Inborn errors in the metabolism of glutathione

Glutathione-Dependent Pathways in Cancer Cells

The most abundant tripeptide-glutathione (GSH)-and the major GSH-related enzymes-glutathione peroxidases (GPxs) and glutathione S-transferases (GSTs)-are highly significant in the regulation of tumor cell viability, initiation of tumor development, its progression, and drug resistance. The high level of GSH synthesis in different cancer types depends not only on the increasing expression of the key enzymes of the γ-glutamyl cycle but also on the changes in transport velocity of its precursor amino acids. The ability of GPxs to reduce hydroperoxides is used for cellular viability, and each member of the GPx family has a different mechanism of action and site for maintaining redox balance. GSTs not only catalyze the conjugation of GSH to electrophilic substances and the reduction of organic hydroperoxides but also take part in the regulation of cellular signaling pathways. By catalyzing the S-glutathionylation of key target proteins, GSTs are involved in the regulation of major cellular processes, including metabolism (e.g., glycolysis and the PPP), signal transduction, transcription regulation, and the development of resistance to anticancer drugs. In this review, recent findings in GSH synthesis, the roles and functions of GPxs, and GST isoforms in cancer development are discussed, along with the search for GST and GPx inhibitors for cancer treatment.

Glutathione-mediated redox regulation in Cryptococcus neoformans impacts virulence

The fungal pathogen Cryptococcus neoformans is well adapted to its host environment. It has several defence mechanisms to evade oxidative and nitrosative agents released by phagocytic host cells during infection. Among them, melanin production is linked to both fungal virulence and defence against harmful free radicals that facilitate host innate immunity. How C. neoformans manipulates its redox environment to facilitate melanin formation and virulence is unclear. Here we show that the antioxidant glutathione is inextricably linked to redox-active processes that facilitate melanin and titan cell production, as well as survival in macrophages and virulence in a murine model of cryptococcosis. Comparative metabolomics revealed that disruption of glutathione biosynthesis leads to accumulation of reducing and acidic compounds in the extracellular environment of mutant cells. Overall, these findings highlight the importance of redox homeostasis and metabolic compensation in pathogen adaptation to the host environment and suggest new avenues for antifungal drug development.

Is 5-Oxoprolinase Deficiency More than Just a Benign Condition?

Introduction

Inherited 5-oxoprolinase (OPLAH) deficiency is a rare inborn condition characterized by 5-oxoprolinuria. The inherited condition of 5-oxoprolinuria, or pyroglutamic aciduria, is primarily caused by mutations in the genes that encode glutathione synthetase (GSS) and 5-oxoprolinase (OPLAH), which are enzymes involved in the gamma-glutamyl cycle in glutathione metabolism. We report a 3-year-old male patient with epilepsy and speech difficulty diagnosed as primary 5-oxoprolinuria due to a novel OPLAH gene mutation.

Case Presentation

A 3-year-old boy who was delivered at full term in an uncomplicated birth to consanguineous parents presented with epilepsy at the age of 2 years. He did not speak fluently. He was using 5-10 words with decreased language fluency. His past medical history revealed postnatal macrocephaly, hydrocephalus, and well-controlled epilepsy with levetiracetam. Progressive cerebral atrophy, hypomyelination, ventriculomegaly, and corpus callosum hypoplasia were striking features in brain MRI. A urine sample was sent for organic acid analysis by gas chromatography-mass spectrometry (GC-MS); quantitation of 5-oxoproline by stable isotope dilution gave a value of 177.9 mmol/mol creatinine (reference values 25.8-92.2). Molecular genetic analysis of the OPLAH gene revealed a novel homozygous variant (OPLAH (NM_017570.5): c.1909C>T p.Arg637Trp).

Conclusion

We conclude that inherited 5-oxoprolinase deficiency is not a benign biochemical condition, and patients with 5-oxoprolinuria should be screened for it. The nature of this inherited metabolic disorder must be determined through long-term observation. We wish to emphasize the significance of molecular genetic analysis in symptomatic patients with persistently elevated levels of 5-oxoproline in the urine, as measured by organic acid analysis.

Diagnosis of Chronic Granulomatous Disease: Strengths and Challenges in the Genomic Era

Chronic granulomatous disease (CGD) is a group of rare primary inborn errors of immunity characterised by a defect in the phagocyte respiratory burst, which leads to severe and life-threatening infective and inflammatory complications. Despite recent advances in our understanding of the genetic and molecular pathophysiology of X-linked and autosomal recessive CGD, and growth in the availability of functional and genetic testing, there remain significant barriers to early and accurate diagnosis. In the current review, we provide an up-to-date summary of CGD pathophysiology, underpinning current methods of diagnostic testing for CGD and closely related disorders. We present an overview of the benefits of early diagnosis and when to suspect and test for CGD. We discuss current and historical methods for functional testing of NADPH oxidase activity, as well as assays for measuring protein expression of NADPH oxidase subunits. Lastly, we focus on genetic and genomic methods employed to diagnose CGD, including gene-targeted panels, comprehensive genomic testing and ancillary methods. Throughout, we highlight general limitations of testing, and caveats specific to interpretation of results in the context of CGD and related disorders, and provide an outlook for newborn screening and the future.

Skeletal muscle vulnerability in a child with Pitt-Hopkins syndrome

BACKGROUND

TCF4 acts as a transcription factor that binds to the immunoglobulin enhancer Mu-E5/KE5 motif. Dominant variants in TCF4 are associated with the manifestation of Pitt-Hopkins syndrome, a rare disease characterized by severe mental retardation, certain features of facial dysmorphism and, in many cases, with abnormalities in respiratory rhythm (episodes of paroxysmal tachypnea and hyperventilation, followed by apnea and cyanosis). Frequently, patients also develop epilepsy, microcephaly, and postnatal short stature. Although TCF4 is expressed in skeletal muscle and TCF4 seems to play a role in myogenesis as demonstrated in mice, potential myopathological findings taking place upon the presence of dominant TCF4 variants are thus far not described in human skeletal muscle.

METHOD

To address the pathological effect of a novel deletion affecting exons 15 and 16 of TCF4 on skeletal muscle, histological and immunofluorescence studies were carried out on a quadriceps biopsy in addition to targeted transcript studies and global proteomic profiling.

RESULTS

We report on muscle biopsy findings from a Pitt-Hopkins patient with a novel heterozygous deletion spanning exon 15 and 16 presenting with neuromuscular symptoms. Microscopic characterization of the muscle biopsy revealed moderate fiber type I predominance, imbalance in the proportion of fibroblasts co-expressing Vimentin and CD90, and indicate activation of the complement cascade in TCF4-mutant muscle. Protein dysregulations were unraveled by proteomic profiling. Transcript studies confirmed a mitochondrial vulnerability in muscle and confirmed reduced TCF4 expression.

CONCLUSION

Our combined findings, for the first time, unveil myopathological changes as phenotypical association of Pitt-Hopkins syndrome and thus expand the current clinical knowledge of the disease as well as support data obtained on skeletal muscle of a mouse model.

Spectrum of Organic Aciduria Diseases in Tunisia: A 35-year Retrospective Study

Background

Organic aciduria diseases (OADs) occur worldwide, with differences in prevalence and patterns between populations.

Objectives

To describe the spectrum of OADs identified in Tunisia over a 35-years period.

Materials and Methods

This retrospective study included patients who were diagnosed with OADs between 1987 and 2022 in the Laboratory of Biochemistry, Rabta Hospital, Tunisia. Organic acids were analyzed using gas chromatography-mass spectrometry.

Results

A total of 30,670 urine samples were analyzed for OADs, of which 471 were positive for OADs. The estimated incidence of OADs in Tunisia was 6.78 per 100,000 live births. Methylmalonic (n = 146) and propionic (n = 90) acidurias were the most common OADs (estimated incidence: 2.10 and 1.30 per 100,000 live births, respectively). There were 54 cases of L-2-hydroxyglutatric acidurias and 30 cases of pyroglutamic acidurias, which makes it one of the highest in the world. The main clinical features were hypotonia (65%) and feeding difficulties (41%). Age at diagnosis was highly variable, ranging from 1 day to 49 years. Only 27% of the patients were diagnosed within the first month of life. The prevalence of OADs was highest in the Center-East and Southeast regions.

Conclusions

In Tunisia, OADs are relatively frequent, but there are shortcomings regarding the diagnosis of these disorders. The frequency and health/social impact of these disorders warrant the need for implementing newborn screening programs and suitable patient management.

The Emerging Roles of γ-Glutamyl Peptides Produced by γ-Glutamyltransferase and the Glutathione Synthesis System

L-γ-Glutamyl-L-cysteinyl-glycine is commonly referred to as glutathione (GSH); this ubiquitous thiol plays essential roles in animal life. Conjugation and electron donation to enzymes such as glutathione peroxidase (GPX) are prominent functions of GSH. Cellular glutathione balance is robustly maintained via regulated synthesis, which is catalyzed via the coordination of γ-glutamyl-cysteine synthetase (γ-GCS) and glutathione synthetase, as well as by reductive recycling by glutathione reductase. A prevailing short supply of L-cysteine (Cys) tends to limit glutathione synthesis, which leads to the production of various other γ-glutamyl peptides due to the unique enzymatic properties of γ-GCS. Extracellular degradation of glutathione by γ-glutamyltransferase (GGT) is a dominant source of Cys for some cells. GGT catalyzes the hydrolytic removal of the γ-glutamyl group of glutathione or transfers it to amino acids or to dipeptides outside cells. Such processes depend on an abundance of acceptor substrates. However, the physiological roles of extracellularly preserved γ-glutamyl peptides have long been unclear. The identification of γ-glutamyl peptides, such as glutathione, as allosteric modulators of calcium-sensing receptors (CaSRs) could provide insights into the significance of the preservation of γ-glutamyl peptides. It is conceivable that GGT could generate a new class of intercellular messaging molecules in response to extracellular microenvironments.

Clinical and biochemical footprints of inherited metabolic diseases. XIV. Metabolic kidney diseases

Kidney disease is a global health burden with high morbidity and mortality. Causes of kidney disease are numerous, extending from common disease groups like diabetes and arterial hypertension to rare conditions including inherited metabolic diseases (IMDs). Given its unique anatomy and function, the kidney is a target organ in about 10% of known IMDs, emphasizing the relevant contribution of IMDs to kidney disease. The pattern of injury affects all segments of the nephron including glomerular disease, proximal and distal tubular damage, kidney cyst formation, built-up of nephrocalcinosis and stones as well as severe malformations. We revised and updated the list of known metabolic etiologies associated with kidney involvement and found 190 relevant IMDs. This represents the 14th of a series of educational articles providing a comprehensive and revised list of metabolic differential diagnoses according to system involvement.

Targeting gamma-glutamyl transpeptidase: A pleiotropic enzyme involved in glutathione metabolism and in the control of redox homeostasis

Gamma-glutamyl transpeptidase (GGT) is an enzyme located on the outer membrane of the cells where it regulates the metabolism of glutathione (GSH), the most abundant intracellular antioxidant thiol. GGT plays a key role in the control of redox homeostasis, by hydrolyzing extracellular GSH and providing the cell with the recovery of cysteine, which is necessary for de novo intracellular GSH and protein biosynthesis. Therefore, the upregulation of GGT confers to the cell greater resistance to oxidative stress and the advantage of growing fast. Indeed, GGT is upregulated in inflammatory conditions and in the progression of various human tumors and it is involved in many physiological disorders related to oxidative stress, such as cardiovascular disease and diabetes. Currently, increased GGT expression is considered a marker of liver damage, cancer, and low-grade chronic inflammation. This review addresses the current knowledge on the structure-function relationship of GGT, focusing on human GGT, and provides information on the pleiotropic biological role and relevance of the enzyme as a target of drugs aimed at alleviating oxidative stress-related diseases. The development of new GGT inhibitors is critically discussed, as are the advantages and disadvantages of their potential use in clinics. Considering its pleiotropic activities and evolved functions, GGT is a potential "moonlighting protein".

Case report: A Chinese patient with glutathione synthetase deficiency and a novel glutathione synthase mutation

Glutathione synthetase deficiency (GSSD) is an autosomal-recessive metabolic disorder caused by glutathione synthetase (GSS) gene mutations. No more than 90 cases of GSSD have been reported worldwide; thus, the spectrum of GSS mutations and the genotype-phenotype association remain unclear. Here, we present a severely affected infant carrying a compound heterozygous GSS variation, c.491G > A, and a novel variant of c.1343_1348delTACTTC. We also summarize the clinical manifestations, treatment protocol, prognosis, and genetic characteristics of previously reported GSSD cases in China. In this case study, our patient presented with tachypnea, jaundice, intractable metabolic acidosis, and hemolytic anemia. Urinary-organic acid analysis revealed elevated 5-oxoproline levels. Further, this patient showed improved outcomes owing to early diagnosis and the timely administration of vitamins C and E. Therefore, our study indicates that in clinical cases of unexplained hemolytic anemia and metabolic acidosis, GSSD should be considered. Additionally, genetic testing and antioxidant application might help identify GSSD and improve the prognosis.

How to Increase Cellular Glutathione

Glutathione (GSH) has special antioxidant properties due to its high intracellular concentration, ubiquity, and high reactivity towards electrophiles of the sulfhydryl group of its cysteine moiety. In most diseases where oxidative stress is thought to play a pathogenic role, GSH concentration is significantly reduced, making cells more susceptible to oxidative damage. Therefore, there is a growing interest in determining the best method(s) to increase cellular glutathione for both disease prevention and treatment. This review summarizes the major strategies for successfully increasing cellular GSH stores. These include GSH itself, its derivatives, NRf-2 activators, cysteine prodrugs, foods, and special diets. The possible mechanisms by which these molecules can act as GSH boosters, their related pharmacokinetic issues, and their advantages and disadvantages are discussed.

Recent topics and advanced therapies in chronic granulomatous disease

Chronic granulomatous disease (CGD) is a primary immunodeficiency characterized by the inability of phagocytes to produce reactive oxygen species (ROS) owing to a defect in any of the five components (CYBB/gp91phox, CYBA/p22phox, NCF1/p47phox, NCF2/p67phox, and NCF4/p40phox) and a concomitant regulatory component of Rac1/2 and CYBC1/Eros of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. Patients with CGD are at an increased risk of life-threatening infections caused by catalase-positive bacteria and fungi and of inflammatory complications such as CGD colitis. Antimicrobial and azole antifungal prophylaxes have considerably reduced the incidence and severity of bacterial and improved fungal infections and overall survival. CGD studies have revealed the precise epidemiology and role of NADPH oxidase in innate immunity which has led to a new understanding of the importance of phagocyte oxygen metabolism in various host-defense systems and the fields leading to cell death processes. Moreover, ROS plays central roles in the determination of cell fate as secondary messengers and by modifying of various signaling molecules. According to this increasing knowledge about the effects of ROS on the inflammasomal system, immunomodulatory treatments, such as IFN-γ and anti-IL-1 antibodies, have been established. This review covers the current topics in CGD and the relationship between ROS and ROS-mediated pathophysiological phenomena. In addition to the shirt summary of hematopoietic stem cell transplantation and gene therapy, we introduce a novel ROS-producing enzyme replacement therapy using PEG-fDAO to compensate for NADPH oxidase deficiency.

Toxic Metabolites and Inborn Errors of Amino Acid Metabolism: What One Informs about the Other

In inborn errors of metabolism, such as amino acid breakdown disorders, loss of function mutations in metabolic enzymes within the catabolism pathway lead to an accumulation of the catabolic intermediate that is the substrate of the mutated enzyme. In patients of such disorders, dietarily restricting the amino acid(s) to prevent the formation of these catabolic intermediates has a therapeutic or even entirely preventative effect. This demonstrates that the pathology is due to a toxic accumulation of enzyme substrates rather than the loss of downstream products. Here, we provide an overview of amino acid metabolic disorders from the perspective of the ‘toxic metabolites’ themselves, including their mechanism of toxicity and whether they are involved in the pathology of other disease contexts as well. In the research literature, there is often evidence that such metabolites play a contributing role in multiple other nonhereditary (and more common) disease conditions, and these studies can provide important mechanistic insights into understanding the metabolite-induced pathology of the inborn disorder. Furthermore, therapeutic strategies developed for the inborn disorder may be applicable to these nonhereditary disease conditions, as they involve the same toxic metabolite. We provide an in-depth illustration of this cross-informing concept in two metabolic disorders, methylmalonic acidemia and hyperammonemia, where the pathological metabolites methylmalonic acid and ammonia are implicated in other disease contexts, such as aging, neurodegeneration, and cancer, and thus there are opportunities to apply mechanistic or therapeutic insights from one disease context towards the other. Additionally, we expand our scope to other metabolic disorders, such as homocystinuria and nonketotic hyperglycinemia, to propose how these concepts can be applied broadly across different inborn errors of metabolism and various nonhereditary disease conditions.

Plasma Metabolomics and Lipidomics Differentiate Obese Individuals by Peripheral Neuropathy Status

CONTEXT

Peripheral neuropathy (PN) is a frequent prediabetes and type 2 diabetes (T2D) complication. Multiple clinical studies reveal that obesity and dyslipidemia can also drive PN progression, independent of glycemia, suggesting a complex interplay of specific metabolite and/or lipid species may underlie PN.

OBJECTIVE

This work aimed to identify the plasma metabolomics and lipidomics signature that underlies PN in an observational study of a sample of individuals with average class 3 obesity.

METHODS

We performed plasma global metabolomics and targeted lipidomics on obese participants with (n = 44) and without PN (n = 44), matched for glycemic status, vs lean nonneuropathic controls (n = 43). We analyzed data by Wilcoxon, logistic regression, partial least squares-discriminant analysis, and group-lasso to identify differential metabolites and lipids by obesity and PN status. We also conducted subanalysis by prediabetes and T2D status.

RESULTS

Lean vs obese comparisons, regardless of PN status, identified the most significant differences in gamma-glutamyl and branched-chain amino acid metabolism from metabolomics analysis and triacylglycerols from lipidomics. Stratification by PN status within obese individuals identified differences in polyamine, purine biosynthesis, and benzoate metabolism. Lipidomics found diacylglycerols as the most significant subpathway distinguishing obese individuals by PN status, with additional contributions from phosphatidylcholines, sphingomyelins, ceramides, and dihydroceramides. Stratifying the obese group by glycemic status did not affect discrimination by PN status.

CONCLUSION

Obesity may be as strong a PN driver as prediabetes or T2D in a sample of individuals with average class 3 obesity, at least by plasma metabolomics and lipidomics profile. Metabolic and complex lipid pathways can differentiate obese individuals with and without PN, independent of glycemic status.

Gamma-glutamyl transferase levels are associated with the occurrence of post-stroke cognitive impairment: a multicenter cohort study

Background

Gamma-glutamyl transferase (GGT) is involved in maintenance of physiological concentrations of glutathione in cells, and protects them from oxidative stress-induced damage. However, its role in post-stroke cognitive impairment (PSCI) remains unknown. Here, we investigated the effects of serum GGT on PSCI.

Methods

We conducted a prospective, multicenter cohort study. A total of 1, 957 participants with a minor ischemic stroke or transient ischemic attack whose baseline GGT levels were measured were enrolled from the Impairment of Cognition and Sleep (ICONS) study of the China National Stroke Registry-3 (CNSR-3). They were categorized into four groups according to quartiles of baseline GGT levels. Cognitive functions were assessed using the Montreal Cognitive Assessment (MoCA) approach. Multiple logistic regression models were performed to evaluate the relationship between GGT and PSCI at 3 months follow-up.

Results

Among the 1957 participants, 671 (34.29%) patients suffered PSCI at 3 months follow-up. The highest GGT level quartile group exhibited a lower risk of PSCI in the fully adjusted model [OR (95% CI): 0.69 (0.50-0.96)], relative to the lowest group. Moreover, incorporation of GGT to the conventional model resulted in slight improvements in PSCI outcomes after 3 months (NRI: 12.00%; IDI: 0.30%).

Conclusions

Serum GGT levels are inversely associated with the risk of PSCI, with extremely low levels being viable risk factors for PSCI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02587-4.

Glutathione in Brain Disorders and Aging

Glutathione is a remarkably functional molecule with diverse features, which include being an antioxidant, a regulator of DNA synthesis and repair, a protector of thiol groups in proteins, a stabilizer of cell membranes, and a detoxifier of xenobiotics. Glutathione exists in two states—oxidized and reduced. Under normal physiological conditions of cellular homeostasis, glutathione remains primarily in its reduced form. However, many metabolic pathways involve oxidization of glutathione, resulting in an imbalance in cellular homeostasis. Impairment of glutathione function in the brain is linked to loss of neurons during the aging process or as the result of neurological diseases such as Huntington’s disease, Parkinson’s disease, stroke, and Alzheimer’s disease. The exact mechanisms through which glutathione regulates brain metabolism are not well understood. In this review, we will highlight the common signaling cascades that regulate glutathione in neurons and glia, its functions as a neuronal regulator in homeostasis and metabolism, and finally a mechanistic recapitulation of glutathione signaling. Together, these will put glutathione’s role in normal aging and neurological disorders development into perspective.

Ligaza γ-glutamylocysteiny – od molekularnych mechanizmów regulacji aktywności enzymatycznej do implikacji terapeutycznych

Glutation (γ-glutamylocysteinyloglicyna, GSH) jest najbardziej rozpowszechnionym tiolowym antyoksydantem wytwarzanym w cytozolu wszystkich komórek ssaków, który pełni ważną rolę ochronną przed stresem oksydacyjnym. GSH jest syntetyzowany de novo przez sekwencyjne działanie dwóch enzymów: ligazy γ-glutamylocysteiny (GCL) i syntetazy glutationowej (GS). GCL katalizuje pierwszy etap biosyntezy GSH, którego produktem jest γ-glutamylocysteina (γ-GC). GCL jest heterodimerycznym enzymem zbudowanym z podjednostki katalitycznej (GCLc) i modulatorowej (GCLm), kodowanych przez dwa różne geny. Podjednostki GCL podlegają złożonej regulacji zarówno na poziomie przed-, jak i potranslacyjnym. Zmiany w ekspresji i aktywności GCL mogą zaburzać poziom GSH i homeostazy redoks. Przyczyną wielu przewlekłych schorzeń związanych ze stresem oksydacyjnym jest upośledzenie aktywności katalitycznej GCL oraz spadek stężenia GSH. Badania przedkliniczne sugerują, że podawanie egzogennej γ-GC podwyższa wewnątrzkomórkowe GSH przez dostarczenie brakującego substratu i może wykazywać potencjał jako terapia uzupełniająca w chorobach związanych z deplecją GSH.

Gas Chromatography Mass Spectrometry Aided Diagnosis of Glutathione Synthetase Deficiency

Glutathione synthetase (GSS) deficiency is a rare disorder, occurring with a frequency of less than 1 in 100,000 individuals worldwide. The clinical presentation may vary from mild to severe, and manifestations include hemolytic anemia, hyperbilirubinemia, metabolic acidosis, neurological problems, and sepsis. Herein, we present a case of a newborn boy with the most severe phenotype of GSS deficiency, diagnosed based on clinical features and increased urinary 5-oxoproline levels determined via gas chromatography mass spectrometry (GCMS) testing.

In Vivo Brain GSH: MRS Methods and Clinical Applications

Glutathione (GSH) is an important antioxidant implicated in several physiological functions, including the oxidation−reduction reaction balance and brain antioxidant defense against endogenous and exogenous toxic agents. Altered brain GSH levels may reflect inflammatory processes associated with several neurologic disorders. An accurate and reliable estimation of cerebral GSH concentrations could give a clear and thorough understanding of its metabolism within the brain, thus providing a valuable benchmark for clinical applications. In this context, we aimed to provide an overview of the different magnetic resonance spectroscopy (MRS) technologies introduced for in vivo human brain GSH quantification both in healthy control (HC) volunteers and in subjects affected by different neurological disorders (e.g., brain tumors, and psychiatric and degenerative disorders). Additionally, we aimed to provide an exhaustive list of normal GSH concentrations within different brain areas. The definition of standard reference values for different brain areas could lead to a better interpretation of the altered GSH levels recorded in subjects with neurological disorders, with insights into the possible role of GSH as a biomarker and therapeutic target.

Quantitative trait mapping in Diversity Outbred mice identifies novel genomic regions associated with the hepatic glutathione redox system

The tripeptide glutathione (GSH) is instrumental to antioxidant protection and xenobiotic metabolism, and the ratio of its reduced and oxidized forms (GSH/GSSG) indicates the cellular redox environment and maintains key aspects of cellular signaling. Disruptions in GSH levels and GSH/GSSG have long been tied to various chronic diseases, and many studies have examined whether variant alleles in genes responsible for GSH synthesis and metabolism are associated with increased disease risk. However, past studies have been limited to established, canonical GSH genes, though emerging evidence suggests that novel loci and genes influence the GSH redox system in specific tissues. The present study marks the most comprehensive effort to date to directly identify genetic loci associated with the GSH redox system. We employed the Diversity Outbred (DO) mouse population, a model of human genetics, and measured GSH and the essential redox cofactor NADPH in liver, the organ with the highest levels of GSH in the body. Under normal physiological conditions, we observed substantial variation in hepatic GSH and NADPH levels and their redox balances, and discovered a novel, significant quantitative trait locus (QTL) on murine chromosome 16 underlying GSH/GSSG; bioinformatics analyses revealed Socs1 to be the most likely candidate gene. We also discovered novel QTL associated with hepatic NADP⁺ levels and NADP⁺/NADPH, as well as unique candidate genes behind each trait. Overall, these findings transform our understanding of the GSH redox system, revealing genetic loci that govern it and proposing new candidate genes to investigate in future mechanistic endeavors.

Malnourishment-Associated Acetaminophen Toxicity in Pregnancy

BACKGROUND

Although acetaminophen is commonly used in pregnancy, it can deplete glutathione concentrations and cause accumulation of 5-oxoproline, with subsequent metabolic acidosis.

CASE

A malnourished 25-year-old woman, G2P1001, with chronic acetaminophen use presented with abdominal pain and high anion gap metabolic acidosis. After ruling out other potential causes, her urine 5-oxoproline level was found to be elevated. She received N-acetylcysteine, with resolution of the acidosis.

CONCLUSION

Those who care for pregnant patients should remain alert to 5-oxoprolinemia as a cause of metabolic acidosis during pregnancy. Care must be taken when using acetaminophen in states of malnutrition. N-acetylcysteine seems to be an effective antidote.

Assay of the Enzymes of Glutathione Biosynthesis

This article is dedicated to the late long-time Editor-in-Chief of Analytical Biochemistry, William Jakoby. As a graduate student, I remember reading many articles in Analytical Biochemistry and Methods in Enzymology, both volumes that Bill edited. I first met him as a graduate student presenting at the American Society of Biochemistry (and Molecular Biology) meetings. My Ph.D. advisor, Alton Meister, would bring over well-known biochemists and introduce me as Dr. Anderson, leaving me a bit tongue-tied being that I was still actually a humble graduate student! I next met Bill at my first Analytical Biochemistry Executive Editors meeting in San Diego when he was Editor-in-Chief Emeritus; I felt honored to be on the same board with him and serving the journal to which he had brought to prominence. His eyes were piercing and he was so sharp; his knowledge was both broad and deep. Since much of the large body of Bill's research was on glutathione S-transferases, my article focuses on the assay of the enzymes that synthesize glutathione, a substrate for glutathione S-transferases.

The Role of Non-Coding RNAs in the Neuroprotective Effects of Glutathione

The establishment of antioxidative defense systems might have been mandatory for most living beings with aerobic metabolisms, because oxygen consumption produces adverse byproducts known as reactive oxygen species (ROS). The brain is especially vulnerable to the effect of ROS, since the brain has large amounts of unsaturated fatty acids, which are a target of lipid oxidation, as well as comparably high-energy consumption compared to other organs that results in ROS release from mitochondria. Thus, dysregulation of the synthesis and/or metabolism of antioxidants-particularly glutathione (GSH), which is one of the most important antioxidants in the human body-caused oxidative stress states that resulted in critical diseases, including neurodegenerative diseases in the brain. GSH plays crucial roles not only as an antioxidant but also as an enzyme cofactor, cysteine storage form, the major redox buffer, and a neuromodulator in the central nervous system. The levels of GSH are precisely regulated by uptake systems for GSH precursors as well as GSH biosynthesis and metabolism. The rapid advance of RNA sequencing technologies has contributed to the discovery of numerous non-coding RNAs with a wide range of functions. Recent lines of evidence show that several types of non-coding RNAs, including microRNA, long non-coding RNA and circular RNA, are abundantly expressed in the brain, and their activation or inhibition could contribute to neuroprotection through the regulation of GSH synthesis and/or metabolism. Interestingly, these non-coding RNAs play key roles in gene regulation and growing evidence indicates that non-coding RNAs interact with each other and are co-regulated. In this review, we focus on how the non-coding RNAs modulate the level of GSH and modify the oxidative stress states in the brain.

Causal relationships between genetically determined metabolites and human intelligence: a Mendelian randomization study

Intelligence predicts important life and health outcomes, but the biological mechanisms underlying differences in intelligence are not yet understood. The use of genetically determined metabotypes (GDMs) to understand the role of genetic and environmental factors, and their interactions, in human complex traits has been recently proposed. However, this strategy has not been applied to human intelligence. Here we implemented a two-sample Mendelian randomization (MR) analysis using GDMs to assess the causal relationships between genetically determined metabolites and human intelligence. The standard inverse-variance weighted (IVW) method was used for the primary MR analysis and three additional MR methods (MR-Egger, weighted median, and MR-PRESSO) were used for sensitivity analyses. Using 25 genetic variants as instrumental variables (IVs), our study found that 5-oxoproline was associated with better performance in human intelligence tests (P_IVW = 9.25 × 10^-5). The causal relationship was robust when sensitivity analyses were applied (P_MR-Egger = 0.0001, P_{Weighted median} = 6.29 × 10^-6, P_MR-PRESSO = 0.0007), and repeated analysis yielded consistent result (P_IVW = 0.0087). Similarly, also dihomo-linoleate (20:2n6) and p-acetamidophenylglucuronide showed robust association with intelligence. Our study provides novel insight by integrating genomics and metabolomics to estimate causal effects of genetically determined metabolites on human intelligence, which help to understanding of the biological mechanisms related to human intelligence.

Glutathione Synthesis in Cancer Cells

Tripeptide GSH is associated not only with the control and maintenance of redox cell homeostasis, but also with the processes of detoxification, proliferation, cell differentiation, and regulation of cell death. Disruptions in GSH synthesis and changes in the GSH/GSSG ratio are common for many pathological conditions, including malignant neoplasms. Numerous data indicate the importance of GSH and the GSH/GSSG ratio in the regulation of tumor cell viability, in the initiation of tumor development, progression, and drug resistance. However, control of the mechanism of GSH synthesis in malignant tumors remains poorly understood. This review discusses the features of GSH synthesis and its regulation in tumor cells. The role of GSH in the mechanisms of apoptosis, necroptosis, ferroptosis, and autophagy is considered.

Non-canonical Glutamate-Cysteine Ligase Activity Protects against Ferroptosis

Cysteine is required for maintaining cellular redox homeostasis in both normal and transformed cells. Deprivation of cysteine induces the iron-dependent form of cell death known as ferroptosis; however, the metabolic consequences of cysteine starvation beyond impairment of glutathione synthesis are poorly characterized. Here, we find that cystine starvation of non-small-cell lung cancer cell lines induces an unexpected accumulation of γ-glutamyl-peptides, which are produced due to a non-canonical activity of glutamate-cysteine ligase catalytic subunit (GCLC). This activity is enriched in cell lines with high levels of NRF2, a key transcriptional regulator of GCLC, but is also inducible in healthy murine tissues following cysteine limitation. γ-glutamyl-peptide synthesis limits the accumulation of glutamate, thereby protecting against ferroptosis. These results indicate that GCLC has a glutathione-independent, non-canonical role in the protection against ferroptosis by maintaining glutamate homeostasis under cystine starvation.

The dark side of gamma-glutamyltransferase (GGT): Pathogenic effects of an 'antioxidant' enzyme

Having long been regarded as just a member in the cellular antioxidant systems, as well as a clinical biomarker of hepatobiliary diseases and alcohol abuse, gamma-glutamyltransferase (GGT) enzyme activity has been highlighted by more recent research as a critical factor in modulation of redox equilibria within the cell and in its surroundings. Moreover, due to the prooxidant reactions which can originate during its metabolic function in selected conditions, experimental and clinical studies are increasingly involving GGT in the pathogenesis of several important disease conditions, such as atherosclerosis, cardiovascular diseases, cancer, lung inflammation, neuroinflammation and bone disorders. The present article is an overview of the laboratory findings that have prompted an evolution in interpretation of the significance of GGT in human pathophysiology.

Glutathione synthetase deficiency: a novel mutation with femur agenesis

Introduction: Glutathione synthetase (GSS) deficiency is an autosomal recessive disorder (frequency < 1/1,000,000) with different varyingly severe clinical manifestations that include metabolic acidosis, hemolytic anemia, hyperbilirubinemia, neurological disorders and sepsis. Case report: This infant was small for gestational age, had hemolytic anemia, metabolic acidosis, bilateral subependymal pseudocysts and increased echogenicity of the basal ganglia. GSS deficiency was confirmed by genetic analysis. The patient also had unilateral right femur agenesis. Conclusion: By using next generation sequencing analysis, we identified a novel homozygous variant c.800G > A, p.Arg267Gln in the GSS gene of this patient. Femur agenesis had not previously been associated with GSS.

Pyroglutamic Acidemia: An Underrecognized and Underdiagnosed Cause of High Anion Gap Metabolic Acidosis - A Case Report and Review of Literature

Pyroglutamic acidemia (oxoprolinemia) is an underrecognized cause of high anion gap acidosis resulting from derangement in the gamma-glutamyl cycle. Pyroglutamic acidemia is most commonly diagnosed in the pediatric population in patients with inherited autosomal recessive enzyme deficiencies. However, acquired pyroglutamic acidemia can present in the adult population. Patients often present with confusion, nausea, and vomiting as well as an elevated anion gap metabolic acidosis. This article describes a case of acquired pyroglutamic acidemia and emphasizes the need to consider this entity.

Boosting GSH Using the Co-Drug Approach: I-152, a Conjugate of N-acetyl-cysteine and β-mercaptoethylamine

Glutathione (GSH) has poor pharmacokinetic properties; thus, several derivatives and biosynthetic precursors have been proposed as GSH-boosting drugs. I-152 is a conjugate of N-acetyl-cysteine (NAC) and S-acetyl-β-mercaptoethylamine (SMEA) designed to release the parent drugs (i.e., NAC and β-mercaptoethylamine or cysteamine, MEA). NAC is a precursor of L-cysteine, while MEA is an aminothiol able to increase GSH content; thus, I-152 represents the very first attempt to combine two pro-GSH molecules. In this review, the in-vitro and in-vivo metabolism, pro-GSH activity and antiviral and immunomodulatory properties of I-152 are discussed. Under physiological GSH conditions, low I-152 doses increase cellular GSH content; by contrast, high doses cause GSH depletion but yield a high content of NAC, MEA and I-152, which can be used to resynthesize GSH. Preliminary in-vivo studies suggest that the molecule reaches mouse organs, including the brain, where its metabolites, NAC and MEA, are detected. In cell cultures, I-152 replenishes experimentally depleted GSH levels. Moreover, administration of I-152 to C57BL/6 mice infected with the retroviral complex LP-BM5 is effective in contrasting virus-induced GSH depletion, exerting at the same time antiviral and immunomodulatory functions. I-152 acts as a pro-GSH agent; however, GSH derivatives and NAC cannot completely replicate its effects. The co-delivery of different thiol species may lead to unpredictable outcomes, which warrant further investigation.

Pyroglutamic acidosis by glutathione regeneration blockage in critical patients with septic shock

AIM

The aim of this study was to evaluate oxidative stress from glutathione depletion in critically ill patients with a septic shock through the abnormal presence of pyroglutamic acid (PyroGlu) in the urine (indirectly) and through its serum level (directly).

METHODS

This was a prospective analytical study of 28 critically ill patients with a septic shock who were monitored from admission (initial) to 3 days of stay (final) in the intensive care unit (ICU). Data collected included PyroGlu and glutamic acid (Glu) using liquid chromatography/mass spectrometry, and glutathione peroxidase (GPX) activity with a colorimetric assay. The differences in Glu, PyroGlu, and GPX activity between the septic shock group and healthy control group serving as reference values were evaluated using the Mann-Whitney test. The correlations between Glu, PyroGlu, and GPX activity and clinical outcomes were determined using Spearman's correlation coefficient.

RESULTS

In patients with septic shock, serum and urine PyroGlu levels were higher, erythrocyte GPX activity/gr Hb was lower, and urine Glu levels were lower compared to healthy control reference values, for both initial and final values. Initial serum Glu levels were also lower. Serum PyroGlu levels had a correlation with both initial and final serum Glu levels; levels also correlated in the urine. Initial serum Glu correlated with the days of mechanical ventilation (P = 0.016) and the days of ICU stay (P = 0.05). Urine Glu/mg creatinine correlated with APACHE II (P = 0.030). This positive correlation observed for serum Glu was not observed for PyroGlu.

CONCLUSIONS

The current study found that septic patients have higher levels of PyroGlu, lower levels of Glu, and lower erythrocyte GPX activity, suggesting that these biomarkers could be used as an indicator of glutathione depletion. In addition, Glu is related to severity parameters. This study can guide future studies on the importance of monitoring the levels of pyroglutamic acidosis in critical patients with septic shock in order to preserve the oxidative status and its evolution during the stay in the ICU.

Pyroglutamic acidosis as a cause for high anion gap metabolic acidosis: a prospective study

5-oxoprolinemia (pyroglutamic acid, PGA) in the absence of acetaminophen use has been rarely reported as a cause for high anion gap metabolic acidosis. We investigated the prevalence and risk factors for elevated PGA concentrations among hospitalized patients with high anion gap metabolic acidosis: We prospectively enrolled patients with high anion gap metabolic acidosis hospitalized in the department of medicine. For each patient we collected the main diagnosis, concurrent medications and laboratory parameters. Spot urine samples were tested for PGA concentration. Levels ≥63 µmol/mmol creatinine were considered elevated. Overall, forty patients were prospectively followed. Mean age was 66.9 (17.9) years. Four (6.3%) patients had a high urine PGA level and demonstrated also lower blood pH (7.2 vs 7.3, p = 0.05) and lower serum lactate concentration (17.5 mg/dl vs 23.0 mg/dl, p = 0.04). Additionally, the high PGA level group consisted of more patients with septic shock [2/4 (50%) vs 3/36 (8.3%)] with a trend towards significance (p = 0.07). In conclusion, PGA might have a role in patients with septic shock and acidosis. Being a treatable condition, PGA should be taken into consideration particularly when no other cause for high anion gap is identified.

An UPLC-MS/MS Assay to Measure Glutathione as Marker for Oxidative Stress in Cultured Cells

Oxidative stress plays a role in the onset and progression of a number of diseases, such as Alzheimer’s disease, diabetes and cancer, as well as ageing. Oxidative stress is caused by an increased production of reactive oxygen species and reduced antioxidant activity, resulting in the oxidation of glutathione. The ratio of reduced to oxidised glutathione is often used as a marker of the redox state in the cell. Whereas a variety of methods have been developed to measure glutathione in blood samples, methods to measure glutathione in cultured cells are scarce. Here we present a protocol to measure glutathione levels in cultured human and yeast cells using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS).

Glutathione as a Marker for Human Disease

Glutathione (GSH), often referred to as "the master antioxidant," participates not only in antioxidant defense systems, but many metabolic processes, and therefore its role cannot be overstated. GSH deficiency causes cellular risk for oxidative damage and thus as expected, GSH imbalance is observed in a wide range of pathological conditions including tuberculosis (TB), HIV, diabetes, cancer, and aging. Consequently, it is not surprising that GSH has attracted the attention of biological researchers and pharmacologists alike as a possible target for medical intervention. Here, we discuss the role GSH plays amongst these pathological conditions to illuminate how it can be used as a marker for human disease.

Glutathione metabolism in cancer progression and treatment resistance

Bansal and Simon discuss strategies to block glutathione synthesis and utilization pathways to inhibit tumor propagation and treatment resistance.

Glutathione (GSH) is the most abundant antioxidant found in living organisms and has multiple functions, most of which maintain cellular redox homeostasis. GSH preserves sufficient levels of cysteine and detoxifies xenobiotics while also conferring therapeutic resistance to cancer cells. However, GSH metabolism plays both beneficial and pathogenic roles in a variety of malignancies. It is crucial to the removal and detoxification of carcinogens, and alterations in this pathway can have a profound effect on cell survival. Excess GSH promotes tumor progression, where elevated levels correlate with increased metastasis. In this review, we discuss recent studies that focus on deciphering the role of GSH in tumor initiation and progression as well as mechanisms underlying how GSH imparts treatment resistance to growing cancers. Targeting GSH synthesis/utilization therefore represents a potential means of rendering tumor cells more susceptible to different treatment options such as chemotherapy and radiotherapy.

A case of severe glutathione synthetase deficiency with novel GSS mutations

Glutathione synthetase deficiency (GSSD) is a rare inborn error of glutathione metabolism with autosomal recessive inheritance. The severe form of the disease is characterized by acute metabolic acidosis, usually present in the neonatal period with hemolytic anemia and progressive encephalopathy. A case of a male newborn infant who had severe metabolic acidosis with high anion gap, hemolytic anemia, and hyperbilirubinemia is reported. A high level of 5-oxoproline was detected in his urine and a diagnosis of generalized GSSD was made. DNA sequence analysis revealed the infant to be compound heterozygous with two mutations, c.738dupG in exon 8 of GSS gene resulting in p.S247fs and a repetitive sequence in exon 3 of GSS gene. Treatment after diagnosis of GSSD included supplementation with antioxidants and oral sodium hydrogen bicarbonate. However, he maintained a variable degree of metabolic acidosis and succumbed shortly after his parents requested discontinuation of therapy because of dismal prognosis and medical futility when he was 18 days old.

Acquired 5-oxoproline acidemia successfully treated with N-acetylcysteine

Acquired 5-oxoprolinemia is increasingly recognized as a cause of anion gap metabolic acidosis. It predominantly occurs in chronically ill, malnourished women with impaired renal function and chronic acetaminophen ingestion. Depletion of glutathione and cysteine stores leads to elevated 5-oxoproline levels. N-acetylcysteine, given its effect in repleting glutathione and cysteine stores, has been proposed as a potential treatment for 5-oxoprolinemia, though reports of its successful use are lacking. We present a case of 5-oxoproline metabolic acidosis that persisted despite discontinuation of acetaminophen. However, the acidosis rapidly resolved with N-acetylcysteine administration.

Glutathione, Glutaredoxins, and Iron

SIGNIFICANCE

Glutathione (GSH) is the most abundant cellular low-molecular-weight thiol in the majority of organisms in all kingdoms of life. Therefore, functions of GSH and disturbed regulation of its concentration are associated with numerous physiological and pathological situations. Recent Advances: The function of GSH as redox buffer or antioxidant is increasingly being questioned. New functions, especially functions connected to the cellular iron homeostasis, were elucidated. Via the formation of iron complexes, GSH is an important player in all aspects of iron metabolism: sensing and regulation of iron levels, iron trafficking, and biosynthesis of iron cofactors. The variety of GSH coordinated iron complexes and their functions with a special focus on FeS-glutaredoxins are summarized in this review. Interestingly, GSH analogues that function as major low-molecular-weight thiols in organisms lacking GSH resemble the functions in iron homeostasis.

CRITICAL ISSUES

Since these iron-related functions are most likely also connected to thiol redox chemistry, it is difficult to distinguish between mechanisms related to either redox or iron metabolisms.

FUTURE DIRECTIONS

The ability of GSH to coordinate iron in different complexes with or without proteins needs further investigation. The discovery of new Fe-GSH complexes and their physiological functions will significantly advance our understanding of cellular iron homeostasis. Antioxid. Redox Signal. 27, 1235-1251.

Role of glutathione in the regulation of epigenetic mechanisms in disease

Epigenetics is a rapidly growing field that studies gene expression modifications not involving changes in the DNA sequence. Histone H3, one of the basic proteins in the nucleosomes that make up chromatin, is S-glutathionylated in mammalian cells and tissues, making Gamma-L-glutamyl-L-cysteinylglycine, glutathione (GSH), a physiological antioxidant and second messenger in cells, a new post-translational modifier of the histone code that alters the structure of the nucleosome. However, the role of GSH in the epigenetic mechanisms likely goes beyond a mere structural function. Evidence supports the hypothesis that there is a link between GSH metabolism and the control of epigenetic mechanisms at different levels (i.e., substrate availability, enzymatic activity for DNA methylation, changes in the expression of microRNAs, and participation in the histone code). However, little is known about the molecular pathways by which GSH can control epigenetic events. Studying mutations in enzymes involved in GSH metabolism and the alterations of the levels of cofactors affecting epigenetic mechanisms appears challenging. However, the number of diseases induced by aberrant epigenetic regulation is growing, so elucidating the intricate network between GSH metabolism, oxidative stress and epigenetics could shed light on how their deregulation contributes to the development of neurodegeneration, cancer, metabolic pathologies and many other types of diseases.

Discovery of a widespread prokaryotic 5-oxoprolinase that was hiding in plain sight

5-Oxoproline (OP) is well-known as an enzymatic intermediate in the eukaryotic γ-glutamyl cycle, but it is also an unavoidable damage product formed spontaneously from glutamine and other sources. Eukaryotes metabolize OP via an ATP-dependent 5-oxoprolinase; most prokaryotes lack homologs of this enzyme (and the γ-glutamyl cycle) but are predicted to have some way to dispose of OP if its spontaneous formation in vivo is significant. Comparative analysis of prokaryotic genomes showed that the gene encoding pyroglutamyl peptidase, which removes N-terminal OP residues, clusters in diverse genomes with genes specifying homologs of a fungal lactamase (renamed prokaryotic 5-oxoprolinase A, pxpA) and homologs of allophanate hydrolase subunits (renamed pxpB and pxpC). Inactivation of Bacillus subtilis pxpA, pxpB, or pxpC genes slowed growth, caused OP accumulation in cells and medium, and prevented use of OP as a nitrogen source. Assays of cell lysates showed that ATP-dependent 5-oxoprolinase activity disappeared when pxpA, pxpB, or pxpC was inactivated. 5-Oxoprolinase activity could be reconstituted in vitro by mixing recombinant B. subtilis PxpA, PxpB, and PxpC proteins. In addition, overexpressing Escherichia coli pxpABC genes in E. coli increased 5-oxoprolinase activity in lysates ≥1700-fold. This work shows that OP is a major universal metabolite damage product and that OP disposal systems are common in all domains of life. Furthermore, it illustrates how easily metabolite damage and damage-control systems can be overlooked, even for central metabolites in model organisms.

Clinical and molecular characterization of 6 children with glutamate-cysteine ligase deficiency causing hemolytic anemia

Glutathione (gamma-glutamylcysteinylglycine) has diverse functions including free radicals scavenging and modulating many critical cellular processes. Glutathione is synthesized by the consecutive action of the enzymes glutamate-cysteine ligase (GCL) and glutathione synthetase. GCL is composed of a catalytic subunit encoded by the GCLC gene and a regulatory subunit encoded by the GCLM gene. GCL deficiency due to homozygous mutations in GCLC has been reported in 6 individuals from 4 independent families. All presented with hemolytic anemia and 4 had additional neurological manifestations including cognitive impairment, neuropathy, ataxia, and myopathy. In this report, we present additional 6 children from 2 independent consanguineous families with GCL deficiency. All the children presented with neonatal hemolytic anemia. Beyond the neonatal period, they did not have jaundice or hemolysis, but continued to have mild anemia. They all had normal development and neurological examination. The affected children from the first family had the homozygous mutation c.1772G>A (p.S591N) and the second family had the homozygous mutation c.514T>A (p.S172T) in GCLC. GCL deficiency can have a mild non-neurological phenotype or a more severe phenotype with neurological manifestations. GCL deficiency can be an underdiagnosed cause of hemolytic anemia, thus awareness may aid in early diagnosis, appropriate genetic counseling, and management.

Pyroglutamate (5-oxoproline) measured with hydrophilic interaction chromatography (HILIC) tandem mass spectrometry in acutely ill patients

BACKGROUND

Pyroglutamic acid (PGA) is challenging to quantify in plasma and is a rare cause of metabolic acidosis that is associated with inherited disorders or acquired after exposure to drugs.

METHOD

We developed a hydrophilic interaction liquid chromatography tandem mass spectrometry method with a short analysis time. We established a reference interval and then measured PGA in acutely ill patients to investigate associations with clinical, pharmaceutical and laboratory parameters.

RESULTS

The assay limit of the blank was 0.14μmol/L and was linear to 5000μmol/L with good precision. In-source formation of PGA from glutamate and glutamine was avoided by chromatographic separation. The PGA in controls had a reference interval of 22.6 to 47.8μmol/L. The median PGA concentration in acutely ill patients was similar (P=0.21), but 18 individuals were above the reference interval with concentrations up to 250μmol/L. We detected an association between PGA concentration and antibiotic and acetaminophen administration as well as renal impairment and severity of illness. Elevations of PGA in this unselected cohort were small compared to those reported in patients with pyroglutamic acidosis.

CONCLUSION

The method is suitable for routine clinical use. We confirmed several expected associations with PGA in an acutely ill population.

The acetaminophen metabolite N-acetyl-p-benzoquinone imine (NAPQI) inhibits glutathione synthetase in vitro; a clue to the mechanism of 5-oxoprolinuric acidosis?

1. Metabolic acidosis due to accumulation of l-5-oxoproline is a rare, poorly understood, disorder associated with acetaminophen treatment in malnourished patients with chronic morbidity. l-5-Oxoprolinuria signals abnormal functioning of the γ-glutamyl cycle, which recycles and synthesises glutathione. Inhibition of glutathione synthetase (GS) by N-acetyl-p-benzoquinone imine (NAPQI) could contribute to 5-oxoprolinuric acidosis in such patients. We investigated the interaction of NAPQI with GS in vitro. 2. Peptide mapping of co-incubated NAPQI and GS using mass spectrometry demonstrated binding of NAPQI with cysteine-422 of GS, which is known to be essential for GS activity. Computational docking shows that NAPQI is properly positioned for covalent bonding with cysteine-422 via Michael addition and hence supports adduct formation. 3. Co-incubation of 0.77 μM of GS with NAPQI (25-400 μM) decreased enzyme activity by 16-89%. Inhibition correlated strongly with the concentration of NAPQI and was irreversible. 4. NAPQI binds covalently to GS causing irreversible enzyme inhibition in vitro. This is an important novel biochemical observation. It is the first indication that NAPQI may inhibit glutathione synthesis, which is pivotal in NAPQI detoxification. Further studies are required to investigate its biological significance and its role in 5-oxoprolinuric acidosis.

Clinical findings and effect of sodium hydrogen carbonate in patients with glutathione synthetase deficiency

BACKGROUND

Glutathione synthetase (GS) deficiency is a rare inborn error of glutathione (GSH) metabolism manifested by severe metabolic acidosis, hemolytic anemia, neurological problems and massive excretion of pyroglutamic acid (5-oxoproline) in the urine. The disorder has mild, moderate, and severe clinical variants. We aimed to report clinical and laboratory findings of four patients, effect of sodium hydrogen carbonate treatment and long-term follow up of three patients.

METHODS

Urine organic acid analysis was performed with gas chromatography-mass spectrometry. Molecular genetic analysis was performed in three patients, mutation was found in two of them. Enzyme analysis was performed in one patient. Clinical and laboratory findings of four patients were evaluated.

RESULTS

One patient died at 4 months old, one patient's growth and development are normal, two patients have developed intellectual disability and seizures in the long term follow up period. Three patients benefited from sodium hydrogen carbonate treatment.

CONCLUSIONS

The clinical picture varies from patient to patient, so it is difficult to predict the prognosis and the effectiveness of treatment protocols. We reported long term follow up of four patients and demonstrated that sodium hydrogen carbonate is effective for treatment of chronic metabolic acidosis in GS deficieny.

Serum γ-Glutamyl Transferase Is Inversely Associated with Bone Mineral Density Independently of Alcohol Consumption

BACKGROUND

γ-Glutamyl transferase (GGT) is a well-known marker of chronic alcohol consumption or hepatobiliary diseases. A number of studies have demonstrated that serum levels of GGT are independently associated with cardiovascular and metabolic disorders. The purpose of this study was to test if serum GGT levels are associated with bone mineral density (BMD) in Korean adults.

METHODS

A total of 462 subjects (289 men and 173 women), who visited Severance Hospital for medical checkup, were included in this study. BMD was measured using dual energy X-ray absorptiometry. Cross-sectional association between serum GGT and BMD was evaluated.

RESULTS

As serum GGT levels increased from the lowest tertile (tertile 1) to the highest tertile (tertile 3), BMD decreased after adjusting for confounders such as age, body mass index, amount of alcohol consumed, smoking, regular exercise, postmenopausal state (in women), hypertension, diabetes mellitus, and hypercholesterolemia. A multiple linear regression analysis showed a negative association between log-transformed serum GGT levels and BMD. In a multiple logistic regression analysis, tertile 3 of serum GGT level was associated with an increased risk for low bone mass compared to tertile 1 (odds ratio, 2.271; 95% confidence interval, 1.340 to 3.850; P=0.002).

CONCLUSION

Serum GGT level was inversely associated with BMD in Korean adults. Further study is necessary to fully elucidate the mechanism of the inverse relationship.

Five Chinese patients with 5-oxoprolinuria due to glutathione synthetase and 5-oxoprolinase deficiencies

OBJECTIVE

5-Oxoprolinuria is a rare inherited metabolic disorder caused by a defective gamma-glutamyl cycle resulting from mutations in the genes encoding 5-oxoprolinase (OPLAH) and glutathione synthetase (GSS). No inherited 5-oxoprolinuria case has been reported in mainland China until now. In this study, clinical, biochemical, and genetic aspects of five Chinese 5-oxoprolinuria patients with OPLAH or GSS gene mutations were investigated.

METHODS

Three boys and two girls from five unrelated Chinese families with symptomatic 5-oxoprolinuria were identified within the past 3years in Peking University First Hospital. OPLAH and GSS genes were analyzed.

RESULTS

Patients were hospitalized between the age of 13days to 1year and 3months for hypersomnia, developmental retardation, feeding deficiency, vomiting, icterus and recurrent pneumonia. All patients had significantly elevated urine 5-oxoproline. Three novel mutations (c.1904G>A and c.2813_2815delGGG in Patient 1, c.2978G>T in Patient 2) on OPLAH, on GSS, one novel mutation (c.1252C>T in Patient 3) and a reported mutation (c.491G>A in Patients 3-5) were detected. Patient 4 has homozygous mutation c.491G>A, the others are heterozygous. After treatment by l-carnitine, vitamin E, B1, B2 and coenzyme Q10, three patients with GSS deficiency improved, but the two 5-oxoprolinase-deficient patients did not respond to treatment.

CONCLUSIONS

5-Oxoprolinase deficiency and GSS deficiency share some clinical and biochemical features. Genetic analysis is important for the deferential diagnosis. In this study, five Chinese patients had severe central nervous system damage. Antioxidant treatments were proved effective for the three patients with GSS deficiency but not for the two patients with 5-oxoprolinase deficiency.

Cerebellar neurochemical alterations in spinocerebellar ataxia type 14 appear to include glutathione deficiency

Autosomal dominant ataxia type 14 (SCA14) is a rare usually adult-onset progressive disorder with cerebellar neurodegeneration caused by mutations in protein kinase C gamma. We set out to examine cerebellar and extracerebellar neurochemical changes in SCA14 by MR spectroscopy. In 13 SCA14 patients and 13 healthy sex- and age-matched controls, 3-T single-voxel brain proton MR spectroscopy was performed in a cerebellar voxel of interest (VOI) at TE = 30 ms to obtain a neurochemical profile of metabolites with short relaxation times. In the cerebellum and in additional VOIs in the prefrontal cortex, motor cortex, and somatosensory cortex, a second measurement was performed at TE = 144 ms to mainly extract the total N-acetyl-aspartate (tNAA) signal besides the signals for total creatine (tCr) and total choline (tCho). The cerebellar neurochemical profile revealed a decrease in glutathione (6.12E-06 ± 2.50E-06 versus 8.91E-06 ± 3.03E-06; p = 0028) and tNAA (3.78E-05 ± 5.67E-06 versus 4.25E-05 ± 5.15E-06; p = 0023) and a trend for reduced glutamate (2.63E-05 ± 6.48E-06 versus 3.15E-05 ± 7.61E-06; p = 0062) in SCA14 compared to controls. In the tNAA-focused measurement, cerebellar tNAA (296.6 ± 42.6 versus 351.7 ± 16.5; p = 0004) and tCr (272.1 ± 25.2 versus 303.2 ± 31.4; p = 0004) were reduced, while the prefrontal, somatosensory and motor cortex remained unaffected compared to controls. Neuronal pathology in SCA14 detected by MR spectroscopy was restricted to the cerebellum and did not comprise cortical regions. In the cerebellum, we found in addition to signs of neurodegeneration a glutathione reduction, which has been associated with cellular damage by oxidative stress in other neurodegenerative diseases such as Parkinson's disease and Friedreich's ataxia.