Polyphenols with antiglycation activity and mechanisms of action: A review of recent findings

Anacardium humile St. Hil as a novel source of antioxidant, antiglycation and α-amylase inhibitors molecules with potential for management of oxidative stress and diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

The substantial increase in diabetes cases worldwide has been a major public health problem, and the use of medicinal plants can be considered an interesting alternative to control the disease and its complications. Anacardium humile St. Hill. (Anacardiaceae) is a typical plant from the Brazilian savanna, popularly known for its antidiarrheal, expectorant, antidiabetic and anti-inflammatory properties, however, few studies have fully described its biological properties. This study aimed to investigate in vitro and ex vivo the antioxidant and antiglycation potential of A. humile ethanolic extract, its organic fractions and three isolated molecules (quercetin, catechin and gallic acid), their capacity to inhibit the glycolytic enzyme α-amylase, as well as their cytotoxic effects against RAW264.7 macrophages.

MATERIAL AND METHODS

The ethanolic extract of A. humile, its organic fractions and three isolated molecules (catechin, quercetin and gallic acid) were tested for their antioxidant (ORAC, FRAP and DPPH) and antiglycation (BSA/Fructose, BSA/Methylglyoxal, Arginine/Methylglyoxal and Lysine/Methylglyoxal) capacities, and also for its potential to inhibit the enzyme α-amylase. Additionally, bioactive compounds present in the A. humile leaves fractions were elucidated by an HPLC-ESIMS/MS analysis.

RESULTS

The analysis showed relevant antioxidant activity of DCM (1264.85 ± 76.90 μM Trolox eq/g ORAC; 216.71 ± 1.04 μM Trolox eq/g FRAP and 3.03 ± 0.08 IC₅₀ μg/mL IC₅₀ DPPH) and EtOAc (1300.11 ± 33.04 ORAC, 236.21 ± 23.86 FRAP and 3.03 ± 0.14 μg/mL IC₅₀ DPPH) fractions and also of the isolated molecules, mainly gallic acid (1291.19 ± 8.41 μM Trolox eq/g ORAC, 1103.52 ± 31.48 μM Trolox eq/g FRAP and 0.78 ± 0.11 μg/mL IC₅₀ DPPH). Concerning the antiglycation activity, all samples inhibited over 88% in the BSA-FRU method. In the BSA-MGO and ARG-MGO methods, the Hex, DCM, EtOAc fractions and the isolated molecule catechin stood out. However, in the LYS-MGO model, only the isolated molecules showed significant results. In α-amylase assay, all fractions, for exception Hex, presented notable inhibition capacity with low IC₅₀ values, especially DCM, EtOAc, ButOH and H₂O (IC₅₀ 0.56 ± 0.10, 0.84 ± 0.01, 0.74 ± 0.03 and 0.79 ± 0.06 μg/mL, respectively). Tests using hepatic tissue showed a notorious capacity of the DCM, AcOEt and ButOH fractions, as well as of the isolated molecules to inhibit lipid peroxidation and ROS production, and also to preserve thiol groups. Molecules of great antioxidant potential were found in our samples, such as kaempferol, quercetin, catechin, gallic acid and luteolin.

CONCLUSION

A. humile extract and its organic fractions showed promising antioxidant and antiglycation potential and a prominent capacity to inhibit the α-amylase enzyme. Hence, this study presents new results and stimulates further research to elucidate the biological properties of A. humile and its capacity to manage DM and its complications.

Investigation of Olea ferruginea Roylebark extracts for potential in vitroantidiabetic and anticancer effects

This study was conducted to investigate the physicochemical, phytochemical, in vitro antidiabetic and anticancer potential of Olea ferruginea R bark. After extraction using Soxhlet, in vitro antidiabetic and cytotoxic activity on human hepatocellular carcinoma (HepG2) cells was assessed by nonenzymatic glycosylation of hemoglobin assay, alpha-amylase inhibition assay, glucose uptake by yeast cells, and 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay, respectively, and gene expression via real-time polymerase chain reaction. Primary and secondary metabolites were present in the extractants; polyphenols (35.61 ± 0.03) and flavonoids (64.33 ± 0.35 ) in the chloroform; and polysaccharides in the ethanol (268.75 ± 0.34), and glycosaponins (78.01 ± 0.07) in the methanol. The chloroform extract exhibited maximum antidiabetic potential, showing inhibition of nonenzymatic glycosylation of hemoglobin (65%), and alpha-amylase inhibition (32%) with maximum percent glucose uptake by the ethanol extract (78%). Only the ethanol extract had dose-dependent cytotoxic potential against the HepG2 cells. After 24-h exposure to the ethanol-extract, the expression of protein kinase B (Akt) remained unchanged, while the expression of B-cell lymphoma 2 (BCL2) and BCL2 associated X (BAX) changed significantly. After 48-h exposure, the expression of Akt decreased significantly, while that of BCL2 and BAX increased significantly. Olea ferruginea R bark possessed in vitro antidiabetic potential and anticancer/cytotoxic effects, attributable to the decline in the prosurvival signals of the Akt signaling pathway.

The Prophylactic Activity of Punica granatum L. mesocarp Protects Preadipocytes against Ribosylated BSA-Induced Toxicity

OBJECTIVE

It was aimed at comparing the glycating capacities of glucose and ribose in bovine serum albumin (BSA) and anti-glycation activity of pomegranate mesocarp extract (PME). The protective mechanism of PME against ribosylated BSA (BSA_RIB)-induced toxicity was also investigated.

METHODS

BSA was incubated with glucose or ribose in the presence or absence of PME for 15 days. In preadipocytes pretreated with PME, cell viability, ROS production, lipid peroxidation and mitochondrial membrane potential were investigated following 1, 6, 12, 18 and 24 h exposure to BSA_RIB. Nuclear translocation of NFκB was assessed at 1 h and 24 h of BSA_RIB insult. Accumulation of oxidized proteins, activities of intrinsic antioxidant enzymes and IL-6 secretion were also determined after 24 h exposure to BSA_RIB.

RESULTS

Ribose was a harsher glycating agent as compared to glucose and PME showed strong anti-glycation activity by suppressing (P < 0.05) the increase in levels of fluorescent AGEs, Amadori products, protein carbonyl and advanced oxidation protein products (AOPP). In preadipocytes, BSA_RIB potentiated pro-apoptotic activity by inhibiting the nuclear translocation of NFκB. BSA_RIB induced a time dependent decrease in cell viability, which was significantly suppressed (P < 0.05) by PME. The extract also significantly reduced (P < 0.05) the time dependent increase in ROS level and associated lipid peroxidation as well as loss in mitochondrial membrane potential caused by BSA_RIB. PME also counteracted the BSA_RIB-induced accumulation of oxidized proteins, decrease in intrinsic antioxidant activity and IL-6 over-secretion.

CONCLUSIONS

PME showed anti-glycation activity and afforded protection against BSA_RIB-induced toxicity, oxidative stress and inflammation in preadipocytes.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

Recent Advances in Histone Glycation: Emerging role in Diabetes and Cancer

Ever increasing information on genome and proteome has offered fascinating details and new opportunities to understand the molecular biology. It is now known that histone proteins surrounding the DNA play a crucial role in the chromatin structure and function. Histones undergo a plethora of post-translational enzymatic modifications that influence nucleosome dynamics and affect DNA activity. Earlier research offered insights into the enzymatic modifications of histones; however attention has been diverted to histone modifications induced by by-products of metabolism without enzymatic engagement in the last decade. Non enzymatic modifications of histones are believed to be crucial for epigenetic landscape, cellular fate and for role in human diseases. Glycation of histone proteins constitutes the major non enzymatic modifications of nuclear proteins that have implications in diabetes and cancer. It has emerged that glycation damages nuclear proteins, modifies amino acids of histones at crucial locations, generates adducts affecting histone chromatin interaction, develops neo-epitopes inducing specific immune response and impacts cell function. Presence of circulating antibodies against glycated histone proteins in diabetes and cancer has shown immunological implications with diagnostic relevance. These crucial details make histone glycation an attractive focus for investigators. This review article, therefore, makes an attempt to exclusively summarize the recent researches in histone glycation, its impact on structural integrity of chromatin and elaborates on their role in diabetes and cancer. The work offers insights for future scientists who investigate the link between metabolism, bio-molecular structures, glycobiology, histone-DNA interactions in relation to diseases in humans.

Protective effects of three structurally similar polyphenolic compounds against oxidative damage and their binding properties to human serum albumin

Brazilin (Bra), hematoxylin (Hto) and hematein (Hte) are structurally similar polyphenols having rich biological activities, but their antioxidant ability has not been well studied. Here, their protective ability against human serum albumin (HSA) oxidative degradation were investigated using 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (AAPH), NaClO and Fenton like reactions methods. The results indicated that polyphenols inhibited the oxidative injuries of HSA in the order: Hto > Bra > Hte. Additionally, the biological effects of polyphenols were mostly influenced by their binding to protein. Therefore, the structure-affinity relationships of polyphenols binding to HSA were also explored. Fluorescence experiments indicated that polyphenols bound to HSA through static quenching mechanism. Furthermore, some conformational changes of HSA could be observed in the presence of polyphenols. Altogether, molecular structure of polyphenols played a significant role in their protective effect against HSA oxidative damage and binding ability, which provided fundamental insights into their application as health care foods.

Polyphenols as a versatile component in tissue engineering

The fabrication of functional tissue or organs substitutes has always been the pursuit of goals in the field of tissue engineering. But even biocompatible tissue-engineered scaffolds still suffer from immune rejection, subsequent long-term oxidative stress and inflammation, which can delay normal tissue repair and regeneration. As a well-known natural antioxidant, polyphenols have been widely used in tissue engineering in recent years. The introduced polyphenols not only reduce the damage of oxidative stress to normal tissues, but show specific affinity to functional molecules, such as receptors, enzyme, transcription and transduction factors, etc. Therefore, polyphenols can promote the recovery process of damaged tissues by both regulating tissue microenvironment and participating in cell events, which embody specifically in antioxidant, anti-inflammatory, antibacterial and growth-promoting properties. In addition, based on its hydrophilic and hydrophobic moieties, polyphenols have been widely used to improve the mechanical properties and anti-degradation properties of tissue engineering scaffolds. In this review, the research advances of tissue engineering scaffolds containing polyphenols is discussed systematically from the aspects of action mechanism, introduction method and regulation effect of polyphenols, in order to provide references for the rational design of polyphenol-related functional scaffolds.

The effect of Kappaphycus alvarezii fraction on plasma glucose, Advanced Glycation End-products formation, and renal RAGE gene expression

BACKGROUND

Kappaphycus alvarezii (Doty) Doty ex P.C.Silva is a red algae with antioxidant and antiglycation activities. Algae still have not been widely used for treating diabetes, especially to prevent complications. The purpose of this study was to examine the effect of active fractions from Kappaphycus alvarezii on plasma glucose level, glycation process and renal RAGE gene expression.

METHODS

This study used bioassay-guided fractionation, consisting of three stages: extraction, partition, and fractionation. These processes were monitored with Thin Layer Chromatography and the BSA-Glucose method to select the best extract with antiglycation activity (calculated as the percentage of inhibition and IC50). The selected active fraction from four fractions was further used for in vivo study, which was conducted with hyperglycemic Wistar male rats. Plasma glucose level was measured using GOD-PAP methods, while plasma glycated albumin (GA) and Nε- (carboxymethyl) lysine (CML) levels were measured using ELISA. Renal RAGE gene expression was analyzed using qPCR.

RESULTS

Fraction II was selected as the active fraction of Kappaphycus alvarezii showing antiglycation activity with the highest percentage of inhibition and the lowest IC50. This fraction significantly reduced plasma GA and CML levels, but it did not significantly reduce plasma glucose level. Furthermore, renal RAGE gene expression was lower in the diabetic rat group treated with this active fraction compared to the untreated group.

CONCLUSIONS

This study successfully identified an active fraction of Kappaphycus alvarezii with antiglycation activity to reduce plasma GA and CML levels as well as renal RAGE gene expression. Therefore, this fraction could be developed as a potential candidate for treating diabetes.

Attenuation of protein glycation by functional polyphenolics of dragon fruit (Hylocereus polyrhizus); an in vitro and in silico evaluation

Chronic hyperglycemia and oxidative stress promote non-enzymatic glycation that leads to the production of advanced glycation end products (AGEs). AGEs casue significant damage to physiological proteins which result in several complications. The scenario also corresponds to the chronic consumption of a diet rich in AGEs. Despite understanding these mechanisms at the molecular level, the discovery of new drugs for these complications is under progress. Natural compounds might have great therapeutic potential for treating glycative consequences. In view of this, the study aimed to evaluate fruit extracts of Hylocereus polyrhizus towards determining its phenolics and flavonoid contents, as well as assessing it's in vitro antiglycative potential through the use of multistage glycation markers (early, intermediate and end stage products of β-aggregation) in sugar-protein model. In vitro hypoglycemic activity of H. polyrhizus extracts was evaluated through α-amylase and α glucosidase inhibitory activities. In vitro antioxidant potential of the fruit extracts was also examined against different free radical types including DPPH and ABTS. Among the different in vitro assays performed, methanolic and acetone extracts of the fruit, with higher phenolics and flavonoid content, have exerted significant antiglycation and antioxidant activities than other extracts namely aqueous, ethanol, hydro-ethanol, hydro-methanol, and petroleum ether. Ultra-Performance Liquid Chromatography coupled with Electrospray Ionization Mass Spectrometry (UPLC-ESI-MS/MS) analysis was employed to identify active polyphenolics that may be responsible for the antiglycative potential of H. polyrhizus. The analysis revealed some high-profile compounds that have well documented for their therapeutic benefits. Additionally, In silico analysis also showed the possible connection between identified compounds and mechanisms of action. 4- Prenylresveratrol, Vicenin, and Luteolin had observed as effectively interact with target protein in molecular docking analysis. This suggests H. polyrhizus as a good source of anti-glycation and antioxidants that may have potential applications for the treatment and prevention of glycation associated diabetic and aging complications.

In Vitro Antioxidant and Anti-Glycation Activity of Resveratrol and Its Novel Triester with Trolox

Resveratrol (RSV) is well known for its many beneficial activities, but its unfavorable physicochemical properties impair its effectiveness after systemic and topical administration; thus, several strategies have been investigated to improve RSV efficacy. With this aim, in this work, we synthesized a novel RSV triester with trolox, an analogue of vitamin E with strong antioxidant activity. The new RSV derivative (RSVTR) was assayed in vitro to evaluate its antioxidant and anti-glycation activity compared to RSV. RSVTR chemical stability was assessed at pH 2.0, 6.8, and 7.2 and different storage temperatures (5 °C, 22 °C, and 37 °C). An influence of pH stronger than that of temperature on RSVTR half-life values was pointed out, and RSVTR greatest stability was observed at pH 7.2 and 5 °C. RSVTR showed a lower antioxidant ability compared to RSV (determined by the oxygen radical absorbance capacity assay) while its anti-glycation activity (evaluated using the Maillard reaction) was significantly greater than that of RSV. The improved ability to inhibit the glycation process was attributed to a better interaction of RSVTR with albumin owing to its increased topological polar surface area value and H-bond acceptor number compared to RSV. Therefore, RSVTR could be regarded as a promising anti-glycation agent worthy of further investigations.

Methylglyoxal-hydroimidazolones (MG-Hs) instead of Nɛ-(carboxymethyl)-l-lysine (CML) is the major advanced glycation end-product during drying process in black tea

This study was to examine the formation of advanced glycation end-products (AGEs) in black tea during drying process at 90, 120, and 150 °C for 1 h. Nine AGEs including Nɛ-(carboxyethyl)-l-lysine (CEL), Nɛ-(carboxymethyl)-l-lysine (CML), three isomers of methylglyoxal-hydroimidazolones (MG-Hs), three isomers of glyoxal-hydroimidazolones (GO-Hs), and argpyrimidine were quantified by using HPLC-MS/MS with isotope-labelled internal standard. Results showed that each AGE during the drying process of 150 °C was significantly higher (p < 0.05) than at 90 and 120 °C, and argpyrimidine was only found in the treatment of 150 °C. MG-H1/3 was first quantified as the major AGE during drying at 120-150 °C, the content respectively reached to (39.66 ± 2.61) μg/g and (58.88 ± 1.76) μg/g after 1 h drying, where CML content only had (19.86 ± 1.02) μg/g and (23.71 ± 1.40) μg/g. This study indicated that arginine derived-AGEs are the key components of black tea AGEs.

Investigation of the Phytochemical Composition, Antioxidant Activity, and Methylglyoxal Trapping Effect of Galega officinalis L. Herb In Vitro

Galega officinalis L. has been known for centuries as an herbal medicine used to alleviate the symptoms of diabetes, but its comprehensive chemical composition and pharmacological activity are still insufficiently known. The current study involved the qualitative and quantitative phytochemical analysis and in vitro evaluation of the antioxidative and methylglyoxal (MGO) trapping properties of galega herb. Ultra high-performance liquid chromatography coupled with both the electrospray ionization mass spectrometer and diode-array detector (UHPLC-ESI-MS and UHPLC-DAD) were used to investigate the composition and evaluate the anti-MGO capability of extracts and their components. Hot water and aqueous methanol extracts, as well as individual compounds representing phytochemical groups, were also assessed for antioxidant activity using DPPH (2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) and ABTS (2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) assays. Quercetin and metformin were used as a positive control. We confirmed the presence of tricyclic quinazoline alkaloids, guanidines, flavonoids, and hydroxycinnamic acids (HCAs) in galega extracts. The polyphenolic fraction was dominated by mono-, di-, and triglycosylated flavonols, as well as monocaffeoylhexaric acids. The in vitro tests indicated which G. officinalis components exhibit beneficial antioxidative and MGO trapping effects. For galega extracts, flavonols, and HCAs, a potent antiradical activity was observed. The ability to trap MGO was noted for guanidines and flavonoids, whereas HCA esters and quinazoline alkaloids were ineffective. The formation of mono-MGO adducts of galegine, hydroxygalegine, and rutin in the examined water infusion was observed.

Coriandrum sativum improve neuronal function via inhibition of oxidative/nitrosative stress and TNF-α in diabetic neuropathic rats

ETHNOPHRAMACOLOGICAL RELEVANCE

Coriandrum sativum L. is traditionally acknowledged for its use in inflammatory disorders, altered blood lipid levels, respiratory and digestive problems.

AIM OF THE STUDY

The present study investigates possible role of hydro-alcoholic extract of C. sativum (CHA) seeds in the attenuation of indices of diabetic peripheral neuropathy (DPN).

MATERIALS AND METHODS

Phytochemical analysis was carried out by employing chromatographic, spectroscopic as well as spectrometric techniques. Diabetes was induced by a single i.p. injection of freshly prepared STZ (65 mg/kg). The indexed markers of DPN, i.e., thermal and mechanical hyperalgesia were found to be prominent on the 60th day of STZ administration. Administration of CHA (100, 200, and 400 mg/kg, p.o.) for 30 days was started on the substantiation of DPN onset. Molecular docking study was performed by targeting TNF-α.

RESULTS

Phytochemical analysis revealed the presence of flavonoids, terpenoids, and phenolic acids. Oral administration of CHA considerably attenuated hyperglycemia and decreased pain threshold in diabetic rats as well as modulated oxidative-nitrosative stress. Docking study suggested good affinity of flavonoids when docked into the binding site of TNF-α.

CONCLUSION

In conclusion, using STZ model, it was successfully predicted that CHA might be beneficial in diabetes-induced neuropathic pain by inhibiting oxidative/nitrosative stress and inflammatory cytokine.

Pathophysiology, Clinical Characteristics of Diabetic Cardiomyopathy: Therapeutic Potential of Natural Polyphenols

Diabetic cardiomyopathy (DCM) is an outcome of disturbances in metabolic activities through oxidative stress, local inflammation, and fibrosis, as well as a prime cause of fatality worldwide. Cardiovascular disorders in diabetic individuals have become a challenge in diagnosis and formulation of treatment prototype. It is necessary to have a better understanding of cellular pathophysiology that reveal the therapeutic targets and prevent the progression of cardiovascular diseases due to hyperglycemia. Critical changes in levels of collagen and integrin have been observed in the extracellular matrix of heart, which was responsible for cardiac remodeling in diabetic patients. This review explored the understanding of the mechanisms of how the phytochemicals provide cardioprotection under diabetes along with the caveats and provide future perspectives on these agents as prototypes for the development of drugs for managing DCM. Thus, here we summarized the effect of various plant extracts and natural polyphenols tested in preclinical and cell culture models of diabetic cardiomyopathy. Further, the potential use of selected polyphenols that improved the therapeutic efficacy against diabetic cardiomyopathy is also illustrated.

Antioxidant and Antiglycation Activities of Syzygium paniculatum Gaertn and Inhibition of Digestive Enzymes Relevant to Type 2 Diabetes Mellitus

Advanced glycation end-products (AGEs) may be a contributing factor in the development of diabetes-specific vascular pathologies that affect the retina, glomerulus and peripheral nerves. In this study, Australian native food plant species Syzygium paniculatum was investigated for activities relevant to Type 2 diabetes mellitus including inhibition of α-amylase, α-glucosidase and protein glycation. A methanolic extract of the leaves showed the strongest α-amylase inhibition (IC₅₀ = 14.29 ± 0.82 μg/mL, p < 0.05) when compared with other extracts. For inhibition of α-glucosidase, the strongest inhibition was shown for the water, methanolic and acetone extracts of leaves with IC₅₀ values ranging from 4.73 ± 0.96 to 7.26 ± 0.92 μg/mL. In the BSA-glucose model, fruit and leaf extracts inhibited formation of protein-bound fluorescent AGEs with IC₅₀ values ranging between 11.82 ± 0.71 and 96.80 ± 13.41 μg/mL. Pearson's correlation analysis showed that the AGE inhibition significantly correlated with DPPH (r_p = -0.8964, p < 0.05) and ABTS (r_p = -0.8326, p < 0.05). α-amylase inhibitory activities strongly correlated with DPPH (r_p = -0.8964, p < 0.001). α-glucosidase inhibition strongly correlated with TPC (r_p = -0.9243, p < 0.05), FRAP (r_p = -0.9502, p < 0.01), DPPH (r_p = -0.9317, p < 0.01) and ABTS (r_p = -0.9486, p < 0.01). This study provides a strong rationale for further investigation aimed at isolating and identifying the active compounds responsible for the observed effects on targets relevant to diabetes.

Dibenzoate esters of cis-tetralin-2,3-diol as analogs of (–)-epigallocatechin gallate: synthesis and crystal structure of anticancer drug candidates

(−)-Epigallocatechin gallate (EGCG), the main component of green tea extract, displays multiple biological activities. However, it cannot be used as a drug due to its low cellular absorption, instability and metabolic degradation. Therefore, there is a need to provide analogs that can overcome the limitations of EGCG. In this work, six synthetic analogs of EGCG sharing a common tetralindiol dibenzoate core were synthesized and fully characterized by 1H NMR, 13C NMR, HRMS and IR spectroscopies, and X-ray crystallography. These are (2R,3S)-1,2,3,4-tetrahydronaphthalene-2,3-diyl bis[3,4,5-tris(benzyloxy)benzoate], C66H56O10, and the analogous esters bis(3,4,5-trimethoxybenzoate), C30H32O10, bis(3,4,5-trifluorobenzoate), C24H14F6O4, bis[4-(benzyloxy)benzoate], C38H32O6, bis(4-methoxybenzoate), C26H24O6, and bis(2,4,6-trifluorobenzoate), C24H14F6O4. Structural analysis revealed that the molecular shapes of these dibenzoate esters of tetralindiol are significantly different from that of previously reported dimandelate esters or monobenzoate esters, as the acid moieties extend far from the bicyclic system without folding back over the tetralin fragment. Compounds with small fluorine substituents take a V-shape, whereas larger methoxy and benzyloxy groups determine the formation of an L-shape or a cavity. Intermolecular interactions are dominated by π–π stacking and C—H...π interactions involving the arene rings in the benzoate fragment and the arene ring in the tetrahydronaphthalene moiety. All six crystal structures are determined in centrosymmetric space groups (either P-1, P21/n, C2/c or I2/a).

Stability and Antiglycoxidant Potential of Bilberry Anthocyanins in Simulated Gastrointestinal Tract Model

Anthocyanins from Vaccinium myrtillus fruits have been reported in vitro to exert potent radical scavenging and antiglycation activities. However, the physiological relevance of such properties remains unclear given the potential susceptibility of anthocyanin derivatives to digestive conditions. A simulated gastrointestinal tract model was thus implemented to assess the impact of gastric and intestinal phases on the chemical integrity of bilberry anthocyanins and their antiglycoxidant effects. Results demonstrated that the investigated activities as well as total and individual anthocyanin contents were marginally affected by gastric conditions. By contrast, with recoveries ranging from 16.1 to 41.2%, bilberry anthocyanins were shown to be highly sensitive to the intestinal phase. Of major interest, a much better preservation was observed for radical scavenging and antiglycation activities as attested by recovery rates ranging from 79.1 to 86.7%. Consistently with previous observations, the present study confirms the moderate bioaccessibility of anthocyanin constituents. It does however provide valuable information supporting the persistence of substantial radical scavenging and antiglycation activities at each step of the digestion process. Taken together, these data indicate that digestive conditions might not abolish the potential positive effects of bilberry consumption on both oxidative and carbonyl stresses.

Antidiabetic effects of Syzygium cumini leaves: A non-hemolytic plant with potential against process of oxidation, glycation, inflammation and digestive enzymes catalysis

ETHNOPHARMACOLOGICAL RELEVANCE

Plant materials are commonly used in traditional medicine in order to treat various diseases such as Diabetes mellitus. Some plants, such as Syzygium cumini, have the capability to act controlling oxidative stress and protein glycation besides their potential to decrease hyperglycemia and hyperlipidemia by the inhibition of the catalysis of digestive enzymes. The aim of this study was to evaluate the antioxidant and antiglicant activity of S. cumini leaves fractions, their capacity to inhibit hydrolases and lipase enzymes, as well as the cytotoxicity effects against erythrocytes and comparate these results with isolate quercetin flavonoid.

MATERIAL AND METHODS

Ethnobotanical researches, carried out by academic studies at the Federal University of Uberlandia, led us to choose S. cumini as a potential plant for treatment of Diabetes mellitus. Fractions from ethanolic extract of S. cumini (hexane/Hex, dichloromethane/DCM, ethyl acetate/EtOAc, n-butanol/ButOH and water/H₂O) were used to evaluate their antioxidant (DPPH, ORAC and FRAP) and antiglycant (BSA/fructose, BSA/methylglyoxal and Arginine/Methylglyoxal) activity as well as the inhibitory potential against α-amylase, α-glucosidase and lipase. In addition, identification of the main bioactive compounds of S. cuimini leaves by HPLC-ESIMS/MS analysis was carried out.

RESULTS

Our results indicate that all fractions, for exception Hex, present noteworthy antioxidant activity, mainly in EtOAc and ButOH fractions (FRAP 1154.49 ± 67.37 and 1178.27 ± 21.26 μmol trolox eq g^-1, respectively; ORAC 1224.63 ± 58.16 and 1313.53 ± 85.23 μmol trolox eq g^-1, respectively; DPPH IC₅₀ 15.7 ± 2.4 and 23.5 ± 2.7 μg mL^-1, respectively). Regarding the antiglycant activity (BSA/fructose and Arginine/Methylglyoxal models), all fraction, for exception Hex, presented inhibition higher than 85%. All fractions were capable to inhibit 100% of α-amylase and the fractions DCM, EtOAc and ButOH inhibited α-glucosidase more than 50%. Regarding the lipase assay, DCM and Hex had the best activity (31.5 ± 14.3 and 44.3 ± 4.5 μg mL^-1, respectively). Various biomolecules known as potent antioxidants were identified in these fractions, such as quercetin, kaempferol, luteolin and (Epi)catechin.

CONCLUSION

S. cumini fractions and quercetin presented promising antioxidant and antiglycation properties as well as the ability to inhibit digestive enzymes. This study presents new biological activities not yet described for S. cumini which provide new possibilities for further studies in order to assess the antidiabetic potential of S. cumini fractions especially EtOAc and ButOH.

Antiglycaemic potentials and molecular docking studies of the extracts of Cassia alata L

Background

This study assessed the antiglycaemic properties of the methanolic extracts of the dried leaf of Cassia alata L. through in vitro and in silico approaches. The methanolic crude extract (MCE) of the dried leaf was prepared and partitioned into n-butanol (BPE) and aqueous (ARE) extracts. The antiglycaemic potential was assessed in vitro by studying the inhibitory actions of the extracts with α-amylase, α-glucosidase, and sucrase. The antiglycation capacity of the extracts was evaluated through the inhibition of albumin glycation, thiol oxidation, and β-fibril formation. Previously identified compounds (emodin, quercetin, chrysoeriol, and kaempferol) were docked with α-amylase (1HNY), α-glucosidase (5ZCB), and sucrase-isomaltase (3LPO) using the Pyrex Virtual Screening tool.

Results

The results revealed that MCE had the highest inhibitory potential with the lowest IC50 values of 69.67 ± 0.88, 65.54 ± 0.34, and 48.35 ± 1.45 μg/mL for α-amylase, α-glucosidase, and sucrase inhibitions, respectively. The molecular docking studies showed that quercetin and kaempferol had the best docking scores with 1HNY while emodin and chrysoeriol had the best scores towards 5ZCB and 3LPO. MCE and BPE significantly (p < 0.05) inhibited glucose-induced albumin glycation and modification.

Conclusion

This study suggested that the extract of the leaf of C. alata could contain a mix of different phytochemicals that could be beneficial in reducing the absorption of glucose and preventing diabetes-induced complications.

Antioxidant compounds from Banisteriopsis argyrophylla leaves as α-amylase, α-glucosidase, lipase, and glycation inhibitors

Banisteriopsis argyrophylla belongs to the Malpighiaceae family, which is a species from Cerrado, also known as "cipó-prata" or "cipó-folha-de-prata." Several species of this family present biological potential. This work reports the chemical identification of the ethanol extract (EE) and its fractions from B. argyrophylla leaves and shows the analysis of the antioxidant activity and inhibitory effects on activities of α-amylase, α-glucosidase and lipase, and non-enzymatic glycation. The ethyl acetate fraction (EAF) and n-butanol fraction (BF) showed antioxidant activity, with IC₅₀ values of 4.1 ± 0.1 and 4.8 ± 0.1 μg mL^-1, respectively, by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, and IC₅₀ values of 6046.3 ± 174.2 and 6264.2 ± 32.2 µmol Trolox eq g^-1 by the oxygen radical absorbance capacity (ORAC) method. Furthermore, the DPPH method with these fractions presented electroactive species with antioxidant potential, as shown by the differential pulse voltammetry (DPV) method. The inhibitory effects of the EAF and BF were demonstrated by the following results: IC₅₀ of 5.1 ± 0.3 and 2.5 ± 0.2 μg mL^-1 for α-amylase, IC₅₀ of 1093.5 ± 26.0 and 1250.8 ± 21.9 μg mL^-1 for α-glucosidase, IC₅₀ of 8.3 ± 4.1 and 4.4 ± 1.0 μg mL^-1 for lipase, and IC₅₀ of 1.3 ± 0.1 and 0.9 ± 0.1 μg mL^-1 for glycation. Some bioactive compounds were identified by (-)-ESI-MS/MS, such as catechin, procyanidins, glycosylated flavonoids, kaempferol, and megastigmane glucosides. The antidiabetic activity of B.argyrophylla has been reported for the first time.

Protection of Polyphenols against Glyco-Oxidative Stress: Involvement of Glyoxalase Pathway

Chronic high glucose (HG) exposure increases methylglyoxal (MGO)-derived advanced glycation end-products (AGEs) and is involved in the onset of pathological conditions, such as diabetes, atherosclerosis and chronic-degenerative diseases. Under physiologic conditions the harmful effects of MGO are contrasted by glyoxalase system that is implicated in the detoxification of Reactive Carbonyl Species (RCS) and maintain the homeostasis of the redox environment of the cell. Polyphenols are the most abundant antioxidants in the diet and present various health benefits. Aims of the study were to investigate the effects of HG-chronic exposure on glyco-oxidation and glyoxalase system in intestinal cells, using CaCo-2 cells. Moreover, we studied the effect of apple polyphenols on glyco-oxidative stress. Our data demonstrated that HG-treatment triggers glyco-oxidation stress with a significant increase in intracellular Reactive Oxygen Species (ROS), lipid peroxidation, AGEs, and increase of Glyoxalase I (GlxI) activity. On the contrary, Glyoxalase II (GlxII) activity was lower in HG-treated cells. We demonstrate that apple polyphenols exert a protective effect against oxidative stress and dicarbonyl stress. The increase of total antioxidant capacity and glutathione (GSH) levels in HG-treated cells in the presence of apple polyphenols was associated with a decrease of GlxI activity.

Pleiotropic ameliorative effects of ellagitannin geraniin against metabolic syndrome induced by high-fat diet in rats

OBJECTIVES

Metabolic syndrome (MetS), a multiplex risk factor for cardiovascular disease and type 2 diabetes, is increasingly prevalent worldwide. Ellagitannin geraniin, a polyphenol found in the rind of rambutan (Nephelium lappaceum), has demonstrated therapeutic effects against metabolism dysfunction. The aim of this study was to characterize the metabolic effects and possible mechanism of geraniin in rats with MetS induced by a high-fat diet (HFD).

METHODS

MetS was induced in Sprague Dawley rats on an HFD, followed by a daily oral gavage of geraniin (25 mg/kg) for 4 wk. The outcomes of geraniin-treated rats were compared with those of untreated rats on either a control diet or an HFD and with rats with MetS treated with metformin on a daily basis (200 mg/kg).

RESULTS

The supplementation of geraniin ameliorated multiple metabolic abnormalities caused by HFD, including hypertension, impaired glucose and lipid metabolism, ectopic fat deposition in the visceral fat and liver, and disturbed antioxidant mechanism and inflammatory response. The benefits conferred by geraniin were comparable to metformin. Transcriptomic analysis revealed a profound influence of geraniin on the hepatic expression profiles. The lipid and steroid metabolic processes that were aberrantly activated by HFD were suppressed by geraniin. Based on the differential transcriptomes, geraniin also exerted a significant modulatory effect on the expression of mitochondrial genes, potentially influencing the mitochondrial activity and leading to the observed beneficial effects.

CONCLUSION

Geraniin supplementation mitigated metabolic anomalies of MetS in rats, making it an attractive drug candidate for further investigation.

Beta-lactoglobulin-nutrition allergen and nanotransporter of different nature ligands therapy with therapeutic action

β-lactoglobulin is one of the nutrition allergens present in the milk of many mammals, with the exception of human. This protein belongs to the family of lipocalins, consisting of nine antiparallel β-strands (β-A to β-I) and one α-helix. This structure allows it to serve as a nanotransporter of various nature ligands in a pH dependent manner, which allows us to confidently consider it as a reliable carrier of drugs directly into the intestine, bypassing the destructive acidic environment of the stomach. Based on the latest data, this review describes the currently known methods of reducing the allergenicity of beta-lactoglobulin, as well as the mechanisms and methods of forming complexes of this protein with ligands, which emphasizes its importance and versatility and explains the growing interest in studying its properties in recent decades, and also opens up prospects for its practical application in medicine and pharmaceuticals.

Influence of Hydroxyl Substitution on the Suppression of Flavonol in Harmful Glycation Product Formation and the Inhibition Mechanism Revealed by Spectroscopy and Mass Spectrometry

Quercetin (Que), kaempferol (Kaem), isorhamnetin (Irh), and myricetin (Myri) are typical flavonols that are abundant in plant resources. This research investigated their ability in attenuating harmful glycation product formation and the effect of hydroxyl substitution. The inhibition mechanisms were elucidated by fluorescence spectroscopy and nano-liquid chromatography Orbitrap tandem mass spectrometry. The results indicated that the 3'-OH on the B-ring is critical in alleviating harmful glycation product formation, methylation reduced its inhibition, and the 5'-OH showed much less contribution than the 3'-OH. Que showed the strongest suppression on initial product, 5-hydroxymethylfurfural, and advanced glycation end product formation, with the corresponding percentage inhibitions at 36.58 μM of 81.1, 56.9, and 95.4%. Que and Myri also clearly inhibited fructosamine and acrylaminde production, while no suppression was observed by Irh and Kaem. The number of glycated sites was reduced from ten to seven, five, six, and nine, respectively, when 36.58 μM Que, Myri, Kaem, and Irh was added. Suppressing the conformational changes of ovalbumin induced by glycation, trapping dicarbonyl compounds, altering the microenvironment around tryptophan, and reducing the glycation activity of potential sites were the major inhibition mechanisms. These results suggest that Que and Myri may be promising natural agents for inhibiting harmful glycation and provide theoretical support for the effective screening of natural antiglycation reagents.

Impact of Particle-Size Reduction on the Solubility and Antidiabetic Activity of Extracts of Leaves of Vinca rosea

Objectives

The present study aimed to enhance the aqueous solubility of methanol extract of leaves of Vinca rosea (family: Apocynaceae) by particle-size reduction using milling and to evaluate its antidiabetic activity.

Materials and Methods

The methanol extract (ME) was micronized using a vibratory ball mill, operated at a vibratory speed of 15 Hz for 60 min at room temperature, and the resulting extract micronized ME (MME) was investigated to determine particle size, solubility, UV/visible profile, and in vitro antidiabetic activity.

Results

The average particle size of MME was 0.753±0.227 μm, which was less than half of that of the ME (2.007±0.965 μm). The solubility of MME was greater than that of the ME. MME exhibited 65.63%, 18.0%, and 96.87% higher antidiabetic activity in the glucose uptake by the yeast cells method, hemoglobin glycosylation assay, and the alpha amylase inhibition assay, respectively (p<0.05).

Conclusion

The results of the present study indicate that micronization effectively enhanced the aqueous solubility and antidiabetic activity of methanol extract of leaves of Vinca rosea.

Chemometric analysis reveals influences of hot air drying on the degradation of polyphenols in red radish

Hot air drying is a commonly used technology in the preservation of red radish. This study was designed to investigate the correlations among total polyphenol content, total flavonoid content, antioxidant activities and polyphenol compounds in hot air dried red radish via chemometric analysis. UHPLC-QqQ-MS/MS analysis detected nine non-anthocyanin polyphenols and one anthocyanin in fresh and dried red radish samples, and found that hot air drying at 80 °C caused an increase in the p-coumaric acid and ferulic acid content of the red radish. The integral effect of hot air drying on the polyphenol profile of red radish was analyzed by principle component analysis, while sparse partial least squares-discriminant analysis showed that hot air drying induced changes mainly in the contents of poncirin, naringenin, phloetin and cyanidin-3-glucoside. These polyphenol degradations occurred as non-spontaneous and endothermic reactions during the hot air drying process, following first-order reaction kinetics.

A New Italian Purple Corn Variety (Moradyn) Byproduct Extract: Antiglycative and Hypoglycemic In Vitro Activities and Preliminary Bioaccessibility Studies

The reuse of byproducts from agricultural and food industries represents the key factor in a circular economy, whose interest has grown in the last two decades. Thus, the extraction of bioactives from agro-industrial byproducts is a potential source of valuable molecules. The aim of this work was to investigate the in vitro capacity of byproducts from a new Italian corn variety, named Moradyn, to inhibit the accumulation of advanced glycation end products (AGEs) involved in several chronic age-related disorders. In addition, the hypoglycemic effect of Moradyn was tested by in vitro enzymatic systems. A Moradyn phytocomplex and its purified anthocyanin fraction were able to inhibit fructosamine formation and exhibited antiglycative properties when tested using BSA-sugars and BSA-methylglyoxal assays. These properties could be attributed to the polyphenols, mainly anthocyanins and flavonols, detected by RP-HPLC-DAD-ESI-MSⁿ. Finally, a Moradyn phytocomplex was submitted to a simulated in vitro digestion process to study its bioaccessibility. Moradyn could be considered as a promising food ingredient in the context of typical type 2 diabetes risk factors and the study will continue in the optimization of the ideal formulation to preserve its bioactivities from digestion.

Spray-dried olive mill wastewater reduces Maillard reaction in cookies model system

The network of the Maillard reaction can be influenced by the presence of polyphenols. In this paper, we evaluated the ability of secoiridoids to interact with asparagine and lysine tuning the formation of dietary advanced glycation end-products (d-AGEs), dicarbonyls and acrylamide. Olive oil mill wastewater polyphenol powders (OMWP) were added to glucose and lysine or asparagine in silica model systems to mimic water activity present in cookies. Results revealed that acrylamide, Amadori compounds and N-ε-carboxyethyllysine (CEL) were reduced to 50%, after 13 min at 180 °C; for the reduction of N-ε-carboxymethyllysine (CML), secoiridoids were effective only in model systems with the addition of acacia fiber and maltodextrin as coating agents. In cookies, OMWP at three different concentrations decreased the concentration of protein bound Amadori compounds, CML, CEL and dicarbonyls. Acrylamide and 5-hydroxymethylfurfural were reduced to 60% and 76% respectively, highlighting the ability of secoiridoids-based functional ingredients in controlling d-AGEs formation.

Glucose and Blood Pressure-Dependent Pathways-The Progression of Diabetic Kidney Disease

The major clinical associations with the progression of diabetic kidney disease (DKD) are glycemic control and systemic hypertension. Recent studies have continued to emphasize vasoactive hormone pathways including aldosterone and endothelin which suggest a key role for vasoconstrictor pathways in promoting renal damage in diabetes. The role of glucose per se remains difficult to define in DKD but appears to involve key intermediates including reactive oxygen species (ROS) and dicarbonyls such as methylglyoxal which activate intracellular pathways to promote fibrosis and inflammation in the kidney. Recent studies have identified a novel molecular interaction between hemodynamic and metabolic pathways which could lead to new treatments for DKD. This should lead to a further improvement in the outlook of DKD building on positive results from RAAS blockade and more recently newer classes of glucose-lowering agents such as SGLT2 inhibitors and GLP1 receptor agonists.

Phenolic Profile, Antioxidant, and Antidiabetic Potential Exerted by Millet Grain Varieties

This study evaluated the potential antioxidant and antidiabetic properties in vitro of four millet grain varieties cultivated in South Korea. The free fractions were tested for their total antioxidant capacity using 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS⁺) and 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays, followed by α-glucosidase, α-amylase, and advanced glycation endproducts (AGEs) formation inhibition assays. The total phenolics, flavonoids, and condensed tannins in the free fractions ranged from 107.8 to 136.4 mg ferulic acid equivalent (FAE)/100 g, 101.3 to 115.8 mg catechin equivalent (CE)/100 g, and 17.65 to 59.54 mg catechin equivalent (CE)/100 g, respectively. Finger Italian millet had the highest total phenolic content (136.4 mg FAE/100 g) and flavonoid content (115.8 mg CE/100 g). Barnyard and finger Italian millet showed the highest DPPH (IC₅₀ = 359.6 µg/mL and 436.25 µg/mL, respectively) and ABTS radical scavenging activity (IC₅₀ = 362.40 µg/mL and 381.65 µg/mL, respectively). Similarly, finger Italian millet also exhibited significantly lower IC₅₀ values for the percentage inhibition of α-glucosidase (18.07 µg/mL) and α-amylase (10.56 µg/mL) as compared with acarbose (IC₅₀ = 59.34 µg/mL and 27.73 µg/mL, respectively) and AGEs formation (33.68 µg/mL) as compared with aminoguanidine (AG) (52.30 µg/mL). All eight phenolic compounds identified in finger Italian millet were flavonoids, with flavanols being the predominant subclass. Taken together, millet flavonoids play important roles in the prevention and management of type 2 diabetes, and hence finger Italian millet has the potential to be developed as a functional food.

Polyphenols and AGEs/RAGE axis. Trends and challenges

The formation of advanced glycation end-products (AGEs) is a key pathophysiological event linked not only to the onset and progression of diabetic complications, but also to neurodegeneration, cardiovascular diseases, cancer, and others important human diseases. AGEs contributions to pathophysiology are mainly through the formation of cross-links and by engaging the receptor for advanced glycation end-products (RAGE). Polyphenols are secondary metabolites found largely in fruits, vegetables, cereals, and beverages, and during many years, important efforts have been made to elucidate their beneficial effects on human health, mainly ascribed to their antioxidant activities. In the present review, we highlighted the beneficial actions of polyphenols aimed to diminish the harmful consequences of advanced glycation, mainly by the inhibition of ROS formation during glycation, the inhibition of Schiff base, Amadori products, and subsequent dicarbonyls group formation, the activation of the glyoxalase system, as well as by blocking either AGEs-RAGE interaction or cell signaling.

Schwann cells apoptosis is induced by high glucose in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus that affects approximately half of patients with diabetes. Current treatment regimens cannot treat DPN effectively. Schwann cells (SCs) are very sensitive to glucose concentration and insulin, and closely associated with the occurrence and development of type 1 diabetic mellitus (T1DM) and DPN. Apoptosis of SCs is induced by hyperglycemia and is involved in the pathogenesis of DPN. This review considers the pathological processes of SCs apoptosis under high glucose, which include the following: oxidative stress, inflammatory reactions, endoplasmic reticulum stress, autophagy, nitrification and signaling pathways (PI3K/AKT, ERK, PERK/Nrf2, and Wnt/β-catenin). The clarification of mechanisms underlying SCs apoptosis induced by high glucose will help us to understand and identify more effective strategies for the treatment of T1DM DPN.

Differential effect of biophenols on attenuation of AGE-induced hemoglobin aggregation

Despite most studied activities of natural biophenols rely on antioxidant properties, little clues explored their key structural components with regard to opposing action on glycation-induced aggregation. Herein, human hemoglobin (hHb)/fructose system used to decipher if structural peculiarities of two biophenols "chlorogenic acid (CGA) and curcumin (CUR)" are effective toward AGEs-bridged aggregate formation. Suppression in amyloid cross-β formation was monitored by CD spectroscopy, fluorescence microscopy, ANS and AGE fluorescence. Reduction in molten globule structure of modified-Hb by CGA was corroborated with helix structure, thiol group and lysine residues content estimation for native, glycated and biophenols treated samples. ThT and Congo red assays showed the cross-β breaking properties of CGA. Molecular docking outcomes revealed the positioning of CGA/CUR is driven by "aromatic interactions" with Trp β₁180 and Tyr α₂540. These interactions are modulated by the structural constraints such as number of hydroxyl groups and their methylation status directing the biophenols to the amyloidogenic core. The results are applicable to formulation of small-molecule nutraceuticals for treatment of conformational diseases.

Mulberry anthocyanins exert anti-AGEs effects by selectively trapping glyoxal and structural-dependently blocking the lysyl residues of β-lactoglobulins

Advanced glycation end-products (AGEs), which instigate many disorders, are mostly mediated by dicarbonyl rearrangements. We studied the corresponding mechanisms of the anti-glycation effects of two anthocyanins purified from mulberry fruits, namely cyanidin 3-glucoside (C3G) and cyanidin 3-rutinoside (C3R), on glycated β-lactoglobulins (β-Lg). Both mulberry anthocyanins (MAs) inhibited the AGEs-formation in a dose-dependent manner, but the effect of C3R was significantly stronger than that of C3G (p < 0.05). MAs inhibited AGEs-formation by selectively trapping dicarbonyls, especially glyoxal. The UPLC-ESI-Q-TOF-MS results characterized that C3R formed mono- and di-glyoxal adducts, where C3G only created di-glyoxal adducts. Additionally, C3R could directly interact with some of the glycation sites of β-Lg. Overall, GO-trapping and β-Lg-MAs covalent/noncovalent binding are disclosed as the key mechanisms of the anti-AGEs activity of MAs on β-Lg, which could be valorised as effectual AGEs inhibitors in proteins-rich matrices.

Lycopene Improves the Metformin Effects on Glycemic Control and Decreases Biomarkers of Glycoxidative Stress in Diabetic Rats

INTRODUCTION

Oxidative stress and exacerbated generation of advanced glycation end products (AGEs) participate in the onset of diabetic complications. Lycopene is a potent antioxidant; evidence accounts for its ability to mitigate diabetic disturbances, including the deleterious events of advanced glycation. Therefore, this carotenoid has emerged as a candidate to be used in combination with antidiabetic drugs, such as metformin, attempting to counteract the glycoxidative stress. This study investigated the effects of the treatments with lycopene or metformin, alone or in combination, on glycoxidative stress biomarkers and antioxidant defenses in diabetic rats.

METHODS

Streptozotocin-induced diabetic rats were treated for 35 days with lycopene (45 mg/kg) or metformin (250 mg/kg), alone or as mixtures in yoghurt. Plasma levels of glucose, triglycerides, cholesterol, thiobarbituric acid reactive substances and protein carbonyl groups (biomarkers of oxidative damage), fluorescent AGEs (biomarkers of advanced glycation), and paraoxonase 1 activity (antioxidant enzyme) were assessed. Changes in the hepatic and renal levels of glycoxidative damage biomarkers and the activities of antioxidant enzymes were investigated.

RESULTS

The combination of lycopene with metformin maintained the beneficial effects of the isolated treatments, improving the glucose tolerance and lipid profile, lessening biomarkers of oxidative damage, and increasing the paraoxonase 1 activity. Besides, the combined therapy caused further decreases in postprandial glycemia, plasma levels of cholesterol and AGEs, avoided lipid peroxidation (plasma, kidney), and increased antioxidant defenses, mainly the activity of superoxide dismutase (liver, kidney), indicating the maintenance of the lycopene effects.

CONCLUSION

Lycopene combined with metformin may act synergistically in the control of postprandial glycemia, dyslipidemia and glycoxidative stress, as well as increased antioxidant defenses, arising as a promising therapeutic strategy to mitigate diabetic complications.

Methylglyoxal, a Highly Reactive Dicarbonyl Compound, in Diabetes, Its Vascular Complications, and Other Age-Related Diseases

The formation and accumulation of methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of type 2 diabetes, vascular complications of diabetes, and several other age-related chronic inflammatory diseases such as cardiovascular disease, cancer, and disorders of the central nervous system. MGO is mainly formed as a byproduct of glycolysis and, under physiological circumstances, detoxified by the glyoxalase system. MGO is the major precursor of nonenzymatic glycation of proteins and DNA, subsequently leading to the formation of advanced glycation end products (AGEs). MGO and MGO-derived AGEs can impact on organs and tissues affecting their functions and structure. In this review we summarize the formation of MGO, the detoxification of MGO by the glyoxalase system, and the biochemical pathways through which MGO is linked to the development of diabetes, vascular complications of diabetes, and other age-related diseases. Although interventions to treat MGO-associated complications are not yet available in the clinical setting, several strategies to lower MGO have been developed over the years. We will summarize several new directions to target MGO stress including glyoxalase inducers and MGO scavengers. Targeting MGO burden may provide new therapeutic applications to mitigate diseases in which MGO plays a crucial role.

B procyanidins of Annona crassiflora fruit peel inhibited glycation, lipid peroxidation and protein-bound carbonyls, with protective effects on glycated catalase

Advanced glycation end-products (AGEs) have been reported as results of increased oxidative stress. Consequently, the search for new antioxidant and anti-glycating agents is under intense investigation. Plant-derived procyanidins have previously demonstrated anti-glycation properties. Thus, this study aimed to isolate procyanidins from Annona crassiflora fruit peel, a species from the Brazilian Savanna, and investigate their antioxidant and anti-glycation effects. Free radical scavenging and quenching properties, formation of reactive oxygen species (ROS), AGEs, protein carbonyl and thiol groups, lipid peroxidation, crosslinked AGEs, as well as glycated catalase activity, were analyzed. In addition, in silico assessment of absorption, distribution, metabolism, excretion and toxicity was carried out. The procyanidins-enriched fraction, named here as F7, showed high antioxidant and anti-glycation capacities, with inhibitory activities against lipid peroxidation, and AGEs and ROS formation. In addition, there were reductions in AGEs-induced crosslinks and protein carbonyls and protective effects against oxidation of thiol groups and glycated-catalase. ADMET predictions of F7 showed favorable absorption and distribution, with no hepatotoxicity or mutagenicity. Together, our results support the anti-glycation activities of the procyanidins-enriched fraction from A. crassiflora, and suggest that these effects are triggered, at least in part, by scavenging free radical and dicarbonyls intermediates.

Potassium Salt of Fullerenylpenta-N-Dihydroxytyrosine Effects on Type 2 Diabetes Mellitus Therapeutic Targets

It was shown for the first time that pentaamino acid derivative of fullerene C₆₀ (potassium salt of fullerenylpenta-N-dihydroxytyrosine) affects three targets of type 2 diabetes mellitus. It competitively inhibits the enzymes aldose reductase and sorbitol dehydrogenase and also has an antiglycation effect on bovine serum albumin. The inhibition constants for these enzymes were calculated.