Quantifying carboxymethyl lysine and carboxyethyl lysine in human plasma: clinical insights into aging research using liquid chromatography-tandem mass spectrometry.

OBJECTIVE: The objective of this study was to establish a methodology for determining carboxymethyl lysine (CML) and carboxyethyl lysine (CEL) concentrations in human plasma using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The test results were also used for clinical aging research. METHODS: Human plasma samples were incubated with aqueous perfluorovaleric acid (NFPA), succeeded by precipitation utilizing trichloroacetic acid, hydrolysis facilitated by hydrochloric acid, nitrogen drying, and ultimate re-dissolution utilizing NFPA, followed by filtration. Cotinine-D3 was added as an internal standard. The separation was performed on an Agela Venusil ASB C18 column (50 mm × 4.6 mm, 5 µm) with a 5 mmol/L NFPA and acetonitrile/water of 60:40 (v/v) containing 0.15% formic acid. The multiple reaction monitoring mode was used for detecting CML, CEL, and cotinine-D3, with ion pairs m/z 205.2 > 84.1 (for quantitative) and m/z 205.2 > m/z 130.0 for CML, m/z 219.1 > 84.1 (for quantitative) and m/z 219.1 > m/z 130.1 for CEL, and m/z 180.1 > 80.1 for cotinine-D3, respectively. RESULTS: The separation of CML and CEL was accomplished within a total analysis time of 6 minutes. The retention times of CML, CEL, and cotinine-D3 were 3.43 minutes, 3.46 minutes, and 4.50 minutes, respectively. The assay exhibited linearity in the concentration range of 0.025-1.500 µmol/L, with a lower limit of quantification of 0.025 µmol/L for both compounds. The relative standard deviations of intra-day and inter-day were both below 9%, and the relative errors were both within the range of ±4%. The average recoveries were 94.24% for CML and 97.89% for CEL. CONCLUSION: The results indicate that the developed methodology is fast, highly sensitive, highly specific, reproducible, and suitable for the rapid detection of CML and CEL in clinical human plasma samples. The outcomes of the clinical research project on aging underscored the important indicative significance of these two indicators for research on human aging.

Chemical synthesis of site-selective advanced glycation end products in α-synuclein and its fragments.

Advanced glycation end products (AGEs) arise from the Maillard reaction between dicarbonyls and proteins, nucleic acids, or specific lipids. Notably, AGEs are linked to aging and implicated in various disorders, spanning from cancer to neurodegenerative diseases. While dicarbonyls like methylglyoxal preferentially target arginine residues, lysine-derived AGEs, such as N(6)-(1-carboxymethyl)lysine (CML) and N(6)-(1-carboxyethyl)lysine (CEL), are also abundant. Predicting protein glycation in vivo proves challenging due to the intricate nature of glycation reactions. In vitro, glycation is difficult to control, especially in proteins that harbor multiple glycation-prone amino acids. α-Synuclein (aSyn), pivotal in Parkinson's disease and synucleinopathies, has 15 lysine residues and is known to become glycated at multiple lysine sites. To understand the influence of glycation in specific regions of aSyn on its behavior, a strategy for site-specific glycated protein production is imperative. To fulfill this demand, we devised a synthetic route integrating solid-phase peptide synthesis, orthogonal protection of amino acid side-chain functionalities, and reductive amination strategies. This methodology yielded two disease-related N-terminal peptide fragments, each featuring five and six CML and CEL modifications, alongside a full-length aSyn protein containing a site-selective E46CEL modification. Our synthetic approach facilitates the broad introduction of glycation motifs at specific sites, providing a foundation for generating glycated forms of synucleinopathy-related and other disease-relevant proteins.

Inhibitory effects and mechanisms of phenolic compounds in rapeseed oil on advanced glycation end product formation in chemical and cellular models in vitro.

Sinapic acid (SA), canolol (CAO) and canolol dimer (CAO dimer) are the main phenolic compounds in rapeseed oil. However, their possible efficacy against glycation remains unclear. This study aims to explore the impacts of these substances on the formation of advanced glycation end products (AGEs) based on chemical and cellular models in vitro. Based on fluorescence spectroscopy results, three chemical models of BSA-fructose, BSA-methylglyoxal (MGO), and arginine (Arg)-MGO showed that SA/CAO/CAO dimer could effectively reduce AGE formation but with different abilities. After SA/CAO/CAO dimer incubation, effective protection against BSA protein glycation was observed and three different MGO adducts were formed. In MGO-induced HUVEC cell models, only CAO and CAO dimer significantly inhibited oxidative stress and cell apoptosis, accompanied by the regulation of the Nrf2-HO-1 pathway. During the inhibition, 20 and 12 lipid mediators were reversed in the CAO and CAO dimer groups compared to the MGO group.

Boronate crosslinking-based ratiometric electrochemical assay of glycated albumin.

As a product of nonenzymatic glycation, glycated albumin (GA) is a promising serum marker for the short-term glycemic monitoring in patients with diabetes. On the basis of the boronate crosslinking (BCL)-enabled direct labeling of ferrocene (Fc) tags to the nonenzymatically glycated (NEG) sites, we report herein a novel aptamer-based ratiometric electrochemical (apt-REC) platform for the point-of-care (POC) assay of GA. This apt-REC platform is based on the recognition of GA proteins by the methylene blue (MB)-modified aptamer receptors and the labeling of the Fc tags to the NEG sites via the BCL. Using MB as the reference tag and Fc as the quantification tag, the ratio of the oxidation currents (i.e., IFc/IMB) can serve as the yardstick for the ratiometric assay of GA. Due to the presence of tens of the NEG sites, each GA protein can be labeled with tens of quantification tags, permitting the amplified assay in a simple, time-saving, and low-cost manner. The ratiometric signal exhibited a good linear response over the range from 0.1 to 100 µg/mL, with a detection limit of 45.5 ng/mL. In addition to the superior reproducibility and robustness, this apt-REC platform is highly selective (capable of discriminating GA against human serum albumin (HSA)) and applicable to GA assay in serum samples. Due to its low cost, high reproducibility and robustness, simple operation, and high sensitivity and selectivity, this apt-REC platform holds great promise in the POC assay of GA for diabetes management.

Development of simultaneous quantitation method for 20 free advanced glycation end products using UPLC-MS/MS and clinical application in kidney injury.

Advanced glycation end products (AGEs), derived from the non-enzymatic glycation reaction, are defined as glycotoxins in various diseases including aging, diabetes and kidney injury. Exploring AGEs as potential biomarkers for these diseases holds paramount significance. Nevertheless, the high chemical structural similarity and great heterogeneity among AGEs present a formidable challenge when it comes to the comprehensive, simultaneous, and accurate detection of multiple AGEs in biological samples. In this study, an UPLC/MS/MS method for simultaneous quantification of 20 free AGEs in human serum was firstly established and applied to quantification of clinical samples from individuals with kidney injury. Simple sample preparation method through protein precipitation without derivatization was used. Method performances including imprecision, accuracy, sensitivity, linearity, and carryover were systematically validated. Intra- and inter- imprecision of 20 free AGEs were 1.93-5.94 % and 2.30-8.55 %, respectively. The method accuracy was confirmed with good recoveries ranging from 96.40 % to 103.25 %. The LOD and LOQ were 0.1-3.13 ng/mL and 0.5-6.25 ng/mL, respectively. Additionally, the 20 free AGEs displayed excellent linearity (R2 >0.9974) across a wide linear range (1.56-400 ng/mL). Finally, through simultaneous quantitation of 20 Free AGEs in 100 participants including kidney injury patient and healthy controls, we identified six free AGEs, including N6-carboxyethyl-L-arginine (CEA), N6-carboxymethyl-L-lysine (CML), methylglyoxal-derived hydroimidazolones (MG-H), N6-formyl-lysine, N6-carboxymethyl-L-arginine (CMA), and glyoxal-derived hydroimidazolone (G-H), could well distinguish kidney injury patients and healthy individuals. Among them, the levels of four free AGEs including CML, CEA, MG-H, and G-H strongly correlate with traditionally clinical markers of kidney disease. The high area under the curve (AUC) values (AUC=0.965) in receiver operating characteristic (ROC) curve indicated that these four free AGEs can be served as combined diagnostic biomarkers for the diagnosis of kidney disease.

Dry-air roasting impact on physicochemical, functional, antioxidant properties, phenolic profile and Maillard reaction products of flaxseed flour and cake flour.

The study investigated and compared physicochemical, functional, antioxidant properties, phenolic profile and Maillard reaction products (MRP) of flaxseed flour (FF) and flaxseed cake flour (FCF) upon dry-air roasting (DaR) of flaxseeds at 140, 160 and 180 °C for 5 and 10 min. This information on FF and FCF is limited and has considerable gaps. The raw FF exhibited higher fat, ash, antioxidant and functional properties while lower protein than the FCF. Upon increasing DaR conditions, the ash and protein increased in FCF and decreased in FF. DaR at 180 °C for 10 min augmented water solubility index, ΔE, MRP, free rutin and syringic acid, bound epicatechin, gallic acid and syringic acid while lowered moisture, L*, b*, hue, chroma, potassium, iron, selenium, emulsion indexes, caffeic acid, flavonoids and free resveratrol in FF and FCF. In conclusion, DaR improves phenolic profile, antioxidant properties, MRP, water solubility and oil absorption capacity of FF and FCF.

Inhibitory effect of baicalein against glycation in HSA: an in vitro approach.

Hyperglycaemia accelerates the aging process significantly. Diabetes problems can be mitigated by inhibiting glycation. To learn more about glycation and antiglycation mediated by methyl glyoxal and baicalein, we studied human serum albumin as a model protein. A Methylglyoxal (MGO) incubation period of seven days at 37 degrees Celsius induced glycation of Human Serum Albumin.s Hyperchromicity, decreased tryptophan and intrinsic fluorescence, increased AGE-specific fluorescence, and reduced mobility were all seen in glycated human serum albumin (MGO-HSA) in sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Fourier transform infrared spectroscopy (FT-IR) and then far ultraviolet dichroism were used to detect secondary and tertiary structural perturbations (CD). The Congo red assay (CR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) all verified the presence of amyloid-like clumps. Structure (carbonyl groups on ketoamine moieties) (CO), physiological problems including diabetes mellitus, and cardiovascular disease, etc. are linked to the structural and functional changes in glycated HSA, as proven by these studies.Communicated by Ramaswamy H. Sarma.

Assessing the effect of Maillard reaction products on the functionality and antioxidant properties of Amaranth-red seaweed blends.

Plant-based proteins, represented by amaranth in our study, embrace a potential as an ingredient for the functional-food formulation. However, their efficacy is hindered by inherent limitations in solubility, emulsification, and antioxidant traits. The Maillard reaction, a complex chemical-process resulting in a diverse array of products, including Maillard conjugates and Maillard reaction products (MRPs), can employ variable effects on these specific attributes. To elucidate the influence of this reaction and the MRPs on the aforementioned properties, we used a complex blend of dehydrated seaweed Gracilaria and amaranth protein to create a conjugate-MRP blend. Our investigations revealed that the resultant incorporation enhanced solubility, emulsification, and antioxidant properties, while the intermediates formed did not progress to advanced glycation stages. This change is likely attributed to the dual effect of conjugates that altered the secondary protein structure, while the generation and/or preservation of MRPs post ultrasonication and spray drying enhanced its antioxidant potential.

UPLC-MS/MS method for quantitative determination of the advanced glycation endproducts Nε-(carboxymethyl)lysine and Nε-(carboxyethyl)lysine.

During blood storage, red blood cells (RBCs) undergo physical, chemical, and metabolic changes that may contribute to post-transfusion complications. Due to the hyperglycemic environment of typical solutions used for RBC storage, the formation of advanced glycation endproducts (AGEs) on the stored RBCs has been implicated as a detrimental chemical change during storage. Unfortunately, there are limited studies involving quantitative determination and differentiation of carboxymethyl-lysine (CML) and carboxyethyl-lysine (CEL), two commonly formed AGEs, and no reported studies comparing these AGEs in experimental storage solutions. In this study, CML and CEL were identified and quantified on freshly drawn blood samples in two types of storage solutions, standard additive solution 1 (AS-1) and a normoglycemic version of AS-1 (AS-1N). To facilitate detection of the AGEs, a novel method was developed to reliably extract AGEs from RBCs, provide Food and Drug Administration (FDA) bioanalytical guidance criteria, and enable acceptable selectivity for these analytes. Ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) was utilized to identify and quantify the AGEs. Results show this method is accurate, precise, has minimal interferences or matrix effects, and overcomes the issue of detecting AGE byproducts. Importantly, AGEs can be detected and quantified in both types of blood storage solutions (AS-1 and AS-1N), thereby enabling long-term (6 weeks) blood storage related studies.

Screening, identification and control of unknown estrogen-like compounds in Maillard reaction products of glucose-arginine/lysine model systems.

It was speculated that estrogen-like compounds may be produced by chemical reactions during food processing, such as Maillard reaction, which would disrupt the endocrine system of organisms. Herein, the Maillard reaction in the process of high temperature for long time was simulated by using model system, and unknown estrogen-like compounds produced during Maillard reaction were screened by colorimetric assay based on dual estrogen receptor (ER)-gold nanoparticles (AuNPs) and enzyme-linked immunosorbent assay (ELISA). Possible structures of estrogen-like compounds were inferred by ultra-performance liquid chromatography-quadrupole time of flight tandem mass spectrometry (UPLC-QTOF/MS) in combination with a mass database, and finally the structure of estrogen-like compound, 2, 4-dihydroxy-1, 4-benzoxazin-3-one-2-o-ß-D-glucopyranoside (DIBOA-glc), was identified by high resolution orbitrap mass spectrometry (Orbitrap HRMS). This is the first study of the screening and identification of unknown estrogen-like compounds produced in Maillard reaction. Additionally, strategy of controlling the formation of DIBOA-glc by adding vitamin B6 in Maillard reaction was proposed, providing effective proposals for the safety control in actual food processing.

Non-canonical food sources: bacterial metabolism of Maillard reaction products and its regulation.

Proteins are an important part of our regular diet. During food processing, their amino acid composition can be chemically altered by the reaction of free amino groups with sugars - a process termed glycation. The resulting Maillard reaction products (MRPs) have low bioavailability and thus predominantly end up in the colon where they encounter our gut microbiota. In the following review, we summarize bacterial strategies to efficiently metabolize these non-canonical amino acids. A particular focus will be on the complex regulatory mechanisms that allow a tightly controlled expression of metabolic genes to successfully occupy the ecological niches that result from the chemical diversity of MRPs.

The relationships between plasma advanced glycation end products level and cognitive function in middle-aged and elderly Chinese subjects.

OBJECTIVES: To determine the relationships between circulating representative advanced glycation end products (AGEs) and cognitive performance in middle-aged and elderly Chinese adults. METHOD: A cross-sectional study with 1834 participants were included. Cognitive performance was assessed using the Mini-Mental State Examination (MMSE). Plasma free AGEs including Nε-carboxymethyl-L-lysine (CML), Nε-(1-carboxyethyl) lysine (CEL), S-carboxymethyl-L-cysteine (CMC) and Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1) were measured by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Multivariate adjusted linear and logistic regression analysis were used to explore the associations between plasma AGEs and cognitive function. RESULTS: The prevalence of mild cognitive impairment (MCI) was 17.94%. Plasma CMC and MG-H1 level were negatively associated with MMSE score (ß = -0.42, p < 0.001 for all) in the multivariate linear regression analysis. In the multivariate logistic regression analysis, compared to the lowest tertile, participants within the highest tertile of CMC and MG-H1 had increased risk of MCI [ORs (95% CI): 1.62 (1.21-2.17), P trend <0.001, and ORs (95% CI): 1.30 (0.97-1.76), P trend = 0.069, respectively]. In addition, the weighted quantile sum (WQS) index was negatively associated with MMSE (ß = -0.48, P < 0.001) and increased risk of MCI [ORs (95% CI): 1.35 (1.20-1.52), P < 0.001]. CONCLUSION: Combined exposure of plasma free AGEs including CML, CEL, CMC and MG-H1 were associated with increased risk of cognitive impairment. Plasma CMC and MG-H1 might the main contributors for cognitive impairment, while further longitudinal studies are required to verify the associations.

Molecular Mechanism of Lotus Seedpod Oligomeric Procyanidins Inhibiting the Absorption of Oligopeptide-Advanced Glycation End Products.

Research on advanced glycation end product (AGEs) inhibition has generally focused on food processing, but many protein-AGEs will still be taken. Oligopeptide (OLP)-AGEs, as the main form after digestion, will damage human health once absorbed. Here, we investigated the ability of lotus seedpod oligomeric procyanidins (LSOPC) to inhibit the absorption of the OLP-AGEs and elucidated the underlying mechanism. Our results showed that the inhibition rate of LSOPC on the absorption of OLP-AGEs was about 50 ± 5.38%. 0.1, 0.2, and 0.3 mg/mL could upregulate the expression of ZO-1 and downregulate the expression of PepT1 and clathrin. Molecular docking showed that LSOPC could compete with the binding of OLP-AGEs to PepT1 and AP-2, thus inhibiting the absorption of OLP-AGEs. Furthermore, the interaction of LSOPC with the OLP-AGEs reduced the surface hydrophobicity of OLP-AGEs. It altered the secondary structure of the OLP-AGEs, thus weakening the affinity of the OLP-AGEs to the transporter protein to inhibit the absorption of OLP-AGEs. Together, our data revealed potential mechanisms by which LSOPC inhibit the absorption of OLP-AGEs and opened up new perspectives on the application of LSOPC in reducing the increasing health risks posed by OLP-AGEs.

Glycated bovine serum albumin for use in feeding trials with animal models - In vitro methodology and characterization of a glycated substrate for modifying feed pellets.

This study investigated different methods to produce Nε-carboxymethyl-lysine (CML)-enriched bovine serum albumin (BSA) as alternatives to the classical approach using glyoxylic acid (GA) and sodium cyanoborohydride (NaBH3CN) which results in toxic hydrogen cyanide (HCN). The reaction of GA (6 mmol/L) and NaBH3CN (21 mmol/L) to produce CML remained the most effective with CML yields of 24-35%, followed by 13-24% using 300 mmol/L glyoxal (GO). GA promoted specific modification of lysine to CML, and fewer structural modifications of the BSA molecule compared with GO, as evidenced by fluorescence and proteomic analyses. GO promoted greater arginine modification compared with GA (76 vs 23%). Despite structural changes to BSA with GO, murine fecal clearance of CML was similar to literature values. Hence, BSA glycation with 300 mmol/L glyoxal is a suitable alternative to GA and NaBH3CN for generating CML-enriched protein free of HCN, but a CML-only fortification model remains to be described.

The Effect of Free and Protein-Bound Maillard Reaction Products N-ε-Carboxymethyllysine, N-ε-Fructosyllysine, and Pyrraline on Nrf2 and NFκB in HCT 116 Cells.

SCOPE: Maillard reaction products (MRPs) are believed to interact with the receptor for advanced glycation endproducts (RAGE) and lead to a pro-inflammatory cellular response. The structural basis for this interaction is scarcely understood. This study investigates the effect of individual lysine modifications in free form or bound to casein on human colon cancer cells. METHODS AND RESULTS: Selectively glycated casein containing either protein-bound N-ε-carboxymethyllysine (CML), N-ε-fructosyllysine (FL), or pyrraline is prepared and up to 94%, 97%, and 61% of lysine modification could be attributed to CML, FL, or pyrraline, respectively. HCT 116 cells are treated with free CML, pyrraline, FL, or modified casein for 24 h. Native casein is used as control. Intracellular MRP content is analyzed by UPLC-MS/MS. Microscopic analysis of the transcription factors shows no activation of NFκB by free or protein-bound FL or CML, whereas casein containing protein-bound pyrraline activates Nrf2. RAGE expression is not influenced by free or casein-bound MRPs. Activation of Nrf2 by pyrraline-modified casein is confirmed by analyzing Nrf2 target proteins NAD(P)H dehydrogenase (quinone 1) (NQO1) and heme oxygenase-1 (HO-1). CONCLUSION: Studies on the biological effects of glycated proteins require an individual consideration of defined structures. General statements on the effect of "AGEs" in biological systems are scientifically unsound.

Formation of advanced glycation end-products in minced pork during frozen-then-chilled storage and subsequent heating.

The influences of frozen-then-chilled storage of minced pork on the formation of advanced glycation end-products (AGEs) including Nε-carboxymethyllysine and Nε-carboxyethyllysine, and their corresponding α-dicarbonyl precursors (α-DPs; glyoxal and methylglyoxal) during storage and subsequent heating were investigated in comparison with chilled storage. During cold storage, the levels of AGEs, trichloroacetic acid-soluble peptides, and Schiff bases in minced pork continuously increased while α-DPs decreased. The 30 min heating (100 °C) resulted in 64-560% increase of AGEs in pork, corresponding with an increase of Schiff bases and decreases of α-DPs. Compared to the chilled storage, the frozen-then-chilled storage led to no significant difference (P > 0.05) on the levels of AGEs and α-DPs in raw or heat-treated pork, implying that the formation and thawing of ice crystals in pork during the frozen-then-chilled storage had minor to no effects on the formation of AGEs and their α-DPs.

Magnetically driven nanorobots based on peptides nanodots with tunable photoluminescence for rapid scavenging reactive α-dicarbonyl species and effective blocking of advanced glycation end products.

The present work constructed magnetically driven nanorobots by conjugating the photoluminescent ß-alanine-histidine (ß-AH) nanodots to superparamagnetic nanoparticles (SPNPs) for simultaneously sensitive determination and fast trapping RDS in food processing, achieving efficient regulation of advanced glycation end products (AGEs) risk. Bio-derivative ß-AH nanodots with orderly self-assembly nanostructure and tunable photoluminescent properties served as both biorecognition elements to effectively bind and scavenge the reactive α-dicarbonyl species (RDS), as well as the indicator with sensitive fluorescence response in the food matrix. The magnetically driven nanorobots with excellent biosafety of endogenous dipeptides displayed a high binding capacity of 80.12 mg g-1 with ultrafast equilibrium time. Furthermore, the magnetically driven nanorobots achieved rapid removal of the RDS with the manipulation of the external magnetic field, which enabled intercepting AGEs generation without byproducts residual as well as ease-of-operation. This work provided a promising strategy with biosafety and versatility for both accurate determination and efficient removal of hazards.

Phytochemical profiling of Symplocos tanakana Nakai and S. sawafutagi Nagam. leaf and identification of their antioxidant and anti-diabetic potential.

Symplocos sp. contains various phytochemicals and is used as a folk remedy for treatment of diseases such as enteritis, malaria, and leprosy. In this study, we discovered that 70% ethanol extracts of Symplocos sawafutagi Nagam. and S. tanakana Nakai leaves have antioxidant and anti-diabetic effects. The components in the extracts were profiled using high-performance liquid chromatography coupled to electrospray ionization and quadrupole time-of-flight mass spectrometry; quercetin-3-O-(6''-O-galloyl)-ß-d-galactopyranoside (6) and tellimagrandin II (7) were the main phenolic compounds. They acted as strong antioxidants with excellent radical scavenging activity and as inhibitors of non-enzymatic advanced glycation end-products (AGEs) formation. Mass fragmentation analysis demonstrated that compounds 6 and 7 could form mono- or di-methylglyoxal adducts via reaction with methylglyoxal, which is a reactive carbonyl intermediate and an important precursor of AGEs. In addition, compound 7 effectively inhibited the binding between AGE2 and receptor for AGEs as well as the activity of α-glucosidase. Enzyme kinetic study revealed that compound 7 acts as a competitive inhibitor of α-glucosidase, through interaction with the active site of the enzyme. Therefore, compounds 6 and 7, the major constituents of S. sawafutagi and S. tanakana leaves, are promising for developing drugs for preventing or treating diseases caused by aging and excessive sugar consumption.

Unveiling the molecular basis of inflamm-aging induced by advanced glycation end products (AGEs)-modified human serum albumin (AGE-HSA) in patients with different immune-mediated diseases.

Increased serum advanced glycation end products (AGEs) are commonly found in the patients with Diabetes mellitus (DM), aging-related diseases, and immune-mediated diseases. These diseases are notorious for vasculopathy, immune dysfunctions, and low-grade inflammation mimicking inflamm-aging. However, the molecular basis of inflamm-aging related to AGEs remains elucidation. In this study, we incubated human serum albumin (HSA) and glucose at 37 °C in 5% CO2 incubator for 0-180 days to generate AGE-HSA. We found the mixture gradually changing the color from transparancy to brown color and increased molecular weight during incubation. The pH value also gradually decreased from 7.2 to 5.4 irrelevant to ionic charge or [Ca2+] concentration, but dependent on gradual glycation of the alkaline amino acids, lysine and arginine. Functionally, 40 µg/mL of AGE-HSA decreased IL-2 production from human Jurkat T cell line via suppressing p-STAT3, p-STAT4, and p-STAT6 with an increased tendency of senescence-associated ß-galactosidase (SA-ßgal) expression but irrelevant to change of Th1/Th2/Treg subpopulations. In contrast, AGE-HSA enhanced CC motif chemokine ligand 5 (CCL-5), IL-8, macrophage migration inhibitor factor (MIF), and interleukin 1 receptor antagonist (IL-1Ra) but suppressed SA-ßgal expression by human macrophage-like THP-1 cells. Interestingly, AGE-HSA abrogated the HSA-induced soluble intercellular adhesion molecules 1 (sICAM-1), sE-selectin and endothelin release from human coronary artery endothelial cells (HCAEC) and enhanced SA-ßgal expression. The accelerated and increased HSA glycations by individual inflammation-related cytokine such as IL-2, IL-6, IL-17, TGF-ß, or TNF-α in the in vitro study reflect increased serum AGE levels in patients with immune-mediated diseases. In conclusion, AGE-HSA can exert immunosuppresive, inflammatory and vasculopathic effects mimicking inflamm-aging in these patients.

Effect of glycation derived from α-dicarbonyl compounds on the in vitro digestibility of ovalbumin: Tracing of advanced glycation end-products and immuno-active peptides.

Currently, the biological consequences of advanced glycation end-products (AGEs) and their link to the antigenicity of food allergens are largely unknown due to the uncertainty in their digestive fates within the body. In this study, the influence of glycation derived from α-dicarbonyl compounds (α-DCs), precursors of AGEs, on digestive behaviors of ovalbumin (OVA) was investigated in a two-step simulated gastrointestinal (GI) model. Methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone were selected as typical α-DCs to obtain glycated OVA with different AGE-modifications (AGE-Ms). It was unveiled that α-DC-glycation reduced the digestibility of OVA via blocking tryptic cleavage sites and inducing steric hindrance, especially seen in the GO- and MGO-OVA groups. The formed AGE-Ms, depending on the precursor type, showed masking effects on the epitopes of OVA, which counteracted the negative effects of reduced digestibility on its antigenicity. Substantial changes in the peptide release patterns were also noted in glycated OVA, including alterations in the sequences and structures of several known protease-resistant epitopes of OVA. This study provides new insights into the nutritional and healthy effects of MRPs in heat-processed foods, as well as their potential connection to the modulation of egg allergy.