Mechanochemistry of Strecker degradation: Interaction of glyoxal with amino acids

Mechanochemistry is rapidly evolving into a versatile and green method for chemical synthesis. Due to its unique reaction conditions, ball milling of sugars and amino acids mainly leads to the formation of Amadori products with minimum degradation. In this study, we milled glyoxal trimer dihydrate with twenty proteogenic amino acids to demonstrate the formation of Strecker degradation products. HS-GC/MS studies indicated that Strecker degradation proceeded to selectively generate Strecker aldehyde and unsubstituted pyrazine as the major volatiles. Moreover, ESI/qToF/MS studies demonstrated for the first time the formation of the proposed key Strecker degradation intermediates, such as the condensation products and their decarboxylated products, indicating the similarity of the mechanism of Strecker reaction under ball milling to that proposed under hydrothermal reaction conditions. These studies provided supporting evidence that ball milling at ambient temperatures could be used as a novel synthetic approach to prepare precursors of aroma-active volatiles through Strecker degradation.

in Mice and Humans

There is considerable research evidence that α-dicarbonyl compounds, including glyoxal (GO) and methylglyoxal (MGO), are closely related to many chronic diseases. In this work, after comparison of the capture capacity, reaction pathway, and reaction rate of synephrine (SYN) and neohesperidin (NEO) on GO/MGO in vitro, experimental mice were administrated with SYN and NEO alone and in combination. Quantitative data from UHPLC-QQQ-MS/MS revealed that SYN/NEO/HES (hesperetin, the metabolite of NEO) could form the GO/MGO-adducts in mice (except SYN-MGO), and the levels of GO/MGO-adducts in mouse urine and fecal samples were dose-dependent. Moreover, SYN and NEO had a synergistic scavenging effect on GO in vivo by promoting each other to form more GO adducts, while SYN could promote NEO to form more MGO-adducts, although it could not form MGO-adducts. Additionally, human experiments showed that the GO/MGO-adducts of SYN/NEO/HES found in mice were also detected in human urine and fecal samples after drinking flowers of Citrus aurantium L. var. amara Engl. (FCAVA) tea using UHPLC-QTOF-MS/MS. These findings provide a novel strategy to reduce endogenous GO/MGO via the consumption of dietary FCAVA rich in SYN and NEO.

Investigations of Major α-Dicarbonyl Content in U.S. Honey of Different Geographical Origins

α-Dicarbonyls are significant degradation products resulting from the Maillard reaction during food processing. Their presence in foods can indicate the extent of heat exposure, processing treatments, and storage conditions. Moreover, they may be useful in providing insights into the potential antibacterial and antioxidant activity of U.S. honey. Despite their importance, the occurrence of α-dicarbonyls in honey produced in the United States has not been extensively studied. This study aims to assess the concentrations of α-dicarbonyls in honey samples from different regions across the United States. The identification and quantification of α-dicarbonyls were conducted using reverse-phase liquid chromatography after derivatization with o-phenylenediamine (OPD) and detected using ultraviolet (UV) and mass spectrometry methods. This study investigated the effects of pH, color, and derivatization reagent on the presence of α-dicarbonyls in honey. The quantification method was validated by estimating the linearity, precision, recovery, method limit of detection, and quantification using known standards for GO, MGO, and 3-DG, respectively. Three major OPD-derivatized α-dicarbonyls including methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), were quantified in all the honey samples. 3-Deoxyglucosone (3-DG) was identified as the predominant α-dicarbonyl in all the U.S. honey samples, with concentrations ranging from 10.80 to 50.24 mg/kg. The total α-dicarbonyl content ranged from 16.81 to 55.74 mg/kg, with the highest concentration measured for Southern California honey. Our results showed no significant correlation between the total α-dicarbonyl content and the measured pH solutions. Similarly, we found that lower amounts of the OPD reagent are optimal for efficient derivatization of MGO, GO, and 3-DG in honey. Our results also indicated that darker types of honey may contain higher α-dicarbonyl content compared with lighter ones. The method validation results yielded excellent recovery rates for 3-DG (82.5%), MGO (75.8%), and GO (67.0%). The method demonstrated high linearity with a limit of detection (LOD) and limit of quantitation (LOQ) ranging from 0.0015 to 0.002 mg/kg and 0.005 to 0.008 mg/kg, respectively. Our results provide insights into the occurrence and concentrations of α-dicarbonyl compounds in U.S. honey varieties, offering valuable information on their quality and susceptibility to thermal processing effects.

Defining an Optimized Workflow for Enriching and Analyzing Residual Tumor Populations Using Intracellular Markers

Tumor relapse is well recognized to arise from treatment-resistant residual populations. Strategies enriching such populations for in-depth downstream analyses focus on tumor-specific surface markers; however, enrichment using intracellular biomarkers remains challenging. Using B-cell lymphoma as an exemplar, we demonstrate feasibility to enrich B-cell lymphoma 2 (BCL2)high populations, a surrogate marker for t(14;18)+ lymphomas, for use in downstream applications. Different fixation protocols were assessed for impact on antibody expression and RNA integrity; glyoxal fixation demonstrated superior results regarding minimal effects on surface and intracellular expression, and RNA quality, compared with alternative fixatives evaluated. Furthermore, t(14;18)+ B cells were effectively detected using intracellular BCL2 overexpression to facilitate tumor cell enrichment. Tumor cell populations were enriched using the cellenONE F1.4 single-cell sorting platform, which detected and dispensed BCL2high-expressing cells directly into library preparation reagents for transcriptome analyses. Sorted glyoxal-fixed cells generated good quality sequencing libraries, with high concordance between live and fixed single-cell transcriptomic profiles, discriminating cell populations predominantly on B-cell biology. Overall, we successfully developed a proof-of-concept workflow employing a robust cell preparation protocol for intracellular markers combined with cell enrichment using the cellenONE platform, providing an alternative to droplet-based technologies when cellular input is low or requires prior enrichment to detect rare populations. This workflow has wider prognostic and therapeutic potential to study residual cells in a pan-cancer setting.

Identification of redox activators for continuous reactivation of glyoxal oxidase from Trametes versicolor in a two-enzyme reaction cascade

Glyoxal oxidases, belonging to the group of copper radical oxidases (CROs), oxidize aldehydes to carboxylic acids, while reducing O2 to H2O2. Their activity on furan derivatives like 5-hydroxymethylfurfural (HMF) makes these enzymes promising biocatalysts for the environmentally friendly synthesis of the bioplastics precursor 2,5-furandicarboxylic acid (FDCA). However, glyoxal oxidases suffer from inactivation, which requires the identification of suitable redox activators for efficient substrate conversion. Furthermore, only a few glyoxal oxidases have been expressed and characterized so far. Here, we report on a new glyoxal oxidase from Trametes versicolor (TvGLOX) that was expressed at high levels in Pichia pastoris (reclassified as Komagataella phaffii). TvGLOX was found to catalyze the oxidation of aldehyde groups in glyoxylic acid, methyl glyoxal, HMF, 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA), but barely accepted alcohol groups as in 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), preventing formation of FDCA from HMF. Various redox activators were tested for TvGLOX reactivation during catalyzed reactions. Among them, a combination of horseradish peroxidase and its substrate 2,2'-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) most efficiently reactivated TvGLOX. Through continuous reactivation of TvGLOX in a two-enzyme system employing a recombinant Moesziomyces antarcticus aryl-alcohol oxidase (MaAAO) almost complete conversion of 8 mM HMF to FDCA was achieved within 24 h.

Comparison of the properties of phenolic resin synthesized from different aldehydes and evaluation of the release and health risks of VOCs

Different amounts of glyoxal and paraformaldehyde were used to synthesize phenol-glyoxal (PG) and phenol-paraformaldehyde (PPF) resins, which were compared with conventional phenol-formaldehyde (PF) resins. Glyoxal oxidation leads to a pH value of 9.83 for PG 2.2. With the addition of polyformaldehyde, PPF 2.2 exhibited the highest viscosity at 17333.33 mPa s. The PPF 2.0 plywood has a maximum bonding strength of 1.94 MPa. The formaldehyde emission of PG 1.8 plywood is found to have a minimum value of 0.025 mg/m3, reaching the ENF limit (≤0.025 mg/m3). Acetaldehyde is found only in volatile organic compound (VOC) emissions from PG plywood and is associated with increased glyoxal. PPF plywood emitted more aromatic and total VOC (TVOC) than the other two plywood types. The measured TVOC for PPF 2.2 is 196.07 μg/m3. The results showed that the total cancer risk (TCR) values of PPF 1.8, PPF 2.0, and PG 1.8 were above the threshold of 1.00E-4, indicating a definite carcinogenic risk. Acetaldehyde in the PG plywood exceeded the safety threshold for noncarcinogenic risk. The use of paraformaldehyde in the wood-based panel production is been considered a possible means of improving the bonding strength of plywood. Glyoxal has also been shown to be a viable method for lowering the formaldehyde emissions from plywood. The VOC emissions from plywood changed significantly depending on the aldehyde used. Limiting VOCs that present high health hazards is crucial for reducing the negative impact of plywood on both indoor environments and human health.

Bi-functionality of glyoxal caged nucleic acid coupled with CRISPR/Cas12a system for Hg2+ determination

A highly sensitive and selective fluorescence method has been conducted for the detection of Hg2+ based on aminophenylboronic acid-modified carboxyl magnetic beads (CMB@APBA) and CRISPR/Cas12a system mediated by glyoxal caged nucleic acid (gcDNA). As a bi-functional DNA linker, gcDNA offers advantages of simultaneous recognition by boronic acid and complementary DNA/RNA. Under acidic condition, gcDNA can be immobilized on CMB@APBA through the formation of borate ester bond. The formed boric acid-esterified gcDNA can further bind with complementary CRISPR RNA through A-T base pairing to activate Cas12a with kcat/Km ratio of 3.4 × 107 s-1 M-1, allowing for amplified signal. Hg2+ can specifically combine with CMB@APBA, resulting in the release of gcDNA from CMB@APBA and the following inhibition on the activation of CRISPR/Cas12a system around magnetic bead. Under optimal conditions, the method exhibits a linear range from 20 to 250 nM, with a detection limit of 2.72 nM. The proposed method can detect Hg2+ in milk and tea beverages, providing a great significance for on-site monitoring of Hg2+ contamination in food.

Alginate-modified surfactants functionalized metal-organic framework-based fluorescent film sensors for detection and adsorption of volatile aldehydes in water

Volatile aldehydes have an adverse impact on both human health and the environment, therefore, a fast, straightforward, highly accurate detection technique for the simultaneous detection and removal of several aldehydes is eagerly anticipated. Herein, novel APGF@ZIF-8 and APOF@ZIF-8 sensing materials were developed by coating fluorescent alginate-modified surfactants (APGF and APOF) into the ZIF-8 MOFs to produce quite porous fluorescent sensors (SBET up to 1519 m2/g). The detection capacity of the prepared sensors for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde has been examined. The detection mechanism was suggested as hydrogen bonding formation between the sensors and volatile aldehydes as confirmed by Gaussian calculations. All the fluorescence spectra of aldehydes display remarkable linear detection relationships in the range of 0.05-200 μM with the limits of detection (LOD) values in the range of 0.001-0.18 μM (0.106-10.44 ppb). These sensors were utilized successfully to detect multiple volatile aldehydes in river water samples with satisfactory recoveries of 96-107 %. Interestingly, fluorescent APGF@ZIF-8/CS and APOF@ZIF-8/CS films as portable disposable removal techniques for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde from water were fabricated. APOF@ZIF-8/CS exhibited an excellent formaldehyde adsorption capacity of 58.30 mg/g and an adsorption removal efficiency of 93.5 %. The adsorption process of biosorbent on various aldehydes was fitted by Freundlich adsorption isotherm. The adsorption kinetics followed Pseudo-second-order kinetic model.

Contribution of Hydroxycinnamic Acids to Color Formation in Nonenzymatic Browning Reactions with Key Maillard Reaction Intermediates

The Maillard reaction is a vital part of food processing, involving a vast number of complex reaction pathways, resulting in high-molecular-weight colorants. So far, studies have been focused on the conversion of carbohydrates and amino compounds, but the literature elaborating the contribution of phenolic compounds to the formation of the colored end-products is still rare. The aim of this study was to characterize early reactions, underlying the formation of phenol-containing melanoidins. For this purpose, binary model systems of the prominent phenolic compounds caffeic acid and ferulic acid combined with α-dicarbonyl compounds typically formed in the Maillard reaction such as glyoxal, methylglyoxal, and diacetyl were analyzed after heat treatment. High-resolution mass spectrometry revealed that decarboxylation, aromatic electrophilic substitution, and nucleophilic addition are important reaction steps that lead to colored heterogeneous oligomers. Polymerization was favored for phenolic compounds with a high electron density in the aromatic system and for α-dicarbonyl compounds carrying aldehyde functions.

Glyoxal-derived advanced glycation end products (GO-AGEs) with UVB critically induce skin inflammaging: in vitro and in silico approaches

Advanced glycation end products (AGEs) have potential implications on several diseases including skin inflammation and aging. AGEs formation can be triggered by several factors such as UVB, glyoxal and methylglyoxal etc. However, little attention has been paid to glyoxal-derived AGEs (GO-AGEs) and UVB-induced skin inflammaging, with none have investigated together. This study aimed to investigate the possible role of GO-AGEs and UVB in skin inflammaging focusing on revealing its molecular mechanisms. The effects of GO-AGEs in the presence or absence of UVB were studied by using enzyme linked immunosorbent assay, western blotting, qPCR, flow cytometry and in silico approaches. In HaCaT cells, GO-AGEs in the presence of UVB irradiation (125 mJ/cm2) dramatically enhanced the release of different pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) with further activation of RAGE signaling pathways (NF-κB, COX 2, and IL- 1β) and increased oxidative stress also noticed in NHEK cells. In NHDF cells, extracellular matrix disruption noted via increasing matrix metalloproteinase release and decreasing collagen type 1 and SIRT1 expression. Besides that, the docking scores obtained from the molecular docking study support the above-mentioned results. This study strongly suggests the pivotal role of GO-AGEs in skin inflammaging and illuminates novel molecular pathways for searching most effective and updated anti-aging therapy.

pH-Dependent Aqueous-Phase Brown Carbon Formation: Rate Constants and Implications for Solar Absorption and Atmospheric Photochemistry

Aqueous-phase reactions of α-dicarbonyls with amines or ammonium have been identified as important sources of secondary brown carbon (BrC). However, the kinetics of BrC formation and the effects of pH are still not very clear. In this study, the kinetics of BrC formation by aqueous reactions of α-dicarbonyls (glyoxal and methylglyoxal) with ammonium, amino acids, or alkylamines in bulk solution at different pH values are investigated. Our results reveal pH-parameterized BrC production rate constants, kBrCII (m-1 [M]-2 s-1), based on the light absorption between 300 and 500 nm: log10(kBrCII) = (1.0 ± 0.1) × pH - (7.4 ± 1.0) for reactions with glyoxal and log10(kBrCII) = (1.0 ± 0.1) × pH - (6.3 ± 0.9) for reactions with methylglyoxal. The linear slopes closing to 1.0 indicate that BrC formation is governed by the nitrogen nucleophilic addition pathway. Consequently, the absorptivities of the produced BrC increase exponentially with the increase of pH. BrC from reactions with methylglyoxal at higher pH (≥6.5) exhibits optical properties comparable to BrC from biomass burning or coal combustion, categorized as the "weakly" absorbing BrC, while BrC from reactions with methylglyoxal at lower pH (<6.0) or reactions with glyoxal (pH 5.0-7.0) falls into the "very weakly" absorbing BrC. The pH-dependent BrC feature significantly affects the solar absorption ability of the produced BrC and thus the atmospheric photochemical processes, e.g., BrC produced at pH 7.0 absorbs 14-16 times more solar power compared to that at pH 5.0, which in turn could lead to a decrease of 1 order of magnitude in the photolysis rate constants of O3 and NO2.

κ-Carrageenan inhibits the formation of advanced glycation end products in cakes: Inhibition mechanism, cake characteristics, and sensory evaluation

Inhibiting the formation of advanced glycation end products (AGEs) in the heat-processed food can reduce health risks related to diabetic complications. However, additives used for this purpose may also affect the sensory characteristics of food products. In this study, the effects of six hydrocolloids on the formation of AGEs were evaluated in the lysine-glucose model, with κ-carrageenan exhibited the highest inhibitory activity. Mechanistic investigations indicated that κ-carrageenan conjugated with the key intermediates of AGEs, namely glyoxal (GO) and methylglyoxal (MGO). Subsequently, the inhibitory effect of κ-carrageenan on AGEs formation in cakes was verified. The data showed that κ-carrageenan in cakes significantly inhibited the formation of fluorescent and non-fluorescent AGEs. In addition, analysis of cake characteristics and sensory evaluation showed that cakes with 1% (w/w) κ-carrageenan had the highest quality and overall acceptance. Overall, κ-carrageenan is an effective inhibitor of AGEs formation in heat-processed food.

The Recycling of Substandard Rocket Fuel N,N-Dimethylhydrazine via the Involvement of Its Hydrazones Derived from Glyoxal, Acrolein, Metacrolein, Crotonaldehyde, and Formaldehyde in Organic Synthesis

"Heptil" (unsymmetrical dimethylhydrazine-UDMH) is extensively employed worldwide as a propellant for rocket engines. However, UDMH constantly loses its properties as a result of its continuous and uncontrolled absorption of moisture, which cannot be rectified. This situation threatens its long-term usability. UDMH is an exceedingly toxic compound (Hazard Class 1), which complicates its transportation and disposal. Incineration is currently the only method used for its disposal, but this process generates oxidation by-products that are even more toxic than the original UDMH. A more benign approach involves its immediate reaction with a formalin solution to form 1,1-dimethyl-2-methylene hydrazone (MDH), which is significantly less toxic by an order of magnitude. MDH can then be polymerized under acidic conditions, and the resulting product can be burned, yielding substantial amounts of nitrogen oxides. This review seeks to shift the focus of MDH from incineration towards its application in the synthesis of relatively non-toxic and readily available analogs of various pharmaceutical substances. We aim to bring the attention of the international chemical community to the distinctive properties of MDH, as well as other hydrazones (such as glyoxal, acrolein, crotonal, and meta-crolyl), wherein each structural fragment can initiate unique transformations that have potential applications in molecular design, pharmaceutical research, and medicinal chemistry.

Effect of edible oil type on the formation of protein-bound Nε-(carboxymethyl)lysine in roasted pork patties

Protein-bound Nε-(carboxymethyl)lysine (CML), an advanced glycation end product within meat products, poses a potential health risk to humans. The objective of this study was to explore the impact of various edible oils on the formation of protein-bound CML in roasted pork patties. Eleven commercially edible oils including lard oil, corn oil, palm oil, olive oil, flaxseed oil, blended oil, camellia oil, walnut oil, soybean oil, peanut oil, and colza oil were added to pork tenderloin mince, respectively, at a proportion of 4 % to prepare raw pork patties. The protein-bound CML contents in the pork patties were determined by HPLC-MS/MS before and after roasting at 200 °C for 20 min. The results indicated that walnut oil, flaxseed oil, colza oil, olive oil, lard oil, corn oil, blended oil, and palm oil significantly reduced the accumulation of protein-bound CML in pork patties, of which the inhibition rate was in the 24.43 %-37.96 % range. Moreover, the addition of edible oil contributed to a marginal reduction in the loss of lysine. Meanwhile, glyoxal contents in pork patties were reduced by 16.72 %-43.21 % after roasting. Other than blend oil, all the other edible oils restrained protein oxidation in pork patties to varying degrees (between 20.16 % and 61.26 %). In addition, camellia oil, walnut oil, and flaxseed oil increased TBARS values of pork patties by 2.2-8.6 times when compared to the CON group. After analyzing the fatty acid compositions of eleven edible oils, five main fatty acids (palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid) were selected to establish Myofibrillar protein-Glucose-fatty acids systems to simulate the roasting process. The results showed that palmitic acid, oleic acid, linoleic acid, and linolenic acid obviously mitigated the formation of myofibrillar protein-bound CML, exhibiting suppression rates ranging from 10.38 % to 40.32 %. In conclusion, the addition of specific edible oil may curb protein-bound CML production in roasted pork patty by restraining protein or lipid oxidation, reducing lysine loss, and suppressing glyoxal production, which may be attributed to the fatty acid compositions of edible oils. This finding provides valuable guidance for the selection of healthy roasting oils in the thermal processing of meat products.

Imperfect cross-linking of xanthan for pH-responsive bio-based composite moist wound dressings by stencil printing

The work addresses the use of bio-based and -degradable materials for the production of a moist, adaptive and anti-microbial wound dressing. The dressing is targeted to exhibit a pH-dependent active agent release. Xanthan hydrogel structures are coated on cellulose fabrics via stencil printing and subsequently cross-linked using glyoxal. By alteration of the cross-linker content from 1 to 6% by mass, the hydrogel elasticity can be tuned within a range of 2-16 kPa storage modulus. Increasing initial glyoxal concentrations also result in higher amounts of glyoxal release. Glyoxal, an anti-microbial agent with approval in veterinary medicine, is mostly released upon wound application supporting infection management. As wound simulation, normal saline, as pH 5 and pH 8 buffer solutions, were used. The release profile and magnitude of approx. 65%-90% glyoxal is pH-dependent. Increased release rates of glyoxal are present in pH 8 fluids, which mostly base on faster hydrogel swelling. Higher total glyoxal release is present in pH 5 fluid and normal saline after 3 days. Accordingly, a pH-dependent release profile was encountered. As glyoxal attacks any cell unselectively, it is expected to be effective against antibiotic resistant bacteria. By stencil printing the dressing size can be adjusted to minimize healthy glyoxal tissue exposure.

Development of a label-free impedimetric aptasensor for the detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is responsible for various nosocomial infections, which is known as a clinically crucial opportunistic pathogen. Therefore, rapid detection of this pathogen is critical to prevent the spread of infection and appropriate treatment. Biological detection probes, such as aptamers and synthetic receptors can be used as diagnostic layers to detect bacteria. In this work, an electrochemical aptasensor was developed for the ultrasensitive detection of A. baumannii by electrochemical impedance spectroscopy (EIS). The aptamer was immobilized on the surface of a CSPE modified with the nanocomposite Fe3O4@SiO2@Glyoxal (Gly) for selective and label-free detection of A. baumannii. The charge transfers resistance (Rct) between redox couple [Fe(CN)63-/4-] and the surface of aptasensor in the Nyquist plot of EIS study was used as electroanalytical signal for detection and determination of A. baumannii. The obtained results showed that the constructed aptasensor could specifically detect A. baumannii in the concentration range from 1.0 × 103-1.0 × 108 Colony-forming unit (CFU)/mL and with a detection limit of 150 CFU/mL (S/N = 3). In addition to its sensitivity, the biosensor exhibits high selectivity over some other pathogens. Therefore, a simple, inexpensive, rapid, label-free, selective, and sensitive electrochemical aptasensor was developed to detect A. baumannii.

Serum levels of autoantibodies against the angiotensin II type I receptor are not associated with serum dicarbonyl or AGE levels in patients with an aldosterone-producing adenoma

Patients with an aldosterone-producing adenoma (APA) carry a higher risk of cardiovascular disease and commonly have high levels of autoantibodies (AT1AA) that may activate the angiotensin II type 1 receptor (AT1R). AT1R activation is linked to an increase of the glucose metabolite methylglyoxal (MGO), a potential precursor of advanced glycation endproducts (AGEs) and driver of vascular inflammation. We investigated whether serum AT1AA levels are associated with serum MGO and AGE levels in APA patients. In a case series of 26 patients with APA we measured levels of dicarbonyls MGO, glyoxal (GO) and 3-deoxyglucosone (3-DG), and dicarbonyl-derived AGEs 5-hydro-5-methylimidazolone (MG-H1), Nε-(carboxyethyl)lysine (CEL) and Nε-(carboxymethyl)lysine (CML) with UPLC-MS/MS. We also measured AT1AA by ELISA. These measurements were repeated 1-month after adrenalectomy in a subset of 14 patients. Panels of inflammation and endothelial function were also measured by immunoassays. Although baseline higher AT1AA levels tended to be correlated with higher baseline serum MGO, GO and 3-DG levels (r = 0.18, p = 0.38; r = 0.20, p = 0.33; r = 0.23, p = 0.26; respectively), these correlations were not statistically significant. We observed no obvious correlations between higher AT1AA levels and protein-bound and free MG-H1, CEL and CML levels, and markers of inflammation and endothelial function. No decrease was observed in any of the dicarbonyls, protein-bound AGE levels and markers of inflammation and endothelial function after adrenalectomy. In patients with APA the serum levels of AT1AA were not significantly correlated with serum dicarbonyls, protein-bound and free AGE levels. Increased signalling of the AT1AA receptor may therefore be unlikely to overtly increase systemic dicarbonyl levels.

Glyoxal as an alternative fixative for single-cell RNA sequencing

Single-cell RNA sequencing has become an important method to identify cell types, delineate the trajectories of cell differentiation in whole organisms, and understand the heterogeneity in cellular responses. Nevertheless, sample collection and processing remain a severe bottleneck for single-cell RNA sequencing experiments. Cell isolation protocols often lead to significant changes in the transcriptomes of cells, requiring novel methods to preserve cell states. Here, we developed and benchmarked protocols using glyoxal as a fixative for single-cell RNA sequencing applications. Using Drop-seq methodology, we detected a large number of transcripts and genes from glyoxal-fixed Drosophila cells after single-cell RNA sequencing. The effective glyoxal fixation of transcriptomes in Drosophila and human cells was further supported by a high correlation of gene expression data between glyoxal-fixed and unfixed samples. Accordingly, we also found highly expressed genes overlapping to a large extent between experimental conditions. These results indicated that our fixation protocol did not induce considerable changes in gene expression and conserved the transcriptome for subsequent single-cell isolation procedures. In conclusion, we present glyoxal as a suitable fixative for Drosophila cells and potentially cells of other species that allow high-quality single-cell RNA sequencing applications.

Glyoxal-based fixation of Drosophila embryos for immunofluorescence staining and RNA in situ hybridization

The dialdehyde glyoxal is an alternative chemical fixative that cross-links tissues faster than formaldehyde, retains higher antigenicity, and is less hazardous than either formaldehyde or glutaraldehyde. Here we present a glyoxal-based fixation protocol for use with Drosophila embryos. We describe steps to prepare acid-free glyoxal, fix embryos, and then stain with antibodies for immunofluorescence (IF). We also describe methods for RNA fluorescence in situ hybridization (FISH) and FISH plus IF (FISH-IF) using glyoxal-fixed embryos. This protocol was adapted for Drosophila embryos from the methods of Bussolati et al.1 and Richter et al.2.

Investigating Bioaccessibility of Advanced Glycation Product Precursors in Gluten-Free Foods Using In Vitro Gastrointestinal System

Background and Objectives: Gluten-free products have been produced as part of medical therapy and have gained popularity among individuals seeking weight loss or healthier dietary options. Assessing the potential risks associated with these products is essential in optimizing their compositions and developing new dietetic approaches. This study aimed to determine the glyoxal (GO) and methylglyoxal (MGO) contents in gluten-free bread, biscuits, and cookies and to examine their bioaccessibility using an in vitro gastrointestinal model. Materials and Methods: A total of 26 gluten-free and 19 gluten-containing (control) products were analyzed for their GO and MGO levels utilizing a high-performance liquid chromatography (HPLC) device. Results: Post-digestion, the GO and MGO values increased significantly across all food groups compared with pre-digestion values (p < 0.05), and the bioaccessibility exceeded 100%. Specifically, gluten-free bread exhibited higher post-digestion GO and MGO values than the control group (p < 0.05). Conversely, gluten-containing biscuits and cookies had higher post-digestion GO and MGO values compared to gluten-free products (p < 0.05). Conclusions: The detection of precursors to advanced glycation end products (AGEs) in gluten-free products has drawn attention to the potential health risks associated with their consumption. Therefore, reevaluation of the formulations and technologies used in these products and the introduction of new strategies are crucial in mitigating AGE content.

Selected Maillard Reaction Products and Their Yeast Metabolites in Commercial Wines

During beer and wine production, Maillard reaction products (MRPs) are formed, which have a particular influence on the taste and aroma of the fermented beverages. Compared to beer, less is known about individual Maillard compounds and especially corresponding yeast metabolites in wine. In this study, 36 selected wines (Amarone, Ripasso, red, and white wines) were analyzed by HPLC-UV and GC-MS concerning the amounts of 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), methylglyoxal (MGO), glyoxal (GO), 5-hydroxymethylfurfural (HMF), and furfural (FF). 3-DG was found to be the dominant compound with values from 3.3 to 35.1 mg/L. The contents of 3-DGal, MGO, GO, HMF, and FF were in a single digit range. In addition to MRPs, the yeast metabolites originating from 3-DG, namely, 3-deoxyfructose and 3-deoxy-2-ketogluconic acid, 2,5-bis(hydroxymethyl)furan and 5-formyl-2-furancarboxylic acid, both formed from HMF, and the FF metabolites furfuryl alcohol and furan-2-carboxylic acid were detected and quantitated in wines for the first time. The amounts were between 0.1 and 53.5 mg/L with especially high contents of the oxidation products. Differences between red and white wines indicate that enological parameters like grape variety, production method, and aging may have an influence on the MRP contents in wines.

Mechanism of Carbon Skeleton Formation of 2,3,5-Trimethylpyrazine via a Conversion Reaction between Methylglyoxal and Glyoxal

Maillard flavor compounds, such as 2,3,5-trimethylpyrazine, have been frequently identified in thermally processed food products, such as popcorn and peanuts. However, the origin of the carbon atoms in 2,3,5-trimethylpyrazine has not been clearly elucidated. Herein, a model reaction showed that precursor methylglyoxal and intermediates glyoxal and formaldehyde contributed to the formation of 2,3,5-trimethylpyrazine via a conversion reaction between methylglyoxal and glyoxal. In addition, carbon module labeling technology and model response validation experiments indicated that this transformation reaction between methylglyoxal and glyoxal brought formaldehyde into the methyl group carbon atoms of the 2,3,5-trimethylpyrazine ring. The proposed novel route provides a new perspective for approaches to control the formation of flavor compounds, such as 2,3,5-trimethylpyrazine.

Identification of volatile organic compound emissions from anthropogenic and biogenic sources based on satellite observation of formaldehyde and glyoxal

Anthropogenic volatile organic compounds (VOCs) are serious pollutants in the atmosphere because of their toxicity and as precursors of secondary organic aerosols and ozone pollution. Although in-situ measurements provide accurate information on VOCs, their spatial coverage is limited and insufficient. In this study, we provide a global perspective for identifying anthropogenic VOC emission sources through the ratio of glyoxal to formaldehyde (RGF) based on satellite observations. We assessed typical cities and polluted areas in the mid latitudes and found that some Asian cities had higher anthropogenic VOC emissions than cities in Europe and America. For heavily polluted areas, such as the Yangtze River Delta (YRD), the areas dominated by anthropogenic VOCs accounted for 23 % of the total study areas. During the COVID-19 pandemic, a significant decline in RGF values was observed in the YRD and western United States, corresponding to a reduction in anthropogenic VOC emissions. Furthermore, developing countries appeared to have higher anthropogenic VOC emissions than developed countries. These observations could contribute to optimising industrial structures and setting stricter pollution standards to reduce anthropogenic VOCs in developing countries.

Investigation on the contents of heat-induced hazards in commercial nuts

The purpose was to investigate the contents of heat-induced hazards by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in 44 commercial nuts. Results showed that content ranges of Acrylamide (AA), 5-hydroxymethylfurfural (5-HMF), N^ε-carboxymethyl-lysine (CML), N^ε-carboxyethyl-lysine (CEL), 3-Deoxyglucosone (3-DG), Glyoxal (GO), and Methylglyoxal (MGO) were ND-123.57 µg/kg, 0.57-213.42 mg/kg, 3.18-18.67 mg/kg, 3.98-57.85 mg/kg, 1.5-133.86 mg/kg, 0.45-1.59 mg/kg and 0.29-13.84 mg/kg, respectively. Sunflower seeds contained more heat-induced hazards followed by pistachios, cashews, almonds, walnuts and hazelnuts. The content of 5-HMF was positively correlated with the content of 3-DG. CML exhibited positive correlation with content of GO while no correlation between CEL and MGO. Higher levels of 3-DG and 5-HMF were observed in nuts produced with sugar and honey. Deep processing had a stronger promoting effect on CML and CEL formation. These data could provide a crucial guide for consumers to select nut products which might reduce heat-induced hazards intake.

Habitual intake of dietary methylglyoxal is associated with less low-grade inflammation: the Maastricht Study

BACKGROUND

Dicarbonyls are major reactive precursors of advanced glycation endproducts (AGEs). Dicarbonyls are formed endogenously and also during food processing. Circulating dicarbonyls and AGEs are associated with inflammation and microvascular complications of diabetes, but for dicarbonyls from the diet these associations are currently unknown.

OBJECTIVES

We sought to examine the associations of dietary dicarbonyl intake with low-grade inflammation and microvascular function.

METHODS

In 2792 participants (mean ± SD age: 60 ± 8 y; 50% men; 26% type 2 diabetes) of the population-based cohort the Maastricht Study, we estimated the habitual intake of the dicarbonyls methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG) by linking FFQ outcome data to our food composition database of the MGO, GO, and 3-DG content of >200 foods. Low-grade inflammation was assessed as six plasma biomarkers, which were compiled in a z score. Microvascular function was assessed as four plasma biomarkers, compiled in a zscore; as diameters and flicker light-induced dilation in retinal microvessels; as heat-induced skin hyperemic response; and as urinary albumin excretion. Cross-sectional associations of dietary dicarbonyls with low-grade inflammation and microvascular function were investigated using linear regression with adjustments for age, sex, potential confounders related to cardiometabolic risk factors, and lifestyle and dietary factors.

RESULTS

Fully adjusted analyses revealed that higher intake of MGO was associated with a lower z score for inflammation [standardized β coefficient (STD β): -0.05; 95% CI: -0.09 to -0.01, with strongest inverse associations for hsCRP and TNF-α: both -0.05; -0.10 to -0.01]. In contrast, higher dietary MGO intake was associated with impaired retinal venular dilation after full adjustment (STD β: -0.07; 95% CI: -0.12 to -0.01), but not with the other features of microvascular function. GO and 3-DG intakes were not consistently associated with any of the outcomes.

CONCLUSION

Higher habitual intake of MGO was associated with less low-grade inflammation. This novel, presumably beneficial, association is the first observation of an association between MGO intake and health outcomes in humans and warrants further investigation.

Analysis of the binding of warfarin to glyoxal- and methylglyoxal-modified human serum albumin by ultrafast affinity extraction

Ultrafast affinity extraction (UAE) and affinity microcolumns containing immobilized human serum albumin (HSA) were employed to evaluate the effect of advanced stage glycation on HSA and its binding to warfarin, a common site-specific probe for Sudlow site I of this protein. The modification of HSA by glyoxal (GO) and methylglyoxal (MGO) was considered, where GO and MGO are known to be important in the formation of many types of advanced glycation end products. Free drug fractions were measured by UAE for warfarin in solutions containing normal HSA or HSA that had been modified by GO or MGO at levels seen in serum during diabetes. The free fractions measured with the GO-modified HSA gave association equilibrium constants that ranged from 2.42-2.63 × 105 M-1 at pH 7.4 and 37 °C. These values were not significantly different from a value of 2.33 (±0.15) × 105 M-1 that was determined by the same method for warfarin with normal HSA. Similar studies using MGO-modified HSA gave association equilibrium constants for warfarin in the range of 3.07-3.31 × 105 M-1, which were 1.32- to 1.42-fold higher than the value seen for normal HSA (differences that were significant at the 95% confidence level). These results will be valuable in future binding studies based on affinity chromatography or other methods that employ warfarin as a probe to examine drug interactions at Sudlow site I of HSA and modified forms of this protein. This work also illustrates how UAE can be used, with analysis times of only minutes, to detect and measure small changes in the binding by drugs with unmodified or modified forms of a soluble binding agent or protein.

Formation Priority of Pyrazines and 2-Acetylthiazole Dependent on the Added Cysteine and Fragments of Deoxyosones during the Thermal Process of the Glycine-Ribose Amadori Compound

In this study, it was found that extra-added cysteine (Cys) became involved in volatile compound formation during the Maillard reaction of the glycine-ribose Amadori rearrangement product (GR-ARP). The priority of the Cys reaction with different α-dicarbonyls and its dependence on the Cys dosage were investigated. At the same concentrations of methylglyoxal (MGO) and glyoxal (GO), it was found that 2-acetylthiazole was the dominant product when the molar ratio of Cys to MGO was 1:1, while formation of pyrazines was improved when the Cys percentage increased. Cys preferentially reacted with MGO first rather than GO to exclusively generate 2-acetylthiazole at a high yield. The concentration of 2-acetylthiazole quickly increased up to a plateau and remained stable during further heat treatment. When MGO was totally consumed, remaining Cys began to react with GO through the predominant pathway where the keto form of carbonylcysteimine derived from Cys and GO was hydrolyzed to recover GO with cysteamine formation, whereas the hydrolysis reactivity of enolized carbonylcysteimine as the Strecker pathway for generation of pyrazines was relatively low. During the heat treatment of GR-ARP, the constantly lower ratios of α-dicarbonyls to Cys led to inhibited formation of 2-aminopropanal, which accounted for the decreased methylpyrazine yields.

Large-scale synthesis of galeterone and lead next generation galeterone analog VNPP433-3β

VNPP433-3β (compound 2, (3β-(1H-imidazole-1-yl)-17-(1H-benzimidazole-1-yl)-androsta-5,16-diene), a multitarget anticancer agent has emerged as our lead next generation galeterone analogs (NGGA). Here, we describe a large multi-gram (92 g) scale synthesis of compound 2 starting from the commercially available dehydroepiandrosterone-3-acetate (DHEA, 6) via Galeterone (Gal, 1), in 8 steps with a 26% overall yield and 99.5% purity. The overall yield for the synthesis of Gal from DHEA improved from previously reported 47% to 59%. The advantages of this synthesis are as follows: (1) In the first two steps of Scheme 2, the change of solvents and reagents enabled the isolation of compounds 7 and 8 from heptane triturations, as column chromatography was eliminated in both steps. (2) In step 3 (deformylation) the catalyst required was reduced from 50% to 10% (wt/wt) of compound 8 which enable easy purification of compound 9, with modest increased yield. (3) The fourth step to produce Gal (1) was improved by using methanol, eliminating the use of tetrahydrofuran (THF) and dichloromethane, solvent which may be a problem as residual solvent contaminant. (4) In the final step 8, the imidazole-ring formation, inexpensive glyoxal (40% aqueous solution) was used in the reaction instead of expensive glyoxal trimer dihydrate. The structure of the target product (2, VNPP433-3β) was established by NMR spectroscopy, mass spectrometry and elemental analysis. Gal and VNPP433-3β exhibit more potent antiproliferative activities against CWR22Rv1 human prostate cancer cells compared to clinical drugs, Abiraterone and Enzalutamide.

Lipid Peroxidation Has Major Impact on Malondialdehyde-Derived but Only Minor Influence on Glyoxal and Methylglyoxal-Derived Protein Modifications in Carbohydrate-Rich Foods

In the present work, the contribution of lipid peroxidation on modifications of lysine and arginine residues of proteins was investigated. Lipid peroxidation had a major impact on malondialdehyde-derived protein modifications; however, the influence on glyoxal and methylglyoxal-derived modifications in flat wafers was negligible. Therefore, vegetable oils (either linseed oil, sunflower oil, or coconut oil) were added to respective batters, and flat wafers were baked (150 °C, 3-10 min). Analysis of malondialdehyde indicated oxidation in linseed wafers, which was supported by the direct quantitation of three malondialdehyde protein adducts in the range of 0.09-23.5 mg/kg after enzymatic hydrolysis. In contrast, levels of free glyoxal and methylglyoxal were independent of the type of oil added, which was in line with the analysis of 13 advanced glycation end products. Comprehensive incubations of 40 mM N²-t-Boc-lysine (100 mM phosphate buffer, pH 7.4) with either 10% oil or an equimolar concentration of carbohydrates led to magnitudes higher (10³-10⁵) amounts of N⁶-carboxymethyl lysine, N⁶-glycolyl lysine, and N⁶-carboxyethyl lysine in the latter. Furthermore, malondialdehyde exceeded glyoxal and methylglyoxal in incubations of pure oils at 150 °C by factors of 30 and 100, respectively.

Formaldehyde-Free Resins for the Wood-Based Panel Industry: Alternatives to Formaldehyde and Novel Hardeners

Due to its carcinogenic properties, the presence of formaldehyde in resins and other industrial products has been a subject of great concern in recent years. The presented review focuses on modern alternatives for the production of wood-based panels; i.e., substitutes for formaldehyde in the production of amino and phenolic resins, as well as novel hardeners for formaldehyde-free wood adhesives. Solutions in which formaldehyde in completely replaced are presented in this review. Recent advances indicate that it is possible to develop new formaldehyde-free systems of resins with compatible hardeners. The formaldehyde substitutes that have primarily been tested are glyoxal, glutaraldehyde, furfural, 5-hydroxymethylfurfural, and dimethoxyethanal. The use of such substitutes eliminates the problem of free formaldehyde emission originating from the resin used in the production of wood-based panels. However, these alternatives are mostly characterized by worse reactivity, and, as a result, the use of formaldehyde-free resins may affect the mechanical and strength properties of wood-based panels. Nonetheless, there are still many substantial challenges for the complete replacement of formaldehyde and further research is needed, especially in the field of transferring the technology to industrial practice.

Photo-Induced Reactions between Glyoxal and Hydroxylamine in Cryogenic Matrices

In this paper, the photochemistry of glyoxal−hydroxylamine (Gly−HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly−HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene−hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species.

Compact glyoxal tanning system: a chrome-free sustainable and green approach towards tanning-cum-upgradation of low-grade raw materials in leather processing

Increased concern over the use of metal salts such as chromium, zirconium, and aluminum for tanning of hides and skins has made the leather production industry to be constantly on the lookout for organic tanning agents in place of the inorganic system. Though glutaraldehyde has been looked at as a viable option, it still lags in imparting superior strength properties to the leather and also it has been reported to have inherent toxicity. With that concept in view, this research work focuses on the usage of glyoxal along with synthetic tanning agents as a replacement for glutaraldehyde and other inorganic tanning systems. The offer level and starting pH for the glyoxal tanning process was optimized as 6% (w/w) and 5.0, respectively, and the shrinkage temperature of the collagen was found to be around 80 °C. Additionally, the controlled shrunken grain effect of the aldehyde tanning system was explored by changing the pH of the process, which helped to improve the thickness of low-grade thinner raw materials by up to 40%. The mechanism for the shrunken grain effect has also been proposed in this work by studying the dimensional changes occurring in the leather matrix upon treating skin/hide with glyoxal at different pH levels. The mechanical and strength properties of the leather were found to be better than the glutaraldehyde tanning system. The BOD/COD ratio of wastewater generated from the glyoxal process was found to be greater than 0.3 making them easily treatable. Considering all these factors, compact glyoxal-based tanning along with synthetic tanning agents can be a game-changing technology for the leather processing industry.

Investigation of formation of well-known AGEs precursors in cookies using an in vitro simulated gastrointestinal digestive system

The present study investigated the influence of in vitro stimulated digestion system on the content of glyoxal and methylglyoxal in commercial cookies. Glyoxal and methylglyoxal levels in different cookie samples were analyzed before and after in vitro digestion with High Performance Liquid Chromatography. Initial glyoxal and methylglyoxal values ranged between 42.9 and 126.6 µg/100 g, and between 22.9 and 507.3 µg/100 g, respectively. After in vitro digestion, formation of glyoxal and methylglyoxal values were increased up to 645% and 698%, respectively. The results revealed that in vitro stimulated digestion conditions strongly increased the amount of glyoxal and methylglyoxal in cookies. The amount of fructose was found to be more effective on the formation of both GO and MGO than those of glucose and sucrose. Further studies are needed to extensively investigate glyoxal and methylglyoxal formation under in vitro conditions in such foods.

The underappreciated role of monocarbonyl-dicarbonyl interconversion in secondary organic aerosol formation during photochemical oxidation of m-xylene

Photochemical oxidation (including photolysis and OH-initiated reactions) of aromatic hydrocarbon produces carbonyls, which are involved in the formation of secondary organic aerosols (SOA). However, the mechanism of this process remains incompletely understood. Herein, the monocarbonyl-dicarbonyl interconversion and its role in SOA production were investigated via a series of photochemical oxidation experiments for m-xylene and representative carbonyls. The results showed that SOA mass concentration peaked at 113.5 ± 3.5 μg m^-3 after m-xylene oxidation for 60 min and then decreased. Change in the main oxidation products from dicarbonyl (e.g., glyoxal, methylglyoxal) to monocarbonyl (e.g., formaldehyde) was responsible for this decrease. The photolysis of methylglyoxal or glyoxal produced formaldehyde, favoring SOA formation, while photopolymerization of formaldehyde to glyoxal decreased SOA production. The presence of ·OH altered the balance of photolysis interconversion, resulting in greater production of formaldehyde and SOA from glyoxal than methylglyoxal. Both photolysis and OH-initiated transformations of glyoxal to formaldehyde were suppressed by methylglyoxal, while glyoxal accelerated the reaction of ·OH with methylglyoxal to generate products which reversibly converted to glyoxal and methylglyoxal. These interconversion reactions reduced SOA production. The present study provides a new research perspective for the contribution mechanism of carbonyls in SOA formation and the findings are also helpful to efficiently evaluate the atmospheric fate of aromatic hydrocarbons.

Characteristic flavor formation of thermally processed N-(1-deoxy-α-d-ribulos-1-yl)-glycine: Decisive role of additional amino acids and promotional effect of glyoxal

The role of amino acids and α-dicarbonyls in the flavor formation of Amadori rearrangement product (ARP) during thermal processing was investigated. Comparisons of the volatile compounds and their concentrations when N-(1-deoxy-α-d-ribulos-1-yl)-glycine reacted with different amino acids or glyoxal (GO) at 100 °C were executed. Additional amino acids, such as glycine (Gly), in ARP models contributed to the diversity of furanoids by the chain elongation of the derived formaldehyde. Whereas the monoanion of additional glutamic acid acted as nucleophile, favored 2-ethyl-3,5-dimethylpyrazine and 2,5-dimethylpyrazine formation; the nonionized amino group of additional lysine were involved in α-dicarbonyls formation, causing pyrazine and methylpyrazine accumulation in the ARP model. Moreover, the high dosage and pH stabilization of additional GO probably promoted the ARP degradation and deoxyosones retro-aldol cleavage, resulting in methylpyrazine rather than furanoids formation. The present work provided the guidance for the controlled flavor formation of ARP in industrial application.

Deciphering Changes in the Structure and IgE-Binding Ability of Ovalbumin Glycated by α-Dicarbonyl Compounds under Simulated Heating

As a complex reaction, biological consequences of the Maillard reaction (MR) on dietary proteins need to be deciphered. Despite previous studies on the structural and antigenic properties of ovalbumin (OVA) by MR, associated changes induced by specific MR intermediates and their downstream products are largely unknown. This study focused on the impacts of glycation by α-dicarbonyl compounds (α-DCs), intermediates of MR and precursors of advanced glycation end-products (AGEs), on the structural and IgE-binding properties of ovalbumin (OVA) under simulated heating. Methylglyoxal (MGO), glyoxal (GO), and butanedione (BU) were selected as typical α-DCs to generate glycated OVA with different AGE-modifications (AGE-Ms). The results showed that reactions between OVA and α-DCs generated OVA-AGE with various degrees of modification and conformational unfolding, and the reactivity of α-DCs followed the order GO > MGO > BU. Depending on the precursor type, the levels of 10 specific AGEs were verified, and the amounts of total AGEs increased with heating temperature and α-DC dosage. Compared to native OVA, glycated OVA showed reduced IgE-binding levels but with sRAGE-binding ligands, the extent of which was associated with the contents of total AGEs and Nε-carboxymethyllysine, and changes in certain protein conformational structures. High-resolution mass spectrometry further identified different AGE-Ms on the Lys and Arg residues of OVA, confirming variations in the glycation sites and their associations with the immunoreactive epitopes of OVA under different conditions.

Analysis of Glyoxal- and Methylglyoxal-Derived Advanced Glycation End Products during Grilling of Porcine Meat

The reaction of the N⁶-amino group of lysine residues and 1,2-dicarbonyl compounds during Maillard processes leads to advanced glycation end products (AGEs). In the present work, we deliver a comprehensive analysis of changes of carbohydrates, dicarbonyl structures, and 11 AGEs during the grilling of porcine meat patties. While raw meat contained mainly glyoxal-derived N⁶-carboxymethyl lysine (CML), grilling led to an increase of predominantly methylglyoxal-derived AGEs N⁶-carboxyethyl lysine (CEL), N⁶-lactoyl lysine, methylglyoxal lysine dimer (MOLD), and methylglyoxal lysine amide (MOLA). Additionally, we identified and quantitated a novel methylglyoxal-derived amidine compound N¹,N²-di-(5-amino-5-carboxypentyl)-2-lactoylamidine (methylglyoxal lysine amide, MGLA) in heated meat. Analysis of carbohydrates suggested that approximately 50% of the methylglyoxal stemmed from the fragmentation of triosephosphates during the heat treatment. Surprisingly, N⁶-lactoyl lysine was the major AGE, and based on model incubations, we propose that approximately 90% must be explained by the nonenzymatic acylation of lysine through S-lactoylglutathione, which was quantitated for the first time in meat herein.

Water Significantly Changes the Ring-Cleavage Process During Aqueous Photooxidation of Toluene

As a major constituent of aromatic compounds, toluene exists widely in environmental aqueous phases. This research investigated the aqueous-phase OH oxidation of toluene to determine how liquid water changes the radical chemistry of ring-cleavage pathways. Results show that ring-cleavage pathways through the C₇ bicyclic peroxy radical (BPR) account for about 70% of total aqueous-phase oxidation pathways, which is similar to that in the gas-phase oxidation. However, detailed ring-cleavage pathways in the aqueous phase change significantly compared with those in the gas phase as shown by the decreased production of glyoxal and methylglyoxal and the enhanced production of formic acid and acetic acid as primary products, which can be attributed to the presence of liquid water. Water facilitates the formation of the BPR whose structure is different from that in the gas-phase oxidation and results in different ring-cleavage pathways through hydrogen-shift reactions. Furthermore, water helps the hydration of acyl radicals formed by the BPR to produce organic acids. With the suggested ring-cleavage mechanisms, a box model can simulate aqueous-phase product distributions better than that with the classical ring-cleavage mechanisms. Given the influence of water on reaction mechanisms, aqueous-phase oxidation of hydrophobic organic compounds may be more important than previously assumed.

Competition of Partitioning and Reaction Controls Brown Carbon Formation from Butenedial in Particles

Organic reactions in atmospheric particles impact human health and climate, such as by the production of brown carbon. Previous work suggests that reactions are faster in particles than in bulk solutions because of higher reactant concentrations and pronounced surface-mediated processes. Additionally, dialdehydes may have accelerated reactions in particles, as has been shown for the glyoxal reaction with ammonium sulfate (AS). Here, we examine the competition between evaporation and reaction of butenedial, a semivolatile dialdehyde, and reduced nitrogen (NH_X) in bulk solutions and levitated particles with mass spectrometry (MS). Pyrrolinone is the major product of butenedial/AS bulk solutions, indicating brown carbon formation via accretion reactions. By contrast, pyrrolinone is completely absent in all MS measurements of comparable levitated particles suspended in a pure N₂ stream. Pyrrolinone is only produced in levitated butenedial particles exposed to gas-phase ammonia, without enhanced reaction kinetics previously observed for glyoxal and other systems. Despite butenedial's large Henry's law constant and fast reaction with NH_X compared to glyoxal, the brown carbon pathway competes with evaporation only in polluted regions with extreme NH_X. Therefore, accurate knowledge of effective volatilities or Henry's law constants for complex aerosol matrices is required when chemistry studied in bulk solutions is extrapolated to atmospheric particles.

Inhibitory Activity on the Formation of Reactive Carbonyl Species in Edible Oil by Synthetic Polyphenol Antioxidants

Food lipids play an important role in food quality, and their attributes contribute to texture, flavor, and nutrition. However, high-temperature processing leads to lipid peroxidation, degradation, and the formation of reactive carbonyl species (RCS), such as acrolein (ACR), glyoxal (GO), and methylglyoxal (MGO). We investigated the changes in the peroxidation value (POV), Rancimat induction time, formation and total amount of RCS, and inhibitory effects of synthetic polyphenol antioxidants on ACR/GO/MGO in plant oils during heating processing through an accelerated oxidation test using Rancimat. With increasing temperature and heating time, the amounts of ACR, GO, and MGO in oil increased and the level of ACR was about several times higher than that of GO and MGO. We also found that some amounts of ACR, GO, and MGO were produced at the initial stage before reaching the peak value of POV, even before oil oxidative rancidity, and the common antioxidant butyl hydroxyanisole (BHA)/butylated hydroxytoluene (BHT) could not remove them once they were generated. This is first time to purify PG-ACR-MGO and elucidate the structure based on analysis of their high resolution mass spectrometry and ¹H, ¹³C, and two-dimensional nuclear magnetic resonance. We further found that PG rather than BHT and BHA efficiently trapped ACR, OG, and MGO to form adducts in oil and roasted beef burgers with corn oil. Additionally, after incubation at 80 °C, the trapping order of PG was as follows: ACR, MGO, and GO, and the adduct of PG-ACR was formed within 1 min; after 10 min, PG-MGO was generated; and three adducts formed at 15 min. However, PG could not trap ACR, GO, or MGO to form adducts at room temperature. This study provided novel knowledge to advance our understanding of the ability of synthetic polyphenol antioxidants to scavenge RCS simultaneously, such as ACR, MGO, and GO. Our findings demonstrated that PG, as an inhibitor of RCS, is suitable for medium- and high-temperature food processing but not for normal-temperature storage.

Novel Amidine Protein Cross-Links Formed by the Reaction of Glyoxal with Lysine

One crucial aspect of the Maillard reaction is the formation of reactive α-dicarbonyl structures like glyoxal, which are prone toward further reactions with proteins, e.g., the N⁶-amino group of lysine. The initially formed labile glyoxal-imine was previously established as a key intermediate in the formation of the advanced glycation end products N⁶-carboxymethyl lysine (CML), glyoxal lysine amide (GOLA), glyoxal lysine dimer (GOLD), and N⁶-glycolyl lysine (GALA). Here, we introduce a novel amidine cross-link structure N¹,N²-bis-(5-amino-5-carboxypentyl)-2-hydroxy-acetamidine (glyoxal lysine amidine, GLA), which is formed exclusively from glyoxal through the same isomerization cascade. After independent synthesis of the authentic reference standard, we were able to quantitate this cross-link in incubations of 40 mM N²-t-Boc-lysine with glyoxal and various sugars (40-100 mM) under mild conditions (pH 7.4, 37 °C) using an HPLC-MS/MS method. Furthermore, incubations of proteins (6 mg/mL) with 50 mM glyoxal confirmed the cross-linking by GLA, which was additionally identified in acidic hydrolyzed proteins of butter biscuits after HPLC enrichment.

High Pressure Inside Nanometer-Sized Particles Influences the Rate and Products of Chemical Reactions

The composition of organic aerosol has a pivotal influence on aerosol properties such as toxicity and cloud droplet formation capability, which could affect both climate and air quality. However, a comprehensive and fundamental understanding of the chemical and physical processes that occur in nanometer-sized atmospheric particles remains a challenge that severely limits the quantification and predictive capabilities of aerosol formation pathways. Here, we investigated the effects of a fundamental and hitherto unconsidered physical property of nanoparticles-the Laplace pressure. By studying the reaction of glyoxal with ammonium sulfate, both ubiquitous and important atmospheric constituents, we show that high pressure can significantly affect the chemical processes that occur in atmospheric ultrafine particles (i.e., particles < 100 nm). Using high-resolution mass spectrometry and UV-vis spectroscopy, we demonstrated that the formation of reaction products is strongly (i.e., up to a factor of 2) slowed down under high pressures typical of atmospheric nanoparticles. A size-dependent relative rate constant is determined and numerical simulations illustrate the reduction in the production of the main glyoxal reaction products. These results established that the high pressure inside nanometer-sized aerosols must be considered as a key property that significantly impacts chemical processes that govern atmospheric aerosol growth and evolution.

Effect of Methionine on the Thermal Degradation of N-(1-Deoxy-d-fructos-1-yl)-methionine Affecting Browning Formation

The effect of additional dl-methionine (Met) on the thermal degradation of a methionine-glucose-derived Amadori rearrangement product (MG-ARP) was investigated under different reaction conditions. The resulting color formation and changes in the concentrations of MG-ARP, Met, and α-dicarbonyl compounds were investigated. Additional Met did not affect the degradation rate of MG-ARP but got involved in subsequent reactions and resulted in a decrease in the contents of C₆-α-dicarbonyl compounds. During MG-ARP degradation, the formation of glyoxal (GO) and methylglyoxal (MGO) was facilitated by additional Met, through retro-aldolization reaction of C₆-α-dicarbonyl compounds. This effect of Met addition was dependent on the reaction temperature, and the consistent conclusion could be made in a buffer system. The improvement of GO and MGO formation as color precursors caused by the additional Met contributed to the acceleration of browning formation.

Production of Formate via Oxidation of Glyoxal Promoted by Particulate Nitrate Photolysis

Particulate nitrate photolysis can produce oxidants (i.e., OH, NO₂, and NO₂^-/HNO₂) in aqueous droplets and may play a potential role in increased atmospheric oxidative capacity. Our earlier works have reported on the SO₂ oxidation promoted by nitrate photolysis to produce sulfate. Here, we used glyoxal as a model precursor to examine the role of particulate nitrate photolysis in the formation of secondary organic aerosol (SOA) from particle-phase oxidation of glyoxal by OH radicals. Particles containing sodium nitrate and glyoxal were irradiated at 300 nm. Interestingly, typical oxidation products of oxalic acid, glyoxylic acid, and higher-molecular-weight products reported in the literature were not found in the photooxidation process of glyoxal during nitrate photolysis in the particle phase. Instead, formic acid/formate production was found as the main oxidation product. At glyoxal concentration higher than 3 M, we found that the formic acid/formate production rate increases significantly with increasing glyoxal concentration. Such results suggest that oxidation of glyoxal at high concentrations by OH radicals produced from nitrate photolysis in aqueous particles may not contribute significantly to SOA formation since formic acid is a volatile species. Furthermore, recent predictions of formic acid/formate concentration from the most advanced chemical models are lower than ambient observations at both the ground level and high altitude. The present study reveals a new insight into the production of formic acid/formate as well as a sink of glyoxal in the atmosphere, which may partially narrow the gap between model predictions and field measurements in both species.

Unexpected Oligomerization of Small α-Dicarbonyls for Secondary Organic Aerosol and Brown Carbon Formation

Large amounts of small α-dicarbonyls (glyoxal and methylglyoxal) are produced in the atmosphere from photochemical oxidation of biogenic isoprene and anthropogenic aromatics, but the fundamental mechanisms leading to secondary organic aerosol (SOA) and brown carbon (BrC) formation remain elusive. Methylglyoxal is commonly believed to be less reactive than glyoxal because of unreactive methyl substitution, and available laboratory measurements showed negligible aerosol growth from methylglyoxal. Herein, we present experimental results to demonstrate striking oligomerization of small α-dicarbonyls leading to SOA and BrC formation on sub-micrometer aerosols. Significantly more efficient growth and browning of aerosols occur upon exposure to methylglyoxal than glyoxal under atmospherically relevant concentrations and in the absence/presence of gas-phase ammonia and formaldehyde, and nonvolatile oligomers and light-absorbing nitrogen-heterocycles are identified as the dominant particle-phase products. The distinct aerosol growth and light absorption are attributed to carbenium ion-mediated nucleophilic addition, interfacial electric field-induced attraction, and synergetic oligomerization involving organic/inorganic species, leading to surface- or volume-limited reactions that are dependent on the reactivity and gaseous concentrations. Our findings resolve an outstanding discrepancy concerning the multiphase chemistry of small α-dicarbonyls and unravel a new avenue for SOA and BrC formation from atmospherically abundant, ubiquitous carbonyls and ammonia/ammonium sulfate.

Glycation by glyoxal leads to profound changes in the behavior of dermal fibroblasts

INTRODUCTION

Diabetes is a worldwide health problem that is associated with severe complications. Advanced Glycation End products (AGEs) such as Nε-(carboxymethyl)lysine, which result from chronic hyperglycemia, accumulate in the skin of patients with diabetes. The effect of AGEs on fibroblast functionality and their impact on wound healing are still poorly understood.

RESEARCH DESIGN AND METHODS

To investigate this, we treated cultured human fibroblasts with 0.6 mM glyoxal to induce acute glycation. The behavior of fibroblasts was analyzed by time-lapse monolayer wounding healing assay, seahorse technology and atomic force microscopy. Production of extracellular matrix was studied by transmission electronic microscopy and western blot. Lipid metabolism was investigated by staining of lipid droplets (LDs) with BODIPY 493/503.

RESULTS

We found that the proliferative and migratory capacities of the cells were greatly reduced by glycation, which could be explained by an increase in fibroblast tensile strength. Measurement of the cellular energy balance did not indicate that there was a change in the rate of oxygen consumption of the fibroblasts. Assessment of collagen I revealed that glyoxal did not influence type I collagen secretion although it did disrupt collagen I maturation and it prevented its deposition in the extracellular matrix. We noted a pronounced increase in the number of LDs after glyoxal treatment. AMPK phosphorylation was reduced by glyoxal treatment but it was not responsible for the accumulation of LDs.

CONCLUSION

Glyoxal promotes a change in fibroblast behavior in favor of lipogenic activity that could be involved in delaying wound healing.

Model studies of advanced glycation end product modification of heterograft biomaterials: The effects of in vitro glucose, glyoxal, and serum albumin on collagen structure and mechanical properties

Glutaraldehyde cross-linked heterograft tissues, bovine pericardium (BP) or porcine aortic valves, are the leaflet materials in bioprosthetic heart valves (BHV) used in cardiac surgery for heart valve disease. BHV fail due to structural valve degeneration (SVD), often with calcification. Advanced glycation end products (AGE) are post-translational, non-enzymatic reaction products from sugars reducing proteins. AGE are present in SVD-BHV clinical explants and are not detectable in un-implanted BHV. Prior studies modeled BP-AGE formation in vitro with glyoxal, a glucose breakdown product, and serum albumin. However, glucose is the most abundant AGE precursor. Thus, the present studies investigated the hypothesis that BHV susceptibility to glucose related AGE, together with serum proteins, results in deterioration of collagen structure and mechanical properties. In vitro experiments studied AGE formation in BP and porcine collagen sponges (CS) comparing ¹⁴C-glucose and ¹⁴C-glyoxal with and without bovine serum albumin (BSA). Glucose incorporation occurred at a significantly lower level than glyoxal (p<0.02). BSA co-incubations demonstrated reduced glyoxal and glucose uptake by both BP and CS. BSA incubation caused a significant increase in BP mass, enhanced by glyoxal co-incubation. Two-photon microscopy of BP showed BSA induced disruption of collagen structure that was more severe with glucose or glyoxal co-incubation. Uniaxial testing of CS demonstrated that glucose or glyoxal together with BSA compared to controls, caused accelerated deterioration of viscoelastic relaxation, and increased stiffness over a 28-day time course. In conclusion, glucose, glyoxal and BSA uniquely contribute to AGE-mediated disruption of heterograft collagen structure and deterioration of mechanical properties.

Effect of Relative Humidity on Secondary Brown Carbon Formation in Aqueous Droplets

Atmospheric brown carbon (BrC) is a significant contributor to particulate light absorption. Reactions between small aldehydes and reduced nitrogen species have been shown to produce secondary BrC in atmospheric droplets. These reactions can be substantially accelerated upon droplet evaporation. Despite aqueous droplets undergoing continuous water evaporation and uptake in response to the surrounding relative humidity (RH), secondary BrC formation in these droplets under various RH conditions remains poorly understood. In this work, we investigate BrC formation from reactions of two aqueous-phase precursors, glyoxal and methylglyoxal, with ammonium sulfate or glycine in aqueous droplets after drying at a range of RH (30-90%). Our results illustrate, for the first time, that BrC production varies as a function of RH. For all four chemical reaction systems being investigated, mass absorption efficiencies (MAE, m²/g C) of aqueous aerosol products (from 270 to 512 nm wavelength range) generally increase with reducing RH to reach a maximum at ∼55-65% RH and subsequently decrease, caused by further drying. Chemical characterization using high-resolution aerosol mass spectrometry shows that the formation of nitrogen-containing organic species also follows a similar variation with RH. Our observations reveal that the acceleration of BrC production from evaporation of water may be diminished by other factors, such as limited particle-phase water content, phase transition, and volatility of reactants and products. Overall, our results highlight that intermediate RH conditions in the atmosphere may be more efficient in secondary BrC formation, indicating that the effect of RH needs to be included in atmospheric models for a more accurate representation of light-absorbing aerosol formation in aqueous droplets.

Synergistic Uptake by Acidic Sulfate Particles of Gaseous Mixtures of Glyoxal and Pinanediol

The uptake of gaseous organic species by atmospheric particles can be affected by the reactive interactions among multiple co-condensing species, yet the underlying mechanisms remain poorly understand. Here, the uptake of unary and binary mixtures of glyoxal and pinanediol by neutral and acidic sulfate particles is investigated. These species are important products from the oxidation of volatile organic compounds (VOCs) under atmospheric conditions. The uptake to acidic aerosol particles greatly increased for a binary mixture of glyoxal and pinanediol compared to the unary counterparts. The strength of the synergism depended on the particle acidity and water content (i.e., relative humidity). The greater uptake was up to 2.5× to 8× at 10% relative humidity (RH) for glyoxal and pinanediol, respectively. At 50% RH, it was 2× and 1.2× for the two species. Possible mechanisms of acid-catalyzed cross reactions between the species are proposed to explain the synergistic uptake. The proposed mechanisms are applicable to a broader extent across atmospheric species having carbonyl and hydroxyl functionalities. The results thus suggest that synergistic uptake reactions can be expected to significantly influence the gas-particle partitioning of VOC oxidation products under atmospheric conditions and thus greatly affect their atmospheric transport and lifetime.

Importance of Wintertime Anthropogenic Glyoxal and Methylglyoxal Emissions in Beijing and Implications for Secondary Organic Aerosol Formation in Megacities

Atmospheric glyoxal (GLY) and methylglyoxal (MGLY) are key precursors of secondary organic aerosol (SOA). However, anthropogenic emissions of GLY and MGLY and their contribution to surface GLY and MGLY concentrations, as well as the secondary organic aerosol (SOA) formation, are not well quantified. By developing an emission inventory of anthropogenic GLY and MGLY and improving the Community Multiscale Air Quality Model (CMAQ) with SOA formation from irreversible surface uptake of GLY and MGLY, as well as a precursor-origin resolved technique, we quantified the source contributions of GLY and MGLY and their impact on wintertime SOA formation in Beijing, China. The total emissions of GLY and MGLY in Beijing in 2017 are 1.1 × 10⁴ kmol and 7.0 × 10³ kmol, respectively. Anthropogenic primary emissions are found to be the dominant contributor to wintertime GLY and MGLY concentrations (∼74% for GLY and ∼63% for MGLY). Anthropogenic primary emissions of GLY and MGLY contributes to 30% of GLY/MGLY SOA daily average concentration and accounts for up to 45% of nighttime GLY/MGLY SOA in winter. The study suggests that the anthropogenic GLY and MGLY emissions, mainly from gasoline vehicles and cooking, are important for SOA formation and shall be strictly controlled in Chinese megacities.