Pyrogallol experimentally and theoretically suppressed advanced glycation end products (AGEs) formation, as one of the mechanisms involved in the chronic complications of the diabetes

This study aimed to explore the inhibitory effect of pyrogallol on AGE formation in the bovine serum albumin (BSA)/glucose system for 21 days at 37 °C. The AGEs formation was measured in terms of Amadori products, total AGEs, argpyrimidine, and pentosidine. Molecular docking was used to investigate the interaction between pyrogallol and BSA. According to the results, in the presence of pyrogallol, the formation of pentosidine and argpyrimidine AGEs decreased. The molecular interaction studies demonstrated that pyrogallol has a high affinity towards arginine residues of albumin. Finally, results proved pyrogallol is a vigorous antiglycation compound and fruitful for AGE inhibition.

Microwave-assisted solid-phase synthesis of lactosylated peptides for food analytical application

The lactosylation of whey proteins affects their properties, especially their allergenicity and nutritional value, which matters in infant feeding. The quantification of lactosylated peptides requires analytically pure standards which are not commercially available. Herein, we proposed a fast, simple, and efficient protocol for the synthesis of lactosylated peptides on solid support based on microwave-assisted synthesis combined with boronate affinity chromatography utilizing the functionalized resin developed in our research group. We have used our method to synthesize identified modified peptides derived from β-lactoglobulin in tryptic digestion. Thus, the standard peptides contain the dabcyl moiety for determination of the amount in a sample and a cleavable linker to obtain tryptic analogs of β-lactoglobulin. Moreover, for the first time, we applied the functionalized resin to enrich the sample of human serum albumin lactosylated in vitro, into lactosylated peptides.

Competent antioxidant and antiglycation properties of zinc oxide nanoparticles (ZnO-NPs) phyto-fabricated from aqueous leaf extract of Boerhaavia erecta L

During the present century, plant-based zinc oxide nanoparticles (ZnO-NPs) are exploited extensively for their vast biological properties due to their unique characteristic features and eco-friendly nature. Diabetes is one of the fast-growing human diseases/abnormalities worldwide, and the need for new/ novel antiglycation products is the need of the hour. The study deals with the phyto-fabrication of ZnO-NPs from Boerhaavia erecta, a medicinally important plant, and to evaluate their antioxidant and antiglycation ability in vitro. UV-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the phyto-fabricated ZnO-NPs. The characterization of nanoparticles revealed that the particles showed an absorption peak at 362 nm and band gap energy of 3.2 eV, approximately 20.55 nm in size, with a ZnO elemental purity of 96.61%. The synthesized particles were found agglomerated when observed under SEM, and the FT-IR studies proved that the phyto-constituents of the extract involved during the different stages (reduction, capping, and stabilization) of nanoparticles synthesis. The antioxidant and metal chelating activities confirmed that ZnO-NPs could inhibit the free radicals generated, which was dose-dependent with an IC₅₀ value between 1.81 and 1.94 mg mL^-1, respectively. In addition, the phyto-fabricated nanoparticles blocked the formation of advanced glycation end products (AGEs) as noticed through inhibition of Amadori products, trapping of reactive dicarbonyl intermediate and breaking the cross-link of glycated protein. It was also noted that the phyto-fabricated ZnO-NPs significantly prevented the damage of red blood corpuscles (RBCs) induced by MGO. The present study's findings will provide an experimental basis for exploring ZnO-NPs in diabetes-related complications.

Modelling Hyperglycaemia in an Epithelial Membrane Model: Biophysical Characterisation

Biomimetic models are valuable platforms to improve our knowledge on the molecular mechanisms governing membrane-driven processes in (patho)physiological conditions, including membrane permeability, transport, and fusion. However, current membrane models are over simplistic and do not include the membrane’s lipid remodelling in response to extracellular stimuli. Our study describes the synthesis of glycated dimyristoyl-phosphatidylethanolamine (DMPE-glyc), which was structurally characterised by mass spectrometry (ESI-MS) and quantified by NMR spectroscopy to be further incorporated in a complex phospholipid (PL) membrane model enriched in cholesterol (Chol) and (glyco)sphingolipids (GSL) designed to mimic epithelial membranes (PL/Chol/GSL) under hyperglycaemia conditions. Characterisation of synthesised DMPE-glyc adducts by tandem mass spectrometry (ESI-MS/MS) show that synthetic DMPE-glyc adducts correspond to Amadori products and quantification by ¹H NMR spectroscopy show that the yield of glycation reaction was 8%. The biophysical characterisation of the epithelial membrane model shows that excess glucose alters the thermotropic behaviour and fluidity of epithelial membrane models likely to impact permeability of solutes. The epithelial membrane models developed to mimic normo- and hyperglycaemic scenarios are the basis to investigate (poly)phenol-lipid and drug–membrane interactions crucial in nutrition, pharmaceutics, structural biochemistry, and medicinal chemistry.

Effect of the consumption of yacon flour and energy-restricted diet on glycation markers, and association between these markers and factors linked to obesity in adults with excess body weight: A randomized, double-blind, placebo-controlled clinical trial

OBJECTIVES

Regardless of the positive effect of yacon on metabolic markers, this food contains fructose molecules, which can originate advanced glycation end products (AGEs). High AGEs serum concentrations can contribute to excess body weight. We evaluated the effect of consuming an energy-restricted diet and yacon flour on glycation markers concentrations, and the associations between these markers and factors linked to obesity in adults with excess body weight.

METHODS

Twenty-six adults with excess body weight were included in this randomized, parallel, double-blind, placebo-controlled, 6-week clinical trial. Subjects were randomly allocated to the control group (n = 13) or the yacon-flour group (n = 13), and daily consumed a breakfast drink either not containing or containing 25 g of yacon flour (8.7 g of fructooligosaccharides). Energy-restricted diets were prescribed for both groups. Biochemical markers, anthropometric variables, and body composition were evaluated at baseline and the end of the study.

RESULTS

AGEs and early glycation products did not increase in the yacon flour group. Soluble receptor for AGEs (sRAGE) decreased regardless of group. Besides, changes in AGEs were positively associated with changes in body fat (β = 0.04, P = 0.038) and in sRAGE, with insulin (β = 0.02, P = 0.035) and homeostasis model assessment index of insulin resistance (β = 0.01, P = 0.049).

CONCLUSIONS

The consumption of 25 g of yacon flour associated with an energy-restricted diet did not increase concentrations of glycation markers. Changes in glycation markers were positively associated with changes in consolidated anthropometric and biochemical markers related to being overweight. Assessing glycation markers may be a useful strategy for monitoring responses to dietary interventions in subjects with excess body weight.

Glycation of Plant Proteins Via Maillard Reaction: Reaction Chemistry, Technofunctional Properties, and Potential Food Application

Plant proteins are being considered to become the most important protein source of the future, and to do so, they must be able to replace the animal-derived proteins currently in use as techno-functional food ingredients. This poses challenges because plant proteins are oftentimes storage proteins with a high molecular weight and low water solubility. One promising approach to overcome these limitations is the glycation of plant proteins. The covalent bonding between the proteins and different carbohydrates created via the initial stage of the Maillard reaction can improve the techno-functional characteristics of these proteins without the involvement of potentially toxic chemicals. However, compared to studies with animal-derived proteins, glycation studies on plant proteins are currently still underrepresented in literature. This review provides an overview of the existing studies on the glycation of the major groups of plant proteins with different carbohydrates using different preparation methods. Emphasis is put on the reaction conditions used for glycation as well as the modifications to physicochemical properties and techno-functionality. Different applications of these glycated plant proteins in emulsions, foams, films, and encapsulation systems are introduced. Another focus lies on the reaction chemistry of the Maillard reaction and ways to harness it for controlled glycation and to limit the formation of undesired advanced glycation products. Finally, challenges related to the controlled glycation of plant proteins to improve their properties are discussed.

Acetoacetate enhancement of glucose mediated DNA glycation

Acetoacetate (AA) is a ketone body, which generates reactive oxygen species (ROS). ROS production is impacted by the formation of covalent bonds between amino groups of biomacromolecules and reducing sugars (glycation). Glycation can damage DNA by causing strand breaks, mutations, and changes in gene expression. DNA damage could contribute to the pathogenesis of various diseases, including neurological disorders, complications of diabetes, and aging. Here we studied the enhancement of glucose-mediated DNA glycation by AA for the first time. The effect of AA on the structural changes, Amadori and advanced glycation end products (AGEs) formation of DNA incubated with glucose for 4 weeks were investigated using various techniques. These included UV-Vis, circular dichroism (CD) and fluorescence spectroscopy, and agarose gel electrophoresis. The results of UV-Vis and fluorescence spectroscopy confirmed that AA increased the DNA-AGE formation. The NBT test showed that AA also increased Amadori product formation of glycated DNA. Based on the CD and agarose gel electrophoresis results, the structural changes of glycated DNA was increased in the presence of AA. The chemiluminescence results indicated that AA increased ROS formation. Thus AA has an activator role in DNA glycation, which could enhance the adverse effects of glycation under high glucose conditions.

Maillard reaction products inhibit the periodontal pathogen Aggregatibacter actinomycetemcomitans by chelating iron

OBJECTIVE

To determine the mechanism of growth inhibition of Aggregatibacter actinomycetemcomitans by Maillard reaction products (MRP).

DESIGN

Growth and cell viabilities in the presence or absence of MRP were measured for both the rough and smooth variants of the bacteria. Effects of addition of ferrous and ferric ions on the inhibition of the bacteria by MRP were determined.

RESULTS

MRPs decreased the extent of complex formation of Chrome Azurol S with iron suggesting that MRPs can chelate iron effectively. The chelation causes growth inhibition of both the rough and smooth strains. At low concentrations of the inhibitor, lag time was extended by approximately 12 h while at high concentrations, cells were killed, decreasing cell viability by up to 8 orders of magnitude. Growth of both the rough and smooth strains could be restored to original level by addition of iron. For the rough strain, both ferrous and ferric ions could relieve the inhibition by MRP while for the smooth strain only ferrous ion was effective.

CONCLUSION

MRPs inhibit the growth of A. actinomycetemcomitans by chelating iron and the inhibition can be relieved by addition of iron.

Formation of Taste-Active Pyridinium Betaine Derivatives Is Promoted in Thermally Treated Oil-in-Water Emulsions and Alkaline pH

The oil-water interface can be used as an efficient reaction controller in foods by carrying specific reactants and products in either the hydrophobic or hydrophilic phase. The formation of the taste-active compounds N-(1-carboxyethyl)-6-hydroxymethyl-pyridinium-3-ol inner salt (alapyridaine) and 1-(1-carboxyethyl)-3-hydroxy-pyridinium inner salt is influenced by the presence of a dispersed saturated triglyceride oil phase and by the pH of the aqueous phase. At pH 6.5, the formation of both betaines was 1.24 and 6 times higher in emulsions than in aqueous solution after 4 min at 140 °C. In alkaline emulsions (pH = 9.5, 4 min), the concentrations of alapyridaine and 1-(1-carboxyethyl)-3-hydroxy-pyridinium ion were 6.2 and 3.8 times higher, respectively, than in unbuffered emulsions as a result of the interaction between the polar head group of the surfactant and pyridinium rings. Here, we reported for the first time the effects of multiphase systems on the formation of nonvolatile, taste-active end products.

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.

Milk-Derived Amadori Products in Feces of Formula-Fed Infants

Food processing of infant formula alters chemical structures, including the formation of Maillard reaction products between proteins and sugars. We detected early Maillard reaction products, so-called Amadori products, in stool samples of formula-fed infants. In total, four Amadori products (N-deoxylactulosyllysine, N-deoxyfructosyllysine, N-deoxylactulosylleucylisoleucine, N-deoxyfructosylleucylisoleucine) were identified by a combination of complementary nontargeted and targeted metabolomics approaches. Chemical structures were confirmed by preparation and isolation of reference compounds, LC-MS/MS, and NMR. The leucylisoleucine Amadori compounds, which most likely originate from β-lactoglobulin, were excreted throughout the first year of life in feces of formula-fed infants but were absent in feces of breastfed infants. Despite high inter- and intraindividual differences of Amadori products in the infants' stool, solid food introduction resulted in a continuous decrease, proving infant formula as the major source of the excreted Amadori products.

The quantification of free Amadori compounds and amino acids allows to model the bound Maillard reaction products formation in soybean products

The quantification of protein bound Maillard reaction products (MRPs) is still a challenge in food chemistry. Protein hydrolysis is the bottleneck step: it is time consuming and the protein degradation is not always complete. In this study, the quantitation of free amino acids and Amadori products (APs) was compared to the percentage of blocked lysine by using chemometric tools. Eighty thermally treated soybean samples were analyzed by mass spectrometry to measure the concentration of free amino acids, free APs and the protein-bound markers of the Maillard reaction (furosine, Nε-(carboxymethyl)-l-lysine, Nε-(carboxyethyl)-l-lysine, total lysine). Results demonstrated that Discriminant Analysis (DA) and Correlated Component Regression (CCR) correctly estimated the percent of blocked lysine in a validation and prediction set. These findings indicate that the measure of free markers reflects the extent of protein damage in soybean samples and it suggests the possibility to obtain rapid information on the quality of the industrial processes.

Salmonella-Mediated Inflammation Eliminates Competitors for Fructose-Asparagine in the Gut

Salmonella enterica elicits intestinal inflammation to gain access to nutrients. One of these nutrients is fructose-asparagine (F-Asn). The availability of F-Asn to Salmonella during infection is dependent upon Salmonella pathogenicity islands 1 and 2, which in turn are required to provoke inflammation. Here, we determined that F-Asn is present in mouse chow at approximately 400 pmol/mg (dry weight). F-Asn is also present in the intestinal tract of germfree mice at 2,700 pmol/mg (dry weight) and in the intestinal tract of conventional mice at 9 to 28 pmol/mg. These findings suggest that the mouse intestinal microbiota consumes F-Asn. We utilized heavy-labeled precursors of F-Asn to monitor its formation in the intestine, in the presence or absence of inflammation, and none was observed. Finally, we determined that some members of the class Clostridia encode F-Asn utilization pathways and that they are eliminated from highly inflamed Salmonella-infected mice. Collectively, our studies identify the source of F-Asn as the diet and that Salmonella-mediated inflammation is required to eliminate competitors and allow the pathogen nearly exclusive access to this nutrient.

Identification of Bacterial Species That Can Utilize Fructose-Asparagine

Salmonella enterica serovar Typhimurium is the only organism demonstrated to utilize fructose-asparagine (F-Asn) as a source of carbon and nitrogen. In this report, we first used a bioinformatics approach to identify other microorganisms that encode homologs of the Salmonella F-Asn utilization enzymes FraB (deglycase), FraD (kinase), and FraE (asparaginase). These candidate organisms were then tested with up to four different methods to confirm their ability to utilize F-Asn. The easiest and most broadly applicable method utilized a biological toxicity assay, which is based on the observation that F-Asn is toxic to a Salmonella fraB mutant. Candidate organisms were grown in a rich medium containing F-Asn, and depletion of F-Asn from the medium was inferred by the growth of a Salmonella fraB mutant in that same medium. For select organisms, the toxicity assay was cross-validated by direct mass spectrometry-aided measurement of F-Asn in the spent-culture media and through demonstration of FraB and FraD enzyme activity in cellular extracts. For prototrophs, F-Asn utilization was additionally confirmed by growth in a minimal medium containing F-Asn as the sole carbon source. Collectively, these studies established that Clostridiumbolteae, Clostridium acetobutylicum, and Clostridium clostridioforme can utilize F-Asn, but Clostridium difficile cannot; Klebsiella oxytoca and some Klebsiella pneumoniae subspecies can utilize F-Asn; and some Citrobacter rodentium and Citrobacter freundii strains can also utilize F-Asn. Within Salmonella enterica, the host-adapted serovars Typhi and Paratyphi A have lost the ability to utilize F-Asn.IMPORTANCE Fructose-asparagine (F-Asn) is a precursor to acrylamide that is found in human foods, and it is also a nutrient source for Salmonella enterica, a foodborne pathogen. Here, we determined that among the normal intestinal microbiota, there are species of Clostridium that encode the enzymes required for F-Asn utilization. Using complementary experimental approaches, we have confirmed that three members of Clostridium, two members of Klebsiella, and two members of Citrobacter can indeed utilize F-Asn. The Clostridium spp. likely compete with Salmonella for F-Asn in the gut and contribute to competitive exclusion. FraB, one of the enzymes in the F-Asn utilization pathway, is a potential drug target because inhibition of this enzyme leads to the accumulation of a toxic metabolite that inhibits the growth of Salmonella species. This study identifies the potential off-target organisms that need to be considered when developing therapeutics directed at FraB.

Measurement of Fructose-Asparagine Concentrations in Human and Animal Foods

The food-borne bacterial pathogen, Salmonella enterica, can utilize fructose-asparagine (F-Asn) as its sole carbon and nitrogen source. F-Asn is the product of an Amadori rearrangement following the nonenzymatic condensation of glucose and asparagine. Heating converts F-Asn via complex Maillard reactions to a variety of molecules that contribute to the color, taste, and aroma of heated foods. Among these end derivatives is acrylamide, which is present in some foods, especially in fried potatoes. The F-Asn utilization pathway in Salmonella, specifically FraB, is a potential drug target because inhibition of this enzyme would lead to intoxication of Salmonella in the presence of F-Asn. However, F-Asn would need to be packaged with the FraB inhibitor or available in human foods. To determine if there are foods that have sufficient F-Asn, we measured F-Asn concentrations in a variety of human and animal foods. The 400 pmol/mg F-Asn found in mouse chow is sufficient to intoxicate a Salmonella fraB mutant in mouse models of salmonellosis, and several human foods were found to have F-Asn at this level or higher (fresh apricots, lettuce, asparagus, and canned peaches). Much higher concentrations (11 000-35 000 pmol/mg dry weight) were found in heat-dried apricots, apples, and asparagus. This report reveals possible origins of F-Asn as a nutrient source for Salmonella and identifies foods that could be used together with a FraB inhibitor as a therapeutic agent for Salmonella.

Simultaneous quantification of twenty Amadori products in soy sauce using liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method using a pentafluorophenylpropyl-bonded silica column was developed to simultaneously quantify twenty Amadori products (APs), including N-(1-Deoxy-d-fructosyl-1-yl)-l-isoleucine (Fru-Ile) and N-(1-Deoxy-d-fructosyl-1-yl)-l-leucine (Fru-Leu), in soy sauce, without the need for an ion-pairing reagent or sample derivatization. The method was applied to six types of soy sauce, to determine the total AP levels and the levels of individual APs. The level of total APs widely varied between the eight samples, from 358mg/L to 24347mg/L. The concentrations of N-ε-(1-deoxy-d-fructosyl-1-yl)-l-lysine (Fru-Lys) and N-(1-deoxy-d-fructosyl-1-yl)-l-pyroglutamic acid (Fru-pGlu) were the highest among the APs and the level of Fru-pGlu was similar to that of Fru-Lys. Furthermore, fermentation periods of up to six months greatly influenced AP levels in soy sauce but the levels remained constant thereafter. Thermal treatment of soy sauce had little effect on AP levels.

The quality of low lactose milk is affected by the side proteolytic activity of the lactase used in the production process

Lactose intolerance syndrome can be efficiently tackled consuming low lactose products. Lactase is the key tool to manufacture low lactose milk (LLM): its addition during milk processing can be done "in batch", i.e. before thermal treatment, or directly "in pack" after sterilization. In this paper data on sensory properties, Maillard Reaction products (MRPs) and free amino acids formation were obtained on six commercial Italian LLMs over six months storage. They showed that the side proteolytic activity of lactase caused the release of amino acids with a significant higher MRPs and off-flavors formation in four out of five samples produced by adding the enzyme in the pack after thermal treatment. We concluded that the in pack addition of lactase after milk sterilization can have negative sensorial and nutritional consequences mainly related to the enzyme side proteolytic activity especially for prolonged storage time.

Enhanced Approaches for Identifying Amadori Products: Application to Peanut Allergens

The dry roasting of peanuts is suggested to influence allergic sensitization as a result of the formation of advanced glycation end products (AGEs) on peanut proteins. Identifying AGEs is technically challenging. The AGEs of a peanut allergen were probed with nano-scale liquid chromatography-electrospray ionization-mass spectrometry (nanoLC-ESI-MS) and tandem mass spectrometry (MS/MS) analyses. Amadori product ions matched to expected peptides and yielded fragments that included a loss of three waters and HCHO. As a result of the paucity of b and y ions in the MS/MS spectrum, standard search algorithms do not perform well. Reactions with isotopically labeled sugars confirmed that the peptides contained Amadori products. An algorithm was developed on the basis of information content (Shannon entropy) and the loss of water and HCHO. Results with test data show that the algorithm finds the correct spectra with high precision, reducing the time needed to manually inspect data. Computational and technical improvements allowed for better identification of the chemical differences between modified and unmodified proteins.

Metabolite Profiling of Italian Tomato Landraces with Different Fruit Types

Increased interest toward traditional tomato varieties is fueled by the need to rescue desirable organoleptic traits and to improve the quality of fresh and processed tomatoes in the market. In addition, the phenotypic and genetic variation preserved in tomato landraces represents a means to understand the genetic basis of traits related to health and organoleptic aspects and improve them in modern varieties. To establish a framework for this approach, we studied the content of several metabolites in a panel of Italian tomato landraces categorized into three broad fruit type classes (flattened/ribbed, pear/oxheart, round/elongate). Three modern hybrids, corresponding to the three fruit shape typologies, were included as reference. Red ripe fruits were morphologically characterized and biochemically analyzed for their content in glycoalkaloids, phenols, amino acids, and Amadori products. The round/elongate types showed a higher content in glycoalkaloids, whereas flattened types had higher levels of phenolic compounds. Flattened tomatoes were also rich in total amino acids and in particular in glutamic acid. Multivariate analysis of amino acid content clearly separated the three classes of fruit types. Making allowance of the very low number of genotypes, phenotype-marker relationships were analyzed after retrieving single nucleotide polymorphisms (SNPs) among the landraces available in the literature. Sixty-six markers were significantly associated with the studied traits. The positions of several of these SNPs showed correspondence with already described genomic regions and QTLs supporting the reliability of the association. Overall the data indicated that significant changes in quality-related metabolites occur depending on the genetic background in traditional tomato germplasm, frequently according to specific fruit shape categories. Such a variability is suitable to harness association mapping for metabolic quality traits using this germplasm as an experimental population, paving the way for investigating their genetic/molecular basis, and facilitating breeding for quality-related compounds in tomato fruits.

Nonenzymatic modification of Ubiquitin under high-pressure and -temperature treatment: mass spectrometric studies

The effect of high-pressure and/or high-temperature on the glycation of a model protein (ubiquitin) was investigated by mass spectrometry. This paper reports the impact of high pressure (up to 1200 MPa) on the modification of a ubiquitin using ESI-MS measurements. The application of glucose labeled with stable isotope allows a quantitative assessment of modification under the conditions of high-pressure (HPG) and high-temperature (HTG) glycation. A higher degree of modification was observed for the sample heated at 80 °C for 25 min under atmospheric pressure than for sample treated under high pressure. In samples treated at pressure below 400 MPa an insignificant increase of glycation level was observed, whereas high pressure (>600 MPa) has only a minor effect on the number of hexose moieties (Fru) attached to the lysine residue side chain.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

[Assays of HbA1c and Amadori products in human biology]

Different Amadori products, formed during the early steps of the non-enzymatic glycation of proteins, may be assayed in current practice in human biology. The most important marker is HbA1c, resulting from the binding of glucose to the N-terminal extremity of HbA beta chains. HbA1c may be evaluated by various techniques (ion exchange or affinity high performance liquid chromatography, capillary electrophoresis, immunoassay, enzymatic technique) and is considered the best marker of diabetic patient survey. Due to its irreversible and cumulative formation, it provides a retrospective information on the glycemic balance over the four to eight weeks preceding blood collection. It benefits from an international standardization, based on a reference method using liquid chromatography coupled to capillary electrophoresis or mass spectrometry, maintained by an international network of reference laboratories. When HbA1c assay cannot be used (anemia, hemolysis, hemoglobinopathy) or when a shorter period of glycemic equilibrium must be evaluated (child and adolescent, pregnancy, therapeutic changes), other Amadori products may be assayed, like plasma fructosamine (all plasma glycated proteins) or glycated albumin. Nevertheless, these assays are less used in practice, because their semiological value has been less evidenced. Besides, fructosamine assay lacks specificity, and glycated albumin assay has been described recently. An expanding use of HbA1c assay is expected, especially for the diagnosis of diabetes mellitus and the evaluation of other risks, especially cardiovascular ones.

Amadori glycated proteins: role in production of autoantibodies in diabetes mellitus and effect of inhibitors on non-enzymatic glycation

Nonenzymatic glycation of macromolecules, especially proteins leading to their oxidation is increased in diabetes mellitus due to hyperglycemia and play an important role in associated complications of the disease. The glycation primarily occurs at intrachain lysine residues of proteins and results in the formation of an early stage stable product as Amadori-lysine which undergo further irreversible chemical reactions to form advanced glycation endproducts. This review deals with the role of Amadori modified proteins in pathogenesis of diabetes. We aim to explain immunogenicity of Amadori-glycated proteins, which might be involve in production of serum autoantibodies in the diabetic patients, and effect of inhibitors on the glycation process.