Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0036341 (schizophrenia)
 60,220 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

D-Serine, an endogenous amino acid, is involved in many physiological processes through its interaction with the glycine binding site of the N-methyl-D-aspartate (NMDA) receptor. It has important roles in development, learning, and cell death signaling. Recent evidence suggests that decreased function of the NMDA receptor is related to the etiology of schizophrenia, and the use of D-serine as add-on therapy is beneficial in alleviating the symptoms of treatment-refractory schizophrenia. The NMDA receptor also plays a major role in neuronal cell death and neurodegeneration mediated by excitatory amino acid toxicity in ischemia, epilepsy, and trauma. Due to its co-activator function, D-serine can markedly potentiate NMDA-mediated excitotoxicity. To investigate potential adverse effects of D-serine treatment, we investigated gene expression changes in the forebrain of male F-344 rats treated with a single intraperitoneal injection of D-serine (5, 20, 50, 200, or 500 mg/kg) at 96 h post-treatment. Gene expression profiling using Affymetrix Rat Genome 230 2.0 arrays revealed that D-serine treatment resulted in up- and down-regulation of 134 and 52 genes, respectively, based on the common genes identified using three statistical methods, i.e. t test (p < 0.01 over two consecutive doses), ANOVA (with adjusted Bonferonni correction for multiple testing) and significance analysis of microarray (SAM). Self organized map (SOM) clustering analysis of the differentially expressed genes showed two clusters, one with all 134 up-regulated probe sets and the other with all 52 down-regulated probe sets. The dose-response pattern of the down-regulated cluster showed nearly a perfect mirror image of that of the up-regulated one. Gene ontology analysis revealed that pathways implicated in neuronal functions and/or neurodegenerative disorders are over-represented among the differentially expressed genes. Specifically, genes involved in vesicle-mediated transport, endocytosis, ubiquitin conjugation pathway, regulation of actin filament polymerization/depolymerization, focal adhesion, Wnt signaling, and insulin signaling were up-regulated, while genes involved in RNA metabolism/splicing/processing and Notch signaling were down-regulated. Consistent with this finding, pathway analysis using GenMAPP showed a significant number of differentially expressed genes in these pathways. In addition, the GenMAPP result also showed activation of the signaling pathways of several proinflammatory cytokines (including IL-2, IL-3, IL-5, IL-6 and TNF-alpha), which might suggest the onset of neuroinflammation. Biological association network analysis showed that several nuclear factors implicated in transcription regulation (including Taf1, Max, Myc, and Hnf4a) are highly connected to a large number of up-regulated genes. While the transcript levels of these transcription factors were not changed, their connections to Ddx3x, a gene involved in mRNA processing and translation initiation, raise the possibility that they may be up-regulated at the post-transcriptional level. The observation that Ubqln1 and Ube2d, two differentially expressed genes involved in ubiquitin-mediated proteolysis and implicated in neurodegenerative disorders, are highly connected in this network suggests a role of ubiquitination proteasome pathway in response to D-serine exposure. This finding is consistent with the result of gene ontology analysis and suggests that D-serine treatment might result in damage to cellular proteins and subsequent up-regulation of ubiquitination proteasome pathway to clear these damaged proteins. In summary, D-serine exposure resulted in perturbation of a number of pathways implicated in neuronal functions and neurodegenerative disorders. However, activation of cellular response to counter the toxic effects of D-serine might be hindered due to the down-regulation of such important cellular machinery like RNA metabolism, splicing and processing. Consequently, cell damage might be further exacerbated. Taken together, these findings highlight the potential impacts of D-serine exposure on neuronal functions.
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PMID:D-Serine exposure resulted in gene expression changes implicated in neurodegenerative disorders and neuronal dysfunction in male Fischer 344 rats. 1921 59

In the brain, the human flavoprotein D-amino acid oxidase (hDAAO) is involved in the degradation of the gliotransmitter D-serine, an important modulator of NMDA-receptor-mediated neurotransmission; an increase in hDAAO activity (that yields a decrease in D-serine concentration) was recently proposed to be among the molecular mechanisms leading to the onset of schizophrenia susceptibility. This human flavoenzyme is a stable homodimer (even in the apoprotein form) that distinguishes from known D-amino acid oxidases because it shows the weakest interaction with the flavin cofactor in the free form. Instead, cofactor binding is significantly tighter in the presence of an active site ligand. In order to understand how hDAAO activity is modulated, we investigated the FAD binding process to the apoprotein moiety and compared the folding and stability properties of the holoenzyme and the apoprotein forms. The apoprotein of hDAAO can be distinguished from the holoenzyme form by the more "open" tertiary structure, higher protein fluorescence, larger exposure of hydrophobic surfaces, and higher sensitivity to proteolysis. Interestingly, the FAD binding only slightly increases the stability of hDAAO to denaturation by urea or temperature. Taken together, these results indicate that the weak cofactor binding is not related to protein (de)stabilization or oligomerization (as instead observed for the homologous enzyme from yeast) but rather should represent a means of modulating the activity of hDAAO. We propose that the absence in vivo of an active site ligand/substrate weakens the cofactor binding, yielding the inactive apoprotein form and thus avoiding excessive D-serine degradation.
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PMID:Relevance of weak flavin binding in human D-amino acid oxidase. 1930 36

D-Amino acid oxidase (DAO) has been established to be involved in the oxidation of D-serine, an allosteric activator of the N-methyl-D-aspartate-type glutamate receptor in the brain, and to be associated with the onset of schizophrenia. The effect of risperidone, a benzisoxazole derivative, atypical antischizophrenic drug, on the activity of human DAO was tested using an in-vitro oxygraph system and rat C6, stable C6 transformant cells overexpressing mouse DAO (designated as C6/DAO) and pig kidney epithelial cells (LLC-PK(1)). Risperidone has a hyperbolic mixed-type inhibition, designated as 'partial uncompetitive inhibition effect', with K(i) value of 41 microM on human DAO. Risperidone exhibited a protective effect from D-amino acid induced cell death in both C6/DAO and LLC-PK(1) cells with 10% increase in viability. These data indicate the involvement of DAO activity in D-serine metabolism and also suggest a new mechanism of action to risperidone as antischizophrenic drug.
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PMID:The effect of risperidone on D-amino acid oxidase activity as a hypothesis for a novel mechanism of action in the treatment of schizophrenia. 1993 69

D-Serine, an endogenous modulator of NMDA receptors has been shown to play a vital role in many neuropsychiatric functions such as learning, memory, nociception and implicated in pathological conditions like schizophrenia and Alzheimer's disease. We propose possible therapeutic approaches for some CNS diseases and chronic pain, targeting the D-serine levels by manipulating its uptake, biosynthesis and metabolism.
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PMID:D-serine regulation: a possible therapeutic approach for central nervous diseases and chronic pain. 1951 6

Schizophrenia is a severe neuropsychiatric disorder for which there is no adequate current treatment. Recent theories about the molecular basis of schizophrenia focus on disturbances of glutamatergic neurotransmission, particularly at NMDA-type glutamate receptors (NMDARs). NMDARs are regulated in vivo by the amino acids glycine and D-serine. Glycine levels, in turn, are regulated by glycine transporter type 1 (GlyT1), which serves to maintain low subsaturating glycine levels in the vicinity of the NMDAR. Therefore, one proposed approach to the treatment of schizophrenia is via the inhibition of GlyT1-mediated transport. During the past decade, several well-tolerated, high-affinity glycine transport inhibitors (GTIs) have been developed that demonstrate the ability to potentiate NMDAR-mediated neurotransmission in animal models relevant to schizophrenia. In addition, clinical trials have been conducted with sarcosine (N-methylglycine), a naturally occurring GTI. Issues related to clinical proof-of-concept studies with high-affinity GTIs in schizophrenia are discussed in this review.
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PMID:Glycine transport inhibitors for the treatment of schizophrenia: symptom and disease modification. 1956 43

Antipsychotics, the drugs used currently for the treatment of schizophrenia, produce their therapeutic effects via the blockade of dopamine receptors. These compounds are, however, limited in their therapeutic efficacy and have side effect liabilities that also limit their use. Agents that produce antipsychotic effects by enhancing NMDA receptor function represent a viable alternative to dopamine antagonists. D-serine, is the prototype of this approach acting as a positive allosteric modulator of the NMDA receptor to enhance antipsychotic efficacy in the clinic. A newer approach to modulating NMDA receptor function, identified by gene association studies, is pLG72/DAOA (D-amino acid oxidase activator) a peptide that modulates D-amino acid oxidase (DAAO) activity, increasing endogenous levels of D-serine. While the initial association of DAOA with schizophrenia and its functional effects on DAAO activity have not been replicated, its identification has led to the development of several DAAO inhibitors, e.g., AS057278, CBIO and Compound 8, that are active in animal models of antipsychotic action. The complications in validating the G72 association with schizoprenia highlight the inherent challenges in translating gene-based, disease-related associations to drug discovery targets.
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PMID:Commentary: genome-based CNS drug discovery: D-amino acid oxidase (DAAO) as a novel target for antipsychotic medications: progress and challenges. 1959 8

D-Amino acid oxidase (DAO) is a peroxisomal flavoenzyme that catalyzes oxidative deamination of a wide range of D-amino acids. Among the possible substrates of DAO in vivo, D-serine is proposed to be a neuromodulator of the N-methyl-D-aspartate (NMDA) type glutamate receptor. The gene for DAO was reported to be associated with schizophrenia. Since DAO is expected to be one of the key enzymes in the regulation of NMDA neurotransmission, the modulation of the enzyme activity is expected to be therapeutical for neuronal disorders. In search of the pathophysiological role of DAO, we analyzed the distribution of DAO mRNA and protein in the rat and human brain. In rat, the distribution of DAO mRNA was newly detected in choroid plexus (CP) epithelial cells in addition to glial cells of pons, medulla oblongata, and especially Bergmann glia of cerebellum. Moreover, to investigate how DAO expression level is altered in schizophrenia, we performed immunohistochemistry in the human brain. In agreement with the results in the rat brain, the immunoreactivity for DAO was detected in glial cells of rhombencephalon and in CP. Furthermore, higher level of DAO expression was observed in schizophrenic CP epithelial cells than that in non-schizophrenic cases. These results suggest that an increase in DAO expression in parts of the brain is involved in aberrant D-amino acid metabolism. In particular, gene expression of DAO in CP suggests that DAO may regulate D-amino acid concentration by modulating the cerebrospinal fluid and may be regarded as a potential therapeutic target for schizophrenia.
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PMID:Potential pathophysiological role of D-amino acid oxidase in schizophrenia: immunohistochemical and in situ hybridization study of the expression in human and rat brain. 1968 98

Hypofunction of the N-methyl-D-aspartate receptor (NMDAR) has been implicated in the pathophysiology of schizophrenia. The NMDAR contains a D-serine/glycine site on the NR1 subunit that may be a promising therapeutic target for psychiatric illness. This review outlines the complex regulation of endogenous NMDAR D-serine/glycine site agonists and explores their contribution to schizophrenia pathogenesis and their potential clinical utility. Genetic studies have associated genes influencing NMDAR D-serine/glycine site activation with an increased susceptibility to schizophrenia. Postmortem studies have identified abnormalities in several transcripts affecting D-serine/glycine site activity, consistent with in vivo reports of alterations in levels of endogenous D-serine/glycine site agonists and antagonists. Genetically modified mice with aberrant NMDAR D-serine/glycine site function model certain features of the negative and cognitive symptoms of schizophrenia, and similar behavioral abnormalities have been observed in other candidate genes models. Compounds that directly activate the NMDAR D-serine/glycine site or inhibit glycine transport have demonstrated beneficial effects in preclinical models and clinical trials. Future pharmacological approaches for schizophrenia treatment may involve targeting enzymes that affect D-serine synthesis and metabolism.
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PMID:The involvement of the NMDA receptor D-serine/glycine site in the pathophysiology and treatment of schizophrenia. 1969 84

Reduced function of the N-methyl-d-aspartate receptor (NMDAR) has been implicated in the pathophysiology of schizophrenia. The NMDAR contains a glycine binding site in its NR1 subunit that may be a useful target for the treatment of schizophrenia. In this study, we assessed the therapeutic potential of long-term increases in the brain levels of the endogenous NMDAR glycine site agonist D-serine, through the genetic inactivation of its catabolic enzyme D-amino acid oxidase (DAO) in mice. The effects of eliminating DAO function were investigated in mice that display schizophrenia-related behavioral deficits due to a mutation (Grin 1(D481N)) in the NR1 subunit that results in a reduction in NMDAR glycine affinity. Grin 1(D481N) mice show deficits in sociability, prolonged latent inhibition, enhanced startle reactivity and impaired spatial memory. The hypofunctional Dao 1(G181R) mutation elevated brain levels of D-serine, but alone it did not affect performance in the behavioral measures. Compared to animals with only the Grin 1(D481N) mutation, mice with both the Dao1(G181R) and Grin 1(D481N) mutations displayed an improvement in social approach and spatial memory retention, as well as a reversal of abnormally persistent latent inhibition and a partial normalization of startle responses. Thus, an increased level of D-serine resulting from decreased catalysis corrected the performance of mice with deficient NMDAR glycine site activation in behavioral tasks relevant to the negative and cognitive symptoms of schizophrenia. Diminished DAO activity and elevations in D-serine may serve as an effective therapeutic intervention for the treatment of psychiatric symptoms.
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PMID:Genetic loss of D-amino acid oxidase activity reverses schizophrenia-like phenotypes in mice. 1975 94

D-amino acid oxidase (DAO) is a flavoenzyme that metabolizes certain D-amino acids, notably the endogenous N-methyl D-aspartate receptor (NMDAR) co-agonist, D-serine. As such, it has the potential to modulate the function of NMDAR and to contribute to the widely hypothesized involvement of NMDAR signalling in schizophrenia. Three lines of evidence now provide support for this possibility: DAO shows genetic associations with the disorder in several, although not all, studies; the expression and activity of DAO are increased in schizophrenia; and DAO inactivation in rodents produces behavioural and biochemical effects, suggestive of potential therapeutic benefits. However, several key issues remain unclear. These include the regional, cellular and subcellular localization of DAO, the physiological importance of DAO and its substrates other than D-serine, as well as the causes and consequences of elevated DAO in schizophrenia. Herein, we critically review the neurobiology of DAO, its involvement in schizophrenia, and the therapeutic value of DAO inhibition. This review also highlights issues that have a broader relevance beyond DAO itself: how should we weigh up convergent and cumulatively impressive, but individually inconclusive, pieces of evidence regarding the role that a given gene may have in the aetiology, pathophysiology and pharmacotherapy of schizophrenia?
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PMID:The neurobiology of D-amino acid oxidase and its involvement in schizophrenia. 1978 63


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