Potential Properties of Plant Sprout Extracts on Amyloid β

The aim of this study is to examine the amyloid β (Aβ) inhibition mechanism of plant sprouts' aqueous extracts (PSAE). In this study, we screened the effects of five plant sprouts' extracts on Aβ (1–42) structure modification using gel electrophoresis. In PSAE, no band of Aβ monomer was recognized in Japanese butterbur. Similarly, the Aβ monomer band became light in buckwheat, red cabbage, broccoli, and brussels. The neuroprotective effects of PSAE were evaluated by measuring levels of Aβ in mixtures (Aβ  and PSAE) with Aβ ELISA assay. The treatment with PSAE decreased Aβ levels. The results indicated that the levels of red cabbage, Japanese butterbur, and broccoli were 9.6, 28.0, and 44.0%, respectively. The lowest value was observed with buckwheat. Furthermore, we carried out a Congo Red (CR) and Aβ binding experiment of PSAE to confirm the modification mechanism of PSAE. The correlation coefficient for the absorption spectrum peak of CR was found to be bigger than 0.8 (r = 0.882) which proved that the Aβ levels could be attributed to the peak of CR. In conclusion, we demonstrated that treatment with PSAE effectively decreases Aβ concentration. Thus, the mechanism that decreased the Aβ levels may be modification by PSAE.

Physicochemical Changes and Glycation Reaction in Intermediate-Moisture Protein-Sugar Foods with and without Addition of Resveratrol during Storage

An intermediate-moisture food (IMF) model consisting of whey protein isolate and glucose and an IMF model fortified with resveratrol were used to study the effect of resveratrol on physicochemical changes and glycation of protein-sugar-rich foods during storage. The water activity (aw) of the storage was controlled at 0.75 or 0.56. The browning rate or hardness of fortified IMFs was significantly lower than that of IMFs after 45-day storage. The rate of Maillard reaction in the samples stored at aw 0.56 was higher than that of samples stored at aw 0.75. The fortified IMFs had lower levels of AGEs (advanced glycation end products), CML (N(ε)-(carboxymethyl)-l-lysine), and insoluble protein during storage. The inhibition capability of resveratrol against glycation was also confirmed by using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), liquid chromatography mass spectrometry (LC-MS), and Fourier transform infrared spectroscopy (FTIR) analysis to monitor glycated proteins and protein aggregation in the samples. The results of this study suggested that resveratrol could be used as an inhibitor to reduce the formation of undesirable AGEs and other Maillard reaction products in foods during storage.

Effect of cranberry (Vaccinium macrocarpon) oligosaccharides on the formation of advanced glycation end-products

BACKGROUND: The formation and accumulation of advanced glycation end-products (AGEs) are implicated in several chronic human illnesses including type-2 diabetes, renal failure, and neurodegenerative diseases. The cranberry (Vaccinium macrocarpon) fruit has been previously reported to show anti-AGEs effects, attributed primarily to its phenolic constituents. However, there is lack of similar data on the non-phenolic constituents found in the cranberry fruit, in particular, its carbohydrate constituents. Herein, a chemically characterized oligosaccharide-enriched fraction purified from the cranberry fruit was evaluated for its potential anti-AGEs and free radical scavenging effects. OBJECTIVE: The aim of this study was to evaluate the in vitro anti-AGEs and free radical scavenging effects of a chemically characterized oligosaccharide-enriched fraction purified from the North American cranberry (Vaccinium macrocarpon) fruit. METHOD: The cranberry oligosaccharide-enriched fraction was purified from cranberry hull powder and characterized based on spectroscopic and spectrometric (NMR, MALDI-TOF-MS, and HPAEC-PAD) data. The oligosaccharide-enriched fraction was evaluated for its anti-AGEs and free radical scavenging effects by the bovine serum albumin-fructose, and DPPH assays, respectively. RESULTS: Fractionation of cranberry hull material yielded an oligosaccharide-enriched fraction named Cranf1b-CL. The ¹H NMR and MALDI-TOF-MS revealed that Cranf1b-CL consists of oligosaccharides ranging primarily from 6-mers to 9-mers. The monosaccharide composition of Cranf1b-CL was arabinose (25%), galactose (5%), glucose (47%) and xylose (23%). In the bovine serum albumin-fructose assay, Cranf1b-CL inhibited AGEs formation in a concentration-dependent manner with comparable activity to the synthetic antiglycating agent, aminoguanidine, used as the positive control (57 vs. 75%; both at 500μg/mL). In the DPPH free radical scavenging assay, Cranf1b-CL showed superior activity to the synthetic commercial antioxidant, butylated hydroxytoluene, used as the positive control (IC₅₀ = 680 vs. 2200μg/mL, respectively). CONCLUSION: The in vitro anti-AGEs and free radical scavenging effects of cranberry oligosaccharides support previous data suggesting that these constituents may also contribute to biological effects of the whole fruit beyond its phenolic constituents alone. Also, this is the first study to evaluate a chemically characterized oligosaccharide fraction purified from the North American cranberry fruit for anti-AGEs and free radical scavenging properties.

Luteolin alleviates methylglyoxal-induced cytotoxicity in osteoblastic MC3T3-E1 cells

Methylglyoxal (MG), a reactive sugar-derived metabolite, exerts harmful effects by inducing oxidative stress, which aggravates a series of diabetic complications, including osteoporosis. The present study was performed to examine the effects of luteolin, a dietary polyphenolic flavonoid, on MG-induced cytotoxicity in MC3T3-E1 osteoblastic cells. Pretreatment of MC3T3-E1 osteoblastic cells with luteolin prevented MG-induced cell death and production of tumor necrosis factor-alpha, intracellular reactive oxygen species, mitochondrial superoxide, and cardiolipin peroxidation. In addition, luteolin increased the levels of glutathione and nuclear factor erythroid 2-related factor 2 (Nrf2) and decreased the inhibition of heme oxygenase-1 activity by MG. Pretreatment with luteolin prior to MG exposure reduced MG-induced mitochondrial dysfunction and increased the peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) and nitric oxide levels, suggesting that luteolin may induce mitochondrial biogenesis. Taken together, these observations indicated that luteolin has potential as a preventive agent against the development of diabetic osteopathy related to MG-induced oxidative stress in diabetes.

Cyanidin-3-rutinoside attenuates methylglyoxal-induced protein glycation and DNA damage via carbonyl trapping ability and scavenging reactive oxygen species

BACKGROUND

Advanced glycation end-products (AGEs) play a significant role in the development and progression of vascular complication in diabetes. Anthocyanin has been recently reported to possess antiglycating activity. This study aimed to determine whether a naturally occurring anthocyanin, cyanidin-3-rutinoside (C3R) inhibits methylglyoxal (MG) induced protein glycation and oxidative protein and DNA damage.

METHODS

C3R (0.125-1 mM) was incubated with bovine serum albumin and MG (1 mM) for 2 weeks. The formation of fluorescent AGEs was measured by using spectrofluorometer and thiol group content were used to detect protein oxidative damage. Gel electrophoresis was used to determine whether C3R (0.125-1 mM) reduced DNA strand breakage in a glycation model comprising lysine, MG and/or Cu(2+). The generation of superoxide anions and hydroxyl radicals were detected by the cytochrome c reduction assay and the thiobarbituric acid reactive substances assay. MG-trapping capacity was assessed by high performance liquid chromatography (HPLC).

RESULTS

C3R (0.25-1 mM) reduced the formation of fluorescent AGEs and depleted protein thiol groups in bovine serum albumin mediated by MG. At 1 mM C3R inhibited oxidative DNA damage in the glycation model (p < 0.05) and at 0.5-1 mM prevented Cu(2+) induced DNA strand breakage in the presence of lysine and MG. The findings showed that C3R reduced the formation of superoxide anion and hydroxyl radicals during the glycation reaction of MG with lysine. C3R directly trapped MG in a concentration and time dependent manner (both p < 0.001).

CONCLUSIONS

These findings suggest that C3R protects against MG-induced protein glycation and oxidative damage to protein and DNA by scavenging free radicals and trapping MG.

Glucitol-core containing gallotannins inhibit the formation of advanced glycation end-products mediated by their antioxidant potential

Glucitol-core containing gallotannins (GCGs) are polyphenols containing galloyl groups attached to a 1,5-anhydro-d-glucitol core, which is uncommon among naturally occurring plant gallotannins. GCGs have only been isolated from maple (Acer) species, including the red maple (Acer rubrum), a medicinal plant which along with the sugar maple (Acer saccharum), are the major sources of the natural sweetener, maple syrup. GCGs are reported to show antioxidant, α-glucosidase inhibitory, and antidiabetic effects, but their antiglycating potential is unknown. Herein, the inhibitory effects of five GCGs (containing 1-4 galloyls) on the formation of advanced glycation end-products (AGEs) were evaluated by MALDI-TOF mass spectroscopy, and BSA-fructose, and G.K. peptide-ribose assays. The GCGs showed superior activities compared to the synthetic antiglycating agent, aminoguanidine (IC50 15.8-151.3 vs. >300 μM) at the early, middle, and late stages of glycation. Circular dichroism data revealed that the GCGs were able to protect the secondary structure of BSA protein from glycation. The GCGs did not inhibit AGE formation by the trapping of reactive carbonyl species, namely, methylglyoxal, but showed free radical scavenging activities in the DPPH assay. The free radical quenching properties of the GCGs were further confirmed by electron paramagnetic resonance spectroscopy using ginnalin A (contains 2 galloyls) as a representative GCG. In addition, this GCG chelated ferrous iron, an oxidative catalyst of AGE formation, supported a potential antioxidant mechanism of antiglycating activity for these polyphenols. Therefore, GCGs should be further investigated for their antidiabetic potential given their antioxidant, α-glucosidase inhibitory, and antiglycating properties.

Antioxidant, antiglycation and insulinotrophic properties of Coccinia grandis (L.) in vitro: Possible role in prevention of diabetic complications

In an attempt to develop Complementary and Alternative Medicine (CAM) for the treatment of diabetes and related complications, the antidiabetic potential of the mature unripe fruits of Coccinia grandis (CGF) was evaluated. Oxidative stress and glycation plays an important role in manifesting of diabetes and vascular complications. Agents with antioxidant and antiglycation properties may retard these pathological alterations. In this study, the edible plant Coccinia grandis was assessed for in vitro estimation of antioxidant and antiglycation potential and its insulinotrophic properties in RINm5F cells. Antioxidant activity was evaluated as DPPH (1,1-diphenyl-2-picrylhydrazyl), hydrogen peroxide and superoxide anion scavenging activities, whereas the protein glycation inhibitory potential was evaluated using in vitro albumin-fructose glycation model. Glycation inhibition was estimated by different biochemical parameters viz. fructosamine, protein carbonyl group and protein aggregation using thioflavin T fluorescence. C. grandis extract exerted a dose dependent radical scavenging activity and exhibited a significant antiglycation potential. The extract also showed a significant insulinotrophic property with 1.28 and 1.71-fold increase in insulin release when compared to control at 0.25 and 0.50 mg/mL, respectively. These data suggest the possible antidiabetic role of CGF extract, presumably by its antioxidant, antiglycation and insulin secretory effects. Present findings provide experimental evidence that the fruits of C. grandis have potential antidiabetic activity which might be used as a functional food and safe remedy for the treatment of diabetes and associated complications. This study also revealed that the plant can be a promising source for development of natural antiglycating agents and novel insulin secretagogues.

Phenolics from Garcinia mangostana Inhibit Advanced Glycation Endproducts Formation: Effect on Amadori Products, Cross-Linked Structures and Protein Thiols

Accumulation of Advanced Glycation Endproducts (AGEs) in body tissues plays a major role in the development of diabetic complications. Here, the inhibitory effect of bioactive metabolites isolated from fruit hulls of Garcinia mangostana on AGE formation was investigated through bio-guided approach using aminoguanidine (AG) as a positive control. Including G. mangostana total methanol extract (GMT) in the reaction mixture of bovine serum albumin (BSA) and glucose or ribose inhibited the fluorescent and non-fluorescent AGEs formation in a dose dependent manner. The bioassay guided fractionation of GMT revealed isolation of four bioactive constituents from the bioactive fraction; which were identified as: garcimangosone D (1), aromadendrin-8-C-glucopyranoside (2), epicatechin (3), and 2,3',4,5',6-pentahydroxybenzophenone (4). All the tested compounds significantly inhibited fluorescent and non-fluorescent AGEs formation in a dose dependent manner whereas compound 3 (epicatechin) was found to be the most potent. In search for the level of action, addition of GMT, and compounds 2-4 inhibited fructosamine (Amadori product) and protein aggregation formation in both glucose and ribose. To explore the mechanism of action, it was found that addition of GMT and only compound (3) to reaction mixture increased protein thiol in both glucose and ribose while compounds 1, 2 and 4 only increased thiol in case of ribose. In conclusion, phenolic compounds 1-4 inhibited AGEs formation at the levels of Amadori product and protein aggregation formation through saving protein thiol.

The hydrolyzable gallotannin, penta-O-galloyl-β-D-glucopyranoside, inhibits the formation of advanced glycation endproducts by protecting protein structure

Glycation is a spontaneous process initiated by a condensation reaction between reducing sugars and proteins that leads to the formation of advanced glycation endproducts (AGEs). The in vivo accumulation of AGEs is associated with several chronic human diseases and, thus, the search for AGE inhibitors is of great research interest. Hydrolyzable tannins (gallotannins and ellagitannins) are bioactive plant polyphenols which show promise as natural inhibitors of glycation and AGE formation. Notably, the gallotannin, 1,2,3,4,6-penta-O-galloyl-β-D-glucose (PGG), is a key intermediate involved in the biosynthesis of hydrolyzable tannins in plants. Herein, we investigated the effects of PGG on the individual stages of protein glycation and on protein structure (using bovine serum albumin; BSA). MALDI-TOF data demonstrated that PGG inhibited early glycation by 75% while the synthetic AGE inhibitor, aminoguanidine (AG), was not active (both at 50 μM). In addition, PGG reduced the formation of middle and late stage AGEs by 90.1 and 60.5%, respectively, which was superior to the positive control, AG. While glycation induced conformational changes in BSA from α-helix to β-sheets (from circular dichroism and congo red binding studies), PGG (at 50 μM) reduced this transition by 50%. Moreover, BSA treated with PGG was more stable in its structure and retained its biophysical properties (based on zeta potential and electrophoretic mobility measurements). The interaction between PGG and BSA was further supported by molecular docking studies. Overall, the current study adds to the growing body of data supporting the anti-AGE effects of hydrolyzable tannins, a ubiquitous class of bioactive plant polyphenols.

The decrease in the IgG-binding capacity of intensively dry heated whey proteins is associated with intense Maillard reaction, structural changes of the proteins and formation of RAGE-ligands

Heat treatment is the most common way of milk processing, inducing structural changes as well as chemical modifications in milk proteins.

Anti-Advanced Glycation End-product and Free Radical Scavenging Activity of Plants from the Yucatecan Flora

Background:

Formation and accumulation of advanced glycation end-products (AGE) is recognized as a major pathogenic process in diabetic complications, atherosclerosis and cardiovascular diseases. In addition, reactive oxygen species and free radicals have also been reported to participate in AGE formation and in cell damage. Natural products with antioxidant and antiAGE activity have great therapeutic potential in the treatment of diabetes, hypertension and related complications. Objective: to test ethanolic extracts and aqueous-traditional preparations of plants used to treat diabetes, hypertension and obesity in Yucatecan traditional medicine for their anti-AGE and free radical scavenging activities.

Materials and Methods:

ethanolic extracts of leaves, stems and roots of nine medicinal plants, together with their traditional preparations, were prepared and tested for their anti-AGE and antioxidant activities using the inhibition of advanced glycation end products and DPPH radical scavenging assays, respectively.

Results:

the root extract of C. fistula (IC₅₀= 0.1 mg/mL) and the leaf extract of P. auritum (IC₅₀= 0.35 mg/mL) presented significant activity against vesperlysine and pentosidine-like AGE. Although none of the aqueous traditional preparations showed significant activity in the anti-AGE assay, both the traditional preparations and the ethanolic extracts of E. tinifolia, M. zapota, O. campechianum and P. auritum showed significant activity in the DPPH reduction assay.

Conclusions:

the results suggest that the metabolites responsible for the detected radical-scavenging activity are different to those involved in inhibiting AGE formation; however, the extracts with antioxidant activity may contain other metabolites which are able to prevent AGE formation through a different mechanism.

SUMMARY

Ethanolic extracts from nine plants used to treat diabetes, hypertension and obesity in Yucatecan traditional medicine were tested for their anti-AGE and free radical scavenging activities.

Significant activity against vesperlysine and pentosidine-like AGE was detected in the root extract of Cassia fistula and the leaf extract of Piper auritum.

Traditional preparations and the ethanolic extracts of Ehretia tinifolia, Manilkara zapota, Ocimum campechianum and Piper auritum showed significant activity in the DPPH reduction assay.

Results suggest that the metabolites responsible for the detected radical-scavenging activity are different to those involved in inhibiting AGE formation.

Abbreviations Used: AGE: Advanced glycation end-product; DPPH: 2,2-Diphenyl-1-picrylhydrazyl; DM: Diabetes mellitus; ROS: Reactive oxygen species; BSA: Bovine serum albumin; EtOH: Ethanol; EtOAc: Ethyl acetate; ANOVA: Analysis of variance; BA: Brosimum alicastrum; BS: Bunchosia swartziana; CF: Cassia fistula; CN: Cocos nucifera; ET: Ehretia tinifolia; MZ: Manilkara zapota; OC: Ocimum campechianum; PA: Piper auritum; RM: Rhizophora mangle; L: Leaves; S: Stems; R: Roots; T: traditional preparation; I: Inflorescences; W: Water

Ameliorating Effect of Akebia quinata Fruit Extracts on Skin Aging Induced by Advanced Glycation End Products

The accumulation of free radicals and advanced glycation end products (AGEs) in the skin plays a very important role in skin aging. Both are known to interact with each other. Therefore, natural compounds or extracts that possess both antioxidant and antiglycation activities might have great antiageing potential. Akebia quinata fruit extract (AQFE) has been used to treat urinary tract inflammatory disease in traditional Korean and Chinese medicines. In the present study, AQFE was demonstrated to possess antioxidant and antiglycation activity. AQFE protects human dermal fibroblasts (HDFs) from oxidative stress and inhibits cellular senescence induced by oxidative stress. We also found that AQFE inhibits glycation reaction between BSA and glucose. The antiglycation activity of AQFE was dose-dependent. In addition, the antiglycation activity of AQFE was confirmed in a human skin explant model. AQFE reduced CML expression and stimulated fibrillin-1 expression in comparison to the methyglyoxal treatment. In addition, the possibility of the extract as an anti-skin aging agent has also been clinically validated. Our analysis of the crow’s feet wrinkle showed that there was a decrease in the depth of deep furrows in RI treated with AQFE cream over an eight-week period. The overall results suggest that AQFE may work as an anti-skin aging agent by preventing oxidative stress and other complications associated with AGEs formation.

Inhibitory effect of herbal medicines and their trapping abilities against methylglyoxal-derived advanced glycation end-products

Background

Methylglyoxal (MG) is one of the most reactive glycating agents, which result the formation of advanced glycation end-products (AGEs) that have been implicated in the progression of age-related diseases. Inhibition of MG-induced AGE formation is the imperative approach for alleviating diabetic complications. The objective of this study was to investigate the MG-trapping abilities of herbal medicines and their inhibitory activities on the formation of MG-derived AGEs.

Methods

The aqueous extract of herbal medicines was measured for the content of total phenolic compounds and the antioxidant activity by Folin-Ciocalteu assay and the 1,1-diphenyl 2-picrylhydrazyl (DPPH) radical scavenging activity, respectively. The extracts were investigated the MG-trapping ability by high performance liquid chromatography (HPLC). The extracts were incubated with BSA and MG at 37 °C for 1 day. The formation of MG-derived AGEs was measured.

Results

Total phenolic compounds of eleven herbal medicines showed marked variations, ranging from 12.16 to 272.36 mg gallic acid equivalents/g extract. All extracts (1 mg/mL) markedly exhibited the DPPH radical scavenging activity (0.31–73.52 %) and the MG-trapping abilities (13.97–58.97 %). In addition, they also inhibited the formation of MG-derived AGEs by 4.01–79.98 %. The results demonstrated that Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus were the potent inhibitors against the formation of MG-derived AGEs. The positive correlations between the contents of phenolics and % MG trapping (r = 0.912, p < 0.01) and % inhibition of MG-derived AGEs (r = 0.716, p < 0.01) were observed in the study. Furthermore, there was a moderate positive correlation between % MG trapping and % inhibition of MG-derived AGEs (r =0.584, p < 0.01).

Conclusions

Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus could reduce the formation of MG-derived AGEs through their MG-trapping abilities. These findings are relevant for focusing on potential herbal medicines to prevent or ameliorate AGE-mediated diabetic complications.

Contribution of dietary advanced glycation end products (AGE) to circulating AGE: role of dietary fat

The purpose of this pilot study was to determine whether macronutrient content (low-fat v. high-fat diet) influences an indicator of advanced glycation end products (AGE), N(ε) carboxymethyl-lysine (CML), in the context of a 1-d, high-AGE diet. The effect of the diets on inflammatory markers was also assessed. A total of nineteen overweight and obese adults (nine men and ten women) without known disease were recruited to participate in a crossover challenge of a high-fat, high-AGE (HFHA) and low-fat, high-AGE (LFHA) diet. In each phase patients had fasting blood drawn, followed by consumption of a high-fat or low-fat breakfast test meal, then three postprandial blood draws at 1, 2 and 3 h after consuming the test meal. After consuming high-AGE meals for the remainder of the day, participants returned the next day for a follow-up analysis. A different pattern in the 3-h post-meal CML and soluble receptor for AGE response to the two diets was observed (P=0·01 and 0·05, respectively). No change in serum CML was observed following consumption of a LFHA breakfast (535 (25th-75th percentile 451-790) to 495 (25th-75th percentile 391-682) ng/ml; P=0·36), whereas a rise in CML occurred after the HFHA breakfast (463 (25th-75th percentile 428-664) to 578 (25th-75th percentile 474-865) ng/ml; P=0·05). High sensitivity C-reactive protein and high molecular weight adiponectin were not affected by either diet. These findings suggest that dietary CML may not be as important in influencing serum CML as other dietary factors. In addition, acute exposure to dietary CML may not influence inflammation in adults without diabetes or kidney disease. This is contrary to previous findings.

Food Processing and the Mediterranean Diet

The benefits of the Mediterranean diet (MD) for protecting against chronic disorders such as cardiovascular disease are usually attributed to high consumption of certain food groups such as vegetables, and low consumption of other food groups such as meat. The influence of food processing techniques such as food preparation and cooking on the nutrient composition and nutritional value of these foods is not generally taken into consideration. In this narrative review, we consider the mechanistic and epidemiological evidence that food processing influences phytochemicals in selected food groups in the MD (olives, olive oil, vegetables and nuts), and that this influences the protective effects of these foods against chronic diseases associated with inflammation. We also examine how the pro-inflammatory properties of meat consumption can be modified by Mediterranean cuisine. We conclude by discussing whether food processing should be given greater consideration, both when recommending a MD to the consumer and when evaluating its health properties.

Effect of diet-derived advanced glycation end products on inflammation

Advanced glycation end products (AGEs) formed via the Maillard reaction during the thermal processing of food contributes to the flavor, color, and aroma of food. A proportion of food-derived AGEs and their precursors is intestinally absorbed and accumulates within cells and tissues. AGEs have been implicated in the pathogenesis of diabetes-related complications and several chronic diseases via interaction with the receptor for AGEs, which promotes the transcription of genes that control inflammation. The dicarbonyls, highly reactive intermediates of AGE formation, are also generated during food processing and may incite inflammatory responses through 1) the suppression of protective pathways, 2) the incretin axis, 3) the modulation of immune-mediated signaling, and 4) changes in gut microbiota profile and metabolite sensors. In animal models, restriction of dietary AGEs attenuates chronic low-grade inflammation, but current evidence from human studies is less clear. Here, the emerging relationship between excess dietary AGE consumption and inflammation is explored, the utility of dietary AGE restriction as a therapeutic strategy for the attenuation of chronic diseases is discussed, and possible avenues for future investigation are suggested.

The inhibitory effects of γ-glutamylcysteine derivatives from fresh garlic on glycation radical formation

The effects of three reactive peptides, γ-glutamylmethylcysteine (γ-GMC), γ-glutamylpropylcysteine (γ-GPC), and γ-glutamylbutylcysteine (γ-GBC) on the suppression of reactive radicals during the heating of l-lysine in the presence or absence of glucose was studied by electron spin resonance spectroscopy. γ-GMC and γ-GPC were extracted from fresh garlic, and γ-GBC was a synthetic peptide. The results showed that γ-GMC and γ-GPC effectively suppress formation of l-lysine radicals, but that γ-GBC exhibits low radical inhibition. The origin of the short peptides, and the length of their side chain, influenced their surface hydrophobicity and subsequent radical inhibition. In addition, the oxidation of l-lysine was inhibited by the peptides in a similar manner to their inhibition of the Maillard reaction (MR), and their radical inhibition was consistent with similar activity towards N(ε)-(carboxymethyl)lysine (CML).

Pomegranate phenolics inhibit formation of advanced glycation endproducts by scavenging reactive carbonyl species

Advanced Glycation Endproducts (AGEs) are a heterogeneous group of molecules produced from non-enzymatic glycation. Accumulation of AGEs in vivo plays an important role in the pathology of chronic human diseases including type-2 diabetes and Alzheimer's disease. Natural AGEs inhibitors such as the pomegranate (Punica granatum) fruit show great potential for the management of these diseases. Herein, we investigated the in vitro anti-glycation effects of a pomegranate fruit extract (PE), its phenolic constituents [punicalagin (PA), ellagic acid (EA) and gallic acid (GA)], and their in vivo derived colonic metabolites [urolithin A (UA) and urolithin B (UB)]. All of the samples showed anti-glycation activities and PE, PA, and EA were more potent inhibitors than the positive control, aminoguanidine. PE and the purified phenolics also exhibited carbonyl scavenger reactivity. Our study suggests that pomegranate may offer an attractive dietary strategy for the prevention and treatment of AGE-related diseases such as type-2 diabetes and Alzheimer's disease.

Emerging Targets for Therapeutic Development in Diabetes and Its Complications: The RAGE Signaling Pathway

Types 1 and 2 diabetes are on the rise worldwide. Although the treatment of hyperglycemia has benefited from recent advances, aggressive efforts to maintain euglycemia may be fraught with risk, especially in older subjects or in subjects vulnerable to hypoglycemic unawareness. Hence, strategies to prevent and treat the complications of hyperglycemia are essential. In this review we summarize recent updates on the biology of the receptor for advanced glycation endproducts (RAGE) in the pathogenesis of both micro- and macrovascular complications of diabetes, insights from the study of mouse models of obesity and diabetic complications, and from associative studies in human subjects. The study of the mechanisms and consequences of the interaction of the RAGE cytoplasmic domain with the formin, mDia1, in RAGE signal transduction, will be discussed. Lastly, we review the "state-of-the-art" on RAGE-directed therapeutics. Tackling RAGE/mDia1 may identify a novel class of therapeutics preventing diabetes and its complications.

Analysis of glycation induced protein cross-linking inhibitory effects of some antidiabetic plants and spices

Background

Protein cross-linking which occurs towards the latter part of protein glycation is implicated in the development of chronic diabetic complications. Glycation induced protein cross-linking inhibitory effects of nine antidiabetic plants and three spices were evaluated in this study using a novel, simple, electrophoresis based method.

Methods

Methanol extracts of thirteen plants including nine antidiabetic plants and three spices were used. Lysozyme and fructose were incubated at 37 °C in the presence or absence of different concentrations of plant extracts up to 31 days. Standard glycation inhibitor aminoguanidine and other appropriate controls were included. A recently established sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) method was used to detect the products of protein cross-linking in the incubation mixtures.

Results

High molecular weight protein products representing the dimer, trimer and tetramer of lysozyme were detected in the presence of fructose. Among the nine antidiabetic plants, seven showed glycation induced protein cross-linking inhibitory effects namely Ficus racemosa (FR) stem bark, Gymnema sylvestre (GS) leaves, Musa paradisiaca (MP) yam, Phyllanthus debilis (PD) whole plant, Phyllanthus emblica (PE) fruit, Pterocarpus marsupium (PM) latex and Tinospora cordifolia (TC) leaves. Inhibition observed with Coccinia grandis (CG) leaves and Strychnos potatorum (SP) seeds were much low. Leaves of Gymnema lactiferum (GL), the plant without known antidiabetic effects showed the lowest inhibition. All three spices namely Coriandrum sativum (CS) seeds, Cinnamomum zeylanicum (CZ) bark and Syzygium aromaticum (SA) flower buds showed cross-link inhibitory effects with higher effects in CS and SA. PD, PE, PM, CS and SA showed almost complete inhibition on the formation of cross-linking with 25 μg/ml extracts.

Conclusions

Methanol extracts of PD, PE, PM, CS and SA have shown promising inhibitory effects on glycation induced protein cross-linking.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-015-0689-1) contains supplementary material, which is available to authorized users.

Resveratrol protects against methylglyoxal-induced hyperglycemia and pancreatic damage in vivo

Methylglyoxal (MG) has been found to cause inflammation and insulin resistance in vitro and in vivo in recent studies. Resveratrol has been proposed as an effective treatment that helps lower the risk of developing complications of diabetes. To study the significance of glycosylation-related stress on the pathology of diabetes, the effects of resveratrol were examined in a mouse model of diabetes induced by MG. Resveratrol was given via oral gavage in MG-treated mice, and diabetes-related tests and markers were assessed using biochemical and immunohistochemical analyses. Treatment with resveratrol markedly improved blood glucose level from the oral glucose tolerance test and promoted nuclear factor erythroid 2-related factor-2 (Nrf2) phosphorylation (p < 0.05) in the pancreas of MG-treated mice. However, these effects were abolished by retinoic acid, Nrf2 inhibitor, in resveratrol and retinoic acid-treated and MG-induced mice. These findings support that resveratrol may be useful in the treatment of type-2 diabetes by protecting against pancreatic cell dysfunction.

The inhibitory effect of selenium nanoparticles on protein glycation in vitro

Selenium nanoparticles (Se NPs) possess well-known excellent biological activities and low toxicity, and have been employed for numerous applications except as inhibitors to protein glycation. Herein, the present study is carried out to investigate the inhibitory effect of Se NPs on protein glycation in a bovine serum albumin (BSA)/glucose system. By measuring the amount of glucose covalently bound onto BSA, the formation of fructosamine and fluorescent products, it is found that Se NPs can hinder the development of protein glycation in a dose-dependent but time-independent manner under the selected reaction conditions (55 °C, 40 h). And after comparing the increase of inhibitory rate in different stages, it is observed that Se NPs show the greatest inhibitory effect in the early stage, then in the advanced stage, but no effect in the intermediate stage. Fourier transform infrared spectroscopy characterization of Se NPs collected after glycation and determination of ·OH influence and glyoxal formation show that the mechanism for the inhibitory efficacy of Se NPs is related to their strong competitive activity against available amino groups in proteins, their great scavenging activity on reactive oxygen species and their inhibitory effect on α-dicarbonyl compounds' formation. In addition, it is proved that Se NPs protect proteins from structural modifications in the system and they do not exhibit significant cytotoxicity towards BV-2 and BRL-3A cells at low concentrations (10 and 50 μg mL(-1)). Consequently, Se NPs may be suitable for further in vivo studies as novel anti-glycation agents.

Aqueous extract of some indigenous medicinal plants inhibits glycation at multiple stages and protects erythrocytes from oxidative damage-an in vitro study

Azadirachta indica, Emblica officinalis, Syzygium cumini and Terminalia bellirica are common in Indian system of traditional medicine for the prevention of diabetes and its complications. The aim of the present study was to comprehensively and comparatively investigate the antiglycation potential of these plant extracts at multiple stages and their possible protective effect against glycated albumin mediated toxicity to erythrocytes. Antiglycation activities of these plant extracts was measured by co-incubation of plant extract with bovine serum albumin-fructose glycation model. The multistage glycation markers- fructosamines (early stage), protein carbonyls (intermediate stage) and AGEs (late stage) are investigated along with measurement of thiols and β aggregation of albumin using amyloid-specific dyes-Congo red and Th T. Protection of erythrocytes from glycated albumin induced toxicity by these plant extracts was assessed by measuring erythrocytes hemolysis, lipid peroxidation, reduced glutathione and intracellular antioxidant capacity. Total phenolics, reducing power and antioxidant activities of the plant extracts were also measured. In vitro glycation assays showed that plant extracts exerted site specific inhibitory effects at multiple stages, with T. bellirica showing maximum attenuation. In erythrocytes, along with the retardation of glycated albumin induced hemolysis and lipid-peroxidation, T. bellirica considerably maintained cellular antioxidant potential. Significant positive correlations were observed between erythrocyte protection parameters with total phenolics. These plant extracts especially T. bellirica prevents glycation induced albumin modifications and subsequent toxicity to erythrocytes which might offer additional protection against diabetic vascular complications.

A novel PPARgamma agonist monascin's potential application in diabetes prevention

Edible fungi of the Monascus species have been used as traditional Chinese medicine in eastern Asia for several centuries. Monascus-fermented products possess a number of functional secondary metabolites, including the anti-inflammatory pigments monascin and ankaflavin. Monascin has been shown to prevent or ameliorate several conditions, including hypercholesterolemia, hyperlipidemia, diabetes, and obesity. Recently, monascin has been shown to improve hyperglycemia, attenuate oxidative stress, inhibit insulin resistance, and suppress inflammatory cytokine production. In our recent study, we have found that monascin is a peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist. The PPARgamma agonist activity had been investigated and its exerted benefits are inhibition of inflammation in methylglyoxal (MG)-treated rats, prevention of pancreas impairment causing advanced glycation endproducts (AGEs), promotion of insulin expression in vivo and in vitro, and attenuated carboxymethyllysine (CML)-induced hepatic stellate cell (HSC) activation in the past several years. Moreover, our studies also demonstrated that monascin also activated nuclear factor-erythroid 2-related factor 2 (Nrf2) in pancreatic RIN-m5F cell line thereby invading methylglyoxal induced pancreas dysfunction. In this review, we focus on the chemo-preventive properties of monascin against metabolic syndrome through PPARgamma and Nrf2 pathways.

Anti-glycation activities of phenolic constituents from Silybum marianum (Milk Thistle) flower in vitro and on human explants

Glycation is an ageing reaction of naturally occurring sugars with dermal proteins, with clinical signs appearing in vivo around age 30, and increasing steadily/regularly with age. The suppleness of the dermis is affected by the formation of bridges between proteins and sugars (Maillard's reaction). The accumulation of advanced glycation end products (AGEs) in skin plays a very important role in skin ageing. Therefore, natural compounds or extracts that possess antiglycation activities may have great anti-ageing potential. In the present study, Silybum marianum flower extract (SMFE) was demonstrated to possess antiglycation activity. We found that SMFE inhibits glycation reaction between BSA and glucose. In addition, antiglycation activity of SMFE was confirmed in a human skin explants model. SMFE reduced Nε-(carboxymethyl) lysine (CML) expression, whereas SMFE stimulated fibrillin-1 expression compared to treatment with methyglyoxal. An active ingredient contributing to the observed activities was identified as silibinin. The antiglycation activity of silibinin was dose-dependent. The beneficial effects of silibinin may be applied to prevention or management of AGE-mediated pathologies, targeting in a pleiotropic and complementary way the biochemical and cellular bases of skin aging.

Inhibitory effect of Clitoria ternatea flower petal extract on fructose-induced protein glycation and oxidation-dependent damages to albumin in vitro

BACKGROUND

The accumulation of advanced glycation end products (AGEs) in body tissue has been implicated in the progression of age-related diseases. Inhibition of AGE formation is the imperative approach for alleviating diabetic complications. Clitoria ternatea extract (CTE) has been demonstrated to possess anti-diabetic activity. However, there is no scientific evidence supporting its anti-glycation activity. The objective of this study was to determine the inhibitory effect of CTE on fructose-induced formation of AGEs and protein oxidation. Antioxidant activity of CTE was also assessed by various methods.

METHODS

The aqueous extract of CTE (0.25-1.00 mg/ml) was measured for the content of total phenolic compounds, flavonoid, and anthocyanin by Folin-Ciocalteu assay, AlCl3 colorimetric method, and pH differential method, respectively. The various concentrations of CTE were incubated with BSA and fructose at 37°C for 28 days. The formation of fluorescent AGEs, the level of fructosamine, protein carbonyl content, and thiol group were measured. The in vitro antioxidant activity was measured by the 1,1-diphenyl 2-picrylhydrazyl (DPPH) scavenging activity, trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant power (FRAP), hydroxyl radical scavenging activity (HRSA), superoxide radical scavenging activity (SRSA), and ferrous ion chelating power (FICP).

RESULTS

The results demonstrated that the content of total phenolics, flavonoids and total anthocyanins in CTE was 53 ± 0.34 mg gallic acid equivalents/g dried extract, 11.2 ± 0.33 mg catechin equivalents/g dried extract, and 1.46 ± 0.04 mg cyanidin-3-glucoside equivalents/g dried extract, respectively. Moreover, CTE (0.25-1.00 mg/ml) significantly inhibited the formation of AGEs in a concentration-dependent manner. CTE also markedly reduced the levels of fructosamine and the oxidation of protein by decreasing protein carbonyl content and preventing free thiol depletion. In the DPPH radical scavenging activity and SRSA, CTE had the IC50 values of 0.47 ± 0.01 mg/ml and 0.58 ± 0.04 mg/ml. Furthermore, the FRAP and TEAC values of CTE were 0.38 ± 0.01 mmol FeSO4 equivalents/mg dried extract and 0.17 ± 0.01 mg trolox equivalents/mg dried extract. However, CTE showed weak scavenging activity on hydroxyl radical and a weak antioxidant iron chelator.

CONCLUSIONS

The results showed that CTE has strong antiglycation and antioxidant properties and might have therapeutic potentials in the prevention of AGE-mediated diabetic complications.

Protective effects of cyanidin-3-rutinoside against monosaccharides-induced protein glycation and oxidation

Cyanidin-3-rutinoside (C3R), a naturally occurring anthocyanin, is present in various fruits and vegetables as a colorant. C3R has been well characterized and demonstrated a number of biological activities attributed to its antioxidant properties. The present study compared the effectiveness of C3R against monosaccharide-induced protein glycation and oxidation in vitro using bovine serum albumin (BSA).The results demonstrated that C3R (0.125-1.00 mM) inhibited the formation of fluorescent AGEs in ribose-glycated BSA (2-52%), fructose-glycated BSA (81-93%), glucose-glycated BSA (30-74%) and galactose-glycated BSA (6-79%).Correspondingly, C3R (1.00 mM) decreased the level of N(ɛ)-(carboxymethyl) lysine (56-86%) in monosaccharide-induced glycation in BSA. C3R also reduced the level of fructosamine, β-amyloid cross structure, protein carbonyl content as well as the depletion of thiol in BSA/monosaccharide system. In summary, C3R might offer a new promising antiglycation agent for the prevention of diabetic complications by inhibiting AGE formation and oxidation-dependent protein damage.

Scopoletin protects against methylglyoxal-induced hyperglycemia and insulin resistance mediated by suppression of advanced glycation endproducts (AGEs) generation and anti-glycation

Recently, several types of foods and drinks, including coffee, cream, and cake, have been found to result in high methylglyoxal (MG) levels in the plasma, thus causing both nutritional and health concerns. MG can be metabolized by phase-II enzymes in liver through the positive regulation of nuclear factor-erythroid 2-related factor 2 (Nrf2). In this study, we investigated the ability of scopoletin (SP) to protect against MG-induced hyperglycemia and insulin resistance. Recently, SP was shown to be a peroxisome proliferator-activated receptor-γ activator to elevate insulin sensitivity. We investigated the effects of oral administration of SP on the metabolic, biochemical, and molecular abnormalities characteristic of type 2 diabetes in MG-treated Wistar rats to understand the potential mechanism of scopoletin for diabetes protection. Our results suggested that SP activated Nrf2 by Ser40 phosphorylation, resulting in the metabolism of MG into d-lactic acid and the inhibition of AGEs generation, which reduced the accumulation of AGEs in the livers of MG-induced rats. In this manner, SP improved the results of the oral glucose tolerance test and dyslipidemia. Moreover, SP also increased the plasma translocation of glucose transporter-2 and promoted Akt phosphorylation caused by insulin treatment in MG-treated FL83B hepatocytes. In contrast, SP effectively suppressed protein tyrosine phosphatase 1B (PTP1B) expression, thereby alleviating insulin resistance. These findings suggest that SP acts as an anti-glycation and anti-diabetic agent, and thus has therapeutic potential for the prevention of diabetes.

Current perspectives on the health risks associated with the consumption of advanced glycation end products: recommendations for dietary management

Advanced glycation end products (AGEs) constitute a complex group of compounds produced endogenously during the aging process and under conditions of hyperglycemia and oxidative stress. AGEs also have an emerging exogenous origin. Cigarette smoke and diet are the two main exogenous sources of AGEs (glycotoxins). Modern Western diets are rich in AGEs which have been implicated in the pathogenesis of several metabolic and degenerative disorders. Accumulating evidence underlies the beneficial effect of the dietary restriction of AGEs not only in animal studies but also in patients with diabetic complications and metabolic diseases. This article reviews the evidence linking dietary glycotoxins to several disorders from diabetic complications and renal failure to liver dysfunction, female reproduction, eye and cognitive disorders as well as cancer. Furthermore, strategies for AGE reduction are discussed with a focus on dietary modification.

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.

Mechanism of reactive carbonyl species trapping by hydroxytyrosol under simulated physiological conditions

This investigation reveals that hydroxytyrosol (HT) could compete with lysine, arginine and histidine to bind methylglyoxal (MGO) and reducing the formation of advanced glycation end products. Kinetic of the degradation of HT in presence/absence of MGO under simulated physiological conditions is monitored by HPLC coupled to a QTOF spectrometer. HT should previously be oxidized to DOPAC (3,4-dihydroxyphenylacetic acid) which reacts with MGO by electrophilic aromatic substitution of the ortho-diphenyl ring. DOPAC was detected as the major degradation product of HT under simulated physiological conditions. Ortho-hydroxyl groups are necessary to promote the nucleophilic addition of MGO by HT and related compounds. The formation of four adducts were described by mass spectrometry, but monoDOPAC-monoMGO adduct (C11H12O6) was predominant. Results suggest that HT and its degradation product DOPAC could have a relevant role in preventing the formation of advanced glycation end products and therefore potentially mitigate the diabetic complications.

Effects of different products of peach (Prunus persica L. Batsch) from a variety developed in southern Brazil on oxidative stress and inflammatory parameters in vitro and ex vivo

Antioxidant, anti-glycation and anti-inflammatory activities of fresh and conserved peach fruits (Prunus persica L. Batsch) were compared. Fresh peach pulps, peels, preserve peach pulps and the preserve syrup were prepared at equal concentrations. Rat liver, kidney and brain cortex tissue slices were pre-incubated with peach samples, subjected to oxidative stress with FeSO₄ and hydrogen peroxide. Fresh peach pulps and peel conferred higher protection against cytotoxicity and oxidative stress than preserve peach pulps in most tissues. Release of tumor necrosis factor-α and interleukin-1β was also significantly decreased by Fresh peach pulps and peel, followed by preserve peach pulps. Total phenolic determination and HPLC analysis of carotenoids showed that the content of secondary metabolites in Fresh peach pulps and peel is significantly higher than in preserve peach pulps, while the syrup had only small or trace amounts of these compounds. Fresh peach pulps and Peel demonstrated high antioxidant and anti-inflammatory effects preventing against induced damage.

Glycation is regulated by isoflavones

The effect of soy isoflavones on the Maillard reaction (MR) was investigated. Model systems composed of the soy protein glycinin (10 mg mL(-1)) and fructose (40 mg mL(-1)) under basic pH (∼12) conditions were employed for testing the anti-glycative effect of the major antioxidant soy isoflavones (genistin and genistein at 10 μg mL(-1)) and a soy isoflavone-rich extract. The contents of total phenols (TPCs) and total flavonoids (TFCs) of the isoflavone-rich extract were determined. Glycinin was pre-incubated with isoflavones for 1 h and 16 h at 60 °C prior to MR. The progress of MR was estimated by analysis of free amino groups by OPA assay; carbohydrate covalently bound to the protein backbone using phenol-sulfuric acid assay, protein-bound N(ε)-(carboxymethyl)lysine (CML) by UPLC-MS and spectral analysis of fluorescent protein-bound AGEs. Genistin (10 μg mL(-1), 23 μM) and its aglycone genistein (10 μg mL(-1), 37 μM) did not prevent protein glycation (p > 0.05). The soy isoflavone-rich extract containing 2.5 mg mL(-1) of TFC efficiently decreased the amount of carbohydrate bound to the protein skeleton (20%) (p < 0.05) and formation of advanced glycation end products (AGEs) (>80%) (p < 0.05). The anti-glycative mechanism of isoflavones may be related to its conjugation to glycation sites of the protein structure (free amino groups), their antioxidant character and trapping of dicarbonyl intermediates. Extracts based on mixtures of isoflavones may be useful for producing glycated conjugates avoiding the substantial formation of AGEs bound to protein.

Protein glycation inhibitory activity and antioxidant capacity of clove extract

Syzygium aromaticum (L.) (clove) is one of the most widely cultivated spices in many tropical countries. The aim of this study was to determine the phytochemical content, the antioxidant properties and the antiglycation properties of aqueous extract of clove against fructose-mediated protein glycation and oxidation. The result showed that the content of total phenolics and flavonoids in clove extract was 239.58 ± 0.70 mg gallic acid equivalents/g dried extract and 65.67 ± 0.01 mg catechin equivalents/g dried extract, respectively. In addition, clove exhibited antioxidant properties including DPPH radical scavenging activity (IC50 = 0.29 ± 0.01 mg/ml), Trolox equivalent antioxidant capacity (4.69 ± 0.03 μmol Trolox equivalents/mg dried extract), ferric reducing antioxidant power (20.55 ± 0.11 μmol ascorbic acid equivalents/mg dried extract), Oxygen radical absorbance capacity (31.12 ± 0.21 μmol Trolox equivalents/mg dried extract), hydroxyl radical scavenging activity (0.15 ± 0.04 mg Trolox equivalents/mg dried extract), and superoxide radical scavenging activity (18.82 ± 0.50 mg Trolox equivalents/mg dried extract). The aqueous extract of clove (0.25-1.00 mg/ml) significantly inhibited the formation of fluorescent advanced glycation end products (AGEs) and non-fluorescent AGEs (N(ɛ)-(carboxymethyl) lysine (CML)) in glycated BSA during 4 weeks of incubation. The extract also markedly prevented oxidation-induced protein damage by decreasing protein carbonyl formation and protecting against the loss of protein thiol group. These results clearly demonstrated that a polyphenol enriched clove extract, owing to its antioxidant, was capable to inhibit the formation of AGEs and protein glycation. The findings might lead to the possibility of using the clove extract for targeting diabetic complications.

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.