Studies of erythrocyte glyoxalase II in various domestic species: discovery of glyoxalase II deficiency in the horse

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.

Diet and Obesity-Induced Methylglyoxal Production and Links to Metabolic Disease

The obesity rate in the United States is 42.4% and has become a national epidemic. Obesity is a complex condition that is influenced by socioeconomic status, ethnicity, genetics, age, and diet. Increased consumption of a Western diet, one that is high in processed foods, red meat, and sugar content, is associated with elevated obesity rates. Factors that increase obesity risk, such as socioeconomic status, also increase consumption of a Western diet because of a limited access to healthier options and greater affordability of processed foods. Obesity is a public health threat because it increases the risk of several pathologies, including atherosclerosis, diabetes, and cancer. The molecular mechanisms linking obesity to disease onset and progression are not well understood, but a proposed mechanism is physiological changes caused by altered lipid peroxidation, glycolysis, and protein metabolism. These metabolic pathways give rise to reactive molecules such as the abundant electrophile methylglyoxal (MG), which covalently modifies nucleic acids and proteins. MG-adducts are associated with obesity-linked pathologies and may have potential for biomonitoring to determine the risk of disease onset and progression. MG-adducts may also play a role in disease progression because they are mutagenic and directly impact protein stability and function. In this review, we discuss how obesity drives metabolic alterations, how these alterations lead to MG production, the association of MG-adducts with disease, and the potential impact of MG-adducts on cellular function.

De novo transcriptome analysis of Rhizophora mucronata Lam. furnishes evidence for the existence of glyoxalase system correlated to glutathione metabolic enzymes and glutathione regulated transporter in salt tolerant mangroves

The accumulation of a metabolic by product - methylglyoxal above a minimal range can be highly toxic in all organisms. Stress induced elevation in methylglyoxal inactivates proteins and nucleic acids. Glutathione dependent glyoxalase enzymes like glyoxalase I and glyoxalase II together with glutathione independent glyoxalase III play inevitable role in methylglyoxal detoxification. Glyoxalase genes are generally conserved but with obvious exceptions. Mangroves being potent harsh land inhabitants, their internal organelles are constantly been exposed to elevated levels of methylglyoxal. First and foremost it is important to detect the presence of glyoxalases in mangroves. De novo transcriptome analysis of mangrove species Rhizophora mucronata Lam., identified eleven putative glyoxalase proteins (RmGLYI-1 to 5, RmGLYII-1 to 5 and RmGLYIII). Molecular characterization proposed PLN02300 or PLN02367 as the key domains of RmGLYI proteins. They possess molecular weight ranging from 26.45 to 32.53 kDa and may localize in cytosol or chloroplast. RmGLYII proteins of molecular weight 28.64-36 kDa, carrying PLN02398 or PLN02469 domains are expected to be localized in diverse cellular compartments. Cytosolic RmGLYIII with DJ-1/PfpI domain carries a molecular weight 26.4 kDa. Detailed structural analysis revealed monomeric nature of RmGLYI-1 and RmGLYII-1 whereas RmGLYIII is found to be homodimer. Molecular phylogenetic analysis and multiple sequence alignment specified conserved metal ion/substrate binding residues of RmGLY proteins. Estimation of relative expression of glyoxalases under salt stress indicated the prominence of RmGLYI and RmGLYII over RmGLYIII. The aforementioned prominence is supported by salt induced expression difference of glutathione metabolic enzymes and glutathione regulated transporter protein.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

A Hypothesis: Moderate Consumption of Alcohol Contributes to Lower Prevalence of Type 2 Diabetes Due to the Scavenging of Alpha-Dicarbonyls by Dietary Polyphenols

The world is experiencing an epidemic of type-2-diabetes mellitus (T2DM). This has led to increased morbidity and mortality, explosive growth in health care budgets, and an even greater adverse, if indirect, impact on societies and economies of affected countries. While genetic susceptibility to T2DM is a major determinant of its prevalence, changes in lifestyles also play a role. One such change has been a transition from traditional diets characterized by low caloric and high nutrient density to calorie-rich but nutrient-poor Western diets. Given this, one solution to the epidemic of T2DM would be to abandon Western diets and revert to traditional eating patterns. However, traditional diets cannot provide enough calories for the increasing global population, so transition from traditional to Western foodstuffs appears to be irreversible. Consequently, the only practical solution to problems caused by these changes is to modify Western diets, possibly by supplementing them with functional foods containing nutrients that would compensate for these dietary deficits. I present in this study a hypothesis to explain why shifts from traditional to Western diets have been so problematic and to suggest nutrients that may counteract these adverse effects. I postulate that the components of traditional diets that may compensate for deficiencies of Westerns diets are scavengers of reactive α-dicarbonyls produced as unavoidable by-products of glucose and lipid metabolism. Most important among these scavengers are some plant secondary metabolites: polyphenols, phlorotannins, and carotenoids. They are found in alcoholic beverages and are abundant in seasonings, cocoa, coffee, tea, whole grains, pigmented vegetables, fruits, and berries.

Presence of unique glyoxalase III proteins in plants indicates the existence of shorter route for methylglyoxal detoxification

Glyoxalase pathway, comprising glyoxalase I (GLY I) and glyoxalase II (GLY II) enzymes, is the major pathway for detoxification of methylglyoxal (MG) into D-lactate involving reduced glutathione (GSH). However, in bacteria, glyoxalase III (GLY III) with DJ-1/PfpI domain(s) can do the same conversion in a single step without GSH. Our investigations for the presence of DJ-1/PfpI domain containing proteins in plants have indicated the existence of GLY III-like proteins in monocots, dicots, lycopods, gymnosperm and bryophytes. A deeper in silico analysis of rice genome identified twelve DJ-1 proteins encoded by six genes. Detailed analysis has been carried out including their chromosomal distribution, genomic architecture and localization. Transcript profiling under multiple stress conditions indicated strong induction of OsDJ-1 in response to exogenous MG. A member of OsDJ-1 family, OsDJ-1C, showed high constitutive expression at all developmental stages and tissues of rice. MG depletion study complemented by simultaneous formation of D-lactate proved OsDJ-1C to be a GLY III enzyme that converts MG directly into D-lactate in a GSH-independent manner. Site directed mutagenesis of Cys-119 to Alanine significantly reduces its GLY III activity indicating towards the existence of functional GLY III enzyme in rice—a shorter route for MG detoxification.

The role of methylglyoxal and the glyoxalase system in diabetes and other age-related diseases

The formation and accumulation of advanced glycation endproducts (AGEs) are related to diabetes and other age-related diseases. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is the major precursor in the formation of AGEs. MGO is mainly formed as a byproduct of glycolysis. Under physiological circumstances, MGO is detoxified by the glyoxalase system into D-lactate, with glyoxalase I (GLO1) as the key enzyme in the anti-glycation defence. New insights indicate that increased levels of MGO and the major MGO-derived AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1), and dysfunctioning of the glyoxalase system are linked to several age-related health problems, such as diabetes, cardiovascular disease, cancer and disorders of the central nervous system. The present review summarizes the mechanisms through which MGO is formed, its detoxification by the glyoxalase system and its effect on biochemical pathways in relation to the development of age-related diseases. Although several scavengers of MGO have been developed over the years, therapies to treat MGO-associated complications are not yet available for application in clinical practice. Small bioactive inducers of GLO1 can potentially form the basis for new treatment strategies for age-related disorders in which MGO plays a pivotal role.

The glyoxalase pathway: the first hundred years... and beyond

The discovery of the enzymatic formation of lactic acid from methylglyoxal dates back to 1913 and was believed to be associated with one enzyme termed ketonaldehydemutase or glyoxalase, the latter designation prevailed. However, in 1951 it was shown that two enzymes were needed and that glutathione was the required catalytic co-factor. The concept of a metabolic pathway defined by two enzymes emerged at this time. Its association to detoxification and anti-glycation defence are its presently accepted roles, since methylglyoxal exerts irreversible effects on protein structure and function, associated with misfolding. This functional defence role has been the rationale behind the possible use of the glyoxalase pathway as a therapeutic target, since its inhibition might lead to an increased methylglyoxal concentration and cellular damage. However, metabolic pathway analysis showed that glyoxalase effects on methylglyoxal concentration are likely to be negligible and several organisms, from mammals to yeast and protozoan parasites, show no phenotype in the absence of one or both glyoxalase enzymes. The aim of the present review is to show the evolution of thought regarding the glyoxalase pathway since its discovery 100 years ago, the current knowledge on the glyoxalase enzymes and their recognized role in the control of glycation processes.

Quantitative assessment of the glyoxalase pathway in Leishmania infantum as a therapeutic target by modelling and computer simulation

The glyoxalase pathway of Leishmania infantum was kinetically characterized as a trypanothione-dependent system. Using time course analysis based on parameter fitting with a genetic algorithm, kinetic parameters were estimated for both enzymes, with trypanothione derived substrates. A K(m) of 0.253 mm and a V of 0.21 micromol.min(-1).mg(-1)for glyoxalase I, and a K(m) of 0.098 mm and a V of 0.18 micromol.min(-1).mg(-1) for glyoxalase II, were obtained. Modelling and computer simulation were used for evaluating the relevance of the glyoxalase pathway as a potential therapeutic target by revealing the importance of critical parameters of this pathway in Leishmania infantum. A sensitivity analysis of the pathway was performed using experimentally validated kinetic models and experimentally determined metabolite concentrations and kinetic parameters. The measurement of metabolites in L. infantum involved the identification and quantification of methylglyoxal and intracellular thiols. Methylglyoxal formation in L. infantum is nonenzymatic. The sensitivity analysis revealed that the most critical parameters for controlling the intracellular concentration of methylglyoxal are its formation rate and the concentration of trypanothione. Glyoxalase I and II activities play only a minor role in maintaining a low intracellular methylglyoxal concentration. The importance of the glyoxalase pathway as a therapeutic target is very small, compared to the much greater effects caused by decreasing trypanothione concentration or increasing methylglyoxal concentration.

Methylglyoxal in living organisms: chemistry, biochemistry, toxicology and biological implications

Despite the growing interest towards methylglyoxal and glyoxalases their real role in metabolic network is still obscure. In the light of developments several reviews have been published in this field mainly dealing with only a narrow segment of this research area. In this article a trial is made to present a comprehensive overview of methylglyoxal research, extending discussion from chemistry to biological implications by reviewing some important characteristics of methylglyoxal metabolism and toxicity in a wide variety of species, and emphasizing the action of methylglyoxal on energy production, free radical generation and cell killing. Special attention is paid to the discussion of alpha-oxoaldehyde production in the environment as a potential risk factor and to the possible role of this a-dicarbonyl in diseases. Concerning the interaction of methylglyoxal with biological macromolecules (DNA, RNA, proteins) an earlier review (Kalapos, Toxicology Letters, 73, 1994, 3-24) means a supplementation to this paper, thus hoping the avoidance of unnecessary bombast. The paper arrives at the conclusion that since the early stage of evolution the function of methylglyoxalase pathway has been related to carbohydrate metabolism, but its significance has been changed over the thousands of years. Namely, at the beginning of evolution methylglyoxalase path was essential for the reductive citric acid cycle as an anaplerotic route, while in the extant metabolism it concerns with the detoxification of methylglyoxal and plays some regulatory role in triose-phosphate household. As there is a tight junction between methylglyoxal and carbohydrate metabolism its pathological role in the events of the development of diabetic complications emerges in a natural manner and further progress is hoped in this field. In contrast, significant advancement cannot be expected in relation to cancer research.

Glyoxalase 2 deficiency in the erythrocytes of a horse: 1H NMR studies of enzyme kinetics and transport of S-lactoylglutathione

In mammalian red blood cells the metabolism of methylglyoxal, and some alpha-ketoaldehydes, takes place via two, generally, highly active enzymes, glyoxalase 1 and 2. The 1H NMR spin-echo spectra of horse erythrocytes, and the various reactants in the glyoxalase system, were characterized as a prelude to obtaining series of spectra in time courses of methylglyoxal metabolism. We characterized the kinetics of the enzyme system in red cells from a normal horse and also from one which had very low activity of glyoxylase 2. The kinetics of the reaction scheme, with methylglyoxal as the starting substrate, were obtained from 1H NMR spectra and analyzed with a computer model of the scheme. The most salient feature of the normal system was the very high feed-forward inhibition (KiHTA = 0.1 microM) of glyoxalase 2 by the hemithioacetal which is the substrate of glyoxalase 1. The glyoxalase-2-deficient red cells were used to test whether S-lactoylglutathione is transported from red cells via the glutathione-S-conjugate transporter; this transport appeared not to occur. Because methylglyoxal is extremely rapidly removed (half-life, approximately 5 min) from normal red cells, it is difficult to assess the effect of this compound on glycolysis but the slow decline evident in the deficient cells allowed a study of the effects on L-lactate production; no effects were apparent.

Genetic heterogeneity of S-formylglutathione hydrolase

S-formylglutathione hydrolase from erythrocytes has been studied by an electrophoretic technique. Three phenotypes were observed in a number of racial groups. The electrophoretic polymorphism was shown to be the product of two alleles at a single locus termed FGH. The product of the type 2 allele was found to be relatively unstable.