Lishuang Lv

Genistein Inhibits Advanced Glycation End Product Formation by Trapping Methylglyoxal

Methylglyoxal (MGO) is a highly reactive endogenous metabolite derived from several nonenzymatic and enzymatic reactions, and identified as a well-known precursor of advanced glycation end products (AGEs). In the present study, genistein, a naturally occurring isoflavone derived from soy products, demonstrated significant trapping effects of MGO and consequently formed mono- and di-MGO adducts under physiological conditions (pH 7.4, 37 °C). More than 80.0% of MGO was trapped within 4 h, and the trapping efficiency could be up to 97.7% at 24 h. The reaction adducts formed from genistein and MGO under different ratios were analyzed using LC/MS. We also successfully purified and identified the major mono- and di-MGO conjugated adducts of genistein. The NMR data showed that positions 6 and 8 of the A ring of genistein were the major active sites for trapping MGO. We further demonstrated that genistein could effectively inhibit the formation of AGEs in the human serum albumin (HSA)-MGO assay. Two mono-MGO adducts and one di-MGO adduct of genistein were detected in this assay using LC/MS. The di-MGO adduct of genistein became the dominant reaction product during prolonged incubation. Results from this study, as well as our previous findings on (-)-epigallocatechin 3-gallate (EGCG), phloridzin and phloretin, indicate that dietary flavonoids that have the same A ring structure as genistein, EGCG, phloridzin, and phloretin may have the potential to inhibit the formation of AGEs by trapping reactive dicarbonyl species.

Stilbene glucoside from Polygonum multiflorum Thunb.: a novel natural inhibitor of advanced glycation end product formation by trapping of methylglyoxal.

Methylglyoxal (MGO), the reactive dicarbonyl intermediate generated during the nonenzymatic glycation between reducing sugars and amino groups of proteins, lipids, and DNA, is the precursor of advanced glycation end products (AGEs). Many studies have shown that AGEs play a major pathogenic role in diabetes and its complications. This study found that 2,3,5,4-tetrahydroxystilbene 2-O-beta-D-glucoside (THSG), the major bioactive compound from Polygonum multiflorum Thunb., can efficiently inhibit the formation of AGEs in a dose-dependent manner by trapping reactive MGO under physiological conditions (pH 7.4, 37 degrees C). More than 60% MGO was trapped by THSG within 24 h, which was much more effective than resveratrol and its methylated derivative, pterostilbene, the two major bioactive dietary stilbenes. The major mono- and di-MGO adducts of THSG were successfully purified and found to be mixtures of tautomers. LC-MS and NMR data showed that positions 4 and 6 of the A ring were the major active sites for trapping MGO. It was also found that THSG could significantly inhibit the formation of AGEs in the human serum albumin (HSA)-MGO assay and both mono- and di-MGO adducts of THSG were detected in this assay using LC-MS. The results suggest that the ability of THSG to trap reactive dicarbonyl species makes it a potential natural inhibitor of AGEs.

Quercetin Inhibits Advanced Glycation End Product Formation by Trapping Methylglyoxal and Glyoxal

Methylglyoxal (MGO) and glyoxal (GO) not only are endogenous metabolites but also exist in exogenous resources, such as foods, beverages, urban atmosphere, and cigarette smoke. They have been identified as reactive dicarbonyl precursors of advanced glycation end products (AGEs), which have been associated with diabetes-related long-term complications. In this study, quercetin, a natural flavonol found in fruits, vegetables, leaves, and grains, could effectively inhibit the formation of AGEs in a dose-dependent manner via trapping reactive dicarbonyl compounds. More than 50.5% of GO and 80.1% of MGO were trapped at the same time by quercetin within 1 h under physiological conditions. Quercetin and MGO (or GO) were combined at different ratios, and the products generated from this reaction were analyzed with LC-MS. Both mono-MGO and di-MGO adducts of quercetin were detected in this assay using LC-MS, but only tiny amounts of mono-GO adducts of quercetin were found. Additionally, di-MGO adducts were observed as the dominant product with prolonged incubation time. In the bovine serum albumin (BSA)-MGO/GO system, quercetin traps MGO and GO directly and then significantly inhibits the formation of AGEs.

Purification, antioxidant activity and antiglycation of polysaccharides from Polygonum multiflorum Thunb

Polysaccharides, one of the most important constituents in Polygonum multiflorum Thunb, a famous Chinese medicinal herb, were isolated by DEAE-52, Sepharose 4B and Sephacryl S-300 column chromatography. Two polysaccharides (PMP-1 and PMP-2) were identified as homogeneous in molecular weight with HPLC. The molecular weights were 4.8 × 10(2) and 6.1 × 10(2) kDa, respectively. Antioxidant activity tests were performed with two polysaccharides at concentrations of 0.1-1.5mg/mL. The results indicated that the inhibitory activity on oxidation and glycation exhibited a dose-dependent response. PMP-2 exhibited a much stronger antioxidant capacity against free radical, lipid oxidation and protein glycation. The IC₅₀ values of PMP-2 were 0.47, 0.6 and 0.93 mg/mL for superoxide anion scavenging, hydroxyl radical scavenging, and hydroxyl peroxide scavenging, respectively. The inhibitory ability of PMP-2 on lipid oxidation was most markedly in rat liver, followed by heart and kidney. Meanwhile, PMP-2 also showed satisfactory suppression of AGEs formation. This suggested that the polysaccharides present in PM can contribute to the biological effects.

Metabolism of [6]-Shogaol in Mice and in Cancer Cells

Ginger has received extensive attention because of its antioxidant, anti-inflammatory, and antitumor activities. However, the metabolic fate of its major components is still unclear. In the present study, the metabolism of [6]-shogaol, one of the major active components in ginger, was examined for the first time in mice and in cancer cells. Thirteen metabolites were detected and identified, seven of which were purified from fecal samples collected from [6]-shogaol-treated mice. Their structures were elucidated as 1-(4′-hydroxy-3′-methoxyphenyl)-4-decen-3-ol (M6), 5-methoxy-1-(4′-hydroxy-3′-methoxyphenyl)-decan-3-one (M7), 3′,4′-dihydroxyphenyl-decan-3-one (M8), 1-(4′-hydroxy-3′-methoxyphenyl)-decan-3-ol (M9), 5-methylthio-1-(4′-hydroxy-3′-methoxyphenyl)-decan-3-one (M10), 1-(4′-hydroxy-3′-methoxyphenyl)-decan-3-one (M11), and 5-methylthio-1-(4′-hydroxy-3′-methoxyphenyl)-decan-3-ol (M12) on the basis of detailed analysis of their 1H, 13C, and two-dimensional NMR data. The rest of the metabolites were identified as 5-cysteinyl-M6 (M1), 5-cysteinyl-[6]-shogaol (M2), 5-cysteinylglycinyl-M6 (M3), 5-N-acetylcysteinyl-M6 (M4), 5-N-acetylcysteinyl-[6]-shogaol (M5), and 5-glutathiol-[6]-shogaol (M13) by analysis of the MSn (n = 1–3) spectra and comparison to authentic standards. Among the metabolites, M1 through M5, M10, M12, and M13 were identified as the thiol conjugates of [6]-shogaol and its metabolite M6. M9 and M11 were identified as the major metabolites in four different cancer cell lines (HCT-116, HT-29, H-1299, and CL-13), and M13 was detected as a major metabolite in HCT-116 human colon cancer cells. We further showed that M9 and M11 are bioactive compounds that can inhibit cancer cell growth and induce apoptosis in human cancer cells. Our results suggest that 1) [6]-shogaol is extensively metabolized in these two models, 2) its metabolites are bioactive compounds, and 3) the mercapturic acid pathway is one of the major biotransformation pathways of [6]-shogaol.

Quantitative Analysis of Ginger Components in Commercial Products Using Liquid Chromatography with Electrochemical Array Detection

For the first time, a sensitive reversed-phase HPLC electrochemical array method has been developed for the quantitative analysis of 8 major ginger components ([6]-, [8]-, and [10]-gingerol, [6]-, [8]-, and [10]-shogaol, [6]-paradol, and [1]-dehydrogingerdione) in 11 ginger-containing commercial products. This method was valid with unrivaled sensitivity as low as 7.3-20.2 pg of limit of detection and a range of 14.5-40.4 pg for the limit of quantification. The levels of 8 ginger components in 11 different commercial products were quantified by use of this method. The results found that both levels and ratios among the 8 compounds vary greatly in commercial products.

6-Gingerdiols as the Major Metabolites of 6-Gingerol in Cancer Cells and in Mice and Their Cytotoxic Effects on Human Cancer Cells

6-Gingerol, a major pungent component of ginger (Zingiber officinale Roscoe, Zingiberaceae), has been reported to have antitumor activities. However, the metabolic fate of 6-gingerol and the contribution of its metabolites to the observed activities are still unclear. In the present study, we investigated the biotransformation of 6-gingerol in different cancer cells and in mice, purified and identified the major metabolites from human lung cancer cells, and determined the effects of the major metabolites on the proliferation of human cancer cells. Our results show that 6-gingerol is extensively metabolized in H-1299 human lung cancer cells, CL-13 mouse lung cancer cells, HCT-116 and HT-29 human colon cancer cells, and in mice. The two major metabolites in H-1299 cells were purified and identified as (3R,5S)-6-gingerdiol (M1) and (3S,5S)-6-gingerdiol (M2) based on the analysis of their 1D and 2D NMR data. Both metabolites induced cytotoxicity in cancer cells after 24 h, with M1 having a comparable effect to 6-gingerol in H-1299 cells.

Protective effects of lotus (Nelumbo nucifera Gaertn) germ oil against carbon tetrachloride-induced injury in mice and cultured PC-12 cells.

The protective effects of lotus germ oil on liver and kidney damage by carbon tetrachloride-induced chronic hepatotoxicity in mice, PC-12 cells, and DNA damage were investigated. The mice were treated orally with lotus germ oil or dl-α-tocopherol after administration CCl(4) for 49 consecutive days. The levels of key antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and the concentration of glutathione (GSH), as well as the concentration of malondialdehyde (MDA), an indicator of lipid peroxidation, were determined in homogenates of the liver and the kidney. The pathological histology of the liver was also examined. The activities of SOD, CAT, and the concentration of GSH were increased significantly (p<0.05-0.01) after treated with lotus germ oil in a concentration-dependent manner. Whereas, the content of the peroxidation product MDA were decreased significantly (p<0.05), similar to the serum levels of hepatic enzyme biomarkers (alanine aminotransferase and aspartate aminotransferase). Furthermore, lotus germ oil could inhibit the conversion of super-coiled pBR322 plasmid DNA to the open circular form and apoptosis of hydrogen peroxide-induced PC-12 cells. The result of this study suggested that the lotus germ oil could be recognized as powerful functional oil against oxidative stress.

Influence of Quercetin and Its Methylglyoxal Adducts on the Formation of α-Dicarbonyl Compounds in a Lysine/Glucose Model System

Increasing evidence has identified α-dicarbonyl compounds, the reactive intermediates generated during Maillard reaction, as the potential factors to cause protein glycation and the development of chronic diseases. Therefore, there is an urgent need to decrease the levels of reactive dicarbonyl compounds in foods. In this study, we investigated the inhibitory effect of quercetin, a major dietary flavonoid, and its major mono- and di-MGO adducts on the formation of dicarbonyl compounds, such as methylglyoxal (MGO) and glyoxal (GO), in a lysine/glucose aqueous system, a model system to reflect the Maillard reaction in food process. Our result indicated that quercetin could efficiently inhibit the formation of MGO and GO in a time-dependent manner. Further mechanistic study was conducted by monitoring the formation of quercetin oxidation and conjugation products using LC-MS/MS. Quercetin MGO adducts, quercetin quinones, and the quinones of quercetin MGO adducts were detected in the system, indicating quercetin plays a dual role in inhibiting the formation of MGO and GO by scavenging free radicals generated in the system and trapping of MGO and GO to form MGO adducts. In addition, we prepared the mono- and di-MGO quercetin adducts and investigated their antioxidant activity and trapping capacity of MGO and GO. Our results indicated that both mono- and di-MGO quercetin adducts could scavenge the DPPH radical in a dose-dependent manner with >40% DPPH scavenged by the MGO adducts at 10 μM, and the di-MGO quercetin adduct could further trap MGO to generate tri-MGO adducts. Therefore, we demonstrate for the first time that quercetin MGO adducts retain the antioxidant activity and trapping capacity of reactive dicarbonyl species.

Levels and formation of α-dicarbonyl compounds in beverages and the preventive effects of flavonoids

Methylglyoxal (MGO) and glyoxal (GO), α-dicarbonyl compounds found in the Maillard reaction, progressively and irreversibly modify proteins. Beverages are an exogenous source of α-dicarbonyl compounds and may potentially increase MGO and GO levels in vivo. Using GC-FID method, we detected the MGO and GO contents of 86 beverages in Chinese supermarkets. The highest MGO and GO 587.5xa0µg/100xa0mL and 716.7xa0µg/100xa0mL respectively found in soyamilk and coffee. Herbal beverages, which contained bioactive components, had lower average levels of MGO (48.1xa0µg/100xa0mL) and GO (25.9xa0µg/100xa0mL). A box-and-whisker plot was used to display variation of the same group drinks, and comparing distributions between six different groups. It was further discovered that fat, protein and flavonoids, in addition to sweeteners, had notable effects on the formation of MGO and GO in soybean milk. The result of LC/MS indicated that quercetin could prevent the formation of MGO by trapping MGO to form the mono-MGO and di-MGO adducts during soybean milk manufacturing.Graphical Abstract