An animal model with relevance to schizophrenia: sex-dependent cognitive deficits in osteogenic disorder-Shionogi rats induced by glutathione synthesis and dopamine uptake inhibition during development

Treatment with aripiprazole and N-acetylcysteine affects anaerobic cysteine metabolism in the hippocampus and reverses schizophrenia-like behavior in the neurodevelopmental rat model of schizophrenia

Preclinical and clinical studies have shown that the antipsychotic drug aripiprazole and the antioxidant N-acetylcysteine have unique biological properties. The aim of the study was to investigate, in a rat model of schizophrenia, the effects of chronic administration of these drugs on schizophrenia-like behaviors and anaerobic cysteine metabolism in the hippocampus (HIP). The schizophrenia-type changes were induced in Sprague-Dawley rats by repeated administration of the glutathione synthesis inhibitor l-butionine-(S,R)-sulfoximine in combination with the dopamine reuptake inhibitor GBR 12909 in the early postnatal period. Adult model rats were chronically treated with aripiprazole (0.3 mg·kg-1 , i.p.) or N-acetylcysteine (30 mg·kg-1 , orally), and their effects on schizophrenia-like behaviors were assessed using the social interaction test and novel object recognition test. In the HIP, the level of anaerobic cysteine metabolites, H2 S, and bound sulfane sulfur were determined by a fluorescence method, while the expression of H2 S-synthetizing enzymes: cystathionine β-synthase (CBS) and mercaptopyruvate sulfurtransferase (MST) by western blot. Long-term treatment with aripiprazole or N-acetylcysteine reversed social and cognitive deficits and reduced the exploratory behaviors. In the HIP of 16-day-old model pups, H2 S levels and MST protein expression were significantly decreased. In adult model rats, H2 S levels remained unchanged, bound sulfane sulfur significantly increased, and the expression of CBS and MST slightly decreased. The studied drugs significantly reduced the level of bound sulfane sulfur and the expression of tested enzymes. The reduction in bound sulfane sulfur level coincided with the attenuation of exploratory behavior, suggesting that modulation of anaerobic cysteine metabolism in the HIP may have therapeutic potential in schizophrenia.

The Effect of Glutathione Deficit During Early Postnatal Brain Development on the Prepulse Inhibition and Monoamine Levels in Brain Structures of Adult Sprague-Dawley Rats

Recent studies suggest that impaired glutathione synthesis and distorted dopaminergic transmission are important factors in the pathophysiology of schizophrenia. In the present study, on the postnatal days p5-p16, male pups were treated with the inhibitor of glutathione synthesis, L-buthionine-(S,R)- sulfoximine (BSO, 3.8 or 7.6 mmol/kg), and the dopamine uptake inhibitor, GBR 12,909 (5 mg/kg) alone or in combination, and prepulse inhibition of the acoustic startle response (PPI) was evaluated in adult 90-day-old rats. Moreover, the monoamine levels in the cortex and hippocampus of 16-day-old rats or 91-day-old rats were measured. The present results showed that administration of BSO at 3.8 mmol/kg led to a decreasing tendency in PPI for all tested prepulse intensities. In contrast, a combined treatment with BSO in both studied doses and GBR 12,909 did not induce significant deficits in PPI. Moreover, the results of biochemical studies indicated that treatment with BSO or GBR 12,909 alone induced a weak increase in the activity of dopaminergic, serotonergic, and noradrenergic systems in the frontal cortex and hippocampus of 16-day-old rats and 91-day-old rats. However, the combined administration of both substances allowed for maintaining the normal activity of monoaminergic systems in the rat brain. The most significant changes in the functioning of monoaminergic systems were observed in the frontal cortex of 16-day-old rats. Therefore, it seems that the frontal cortex of rat puppies is most sensitive to glutathione deficiencies resulting in increased oxidative stress in neurons. As a result, it can lead to cognitive and memory impairment.

Impact of repeated co-treatment with escitalopram and aripiprazole on the schizophrenia-like behaviors and BDNF mRNA expression in the adult Sprague-Dawley rats exposed to glutathione deficit during early postnatal development of the brain

BACKGROUND

Preclinical and clinical studies have indicated that impaired endogenous synthesis of glutathione during early postnatal development plays a significant role in the pathophysiology of schizophrenia. Moreover, some studies have suggested that antidepressants are able to increase the activity of atypical antipsychotics which may efficiently improve the treatment of negative and cognitive symptoms of schizophrenia.

METHODS

In the present study, we investigated the influence of repeated co-treatment with escitalopram and aripiprazole on the schizophrenia-like behavior and BDNF mRNA expression in adult rats exposed to glutathione deficit during early postnatal development. Male pups between the postnatal days p5-p16 were treated with the inhibitor of glutathione synthesis, BSO (L-buthionine-(S,R)-sulfoximine) and the dopamine uptake inhibitor, GBR 12,909 alone or in combination. Escitalopram and aripiprazole were given repeatedly for 21 days before the tests. On p90-92 rats were evaluated in the behavioral and biochemical tests.

RESULTS

BSO given alone and together with GBR 12,909 induced deficits in the studied behavioral tests and decreased the expression of BDNF mRNA. Repeated aripiprazole administration at a higher dose reversed these behavioral deficits. Co-treatment with aripiprazole and an ineffective dose of escitalopram also abolished the behavioral deficits in the studied tests.

CONCLUSION

The obtained data indicated that the inhibition of glutathione synthesis in early postnatal development induced long-term deficits corresponding to schizophrenia-like behavior and decreased the BDNF mRNA expression in adult rats, and these behavioral deficits were reversed by repeated treatment with a higher dose of aripiprazole and also by co-treatment with aripiprazole and ineffective dose of escitalopram.

Glutathione Deficiency during Early Postnatal Development Causes Schizophrenia-Like Symptoms and a Reduction in BDNF Levels in the Cortex and Hippocampus of Adult Sprague-Dawley Rats

Growing body of evidence points to dysregulation of redox status in the brain as an important factor in the pathogenesis of schizophrenia. The aim of our study was to evaluate the effects of l-buthionine-(S,R)-sulfoximine (BSO), a glutathione (GSH) synthesis inhibitor, and 1-[2-Bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine dihydrochloride (GBR 12909), a dopamine reuptake inhibitor, given alone or in combination, to Sprague–Dawley pups during early postnatal development (p5–p16), on the time course of the onset of schizophrenia-like behaviors, and on the expression of brain-derived neurotrophic factor (BDNF) mRNA and its protein in the prefrontal cortex (PFC) and hippocampus (HIP) during adulthood. BSO administered alone decreased the levels of BDNF mRNA and its protein both in the PFC and HIP. Treatment with the combination of BSO + GBR 12909 also decreased BDNF mRNA and its protein in the PFC, but in the HIP, only the level of BDNF protein was decreased. Schizophrenia-like behaviors in rats were assessed at three time points of adolescence (p30, p42–p44, p60–p62) and in early adulthood (p90–p92) using the social interaction test, novel object recognition test, and open field test. Social and cognitive deficits first appeared in the middle adolescence stage and continued to occur into adulthood, both in rats treated with BSO alone or with the BSO + GBR 12909 combination. Behavior corresponding to positive symptoms in humans occurred in the middle adolescence period, only in rats treated with BSO + GBR 12909. Only in the latter group, amphetamine exacerbated the existing positive symptoms in adulthood. Our data show that rats receiving the BSO + GBR 12909 combination in the early postnatal life reproduced virtually all symptoms observed in patients with schizophrenia and, therefore, can be considered a valuable neurodevelopmental model of this disease.

Timely N-Acetyl-Cysteine and Environmental Enrichment Rescue Oxidative Stress-Induced Parvalbumin Interneuron Impairments via MMP9/RAGE Pathway: A Translational Approach for Early Intervention in Psychosis

Research in schizophrenia (SZ) emphasizes the need for new therapeutic approaches based on antioxidant/anti-inflammatory compounds and psycho-social therapy. A hallmark of SZ is a dysfunction of parvalbumin-expressing fast-spiking interneurons (PVI), which are essential for neuronal synchrony during sensory/cognitive processing. Oxidative stress and inflammation during early brain development, as observed in SZ, affect PVI maturation. We compared the efficacy of N-acetyl-cysteine (NAC) and/or environmental enrichment (EE) provided during juvenile and/or adolescent periods in rescuing PVI impairments induced by an additional oxidative insult during childhood in a transgenic mouse model with gluthation deficit (Gclm KO), relevant for SZ. We tested whether this rescue was promoted by the inhibition of MMP9/RAGE mechanism, both in the mouse model and in early psychosis (EP) patients, enrolled in a double-blind, randomized, placebo-controlled clinical trial of NAC supplementation for 6 months. We show that a sequential combination of NAC+EE applied after an early-life oxidative insult recovers integrity and function of PVI network in adult Gclm KO, via the inhibition of MMP9/RAGE. Six-month NAC treatment in EP patients reduces plasma sRAGE in association with increased prefrontal GABA, improvement of cognition and clinical symptoms, suggesting similar neuroprotective mechanisms. The sequential combination of NAC+EE reverses long-lasting effects of an early oxidative insult on PVI/perineuronal net (PNN) through the inhibition of MMP9/RAGE mechanism. In analogy, patients vulnerable to early-life insults could benefit from a combined pharmacological and psycho-social therapy.

PPARD May Play a Protective Role against the Development of Schizophrenia

PPARD has been suggested to contribute to the etiology of schizophrenia (SCZ) with the underlying mechanisms largely unknown. Here, we first collected and analyzed the PPARD expression profile from three groups: (1) 18 healthy control (HC) subjects, (2) 14 clinical high-risk (CHR) patients, and (3) 19 early onset of SCZ (EOS) patients. After that, we conducted a systematical pathway analysis to explore the potential mechanisms involved in PPARD exerting influence on the pathological development of SCZ. Compared to the HC group, the expression of PPARD was slightly decreased in the EOS group (LFC = −0.34; p = 0.23) and increased in the CHR group (LFC = 0.65; p = 0.20). However, there was a significant difference between the EOS group and the CHR group (LFC = −0.99; p = 0.015), reflecting the amount of variation in PPARD expression before and after the onset of SCZ. Pathway analysis suggested that overexpression of PPARD may regulate ten proteins or molecules to inhibit the pathological development of SCZ, including the deactivation of eight SCZ promoters and stimulation of two SCZ inhibitors. Our results support the association between PPARD and SCZ. The pathways identified may help in the understanding of the potential mechanisms by which PPARD contributes to the etiology of SCZ.

Alterations in the Antioxidant Enzyme Activities in the Neurodevelopmental Rat Model of Schizophrenia Induced by Glutathione Deficiency during Early Postnatal Life

The aim of the present study was to assess the effects of l-buthionine-(S,R)-sulfoximine (BSO), a glutathione (GSH) synthesis inhibitor, and GBR 12909, a dopamine reuptake inhibitor, administered alone or in combination to Sprague-Dawley rats during early postnatal development (p5-p16), on the levels of reactive oxygen species (ROS), lipid peroxidation (LP) and the activities of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione disulfide reductase (GR) in peripheral tissues (liver, kidney) and selected brain structures (prefrontal cortex, PFC; hippocampus, HIP; and striatum, STR) of 16-day-old rats. The studied parameters were analyzed with reference to the content of GSH and sulfur amino acids, methionine (Met) and cysteine (Cys) described in our previous study. This analysis showed that treatment with a BSO + GBR 12909 combination caused significant decreases in the lipid peroxidation levels in the PFC and HIP, in spite of there being no changes in ROS. The reduction of lipid peroxidation indicates a weakening of the oxidative power of the cells, and a shift in balance in favor of reducing processes. Such changes in cellular redox signaling in the PFC and HIP during early postnatal development may result in functional changes in adulthood.

Glutathione Deficiency and Alterations in the Sulfur Amino Acid Homeostasis during Early Postnatal Development as Potential Triggering Factors for Schizophrenia-Like Behavior in Adult Rats

Impaired glutathione (GSH) synthesis and dopaminergic transmission are important factors in the pathophysiology of schizophrenia. Our research aimed to assess the effects of l-buthionine-(S,R)-sulfoximine (BSO), a GSH synthesis inhibitor, and GBR 12909, a dopamine reuptake inhibitor, administered alone or in combination, to Sprague–Dawley rats during early postnatal development (p5–p16), on the levels of GSH, sulfur amino acids, global DNA methylation, and schizophrenia-like behavior. GSH, methionine (Met), homocysteine (Hcy), and cysteine (Cys) contents were determined in the liver, kidney, and in the prefrontal cortex (PFC) and hippocampus (HIP) of 16-day-old rats. DNA methylation in the PFC and HIP and schizophrenia-like behavior were assessed in adulthood (p90–p93). BSO caused the tissue-dependent decreases in GSH content and alterations in Met, Hcy, and Cys levels in the peripheral tissues and in the PFC and HIP. The changes in these parameters were accompanied by alterations in the global DNA methylation in the studied brain structures. Parallel to changes in the global DNA methylation, deficits in the social behaviors and cognitive functions were observed in adulthood. Only BSO + GBR 12909-treated rats exhibited behavioral alterations resembling positive symptoms in schizophrenia patients. Our results suggest the usefulness of this neurodevelopmental model for research on the pathomechanism of schizophrenia.

Two-hit model of schizophrenia induced by neonatal immune activation and peripubertal stress in rats: Study of sex differences and brain oxidative alterations

Schizophrenia is considered to be a developmental disorder with distinctive sex differences. Aiming to simulate the vulnerability of the third trimester of human pregnancy to the developmental course of schizophrenia, an animal model was developed, using neonatal poly(I:C) as a first-hit, and peripubertal stress as a second-hit, i.e. a two-hit model. Since, to date, there have been no references to sex differences in the two-hit model, our study sought to determine sex influences on the development of behavior and brain oxidative change in adult rats submitted to neonatal exposure to poly(I:C) on postnatal days 5-7 as well as peripubertal unpredictable stress (PUS). Our results showed that adult two-hit rats present sex-specific behavioral alterations, with females showing more pronounced deficits in prepulse inhibition of the startle reflex and hyperlocomotion, while males showing more deficits in social interaction. Male and female animals exhibited similar working memory deficits. The levels of the endogenous antioxidant, reduced glutathione, were decreased in the prefrontal cortex (PFC) of both male and female animals exposed to both poly(I:C) and poly(I:C)+PUS. Only females presented decrements in GSH levels in the striatum. Nitrite levels were increased in the PFC of male and in the striatum of female poly(I:C)+PUS rats. Increased lipid peroxidation was observed in the PFC of females and in the striatum of males and females exposed to poly(I:C) and poly(I:C)+PUS. Thus, the present study presents evidence for sex differences in behavior and oxidative brain change induced by a two-hit model of schizophrenia.

Anxiety modulates cognitive deficits in a perinatal glutathione deficit animal model of schizophrenia

In this study, we investigated long-term repercussion of early glutathione deficit by l-buthionine-(S,R)-sulfoximine (BSO) injections as a rat model of schizophrenia. BSO rats were tested through various behavioral tasks requiring animals to take into account previously delivered information. We showed that relative to controls, BSO rats (1) were less active and more anxious in an Elevated Plus Maze test, allowing us to split them into two subgroups with high and low anxiety levels; (2) demonstrated normal abilities of behavioral flexibility tested with a rat-adapted version of the Wisconsin Card Sorting Test (WCST), with even higher abilities in anxious BSO rats suggesting reduced interference of previously acquired rules; (3) did not forage normally in radial arm mazes and mainly used clockwise strategies; (4) exhibited a lack of habituation during a startle response task; and (5) showed a normal prepulse inhibition of the startle response (PPI) and a normal conditioned taste aversion (CTA). All these results indicate that early glutathione deficit provokes persistent changes in adulthood and improves the validity of this animal model of schizophrenia. They further suggest difficulties binding temporally separated events (WCST), except when the salience of this information is very strong (CTA). We propose that the transient glutathione deficit during cerebral development could alter a "cognitive binding" process in interaction with the emotional state that could possibly account for the disruption of integrative function that characterizes schizophrenia.

Gender and estrous cycle influences on behavioral and neurochemical alterations in adult rats neonatally administered ketamine

Neonatal N-methyl-D-aspartate (NMDA) receptor blockade in rodents triggers schizophrenia (SCZ)-like alterations during adult life. SCZ is influenced by gender in age of onset, premorbid functioning, and course. Estrogen, the hormone potentially driving the gender differences in SCZ, is known to present neuroprotective effects such as regulate oxidative pathways and the expression of brain-derived neurotrophic factor (BDNF). Thus, the aim of this study was to verify if differences in gender and/or estrous cycle phase during adulthood would influence the development of behavioral and neurochemical alterations in animals neonatally administered ketamine. The results showed that ketamine-treated male (KT-male) and female-in-diestrus (KTF-diestrus, the low estrogen phase) presented significant deficits in prepulse inhibition of the startle reflex and spatial working memory, two behavioral SCZ endophenotypes. On the contrary, female ketamine-treated rats during proestrus (KTF-proestrus, the high estradiol phase) had no behavioral alterations. This correlated with an oxidative imbalance in the hippocampus (HC) of both male and KTF-diestrus female rats, that is, decreased levels of GSH and increased levels of lipid peroxidation and nitrite. Similarly, BDNF was decreased in the KTF-diestrus rats while no alterations were observed in KTF-proestrus and male animals. The changes in the HC were in contrast to those in the prefrontal cortex in which only increased levels of nitrite in all groups studied were observed. Thus, there is a gender difference in the adult rat HC in response to ketamine neonatal administration, which is based on the estrous cycle. This is discussed in relation to neuropsychiatric conditions and in particular SCZ.

Repeated exposure of adult rats to transient oxidative stress induces various long-lasting alterations in cognitive and behavioral functions

Exposure of neonates to oxidative stress may increase the risk of psychiatric disorders such as schizophrenia in adulthood. However, the effects of moderate oxidative stress on the adult brain are not completely understood. To address this issue, we systemically administrated 2-cyclohexen-1-one (CHX) to adult rats to transiently reduce glutathione levels. Repeated administration of CHX did not affect the acquisition or motivation of an appetitive instrumental behavior (lever pressing) rewarded by a food outcome under a progressive ratio schedule. In addition, response discrimination and reversal learning were not affected. However, acute CHX administration blunted the sensitivity of the instrumental performance to outcome devaluation, and this effect was prolonged in rats with a history of repeated CHX exposure, representing pro-depression-like phenotypes. On the other hand, repeated CHX administration reduced immobility in forced swimming tests and blunted acute cocaine-induced behaviors, implicating antidepressant-like effects. Multivariate analyses segregated a characteristic group of behavioral variables influenced by repeated CHX administration. Taken together, these findings suggest that repeated administration of CHX to adult rats did not cause a specific mental disorder, but it induced long-term alterations in behavioral and cognitive functions, possibly related to specific neural correlates.

Evaluating negative-symptom-like behavioural changes in developmental models of schizophrenia

Many lines of evidence suggest that schizophrenia has a major developmental component and that environmental factors that disrupt key stages of development, such as maternal stress during pregnancy as a result of infection or malnutrition, can increase the risk of developing schizophrenia in later life. This review examines how non-clinical neurodevelopmental models pertinent to schizophrenia have been evaluated for their ability to reproduce behavioural deficits related to the negative symptoms of schizophrenia. The more frequently used are the prenatal application of the mitotoxic agent methylazoxymethanol, prenatal immune challenge and the neonatal ventral hippocampus lesion model. In general they have been extensively evaluated in models considered relevant to positive symptoms of schizophrenia. In contrast, very few studies have examined tests related to negative symptoms and, when they have, it has almost exclusively been a social interaction model. Other aspects related to negative symptoms such as anhedonia, affective flattening and avolition have almost never been studied. Further studies examining other components of negative symptomatology are needed to more clearly associate these deficits with a schizophrenia-like profile as social withdrawal is a hallmark of many disorders. Although there are no truly effective treatments for negative symptoms, better characterisation with a broader range of drugs used in schizophrenia will be necessary to better evaluate the utility of these models. In summary, developmental models of schizophrenia have been extensively studied as models of positive symptoms but, given the unmet need in the clinic, the same effort now needs to be made with regard to negative symptoms.

Redox dysregulation in the pathophysiology of schizophrenia and bipolar disorder: insights from animal models

SIGNIFICANCE

Schizophrenia (SZ) and bipolar disorder (BD) are classified as two distinct diseases. However, accumulating evidence shows that both disorders share genetic, pathological, and epidemiological characteristics. Based on genetic and functional findings, redox dysregulation due to an imbalance between pro-oxidants and antioxidant defense mechanisms has been proposed as a risk factor contributing to their pathophysiology.

RECENT ADVANCES

Altered antioxidant systems and signs of increased oxidative stress are observed in peripheral tissues and brains of SZ and BD patients, including abnormal prefrontal levels of glutathione (GSH), the major cellular redox regulator and antioxidant. Here we review experimental data from rodent models demonstrating that permanent as well as transient GSH deficit results in behavioral, morphological, electrophysiological, and neurochemical alterations analogous to pathologies observed in patients. Mice with GSH deficit display increased stress reactivity, altered social behavior, impaired prepulse inhibition, and exaggerated locomotor responses to psychostimulant injection. These behavioral changes are accompanied by N-methyl-D-aspartate receptor hypofunction, elevated glutamate levels, impairment of parvalbumin GABA interneurons, abnormal neuronal synchronization, altered dopamine neurotransmission, and deficient myelination.

CRITICAL ISSUES

Treatment with the GSH precursor and antioxidant N-acetylcysteine normalizes some of those deficits in mice, but also improves SZ and BD symptoms when given as adjunct to antipsychotic medication.

FUTURE DIRECTIONS

These data demonstrate the usefulness of GSH-deficient rodent models to identify the mechanisms by which a redox imbalance could contribute to the development of SZ and BD pathophysiologies, and to develop novel therapeutic approaches based on antioxidant and redox regulator compounds.

Glutathione precursor N-acetyl-cysteine modulates EEG synchronization in schizophrenia patients: a double-blind, randomized, placebo-controlled trial

Glutathione (GSH) dysregulation at the gene, protein, and functional levels has been observed in schizophrenia patients. Together with disease-like anomalies in GSH deficit experimental models, it suggests that such redox dysregulation can play a critical role in altering neural connectivity and synchronization, and thus possibly causing schizophrenia symptoms. To determine whether increased GSH levels would modulate EEG synchronization, N-acetyl-cysteine (NAC), a glutathione precursor, was administered to patients in a randomized, double-blind, crossover protocol for 60 days, followed by placebo for another 60 days (or vice versa). We analyzed whole-head topography of the multivariate phase synchronization (MPS) for 128-channel resting-state EEGs that were recorded at the onset, at the point of crossover, and at the end of the protocol. In this proof of concept study, the treatment with NAC significantly increased MPS compared to placebo over the left parieto-temporal, the right temporal, and the bilateral prefrontal regions. These changes were robust both at the group and at the individual level. Although MPS increase was observed in the absence of clinical improvement at a group level, it correlated with individual change estimated by Liddle's disorganization scale. Therefore, significant changes in EEG synchronization induced by NAC administration may precede clinically detectable improvement, highlighting its possible utility as a biomarker of treatment efficacy.

Behavioral phenotyping of glutathione-deficient mice: relevance to schizophrenia and bipolar disorder

Redox-dysregulation represents a common pathogenic mechanism in schizophrenia (SZ) and bipolar disorder (BP). It may in part arise from a genetically compromised synthesis of glutathione (GSH), the major cellular antioxidant and redox-regulator. Allelic variants of the genes coding for the rate-limiting GSH synthesizing enzyme glutamate-cysteine-ligase modifier (GCLM) and/or catalytic (GCLC) subunit have been associated with SZ and BP. Using mice knockout (KO) for GCLM we have previously shown that impaired GSH synthesis is associated with morphological, functional and neurochemical anomalies similar to those in patients. Here we asked whether GSH deficit is also associated with SZ- and BP-relevant behavioral and cognitive anomalies. Accordingly, we subjected young adult GCLM-wildtype (WT), heterozygous and KO males to a battery of standard tests. Compared to WT, GCLM-KO mice displayed hyperlocomotion in the open field and forced swim test but normal activity in the home cage, suggesting that hyperlocomotion was selective to environmental novelty and mildly stressful situations. While spatial working memory and latent inhibition remained unaffected, KO mice showed a potentiated hyperlocomotor response to an acute amphetamine injection, impaired sensorymotor gating in the form of prepulse inhibition and altered social behavior compared to WT. These anomalies resemble important aspects of both SZ and the manic component of BP. As such our data support the notion that redox-dysregulation due to GSH deficit is implicated in both disorders. Moreover, our data propose the GCLM-KO mouse as a valuable model to study the behavioral and cognitive consequences of redox dysregulation in the context of psychiatric disease.

Is it time to reassess alpha lipoic acid and niacinamide therapy in schizophrenia?

As sulfur containing thiols, alpha lipoic acid (ALA) and its reduced form dihydrolipoic acid (DHLA) are powerful antioxidants and free radical scavengers capable of performing many of the same functions as glutathione (GSH). ALA supplementation may help protect mitochondria from oxidative stress, a possible mechanism contributing to certain forms of brain diseases called schizophrenia. Shortly before the advent of antipsychotic medications, two small studies found ALA relieved psychiatric symptoms in schizophrenia. More recently, animal studies have shown ALA augmentation improves mitochondrial function. At pharmaceutical levels, niacinamide helps preserve mitochondrial membrane integrity and acts as an antioxidant. ALA is a precursor for lipoamide, an essential mitochondrial coenzyme and niacinamide is a component of niacinamide adenine dinucleotide (NAD). NADH, the reduced form of NAD, is involved in the reduction of ALA to DHLA within the mitochondria. This is relevant to contemporary research because DHLA increases GSH and low GSH levels contribute to mitochondrial dysfunction and oxidative stress which have been implicated in the pathophysiology of schizophrenia.

Preclinical behavioral models for predicting antipsychotic activity

Schizophrenia is a major psychiatric disease that is characterized by three distinct symptom domains: positive symptoms, negative symptoms, and cognitive impairment. Additionally, treatment with classical antipsychotic medication can be accompanied by important side effects that involve extrapyramidal symptoms (EPS). The discovery of clozapine in the 1970s, which is efficacious in all three symptom domains and has a reduced propensity to induce EPS, has driven research for new antipsychotic agents with a wider spectrum of activity and a lower propensity to induce EPS. The following chapter reviews existing behavioral procedures in animals for their ability to predict compound efficacy against schizophrenia symptoms and liability to induce EPS. Rodent models of positive symptoms include procedures related to hyperfunction in central dopamine and serotonin (5-hydroxytryptamine) systems and hypofunction of central glutamatergic (N-methyl-d-aspartate) neurotransmission. Procedures for evaluating negative symptoms include rodent models of anhedonia, affective flattening, and diminished social interaction. Cognitive deficits can be assessed in rodent models of attention (prepulse inhibition (PPI), latent inhibition) and of learning and memory (passive avoidance, object and social recognition, Morris water maze, and operant-delayed alternation). The relevance of the conditioned avoidance response (CAR) is also discussed. A final section reviews animal procedures for assessing EPS liability, in particular parkinsonism (catalepsy), acute dystonia (purposeless chewing in rodents, dystonia in monkeys), akathisia (defecation in rodents), and tardive dyskinesia (long-term antipsychotic treatment in rodents and monkeys).

Redox dysregulation, neurodevelopment, and schizophrenia

In schizophrenia, a developmental redox dysregulation constitutes one 'hub' on which converge genetic impairments of glutathione synthesis and environmental vulnerability factors generating oxidative stress. Their timing at critical periods of neurodevelopment could play a decisive role in inducing impairment of neural connectivity and synchronization as observed in schizophrenia. In experimental models, such redox dysregulation induces anomalies strikingly similar to those observed in patients. This is mediated by hypoactive NMDA receptors, impairment of fast-spiking parvalbumin GABA interneurons and deficit in myelination. A treatment restoring the redox balance without side effects yields improvements of negative symptoms in chronic patients. Novel interventions based on these mechanisms if applied in early phases of the disease hold great therapeutic promise.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Glutathione depletion in the brain disrupts short-term spatial memory in the Y-maze in rats and mice

Oxidative stress and reduced brain glutathione (GSH) levels have been reported in psychiatric illnesses including schizophrenia and bipolar disorder. However the role of GSH in cognitive impairment in the illness remains unclear. Treatment of Sprague-Dawley rats and C57Bl/6 mice with 2-cyclohexene-1-one (CHX) dose-dependently reduced striatal and frontal cortical GSH levels similar to those in schizophrenia. In both species, GSH depletion resulted in disruption of short-term spatial recognition memory in a Y-maze test. In conclusion, GSH depletion induces cognitive impairment, which may be relevant to the role of GSH in psychiatric illnesses.

Glutathione precursor, N-acetyl-cysteine, improves mismatch negativity in schizophrenia patients

In schizophrenia patients, glutathione dysregulation at the gene, protein and functional levels, leads to N-methyl-D-aspartate (NMDA) receptor hypofunction. These patients also exhibit deficits in auditory sensory processing that manifests as impaired mismatch negativity (MMN), which is an auditory evoked potential (AEP) component related to NMDA receptor function. N-acetyl-cysteine (NAC), a glutathione precursor, was administered to patients to determine whether increased levels of brain glutathione would improve MMN and by extension NMDA function. A randomized, double-blind, cross-over protocol was conducted, entailing the administration of NAC (2 g/day) for 60 days and then placebo for another 60 days (or vice versa). 128-channel AEPs were recorded during a frequency oddball discrimination task at protocol onset, at the point of cross-over, and at the end of the study. At the onset of the protocol, the MMN of patients was significantly impaired compared to sex- and age- matched healthy controls (p=0.003), without any evidence of concomitant P300 component deficits. Treatment with NAC significantly improved MMN generation compared with placebo (p=0.025) without any measurable effects on the P300 component. MMN improvement was observed in the absence of robust changes in assessments of clinical severity, though the latter was observed in a larger and more prolonged clinical study. This pattern suggests that MMN enhancement may precede changes to indices of clinical severity, highlighting the possible utility AEPs as a biomarker of treatment efficacy. The improvement of this functional marker may indicate an important pathway towards new therapeutic strategies that target glutathione dysregulation in schizophrenia.

Impaired glutathione synthesis in schizophrenia: convergent genetic and functional evidence

Schizophrenia is a complex multifactorial brain disorder with a genetic component. Convergent evidence has implicated oxidative stress and glutathione (GSH) deficits in the pathogenesis of this disease. The aim of the present study was to test whether schizophrenia is associated with a deficit of GSH synthesis. Cultured skin fibroblasts from schizophrenia patients and control subjects were challenged with oxidative stress, and parameters of the rate-limiting enzyme for the GSH synthesis, the glutamate cysteine ligase (GCL), were measured. Stressed cells of patients had a 26% (P = 0.002) decreased GCL activity as compared with controls. This reduction correlated with a 29% (P < 0.001) decreased protein expression of the catalytic GCL subunit (GCLC). Genetic analysis of a trinucleotide repeat (TNR) polymorphism in the GCLC gene showed a significant association with schizophrenia in two independent case-control studies. The most common TNR genotype 7/7 was more frequent in controls [odds ratio (OR) = 0.6, P = 0.003], whereas the rarest TNR genotype 8/8 was three times more frequent in patients (OR = 3.0, P = 0.007). Moreover, subjects with disease-associated genotypes had lower GCLC protein expression (P = 0.017), GCL activity (P = 0.037), and GSH contents (P = 0.004) than subjects with genotypes that were more frequent in controls. Taken together, the study provides genetic and functional evidence that an impaired capacity to synthesize GSH under conditions of oxidative stress is a vulnerability factor for schizophrenia.

Transitory glutathione deficit during brain development induces cognitive impairment in juvenile and adult rats: Relevance to schizophrenia

Glutathione (GSH) metabolism dysfunction is one risk factor in schizophrenia. A transitory brain GSH deficit was induced in Wistar (WIS) and mutant (ODS; lacking ascorbic acid synthesis) rats using BSO (l-buthionine-(S,R)-sulfoximine) from post-natal days 5-16. When GSH was re-established to physiological levels, juvenile BSO-ODS rats were impaired in the water maze task. Long after treatment cessation, adult BSO-WIS/-ODS rats showed impaired place discrimination in the homing board with distributed visual or olfactory cues. Their accuracy was restored when a single cue marked the trained position. Similarly, more working memory errors were made by adult BSO-WIS in the radial maze when several olfactory cues were present. These results reveal that BSO rats did not suffer simple sensory impairment. They were selectively impaired in spatial memory when the task required the integration of multimodal or olfactory cues. These results, in part, resemble some of the reported olfactory discrimination and cognitive impairment in schizophrenia.

Neurodevelopmental damage after prenatal infection: role of oxidative stress in the fetal brain

Prenatal infection is a major risk responsible for the occurrence of psychiatric conditions in infants. Mimicking maternal infection by exposing pregnant rodents to bacterial endotoxin lipopolysaccharide (LPS) also leads to major brain disorders in the offspring. The mechanisms of LPS action remain, however, unknown. Here, we show that LPS injection during pregnancy in rats, 2 days before delivery, triggered an oxidative stress in the hippocampus of male fetuses, evidenced by a rapid rise in protein carbonylation and by decreases in alpha-tocopherol levels and in the ratio of reduced/oxidized forms of glutathione (GSH/GSSG). Neither protein carbonylation increase nor decreases in alpha-tocopherol levels and GSH/GSSG ratio were observed in female fetuses. NMDA synaptic currents and long-term potentiation in CA1, as well as spatial recognition in the water maze, were also impaired in male but not in female 28-day-old offspring. Pretreatment with the antioxidant N-acetylcysteine prevented the LPS-induced changes in the biochemical markers of oxidative stress in male fetuses, and the delayed detrimental effects in male 28-day-old offspring, completely restoring both long-term potentiation in the hippocampus and spatial recognition performance. Oxidative stress in the hippocampus of male fetuses may thus participate in the neurodevelopmental damage induced by a prenatal LPS challenge.

Schizophrenia and oxidative stress: glutamate cysteine ligase modifier as a susceptibility gene

Oxidative stress could be involved in the pathophysiology of schizophrenia, a major psychiatric disorder. Glutathione (GSH), a redox regulator, is decreased in patients' cerebrospinal fluid and prefrontal cortex. The gene of the key GSH-synthesizing enzyme, glutamate cysteine ligase modifier (GCLM) subunit, is strongly associated with schizophrenia in two case-control studies and in one family study. GCLM gene expression is decreased in patients' fibroblasts. Thus, GSH metabolism dysfunction is proposed as one of the vulnerability factors for schizophrenia.

Glutathione deficit during development induces anomalies in the rat anterior cingulate GABAergic neurons: Relevance to schizophrenia

A series of studies in schizophrenic patients report a decrease of glutathione (GSH) in prefrontal cortex (PFC) and cerebrospinal fluid, a decrease in mRNA levels for two GSH synthesizing enzymes and a deficit in parvalbumin (PV) expression in a subclass of GABA neurons in PFC. GSH is an important redox regulator, and its deficit could be responsible for cortical anomalies, particularly in regions rich in dopamine innervation. We tested in an animal model if redox imbalance (GSH deficit and excess extracellular dopamine) during postnatal development would affect PV-expressing neurons. Three populations of interneurons immunolabeled for calcium-binding proteins were analyzed quantitatively in 16-day-old rat brain sections. Treated rats showed specific reduction in parvalbumin immunoreactivity in the anterior cingulate cortex, but not for calbindin and calretinin. These results provide experimental evidence for the critical role of redox regulation in cortical development and validate this animal model used in schizophrenia research.

Synaptic plasticity impairment and hypofunction of NMDA receptors induced by glutathione deficit: Relevance to schizophrenia

Increasing evidence suggests that the metabolism of glutathione, an endogenous redox regulator, is abnormal in schizophrenia. Patients show a deficit in glutathione levels in the cerebrospinal fluid and prefrontal cortex and a reduction in gene expression of the glutathione synthesizing enzymes. We investigated whether such glutathione deficit altered synaptic transmission and plasticity in slices of rat hippocampus, with particular emphasis on NMDA receptor function. An approximately 40% decrease in brain glutathione levels was induced by s.c. administration of L-buthionine-(S,R)-sulfoximine, an inhibitor of glutathione synthesis. Such glutathione deficit did not affect the basal synaptic transmission, but produced several NMDA receptor-dependent and -independent effects. Glutathione deficit caused an increase in excitability of CA1 pyramidal cells. The paired-pulse facilitation was diminished in glutathione-depleted slices, in a manner that was independent of NMDA receptor activity. This suggests that lowering glutathione levels altered presynaptic mechanisms involved in neurotransmitter release. NMDA receptor-dependent long-term potentiation induced by high-frequency stimulation was impaired in glutathione-depleted slices. Pharmacologically isolated NMDA receptor-mediated field excitatory postsynaptic potentials were significantly smaller in L-buthionine-(S,R)-sulfoximine-treated than in control slices. Hypofunction of NMDA receptors under glutathione deficit was explained at least in part by an excessive oxidation of the extracellular redox-sensitive sites of the NMDA receptors. These results indicate that a glutathione deficit, like that observed in schizophrenics, alters short- and long-term synaptic plasticity and affects NMDA receptor function. Thus, glutathione deficit could be one causal factor for the hypofunction of NMDA receptors in schizophrenia.

Monoaminergic dysregulation in glutathione-deficient mice: Possible relevance to schizophrenia?

Several lines of research have implicated glutathione (GSH) in schizophrenia. For instance, GSH deficiency has been reported in the prefrontal cortex of schizophrenics in vivo. Further, in rats postnatal GSH-deficiency combined with hyperdopaminergia led to cognitive impairments in the adult. In the present report we studied the effects of 2-day GSH-deficiency with L-buthionine-(S,R)-sulfoximine on monoaminergic function in mice. The effect of GSH-deficiency per se and when combined with the amphetamine and phencyclidine (PCP) models of schizophrenia was investigated. GSH-deficiency significantly altered tissue levels of dopamine (DA), 5-hydroxytryptamine (5-HT) and their respective metabolites homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in a region-specific fashion. The effects of GSH-deficiency on tissue monoamines were distinct from and, generally, did not interact with the effects of amphetamine (5 mg/kg; i.p.) on tissue monoamines. Microdialysis studies showed that extracellular DA-release after amphetamine (5 mg/kg, i.p.) was two-fold increased in the nucleus accumbens of GSH-deficient mice as compared with control mice. Basal DA was unaltered. Further, extracellular levels of HVA in the frontal cortex and hippocampus and 5-HIAA in the nucleus accumbens were elevated by GSH-deficiency per se. Spontaneous locomotor activity in the open field was unchanged in GSH-deficient mice. In contrast, GSH-deficiency modulated the locomotor responses to mid-range doses of amphetamine (1.5 and 5 mg/kg, i.p.). Further, GSH-deficient mice displayed an increased locomotor response to low (2 and 3 mg/kg, i.p.) doses of phencyclidine (PCP). In conclusion, the data presented here show that even short-term GSH-deficiency has consequences for DA and 5-HT function. This was confirmed on both neurochemical and behavioral levels. How GSH and the monoamines interact needs further scrutiny. Moreover, the open field findings suggest reduced or altered N-methyl-d-aspartate (NMDA) receptor function in GSH-deficient mice. Thus, GSH-deficiency can lead to disturbances in DA, 5-HT and NMDA function, a finding that may have relevance for schizophrenia.