D-amino acid oxidase controls motoneuron degeneration through D-serine

Characterisation of a microelectrochemical biosensor for real-time detection of brain extracellular d-serine

A modified development protocol and concomitant characterisation of a first generation biosensor for the detection of brain extracellular d-serine is reported. Functional parameters important for neurochemical monitoring, including sensor sensitivity, O2 interference, selectivity, shelf-life and biocompatibility were examined. Construction and development involved the enzyme d-amino acid oxidase (DAAO), utilising a dip-coating immobilisation method employing a new extended drying approach. The resultant Pt-based polymer enzyme composite sensor achieved high sensitivity to d-serine (0.76 ± 0.04 nA mm-2. μM-1) and a low μM limit of detection (0.33 ± 0.02 μM). The in-vitro response time was within the solution stirring time, suggesting potential sub-second in-vivo response characteristics. Oxygen interference studies demonstrated a 1 % reduction in current at 50 μM O2 when compared to atmospheric O2 levels (200 μM), indicating that the sensor can be used for reliable neurochemical monitoring of d-serine, free from changes in current associated with physiological O2 fluctuations. Potential interference signals generated by the principal electroactive analytes present in the brain were minimised by using a permselective layer of poly(o-phenylenediamine), and although several d-amino acids are possible substrates for DAAO, their physiologically relevant signals were small relative to that for d-serine. Additionally, changing both temperature and pH over possible in vivo ranges (34-40 °C and 7.2-7.6 respectively) resulted in no significant effect on performance. Finally, the biosensor was implanted in the striatum of freely moving rats and used to monitor physiological changes in d-serine over a two-week period.

Blood D-serine levels correlate with aging and dopaminergic treatment in Parkinson's disease

We recently described increased D- and L-serine concentrations in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys, the post-mortem caudate-putamen of human Parkinson's disease (PD) brains and the cerebrospinal fluid (CSF) of de novo living PD patients. However, data regarding blood D- and L-serine levels in PD are scarce. Here, we investigated whether the serum profile of D- and L-serine, as well as the other glutamate N-methyl-D-aspartate ionotropic receptor (NMDAR)-related amino acids, (i) differs between PD patients and healthy controls (HC) and (ii) correlates with clinical-demographic features and levodopa equivalent daily dose (LEDD) in PD. Eighty-three consecutive PD patients and forty-one HC were enrolled. PD cohort underwent an extensive clinical characterization. Serum levels of D- and L-serine, L-glutamate, L-glutamine, L-aspartate, L-asparagine and glycine were determined using High Performance Liquid Chromatography. In age- and sex-adjusted analyses, no differences emerged in the serum levels of D-serine, L-serine and other NMDAR-related amino acids between PD and HC. However, we found that D-serine and D-/Total serine ratio positively correlated with age in PD but not in HC, and also with PD age at onset. Moreover, we found that higher LEDD correlated with lower levels of D-serine and the other excitatory amino acids. Following these results, the addition of LEDD as covariate in the analyses disclosed a selective significant increase of D-serine in PD compared to HC (Δ ≈ 38%). Overall, these findings suggest that serum D-serine and D-/Total serine may represent a valuable biochemical signature of PD.

Investigating D-Amino Acid Oxidase Expression and Interaction Network Analyses in Pathways Associated With Cellular Stress: Implications in the Biology of Aging

D-amino acid oxidase (DAO) is a flavoenzyme that metabolizes D-amino acids by oxidative deamination, producing hydrogen peroxide (H2O2) as a by-product. The generation of intracellular H2O2 may alter the redox-homeostasis mechanism of cells and increase the oxidative stress levels in tissues, associated with the pathogenesis of age-related diseases and organ decline. This study investigates the effect of DAO knockdown using clustered regularly interspaced short palindromic repeats (CRISPR) through an in silico approach on its protein-protein interactions (PPIs) and their potential roles in the process of aging. The target sequence and guide RNA of DAO were designed using the CCTop database, PPI analysis using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses, Reactome biological pathway, protein docking using GalaxyTongDock database, and structure analysis. The translated target sequence of DAO lies between amino acids 43 to 50. The 10 proteins that were predicted to interact with DAO are involved in peroxisome pathways such as acyl-coenzyme A oxidase 1 (ACOX1), alanine-glyoxylate and serine-pyruvate aminotransferase (AGXT), catalase (CAT), carnitine O-acetyltransferase (CRAT), glyceronephosphate O-acyltransferase (GNPAT), hydroxyacid oxidase 1 (HAO1), hydroxyacid oxidase 2 (HAO2), trans-L-3-hydroxyproline dehydratase (L3HYPDH), polyamine oxidase (PAOX), and pipecolic acid and sarcosine oxidase (PIPOX). In summary, DAO mutation would most likely reduce activity with its interacting proteins that generate H2O2. However, DAO mutation may result in peroxisomal disorders, and thus, alternative techniques should be considered for an in vivo approach.

Enantioselective Glutamic Acid Discrimination and Nanobiological Imaging by Chiral Fluorescent Silicon Nanoparticles

Enantioselective discrimination of chiral molecules is essential in chemistry, biology, and medical science due to the configuration-dependent activities of enantiomers. Therefore, identifying a specific amino acid and distinguishing it from its enantiomer by using nanomaterials with outstanding performance are of great significance. Herein, blue- and green-emitting chiral silicon nanoparticles named bSiNPs and gSiNPs, respectively, with excellent water solubility, salt resistance, pH stability, photobleaching resistance, biocompatibility, and ability to promote soybean germination, were fabricated in a facile one-step method. Especially, chiral gSiNPs presented excellent fluorescence recognition ability for glutamic acid enantiomers within 1 min, and the enantiomeric recognition difference factor was as high as 9.0. The mechanism for enantiomeric fluorescence recognition was systematically explored by combining the fluorescence spectra with density functional theory (DFT) calculation. Presumably, the different Gibbs free energy and hydrogen-bonding interaction of the chiral recognition module with glutamic acid enantiomers mainly contributed to the difference in the fluorescence signals. Most noteworthy was the fact that the chiral gSiNPs can showcase not only the ability to recognize l- and d-glutamic acids in living cells but also the test strips fabricated by soaking gSiNPs can be applied for d-glutamic acid visual detection. As a result, this study provided insights into the design of multifunctional chiral sensing nanoplatforms for enantiomeric detection and other applications.

Gut Symptoms, Gut Dysbiosis and Gut-Derived Toxins in ALS

Many pathogenetic mechanisms have been proposed for amyotrophic lateral sclerosis (ALS). Recently, there have been emerging suggestions of a possible role for the gut microbiota. Gut microbiota have a range of functions and could influence ALS by several mechanisms. Here, we review the possible role of gut-derived neurotoxins/excitotoxins. We review the evidence of gut symptoms and gut dysbiosis in ALS. We then examine a possible role for gut-derived toxins by reviewing the evidence that these molecules are toxic to the central nervous system, evidence of their association with ALS, the existence of biochemical pathways by which these molecules could be produced by the gut microbiota and existence of mechanisms of transport from the gut to the blood and brain. We then present evidence that there are increased levels of these toxins in the blood of some ALS patients. We review the effects of therapies that attempt to alter the gut microbiota or ameliorate the biochemical effects of gut toxins. It is possible that gut dysbiosis contributes to elevated levels of toxins and that these could potentially contribute to ALS pathogenesis, but more work is required.

Aggregation of E121K mutant D-amino acid oxidase and ubiquitination-mediated autophagy mechanisms leading to amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a terminal adult-onset neuromuscular disorder. Our group has been studying this illness and previously reported novel mutations and rare mutations in a study using next-generation sequencing of DNA samples from Indian ALS patients. In this paper, we focus on the E121K mutation in the DAO gene to understand how it leads to ALS. Our experiments in SH-SY5Y cells indicate that the E121K mutation results in the accumulation of mutant protein aggregates, a change in cell morphology, and the death of neuronal cells. These protein aggregates get ubiquitinated and cause an imbalance in autophagy regulation. We observed an increase in the cellular concentrations of p62, OPTN, and LC3II. Through confocal microscopy studies, we show that the binding of p62 with ubiquitinated aggregates and its recruitment to LC3II mediates autophagosome generation. These relative changes in the key partners in autophagy increase cell death in cells harboring the E121K mutation and is a probable mechanism leading to ALS.

Biosynthesis and Degradation of Free D-Amino Acids and Their Physiological Roles in the Periphery and Endocrine Glands

It was long believed that D-amino acids were either unnatural isomers or laboratory artifacts, and that the important functions of amino acids were exerted only by L-amino acids. However, recent investigations have revealed a variety of D-amino acids in mammals that play important roles in physiological functions, including free D-serine and D-aspartate that are crucial in the central nervous system. The functions of several D-amino acids in the periphery and endocrine glands are also receiving increasing attention. Here, we present an overview of recent advances in elucidating the physiological roles of D-amino acids, especially in the periphery and endocrine glands.

d-Amino acids: new clinical pathways for brain diseases

Free d-amino acids (d-AAs) are emerging as a novel and important class of signaling molecules in many organs, including the brain and endocrine systems. There has been considerable progress in our understanding of the fundamental roles of these atypical messengers, with increasingly recognized implications in a wide range of neuropathologies, including schizophrenia (SCZ), epilepsy, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), substance abuse, and chronic pain, among others. Research has enabled the discovery that d-serine, d-aspartate and more recently d-cysteine are essential for the healthy development and function of the central nervous system (CNS). We discuss recent progress that has profoundly transformed our vision of numerous physiological processes but has also shown how d-AAs are now offering therapeutic promise in clinical settings for several human diseases.

Two-dimensional LC-MS/MS and three-dimensional LC analysis of chiral amino acids and related compounds in real-world matrices

Amino acids normally have a chiral carbon and d/l-enantiomers are present. Due to the homochirality features on the present Earth, l-enantiomers are predominant in the living beings and the d-enantiomers are rare. Along with the progress and development of cutting edge analytical methods, several d-amino acids were found even in the higher animals including humans, and their biological functions and diagnostic values have also been reported. However, the amounts of these d-amino acids are much lower than the l-forms, and development/utilization of highly sensitive and selective methods are practically essential to avoid the disturbance from uncountable intrinsic substances. In the present review, multi-dimensional HPLC methods for the determination of chiral amino acids, especially two-dimensional LC-MS/MS and three-dimensional LC methods, and their applications to a variety of real-world matrices are summarized.

Chirality in Light-Matter Interaction

The scientific effort to control the interaction between light and matter has grown exponentially in the last 2 decades. This growth has been aided by the development of scientific and technological tools enabling the manipulation of light at deeply sub-wavelength scales, unlocking a large variety of novel phenomena spanning traditionally distant research areas. Here, the role of chirality in light-matter interactions is reviewed by providing a broad overview of its properties, materials, and applications. A perspective on future developments is highlighted, including the growing role of machine learning in designing advanced chiroptical materials to enhance and control light-matter interactions across several scales.

Perturbation of serine enantiomers homeostasis in the striatum of MPTP-lesioned monkeys and mice reflects the extent of dopaminergic midbrain degeneration

Loss of dopaminergic midbrain neurons perturbs l-serine and d-serine homeostasis in the post-mortem caudate putamen (CPu) of Parkinson's disease (PD) patients. However, it is unclear whether the severity of dopaminergic nigrostriatal degeneration plays a role in deregulating serine enantiomers' metabolism. Here, through high-performance liquid chromatography (HPLC), we measured the levels of these amino acids in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys and MPTP-plus-probenecid (MPTPp)-treated mice to determine whether and how dopaminergic midbrain degeneration affects the levels of serine enantiomers in various basal ganglia subregions. In addition, in the same brain regions, we measured the levels of key neuroactive amino acids modulating glutamatergic neurotransmission, including L-glutamate, glycine, l-aspartate, d-aspartate, and their precursors l-glutamine, L-asparagine. In monkeys, MPTP treatment produced severe denervation of nigrostriatal dopaminergic fibers (⁓75%) and increased the levels of serine enantiomers in the rostral putamen (rPut), but not in the subthalamic nucleus, and the lateral and medial portion of the globus pallidus. Moreover, this neurotoxin significantly reduced the protein expression of the astrocytic serine transporter ASCT1 and the glycolytic enzyme GAPDH in the rPut of monkeys. Conversely, concentrations of d-serine and l-serine, as well as ASCT1 and GAPDH expression were unaffected in the striatum of MPTPp-treated mice, which showed only mild dopaminergic degeneration (⁓30%). These findings unveil a link between the severity of dopaminergic nigrostriatal degeneration and striatal serine enantiomers concentration, ASCT1 and GAPDH expression. We hypothesize that the up-regulation of d-serine and l-serine levels occurs as a secondary response within a homeostatic loop to support the metabolic and neurotransmission demands imposed by the degeneration of dopaminergic neurons.

Homeostasis of serine enantiomers is disrupted in the post-mortem caudate putamen and cerebrospinal fluid of living Parkinson's disease patients

L-serine generated in astrocytes plays a pivotal role in modulating essential neurometabolic processes, while its enantiomer, D-serine, specifically regulates NMDA receptor (NMDAR) signalling. Despite their physiological relevance in modulating cerebral activity, serine enantiomers metabolism in Parkinson's disease (PD) remains elusive. Using High-Performance Liquid Chromatography (HPLC), we measured D- and L-serine levels along with other amino acids known to modulate NMDAR function, such as L-glutamate, L-aspartate, D-aspartate, and glycine, in the post-mortem caudate putamen (CPu) and superior frontal gyrus (SFG) of PD patients. Moreover, we examined these amino acids in the cerebrospinal fluid (CSF) of de novo living PD, Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS) patients versus subjects with other neurological disorders (OND), used as control. We found higher D-serine and L-serine levels in the CPu of PD patients but not in the SFG, a cerebral region that, in contrast to the CPu, is not innervated by nigral dopaminergic terminals. We also highlighted a significant elevation of both serine enantiomers in the CSF samples from PD but not in those of AD and ALS patients, compared with control subjects. By contrast, none or only minor changes were found in the amount of other neuroactive amino acids mentioned above. Our findings identify D-serine and L-serine level upregulation as a biochemical signature associated with nigrostriatal dopaminergic degeneration in PD.

Differential relationships of NMDAR hypofunction and oxidative stress with cognitive decline

NMDAR hypofunction and oxidative stress are implicated in the pathogenesis of Alzheimer's disease. D-amino acid oxidase (DAO) regulates NMDAR function. Glutathione, superoxide dismutase, and catalase are three first-line endogenous antioxidants. This study explored the associations of these potential biomarkers with mild cognitive impairment. Cognitive function and blood levels of DAO, glutathione, superoxide dismutase, and catalase were measured in 63 mild cognitive impairment patients and 24 healthy individuals every 6 months for 2 years. Among the patients, DAO and glutathione levels at baseline contributed to the cognitive decline 2 years later. Among the healthy individuals, only glutathione levels were associated with cognitive change. The four biomarkers differed in change directions (upward vs. downward) in the patients and in the healthy individuals. Among patients, glutathione levels were negatively correlated with superoxide dismutase and positively correlated with catalase, and DAO levels were negatively correlated with superoxide dismutase. To our knowledge, this is the first study to demonstrate the differential associations of NMDAR hypofunction and oxidative stress with cognitive change between the mild cognitive impairment patients and healthy people. Glutathione may be regarded as an aging marker for both mild cognitive impairment and normal aging; and DAO, a biomarker exclusively for mild cognitive impairment.

Detection and analysis of chiral molecules as disease biomarkers

The chirality of small metabolic molecules is important in controlling physiological processes and indicating the health status of humans. Abnormal enantiomeric ratios of chiral molecules in biofluids and tissues occur in many diseases, including cancers and kidney and brain diseases. Thus, chiral small molecules are promising biomarkers for disease diagnosis, prognosis, adverse drug-effect monitoring, pharmacodynamic studies and personalized medicine. However, it remains difficult to achieve cost-effective and reliable analysis of small chiral molecules in clinical procedures, in part owing to their large variety and low concentration. In this Review, we describe current and emerging techniques that detect and quantify small-molecule enantiomers and their biological importance.

Mammals sustain amino acid homochirality against chiral conversion by symbiotic microbes

Mammals exhibit systemic homochirality of amino acids in L-configurations. While ribosomal protein synthesis requires rigorous chiral selection for L-amino acids, both endogenous and microbial enzymes convert diverse L-amino acids to D-configurations in mammals. However, it is not clear how mammals manage such diverse D-enantiomers. Here, we show that mammals sustain systemic stereo dominance of L-amino acids through both enzymatic degradation and excretion of D-amino acids. Multidimensional high performance liquidchromatography analyses revealed that in blood, humans and mice maintain D-amino acids at less than several percent of the corresponding L-enantiomers, while D-amino acids comprise ten to fifty percent of the L-enantiomers in urine and feces. Germ-free experiments showed that vast majority of D-amino acids, except for D-serine, detected in mice are of microbial origin. Experiments involving mice that lack enzymatic activity to catabolize D-amino acids showed that catabolism is central to the elimination of diverse microbial D-amino acids, whereas excretion into urine is of minor importance under physiological conditions. Such active regulation of amino acid homochirality depends on maternal catabolism during the prenatal period, which switches developmentally to juvenile catabolism along with the growth of symbiotic microbes after birth. Thus, microbial symbiosis largely disturbs homochirality of amino acids in mice, whereas active host catabolism of microbial D-amino acids maintains systemic predominance of L-amino acids. Our findings provide fundamental insight into how the chiral balance of amino acids is governed in mammals and further expand the understanding of interdomain molecular homeostasis in host-microbial symbiosis.

An integrated strategy to study the combination mechanisms of Bupleurum chinense DC and Paeonia lactiflora Pall for treating depression based on correlation analysis between serum chemical components profiles and endogenous metabolites profiles

ETHNOPHARMACOLOGICAL RELEVANCE

Bupleurum chinense DC-Paeonia lactiflora Pall (BCD-PLP) is a common clinical herb pair in traditional Chinese medicine (TCM) prescriptions commonly used to treat depression. However, its combination mechanisms with its anti-depressive effects remain highly unclear.

AIM OF THE STUDY

Here, an effective strategy has been developed to study the combination mechanisms of Bupleurum chinense DC (BCD) and Paeonia lactiflora Pall (PLP) by integrating serum pharmacochemistry analysis, metabolomics technology, and molecular docking technology.

MATERIALS AND METHODS

First, the depression model rats were replicated by the chronic unpredictable mild stress (CUMS) procedure, and the difference in the chemical composition in vivo before and after the combination of BCD and PLP was analyzed by integrating background subtraction and multivariate statistical analysis techniques. Then, UPLC/HRMS-based serum metabolomics was performed to analyze the synergistic effect on metabolite regulation before and after the combination of BCD and PLP. Further, the correlation analysis between the differential exogenous chemical components and the differential endogenous metabolites before and after the combination was employed to dissect the combination mechanisms from a global perspective of combining metabolomics and serum pharmacochemistry. Finally, the molecular docking between the differential chemical components and the key metabolic enzymes was applied to verify the regulatory effect of the differential exogenous chemical components on the differential endogenous metabolites.

RESULTS

The serum pharmacochemistry analysis results demonstrated that the combination of BCD and PLP could significantly affect the content of 10 components in BCD (including 5 prototype components were significantly decreased and 5 metabolites were significantly increased) and 8 components in PLP (including 4 prototype components and 3 metabolites were significantly increased, 1 metabolite was significantly decreased), which indicated that the combination could enhance BCD prototype components' metabolism and the absorption of the PLP prototype components. Besides, metabolomics results indicated that the BCD-PLP herb pair group significantly reversed more metabolites (8) than BCD and PLP single herb group (5 & 4) and has a stronger regulatory effect on metabolite disorders caused by CUMS. Furthermore, the correlation analysis results suggested that saikogenin F and saikogenin G were significantly positively correlated with the endogenous metabolite itaconate, an endogenous anti-inflammatory metabolite; and benzoic acid was significantly positively correlated with D-serine, an endogenous metabolite with an antidepressant effect. Finally, the molecular docking results further confirmed that the combination of BCD and PLP could affect the activities of cis-aconitic acid decarboxylase and D-amino acid oxidase by increasing the in vivo concentration of saikogenin F and benzoic acid, which further enhances its anti-inflammatory activity and anti-depressive effect.

CONCLUSIONS

In this study, an effective strategy has been developed to study the combination mechanisms of BCD and PLP by integrating serum pharmacochemistry analysis, multivariate statistical analysis, metabolomics technology, and molecular docking technology. Based on this strategy, the present study indicated that the combination of BCD and PLP could affect the activities of cis-aconitic acid decarboxylase and D-amino acid oxidase by increasing the concentration of saikogenin F and benzoic acid in vivo, which further enhances its anti-depressive effect. In short, this strategy will provide a reliable method for elucidating the herb-herb compatibility mechanism of TCM.

Sodium benzoate attenuates 2,8-dihydroxyadenine nephropathy by inhibiting monocyte/macrophage TNF-α expression

Sodium benzoate (SB), a known D-amino acid oxidase (DAO) enzyme inhibitor, has an anti-inflammatory effect, although its role in renal damage has not been explored. 2,8-dihydroxyadenine crystal induced chronic kidney disease, in which TNF-α is involved in the pathogenesis, was established by oral adenine administration in C57BL/6JJcl mice (AdCKD) with or without SB to investigate its renal protective effects. SB significantly attenuated AdCKD by decreasing serum creatinine and urea nitrogen levels, and kidney interstitial fibrosis and tubular atrophy scores. The survival of AdCKD mice improved 2.6-fold by SB administration. SB significantly decreased the number of infiltrating macrophages observed in the positive F4/80 immunohistochemistry area and reduced the expression of macrophage markers and inflammatory genes, including TNF-α, in the kidneys of AdCKD. Human THP-1 cells stimulated with either lipopolysaccharide or TNF-α showed increased expression of inflammatory genes, although this was significantly reduced by SB, confirming the anti-inflammatory effects of SB. SB exhibited renal protective effects in AdCKD in DAO enzyme deficient mice, suggesting that anti-inflammatory effect of SB was independent of DAO enzyme activity. Moreover, binding to motif DNA sequence, protein level, and mRNA level of NF-κB RelB were significantly inhibited by SB in AdCKD kidneys and lipopolysaccharide treated THP-1 cells, respectively. We report that anti-inflammatory property of SB is independent of DAO enzymatic activity and is associated with down regulated NF-κB RelB as well as its downstream inflammatory genes such as TNF-α in AdCKD.

Connexin 30 Deficiency Ameliorates Disease Progression at the Early Phase in a Mouse Model of Amyotrophic Lateral Sclerosis by Suppressing Glial Inflammation

Connexin 30 (Cx30), which forms gap junctions between astrocytes, regulates cell adhesion and migration, and modulates glutamate transport. Cx30 is upregulated on activated astroglia in central nervous system inflammatory lesions, including spinal cord lesions in mutant superoxide dismutase 1 (mSOD1) transgenic amyotrophic lateral sclerosis (ALS) model mice. Here, we investigated the role of Cx30 in mSOD1 mice. Cx30 was highly expressed in the pre-onset stage in mSOD1 mice. mSOD1 mice with knockout (KO) of the Cx30 gene (Cx30KO-mSOD1 mice) showed delayed disease onset and tended to have an extended survival period (log-rank, p = 0.09). At the progressive and end stages of the disease, anterior horn cells were significantly preserved in Cx30KO-mSOD1 mice. In lesions of these mice, glial fibrillary acidic protein/C3-positive inflammatory astroglia were decreased. Additionally, the activation of astrocytes in Cx30KO-mSOD1 mice was reduced compared with mSOD1 mice by gene expression microarray. Furthermore, expression of connexin 43 at the pre-onset stage was downregulated in Cx30KO-mSOD1 mice. These findings suggest that reduced expression of astroglial Cx30 at the early disease stage in ALS model mice protects neurons by attenuating astroglial inflammation.

Blood-Brain Barrier Solute Carrier Transporters and Motor Neuron Disease

Defective solute carrier (SLC) transporters are responsible for neurotransmitter dysregulation, resulting in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). We provided the role and kinetic parameters of transporters such as ASCTs, Taut, LAT1, CAT1, MCTs, OCTNs, CHT, and CTL1, which are mainly responsible for the transport of essential nutrients, acidic, and basic drugs in blood-brain barrier (BBB) and motor neuron disease. The affinity for LAT1 was higher in the BBB than in the ALS model cell line, whereas the capacity was higher in the NSC-34 cell lines than in the BBB. Affinity for MCTs was lower in the BBB than in the NSC-34 cell lines. CHT in BBB showed two affinity sites, whereas no expression was observed in ALS cell lines. CTL1 was the main transporter for choline in ALS cell lines. The half maximal inhibitory concentration (IC50) analysis of [3H]choline uptake indicated that choline is sensitive in TR-BBB cells, whereas amiloride is most sensitive in ALS cell lines. Knowledge of the transport systems in the BBB and motor neurons will help to deliver drugs to the brain and develop the therapeutic strategy for treating CNS and neurological diseases.

Brain Energy Metabolism: Astrocytes in Neurodegenerative Diseases

Astrocytes are the most abundant cells in the brain. They have many important functions in the central nervous system (CNS), including the maintenance of glutamate and ion homeostasis, the elimination of oxidative stress, energy storage in glycogen, tissue repair, regulating synaptic activity by releasing neurotransmitters, and participating in synaptic formation. Astrocytes have special highly ramified structure. Their branches contact with synapses of neurons inwardly, with fine structure and wrapping synapses; their feet contact with blood vessels of brain parenchyma outward, almost wrapping the whole brain. The adjacent astrocytes rarely overlap and communicate with each other through gap junction channels. The ideal location of astrocytes enables them to sense the weak changes of their surroundings and provide the structural basis for the energy supply of neurons. Neurons and astrocytes are closely coupled units of energy metabolism in the brain. Neurons consume a lot of ATPs in the process of neurotransmission. Astrocytes provide metabolic substrates for neurons, maintain high activity of neuron, and facilitate information transmission of neurons. This article reviews the characteristics of glucose metabolism, lipid metabolism, and amino acid metabolism of astrocytes. The metabolic interactions between astrocytes and neurons, astrocytes and microglia were also detailed discussed. Finally, we classified analyzed the role of metabolic disorder of astrocytes in the occurrence and development of neurodegenerative diseases.

Pharmacokinetics and Safety of Sodium Benzoate, a d-Amino Acid Oxidase (DAAO) Inhibitor, in Healthy Subjects: A Phase I, Open-Label Study

PURPOSE

N-methyl-d-aspartate receptor (NMDAR)-mediated neurotransmission plays a critical role in cognition and memory, and d-serine is a co-agonist of the receptor. d-serine is metabolized by d-amino acid oxidase (DAAO). Sodium benzoate is a DAAO inhibitor that leads to the elevation of d-serine levels and enhances NMDAR functions as a therapeutic for wide-spectrum central nervous system (CNS) disorders, including schizophrenia and dementia. For therapeutic application of sodium benzoate in CNS disorders, we conducted a Phase I study to evaluate its safety, tolerability, and pharmacokinetic profile after single-dose oral administration in healthy volunteers. In contrast to the accumulation in the CNS, sodium benzoate has a rapid pharmacokinetic profile when measured peripherally.

METHODS

In this Phase I study, subjects were randomized into 4 different dose groups after a single oral administration. The pharmacokinetic parameters of sodium benzoate were assessed after exposure to 250, 500, 1000, and 2000 mg of sodium benzoate. All adverse events were investigated and recorded.

FINDINGS

The C_max and AUC of sodium benzoate exhibited a higher than dose-proportional increase within the dose range from 250 to 2000 mg under fasting conditions. The slopes were 1.78 and 2.61 and the 90% CIs were 1.41 to 2.15 and 2.20 to 3.03 for C_max and AUC, respectively. Sodium benzoate was absorbed and converted to benzoic acid rapidly, reaching C_max after ∼0.5 hour and elimination t_1/2 after ∼0.3 hour. No subjects reported adverse events that were sodium benzoate related.

IMPLICATIONS

The nonlinear pharmacokinetic response was observed within the dose range up to 2000 mg. Sodium benzoate treatment exhibited a favorable safety profile and was well tolerated at all dose levels. The study results serve as a foundation that should be useful for investigating efficacy and safety in the drug's subsequent clinical development.

TRIAL REGISTRATION

TFDA-103607047.

Diagnosing Alzheimer's Disease Specifically and Sensitively With pLG72 and Cystine/Glutamate Antiporter SLC7A11 AS Blood Biomarkers

BACKGROUND

Reliable blood biomarkers for Alzheimer's disease (AD) have been lacking. The D-amino acids oxidase modulator (named pLG72) modulates glutamate N-methyl-D-aspartate receptor activity. The cystine/glutamate antiporter contains a SLC7A11 subunit, which mediates glutamate release. This study aimed to determine the accuracy of pLG72 protein and SLC7A11 mRNA in diagnosing AD.

METHODS

This study enrolled 130 healthy controls and 109 unmatched AD patients; among them, 40 controls and 70 patients were selected to match by age. We measured their pLG72 protein in plasma and SLC7A11 mRNA in white blood cells.

RESULTS

AD patients had markedly higher pLG72 levels and SLC7A11 mRNA ΔCT values than healthy controls (in both unmatched and matched cohorts; all 4 P values <.001). The receiver operating characteristics analysis in the unmatched cohorts demonstrated that the pLG72 level had a high specificity (0.900) at the optimal cutoff value of 2.3285, the ΔCT of SLC7A11 mRNA displayed an excellent sensitivity (0.954) at the cutoff of 12.185, and the combined value of pLG72 and SLC7A11 ΔCT determined a favorable area under the curve (AUC) (0.882) at the cutoff of 21.721. The AUC of the combined value surpassed that of either biomarker. The specificity, sensitivity, and AUC of the matched cohort were like those of the unmatched cohort.

CONCLUSIONS

The findings suggest that pLG72 protein and SLC7A11 mRNA can distinguish AD patients from healthy controls with excellent specificity and sensitivity, respectively. The combination of pLG72 and SLC7A11 yields better AUC than either, suggesting the superiority of simultaneously measuring both biomarkers in identifying AD patients.

Indirect Enantioseparations: Recent Advances in Chiral Metabolomics for Biomedical Research

Chiral metabolomics is starting to become a well-defined research field, powered by the recent advances in separation techniques. This review aimed to cover the most relevant advances in indirect enantioseparations of endogenous metabolites that were published over the last 10 years, including improvements and development of new chiral derivatizing agents, along with advances in separation methodologies. Moreover, special emphasis is put on exciting advances in separation techniques combined with mass spectrometry, such as chiral discrimination by ion-mobility mass spectrometry together with untargeted strategies for profiling of chiral metabolites in complex matrices. These advances signify a leap in chiral metabolomics technologies that will surely offer a solid base to better understand the specific roles of enantiomeric metabolites in systems biology.

Astrocytic D -amino acid oxidase degrades D -serine in the hindbrain

_D -serine modulates excitatory neurotransmission by binding to N-methyl-_D -aspartate glutamate receptors. _D- amino acid oxidase (DAO) degrades _D -amino acids, such as _D -serine, in the central nervous system, and is associated with neurological and psychiatric disorders. However, cell types that express brain DAO remain controversial, and whether brain DAO influences systemic _D -amino acids in addition to brain _D -serine remains unclear. Here, we created astrocyte-specific DAO-conditional knockout mice. Knockout in glial fibrillary acidic protein (GFAP)-positive cells eliminated DAO expression in the hindbrain and increased _D -serine levels significantly in the cerebellum. Brain DAO did not influence levels of _D -amino acids in the forebrain or periphery. These results show that astrocytic DAO regulates _D -serine specifically in the hindbrain.

Complex Processes Underlying the Dynamic Changes of D-serine Levels in AD Brains

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by extracellular β-amyloid (Aβ) plaques and cognitive impairments. D-Serine, produced by the enzyme serine racemase (SR) in the brain, functions as an endogenous co-agonist at the glycine-binding site of N-methyl-D-aspartate receptor (NMDAR), has been implicated in the pathophysiological progression of AD.

OBJECTIVES

Evidence regarding the understanding of the role and dynamic modulation of D-serine during AD progression remains controversial. This literature review aims to offer novel research directions for studying the functions and metabolisms of D-serine in AD brains.

METHODS

We searched PubMed, using D-serine/SR and AD as keywords. Studies related to NMDAR dysfunction, neuronal excitotoxicity, D-serine dynamic changes and inflammatory response were included.

RESULTS

This review primarily discusses: (i) Aβ oligomers' role in NMDAR dysregulation, and the subsequent synaptic dysfunction and neuronal damage in AD, (ii) D-serine's role in NMDAR-elicited excitotoxicity, and (iii) the involvement of D-serine and SR in AD-related inflammatory pathological progression.

CONCLUSION

We also presented supposed metabolism and dynamic changes of D-serine during AD progression and hypothesized that: (i) the possible modulation of D-serine levels or SR expression as an effective method of alleviating neurotoxicity during AD pathophysiological progression, and (ii) the dynamic changes of D-serine levels in AD brains possibly resulting from complex processes.

Blood D-Amino Acid Oxidase Levels Increased With Cognitive Decline Among People With Mild Cognitive Impairment: A Two-Year Prospective Study

BACKGROUND

Dysregulation of N-methyl-D-aspartate receptor (NMDAR) neurotransmission has been reported to be implicated in the pathogenesis of Alzheimer's disease (AD). D-amino acid oxidase (DAO), responsible for degradation of NMDAR-related D-amino acids such as D-serine, regulates NMDAR function. A cross-section study found that serum DAO levels were positively related with the severity of cognitive aging among elderly individuals. This 2-year prospective study aimed to explore the role of DAO levels in predicting the outcome of patients with very early-phase AD, such as mild cognitive impairment (MCI).

METHODS

Fifty-one patients with MCI and 21 healthy individuals were recruited. Serum DAO levels and cognitive function, measured by the AD assessment scale-cognitive subscale and the Mini-Mental Status Examination, were monitored every 6 months. We employed multiple regressions to examine the role of DAO concentration in cognitive decline in the 2-year period.

RESULTS

From baseline to endpoint (24 months), serum DAO levels increased significantly, and cognitive ability declined according to both cognitive tests in the MCI patients. Among the healthy individuals, DAO concentrations also increased and Mini-Mental Status Examination scores declined; however, AD assessment scale-cognitive subscale scores did not significantly change. Further, DAO levels at both months 12 and 18 were predictive of cognitive impairment at month 24 among the MCI patients.

CONCLUSIONS

To our knowledge, this is the first study to demonstrate that blood DAO levels increased with cognitive deterioration among the MCI patients in a prospective manner. If replicated by future studies, blood DAO concentration may be regarded as a biomarker for monitoring cognitive change in the patients with MCI.

Separation and identification of the DL-forms of short-chain peptides using a new chiral resolution labeling reagent

There are several reports of D-amino acids being the causative molecules of serious diseases, resulting in the formation of, for example, prion protein and amyloid β. D-Amino acids in peptides and proteins are typically identified by sequencing each residue by Edman degradation or by hydrolysis with hydrochloric acid for amino acid analysis. However, these approaches can result in racemization of the L-form to the D-form by hydrolysis and long pre-treatment for hydrolysis. To address these problems, we aimed to identify the DL-forms of amino acids in peptides without hydrolysis. Here, we showed that the DL-forms in peptides which are difficult to separate on a chiral column can be precisely separated by labeling with 1-fluoro-2,4-dinitrophenyl-5-D-leucine-N,N-dimethylethylenediamine-amide (D-FDLDA). Additionally, the peptides could be quantitatively analyzed using the same labeling method as for amino acids. Furthermore, the detection sensitivity of a sample labeled with D-FDLDA was higher than that of the conventional reagents Nα-(5-fluoro-2,4-dinitrophenyl)-L-alaninamide (L-FDAA) and Nα-(5-fluoro-2,4-dinitrophenyl)-L-leucinamide (L-FDLA) used in Marfey's method. The proposed method for identifying DL-forms of amino acids in peptides is a powerful tool for use in organic chemistry, biochemistry, and medical science.

Modelling amyotrophic lateral sclerosis in rodents

The efficient study of human disease requires the proper tools, one of the most crucial of which is an accurate animal model that faithfully recapitulates the human condition. The study of amyotrophic lateral sclerosis (ALS) is no exception. Although the majority of ALS cases are considered sporadic, most animal models of this disease rely on genetic mutations identified in familial cases. Over the past decade, the number of genes associated with ALS has risen dramatically and, with each new genetic variant, there is a drive to develop associated animal models. Rodent models are of particular importance as they allow for the study of ALS in the context of a living mammal with a comparable CNS. Such models not only help to verify the pathogenicity of novel mutations but also provide critical insight into disease mechanisms and are crucial for the testing of new therapeutics. In this Review, we aim to summarize the full spectrum of ALS rodent models developed to date.

Enantioselective metabolomics by liquid chromatography-mass spectrometry

Metabolomics strives to capture the entirety of the metabolites in a biological system by comprehensive analysis, often by liquid chromatography hyphenated to mass spectrometry. A particular challenge thereby is the differentiation of structural isomers. Common achiral targeted and untargeted assays do not distinguish between enantiomers. This may lead to information loss. An increasing number of publications demonstrate that the enantiomeric ratio of certain metabolites can be meaningful biomarkers of certain diseases emphasizing the importance of introducing enantioselective analytical procedures in metabolomics. In this work, the state-of-the-art in the field of LC-MS based metabolomics is summarized with focus on developments in the recent decade. Methodologies, tagging strategies, workflows and general concepts are outlined. Selected biological applications in which enantioselective metabolomics has documented its usefulness are briefly discussed. In general, targeted enantioselective metabolomics assays are often based on a direct approach using chiral stationary phases (CSP) with polysaccharide derivatives, macrocyclic antibiotics, chiral crown ethers, chiral ion exchangers, donor-acceptor phases as chiral selectors. Rarely, these targeted assays focus on more than 20 analytes and usually are restricted to a certain metabolite class. In a variety of cases, pre-column derivatization of metabolites has been performed, especially for amino acids, to improve separation and detection sensitivity. Triple quadrupole instruments are the detection methods of first choice in targeted assays. Here, issues like matrix effect, absence of blank matrix impair accuracy of results. In selected applications, multiple heart cutting 2D-LC (RP followed by chiral separation) has been pursued to overcome this problem and alleviate bias due to interferences. Non-targeted assays, on the other hand, are based on indirect approach involving tagging with a chiral derivatizing agent (CDA). Besides classical CDAs numerous innovative reagents and workflows have been proposed and are discussed. Thereby, a critical issue for the accuracy is often neglected, viz. the validation of the enantiomeric impurity in the CDA. The majority of applications focus on amino acids, hydroxy acids, oxidized fatty acids and oxylipins. Some potential clinical applications are highlighted.

d-Amino Acids and pLG72 in Alzheimer's Disease and Schizophrenia

Numerous studies over the last several years have shown that d-amino acids, especially d-serine, have been related to brain and neurological disorders. Acknowledged neurological functions of d-amino acids include neurotransmission and learning and memory functions through modulating N-methyl-d-aspartate type glutamate receptors (NMDARs). Aberrant d-amino acids level and polymorphisms of genes related to d-amino acids metabolism are associated with neurodegenerative brain conditions. This review summarizes the roles of d-amino acids and pLG72, also known as d-amino acid oxidase activator, on two neurodegenerative disorders, schizophrenia and Alzheimer’s disease (AD). The scope includes the changes in d-amino acids levels, gene polymorphisms of G72 genomics, and the role of pLG72 on NMDARs and mitochondria in schizophrenia and AD. The clinical diagnostic value of d-amino acids and pLG72 and the therapeutic importance are also reviewed.

Cystine/Glutamate Antiporter in Schizophrenia: From Molecular Mechanism to Novel Biomarker and Treatment

Glutamate, a crucial excitatory neurotransmitter, plays a major role in the modulation of schizophrenia’s pathogenesis. New drug developments for schizophrenia have been prompted by the hypoglutamatergic hypothesis of schizophrenia. The cystine/glutamate antiporter system x_c⁻ is related to glutamate-release regulation. Patients with schizophrenia were recently discovered to exhibit downregulation of x_c⁻ subunits—the solute carrier (SLC) family 3 member 2 and the SLC family 7 member 11. We searched for relevant studies from 1980, when Bannai and Kitamura first identified the protein subunit system x_c⁻ in lung fibroblasts, with the aim of compiling the biological, functional, and pharmacological characteristics of antiporter x_c⁻, which consists of several subunits. Some of them can significantly stimulate the human brain through the glutamate pathway. Initially, extracellular cysteine activates neuronal x_c⁻, causing glutamate efflux. Next, excitatory amino acid transporters enhance the unidirectional transportation of glutamate and sodium. These two biochemical pathways are also crucial to the production of glutathione, a protective agent for neural and glial cells and astrocytes. Investigation of the expression of system x_c⁻ genes in the peripheral white blood cells of patients with schizophrenia can facilitate better understanding of the mental disorder and future development of novel biomarkers and treatments for schizophrenia. In addition, the findings further support the hypoglutamatergic hypothesis of schizophrenia.

Role of EphA4 in Mediating Motor Neuron Death in MND

Motor neuron disease (MND) comprises a group of fatal neurodegenerative diseases with no effective cure. As progressive motor neuron cell death is one of pathological characteristics of MND, molecules which protect these cells are attractive therapeutic targets. Accumulating evidence indicates that EphA4 activation is involved in MND pathogenesis, and inhibition of EphA4 improves functional outcomes. However, the underlying mechanism of EphA4’s function in MND is unclear. In this review, we first present results to demonstrate that EphA4 signalling acts directly on motor neurons to cause cell death. We then review the three most likely mechanisms underlying this effect.

D-Serine: A Cross Species Review of Safety

Background:D-Serine, a direct, full agonist at the D-serine/glycine modulatory site of the N-methyl-D-aspartate-type glutamate receptors (NMDAR), has been assessed as a treatment for multiple psychiatric and neurological conditions. Based on studies in rats, concerns of nephrotoxicity have limited D-serine research in humans, particularly using high doses. A review of D-serine's safety is timely and pertinent, as D-serine remains under active study for schizophrenia, both directly (R61 MH116093) and indirectly through D-amino acid oxidase (DAAO) inhibitors. The principal focus is on nephrotoxicity, but safety in other physiologic and pathophysiologic systems are also reviewed. Methods: Using the search terms "D-serine," "D-serine and schizophrenia," "D-serine and safety," "D-serine and nephrotoxicity" in PubMed, we conducted a systematic review on D-serine safety. D-serine physiology, dose-response and efficacy in clinical studies and dAAO inhibitor safety is also discussed. Results: When D-serine doses >500 mg/kg are used in rats, nephrotoxicity, manifesting as an acute tubular necrosis syndrome, seen within hours of administration is highly common, if not universal. In other species, however, D-serine induced nephrotoxicity has not been reported, even in other rodent species such as mice and rabbits. Even in rats, D--serine related toxicity is dose dependent and reversible; and does not appear to be present in rats at doses producing an acute Cmax of <2,000 nmol/mL. For comparison, the Cmax of D-serine 120 mg/kg, the highest dose tested in humans, is ~500 nmol/mL in acute dosing. Across all published human studies, only one subject has been reported to have abnormal renal values related to D-serine treatment. This abnormality did not clearly map on to the acute tubular necrosis syndrome seen in rats, and fully resolved within a few days of stopping treatment. DAAO inhibitors may be nephroprotective. D-Serine may have a physiologic role in metabolic, extra-pyramidal, cardiac and other systems, but no other clinically significant safety concerns are revealed in the literature. Conclusions: Even before considering human to rat differences in renal physiology, using current FDA guided monitoring paradigms, D-serine appears safe at currently studied maximal doses, with potential safety in combination with DAAO inhibitors.

Oral administration of D-serine prevents the onset and progression of colitis in mice

BACKGROUND

L-amino acids are the predominant forms of organic molecules on the planet, but recent studies have revealed that various foods contain D-amino acids, the enantiomers of L-amino acids. Though diet plays important roles in both the development and progression of inflammatory bowel disease (IBD), to our best knowledge, there has been no report on any potential interactions between D-amino acids and IBD. In this report, we aim to assess the effects of D-serine in a murine model of IBD.

MATERIALS AND METHODS

To induce chronic colitis, naïve CD4 T cells (CD4⁺ CD62⁺ CD44^low) from wild-type mice were adoptively transferred into Rag2^-/- mice, after or before the mice were orally administered with D-serine. In vitro proliferation assays were performed to assess naïve CD4 T cell activation under the Th-skewing conditions in the presence of D-serine.

RESULTS

Mice treated with D-serine prior to the induction of colitis exhibited a reduction in T-cell infiltration into the lamina propria and colonic inflammation that were not seen in mice fed with water alone or L-serine. Moreover, D-serine suppressed the progression of chronic colitis when administered after the disease induction. Under in vitro conditions, D-serine suppressed the proliferation of activated CD4 T cells and limited their ability to differentiate to Th1 and Th17 cells.

CONCLUSION

Our results suggest that D-serine not only can prevent, but also has efficacious effects as a treatment for IBD.

Enantiospecific Detection of D-Amino Acid through Synergistic Upconversion Energy Transfer

D-amino acids (DAAs) are indispensable in regulating diverse metabolic pathways. Selective and sensitive detection of DAAs is crucial for understanding the complexity of metabolic processes and managing associated diseases. However, current DAA detection strategies mainly rely on bulky instrumentation or electrochemical probes, limiting their cellular and animal applications. Here we report an enzyme-coupled nanoprobe that can detect enantiospecific DAAs through synergistic energy transfer. This nanoprobe offers near-infrared upconversion capability, a wide dynamic detection range, and a detection limit of 2.2 μM, providing a versatile platform for in vivo noninvasive detection of DAAs with high enantioselectivity. These results potentially allow real-time monitoring of biomolecular handedness in living animals, as well as developing antipsychotic treatment strategies.

Human D-aspartate Oxidase: A Key Player in D-aspartate Metabolism

In recent years, the D-enantiomers of amino acids have been recognized as natural molecules present in all kingdoms, playing a variety of biological roles. In humans, d-serine and d-aspartate attracted attention for their presence in the central nervous system. Here, we focus on d-aspartate, which is involved in glutamatergic neurotransmission and the synthesis of various hormones. The biosynthesis of d-aspartate is still obscure, while its degradation is due to the peroxisomal flavin adenine dinucleotide (FAD)-containing enzyme d-aspartate oxidase. d-Aspartate emergence is strictly controlled: levels decrease in brain within the first days of life while increasing in endocrine glands postnatally and through adulthood. The human d-aspartate oxidase (hDASPO) belongs to the d-amino acid oxidase-like family: its tertiary structure closely resembles that of human d-amino acid oxidase (hDAAO), the enzyme that degrades neutral and basic d-amino acids. The structure-function relationships of the physiological isoform of hDASPO (named hDASPO_341) and the regulation of gene expression and distribution and properties of the longer isoform hDASPO_369 have all been recently elucidated. Beyond the substrate preference, hDASPO and hDAAO also differ in kinetic efficiency, FAD-binding affinity, pH profile, and oligomeric state. Such differences suggest that evolution diverged to create two different ways to modulate d-aspartate and d-serine levels in the human brain. Current knowledge about hDASPO is shedding light on the molecular mechanisms underlying the modulation of d-aspartate levels in human tissues and is pushing novel, targeted therapeutic strategies. Now, it has been proposed that dysfunction in NMDA receptor-mediated neurotransmission is caused by disrupted d-aspartate metabolism in the nervous system during the onset of various disorders (such as schizophrenia): the design of suitable hDASPO inhibitors aimed at increasing d-aspartate levels thus represents a novel and useful form of therapy.

Effect of Sodium Benzoate on Cognitive Function Among Patients With Behavioral and Psychological Symptoms of Dementia: Secondary Analysis of a Randomized Clinical Trial

IMPORTANCE

Female gender is a major risk factor for dementia; however, gender has not yet been adequately addressed by clinical trials. A recent study demonstrated that sodium benzoate, a D-amino acid oxidase inhibitor, improved cognitive function in early-phase Alzheimer disease.

OBJECTIVE

To examine the potential gender difference in the effects of benzoate treatment on the behavioral and psychological symptoms of dementia (BPSD).

DESIGN, SETTING, AND PARTICIPANTS

This post hoc secondary analysis used data from a randomized, double-masked, placebo-controlled trial conducted in 3 major medical centers in Taiwan and enrolled 97 patients with BPSD. Data were analyzed between February 2014 and November 2017.

INTERVENTIONS

Six weeks of treatment of 250 to 1500 mg/d of sodium benzoate or placebo.

MAIN OUTCOMES AND MEASURES

The primary outcome measures were Alzheimer disease assessment scale-cognitive subscale (ADAS-cog) and Behavioral Pathology in Alzheimer Disease Rating Scale (BEHAVE-AD) scores.

RESULTS

Among 97 total participants (62 [64%] women; mean [SD] age, 75.4 [7.7] years), 49 patients (30 women and 19 men) were randomized to sodium benzoate, and 48 (32 women and 16 men) were randomized to placebo. Among 62 women, 6-week benzoate treatment significantly surpassed placebo in the effects on ADAS-cog performance (mean [SD] difference in score between baseline and end point, -3.1 [6.4] points vs 0 [4.5] points; Cohen d = 0.56; P = .04) but not BEHAVE-AD performance. In contrast, among 35 men, the 2 treatment groups did not differ significantly in both ADAS-cog and BEHAVE-AD scores. Compared with placebo, benzoate treatment also increased estradiol to follicle-stimulating hormone ratios among women (mean [SD] difference between baseline and end point, 0 [0.2] vs -0.1 [0.3]; P = .03).

CONCLUSIONS AND RELEVANCE

These findings suggest that benzoate treatment may improve cognitive function in women with later-phase dementia. In the future, longer dose-finding trials are warranted to further clarify the efficacy of benzoate for later-phase dementia and investigate the role of sex hormones and other factors in the pathogenesis of dementia.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02103673.

Racemization in Post-Translational Modifications Relevance to Protein Aging, Aggregation and Neurodegeneration: Tip of the Iceberg

Homochirality of DNA and prevalent chirality of free and protein-bound amino acids in a living organism represents the challenge for modern biochemistry and neuroscience. The idea of an association between age-related disease, neurodegeneration, and racemization originated from the studies of fossils and cataract disease. Under the pressure of new results, this concept has a broader significance linking protein folding, aggregation, and disfunction to an organism's cognitive and behavioral functions. The integrity of cognitive function is provided by a delicate balance between the evolutionarily imposed molecular homo-chirality and the epigenetic/developmental impact of spontaneous and enzymatic racemization. The chirality of amino acids is the crucial player in the modulation the structure and function of proteins, lipids, and DNA. The collapse of homochirality by racemization is the result of the conformational phase transition. The racemization of protein-bound amino acids (spontaneous and enzymatic) occurs through thermal activation over the energy barrier or by the tunnel transfer effect under the energy barrier. The phase transition is achieved through the intermediate state, where the chirality of alpha carbon vanished. From a thermodynamic consideration, the system in the homo-chiral (single enantiomeric) state is characterized by a decreased level of entropy. The oscillating protein chirality is suggesting its distinct significance in the neurotransmission and flow of perceptual information, adaptive associative learning, and cognitive laterality. The common pathological hallmarks of neurodegenerative disorders include protein misfolding, aging, and the deposition of protease-resistant protein aggregates. Each of the landmarks is influenced by racemization. The brain region, cell type, and age-dependent racemization critically influence the functions of many intracellular, membrane-bound, and extracellular proteins including amyloid precursor protein (APP), TAU, PrP, Huntingtin, α-synuclein, myelin basic protein (MBP), and collagen. The amyloid cascade hypothesis in Alzheimer's disease (AD) coexists with the failure of amyloid beta (Aβ) targeting drug therapy. According to our view, racemization should be considered as a critical factor of protein conformation with the potential for inducing order, disorder, misfolding, aggregation, toxicity, and malfunctions.

Host-microbe cross-talk governs amino acid chirality to regulate survival and differentiation of B cells

Organisms use l-amino acids (l-aa) for most physiological processes. Unlike other organisms, bacteria chiral-convert l-aa to d-configurations as essential components of their cell walls and as signaling molecules in their ecosystems. Mammals recognize microbe-associated molecules to initiate immune responses, but roles of bacterial d-amino acids (d-aa) in mammalian immune systems remain largely unknown. Here, we report that amino acid chirality balanced by bacteria-mammal cross-talk modulates intestinal B cell fate and immunoglobulin A (IgA) production. Bacterial d-aa stimulate M1 macrophages and promote survival of intestinal naïve B cells. Mammalian intestinal d-aa catabolism limits the number of B cells and restricts growth of symbiotic bacteria that activate T cell-dependent IgA class switching of the B cells. Loss of d-aa catabolism results in excessive IgA production and dysbiosis with altered IgA coating on bacteria. Thus, chiral conversion of amino acids is linked to bacterial recognition by mammals to control symbiosis with bacteria.

Brain Activity of Benzoate, a D-Amino Acid Oxidase Inhibitor, in Patients With Mild Cognitive Impairment in a Randomized, Double-Blind, Placebo Controlled Clinical Trial

BACKGROUND

Current anti-dementia drugs cannot benefit mild cognitive impairment (MCI). Sodium benzoate (a D-amino acid oxidase [DAO] inhibitor) has been found to improve the cognitive function of patients with early-phase Alzheimer's disease (mild Alzheimer's disease or MCI). However, its effect on brain function remains unknown. This study aimed to evaluate the influence of benzoate on functional magnetic resonance imaging in patients with amnestic MCI.

METHODS

This was a 24-week, randomized, double-blind, placebo-controlled trial that enrolled 21 patients with amnestic MCI and allocated them randomly to either of 2 treatment groups: (1) benzoate group (250-1500 mg/d), or (2) placebo group. We assessed the patients' working memory, verbal learning and memory, and resting-state functional magnetic resonance imaging and regional homogeneity (ReHo) maps at baseline and endpoint.

RESULTS

Resting-state ReHo decreased in right orbitofrontal cortex after benzoate treatment but did not change after placebo. Moreover, after benzoate treatment, the change in working memory was positively correlated with the change in ReHo in right precentral gyrus and right middle occipital gyrus; and the change in verbal learning and memory was positively correlated with the change in ReHo in left precuneus. In contrast, after placebo treatment, the change in working memory or in verbal learning and memory was not correlated with the change in ReHo in any brain region.

CONCLUSION

The current study is the first to our knowledge to demonstrate that a DAO inhibitor, sodium benzoate herein, can alter brain activity as well as cognitive functions in individuals with MCI. The preliminary finding lends supports for DAO inhibition as a novel approach for early dementing processes.

Candidate Strategies for Development of a Rapid-Acting Antidepressant Class That Does Not Result in Neuropsychiatric Adverse Effects: Prevention of Ketamine-Induced Neuropsychiatric Adverse Reactions

Non-competitive N-methyl-D-aspartate/glutamate receptor (NMDAR) antagonism has been considered to play important roles in the pathophysiology of schizophrenia. In spite of severe neuropsychiatric adverse effects, esketamine (racemic enantiomer of ketamine) has been approved for the treatment of conventional monoaminergic antidepressant-resistant depression. Furthermore, ketamine improves anhedonia, suicidal ideation and bipolar depression, for which conventional monoaminergic antidepressants are not fully effective. Therefore, ketamine has been accepted, with rigorous restrictions, in psychiatry as a new class of antidepressant. Notably, the dosage of ketamine for antidepressive action is comparable to the dose that can generate schizophrenia-like psychotic symptoms. Furthermore, the psychotropic effects of ketamine precede the antidepressant effects. The maintenance of the antidepressive efficacy of ketamine often requires repeated administration; however, repeated ketamine intake leads to abuse and is consistently associated with long-lasting memory-associated deficits. According to the dissociative anaesthetic feature of ketamine, it exerts broad acute influences on cognition/perception. To evaluate the therapeutic validation of ketamine across clinical contexts, including its advantages and disadvantages, psychiatry should systematically assess the safety and efficacy of either short- and long-term ketamine treatments, in terms of both acute and chronic outcomes. Here, we describe the clinical evidence of NMDAR antagonists, and then the temporal mechanisms of schizophrenia-like and antidepressant-like effects of the NMDAR antagonist, ketamine. The underlying pharmacological rodent studies will also be discussed.

Elevated plasma levels of D-serine in some patients with amyotrophic lateral sclerosis

D-serine is an endogenous co-agonist with glutamate for activation of the N-methyl-D-aspartate receptor (NMDAR). D-serine exacerbates neuronal death and is elevated in the spinal cord from patients with sporadic/familial ALS. The present study was undertaken to examine whether plasma levels of D-serine of patients with ALS are different from those of healthy controls. Levels of D-serine in plasma (30 patients and 30 controls) were measured by high-performance liquid chromatography mass spectrometry. Plasma levels of D-serine in ALS patients (mean 39.27 ± 28.61 ng/ml) were significantly higher (p = 0.0293) than those of healthy control subjects (mean 21.07 ± 14.03 ng/ml) as well as previously reported values for healthy controls; ∼43% of patients had plasma D-serine levels that were 2 to 4-folds higher than those of controls. There was no association of plasma D-serine levels with disability, the duration of disease or with the age of subjects. In conclusion, we show that D-serine levels are elevated in the plasma of some ALS patients. Since D-serine serves as a co-agonist/activator of NMDAR, increases in D-serine could have a direct influence on glutamatergic neurotransmission and potentially contribute to excitotoxicity in some ALS patients.

L-Citrulline Level and Transporter Activity Are Altered in Experimental Models of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease caused by the death of the neurons regulating the voluntary muscles which leads to the progressive paralysis. We investigated the difference of transport function of L-citrulline in ALS disease model (NSC-34/hSOD1^G93A, MT) and a control model (NSC-34/hSOD1^wt, WT). The [¹⁴C]L-citrulline uptake was significantly reduced in MT cells as compared with that of control. The Michaelis-Menten constant (K_m) for MT cells was 0.67 ± 0.05 mM, whereas it was 1.48 ± 0.21 mM for control. On the other hand, the V_max values for MT and control were 10.9 ± 0.8 nmol/mg protein/min and 18.3 ± 2.9 nmol/mg protein/min, respectively. The K_m and V_max values showed the high affinity and low capacity for MT as compared with control. Moreover, the uptake of [¹⁴C]L-citrulline was significantly inhibited by 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) and harmaline which is the inhibitor of the large neutral amino acid transporter1 (LAT1) in NSC-34 cell lines. Furthermore, [¹⁴C]L-citrulline uptakes took place in Na⁺-independent manner. It was also inhibited by the neutral amino acids such as citrulline and phenylalanine. Likewise, L-dopa, gabapentin, and riluzole significantly inhibited the [¹⁴C]L-citrulline uptake. It shows the competitive inhibition for L-dopa in ALS cell lines. On the other hand, [¹⁴C]L-citrulline uptake in the presence of riluzole showed competitive inhibition in WT cells, whereas it was uncompetitive for MT cells. The small interfering RNA experiments showed that LAT1 is involved in the [¹⁴C]L-citrulline uptake in NSC-34 cell lines. On the other hand, in the examination of the alteration in the expression level of LAT1, it was significantly lower in MT cells as compared with that of control. Similarly, in the spinal cord of ALS, transgenic mice revealed a slight but significant decrease in LAT1 immunoreactivity in motor neurons of ALS mice compared with control. However, the LAT1 immunoreactivity in non-motor neurons and in astrocytes was relatively increased in the spinal cord gray matter of ALS mice. The experimental evidences of our results suggest that the change of transport activity of [¹⁴C]L-citrulline may be partially responsible for the pathological alteration in ALS.

Determination of phenylalanine enantiomers in the plasma and urine of mammals and ᴅ-amino acid oxidase deficient rodents using two-dimensional high-performance liquid chromatography

A two-dimensional (2D) HPLC system focusing on the determination of phenylalanine (Phe) enantiomers in mammalian physiological fluids has been developed. ᴅ-Phe is indicated to have potential values as a disease biomarker and therapeutic molecule in several neuronal and metabolic disorders, thus the regulation of ᴅ-Phe in mammals is a matter of interest. However, the precise determination of amino acid enantiomers is difficult in complex biological samples, and the development of an analytical method with practically acceptable sensitivity, selectivity and throughput is expected. In the present study, a 2D-HPLC system equipped with a reversed-phase column in the 1st dimension and an enantioselective column in the 2nd dimension has been designed, following the fluorescence derivatization of the target amino acid enantiomers with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). The analytical method was validated using both plasma and urine samples, and successfully applied to human, rat and mouse fluids. Trace levels of ᴅ-Phe were determined in the plasma, and the %ᴅ values were around 0.1% for all species. In the urine, relatively large amounts of ᴅ-Phe were observed, and the %ᴅ values for humans, rats and mice were 3.99, 1.76 and 5.25%, respectively. The relationships between the enzymatic activity of ᴅ-amino acid oxidase (DAO) and the amounts of intrinsic ᴅ-Phe have also been clarified, and high ᴅ-Phe amounts were observed (around 0.3% in the plasma and around 50% in the urine) in the DAO deficient rats and mice.

Synthesis and preliminary evaluation of 4-hydroxy-6-(3-[11C]methoxyphenethyl)pyridazin-3(2H)-one, a 11C-labeled d-amino acid oxidase (DAAO) inhibitor for PET imaging

Selective DAAO inhibitors have demonstrated promising therapeutic effects in clinical studies, including clinically alleviating symptoms of schizophrenic patients and ameliorating cognitive function in Alzheimer's patients with early phase. Herein we report the synthesis and preliminary evaluation of a ¹¹C-labeled positron emission tomography ligand based on a DAAO inhibitor, DAO-1903 (8). ¹¹C-Isotopologue of 8 was prepared in high radiochemical yield with high radiochemical purity (>99%) and high molar activity (>37 GBq/µmol). In vitro autoradiography studies indicated that the ligand possessed high in vitro specific binding to DAAO, while in vivo dynamic PET studies demonstrated that [¹¹C]8 failed to cross the blood-brain barrier possibly due to moderate brain efflux mechanism. Further chemical scaffold optimization is necessary to overcome limited brain permeability and improve specific binding.

Glia Crosstalk in Neuroinflammatory Diseases

Neuroinflammation constitutes a fundamental cellular process to signal the loss of brain homeostasis. Glial cells play a central role in orchestrating these neuroinflammation processes in both deleterious and beneficial ways. These cellular responses depend on their intercellular interactions with neurons, astrocytes, the blood–brain barrier (BBB), and infiltrated T cells in the central nervous system (CNS). However, this intercellular crosstalk seems to be activated by specific stimuli for each different neurological scenario. This review summarizes key studies linking neuroinflammation with certain neurodegenerative diseases such as Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS) and for the development of better therapeutic strategies based on immunomodulation.

In vivo detection of d-amino acid oxidase with hyperpolarized d-[1-13 C]alanine

d-amino acid oxidase (DAO) is a peroxisomal enzyme that catalyzes the oxidative deamination of several neutral and basic d-amino acids to their corresponding α-keto acids. In most mammalian species studied, high DAO activity is found in the kidney, liver, brain and polymorphonuclear leukocytes, and its main function is to maintain low circulating d-amino acid levels. DAO expression and activity have been associated with acute and chronic kidney diseases and with several pathologies related to N-methyl-d-aspartate (NMDA) receptor hypo/hyper-function; however, its precise role is not completely understood. In the present study we show that DAO activity can be detected in vivo in the rat kidney using hyperpolarized d-[1-¹³ C]alanine. Following a bolus of hyperpolarized d-alanine, accumulation of pyruvate, lactate and bicarbonate was observed only when DAO activity was not inhibited. The measured lactate-to-d-alanine ratio was comparable to the values measured when the l-enantiomer was injected. Metabolites downstream of DAO were not observed when scanning the liver and brain. The conversion of hyperpolarized d-[1-¹³ C]alanine to lactate and pyruvate was detected in blood ex vivo, and lactate and bicarbonate were detected on scanning the blood pool in the heart in vivo; however, the bicarbonate-to-d-alanine ratio was significantly lower compared with the kidney. These results demonstrate that the specific metabolism of the two enantiomers of hyperpolarized [1-¹³ C]alanine in the kidney and in the blood can be distinguished, underscoring the potential of d-[1-¹³ C]alanine as a probe of d-amino acid metabolism.

Exciting Complexity: The Role of Motor Circuit Elements in ALS Pathophysiology

Amyotrophic lateral sclerosis (ALS) is a fatal disease, characterized by the degeneration of both upper and lower motor neurons. Despite decades of research, we still to date lack a cure or disease modifying treatment, emphasizing the need for a much-improved insight into disease mechanisms and cell type vulnerability. Altered neuronal excitability is a common phenomenon reported in ALS patients, as well as in animal models of the disease, but the cellular and circuit processes involved, as well as the causal relevance of those observations to molecular alterations and final cell death, remain poorly understood. Here, we review evidence from clinical studies, cell type-specific electrophysiology, genetic manipulations and molecular characterizations in animal models and culture experiments, which argue for a causal involvement of complex alterations of structure, function and connectivity of different neuronal subtypes within the cortical and spinal cord motor circuitries. We also summarize the current knowledge regarding the detrimental role of astrocytes and reassess the frequently proposed hypothesis of glutamate-mediated excitotoxicity with respect to changes in neuronal excitability. Together, these findings suggest multifaceted cell type-, brain area- and disease stage- specific disturbances of the excitation/inhibition balance as a cardinal aspect of ALS pathophysiology.