Glyoxalase I activity and immunoreactivity in the aging human lens

Combined Treatment of Monopolar and Bipolar Radiofrequency Increases Skin Elasticity by Decreasing the Accumulation of Advanced Glycated End Products in Aged Animal Skin

It is well known that skin aging is related to the destruction of collagen and elastin fibers by metalloproteinases (MMPs). Aged fibroblasts have a decreased ability to synthesize collagen and elastin. Nuclear factor erythroid 2-related factor 2 (NRF2) involves glyoxalase (GLO) activation, which inhibits the production of advanced glycated end products (AGE) and the expression of its receptor (RAGE). RAGE increases nuclear transcription factor-kappa B (NF-κB), which upregulates MMPs and decreases skin elasticity. NRF2 also decreases M1 macrophages, which secrete tumor necrosis factor-alpha (TNF-α), thereby decreasing AGE production. It is well known that radiofrequency (RF) decreases skin elasticity by increasing collagen synthesis. We evaluated whether RF increases skin elasticity via NRF2/GLO and whether they decrease AGE and RAGE expression in aged animal skin. We also compared the effects of RF based on the modes (monopolar or bipolar) or the combination used. In aged skin, NRF2, GLO-1, and M2 macrophage expression was decreased, and their expression increased when RF was applied. M1 and TNF-α demonstrated increased expression in the aged skin and decreased expression after RF application. AGE accumulation and RAGE, NF-κB, and MMP2/3/9 expression were increased in the aged skin, and they were decreased by RF. The papillary and reticular fibroblast markers showed decreased expression in young skin and increased expression in aged skin. The densities of collagen and elastin fiber in the aged skin were low, and they were increased by RF. In conclusion, RF leads to increased collagen and elastin fibers by increasing NRF2/GLO-1 and modulating M1/M2 polarization, which leads to decreased AGE and RAGE and, consequently, decreased NF-κB, which eventually slows collagen and elastin destruction. RF also leads to increased collagen and elastin fiber synthesis by increasing papillary and reticular fibroblast expression.

The Glyoxalase System in Age-Related Diseases: Nutritional Intervention as Anti-Ageing Strategy

The glyoxalase system is critical for the detoxification of advanced glycation end-products (AGEs). AGEs are toxic compounds resulting from the non-enzymatic modification of biomolecules by sugars or their metabolites through a process called glycation. AGEs have adverse effects on many tissues, playing a pathogenic role in the progression of molecular and cellular aging. Due to the age-related decline in different anti-AGE mechanisms, including detoxifying mechanisms and proteolytic capacities, glycated biomolecules are accumulated during normal aging in our body in a tissue-dependent manner. Viewed in this way, anti-AGE detoxifying systems are proposed as therapeutic targets to fight pathological dysfunction associated with AGE accumulation and cytotoxicity. Here, we summarize the current state of knowledge related to the protective mechanisms against glycative stress, with a special emphasis on the glyoxalase system as the primary mechanism for detoxifying the reactive intermediates of glycation. This review focuses on glyoxalase 1 (GLO1), the first enzyme of the glyoxalase system, and the rate-limiting enzyme of this catalytic process. Although GLO1 is ubiquitously expressed, protein levels and activities are regulated in a tissue-dependent manner. We provide a comparative analysis of GLO1 protein in different tissues. Our findings indicate a role for the glyoxalase system in homeostasis in the eye retina, a highly oxygenated tissue with rapid protein turnover. We also describe modulation of the glyoxalase system as a therapeutic target to delay the development of age-related diseases and summarize the literature that describes the current knowledge about nutritional compounds with properties to modulate the glyoxalase system.

Consequences of Dicarbonyl Stress on Skeletal Muscle Proteins in Type 2 Diabetes

Skeletal muscle is the largest organ in the body and constitutes almost 40% of body mass. It is also the primary site of insulin-mediated glucose uptake, and skeletal muscle insulin resistance, that is, diminished response to insulin, is characteristic of Type 2 diabetes (T2DM). One of the foremost reasons posited to explain the etiology of T2DM involves the modification of proteins by dicarbonyl stress due to an unbalanced metabolism and accumulations of dicarbonyl metabolites. The elevated concentration of dicarbonyl metabolites (i.e., glyoxal, methylglyoxal, 3-deoxyglucosone) leads to DNA and protein modifications, causing cell/tissue dysfunctions in several metabolic diseases such as T2DM and other age-associated diseases. In this review, we recapitulated reported effects of dicarbonyl stress on skeletal muscle and associated extracellular proteins with emphasis on the impact of T2DM on skeletal muscle and provided a brief introduction to the prevention/inhibition of dicarbonyl stress.

Glyoxalase System as a Therapeutic Target against Diabetic Retinopathy

Hyperglycemia, a defining characteristic of diabetes, combined with oxidative stress, results in the formation of advanced glycation end products (AGEs). AGEs are toxic compounds that have adverse effects on many tissues including the retina and lens. AGEs promote the formation of reactive oxygen species (ROS), which, in turn, boost the production of AGEs, resulting in positive feedback loops, a vicious cycle that compromises tissue fitness. Oxidative stress and the accumulation of AGEs are etiologically associated with the pathogenesis of multiple diseases including diabetic retinopathy (DR). DR is a devastating microvascular complication of diabetes mellitus and the leading cause of blindness in working-age adults. The onset and development of DR is multifactorial. Lowering AGEs accumulation may represent a potential therapeutic approach to slow this sight-threatening diabetic complication. To set DR in a physiological context, in this review we first describe relations between oxidative stress, formation of AGEs, and aging in several tissues of the eye, each of which is associated with a major age-related eye pathology. We summarize mechanisms of AGEs generation and anti-AGEs detoxifying systems. We specifically feature the potential of the glyoxalase system in the retina in the prevention of AGEs-associated damage linked to DR. We provide a comparative analysis of glyoxalase activity in different tissues from wild-type mice, supporting a major role for the glyoxalase system in the detoxification of AGEs in the retina, and present the manipulation of this system as a therapeutic strategy to prevent the onset of DR.

Potential Markers of Dietary Glycemic Exposures for Sustained Dietary Interventions in Populations without Diabetes

There is considerable interest in dietary and other approaches to maintaining blood glucose concentrations within the normal range and minimizing exposure to postprandial hyperglycemic excursions. The accepted marker to evaluate the sustained maintenance of normal blood glucose concentrations is glycated hemoglobin A1c (HbA1c). However, although this is used in clinical practice to monitor glycemic control in patients with diabetes, it has a number of drawbacks as a marker of efficacy of dietary interventions that might beneficially affect glycemic control in people without diabetes. Other markers that reflect shorter-term glycemic exposures have been studied and proposed, but consensus on the use and relevance of these markers is lacking. We have carried out a systematic search for studies that have tested the responsiveness of 6 possible alternatives to HbA1c as markers of sustained variation in glycemic exposures and thus their potential applicability for use in dietary intervention trials in subjects without diabetes: 1,5-anhydroglucitol (1,5-AG), dicarbonyl stress, fructosamine, glycated albumin (GA), advanced glycated end products (AGEs), and metabolomic profiles. The results suggest that GA may be the most promising for this purpose, but values may be confounded by effects of fat mass. 1,5-AG and fructosamine are probably not sensitive enough to the range of variation in glycemic exposures observed in healthy individuals. Use of measures based on dicarbonyls, AGEs, or metabolomic profiles would require further research into possible specific molecular species of interest. At present, none of the markers considered here is sufficiently validated and sensitive for routine use in substantiating the effects of sustained variation in dietary glycemic exposures in people without diabetes.

Glycation-mediated inter-protein cross-linking is promoted by chaperone-client complexes of α-crystallin: Implications for lens aging and presbyopia

Lens proteins become increasingly cross-linked through nondisulfide linkages during aging and cataract formation. One mechanism that has been implicated in this cross-linking is glycation through formation of advanced glycation end products (AGEs). Here, we found an age-associated increase in stiffness in human lenses that was directly correlated with levels of protein-cross-linking AGEs. α-Crystallin in the lens binds to other proteins and prevents their denaturation and aggregation through its chaperone-like activity. Using a FRET-based assay, we examined the stability of the αA-crystallin-γD-crystallin complex for up to 12 days and observed that this complex is stable in PBS and upon incubation with human lens-epithelial cell lysate or lens homogenate. Addition of 2 mm ATP to the lysate or homogenate did not decrease the stability of the complex. We also generated complexes of human αA-crystallin or αB-crystallin with alcohol dehydrogenase or citrate synthase by applying thermal stress. Upon glycation under physiological conditions, the chaperone-client complexes underwent greater extents of cross-linking than did uncomplexed protein mixtures. LC-MS/MS analyses revealed that the levels of cross-linking AGEs were significantly higher in the glycated chaperone-client complexes than in glycated but uncomplexed protein mixtures. Mouse lenses subjected to thermal stress followed by glycation lost resilience more extensively than lenses subjected to thermal stress or glycation alone, and this loss was accompanied by higher protein cross-linking and higher cross-linking AGE levels. These results uncover a protein cross-linking mechanism in the lens and suggest that AGE-mediated cross-linking of α-crystallin-client complexes could contribute to lens aging and presbyopia.

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.

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

Both cancer and Alzheimer's disease (AD) are emerging as metabolic diseases in which aberrant/dysregulated glucose metabolism and bioenergetics occur, and play a key role in disease progression. Interestingly, an enhancement of glucose uptake, glycolysis and pentose phosphate pathway occurs in both cancer cells and amyloid-β-resistant neurons in the early phase of AD. However, this metabolic shift has its adverse effects. One of them is the increase in methylglyoxal production, a physiological cytotoxic by-product of glucose catabolism. Methylglyoxal is mainly detoxified via cytosolic glyoxalase route comprising glyoxalase 1 and glyoxalase 2 with the production of S-D-lactoylglutathione and D-lactate as intermediate and end-product, respectively. Due to the existence of mitochondrial carriers and intramitochondrial glyoxalase 2 and D-lactate dehydrogenase, the transport and metabolism of both S-D-lactoylglutathione and D-lactate in mitochondria can contribute to methylglyoxal elimination, cellular antioxidant power and energy production. In this review, it is supposed that the different ability of cancer cells and AD neurons to metabolize methylglyoxal, S-D-lactoylglutathione and D-lactate scores cell fate, therefore being at the very crossroad of the "eternal youth" of cancer and the "premature death" of AD neurons. Understanding of these processes would help to elaborate novel metabolism-based therapies for cancer and AD treatment.

A monoclonal antibody targeted to the functional peptide of αB-crystallin inhibits the chaperone and anti-apoptotic activities

αB-Crystallin is a member of the small heat shock protein family. It is a molecular chaperone and an anti-apoptotic protein. Previous studies have shown that the peptide (⁷³DRFSVNLDVKHFSPEELKVKV⁹³, hereafter referred to as peptain-1) from the core domain of αB-crystallin exhibits both chaperone and anti-apoptotic properties similar to the parent protein. We developed a mouse monoclonal antibody against peptain-1 with the aim of blocking the functions of αB-crystallin. The antibody reacted with peptain-1, it did not react with the chaperone peptide of αA-crystallin. The antibody strongly reacted with human recombinant αB-crystallin but weakly with Hsp20; it did not react with αA-crystallin or Hsp27. The antibody specifically reacted with αB-crystallin in human and mouse lens proteins but not with αA-crystallin. The antibody reacted with αB-crystallin in human lens epithelial cells, human retinal endothelial cells, and with peptain-1 in peptain-1-transduced cells. Unlike the commercial antibodies against αB-crystallin, the antibody against peptain-1 inhibited the chaperone and anti-apoptotic activities of peptain-1. The antibody might find use in inhibiting αB-crystallin's chaperone and anti-apoptotic activities in diseases where αB-crystallin is a causative or contributing factor.

Mechanistic targeting of advanced glycation end-products in age-related diseases

Glycative stress, caused by the accumulation of cytotoxic and irreversibly-formed sugar-derived advanced glycation end-products (AGEs), contributes to morbidity associated with aging, age-related diseases, and metabolic diseases. In this review, we summarize pathways leading to formation of AGEs, largely from sugars and glycolytic intermediates, and discuss detoxification of AGE precursors, including the glyoxalase system and DJ-1/Park7 deglycase. Disease pathogenesis downstream of AGE accumulation can be cell autonomous due to aggregation of glycated proteins and impaired protein function, which occurs in ocular cataracts. Extracellular AGEs also activate RAGE signaling, leading to oxidative stress, inflammation, and leukostasis in diabetic complications such as diabetic retinopathy. Pharmaceutical agents have been tested in animal models and clinically to diminish glycative burden. We summarize existing strategies and point out several new directions to diminish glycative stress including: plant-derived polyphenols as AGE inhibitors and glyoxalase inducers; improved dietary patterns, particularly Mediterranean and low glycemic diets; and enhancing proteolytic capacities of the ubiquitin-proteasome and autophagy pathways that are involved in cellular clearing of AGEs.

Association of advanced glycation end products, evaluated by skin autofluorescence, with lifestyle habits in a general Japanese population

Objective

Accumulation of advanced glycation end products (AGEs) occurs during normal aging but markedly accelerates in people with diabetes. AGEs may play a role in various age-related disorders. Several studies have demonstrated that skin autofluorescence (SAF) reflects accumulated tissue levels of AGEs. However, very few studies have investigated SAF in the general population. The purpose of the present study was to more thoroughly evaluate the potential association among SAF, chronological age, and lifestyle habits in the general population.

Methods

A large cross-sectional survey of 10,946 Japanese volunteers aged 20 to 79 years was conducted. Volunteers completed a self-administered questionnaire and underwent SAF measurement on their dominant forearms. The associations of SAF with age and lifestyle habits were analyzed using a multiple stepwise regression analysis.

Results

Age was independently correlated with SAF. Lifestyle habits such as physical activity, nonsmoking, adequate sleep, low mental stress level, eating breakfast, and abstaining from sugary food were each independently associated with lower SAF.

Conclusions

SAF was associated with age and healthy lifestyle habits in this general Japanese population. The present study suggests that SAF measurement is a convenient tool for evaluating habitual lifestyle behaviors and may have potential for preventative health education.

Methylglyoxal-induced dicarbonyl stress in aging and disease: first steps towards glyoxalase 1-based treatments

Dicarbonyl stress is the abnormal accumulation of dicarbonyl metabolites leading to increased protein and DNA modification contributing to cell and tissue dysfunction in aging and disease. It is produced by increased formation and/or decreased metabolism of dicarbonyl metabolites. MG (methylglyoxal) is a dicarbonyl metabolite of relatively high flux of formation and precursor of the most quantitatively and functionally important spontaneous modifications of protein and DNA clinically. Major MG-derived adducts are arginine-derived hydroimidazolones of protein and deoxyguanosine-derived imidazopurinones of DNA. These are formed non-oxidatively. The glyoxalase system provides an efficient and essential basal and stress-response-inducible enzymatic defence against dicarbonyl stress by the reduced glutathione-dependent metabolism of methylglyoxal by glyoxalase 1. The GLO1 gene encoding glyoxalase 1 has low prevalence duplication and high prevalence amplification in some tumours. Dicarbonyl stress contributes to aging, disease and activity of cytotoxic chemotherapeutic agents. It is found at a low, moderate and severe level in obesity, diabetes and renal failure respectively, where it contributes to the development of metabolic and vascular complications. Increased glyoxalase 1 expression confers multidrug resistance to cancer chemotherapy and has relatively high prevalence in liver, lung and breast cancers. Studies of dicarbonyl stress are providing improved understanding of aging and disease and the basis for rational design of novel pharmaceuticals: glyoxalase 1 inducers for obesity, diabetes and cardiovascular disease and glyoxalase 1 inhibitors for multidrug-resistant tumours. The first clinical trial of a glyoxalase 1 inducer in overweight and obese subjects showed improved glycaemic control, insulin resistance and vascular function.

The structural damages of lens crystallins induced by peroxynitrite and methylglyoxal, two causative players in diabetic complications and preventive role of lens antioxidant components

Peroxynitrite (PON) and methylglyoxal (MGO), two diabetes-associated compounds, are believed to be important causative players in development of diabetic cataracts. In the current study, different spectroscopic methods, gel electrophoresis, lens culture and microscopic assessments were applied to examine the impact of individual, subsequent or simultaneous modification of lens crystallins with MGO and PON on their structure, oligomerization and aggregation. The protein modifications were confirmed with detection of the significantly increased quantity of carbonyl groups and decreased levels of sulfhydryl, tyrosine and tryptophan. Also, lens proteins modification with these chemical agents was accompanied with important structural alteration, oligomerization, disulfide/chromophore mediated protein crosslinking and important proteolytic instability. All these structural damages were more pronounced when the lens proteins were modified in the presence of both mentioned chemical agents, either in sequential or simultaneous manner. Ascorbic acid and glutathione, as the main components of lens antioxidant defense mechanism, were also capable to markedly prevent the damaging effects of PON and MGO on lens crystallins, as indicated by gel electrophoresis. The results of this study may highlight the importance of lens antioxidant defense system in protection of crystallins against the structural insults induced by PON and MGO during chronic hyperglycemia in the diabetic patients.

Prevention of dicarbonyl-mediated advanced glycation by glyoxalases: implication in skin aging

Skin aging is the result of intrinsic chronological aging and photoaging, due to UV exposure, that both share important histological modifications and molecular features, including alterations of proteins. One of the main damage is glycation that occurs when reducing sugars react non-enzymatically with proteins. This reaction also happens when the dicarbonyl compounds GO (glyoxal) and MG (methylglyoxal), which are glucose derivatives, react with proteins. These compounds can be detoxified by the glyoxalase system composed of two enzymes, Glo1 (glyoxalase I) and Glo2 (glyoxalase II). The aims of the present mini-review are to briefly summarize our current knowledge of the biological roles of these enzymes in aging and then discuss the relevance of studying the role of glycation and of detoxifying systems in human skin aging.

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 GLO1 C332 (Ala111) allele confers autism vulnerability: family-based genetic association and functional correlates

Glyoxalase I (GLO1) is a homodimeric Zn(2+)-dependent isomerase involved in the detoxification of methylglyoxal and in limiting the formation of advanced glycation end-products (AGE). We previously found the rs4746 A332 (Glu111) allele of the GLO1 gene, which encodes for glyoxalase I, associated with "unaffected sibling" status in families with one or more children affected by Autism Spectrum Disorder (ASD). To identify and characterize this protective allele, we sequenced GLO1 exons and exon-intron junctions, detecting two additional SNPs (rs1049346, rs1130534) in linkage disequilibrium with rs4746. A family-based association study involving 385 simplex and 20 multiplex Italian families yielded a significant association with autism driven only by the rs4746 C332 (Ala111) allele itself (P < 0.05 and P < 0.001 under additive and dominant/recessive models, respectively). Glyoxalase enzymatic activity was significantly reduced both in leukocytes and in post-mortem temporocortical tissue (N = 38 and 13, respectively) of typically developing C332 allele carriers (P < 0.05 and <0.01), with no difference in Glo1 protein levels. Conversely, AGE amounts were significantly higher in the same C332 post-mortem brains (P = 0.001), with a strong negative correlation between glyoxalase activity and AGE levels (τ = -0.588, P < 0.01). Instead, 19 autistic brains show a dysregulation of the glyoxalase-AGE axis (τ = -0.209, P = 0.260), with significant blunting of glyoxalase activity and AGE amounts compared to controls (P < 0.05), and loss of rs4746 genotype effects. In summary, the GLO1 C332 (Ala111) allele confers autism vulnerability by reducing brain glyoxalase activity and enhancing AGE formation, but years after an autism diagnosis the glyoxalase-AGE axis appears profoundly disrupted, with loss of C332 allelic effects.

Molecular strategies to prevent, inhibit, and degrade advanced glycoxidation and advanced lipoxidation end products

The advanced glycoxidation end products (AGEs) and lipoxidation end products (ALEs) contribute to the development of diabetic complications and of other pathologies. The review discusses the possibilities of counteracting the formation and stimulating the degradation of these species by pharmaceuticals and natural compounds. The review discusses inhibitors of ALE and AGE formation, cross-link breakers, ALE/AGE elimination by enzymes and proteolytic systems, receptors for advanced glycation end products (RAGEs) and blockade of the ligand-RAGE axis.

The combined effect of acetylation and glycation on the chaperone and anti-apoptotic functions of human α-crystallin

N(ε)-acetylation occurs on select lysine residues in α-crystallin of the human lens and alters its chaperone function. In this study, we investigated the effect of N(ε)-acetylation on advanced glycation end product (AGE) formation and consequences of the combined N(ε)-acetylation and AGE formation on the function of α-crystallin. Immunoprecipitation experiments revealed that N(ε)-acetylation of lysine residues and AGE formation co-occurs in both αA- and αB-crystallin of the human lens. Prior acetylation of αA- and αB-crystallin with acetic anhydride (Ac(2)O) before glycation with methylglyoxal (MGO) resulted in significant inhibition of the synthesis of two AGEs, hydroimidazolone (HI) and argpyrimidine. Similarly, synthesis of ascorbate-derived AGEs, pentosidine and N(ε)-carboxymethyl lysine (CML), was inhibited in both proteins by prior acetylation. In all cases, inhibition of AGE synthesis was positively related to the degree of acetylation. While prior acetylation further increased the chaperone activity of MGO-glycated αA-crystallin, it inhibited the loss of chaperone activity by ascorbate-glycation in both proteins. BioPORTER-mediated transfer of αA- and αB-crystallin into CHO cells resulted in significant protection against hyperthermia-induced apoptosis. This effect was enhanced in acetylated and MGO-modified αA- and αB-crystallin. Caspase-3 activity was reduced in α-crystallin transferred cells. Glycation of acetylated proteins with either MGO or ascorbate produced no significant change in the anti-apoptotic function. Collectively, these data demonstrate that lysine acetylation and AGE formation can occur concurrently in α-crystallin of human lens, and that lysine acetylation improves anti-apoptotic function of α-crystallin and prevents ascorbate-mediated loss of chaperone function.

Oxidative stress and aging: is methylglyoxal the hidden enemy?

Aging is a multifactorial process that involves changes at the cellular, tissue, organ and the whole body levels resulting in decreased functioning, development of diseases, and ultimately death. Oxidative stress is believed to be a very important factor in causing aging and age-related diseases. Oxidative stress is caused by an imbalance between oxidants such as reactive oxygen species (ROS) and antioxidants. ROS are produced from the mitochondrial electron transport chain and many oxidative reactions. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite formed during glucose, protein and fatty acid metabolism. MG levels are elevated in hyperglycemia and other conditions. An excess of MG formation can increase ROS production and cause oxidative stress. MG reacts with proteins, DNA and other biomolecules, and is a major precursor of advanced glycation end products (AGEs). AGEs are also associated with the aging process and age-related diseases such as cardiovascular complications of diabetes, neurodegenerative diseases and connective tissue disorders. AGEs also increase oxidative stress. In this review we discuss the potential role of MG in the aging process through increasing oxidative stress besides causing AGEs formation. Specific and effective scavengers and crosslink breakers of MG and AGEs are being developed and can become potential treatments to slow the aging process and prevent many diseases.

Inhibition of methylglyoxal-mediated protein modification in glyoxalase I overexpressing mouse lenses

Objective. Here we tested the role of Glo I in the prevention of advanced glycation end product (AGE) formation in transgenic mouse lenses. Methods. A transgenic animal line that expressed high levels of human Glo I in the lens was developed from the C57B6 mouse strain. The role of Glo I in the inhibition of MGO-AGE formation was tested in organ-cultured lenses. Results. Organ culture of Wt and Glo I lenses with 5 mM D, L-glyceraldehyde (GLD) enhanced MGO by 29-fold and 17-fold in Wt lenses and Glo I lenses, respectively. Argpyrimidine levels were 192 ± 73 pmoles/mg protein, and hydroimidazolone levels were 22 ± 0.7 units/μg protein in GLD-incubated Wt lenses. In Glo I lenses, formation of AGEs was significantly inhibited; the argpyrimidine levels were 82 ± 18 pmoles/mg protein, and the HI levels were 2.6 ± 2.3 units/μg protein. Incubation of Wt lens proteins with 5 mM ribose for 7 days resulted in the formation of pentosidine. However, the levels were substantially higher in Glo I lens proteins incubated with ribose. Conclusion. Our study provides direct evidence that Glo I activity plays an important role in the regulation of AGE synthesis in the lens; while Glo I activity blocks the formation of MGO-AGEs, it might promote the formation of sugar-derived AGEs.

The RAGE axis: a fundamental mechanism signaling danger to the vulnerable vasculature

The immunoglobulin superfamily molecule RAGE (receptor for advanced glycation end product) transduces the effects of multiple ligands, including AGEs (advanced glycation end products), advanced oxidation protein products, S100/calgranulins, high-mobility group box-1, amyloid-beta peptide, and beta-sheet fibrils. In diabetes, hyperglycemia likely stimulates the initial burst of production of ligands that interact with RAGE and activate signaling mechanisms. Consequently, increased generation of proinflammatory and prothrombotic molecules and reactive oxygen species trigger further cycles of oxidative stress via RAGE, thus setting the stage for augmented damage to diabetic tissues in the face of further insults. Many of the ligand families of RAGE have been identified in atherosclerotic plaques and in the infarcted heart. Together with increased expression of RAGE in diabetic settings, we propose that release and accumulation of RAGE ligands contribute to exaggerated cellular damage. Stopping the vicious cycle of AGE-RAGE and RAGE axis signaling in the vulnerable heart and great vessels may be essential in controlling and preventing the consequences of diabetes.