanoate, and methyloctanoate decrease intracellular inositol levels and increase the expression of INO1, the gene encoding myo-inositol-3-phosphate synthase (MIPS). Similar to valproate, these inositol-depleting carboxylic acids inhibited MIPS indirectly. A correlation was shown between cell growth inhibition and the increase in INO1 expression by the carboxylic acids, factors that were reversed in the presence of inositol. Inositol depletion in yeast may be exploited as an easy and inexpensive screening test for potential new inositol depleting anti-bipolar drugs.

Lithium preferentially inhibits adenylyl cyclase V and VII isoforms.

Lithium ions' inhibition of adenylyl cyclase (AC) has not been previously studied for the newly discovered AC isoforms. COS7 cells were transfected with each of the nine membrane-bound AC isoforms cDNAs with or without D1- or D2-dopamine receptor cDNA. AC activity was measured as [3H]cAMP accumulation in cells pre-incubated with [3H]adenine followed by incubation with phosphodiesterase inhibitors together with either the D1 agonist SKF-82958 alone, or forskolin, in the presence or absence of the D2 agonist quinpirole. At 1 mm or 2 mm lithium inhibited only AC-V activity when the enzyme was stimulated by forskolin, a direct activator of AC. Lithium inhibited AC-V (by 50%), AC-VII (by 40%) and AC-II (by 25%) when stimulated via the D1 receptors, but did not affect the Ca2+-activated isoforms when stimulated by the Ca2+ ionophore A23187. Quinpirole inhibits AC via the Gi protein. Lithium did not affect quinpirole-inhibited FSK-activated AC-V activity nor did it affect superactivated AC-V or AC-I following the removal of quinpirole. The data suggest interference of lithium with transduction pathways mediated via AC-V or AC-VII; only the active conformation of these AC isoforms is inhibited by lithium; the inhibitory effect of lithium is abolished when the enzyme is superactivated. The marked inhibition of AC-V and AC-VII by lithium suggests that these two isoforms may be involved in mediating the mood-stabilizing effect of lithium.

Possible involvement of post-dopamine D2 receptor signalling components in the pathophysiology of schizophrenia.

Par-4 has been suggested to mediate dopamine neurotransmission. Dopamine D2 receptor (DRD2) activation induces a signalling complex of AKT1, PP2A and beta-arrestin2 which dephosphorylates/inactivates AKT1 thereby activating GSK-3beta, transducing dopamine-dependent behaviour. DRD2 activation also results in down-regulation of PKA activity. Among other substrates PKA phosphorylates GSK-3beta. Prolonged DRD2 activation leads to its 'desensitization' which involves GRKs and beta-arrestins. beta-arrestin1 binds to phosphorylated receptors preventing further G-protein stimulation. This study examined whether Par-4, beta-arrestin1, AKT1 and GSK-3beta are involved in the pathophysiology of schizophrenia. Lymphocytes obtained from schizophrenia and bipolar patients and healthy controls recruited from the Beer-Sheva Mental Health Center were transformed by Epstein-Barr virus (EBV) into lymphocyte-derived cell lines (LDCL). Post-mortem brain samples were obtained from the Rebecca L. Cooper Brain Bank, Parkville, Australia. The study was approved by the IRB committees of Beer-Sheva, Israel and Parkville, Australia. Levels of the specific proteins were assayed by Western blotting. beta-arrestin1 protein levels were significantly ~2-fold increased in LDCL from schizophrenia patients while Par-4 protein levels were unaltered. A 63% significant decrease was found in frontal cortex phospho-Ser9-GSK-3beta protein levels in schizophrenia but not in those of AKT1, Par-4 or beta-arrestin1. Elevated beta-arrestin1 protein levels in LDCL and decreased phospho-Ser9-GSK-3beta protein levels in post-mortem frontal cortex of schizophrenia patients vs. control groups support the possible involvement of these proteins in the pathophysiology of schizophrenia. However, since we did not find differences in beta-arrestin1, AKT1 and Par-4 protein levels in post-mortem frontal cortex of schizophrenia patients and although GSK-3beta participates in other signalling cascades we can not rule out the possibility that the differences found reflect deviation in DRD2 signalling.

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.

Effect of valproate derivatives on human brain myo-inositol-1-phosphate (MIP) synthase activity and amphetamine-induced rearing.

We have recently shown that valproate (VPA) decreases intracellular concentrations of inositol, like lithium but via a different mechanism, namely by inhibiting myo-inositol-1-phosphate (MIP) synthase. Valnoctamide (VCD) and valrocemide (VGD) are VPA derivatives which are anticonvulsants and have been shown in animal models to be significantly less teratogenic than VPA. We now show that 1 mM of either VCD or VGD drastically inhibits human brain crude homogenate MIP synthase activity. We studied the mechanism of the effect of VCD and found that it reduced the enzyme activity by an apparent competitive mode of inhibition at concentrations within the therapeutic range of VPA(Ki = 0.18 mM). We studied the behavioral effect of VGD and found that both lithium and VGD attenuated amphetamine-induced increase in rearing. These data support clinical study of these VPA-derivatives in bipolar disorder.

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.

Neurotrophic signaling cascades in the pathophysiology and treatment of bipolar disorder.

Increasing evidence suggests that bipolar disorder (BPD) is associated with regional brain volumetric reductions, accompanied by cellular atrophy and/or loss. Considerable data suggest that the protypical drugs for BPD--lithium and valproate--when administered in therapeutically relevant paradigms regulate neurotrophic signaling cascades. Notably, brain-derived neurotrophic factor, the extracellular signal-regulated kinase pathway, the glycogen synthase kinase-3-mediated pathway and Bcl-2 are major targets for mood stabilizers. Further data suggest that agents which directly target neurotrophic signaling cascades may have considerable utility for the treatment of this devastating illness.

Lymphocyte G-protein receptor kinase (GRK)3 mRNA levels in bipolar disorder.

Linkage studies in bipolar disorder were positive for markers in the region of chromosome 22q12.1 including the gene coding for G-protein receptor kinase (GRK)3. Two of six variants of the GRK3 5'-UTR/promoter were reported to be associated with bipolar disorder. GRK3 protein levels in lymphoblastoid cell lines derived from bipolar patients originating from families with linkage to chromosome 22q11 were reported to be decreased compared to those of control subjects and correlated with disease severity. We compared GRK3 mRNA levels in fresh lymphocytes from 31 bipolar patients vs. 26 control subjects, using real-time RT-PCR. No overall difference was found between patients and controls. However, GRK3 mRNA levels were markedly and significantly reduced in the subgroup of patients with no family history of a major psychiatric disorder compared with patients with family history.

Postmortem parietal cortex TPH2 expression is not altered in schizophrenic, unipolar-depressed, and bipolar patients vs control subjects.

Serotonin (5-hydroxytryptamine [5-HT]) is a neurotransmitter synthesized in the raphe nuclei of the brain stem in the central nervous system (CNS) and also in the periphery. Dysfunction of the serotonergic system has been implicated in the pathogenesis of psychiatric disorders. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in 5-HT biosynthesis. For more than a decade, only one gene encoding TPH was identified in vertebrates. Recently, a second TPH gene, designated TPH2, was detected, located on human chromosome 12, a susceptibility region for affective disorders. TPH2 is predominantly expressed in the brain, whereas the classical TPH gene, TPH1, is expressed in peripheral tissues. The discovery of the brain-abundant TPH2 gene justifies a new concept of the CNS serotonergic system. TPH2, rather than TPH1, has now become a candidate gene for 5-HT-related affective disorders. We compared TPH2 mRNA levels in postmortem parietal cortex of unipolar-depressed, bipolar, and schizophrenic patients vs control subjects, using real-time reverse transcription polymerase chain reaction. No significant difference in TPH2 mRNA levels was found among the four diagnostic groups. The lack of difference might suggest that this gene is not involved in the etiology of of these psychiatric disorders. Alternatively, it is possible that the parietal cortex is not the relevant brain area involved in the pathophysiology of these disorders or that posttranscriptional modifications of TPH2 mRNA occur in these patients, causing changes in protein levels and/or enzymatic activity.

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.

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.

Chronic lithium treatment affects rat brain and serum dehydroepiandrosterone (DHEA) and DHEA-sulphate (DHEA-S) levels.

Lithium (Li) is an established effective treatment for bipolar disorder. However, the molecular mechanism of its action is still unknown. Dehydroepiandrosterone (DHEA) and its sulphate ester (DHEA-S) are adrenal hormones also synthesized de novo in the brain as neurosteroids. Recent studies have suggested that DHEA has mood-elevating properties and may demonstrate antidepressant effects. 3(2)-Phosphoadenosine 5-phosphate (PAP) phosphatase is a novel Li-inhibitable enzyme involved in sulphation processes. In the present study we examined the impact of 10 d Li treatment on serum and brain DHEA and DHEA-S levels in rats. Our results show that Li administration lowered frontal cortex and hippocampus DHEA and DHEA-S levels, in line with our hypothesis assuming that Lis inhibition of PAP phosphatase leads to elevated PAP levels resulting in inhibition of sulphation and reduction in brain DHEA-S levels. Future studies should address the involvement of neurosteroids in the mechanism of Lis mood stabilization.

Possible role of 3'(2')-phosphoadenosine-5'-phosphate phosphatase in the etiology and therapy of bipolar disorder.

Bipolar affective disorder (BPD) is a multifactorial, severe, chronic and disabling illness with 50% heritability that affects 1-2% of the population. Lithium ions (Li) are the drug of choice for BPD. Yet, 20-40% of patients fail to respond to Li. Although numerous biochemical and cellular effects have been attributed to Li, its therapeutic mechanism of action has not been elucidated. This review presents the possible involvement of 3'(2')-phosphoadenosine-5'-phosphate (PAP) phosphatase in the etiology of bipolar disorder and the mechanism of action of Li. Of the enzymes inhibited by Li, PAP phosphatase is inhibited with the lowest Ki (0.3 mM). At therapeutic concentrations of Li (0.5-1.5 mM), inhibition is greater than 80%. Therefore, PAP phosphatase is a strong candidate for Li's therapeutic mechanism of action. In yeast, a PAP phosphatase knockout mutation leads to the accumulation of PAP, which affects ribosomal-, transfer- and small nucleolar-RNA processing. PAP accumulation in the mammalian brain following Li inhibition of PAP phosphatase may very well account for the observed effects of Li on gene expression and behavior. Furthermore, we have reported significant changes in PAP phosphatase levels in postmortem frontal cortex of bipolar patients.

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

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

Lithium inhibitable enzymes in postmortem brain of bipolar patients.

Despite considerable ongoing efforts at the epidemiological, genetic and molecular level, the etiology of bipolar disorder had not yet been elucidated. To study possible contributing components to the pathophysiology of this disorder, we have hypothesized that levels of enzymes inhibited by therapeutically relevant lithium ion concentrations in the brain of patients may differ from those in normal controls and may be involved in the etiology of the disorder. Three Li-inhibitable enzymes were studied in postmortem brain samples of bipolar patients and normal controls. The expression and function of the two enzymes that are obviously involved in signaling cascades, IMPase, involved in the second messenger system of the phosphatidylinositol cycle, and GSK-3, a mediator of an array of signaling cascades, were not found to be different in postmortem frontal and occipital cortex of bipolar patients and normal controls. Only PAP phosphatase protein levels, but not its mRNA levels or enzymatic activity, were found to be significantly decreased in frontal cortex of bipolar patients compared with normal controls.

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.