Identification and inhibitory activities of ellagic acid- and kaempferol-derivatives from Mongolian oak cups against α-glucosidase, α-amylase and protein glycation linked to type II diabetes and its complications and their influence on HepG2 cells’ viability

Inhibition of human starch digesting enzymes and intestinal glucose transport by walnut polyphenols

One approach to controlling type 2 diabetes (T2D) is to lower postprandialglucose spikesby slowing down the digestion of carbohydrates and the absorption of glucose in the small intestine. The consumption of walnuts is associated with a reduced risk of chronic diseases such as T2D, suggested to be partly due to the high content of (poly)phenols. This study evaluated, for the first time, the inhibitory effect of a (poly)phenol-rich walnut extract on human carbohydrate digesting enzymes (salivary and pancreatic α-amylases, brush border sucrase-isomaltase) and on glucose transport across fully differentiated human intestinal Caco-2/TC7 monolayers. The walnut extract was rich in multiple (poly)phenols (70 % w/w) as analysed by Folin-Ciocalteau and by LCMS. It exhibited potent inhibition of both human salivary (IC50: 32.2 ± 2.5 µg walnut (poly)phenols (WP)/mL) and pancreatic (IC50: 56.7 ± 1.7 µg WP/mL) α-amylases, with weaker effects on human sucrase (IC50: 990 ± 20 µg WP/mL), maltase (IC50: 1300 ± 80 µg WP/mL), and isomaltase (IC25: 830 ± 60 µg WP/mL) activities. Selected individual walnut (poly)phenols inhibited human salivary α-amylase in the order: 1,3,4,6-tetragalloylglucose > ellagic acid pentoside > 1,2,6-tri-O-galloyl-β-D-glucopyranose, with no inhibition by ellagic acid, gallic acid and 4-O-methylgallic acid. The (poly)phenol-rich walnut extract also attenuated (up to 59 %) the transfer of 2-deoxy-D-glucose across differentiated Caco-2/TC7 cell monolayers. This is the first report on the effect of (poly)phenol-rich extracts from any commonly-consumed nut kernel on any human starch-digesting enzyme, and suggests a mechanism through which walnut consumption may lower postprandial glucose spikes and contribute to their proposed health benefits.

Clinical applications and mechanism insights of natural flavonoids against type 2 diabetes mellitus

Diabetes is a complex disease that affects a large percentage of the world's population, and it is associated with several risk factors. Self-management poses a significant challenge, but natural sources have shown great potential in providing effective glucose reducing solutions. Flavonoids, a class of bioactive substances found in different natural sources including medicinal plants, have emerged as promising candidates in this regard. Indeed, several flavonoids, including apigenin, arbutin, catechins, and cyanidin, have demonstrated remarkable anti-diabetic properties. The clinical effectiveness of these flavonoids is linked to their potential to decrease blood glucose concentration and increase insulin concentration. Thus, the regulation of certain metabolic pathways such as glycolysis and neoglycogenesis has also been demonstrated. In vitro and in vivo investigations revealed different mechanisms of action related to flavonoid compounds at subcellular, cellular, and molecular levels. The main actions reside in the activation of glycolytic signaling pathways and the inhibition of signaling that promotes glucose synthesis and storage. In this review, we highlight the clinical efficiency of natural flavonoids as well as the molecular mechanisms underlying this effectiveness.

UHPLC-ESI-QTOF-MS metabolite profiles of different extracts from Pelargonium endlicherianum parts and their biological properties based on network pharmacological approaches

In the present study, we aimed to investigate the chemical profiles and biological activities of different extracts (ethyl acetate, dichloromethane, ethanol, and water) of Pelargonium endlicherianum parts (aerial parts and roots). Free radical scavenging, reducing power, phosphomolybdenum, and metal chelating were assayed for antioxidant properties. To detect enzyme inhibitory properties, cholinesterase, amylase, glucosidase, and tyrosinase were chosen as target enzymes. The ethanol extract of the aerial parts contained higher amounts of total bioactive compounds (120.53 mg GAE/g-24.46 mg RE/g). The ethanol and water extracts of these parts were tentatively characterized by UHPLC-ESI-QTOF-MS and 95 compounds were annotated. In addition, the highest acetylcholiesterase (3.74 mg GALAE/g) and butyrylcholinesterase (3.92 mg GALAE/g) abilities were observed by the ethanol extract of roots. The water extract from aerial parts exhibited the most pronounced inhibitory effects on multiple cancer cell lines, especially A549 (IC50: 23.2 µg/mL) and HT-29 (IC50: 27.43 µg/mL) cells. Using network pharmacology, P. endlicherianum compounds were studied against cancer, revealing well-connected targets such as epidermal growth factor receptor (EGFR), phosphoinositide-3-kinase (PI3K), AKT, receptor tyrosine-protein kinase erbB-2, and growth factor receptor bound protein 2 (GRB2) with significant impact on cancer-related pathways. The results could open a new path from natural treasure to functional applications with P. endlicherianum and highlight a new study on other uninvestigated Pelargonium species.

(Poly)phenol-related gut metabotypes and human health: an update

Dietary (poly)phenols have received great interest due to their potential role in the prevention and management of non-communicable diseases. In recent years, a high inter-individual variability in the biological response to (poly)phenols has been demonstrated, which could be related to the high variability in (poly)phenol gut microbial metabolism existing within individuals. An interplay between (poly)phenols and the gut microbiota exists, with (poly)phenols being metabolised by the gut microbiota and their metabolites modulating gut microbiota diversity and composition. A number of (poly)phenol metabolising phenotypes or metabotypes have been proposed, however, potential metabotypes for most (poly)phenols have not been investigated, and the relationship between metabotypes and human health remains ambiguous. This review presents updated knowledge on the reciprocal interaction between (poly)phenols and the gut microbiome, associated gut metabotypes, and subsequent impact on human health.

A discovery of potent kaempferol derivatives as multi-target medicines against diabetes as well as bacterial infections: an in silico approach

Flavonoids demonstrate beneficial effects on human health because flavonoids contain important biological properties. Kaempferol is a flavonol, type of flavonoid found in eatable plants and in plants usually employed in ancient drugs (Moringa oleifera, Tilia spp., fern genus spp. and gingko etc.). Some medicinal studies have shown that the use of foods full of kaempferol decreases the risk of many (cancer, vascular) diseases. All the data of 50 kaempferol derivatives were collected from PubChem database. Through Schrödinger software, 3D-QSAR study was performed for 50 compounds by using method of field base. Conformer of kaempferol derivatives was docked against anti-diabetic, anti-microbial co-crystal structures and protein. To monitor the best anti-diabetic and antibacterial agent, particular kaempferol derivatives were downloaded from PubChem database. Virtual screening by molecular docking provided four lead compounds with four different proteins. These hit compounds were found to be potent inhibitor for diabetic enzymes alpha-amylase and DPP IV and had the potential to suppress DNA gyrase and dihydrofolate reductase synthesis. Molecular dynamic simulation of docked complexes evaluates the value of root mean square fluctuation by iMOD server. Kaempferol 3-O-alpha-L-(2, 3-di-Z-p-coumaroyl) rhamnoside (42) compound used as anti-diabetic and kaempferol 3-O-gentiobioside (3) as antibacterial with good results can be used for drug discovery.Communicated by Ramaswamy H. Sarma.

Simulated Gastrointestinal Digestion of Chestnut (Castanea sativa Mill.) Shell Extract Prepared by Subcritical Water Extraction: Bioaccessibility, Bioactivity, and Intestinal Permeability by In Vitro Assays

Chestnut shells (CSs) are an appealing source of bioactive molecules, and constitute a popular research topic. This study explores the effects of in vitro gastrointestinal digestion and intestinal permeability on the bioaccessibility and bioactivity of polyphenols from CS extract prepared by subcritical water extraction (SWE). The results unveiled higher phenolic concentrations retained after gastric and intestinal digestion. The bioaccessibility and antioxidant/antiradical properties were enhanced in the following order: oral < gastric ≤ intestinal digests, attaining 40% of the maximum bioaccessibility. Ellagic acid was the main polyphenol in the digested and undigested extract, while pyrogallol-protocatechuic acid derivative was only quantified in the digests. The CS extract revealed potential mild hypoglycemic (<25%) and neuroprotective (<75%) properties before and after in vitro digestion, along with upmodulating the antioxidant enzymes' activities and downregulating the lipid peroxidation. The intestinal permeation of ellagic acid achieved 22.89% after 240 min. This study highlighted the efficacy of the CS extract on the delivery of polyphenols, sustaining its promising use as nutraceutical ingredient.

Potential Use of Quercus dalechampii Ten. and Q. frainetto Ten. Barks Extracts as Antimicrobial, Enzyme Inhibitory, Antioxidant and Cytotoxic Agents

The bark resulted as a by-product after different Quercus sp. processing is a valuable alternative source of phenolic compounds (mainly tannins). Hence, the focus of the present work was to obtain eight extracts from the rhytidome of the less-studied Q. dalechampii and Q. frainetto and characterize them in terms of chemical and bioactive profiles. Ultrasound and microwave-assisted extraction methods were used for the preparation of the extracts. Total phenolic and tannin contents were assessed through classic spectrophotometric methods, while several individual phenolic compounds were identified and quantified using UPLC-PDA. Antioxidant, enzyme-inhibitory, antibacterial, and cytotoxic activities were tested using in vitro assays; additionally being evaluated was the ability of the extracts to inhibit the adherence of MRSA to suture wires. The UPLC analysis confirmed the presence of gallic acid, catechin, taxifolin, vanillic acid, epicatechin, and caffeic acid. The results showed that tested extracts were able to exert cytotoxic effects, at 6% and 3% concentrations, on confluent cells. The tested solutions inhibit α-glucosidase activity and the antibacterial potential suggested a mild to moderate effect against the Gram-positive strains. Overall, the obtained results revealed rich phenolic and tannin contents for the extracts obtained from both species through microwave-assisted extraction, probably responsible for their mild antibacterial and cytotoxic effects.

Chemical and Biological Investigations of Allium scorodoprasum L. Flower Extracts

This study was designed to investigate the impact of different extraction solvent systems on the chemical composition and biological activities of Allium scorodoprasum L. (Amaryllidaceae)-the medicinal plant that was traditionally used as a remedy in the medieval period in the Balkans. Targeted chemical analysis of nine different extracts was performed by UHPLC(-)HESI-QqQ-MS/MS. Antimicrobial and antibiofilm activities of the extracts were investigated on sixteen clinical isolates of bacteria, yeasts and dermatomycetes, all isolated from infected human skin and corneal formations. Cytotoxicity and wound-healing properties were tested on human immortalized keratinocytes (HaCaT cell line). Antioxidant activity was assessed by six different assays, while beneficial potential against certain neurodegenerative diseases and type 2 diabetes was determined in selected enzyme inhibition assays coupled with molecular modeling. The results showed that the obtained extracts were rich in phenolic compounds, especially flavonoid glycosides such as rutin and kaempferol 3-O-glucoside. All of the extracts showed antimicrobial, wound-healing, antioxidant and anti-enzymatic properties. This study is the first of its kind, linking the medieval medicinal use of wild-growing flowers of A. scorodoprasum with contemporary in vitro scientific approaches.

Biological Activity of Bark Extracts from Northern Red Oak (Quercus rubra L.): An Antioxidant, Antimicrobial and Enzymatic Inhibitory Evaluation

The northern red oak (Quercus rubra L.) is an ornamental oak species native to eastern America, being an invasive species in Europe, with increasing coverage. The aim of this work was to evaluate the biological potential of red oak bark extracts. Aqueous and ethanolic preparations were obtained by two extraction methods: ultrasonic-assisted extraction (UAE) and microwave assisted extraction (MAE). The total phenolic and tannin contents were measured using spectrophotometric methods. The antioxidant activity was evaluated by two complementary methods (DPPH and ABTS). Antimicrobial potential was tested against five bacteria and three Candida species, and the effect on biofilm formation and synergism with gentamicin was also evaluated. Finally, enzyme inhibitory properties were assessed for α-glucosidase, tyrosinase, and acetylcholinesterase. The results indicated a higher phenolic content for the extracts obtained through MAE, while UAE bark extracts were rich in tannins. All the extracts exhibited antioxidant, anti-glucosidase, and anti-tyrosinase activity, while the antibacterial potential was mostly observed for the MAE extracts, especially against S. aureus, C. parapsilopsis, and C. krusei; inhibition of biofilm formation was observed only for MRSA. These findings show that the red oak bark might be an important source of bioactive compounds with antioxidant and antimicrobial properties.

Physicochemical Characterization of In Vitro LDL Glycation and Its Inhibition by Ellagic Acid (EA): An In Vivo Approach to Inhibit Diabetes in Experimental Animals

Hundreds of millions of people around the globe are afflicted by diabetes mellitus. The alteration in glucose fixation process might result into hyperglycaemia and could affect the circulating plasma proteins to undergo nonenzymatic glycation reaction. If it is unchecked, it may lead to diabetes with increase in advanced glycation end products (AGEs). Therefore, the present study was designed to inhibit the diabetes and glycation by using natural antioxidant “ellagic acid” (EA). In this study, we explored the antidiabetes and antiglycation potential of EA in both in vitro (EA at micromolar concentration) and in vivo systems. The EA concentrations of 10 and 20 mg kg⁻¹B.W./day were administered orally for 25 days to alloxan-induced diabetic rats, a week after confirmation of stable diabetes in animals. Intriguingly, EA supplementation in diabetic rats reversed the increase in fasting blood sugar (FBS) and hemoglobin A1c (HbA1c) level. EA also showed an inhibitory role against glycation intermediates including dicarbonyls, as well as AGEs, investigated in a glycation mixture with in vitro and in vivo animal plasma samples. Additionally, EA treatment resulted in inhibition of lipid peroxidation-mediated malondialdehyde (MDA) and conjugated dienes (CD). Furthermore, EA exhibited an antioxidant property, increased the level of plasma glutathione (GSH), and also helped to decrease histological changes evaluated by histoimmunostaining of animal kidney tissues. The results from our investigation clearly indicates the antiglycative property of EA, suggesting EA as an adequate inhibitor of glycation and diabetes, which can be investigated further in preclinical settings for the treatment and management of diabetes-associated complications.

A Review on Antidiabetic Activity of Centaurea spp.: A New Approach for Developing Herbal Remedies

Objective

Diabetes mellitus (DM) is a long-life metabolic disorder, characterized by high blood glucose levels. The hyperglycemic condition generally leads to irreversible nerve injury and vascular damage. Among different types of diabetes, type 2 is more common and has spread all over the world. Although various therapeutic approaches have been developed to control type 2 DM, regulating blood glucose levels has still remained a controversial challenge for patients. Also, most prescription drugs cause different side effects, such as gastrointestinal disorders. Thus, developing novel and efficient antidiabetic agents possessing fewer adverse effects is in high demand.

Method

The literature was comprehensively surveyed via search engines such as Google Scholar, PubMed, and Scopus using appropriate keywords.

Results

Medicinal plants, both extracts and isolated active components, have played a significant role in controlling the blood glucose levels. Good-to-excellent results documented in the literature have made them a precious origin for developing and designing drugs and supplements against DM. Centaurea spp. have been traditionally used for controlling high blood glucose levels. Also, the antidiabetic properties of different species of Centaurea have been confirmed in recent studies through in vitro assays as well as in vivo experiments.

Conclusion

Potent results encouraged us to review their efficacy to open a new horizon for development of herbal antidiabetic agents.

Ellagic Acid as a Tool to Limit the Diabetes Burden: Updated Evidence

Oxidative stress contributes not only to the pathogenesis of type 2 diabetes (T2D) but also to diabetic vascular complications. It follows that antioxidants might contribute to limiting the diabetes burden. In this review we focus on ellagic acid (EA), a compound that can be obtained upon intestinal hydrolysis of dietary ellagitannins, a family of polyphenols naturally found in several fruits and seeds. There is increasing research on cardiometabolic effects of ellagitannins, EA, and urolithins (EA metabolites). We updated research conducted on these compounds and (I) glucose metabolism; (II) inflammation, oxidation, and glycation; and (III) diabetic complications. We included studies testing EA in isolation, extracts or preparations enriched in EA, or EA-rich foods (mostly pomegranate juice). Animal research on the topic, entirely conducted in murine models, mostly reported glucose-lowering, antioxidant, anti-inflammatory, and anti-glycation effects, along with prevention of micro- and macrovascular diabetic complications. Clinical research is incipient and mostly involved non-randomized and low-powered studies, which confirmed the antioxidant and anti-inflammatory properties of EA-rich foods, but without conclusive results on glucose control. Overall, EA-related compounds might be potential agents to limit the diabetes burden, but well-designed human randomized controlled trials are needed to fill the existing gap between experimental and clinical research.

Dual electrophoretically-mediated microanalysis in multiple injection mode for the simultaneous determination of acetylcholinesterase and α-glucosidase activity applied to selected polyphenols

Acetylcholinesterase (AChE) and α-glucosidase (α-glu) are key target enzymes in the search for novel strategies in the treatment of Alzheimer's disease and type II diabetes. Therefore, methods to assess the enzyme inhibition are of great value in the research field. Here is proposed a novel a dual electrophoretically-mediated microanalysis for the simultaneous determination of both enzymes' activity. In order to do so, the various solutions required for both assays were introduced in the capillary electrophoresis system using the multiple injections approach. Enzymatic kinetic parameters were tested, K_m for AChE and α-glu were 3.81 and 0.43 mmol L^-1. K_i values were 4.27 μmol L^-1 for neostigmine (an AChE inhibitor) and 0.40 mmol L^-1 for acarbose (an α-glu inhibitor). Results of IC₅₀ (concentration for 50% of inhibition) were 5.11 ± 0.47 μmol L^-1 and 0.58 ± 0,02 mmol L^-1 for neostigmine and acarbose, respectively. All parameters (except for K_i of neostigmine) were comparable with the literature, indicating a good reliability of the proposed method to evaluate these enzymes activity. Total time analysis was approximately 10 min, being possible to perform around 12 enzymatic assays per hour, with low sample and reagent consumption, thus satisfying some of the principles of green chemistry. The method was applied to evaluate 10 phenolic compounds, of wich p-coumaric acid showed the best inhibitory activity for AChE (40.14 ± 4.75% at 10 mg L^-1); and quercetin for α-glu (46.53 ± 4.90% at 10 mg L^-1).

Medicinal Uses, Phytochemistry, and Pharmacological Activities of Quercus Species

Quercus species, also known as oak, represent an important genus of the Fagaceae family. It is widely distributed in temperate forests of the northern hemisphere and tropical climatic areas. Many of its members have been used in traditional medicine to treat and prevent various human disorders such as asthma, hemorrhoid, diarrhea, gastric ulcers, and wound healing. The multiple biological activities including anti-inflammatory, antibacterial, hepatoprotective, antidiabetic, anticancer, gastroprotective, antioxidant, and cytotoxic activities have been ascribed to the presence of bioactive compounds such as triterpenoids, phenolic acids, and flavonoids. This paper aimed to provide available information on the medicinal uses, phytochemicals, and pharmacology of species from Quercus. However, further investigation is needed to fully clarify the mode of action of its bioactive compounds and to evaluate in vivo chronic toxicity, before exploring their potential use as a supplement in functional foods and natural pharmaceutics.

Antifungal, Antitumoral and Antioxidant Potential of the Danube Delta Nymphaea alba Extracts

This study aimed to explore for the first time the biological properties such as antifungal, antitumoral and antioxidant of Danube Delta Nymphaea alba (N. alba) leaf and root methanolic extracts. The toxicity studies of N. alba extracts showed no inhibitory effect on wheat seed germination by evaluating the most sensitive physiological parameters (Germination %, Germination index, Vigor index) and using confocal laser scanning microscopy images. The analyzed extracts were found to have high antifungal activity against Candida glabrata with MIC values of 1.717 µg/mL for leaf and 1.935 µg/mL for root. The antitumor activity of the both extracts against A2780/A2780cisR ovarian, LNCaP prostate and MCF-7 breast cancer cells was promising with IC₅₀ values ranging from 23–274 µg/mL for leaf and 18–152 µg/mL for root, and the combination of N. alba extracts with cisplatin showed a synergistic effect (coefficient of drug interaction <1). The antioxidant properties were assessed by β-carotene bleaching, ABTS and FRAP assays and cyclic voltammetry. Quercetin, the most prominent antioxidant, was quantified in very good yields by spectroelectrochemical assay.

Bioactivity of dietary polyphenols: The role of metabolites

A polyphenol-rich diet protects against chronic pathologies by modulating numerous physiological processes, such as cellular redox potential, enzymatic activity, cell proliferation and signaling transduction pathways. However, polyphenols have a low oral bioavailability mainly due to an extensive biotransformation mediated by phase I and phase II reactions in enterocytes and liver but also by gut microbiota. Despite low oral bioavailability, most polyphenols proved significant biological effects which brought into attention the low bioavailability/high bioactivity paradox. In recent years, polyphenol metabolites have attracted great interest as many of them showed similar or higher intrinsic biological effects in comparison to the parent compounds. There is a huge body of literature reporting on the biological functions of polyphenol metabolites generated by phase I and phase II metabolic reactions and gut microbiota-mediated biotransformation. In this respect, the review highlights the pharmacokinetic fate of the major dietary polyphenols (resveratrol, curcumin, quercetin, rutin, genistein, daidzein, ellagitannins, proanthocyanidins) in order to further address the efficacy of biometabolites as compared to parent molecules. The present work strongly supports the contribution of metabolites to the health benefits of polyphenols, thus offering a better perspective in understanding the role played by dietary polyphenols in human health.

Hypoglycemic Effects in Alloxan-Induced Diabetic Rats of the Phenolic Extract from Mongolian Oak Cups Enriched in Ellagic Acid, Kaempferol and Their Derivatives

Our previous reports showed that crude extract prepared with 50% ethanol (ethanol crude extract, ECE) from Mongolian oak cups possessed excellent in vitro antioxidant capacities as well as inhibitory activities against α-glucosidase, α-amylase and protein glycation caused by its enrichment in phenolics, including mainly ellagic acid, kaempferol and their derivatives. Nevertheless, few in vivo studies on antidiabetic activities of these phenolics were conducted. The present study investigated hypoglycemic effects with normal and diabetic rats being administrated orally without or with ECE at 200 and 800 mg/kg for 15 days. In normal rats, no significant differences were exhibited after ECE administration in body weight, fasting blood glucose level, levels of cholesterol, triglyceride, LDL and AST in serum, organ indexes, and levels of GSH and MDA in organs. In diabetic rats, the fasting blood glucose level, indexes of heart and liver, and levels of cholesterol and triglyceride in serum and MDA in heart tissue were significantly decreased. Moreover, HDL levels in serum and SOD activities in the four organs of diabetic rats were significantly improved after ECE administration at 800 mg/kg. Thus, in addition to inhibiting α-glucosidase, α-amylase and protein glycation reported previously, oak cups might contain novel dietary phytonutrients in preventing abnormal changes in blood glucose and lipid profile and attenuating oxidant stress in vivo. The results also implied that it is ellagic acid, kaempferol and their derivatives enriched in ECE that might play vital roles in managing type 1 as well as type 2 diabetes.