Involvement of D-amino acid oxidase in elimination of free D-amino acids in mice.
Ontology highlight
ABSTRACT:
SUBMITTER: Nagata Y
PROVIDER: S-EPMC1135571 | biostudies-other | 1989 Jan
REPOSITORIES: biostudies-other
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Project description: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?
| S-EPMC2811712 | biostudies-literature
Project description:Feasible peripheral biomarker for Alzheimer's disease (AD) is lacking. Dysregulation of N-methyl-D-aspartate (NMDA) receptor is implicated in the pathogenesis of AD. D-amino acid oxidase (DAO) and amino acids can regulate the NMDA receptor function. This study aimed to examine whether peripheral DAO and amino acids levels are characteristic of age-related cognitive decline. We enrolled 397 individuals (including amnestic mild cognitive impairment (MCI), mild AD, moderate to severe AD, and healthy elderly). DAO levels in the serum were measured using ELISA. Amino acids levels in serum were measured by high performance liquid chromatography. Severity of the cognitive deficits in subjects was assessed using Clinical Dementia Rating Scale (CDR). The DAO levels increased with the severity of the cognitive deficits. DAO levels were significantly associated with D-glutamate and D-serine levels. The Receiver Operating Characteristics analysis of DAO levels for AD patients vs. healthy controls determined the optimal cutoff value, 30.10, with high sensitivity (0.842) and specificity (0.889) (area under curve = 0.928). This is the first study indicating that the peripheral DAO levels may increase with age-related cognitive decline. The finding supports the hypofunction of NMDA receptor hypothesis in AD. Whether DAO could serve as a potential surrogate biomarker needs further studies.
| S-EPMC5665939 | biostudies-literature
Project description:BACKGROUND AND PURPOSE:d-Amino acid oxidase (DAAO) is a flavine adenine dinucleotide-containing flavoenzyme and specifically catalyses oxidative deamination of d-amino acids. This study aimed to explore the association between increased cerebral DAAO expression or enzymic activity and the development of cerebral ischaemia. EXPERIMENTAL APPROACH:A mouse model of transient (90 min) middle cerebral artery occlusion (MCAO) was established, and western blotting, enzymic activity assay, and fluorescent immunostaining techniques were used. KEY RESULTS:The expression and enzymic activity of DAAO increased over time in the cortical peri-infarct area of the mice subjected to transient MCAO. The DAAO was specifically expressed in astrocytes, and its double immunostaining with the astrocytic intracellular marker, glial fibrillary acidic protein, in the cortical peri-infarct area was up-regulated following ischaemic insult, with peak increase on Day 5 after MCAO. Single intravenous injection of the specific and potent DAAO inhibitor Compound SUN reduced the cerebral DAAO enzymic activity and attenuated neuronal infarction and neurobehavioural deficits with optimal improvement apparent immediately after the MCAO procedure. The neuroprotective effect was dose dependent, with ED50 values of 3.9-4.5 mg·kg-1 . Intracerebroventricular injection of the DAAO gene silencer siRNA/DAAO significantly reduced cerebral DAAO expression and attenuated MCAO-induced neuronal infarction and behavioural deficits. CONCLUSIONS AND IMPLICATIONS:Our results, for the first time, demonstrated that increased cerebral astrocytic DAAO expression and enzymic activity were causally associated with the development of neuronal destruction following ischaemic insults, suggesting that targeting cerebral DAAO could be a potential approach for treatment of neurological conditions following cerebral ischaemia.
| S-EPMC6692583 | biostudies-literature
Project description:Amino acids participate directly and indirectly in many important biochemical functions in the brain. We focused on one amino acid metabolic enzyme, L-amino acid oxidase (LAO), and investigated the importance of LAO in brain function using LAO1 knockout (KO) mice. Compared to wild-type mice, LAO1 KO mice exhibited impaired fear learning and memory function in a passive avoidance test. This impairment in LAO1 KO mice coincided with significantly reduced hippocampal acetylcholine levels compared to wild-type mice, while treatment with donepezil, a reversible acetylcholine esterase inhibitor, inhibited this reduction. Metabolomic analysis revealed that knocking out LAO1 affected amino acid metabolism (mainly of phenylalanine [Phe]) in the hippocampus. Specifically, Phe levels were elevated in LAO1 KO mice, while phenylpyruvic acid (metabolite of Phe produced largely by LAO) levels were reduced. Moreover, knocking out LAO1 decreased hippocampal mRNA levels of pyruvate kinase, the enzymatic activity of which is known to be inhibited by Phe. Based on our findings, we propose that LAO1 KO mice exhibited impaired fear learning and memory owing to low hippocampal acetylcholine levels. Furthermore, we speculate that hippocampal Phe metabolism is an important physiological mechanism related to glycolysis and may underlie cognitive impairments, including those observed in Alzheimer's disease.
| S-EPMC6056520 | biostudies-literature
Project description:Dietary proteins can influence the maturation of the immune system, particularly the gut-associated lymphoid tissue, when consumed from weaning to adulthood. Moreover, replacement of dietary proteins by amino acids at weaning has been shown to impair the generation of regulatory T cells in the gut as well as immune activities such as protective response to infection, induction of oral and nasal tolerance as well as allergic responses. Polymeric and elemental diets are used in the clinical practice, but the specific role of intact proteins and free amino acids during the intestinal inflammation are not known. It is plausible that these two dietary nitrogen sources would yield distinct immunological outcomes since proteins are recognized by the immune system as antigens and amino acids do not bind to antigen-recognition receptors but instead to intracellular receptors such as mammalian target of rapamycin (mTOR). In this study, our aim was to evaluate the effects of consumption of an amino acid-containing diet (AA diet) versus a control protein-containing diet in adult mice at steady state and during colitis development. We showed that consumption of a AA diet by adult mature mice lead to various immunological changes including decrease in the production of serum IgG as well as increase in the levels of IL-6, IL-17A, TGF-β, and IL-10 in the small and large intestines. It also led to changes in the intestinal morphology, to increase in intestinal permeability, in the number of total and activated CD4+ T cells in the small intestine as well as in the frequency of proliferating cells in the colon. Moreover, consumption of AA diet during and prior to development of dextran sodium sulfate-induced colitis exacerbated gut inflammation. Administration of rapamycin during AA diet consumption prevented colitis exacerbation suggesting that mTOR activation was involved in the effects triggered by the AA diet. Therefore, our study suggests that different outcomes can result from the use of diets containing either intact proteins or free amino acids such as elemental, semielemental, and polymeric diets during intestinal inflammation. These results may contribute to the design of nutritional therapeutic intervention for inflammatory bowel diseases.
| S-EPMC5701921 | biostudies-literature
Project description:A series of thiophene-2-carboxylic acids and thiophene-3-carboxylic acids were identified as a new class of DAO inhibitors. Structure-activity relationship (SAR) studies revealed that small substituents are well-tolerated on the thiophene ring of both the 2-carboxylic acid and 3-carboxylic acid scaffolds. Crystal structures of human DAO in complex with potent thiophene carboxylic acids revealed that Tyr224 was tightly stacked with the thiophene ring of the inhibitors, resulting in the disappearance of the secondary pocket observed with other DAO inhibitors. Molecular dynamics simulations of the complex revealed that Tyr224 preferred the stacked conformation irrespective of whether Tyr224 was stacked or not in the initial state of the simulations. MM/GBSA indicated a substantial hydrophobic interaction between Tyr244 and the thiophene-based inhibitor. In addition, the active site was tightly closed with an extensive network of hydrogen bonds including those from Tyr224 in the stacked conformation. The introduction of a large branched side chain to the thiophene ring markedly decreased potency. These results are in marked contrast to other DAO inhibitors that can gain potency with a branched side chain extending to the secondary pocket due to Tyr224 repositioning. These insights should be of particular importance in future efforts to optimize DAO inhibitors with novel scaffolds.
| S-EPMC6193832 | biostudies-literature
Project description:L-Amino acids are the building blocks for proteins synthesized in ribosomes in all kingdoms of life, but d-amino acids (d-aa) have important non-ribosome-based functions(1). Mammals synthesize d-Ser and d-Asp, primarily in the central nervous system, where d-Ser is critical for neurotransmission(2). Bacteria synthesize a largely distinct set of d-aa, which become integral components of the cell wall and are also released as free d-aa(3,4). However, the impact of free microbial d-aa on host physiology at the host-microbial interface has not been explored. Here, we show that the mouse intestine is rich in free d-aa that are derived from the microbiota. Furthermore, the microbiota induces production of d-amino acid oxidase (DAO) by intestinal epithelial cells, including goblet cells, which secrete the enzyme into the lumen. Oxidative deamination of intestinal d-aa by DAO, which yields the antimicrobial product H2O2, protects the mucosal surface in the small intestine from the cholera pathogen. DAO also modifies the composition of the microbiota and is associated with microbial induction of intestinal sIgA. Collectively, these results identify d-aa and DAO as previously unrecognized mediators of microbe-host interplay and homeostasis on the epithelial surface of the small intestine.
| S-EPMC5074547 | biostudies-literature
Project description:Pigs exposed to heat stress (HS) increase body temperature in which can damage the intestinal epithelia and affect the absorption and availability of amino acids (AA). Protein digestion and metabolism further increase body temperature. An experiment was conducted with six pairs of pigs (of 47.3 ± 1.3 kg initial body weight) exposed to natural HS to assess the effect of substituting dietary protein-bound AA by free AA on morphology and gene expression of intestinal epithelial and serum concentration (SC) of free AA. Treatments were: high protein, 21.9% crude protein (CP) diet (HShp) and low protein, 13.5% CP diet supplemented with crystalline Lys, Thr, Met, Trp, His, Ile, Leu, Phe, and Val (HSaa). The HShp diet met or exceeded all AA requirements. The HSaa diet was formulated on the basis of ideal protein. Pigs were fed the same amount at 0700 and 1900 hours during the 21-d study. Blood samples were collected at 1700 hours (2.0 h before the evening meal), 2030 hours, and 2130 hours (1.5 and 2.5 h after the evening meal). At the end, all pigs were sacrificed to collect intestinal mucosa and a 5-cm section from each segment of the small intestine from each pig. Villi measures, expression of AA transporters (y+L and B0) in mucosa, and SC of AA were analyzed. Ambient temperature fluctuated daily from 24.5 to 42.6 °C. Weight gain and G.F were not affected by dietary treatment. Villi height tended to be larger (P ≤ 0.10) and the villi height:crypt depth ratio was higher in duodenum and jejunum of pigs fed the HSaa diet (P < 0.05). Gene expression of transporter y+L in jejunum tended to be lower (P < 0.10) and transporter B0 in the ileum was lower (P < 0.05) in HSaa pigs. Preprandial (1700 hours) SC of Arg, His, Ile, Leu, Thr, Trp, and Val was higher (P < 0.05), and Phe tended to be higher (P < 0.10) in HShp pigs. At 2030 hours (1.5 h postprandial), serum Lys, Met, and Thr were higher in the HSaa pigs (P < 0.05). At 2130 hours (2.5 h), Arg, His, Ile, Phe, and Trp were lower (P < 0.05); Met was higher (P < 0.05); and Lys tended to be higher (P < 0.10) in HSaa pigs. In conclusion, feeding HS pigs with low protein diets supplemented with free AA reduces the damage of the intestinal epithelia and seems to improve its absorption capacity, in comparison with HS pigs fed diets containing solely protein-bound AA. This information is useful to formulate diets that correct the reduced AA consumption associated with the decreased voluntary feed intake of pigs under HS.
| S-EPMC7082100 | biostudies-literature
Project description:BackgroundGlobal residue-specific amino acid mutagenesis can provide important biological insight and generate proteins with altered properties, but at the risk of protein misfolding. Further, targeted libraries are usually restricted to a handful of amino acids because there is an exponential correlation between the number of residues randomized and the size of the resulting ensemble. Using GFP as the model protein, we present a strategy, termed protein evolution via amino acid and codon elimination, through which simplified, native-like polypeptides encoded by a reduced genetic code were obtained via screening of reduced-size ensembles.Methodology/principal findingsThe strategy involves combining a sequential mutagenesis scheme to reduce library size with structurally stabilizing mutations, chaperone complementation, and reduced temperature of gene expression. In six steps, we eliminated a common buried residue, Phe, from the green fluorescent protein (GFP), while retaining activity. A GFP variant containing 11 Phe residues was used as starting scaffold to generate 10 separate variants in which each Phe was replaced individually (in one construct two adjacent Phe residues were changed simultaneously), while retaining varying levels of activity. Combination of these substitutions to generate a Phe-free variant of GFP abolished fluorescence. Combinatorial re-introduction of five Phe residues, based on the activities of the respective single amino acid replacements, was sufficient to restore GFP activity. Successive rounds of mutagenesis generated active GFP variants containing, three, two, and zero Phe residues. These GFPs all displayed progenitor-like fluorescence spectra, temperature-sensitive folding, a reduced structural stability and, for the least stable variants, a reduced steady state abundance.Conclusions/significanceThe results provide strategies for the design of novel GFP reporters. The described approach offers a means to enable engineering of active proteins that lack certain amino acids, a key step towards expanding the functional repertoire of uniquely labeled proteins in synthetic biology.
| S-EPMC2859931 | biostudies-literature
Project description:Amidation of unprotected amino acids has been investigated using a variety of 'classical" coupling reagents, stoichiometric or catalytic group(IV) metal salts, and boron Lewis acids. The scope of the reaction was explored through the attempted synthesis of amides derived from twenty natural, and several unnatural, amino acids, as well as a wide selection of primary and secondary amines. The study also examines the synthesis of medicinally relevant compounds, and the scalability of this direct amidation approach. Finally, we provide insight into the chemoselectivity observed in these reactions.
| S-EPMC5969221 | biostudies-other