Taurine and Brain Development: Trophic or Cytoprotective Actions?

Protective effects of taurine on heat Stress-Induced cognitive impairment through Npas4 and Lcn2

Heat stress (HS) induces various pathophysiological responses in the brain, encompassing neuroinflammation and cognitive impairments. Although taurine has been reported to possess anti-inflammatory and cognitive-enhancing properties, its role and mechanisms in HS-induced cognitive impairment remain unclear. This study supplemented mice exposed to HS with taurine to assess its effect on cognitive function in a HS-induced mouse model. The results revealed that taurine ameliorated cognitive deficits following HS in mice and mitigated HS-induced astrocyte and microglia activation as well as blood-brain barrier (BBB) damage in the hippocampus. Mechanistically, Mechanistically, transcriptome sequencing was employed to identify that taurine regulates neuronal PAS domain protein (Npas4) and lipocalin 2 (Lcn2) during HS. Taurine was found to modulate hippocampal inflammation and influence cognitive function by upregulating Npas4 and downregulating Lcn2 after HS. Subsequently, molecular docking and AnimalTFDB database calculations were conducted, revealing that taurine might regulate the expression of Npas4 and Lcn2 by modulating the regulatory transcription factors (TFs) RE1 silencing transcription factor (REST) and nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (NFKB1). Our findings demonstrate that taurine enhances the recovery of cognitive function through Npas4 and Lcn2 following HS, providing a theoretical basis for the clinical application of taurine in preventing or treating HS-induced cognitive impairment.

Taurine induces hormesis in multiple biological models: May have transformative implications for overall societal health

This paper represents the first integrative assessment and documentation of taurine-induced hormetic effects in the biological and biomedical areas, their dose response features, mechanistic frameworks, and possible public health, therapeutic and commercial applications. Taurine-induced hormetic effects are documented in a wide range of experimental models, cell types and for numerous biological endpoints, with most of these experimental findings being reported within the past five years. It is suggested that the concept of hormesis may have a transformative effect on taurine research and its public health and therapeutic applications.

Metabolomics on depression: A comparison of clinical and animal research

BACKGROUND

Depression is a major cause of suicide and mortality worldwide. This study aims to conduct a systematic review to identify metabolic biomarkers and pathways for major depressive disorder (MDD), a prevalent subtype of clinical depression.

METHODS

We searched for metabolomics studies on depression published between January 2000 and January 2023 in the PubMed and Web of Science databases. The reported metabolic biomarkers were systematically evaluated and compared. Pathway analysis was implemented using MetaboAnalyst 5.0.

RESULTS

We included 26 clinical studies on MDD and 78 metabolomics studies on depressive-like animal models. A total of 55 and 77 high-frequency metabolites were reported consistently in two-thirds of clinical and murine studies, respectively. In the comparison between murine and clinical studies, we identified 9 consistently changed metabolites (tryptophan, tyrosine, phenylalanine, methionine, fumarate, valine, deoxycholic acid, pyruvate, kynurenic acid) in the blood, 1 consistently altered metabolite (indoxyl sulfate) in the urine and 14 disturbed metabolic pathways in both types of studies. These metabolic dysregulations and pathways are mainly implicated in enhanced inflammation, impaired neuroprotection, reduced energy metabolism, increased oxidative stress damage and disturbed apoptosis, laying solid molecular foundations for MDD.

LIMITATIONS

Due to unavailability of original data like effect-size results in many metabolomics studies, a meta-analysis cannot be conducted, and confounding factors cannot be fully ruled out.

CONCLUSIONS

This systematic review delineated metabolic biomarkers and pathways related to depression in the murine and clinical samples, providing opportunities for early diagnosis of MDD and the development of novel diagnostic targets.

Effect of Noise and Music on Neurotransmitters in the Amygdala: The Role Auditory Stimuli Play in Emotion Regulation

Stress caused by noise is becoming widespread globally. Noise may lead to deafness, endocrine disorders, neurological diseases, and a decline in mental health. The mechanism behind noise-induced neurodevelopmental abnormalities is unclear, but apoptosis and pro-inflammatory signals may play an important role. In this study, weaned piglets were used as a model to explore noise-induced neurodevelopmental abnormalities. We hypothesized that long-term noise exposure would induce anxiety and cause acute stress, exhibited by alterations in neurotransmission in the amygdala. A total of 72 hybrid piglets (Large White × Duroc × Min Pig) were randomly divided into three groups, including noise (exposed to mechanical noise, 80-85 dB), control (blank, exposed to natural background sound, <40 dB), and music (positive control, exposed to Mozart K.448, 60-70 dB) groups. The piglets were exposed to 6 h of auditory noise daily (10:00-16:00) for 28 days. Compared with the control group, piglets exposed to noise showed more aggressive behavior. The expression of Caspase3, Caspase9, Bax, NF-κB (p56), TLR4, MYD88, I κ B α, IL-1 β, TNF-α, and IL-12RB2 was significantly upregulated in the amygdala, while the expression of Nrf2, HO-1, CAT, and SOD was downregulated in piglets in the noise group. Cell death occurred, and numerous inflammatory cells accumulated in the amygdala of piglets in the noise group. Targeted metabolomics showed that the content of inhibitory neurotransmitter GABA was higher in the amygdala of piglets in the noise group. Compared with the noise group, piglets in the music group displayed more positive emotion-related behaviors. Compared with the noise group, the expression of genes related to apoptosis, inflammation, and oxidative damage was lower in the music group. Cells of the amygdala in the music group were also of normal morphology. Our results show that noise-induced stress causes apoptosis and neuroinflammation in the amygdala and induces anxiety during the early neonatal neural development of piglets. In contrast, to some extent, music alleviates noise-induced anxiety.

Neurometabolic changes in a rat pup model of type C hepatic encephalopathy depend on age at liver disease onset

Chronic liver disease (CLD) is a serious condition where various toxins present in the blood affect the brain leading to type C hepatic encephalopathy (HE). Both adults and children are impacted, while children may display unique vulnerabilities depending on the affected window of brain development.We aimed to use the advantages of high field proton Magnetic Resonance Spectroscopy (1H MRS) to study longitudinally the neurometabolic and behavioural effects of Bile Duct Ligation (animal model of CLD-induced type C HE) on rats at post-natal day 15 (p15) to get closer to neonatal onset liver disease. Furthermore, we compared two sets of animals (p15 and p21-previously published) to evaluate whether the brain responds differently to CLD according to age onset.We showed for the first time that when CLD was acquired at p15, the rats presented the typical signs of CLD, i.e. rise in plasma bilirubin and ammonium, and developed the characteristic brain metabolic changes associated with type C HE (e.g. glutamine increase and osmolytes decrease). When compared to rats that acquired CLD at p21, p15 rats did not show any significant difference in plasma biochemistry, but displayed a delayed increase in brain glutamine and decrease in total-choline. The changes in neurotransmitters were milder than in p21 rats. Moreover, p15 rats showed an earlier increase in brain lactate and a different antioxidant response. These findings offer tentative pointers as to which neurodevelopmental processes may be impacted and raise the question of whether similar changes might exist in humans but are missed owing to 1H MRS methodological limitations in field strength of clinical magnet.

Study on multi-target effects of PIMPC on Aβ/Cu2+-induced Alzheimer's disease model of rats

Glycogen synthase kinase-3 (GSK-3), a key role in the pathogenesis of Alzheimer's disease (AD), has been linked with the formation of β-amyloid (Aβ), tubulin-associated unit (tau) protein phosphorylation and apoptosis. Moreover, the excessive presence of elements such as copper (Cu) can promote Aβ aggregation and increase the risk of AD. Combined with the role of GSK-3 and metal elements in AD, a metal-chelating imine GSK-3 inhibitor N-(4-{[(2-amino-5-phenylpyridin-3-ylidene)imino]methyl}pyridin-2-yl)cyclopropanecarboxamide (PIMPC) was designed and synthesized. In our study, Aβ/Cu²⁺-induced AD rat model was established and treated with PIMPC. The results indicated that PIMPC can not only down-regulate the high expression levels of Aβ, tau and p-tau proteins of the AD rats, but also chelate Cu and aluminum (Al) elements in the brain. In addition, PIMPC may play an anti-apoptotic effect by down-regulating the high expression of cleaved Caspase-3 protein, and it can modulate ATPase and nitric oxide synthase (NOS) levels, oxidative stress and neurotransmitter disturbance. In summary, PIMPC acts on multiple targets to relieve the learning and memory impairment of AD rats induced by Aβ/Cu²⁺.

Natural variation in developmental condition has limited effect on spatial cognition in a wild food-caching bird

Laboratory studies show that increased physiological burden during development results in cognitive impairment. In the wild, animals experience a wide range of developmental conditions, and it is critical to understand how variation in such conditions affects cognitive abilities later in life, especially in species that strongly depend on such abilities for survival. We tested whether variation in developmental condition is associated with differences in spatial cognitive abilities in wild food-caching mountain chickadees. Using tail feathers grown during development in juvenile birds, we measured feather corticosterone (Cortf) levels and growth rates and tested these birds during their first winter on two spatial learning tasks. In only 1 of the 3 years, higher feather Cortf was negatively associated with memory acquisition. No significant associations between feather Cortf and any other measurement of spatial cognition were detected in the other 2 years of the study or between feather growth rate and any measurement of cognition during the entire study. Our results suggest that in the wild, naturally existing variation in developmental condition has only a limited effect on spatial cognitive abilities, at least in a food-caching species. This suggests that there may be compensatory mechanisms to buffer specialized cognitive abilities against developmental perturbations.

TMT-based proteomics analysis of the cerebral cortex of TauT knockout rats

Background

Taurine serves a variety of nutritional and physiological roles, and it is mostly transported in cells via taurine transporter (TauT). The effect of taurine transporter in cerebral cortex is still unknown. We employed TMT label-based proteomics to find differences in proteins in the cerebral cortex of TauT knockout rats in this investigation. The goal of this research was to see how TauT deletion affected protein alterations in brain tissue and to see if there was a new research area for TauT.

Methods

The cerebral cortex of TauT knockout rats and wild-type control rats were analyzed using TMT-based proteomics, and differentially expressed proteins were analyzed by bioinformatics analysis means such as GO and KEGG, the association between the proteins was found by PPI, and biologically significant and interesting proteins were selected for verification by WB and immunohistochemistry.

Results

There were total of 8275 proteins found, but only 35 differentially expressed proteins were identified (27 up-regulated and 8 down-regulated), and gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to predict the biological pathways and functional classification of the proteins. The results show that these differentially expressed proteins are mainly enriched in lysine degradation, cell cycle, chronic myeloid leukemia, and longevity regulating pathways-multiple species, renal cell carcinoma, pathways in cancer, etc. To verify the proteomic data, we analyzed the expression of Annexin6 and Pik3r2 by western blotting and immunofluorescence. The results are consistent with proteomics, which proves the reliability of our proteomics data.

Conclusion

Through TMT-based proteomics, we have a comprehensive understanding of the effect of TauT knockout on the changes of other proteins in the cerebral cortex, providing new evidence for further understanding the function of TauT.

Quantification of magnetic resonance spectroscopy data using a combined reference: Application in typically developing infants

Quantification of proton magnetic resonance spectroscopy (¹ H-MRS) data is commonly performed by referencing the ratio of the signal from one metabolite, or metabolite group, to that of another, or to the water signal. Both approaches have drawbacks: ratios of two metabolites can be difficult to interpret because study effects may be driven by either metabolite, and water-referenced data must be corrected for partial volume and relaxation effects in the water signal. Here, we introduce combined reference (CRef) analysis, which compensates for both limitations. In this approach, metabolites are referenced to the combined signal of several reference metabolites or metabolite groups. The approach does not require the corrections necessary for water scaling and produces results that are less sensitive to the variation of any single reference signal, thereby aiding the interpretation of results. We demonstrate CRef analysis using 202 ¹ H-MRS acquisitions from the brains of 140 infants, scanned at approximately 1 and 3 months of age. We show that the combined signal of seven reference metabolites or metabolite groups is highly correlated with the water signal, corrected for partial volume and relaxation effects associated with cerebral spinal fluid. We also show that the combined reference signal is equally or more uniform across subjects than the reference signals from single metabolites or metabolite groups. We use CRef analysis to quantify metabolite concentration changes during the first several months of life in typically developing infants.

Structure and substrate specificity determinants of the taurine biosynthetic enzyme cysteine sulphinic acid decarboxylase

Pyridoxal 5́-phosphate (PLP) is an important cofactor for amino acid decarboxylases with many biological functions, including the synthesis of signalling molecules, such as serotonin, dopamine, histamine, γ-aminobutyric acid, and taurine. Taurine is an abundant amino acid with multiple physiological functions, including osmoregulation, pH regulation, antioxidative protection, and neuromodulation. In mammalian tissues, taurine is mainly produced by decarboxylation of cysteine sulphinic acid to hypotaurine, catalysed by the PLP-dependent cysteine sulphinic acid decarboxylase (CSAD), followed by oxidation of the product to taurine. We determined the crystal structure of mouse CSAD and compared it to other PLP-dependent decarboxylases in order to identify determinants of substrate specificity and catalytic activity. Recognition of the substrate involves distinct side chains forming the substrate-binding cavity. In addition, the backbone conformation of a buried active-site loop appears to be a critical determinant for substrate side chain binding in PLP-dependent decarboxylases. Phe94 was predicted to affect substrate specificity, and its mutation to serine altered both the catalytic properties of CSAD and its stability. Using small-angle X-ray scattering, we further showed that CSAD presents open/close motions in solution. The structure of apo-CSAD indicates that the active site gets more ordered upon internal aldimine formation. Taken together, the results highlight details of substrate recognition in PLP-dependent decarboxylases and provide starting points for structure-based inhibitor design with the aim of affecting the biosynthesis of taurine and other abundant amino acid metabolites.

Lopata A, Li L, Dasouki M, Rahman AMA. Metabolomics Distinguishes DOCK8 Deficiency from Atopic Dermatitis: Towards a Biomarker Discovery

Bi-allelic mutations in the dedicator of cytokinesis 8 (DOCK8) are responsible for a rare autosomal recessive primary combined immunodeficiency syndrome, characterized by atopic dermatitis, elevated serum Immunoglobulin E (IgE) levels, recurrent severe cutaneous viral infections, autoimmunity, and predisposition to malignancy. The molecular link between DOCK8 deficiency and atopic skin inflammation remains unknown. Severe atopic dermatitis (AD) and DOCK8 deficiency share some clinical symptoms, including eczema, eosinophilia, and increased serum IgE levels. Increased serum IgE levels are characteristic of, but not specific to allergic diseases. Herein, we aimed to study the metabolomic profiles of DOCK8-deficient and AD patients for potential disease-specific biomarkers using chemical isotope labeling liquid chromatography-mass spectrometry (CIL LC-MS). Serum samples were collected from DOCK8-deficient (n = 10) and AD (n = 9) patients. Metabolomics profiling using CIL LC-MS was performed on patient samples and compared to unrelated healthy controls (n = 33). Seven metabolites were positively identified, distinguishing DOCK8-deficient from AD patients. Aspartic acid and 3-hydroxyanthranillic acid (3HAA, a tryptophan degradation pathway intermediate) were up-regulated in DOCK8 deficiency, whereas hypotaurine, leucyl-phenylalanine, glycyl-phenylalanine, and guanosine were down-regulated. Hypotaurine, 3-hydroxyanthranillic acid, and glycyl-phenyalanine were identified as potential biomarkers specific to DOCK8 deficiency. Aspartate availability has been recently implicated as a limiting metabolite for tumour growth and 3HAA; furthermore, other tryptophan metabolism pathway-related molecules have been considered as potential novel targets for cancer therapy. Taken together, perturbations in tryptophan degradation and increased availability of aspartate suggest a link of DOCK8 deficiency to oncogenesis. Additionally, perturbations in taurine and dipeptides metabolism suggest altered antixidation and cell signaling states in DOCK8 deficiency. Further studies examining the mechanisms underlying these observations are necessary.

Comparative metabolomics analysis of donkey colostrum and mature milk using ultra-high-performance liquid tandem chromatography quadrupole time-of-flight mass spectrometry

Donkey milk has been widely shown to be an ideal substitute for human milk because of its similar composition. However, alterations to the composition of donkey milk during lactation have not been well studied. In this study, untargeted metabolomics with ultra-high-performance liquid tandem chromatography quadrupole time-of-flight mass spectrometry were used to analyze and compare the metabolites in donkey colostrum (DC) and mature milk (DMM). Two hundred seventy metabolites were characterized in both DC and DMM. Fifty-two of the metabolites in the DC were significantly different from those in the DMM; 8 were downregulated and 44 were upregulated. This demonstrated that the composition of the donkey milk changed with lactation. Additionally, the interactions and metabolic pathways were further analyzed to explore the mechanisms that altered the milk during lactation. Our results provide comprehensive insights into the alterations in donkey milk during lactation. The results will aid in future investigations into the nutrition of donkey milk and provide practical information for the dairy industry.

Growth, antioxidant capacity, intestinal morphology, and metabolomic responses of juvenile Oriental river prawn (Macrobrachium nipponense) to chronic lead exposure

Understanding the mechanisms of metal toxicity to organisms farmed for food may suggest mitigation strategies. We determined the 24-, 48-, 72-, and 96-h median lethal concentrations of lead in juvenile oriental river prawn (Macrobrachium nipponense). The prawns were then exposed to sub-lethal concentrations (13.13 and 26.26 μg/L) of lead for 60 days and growth, antioxidant enzyme activity, intestinal morphology, and metabolite profiles were assessed. Prawns exposed to 26.26 μg/L but not to 13.13 μg/L lead exhibited lower weight gain than controls. The lead burden in muscle was 0.067 and 0.25 μg/g of dry weight exposed to 13.13 and 26.26 μg/L, respectively. Levels of glutamic oxaloacetic transaminase and glutamic-pyruvic transaminase were not altered following exposure. Exposure increased malondialdehyde activity in the hepatopancreas and decreased superoxide dismutase and glutathione peroxidase activities. Catalase activity first increased and then decreased as lead concentrations increased. Some intestinal epithelial cells disassociated from the basement membrane in prawns exposed to 13.13 μg/L lead. Intestinal epithelial cells in prawns exposed to 26.26 μg/L lead separated completely from the basement membrane. Gas chromatography-mass spectrometry metabolomics assays showed the 13.13-μg/L exposure did not elicit significant metabolic alterations. Exposure to 26.26 μg/L lead differentially up-regulated 58 metabolites and down-regulated 21 metabolites. The metabolites identified were involved in galactose, purine, glutathione, and carbon metabolism, biosynthesis of amino acids and steroids, and neuroactive ligand-receptor interaction. These data indicate that chronic lead exposure can adversely affect growth, increase accumulation in muscle, impair intestinal morphology, and induce oxidant stress or neurotoxicity-related effects in M. nipponense.

Oligodendrocyte Bioenergetics in Health and Disease

The human brain weighs approximately 2% of the body; however, it consumes about 20% of a person’s total energy intake. Cellular bioenergetics in the central nervous system involves a delicate balance between biochemical processes engaged in energy conversion and those responsible for respiration. Neurons have high energy demands, which rely on metabolic coupling with glia, such as with oligodendrocytes and astrocytes. It has been well established that astrocytes recycle and transport glutamine to neurons to make the essential neurotransmitters, glutamate and GABA, as well as shuttle lactate to support energy synthesis in neurons. However, the metabolic role of oligodendrocytes in the central nervous system is less clear. In this review, we discuss the energetic demands of oligodendrocytes in their survival and maturation, the impact of altered oligodendrocyte energetics on disease pathology, and the role of energetic metabolites, taurine, creatine, N-acetylaspartate, and biotin, in regulating oligodendrocyte function.

Regional dysregulation of taurine and related amino acids in the fetal rat brain following gestational alcohol exposure

The fetal brain exhibits exquisite alcohol-induced regional neuronal vulnerability. A candidate mechanism for alcohol-mediated brain deficits is disruption of amino acid (AA) bioavailability. AAs are vitally important for proper neurodevelopment, as they comprise the most abundant neurotransmitters in the brain and act as neurotransmitter precursors, nitric oxide donors, antioxidants, and neurotrophic factors, which induce synaptogenesis, neuronal proliferation, and migration. We hypothesized that gestational alcohol alters brain AA concentrations, disrupts AAs associated with neuropathogenesis, and that alterations are region-specific. We assigned pregnant Sprague-Dawley rats to either a pair-fed control or a binge alcohol treatment group on gestational day (GD) 4. Alcohol animals were acclimatized via a once-daily orogastric gavage of a 4.5 g/kg alcohol dose from GD 5-10, and progressed to a 6 g/kg alcohol dose from GD 11-20. Pair-fed animals received isocaloric maltose dextrin (once daily; GD 5-20). Fetal cerebral cortex, cerebellum, and hippocampus were collected on GD 21. Following collection, Fluorometric High Performance Liquid Chromatography (HPLC) involving pre-column derivatization with o-phthaldialdehyde quantified regional content of 22 AAs. Chronic binge alcohol administration to pregnant dams regionally altered AA concentrations in all three structures, with the cerebral cortex exhibiting the least vulnerability and the hippocampus exhibiting maximal vulnerability. We conjecture that the AA imbalances observed in this study are critically implicated in pathological and compensatory processes occurring in the brain in response to gestational alcohol exposure.

Metabolic profiling of the three neural derived embryonal pediatric tumors retinoblastoma, neuroblastoma and medulloblastoma, identifies distinct metabolic profiles

The rare pediatric embryonal tumors retinoblastoma, medulloblastoma and neuroblastoma derive from neuroectodermal tissue and share similar histopathological features despite different anatomical locations and diverse clinical outcomes. As metabolism can reflect genetic and histological features, we investigated whether the metabolism of embryonal tumors reflects their similar histology, shared developmental and neural origins, or tumor location. We undertook metabolic profiling on 50 retinoblastoma, 39 medulloblastoma and 70 neuroblastoma using high resolution magic angle spinning magnetic resonance spectroscopy (1H-MRS). Mean metabolite concentrations identified several metabolites that were significantly different between the tumor groups including taurine, hypotaurine, glutamate, glutamine, GABA, phosphocholine, N-acetylaspartate, creatine, glycine and myoinositol, p < 0.0017. Unsupervised multivariate analysis found that each tumor group clustered separately, with a unique metabolic profile, influenced by their underlying clinical diversity. Taurine was notably high in all tumors consistent with prior evidence from embryonal tumors. Retinoblastoma and medulloblastoma were more metabolically similar, sharing features associated with the central nervous system (CNS). Neuroblastoma had features consistent with neural tissue, but also contained significantly higher myoinositol and altered glutamate-glutamine ratio, suggestive of differences in the underlying metabolism of embryonal tumors located outside of the CNS. Despite the histological similarities and shared neural metabolic features, we show that individual neuroectodermal derived embryonal tumors can be distinguished by tissue metabolic profile. Pathway analysis suggests the alanine-aspartate-glutamate and taurine-hypotaurine metabolic pathways may be the most pertinent pathways to investigate for novel therapeutic strategies. This work strengthens our understanding of the biology and metabolic pathways underlying neuroectodermal derived embryonal tumors of childhood.

Cerebellar networks and neuropathology of cerebellar developmental disorders

The cerebellar system is a series of axonal projections and synaptic circuits as networks, similar to those of the limbic system and those subserving the propagation and spread of seizures. Three principal cerebellar networks are identified and cerebellar disease often affects components of the networks other than just the cerebellar cortex. Contemporary developmental neuropathology of the cerebellum is best considered in the context of alterations of developmental processes: embryonic segmentation and genetic gradients along the three axes of the neural tube, individual neuronal and glial cell differentiation, migration, synaptogenesis, and myelination. Precisely timed developmental processes may be delayed or precocious rhombencephalosynapsis and pontocerebellar hypoplasia exemplify opposite gradients in the horizontal axis. Chiari II malformation may be reconsidered as a disorder of segmentation rather than simply due to mechanical forces upon normally developing hindbrain structures. Cellular nodules in the roof of the fourth ventricle are heterotopia of histologically differentiated but architecturally disoriented and disorganized neurons and glial cells; they often are less mature immunocytochemically than similar cells in adjacent normal folia. Cell rests are nodules of undifferentiated neuroepithelial cells. Both are frequent in human fetuses and neonates. Axonal projections from heterotopia to adjacent cerebellar folia or nuclei are few or absent, hence these nodules are clinically silent despite neuronal differentiation.

The role of taurine in improving neural stem cells proliferation and differentiation

OBJECTIVES

Taurine is one of the most abundant amino acids in the central nervous system and has important functions in the promotion of brain development. This study aimed to determine the mechanistic role of taurine in improving neuronal proliferation, stem cell proliferation, and neural differentiation.

METHODS

The data for this review were primarily retrieved from the PubMed database from 1985 to 2015 in English. The search string included the keywords taurine, brain development, neuronal, stem cell, proliferation, differentiation, and others. Relevant publications were identified, retrieved, and reviewed.

RESULTS

This review introduces the source, function, and mechanisms of taurine in brain development and provides additional detail regarding the mechanistic role of taurine in improving neuronal proliferation, stem cell proliferation, and neural differentiation. Many studies concerning these aspects are discussed.

CONCLUSIONS

Taurine plays an important role in brain development, including neuronal proliferation, stem cell proliferation, and differentiation, via several mechanisms. Taurine can be directly used in clinical applications to improve brain development because it has no toxic effects on humans.

A Cultivated Form of a Red Seaweed (Chondrus crispus), Suppresses β-Amyloid-Induced Paralysis in Caenorhabditis elegans

We report here the protective effects of a methanol extract from a cultivated strain of the red seaweed, Chondrus crispus, against β-amyloid-induced toxicity, in a transgenic Caenorhabditis elegans, expressing human Aβ_1-42 gene. The methanol extract of C. crispus (CCE), delayed β-amyloid-induced paralysis, whereas the water extract (CCW) was not effective. The CCE treatment did not affect the transcript abundance of amy1; however, Western blot analysis revealed a significant decrease of Aβ species, as compared to untreated worms. The transcript abundance of stress response genes; sod3, hsp16.2 and skn1 increased in CCE-treated worms. Bioassay guided fractionation of the CCE yielded a fraction enriched in monogalactosyl diacylglycerols (MGDG) that significantly delayed the onset of β-amyloid-induced paralysis. Taken together, these results suggested that the cultivated strain of C. crispus, whilst providing dietary nutritional value, may also have significant protective effects against β-amyloid-induced toxicity in C. elegans, partly through reduced β-amyloid species, up-regulation of stress induced genes and reduced accumulation of reactive oxygen species (ROS).

Mammalian CSAD and GADL1 have distinct biochemical properties and patterns of brain expression

Variants in the gene encoding the enzyme glutamic acid decarboxylase like 1 (GADL1) have been associated with response to lithium therapy. Both GADL1 and the related enzyme cysteine sulfinic acid decarboxylase (CSAD) have been proposed to be involved in the pyridoxal-5'-phosphate (PLP)-dependent biosynthesis of taurine. In the present study, we compared the catalytic properties, inhibitor sensitivity and expression profiles of GADL1 and CSAD in brain tissue. In mouse and human brain we observed distinct patterns of expression of the PLP-dependent decarboxylases CSAD, GADL1 and glutamic acid decarboxylase 67 (GAD67). CSAD levels were highest during prenatal and early postnatal development; GADL1 peaked early in prenatal development, while GAD67 increased rapidly after birth. Both CSAD and GADL1 are being expressed in neurons, whereas only CSAD mRNA was detected in astrocytes. Cysteine sulfinic acid was the preferred substrate for both mouse CSAD and GADL1, although both enzymes also decarboxylated cysteic acid and aspartate. In silico screening and molecular docking using the crystal structure of CSAD and in vitro assays led to the discovery of eight new enzyme inhibitors with partial selectivity for either CSAD or GADL1. Lithium had minimal effect on their enzyme activities. In conclusion, taurine biosynthesis in vertebrates involves two structurally related PLP-dependent decarboxylases (CSAD and GADL1) that have partially overlapping catalytic properties but different tissue distribution, indicating divergent physiological roles. Development of selective enzyme inhibitors targeting these enzymes is important to further dissect their (patho)physiological roles.

Ethanol- and/or Taurine-Induced Oxidative Stress in Chick Embryos

Because taurine alleviates ethanol- (EtOH-) induced lipid peroxidation and liver damage in rats, we asked whether exogenous taurine could alleviate EtOH-induced oxidative stress in chick embryos. Exogenous EtOH (1.5 mmol/Kg egg or 3 mmol/Kg egg), taurine (4 μmol/Kg egg), or EtOH and taurine (1.5 mmol EtOH and 4 μmol taurine/Kg egg or 3 mmol EtOH and 4 μmol taurine/Kg egg) were injected into fertile chicken eggs during the first three days of embryonic development (E_0–2). At 11 days of development (midembryogenesis), serum taurine levels and brain caspase-3 activities, homocysteine (HoCys) levels, reduced glutathione (GSH) levels, membrane fatty acid composition, and lipid hydroperoxide (LPO) levels were measured. Early embryonic EtOH exposure caused increased brain apoptosis rates (caspase-3 activities); increased brain HoCys levels; increased oxidative-stress, as measured by decreased brain GSH levels; decreased brain long-chain polyunsaturated levels; and increased brain LPO levels. Although taurine is reported to be an antioxidant, exogenous taurine was embryopathic and caused increased apoptosis rates (caspase-3 activities); increased brain HoCys levels; increased oxidative-stress (decreased brain GSH levels); decreased brain long-chain polyunsaturated levels; and increased brain LPO levels. Combined EtOH and taurine treatments also caused increased apoptosis rates and oxidative stress.

Volume-sensitive release of organic osmolytes in the human lung epithelial cell line A549: role of the 5-lipoxygenase

Pathophysiological conditions challenge cell volume homeostasis and perturb cell volume regulatory mechanisms leading to alterations of cell metabolism, active transepithelial transport, cell migration, and death. We report that inhibition of the 5-lipoxygenase (5-LO) with AA861 or ETH 615-139, the cysteinyl leukotriene 1 receptor (CysLT₁) with the antiasthmatic drug Zafirlukast, or the volume-sensitive organic anion channel (VSOAC) with DIDS blocks the release of organic osmolytes (taurine, meAIB) and the concomitant cell volume restoration following hypoosmotic swelling of human type II-like lung epithelial cells (A549). Reactive oxygen species (ROS) are produced in A549 cells upon hypotonic cell swelling by a diphenylene iodonium-sensitive NADPH oxidase. The swelling-induced taurine release is suppressed by ROS scavenging (butylated hydroxytoluene, N-acetyl cysteine) and potentiated by H₂O₂. Ca²⁺ mobilization with ionomycin or ATP stimulates the swelling-induced taurine release whereas calmodulin inhibition (W7) inhibits the release. Chelation of the extracellular Ca²⁺ (EGTA) had no effect on swelling-induced taurine release but prevented ATP-induced stimulation. H₂O₂, ATP, and ionomycin were unable to stimulate the taurine release in the presence of AA861 or Zafirlukast, placing 5-LO and CysLT₁ as essential elements in the swelling-induced activation of VSOAC with ROS and Ca²⁺ as potent modulators. Inhibition of tyrosine kinases (genistein, cucurbitacin) reduces volume-sensitive taurine release, adding tyrosine kinases (Janus kinase) as regulators of VSOAC activity. Caspase-3 activity during hypoxia is unaffected by inhibition of 5-LO/CysLT₁ but reduced when swelling-induced taurine loss via VSOAC is prevented by DIDS excess extracellular taurine, indicating a beneficial role of taurine under hypoxia.

Metabolic maturation of the human brain from birth through adolescence: insights from in vivo magnetic resonance spectroscopy

Between birth and late adolescence, the human brain undergoes exponential maturational changes. Using in vivo magnetic resonance spectroscopy, we determined the developmental profile for 6 metabolites in 5 distinct brain regions based on spectra from 309 children from 0 to 18 years of age. The concentrations of N-acetyl-aspartate (an indicator for adult-type neurons and axons), creatine (energy metabolite), and glutamate (excitatory neurotransmitter) increased rapidly between birth and 3 months, a period of rapid axonal growth and synapse formation. Myo-inositol, implicated in cell signaling and a precursor of membrane phospholipid, as well as an osmolyte and astrocyte marker, declined rapidly during this period. Choline, a membrane metabolite and indicator for de novo myelin and cell membrane synthesis, peaked from birth until approximately 3 months, and then declined gradually, reaching a plateau at early childhood. Similarly, taurine, involved in neuronal excitability, synaptic potentiation, and osmoregulation, was high until approximately 3 months and thereafter declined. These data indicate that the first 3 months of postnatal life are a critical period of rapid metabolic changes in the development of the human brain. This study of the developmental profiles of the major brain metabolites provides essential baseline information for future analyses of the pediatric health and disease.

Taurine stimulates proliferation and promotes neurogenesis of mouse adult cultured neural stem/progenitor cells

This study reports an effect of taurine (1-10 mM) increasing markedly (120%) the number of neural precursor cells (NPCs) from adult mouse subventricular zone, cultured as neurospheres. This effect is one of the highest reported for adult neural precursor cells. Taurine-containing cultures showed 73-120% more cells than controls, after 24 and 96 h in culture, respectively. Taurine effect is due to enhanced proliferation as assessed by BrdU incorporation assays. In taurine cultures BrdU incorporation was markedly higher than controls from 1.5 to 48 h, with the maximal difference found at 1.5 h. This effect of taurine reproduced at every passage with the same window time. Taurine effects are not mimicked by glycine, alanine or GABA. Clonal efficiency values of 3.6% for taurine cultures and 1.3% for control cultures suggest a taurine influence on both, progenitor and stem cells. Upon differentiation, the proportion of neurons in control and taurine cultures was 3.1% (±0.5) and 10.2% (±0.8), respectively. These results are relevant for taurine implication in brain development as well as in adult neurogenesis. Possible mechanisms underlying taurine effects on cell proliferation are discussed.