Second-generation antipsychotic drugs, olanzapine, quetiapine, and clozapine enhance neurite outgrowth in PC12 cells via PI3K/AKT, ERK, and pertussis toxin-sensitive pathways

Neuroinflammation in schizophrenia especially focused on the role of microglia

An accumulating body of evidence point to the significance of neuroinflammation and immunogenetics also in schizophrenia. Recent genome-wide studies in schizophrenia suggest immune involvement in schizophrenia. Microglia are the resident macrophage of the brain and major players in innate immunity in the CNS. They respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia is closely associated with microglial activation. We and other researchers have shown the inhibitory effects of some typical or atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which are not only directly toxic to neurons but also cause a decrease in neurogenesis as well as white matter abnormalities in the brains of the patients with schizophrenia. The treatment through the inhibition of microglial activation may shed new light on the therapeutic strategy of schizophrenia.

Improving myelin/oligodendrocyte-related dysfunction: a new mechanism of antipsychotics in the treatment of schizophrenia?

Schizophrenia is a severe psychiatric disorder with complex clinical manifestations and its aetiological factors remain unclear. During the past decade, the oligodendrocyte-related myelin dysfunction was proposed as a hypothesis for schizophrenia, supported initially by a series of neuroimaging studies and genetic evidence. Recently, the effects of antipsychotics on myelination and oligodendroglial lineage development and their underlying molecular mechanisms were evaluated. Data from those studies suggest that the antipsychotics-resulting improvement in myelin/oligodendrocyte-related dysfunction may contribute, at least in part, to their therapeutic effect on schizophrenia. Importantly, these findings may provide the basis for a new insight into the therapeutic strategy by targeting the oligodendroglia lineage cells against schizophrenia.

Interferon-α induces nitric oxide synthase expression and haem oxygenase-1 down-regulation in microglia: implications of cellular mechanism of IFN-α-induced depression

Substantiating evidence for the inflammation theory of depression is that interferon-alpha (IFN-α) induces clinical depression. Despite numerous researches on neurochemical and neuroendocrinological mechanisms from human and animal studies, the direct mechanisms of IFN-α at cellular levels are still lacking. In this study, we aimed to identify the cellular mechanisms for IFN-α-induced neuroinflammatory response with the murine BV-2 microglia cell line. IFN-α potently induced nitric oxide synthase (iNOS) and nitric oxide (NO) release and down-regulated haem oxygenase-1 (HO-1) expression, which could be dampened by Janus kinase 1 (JAK1) and c-Jun NH2-terminal kinase (JNK) inhibition, respectively. IFN-α activated JAK1, JNK, signal transducers and activators of transcription (STAT)1 and STAT3, but not extracellular signal-regulated kinases (ERK) and phosphoinositide 3 (PI3) kinase, signal pathways. The transfection with STAT1 and STAT3 siRNA also inhibited IFN-α-induced iNOS/NO expression and HO-1 down-regulation. The HO-1 activator, CoppIX, reversed iNOS/NO up-regulation and HO-1 down-regulation induced by IFN-α. On the other hand, a knockdown of HO-1 expression enhanced IFN-α-induced iNOS/NO expression. The effects of IFN-α-induced iNOS/NO up-regulation and HO-1 down-regulation in microglia are associated with JAK1/JNK/STAT1 and STAT3 signalling pathways. The different effects between IFN-α and IFN-γ on HO-1 regulation and ERK phosphorylation might provide a possible explanation of different risk in their induction of neuropsychiatric adverse effects in clinical and animal studies. The results from this study add the missing part of direct cellular mechanisms for IFN-α-induced depression.

Effects of antipsychotic drugs on the expression of synaptic proteins and dendritic outgrowth in hippocampal neuronal cultures

Recent evidence has suggested that atypical antipsychotic drugs regulate synaptic plasticity. We investigated whether some atypical antipsychotic drugs (olanzapine, aripiprazole, quetiapine, and ziprasidone) altered the expression of synapse-associated proteins in rat hippocampal neuronal cultures under toxic conditions induced by B27 deprivation. A typical antipsychotic, haloperidol, was used for comparison. We measured changes in the expression of various synaptic proteins including postsynaptic density protein-95 (PSD-95), brain-derived neurotrophic factor (BDNF), and synaptophysin (SYP). Then we examined whether these drugs affected the dendritic morphology of hippocampal neurons. We found that olanzapine, aripiprazole, and quetiapine, but not haloperidol, significantly hindered the B27 deprivation-induced decrease in the levels of these synaptic proteins. Ziprasidone did not affect PSD-95 or BDNF levels, but significantly increased the levels of SYP under B27 deprivation conditions. Moreover, olanzapine and aripiprazole individually significantly increased the levels of PSD-95 and BDNF, respectively, even under normal conditions, whereas haloperidol decreased the levels of PSD-95. These drugs increased the total outgrowth of hippocampal dendrites via PI3K signaling, whereas haloperidol had no effect in this regard. Together, these results suggest that the up-regulation of synaptic proteins and dendritic outgrowth may represent key effects of some atypical antipsychotic drugs but that haloperidol may be associated with distinct actions.

Neurite outgrowth mediated by the heat shock protein Hsp90α: a novel target for the antipsychotic drug aripiprazole

Aripiprazole is an atypical antipsychotic drug approved for the treatment of psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder and autism. The drug shows partial agonistic activity at dopamine D(2) receptors and 5-hydroxytryptamine (5-HT) 5-HT(1A) receptors, and antagonistic activity at 5-HT(2A) receptors. However, the precise mechanistic pathways remain unclear. In this study, we examined the effects of aripiprazole on neurite outgrowth. Aripiprazole significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration-dependent manner. The 5-HT(1A) receptor antagonist WAY-100635, but not the dopamine D(2) receptor antagonist sulpiride, blocked the effects of aripiprazole, although, only partially. Specific inhibitors of inositol 1,4,5-triphosphate (IP(3)) receptors and BAPTA-AM, a chelator of intracellular Ca(2+), blocked the effects of aripiprazole. Moreover, specific inhibitors of several common signaling pathways phospholipase C-γ (PLC-γ), phosphatidylinositol-3 kinase (PI3K), mammalian target of rapamycin, p38 MAPK, c-Jun N-terminal kinase, Akt, Ras, Raf, ERK, MAPK) also blocked the effects of aripiprazole. Using proteomic analysis, we found that aripiprazole significantly increased levels of the heat shock protein Hsp90α in cultured cells. The effects of aripiprazole on NGF-induced neurite outgrowth were significantly attenuated by treatment with Hsp90α RNA interference, but not by the negative control of Hsp90α. These findings suggest that both 5-HT(1A) receptor activation and Ca(2+) signaling via IP(3) receptors, as well as their downstream cellular signaling pathways play a role in the promotion of aripiprazole-induced neurite outgrowth. Furthermore, aripiprazole-induced increases in Hsp90α protein expression may form part of the therapeutic mechanism for this drug.

Clozapine induction of ERK1/2 cell signalling via the EGF receptor in mouse prefrontal cortex and striatum is distinct from other antipsychotic drugs

Treatment resistance remains a major obstacle in schizophrenia, with antipsychotic drugs (APDs) being ineffective in about one third of cases. Poor response to standard therapy leaves the APD clozapine as the only effective treatment for many patients. The reason for the superior efficacy of clozapine is unknown, but as we have proposed previously it may involve modulation of neuroplasticity and connectivity through induction of interconnected mitogenic signalling pathways. These include the mitogen-activated protein kinase-extracellular signal regulated kinase (MAPK-ERK) cascade and epidermal growth factor (EGF)/ErbB systems. Clozapine, distinct from other APDs, induced initial inhibition and subsequent activation of the ERK response in prefrontal cortical (PFC) neurons in vitro and in vivo, an action mediated by the EGF receptor (ErbB1). Here we examine additionally the striatum of C57Bl/6 mice to determine if clozapine, olanzapine, and haloperidol differentially regulate the ERK1/2 pathway in a region or time-specific manner conditional on the EGF receptor. Following acute treatment, only clozapine caused delayed striatal ERK phosphorylation through EGF receptor phosphorylation (tyrosine 1068 site) and MEK that paralleled cortical ERK phosphorylation. Olanzapine induced initial pERK1-specific blockade and an elevation 24-h later in PFC but had no effect in the striatum. By contrast, haloperidol significantly stimulated pERK1 in striatum for up to 8 h, but exerted limited effect in PFC. Clozapine but not olanzapine or haloperidol recruited the EGF receptor to signal to ERK. These in-vivo data reinforce our previous findings that clozapine's action may be uniquely linked to the EGF signalling system, potentially contributing to its distinctive clinical profile.

A chemical genetic approach identifies piperazine antipsychotics as promoters of CNS neurite growth on inhibitory substrates

Injury to the central nervous system (CNS) can result in lifelong loss of function due in part to the regenerative failure of CNS neurons. Inhibitory proteins derived from myelin and the astroglial scar are major barriers for the successful regeneration of injured CNS neurons. Previously, we described the identification of a novel compound, F05, which promotes neurite growth from neurons challenged with inhibitory substrates in vitro, and promotes axonal regeneration in vivo (Usher et al., 2010). To identify additional regeneration-promoting compounds, we used F05-induced gene expression profiles to query the Broad Institute Connectivity Map, a gene expression database of cells treated with >1300 compounds. Despite no shared chemical similarity, F05-induced changes in gene expression were remarkably similar to those seen with a group of piperazine phenothiazine antipsychotics (PhAPs). In contrast to antipsychotics of other structural classes, PhAPs promoted neurite growth of CNS neurons challenged with two different glial derived inhibitory substrates. Our pharmacological studies suggest a mechanism whereby PhAPs promote growth through antagonism of calmodulin signaling, independent of dopamine receptor antagonism. These findings shed light on mechanisms underlying neurite-inhibitory signaling, and suggest that clinically approved antipsychotic compounds may be repurposed for use in CNS injured patients.

Clozapine impairs insulin action by up-regulating Akt phosphorylation and Ped/Pea-15 protein abundance

Clinical and experimental evidence indicates that atypical antipsychotics impair glucose metabolism. We investigated whether clozapine may directly affect insulin action by analyzing insulin signaling in vitro and in vivo. Clozapine reduced insulin-stimulated glucose uptake in PC12 and in L6 cells, representative models of neuron and skeletal muscle, respectively. Consistently, clozapine reduced insulin effect on insulin receptor (IR) by 40% and on IR substrate-1 (IRS1) tyrosine phosphorylation by 60%. Insulin-stimulated Akt phosphorylation was also reduced by about 40%. Moreover, insulin-dependent phosphorylation of protein kinase C-ζ (PKC-ζ) was completely blunted in clozapine-treated cells. Interestingly, clozapine treatment was accompanied by an insulin-independent increase of Akt phosphorylation, with no change of IR, IRS1, and PKC-ζ basal phosphorylation. The cellular abundance of Ped/Pea-15, an Akt substrate and inducer of insulin resistance, was also increased following clozapine exposure, both in the absence and in the presence of cyclohexymide, a protein synthesis inhibitor. Similar as in cellular models, in the caudate-putamen and in the tibialis muscle of clozapine-treated C57/BL/KsJ mice, Akt phosphorylation and Ped/Pea-15 protein levels were increased and PKC-ζ phosphorylation was decreased. Thus, in these experimental models, clozapine deranged Akt function and up-regulated Ped/Pea-15, thereby inhibiting insulin stimulation of PKC-ζ and of glucose uptake.

Clozapine protects dopaminergic neurons from inflammation-induced damage by inhibiting microglial overactivation

Increasing evidence suggests a possible involvement of neuroinflammation in some psychiatric disorders, and also pharmacological reports indicate that anti-inflammatory effects are associated with therapeutic actions of psychoactive drugs, such as anti-depressants and antipsychotics. The purpose of this study was to explore whether clozapine, a widely used antipsychotic drugs, displays anti-inflammatory and neuroprotective effects. Using primary cortical and mesencephalic neuron-glia cultures, we found that clozapine was protective against inflammation-related neurodegeneration induced by lipopolysaccharide (LPS). Pretreatment of cortical or mesencephalic neuron-glia cultures with clozapine (0.1 or 1 μM) for 24 h attenuated LPS-induced neurotoxicity. Clozapine also protected neurons against 1-methyl-4-phenylpyridinium(+) (MPP(+))-induced neurotoxicity, but only in cultures containing microglia, indicating an indispensable role of microglia in clozapine-afforded neuroprotection. Further observation revealed attenuated LPS-induced microglial activation in primary neuron-glia cultures and in HAPI microglial cell line with clozapine pretreatment. Clozapine ameliorated the production of microglia-derived superoxide and intracellular reactive oxygen species (ROS), as well as the production of nitric oxide and TNF-α following LPS. In addition, the protective effect of clozapine was not observed in neuron-glia cultures from mice lacking functional NADPH oxidase (PHOX), a key enzyme for superoxide production in immune cells. Further mechanistic studies demonstrated that clozapine pretreatment inhibited LPS-induced translocation of cytosolic subunit p47(phox) to the membrane in microglia, which was most likely through inhibiting the phosphoinositide 3-kinase (PI3K) pathway. Taken together, this study demonstrates that clozapine exerts neuroprotective effect via the attenuation of microglia activation through inhibition of PHOX-generated ROS production and suggests potential use of antipsychotic drugs for neuroprotection.

Dysregulated mTORC1-Dependent Translational Control: From Brain Disorders to Psychoactive Drugs

In the last decade, a plethora of studies utilizing pharmacological, biochemical, and genetic approaches have shown that precise translational control is required for long-lasting synaptic plasticity and the formation of long-term memory. Moreover, more recent studies indicate that alterations in translational control are a common pathophysiological feature of human neurological disorders, including developmental disorders, neuropsychiatric disorders, and neurodegenerative diseases. Finally, translational control mechanisms are susceptible to modification by psychoactive drugs. Taken together, these findings point to a central role for translational control in the regulation of synaptic function and behavior.

Mechanisms of antidepressant action: an integrated dopaminergic perspective

The molecular mechanisms that cause and maintain the major depressive disorder (MDD) are currently unknown. Consistently, antidepressant treatments are characterized by insufficient success rates. This causes high social costs and severe personal sufferings. In the present review we analyze some of the paradigms that are used to explain MDD, particularly from the perspective of the dopaminergic (DA) system. DA has been more classically associated with psychosis and substance abuse disorders, even though a role of DA in MDD has been proposed as well and some antidepressants with DA profile exist. In the present work, we review some of the molecular mechanisms that underpin MDD from the perspective of the dopaminergic system, in the hope of unifying some of the major theories of MDD - the monoaminergic, inflammatory, epigenetics, neurotrophin and anti-apoptotic theories. Several shared components of these theories are highlighted, partially accounted by the functions of the DA system (see supplementary video).

Clozapine and lithium require Caenorhabditis elegans β-arrestin and serum- and glucocorticoid-inducible kinase to affect Daf-16 (FOXO) localization

Numerous studies have implicated low levels of signaling in the Akt network with psychotic illnesses, and a growing body of literature has shown that all classes of antipsychotic drugs increase Akt signaling. The most clinically effective antipsychotic drug is clozapine. With Caenorhabditis elegans as a model system, this study demonstrates that clozapine is unique among antipsychotic drugs because it requires β-arrestin and serum and glucocorticoid-inducible kinase (SGK) in addition to Akt to suppress the nuclear localization of DAF-16 (Forkhead box O [FOXO]). Lithium, a mood stabilizer often used to treat psychosis, also requires β-arrestin and SGK to suppress the nuclear localization of DAF-16.

Inhibition of Akt with small molecules and biologics: historical perspective and current status of the patent landscape

INTRODUCTION

Akt plays a pivotal role in cell survival and proliferation through a number of downstream effectors; unregulated activation of the PI3K/PTEN/Akt pathway is a prominent feature of many human cancers. Akt is considered an attractive target for cancer therapy by the inhibition of Akt alone or in combination with standard cancer chemotherapeutics. Both preclinical animal studies and clinical trials in humans have validated Akt as an important target of cancer drug discovery.

AREA COVERED

A historical perspective of Akt inhibitors, including PI analogs, ATP-competitive and allosteric Akt inhibitors, along with other inhibitory mechanisms are reviewed in this paper with a focus on issued patents, patent applications and a summary of clinical trial updates since the last review in 2007.

EXPERT OPINION

A vast diversity of inhibitors of Akt, both small molecule and biologic, have been developed in the past 5 years, with over a dozen in various phases of clinical development, and several displaying efficacy in humans. While it is not yet clear which mechanism of Akt inhibition will be optimal in humans, or which Akt isoforms to inhibit, or whether a small molecule or biologic agent will be best, data to all of these points will be available in the near future.

Weight gain, schizophrenia and antipsychotics: new findings from animal model and pharmacogenomic studies

Excess body weight is one of the most common physical health problems among patients with schizophrenia that increases the risk for many medical problems, including type 2 diabetes mellitus, coronary heart disease, osteoarthritis, and hypertension, and accounts in part for 20% shorter life expectancy than in general population. Among patients with severe mental illness, obesity can be attributed to an unhealthy lifestyle, personal genetic profile, as well as the effects of psychotropic medications, above all antipsychotic drugs. Novel "atypical" antipsychotic drugs represent a substantial improvement on older "typical" drugs. However, clinical experience has shown that some, but not all, of these drugs can induce substantial weight gain. Animal models of antipsychotic-related weight gain and animal transgenic models of knockout or overexpressed genes of antipsychotic receptors have been largely evaluated by scientific community for changes in obesity-related gene expression or phenotypes. Moreover, pharmacogenomic approaches have allowed to detect more than 300 possible candidate genes for antipsychotics-induced body weight gain. In this paper, we summarize current thinking on: (1) the role of polymorphisms in several candidate genes, (2) the possible roles of various neurotransmitters and neuropeptides in this adverse drug reaction, and (3) the state of development of animal models in this matter. We also outline major areas for future research.

Docosahexaenoic acid suppresses neuroinflammatory responses and induces heme oxygenase-1 expression in BV-2 microglia: implications of antidepressant effects for ω-3 fatty acids

Accumulating evidence suggests that the pathophysiology of depression might be associated with neuroinflammation, which could be attenuated by pharmacological treatment for depression. Omega-3 polyunsaturated fatty acids (PUFAs) are anti-inflammatory and exert antidepressant effects. The aim of this study was to identify the molecular mechanisms through which docosahexaenoic acid (DHA), the main omega-3 PUFA in the brain, modulates oxidative reactions and inflammatory cytokine production in microglial and neuronal cells. The results of this study showed that DHA reduced expressions of tumor necrosis factor-α, interleukin-6, nitric oxide synthase, and cyclo-oxygenase-2, induced by interferon-γ, and induced upregulation of heme oxygenase-1 (HO-1) in BV-2 microglia. The inhibitory effect of DHA on nitric oxide production was abolished by HO-1 inhibitor zinc protoporphyrin IX. In addition, DHA caused AKT and ERK activation in a time-dependent manner, and the DHA-induced HO-1 upregulation could be attenuated by PI-3 kinase/AKT and MEK/ERK inhibitors. DHA also increased IKKα/β phosphorylation, IκBα phosphorylation, and IκBα degradation, whereas both nuclear factor-κB and IκB protease inhibitors could inhibit DHA-induced HO-1 expressions. The other major n-3 PUFA, eicosapentaenoic acid, showed similar effects of DHA on inflammation and HO-1 in repeated key experiments. In connecting with inflammation hypothesis of depression and clinical studies supporting the antidepressant effects of omega-3 PUFAs, this study provides a novel implication of the antidepressant mechanisms of DHA.

Antipsychotic drugs activate the C. elegans akt pathway via the DAF-2 insulin/IGF-1 receptor

The molecular modes of action of antipsychotic drugs are poorly understood beyond their effects at the dopamine D2 receptor. Previous studies have placed Akt signaling downstream of D2 dopamine receptors, and recent data have suggested an association between psychotic illnesses and defective Akt signaling. To characterize the effect of antipsychotic drugs on the Akt pathway, we used the model organism C. elegans, a simple system where the Akt/forkhead box O transcription factor (FOXO) pathway has been well characterized. All major classes of antipsychotic drugs increased signaling through the insulin/Akt/FOXO pathway, whereas four other drugs that are known to affect the central nervous system did not. The antipsychotic drugs inhibited dauer formation, dauer recovery, and shortened lifespan, three biological processes affected by Akt signaling. Genetic analysis showed that AKT-1 and the insulin and insulin-like growth factor receptor, DAF-2, were required for the antipsychotic drugs to increase signaling. Serotonin synthesis was partially involved, whereas the mitogen activated protein kinase (MAPK), SEK-1 is a MAP kinase kinase (MAPKK), and calcineurin were not involved. This is the first example of a common but specific molecular effect produced by all presently known antipsychotic drugs in any biological system. Because untreated schizophrenics have been reported to have low levels of Akt signaling, increased Akt signaling might contribute to the therapeutic actions of antipsychotic drugs.

Dysregulation of the norepinephrine transporter sustains cortical hypodopaminergia and schizophrenia-like behaviors in neuronal rictor null mice

The mammalian target of rapamycin (mTOR) complex 2 (mTORC2) is a multimeric signaling unit that phosphorylates protein kinase B/Akt following hormonal and growth factor stimulation. Defective Akt phosphorylation at the mTORC2-catalyzed Ser473 site has been linked to schizophrenia. While human imaging and animal studies implicate a fundamental role for Akt signaling in prefrontal dopaminergic networks, the molecular mechanisms linking Akt phosphorylation to specific schizophrenia-related neurotransmission abnormalities have not yet been described. Importantly, current understanding of schizophrenia suggests that cortical decreases in DA neurotransmission and content, defined here as cortical hypodopaminergia, contribute to both the cognitive deficits and the negative symptoms characteristic of this disorder. We sought to identify a mechanism linking aberrant Akt signaling to these hallmarks of schizophrenia. We used conditional gene targeting in mice to eliminate the mTORC2 regulatory protein rictor in neurons, leading to impairments in neuronal Akt Ser473 phosphorylation. Rictor-null (KO) mice exhibit prepulse inhibition (PPI) deficits, a schizophrenia-associated behavior. In addition, they show reduced prefrontal dopamine (DA) content, elevated cortical norepinephrine (NE), unaltered cortical serotonin (5-HT), and enhanced expression of the NE transporter (NET). In the cortex, NET takes up both extracellular NE and DA. Thus, we propose that amplified NET function in rictor KO mice enhances accumulation of both NE and DA within the noradrenergic neuron. This phenomenon leads to conversion of DA to NE and ultimately supports both increased NE tissue content as well as a decrease in DA. In support of this hypothesis, NET blockade in rictor KO mice reversed cortical deficits in DA content and PPI, suggesting that dysregulation of DA homeostasis is driven by alteration in NET expression, which we show is ultimately influenced by Akt phosphorylation status. These data illuminate a molecular link, Akt regulation of NET, between the recognized association of Akt signaling deficits in schizophrenia with a specific mechanism for cortical hypodopaminergia and hypofunction. Additionally, our findings identify Akt as a novel modulator of monoamine homeostasis in the cortex.

Effect of dopamine D3 receptor gene polymorphisms and clozapine treatment response: exploratory analysis of nine polymorphisms and meta-analysis of the Ser9Gly variant

D2 blockade has been implicated in having a central role in antipsychotic response. However, treatment refractoriness, in spite of complete D2 blockade, as well as the efficacy of clozapine (CLZ) in a portion of this patient population, indicates the involvement of other factors as well. Several lines of evidence suggest a role for D3. Furthermore, an earlier meta-analysis by Jönsson et al. (2003) (n=233) suggested a role for genetic variation in the D3 gene. Relevant to this study, Jönsson et al. found the Ser allele of the D3 serine-to-glycine substitution at amino acid position 9 (Ser9Gly) polymorphism to be associated with worse CLZ response compared with the Gly allele. In this study, we attempt to validate these findings by performing a meta-analysis in a much larger sample (n=758). Eight other variants were also tested in our own sample to explore the possible effect of other regions of the gene. We report a negative but consistent trend across individual studies in our meta-analysis for the DRD3 Ser allele and poor CLZ response. A possible minor role for this single-nucleotide polymorphism cannot be disregarded, as our sample size may have been insufficient. Other DRD3 variants and haplotypes of possible interest were also identified for replication in future studies.

Nerve growth factor mediated SH2-Bbeta/Akt signal pathway activated in allergic airway challenge in mice

BACKGROUND AND OBJECTIVE

Nerve growth factor (NGF) contributes to airway inflammation and bronchoconstriction in allergic asthma. The Src homology 2beta/serine/threonine kinase (SH2-Bbeta/Akt) pathway is one of the avenues through which NGF regulates the biological activity of pheochromocytoma (PC)12 cells. It has also been reported that NGF upregulates the expression of SH2-Bbeta in the lung tissue of asthmatic mice. The present study investigated the effects of NGF and SH2-Bbeta on Akt activation during allergic airway challenge.

METHODS

BALB/c mice were sensitized and challenged with ovalbumin. The effects of NGF and SH2-Bbeta on Akt in allergic airway challenge were assessed by intravenously administering anti-NGF antibody or a mutant of SH2-Bbeta (R555E) to these mice. Pulmonary histological changes were then assessed and the inflammatory cells in the BAL fluid (BALF) were counted. Additionally, phosphorylated Akt (p-Akt) expression was determined by fluorescence microscopy, western blotting and quantitative RT-PCR. Airway resistance was also measured using closed-type body plethysmography.

RESULTS

We observed p-Akt overexpression in the lungs after allergen challenge by fluorescence microscopy, Western blotting and RT-PCR, as compared with the control. However, after treatment with anti-NGF or R555E, p-Akt levels and allergen-induced airway inflammation were reduced in comparison with those of allergen-challenged mice. Anti-NGF and R555E also decreased airway hyperresponsiveness caused by allergen challenge in response to methacholine (MCH).

CONCLUSIONS

These results suggest that SH2-Bbeta regulation of Akt partly participates in the NGF-mediated development of allergic airway challenge.

The neurotrophic and neuroprotective effects of psychotropic agents

Accumulating evidence suggests that psychotropic agents such as mood stabilizers, antidepressants, and antipsychotics realize their neurotrophic/neuroprotective effects by activating the mitogen activated protein kinaselextracellular signal-related kinase, PI3-kinase, and winglesslglycogen synthase kinase (GSK) 3 signaling pathways. These agents also upregulate the expression of trophic/protective molecules such as brain-derived neurotrophic factor, nerve growth factor, B-cell lymphoma 2, serine-threonine kinase, and Bcl-2 associated athanogene 1, and inactivate proapoptotic molecules such as GSK-3, They also promote neurogenesis and are protective in models of neurodegenerative diseases and ischemia. Most if not all, of this evidence was collected from animal studies that used clinically relevant treatment regimens. Furthermore, human imaging studies have found that these agents increase the volume and density of brain tissue, as well as levels of N-acetyl aspartate and glutamate in selected brain regions. Taken together, these data suggest that the neurotrophic/neuroprotective effects of these agents have broad therapeutic potential in the treatment, not only of mood disorders and schizophrenia, but also neurodegenerative diseases and ischemia.

Structure-based discovery of low molecular weight compounds that stimulate neurite outgrowth and substitute for nerve growth factor

Olanzapine, an atypical antipsychotic drug, was previously shown to protect neuronal cells against nutrient deprivation and to enhance neurite outgrowth. In an effort to identify small molecules with greater potency, the structure of olanzapine was used as a template to search commercially available chemical inventories for compounds with similar features. These compounds were evaluated for their ability to protect cells against glutamine deprivation and low-serum conditions. Positive compounds, 'hits' from initial screening, were then tested for stimulation of neurite outgrowth, alone and in combination with suboptimum concentrations of nerve growth factor (NGF). Numerous neuroprotective compounds (mw < 550 Da) were identified that significantly stimulated neurite outgrowth in PC12 cells. These included 4', 6'-diamidino-2-phenylindole, a nuclear stain; staurosporine, an antibiotic and kinase inhibitor; and 2-phenylamino-adenosine, an adenosine analog. The small molecules were comparable with NGF, and in fact, replaced NGF in outgrowth assays. Pharmacophore analysis of the hits led to the design and synthesis of an active compound, LSU-D84, which represented an initial lead for drug discovery efforts.

Cytokines and schizophrenia: Microglia hypothesis of schizophrenia

The etiology of schizophrenia remains unclear, while there has been a growing amount of evidence for the neuroinflammation and immunogenetics, which are characterized by an increased serum concentration of several pro-inflammatory cytokines. Despite the fact that microglia comprise only <10% of the total brain cells, microglia respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia has recently been reported to be closely associatedwith microglial activation. Previous studies have shown the inhibitory effects of some typical/atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which have recently been known to cause a decrease in neurogenesis as well as white matter abnormalities in the brains of patients with schizophrenia. The microglia hypothesis of schizophrenia may shed new light on the therapeutic strategy for schizophrenia.

Clozapine-induced ERK1 and ERK2 signaling in prefrontal cortex is mediated by the EGF receptor

The atypical antipsychotic drug clozapine is effective in treatment-refractory schizophrenia. The intracellular signaling pathways that mediate clozapine action remain unknown. A potential candidate is the mitogen-activated protein kinase extracellular signal-regulated kinase (MAPK-ERK) cascade that links G-protein-coupled receptor and ErbB growth factor signaling systems, thereby regulating synaptic plasticity and connectivity, processes impaired in schizophrenia. Here, we examined how clozapine differentially modulated phosphorylation of the MAPK isoforms, ERK1/ERK2 in primary murine prefrontal cortical neurons compared to the typical antipsychotic drug haloperidol. While clozapine and haloperidol acutely decreased cortical pERK1 activation, only clozapine but not haloperidol stimulated pERK1 and pERK2 with continued drug exposure. This delayed ERK increase however, did not occur via the canonical dopamine D(2)-Gi/o-PKA or serotonin 5HT(2A)-Gq-phospholipase-C-linked signaling pathways. Rather, epidermal growth factor (EGF) receptor signaling mediated clozapine-induced ERK activation, given dose-dependent reduction of pERK1 and pERK2 stimulation with the EGF receptor inhibitor, AG1478. Immunocytochemical studies indicated that clozapine treatment increased EGF receptor (Tyr1068) phosphorylation. In vivo mouse treatment studies supported the in vitro findings with initial blockade, subsequent activation, and normalization of the cortical ERK response over 24 h. Furthermore, in vivo clozapine-induced ERK activation was significantly reduced by AG1478. This is the first report that clozapine action on prefrontal cortical neurons involves the EGF signaling system. Since EGF receptor signaling has not been previously linked to antipsychotic drug action, our findings may implicate the EGF system as a molecular substrate in treatment-resistant schizophrenia.

Increased grey matter densities in schizophrenia patients with negative symptoms after treatment with quetiapine: a voxel-based morphometry study

Among new-generation antipsychotics, quetiapine was found to be associated with a partial 'normalization' of reduced functional activation in prefrontal and temporal areas and studies conducted by our group found a clinical improvement in negative symptoms in addition to restoration of frontal activation in schizophrenia patients with blunted affect after treatment with quetiapine. Here we investigated the parallelism between improved clinical symptoms and grey mater density (GMD) changes in the frontal region after quetiapine treatment in 15 schizophrenia patients. We hypothesize that improvement in clinical symptoms will be associated with change in GMD in prefrontal regions of interest. By using voxel-based morphometry, paired t-test random-effect analysis showed a significant increase in GMD bilaterally in the inferior frontal cortex/orbitofrontal gyrus and anterior cingulate cortex after 5.5 months of treatment with quetiapine. This GMD increase was associated with a significant improvement in negative symptoms. When GMD was correlated with psychiatric assessment scores, there was a negative correlation between GMD in the anterior cingulate cortex and the Rating Scale for Emotional Blunting score (r=-665, P=0.008) and between the orbitofrontal gyrus and the total Positive and Negative Syndrome Scale negative score (r=-764, P=0.001). Results suggest that increased GMD in some frontal regions are associated with an improvement of negative symptoms. Although not unique to quetiapine, it would be reasonable to attribute the GMD changes in the study to treatment.

Antipsychotic drug mechanisms: links between therapeutic effects, metabolic side effects and the insulin signaling pathway

The exact therapeutic mechanism of action of antipsychotic drugs remains unclear. Recent evidence has shown that second-generation antipsychotic drugs (SGAs) are differentially associated with metabolic side effects compared to first-generation antipsychotic drugs (FGAs). Their proclivity to cause metabolic disturbances correlates, to some degree, with their comparative efficacy. This is particularly the case for clozapine and olanzapine. In addition, the insulin signaling pathway is vital for normal brain development and function. Abnormalities of this pathway have been found in persons with schizophrenia and antipsychotic drugs may ameliorate some of these alterations. This prompted us to hypothesize that the therapeutic antipsychotic and adverse metabolic effects of antipsychotic drugs might be related to a common pharmacologic mechanism. This article reviews insulin metabolism in the brain and related abnormalities associated with schizophrenia with the goals of gaining insight into antipsychotic drug effects and possibly also into the pathophysiology of schizophrenia. Finally, we speculate about one potential mechanism of action (that is, functional selectivity) that would be consistent with the data reviewed herein and make suggestions for the future investigation that is required before a therapeutic agent based on these data can be realized.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Protective effects of olanzapine and haloperidol on serum withdrawal-induced apoptosis in SH-SY5Y cells

PURPOSE

Recent clinical studies have suggested that treatment with second generation antipsychotic drugs such as olanzapine may prevent progressive alterations of brain structure in patients with schizophrenia. However, the molecular mechanisms underlying these different effects remain to be determined. We investigated the mechanisms of action of olanzapine and haloperidol, on serum withdrawal apoptosis in human neuroblastoma SH-SY5Y cells.

METHODS

SH-SY5Y cells were cultured with olanzapine and haloperidol in medium with or without serum. We determined the effects of the drugs on cell viability against serum withdrawal by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Additionally, to explore the drugs' actions, Western blot was performed to examine the expression of key genes involved in GSK-3beta-mediated signaling, notably GSK-3beta, beta-catenin, and Bcl-2.

RESULTS

SH-SY5Y cells suffered about a 38% loss in cell number under serum-free conditions for 48 h. Olanzapine (10-200 muM) up to 100 muM significantly attenuated serum withdrawal-induced cell loss (p<0.01), and a dose of 100 muM also increased cell viability (p<0.05). In contrast, haloperidol (0.01-10 muM) did not affect cell viability but exacerbated cell death at 10 muM under serum-free conditions (p<0.01). Western blot analysis showed that olanzapine, but not haloperidol, prevented the serum withdrawal-induced decrease in levels of neuroprotective proteins such as p-GSK-3beta, beta-catenin, and Bcl-2 (p<0.01), whereas haloperidol robustly reduced the levels of these proteins at a 10 muM dose in serum-starved cells (p<0.05). Moreover, olanzapine alone significantly increased phosphorylation of GSK-3beta under normal conditions (p<0.05).

CONCLUSIONS

This study showed that olanzapine may have neuroprotective effects, whereas haloperidol was apparently neurotoxic. The actions of signaling systems associated with GSK-3beta may be key targets for olanzapine and haloperidol, but their effects are distinct. These differences suggest different therapeutic effects of first and second generation antipsychotic drugs in patients with schizophrenia.

The effect of atypical antipsychotics, perospirone, ziprasidone and quetiapine on microglial activation induced by interferon-gamma

An accumulating body of evidences point to the significance of neuroinflammation and immunogenetics in schizophrenia, characterized by increased serum concentration of several pro-inflammatory cytokines. In the central nervous system (CNS), the microglial cells are the major immunocompetent cells which release pro-inflammatory cytokines, nitric oxide (NO) and reactive oxygen species to mediate the inflammatory process. In the present study, we investigated whether or not atypical antipsychotics, namely perospirone, quetiapine and ziprasidone, would have anti-inflammatory effects on the activated microglia which may potentiate neuroprotection. All three atypical antipsychotics significantly inhibited NO generation from activated microglia while perospirone and quetiapine significantly inhibited the TNF-alpha release from activated microglia. Antipsychotics, especially perospirone and quetiapine may have an anti-inflammatory effect via the inhibition of microglial activation, which is not only directly toxic to neurons but also has an inhibitory effect on neurogenesis and oligodendrogenesis, both of which have been reported to play a crucial role in the pathology of schizophrenia.

In vitro functional characteristics of dopamine D2 receptor partial agonists in second and third messenger-based assays of cloned human dopamine D2Long receptor signalling

Aripiprazole, (+)terguride, OPC-4392 and (-)3-PPP have been classified as dopamine D(2) receptor partial agonists based largely on their activity in second messenger-based assays of dopamine D(2) receptor signalling. Nevertheless, signal transduction amplification might result in these compounds behaving as dopamine D(2) receptor full agonists at a more downstream level of signalling. We compared the intrinsic activity (E(max), expressed as a percentage of the maximal effect of dopamine) of aripiprazole, (+)terguride, OPC-4392 and (-)3-PPP using second (calcium (Ca(2+)) mobilization) and third (extracellular signal-regulated kinase 2 (ERK2) phosphoprotein expression) messenger readouts of cloned human dopamine D(2long) (hD(2L)) receptor signalling in CHO cells. These compounds were all less potent and displayed lower intrinsic activity in the Ca(2+) assay (aripiprazole = 24.3%, (+)terguride = 56.9%, OPC-4392 = 58.6% and (-)3-PPP = 75.1%), and aripiprazole (E(max) = 54.5%) displayed a substantially lower intrinsic activity than (+)terguride (E(max) = 92.3%), OPC-4392 (E(max) = 93.1%) and (-)3-PPP (E(max) = 101.1%) in the more downstream-based ERK2 phosphoprotein expression assay. These drug effects on Ca(2+) mobilization and ERK2 phosphoprotein expression were mediated through dopamine hD(2L) receptors, as they all were blocked by (-)raclopride, whereas (-)raclopride and other dopamine D(2) receptor antagonists (haloperidol, risperidone, ziprasidone, olanzapine, clozapine and quetiapine) were inactive on their own in both assays. These data are consistent with clinical evidence that only dopamine D(2) receptor partial agonists with a sufficiently low enough intrinsic activity will prove effective against the positive symptoms of schizophrenia, and also highlight the importance of using downstream-based assays in the discovery of novel D(2) receptor partial agonist therapeutics.

Induction of neurite outgrowth in PC12 cells by the medium-chain fatty acid octanoic acid

It has been shown that polyunsaturated fatty acids such as arachinonic and docosahexanoic acids but not monounsaturated and saturated long-chain fatty acids promote basal and nerve growth factor (NGF)-induced neurite extension of PC12 cells, a line derived from a rat pheochromocytoma. On the other hand, short-chain fatty acids and valproic acid (2-propylpentanoic acid) enhance the growth of neurite processes of the cells only in the presence of inducers. In this study, we demonstrated that straight medium-chain fatty acids (MCFAs) at millimolar concentrations alone potently induced neuronal differentiation of PC12 cells. Hexanoic, heptanoic and octanoic acids dose-dependently induced neurite outgrowth of the cells: their maximal effects determined 2 days after addition to the culture medium were more marked than the effect of NGF. PC12 cells exposed to octanoic acid expressed increased levels of the neuronal marker beta-tubulin isotype III. Nonanoic, decanoic, and dodecanoic acids also induced growth of neurite processes, but their maximal effects were less marked than that of octanoic acid. In contrast, the polyunsaturated fatty acid linoleic acid and short-chain fatty acids had only slight or almost no effects on neurite formation in the absence of NGF. The effect of octanoic acid was synergistic with or additive to the effects of NGF and dibutyryl cyclic AMP. Octanoic acid upregulated phosphorylation of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK), critical signaling molecules in neuronal differentiation, but not phosphorylation of Akt, a signaling molecule downstream of phosphatidylinositol 3-kinase (PI3K). Moreover, growth of neurites induced by octanoic acid was potently inhibited by treatment of cells with the p38 MAPK inhibitor SB203580 and the ERK kinase inhibitor PD98059 but not inhibited and only slightly inhibited by the JNK inhibitor SP600125 and the PI3K inhibitor wortmannin, respectively. Taken together, our results indicate that MCFAs, including octanoic acid, induced neurite outgrowth of PC12 cells in the absence of NGF and suggest that the activation of p38 MAPK and ERK pathways is involved in this process.

Clozapine, a neuroleptic agent, inhibits Akt by counteracting Ca2+/calmodulin in PTEN-negative U-87MG human glioblastoma cells

Clozapine (CZP), a dibenzodiazepine derivative with a piperazinyl side chain, is in clinical use as an antipsychotic drug. This study investigated the effect of CZP on the modulation of the PI3K/Akt/GSK-3beta pathway in PTEN-negative U-87MG glioblastoma cells. Treatment with CZP rapidly inhibited the basal and EGF-induced phosphorylation of Akt. The inhibition of Akt resulted in the dephosphorylation of GSK-3beta and increased GSK-3beta kinase activity. A voltage-sensitive Ca(2+) channel blocker and calmodulin (CaM) antagonists inhibited Akt phosphorylation, whereas elevation of the intracellular Ca(2+) concentration prevented CZP-induced dephosphorylation of Akt and GSK-3beta, suggesting that Ca(2+)/CaM participates in the inhibition of Akt by CZP in U-87MG cells. In addition, similar to LY294002, CZP arrested cell cycle progression at G0/G1 phase, which was accompanied by decreased expression of cyclin D1. The reduction in the cyclin D1 level induced by CZP was abrogated by the inhibition of GSK-3beta, the inhibition of proteasome-dependent proteolysis, or an increase in the intracellular Ca(2+) concentration. These results suggest that the antipsychotic drug CZP modulates the PI3K/Akt/GSK-3beta pathway by counteracting Ca(2+)/CaM in PTEN-negative U-87MG glioblastoma cells.

Antipsychotic induced metabolic abnormalities: An interaction study with various PPAR modulators in mice

Abnormalities in glucose and lipid regulation have been reported in schizophrenia during antipsychotic medications. The objectives of the present study were to evaluate the effect of various peroxisome proliferator-activated receptor modulators viz. glimepiride, rosiglitazone and fenofibrate on chlorpromazine, clozapine and ziprasidone induced hyperglycemia and hyperlipidemia in mice. Male Swiss albino mice were orally treated with chlorpromazine, clozapine and ziprasidone concurrently with the antidiabetic medications for 7 days. Plasma glucose, insulin and triglyceride levels were determined at the end of the study. Chlorpromazine and clozapine elevated the glucose and triglyceride levels in normal mice, with no effect on insulin but ziprasidone increased the basal triglyceride and insulin levels and did not have any effect on glucose. Glimepiride and rosiglitazone showed beneficial glucose and triglyceride lowering effects in chlorpromazine and clozapine animals and no effect on insulin levels. Fenofibrate significantly reduced the glucose levels only in animals treated with clozapine, and exhibited significant reduction of triglyceride levels in chlorpromazine, clozapine and ziprasidone treated animals. All three antidiabetic/hypolipidemic agents lowered triglyceride and insulin levels in ziprasidone treated animals. The results of the present studies suggest that hyperglycemia, hyperinsulinemia and hypertriglyceridemia induced by various antipsychotics may involve diverse mechanisms.

Antipsychotic drugs disrupt normal development in Caenorhabditis elegans via additional mechanisms besides dopamine and serotonin receptors

Antipsychotic drugs may produce adverse effects during development in humans and rodents. However, the extent of these effects has not been systematically characterized nor have molecular mechanisms been identified. Consequently, we sought to evaluate the effects of an extensive panel of antipsychotic drugs in a model organism, Caenorhabditis elegans, whose development is well characterized and which offers the possibility of identifying novel molecular targets. For these studies, animals were grown from hatching in the presence of vehicle (control) or antipsychotic drugs over a range of concentrations (20-160microM) and growth was analyzed by measuring head-to-tail length at various intervals. First-generation antipsychotics (e.g., fluphenazine) generally slowed growth and maturation more than second-generation drugs such as quetiapine and olanzapine. This is consistent with in vitro effects on human neuronal cell lines. Clozapine, a second-generation drug, produced similar growth deficits as haloperidol. Converging lines of evidence, including the failure to rescue growth with high concentrations of agonists, suggested that the drug-induced delay in development was not mediated by the major neurotransmitter receptors recognized by the antipsychotic drugs. Moreover, in serotonin-deficient tph-1 mutants, the drugs dramatically slowed development and led to larval arrest (including dauer formation) and neuronal abnormalities. Evaluation of alternative targets of the antipsychotics revealed a potential role for calmodulin and underscored the significance of Ca(2+)-calmodulin signaling in development. These findings suggest that antipsychotic drugs may interfere with normal developmental processes and provide a tool for investigating the key signaling pathways involved.

Haloperidol and atypical antipsychotics share a same action of decreasing P75NTR mRNA levels in PC12 cells

P75(NTR) is a common neurotrophin receptor which binds all neurotrophins with similar affinities and has been shown to be capable of mediating programmed cell death. In this study, we investigated effects of the antipsychotic drugs (APDs) haloperidol, clozapine, quetiapine, and risperidone on p75(NTR) mRNA levels in PC12 cells. Haloperidol is a prototype of typical APDs, and the other three drugs are atypical APDs, which are effective in reducing negative symptoms and cognitive deficits of schizophrenia, cause less side effects, and are more tolerable compared to haloperidol. PC12 cells were cultured with various concentrations of haloperidol, clozapine, quetiapine, or risperidone, in their media. After culture for 48h, the cell viabilities and p75(NTR) mRNA levels were measured. It was shown that both haloperidol and the atypical APDs used in this study deceased p75(NTR) mRNA levels in PC12 cells in a dose dependent manner, while not affecting cell viabilities. In further experiments, doses that produced significant/greatest effects were chosen and provided in the culture media for various periods. Decreases in p75(NTR) mRNA levels were observed in cultures treated for 12h with quetiapine, 24h with clozapine or risperidone, or for 48h with haloperidol. These results suggest that both haloperidol and atypical APDs have the same action of decreasing p75(NTR) mRNA levels in PC12 cells. Although the underlying molecular mechanism of this action remains to be elucidated, this finding is particularly relevant given the neurodevelopmental deficits associated with schizophrenia and important roles of p75(NTR) in mediating cell death.

The extracellular signal-regulated kinase pathway: an emerging promising target for mood stabilizers

PURPOSE OF REVIEW

There exists a growing appreciation that, though not classical neurodegenerative disorders, severe mood disorders are associated with regional impairments of structural plasticity and cellular resilience. Exciting recent data suggest that synaptic plasticity probably is involved in mechanisms of actions of mood stabilizers and antidepressants. Notably, the extracellular signal-regulated kinase pathway is a critical 'plasticity pathway' in the brain. The present review summarizes neurobiological, pharmacological, and behavioral data on the role of the extracellular signal-regulated kinase pathway in regulating some of the symptoms of bipolar disorder and as a therapeutically relevant target for mood stabilizers.

RECENT FINDINGS

The extracellular signal-regulated kinase pathway is known to mediate neurotrophic actions and synaptic plasticity. Treatment with lithium and valproate activates the extracellular signal-regulated kinase pathway in cultured cells and in prefrontal cortex and hippocampus. In addition, lithium or valproate treatment promotes neurogenesis, neurite growth, and cell survival. The extracellular signal-regulated kinase pathway is also targeted by antipsychotics. Modulation of the central nervous system extracellular signal-regulated kinase pathway induces animal behavioral alterations reminiscent of manic symptoms; these complex behaviors probably depend on the effects of extracellular signal-regulated kinase on discrete brain regions and the presence of other interacting molecules.

SUMMARY

The extracellular signal-regulated kinase pathway may represent a novel target for the development of improved therapeutics for bipolar disorder.