Uriel Heresco-Levy

D-serine efficacy as add-on pharmacotherapy to risperidone and olanzapine for treatment-refractory schizophrenia

BACKGROUND D-serine, a selective full agonist at the glycine site of N-methyl-D-aspartate glutamate receptor, might presently be the compound of choice for counteracting the hypothesized dysfunction of this receptor class in schizophrenia. Studies performed with Taiwanese patients indicate that D-serine significantly improves schizophrenia symptoms when used as adjuvant to conventional neuroleptics but not to clozapine. We assessed the efficacy and safety of D-serine adjuvant treatment for Occidental schizophrenia patients treated with newer atypical antipsychotics. METHODS Thirty-nine risperidone- or olanzapine-treated schizophrenia patients participated in a double-blind, placebo-controlled, 6-week crossover trial with 30 mg/kg/day D-serine added to their antipsychotic medication. Measures of clinical efficacy and side effects were determined biweekly throughout the study. Clinical laboratory parameters and amino acid serum levels were monitored. RESULTS D-serine administration induced increased serine serum levels (p < .001) and resulted in significant (p < .001) improvements in negative, positive, cognitive, and depression symptoms, as measured by the Positive and Negative Syndrome Scale. For approximately one third of the sample, D-serine treatment resulted in significant (>20%) reductions in Brief Psychiatric Rating Scale total scores. D-serine was well tolerated, and no detrimental changes in clinical laboratory parameters were noted. CONCLUSIONS These findings 1) indicate that risperidone and olanzapine efficacy might be augmented with D-serine adjuvant treatment; 2) confirm D-serine efficacy against main schizophrenia symptom domains; and 3) warrant the assessment of D-serine antipsychotic monotherapy for this illness.

High-dose glycine added to olanzapine and risperidone for the treatment of schizophrenia

Abstract Background Clinical trials indicate that glycine site agonists of the N-methyl-D-aspartate (NMDA) receptors may reduce negative and cognitive symptoms in treatment-resistant schizophrenia when used as adjuvants to conventional antipsychotics but possibly not to clozapine. In this study, we assessed whether high-dose glycine may also be therapeutically beneficial when added to olanzapine and risperidone treatment. Methods Seventeen olanzapine- or risperidone-treated schizophrenia patients participated in a double-blind, placebo-controlled, 6-week crossover treatment trial with .8 g/kg/day glycine added to their ongoing antipsychotic medication. Clinical assessments were performed biweekly throughout the study. Clinical laboratory parameters and amino acid serum levels were monitored. Results Glycine treatment was well tolerated and resulted in a significant ( p r = .60) clinical response. Conclusions These findings indicate that the efficacy of olanzapine and risperidone may be augmented using high-dose adjuvant glycine treatment and suggest that these atypical antipsychotics may affect NMDA receptor-mediated neurotransmission differently than clozapine.

Has an Angel Shown the Way? Etiological and Therapeutic Implications of the PCP/NMDA Model of Schizophrenia

Over the last 20 years, glutamatergic models of schizophrenia have become increasingly accepted as etiopathological models of schizophrenia, based on the observation that phencyclidine (PCP) induces a schizophrenia-like psychosis by blocking neurotransmission at N-methyl-D-aspartate (NMDA)-type glutamate receptors. This article reviews developments in two key predictions of the model: first, that neurocognitive deficits in schizophrenia should follow the pattern of deficit predicted based on underlying NMDAR dysfunction and, second, that agents that stimulate NMDAR function should be therapeutically beneficial. As opposed to dopamine receptors, NMDAR are widely distributed throughout the brain, including subcortical as well as cortical brain regions, and sensory as well as association cortex. Studies over the past 20 years have documented severe sensory dysfunction in schizophrenia using behavioral, neurophysiological, and functional brain imaging approaches, including impaired generation of key sensory-related potentials such as mismatch negativity and visual P1 potentials. Similar deficits are observed in humans following administration of NMDAR antagonists such as ketamine in either humans or animal models. Sensory dysfunction, in turn, predicts impairments in higher order cognitive functions such as auditory or visual emotion recognition. Treatment studies have been performed with compounds acting directly at the NMDAR glycine site, such as glycine, D-serine, or D-cycloserine, and, more recently, with high-affinity glycine transport inhibitors such as RG1678 (Roche). More limited studies have been performed with compounds targeting the redox site. Overall, these compounds have been found to induce significant beneficial effects on persistent symptoms, suggesting novel approaches for treatment and prevention of schizophrenia.

The role of N-Methyl-D-Aspartate (NMDA) receptor-mediated neurotransmission in the pathophysiology and therapeutics of psychiatric syndromes

The study of excitatory amino acids (EAAs) has recently resulted in new and fundamental concepts in neuroscience. This progress has led to a growing awareness of the crucial role that brain EAAs systems play in a variety of physiological and pathological processes. The N-methyl-D-aspartate (NMDA) receptor, presently the most well understood subtype of EAAs receptors, has been implicated in crucial physiological processes such as synaptogenesis, learning and memory. Dysfunctions of NMDA receptors seem to play a crucial role in the neurobiology of disorders such as Parkinsons disease, Alzheimers disease, epilepsy and ischemic stroke. This paper is a review of emerging data indicating that alterations of NMDA receptor function may be pivotal to the pathophysiology of four common psychiatric syndromes: schizophrenia, major depression, posttraumatic stress disorder, and alcoholism. Special emphasis is placed on the current state of development of pharmacological strategies aiming at the modulation of NMDA receptor-mediated neurotransmission in these disorders.

Comparative effects of glycine and d-cycloserine on persistent negative symptoms in schizophrenia: a retrospective analysis

Phencyclidine (PCP), ketamine and other N-methyl-D-aspartate (NMDA) antagonists induce schizophrenia-like symptoms in normal volunteers, suggesting that endogenous dysfunction or dysregulation of NMDA receptors may contribute to the pathophysiology of schizophrenia. Glycine and D-cycloserine are potential treatments for persistent negative symptoms of schizophrenia. Seventeen patients were identified who participated in double-blind trials of both agents. Significant clinical improvement was observed during both trials. However, the degree of improvement was significantly larger during glycine, than D-cycloserine, treatment on both an individual subject and group level. Previous analyses have documented effectiveness of glycine, and to a lesser extent D-cycloserine, within separate patient populations. This analysis provides the first direct comparison of glycine and D-cycloserine effects within the same population, and suggests first, that NMDA agonists are effective in treatment of persistent negative symptoms of schizophrenia, and, second, that full agonists, such as glycine and D-serine, may be more effective than partial agonists such as D-cycloserine. Similar findings are apparent when data are considered from all trials with NMDA agonists performed to date. Overall, the findings indicate that agents which potentiate NMDA transmission may be therapeutically beneficial in treatment of persistent symptoms of schizophrenia.

Combined analysis of 635 patients confirms an age-related association of the serotonin 2A receptor gene with tardive dyskinesia and specificity for the non-orofacial subtype

Tardive dyskinesia (TD) is an important limiting factor in the use of typical antipsychotic drugs. Genetic variability in the serotonin 2A (5-HT(2A)) receptor may influence risk for TD but the results of prior studies are not confirmatory. The objective of this study was to determine association of T102C and His452Tyr polymorphisms in the 5-HT(2A) receptor gene (HTR(2A)) with TD in a large, multicentre patient sample. The design employed case-control analysis controlling for possible confounders using pooled, original data from published and available unpublished samples and employing logistic regression, analysis of variance and meta-analysis. The study sample consisted of 635 patients with schizophrenia or schizoaffective disorder (256 with TD and 379 without TD) drawn from five research centres, divided into six groups based on population origin. The main outcome measure was association of a categorical diagnosis of TD based on the Research Diagnostic Criteria for TD with HTR(2A) T102C and His452Tyr genotypes and haplotypes. The findings indicate significant association of TD with HTR(2A) T102C genotype (p=0.002) over and above the effect of population group, also when controlling for age and gender (p=0.0008), but not with His452Tyr genotype. The T102C genotype was significantly associated with TD in older (>median age 47 yr, p=0.002) but not younger patients and in patients with non-orofacial (limb-truncal) (p=0.001) but not orofacial TD. By meta-analysis the Mantel-Haenszel (M-H) pooled odds ratio (OR) across all the available data was 1.64. A T102C-His452Tyr haplotype was significantly associated with TD (p=0.0008). These findings confirm that genetic variability in HTR(2A) contributes a small but significant degree of risk for the expression of TD, particularly in older patients and specifically for the non-orofacial (limb-truncal) type. Together with other genetic variants associated with TD the findings could be used to assess risk in patients who are candidates for treatment with typical antipsychotic medications.

Glutamatergic neurotransmission modulation and the mechanisms of antipsychotic atypicality

The neurotransmission mediated by the excitatory amino acids (EAA) glutamate (GLU) and aspartate is of interest to the pharmacotherapy of psychosis due to its role in neurodevelopment and neurotoxicity, its complex interactions with dopaminergic and other neurotransmitter systems and its pivotal importance in recent models of schizophrenia. Accumulating evidence indicates that modulation of glutamatergic neurotransmission may play an important role in the mechanisms of action of atypical antipsychotic drugs. The principles of the phencyclidine (PCP) model of schizophrenia suggest that conventional neuroleptics cannot counteract all aspects of schizophrenia symptomatology, while a more favorable outcome, including anti-negative and cognitive symptoms effects, would be expected with the use of treatment modalities targeting glutamatergic neurotransmission. Clozapine and other presently used atypical antipsychotics differ from conventional neuroleptics in the way they affect various aspects of glutamatergic receptors function. In this context, a specific hypothesis suggesting an agonistic role of clozapine at the N-methyl-D-aspartate (NMDA) subtype of GLU receptors has been postulated. Furthermore, the results of the first generation of clinical trials with glycine (GLY) site agonists of the NMDA receptor in schizophrenia suggest that this type of compounds (1) have efficacy and side effects profiles different than those of conventional neuroleptics and (2) differ in their synergic effects when used in addition to conventional neuroleptics versus clozapine and possibly additional atypical antipsychotics. These findings (1) bring further support to the hypothesis that glutamatergic effects may play an important role in the mechanism of action of atypical antipsychotics, (2) help explain the unique clinical profile of clozapine, and (3) suggest that GLY site agonists of the NMDA receptor may represent a new class of atypical antipsychotic medication. Future research in this area is bound to bring about a better understanding of the role of glutamatergic neurotransmission manipulation in the pharmacotherapy of psychosis and the development of novel pharmacological strategies targeting GLU brain systems.

Double-blind, placebo-controlled, crossover trial of D -cycloserine adjuvant therapy for treatment-resistant schizophrenia

Dysfunction of N-methyl-D-aspartate (NMDA) receptor-mediated glutamatergic neurotransmission may be relevant to the pathogenesis of negative symptoms in schizophrenia. The tuberculostatic compound D-cycloserine (DCS) acts as a partial agonist at the strychnine-insensitive glycine regulatory site on the NMDA receptor complex. Dose-finding trials suggest that DCS doses of 50-100 mg/d may be beneficial in the treatment of negative symptoms in schizophrenia. Nine treatment-resistant chronic schizophrenic patients participated in a double-blind, placebo-controlled, adjuvant treatment trial with 50 mg/d DCS. Between treatment-groups differences in symptom changes were not significant. However, a significant (p<0.05) reduction in negative symptoms was registered during treatment with DCS but not placebo. Greater reductions were registered in patients with lower baseline serum glycine levels (p<0.008). No side effects were registered. These preliminary findings indicate a potential role of DCS in the treatment of negative symptoms in schizophrenia. However, the degree of symptom reduction may be modest, at least among treatment-resistant inpatients.

A randomized add-on trial of high-dose d-cycloserine for treatment-resistant depression

Antagonism of N-methyl-D-aspartate glutamatergic receptors (NMDAR) may represent an effective antidepressant mechanism. D-cycloserine (DCS) is a partial agonist at the NMDAR-associated glycine modulatory site that at high doses acts as a functional NMDAR antagonist. Twenty-six treatment-resistant major depressive disorder patients participated in a double blind, placebo-controlled, 6-wk parallel group trial with a gradually titrated high dose (1000 mg/d) of DCS added to their antidepressant medication. DCS treatment was well tolerated, had no psychotomimetic effects and led to improvement in depression symptoms as measured by Hamilton Depression Rating Scale (HAMD; p = 0.005) and Beck Depression Inventory (p = 0.046). Of the 13 subjects treated with DCS, 54% had a ≥ 50% HAMD score reduction vs. 15% of the 13 patients randomized to placebo (p = 0.039). A significant (p = 0.043) treatment× pre-treatment glycine serum levels interaction was registered. These findings indicate that NMDAR glycine site antagonism may be a cost-effective target for development of mechanistically novel antidepressants. Larger-sized DCS trials are warranted.

A Multicenter, Add-On Randomized Controlled Trial of Low-Dose d -Serine for Negative and Cognitive Symptoms of Schizophrenia

BACKGROUND Observations that antagonists of the N-methyl-d-aspartate (NMDA) receptor of glutamatergic neurons can mimic symptoms of schizophrenia have raised the hope that NMDA agonists can improve symptoms. On the basis of encouraging results of trials in which NMDA agonists were added to antipsychotics, we conducted an adequately powered randomized controlled trial adding d-serine, an NMDA modulator, to antipsychotics. METHOD This study was a 195-patient, multicenter, double-blind, randomized, placebo-controlled, 16-week trial of d-serine 2 g/d as an add-on treatment to antipsychotics. Subjects had DSM-IV schizophrenia or schizoaffective disorder and were inpatients or outpatients stabilized on antipsychotics, with persistent negative symptoms. The primary outcome measures were changes in negative symptoms and cognition as measured by the Scale for the Assessment of Negative Symptoms (SANS) and the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) battery, respectively. The study was performed between 2003 and 2007. RESULTS Mean total Positive and Negative Syndrome Scale scores at baseline were 75.5. Subjects receiving d-serine and placebo improved in scores on the SANS and MATRICS, but no significant differences were observed between groups: improvement on SANS was 11.4% for d-serine vs 14.8% for placebo, F1,147=1.18, P=.32; and improvement on MATRICS was 6.8% for d-serine vs 6.1% for placebo, F1,125=0.96, P=.39, respectively. d-Serine was well tolerated. DISCUSSION This study did not find a significant difference between drug and placebo. However, the results are limited by a relatively large placebo response and somewhat lower-achieved doses than in prior studies. Future studies will administer higher doses and will attempt to affect the NMDA receptor using other mechanisms, such as agonists of the presynaptic metabotropic glutamate 2/3 receptor or glycine reuptake inhibitors. TRIAL REGISTRATION ClinicalTrials.gov identifier: NCT00138775.