Trapping Methylglyoxal by Myricetin and Its Metabolites in Mice

Dose-Dependent Scavenging of Methylglyoxal by Naringenin in Diabetic Mice

Methylglyoxal (MGO) has driven interest as a major precursor of advanced glycation end products due to it being closely implicated in the pathogenesis of diabetic kidney disease (DKD). Therefore, it is critical for seeking active scavenger-targeted MGO to mitigate the development of DKD. Previous studies demonstrated that naringenin (Nar) has a remarkable therapeutic effect on DKD. However, whether Nar could scavenge MGO in diabetic mice remains virtually unknown. This work aims to investigate the effect and mechanism of scavenging MGO by Nar in diabetic mice. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was applied for investigating the scavenging capacity and mechanism of Nar on MGO in diabetic mice. The results indicated that Nar could significantly scavenge MGO in diabetic mice based on the formation of mono-MGO-Nar. In addition, two mono-MGO-Nar nanoparticles were purified, and their structures were deduced as 3-MGO-Nar using LC-MS/MS and NMR spectroscopic analyses. Furthermore, the dose-dependent scavenge effect of Nar on MGO in diabetic mice was elucidated by quantifying mono-MGO-Nar in urine and feces using LC-MS/MS. In summary, our results first demonstrated that targeting the MGO burden may be the new mechanism of Nar combating DKD.

Enhancement of antioxidant, carbonyl scavenging and anti-glycation activities of polysaccharide-based hydrocolloids by covalent grafting with gallic acid

Carbonyl stress contributes to pathological disorders leading to the progression of a variety of chronic diseases. Exploration of food ingredients with carbonyl scavenging capacities became one of the most potential strategies for the prevention of these diseases. Polysaccharide-based hydrocolloids have wide application approaches in the food industry. However, the carbonyl scavenging capacity of some natural polysaccharide-based hydrocolloids is unsatisfactory due to structural limitations. In this research, gallic acid (GA) was grafted onto different hydrocolloids (xanthan gum, carrageenan, carboxymethylcellulose, carboxymethyl chitosan (CMCS), and sodium alginate) by a free radical-mediated reaction to improve their antioxidant, carbonyl scavenging, and anti-glycation activities. The antioxidant activity of hydrocolloids was significantly improved after GA grafting. Among them, CMCS-GA (graft ratio 15.45 mg GA/g) exhibited the same ABTS scavenging ability as the equivalent amount of free GA and Vc. The carbonyl scavenging capacity, and the inhibitory effects on the fluorescent advanced glycation end products (AGEs) and protein oxidation products of some hydrocolloids also increased significantly GA grafting. The scavenging capacity of CMCS-GA on MGO, GO, ACR, and MDA in the model reaction increased by 220 %, 100 %, 6 %, and 58 %, respectively. Overall, CMCS-GA showed the best performance in radical scavenging, carbonyl scavenging, and AGEs inhibition compared to all the other hydrocolloids investigated. The findings showed that grafting GA onto hydrocolloids is a viable strategy to enhance the carbonyl scavenging capacity and anti-glycation activity of hydrocolloids.

Influence of hydroxyl substitution on the inhibition of flavonoids in advanced glycation end-products formation in glucose-lysine-arginine Maillard reaction models

Advanced glycation end products (AGEs) generated from the Maillard reaction (MR) during food processing in the human physiological environment, have been proven to be significantly associated with various chronic metabolic diseases. In this study, 18 flavonoids were investigated to study their effects on AGEs formation during MR within a glucose-lysine-arginine model system. Five AGEs- Nε-carboxymethyl-lysine (CML), Nε-carboxyethyl-lysine (CEL), pyrraline, pentosidine, and argpyrimidine-were determined by high-performance liquid chromatography-mass spectrometry, with inhibitory rates ranging between 0 % and 71.35 %. Isorhamnetin and naringenin exhibited the strongest inhibitory effect on the formation of CML and CEL, respectively, whereas myricetin exhibited the strongest inhibitory effect on pyrraline, pentosidine, and argpyrimidine formation. In addition, each flavonoid was reacted with glyoxal (GO) and methylglyoxal (MGO) to investigate their trapping activities and adducts. The results showed that the 18 flavonoids could effectively clear GO and MGO, with clearance rates of 1.03 %-71.42 % and 0.93 %-69.37 % for GO and MGO, respectively. Six flavonoids-chrysin, naringenin, apigenin, luteolin, diosmetin, and kaempferol-could form adduct products with mono-/di-MGO, with flavonoid to mono-/di-MGO adduct ratios of approximately 6:1, 2:1, 8:1, 23:1, 10:1, and 3:1, respectively. The number and site of phenolic hydroxyl groups, as well as methoxy substitution on the B-ring in flavonoids, had little effect, but phenolic hydroxyl groups at the C-3 position in the C-ring impeded adduct formation. The flavonoids lowered the degradation of glucose itself, and decreased ammonia-induced degradation and Amadori rearrangement product oxidation due to their antioxidant activities, and they trapped the reactive 1,2-di‑carbonyl species via nucleophilic addition reaction to form AGEs.

Glycation of Proteins and Its End Products: From Initiation to Natural Product-Based Therapeutic Preventions

Diabetes is a chronic metabolic disorder characterized by elevated blood glucose levels, which lead to the glycation of proteins and the formation of advanced glycation end products (AGEs). These AGEs contribute to oxidative stress, inflammation, and the development of complications such as cardiovascular disease, nephropathy, and anemia, significantly increasing mortality rates among diabetic patients. This Review focuses on the role of glycation inhibitors as a potential strategy to prevent AGE-related pathologies. While synthetic glycation inhibitors have shown promise, their adverse effects highlight the need for safer alternatives. We specifically explore a range of natural compounds-flavonoids, curcuminoids, terpenes, stilbenes, lignans, and coumarins-that have demonstrated significant antiglycating properties. The mechanisms through which these natural products inhibit glycation, including antioxidant activity, metal ion chelation, and direct interference with the glycation process, are discussed in detail. This review underscores the potential of natural products as effective and safer glycation inhibitors, offering a promising avenue for the development of therapeutic strategies against diabetes and AGE-related disorders.

Italian Biodiversity: A Source of Edible Plant Extracts with Protective Effects Against Advanced Glycation End Product-Related Diseases

Background: Italy's plant biodiversity, characterized by many plant species, is an important source of bioactive secondary metabolites that help reduce the risk of the development of advanced glycation end product (AGE)-related diseases. AGEs are involved in various diseases, such as diabetes, cardiovascular, and neurodegenerative disorders. Therefore, the aim of the study was to investigate the antiglycative, hypoglycemic, and neuroprotective properties of nine edible plant extracts using different in vitro assays. Methods: The ability of the extracts to counteract AGE formation was evaluated at different stages of the glycation reaction using in vitro systems based on the determination of Amadori products and the co-incubation of a model protein with a dicarbonyl compound under different experimental conditions. In addition, the extracts' methylglyoxal (MGO) and glyoxal (GO) trapping ability was investigated. Hypoglycemic activity was assessed by measuring α-amylase inhibition, while the neuroprotective effects were explored by testing amyloid β peptide 1-42 (Aβ1-42) fibrillogenesis inhibition. Results: All extracts generally had a dose-related capacity for the inhibition of AGE formation, mainly at the intermediate stage of the glycation reaction; high trapping capacity against MGO and GO; and promising hypoglycemic properties. In addition, they affected the fibrillogenesis process by reducing mature amyloid fibril formation and altering fibril morphology. Conclusions: All tested extracts had promising anti-fibrillogenic properties. Rosa canina extract was the most active among the tested plant species given its antiglycative activity (about 80% inhibition of AGE formation), trapping capacity against MGO and GO (almost 100%), hypoglycemic effects (66.20 ± 0.88%), and anti-fibrillogenic effects (69.00 ± 4.49% inhibition), indicating its suitability in the management of AGE-related diseases and for the potential development of a novel food ingredient.

Effects of myricetin and its derivatives on nonenzymatic glycation: A mechanism study based on proteomic modification and fluorescence spectroscopy analysis

Myricetin and its derivatives, myricitrin and dihydromyricetin, are flavonoids widely presented in foods and phytomedicine that possess tremendous health potential. In this study, we compared the antiglycation activity of myricetin and its derivatives, then investigated the underlying mechanism using proteomic modification and fluorescence spectroscopy analysis. All three compounds exhibited thorough inhibition on nonenzymatic glycation process, with the inhibitory effects on AGEs reaching 85% at 40 μmol/L. They effectively protected bovine serum albumin (BSA) structure by inhibiting protein oxidation, preventing the conversion from α-helix to β-sheet, and reducing amyloid-like cross-β structure formation. Among the three compounds, myricetin showed a predominant antiglycation activity. Proteomic analysis identified the early glycated sites that were protected by myricetin, including lysine K235, 256, 336, 421, 420, 489, etc. Additionally, fluorescence spectroscopy revealed spontaneous interactions between BSA and myricetin. Overall, myricetin holds promise as an antiglycation agent in both the food and drug industries.

Quantitative NMR Analysis of Marine Macroalgae for AGE Inhibition by Methylglyoxal Scavenging

Reactive carbonyl species (RCS) induce a fundamental form of biological stress that has driven the evolution of diverse mechanisms for minimizing its impact on organismal health. The complications that accompany uncontrolled hyperglycemia exemplify the health implications when RCS stress exceeds the body's capacity to prevent the excessive formation of advanced glycation end-products. Presented here is a novel quantitative NMR (qNMR) technique for evaluating scavengers of the prominent sugar-derived carbonyl methylglyoxal (MGO). This tool was employed to screen the chemical diversity of marine macroalgae extracts, with a focus on species that have a history of consumption by the World's healthiest populations and are subject to global scale aquacultural production. Fucus vesiculosus demonstrated the highest capacity for inhibiting glycation and scavenging MGO. Additionally, the Chondrus cripsus, Gracilaria vermiculophyla, and Gracilaria tikvahiae extracts had a high capacity for scavenging MGO, representing the first report of this activity. This new qNMR methodology presented is highly applicable for screening extracts and compounds from diverse sources, and the results highlight the potential of macroalgae extracts to be employed as RCS and AGE targeting therapeutics and food additives.

Scavenging of Methylglyoxal by the Total Flavonoids of Apocyni Veneti Folium in Mice

Scavenging MGO has been considered as an effective strategy for preventing atherosclerosis. A previous study showed that the total flavonoids of Apocyni Veneti Folium (TFAVF) had a significant antiatherosclerotic effect. However, there are no studies that have investigated the MGO scavenging capacities of TFAVF in mice. We found that TFAVF consisted mainly of quercetin glycosides and kaempferol glycosides using ultrahigh performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS). TFAVF was first demonstrated to effectively scavenge MGO in mice based on the formation of mono-MGO-quercetin, mono-MGO-dehydroquercetin, mono-MGO-isorhamnetin, mono-MGO-dehydroisorhamnetin, mono-MGO-kaempferol, and mono-MGO-dehydrokaempferol. In addition, one mono-MGO-quercetin was separated and purified, and its structure was elucidated as 8-MGO-quercetin based on UHPLC-QTOF-MS/MS and NMR data. Quantification studies have demonstrated that kaempferol, dehydrokaempferol, quercetin, dehydroquercetin, isorhamnetin, and dehydroisorhamnetin can dose dependently scavenge MGO in mice. Taken together, these results indicated that TFAVF showed a significant antiatherosclerotic effect, which might be based on MGO detoxification.

Theanine Capture of Reactive Carbonyl Species in Humans after Consuming Theanine Capsules or Green Tea

Acrolein (ACR), methylglyoxal (MGO), and glyoxal (GO) are a class of reactive carbonyl species (RCS), which play a crucial role in the pathogenesis of chronic and age-related diseases. Here, we explored a new RCS inhibitor (theanine, THE) and investigated its capture capacity on RCS in vivo by human experiments. After proving that theanine could efficiently capture ACR instead of MGO/GO by forming adducts under simulated physiological conditions, we further detected the ACR/MGO/GO adducts of theanine in the human urine samples after consumption of theanine capsules (200 and 400 mg) or green tea (4 cups, containing 200 mg of theanine) by using ultraperformance liquid chromatography-time-of-flight-high-resolution mass spectrometry. Quantitative assays revealed that THE-ACR, THE-2ACR-1, THE-MGO, and THE-GO were formed in a dose-dependent manner in the theanine capsule groups; the maximum value of the adducts of theanine was also tested. Furthermore, besides the RCS adducts of theanine, the RCS adducts of catechins could also be detected in the drinking tea group. Whereas, metabolite profile analysis showed that theanine could better capture RCS produced in the renal metabolic pathway than catechins. Our findings indicated that theanine could reduce RCS in the body in two ways: as a pure component or contained in tea leaves.

Berry anthocyanins prevent α-dicarbonyls and advanced glycation end product formation in phosphate-buffered saline-based model systems, cookie and ground pork

α-Dicarbonyls and advanced glycation end products (AGEs) are the heat-induced potential toxicants commonly found in thermally processed foods due to the Maillard reaction. Research has shown that both α-dicarbonyls and AGEs can cause oxidative stress and inflammation and have a positive link with several chronic diseases, such as diabetes. This study found that commonly consumed berry fruits exhibited excellent methylglyoxal (MGO)-trapping and antiglycative activities, positively associated with their total phenolic and flavonoid contents. Blackcurrant exhibited the strongest MGO-trapping and antiglycative activities among the tested berry fruits. In addition, we demonstrated that fortification with blackcurrant significantly reduced α-dicarbonyls and AGEs formation in the chocolate cookies and marinated ground pork. Delphinidin and cyanidin glycosides were identified as the primary bioactive compounds of blackcurrant that trapped MGO to form the corresponding mono- and di-MGO adducts. This study suggested that blackcurrant anthocyanins might serve as a novel additive to reduce the consumption of dietary reactive carbonyl species and AGEs from both animal- and plant-derived processed foods. PRACTICAL APPLICATION: The levels of α-dicarbonyls and advanced glycation end products in ground pork and cookies were significantly reduced when fortified with blackcurrant. The blackcurrant anthocyanins might be a novel agent inhibiting α-dicarbonyls and dietary advanced glycation end products formation in thermally processed foods.

Formation of Hesperetin-Methylglyoxal Adducts in Food and In Vivo, and Their Metabolism In Vivo and Potential Health Impacts

Polyphenols with a typical meta-phenol structure have been intensively investigated for scavenging of methylglyoxal (MGO) to reduce harmful substances in food. However, less attention has been paid to the formation level of polyphenol-MGO adducts in foods and in vivo and their absorption, metabolism, and health impacts. In this study, hesperitin (HPT) was found to scavenge MGO by forming two adducts, namely, 8-(1-hydroxyacetone)-hesperetin (HPT-mono-MGO) and 6-(1-hydroxyacetone)-8-(1-hydroxyacetone)-hesperetin (HPT-di-MGO). These two adducts were detected (1.6-15.9 mg/kg in total) in cookies incorporated with 0.01%-0.5% HPT. HPT-di-MGO was the main adduct detected in rat plasma after HPT consumption. The adducts were absorbed 8-30 times faster than HPT, and they underwent glucuronidation and sulfation in vivo. HPT-mono-MGO would continue to react with endogenous MGO in vivo to produce HPT-di-MGO, which effectively reduced the cytotoxicity of HPT and HPT-mono-MGO. This study provided data on the safety of employing HPT as a dietary supplement to scavenge MGO in foods.

Novel inhibitory effect of black chokeberry (Aronia melanocarpa) from selected eight berries extracts on advanced glycation end-products formation and corresponding mechanism study

Numerous health hazards have been connected to advanced glycation end products (AGEs). In this investigation, using reaction models including BSA-fructose, BSA- methylglyoxal (MGO), and BSA-glyoxal (GO), we examined the anti-glycation potential of eight different berry species on AGEs formation. Our results indicate that black chokeberry (Aronia melanocarpa) exhibited the highest inhibitory effects, with IC50 values of 0.35 ± 0.02, 0.45 ± 0.03, and 0.48 ± 0.11 mg/mL, respectively. Furthermore, our findings suggest that black chokeberry inhibits AGE formation by binding to BSA, which alleviates the conformation alteration, prevents protein cross-linking, and traps reactive α-dicarbonyls to form adducts. Notably, three major polyphenols, including cyanidin-3-O-galactoside, cyanidin-3-O-arabinoside, and procyanidin B2 from black chokeberry, showed remarkably inhibitory effect on MGO/GO capture, and new adducts formation was verified through LC-MS/MS analysis. In summary, our research provides a theoretical basis for the use of berries, particularly black chokeberry, as natural functional food components with potential anti-glycation effects.

Influence of in vitro gastrointestinal digestion and colonic fermentation on carbonyl scavenging capacity of fiber-bound polyphenols from quinoa

Whole grain insoluble dietary fiber (IDF) is a good source of bound-form polyphenols. In the present study, insoluble dietary fiber rich in bound polyphenols (BP-IDF) from quinoa, rye and wheat was prepared. The carbonyl scavenging capacities of these three BP-IDFs and the effects of in vitro gastrointestinal (GI) digestion and colonic fermentation on their scavenging activities were studied. The results indicated that the fiber-bound polyphenols from quinoa showed the highest carbonyl scavenging capacity compared to those from rye and wheat. After colonic fermentation, more than 73% of the bound polyphenols were still retained in the fermented residues of the quinoa BP-IDF. The fiber-bound polyphenols in the GI-digested residues of quinoa retained considerable carbonyl scavenging activities. During the fermentation process, the residual fiber-bound polyphenols in the fermented residues still scavenged 35.8% to 45.2% of methylglyoxal, 19.3% to 25.4% of glyoxal, 50.7% to 60.5% of acrolein and 5.2% to 9.7% of malondialdehyde, showing a critical role in the scavenging of carbonyl compounds compared to the released and metabolized polyphenols. These findings confirm the capacity of fiber-bound polyphenols from three whole grains to scavenge carbonyls during in vitro digestion and fermentation processes, suggesting that they could be used as functional ingredients to maintain continuous defenses against carbonyls along the digestive tract.

Theanine in Tea: An Effective Scavenger of Single or Multiple Reactive Carbonyl Species at the Same Time

Reactive carbonyl species (RCS) are generated during thermal food processing, and their accumulation in the body increases the risk of various chronic diseases. Herein, the RCS-scavenging ability of theanine, a unique nonproteinogenic amino acid, was evaluated in terms of the scavenging rate, reaction kinetics, and reaction pathway using LC-MS/MS. Three major products of theanine conjugated with acrolein (ACR) and glyoxal (GO) were prepared and identified using nuclear magnetic resonance. Thereafter, the simultaneous reactions of four types of RCS (namely, ACR, crotonaldehyde, methylglyoxal, and GO) with theanine were discussed in RCS-theanine and RCS-tea models. Under different reaction ratios, theanine could nonspecifically scavenge the four coexisting RCS by forming adducts with them. The amount of theanine-RCS adducts in green and black tea was more than that of catechin (epigallocatechin gallate, epigallocatechin, epicatechin gallate, and epicatechin)-RCS adducts despite the lower content of theanine than catechins. Thus, theanine, as a food additive and dietary supplement, could demonstrate new bioactivity as a promising RCS scavenger in food processing.

A Comparative Study of the Inhibitory Effect of Some Flavonoids and a Conjugate of Taxifolin with Glyoxylic Acid on the Oxidative Burst of Neutrophils

During the storage, processing, and digestion of flavonoid-rich foods and beverages, a condensation of flavonoids with toxic carbonyl compounds occurs. The effect of the resulting products on cells remains largely unknown. The aim of the present study was to evaluate the effects of quercetin, taxifolin, catechin, eriodictyol, hesperetin, naringenin, and a condensation product of taxifolin with glyoxylic acid on the oxidative burst of neutrophils. It was found that the flavonoids and the condensation product inhibited the total production of ROS. Flavonoids decreased both the intra and extracellular ROS production. The condensation product had no effect on intracellular ROS production but effectively inhibited the extracellular production of ROS. Thus, the condensation of flavonoids with toxic carbonyl compounds may lead to the formation of compounds exhibiting potent inhibitory effects on the oxidative burst of neutrophils. The data also suggest that, during these reactions, the influence of a fraction of flavonoids and their polyphenolic derivatives on cellular functions may change. On the whole, the results of the study provide a better understanding of the effects of polyphenols on human health. In addition, these results reveal the structure-activity relationship of these polyphenols and may be useful in a search for new therapeutic agents against diseases associated with oxidative stress.

Zinc-Rutin Particles Ameliorate DSS-Induced Acute and Chronic Colitis via Anti-inflammatory and Antioxidant Protection of the Intestinal Epithelial Barrier

In patients suffering from inflammatory bowel diseases (IBDs), the immune system is disrupted and the intestinal barrier function is compromised. Here, six zinc-flavonoid particles were produced by one-step reaction via changing flavonoids (myricetin, quercetin, and rutin) and solvent (water and ethanol), and then their cytocompatibility and ability to scavenge H2O2, free radicals, and LPS-induced ROS were compared. Zinc-rutin particles (W-ZnRT) composed of rutin (78.92 wt %), Na12[ZnPO4]12·12H2O (6.76 wt %), and crystal water were screened out because W-ZnRT exhibited 80.8 ± 15% cell viability against RAW264.7, could rapidly scavenge 78.1 ± 1% of H2O2 and 71.6 ± 2% of DPPH within 30 min, and reduced LPS-increased intracellular ROS to normal levels. In addition, the therapeutic effects of rutin and W-ZnRT were also compared in dextran sulfate sodium (DSS)-induced acute and chronic colitis in mice. W-ZnRT was superior to rutin alone in chronic colitis (n = 9), although they were equally effective in acute colitis (n = 7). Compared to rutin, 11 oral doses of W-ZnRT (40 mg kg-1) significantly improved intestinal permeability (p = 0.0299) and colon length (p = 0.0025), reduced intestinal proinflammatory factors (IL-6, IL-1β, and TNF-α), and upregulated tight junction proteins to maintain intestinal barrier function. Taken together, these results identified W-ZnRT as an efficient and safe therapeutic strategy for IBD.

A Citrus and Pomegranate Complex Reduces Methylglyoxal in Healthy Elderly Subjects: Secondary Analysis of a Double-Blind Randomized Cross-Over Clinical Trial

Reactive α-dicarbonyls (α-DCs), such as methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), are potent precursors in the formation of advanced glycation end products (AGEs). In particular, MGO and MGO-derived AGEs are thought to be involved in the development of vascular complications in diabetes. Experimental studies showed that citrus and pomegranate polyphenols can scavenge α-DCs. Therefore, the aim of this study was to evaluate the effect of a citrus and pomegranate complex (CPC) on the α-DCs plasma levels in a double-blind, placebo-controlled cross-over trial, where thirty-six elderly subjects were enrolled. They received either 500 mg of Citrus sinensis peel extract and 200 mg of Punica granatum concentrate in CPC capsules or placebo capsules for 4 weeks, with a 4-week washout period in between. For the determination of α-DCs concentrations, liquid chromatography tandem mass spectrometry was used. Following four weeks of CPC supplementation, plasma levels of MGO decreased by 9.8% (-18.7 nmol/L; 95% CI: -36.7, -0.7 nmol/L; p = 0.042). Our findings suggest that CPC supplementation may represent a promising strategy for mitigating the conditions associated with MGO involvement. This study was registered on clinicaltrials.gov as NCT03781999.

Recent updates in anti-glycation strategies: selection of natural products and lactic acid bacteria as potential inhibitors based on the multi-pathway anti-glycation targets

The prevalence of high-sugar diets and unhealthy habits exacerbates the production of advanced glycation end products (AGEs) in the body. When AGEs excessively accumulate in the body, they accelerate the aging process while directly or indirectly causing other complications that can seriously damage the body. Prevention of glycation damage is gaining increasing attention; however, a systematic strategy to combat glycation and specific glycation inhibitors is still lacking. By analyzing the process of glycation damage, we suggest that glycation damage can be mitigated by the inhibition of AGEs production, binding to proteins, and binding to receptors for advanced glycation end products, as well as the attenuation of downstream linkage reactions. This review summarizes the process of glycation damage. According to each step of the process, the review presents the corresponding anti-glycation strategies. Based on recent anti-glycation studies, we support the fabrication of glycation inhibitors by using natural plant products and fermentation products of lactic acid bacteria that partially exhibit anti-glycation properties. This review summarizes the mechanisms by which these dietary ingredients perform anti-glycation functions, providing relevant research evidence. We hope that this review will support and assist subsequent investigations in the development of anti-glycation inhibitors.

Inhibitory effect of Ginkgo biloba seeds peptides on methylglyoxal-induced glycations

The aim of this study was to investigate the antiglycation activity and mechanism of two identified peptides, Valine-Valine-Phenylalanine-Proline-Glycine-Cysteine-Proline-Glutamic acid (VVFPGCPE) and Serine-Valine-Aspartic acid-Aspartic acid-Proline-Arginine-Threonine-Lysine (SVDDPRTL), from Ginkgo biloba seeds protein hydrolysates. Both VVFPGCPE and SVDDPRTL were efficient in bovine serum albumin (BSA)-methylglyoxal (MGO) model to inhibit BSA glycation, while VVFPGCPE showed higher antiglycation activity than SVDDPRTL. In antioxidant assays, VVFPGCPE scavenged more hydroxyl and super anion radicals, and chelated more Fe²⁺. Moreover, VVFPGCPE was more efficient in alleviating glycoxidation since it retained higher content of tryptophan and reduced dityrosine and kynurenine generation. Compared with SVDDPRTL, VVFPGCPE showed better performance in inhibiting protein aggregation and amyloid-like fibrillation formation. Therefore, VVFPGCPE was selected for further mechanism study. The circular dichroism analysis suggested VVFPGCPE could preserve α-helix structure and stabilize protein structure. The MGO trapping assay indicated VVFPGCPE (5 mg/mL) could capture 66.25% MGO within 24 h, and the mass spectrometry revealed VVFPGCPE could trap MGO by forming VVFPGCPE-mono-MGO adducts. Besides, molecular simulations suggested VVFPGCPE could interact with key glycation residues, arginine and lysine residues, of BSA mainly through van der Waals and hydrogen bonds. This study might supply a theoretical basis for the development of VVFPGCPE as an effective antiglycation agent.

Potential roles of gut microbes in biotransformation of natural products: An overview

Natural products have been extensively applied in clinical practice, characterized by multi-component and multi-target, many pharmacodynamic substances, complex action mechanisms, and various physiological activities. For the oral administration of natural products, the gut microbiota and clinical efficacy are closely related, but this relationship remains unclear. Gut microbes play an important role in the transformation and utilization of natural products caused by the diversity of enzyme systems. Effective components such as flavonoids, alkaloids, lignans, and phenols cannot be metabolized directly through human digestive enzymes but can be transformed by enzymes produced by gut microorganisms and then utilized. Therefore, the focus is paid to the metabolism of natural products through the gut microbiota. In the present study, we systematically reviewed the studies about gut microbiota and their effect on the biotransformation of various components of natural products and highlighted the involved common bacteria, reaction types, pharmacological actions, and research methods. This study aims to provide theoretical support for the clinical application in the prevention and treatment of diseases and provide new ideas for studying natural products based on gut biotransformation.

Myricetin alleviates the formaldehyde-enhanced Warburg effect in tumor cells through inhibition of HIF-1α

Myricetin is a flavonoid widely-distributed in foods with many beneficial health effects, which has been marketed in health products. Formaldehyde is an environmental carcinogen which can enhance the Warburg effect through the induction of human hypoxia-inducible factor 1 subunit alpha (HIF-1α), the primary regulator of cellular glycolysis. HIF-1α was verified as an important target in lung and ovarian tumors, which was also identified as a receptor for myricetin via molecular docking. The reinforced HIF-1α signaling, the Warburg effect and T cell suppression induced by 50 μM formaldehyde in both A549 and Caov-3 cells were dose-dependently attenuated by myricetin from 20 to 100 μM, and the attenuative effects were diminished by the stabilization of HIF-1α with deferoxamine. Exposure to 2.0 mg/m³ formaldehyde also stimulated tumor growth and elevated HIF-1α expression in tumor tissues of A549 xenograft mice, which were also alleviated by oral administration of 100 mg/kg myricetin. These results demonstrated that myricetin alleviated formaldehyde-enhanced Warburg effect in tumor cells through HIF-1α inhibition, which could be further developed as a therapeutic or complementary agent for formaldehyde-induced carcinogenesis.

Protections of transcription factor BACH2 and natural product myricetin against pathological cardiac hypertrophy and dysfunction

Pathological hypertrophic myocardium under consistent adverse stimuli eventually can cause heart failure. This study aims to explore the role of BACH2, a member of the basic region leucine zipper transcription factor family, in cardiac hypertrophy and failure. Transverse aortic constriction surgery was operated to induce cardiac hypertrophy and failure in mice. BACH2 was overexpressed in mice through tail vein injection of AAV9-Bach2. Mice with systemic or cardiac-specific knockdown of Bach2 were adopted. Neonatal rat ventricular myocytes (NRVMs) were isolated and infected with lentivirus to overexpress Bach2 or transfected with siRNA to knock down Bach2. Our data showed that overexpression of BACH2 ameliorated TAC-induced cardiac hypertrophy and failure in mice and decreased isoproterenol (ISO)-triggered myocyte hypertrophy in NRVMs. Systemic or cardiac-specific knockdown of Bach2 worsened the cardiac hypertrophy and failure phenotype in mice. Further assays showed that BACH2 bound to the promotor region of Akap6 at the -600 to -587 site and repressed its expression, which functioned as a crucial scaffold for cardiac hypertrophy and failure signaling pathways. Small molecular natural product library screening suggested that myricetin could up-regulate expression of Bach2 and simultaneously suppress the transcriptional levels of hypertrophic marker genes Bnp and Myh7. Further studies showed that myricetin exerted a BACH2-dependent protective effect against cardiac hypertrophy in vivo and in vitro. Taken together, our findings demonstrated that BACH2 plays a crucial role in the regulation of cardiac hypertrophy and failure and can be a potential therapeutic target in the future.

Formation and metabolism of 6-(1-acetol)-8-(1-acetol)-rutin in foods and in vivo, and their cytotoxicity

Methylglyoxal (MGO) is a highly reactive precursor which forms advanced glycation end-products (AGEs) in vivo, which lead to metabolic syndrome and chronic diseases. It is also a precursor of various carcinogens, including acrylamide and methylimidazole, in thermally processed foods. Rutin could efficiently scavenge MGO by the formation of various adducts. However, the metabolism and safety concerns of the derived adducts were paid less attention to. In this study, the optical isomers of di-MGO adducts of rutin, namely 6-(1-acetol)-8-(1-acetol)-rutin, were identified in foods and in vivo. After oral administration of rutin (100 mg/kg BW), these compounds reached the maximum level of 15.80 μg/L in plasma at 15 min, and decreased sharply under the quantitative level in 30 min. They were detected only in trace levels in kidney and fecal samples, while their corresponding oxidized adducts with dione structures presented as the predominant adducts in kidney, heart, and brain tissues, as well as in urine and feces. These results indicated that the unoxidized rutin-MGO adducts formed immediately after rutin ingestion might easily underwent oxidation, and finally deposited in tissues and excreted from the body in the oxidized forms. The formation of 6-(1-acetol)-8-(1-acetol)-rutin significantly mitigated the cytotoxicity of MGO against human gastric epithelial (GES-1), human colon carcinoma (Caco-2), and human umbilical vein endothelial (HUVEC) cells, which indicated that rutin has the potential to be applied as a safe and effective MGO scavenger and detoxifier, and AGEs inhibitor.

Identification and cytotoxic evaluation of the novel rutin-methylglyoxal adducts with dione structures in vivo and in foods

Flavonoids with meta-hydroxyl groups have been proven to react with methylglyoxal (MGO) and form mono- and di-MGO adducts via nucleophilic addition reactions. Rutin, a rutinoside of quercetin with typical meta-phenol structure, is widely distributed in plant-sourced materials. Interestingly, different from the adducts reported between flavonoids and MGO, new rutin-MGO adducts with dione structures on the moiety of MGO were identified and proven to occur in various foods (0.66-6.58 mg/kg in total) and in vivo (up to 5.01 μg/L in plasma of rats administered with 100 mg/kg bodyweight of rutin). The three adducts discovered were assigned as 6-(1,2-propanedione)-8-(1-acetol)-rutin, 6-(1-acetol)-8-(1,2-propanedione)-rutin, and 6-(1,2-propanedione)-8-(1,2-propanedione)-rutin. Cytotoxicity evaluation in different cell lines indicated that the formation of these rutin-MGO adducts remarkably reduced the toxicity of MGO, which provide further promise for the application of rutin as a scavenger of dicarbonyl compounds by dietary supplement and addition in foods.

Trapping Methylglyoxal by Taxifolin and Its Metabolites in Mice

Trapping of methylglyoxal (MGO), an important precursor of advanced glycation end products (AGEs), is considered an effective therapy for alleviating AGE-induced chronic metabolic diseases. In this paper, taxifolin (Tax) was first found to effectively trap MGO by forming mono- and di-MGO adducts under in vitro conditions. In addition, the mechanism of trapping MGO by Tax was also studied in vivo. Tax was demonstrated to efficiently trap endogenous MGO via formation of mono-MGO adducts in urine and fecal samples of C57BL/6J mice after oral administration of Tax and MGO. Mono-MGO adducts of Tax metabolites, including methylated Tax, aromadendrin, quercetin, and isorhamnetin, were identified in C57BL/6J mice urine and fecal samples by ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS/MS). One mono-MGO-Tax was purified from the in vitro reaction mixture, and its structure was elucidated as 6-MGO-Tax based on the analysis of UHPLC-QTOF-MS/MS and detailed nuclear magnetic resonance (NMR) data. Quantification studies demonstrated that Tax and its metabolites trapped MGO in a dose-dependent manner in C57BL/6J mice urine and fecal samples. Furthermore, we also detected mono-MGO adducts of Tax and methylated Tax in urine and fecal samples of diabetic db/db mice after oral administration of Tax. Taken together, our results demonstrated that dietary Tax has the potential to detoxify MGO and treat AGE-associated chronic diseases.

Antioxidant and Antiglycation Effects of Cistus × incanus Water Infusion, Its Phenolic Components, and Respective Metabolites

Reactive oxygen and carbonyl species promote oxidative and carbonyl stress, and the development of diabetes, metabolic syndrome, cardiovascular diseases, and others. The traditional herb Cistus × incanus is known for its antioxidant properties; therefore, the current study aimed to assess how the chemical composition of a C. incanus water infusion corresponds with its antioxidative and antiglycative effects in vitro. The composition of infusions prepared from commercial products was analyzed with UHPLC-ESI-qTOF-MS. Total phenolics, flavonoids, and non-flavonoid polyphenols were determined. Antioxidant activity of infusions and selected polyphenols was investigated using DPPH, ABTS, and FRAP. Fluorometric measurements and methylglyoxal capture were performed to investigate the antiglycation activity. PCA and PLS-DA models were applied to explore the correlation between chemical and antioxidant results. The principal flavonoids in C. incanus were flavonols. In vitro tests revealed that a stronger antioxidant effect was demonstrated by plant material from Turkey rich in flavonoids, followed by Albania and Greece. Flavonols and ellagic acid displayed stronger antiradical and reducing power than EA-derived urolithins. Hyperoside was the most potent inhibitor of glycation. The results indicate that flavonoids are primarily responsible for rock rose antioxidant and antiglycation properties. PLS-DA modeling can be used to identify the origin of plant material with sensitivity and specificity exceeding 86%.

Interconversion and Acrolein-Trapping Capacity of Cardamonin/Alpinetin and Their Metabolites In Vitro and In Vivo

People are at high risk of exposure to endogenous and exogenous acrolein (ACR). ACR can cause a multitude of illnesses, including cardiovascular disease, Alzheimer's disease, and diabetes. In this study, we investigated the reaction pathway of cardamonin (CAR) or alpinetin (ALP) with ACR and the interconversion of CAR and ALP in vitro at 37 °C in phosphate-buffered saline using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Subsequently, ACR adducts of CAR, ALP, and their metabolites, for example, CAR-ACR-1, ALP-ACR, mono-ACR-pinocembrin chalcone (PIN-ACR), and mono- and di-ACR-naringenin (NAR-ACR and NAR-2ACR), were detected in urine samples, but only CAR-ACR-1 and ALP-ACR were detected in fecal samples from the CAR- and ALP-treated mouse groups using ultraperformance liquid chromatography-MS/MS, respectively. Quantitative analyses showed that CAR, ALP, and their metabolites markedly scavenged ACR in a dose-dependent manner in vivo. Furthermore, we also found that the metabolites of CAR or ALP remained and promoted the ACR-trapping ability.

Potential of Vasoprotectives to Inhibit Non-Enzymatic Protein Glycation, and Reactive Carbonyl and Oxygen Species Uptake

Reactive carbonyl species (RCS) such as methylglyoxal (MGO) or glyoxal (GO) are the main precursors of the formation of advanced glycation end products (AGEs). AGEs are a major factor in the development of vascular complications in diabetes. Vasoprotectives (VPs) exhibit a wide range of activities beneficial to cardiovascular health. The present study aimed to investigate selected VPs and their structural analogs for their ability to trap MGO/GO, inhibit AGE formation, and evaluate their antioxidant potential. Ultra-high-performance liquid chromatography coupled with an electrospray ionization mass spectrometer (UHPLC-ESI-MS) and diode-array detector (UHPLC-DAD) was used to investigate direct trapping capacity and kinetics of quenching MGO/GO, respectively. Fluorimetric and colorimetric measurements were used to evaluate antiglycation and antioxidant action. All tested substances showed antiglycative effects, but hesperetin was the most effective in RCS scavenging. We demonstrated that rutin, diosmetin, hesperidin, and hesperetin could trap both MGO and GO by forming adducts, whose structures we proposed. MGO-derived AGE formation was inhibited the most by hesperetin, and GO-derived AGEs by diosmetin. High reducing and antiradical activity was confirmed for quercetin, rutin, hesperetin, and calcium dobesilate. Therefore, in addition to other therapeutic applications, some VPs could be potential candidates as antiglycative agents to prevent AGE-related complications of diabetes.

Maillard Browning Inhibition by Ellagic Acid via Its Adduct Formation with the Amadori Rearrangement Product

The Maillard reaction performed under a stepwise increase of temperature was applied for researching the inhibition of Maillard browning caused by ellagic acid. Ellagic acid was found effective for the inhibition of melanoidin formation in the xylose-glycine Maillard reaction but depended on its dosage and the point of time it was added in the reaction system. The lightest color of the Maillard reaction products was observed when ellagic acid was added at the 90th min, which was the point of time when the Amadori rearrangement product (ARP) developed the most. LC-ESI-MS/MS analysis results showed a significant tendency of the ellagic acid hydrolysis product to react with the predominant intermediate ARP to yield an adduct. The adduct stabilized the ARP and delayed its decomposition and inhibited the downstream reactions toward browning. After the ARP was depleted, ellagic acid also showed an effect on scavenging some short-chain dicarbonyls which contributed to the inhibition of Maillard browning.

Chinese bayberry (Myrica rubra) phenolics mitigated protein glycoxidation and formation of advanced glycation end-products: A mechanistic investigation

Protein glycation and formation of advanced glycation end-products (AGEs) impose threats to the human health. This study firstly investigated the inhibition of Chinese bayberry (Myrica rubra) phenolics on AGEs formation through mechanistic analysis. Four common Chinese bayberry cultivars were selected to prepare phenolic-rich extracts (CBEs) and characterized for phenolic composition, and their anti-AGE properties were evaluated in multiple in vitro systems. Total sixteen phenolics were quantified in CBEs by UPLC-ESI-MS/MS. CBEs reduced total and specific fluorescent AGEs formation in various simulating models, and protected the protein from structural modification, oxidation, and cross-linking. Mechanistic analysis unveiled that scavenging of free radicals, inactivation of transition metals, interaction with protein to form complexes, and trapping of reactive α-dicarbonyls to form adducts underlain the mechanisms of the anti-glycative actions of CBEs. Chinese bayberry fruits, especially the cultivars Biqi and Wuzi, may be a promising dietary strategy to mitigate AGEs load in the human body.

Cytotoxicity of adducts formed between quercetin and methylglyoxal in PC-12 cells

Quercetin (Que) or quercetin-containing food stuffs are widely incorporated in bakery foods for improving food texture and health effects, and scavenging reactive aldehydes, such as methylglyoxal (MGO) that exhibits various deleterious effects including contribution to neurodegeneration. This study aimed to investigate the cytotoxicity of the adducts formed between quercetin and MGO resulted from the incorporation of quercetin in foods. Two highly-purified adducts (Que-mono-MGO and Que-di-MGO) were found to display higher cytotoxicity than their precursor MGO and quercetin. They elevated apoptosis via upregulation of expression of apoptotic markers, including p-P38, cleaved caspase-9 and -3, and pro-apoptotic Bax. They induced mitochondrial dysfunction via decreasing mitochondrial membrane potential and increasing lactate dehydrogenase release. Moreover, they attenuated levels of p-Akt, Nrf2, NQO-1, and HO-1, proving that they induced neurodegeneration apoptosis through mitochondria-mediated signaling pathways (PI3K-Akt and Nrf2-HO-1/NQO-1). These findings indicated that the safety consequence of MGO after scavenged by polyphenols needs to be concerned.