Determination of α-Dicarbonyl compounds in traditional Chinese herbal medicines

α-DCs (α-dicarbonyls) have been proven to be closely related to aging and the onset and development of many chronic diseases. The wide presence of this kind of components in various foods and beverages has been unambiguously determined, but their occurrence in various phytomedicines remains in obscurity. In this study, we established and evaluated an HPLC-UV method and used it to measure the contents of four α-DCs including 3-deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), and diacetyl (DA) in 35 Chinese herbs after they have been derivatized with 4-nitro-1,2-phenylenediamine. The results uncover that 3-DG is the major component among the α-DCs, being detectable in all the selected herbs in concentrations ranging from 22.80 μg/g in the seeds of Alpinia katsumadai to 7032.75 μg/g in the fruit of Siraitia grosuenorii. The contents of the other three compounds are much lower than those of 3-DG, with GO being up to 22.65 μg/g, MGO being up to 55.50 μg/g, and DA to 18.75 μg/g, respectively. The data show as well the contents of the total four α-DCs in the herbs are generally in a comparable level to those in various foods, implying that herb medicines may have potential risks on human heath in view of the α-DCs.

Simultaneous determination of carbonyl compounds related to thermal treatment and oxidative stability of infant formulas by gas-diffusion microextraction and high-performance liquid chromatography with ultraviolet detection

Infant formulae are the only possible alternative to breastfeeding during the first year of life, so it is crucial to assure their innocuousness. Infant formula undergoes heat treatments to ensure safety and shelf life. However, such processes impact health as they lead to the formation of malondialdehyde, acrolein, and α-dicarbonyl compounds, related to Maillard reaction. Thus, there is a need for improved analytical methods to ensure the safety, quality, and nutritional value of infant formulae, and also exploring the potential of specific compounds as indicators for quality control and monitoring purposes. We developed and validated a novel, efficient, and cost-effective method using gas-diffusion microextraction for the simultaneous quantification of carbonyl compounds in infant formula. Malondialdehyde, acrolein, glyoxal, methylglyoxal, and diacetyl were detected as o-phenylenediamine derivatives using HPLC with UV detection. Parameters influencing extraction efficiency were studied using an asymmetric screening design. The validated method has shown excellent linearity, sensitivity, accuracy, and precision. It was applied to analyze 26 infant formula samples, including starter, follow-up, and special formulated powdered infant formula. Methylglyoxal was found in all samples (0.201-3.153 μg mL-1), while malondialdehyde was present only in certain starter formulas (1.033-1.802 μg mL-1). Acrolein (0.510-3.246 μg mL-1), glyoxal (0.109-1.253 μg mL-1), and diacetyl (0.119-2.001 μg mL-1) were detected in various sample types. Principal components and hierarchical cluster analyses have showcased distinct sample clustering based on analyte contents. This study presents a novel methodology for the analysis of markers of thermal treatment and oxidative stability in infant formula. It contributes to the characterization of the products' composition and quality control of infant formulae, thereby enhancing their safety and nutritional adequacy. This study also presents the first reported quantification of acrolein in infant formula and introduces the application of the acrolein-o-phenylenediamine derivative for food analysis.

Study on the non-enzymatic browning of lotus rhizome juice during sterilization mediated by 1,2-dicarboxyl and heterocyclic compounds

BACKGROUND

Lotus rhizome juice (LRJ) is susceptible to the Maillard reaction (MR) and caramelization, which tend to cause a reduction in quality and lower consumer acceptance of the product. 1,2-Dicarbonyl compounds (DCs) and heterocyclic compounds have attracted increasing attention as key intermediates responsible for the formation of brown pigments during MR and caramelization. However, little is known about the effects of these two types of compounds on brown pigments in LRJ during sterilization. This study quantified the changes in brown intensity (A420), DCs, and heterocyclic compounds before and after spiking, and identified the precursors and intermediates for brown pigment formation as well as the formation pathways of the intermediates.

RESULTS

The spiking experiments suggested that spiking with fructose resulted in more 3-deoxyglucosone (3-DG) and 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP), while that with lysine led to more glucosone (GS) and 2,3-butanedione (2,3-BD) in LRJ. The addition of glucose, asparagine, and glutamine promoted the formation of 5-hydroxymethylfurfural (HMF) significantly, whereas the addition of glucose, lysine, and asparagine resulted in more norfuraneol. Spiking with reducing sugars and amino acids promoted both glyoxal (GO) and methylglyoxal (MGO), and the effect of glucose on GO was particularly significant. Correlation analysis showed that A420 had the highest correlation with 3-DG in the fructose- and lysine-spiked group, and with HMF in the glucose-, asparagine-, and glutamine-spiked groups.

CONCLUSION

This study revealed that fructose, glucose, asparagine, glutamine, and lysine were essential precursors of MR and caramelization in LRJ during sterilization. 3-Deoxyglucosone and DDMP were mainly produced by caramelization with fructose as the primary precursor, whereas GS and 2,3-BD were primarily formed via MR with lysine catalysis. The MR and caramelization were the main formation pathways of HMF (catalyzed by asparagine and glutamine) and norfuraneol (catalyzed by lysine and asparagine), with glucose as the critical precursor. Methylglyoxal was mainly produced by MR or caramelization, and caramelization was the main formation pathway of GO, with glucose as the precursor. Dor brown pigment formation from fructose and lysine, 3-DG was identified as the most crucial intermediate, while for that from glucose, asparagine, and glutamine, HMF was found to be the most important intermediate. © 2023 Society of Chemical Industry.

Application of tea polyphenols as additives in brown fermented milk: Potential analysis of mitigating Maillard reaction products

Brown fermented milk (BFM) is favored by consumers in the dairy market for its unique burnt flavor and brown color. However, Maillard reaction products (MRP) from high-temperature baking are also noteworthy. In this study, tea polyphenols (TP) were initially developed as potential inhibitors of MRP formation in BFM. The results showed that the flavor profile of BFM did not change after adding 0.08% (wt/wt) of TP, and its inhibition rates on 5-hydroxymethyl-2-furaldehyde (5-HMF), glyoxal (GO), methylglyoxal (MGO), Nε-carboxymethyl lysine (CML), and Nε-carboxyethyl lysine (CEL) were 60.8%, 27.12%, 23.44%, 57.7%, and 31.28%, respectively. After 21 d of storage, the levels of 5-HMF, GO, MGO, CML, and CEL in BFM with TP were 46.3%, 9.7%, 20.6%, 5.2%, and 24.7% lower than the control group, respectively. Moreover, a smaller change occurred in their color and the browning index was lower than that of the control group. The significance of this study was to develop TP as additives to inhibit the production of MRP in brown fermented yogurt without changing color and flavors, thereby making dairy products safer for consumers.

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.

A fast and efficient method for the analysis of α-dicarbonyl compounds in aqueous solutions: Development and application

Among the highly oxygenated species formed in situ in the atmosphere, α-dicarbonyl compounds are the most reactive species, thus contributing to the formation of secondary organic aerosols that affect both air quality and climate. They are ubiquitous in the atmosphere and are easily transferred to the atmospheric aqueous phase due to their high solubility. In addition, α-dicarbonyl compounds are toxic compounds found in food in biochemistry studies as they can be produced endogenously through various pathways and exogenously through the Maillard reaction. In this work, we take advantage of the high reactivity of α-dicarbonyl compounds in alkaline solutions (intramolecular Cannizzaro reaction) to develop an analytical method based on high performance ion chromatography. This fast and efficient method is suitable for glyoxal, methylglyoxal and phenylglyoxal which are detected as glycolate, lactate and mandelate anions respectively, with 100% conversion at pH > 12 and room temperature for exposure times to hydroxide ranging from 5 min to 4 h. Diacetyl is detected as 2,4-dihydroxy-2,4-dimethyl-5-oxohexanoate due to a base-catalysed aldol reaction that occurs before the Cannizzaro reaction. The analytical method is successfully applied to monitor glyoxal consumption during aqueous phase HO∙-oxidation, an atmospherically relevant reaction using concentrations that can be observed in fog and cloud water. The method also reveals potential analytical artifacts that can occur in the use of ion chromatography for α-hydroxy carboxylates measurements in complex matrices due to α-dicarbonyl conversion during the analysis time. An estimation of the artifact is given for each of the studied α-hydroxy carboxylates. Other polyfunctional and pH-sensitive compounds that are potentially present in environmental samples (such as nitrooxycarbonyls) can also be converted into α-hydroxy carboxylates and/or nitrite ions within the HPIC run. This shows the need for complementary analytical measurements when complex matrices are studied.

Direct emissions of particulate glyoxal and methylglyoxal from biomass burning and coal combustion

Glyoxal (Gly) and methylglyoxal (Mgly) are key precursors globally for secondary organic aerosol (SOA) formation. These two species were often thought to be formed in the atmosphere via photochemical oxidation of organics from biogenic and anthropogenic origins, although few studies have shown their direct emissions. In this study, we report direct emissions of particulate Gly and Mgly from different residential fuels typically used in north China. The emission ratios (ERs) and emission factors (EFs) of particulate Gly and Mgly for biomass burning were approximate 5-fold and 7-fold higher than those for coal combustion, respectively. The large variances in emissions of Gly and Mgly could be attributed to the different combustion processes, which influenced by the fuel types and combustion conditions. The averaged ERs and EFs of particulate Gly and Mgly were about one order of magnitude lower than their gaseous counterparts due to the low Henry's law constant, which was also consistent with the low particle-to-gas ratio of Gly (0.04) and Mgly (0.02). Our results suggest that the direct emissions of Gly and Mgly from emission sources should be considered when estimating the formation of SOA from Gly and Mgly.

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.

Antiglycation Effects of Adlay Seed and Its Active Polyphenol Compounds: An In Vitro Study

This study aimed to evaluate the antiglycation effects of adlay on protein glycation using in vitro glycation assays. Adlay seed was divided into the following four parts: the hull (AH), testa (AT), bran (AB), and polished adlay (PA). A solvent extraction technique and column chromatography were utilized to investigate the active fractions and components of adlay. Based on a BSA-glucose assay, the ethanolic extracts of AT (ATE) and AB (ABE) revealed a greater capacity to inhibit protein glycation. ATE was further consecutively partitioned into four solvent fractions with n-hexane, ethyl acetate (ATE-Ea), 1-butanol (ATE-BuOH), and water. ATE-BuOH and -Ea show marked inhibition of glucose-mediated glycation. Medium–high polarity subfractions eluted from ATE-BuOH below 50% methanol with Diaion HP-20, ATE-BuOH-c to -f, exhibited superior antiglycation activity, with a maximum inhibitory percentage of 88%. Two phenolic compounds, chlorogenic acid and ferulic acid, identified in ATE-BuOH with HPLC, exhibited potent inhibition of the individual stage of protein glycation and its subsequent crosslinking, as evaluated by the BSA-glucose assay, BS-methylglyoxal (MGO) assay, and G.K. peptide-ribose assay. In conclusion, this study demonstrated the antiglycation properties of ATE in vitro that suggest a beneficial effect in targeting hyperglycemia-mediated protein modification.

Rapid increase in atmospheric glyoxal and methylglyoxal concentrations in Lhasa, Tibetan Plateau: Potential sources and implications

Glyoxal (Gly) and methylglyoxal (Mgly) are the intermediate products of several volatile organic compounds (VOCs) as well as the precursors of brown carbon and may play key roles in photochemical pollution and regional climate change in the Tibetan Plateau (TP). However, their sources and atmospheric behaviors in the TP remain unclear. During the second Tibetan Plateau Scientific Expedition and Research in the summer of 2020, the concentrations of Gly (0.40 ± 0.30 ppbv) and Mgly (0.57 ± 0.16 ppbv) observed in Lhasa, the most densely populated city in the TP, had increased by 20 and 15 times, respectively, compared to those measured a decade previously. Owing to the strong solar radiation, secondary formations are the dominant sources of both Gly (71%) and Mgly (62%) in Lhasa. In addition, primary anthropogenic sources also play important roles by emitting Gly and Mgly directly and providing abundant precursors (e.g., aromatics). During ozone pollution episodes, local anthropogenic sources (industries, vehicles, solvent usage, and combustion activities) contributed up to 41% and 45% in Gly and Mgly levels, respectively. During non-episode periods, anthropogenic emissions originating from the south of Himalayas also have non-negligible contributions. Our results suggest that in the previous decade, anthropogenic emissions have elevated the levels of Gly and Mgly in the TP dramatically. This study has important implications for understanding the impact of human activities on air quality and climate change in this ecologically fragile area.

Fructose and methylglyoxal-induced glycation alters structural and functional properties of salivary proteins, albumin and lysozyme

Glycation process refers to reactions between reduction sugars and amino acids that can lead to formation of advanced glycation end products (AGEs) which are related to changes in chemical and functional properties of biological structures that accumulate during aging and diseases. The aim of this study was to perform and analyze in vitro glycation by fructose and methylglyoxal (MGO) using salivary fluid, albumin, lysozyme, and salivary α-amylase (sAA). Glycation effect was analyzed by biochemical and spectroscopic methods. The results were obtained by fluorescence analysis, infrared spectroscopy (total attenuated reflection-Fourier transform, ATR-FTIR) followed by multivariate analysis of principal components (PCA), protein profile, immunodetection, enzymatic activity and oxidative damage to proteins. Fluorescence increased in all glycated samples, except in saliva with fructose. The ATR-FTIR spectra and PCA analysis showed structural changes related to the vibrational mode of glycation of albumin, lysozyme, and salivary proteins. Glycation increased the relative molecular mass (Mr) in protein profile of albumin and lysozyme. Saliva showed a decrease in band intensity when glycated. The analysis of sAA immunoblotting indicated a relative reduction in intensity of its correspondent Mr after sAA glycation; and a decrease in its enzymatic activity was observed. Carbonylation levels increased in all glycated samples, except for saliva with fructose. Thiol content decreased only for glycated lysozyme and saliva with MGO. Therefore, glycation of salivary fluid and sAA may have the potential to identify products derived by glycation process. This opens perspectives for further studies on the use of saliva, an easy and non-invasive collection fluid, to monitor glycated proteins in the aging process and evolution of diseases.

Effect of sugar metabolite methylglyoxal on equine lamellar explants: An ex vivo model of laminitis

Laminitis is one of the most devastating diseases in equine medicine, and although several etiopathogenetic mechanisms have been proposed, few clear answers have been identified to date. Several lines of evidence point towards its underlying pathology as being metabolism-related. In the carbonyl stress pathway, sugars are converted to methylglyoxal (MG)-a highly reactive α-oxoaldehyde, mainly derived during glycolysis in eukaryotic cells from the triose phosphates: D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. One common hypothesis is that MG could be synthesized during the digestive process in horses, and excessive levels absorbed into peripheral blood could be delivered to the foot and lead to alterations in the hoof lamellar structure. In the present study, employing an ex vivo experimental design, different concentrations of MG were applied to hoof explants (HE), which were then incubated and maintained in a specific medium for 24 and 48 h. Macroscopic and histological analyses and a separation force test were performed at 24 and 48 h post-MG application. Gene expression levels of matrix metalloproteinase (MMP)-2 and -14 and tissue inhibitor of metalloproteinase (TIMP)-2 were also measured at each time point for all experimental conditions. High concentrations of MG induced macroscopic and histological changes mimicking laminitis. The separation force test revealed that hoof tissue samples incubated for 24 h in a high concentration of MG, or with lower doses but for a longer period (48 h), demonstrated significant weaknesses, and samples were easily separated. All results support that high levels of MG could induce irreversible damage in HEs, mimicking laminitis in an ex vivo model.

Evaluation of the nephrotoxicity and safety of low-dose aristolochic acid, extending to the use of Xixin (Asurum), by determination of methylglyoxal and d-lactate

ETHNOPHARMACOLOGICAL RELEVANCE

Most Aristolochiaceae plants are prohibited due to aristolochic acid nephropathy (AAN), except Xixin (Asarum spp.). Xixin contains trace amounts of aristolochic acid (AA) and is widely used in Traditional Chinese Medicine. Methylglyoxal and d-lactate are regarded as biomarkers for nephrotoxicity.

AIM OF THE STUDY

The use of Xixin (Asarum spp.) is essential and controversial. This study aimed to evaluate tubulointerstitial injury and interstitial renal fibrosis by determining urinary methylglyoxal and d-lactate after withdrawal of low-dose AA in a chronic mouse model.

MATERIALS AND METHODS

C3H/He mice in the AA group (n = 24/group) were given ad libitum access to distilled water containing 3 μg/mL AA (0.5 mg/kg/day) for 56 days and drinking water from days 57 to 84. The severity of tubulointerstitial injury and fibrosis were evaluated using the tubulointerstitial histological score (TIHS) and Masson's trichrome staining. Urinary and serum methylglyoxal were determined by high-performance liquid chromatography (HPLC); urinary d-lactate were determined by column-switching HPLC.

RESULTS

After AA withdrawal, serum methylglyoxal in the AA group increased from day 56 (429.4 ± 48.3 μg/L) to 84 (600.2 ± 99.9 μg/L), and peaked on day 70 (878.3 ± 171.8 μg/L; p < 0.05); TIHS and fibrosis exhibited similar patterns. Urinary methylglyoxal was high on day 56 (3.522 ± 1.061 μg), declined by day 70 (1.583 ± 0.437 μg) and increased by day 84 (2.390 ± 0.130 μg). Moreover, urinary d-lactate was elevated on day 56 (82.10 ± 18.80 μg) and higher from day 70 (201.10 ± 90.82 μg) to 84 (193.28 ± 61.32 μg).

CONCLUSIONS

Methylglyoxal is induced after AA-induced tubulointerstitial injury, so methylglyoxal excretion and metabolism may be a detoxification and repair strategy. A low cumulative AA dose is the key factor that limits tubulointerstitial injury and helps to repair. Thus, AA-containing herbs, especially Xixin, should be used at low doses for short durations (less than one month).

Silicon-regulated antioxidant and osmolyte defense and methylglyoxal detoxification functions co-ordinately in attenuating fluoride toxicity and conferring protection to rice seedlings

The objective of this manuscript was to demonstrate the efficacy of silicon supplementation in relieving the fluoride-induced damages in rice cultivar, Khitish. The exposure of seedlings to two different concentrations of fluoride, viz., 25 and 50 mg L^-1 NaF caused increase in fluoride accumulation, as a result of which the seedlings suffered severe oxidative stress, as evident from growth inhibition, reduction in seed germination, tissue biomass, root and shoot length, decline in chlorophyll content, increases in electrolyte leakage, H₂O₂ content, lipid peroxidation (malondialdehyde content and lipoxygenase activity), protein carbonylation and protease activity. The extent of damage was more at higher fluoride concentration. Silicon amendment, irrespective of fluoride concentrations, led to large build-up of endogenous silicon level and brought considerable improvement in all the parameters examined with respect to fluoride stress. The fluoride-mediated enhancement in methylglyoxal level was lowered by silicon, because of the prominent activation of glyoxalase I and glyoxalase II. While the stress-mediated induction in antioxidative enzymes like GPOX, APX, SOD, GPX and GR was lowered by silicon, the inhibition in CAT activity was relieved. The antioxidative defense mechanism was also boosted up via enhanced content of total phenolics and carotenoids. However, the fluoride-mediated increase in anthocyanins, flavonoids, xanthophyll, ascorbate and reduced glutathione, and osmolytes like total amino acids, proline and glycine-betaine, were all lowered in presence of silicon, together with reduced PAL and P5CS activity. Overall, silicon reduced oxidative damages to develop fluoride-tolerant rice plants through augmentation of different antioxidant and osmolyte defense and methylglyoxal detoxification system.

Impact of methylglyoxal modification of chicken sarcoplasmic protein emulsions on emulsifying properties, rheological behavior and advanced glycation end products

BACKGROUND

Protein modification is used to improve emulsion properties. However, there are limited reports on the effect of methylglyoxal (MGO) modification on emulsifying properties and on the production of advanced glycation end-products (AGEs) in chicken sarcoplasmic protein emulsion (SPE). In this study, MGO solution was dispersed into prepared emulsion (17 mg mL^-1 sarcoplasmic-soybean oil (v/v 5:1)) at 0, 0.5, 5, 10, 30 and 50 mmol L^-1 concentrations. Emulsifying activity index (EAI), emulsifying stability index (ESI), Z-average diameter, polydispersity index (PDI), zeta potential, rheological behavior (thermal condensation characteristics and fluidity) and AGEs in different concentrations of MGO SPE were measured. In addition, the effect of MGO on the levels of AGEs, lipid and protein oxidation of the emulsion as well as their relationship has also been analyzed.

RESULTS

Our findings showed that ESI had the lowest value when MGO was added at a concentration of 10 mmol L^-1 , while Z-average, PDI, carbonyl and AGEs had the highest value at the same concentration. Also, 10 mmol L^-1 MGO played an important role in affecting the rheology of the emulsion. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that the presence of myofibrillar proteins (MPs) in SPE was the main reason for the crosslinking of polymers which could be damaged by high concentration of MGO (>10 mmol L^-1 ).

CONCLUSION

Different concentration of MGO showed varying effects on emulsion properties and on the formation of AGEs in chicken SPE. Pearson's correlation analysis concluded that protein oxidation played a significant positive role during MGO modification. © 2020 Society of Chemical Industry.

Methylglyoxal and D-lactate in cisplatin-induced acute kidney injury: Investigation of the potential mechanism via fluorogenic derivatization liquid chromatography-tandem mass spectrometry (FD-LC-MS/MS) proteomic analysis

Nephrotoxicity severely limits the chemotherapeutic efficacy of cisplatin (CDDP). Oxidative stress is associated with CDDP-induced acute kidney injury (AKI). Methylglyoxal (MG) forms advanced glycation end products that elevate oxidative stress. We aimed to explore the role of MG and its metabolite D-lactate and identify the proteins involved in CDDP-induced AKI. Six-week-old female BALB/c mice were intraperitoneally administered CDDP (5 mg/kg/day) for 3 or 5 days. Blood urea nitrogen (42.6 ± 7.4 vs. 18.3 ± 2.5; p < 0.05) and urinary N-acetyl-β-D-glucosaminide (NAG; 4.89 ± 0.61 vs. 2.43 ± 0.31 U/L; p < 0.05) were significantly elevated in the CDDP 5-day group compared to control mice. Histological analysis confirmed AKI was successfully induced. Confocal microscopy revealed TNF-α was significantly increased in the CDDP 5-day group. Fluorogenic derivatized liquid chromatography-tandem mass spectrometry (FD-LC-MS/MS) showed the kidney MG (36.25 ± 1.68 vs. 18.95 ± 2.24 mg/g protein, p < 0.05) and D-lactate (1.78 ± 0.29 vs. 1.12 ± 0.06 mol/g protein, p < 0.05) contents were significantly higher in the CDDP 5-day group than control group. FD-LC-MS/MS proteomics identified 33 and nine altered peaks in the CDDP 3-day group and CDDP 5-day group (vs. control group); of the 35 proteins identified using the MOSCOT database, 11 were antioxidant-related. Western blotting confirmed that superoxide dismutase 1 (SOD-1) and parkinson disease protein 7 (DJ-1) are upregulated and may participate with MG in CDDP-induced AKI. This study demonstrates TNF-α, MG, SOD-1 and DJ-1 play crucial roles in CDDP-induced AKI.

Formation and migration of α-dicarbonyl compounds during storage and reheating of a sugary food simulation system

BACKGROUND

The thermal processing of food results in the formation of α-dicarbonyl compounds (α-DCs) such as glyoxal (GO), methylglyoxal (MGO), 2,3-butanedione (2,3-BD), and 3-deoxyglucosone (3-DG), which are precursors of potentially harmful advanced glycation end products. Some of the α-DCs found in food products might result from chemical deterioration reactions during storage and reheating. A range of sugary food simulation systems were stored at three different temperatures (4, 25, and 37 °C) and reheated using three different processing methods to investigate the formation and migration of α-DCs.

RESULTS

During 20 days of storage, the concentration of α-DCs declined, following which the concentration remained approximately constant. Methylglyoxal was the major α-DC affected during storage, its relative content decreasing from 233.71 to 44.12 μg mL^-1 in the glucose-lysine system. The concentration of α-DCs decreased with increasing temperature. Microwave reheating increased the formation of α-DC compounds. The largest increases in 3-DG concentrations were observed in the maltose-lysine systems (24.94 to 35.74 μg mL^-1 ). The concentration of α-DCs only changed a little in response to reheating at 100 °C, but declined when reheated at 150 °C.

CONCLUSION

The concentration of α-DCs following storage and reheating depends on the type of sugar, lysine content, temperature, and method of reheating. © 2020 Society of Chemical Industry.

Measurement of α-dicarbonyl compounds in human saliva by pre-column derivatization HPLC

Background α-Dicarbonyl compounds (α-DCs) have been detected in body fluids including plasma and urine and elevation of this sort of compounds in vivo has been associated with the development of many kinds of chronic diseases. However whether α-DCs are present in human saliva, and if their presence/absence can be related with various chronic diseases is yet to be determined. Methods In this study, a pre-column derivatization HPLC-UV method was developed to measure 3-deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), diacetyl (DA), and pentane-2,3-dione (PD) in human saliva employing 4-(2,3-dimethyl-6-quinoxalinyl)-1,2-benzenediamine (DQB) as a derivatizing reagent. The derivatization of the α-DCs is fast and the conditions are facile. The method was evaluated and the results show that it is suitable for the quantification of α-DCs in human saliva. Results In the measurements of these α-DCs in the saliva of 15 healthy subjects and 23 type 2 diabetes mellitus (T2DM) patients, we found that the concentrations of GO and MGO in the saliva of the diabetic patients were significantly higher than those in healthy subjects. As far as we know, this is the first time that salivary α-DC concentrations have been determined and associated with T2DM. Conclusions The developed method would be useful for the measurement of the salivary α-DC levels and the data acquired could be informative in the early screening for diabetes.

Quantitation of α-Dicarbonyls and Advanced Glycation Endproducts in Conventional and Lactose-Hydrolyzed Ultrahigh Temperature Milk during 1 Year of Storage

A comprehensive quantitative characterization of Maillard reaction products was carried out for conventional (CON) and lactose-hydrolyzed (LH) ultrahigh temperature (UHT) milk during storage at 20, 30, and 40 °C for 1 year. The accumulation of 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) in LH-UHT milk ranged from 20-fold (at 20 °C) to 44-fold (at 40 °C) higher than that in CON-UHT milk. High temperature storage (40 °C) significantly accelerated the accumulation of 3-DG, 3-DGal, and 5-hydroxymethyl furfural but not the majority of the analyzed advanced glycation endproducts (AGEs). The concentrations of major AGEs including N-ε-carboxymethyllysine (CML), N-ε-carboxyethyllysine (CEL), methylglyoxal-hydroimidazolone isomers (MG-H1/H3), glyoxal-hydroimidazolone isomers (G-H1/H3), and G-H2 detected in CON milk during storage were in the range 12-700, 1-14, 8-45, 4-13, and 1-30 μM, respectively, while they were 30-570, 2-88, 17-150, 9-20, and 5-34 μM, respectively, in LH milk. Pyrraline, S-(carboxymethyl)cysteine (CMC), and glyoxal-lysine dimer were detected in lower levels, while MG-H2, methylglyoxal-lysine dimer, argpyrimidine, glyoxal-lysine-amide, glycolic acid-lysine-amide, and pentosidine were not detected in any of the milk samples. This work demonstrates for the first time that five of the analyzed AGEs (CML, CEL, MG-H1/H3, G-H1/H3, and G-H2) could be selected as markers for evaluation of the extent of the Maillard reaction in UHT milk. These results contribute to a better understanding of how Maillard reactions progress during storage of UHT milk and can be used to develop strategies to inhibit Maillard reactions in LH milk.

Antibacterial activity of varying UMF-graded Manuka honeys

Honey has been used as a traditional remedy for skin and soft tissue infections due to its ability to promote wound healing. Manuka honey is recognized for its unusually abundant content of the antibacterial compound, methylglyoxal (MGO). The Unique Manuka Factor (UMF) grading system reflects the MGO concentration in Manuka honey sold commercially. Our objective was to observe if UMF values correlated with the antibacterial activity of Manuka honey against a variety of pathogens purchased over the counter. The antibacterial effect of Manuka honey with UMF values of 5+, 10+, and 15+ from the same manufacturer was assessed by the broth microdilution method. Minimum inhibitory concentration (MIC) values were determined against 128 isolates from wound cultures representing gram-positive, gram-negative, drug-susceptible, and multi-drug resistant (MDR) organisms. Lower MICs were observed with UMF 5+ honey for staphylococci (n = 73, including 25 methicillin-resistant S. aureus) and Pseudomonas aeruginosa (n = 22, including 10 MDR) compared to UMF 10+ honey (p<0.05) and with UMF 10+ compared to UMF 15+ (p = 0.01). For Enterobacteriaceae (n = 33, including 14 MDR), MIC values were significantly lower for UMF 5+ or UMF 10+ compared to UMF 15+ honey (p<0.01). MIC₅₀ for UMF 5+, UMF 10+, and UMF 15+ honey against staphylococci was 6%, 7%, and 15%, and for Enterobacteriaceae was 21%, 21%, and 27%, respectively. For Pseudomonas aeruginosa MIC₅₀ was 21% and MIC₉₀ was 21–27% for all UMFs. Manuka honey exhibited antimicrobial activity against a spectrum of organisms including those with multi-drug resistance, with more potent activity overall against gram-positive than gram-negative bacteria. Manuka honey with lower UMF values, in our limited sampling, paradoxically demonstrated increased antimicrobial activity among the limited samples tested, presumably due to changes in MGO content of honey over time. The UMF value by itself may not be a reliable indicator of antibacterial effect.

Effects of Catechins on Nε-(Carboxymethyl)lysine and Nε-(Carboxyethyl)lysine Formation in Green Tea and Model Systems

The effects of catechins on N^ε-(carboxymethyl)lysine (CML) and N^ε-(carboxyethyl)lysine (CEL) formation in green tea and related model systems were investigated in this study. Since the first step of green tea processing entails enzyme inactivation, the catechin content was maintained at a high level during processing. However, drying still had a great effect on CML and CEL formation, while other steps also contributed. Hence, model systems were developed to analyze the effects of catechins on CML and CEL formation. Catechins ((-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epigallocatechin gallate) could inhibit CML formation in the model imitating the condition of green tea processing, though the inhibitory efficiency was reduced by transition metals. This suggested that catechins could inhibit CML formation in the real tea system, though the inhibitory efficiency may be reduced by tea components which promote its synthesis. However, CEL formation was not always inhibited by the tested catechins, though catechins could significantly decrease the content of methylglyoxal which is considered an important intermediate. Consequently, the main pathway of CEL formation may not be through methylglyoxal.

Effect of Roasting and Storage on the Formation of Maillard Reaction and Sugar Degradation Products in Hazelnuts ( Corylus avellana L.)

This study investigated the effect of roasting (150 °C for 30 min) and storage (12 months at 4 °C, 25 °C, and 25 °C in vacuum package), conditions of which are generally applied in the industry and markets, on the formation of Maillard reaction and sugar degradation products, namely dicarbonyl compounds, 5-hydroxymethylfurfural, N-ε-fructosyllysine, and N-ε-carboxymethyllysine in Tombul and Levant hazelnuts. Roasting increased all dicarbonyl compounds significantly ( p < 0.05). The concentration of methylglyoxal was the highest while 1-deoxyglucosone was the lowest in roasted hazelnuts. 5-Hydroxymethylfurfural and N-ε-carboxymethyllysine also increased significantly ( p < 0.05) with roasting while furosine decreased. Roasting changed the progress of the Maillard reaction from the early stage to the advanced stage. On the other hand, there were no significant changes ( p > 0.05) in the concentration of Maillard reaction and sugar degradation products independent of the storage conditions or time and hazelnut variety, except for glyoxal, diacetyl, and 1-deoxyglucosone. Therefore, neither 5-hydroxymethylfurfural nor furosine is suggested as a storage marker of the Maillard reaction and sugar degradation.

Identification of Pinocembrin as an Anti-Glycation Agent and α-Glucosidase Inhibitor from Fingerroot (Boesenbergia rotunda): The Tentative Structure⁻Activity Relationship towards MG-Trapping Activity

Diabetes mellitus (DM) is a disease that is caused by a malfunction of carbohydrate metabolism, which plays an important role in the development of long-term diabetic complications. The excess glucose can be transformed to methylglyoxal (MG), a potential precursor of glycation. Glycation is a spontaneous non-enzymatic reaction that initially yields advanced glycation end-products (AGEs), which ultimately triggers several severe complications. Therefore, the inhibition of AGEs formation is the imperative approach for alleviating diabetic complications. The aim of this research was to investigate the glycation and α-glucosidase inhibitory abilities of compounds isolated from fingerroot. The dichloromethane extract afforded three flavanones, two chalcones, two dihydrochalcones, and one kavalactone. Most of the isolated compounds showed higher inhibition effect against AGEs formation than aminoguanidine (AG). Subsequent evaluation in MG-trapping assay indicated that their trapping potency was relatively comparable to AG. Their structure-activity relationships (SAR) of MG-trapping activity were investigated using the comparison of the structures of flavonoids. In addition, pinocembrin displayed moderate α-glucosidase inhibition against both maltase and sucrose, with IC₅₀ values of 0.35 ± 0.021 and 0.39 ± 0.020 mM, respectively.

Manipulation of glyoxalase pathway confers tolerance to multiple stresses in rice

Crop plants face a multitude of diverse abiotic and biotic stresses in the farmers' fields. Although there now exists a considerable knowledge of the underlying mechanisms of response to individual stresses, the crosstalk between response pathways to various abiotic and biotic stresses remains enigmatic. Here, we investigated if the cytotoxic metabolite methylglyoxal (MG), excess of which is generated as a common consequence of many abiotic and biotic stresses, may serve as a key molecule linking responses to diverse stresses. For this, we generated transgenic rice plants overexpressing the entire two-step glyoxalase pathway for MG detoxification. Through assessment of various morphological, physiological and agronomic parameters, we found that glyoxalase-overexpression imparts tolerance towards abiotic stresses like salinity, drought and heat and also provides resistance towards damage caused by the sheath blight fungus (Rhizoctonia solani) toxin phenylacetic acid. We show that the mechanism of observed tolerance of the glyoxalase-overexpressing plants towards these diverse abiotic and biotic stresses involves improved MG detoxification and reduced oxidative damage leading to better protection of chloroplast and mitochondrial ultrastructure and maintained photosynthetic efficiency under stress conditions. Together, our findings indicate that MG may serve as a key link between abiotic and biotic stress response in plants.

Analysis of Advanced Glycation Endproducts in Rat Tail Collagen and Correlation to Tendon Stiffening

Methylglyoxal is a major 1,2-dicarbonyl compound in vivo and leads to nonenzymatic protein modifications, known as advanced glycation endproducts. Especially long-lived proteins like collagen are prone to changes of the mechanical or biological function, respectively, by accumulation of Maillard-derived modifications. Specifically, the resulting nonenzymatic cross-link structures in parallel to the natural maturation process of collagen fibrils lead to complications with age or during disease. A novel lysine-lysine amide cross-link derived from methylglyoxal, 2,15-diamino-8-methyl-9-oxo-7,10-diaza-1,16-hexadecanedioic acid, named MOLA, was synthesized and identified in vitro and in vivo. Tail tendons of young, adult, and old rats (3, 12, and 22 months) were enzymatically digested prior to analysis of acid-labile glycation products via liquid chromatography-tandem mass spectrometry (LC-MS/MS). As a result, nine monovalent amino acid modifications, mostly originating from methylglyoxal (36 μmol/mol leucine-equivalents in total), and four glycation cross-links (0.72 μmol/mol glucosepane, 0.24 μmol/mol DODIC (3-deoxyglucosone-derived imidazoline cross-link), 0.04 μmol/mol MODIC (methylglyoxal-derived imidazoline cross-link), 0.34 μmol/mol MOLA) were quantitated in senescent tendon collagen. The results correlated with increased tail tendon breaking time from 10 to 190 min and indicate that methylglyoxal is a major player in the aging process of connective tissue.

Ketone Body Acetoacetate Buffers Methylglyoxal via a Non-enzymatic Conversion during Diabetic and Dietary Ketosis

The α-oxoaldehyde methylglyoxal is a ubiquitous and highly reactive metabolite known to be involved in aging- and diabetes-related diseases. If not detoxified by the endogenous glyoxalase system, it exerts its detrimental effects primarily by reacting with biopolymers such as DNA and proteins. We now demonstrate that during ketosis, another metabolic route is operative via direct non-enzymatic aldol reaction between methylglyoxal and the ketone body acetoacetate, leading to 3-hydroxyhexane-2,5-dione. This novel metabolite is present at a concentration of 10%-20% of the methylglyoxal level in the blood of insulin-starved patients. By employing a metabolite-alkyne-tagging strategy it is clarified that 3-hydroxyhexane-2,5-dione is further metabolized to non-glycating species in human blood. The discovery represents a new direction within non-enzymatic metabolism and within the use of alkyne-tagging for metabolism studies and it revitalizes acetoacetate as a competent endogenous carbon nucleophile.

The Antibacterial Activity of Australian Leptospermum Honey Correlates with Methylglyoxal Levels

Most commercially available therapeutic honey is derived from flowering Leptospermum scoparium (manuka) plants from New Zealand. Australia has more than 80 Leptospermum species, and limited research to date has found at least some produce honey with high non-peroxide antibacterial activity (NPA) similar to New Zealand manuka, suggesting Australia may have a ready supply of medical-grade honey. The activity of manuka honey is largely due to the presence of methylglyoxal (MGO), which is produced non-enzymatically from dihydroxyacetone (DHA) present in manuka nectar. The aims of the current study were to chemically quantify the compounds contributing to antibacterial activity in a collection of Australian Leptospermum honeys, to assess the relationship between MGO and NPA in these samples, and to determine whether NPA changes during honey storage. Eighty different Leptospermum honey samples were analysed, and therapeutically useful NPA was seen in samples derived from species including L. liversidgei and L. polygalifolium. Exceptionally high levels of up to 1100 mg/kg MGO were present in L. polygalifolium honey samples sourced from the Northern Rivers region in NSW and Byfield, QLD, with considerable diversity among samples. There was a strong positive relationship between NPA and MGO concentration, and DHA was present in all of the active honey samples, indicating a potential for ongoing conversion to MGO. NPA was stable, with most samples showing little change following seven years of storage in the dark at 4°C. This study demonstrates the potential for Australian Leptospermum honey as a wound care product, and argues for an extension of this analysis to other Leptospermum species.

Identification and Quantitation of 2-Acetyl-1-pyrroline in Manuka Honey (Leptospermum scoparium)

Manuka honey from New Zealand is known for its exceptional antibacterial activity, which is due to high amounts of the 1,2-dicarbonyl compound methylglyoxal (MGO). MGO in manuka honey is formed via non-enzymatic dehydration from dihydroxyacetone (DHA) during honey maturation. MGO and DHA are highly reactive substances, leading to a variety of unique chemical reactions. During Strecker reaction between proline and MGO, 2-acetyl-1-pyrroline (2-AP), an important aroma compound, is formed. Using liquid-liquid extraction and gas chromatography-mass spectrometry analysis, 2-AP was identified unambiguously in manuka honey for the first time. Quantitation was carried out via external matrix calibration, using a synthetic 2-AP standard and artificial honey. The 2-AP concentration in 11 commercial samples of manuka honey ranged from 0.08 to 0.45 mg/kg. For manuka honey samples containing MGO in concentrations above 250 mg/kg, significantly higher amounts of 2-AP were found when compared to non-manuka honeys. When high amounts of MGO were artificially added to non-manuka multifloral honey, an increase of the 2-AP concentration from 0.07 to 0.40 mg/kg after 12 weeks of storage at 37 °C was observed, concomitant with a significant increase in the concentration of 5-hydroxymethylfurfural (HMF). No increase of 2-AP was found during storage at ambient temperature. 2-AP together with MGO can be a suitable parameter for the quality control of manuka honey.

Carbon Nanomaterials Based Electrochemical Sensors/Biosensors for the Sensitive Detection of Pharmaceutical and Biological Compounds

Electrochemical sensors and biosensors have attracted considerable attention for the sensitive detection of a variety of biological and pharmaceutical compounds. Since the discovery of carbon-based nanomaterials, including carbon nanotubes, C₆₀ and graphene, they have garnered tremendous interest for their potential in the design of high-performance electrochemical sensor platforms due to their exceptional thermal, mechanical, electronic, and catalytic properties. Carbon nanomaterial-based electrochemical sensors have been employed for the detection of various analytes with rapid electron transfer kinetics. This feature article focuses on the recent design and use of carbon nanomaterials, primarily single-walled carbon nanotubes (SWCNTs), reduced graphene oxide (rGO), SWCNTs-rGO, Au nanoparticle-rGO nanocomposites, and buckypaper as sensing materials for the electrochemical detection of some representative biological and pharmaceutical compounds such as methylglyoxal, acetaminophen, valacyclovir, β-nicotinamide adenine dinucleotide hydrate (NADH), and glucose. Furthermore, the electrochemical performance of SWCNTs, rGO, and SWCNT-rGO for the detection of acetaminophen and valacyclovir was comparatively studied, revealing that SWCNT-rGO nanocomposites possess excellent electrocatalytic activity in comparison to individual SWCNT and rGO platforms. The sensitive, reliable and rapid analysis of critical disease biomarkers and globally emerging pharmaceutical compounds at carbon nanomaterials based electrochemical sensor platforms may enable an extensive range of applications in preemptive medical diagnostics.

Significant Contributions of Isoprene to Summertime Secondary Organic Aerosol in Eastern United States

A modified SAPRC-11 (S11) photochemical mechanism with more detailed treatment of isoprene oxidation chemistry and additional secondary organic aerosol (SOA) formation through surface-controlled reactive uptake of dicarbonyls, isoprene epoxydiol and methacrylic acid epoxide was incorporated in the Community Multiscale Air Quality Model (CMAQ) to quantitatively determine contributions of isoprene to summertime ambient SOA concentrations in the eastern United States. The modified model utilizes a precursor-origin resolved approach to determine secondary glyoxal and methylglyoxal produced by oxidation of isoprene and other major volatile organic compounds (VOCs). Predicted OC concentrations show good agreement with field measurements without significant bias (MFB ∼ 0.07 and MFE ∼ 0.50), and predicted SOA reproduces observed day-to-day and diurnal variation of Oxygenated Organic Aerosol (OOA) determined by an aerosol mass spectrometer (AMS) at two locations in Houston, Texas. On average, isoprene SOA accounts for 55.5% of total predicted near-surface SOA in the eastern U.S., followed by aromatic compounds (13.2%), sesquiterpenes (13.0%) and monoterpenes (10.9%). Aerosol surface uptake of isoprene-generated glyoxal, methylglyoxal and epoxydiol accounts for approximately 83% of total isoprene SOA or more than 45% of total SOA. A domain wide reduction of NOx emissions by 40% leads to a slight decrease of domain average SOA by 3.6% and isoprene SOA by approximately 2.6%. Although most of the isoprene SOA component concentrations are decreased, SOA from isoprene epoxydiol is increased by ∼16%.

High glucose, glucose fluctuation and carbonyl stress enhance brain microvascular endothelial barrier dysfunction: Implications for diabetic cerebral microvasculature

We previously demonstrated that in normal glucose (5 mM), methylglyoxal (MG, a model of carbonyl stress) induced brain microvascular endothelial cell (IHEC) dysfunction that was associated with occludin glycation and prevented by N-acetylcysteine (NAC). Herein, we investigated the impact of high glucose and low GSH, conditions that mimicked the diabetic state, on MG-induced IHEC dysfunction. MG-induced loss of transendothelial electrical resistance (TEER) was potentiated in IHECs cultured for 7 or 12 days in 25 mM glucose (hyperglycemia); moreover, barrier function remained disrupted 6 h after cell transfer to normal glucose media (acute glycemic fluctuation). Notably, basal occludin glycation was elevated under these glycemic states. TEER loss was exaggerated by inhibition of glutathione (GSH) synthesis and abrogated by NAC, which corresponded to GSH decreases and increases, respectively. Significantly, glyoxalase II activity was attenuated in hyperglycemic cells. Moreover, hyperglycemia and GSH inhibition increased MG accumulation, consistent with a compromised capacity for MG elimination. α-Oxoaldehydes (MG plus glyoxal) levels were elevated in streptozotocin-induced diabetic rat plasma. Immunohistochemistry revealed a prevalence of MG-positive, but fewer occludin-positive microvessels in the diabetic brain in vivo, and Western analysis confirmed an increase in MG–occludin adducts. These results provide the first evidence that hyperglycemia and acute glucose fluctuation promote MG–occludin formation and exacerbate brain microvascular endothelial dysfunction. Low occludin expression and high glycated-occludin contents in diabetic brain in vivo are factors that would contribute to the dysfunction of the cerebral microvasculature during diabetes.

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Methylglyoxal (MG) induced electrical resistance (TEER)loss in brain microvascular endothelial cells.

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TEER loss was potentiated by hyperglycemia, and low glutathione.

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TEER loss was correlated with occludin-glycation and was attenuated and exacerbated by NAC and BSO, respectively.

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Hyperglycemia decreased glyoxalase II activity and promoted free MG accumulation.

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Diabetic brain in vivo exhibiteda prevalence of MG-positive microvessels and increased occludin–MG adducts.

Investigation of α-dicarbonyl compounds in baby foods by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry

Baby foods are exposed to elevated temperatures during processing treatments such as sterilization or spray drying. These treatments decompose sugars leading to the formation of α-dicarbonyl compounds that are of importance since they have been associated with several metabolic disorders. In this study, an analytical method based on high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) was used to determine α-dicarbonyl compounds in baby foods. The method entailed aqueous extraction of α-dicarbonyl compounds from the samples and derivatization with o-phenylenediamine prior to chromatographic analysis. The results indicated that major degradation product was 3-deoxyglucosone in the samples including cereal-based infant formula, canned fruit and vegetable puree. Its concentration ranged between 3.9 and 827.1 mg/kg in infant formula and between 26.7 and 92.3 mg/kg in fruit puree samples. The concentrations of glucosone, 1-deoxyglucosone, 5-hydroxymethyl-2-furfural, furfural, glyoxal, methylglyoxal, and dimethylglyoxal levels were rather low.

Occurrence and fate of ozonation by-products at a full-scale drinking water treatment plant

The occurrence and fate of carbonyl compounds as ozonation by-products at a full scale drinking water treatment plant (DWTP) were studied for one year. Raw water and samples after the main treatment processes (pre-ozonation, coagulation/flocculation, sand filtration, main ozonation, filtration through granular activated carbon and chlorination) were collected on a monthly basis. Pre-ozonation led to the formation of carbonyl compounds at concentrations of 67.3 ± 43.3 μg/l as sum of 14 carbonyl compounds whereas lower concentrations were determined after the main ozonation process, 32.8 ± 22.3 μg/l. The dominant compounds were formaldehyde, acetaldehyde, glyoxal and methyl glyoxal contributing to 65% of total carbonyl content. The DOC reactivity in formation of carbonyl compounds varied through the year exhibiting the higher values in spring. Coagulation/flocculation and sand filtration significantly removed (64-80%) the carbonyl compounds formed at the pre-ozonation step. The removal efficiency of filtration through granular activated carbon showed great variation ranging from 15 to 62%. Finally, the concentrations of carbonyl compounds in finished water were low, close to detection limits, revealing the efficiency of DWTP in the removal of this class of ozonation by-products.

The unique manuka effect: why New Zealand manuka honey fails the AOAC 998.12 C-4 sugar method

Conversion of dihydroxyacteone (DHA) to methylglyoxal (MGO) has been shown to be the key mechanism for the growth in "apparent" C-4 sugar content in nonperoxide activity (NPA) manuka honey. This reaction is enhanced by heating and storage time and is demonstrated for the first time in clover honey adulterated with DHA purchased from a chemical supplier and in manuka honey containing naturally occurring DHA and MGO. After heating at 37 °C for 83 days, pure clover honey with no added DHA has the same apparent C-4 sugar content as at t = 0 days. The same clover honey adulterated with synthetic DHA added at t = 0 days and heated at 37 °C over the same time scale shows a change in apparent C-4 sugars from 2.8 to 5.0%. Four NPA manuka honeys heated over longer periods show an increase in apparent C-4 sugars of up to 280% after 241 days. This study strongly suggests that a protein fractionation effect occurs in the conversion of DHA to MGO in higher NPA manuka honey, rendering the remaining δ(13)C protein value more negative and falsely indicating C-4 sugar addition when using the AOAC 998.12 method.

Methylglyoxal may affect hydrogen peroxide accumulation in manuka honey through the inhibition of glucose oxidase

Although hydrogen peroxide (H₂O₂) is one of the major antibacterial factors in most honeys, it does not accumulate in medical-grade manuka honey. The goal of this study was to investigate the effect of artificially added methylglyoxal (MGO) on H₂O₂ accumulation in natural non-manuka honeys. H₂O₂ concentrations in the honey solutions were determined using a fluorimetric assay. Two, the most potent H₂O₂ producers honeydew honeys were mixed with MGO at final concentrations of 250, 500, and 1000 mg/kg, and incubated for 4 days at 37°C. Subsequently, H₂O₂ concentrations were determined in 50% (wt/vol) MGO supplemented honey solutions. In vitro crosslinking of the enzyme glucose oxidase (GOX) after incubation with MGO was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Tested honeys at a concentration of 50% (wt/vol) accumulated up to 495.8±9.1 μM H₂O₂ in 24 h. The most potent producers were the two honeydew honeys, whose 50% solutions accumulated 306.9±6.8 and 495.8±9.1 μM H₂O₂, respectively. Levels of H₂O₂ increased significantly over time in both honey solutions. Contrary to this, the MGO-treated honeys generated significantly lower amounts of H₂O₂ (P<.001), and this reduction was dose dependent. In addition, MGO-treated GOX formed high molecular weight adducts with increasing time of incubation accompanied by loss of its enzymatic activity. High levels of MGO in manuka honey, by modifying the enzyme GOX, might be responsible for suppressing H₂O₂ generation. These data highlight the detrimental effect of MGO on significant proteinaceous components of manuka honey.

A mitochondria-targeted mass spectrometry probe to detect glyoxals: implications for diabetes

The glycation of protein and nucleic acids that occurs as a consequence of hyperglycemia disrupts cell function and contributes to many pathologies, including those associated with diabetes and aging. Intracellular glycation occurs after the generation of the reactive 1,2-dicarbonyls methylglyoxal and glyoxal, and disruption of mitochondrial function is associated with hyperglycemia. However, the contribution of these reactive dicarbonyls to mitochondrial damage in pathology is unclear owing to uncertainties about their levels within mitochondria in cells and in vivo. To address this we have developed a mitochondria-targeted reagent (MitoG) designed to assess the levels of mitochondrial dicarbonyls within cells. MitoG comprises a lipophilic triphenylphosphonium cationic function, which directs the molecules to mitochondria within cells, and an o-phenylenediamine moiety that reacts with dicarbonyls to give distinctive and stable products. The extent of accumulation of these diagnostic heterocyclic products can be readily and sensitively quantified by liquid chromatography-tandem mass spectrometry, enabling changes to be determined. Using the MitoG-based analysis we assessed the formation of methylglyoxal and glyoxal in response to hyperglycemia in cells in culture and in the Akita mouse model of diabetes in vivo. These findings indicated that the levels of methylglyoxal and glyoxal within mitochondria increase during hyperglycemia both in cells and in vivo, suggesting that they can contribute to the pathological mitochondrial dysfunction that occurs in diabetes and aging.

Formation of 4(5)-methylimidazole and its precursors, α-dicarbonyl compounds, in Maillard model systems

Glyoxal, methylglyoxal, and diacetyl formed from sucrose alone and from a D-glucose/ammonia Maillard model system were analyzed by gas chromatography. They are known as precursors of 4(5)-methylimidazole (MI). Glyoxal and methylglyoxal formed more in acidic conditions than in basic conditions, whereas diacetyl formed the most at the highest basic condition of pH 12. Glyoxal formation from sucrose ranged from 0.33 to 32.90 μg/g under four different time and temperature conditions. Amounts of glyoxal, methylglyoxal, and diacetyl formed in Maillard model systems ranged from 2.98 to 46.12 μg/mL, from 8.27 to 156.61 μg/mL, and from 14.94 to 1588.45 μg/mL, respectively. 4(5)-MI formation in the same model systems ranged from 28.56 to 1269.71 μg/mL. Addition of sodium sulfite reduced formation of these chemicals significantly. Total α-dicarbonyl compounds in 12 commercial soft drinks ranged from 5.75 to 50.72 μg/mL. 4(5)-MI was found in levels ranging from 1.76 to 28.11 ng/mL in 10 commercial soft drinks.

Aldehyde concentrations in wet deposition and river waters

The process of pollutants removal from the atmosphere can be responsible for the appearance of aldehydes in surface waters. We observed that formaldehyde, acetaldehyde, propanal, glyoxal, methylglyoxal and acetone were commonly present in precipitations as well as in surface water samples, while semi-volatile and poorly soluble aldehydes as nonanal and decanal were observed seasonally. Particularly high level of carbonyls concentration was noted after periods of drought and at the beginning of rainy periods. We estimated that ca. 40% of aldehydes from wet precipitations were delivered into river waters. The level of carbonyl concentration in river was positively correlated with specific local meteorological conditions such as solar radiation and ozone concentration, in contrast, there was negative correlation between aldehyde concentration in the river samples and the precipitation intensity.

Influence of in vitro simulated gastroduodenal digestion on methylglyoxal concentration of Manuka ( Lectospermum scoparium ) honey

Manuka honey (MH) is a functional food that shows in vitro antimicrobial activity and to which wound healing properties, positive effects on oral health, and beneficial properties during the treatment of gastrointestinal infection diseases and upper gastrointestinal dyspepsia are assigned. The antibacterial activity of MH is mainly due to its high concentration of methylglyoxal (MGO), a highly bifunctional alkylating agent that can induce rapid nonenzymatic modifications of proteins. The aim of the present study was to investigate the influence of in vitro simulated gastric and gastroduodenal digestion on MGO content of MH. To this aim commercial MH samples, with different MGO concentrations, were submitted to digestion, and MGO was determined before and after digestion by a validated RP-HPLC-DAD method. Moreover, the role of MGO in causing carbonylation of the digestive proteins and influencing their enzymatic activities was investigated. The results showed that after digestion MGO concentration decreases because it reacts with digestive enzymes by carbonylating their free amino groups. Nevertheless, carbonylation of pepsin and pancreatin does not influence their physiological activity and therefore does not seem to interfere with the digestion process.

Determination of toxic α-dicarbonyl compounds, glyoxal, methylglyoxal, and diacetyl, released to the headspace of lipid commodities upon heat treatment

Toxic α-dicarbonyl compounds, glyoxal, 2-methylglyoxal, and diacetyl, released from the headspace from butter, margarine, safflower oil, beef fat, and cheese heated at 100 and 200 °C were analyzed by gas chromatography as quinoxaline derivatives. Total amounts of α-dicarbonyl compounds ranged from 40.5 ng/g (butter) to 331.2 ng/g (beef fat) at 100 °C and from 302.4 ng/g (safflower oil) to 4521.5 ng/g (margarine) at 200 °C. The total amount of α-dicarbonyl compounds increased approximately 55- and 15-fold in the headspace of heated butter and margarine, respectively, when the temperature was increased from 100 to 200 °C. However, only slight differences associated with temperature variation were observed in the cases of safflower oil and beef fat (1.3- and 1.1-fold, respectively). Diacetyl was found in the highest amounts among all samples, ranging from 13.9 ± 0.3 ng/g (butter) to 2835.7 ng/g (cheese) at 100 °C and from 112.5 ± 102 ng/g (safflower oil) to 2274.5 ± 442.6 ng/g (margarine) at 200 °C, followed by methylglyoxal, ranging from 13.0 ± 0.5 to 112.7 ± 10.1 ng/g (cheese) at 100 °C and from 34.7 ± 5.0 ng/g (safflower oil) to 1790 ± 372.3 ng/g (margarine) at 200 °C. Much less glyoxal formed, in amounts ranging from 13.6 ± 0.7 ng/g (butter) to 53.4 ± 11.2 ng/g (beef fat) at both temperatures. The amounts of α-dicarbonyl compounds released into the vapor phase from lipid commodities during heating were satisfactorily analyzed.

Classification and characterization of manuka honeys based on phenolic compounds and methylglyoxal

Manuka honey from New Zealand is often considered to be a medicinal product of special value due to its high level of antimicrobial activity. Therefore, the distinct authentication of its botanical origin is of great importance. Aside from the common pollen analysis, it is in this respect particularly the analysis of the phenolic acids, flavonoids, and norisoprenoids that is described as useful. In the present study, numerous manuka honeys were analyzed by UPLC-PDA-MS/MS after solid-phase extraction and compared to other kinds of honey to define marker substances characteristic for manuka honeys. The PDA profiles obtained differed markedly from each other so that the individual honey samples could be assigned to three groups. For the honeys of group 1 the comparably high concentrations of 4-hydroxybenzoic acid, dehydrovomifoliol, and benzoic acid proved to be typical, whereas the profiles of group 2 showed high kojic acid and 2-methoxybenzoic acid intensities. The manuka honeys of group 3, on the other hand, yielded high amounts of syringic acid, 4-methoxyphenyllactic acid, and methyl syringate. Furthermore, the comprehensive comparison of manuka honeys to other unifloral honeys revealed that especially kojic acid, 5-methyl-3-furancarboxylic acid, leptosin, unedone, 2-methoxybenzoic acid, 4-methoxyphenyllactic acid, 3-hydroxy-1-(2-methoxyphenyl)penta-1,4-dione, and methyl syringate were useful for distinguishing manuka honeys from the other kinds of investigated honeys. Moreover, kojic acid, unedone, 5-methyl-3-furancarboxylic acid, 3-hydroxy-1-(2-methoxyphenyl)penta-1,4-dione, and lumichrome were identified in manuka honey for the first time.

1,2-dicarbonyl compounds in commonly consumed foods

1,2-Dicarbonyl compounds, formed from carbohydrates during thermal processing in the course of caramelization and Maillard reactions, are intensively discussed as precursors for advanced glycation endproducts in foods and in vivo. To obtain information about the uptake of individual compounds with commonly consumed foods, a comprehensive analysis of the content of 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), and methylglyoxal (MGO) together with 5-hydroxymethylfurfural (HMF) in 173 food items like bakery products, pasta, nonalcoholic and alcoholic beverages, sweet spreads, and condiments was performed. Following suitable cleanup procedures, 1,2-dicarbonyl compounds were quantitated after derivatization with o-phenylenediamine via RP-HPLC with UV detection. 3-DG proved to be the predominant 1,2-dicarbonyl compound with concentrations up to 410 mg/L in fruit juices, 2622 mg/L in balsamic vinegars, and 385 mg/kg in cookies, thus exceeding the corresponding concentrations of HMF. 3-DGal was found to be of relevance in many foods even in the absence of galactose. MGO was only of minor quantitative importance in all foods studied, except for manuka honey. Dietary intake was estimated to range between 20 and 160 mg/day for 3-DG and 5 and 20 mg/day for MGO, respectively.

Fibrin(ogen) may be an important target for methylglyoxal-derived AGE modification in elastic arteries of humans

Diabetes is associated with increased risk of cardiovascular disease. Advanced glycation end-products (AGEs) are considered to be a major pathogenic factor for diabetic vascular complications. The levels of AGEs are increased in diabetic patients. We have studied the presence of the major AGE methylglyoxal (MGO)-derived hydroimidazolone in human aorta and carotid arteries, using immunohistochemistry (IHC), western blotting and mass spectrometry. By IHC, MGO-derived modifications were detected mainly associated with cells in intimal thickenings and cells in microvessels in adventitia. In type V lesions MGO-derived AGE was also present, extracellular in the necrotic core and in cells at the border of the core. The highest degree of modification was probably associated with cell nuclei. By western blotting and mass spectrometry fibrin(ogen), the cytoskeleton-associated protein moesin and the nuclear proteins lamin A and C were identified as putative main targets for MGO-derived modification. LC-MS/MS studies of fibrin(ogen) modified in vitro with low concentrations of MGO identified the sites that were most prone to modification. These results indicate that AGE modifications occur preferentially on specific proteins. The modification of these proteins may play a role in vascular dysfunction and development of atherosclerosis in diabetes.

[Methylglyoxal--a test for impaired biological functions of exotrophy and endoecology, low glucose level in the cytosol and gluconeogenesis from fatty acids (a lecture)]

In philogenesis, due to the failure to store a great deal of carbohydrates in vivo as glycogen, all animal species began synthesizing from glucose palminitic fatty acid and depositing it as triglycerides. During biological dysfunction of exotrophy (long starvation, early postnatality, hibernation), cells also accomplish a reverse synthesis of glucose from fatty acids under aerobic conditions. Under physiological conditions, acetyl-CoA that is converted to malate and pyruvate in the glyoxalate cycle is a substrate of glyconeogenesis. Under pathological conditions of hypoxia and deficiency of macroerges, gluconeogenesis occurs without ATP consumption through the methylglyoxal pathway when used as a substrate of ketone bodies via the pathway: butyric acid (butyrate) --> beta-hydroxybutyrate --> acetoacetate --> acetone --> acetol --> methylglyoxal --> S-D-lactol-glutathione --> D-lactate --> pyruvate --> D-lactate. Under physiological conditions, this gluconeogenesis pathway does not function. We believe that with low glucose levels in the cell cytosole (glycopenia), under pathological conditions of hypoxia and due to failure to mitochondria to oxidize fatty acids, gene expression and gluconeogenesis occur through the methylglyoxal pathway. At the same time, the cytosol, intercellular environment, and plasma shows the elevated levels of methylglyoxal and D-lactate that it is converted to by the action of glyoxalases I and II. Under pathological conditions, glycopenia develops in starvation, diabetes, and metabolic acidosis, neoplasms, renal failure, and possibly, metabolic syndrome. The chemical interaction of methylglyoxal with the amino acid residues of lysine and arginine results in the denaturation of circulating and structurized proteins via carbonylation--glycosylation.

[Methylglyoxal--test for biological dysfunctions of homeostasis and endoecology, low cytosolic glucose level, and gluconeogenesis from fatty acids]

If a lot of carbohydrates cannot be in vivo stored as glycogen, the synthesis of palmitic fatty acid (FA) from glucose and its adipocyte deposition as triglycerides are under way in phylogenesis. With impaired biological function of exotrophy (fasting, early postnatality, hibernation), the cells perform a reverse process--the synthesis of glucose from FA. Physiologically, the substrate of gluconeogenesis is acetyl-CoA that is converted by the malate --> 9 piruvate --> glucose pathway in the glyoxalate cycle. Under the pathological conditions of hypoxia and energy deficiency, gluconeogenesis occurs without ATP consumption via the methylglyoxalate pathway (MGP) while using as a substrate of ketone bodies: butyric acid (butyrate) --> beta-hydroxybutyrate --> acetoacetate --> acetone --> acetol --> methylglyoxal (MG) --> S-D-lactolglutathione --> D-lactate --> piruvate --> D-lactate. Under physiological conditions, this pathway of gluconeogenesis does not work. The authors hold that gene expression and gluconeogenesis occur via the MGP when glucose levels are low in the cell cytosol (glycopenia) and FA cannot be oxidized in the mitochondria. Cytosol, intercellular medium, plasma show elevated levels of MG and D-lactate, to which it converts under the action of glyoxalases I and II. Glycopenia develops in fasting, diabetes mellitus, metabolic syndrome, renal failure, phenofibrate therapy, impaired function of exotrophy--excessive dietary intake of saturated and trans fatty acids. The chemical interaction of MG with amino acid residues of lysine and arginine leads to protein denaturation during carbonylation--glycosylation and impaired biological function of endoecology. The determination of plasma MG and D-lactate may be a test for glycopenia, compensatory activation of gluconeogenesis from FA or for the evaluation of endogenous intoxication.

Characterization and the possible formation mechanism of 2-acetyl-1-pyrroline in aromatic vegetable soybean (Glycine max L.)

2-Acetyl-1-pyrroline (2-AP) was identified as an important aroma compound of aromatic vegetable soybean. The level of 2-AP in 6 aromatic vegetable soybean lines was found to be positively correlated with popcorn-like aroma score. Comparison between aromatic and nonaromatic vegetable soybeans found that aromatic vegetable soybean contains higher concentration of methylglyoxal (MG) and Delta(1)-pyrroline-5-carboxylate (P5C) than a nonaromatic one. For MG formation-related genes, GapC was down-regulated and TPI was up-regulated in aromatic cultivar (Aromatic 7) as compared to nonaromatic control, which may contribute to the increase of MG level. Based on the data presented, a formation mechanism for 2-AP via interaction between MG and P5C in aromatic vegetable soybean was proposed.

Methylglyoxal, protein binding and biological samples: are we getting the true measure?

Methylglyoxal (MG), a reactive metabolic byproduct and a precursor of advanced glycation endproducts (AGEs), is elevated in diabetes. In the body MG is free or reversibly or irreversibly bound (mostly with proteins). Variable plasma MG values have been reported. MG is commonly measured using high performance liquid chromatography. We tested several protocols on different biological samples, which resulted in significant differences in MG values measured in a given sample. The different values do not appear due to the release and detection of bound MG under assay conditions. Protocols that provide consistent values of MG in biological samples are recommended.

Biosynthetic mechanism of 2-acetyl-1-pyrroline and its relationship with Delta1-pyrroline-5-carboxylic acid and methylglyoxal in aromatic rice (Oryza sativa L.) callus

2-Acetyl-1-pyrroline (2-AP) was identified as the major flavor compound in aromatic rice varieties Tainung 71 and 72. In order to understand the mechanism of 2-AP biosynthesis in aromatic rice, we studied the formation of putative precursors, Delta(1)-pyrroline-5-carboxylic acid and methylglyoxal. The endogenous Delta(1)-pyrroline-5-carboxylic acid contents of Tainung 71 and 72 calli reached 191 to 276%, compared to nonaromatic rice Tainung 67. In addition, calli of Tainung 71 and 72 contained 1.30- and 1.36-fold, respectively, higher methylglyoxal levels than that of Tainung 67. Specific enzyme activities of Delta(1)-pyrroline-5-carboxylic acid-synthetic enzyme including Delta(1)-pyrolline-5-carboxylic acid synthetase (P5CS) and ornithine aminotransferase (OAT) increased significantly in aromatic rice varieties. The expression levels of P5CS1 and P5CS2 genes were found to be significantly higher in aromatic rice than nonaromatic rice. Results of a tracer experiment with (15)N-labeled glutamic acid revealed that the nitrogen atom of 2-acetyl-1-pyrroline was derived from glutamic acid. Upregulation of P5CS in aromatic rice Tainung 72 may contribute to the increase of Delta(1)-pyrroline-5-carboxylic acid level and thus leads to the accumulation of an extra amount of 2-acetyl-1-pyrroline.

Isolation and determination of alpha-dicarbonyl compounds by RP-HPLC-DAD in green and roasted coffee

Glyoxal, methylglyoxal, and diacetyl formed as Maillard reaction products in heat-treated food were determined in coffee extracts (coffee brews) obtained from green beans and beans with different degrees of roast. The compounds have been reported to be mutagenic in vitro and genotoxic in experimental animals in a number of papers. More recently, alpha-dicarbonyl compounds have been implicated in the glycation process. Our data show that small amounts of glyoxal and methylglyoxal occur naturally in green coffee beans. Their concentrations increase in the early phases of the roasting process and then decline. Conversely, diacetyl is not found in green beans and forms later in the roasting process. Therefore, light and medium roasted coffees had the highest glyoxal and methylglyoxal content, whereas dark roasted coffee contained smaller amounts of glyoxal, methylglyoxal, and diacetyl. For the determination of coffee alpha-dicarbonyl compounds, a reversed-phase high performance liquid chromatography with a diode array detector (RP-HPLC-DAD) method was devised that involved the elimination of interfering compounds, such as chlorogenic acids, by solid phase extraction (SPE) and their derivatization with 1,2-diaminobenzene to give quinoxaline derivatives. Checks of SPE and derivatization conditions to verify recovery and yield, respectively, resulted in rates of 100%. The results of the validation procedure showed that the proposed method is selective, precise, accurate, and sensitive.