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

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.

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.

Synergistic Effect of Flavonoids and Metformin on Protection of the Methylglyoxal-Induced Damage in PC-12 Neuroblastoma Cells: Structure-Activity Relationship and Potential Target

Methylglyoxal-induced ROS elevation is the primary cause of neuronal damage. Metformin is a traditional hypoglycemic drug that has been reported to be beneficial to the nervous system. In this study, flavonoids were found to enhance the protective effect of metformin when added at a molar concentration of 0.5%. The structure-activity relationship (SAR) analysis indicated that ortho- substitution in the B ring, and the absence of double bonds between the 2 and 3 position combined with the gallate substitution with R configuration at the 3 position in the C ring played crucial roles in the synergistic effects, which could be beneficial for designing a combination of the compounds. Additionally, the mechanism study revealed that a typical flavonoid, EGCG, enhanced ROS scavenging and anti-apoptotic ability via the BCL2/Bax/Cyto C/Caspase-3 pathway, and synergistically inhibited the expression of GSK-3β, BACE-1, and APP in PC-12 cells when used in combination with metformin. The dose of metformin used in the combination was only 1/4 of the conventional dose when used alone. These results suggested that ROS-mediated apoptosis and the pathways related to amyloid plaques (Aβ) formation can be the targets for the synergistic neuroprotective effects of flavonoids and metformin.

Comparison of the methylglyoxal scavenging effects of kaempferol and glutathione and the consequences for the toxicity of methylglyoxal in SH-SY5Y cells

This study aimed to characterize the methylglyoxal (MGO) scavenging capacity of glutathione (GSH) and kaempferol in more detail with special emphasis on the possible reversible nature of the adduct formation and their competition for MGO, and the safety consequences of their MGO-scavenging effects. GSH showed immediate and concentration-dependent MGO-scavenging effects, while the scavenging effects by kaempferol appeared concentration- but also time-dependent, with stable adducts formed over time. The GSH adduct gradually disappeared in a competition reaction with kaempferol, and kaempferol became the preferred scavenger over time. Furthermore, the scavenging of MGO by kaempferol provided better protection than GSH against extracellular MGO in SH-SY5Y cells. It is concluded that flavonoids like kaempferol provide better scavengers for food-borne MGO than thiol-based scavengers such as GSH, while, given the endogenous concentrations of both scavengers and the detoxification of the GSH-MGO adduct by the glyoxalase system, GSH will be dominant for intracellular MGO protection.

Modulation of redox-sensitive transcription factors with polyphenols as pathogenetically grounded approach in therapy of systemic inflammatory response

One of the adverse outcomes of acute inflammatory response is progressing to the chronic stage or transforming into an aggressive process, which can develop rapidly and result in the multiple organ dysfunction syndrome. The leading role in this process is played by the Systemic Inflammatory Response that is accompanied by the production of pro- and anti-inflammatory cytokines, acute phase proteins, and reactive oxygen and nitrogen species. The purpose of this review that highlights both the recent reports and the results of the authors' own research is to encourage scientists to develop new approaches to the differentiated therapy of various SIR manifestations (low- and high-grade systemic inflammatory response phenotypes) by modulating redox-sensitive transcription factors with polyphenols and to evaluate the saturation of the pharmaceutical market with appropriate dosage forms tailored for targeted delivery of these compounds. Redox-sensitive transcription factors such as NFκB, STAT3, AP1 and Nrf2 have a leading role in mechanisms of the formation of low- and high-grade systemic inflammatory phenotypes as variants of SIR. These phenotypic variants underlie the pathogenesis of the most dangerous diseases of internal organs, endocrine and nervous systems, surgical pathologies, and post-traumatic disorders. The use of individual chemical compounds of the class of polyphenols, or their combinations can be an effective technology in the therapy of SIR. Administering natural polyphenols in oral dosage forms is very beneficial in the therapy and management of the number of diseases accompanied with low-grade systemic inflammatory phenotype. The therapy of diseases associated with high-grade systemic inflammatory phenotype requires medicinal phenol preparations manufactured for parenteral administration.

Protective Effect of Flavonoids against Methylglyoxal-Induced Oxidative Stress in PC-12 Neuroblastoma Cells and Its Structure-Activity Relationships

Methylglyoxal-induced oxidative stress and cytotoxicity are the main factors causing neuronal death-related, diabetically induced memory impairment. Antioxidant and anti-apoptotic therapy are potential intervention strategies. In this study, 25 flavonoids with different substructures were assayed for protecting PC-12 cells from methylglyoxal-induced damage. A structure-activity relationship (SAR) analysis indicated that the absence of the double bond at C-2 and C-3, substitutions of the gallate group at the 3 position, the pyrogallol group at the B-ring, and the R configuration of the 3 position enhanced the protection of flavan-3-ols, and a hydroxyl substitution at the 4' and meta-positions were important for the protection of flavonol. These SARs were further confirmed by molecular docking using the active site of the Keap1-Nrf2 complex as the receptor. The mechanistic study demonstrated that EGCG with the lowest EC₅₀ protected the PC-12 cells from methylglyoxal-induced damage by reducing oxidative stress via the Nrf2/Keap1/HO-1 and Bcl-2/Bax signaling pathways. These results suggested that flavan-3-ols might be a potential dietary supplement for protection against diabetic encephalopathy.

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.

Rutin alleviated acrolein-induced cytotoxicity in Caco-2 and GES-1 cells by forming a cyclic hemiacetal product

Acrolein (ACR), an α, β-unsaturated aldehyde, is a toxic compound formed during food processing, and the use of phenolics derived from dietary materials to scavenge ACR is a hot spot. In this study, rutin, a polyphenol widely present in various dietary materials, was used to investigate its capacity to scavenge ACR. It was shown that more than 98% of ACR was eliminated under the conditions of reaction time of 2 h, temperature of 80 °C, and molar ratio of rutin/ACR of 2/1. Further structural characterization of the formed adduct revealed that the adduct of rutin to ACR to form a cyclic hemiacetal compound (RAC) was the main scavenging mechanism. Besides, the stability of RAC during simulated in vitro digestion was evaluated, which showed that more than 83.61% of RAC was remained. Furthermore, the cytotoxicity of RAC against Caco-2 and GES-1 cells was significantly reduced compared with ACR, where the IC50 values of ACR were both below 20 μM while that of RAC were both above 140 μM. And the improvement of the loss of mitochondrial membrane potential (MMP) by RAC might be one of the detoxification pathways. The present study indicated that rutin was one of the potential ACR scavengers among natural polyphenols.

Origin and Fate of Acrolein in Foods

Acrolein is a highly toxic agent that may promote the occurrence and development of various diseases. Acrolein is pervasive in all kinds of foods, and dietary intake is one of the main routes of human exposure to acrolein. Considering that acrolein is substantially eliminated after its formation during food processing and re-exposed in the human body after ingestion and metabolism, the origin and fate of acrolein must be traced in food. Focusing on molecular mechanisms, this review introduces the formation of acrolein in food and summarises both in vitro and in vivo fates of acrolein based on its interactions with small molecules and biomacromolecules. Future investigation of acrolein from different perspectives is also discussed.

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.

Field application of nanoliposomes delivered quercetin by inhibiting specific hsp70 gene expression against plant virus disease

BACKGROUND

The annual economic loss caused by plant viruses exceeds 10 billion dollars due to the lack of ideal control measures. Quercetin is a flavonol compound that exerts a control effect on plant virus diseases, but its poor solubility and stability limit the control efficiency. Fortunately, the development of nanopesticides has led to new ideas.

RESULTS

In this study, 117 nm quercetin nanoliposomes with excellent stability were prepared from biomaterials, and few surfactants and stabilizers were added to optimize the formula. Nbhsp70er-1 and Nbhsp70c-A were found to be the target genes of quercetin, through abiotic and biotic stress, and the nanoliposomes improved the inhibitory effect at the gene and protein levels by 33.6 and 42%, respectively. Finally, the results of field experiment showed that the control efficiency was 38% higher than that of the conventional quercetin formulation and higher than those of other antiviral agents.

CONCLUSION

This research innovatively reports the combination of biological antiviral agents and nanotechnology to control plant virus diseases, and it significantly improved the control efficiency and reduced the use of traditional chemical pesticides.