Enzymatic deglycation of proteins

Metabolization of the Amadori Product N-ε-Fructosyllysine by Probiotic Bacteria

Glycation reactions in food lead to the formation of the Amadori rearrangement product (ARP) N-ε-fructosyllysine (fructoselysine, FL), which is taken up with the daily diet and comes into contact with the gut microbiota during digestion. In the present study, nine commercially available probiotic preparations as well as single pure strains thereof were investigated for their FL-degrading capability under anaerobic conditions. One of the commercial preparations as well as three single pure strains thereof was able to completely degrade 0.25 mM FL within 72 h. Three new deglycating lactic acid bacteria species, namely, Lactobacillus buchneri DSM 20057, Lactobacillus jensenii DSM 20557, and Pediococcus acidilactici DSM 25404, could be identified. Quantitative experiments showed that FL was completely deglycated to lysine. Using 13C6-labeled FL as the substrate, it could be proven that the sugar moiety of the Amadori product is degraded to lactic acid, showing for the first time that certain lactic acid bacteria can utilize the sugar moiety as a substrate for lactic acid fermentation.

Blood and Tissue Advanced Glycation End Products as Determinants of Cardiometabolic Disorders Focusing on Human Studies

Cardiometabolic disorders are characterised by a cluster of interactive risk determinants such as increases in blood glucose, lipids and body weight, as well as elevated inflammation and oxidative stress and gut microbiome changes. These disorders are associated with onset of type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). T2DM is strongly associated with CVD. Dietary advanced glycation end products (dAGEs) attributable from modern diets high in sugar and/or fat, highly processed foods and high heat-treated foods can contribute to metabolic etiologies of cardiometabolic disorders. This mini review aims to determine whether blood dAGEs levels and tissue dAGEs levels are determinants of the prevalence of cardiometabolic disorders through recent human studies. ELISA (enzyme-linked immunosorbent assay), high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) for blood dAGEs measurement and skin auto fluorescence (SAF) for skin AGEs measurement can be used. Recent human studies support that a diet high in AGEs can negatively influence glucose control, body weight, blood lipid levels and vascular health through the elevated oxidative stress, inflammation, blood pressure and endothelial dysfunction compared with a diet low in AGEs. Limited human studies suggested a diet high in AGEs could negatively alter gut microbiota. SAF could be considered as one of the predictors affecting risks for cardiometabolic disorders. More intervention studies are needed to determine how dAGEs are associated with the prevalence of cardiometabolic disorders through gut microbiota changes. Further human studies are conducted to find the association between CVD events, CVD mortality and total mortality through SAF measurement, and a consensus on whether tissue dAGEs act as a predictor of CVD is required.

Diabetic Foot: The Role of Fasciae, a Narrative Review

Simple Summary

Diabetes mellitus and its complications are increasingly prevalent worldwide with severe impacts on patients and health care systems. Diabetic foot ulcers have an important impact on disability, morbidity, and mortality. The mechanism of diabetic wound chronicity has not yet been understood in a complete way. Regarding the involved soft tissues, little space has been given to the fasciae, even if nowadays there is more and more evidence of their role in proprioception, muscular force transmission, skin vascularization and tropism, and wound healing. Thus, we aimed to deepen the fascial involvement in diabetic wounds. Based on this review, we suggest that a clear scientific perception of fascial role can improve treatment strategies and create new perspectives of treatment.

Abstract

Wound healing is an intricate, dynamic process, in which various elements such as hyperglycemia, neuropathy, blood supply, matrix turnover, wound contraction, and the microbiome all have a role in this “out of tune” diabetic complex symphony, particularly noticeable in the complications of diabetic foot. Recently it was demonstrated that the fasciae have a crucial role in proprioception, muscular force transmission, skin vascularization and tropism, and wound healing. Indeed, the fasciae are a dynamic multifaceted meshwork of connective tissue comprised of diverse cells settled down in the extracellular matrix and nervous fibers; each constituent plays a particular role in the fasciae adapting in various ways to the diverse stimuli. This review intends to deepen the discussion on the possible fascial role in diabetic wounds. In diabetes, the thickening of collagen, the fragmentation of elastic fibers, and the changes in glycosaminoglycans, in particular hyaluronan, leads to changes in the stiffness, gliding, and the distribution of force transmission in the fasciae, with cascading repercussions at the cellular and molecular levels, consequently feeding a vicious pathophysiological circle. A clear scientific perception of fascial role from microscopic and macroscopic points of view can facilitate the identification of appropriate treatment strategies for wounds in diabetes and create new perspectives of treatment.

A Hypothesis: Fructosamine-3-Kinase-Related-Protein (FN3KRP) Catalyzes Deglycation of Maillard Intermediates Directly Downstream from Fructosamines

Non-enzymatic glycation (a.k.a. Maillard reaction) is a series of random spontaneous reactions between reducing sugars and amines, resulting in the formation of irreversible advanced glycation endproducts (AGE's). In food chemistry, this process is beneficial by contributing to the flavor, aroma, texture, and appearance of cooked foods. In vivo, however, Maillard reaction is deleterious because uncontrolled modification and crosslinking of biological macromolecules impairs their function. Consequently, chronic hyperglycemia of diabetes mellitus, for instance, leads to increased non-enzymatic glycation and diverse, multi-organ pathologies of diabetic complications. Based on the fact that toxic compounds, such as free radicals, are detoxified in vivo by specific defense mechanisms, one would expect to find mechanisms to control glucose toxicity as well. Thus far, only one such enzyme, fructosamine-3-kinase (FN3K), has been characterized. It operates intracellularly by catalyzing ATP-dependent removal of Maillard adducts, D-fructoselysines, from proteins, thereby reducing the Maillard reaction flux from glucose to AGE's. When FN3K was isolated, a closely related but distinct protein copurified with it. Unlike FN3K, however, this enzyme, fructosamine-3-kinase-related protein (FN3KRP), does not phosphorylate D-fructoselysines but it does phosphorylate several other (non-physiological) substrates. Interestingly, the distribution of FN3KRP in nature appears to be nearly universal whereas that of FN3K is limited to endotherms. In this article, it is suggested that the function of FN3KRP is deglycation of Maillard adducts downstream from fructoselysines. Such a mechanism, if proven correct, would be valuable given reports on apparent correlations between FN3KRP and some chronic conditions and/or diseases, such as a recent publication which proposes that the FN3KRP gene may be a longevity gene.

The effect of Salaciareticulata, Syzygiumcumini, Artocarpusheterophyllus, and Cassiaauriculata on controlling the rapid formation of advanced glycation end-products

BACKGROUND

The excessive formation of Advanced Glycation End-products (AGEs) by non-enzymatic glycation mediates many health complications in the human body and the formation of AGEs largely accelerated under the hyperglycaemic condition.

OBJECTIVE

The prospect of the study to assess the strength of inhibiting the rapid AGE formations in four Ayurvedic medicinal plants, namely; Salacia reticulata (stems), Syzygium cumini (barks), Artocarpus heterophyllus (mature leaves) and, Cassia auriculata (flowers).

MATERIALS AND METHODS

Herbal decoctions of four medicinal plant materials were prepared by simmering with hot water as prescribed by the Ayurvedic medicine. The effectiveness of the decoctions was analyzed in vitro based on their Anti-AGE formation activity, glycation reversing, and anti-oxidant potentials.

RESULTS

According to the results, the decoctions of S. reticulata, A. heterophyllus and C. auriculata indicated the strong Anti-AGE forming (IC₅₀: 23.01 ± 2.70, 32.01 ± 2.09, 43.66 ± 2.11 mg/mL, respectively), glycation reversing (EC₅₀: 183.15 ± 7.67, 91.85 ± 1.93, 252.35 ± 4.03 mg/mL, respectively) and antioxidant potentials in terms of total polyphenol content (TPC), total flavonoid content (TFC), ferric ion reducing power (FRAP), ABTS and DPPH radical scavenging activities. However, the decoction of S. cumini reported the significantly high (p < 0.05) Anti-AGE forming, (IC₅₀: 9.75 ± 0.32 mg/mL), glycation reversing (EC₅₀: 66.45 ± 4.51 mg/mL), and antioxidant potentials against the decoctions of the other three plant materials.

CONCLUSION

S. cumini bark extract was identified as the best source in controlling the formation of AGEs excessively. Further, the other three plant extracts can also be effectively used as potential therapeutic agents to control the pathological conditions associated with AGEs-mediated health complications.

Perspectives on signaling for biological- and processed food-related advanced glycation end-products and its role in cancer progression

Receptor for advanced glycation end-products (RAGE) is a multifunctional receptor binds a broad spectrum of ligands and mediates responses to cell damage and stress conditions. It also activates programs leading to acute and chronic inflammation and implicated in several pathological diseases, including cancer. In this review, we presented the non-enzymatic reaction of reducing sugar with the amino groups of proteins, lipids, and nucleic acids. This reaction initiates a complex series of rearrangements and dehydrations, and then produces a class of irreversibly cross-linked heterogeneous fluorescent moieties, termed advanced glycation end products (AGEs). There is a growing body of evidence that interaction of processes food-related AGEs with a cell surface receptor RAGE brings out the generation of oxidative stress and subsequently evokes proliferative, angiogenic and inflammatory reactions, thereby being involved in the development and progression of various types of cancers. This review is an insightful assessment of molecular mechanisms through which RAGE signaling contributes to the enhancement and survival of the tumorigenic cell. Here we summarize the procurement of individual ligands of RAGE like amphoterin, calcium-binding proteins, and resultant mediation of RAGE signaling pathway, which partially can elucidate the elevated risk of several cancers. Besides, we summarize many factors or conditions including APE1 (apurinic/apyrimidinic endonuclease 1), retinol mutations, retinoblastoma (Rb), proteinase 3 (PR3) hypoxia and so on through which RAGE signaling presents an establishment of cancerous environment. Additionally, we also reviewed some recent findings that give shreds of evidence for presenting the role of RAGE and its ligands in the advanced stage of cancers.

The vast repertoire of carbohydrate oxidases: An overview

Carbohydrates are widely abundant molecules present in a variety of forms. For their biosynthesis and modification, nature has evolved a plethora of carbohydrate-acting enzymes. Many of these enzymes are of particular interest for biotechnological applications, where they can be used as biocatalysts or biosensors. Among the enzymes catalysing conversions of carbohydrates are the carbohydrate oxidases. These oxidative enzymes belong to different structural families and use different cofactors to perform the oxidation reaction of CH-OH bonds in carbohydrates. The variety of carbohydrate oxidases available in nature reflects their specificity towards different sugars and selectivity of the oxidation site. Thanks to their properties, carbohydrate oxidases have received a lot of attention in basic and applied research, such that nowadays their role in biotechnological processes is of paramount importance. In this review we provide an overview of the available knowledge concerning the known carbohydrate oxidases. The oxidases are first classified according to their structural features. After a description on their mechanism of action, substrate acceptance and characterisation, we report on the engineering of the different carbohydrate oxidases to enhance their employment in biocatalysis and biotechnology. In the last part of the review we highlight some practical applications for which such enzymes have been exploited.

The effect of cold atmospheric plasma on diabetes-induced enzyme glycation, oxidative stress, and inflammation; in vitro and in vivo

Cold atmospheric plasma (CAP) is known as the versatile tool in different biological, and medical applications. In this study, we investigated the effect of cold plasma on diabetes via in vitro and in vivo assessments. We performed the in vitro assay to evaluate the impact of CAP on glycated glutathione peroxidase (GPx) through enzyme activity measurement as a function index and far- and near-UV circular dichroism (CD) and fluorescence analysis as structure indices. The result of in vitro assessment showed that the exposure of glycated GPx to plasma causes a considerable increase in enzyme activity up to 30%. Also, the evaluation of far- and near-UV CD and fluorescence analysis indicated a modification in the protein structure. According to obtained result from in vitro assessment, in vivo assay evaluated the effect of CAP on diabetic mice through analyzing of blood glucose level (BGL), advanced glycation end products (AGEs), antioxidant activity, oxidative stress biomarkers such as malondialdehyde (MDA), advanced oxidation protein products (AOPP), and oxidized low-density lipoprotein (oxLDL), and inflammation factors including tumor necrosis factor (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6). The result of in vivo experiment also showed a 20% increase in antioxidant activity. Also, the reduction in AGEs, oxidative stress biomarkers, and inflammatory cytokines concentrations was observed. The result of this study revealed that CAP could be useful in diabetes treatment and can be utilized as a complementary method for diabetes therapy.

Integrated Use of Biochemical, Native Mass Spectrometry, Computational, and Genome-Editing Methods to Elucidate the Mechanism of a Salmonella deglycase

Salmonellais a foodborne pathogen that causes annually millions of cases of salmonellosis globally, yet Salmonella-specific antibacterials are not available. During inflammation, Salmonella utilizes the Amadori compound fructose-asparagine (F-Asn) as a nutrient through the successive action of three enzymes, including the terminal FraB deglycase. Salmonella mutants lacking FraB are highly attenuated in mouse models of inflammation due to the toxic build-up of the substrate 6-phosphofructose-aspartate (6-P-F-Asp). This toxicity makes Salmonella FraB an appealing drug target, but there is currently little experimental information about its catalytic mechanism. Therefore, we sought to test our postulated mechanism for the FraB-catalyzed deglycation of 6-P-F-Asp (via an enaminol intermediate) to glucose-6-phosphate and aspartate. A FraB homodimer model generated by RosettaCM was used to build substrate-docked structures that, coupled with sequence alignment of FraB homologs, helped map a putative active site. Five candidate active-site residues-including three expected to participate in substrate binding-were mutated individually and characterized. Native mass spectrometry and ion mobility were used to assess collision cross sections and confirm that the quaternary structure of the mutants mirrored the wild type, and that there are two active sites/homodimer. Our biochemical studies revealed that FraB Glu214Ala, Glu214Asp, and His230Ala were inactive in vitro, consistent with deprotonated-Glu214 and protonated-His230 serving as a general base and a general acid, respectively. Glu214Ala or His230Ala introduced into the Salmonella chromosome by CRISPR/Cas9-mediated genome editing abolished growth on F-Asn. Results from our computational and experimental approaches shed light on the catalytic mechanism of Salmonella FraB and of phosphosugar deglycases in general.

Multicentered hydrogen bonding in 1-[(1-de-oxy-β-d-fructo-pyranos-1-yl)aza-nium-yl]cyclo-pentane-carboxyl-ate ('d-fructose-cyclo-leucine')

The title compound, C12H21NO7, (I), is conformationally unstable; the predominant form present in its solution is the β-pyran-ose form (74.3%), followed by the β- and α-furan-oses (12.1 and 10.2%, respectively), α-pyran-ose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the 2 C 5 β-pyran-ose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclo-pentane ring assuming the E 9 envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of anti-parallel infinite chains of fused R 3 3(6) and R 3 3(8) rings. The mol-ecule features extensive intra-molecular hydrogen bonding, which is uniquely multicentered and involves the carboxyl-ate, ammonium and carbohydrate hy-droxy groups. In contrast, the contribution of inter-molecular O⋯H/H⋯O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other d-fructose-amino acids. The 1H NMR data suggest a slow rotation around the C1-C2 bond in (I), indicating that the intra-molecular heteroatom contacts survive in aqueous solution of the mol-ecule as well.

Recent findings on the physiological function of DJ-1: Beyond Parkinson's disease

Several mutations in the gene coding for DJ-1 have been associated with early onset forms of parkinsonism. In spite of the massive effort spent by the scientific community in understanding the physiological role of DJ-1, a consensus on what DJ-1 actually does within the cells has not been reached, with several diverse functions proposed. At present, the most accepted function for DJ-1 is a neuronal protective role against oxidative stress. However, how exactly this function is exerted by DJ-1 is not clear. In recent years, novel molecular mechanisms have been suggested that may account for the antioxidant properties of DJ-1. In this review, we critically analyse the experimental evidence, including some very recent findings, supporting the purported neuroprotective role of DJ-1 through different mechanisms linked to oxidative stress handling, as well as the relevance of these processes in the context of Parkinson's disease.

Advanced glycation end products mediated cellular and molecular events in the pathology of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetic patients and a leading cause of end-stage renal disease (ESRD). Degenerative changes such as glomerular hypertrophy, hyperfiltration, widening of basement membranes, tubulointerstitial fibrosis, glomerulosclerosis and podocytopathy manifest in various degrees of proteinuria in DN. One of the key mechanisms implicated in the pathogenesis of DN is non-enzymatic glycation (NEG). NEG is the irreversible attachment of reducing sugars onto free amino groups of proteins by a series of events, which include the formation of Schiff’s base and an Amadori product to yield advanced glycation end products (AGEs). AGE modification of client proteins from the extracellular matrix induces crosslinking, which is often associated with thickening of the basement membrane. AGEs activate several intracellular signaling cascades upon interaction with receptor for AGEs (RAGE), which manifest in aberrant cellular responses such as inflammation, apoptosis and autophagy, whereas other receptors such as AGE-R1, AGE-R3 and scavenger receptors also bind to AGEs and ensue endocytosis and degradation of AGEs. Elevated levels of both serum and tissue AGEs are associated with adverse renal outcome. Increased evidence supports that attenuation of AGE formation and/or inhibition of RAGE activation manifest(s) in improving renal function. This review provides insights of NEG, discusses the cellular and molecular events triggered by AGEs, which manifest in the pathogenesis of DN including renal fibrosis, podocyte epithelial-mesenchymal transition and activation of renin-angiotensin system. Therapies designed to target AGEs, such as inhibitors of AGEs formation and crosslink breakers, are discussed.

Advanced glycation end-products: Mechanics of aged collagen from molecule to tissue

Concurrent with a progressive loss of regenerative capacity, connective tissue aging is characterized by a progressive accumulation of Advanced Glycation End-products (AGEs). Besides being part of the typical aging process, type II diabetics are particularly affected by AGE accumulation due to abnormally high levels of systemic glucose that increases the glycation rate of long-lived proteins such as collagen. Although AGEs are associated with a wide range of clinical disorders, the mechanisms by which AGEs contribute to connective tissue disease in aging and diabetes are still poorly understood. The present study harnesses advanced multiscale imaging techniques to characterize a widely employed in vitro model of ribose induced collagen aging and further benchmarks these data against experiments on native human tissues from donors of different age. These efforts yield unprecedented insight into the mechanical changes in collagen tissues across hierarchical scales from molecular, to fiber, to tissue-levels. We observed a linear increase in molecular spacing (from 1.45nm to 1.5nm) and a decrease in the D-period length (from 67.5nm to 67.1nm) in aged tissues, both using the ribose model of in vitro glycation and in native human probes. Multiscale mechanical analysis of in vitro glycated tendons strongly suggests that AGEs reduce tissue viscoelasticity by severely limiting fiber-fiber and fibril-fibril sliding. This study lays an important foundation for interpreting the functional and biological effects of AGEs in collagen connective tissues, by exploiting experimental models of AGEs crosslinking and benchmarking them for the first time against endogenous AGEs in native tissue.

Proteomic response of the phytopathogen Phyllosticta citricarpa to antimicrobial volatile organic compounds from Saccharomyces cerevisiae

Volatile organic compounds (VOCs) released by Saccharomyces cerevisiae inhibit plant pathogens, including the filamentous fungus Phyllosticta citricarpa, causal agent of citrus black spot. VOCs mediate relevant interactions between organisms in nature, and antimicrobial VOCs are promising, environmentally safer fumigants to control phytopathogens. As the mechanisms by which VOCs inhibit microorganisms are not well characterized, we evaluated the proteomic response in P. citricarpa after exposure for 12h to a reconstituted mixture of VOCs (alcohols and esters) originally identified in S. cerevisiae. Total protein was extracted and separated by 2D-PAGE, and differentially expressed proteins were identified by LC-MS/MS. About 600 proteins were detected, of which 29 were downregulated and 11 were upregulated. These proteins are involved in metabolism, genetic information processing, cellular processes, and transport. Enzymes related to energy-generating pathways, particularly glycolysis and the tricarboxylic acid cycle, were the most strongly affected. Thus, the data indicate that antimicrobial VOCs interfere with essential metabolic pathways in P. citricarpa to prevent fungal growth.

A Mannose Family Phosphotransferase System Permease and Associated Enzymes Are Required for Utilization of Fructoselysine and Glucoselysine in Salmonella enterica Serovar Typhimurium

Salmonella enteric serovar Typhimurium, a major cause of food-borne illness, is capable of using a variety of carbon and nitrogen sources. Fructoselysine and glucoselysine are Maillard reaction products formed by the reaction of glucose or fructose, respectively, with the ε-amine group of lysine. We report here that S. Typhimurium utilizes fructoselysine and glucoselysine as carbon and nitrogen sources via a mannose family phosphotransferase (PTS) encoded by gfrABCD (glucoselysine/fructoselysine PTS components EIIA, EIIB, EIIC, and EIID; locus numbers STM14_5449 to STM14_5454 in S. Typhimurium 14028s). Genes coding for two predicted deglycases within the gfr operon, gfrE and gfrF, were required for growth with glucoselysine and fructoselysine, respectively. GfrF demonstrated fructoselysine-6-phosphate deglycase activity in a coupled enzyme assay. The biochemical and genetic analyses were consistent with a pathway in which fructoselysine and glucoselysine are phosphorylated at the C-6 position of the sugar by the GfrABCD PTS as they are transported across the membrane. The resulting fructoselysine-6-phosphate and glucoselysine-6-phosphate subsequently are cleaved by GfrF and GfrE to form lysine and glucose-6-phosphate or fructose-6-phosphate. Interestingly, although S. Typhimurium can use lysine derived from fructoselysine or glucoselysine as a sole nitrogen source, it cannot use exogenous lysine as a nitrogen source to support growth. Expression of gfrABCDEF was dependent on the alternative sigma factor RpoN (σ(54)) and an RpoN-dependent LevR-like activator, which we designated GfrR.

IMPORTANCE

Salmonella physiology has been studied intensively, but there is much we do not know regarding the repertoire of nutrients these bacteria are able to use for growth. This study shows that a previously uncharacterized PTS and associated enzymes function together to transport and catabolize fructoselysine and glucoselysine. Knowledge of the range of nutrients that Salmonella utilizes is important, as it could lead to the development of new strategies for reducing the load of Salmonella in food animals, thereby mitigating its entry into the human food supply.

Glycated proteome: from reaction to intervention

Glycation, a nonenzymatic reaction between reducing sugars and proteins, is a proteome wide phenomenon, predominantly observed in diabetes due to hyperglycemia. Glycated proteome of plasma, kidney, lens, and brain are implicated in the pathogenesis of various diseases, including diabetic complications, neurodegenerative diseases, cancer, and aging. This review discusses the strategies to characterize protein glycation, its functional implications in different diseases, and intervention strategies to protect the deleterious effects of protein glycation.

Hydrolysates of glycated and heat-treated peanut 7S globulin (Ara h 1) modulate human gut microbial proliferation, survival and adhesion

AIMS

Evaluation of an effect of glycation of Ara h 1 on proliferation and survival rate and adhesion of intestinal Enterococcus faecalis, Escherichia coli and Lactobacillus acidophilus.

METHODS AND RESULTS

Pure Ara h 1 heated at three different temperature conditions (G37, G60 and C145°C) in the presence or absence of glucose was subjected to enzymatic hydrolysis. Impacts of Ara h 1 hydrolysates on the bacterial proliferation, survival rate and adhesion to Caco-2 cells in mono and heterogeneous cultures were studied with fluorescent techniques: DAPI, LIVE/DEAD staining and FISH. Examined hydrolysates hindered proliferation of E. coli and Ent. faecalis with simultaneous decrease in their survival. Maillard reaction (MR, glycation) of Ara h 1 did not alter the effect of hydrolysates on bacterial proliferation rate. Hydrolysates modified at 60 and 145°C with glucose altered the profile of immobilized bacteria, mostly by lowering the number of adhering E. coli and promoting the adhesion of bacteria from genera Lactobacillus and Enterococcus.

CONCLUSIONS

Ara h1 hydrolysates processed in various ways demonstrated their strong modulatory effect on bacterial proliferation, survival rate and adhesion.

SIGNIFICANCE AND IMPACT OF THE STUDY

Reducing the adhesion of opportunistic bacteria by hydrolysates of Ara h 1 glycated at 60 and 145°C, together with modulation of immobilization of beneficial lactobacilli and enterococci, may be of relevance in terms of the physiological status of the intestinal barrier.

Advanced glycation end products: Key players in skin aging?

Aging is the progressive accumulation of damage to an organism over time leading to disease and death. Aging research has been very intensive in the last years aiming at characterizing the pathophysiology of aging and finding possibilities to fight age-related diseases. Various theories of aging have been proposed. In the last years advanced glycation end products (AGEs) have received particular attention in this context. AGEs are formed in high amounts in diabetes but also in the physiological organism during aging. They have been etiologically implicated in numerous diabetes- and age-related diseases. Strategies inhibiting AGE accumulation and signaling seem to possess a therapeutic potential in these pathologies. However, still little is known on the precise role of AGEs during skin aging. In this review the existing literature on AGEs and skin aging will be reviewed. In addition, existing and potential anti-AGE strategies that may be beneficial on skin aging will be discussed.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

The emerging challenge in diabetes: the "metabolic memory"

Large randomized studies have established that early intensive glycemic control reduces the risk of diabetic complications, both micro and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as "metabolic memory." Potential mechanisms for propagating this "memory" may be the production of reactive species unrelated to the presence of hyperglycemia, depending on the previous production of AGEs which can maintain RAGE over-expression, on the level of glycation of mitochondrial proteins and on the amount of mtDNA produced, all conditions able to induce an altered gene expression which may be persistent even when glycemia is normalized. Clinically, the emergence of this "metabolic memory" suggests the need for a very early aggressive treatment aiming to "normalize" the metabolic control and the addition of agents which reduce cellular reactive species and glycation in addition to normalizing glucose levels in diabetic patients in order to minimize long-term diabetic complications.

Prognostic potential and tumor growth-inhibiting effect of plasma advanced glycation end products in non-small cell lung carcinoma

The plasma fluorescence related to the standard fluorescence of advanced glycation end products (AGEs) is a simple measurable blood parameter for distinct diseases but its importance in human cancer, including non-small cell lung carcinoma (NSCLC), is unknown. Plasma samples of 70 NSCLC patients who underwent resection surgery of the tumor were analyzed for the distinct AGE-related fluorescence at 370 nm excitation/440 nm emission. In a retrospective study, we tested the prognostic relevance of this AGE-related plasma fluorescence. The effect of circulating AGEs on the NSCLC growth was studied experimentally in vitro and in vivo. NSCLC patients with high (> median) AGE-related plasma fluorescence were characterized by a later reoccurrence of the tumor after curative surgery and a higher survival rate compared with patients with low plasma fluorescence (25% versus 47% 5-y survival, P = 0.011). Treating NSCLC cell spheroids with patients' plasma showed an inverse correlation between the growth of spheroids in vitro and the individual AGE-related fluorescence of each plasma sample. To confirm the impact of circulating AGEs on the NSCLC progression, we studied the NSCLC growth in mice whose circulating AGE level was elevated by AGE-rich diet. In vivo tumorigenicity assays demonstrated that mice with higher levels of circulating AGEs developed smaller tumors than mice with normal AGE levels. The AGE-related plasma fluorescence has prognostic relevance for NSCLC patients in whom the tumor growth-inhibiting effect of circulating AGEs might play a critical role.

Limited joint mobility (LJM) in elderly subjects with type II diabetes mellitus

LJM is frequently observed in young subjects with insulin-dependent diabetes mellitus (IDDM). Aim of this study was to evaluate whether non-insulin-dependent diabetes mellitus (NIDDM) increases the risk of LJM in elderly subjects. Thirty patients (15 males, 15 females, mean age 73.93 ± 12.72 years) with NIDDM in good glycemic control were compared with thirty non-diabetic elderly, well matched for sex and age (15 males, 15 females, mean age 74.3 ± 4.24 years), and with ten young normal subjects (5 males, 5 females, mean age 26.3 ± 1.56 years). In these subjects, the range of motion (ROM) of ankle, knee, hip, elbow and shoulder were measured with a double-armed goniometer. Moreover, abnormalities of supraspinatus, patellar and Achilles tendons were evaluated with a standardized ultrasound (US) procedure. A significant reduction in the mobility of all joints was found in elderly subjects, compared to younger ones, with exception for the knee and elbow flexion. Elderly patients with diabetes, compared with their age-matched counterpart, showed LJM for ankle dorso- and plantar flexion, hip flexion and adduction, shoulder abduction and flexion. Moreover, tendons sonographic abnormalities were more frequently observed in diabetics. Our data confirm that diabetes worsens the LJM in the elderly, increasing the cross-linking of collagen by the non-enzymatic advanced glycation end products formation.

Hypothesis: the "metabolic memory", the new challenge of diabetes

Large randomized studies have established that early intensive glycaemic control reduces the risk of diabetic complications, both micro and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as "metabolic memory". Potential mechanisms for propagating this "memory" are the non-enzymatic glycation of cellular proteins and lipids, and an excess of cellular reactive oxygen and nitrogen species, in particular originated at the level of glycated-mitochondrial proteins, perhaps acting in concert with one another to maintain stress signaling. Furthermore, the emergence of this "metabolic memory" suggests the need of a very early aggressive treatment aiming to "normalize" the metabolic control and the addition of agents which reduce cellular reactive species and glycation in addition to normalizing glucose levels in diabetic patients in order to minimize long-term diabetic complications.

Hypothesis: the 'metabolic memory', the new challenge of diabetes

Large randomized studies have established that early intensive glycaemic control reduces the risk of diabetic complications, both micro- and macrovascular. However, epidemiological and prospective data support a long-term influence of early metabolic control on clinical outcomes. This phenomenon has recently been defined as 'metabolic memory.' Potential mechanisms for propagating this 'memory' are the non-enzymatic glycation of cellular proteins and lipids, and an excess of cellular reactive oxygen and nitrogen species, in particular originated at the level of glycated-mitochondrial proteins, perhaps acting in concert with one another to maintain stress signalling. Furthermore, the emergence of this 'metabolic memory' suggests the need for very early aggressive treatment aiming to 'normalize' glycaemic control and the addition of agents which reduce cellular reactive species and glycation in order to minimize long-term diabetic complications.

The effects of the Maillard reaction on the physical properties and cell interactions of collagen

The non-enzymic glycation of collagen occurs as its turnover decreases during maturation, with complex carbohydrates accumulating slowly and the end-products of these reactions being permanent. The nature of these advanced glycation end-reaction products (AGEs) can be categorised as: 1) cross-linking: intermolecular cross-linking may occur between two adjacent molecules and involve lysine to lysine or lysine to arginine residues. Several compounds have been characterised. They are believed to be located between the triple helical domains of adjacent molecules in the fibre resulting in major changes of the physical properties, primarily, fibre stiffness, thermal denaturation temperature and enzyme resistance, all of which increase slowly with age but the rate is accelerated in diabetes mellitus due to high glucose levels: 2) side-chain modifications: these changes alter the charge profile of the molecule affecting the interactions within the fibre and if they occur at specific sites can affect the cell-collagen interaction. Modification of arginine within the sites RGD and GFOGER recognised by the two specific integrins (alpha1beta2 and alpha2beta1) for collagen reduce cell interactions during turnover and for platelet interactions (alpha1beta2). These changes can ultimately affect repair of, for example, vascular damage and dermal wound healing in diabetes mellitus. Both types of modification are deleterious to the optimal properties of collagen as a supporting framework structure and as a controlling factor in cell matrix interactions. Glycation during ageing and diabetes is therefore responsible for malfunctioning of the diverse collagenous tissues throughout the body.

Protection against glycation and similar post-translational modifications of proteins

Glycation and other non-enzymic post-translational modifications of proteins have been implicated in the complications of diabetes and other conditions. In recent years there has been extensive progress in the search for ways to prevent the modifications and prevent the consequences of the modifications. These areas are covered in this review together with newer ideas on possibilities of reversing the chemical modifications.

Identification of glucoselysine-6-phosphate deglycase, an enzyme involved in the metabolism of the fructation product glucoselysine

The metabolism of the glycation product fructose-epsilon-lysine in Escherichia coli involves its ATP-dependent phosphorylation by a specific kinase (FrlD), followed by the conversion of fructoselysine 6-phosphate into glucose 6-phosphate and lysine by fructoselysine-6-phosphate deglycase (FrlB), which is distantly related to the isomerase domain of glucosamine-6-phosphate synthase. As shown in the present work, several bacterial operons comprise: (1) a homologue of fructoselysine-6-phosphate deglycase; (2) a second homologue of the isomerase domain of glucosamine-6-phosphate synthase, more closely related to it; and (3) components of a novel phosphotransferase system, but no FrlD homologue. The FrlB homologue (GfrF) and the closer glucosamine-6-phosphate synthase homologue (GfrE) encoded by an Enterococcus faecium operon were expressed in E. coli and purified. Similar to FrlB, GfrF catalysed the reversible conversion of fructoselysine 6-phosphate into glucose 6-phosphate and lysine. When incubated with fructose 6-phosphate and elevated concentrations of lysine, GfrE catalysed the formation of a compound identified as 2-epsilon-lysino-2-deoxy-6-phospho-glucose (glucoselysine 6-phosphate) by NMR. GfrE also catalysed the reciprocal conversion, i.e. the formation of fructose 6-phosphate (but not glucose 6-phosphate) from glucoselysine 6-phosphate. The equilibrium constant of this reaction (0.8 M) suggests that the enzyme serves to degrade glucoselysine 6-phosphate. In conclusion, GfrF and GfrE serve to metabolize glycation products formed from lysine and glucose (fructoselysine) or fructose (glucoselysine), via their 6-phospho derivatives. The latter are presumably formed by the putative phosphotransferase system encoded by gfrA-gfrD. The designation gfr (glycation and fructation product degradation) is proposed for this operon. This is the first description of an enzyme participating in the metabolism of fructation products.

Catalytic amounts of fructose may improve glucose tolerance in subjects with uncontrolled non-insulin-dependent diabetes

BACKGROUND

It was suggested that acute ingestion of small amounts of fructose can improve glucose homeostasis.

AIM

To study the effect of a long-term tri-daily supplementation of catalytic amounts of fructose on glucose tolerance of subjects with type 2 diabetes (NIDDM).

METHODS

A double-blind, placebo-controlled study. Twenty-six subjects with uncontrolled NIDDM as indicated by high levels of hemoglobin A1C (Hgb(A1c)) and 2-h postprandial glucose levels >200 mg% were assigned to either fructose or maltodextrin supplementation (7.5 g) tri-daily after each main meal. The subjects were challenged with a fixed meal and blood was drawn for determining levels of glucose, insulin and triglycerides before and 2 h after meal at baseline and 1 month after study entry. Blood was drawn for total cholesterol, high-density and low-density lipoprotein cholesterol (LDL-c), fructosamine and Hgb(A1C) before study entry and at 1, 2 and 3 months into the study.

RESULTS

No changes were observed in the difference between postprandial and pre-meal glucose, insulin or triglyceride levels in each group or between groups. No significant statistical differences were found in weight, total cholesterol, LDL-c and high-density lipoprotein cholesterol (HDL-c) in each group or between groups along the study period. After 1 month fructosamin levels decreased in the fructose-supplemented group but not in the maltodextrin-supplemented group (P<0.052). Hgb(A1C) levels decreased with time in both groups but were significantly lower at 2 months in the fructose group as compared to the maltodextrin group (P<0.03).

CONCLUSIONS

Subjects with NIDDM may benefit from daily supplementation of catalytic amounts of fructose in their diet.

Glycation and carboxymethyllysine levels in skin collagen predict the risk of future 10-year progression of diabetic retinopathy and nephropathy in the diabetes control and complications trial and epidemiology of diabetes interventions and complications participants with type 1 diabetes

Several mechanistic pathways linking hyperglycemia to diabetes complications, including glycation of proteins and formation of advanced glycation end products (AGEs), have been proposed. We investigated the hypothesis that skin collagen glycation and AGEs predict the risk of progression of microvascular disease. We measured glycation products in the skin collagen of 211 Diabetes Control and Complications Trial (DCCT) volunteers in 1992 who continued to be followed in the Epidemiology of Diabetes Interventions and Complications study for 10 years. We determined whether the earlier measurements of glycated collagen and AGE levels correlated with the risk of progression of retinopathy and nephropathy from the end of the DCCT to 10 years later. In multivariate analyses, the combination of furosine (glycated collagen) and carboxymethyllysine (CML) predicted the progression of retinopathy (chi2 = 59.4, P < 0.0001) and nephropathy (chi2 = 18.2, P = 0.0001), even after adjustment for mean HbA(1c) (A1C) (chi2 = 32.7, P < 0.0001 for retinopathy) and (chi2 = 12.8, P = 0.0016 for nephropathy). The predictive effect of A1C vanished after adjustment for furosine and CML (chi2 = 0.0002, P = 0.987 for retinopathy and chi2 = 0.0002, P = 0.964 for nephropathy). Furosine explained more of the variation in the 10-year progression of retinopathy and nephropathy than did CML. These results strengthen the role of glycation of proteins and AGE formation in the pathogenesis of retinopathy and nephropathy. Glycation and subsequent AGE formation may explain the risk of these complications associated with prior A1C and provide a rational basis for the phenomenon of "metabolic memory" in the pathogenesis of these diabetes complications.

Tissue-specific variation in glycation of proteins in diabetes: evidence for a functional role of amadoriase enzymes

The Amadori product fructoselysine (FL), an intermediate in the formation of many advanced glycation end products, may be deglycated by various pathways. These include spontaneous chemical degradation or enzymatic deglycation by amadoriases. This study was designed to compare changes in FL in various tissues in response to changes in glycemia, thereby testing tissue-specific deglycation. FL content in skin collagen, red cell hemoglobin, and total muscle, liver, and brain protein was analyzed by isotope dilution gas chromatography-mass spectrometry. Mean blood glucose increased over fourfold in diabetic versus control rats, whereas changes in glycation of proteins varied from fivefold in collagen to no change in the liver and brain. These results suggest significant differences among tissues in the activity of deglycating enzymes and/or protein turnover.

Alternative antiglycation mechanisms: are spermine and fructosamine-3-kinase part of a carbonyl damage control pathway?

Spermine is an ubiquitous molecule that bears unique structural features of regularly spaced positive charges interrupted by hydrophobic methylene bridges. In previous studies we have shown significant antiglycation effects of physiological concentrations of spermine and spermidine. The effect is apparent in four different protein models, two targeting structural changes on histones and ubiquitin, and two targeting impairment of catalytic activities of AT III and plasminogen. We hypothesize that polyamines inhibit glycation and that might be one of their elusive molecular functions. A mammalian fructosamine-3-kinase (FN-3-K), which phosphorylates fructoselysine (FL) residues on glycated proteins, to FL-3-phosphate has been isolated and cloned by two independent groups. This enzyme may function as a deglycating enzyme. Being its Km for FL two orders of magnitude lower than for its protein substrate, we propose the enzyme has a dual role and also functions as a recycler of spermine-carbonyl adducts. Spermine and FN-3-K may be part of a carbonyl damage control pathway. Thirdly, due to critically functional lysine residues, we underscore the vulnerability to glycation of ornithine decarboxylase, the main enzyme in spermine biosynthesis. If glycation is modulated by polyamines and glycation itself impairs polyamine synthesis, a dangerous loop of excessive spermine consumption and slower spermine biosynthesis might ensue in chronic hyperglycemic conditions. In this perspective, small changes in flow rates in the spermine (where ODC and antizyme are key players) and/or FN-3-K pathway could contribute to enhance the effects of hyperglycemia and explain why there are diabetic subjects with higher glycation phenotypes and incidence of complications. They could have altered steady state levels of polyamines and/or decreased FN-3-K expression or activity.

Genetic variability in the RAGE gene: Possible implications for nutrigenetics, nutrigenomics, and understanding the susceptibility to diabetic complications

Complex chemical processes called nonenzymatic glycation and glycoxidation are one of the interesting examples of potentially harmful interaction between nutrition and disease. This review summarizes factors influencing the extent of glycoxidation in health and disease and especially focuses on the role of genetic variability in "glycoxidation-related genes" in a disease and diet-related pathogenesis. Possible interaction between genetic variability in relevant loci and dietary advanced glycation end products (AGEs) is considered. As AGEs possess a wide range of chemical and biological effects, the interindividual functional variability in systems dealing with glycoxidation could have a significant nutrigenomic and nutrigenetic consequences.

A continuous enzyme assay and characterisation of fructosyl amine oxidase enzymes (EC 1.5.3)

Enzymatic reversal of the Maillard reaction is a growing area of research. Fructosyl amine oxidase enzymes (EC 1.5.3) have attracted recent attention through demonstration of their ability to deglycate Amadori products, low molecular weight intermediates formed during the early stage of the Maillard reaction. Although stopped assays have been described, a bottleneck in current studies is the lack of continuous kinetic assays. Here, we describe the development of a continuous, coupled enzyme assay and its successful application to determining optimal storage conditions and the steady-state kinetic parameters of an enzyme from this group, amadoriase I. A K(m)(app) of 11 microM and a K(cat)(app) of 3.5s(-1) were determined using this assay using fructosyl propylamine as a substrate, which differ from previous reports. This method was also used to test the activity of two site-directed mutants of amadoriase I, H357N and S370A, which were found to be catalytically inactive.

Cloning and expression of fructosyl-amine oxidase from marine yeast Pichia species N1-1

The gene encoding the fructosyl-amine oxidase (FAOD) from the marine yeast Pichia sp. N1-1 was cloned and expressed in Escherichia coli. Partial amino acid sequence analysis of the Pichia sp. N1-1 FAOD allowed the design of oligonucleotide primers for the amplification of the gene by inverse polymerase chain reaction. The FAOD gene was found to be devoid of introns and to encode a 48-kDa protein composed of 429 amino acid residues. The FAD-binding consensus sequence GXGXXG: and the FAD covalent attachment-site cysteine residue have been identified within the predicted amino acid sequence. Comparisons with the amino acid sequences of other eukaryotic FAODs showed only 30% to 40% identities, establishing that the isolated Pichia N1-1 gene encodes a unique FAOD. Recombinant FAOD expression levels in E. coli reached 0.48 U/mg of soluble protein, which is considerably greater than native expression levels by inducing Pichia sp. N1-1 with fructosyl-valine (f-Val). The kinetic properties of the recombinant enzyme were almost indistinguishable from those of the native enzyme. We previously reported on the construction of a number of effective Pichia sp. N1-1 FAOD-based biosensors for measuring f-Val, a model compound for glycated hemoglobin. The further development of these biosensor systems can now greatly benefit from protein engineering and recombinant expression of the FAOD from Pichia N1-1.

Identification of enzymes acting on α-glycated amino acids inBacillus subtilis

We have characterized the Bacillus subtilis homologs of fructoselysine 6-kinase and fructoselysine-6-phosphate deglycase, two enzymes that specifically metabolize the Amadori compound fructose-epsilon-lysine in Escherichia coli. The B. subtilis enzymes also catalyzed the phosphorylation of fructosamines to fructosamine 6-phosphates (YurL) and the conversion of the latter to glucose 6-phosphate and a free amino acid (YurP). However, their specificity was totally different from that of the E. coli enzymes, since they acted on fructoseglycine, fructosevaline (YurL) or their 6-phosphoderivatives (YurP) with more than 30-fold higher catalytic efficiencies than on fructose-alpha-lysine (6-phosphate). These enzymes are therefore involved in the metabolism of alpha-glycated amino acids.