Synthesis and metabolism of methylglyoxal, S-D-lactoylglutathione and D-lactate in cancer and Alzheimer's disease. Exploring the crossroad of eternal youth and premature aging

The emerging role of lactate in tumor microenvironment and its clinical relevance

In recent years, the significant impact of lactate in the tumor microenvironment has been greatly documented. Acting not only as an energy substance in tumor metabolism, lactate is also an imperative signaling molecule. It plays key roles in metabolic remodeling, protein lactylation, immunosuppression, drug resistance, epigenetics and tumor metastasis, which has a tight relation with cancer patients' poor prognosis. This review illustrates the roles lactate plays in different aspects of tumor progression and drug resistance. From the comprehensive effects that lactate has on tumor metabolism and tumor immunity, the therapeutic targets related to it are expected to bring new hope for cancer therapy.

Metabolomics and transcriptomics of embryonic livers reveal hypoxia adaptation of Tibetan chickens

BACKGROUND

Exploring the hypoxia adaptation mechanism of Tibetan chicken is of great significance for revealing the survival law of Tibetan chicken and plateau animal husbandry production. To investigate the hypoxia adaptation of Tibetan chickens (TBCs), an integrative metabolomic-transcriptomic analysis of the liver on day 18 of embryonic development was performed. Dwarf laying chickens (DLCs), a lowland breed, were used as a control.

RESULTS

A total of 1,908 metabolites were identified in both TBCs and DLCs. Energy metabolism and amino acid metabolism related differentially regulated metabolites (DRMs) were significantly enriched under hypoxia. Important metabolic pathways including the TCA cycle and arginine and proline metabolism were screened; PCK1, SUCLA2, and CPS1 were found to be altered under hypoxic conditions. In addition, integrated analysis suggested potential differences in mitochondrial function, which may play a crucial role in the study of chicken oxygen adaptation.

CONCLUSIONS

These results suggest that hypoxia changed the gene expression and metabolic patterns of embryonic liver of TBCs compared to DLCs. Our study provides a basis for uncovering the molecular regulation mechanisms of hypoxia adaptation in TBCs with the potential application of hypoxia adaptation research for other animals living on the Qinghai-Tibet plateau, and may even contribute to the study of diseases caused by hypoxia.

CDK7-YAP-LDHD axis promotes D-lactate elimination and ferroptosis defense to support cancer stem cell-like properties

Reprogrammed cellular metabolism is essential for maintaining cancer stem cells (CSCs) state. Here, we report that mitochondrial D-lactate catabolism is a necessary initiating oncogenic event during tumorigenesis of esophageal squamous cell carcinoma (ESCC). We discover that cyclin-dependent kinase 7 (CDK7) phosphorylates nuclear Yes-associated protein 1 (YAP) at S127 and S397 sites and enhances its transcription function, which promotes D-lactate dehydrogenase (LDHD) protein expression. Moreover, LDHD is enriched significantly in ESCC-CSCs rather than differentiated tumor cells and high LDHD status is connected with poor prognosis in ESCC patients. Mechanistically, the CDK7-YAP-LDHD axis helps ESCC-CSCs escape from ferroptosis induced by D-lactate and generates pyruvate to satisfy energetic demands for their elevated self-renewal potential. Hence, we conclude that esophageal CSCs adopt a D-lactate elimination and pyruvate accumulation mode dependent on CDK7-YAP-LDHD axis, which drives stemness-associated hallmarks of ESCC-CSCs. Reasonably, targeting metabolic checkpoints may serve as an effective strategy for ESCC therapy.

Early detection of plasma d-lactate: Toward a new highly-specific biomarker of bacteraemia?

Background

Bloodstream infections are a leading cause of mortality. Their detection relies on blood cultures (BCs) but time to positivity is often between tens of hours and days. d-lactate is a metabolite widely produced by bacteria but very few in human. We aimed to evaluate d-lactate, d-lactate/l-lactate ratio and d-lactate/total lactate ratio in plasma as potential early biomarkers of bacteraemia on a strictly biological standpoint.

Methods

A total of 228 plasma specimens were collected from patients who had confirmed bacteraemia (n = 131) and healthy outpatients (n = 97). Specific l-lactate and d-lactate analyses were performed using enzymatic assays and analytical performances of d-lactate, d-lactate/total lactate and d-lactate/l-lactate ratios for the diagnosis of bacteraemia were assessed.

Results

A preliminary in vitro study confirmed that all strains of Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus were able to produce d-lactate at significant levels. In patients, plasma d-lactate level was the most specific biomarker predicting a bacteraemia profile with a specificity and predictive positive value of 100% using a cut-off of 131 μmol.L^-1. However, sensitivity and negative predictive value were rather low, estimated at 31% and 52%, respectively. d-lactate displayed an Area Under Receiver Operating Characteristic (AUROC) curve of 0.696 with a P value < 0.0001. There was no difference of d-lactate levels between BCs bottles positive for Gram-positive or Gram-negative bacteria (p = 0.55).

Conclusion

d-lactate shows promise as a specific early biomarker of bacterial metabolism. The development of rapid automated assays could raise clinical applications for infectious diseases diagnosis including early bacteraemia prediction.

Lactate and Lactylation in the Brain: Current Progress and Perspectives

As the final product of glycolysis, lactate features not only as an energy substrate, a metabolite, and a signaling molecule in a variety of diseases-such as cancer, inflammation, and sepsis-but also as a regulator of protein lactylation; this is a newly proposed epigenetic modification that is considered to be crucial for energy metabolism and signaling in brain tissues under both physiological and pathological conditions. In this review, evidence on lactylation from studies on lactate metabolism and disease has been summarized, revealing the function of lactate and its receptors in the regulation of brain function and summarizing the levels of lactylation expression in various brain diseases. Finally, the function of lactate and lactylation in the brain and the potential mechanisms of intervention in brain diseases are presented and discussed, providing optimal perspectives for future research on the role of lactylation in the brain.

Highly sensitive spectrofluorimetric method for the determination of the genotoxic methylglyoxal in glycerol-containing pharmaceuticals and dietary supplements

Methylglyoxal (MGO) is a genotoxic α-dicarbonyl compound. Recently, it was found to be formed in glycerol preparations during storage through auto-oxidation. A simple fluorimetric determination of the carcinogenic degradation product of glycerol, MGO, was developed and validated. The proposed method is based on the derivatization of MGO with 4-carbomethoxybenzaldehyde (CMBA) and ammonium acetate to yield a fluorescent imidazole derivative that can be measured at 415 nm after excitation at 322 nm. The optimized conditions were determined to be 0.2 M CMBA, 1.0 M ammonium acetate and a reaction time of 40 min at 90°C using ethanol as diluting solvent. The linear range was 10.0-200.0 ng/ml. Detection and quantification limits were 2.22 and 6.72 ng/ml, respectively. The proposed method was validated according to International Council for Harmonisation (ICH) guidelines and compared with the reported method and no significant difference was found. It was successfully applied for the determination of MGO in six different glycerol-containing pharmaceutical preparations and dietary supplements.

Glyoxalase 2: Towards a Broader View of the Second Player of the Glyoxalase System

Glyoxalase 2 is a mitochondrial and cytoplasmic protein belonging to the metallo-β-lactamase family encoded by the hydroxyacylglutathione hydrolase (HAGH) gene. This enzyme is the second enzyme of the glyoxalase system that is responsible for detoxification of the α-ketothaldehyde methylglyoxal in cells. The two enzymes glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) form the complete glyoxalase pathway, which utilizes glutathione as cofactor in eukaryotic cells. The importance of Glo2 is highlighted by its ubiquitous distribution in prokaryotic and eukaryotic organisms. Its function in the system has been well defined, but in recent years, additional roles are emerging, especially those related to oxidative stress. This review focuses on Glo2 by considering its genetics, molecular and structural properties, its involvement in post-translational modifications and its interaction with specific metabolic pathways. The purpose of this review is to focus attention on an enzyme that, from the most recent studies, appears to play a role in multiple regulatory pathways that may be important in certain diseases such as cancer or oxidative stress-related diseases.

Lactylation, an emerging hallmark of metabolic reprogramming: Current progress and open challenges

Lactate, the end product of glycolysis, efficiently functions as the carbon source, signaling molecules and immune regulators. Lactylation, being regulated by lactate, has recently been confirmed as a novel contributor to epigenetic landscape, not only opening a new era for in-depth exploration of lactate metabolism but also offering key breakpoints for further functional and mechanistic research. Several studies have identified the pivotal role of protein lactylation in cell fate determination, embryonic development, inflammation, cancer, and neuropsychiatric disorders. This review summarized recent advances with respect to the discovery, the derivation, the cross-species landscape, and the diverse functions of lactylation. Further, we thoroughly discussed the discrepancies and limitations in available studies, providing optimal perspectives for future research.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

Lactate Is Answerable for Brain Function and Treating Brain Diseases: Energy Substrates and Signal Molecule

Research to date has provided novel insights into lactate's positive role in multiple brain functions and several brain diseases. Although notable controversies and discrepancies remain, the neurobiological role and the metabolic mechanisms of brain lactate have now been described. A theoretical framework on the relevance between lactate and brain function and brain diseases is presented. This review begins with the source and route of lactate formation in the brain and food; goes on to uncover the regulatory effect of lactate on brain function; and progresses to gathering the application and concentration variation of lactate in several brain diseases (diabetic encephalopathy, Alzheimer's disease, stroke, traumatic brain injury, and epilepsy) treatment. Finally, the dual role of lactate in the brain is discussed. This review highlights the biological effect of lactate, especially L-lactate, in brain function and disease studies and amplifies our understanding of past research.

Role of Lactate in Inflammatory Processes: Friend or Foe

During an inflammatory process, shift in the cellular metabolism associated with an increase in extracellular acidification are well-known features. This pH drop in the inflamed tissue is largely attributed to the presence of lactate by an increase in glycolysis. In recent years, evidence has accumulated describing the role of lactate in inflammatory processes; however, there are differences as to whether lactate can currently be considered a pro- or anti-inflammatory mediator. Herein, we review these recent advances on the pleiotropic effects of lactate on the inflammatory process. Taken together, the evidence suggests that lactate could exert differential effects depending on the metabolic status, cell type in which the effects of lactate are studied, and the pathological process analyzed. Additionally, various targets, including post-translational modifications, G-protein coupled receptor and transcription factor activation such as NF-κB and HIF-1, allow lactate to modulate signaling pathways that control the expression of cytokines, chemokines, adhesion molecules, and several enzymes associated with immune response and metabolism. Altogether, this would explain its varied effects on inflammatory processes beyond its well-known role as a waste product of metabolism.

Design of an activatable NIR-II nanoprobe for the in vivo elucidation of Alzheimer's disease-related variations in methylglyoxal concentrations

A biocompatible Fe3O4 nanoparticle integrating methylglyoxal-activatable NIR-II fluorescent probe and brain-targeting peptide was developed for visualizing Alzheimer's disease (AD)-related methylglyoxal variation in vivo.

The Roles of Coenzyme Q in Disease: Direct and Indirect Involvement in Cellular Functions

Coenzyme Q (CoQ) is a key component of the respiratory chain of all eukaryotic cells. Its function is closely related to mitochondrial respiration, where it acts as an electron transporter. However, the cellular functions of coenzyme Q are multiple: it is present in all cell membranes, limiting the toxic effect of free radicals, it is a component of LDL, it is involved in the aging process, and its deficiency is linked to several diseases. Recently, it has been proposed that coenzyme Q contributes to suppressing ferroptosis, a type of iron-dependent programmed cell death characterized by lipid peroxidation. In this review, we report the latest hypotheses and theories analyzing the multiple functions of coenzyme Q. The complete knowledge of the various cellular CoQ functions is essential to provide a rational basis for its possible therapeutic use, not only in diseases characterized by primary CoQ deficiency, but also in large number of diseases in which its secondary deficiency has been found.

Methylglyoxal affects cognitive behaviour and modulates RAGE and Presenilin-1 expression in hippocampus of aged mice

Methylglyoxal (MG), a potent glycotoxin that can be found in the diet, is one of the main precursors of Advanced glycation end products (AGEs). It is well known that modifications in lifestyle such as nutritional interventions can be of great value for preventing brain deterioration. This study aimed to evaluate in vivo how an oral MG treatment, that mimics a high MG dietary intake, could affect brain health. From our results, we demonstrated that MG administration affected working memory, and induced neuroinflammation and oxidative stress by modulating the Receptor for Advanced glycation end products (RAGE). The gene and protein expressions of RAGE were increased in the hippocampus of MG mice, an area where the activity of glyoxalase 1, one of the main enzymes involved in MG detoxification, was found reduced. Furthermore, at hippocampus level, MG mice showed increased expression of proinflammatory cytokines and increased activities of NADPH oxidase and catalase. MG administration also increased the gene and protein expressions of Presenilin-1, a subunit of the gamma-secretase protein complex linked to Alzheimer's disease. These findings suggest that high MG oral intake induces alteration directly in the brain and might establish an environment predisposing to AD-like pathological conditions.

Untargeted and targeted metabolomics profiling reveals the underlying pathogenesis and abnormal arachidonic acid metabolism in laying hens with fatty liver hemorrhagic syndrome

As a metabolic disease, fatty liver hemorrhagic syndrome (FLHS) has become the major factor responsible for the noninfectious cause of mortality in laying hens, which lead to huge economic losses to poultry industry. However, the pathogenesis of FLHS remains unclear. The aim of present study was to identify novel liver metabolites associated with FLHS. Twenty healthy Chinese commercial Jing Fen laying hens aged 90 d were used in present study. After acclimatization for 2 wk, the hens were divided into 2 treatments (n = 10): control group (normal diet) and FLHS group (high-energy low-protein diet). The experiment lasted for 48 d, and the laying hens were killed for blood and liver sampling at the end of the experiment. Blood biochemical indicators and liver pathological changes were examined. Meanwhile, the changes in liver metabolic profile were investigated with the application of metabolomics approach. Significant increased levels of alanine aminotransferase, aspartate aminotransferase, low density lipoprotein, total cholesterol and triglycerides, decreased high density lipoprotein (P < 0.01), and hepatic steatosis were observed in hens of FLHS group, which suggested FLHS was successfully established in this study. Distinct changes in metabolite patterns in liver between control and FLHS group were observed by partial least-squares discriminant analysis. In total, 42 liver metabolites including tyrosine, glutathione, carnitine, linoleic acid, uric acid, arachidonic acid (ARA), lactate and lysophosphatidylcholine (14: 0) were identified and considered to be related with pathogenesis of FLHS. Pathway analysis revealed that these metabolites were mainly involved in amino acid metabolism, fatty acid metabolism, ARA metabolism, glucose metabolism and glycerophospholipid metabolism. Furthermore, targeted metabolomics found that ARA metabolites such as prostaglandins and hydroxyeicosatetraenoic acids were significantly increased in FLHS group (P < 0.05). In conclusion, our data showed that liver metabolites and ARA metabolism were linked to the pathophysiology of FLHS, which provided a basis for understanding the pathogenesis of FLHS in laying hens.

Mitochondrial Retrograde Signaling Contributes to Metabolic Differentiation in Yeast Colonies

During development of yeast colonies, various cell subpopulations form, which differ in their properties and specifically localize within the structure. Three branches of mitochondrial retrograde (RTG) signaling play a role in colony development and differentiation, each of them activating the production of specific markers in different cell types. Here, aiming to identify proteins and processes controlled by the RTG pathway, we analyzed proteomes of individual cell subpopulations from colonies of strains, mutated in genes of the RTG pathway. Resulting data, along with microscopic analyses revealed that the RTG pathway predominantly regulates processes in U cells, long-lived cells with unique properties, which are localized in upper colony regions. Rtg proteins therein activate processes leading to amino acid biosynthesis, including transport of metabolic intermediates between compartments, but also repress expression of mitochondrial ribosome components, thus possibly contributing to reduced mitochondrial translation in U cells. The results reveal the RTG pathway's role in activating metabolic processes, important in U cell adaptation to altered nutritional conditions. They also point to the important role of Rtg regulators in repressing mitochondrial activity in U cells.

Methylglyoxal Has Different Impacts on the Fungistatic Roles of Ammonia and Benzaldehyde, and Lactoylglutathione Lyase Is Necessary for the Resistance of Arthrobotrys oligospora to Soil Fungistasis

Biocontrol of root-knot nematode has attracted increasing attention over the past two decades. The inconsistent field performance of biocontrol agents, which is caused by soil fungistasis, often restricts their commercial application. There is still a lack of research on the genes involved in biocontrol fungi response to soil fungistasis, which is important for optimizing practical applications of biocontrol fungi. In this study, the lactoylglutathione lyase-encoding AOL_s00004g335 in the nematophagous fungi Arthrobotrys oligospora was knocked out, and three mutant strains were obtained. The hyphal growth of mutants on the three media was almost the same as that of the wild-type strain, but mutants had slightly higher resistance to NaCl, SDS, and H₂O₂. Methylglyoxal (MG) significantly increased the resistance of A. oligospora to ammonia, but decreased the resistance to benzaldehyde. Furthermore, the resistance of the mutants to soil fungistasis was largely weakened and MG could not increase the resistance of A. oligospora to soil fungistasis. Our results revealed that MG has different effects on the fungistatic roles of ammonia and benzaldehyde and that lactoylglutathione lyase is very important for A. oligospora to resist soil fungistasis.

Aerobic co-oxidation of hemoglobin and aminoacetone, a putative source of methylglyoxal

Aminoacetone (1-aminopropan-2-one), a putative minor biological source of methylglyoxal, reacts like other α-aminoketones such as 6-aminolevulinic acid (first heme precursor) and 1,4-diaminobutanone (a microbicide) yielding electrophilic α-oxoaldehydes, ammonium ion and reactive oxygen species by metal- and hemeprotein-catalyzed aerobic oxidation. A plethora of recent reports implicates triose phosphate-generated methylglyoxal in protein crosslinking and DNA addition, leading to age-related disorders, including diabetes. Importantly, methylglyoxal-treated hemoglobin adds four water-exposed arginine residues, which may compromise its physiological role and potentially serve as biomarkers for diabetes. This paper reports on the co-oxidation of aminoacetone and oxyhemoglobin in normally aerated phosphate buffer, leading to structural changes in hemoglobin, which can be attributed to the addition of aminoacetone-produced methylglyoxal to the protein. Hydroxyl radical-promoted chemical damage to hemoglobin may also occur in parallel, which is suggested by EPR-spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide and ethanol. Concomitantly, oxyhemoglobin is oxidized to methemoglobin, as indicated by characteristic CD spectral changes in the Soret and visible regions. Overall, these findings may contribute to elucidate the molecular mechanisms underlying human diseases associated with hemoglobin dysfunctions and with aminoacetone in metabolic alterations related to excess glycine and threonine.

Interplay among Oxidative Stress, Methylglyoxal Pathway and S-Glutathionylation

Reactive oxygen species (ROS) are produced constantly inside the cells as a consequence of nutrient catabolism. The balance between ROS production and elimination allows to maintain cell redox homeostasis and biological functions, avoiding the occurrence of oxidative distress causing irreversible oxidative damages. A fundamental player in this fine balance is reduced glutathione (GSH), required for the scavenging of ROS as well as of the reactive 2-oxoaldehydes methylglyoxal (MGO). MGO is a cytotoxic compound formed constitutively as byproduct of nutrient catabolism, and in particular of glycolysis, detoxified in a GSH-dependent manner by the glyoxalase pathway consisting in glyoxalase I and glyoxalase II reactions. A physiological increase in ROS production (oxidative eustress, OxeS) is promptly signaled by the decrease of cellular GSH/GSSG ratio which can induce the reversible S-glutathionylation of key proteins aimed at restoring the redox balance. An increase in MGO level also occurs under oxidative stress (OxS) conditions probably due to several events among which the decrease in GSH level and/or the bottleneck of glycolysis caused by the reversible S-glutathionylation and inhibition of glyceraldehyde-3-phosphate dehydrogenase. In the present review, it is shown how MGO can play a role as a stress signaling molecule in response to OxeS, contributing to the coordination of cell metabolism with gene expression by the glycation of specific proteins. Moreover, it is highlighted how the products of MGO metabolism, S-D-lactoylglutathione (SLG) and D-lactate, which can be taken up and metabolized by mitochondria, could play important roles in cell response to OxS, contributing to cytosol-mitochondria crosstalk, cytosolic and mitochondrial GSH pools, energy production, and the restoration of the GSH/GSSG ratio. The role for SLG and glyoxalase II in the regulation of protein function through S-glutathionylation under OxS conditions is also discussed. Overall, the data reported here stress the need for further studies aimed at understanding what role the evolutionary-conserved MGO formation and metabolism can play in cell signaling and response to OxS conditions, the aberration of which may importantly contribute to the pathogenesis of diseases associated to elevated OxS.

Metabolic Dysregulation Contributes to the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease. Numerous studies have demonstrated a critical role for dysregulated glucose metabolism in its pathogenesis. In this review, we summarize metabolic alterations in aging brain and AD-related metabolic deficits associated with glucose metabolism dysregulation, glycolysis dysfunction, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS) deficits, and pentose phosphate pathway impairment. Additionally, we discuss recent treatment strategies targeting metabolic defects in AD, including their limitations, in an effort to encourage the development of novel therapeutic strategies.

Protection of Polyphenols against Glyco-Oxidative Stress: Involvement of Glyoxalase Pathway

Chronic high glucose (HG) exposure increases methylglyoxal (MGO)-derived advanced glycation end-products (AGEs) and is involved in the onset of pathological conditions, such as diabetes, atherosclerosis and chronic-degenerative diseases. Under physiologic conditions the harmful effects of MGO are contrasted by glyoxalase system that is implicated in the detoxification of Reactive Carbonyl Species (RCS) and maintain the homeostasis of the redox environment of the cell. Polyphenols are the most abundant antioxidants in the diet and present various health benefits. Aims of the study were to investigate the effects of HG-chronic exposure on glyco-oxidation and glyoxalase system in intestinal cells, using CaCo-2 cells. Moreover, we studied the effect of apple polyphenols on glyco-oxidative stress. Our data demonstrated that HG-treatment triggers glyco-oxidation stress with a significant increase in intracellular Reactive Oxygen Species (ROS), lipid peroxidation, AGEs, and increase of Glyoxalase I (GlxI) activity. On the contrary, Glyoxalase II (GlxII) activity was lower in HG-treated cells. We demonstrate that apple polyphenols exert a protective effect against oxidative stress and dicarbonyl stress. The increase of total antioxidant capacity and glutathione (GSH) levels in HG-treated cells in the presence of apple polyphenols was associated with a decrease of GlxI activity.

Mitochondrial Glutathione: Recent Insights and Role in Disease

Mitochondria are the main source of reactive oxygen species (ROS), most of them deriving from the mitochondrial respiratory chain. Among the numerous enzymatic and non-enzymatic antioxidant systems present in mitochondria, mitochondrial glutathione (mGSH) emerges as the main line of defense for maintaining the appropriate mitochondrial redox environment. mGSH’s ability to act directly or as a co-factor in reactions catalyzed by other mitochondrial enzymes makes its presence essential to avoid or to repair oxidative modifications that can lead to mitochondrial dysfunction and subsequently to cell death. Since mitochondrial redox disorders play a central part in many diseases, harboring optimal levels of mGSH is vitally important. In this review, we will highlight the participation of mGSH as a contributor to disease progression in pathologies as diverse as Alzheimer’s disease, alcoholic and non-alcoholic steatohepatitis, or diabetic nephropathy. Furthermore, the involvement of mitochondrial ROS in the signaling of new prescribed drugs and in other pathologies (or in other unmet medical needs, such as gender differences or coronavirus disease of 2019 (COVID-19) treatment) is still being revealed; guaranteeing that research on mGSH will be an interesting topic for years to come.

Quantitative Evaluation of D-Lactate Pathophysiology: New Insights into the Mechanisms Involved and the Many Areas in Need of Further Investigation

In contrast to L-lactate, D-lactate is produced in minimal quantities by human cells, and the plasma D-lactate concentration normally is maintained at a concentration of only about 0.01 mM. However, in short bowel syndrome, colonic bacterial production of D-lactate may lead to plasma concentrations >3mM with accompanying acidosis and neurological symptoms - a syndrome known as D-lactic acidosis. Minor increases in plasma D-lactate have been observed in various gastrointestinal conditions such as ischemia, appendicitis and Crohn's disease, a finding touted to have diagnostic utility. The novel aspect of this review paper is the application of numerical values to the processes involved in D-lactate homeostasis that previously have been described only in qualitative terms. This approach provides a number of new insights into normal and disordered production, catabolism and excretion of D-lactate, and identifies multiple gaps in our understanding of D-lactate physiology that should be amenable to relatively simple investigative study.

Interplay between NADH oxidation by complex I, glutathione redox state and sirtuin-3, and its role in the development of insulin resistance

Metabolic diseases are characterized by high NADH/NAD⁺ ratios due to excessive electron supply, causing defective mitochondrial function and impaired sirtuin-3 (SIRT-3) activity, the latter driving to oxidative stress and altered fatty acid β-oxidation. NADH is oxidized by the complex I in the electron transport chain, thereby factors inhibiting complex I like acetylation, cardiolipin peroxidation, and glutathionylation by low GSH/GSSG ratios affects SIRT3 function by increasing the NADH/NAD⁺ ratio. In this review, we summarized the evidence supporting a role of the above events in the development of insulin resistance, which is relevant in the pathogenesis of obesity and diabetes. We propose that maintenance of proper NADH/NAD⁺ and GSH/GSSG ratios are central to ameliorate insulin resistance, as alterations in these redox couples lead to complex I dysfunction, disruption of SIRT-3 activity, ROS production and impaired β-oxidation, the latter two being key effectors of insulin resistance.

Dicarbonyl Stress and S-Glutathionylation in Cerebrovascular Diseases: A Focus on Cerebral Cavernous Malformations

Dicarbonyl stress is a dysfunctional state consisting in the abnormal accumulation of reactive α-oxaldehydes leading to increased protein modification. In cells, post-translational changes can also occur through S-glutathionylation, a highly conserved oxidative post-translational modification consisting of the formation of a mixed disulfide between glutathione and a protein cysteine residue. This review recapitulates the main findings supporting a role for dicarbonyl stress and S-glutathionylation in the pathogenesis of cerebrovascular diseases, with specific emphasis on cerebral cavernous malformations (CCM), a vascular disease of proven genetic origin that may give rise to various clinical signs and symptoms at any age, including recurrent headaches, seizures, focal neurological deficits, and intracerebral hemorrhage. A possible interplay between dicarbonyl stress and S-glutathionylation in CCM is also discussed.

SIRT1-Dependent Upregulation of Antiglycative Defense in HUVECs Is Essential for Resveratrol Protection against High Glucose Stress

Uncontrolled accumulation of methylglyoxal (MG) and reactive oxygen species (ROS) occurs in hyperglycemia-induced endothelial dysfunction associated with diabetes. Resveratrol (RSV) protects the endothelium upon high glucose (HG); however, the mechanisms underlying such protective effects are still debated. Here we identified key molecular players involved in the glycative/oxidative perturbations occurring in endothelial cells exposed to HG. In addition, we determined whether RSV essentially required SIRT1 to trigger adaptive responses in HG-challenged endothelial cells. We used primary human umbilical vein endothelial cells (HUVECs) undergoing a 24-h treatment with HG, with or without RSV and EX527 (i.e., SIRT1 inhibitor). We found that HG-induced glycative stress (GS) and oxidative stress (OS), by reducing SIRT1 activity, as well as by diminishing the efficiency of MG- and ROS-targeting protection. RSV totally abolished the HG-dependent cytotoxicity, and this was associated with SIRT1 upregulation, together with increased expression of GLO1, improved ROS-scavenging efficiency, and total suppression of HG-related GS and OS. Interestingly, RSV failed to induce effective response to HG cytotoxicity when EX527 was present, thus suggesting that the upregulation of SIRT1 is essential for RSV to activate the major antiglycative and antioxidative defense and avoid MG- and ROS-dependent molecular damages in HG environment.

Preliminary Characterization of a Ni2+-Activated and Mycothiol-Dependent Glyoxalase I Enzyme from Streptomyces coelicolor

The glyoxalase system consists of two enzymes, glyoxalase I (Glo1) and glyoxalase II (Glo2), and converts a hemithioacetal substrate formed between a cytotoxic alpha-ketoaldehyde, such as methylglyoxal (MG), and an intracellular thiol, such as glutathione, to a non-toxic alpha-hydroxy acid, such as d-lactate, and the regenerated thiol. Two classes of Glo1 have been identified. The first is a Zn2+-activated class and is exemplified by the Homo sapiens Glo1. The second class is a Ni2+-activated enzyme and is exemplified by the Escherichia coli Glo1. Glutathione is the intracellular thiol employed by Glo1 from both these sources. However, many organisms employ other intracellular thiols. These include trypanothione, bacillithiol, and mycothiol. The trypanothione-dependent Glo1 from Leishmania major has been shown to be Ni2+-activated. Genetic studies on Bacillus subtilis and Corynebacterium glutamicum focused on MG resistance have indicated the likely existence of Glo1 enzymes employing bacillithiol or mycothiol respectively, although no protein characterizations have been reported. The current investigation provides a preliminary characterization of an isolated mycothiol-dependent Glo1 from Streptomyces coelicolor. The enzyme has been determined to display a Ni2+-activation profile and indicates that Ni2+-activated Glo1 are indeed widespread in nature regardless of the intracellular thiol employed by an organism.