Mind the Anion Gap: 5-Oxoproline-Induced High Anion Gap Metabolic Acidosis in End-Stage Renal Disease.

A rare complication, 5-oxoproline-induced high anion gap metabolic acidosis (HAGMA) is associated with chronic acetaminophen use, predominantly reported in outpatient settings. However, its occurrence in hospitalized patients, particularly those with end-stage renal disease (ESRD), remains underreported. We present a case of a 74-year-old female with ESRD on hemodialysis who developed HAGMA highly suspicious for 5-oxoproline toxicity from acetaminophen usage following cardiac surgery. Despite a standard analgesic dose, the patient's renal impairment likely predisposed her to 5-oxoproline accumulation, resulting in severe metabolic acidosis. Discontinuation of acetaminophen led to the resolution of HAGMA, highlighting the importance of recognizing this rare but potentially life-threatening complication in the inpatient and critical care setting. This case suggests a potential interaction between acetaminophen metabolism and renal dysfunction in the pathogenesis of 5-oxoproline-induced HAGMA.

Pyroglutamate acidosis 2023. A review of 100 cases.

This review concerns the rare, acquired, usually iatrogenic, high-anion-gap metabolic acidosis, pyroglutamic acidosis. Pyroglutamate is a derivative of the amino acid glutamate, and is an intermediate in the 'glutathione cycle', by which glutathione is continuously synthesized and broken down. The vast majority of pyroglutamic acidosis cases occur in patients on regular, therapeutic doses of paracetamol. In about a third of cases, flucloxacillin is co-prescribed. In addition, the patients are almost always seriously unwell in other ways, typically with under-nourishment of some form. Paracetamol, with underlying disorders, conspires to divert the glutathione cycle, leading to the overproduction of pyroglutamate. Hypokalaemia is seen in about a third of cases. Once the diagnosis is suspected, it is simple to stop the paracetamol and change the antibiotic (if flucloxacillin is present), pending biochemistry. N-acetyl-cysteine can be given, but while the biochemical justification is compelling, the clinical evidence base is anecdotal.

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.

Synthesis and Assessment of Antiplatelet and Antithrombotic Activity of 4-Amino-Substituted 5-Oxoproline Amides and Peptides.

Venous thromboembolism is a serious problem because it significantly increases the risk of developing vascular complications in elderly patients with obesity or immobilization, cancer, and many other diseases. Thus, there is a need to study new therapeutic strategies, including new medicinal agents for the efficient and safe correction of thrombus disorders. In this work, we have synthesized a number of new amides and peptides of 4-amino-5-oxoprolines and studied their antiplatelet and antithrombotic activity in experiments in vitro and in vivo. It has been found that the newly obtained compounds slow down the process of thrombus formation in a model of arterial and venous thrombosis, without affecting plasma hemostasis parameters. (2S,4S)-4-Amino-1-(4-fluorophenyl)-5-oxoprolyl-(S)-phenylalanine proved to be the most efficient among the studied derivatives. The results obtained indicate the advisability of further studies on 5-oxoproline derivatives in order to design pharmaceutical agents for the prevention and treatment of the consequences of thrombosis.

Identification of the γ-glutamyl cycle as a novel therapeutic target and 5-oxoproline as a new biomarker for diagnosing pancreatic cancer.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignant solid tumours, and abnormal metabolic reprogramming in the tumour microenvironment is regarded as an important contributor to its pathogenesis. OBJECTIVES: As there is an urgency to identify new targets based on the metabolic features that are highly refractory to PDAC treatment, this study aimed to identify suitable therapeutic targets for PDAC. METHODS: In this study, gene set enrichment and Kyoto Encyclopedia of Genes and Genomes analyses were performed on 163 PDAC tissue samples and 165 normal pancreatic tissue samples from The Cancer Genome Atlas and Genotype-Tissue Expression databases to identify alterations in critical metabolites that may contribute to PDAC pathogenesis. Furthermore, ultra-performance liquid chromatography-tandem mass spectrometry was performed to identify significant metabolic pathways between 24 pairs of tumour and adjacent non-tumour tissues and between serum samples from PDAC patients and healthy donors. RESULTS: Fifty-one tissue metabolites and 26 serum metabolites were altered in PDAC. Among them, those in the γ-glutamyl cycle were the most substantially changed, and 5-oxoproline was the biomarker of PDAC with the most significantly decreased levels. CONCLUSIONS: The γ-glutamyl cycle and 5-oxoproline might be potential biomarkers and therapeutic targets to improve the diagnosis, therapy, and prognosis of PDAC.

Characterization of glutathione-specific gamma glutamyl cyclotransferase (ChaC) in Bombyx mori.

Glutathione (GSH) contributes to redox maintenance and detoxification of various xenobiotic and endogenous substances. γ-glutamyl cyclotransferase (ChaC) is involved in GSH degradation. However, the molecular mechanism underlying GSH degradation in silkworms (Bombyx mori) remains unknown. Silkworms are lepidopteran insects that are considered to be an agricultural pest model. We aimed to examine the metabolic mechanism underlying GSH degradation mediated by B. mori ChaC and successfully identified a novel ChaC gene in silkworms (herein, bmChaC). The amino acid sequence and phylogenetic tree revealed that bmChaC was closely related to mammalian ChaC2. We overexpressed recombinant bmChaC in Escherichia coli, and the purified bmChaC showed specific activity toward GSH. Additionally, we examined the degradation of GSH to 5-oxoproline and cysteinyl glycine via liquid chromatography-tandem mass spectrometry. Quantitative real-time polymerase chain reaction revealed that bmChaC mRNA expression was observed in various tissues. Our results suggest that bmChaC participates in tissue protection via GSH homeostasis. This study provides new insights into the activities of ChaC and the underlying molecular mechanisms that can aid the development of insecticides to control agricultural pests.

Bone Marrow Mesenchymal Stem Cells Exert Protective Effects After Ischemic Stroke Through Upregulation of Glutathione.

Bone marrow mesenchymal stem cells (BMSCs) have been shown to promote stroke recovery, however, the underlying mechanisms are not well understood. In this study naïve rats were intravenously injected with syngeneic BMSCs to screen for potential differences in brain metabolite spectrum versus vehicle-treated controls by capillary electrophoresis-mass spectrometry. A total of 65 metabolites were significantly changed after BMSC treatment. Among them, 5-oxoproline, an intermediate in the biosynthesis of the endogenous glutathione (GSH), was increased. To confirm the obtained results and investigate the metabolic pathways, BMSCs were injected into rats 24 h after middle cerebral artery occlusion (MCAO). Rats receiving vehicle solution and sham-operated animals served as controls. High performance liquid chromatography, reverse transcription-quantitative polymerase chain reaction, and Western blotting revealed that intravenous BMSC application increased the levels of 5-oxoproline and GSH in MCAO rats, as well as the expression of key enzymes involved in GSH synthesis including, gamma-glutamylcyclotransferase and gamma-glutamylcysteine ligase. Subsequent clinical investigation confirmed that acute ischemic stroke patients had higher plasma 5-oxoproline and GSH levels than age- and sex-matched non-stroke controls. The optimal cutoff value for 5-oxoproline diagnosing acute ischemic stroke (≤ 7d) was 3.127 µg/mL (sensitivity, 63.4 %; specificity, 81.2 %) determined by receiver characteristic operator curve. The area under the curve was 0.782 (95 % confidence interval: 0.718-0.845). Our findings indicate that BMSCs play a protective role in ischemic stroke through upregulation of GSH and 5-oxoproline is a potential biomarker for acute ischemic stroke. Ischemic stroke causes oxidative stress and induction of endogenous, glutathione-dependent anti-oxidative mechanisms. 5-oxoproline, an important metabolite in glutathione biosynthesis, could serve as a biomarker of acute ischemic stroke. Moreover, intravenous bone marrow mesenchymal stem cell (BMSC) treatment after experimental stroke upregulates the expression of key enzymes involved in glutathione synthesis, which results in better antioxidative defense and improved stroke outcome.

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.

Cyst fluid metabolites distinguish malignant from benign pancreatic cysts.

OBJECTIVES: Current standard of care imaging, cytology, or cystic fluid analysis cannot reliably differentiate malignant from benign pancreatic cystic neoplasms. This study sought to determine if the metabolic profile of cystic fluid could distinguish benign and malignant lesions, as well as mucinous and non-mucinous lesions. METHODS: Metabolic profiling by untargeted mass spectrometry and quantitative nuclear magnetic resonance was performed in 24 pancreatic cyst fluid from surgically resected samples with pathological diagnoses and clinicopathological correlation. RESULTS: (Iso)-butyrylcarnitine distinguished malignant from benign pancreatic cysts, with a diagnostic accuracy of 89%. (Iso)-butyrylcarnitine was 28-fold more abundant in malignant cyst fluid compared with benign cyst fluid (P=.048). Furthermore, 5-oxoproline (P=.01) differentiated mucinous from non-mucinous cysts with a diagnostic accuracy of 90%, better than glucose (82% accuracy), a previously described metabolite that distinguishes mucinous from non-mucinous cysts. Combined analysis of glucose and 5-oxoproline did not improve the diagnostic accuracy. In comparison, standard of care cyst fluid carcinoembryonic antigen (CEA) and cytology had a diagnostic accuracy of 40% and 60% respectively for mucinous cysts. (Iso)-butyrylcarnitine and 5-oxoproline correlated with cyst fluid CEA levels (P<.0001 and P<.05 respectively). For diagnosing malignant pancreatic cysts, the diagnostic accuracies of cyst size > 3 cm, ≥ 1 high-risk features, cyst fluid CEA, and cytology are 38%, 75%, 80%, and 75%, respectively. CONCLUSIONS: (Iso)-butyrylcarnitine has potential clinical application for accurately distinguishing malignant from benign pancreatic cysts, and 5-oxoproline for distinguishing mucinous from non-mucinous cysts.

Catalytic and structural properties of ATP-dependent caprolactamase from Pseudomonas jessenii.

Caprolactamase is the first enzyme in the caprolactam degradation pathway of Pseudomonas jessenii. It is composed of two subunits (CapA and CapB) and sequence-related to other ATP-dependent enzymes involved in lactam hydrolysis, like 5-oxoprolinases and hydantoinases. Low sequence similarity also exists with ATP-dependent acetone- and acetophenone carboxylases. The caprolactamase was produced in Escherichia coli, isolated by His-tag affinity chromatography, and subjected to functional and structural studies. Activity toward caprolactam required ATP and was dependent on the presence of bicarbonate in the assay buffer. The hydrolysis product was identified as 6-aminocaproic acid. Quantum mechanical modeling indicated that the hydrolysis of caprolactam was highly disfavored (ΔG0 '= 23 kJ/mol), which explained the ATP dependence. A crystal structure showed that the enzyme exists as an (αß)2 tetramer and revealed an ATP-binding site in CapA and a Zn-coordinating site in CapB. Mutations in the ATP-binding site of CapA (D11A and D295A) significantly reduced product formation. Mutants with substitutions in the metal binding site of CapB (D41A, H99A, D101A, and H124A) were inactive and less thermostable than the wild-type enzyme. These residues proved to be essential for activity and on basis of the experimental findings we propose possible mechanisms for ATP-dependent lactam hydrolysis.

Heart failure and the glutathione cycle: an integrated view.

Heart failure results from the heart's inability to carryout ventricular contraction and relaxation, and has now become a worldwide problem. During the onset of heart failure, several signatures are observed in cardiomyocytes that includes fetal reprogramming of gene expression where adult genes are repressed and fetal genes turned on, endoplasmic reticulum stress and oxidative stress. In this short review and analysis, we examine these different phenomenon from the viewpoint of the glutathione cycle and the role of the recently discovered Chac1 enzyme. Chac1, which belongs to the family of γ-glutamylcyclotransferases, is a recently discovered member of the glutathione cycle, being involved in the cytosolic degradation of glutathione. This enzyme is induced during the Endoplasmic Stress response, but also in the developing heart. Owing to its exclusive action on reduced glutathione, its induction leads to an increase in the oxidative redox potential of the cell that also serves as signaling mechanism for calcium ions channel activation. The end product of Chac1 action is 5-oxoproline, and studies with 5-oxoprolinase (OPLAH), an enzyme of the glutathione cycle has revealed that down-regulation of OPLAH can lead to the accumulation of 5-oxproline which is an important factor in heart failure. With these recent findings, we have re-examined the roles and regulation of the enzymes in the glutathione cycle which are central to these responses. We present an integrated view of the glutathione cycle in the cellular response to heart failure.

[The Sour Patient]. / Die saure Patientin.

The Sour Patient Abstract. We report the case of a 75-year-old woman presenting with an elevated anion gap metabolic acidosis. The evaluation proved a 5-oxoprolin acidosis due to acetaminophen in therapeutic dose and concomitant risk factors such as malnutrition, chronic alcohol abuse, renal insufficiency, hepatopathy, and female sex. After stopping paracetamol medication and admission of bicarbonate and N-acetylcysteine, there was a rapid improvement in clinical symptoms and blood analysis.

[Acetaminophen induced 5-oxoproline acidosis: An uncommon case of high anion gap metabolic acidosis]. / Acidose à la 5-oxoproline induite par le paracétamol : une cause rare d'acidose métabolique à trou anionique augmenté.

The most common causes of high anion gap metabolic acidosis (HAGMA) are lactic acidosis, ketoacidosis, and intoxications. Nevertheless, clinicians can be faced with unexplained HAGMA, with a need to look for less common etiologies. We describe a case of 5-oxoproline (pyroglutamate) acidosis due to chronic acetaminophen ingestion at therapeutic dose in a 79-year-old inpatient. The pathophysiology of this condition is detailed, with abnormalities in the gamma-glutamyl cycle due to acetaminophen ingestion and severe chronic morbidities, resulting in glutathione and cysteine deficiency and then accumulation of 5-oxoproline. In HAGMA, when usual causes have been excluded, 5-oxoproline acidosis should be suspected in patients with chronic morbidities and acetaminophen ingestion. This diagnosis should be kept in mind because it generally resolves quickly with cessation of acetaminophen and administration of intravenous fluids.

High anion gap metabolic acidosis induced by cumulation of ketones, L- and D-lactate, 5-oxoproline and acute renal failure.

INTRODUCTION: Frequent causes of high anion gap metabolic acidosis (HAGMA) are lactic acidosis, ketoacidosis and impaired renal function. In this case report, a HAGMA caused by ketones, L- and D-lactate, acute renal failure as well as 5-oxoproline is discussed. CASE PRESENTATION: A 69-year-old woman was admitted to the emergency department with lowered consciousness, hyperventilation, diarrhoea and vomiting. The patient had suffered uncontrolled type 2 diabetes mellitus, underwent gastric bypass surgery in the past and was chronically treated with high doses of paracetamol and fosfomycin. Urosepsis was diagnosed, whilst laboratory analysis of serum bicarbonate concentration and calculation of the anion gap indicated a  HAGMA. L-lactate, D-lactate, ß-hydroxybutyric acid, acetone and 5-oxoproline serum levels were markedly elevated and renal function was impaired. DISCUSSION: We concluded that this case of HAGMA was induced by a variety of underlying conditions: sepsis, hyperglycaemia, prior gastric bypass surgery, decreased renal perfusion and paracetamol intake. Risk factors for 5-oxoproline intoxication present in this case are female gender, sepsis, impaired renal function and uncontrolled type 2 diabetes mellitus. Furthermore, chronic antibiotic treatment with fosfomycin might have played a role in the increased production of 5-oxoproline. CONCLUSION: Paracetamol-induced 5-oxoproline intoxication should be considered as a cause of HAGMA in patients with female gender, sepsis, impaired renal function or uncontrolled type 2 diabetes mellitus, even when other more obvious causes of HAGMA such as lactate, ketones or renal failure can be identified.

Use of anion gap in the evaluation of a patient with metabolic acidosis.

High anion gap (AG) metabolic acidosis, a common laboratory abnormality encountered in clinical practice, frequently is due to accumulation of organic acids such as lactic acid, keto acids, alcohol metabolites, and reduced kidney function. The cause of high AG metabolic acidosis often is established easily using historical and simple laboratory data. Despite this, several challenges in the diagnosis and management of high AG metabolic acidosis remain, including quantifying the increase in AG, understanding the relationship between changes in AG and serum bicarbonate level, and identifying the cause of high AG metabolic acidosis when common causes are ruled out. The present case was selected to highlight the importance of the correction of AG for serum albumin level, the use of actual baseline AG rather than mean normal AG, the relationship between changes in serum bicarbonate level and AG, and a systematic diagnostic approach to uncommon causes of high AG metabolic acidosis, such as 5-oxoproline acidosis (pyroglutamic acidosis).