Increased serum adenosine deaminase activity in schizophrenic receiving antipsychotic treatment

The adenosine hypothesis of schizophrenia into its third decade: From neurochemical imbalance to early life etiological risks

The adenosine hypothesis of schizophrenia was conceptualized about two decades ago in an attempt to integrate two prominent theories of neurochemical imbalance that attribute the pathogenesis of schizophrenia to hyperfunction of the mesocorticolimbic dopamine neurotransmission and hypofunction of cortical glutamate neurotransmission. Given its unique position as an endogenous modulator of both dopamine and glutamate signaling in the brain, adenosine was postulated as a potential new drug target to achieve multiple antipsychotic actions. This new strategy may offer hope for improving treatment, especially in alleviating negative symptoms and cognitive deficits of schizophrenia that do not respond to current medications. To date, however, the adenosine hypothesis has yet led to any significant therapeutic breakthroughs. Here, we address two possible reasons for the impasse. First, neither the presence of adenosine functional deficiency in people with schizophrenia nor its causal relationship to symptom production has been satisfactorily examined. Second, the lack of novel adenosine-based drugs also impedes progress. This review updates the latest preclinical and clinical data pertinent to the construct validity of the adenosine hypothesis and explores novel molecular processes whereby dysregulation of adenosine signaling could be linked to the etiology of schizophrenia. It is intended to stimulate and revitalize research into the adenosine hypothesis towards the development of a new and improved generation of antipsychotic drugs that has eluded us for decades.

Adenosine Receptors in Neuropsychiatric Disorders: Fine Regulators of Neurotransmission and Potential Therapeutic Targets

Adenosine exerts an important role in the modulation of central nervous system (CNS) activity. Through the interaction with four G-protein coupled receptor (GPCR) subtypes, adenosine subtly regulates neurotransmission, interfering with the dopaminergic, glutamatergic, noradrenergic, serotoninergic, and endocannabinoid systems. The inhibitory and facilitating actions of adenosine on neurotransmission are mainly mediated by A₁ and A_2A adenosine receptors (ARs), respectively. Given their role in the CNS, ARs are promising therapeutic targets for neuropsychiatric disorders where altered neurotransmission represents the most likely etiological hypothesis. Activating or blocking ARs with specific pharmacological agents could therefore restore the balance of altered neurotransmitter systems, providing the rationale for the potential treatment of these highly debilitating conditions. In this review, we summarize and discuss the most relevant studies concerning AR modulation in psychotic and mood disorders such as schizophrenia, bipolar disorders, depression, and anxiety, as well as neurodevelopment disorders such as autism spectrum disorder (ASD), fragile X syndrome (FXS), attention-deficit hyperactivity disorder (ADHD), and neuropsychiatric aspects of neurodegenerative disorders.

A Potential Interface between the Kynurenine Pathway and Autonomic Imbalance in Schizophrenia

Schizophrenia is a neuropsychiatric disorder characterized by various symptoms including autonomic imbalance. These disturbances involve almost all autonomic functions and might contribute to poor medication compliance, worsened quality of life and increased mortality. Therefore, it has a great importance to find a potential therapeutic solution to improve the autonomic disturbances. The altered level of kynurenines (e.g., kynurenic acid), as tryptophan metabolites, is almost the most consistently found biochemical abnormality in schizophrenia. Kynurenic acid influences different types of receptors, most of them involved in the pathophysiology of schizophrenia. Only few data suggest that kynurenines might have effects on multiple autonomic functions. Publications so far have discussed the implication of kynurenines and the alteration of the autonomic nervous system in schizophrenia independently from each other. Thus, the coupling between them has not yet been addressed in schizophrenia, although their direct common points, potential interfaces indicate the consideration of their interaction. The present review gathers autonomic disturbances, the impaired kynurenine pathway in schizophrenia, and the effects of kynurenine pathway on autonomic functions. In the last part of the review, the potential interaction between the two systems in schizophrenia, and the possible therapeutic options are discussed.

Inosine as a Tool to Understand and Treat Central Nervous System Disorders: A Neglected Actor?

Since the 1970s, when ATP was identified as a co-transmitter in sympathetic and parasympathetic nerves, it and its active metabolite adenosine have been considered relevant signaling molecules in biological and pathological processes in the central nervous system (CNS). Meanwhile, inosine, a naturally occurring purine nucleoside formed by adenosine breakdown, was considered an inert adenosine metabolite and remained a neglected actor on the purinergic signaling scene in the CNS. However, this scenario began to change in the 1980s. In the last four decades, an extensive group of shreds of evidence has supported the importance of mediated effects by inosine in the CNS. Also, inosine was identified as a natural trigger of adenosine receptors. This evidence has shed light on the therapeutic potential of inosine on disease processes involved in neurological and psychiatric disorders. Here, we highlight the clinical and preclinical studies investigating the involvement of inosine in chronic pain, schizophrenia, epilepsy, depression, anxiety, and in neural regeneration and neurodegenerative diseases, such as Parkinson and Alzheimer. Thus, we hope that this review will strengthen the knowledge and stimulate more studies about the effects promoted by inosine in neurological and psychiatric disorders.

Integration analysis of GWAS and expression quantitative trait loci to identify candidate genes and pathways for clozapine-related neutropaenia

AIMS

Little is known about the genetic basis of clozapine-related neutropaenia. This study aims to explore candidate genes and pathways involved in clozapine-related neutropaenia.

METHODS

This study conducted a two-stage integrative analysis of the summary statistics from the genome-wide association study (GWAS, n = 552) of the lowest absolute neutrophil count (ANC) during clozapine treatment and the summary data of the expressed quantitative trait locus (eQTL). First, we use the probabilistic Mendelian randomization (PMR-Egger) to identify genes whose expression is causally related to ANC, and then use Bayesian co-localization analysis to investigate whether there are shared causal variants between them [posterior probability for hypotheses 4 (PP.H4) > 0.80]. Finally, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were conducted to explore the pathways that may be associated with ANC during clozapine treatment.

RESULTS

PMR-Egger analysis identified 146 genes that may be causally associated with ANC after Bonferroni correction (P-value < 3.25e-6). Bayesian co-localization analysis identified six further genes whose gene expression shared common variants with ANC, including NT5E (PP.H4 = 0.96), GLDC (PP.H4 = 0.82), NUDT17 (PP.H4 = 0.88), MSH4 (PP.H4 = 0.88), PTER (PP.H4 = 0.89) and SERPINB6 (PP.H4 = 0.83). Enrichment analysis identified 52 GO terms and seven pathways associated with ANC, such as NAD metabolic process, drug catabolic process and glyoxylate and dicarboxylate metabolism.

CONCLUSION

This study identified multiple candidate genes and pathways that may be involved in clozapine-related neutropaenia, providing novel clues for the mechanism of clozapine-related neutropaenia.

Abnormal Behavior of Zebrafish Mutant in Dopamine Transporter Is Rescued by Clozapine

Dopamine transporter (SLC6A3) deficiency causes infantile Parkinson disease, for which there is no effective therapy. We have explored the effects of genetically deleting SLC6A3 in zebrafish. Unlike the wild-type, slc6a3−/− fish hover near the tank bottom, with a repetitive digging-like behavior. slc6a3−/− fish manifest pruning and cellular loss of particular tyrosine hydroxylase-immunoreactive neurons in the midbrain. Clozapine, an effective therapeutic for treatment-resistant schizophrenia, rescues the abnormal behavior of slc6a3−/− fish. Clozapine also reverses the abnormalities in the A8 region of the mutant midbrain. By RNA sequencing analysis, clozapine increases the expression of erythropoietin pathway genes. Transgenic over-expression of erythropoietin in neurons of slc6a3−/− fish partially rescues the mutant behavior, suggesting a potential mechanistic basis for clozapine's efficacy.

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DAT mutation in zebrafish causes digging behavior and loss of specific midbrain neurons

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Clozapine restores normal behavior and neuronal morphology of mutant fish

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Clozapine increases expression of erythropoietin pathway genes

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Transgenic expression of erythropoietin partially rescues the mutant behavior

Cell-subtype-specific changes in adenosine pathways in schizophrenia

Prior work in animal models implicates abnormalities of adenosine metabolism in astrocytes as a possible pathophysiological mechanism underlying the symptoms of schizophrenia. In the present study, we sought to reverse-translate these findings back to the human brain in schizophrenia, focusing on the following questions: (1) Which components of the adenosine system are dysregulated in schizophrenia, and (2) are these changes limited to astrocytes? To address these questions, we captured enriched populations of DLPFC pyramidal neurons and astrocytes from schizophrenia and control subjects using laser capture microdissection and assessed expression of adenosine system components using qPCR. Interestingly, we found changes in enriched populations of astrocytes and neurons spanning metabolic and catabolic pathways. Ectonucleoside triphosphate diphosphohydrolase-1 (ENTPD1) and ENTPD2 mRNA levels were significantly decreased (p < 0.05, n = 16 per group) in enriched populations of astrocytes; in pyramidal neurons equilibrative nucleoside transporter 1 (ENT1) and adenosine A₁ receptor mRNA levels were significantly decreased, with an increase in adenosine deaminase (ADA) (p < 0.05, n = 16 per group). Rodent studies suggest that some of our findings (A₁R and ENTPD2) may be due to treatment with antipsychotics. Our findings suggest changes in expression of genes involved in regulating metabolism of ATP in enriched populations of astrocytes, leading to lower availability of substrates needed to generate adenosine. In pyramidal neurons, changes in ENT1 and ADA mRNA may suggest increased catabolism of adenosine. These results offer new insights into the cell-subtype-specific pathophysiology of the adenosine system in this illness.

Antacids' side effect hyperuricaemia could be alleviated by long-term aerobic exercise via accelerating ATP turnover rate

Hyperuricemia is the term for an abnormally high serum uric acid level. Many factors contribute to hyperuricemia, however no definite correlation between proton pump inhibitors (PPIs) and hyperuricemia has been reported before. Physical exercise also decreases serum uric acid levels. However, the detailed biochemical-regulatory mechanisms remain unknown. Here we found that adenylate deaminase activities are much higher in hyperuricemia patients than in the healthy people. Therefore, the patients have higher levels of adenosine metabolites hypoxanthine and uric acid. Acid-inhibitory drugs (antacids) significantly increased serum uric acid level and may lead to gout in the hyperuricemia patient. Long-term aerobic exercise significantly increased serum phosphorus and decreased serum ATP and its metabolites, and therefore decreased serum uric acid. Antacids slow down the ATP turnover rate and result in serum uric acid elevation subsequently. While the long-term aerobic exercise decreases serum uric acid levels by accelerating ATP turnover rate. The results imply that long-term aerobic exercise may be a useful strategy to prevent and treat hyperuricaemia.

Elevated serum adenosine deaminase levels in neuroleptic-naïve patients with recent-onset schizophrenia

The present study examined serum levels of adenosine deaminase (ADA), an adenosine metabolizing enzyme, in neuroleptic-naive patients with recent-onset schizophrenia and age-matched healthy comparison subjects. ADA levels were found to be higher among patients, and revealed a possible link between evening rise and severity of auditory hallucinations as well as morning rise and severity of avolition-apathy in patients with schizophrenia. These findings suggest the potential utility of serum ADA as a peripheral biomarker of schizophrenia.

Genetic blockade of adenosine A2A receptors induces cognitive impairments and anatomical changes related to psychotic symptoms in mice

Schizophrenia is a chronic severe mental disorder with a presumed neurodevelopmental origin, and no effective treatment. Schizophrenia is a multifactorial disease with genetic, environmental and neurochemical etiology. The main theories on the pathophysiology of this disorder include alterations in dopaminergic and glutamatergic neurotransmission in limbic and cortical areas of the brain. Early hypotheses also suggested that nucleoside adenosine is a putative affected neurotransmitter system, and clinical evidence suggests that adenosine adjuvants improve treatment outcomes, especially in poorly responsive patients. Hence, it is important to elucidate the role of the neuromodulator adenosine in the pathophysiology of schizophrenia. A2A adenosine receptor (A2AR) subtypes are expressed in brain areas controlling motivational responses and cognition, including striatum, and in lower levels in hippocampus and cerebral cortex. The aim of this study was to characterize A2AR knockout (KO) mice with complete and specific inactivation of A2AR, as an animal model for schizophrenia. We performed behavioral, anatomical and neurochemical studies to assess psychotic-like symptoms in adult male and female KO and wild-type (WT) littermates. Our results show impairments in inhibitory responses and sensory gating in A2AR KO animals. Hyperlocomotion induced by d-amphetamine and MK-801 was reduced in KO animals when compared to WT littermates. Moreover, A2AR KO animals show motor disturbances, social and cognitive alterations. Finally, behavioral impairments were associated with enlargement of brain lateral ventricles and decreased BDNF levels in the hippocampus. These data highlight the role of adenosine in the pathophysiology of schizophrenia and provide new possibilities for the therapeutic management of schizophrenia.

Biomarkers in schizophrenia: A focus on blood based diagnostics and theranostics

Identifying biomarkers that can be used as diagnostics or predictors of treatment response (theranostics) in people with schizophrenia (Sz) will be an important step towards being able to provide personalized treatment. Findings from the studies in brain tissue have not yet been translated into biomarkers that are practical in clinical use because brain biopsies are not acceptable and neuroimaging techniques are expensive and the results are inconclusive. Thus, in recent years, there has been search for blood-based biomarkers for Sz as a valid alternative. Although there are some encouraging preliminary data to support the notion of peripheral biomarkers for Sz, it must be acknowledged that Sz is a complex and heterogeneous disorder which needs to be further dissected into subtype using biological based and clinical markers. The scope of this review is to critically examine published blood-based biomarker of Sz, focusing on possible uses for diagnosis, treatment response, or their relationship with schizophrenia-associated phenotype. We sorted the studies into six categories which include: (1) brain-derived neurotrophic factor; (2) inflammation and immune function; (3) neurochemistry; (4) oxidative stress response and metabolism; (5) epigenetics and microRNA; and (6) transcriptome and proteome studies. This review also summarized the molecules which have been conclusively reported as potential blood-based biomarkers for Sz in different blood cell types. Finally, we further discusses the pitfall of current blood-based studies and suggest that a prediction model-based, Sz specific, blood oriented study design as well as standardize blood collection conditions would be useful for Sz biomarker development.

Comorbidities in Neurology: Is adenosine the common link?

Comorbidities in Neurology represent a major conceptual and therapeutic challenge. For example, temporal lobe epilepsy (TLE) is a syndrome comprised of epileptic seizures and comorbid symptoms including memory and psychiatric impairment, depression, and sleep dysfunction. Similarly, Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) are accompanied by various degrees of memory dysfunction. Patients with AD have an increased likelihood for seizures, whereas all four conditions share certain aspects of psychosis, depression, and sleep dysfunction. This remarkable overlap suggests common pathophysiological mechanisms, which include synaptic dysfunction and synaptotoxicity, as well as glial activation and astrogliosis. Astrogliosis is linked to synapse function via the tripartite synapse, but astrocytes also control the availability of gliotransmitters and adenosine. Here we will specifically focus on the 'adenosine hypothesis of comorbidities' implying that astrocyte activation, via overexpression of adenosine kinase (ADK), induces a deficiency in the homeostatic tone of adenosine. We present evidence from patient-derived samples showing astrogliosis and overexpression of ADK as common pathological hallmark of epilepsy, AD, PD, and ALS. We discuss a transgenic 'comorbidity model', in which brain-wide overexpression of ADK and resulting adenosine deficiency produces a comorbid spectrum of seizures, altered dopaminergic function, attentional impairment, and deficits in cognitive domains and sleep regulation. We conclude that dysfunction of adenosine signaling is common in neurological conditions, that adenosine dysfunction can explain co-morbid phenotypes, and that therapeutic adenosine augmentation might be effective for the treatment of comorbid symptoms in multiple neurological conditions.

Paliperidone regulates intracellular redox system in rat brain: Role of purine mechanism

OBJECTIVE

The treatment of schizophrenia is multifactorial, with antipsychotic medications comprising a major part of treatment. Paliperidone is a newly commercialized antipsychotic whose formulation includes the principal active metabolite risperidone, 9-hydroxyrisperidone. Ever since the relationship between schizophrenia and oxidative stress was first demonstrated, many studies have been conducted in order to probe the potential protective effects of antipsychotic drugs on the oxidant-antioxidant system and lipid peroxidation. The basic aim of this study is to determine the effects of the newly marketed drug paliperidone on the activities of the enzymes adenosine deaminase (ADA), xanthine oxidase (XO), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) as well as on malondialdehyde (MDA) and nitric oxide (NO) levels in rat brain tissues.

METHODS

Twenty male Sprague-Dawley rats were used for the study, which were divided into two equal groups. The first was the control group (n = 10) and the second was the paliperidone group (n = 10). Saline was administered once daily for 14 days in the control group. In the paliperidone group, paliperidone was administered once daily with a dose of 1 mg/kg for 14 days. All rats were sacrificed at the end of the fourteenth day. Brain samples were collected and then analyzed.

RESULTS

Our results demonstrated that paliperidone significantly decreased the activities of ADA (P = 0.015), XO (P = 0.0001), and CAT (P = 0.004) while insignificantly increasing the activity of SOD (P = 0.49), MDA (P = 0.71), and NO (P = 0.26) levels in rat brain tissues. In addition, paliperidone insignificantly decreased the activity of GSH-Px (P = 0.30) compared to the control group in rat brain tissues.

DISCUSSION

In conclusion, the data obtained in this study suggest that paliperidone can positively alter antioxidant status and, accordingly, can offer positive outcomes in the treatment of schizophrenia by reducing activity in the enzymes ADA and XO, which are associated with purine metabolism. We believe that such a comprehensive approach used with other antipsychotic drugs warrants further study.

Reduced striatal adenosine A2A receptor levels define a molecular subgroup in schizophrenia

Schizophrenia (SZ) is a mental disorder of unknown origin. Some scientific evidence seems to indicate that SZ is not a single disease entity, since there are patient groups with clear symptomatic, course and biomarker differences. SZ is characterized by a hyperdopaminergic state related to high dopamine D2 receptor activity. It has also been proposed that there is a hypoadenosynergic state. Adenosine is a nucleoside widely distributed in the organism with neuromodulative and neuroprotective activity in the central nervous system. In the brain, the most abundant adenosine receptors are A1R and A2AR. In the present report, we characterize the presence of both receptors in human postmortem putamens of patients suffering SZ with real time TaqMan PCR, western blotting and radioligand binding assay. We show that A1R levels remain unchanged with respect to age-matched controls, whereas nearly fifty percent of patients have reduced A2AR, at the transcriptional and translational levels. Moreover, we describe how DNA methylation plays a role in the pathological A2AR levels with the bisulfite-sequencing technique. In fact, an increase in 5-methylcytosine percentage in the 5' UTR region of ADORA2A was found in those SZ patients with reduced A2AR levels. Interestingly, there was a relationship between the A2A/β-actin ratio and motor disturbances as assessed with some items of the PANSS, AIMS and SAS scales. Therefore, there may be a subgroup of SZ patients with reduced striatal A2AR levels accompanied by an altered motor phenotype.

Reduced striatal ecto-nucleotidase activity in schizophrenia patients supports the "adenosine hypothesis"

Schizophrenia (SZ) is a major chronic neuropsychiatric disorder characterized by a hyperdopaminergic state. The hypoadenosinergic hypothesis proposes that reduced extracellular adenosine levels contribute to dopamine D2 receptor hyperactivity. ATP, through the action of ecto-nucleotidases, constitutes a main source of extracellular adenosine. In the present study, we examined the activity of ecto-nucleotidases (NTPDases, ecto-5'-nucleotidase, and alkaline phosphatase) in the postmortem putamen of SZ patients (n = 13) compared with aged-matched controls (n = 10). We firstly demonstrated, by means of artificial postmortem delay experiments, that ecto-nucleotidase activity in human brains was stable up to 24 h, indicating the reliability of this tissue for these enzyme determinations. Remarkably, NTPDase-attributable activity (both ATPase and ADPase) was found to be reduced in SZ patients, while ecto-5'-nucleotidase and alkaline phosphatase activity remained unchanged. In the present study, we also describe the localization of these ecto-enzymes in human putamen control samples, showing differential expression in blood vessels, neurons, and glial cells. In conclusion, reduced striatal NTPDase activity may contribute to the pathophysiology of SZ, and it represents a potential mechanism of adenosine signalling impairment in this illness.

Adenosine augmentation ameliorates psychotic and cognitive endophenotypes of schizophrenia

An emerging theory of schizophrenia postulates that hypofunction of adenosine signaling may contribute to its pathophysiology. This study was designed to test the "adenosine hypothesis" of schizophrenia and to evaluate focal adenosine-based strategies for therapy. We found that augmentation of adenosine by pharmacologic inhibition of adenosine kinase (ADK), the key enzyme of adenosine clearance, exerted antipsychotic-like activity in mice. Further, overexpression of ADK in transgenic mice was associated with attentional impairments linked to schizophrenia. We observed that the striatal adenosine A2A receptor links adenosine tone and psychomotor response to amphetamine, an indicator of dopaminergic signaling. Finally, intrastriatal implants of engineered adenosine-releasing cells restored the locomotor response to amphetamine in mice overexpressing ADK, whereas the same grafts placed proximal to the hippocampus of transgenic mice reversed their working memory deficit. This functional double dissociation between striatal and hippocampal adenosine demonstrated in Adk transgenic mice highlights the independent contributions of these two interconnected brain regions in the pathophysiology of schizophrenia and thus provides the rationale for developing local adenosine augmentation therapies for the treatment of schizophrenia.

Correlation of adenosinergic activity with superior efficacy of clozapine for treatment of chronic schizophrenia: a double blind randomised trial

OBJECTIVE

It has been proposed that a deficit of adenosinergic activity could contribute to the pathophysiology of schizophrenia. The authors undertook this study to further evaluate the level of adenosine deaminase (ADA) in patients with chronic schizophrenia treated with monotherapy of haloperidol, risperidone or clozapine and correlation between the ADA level with response to treatment.

METHODS

The trial was a prospective, 8-week, double blind study of parallel groups of patients with chronic schizophrenia. Eligible participants in the study were 51 patients with chronic schizophrenia with ages ranging from 20 to 45 years. All participants were inpatients, in the active phase of illness, and met DSM-IV-TR criteria for schizophrenia. Patients were randomly allocated (17 patients in each group) to risperidone (6 mg/day) or haloperidol 15 mg/day or clozapine (300 mg/day). Serum ADA activity was measured at baseline and week 8.

RESULTS

The plasma levels of ADA in patients with chronic schizophrenia who received clozapine were significantly higher than patients who received haloperidol. In addition, response to treatment was positively correlated with plasma levels of ADA only in the clozapine group (r = 0.46 and p = 0.04).

CONCLUSION

The results indicate an increased activity of the enzyme ADA in the serum of schizophrenic patients being treated with clozapine and this increase may be correlated with clozapine's superior antipsychotic efficacy.

Clozapine mobilizes CD34+ hematopoietic stem and progenitor cells and increases plasma concentration of interleukin 6 in patients with schizophrenia

The blood of 8 European patients with schizophrenia without manifest comorbidity was studied whether the classical atypical antipsychotic drug clozapine altered the amount of circulating CD34(+) hematopoietic cells. As assessed by flow cytometry, the number of CD34(+) cells increased by 433% (from 1.49 ± 1.07 × 10(6)/L, mean ± SD pretreatment, to a peak of 6.45 ± 3.47 × 10(6)/L) following first-time therapy with clozapine for 12 weeks. The increase of CD34(+) cell, neutrophil, and leukocyte counts was statistically significant (P = 0.012). A transversal investigation of 23 long-term patients and 58 controls showed elevated neutrophil counts in the clozapine-monotreated group, whereas CD34(+) cell numbers were unaltered. A transversal investigation of 12 clozapine-monotreated long-term patients and 10 controls revealed a 1.3-fold elevation of plasma interleukin 6 levels in patients on clozapine (P = 0.017). In conclusion, clozapine treatment results in an initial mobilization of CD34(+) stem and progenitor cells into the peripheral blood and in a slight long-term elevation of interleukin 6.

Lower frequency of the low activity adenosine deaminase allelic variant (ADA1*2) in schizophrenic patients

OBJECTIVE: Adenosine may play a role in the pathophysiology of schizophrenia, since it modulates the release of several neurotransmitters such as glutamate, dopamine, serotonin and acetylcholine, decreases neuronal activity by pos-synaptic hyperpolarization and inhibits dopaminergic activity. Adenosine deaminase participates in purine metabolism by converting adenosine into inosine. The most frequent functional polymorphism of adenosine deaminase (22G→A) (ADA1*2) exhibits 20-30% lower enzymatic activity in individuals with the G/A genotype than individuals with the G/G genotype. The aim of this study was to evaluate the ADA polymorphism 22G→A (ADA1*2) in schizophrenic patients and healthy controls. METHOD: The genotypes of the ADA 22G→A were identified with allele-specific PCR strategy in 152 schizophrenic patients and 111 healthy individuals. RESULTS: A significant decrease in the frequency of the G/A genotype was seen in schizophrenic patients (7/152 - 4.6%) relative to controls (13/111 - 11.7%, p = 0.032, OR = 2.6). CONCLUSION: These results suggest that the G/A genotype associated with low adenosine deaminase activity and, supposingly, with higher adenosine levels is less frequent among schizophrenic patients.

Antipsychotic drugs inhibit nucleotide hydrolysis in zebrafish (Danio rerio) brain membranes

Haloperidol (HAL), olanzapine (OLZ), and sulpiride (SULP) are antipsychotic drugs widely used in the pharmacotherapy of psychopathological symptoms observed in schizophrenia or mood-related psychotic symptoms in affective disorders. Here, we tested the in vitro effects of different concentrations of a typical (HAL) and two atypical (OLZ and SULP) antipsychotic drugs on ectonucleotidase activities from zebrafish brain membranes. HAL inhibited ATP (28.9%) and ADP (26.5%) hydrolysis only at 250 microM. OLZ decreased ATPase activity at all concentrations tested (23.8-60.7%). SULP did not promote significant changes on ATP hydrolysis but inhibited ADP hydrolysis at 250 microM (25.6%). All drugs tested, HAL, OLZ, and SULP, did not promote any significant changes on 5'-nucleotidase activity in the brain membranes of zebrafish. These findings demonstrated that antipsychotic drugs could inhibit NTPDase activities whereas did not change 5'-nucleotidase. Such modulation can alter the adenosine levels, since the ectonucleotidase pathway is an important source of extracellular adenosine. Thus, it is possible to suggest that changes promoted by antipsychotic drugs in the bilayer membrane could alter the NTPDase activities, modulating extracellular ATP and adenosine levels.

A placebo controlled study of the propentofylline added to risperidone in chronic schizophrenia

Impaired activity of the purinergic system is a plausible common factor that could be responsible for many aspects of schizophrenia. Based on purinegic hypothesis of schizophrenia, pharmacological treatments enhancing adenosine activity could be effective treatment in schizophrenia. Propentofylline is a novel xantine derivative which is being developed for treatment of degenerative and vascular dementia. It enhances extracellular adenosine level via inhibition of adenosine uptake. The purpose of the present investigation was to assess the efficacy of propentofylline as an adjuvant agent in the treatment of chronic schizophrenia in an 8-week double blind and placebo controlled trial. Eligible participants in this study were 50 patients with chronic schizophrenia. All patients were inpatients and were in the active phase of the illness, and met DSM-IV-TR criteria for schizophrenia. Patients were allocated in a random fashion, 25 to risperidone 6 mg/day plus propentofylline 900 mg/day (300 mg TDS) and 25 to risperidone 6 mg/day plus placebo. The principal measure of the outcome was Positive and Negative Syndrome Scale (PANSS). Although both protocols significantly decreased the score of the positive, negative and general psychopathological symptoms over the trial period, the combination of risperidone and propentofylline showed a significant superiority over risperidone alone in the treatment of positive symptoms, general psychopathology symptoms as well as PANSS total scores. The means Extrapyramidal Symptoms Rating Scale for the placebo group were higher than in the propentofylline group over the trial. However, the differences were not significant. The present study indicates propentofylline as a potential adjunctive treatment strategy for chronic schizophrenia. Nevertheless, results of larger controlled trials are needed, before recommendation for a broad clinical application can be made.