Mesona Chinensis Benth extract prevents AGE formation and protein oxidation against fructose-induced protein glycation in vitro

BACKGROUND

Mesona chinensis Benth (Chinese Mesona), an economically significant agricultural plant, is the most widely consumed as an herbal beverage in Southeast Asia and China. The objective of this study was to evaluate the inhibitory activity of Mesona chinensis (MC) extract on the formation of advanced glycation end products (AGEs) and protein oxidation in an in vitro model of fructose-mediated protein glycation.

METHODS

The content of total polyphenolic compounds was measured by using Folin-Ciocalteu assay. Antiglycation activity was determined using the formation of AGE fluorescence intensity, Nϵ-(carboxymethyl)lysine (CML), the level of fructosamine, and the formation of amyloid cross β-structure. The protein oxidation was examined using the level of protein carbonyl content and thiol group.

RESULTS

Our results revealed that the content of total polyphenolic compound in MC extract was 212.4 ± 5.6 mg gallic acid equivalents/g dried extract. MC extract (0.25-1.00 mg/mL) significantly inhibited the formation of fluorescence AGEs in fructose-glycated bovine serum albumin (BSA) during 4 weeks of study. Furthermore, MC extract also decreased the level of Nϵ-CML, fructosamine, and amyloid cross β-structure in fructose-glycated BSA. While the total thiol group was elevated and the protein carbonyl content was decreased in BSA incubated with fructose and MC extract.

CONCLUSIONS

The extract of MC inhibits fructose-mediated protein glycation and protein oxidation. This edible plant could be a natural rich source of antiglycation agent for preventing AGE-mediated diabetic complication.

Effects of plant extracts on the reversal of glucose-induced impairment of stress-resistance in Caenorhabditis elegans

Enhanced blood glucose levels are a hallmark of diabetes and are associated with diabetic complications and a reduction of lifespan. In order to search for plant extracts that display preventive activities in such a scenario, we tested 16 extracts used in human nutrition for their survival enhancing activities in the nematode Caenorhabditis elegans. Nematodes were exposed for 48 h to 10 mM glucose in the absence or presence of 0.1% extract. Thereafter, survival was measured at 37 °C. Extracts made from coffee, kola, rooibos and cinnamon, did not influence the glucose-induced reduction of survival. Those made from ginseng, camomile, lime blossom, paraguay tea, balm, rhodiola, black tea, or knotgrass all extended the lifespan of the glucose-treated nematodes significantly but did not rescue survival completely. Extracts from the leaves of blackberries, from hibiscus, elderberries, or jiaogulan completely countered the glucose-induced survival reduction. A potent activation of the proteasome was shown for the most preventive extracts suggesting a more efficient degradation of proteins impaired by glucose. In conclusion, we present a simple animal model to screen for plant extracts with potency to reverse glucose toxicity. Extracts from blackberry leaves, hibiscus, elderberries, and jiaogulan were identified as very potent in this regard whose exact mechanisms of action appear worthwile to investigate at the molecular level.

Tuning a 96-well microtiter plate fluorescence-based assay to identify AGE inhibitors in crude plant extracts

Advanced glycation end-products (AGEs) are involved in the pathogenesis of numerous diseases. Among them, cellular accumulation of AGEs contributes to vascular complications in diabetes. Besides using drugs to lower blood sugar, a balanced diet and the intake of herbal products potentially limiting AGE formation could be considered beneficial for patients’ health. The current paper presents a simple and cheap high-throughput screening (HTS) assay based on AGE fluorescence and suitable for plant extract screening. We have already implemented an HTS assay based on vesperlysines-like fluorescing AGEs quickly (24 h) formed from BSA and ribose under physiological conditions. However, interference was noted when fluorescent compounds and/or complex mixtures were tested. To overcome these problems and apply this HTS assay to plant extracts, we developed a technique for systematic quantification of both vesperlysines (λ_exc 370 nm; λ_em 440 nm) and pentosidine-like (λ_exc 335 nm; λ_em 385 nm) AGEs. In a batch of medicinal and food plant extracts, hits were selected as soon as fluorescence decreased under a fixed threshold for at least one wavelength. Hits revealed during this study appeared to contain well-known and powerful anti-AGE substances, thus demonstrating the suitability of this assay for screening crude extracts (0.1 mg/mL). Finally, quercetin was found to be a more powerful reference compound than aminoguanidine in such assay.

A comparative study of ferulic acid on different monosaccharide-mediated protein glycation and oxidative damage in bovine serum albumin

Three dietary monosaccharides, (glucose, fructose, and ribose), have different rates of protein glycation that accelerates the production of advanced glycation end-products (AGEs). The present work was conducted to investigate the effect of ferulic acid (FA) on the three monosaccharide-mediated protein glycations and oxidation of BSA. Comparing the percentage reduction, FA (1-5 mM) reduced the level of fluorescence AGEs (F-AGEs) and N(ε)-(carboxymethyl) lysine (N(ε)-CML) in glucose-glycated BSA (F-AGEs = 12.61%-36.49%; N(ε)-CML = 33.61%-66.51%), fructose-glycated BSA (F-AGEs = 25.28%-56.42%; N(ε)-CML = 40.21%-62.91%), and ribose-glycated BSA (F-AGEs = 25.63%-51.18%; N(ε)-CML = 26.64%-64.08%). In addition, the percentages of FA reduction of fructosamine (Frc) and amyloid cross β-structure (Amy) were Frc = 20.45%-43.81%; Amy = 17.84%-34.54% in glucose-glycated BSA, Frc = 25.17%-36.92%; Amy = 27.25%-39.51% in fructose-glycated BSA, and Frc = 17.34%-29.71%; Amy = 8.26%-59.92% in ribose-glycated BSA. FA also induced a reduction in protein carbonyl content (PC) and loss of protein thiol groups (TO) in glucose-glycated BSA (PC = 37.78%-56.03%; TO = 6.75%-13.41%), fructose-glycated BSA (PC = 36.72%-52.74%; TO = 6.18%-20.08%), and ribose-glycated BSA (PC = 25.58%-33.46%; TO = 20.50%-39.07%). Interestingly, the decrease in fluorescence AGEs by FA correlated with the level of N(ε)-CML, fructosamine, amyloid cross β-structure, and protein carbonyl content. Therefore, FA could potentially be used to inhibit protein glycation and oxidative damage caused by monosaccharides, suggesting that it might prevent AGEs-mediated pathologies during diabetic complications.

Suppression of dimerumic acid on hepatic fibrosis caused from carboxymethyl-lysine (CML) by attenuating oxidative stress depends on Nrf2 activation in hepatic stellate cells (HSCs)

Hyperglycemia facilitates the formation of advanced glycation end-products (AGEs) in type-2 diabetes. Evidence indicates that carboxymethyl-lysine (CML) is highly prevalent in diabetes, resulting in hepatic fibrosis. The current study was designed to evaluate the effects of dimerumic acid (DMA) identified from Monascus-fermented products on receptor for AGEs (RAGE) signal and hepatic stellate cells (HSCs) activation by CML treatment. We found that DMA (50 μM) eliminated collagen generation, mRNA expressions of α-smooth muscle actin (α-SMA), platelet-derived growth factor-β receptor (PDGF-βR), and procollagen 1a1 (proCol-1a1) in CML (100 μg/ml)-treated HSCs, and these effects were similar to allyl isothiocyanate (AITC; 50 μM). In addition, the suppression of α-SMA, PDGF-βR, proCol-1a1 by DMA were abolished while nuclear factor-erythroid 2-related factor 2 (Nrf2) silence in CML-treated HSCs. These findings suggested that DMA and AITC increased Nrf2 and glutamate-cysteine ligase (GCL) activities thereby inhibiting oxidative stress caused by CML and showing anti-fibrogentic effect in HSCs.

Graptopetalum paraguayense and resveratrol ameliorates carboxymethyllysine (CML)-induced pancreas dysfunction and hyperglycemia

Hyperglycemia is associated with advanced glycation end products (AGEs). Recently, AGEs were found to cause pancreatic damage, oxidative stress, and hyperglycemia through the AGE receptor. Carboxymethyllysine (CML) is an AGE but whether it induces pancreatic dysfunction remains unclear. Graptopetalum paraguayense, a vegetable consumed in Taiwan, has been used in folk medicine and is an antioxidant that protects against liver damage. We investigated the protective properties of G. paraguayense 95% ethanol extracts (GPEs) against CML-induced pancreatic damage. The results indicated that resveratrol, GPE, and gallic acid (the active compound of GPE) increased insulin synthesis via upregulation of pancreatic peroxisome proliferator activated-receptor-γ (PPARγ) and pancreatic-duodenal homeobox-1 (PDX-1) but inhibited the expression of CML-mediated CCAAT/enhancer binding protein-β (C/EBPβ), a negative regulator of insulin production. Moreover, resveratrol and GPE also strongly activated nuclear factor-erythroid 2-related factor 2 (Nrf2) to attenuate oxidative stress and improve insulin sensitivity in the liver and muscle of CML-injected C57BL/6 mice and resulted in reduced blood glucose levels. Taken together, these findings suggested that GPE and gallic acid could potentially be used as a food supplement to protect against pancreatic damage and the development of diabetes.

Advanced glycation endproducts in food and their effects on health

Advanced glycation endproducts (AGEs) form by Maillard-reactions after initial binding of aldehydes with amines or amides in heated foods or in living organisms. The mechanisms of formation may include ionic as well as oxidative and radical pathways. The reactions may proceed within proteins to form high-molecular weight (HMW) AGEs or among small molecules to form low-molecular weight (LMW) AGEs. All free amino acids form AGEs, but lysine or arginine side chains dominate AGE formation within proteins. The analysis of AGEs in foods and body fluids is most often performed by ELISA or LC-MS; however, none of the methodologies cover all HMW and LMW AGEs. Most research is, therefore, carried out using 'representative' AGE compounds, most often N(ε)-carboxymethyl-lysine (CML). Only LMW AGEs, including peptide-bound forms, and carbonyls may be absorbed from the gut and contribute to the body burden of AGEs. Some AGEs interact with specific pro- or anti-inflammatory receptors. Most studies on the biological effects of AGEs have been carried out by administering heated foods. The pro-inflammatory and deteriorating biological effects of AGEs in these studies, therefore, need further confirmation. The current review points out several research needs in order to address important questions on AGEs in foods and health.

Inhibition of advanced glycation end products by red grape skin extract and its antioxidant activity

BACKGROUND

The objective of the present study was to determine the phytochemical content and the protective effect of red grape skin extract (RGSE) against fructose-mediated protein oxidation. In addition, RGSE was screened for its potential as an antioxidant using various in vitro models.

METHODS

Antioxidant activity was measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical scavenging activity, superoxide radical scavenging activity, trolox equivalent antioxidant capacity, ferric reducing antioxidant power (FRAP), ferrous ion chelating power. The total phenols content was measured by Folin-Ciocalteu assay, the flavonoids content by the AlCl3 colorimetric method. Antiglycation activity was determined using the formation of AGE fluorescence intensity, Nε-(carboxymethyl)lysine, and the level of fructosamine. The protein oxidation was examined using the level of protein carbonyl content and thiol group.

RESULTS

The results showed that the content of total phenolics, flavonoids and total anthocyanins in RGSE was 246.3 ± 0.9 mg gallic acid equivalent/g dried extract, 215.9 ± 1.3 mg catechin equivalent/g dried extract, and 36.7 ± 0.8 mg cyanidin-3-glucoside equivalent/g dried extract, respectively. In the DPPH radical scavenging activity, hydroxyl radical scavenging activity, and superoxide radical scavenging activity, RGSE had the IC50 values of 0.03 ± 0.01 mg/ml, 5.40 ± 0.01 mg/ml, and 0.58 ± 0.01 mg/ml, respectively. In addition, RGSE had trolox equivalent antioxidant capacity assay (395.65 ± 1.61 mg trolox equivalent/g dried extract), ferric reducing antioxidant power (114.24 ± 0.03 mM FeSO4/g dried extract), and ferrous ion chelating power (3,474.05 ± 5.55 mg EDTA/g dried extract), respectively. The results showed that RGSE at different concentrations (0.031-0.500 mg/ml) has significantly inhibited the formation of AGEs in terms of the fluorescence intensity of glycated BSA during 4 weeks of study. The RGSE markedly decreased the level of fructosamine, which is directly associated with the reduction of AGE formation and Nε-(carboxymethyl)lysine (CML). The results demonstrated the significant effect of RGSE on preventing protein oxidative damages, including effects on the thiol and protein carbonyl oxidation.

CONCLUSIONS

The present study revealed that RGSE would exert beneficial effects by virtue of its antioxidants and antiglycation. The findings could provide a new insight into the naturally occurring antiglycation properties of RGSE for preventing AGE-mediated diabetic complication.

Antioxidation and antiglycation of Fagopyrum tataricum ethanol extract

Fagopyrum tataricum is used for the treatment of type 2 diabetes mellitus in Taiwan. The aim of this study was to evaluate the inhibitory effects of 75 % ethanol extract of buckwheat (EEB) and rutin on carbohydrate-metabolized enzymes, including α-amylase and α-glucosidase, which are related to hyperglycemia. The rutin dosage (40 μg/mL) was equivalent to that of EEB (200 μg/mL). In addition, the antioxidant and antiglycation activities of EEB and rutin were investigated. Results showed that both EEB and rutin exerted free radical (DPPH and ABTS) scavenging activity. They also attenuated protein glycation to lower the generation of advanced glycation end-products (AGEs) through the suppression of fructosamine and α-dicarbonyl compounds. Moreover, EEB and rutin also inhibited α-amylase and α-glucosidase activity. Taken together, these findings suggest that EEB and rutin may reduce oxidative stress, AGEs formation, and carbohydrate-metabolized enzymes hence EEB may use as protection agent in diabetic patients.

Dimerumic acid attenuates receptor for advanced glycation endproducts signal to inhibit inflammation and diabetes mediated by Nrf2 activation and promotes methylglyoxal metabolism into d-lactic acid

This study was designed to evaluate the effects of dimerumic acid (DMA) on receptor for advanced glycation endproducts (RAGE) signal activation and THP-1 monocyte inflammation treated with S100b, a specific ligand of RAGE. We found that DMA inhibited inflammatory cytokine production via upregulation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and alleviated oxidative stress through attenuation of p47phox translocation to the membrane of S100b-treated THP-1 monocytes. We found that DMA activated Nrf2 mediated by the p38 kinase pathway in THP-1 monocytes. However, anti-inflammatory activity of DMA was attenuated by Nrf2 siRNA treatment. In an animal model, methylglyoxal (MG; 200mg/kg bw) was chosen to induce diabetes in Balb/C mice (6 weeks) in this work. The in vivo verification of anti-inflammation in peripheral blood mononuclear cells by DMA treatment was confirmed by tumor necrosis factor-α and interleukin-1β measurements. Oral glucose tolerance test, insulin tolerance test, hyperinsulinemia, and hyperglycemia were improved in MG-treated mice by DMA treatment and these effects were greater than those of silymarin and N-acetylcysteine. Furthermore, DMA increased hepatic glyoxalase mRNA and glutathione mediated by Nrf2 activation to metabolize MG into d-lactic acid, thereby reducing serum and hepatic AGE levels and suppressing inflammatory factor generation in MG-treated mice. However, DMA did not exert the antiglycation activity in MG-bovine serum albumin incubation. Taken together, the results indicate that DMA is a novel antioxidant and Nrf2 activator that lowers AGE levels and may prove to be an effective treatment for diabetes.

Isoferulic acid, a new anti-glycation agent, inhibits fructose- and glucose-mediated protein glycation in vitro

The inhibitory activity of isoferulic acid (IFA) on fructose- and glucose-mediated protein glycation and oxidation of bovine serum albumin (BSA) was investigated. Our data showed that IFA (1.25–5 mM) inhibited the formation of fluorescent advanced glycation end products (AGEs) and non-fluorescent AGE [N^ε-(carboxymethyl) lysine: CML], as well as the level of fructosamine. IFA also prevented protein oxidation of BSA indicated by decreasing protein carbonyl formation and protein thiol modification. Furthermore, IFA suppressed the formation of β-cross amyloid structures of BSA. Therefore, IFA might be a new promising anti-glycation agent for the prevention of diabetic complications via inhibition of AGEs formation and oxidation-dependent protein damage.

Potent nematicidal activity of phthalaldehyde, salicylaldehyde, and cinnamic aldehyde against Meloidogyne incognita

The nematicidal activity of selected aromatic aldehydes was tested against the root knot nematode Meloidogyne incognita. The most active aldehyde was phthalaldehyde (1) with an EC(50) value of 11 ± 6 mg/L followed by salicylaldehyde (2) and cinnamic aldehyde (3) with EC(50) values of 11 ± 1 and 12 ± 5 mg/L, respectively. On the other hand, structurally related aldehydes such as 2-methoxybenzaldehyde (21), 3,4-dimethoxybenzaldehyde, and vanillin (23) were not active at the concentration of 1000 mg/L. By liquid chromatography-mass spectrometry the reactivity of tested aldehydes against a synthetic peptide resembling the nematode cuticle was characterized. At the test concentration of 1 mM, the main adduct formation was observed for 3,4-dihydroxybenzaldehyde (22), 2-methoxybenzaldehyde (21), and 3,4-dimethoxybenzaldehyde. Considering that 2-methoxybenzaldehyde (21) and 3,4-dimethoxybenzaldehyde were not active against M. incognita in in vitro experiments led us to hypothesize a different mechanism of action rather than an effect on the external cuticle modification of nematodes. When the toxicity of the V-ATPase inhibitor pyocyanin (10) was tested against M. incognita J2 nematodes, an EC(50) at 24 h of 72 ± 25 mg/L was found. The redox-active compounds such as phthalaldehyde (1) and salicylaldehyde (2) may share a common mode of action inhibiting nematode V-ATPase enzyme. The results of this investigation reveal that aromatic redox-active aldehydes can be considered as potent nematicides, and further investigation is needed to completely clarify their mode of action.

Effects of monascin on anti-inflammation mediated by Nrf2 activation in advanced glycation end product-treated THP-1 monocytes and methylglyoxal-treated wistar rats

Hyperglycemia is associated with advanced glycation end products (AGEs). This study was designed to evaluate the inhibitory effects of monascin on receptor for advanced glycation end product (RAGE) signal and THP-1 monocyte inflammation after treatment with S100b, a specific ligand of RAGE. Monascin inhibited cytokine production by S100b-treated THP-1 monocytes via up-regulation of nuclear factor-erythroid 2-related factor-2 (Nrf2) and alleviated p47phox translocation to the membrane. Methylglyoxal (MG, 600 mg/kg bw) was used to induce diabetes in Wistar rats. Inhibitions of RAGE and p47phox by monascin were confirmed by peripheral blood mononuclear cells (PBMCs) of MG-induced rats. Silymarin (SM) was used as a positive control group. It was found that monascin promoted heme oxygenase-1 (HO-1) expression mediated by Nrf2. Suppressions of AGEs, tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-β) in serum of MG-induced rats were attenuated in the monascin administration group treated with retinoic acid (RA). RA treatment resulted in Nrf2 inactivation by increasing RA receptor-α (RARα) activity, suggesting that RA acts as an inhibitor of Nrf2. The results showed that monascin exerted anti-inflammatory and antioxidative effects mediated by Nrf2 to prevent the development of diseases such as type 2 diabetes caused by inflammation.

Ankaflavin: a natural novel PPARγ agonist upregulates Nrf2 to attenuate methylglyoxal-induced diabetes in vivo

Ankaflavin (AK) is an active compound having anti-inflammatory, anti-cancer, antiatherosclerotic, and hypolipidemic effects. We have previously reported that AK acts as an antioxidant and antidiabetic drug; however, the mechanism by which AK prevents diabetes remains unknown. Hyperglycemia is associated with protein glycation, which produces advanced glycation end-products (AGEs). Methylglyoxal (MG)-a metabolite of carbohydrates-is believed to cause insulin resistance by inducing inflammation and pancreas damage. In this work, diabetes was induced in Wistar rats (4 weeks of age) by treating them with MG (600 mg/kg bw) for 4 weeks. We observed that AK (10mg/kg bw) exerted peroxisome proliferator-activated receptor-γ (PPARγ) agonist activity, thereby enhancing insulin sensitivity (as indicated by hepatic GLUT2 translocation, PTP1B suppression, and glucose uptake) by downregulating blood glucose and upregulating pancreatic and duodenal homeobox-1 and Maf-A expression and increasing insulin production in MG-induced rats. However, these effects were abolished by the administration of GW9662 (PPARγ antagonist), but the expression of hepatic heme oxygenase-1 (HO-1) and glutamate-cysteine ligase (GCL) was not suppressed in MG-induced rats. Therefore, the nuclear factor erythroid-related factor-2 (Nrf2) activation was investigated. AK did not affect hepatic Nrf2 mRNA or protein expression but significantly increased Nrf2 phosphorylation (serine 40), which was accompanied by increased transcriptional activation of hepatic HO-1 and GCL. These data indicated that AK protected rats from oxidative stress resulting from MG-induced insulin resistance. In contrast, these effects were not detected when the rats were treated with the antidiabetic drug rosiglitazone (10mg/kg bw). Moreover, we found that AK did not inhibit the generation of AGEs in vitro; however, the glutathione (GSH) levels in liver and pancreas of MG-induced rats were elevated in rats administered AK. Therefore, we believe that GSH may lower the MG level, which attenuates the formation of AGEs in the serum, kidney, liver, and pancreas of MG-induced rats. We also found that AK treatment reduced the production of inflammatory factors, such as tumor necrosis factor-α and interleukin-1β. Taken together, the results of our mechanistic study of MG-induced rats suggest that the protective effects of AK against diabetes are mediated by the upregulation of the signaling pathway of Nrf2, which enhances antioxidant activity and serves as a PPARγ agonist to enhance insulin sensitivity.

Role of Dietary Advanced Glycation End Products in Diabetes Mellitus

Dietary advanced glycation end products (AGEs) can be formed via the Maillard reaction and several alternative pathways. AGEs exert their deleterious effects by damaging protein structure and function, as well as through activation of cellular mechanisms. At the cellular level, the damaging effects of AGEs have been attributed to several AGE-binding proteins. Increased levels of AGEs have been implicated in several chronic diseases, including diabetes-related complications such as renal diseases, retinopathy, neuropathy, and cardiovascular diseases, as well as delayed wound healing. To investigate the role of AGEs thoroughly, a reliable assessment of dietary AGEs is needed. Varying methodology, diverse food preparation, and quantification of a variety of dietary AGEs makes this a complex goal. In addition, some antiglycation food products may balance or offset the negative impact of dietary AGEs.

Resveratrol upregulates Nrf2 expression to attenuate methylglyoxal-induced insulin resistance in Hep G2 cells

Oxidative stress can result in insulin resistance, a primary cause of type-2 diabetes. Methylglyoxal (MG), a highly reactive dicarbonyl metabolite generated during glucose metabolism, has also been confirmed to cause pancreatic injury and induce inflammation, thereby resulting in insulin resistance. Recently, resveratrol has been reported to exert antioxidant properties, protecting cells from the generation of reactive oxygen species (ROS). The aim of this study was to evaluate resveratrol activation of nuclear factor erythroid 2-related factor 2 (Nrf2) to attenuate MG-induced insulin resistance in Hep G2 cells. Therefore, the molecular signaling events affecting resveratrol-mediated heme oxygenase-1 (HO-1) and glyoxalase expression levels were further investigated in this study. Our findings indicated that resveratrol activated the extracellular signal-regulated kinase (ERK) pathway but not the p38 or c-Jun N-terminal kinase (JNK) pathways, subsequently leading to Nrf2 nuclear translocation and elevation of HO-1 and glyoxalase expression levels. Moreover, resveratrol significantly elevated glucose uptake and protected against MG-induced insulin resistance in Hep G2 cells. In contrast, depletion of Nrf2 by small interfering RNA (si-RNA) resulted in the abrogation of HO-1 and glyoxalase expression in the MG-treated resveratrol group in Hep G2 cells. Administration of an appropriate chemopreventive agent, such as resveratrol, may be an alternative strategy for protecting against MG-induced diabetes.

Trapping of methylglyoxal by curcumin in cell-free systems and in human umbilical vein endothelial cells

Curcumin, the most active compound of curcuminoids, has been shown to inhibit formation of advanced glycation end products (AGEs) in streptozotocin-induced diabetic rats. However, little is known on whether curcumin may trap methylglyoxal (MGO), a major reactive dicarbonyl compound, to inhibit AGE formation. We found that one molecule of curcumin effectively trapped one molecule of MGO at a 1:3 ratio at 24 h of incubation under physiological conditions (pH 7.4, 37 °C). Curcumin decreased N(ε)-(carboxymethyl)lysine (CML) expression in human umbilical vein endothelial cells. We further used two curcumin analogues, dimethoxycurcumin (DIMC) and ferulic acid, to investigate the possible MGO-trapping mechanism of curcumin. Results reveal that DIMC, but not ferulic acid, exhibited MGO-trapping capacity, indicating curcumin traps MGO at the electron-dense carbon atom (C10) between the two keto carbon groups. Thus, curcumin may prevent MGO-induced endothelial dysfunction by directly trapping MGO.

Oral administration of ethyl acetate-soluble portion of Terminalia chebula conferring protection from streptozotocin-induced diabetic mellitus and its complications

Terminalia chebula has been widely used in India as a folk medicine. This study investigated the in vivo anti-hyperglycemia and anti-diabetic complication effects of the EtOAc-soluble portion of ethanolic extract of T. chebula fruit (EETC) containing 29.4% chebulic acid. Rats were divided into non-diabetic, untreated diabetic and diabetic groups. Streptozotocin (40 mg/kg body weight (BW))-induced diabetic rats were orally administered the aminoguanidine (100 mg/kg BW), high dose (500 mg/kg BW; HEETC) and low dose (100 mg/kg BW; LEETC) for 13 weeks. HEETC administration reduced the levels of blood glucose and serum lipids, decreased malondialdehyde concentrations of serum and thoracic aorta in diabetic rats, and significantly improved serum biochemical values and the pathomorphological changes of the liver and kidney in diabetic rats. Also, HEETC decreased the advanced glycation end products (AGEs) distribution in testis seminiferous tubules. Therefore, HEETC has a merit to be a potent candidate to control glycemic and diabetic complications.

Cynarin-rich sunflower (Helianthus annuus) sprouts possess both antiglycative and antioxidant activities

The present study examined the antiglycative and antioxidant properties of four edible sprouts popular in Chinese markets. In a protein-reducing sugar model, the sunflower sprout Helianthus annuus exhibited the strongest inhibitory effects against the formation of advanced glycation end products (AGEs). At a concentration of 1.0 mg/mL, its inhibitory rate achieved 83.29%, which is stronger than that of aminoguanidine (1 mM), a well-known synthetic antiglycative agent (with an inhibitory rate of 80.88%). The antioxidant capacity of H. annuus was also much stronger than other sprout samples in terms of free radical scavenging and reducing properties. An active ingredient contributing to the observed activities was identified as cynarin (1,5-dicaffeoylquinic acid). This is the first report of the novel function of cynarin to intervene against glycoxidation. Given the key roles of AGEs and oxidation in the pathogenesis of diabetes, the sunflower sprout H. annuus rich in cynarin may be regarded as a beneficial food choice for diabetic patients.

Cinnamic acid and its derivatives inhibit fructose-mediated protein glycation

Cinnamic acid and its derivatives have shown a variety of pharmacologic properties. However, little is known about the antiglycation properties of cinnamic acid and its derivatives. The present study sought to characterize the protein glycation inhibitory activity of cinnamic acid and its derivatives in a bovine serum albumin (BSA)/fructose system. The results demonstrated that cinnamic acid and its derivatives significantly inhibited the formation of advanced glycation end products (AGEs) by approximately 11.96–63.36% at a concentration of 1 mM. The strongest inhibitory activity against the formation of AGEs was shown by cinnamic acid. Furthermore, cinnamic acid and its derivatives reduced the level of fructosamine, the formation of N^ɛ-(carboxymethyl) lysine (CML), and the level of amyloid cross β-structure. Cinnamic acid and its derivatives also prevented oxidative protein damages, including effects on protein carbonyl formation and thiol oxidation of BSA. Our findings may lead to the possibility of using cinnamic acid and its derivatives for preventing AGE-mediated diabetic complications.

Polyphenolic content and comparative antioxidant capacity of flavoured black teas

The content of selected flavonoids and phenolic acids of 12 commercial flavoured black tea infusions was determined by high-performance liquid chromatography with tandem mass spectrometry in the negative electrospray ionization mode. Assays for the evaluation of their antioxidant capacity were carried out by cupric ion reducing antioxidant capacity, Folin-Ciocalteu assay, cyclic voltammetry and potentiometry. Flavonoids were predominantly present as glycosides in the studied infusions. Only quercetin as a free aglycone was found at trace levels. Notable amount of naringin and hesperidin was determined in teas with citrus aromas or fruits. These compounds were not found in premium black tea. Two principal groups of the studied teas were found using cluster analysis in relation to the values of their antioxidant activities.