Metabolism of galactose in the brain and liver of rats and its conversion into glutamate and other amino acids

Enzymatic biosynthesis of D-galactose derivatives: Advances and perspectives

D-Galactose derivatives, including galactosyl-conjugates and galactose-upgrading compounds, provide various physiological benefits and find applications in industries such as food, cosmetics, feed, pharmaceuticals. Many research on galactose derivatives focuses on identification, characterization, development, and mechanistic aspects of their physiological function, providing opportunities and challenges for the development of practical approaches for synthesizing galactose derivatives. This study focuses on recent advancements in enzymatic biosynthesis of galactose derivatives. Various strategies including isomerization, epimerization, transgalactosylation, and phosphorylation-dephosphorylation were extensively discussed under the perspectives of thermodynamic feasibility, theoretical yield, cost-effectiveness, and by-product elimination. Specifically, the enzymatic phosphorylation-dephosphorylation cascade is a promising enzymatic synthesis route for galactose derivatives because it can overcome the thermodynamic equilibrium of isomerization and utilize cost-effective raw materials. The study also elucidates the existing challenges and future trends in enzymatic biosynthesis of galactose derivatives. Collectively, this review provides a real-time summary aimed at promoting the practical biosynthesis of galactose derivatives through enzymatic catalysis.

A GC-MS-based untargeted metabolomics approach for comprehensive metabolic profiling of mycophenolate mofetil-induced toxicity in mice

Background: Mycophenolate mofetil (MMF), the morpholinoethyl ester of mycophenolic acid, is widely used for maintenance immunosuppression in transplantation. The gastrointestinal toxicity of MMF has been widely uncovered. However, the comprehensive metabolic analysis of MMF-induced toxicity is lacking. This study is aimed to ascertain the metabolic changes after MMF administration in mice. Methods: A total of 700 mg MMF was dissolved in 7 mL dimethyl sulfoxide (DMSO), and then 0.5 mL of mixture was diluted with 4.5 mL of saline (100 mg/kg). Mice in the treatment group (n = 9) were given MMF (0.1 mL/10 g) each day via intraperitoneal injection lasting for 2 weeks, while those in the control group (n = 9) received the same amount of blank solvent (DMSO: saline = 1:9). Gas chromatography-mass spectrometry was utilized to identify the metabolic profiling in serum samples and multiple organ tissues of mice. The potential metabolites were identified using orthogonal partial least squares discrimination analysis. Meanwhile, we used the MetaboAnalyst 5.0 (http://www.metaboanalyst.ca) and Kyoto Encyclopedia of Genes and Genomes database (http://www.kegg.jp) to depict the metabolic pathways. The percentages of lymphocytes in spleens were assessed by multiparameter flow cytometry analysis. Results: Compared to the control group, we observed that MMF treatment induced differential expression of metabolites in the intestine, hippocampus, lung, liver, kidney, heart, serum, and cortex tissues. Subsequently, we demonstrated that multiple amino acids metabolism and fatty acids biosynthesis were disrupted following MMF treatment. Additionally, MMF challenge dramatically increased CD4+ T cell percentages but had no significant influences on other types of lymphocytes. Conclusion: MMF can affect the metabolism in various organs and serum in mice. These data may provide preliminary judgement for MMF-induced toxicity and understand the metabolic mechanism of MMF more comprehensively.

Identification of Therapeutic Targets for Medulloblastoma by Tissue-Specific Genome-Scale Metabolic Model

Medulloblastoma (MB), occurring in the cerebellum, is the most common childhood brain tumor. Because conventional methods decline life quality and endanger children with detrimental side effects, computer models are needed to imitate the characteristics of cancer cells and uncover effective therapeutic targets with minimum toxic effects on healthy cells. In this study, metabolic changes specific to MB were captured by the genome-scale metabolic brain model integrated with transcriptome data. To determine the roles of sphingolipid metabolism in proliferation and metastasis in the cancer cell, 79 reactions were incorporated into the MB model. The pathways employed by MB without a carbon source and the link between metastasis and the Warburg effect were examined in detail. To reveal therapeutic targets for MB, biomass-coupled reactions, the essential genes/gene products, and the antimetabolites, which might deplete the use of metabolites in cells by triggering competitive inhibition, were determined. As a result, interfering with the enzymes associated with fatty acid synthesis (FAs) and the mevalonate pathway in cholesterol synthesis, suppressing cardiolipin production, and tumor-supporting sphingolipid metabolites might be effective therapeutic approaches for MB. Moreover, decreasing the activity of succinate synthesis and GABA-catalyzing enzymes concurrently might be a promising strategy for metastatic MB.

Identification of a glutamine metabolism reprogramming signature for predicting prognosis, immunotherapy efficacy, and drug candidates in bladder cancer

Background

Bladder cancer is the most common malignancy of the urinary system. However, patient prognosis and treatment outcomes in bladder cancer are difficult to predict owing to high tumor heterogeneity. Given that abnormal glutamine metabolism has been identified as a key factor driving the progression of bladder cancer, it is necessary to assess the prognosis and therapeutic efficacy of bladder cancer treatments based on an analysis of glutamine metabolism-related genes.

Methods

We used bladder cancer sample data downloaded from The Cancer Genome Atlas to identify glutamine metabolism-related genes as prognostic markers, and established a novel Glutamine Metabolism Immunity Index (GMII) based on univariate and multivariate COX regression analyses. On the basis of GMII values, bladder cancer patients were divided into high- and low-risk groups, and systematic analysis was conducted for clinical features, somatic mutations, immune cell infiltration, chemotherapeutic response, and immunotherapeutic efficacy. Candidate small-molecule drugs targeting the GMII core target proteins were identified based on molecular docking analysis.

Results

The GMII consisting of eight independent prognostic genes was established to be an excellent tool for predicting the survival in patients with bladder cancer and was validated using multiple datasets. Compared with patients in the high-risk group, those in the low-risk group had significantly better responses to gemcitabine and immune checkpoint blockade. In addition, we predicted 12 potential small-molecule drugs that could bind to three of the GMII core target proteins.

Conclusions

The GMII can be used to accurately predict the prognosis and immunotherapeutic response of bladder cancer patients, as well as candidate small-molecule drugs. Furthermore, the novel "Glutamine Metabolism-related Gene"-guided strategy for predicting survival and chemo-immunotherapeutic efficacy may also be applicable for cancers other than bladder cancer.

The effects of ruminant milk treatments on hippocampal, striatal, and prefrontal cortex gene expression in pigs as a model for the human infant

While infant formula is usually bovine milk-based, interest in other ruminant milk-based formulas is growing. However, whether different ruminant milk treatments with varying nutrient compositions influence the infant’s brain development remains unknown. The aim was to determine the effects of consuming bovine, caprine, or ovine milk on brain gene expression in the early postnatal period using a pig model of the human infant. Starting at postnatal day 7 or 8, pigs were exclusively fed bovine, ovine, or caprine milk for 15 days. The mRNA abundance of 77 genes in the prefrontal cortex, hippocampus, and striatum regions was measured at postnatal day 21 or 22 using NanoString. The expression level of two hippocampal and nine striatal genes was most affected by milk treatments, particularly ovine milk. These modulatory genes are involved in glutamate, gamma-aminobutyric acid, serotonin, adrenaline and neurotrophin signaling and the synaptic vesicle cycle. The expression level of genes involved in gamma-aminobutyric acid signaling was associated with pigs’ lactose intake. In contrast, milk treatments did not affect the mRNA abundance of the genes in the prefrontal cortex. This study provides the first evidence of the association of different ruminant milk treatments with brain gene expression related to cognitive function in the first 3 months of postnatal life.

Association of age-related cataract risk high polygenetic risk scores involved in galactose-related metabolism and dietary interactions

INTRODUCTION

Cataracts are associated with the accumulation of galactose and galactitol in the lens. We determined the polygenetic risk scores for the best model(PRSBM) associated with age-related cataract(ARC) risk and their interaction with diets and lifestyles in 40,262 Korean adults aged over 50 years belonged to a hospital-based city cohort.

METHODS

The genetic variants for ARC risk were selected in lactose and galactose metabolism-related genes with multivariate logistic regression using the PLINK 1.9 version. PRSBM from the selected genetic variants was estimated by generalized multifactor dimensionality reduction (GMDR) after adjusting covariates. The interactions between the PRSBM and each lifestyle factor were determined to modulate ARC risk.

RESULTS

The genetic variants for ARC risk related to lactose- and galactose metabolism were SLC2A1_rs3729548, ST3GAL3_rs3791047, LCT_rs2304371, GALNT5_rs6728956, ST6GAL1_rs2268536, GALNT17_rs17058752, CSGALNACT1_rs1994788, GALNTL4_rs10831608, B4GALT6_rs1667288, and A4GALT_ rs9623659. In GMDR, the best model included all ten genetic variants. The highest odds ratio (OR) for a single SNP in the PRSBM was 1.26. However, subjects with a high-PRSBM had a higher ARC risk by 2.1-fold than a low-PRSBM after adjusting for covariates. Carbohydrate, dairy products, kimchi, and alcohol intake interacted with PRSBM for ARC risk: the participants with high-PRSBM had a much higher ARC risk than those with low-PRSBM when consuming diets with high carbohydrate and low dairy product and kimchi intake. However, only with low alcohol intake, the participants with high-PRSBM had a higher ARC risk than those with low-PRSBM.

CONCLUSION

Adults aged >50 years having high-PRSBM may modulate dietary habits to reduce ARC risk.

Is Galactose a Hormetic Sugar? An Exploratory Study of the Rat Hippocampal Redox Regulatory Network

SCOPE

Galactose, a ubiquitous monosaccharide with incompletely understood physiology is often exploited for inducing oxidative-stress mediated aging in animals. Recent research demonstrates that galactose can conserve cellular function during periods of starvation and prevent/alleviate cognitive deficits in a rat model of sporadic Alzheimer's disease. The present aim is to examine the acute effects of oral galactose on the redox regulatory network (RRN).

METHODS AND RESULTS

Rat plasma and hippocampal RRNs are analyzed upon acute orogastric gavage of galactose (200 mg kg^-1 ). No systemic RRN disbalance is observed; however, a mild pro-oxidative shift accompanied by a paradoxical increment in tissue reductive capacity suggesting overcompensation of endogenous antioxidant systems is observed in the hippocampus. Galactose-induced increment of reductive capacity is accompanied by inflation of the hippocampal pool of nicotinamide adenine dinucleotide phosphates indicating ROS detoxification through disinhibition of the oxidative pentose phosphate pathway flux, reduced neuronal activity, and upregulation of Leloir pathway gatekeeper enzyme galactokinase-1.

CONCLUSION

Based on the observed findings, and in the context of previous work on galactose, a hormetic hypothesis of galactose is proposed suggesting that the protective effects may be inseparable from its pro-oxidative action at the biochemical level.

Antidementia Effects of Alternanthera philoxeroides in Ovariectomized Mice Supported by NMR-Based Metabolomic Analysis

The crude ethanol extract of the whole plant of Alternanthera philoxeroides (Mart.) Griseb was investigated for its potential as antidementia, induced by estrogen deprivation, based on in vitro antioxidant activity, β-amyloid aggregation inhibition and cholinesterase inhibitory activity, as well as in vivo Morris water maze task (MWMT), novel object recognition task (NORT), and Y-maze task. To better understand the effect of the extract, oxidative stress-induced brain membrane damage through lipid peroxidation in the whole brain was also investigated. Additionally, expressions of neuroinflammatory cytokines (IL-1β, IL-6 and TNF-α) and estrogen receptor-mediated facilitation genes such as PI3K and AKT mRNA in the hippocampus and frontal cortex were also evaluated. These effects were confirmed by the determination of its serum metabolites by NMR metabolomic analysis. Both the crude extract of A. philoxeroides and its flavone constituents were found to inhibit β-amyloid (Aβ) aggregation.

Translating traditional herbal formulas into modern drugs: a network-based analysis of Xiaoyao decoction

Background

Traditional Chinese medicine (TCM) encompasses numerous herbal formulas which play critical therapeutic roles through "multi-components, multi-targets and multi-pathways" mechanisms. Exploring the interaction among these mechanisms can certainly help to depict the core therapeutic function of herbal formulas. Xiaoyao decoction (XYD) is one of the most well-known traditional Chinese medicine formulas which has been widely applied to treat various diseases. In this study, taking XYD as an example, we proposed a network pharmacology-based method to identify the main therapeutic targets of this herbal concoctions.

Methods

Chemical data of XYD were retrieved from the Traditional Chinese Medicine Systems Pharmacology Database (TCMSP), Traditional Chinese Medicines Integrated Database (TCMID) and Compound Reference Database (CRD) and screened oral bioavailability attributes from SwissADME using Veber's filter. Targets of sample chemicals were identified using the online tool similarity ensemble approach (SEA), and pathways were enriched using STRING database. On the basis of targets-pathways interactions from the enrichment, a "targets-pathways-targets" (TPT) network was constructed. In the TPT network, the importance of each target was calculated by the declining value of network efficiency, which represents the influential strength of a specific set-off target on the whole network. Network-based predictive results were statistically validated with existing experimental evidence.

Results

The TPT network was comprised of 279 nodes and 6549 edges. The declining value of network efficiency of the sample targets was significantly correlated with their involvement frequency in existing studies of XYD using Spearman's test (p < 0.001). The top 10% of candidate targets, such as AKT1, PIK3R1, NFKB1 and RELA, etc., were chosen as XYD's main therapeutic targets, which further show pharmacological functions synergistically through 11 main pathways. These pathways are responsible for endocrine, nutritional or metabolic diseases, neoplasms and diseases of the nervous system, etc.

Conclusions

The network pharmacology-based approach in the present study shows promising potential for identifying the main therapeutic targets from TCM formulas. This study provides valuable information for TCM researchers and clinicians for better understanding the main therapeutic targets and therapeutic roles of herbal decoctions in clinical settings.

Mitochondrial Complex I Activity Is Required for Maximal Autophagy

Cells adapt to nutrient and energy deprivation by inducing autophagy, which is regulated by the mammalian target of rapamycin (mTOR) and AMP-activated protein kinases (AMPKs). We found that cell metabolism significantly influences the ability to induce autophagy, with mitochondrial complex I function being an important factor in the initiation, amplitude, and duration of the response. We show that phenformin or genetic defects in complex I suppressed autophagy induced by mTOR inhibitors, whereas autophagy was enhanced by strategies that increased mitochondrial metabolism. We report that mTOR inhibitors significantly increased select phospholipids and mitochondrial-associated membranes (MAMs) in a complex I-dependent manner. We attribute the complex I autophagy defect to the inability to increase MAMs, limiting phosphatidylserine decarboxylase (PISD) activity and mitochondrial phosphatidylethanolamine (mtPE), which support autophagy. Our data reveal the dynamic and metabolic regulation of autophagy.

Cognitive, behavioral and metabolic effects of oral galactose treatment in the transgenic Tg2576 mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder associated with insulin resistance and glucose hypometabolism in the brain. Oral administration of galactose, a nutrient that provides an alternative source of energy, prevents and ameliorates early cognitive impairment in a streptozotocin-induced model (STZ-icv) of the sporadic AD (sAD). Here we explored the influence of 2-month oral galactose treatment (200 mg/kg/day) in the familial AD (fAD) by using 5- (5M) and 10- (10M) month-old transgenic Tg2576 mice mimicking the presymptomatic and the mild stage of fAD, and compared it to that observed in 7-month old STZ-icv rats mimicking mild-to-moderate sAD. Cognitive and behavioral performance was tested by Morris Water Maze, Open Field and Elevated Plus Maze tests, and metabolic status by intraperitoneal glucose tolerance test and fluorodeoxyglucose Positron-Emission Tomography scan. The level of insulin, glucagon-like peptide-1 (GLP-1) and soluble amyloid β1-42 (sAβ1-42) was measured by ELISA and the protein expression of insulin receptor (IR), glycogen synthase kinase-3β (GSK-3β), and pre-/post-synaptic markers by Western blot analysis. Although galactose normalized alterations in cerebral glucose metabolism in all Tg2576 mice (5M+2M; 10M+2M) and STZ-icv rats, it did not improve cognitive impairment in either model. Improvement of reduced grooming behavior and normalization in reduced plasma insulin levels were seen only in 5M+2M Tg2576 mice while in 10M+2M Tg2576 mice oral galactose induced metabolic exacerbation at the level of plasma insulin, GLP-1 homeostasis and glucose intolerance, and additionally increased hippocampal sAβ1-42 level, decreased IR expression and increased GSK-3β activity. The results indicate that therapeutic potential of oral galactose seems to depend on the stage and the type/model of AD and to differ in the absence and the presence of AD-like pathology.

Galactose metabolism and health

PURPOSE OF REVIEW

Galactose - a key source of energy and a crucial structural element in complex molecules - is particularly important for early human development. However, galactose metabolism might be important not only for fetal and neonatal development but also for adulthood, as evidenced by the inherited disorders of galactose metabolism. The purpose of this review is to summarize the current evidence of galactose metabolism in health and disease.

RECENT FINDINGS

The biological importance of galactose goes beyond its importance as a nutrient and a metabolite. Galactose has been selected by evolutionary pressure to exert also a crucial structural role in macromolecules. Additionally, galactose has recently been reported as beneficial in a number of diseases, particularly in those affecting the brain.

SUMMARY

Galactose is crucial for human metabolism, with an established role in energy delivery and galactosylation of complex molecules, and evidence for other roles is emerging.

[Particularities of γ-aminobutyric acid metabolism in the liver of rats during different types of alcohol withdrawal]

Activities of GABA-catabolising enzymes and the contents of some amino acids have been studied in the liver of the rats with different types of alcohol cessation after its systemic administration. Intermittent alcohol intoxication was accompanied by activation of liver GABA catabolism in case of the lowest alcohol load. However ethanol in higher doses and prolongation of intermittent alcohol administration decreased GABA catabolism. It is suggested that the observed changes may reflect non-specific adaptation of hepatocytes to the excessive alcohol consumption and its further cessation.

Multiplatform metabolome and proteome profiling identifies serum metabolite and protein signatures as prospective biomarkers for schizophrenia

Schizophrenia is a severe mental illness with a biological basis. However, the search for reliable biomarkers suitable for clinical routine has been futile so far. Accordingly, there is a need for innovative approaches such as genomics and proteomics to achieve this goal. In the present study, we compared metabolomic and proteomic data from 26 schizophrenia patients as well as from unaffected controls carefully matched for age and gender in a multi-platform approach. The combined analysis identified many signatures with initially good biomarker characteristics. After statistical analysis and comparison of these identified serum metabolites (analysed by Gas Chromatography Mass Spectrometry) and hydrophobic serum proteins (analysed by matrix-assisted laser desorption ionisation mass spectrometry), several markers (e.g., 2-piperidinec carboxylic acid, 6-deoxy-mannofuranose, galactoseoxime and a serum peptide of m/z 3177) were determined as having the best discriminating value between the groups. Our findings represent a proof of principle indicating that metabolomic and proteomic approaches can be successfully used in psychiatric biomarker research, even though the results should be regarded as preliminary with a need for replication in larger samples.

Long-term oral galactose treatment prevents cognitive deficits in male Wistar rats treated intracerebroventricularly with streptozotocin

Basic and clinical research has demonstrated that dementia of sporadic Alzheimer's disease (sAD) type is associated with dysfunction of the insulin-receptor (IR) system followed by decreased glucose transport via glucose transporter GLUT4 and decreased glucose metabolism in brain cells. An alternative source of energy is d-galactose (the C-4-epimer of d-glucose) which is transported into the brain by insulin-independent GLUT3 transporter where it might be metabolized to glucose via the Leloir pathway. Exclusively parenteral daily injections of galactose induce memory deterioration in rodents and are used to generate animal aging model, but the effects of oral galactose treatment on cognitive functions have never been tested. We have investigated the effects of continuous daily oral galactose (200 mg/kg/day) treatment on cognitive deficits in streptozotocin-induced (STZ-icv) rat model of sAD, tested by Morris Water Maze and Passive Avoidance test, respectively. One month of oral galactose treatment initiated immediately after the STZ-icv administration, successfully prevented development of the STZ-icv-induced cognitive deficits. Beneficial effect of oral galactose was independent of the rat age and of the galactose dose ranging from 100 to 300 mg/kg/day. Additionally, oral galactose administration led to the appearance of galactose in the blood. The increase of galactose concentration in the cerebrospinal fluid was several times lower after oral than after parenteral administration of the same galactose dose. Oral galactose exposure might have beneficial effects on learning and memory ability and could be worth investigating for improvement of cognitive deficits associated with glucose hypometabolism in AD.

Application of GC/MS-based metabonomic profiling in studying the lipid-regulating effects of Ginkgo biloba extract on diet-induced hyperlipidemia in rats

AIM

To evaluate the lipid-regulating effects of extract from Ginkgo biloba leaves (EGB) using pharmacological methods and metabonomic profiling in a rat model of diet-induced hyperlipidemia.

METHODS

EGB was orally administered at a dose level of 40 mg/kg in both the EGB-prevention and -treatment groups. All rat samples obtained were examined for known and potential biomarkers and enzyme activity using commercial assay kits and GC/MS-based metabonomic profiling coupled with principal component analysis (PCA).

RESULTS

The data obtained from the assay kits indicated that EGB reduced total cholesterol and low density lipoprotein cholesterol levels and increased high density lipoprotein cholesterol levels in rat plasma obtained from both the EGB-prevention and -treatment groups compared with those of the diet-induced hyperlipidemia group. EGB also increased the activities of lipoprotein lipase and hepatic lipase and excretion of fecal bile acid in rats from the EGB-prevention and-treatment groups. Using GC/MS-based metabonomic analysis, more than 40 endogenous metabolites were identified in rat plasma. PCA of rat plasma samples obtained using GC/MS produced a distinctive separation of the four treatment groups and sampling points within each group. Metabolic changes during hyperlipidemia formation and improvement resulting from EGB treatment were definitively monitored with PCA score plots. Furthermore, elevated levels of sorbitol, tyrosine, glutamine and glucose, and decreased levels of citric acid, galactose, palmitic acid, arachidonic acid, acetic acid, cholesterol, butyrate, creatinine, linoleate, ornithine and proline, were observed in the plasma of rats treated with EGB.

CONCLUSION

EGB exerts multi-directional lipid-lowering effects on the rat metabonome, including limitation of the absorption of cholesterol, inactivation of HMGCoA and favorable regulation of profiles of essential polyunsaturated fatty acid (EFA). Further experiments are warranted to explore the mechanisms of action underlying the lipid-regulating effects of EGB against hyperlipidemia.