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

Scavenging Glyoxal and Methylglyoxal by Synephrine Alone or in Combination with Neohesperidin at High Temperatures

α-Dicarbonyl compounds, such as glyoxal (GO) and methylglyoxal (MGO), are a series of chemical hazards that exist in vivo and in vitro, posing a threat to human health. We aimed to explore the scavenging effects on GO/MGO by synephrine (SYN) alone or in combination with neohesperidin (NEO). First, through LC-MS/MS, we confirmed that both SYN and NEO could effectively remove GO and form GO adducts, while NEO could also clear MGO by forming MGO adducts, and its ability to clear MGO was stronger than that of GO. Second, a synergistic inhibitory effect on GO was found when SYN and NEO were used in combination by using the Chou-Talalay method; on the other hand, SYN could promote NEO to clear more MGO, although SYN could not capture MGO. Third, after synthesizing four GO/MGO-adducts (SYN-GO-1, SYN-GO-3, NEO-GO-7, and NEO-MGO-2) and identifying their structure through NMR, strict correlations between the GO/MGO-adducts and the GO/MGO-clearance rate were found when using SYN and NEO alone or in combination. Furthermore, it was inferred that the synergistic effect between SYN and NEO stems from their mutual promotion in capturing more GO by the quantitative analysis of the adducts in the combined model. Finally, a study was conducted on flowers of Citrus aurantium L. var. amara Engl. (FCAVA, an edible tea) rich in SYN and NEO, which could serve as an effective GO and MGO scavenger in the presence of both GO and MGO. Therefore, our study provided well-defined evidence that SYN and NEO, alone or in combination, could efficiently scavenge GO/MGO at high temperatures, whether in the pure form or located in FCAVA.

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.

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.

α-Dicarbonyl compounds in food products: Comprehensively understanding their occurrence, analysis, and control

α-Dicarbonyl compounds (α-DCs) are readily produced during the heating and storage of foods, mainly through the Maillard reaction, caramelization, lipid-peroxidation, and enzymatic reaction. They contribute to both the organoleptic properties (i.e., aroma, taste, and color) and deterioration of foods and are potential indicators of food quality. α-DCs are also important precursors to hazardous substances, such as acrylamide, furan, advanced lipoxidation end products, and advanced glycation end products, which are genotoxic, neurotoxic, and linked to several diseases. Recent studies have indicated that dietary α-DCs can elevate plasma α-DC levels and lead to "dicarbonyl stress." To accurately assess their health risks, quantifying α-DCs in food products is crucial. Considering their low volatility, inability to absorb ultraviolet light, and high reactivity, the analysis of α-DCs in complex food systems is a challenge. In this review, we comprehensively cover the development of scientific approaches, from extraction, enrichment, and derivatization, to sophisticated detection techniques, which are necessary for quantifying α-DCs in different foods. Exposure to α-DCs is inevitable because they exist in most foods. Recently, novel strategies for reducing α-DC levels in foods have become a hot research topic. These strategies include the use of new processing technologies, formula modification, and supplementation with α-DC scavengers (e.g., phenolic compounds). For each strategy, it is important to consider the potential mechanisms underlying the formation and removal of process contaminants. Future studies are needed to develop techniques to control α-DC formation during food processing, and standardized approaches are needed to quantify and compare α-DCs in different foods.

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.

Modulation of 1,2-Dicarbonyl Compounds in Postprandial Responses Mediated by Food Bioactive Components and Mediterranean Diet

Glycoxidative stress with the consequent generation of advanced glycation end products has been implied in the etiology of numerous non-communicable chronic diseases. During the postprandial state, the levels of 1,2-dicarbonyl compounds can increase, depending on numerous factors, including characteristics of the subjects mainly related to glucose metabolism disorders and nutritional status, as well as properties related to the chemical composition of meals, including macronutrient composition and the presence of dietary bioactive molecules and macromolecules. In this review, we examine the chemical, biochemical, and physiological pathways that contribute to postprandial generation of 1,2-dicarbonyl compounds. The modulation of postprandial 1,2-dicarbonyl compounds is discussed in terms of biochemical pathways regulating the levels of these compounds, as well as the effect of phenolic compounds, dietary fiber, and dietary patterns, such as Mediterranean and Western diets.