Cerebrospinal fluid metabolomics identifies a key role of isocitrate dehydrogenase in bipolar disorder: evidence in support of mitochondrial dysfunction hypothesis

Although evidence for mitochondrial dysfunction in the pathogenesis of bipolar disorder (BD) has been reported, the precise biological basis remains unknown, hampering the search for novel biomarkers. In this study, we performed metabolomics of cerebrospinal fluid (CSF) from male BD patients (n=54) and age-matched male healthy controls (n=40). Subsequently, post-mortem brain analyses, genetic analyses, metabolomics of CSF samples from rats treated with lithium or valproic acid were also performed. After multivariate logistic regression, isocitric acid (isocitrate) levels were significantly higher in the CSF from BD patients than healthy controls. Furthermore, gene expression of two subtypes (IDH3A and IDH3B) of isocitrate dehydrogenase (IDH) in the dorsolateral prefrontal cortex from BD patients was significantly lower than that of controls, although the expression of other genes including, aconitase (ACO1, ACO2), IDH1, IDH2 and IDH3G, were not altered. Moreover, protein expression of IDH3A in the cerebellum from BD patients was higher than that of controls. Genetic analyses showed that IDH genes (IDH1, IDH2, IDH3A, IDH3B) and ACO genes (ACO1, ACO2) were not associated with BD. Chronic (4 weeks) treatment with lithium or valproic acid in rats did not alter CSF levels of isocitrate, and mRNA levels of Idh3a, Idh3b, Aco1 and Aco2 genes in the rat brain. These findings suggest that abnormality in the metabolism of isocitrate by IDH3A in the mitochondria plays a key role in the pathogenesis of BD, supporting the mitochondrial dysfunction hypothesis of BD. Therefore, IDH3 in the citric acid cycle could potentially be a novel therapeutic target for BD.

Glutamate Signaling in Synaptogenesis and NMDA Receptors as Potential Therapeutic Targets for Psychiatric Disorders

Glutamate, a major excitatory neurotransmitter, plays important roles in synaptic plasticity, such as long-term potentiation (LTP) and new synapse formation. Growing evidence suggests that glutamate signaling is involved in the neurobiology of psychiatric disorders, including schizophrenia, major depressive disorder (MDD) and bipolar disorder (BP). Postmortem brain studies demonstrated altered spine density in brains from patients with these psychiatric disorders, indicating that remodeled neuronal circuits may contribute to the pathobiology of these psychiatric diseases. Drugs targeting the glutamate system have typically attracted attention as they show efficacy in animal studies and potential therapeutic effects in the clinical setting. In particular, the Nmethyl- D-aspartate (NMDA) receptor antagonist, ketamine exerts a rapid and robust antidepressant effect in treatment-resistant patients with MDD and BP, whereas conventional antidepressants require several weeks for therapeutic onset. Animal studies showed that ketamine induced rapid synaptogenesis, suggestive of synaptic plasticity via NMDA receptor signaling being an essential event in the treatment of depression. Therefore, drugs modulating glutamate signaling could also be potential therapeutic drugs for psychiatric disorders. First, we summarize the role of glutamate signaling on dendritic spine formation, maintenance and remodeling. Then, we discuss the abnormalities identified in dendritic spine and glutamate signaling from postmortem brain studies and animal models of psychiatric disorders. Finally, we review the potential benefits of drugs acting on the NMDA receptor in clinical and animal models of psychiatric disorders.

Cannabidivarin is anticonvulsant in mouse and rat

BACKGROUND AND PURPOSE

Phytocannabinoids in Cannabis sativa have diverse pharmacological targets extending beyond cannabinoid receptors and several exert notable anticonvulsant effects. For the first time, we investigated the anticonvulsant profile of the phytocannabinoid cannabidivarin (CBDV) in vitro and in in vivo seizure models.

EXPERIMENTAL APPROACH

The effect of CBDV (1-100 μM) on epileptiform local field potentials (LFPs) induced in rat hippocampal brain slices by 4-aminopyridine (4-AP) application or Mg(2+) -free conditions was assessed by in vitro multi-electrode array recordings. Additionally, the anticonvulsant profile of CBDV (50-200 mg·kg(-1) ) in vivo was investigated in four rodent seizure models: maximal electroshock (mES) and audiogenic seizures in mice, and pentylenetetrazole (PTZ) and pilocarpine-induced seizures in rats. The effects of CBDV in combination with commonly used antiepileptic drugs on rat seizures were investigated. Finally, the motor side effect profile of CBDV was investigated using static beam and grip strength assays.

KEY RESULTS

CBDV significantly attenuated status epilepticus-like epileptiform LFPs induced by 4-AP and Mg(2+) -free conditions. CBDV had significant anticonvulsant effects on the mES (≥100 mg·kg(-1) ), audiogenic (≥50 mg·kg(-1) ) and PTZ-induced seizures (≥100 mg·kg(-1) ). CBDV (200 mg·kg(-1) ) alone had no effect against pilocarpine-induced seizures, but significantly attenuated these seizures when administered with valproate or phenobarbital at this dose. CBDV had no effect on motor function.

CONCLUSIONS AND IMPLICATIONS

These results indicate that CBDV is an effective anticonvulsant in a broad range of seizure models. Also it did not significantly affect normal motor function and, therefore, merits further investigation as a novel anti-epileptic in chronic epilepsy models.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

Kojic acid production in an airlift bioreactor using partially hydrolyzed raw corn starch

In a culture of Aspergillus oryzae MK-107-39 in a 3-l airlift bioreactor, kojic acid was not produced when glucose/wheat germ medium (GM1) was used. However, when a jar fermentor was used, the kojic acid yield was high. A suitable medium for culture in an airlift bioreactor consisting of partially hydrolyzed corn starch and a small amount of corn steep liquor (CSL) (SM1) was selected. In the cultivation in the airlift bioreactor using SM1, nearly 40 g/l of kojic acid was produced, which was the same as the amount produced in the jar fermentor containing GM1. The optimum aeration rate for the airlift bioreactor was 2.0 vvm (0.66 cm/s of superficial linear velocity (Vs)). The cost of SM1 using the airlift bioreactor was reduced to 40% that of GM1 using the jar fermentor. Furthermore, the energy cost of kojic acid production using SM1 in the airlift bioreactor was less than one-fourth of that for the jar fermentor using GM1.

Improvement of production of Kojic acid by a mutant strain Aspergillus oryzae, MK107-39

A strain designated MK107-39, producing kojic acid with a high yield, was obtained by a new screening method using a 96-well microtiter plate after NTG treatment of Aspergillus oryze ATCC 22788. The amount of kojic acid produced by strain MK107-39 in a shaking flask was 28 g/l from 100 g/l of glucose, which was 7.7-times higher than that produced by parent strain. The kojic acid yields per cell and the amount of glucose consumed were 9.8 and 6.0-times higher than those of the parent strain. Based on differences in the use of carbohydrates and organic acids, it seems that strain MK107-39 has some mutation regarding carbohydrate metabolism. By customizing the medium and culture conditions such as glucose concentration, dissolved oxygen concentration and pH of the fermentation broth, more than 110 g/l of kojic acid was produced in a 3-l jar fermentor. Upon scale up to a 600-l pilot fermentor, enhanced production of kojic acid was successfully achieved. The kojic acid yield from glucose consumed, Y(P/S), was 0.43 (g/g) in this pilot plant-scale fermentation.

Abnormal expression of epidermal growth factor and its receptor in the forebrain and serum of schizophrenic patients

Epidermal growth factor (EGF) comprises a structurally related family of proteins containing heparin-binding EGF-like growth factor (HB-EGF) and transforming growth factor alpha (TGFalpha) that regulates the development of dopaminergic neurons as well as monoamine metabolism. We assessed the contribution of EGF to schizophrenia by measuring EGF family protein levels in postmortem brains and in fresh serum of schizophrenic patients and control subjects. EGF protein levels were decreased in the prefrontal cortex and striatum of schizophrenic patients, whereas the levels of HB-EGF and TGFalpha were not significantly different in any of the regions examined. Conversely, EGF receptor expression was elevated in the prefrontal cortex. Serum EGF levels were markedly reduced in schizophrenic patients, even in young, drug-free patients. Chronic treatment of animals with the antipsychotic drug haloperidol had no influence on EGF levels in the brain or serum. These findings suggest that there is abnormal EGF production in various central and peripheral tissues of patients with both acute and chronic schizophrenia. EGF might thus provide a molecular substrate for the pathologic manifestation of the illness, although additional studies are required to determine a potential link between impaired EGF signaling and the pathology/etiology of schizophrenia.

Neonatal perturbation of neurotrophic signaling results in abnormal sensorimotor gating and social interaction in adults: implication for epidermal growth factor in cognitive development

Epidermal growth factor (EGF) and its structurally related proteins are implicated in the developmental regulation of various brain neurons, including midbrain dopaminergic neurons. There are EGF and EGF receptor abnormalities in both brain tissues and blood from schizophrenic patients. We administered EGF to neonatal rats to transiently perturb endogenous EGF receptor signaling and evaluated the neurobehavioral consequences. EGF-treatment-induced transient impairment in tyrosine hydroxylase expression. The animals grew normally, exhibited normal weight increase, glial growth, and gross brain structures, and later lost the tyrosine hydroxylase abnormality. During and after development, however, the rats began to display various behavioral abnormalities. Abnormal sensorimotor gating was apparent, as measured by deficits in prepulse inhibition of acoustic startle. Motor activity and social interaction scores of the EGF-treated animals were also impaired in adult rats, though not in earlier developmental stages. In parallel, there was a significant abnormality in dopamine metabolism in the brain stem of the adult animals. Gross learning ability appeared to be normal as measured by active avoidance. These behavioral alterations, which are often present in schizophrenic models, were ameliorated by subchronic treatment with clozapine. Although the molecular and/or physiologic background(s) of these behavioral abnormalities await further investigation, the results of the present experiment indicate that abnormal EGF receptor stimulation given during limited neonatal stages can result in severe and persistent cognitive/behavioral dysfunctions, which appear only in adulthood.

Neurotrophins induce BDNF expression through the glutamate receptor pathway in neocortical neurons

Neurotrophins jointly exert various functions in the nervous system, including neuronal differentiation, survival, and regulation of synaptic plasticity. However, the functional interactions of neurotrophins or mechanisms through which neurotrophins regulate each other are still not clear. In the present study, brain-derived neurotrophic factor (BDNF) mRNA expression is induced by neurotrophin-4/5 (NT-4/5) and by BDNF itself in neocortical neurons. K252a, a specific tyrosine kinase (Trk) inhibitor, completely suppresses BDNF- and NT-4/5-enhanced BDNF mRNA expression. NT-4/5 significantly augments BDNF protein production, which is also reversed by K252a. When neurons are incubated with neurotrophin-3 (NT-3) or nerve growth factor (NGF), there are no significant changes in BDNF mRNA or protein expression. Interestingly, the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or the N-methyl-D-aspartate (NMDA) receptor blocker AP-5 completely suppresses NT-4/5-enhanced BDNF protein production, while tetrodotoxin (TTX) only suppresses NT-4/5-enhanced BDNF production by 50%. Additionally, the mitogen activated protein (MAP) kinase inhibitor PD98059 enhances BDNF-induced glutamate receptor-1 (GluR1) protein expression, but a phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 strongly reduces BDNF-induced GluR1 protein expression. Taken together, glutamate receptors are important for the regulation of BDNF expression by neurotrophins, and MAP and PI3K kinases differentially modulate AMPA receptor expression in the cortical neurons.

[The affinities of mosapramine for the dopamine receptor subtypes in human cell lines expressing D2, D3 and D4 receptors]

The affinities of mosapramine hydrochloride, an iminodibenzyl antipsychotic drug, for dopamine receptor subtypes were determined by human dopamine D2, D3 and D4 receptors expressed in several cell lines and compared with those of other neuroleptics. Tritiated spiperone bound to the membrane of transfected cells in a saturable manner, and the Kd values for dopamine D2, D3 and D4 receptors were 0.021, 0.12 and 0.10 nM, respectively. Mosapramine showed the highest affinities for these receptor subtypes among the antipsychotics tested. The ratio of Ki values between D2 and D3 (D2 Ki/D3 Ki ratio) in mosapramine was higher than that of haloperidol, indicating that the effects of mosapramine on D3 receptors were more potent than those of haloperidol. On the other hand, clozapine, risperidone and raclopride had higher affinity to D4, D2 and D3 subtypes, respectively. The affinities of mosapramine for D4 receptors was 8 times higher than that of clozapine, and the affinity for D3 receptors was 40 times higher than that of raclopride. These results suggest that the effect on D3 receptors may underlie at least a portion of mosapramine's atypical clinical profile.

[Quantitative autoradiographic analysis of the binding of mosapramine to dopamine D3-receptors]

The affinity of mosapramine, an iminodibenzyl antipsychotic, to dopamine D3-receptors in rat brain was investigated by quantitative autoradiography of [3H]-7-OH-DPAT, a selective D3-ligand. Autoradiograms showed restricted distribution of [3H]7-OH-DPAT binding sites, with very high levels on the islands of Calleja (ICj), olfactory tubercle (Tu) and nucleus accumbens, while low but distinct labeling was observed in the molecular layer of lobule 10 of the cerebellum and caudate putamen (CPu). Binding of [3H]7-OH-DPAT completely disappeared when 1 microM dopamine was added, and it was reduced by the addition of mosapramine in a concentration-dependent manner. The displacing effect of mosapramine was more potent than that of haloperidol or clozapine in the brain regions examined. Mosapramine showed more potent affinity to receptors in Tu and ICj than those in CPu. On the other hand, haloperidol and clozapine did not show such regional differences. These results suggest that the high affinity of mosapramine to D3-receptors participates in, at least in part, the development of the clinical effects of mosapramine.