6-hydroxyflavonoids as alpha-glucosidase inhibitors from marjoram (Origanum majorana) leaves

Exploring antidiabetic potential of a polyherbal formulation Madhurakshak Activ: An in vitro and in silico study

Madhurakshak Activ (MA), a commercial polyherbal antidiabetic preparation is known to manage diabetes mellitus (DM) by reducing blood glucose levels. However, lacks systematic mechanistic evaluation for their molecular and cellular mode of actions. In the present study, hydro-alcoholic and aqueous extract of MA were evaluated for their effects on glucose adsorption, diffusion, amylolysis kinetics and transport across the yeast cells using in vitro techniques. Bioactive compounds identified from MA by LC-MS/MS were assessed for their binding potential against DPP-IV and PPARγ via an in silico approach. Our results revealed that the adsorption of glucose increased dose dependently (5 mM -100 mM). Both extracts exhibited linear glucose uptake into the yeast cells (5 mM - 25 mM), whereas glucose diffusion was directly proportional to time (30-180 min). Pharmacokinetic analysis revealed drug-like properties and low toxicity levels for all the selected compounds. Among the tested compounds, 6-hydroxyluteolin (-8.9 against DPP-IV and PPARγ) and glycyrrhetaldehyde (DPP-IV -9.7 and PPARγ -8.5) have exhibited higher binding affinity compared to the positive control. Therefore, the above compounds were further considered for molecular dynamics simulation which showed stability of the docked complexes. Hence, studied mode of actions might produce a concerted role of MA in increasing the rate of glucose absorption and uptake followed by the in silico studies which suggest that the compounds identified from MA may inhibit DPP-IV and PPARγ phosphorylation.

Globularia alypum L. and Related Species: LC-MS Profiles and Antidiabetic, Antioxidant, Anti-Inflammatory, Antibacterial and Anticancer Potential

Species from the genus Globularia L. have been used as healing agents for various ailments, with utilization of Globularia alypum L. being most frequently reported. The aim of this study was to evaluate the antidiabetic, antioxidant, anti-inflammatory, antibacterial and anticancer potential of G. alypum and three related species, G. punctata Lapeyr., G. cordifolia L. and G. meridionalis (Podp.) O.Schwarz, in relation to their phytochemical compositions. Globularin and verbascoside were identified using LC-PDA-ESI-MSn as the major metabolites of G. alypum with known biological activities. G. alypum demonstrated the greatest α-glucosidase inhibitory activity and DPPH radical scavenging activity (IC50 = 17.25 μg/mL), while its anti-inflammatory activity was not significantly different from those of related species. All investigated species showed considerable antibacterial activity against methicillin-resistant Staphylococcus aureus in the broth microdilution method (MIC = 1.42-3.79 mg/mL). G. punctata also showed antibacterial activities against Escherichia coli (MIC = 1.42 mg/mL), Bacillus subtilis (MIC = 1.89 mg/mL), B. cereus (MIC = 2.84 mg/mL) and Enterococcus faecalis (MBC = 5.68 mg/mL). G. punctata, G. cordifolia and G. meridionalis showed greater anticancer potential than G. alypum. Obtained results indicate investigated Globularia species could serve as sources of diverse bioactive molecules, with G. punctata having the greatest antibacterial potential.

Biological Activity of Extracts of Red and Yellow Fruits of Cornus mas L.-An In Vitro Evaluation of Antioxidant Activity, Inhibitory Activity against α-Glucosidase, Acetylcholinesterase, and Binding Capacity to Human Serum Albumin

Although extracts are broadly used in order to support the treatment of numerous diseases, only in a limited number of cases is the process of applying and establishing their mechanisms of action scientifically analyzed. Fruits of Cornelian cherry are an abundant source of iridoids, anthocyanins, flavonols and phenolic acids. The aim of the present study was to evaluate the in vitro bioactivity of red and yellow Cornelian cherry fruits’ extracts. The biological potential of extracts, in a broad sense, involved antioxidant activity in relation to phosphatidylcholine liposomes, inhibitory ability against α-glucosidase and acetylcholinesterase enzymes, as well as interactions with human serum albumin. Studies showed that both extracts were more effective in protecting liposome membranes against free radicals produced by AAPH in an aqueous environment due to the fact that they can be better eliminated by the hydrophilic components of the extracts than those produced by UVB radiation. Extracts exhibited inhibitory activity against acetylcholinesterase and α-glucosidase, wherein loganic acid extract showed noncompetitive inhibition of the enzyme. Moreover, extracts binded to albumin mainly through hydrogen bonds and van der Waals forces. Taken together, red and yellow cherry fruits’ extracts exhibit diverse biological properties and can be exploited as a source of natural therapeutic agents.

Updates on the chemistry, processing characteristics, and utilization of tea flavonoids in last two decades (2001-2021)

Tea flavonoids are widely recognized as critical flavor contributors and crucial health-promoting bioactive compounds, and have long been the focus of research worldwide in food science. The aim of this review paper is to summarize the major progress in tea flavonoid chemistry, their dynamics of constituents and concentrations during tea processing as well as storage, and their health functions studied between 2001 and 2021. Moreover, the utilization of tea flavonoids in the human body has also been discussed for a detailed understanding of their uptake, metabolism, and interaction with the gut microbiota. Many novel tea flavonoids have been identified, including novel A- and B-ring substituted flavan-3-ol derivatives, condensed and oxidized flavan-3-ol derivatives, and glycosylated and methylated flavonoids, and are found to be closely associated with the characteristic color, flavor, and health benefits of tea. Flavoalkaloids exist widely in various teas, particularly 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols. Tea flavonoids behave significantly difference in constituents and concentrations depending on tea cultivars, plantation conditions, multiple stresses, the tea-specified manufacturing steps, and even the long-term storage period. Tea flavonoids exhibit multiple health-promoting effects, particularly their anti-inflammatory in alleviating metabolic syndromes. Interaction of tea flavonoids with the gut microbiota plays vital roles in their health function.

Phenolic compounds as antidiabetic, anti-inflammatory, and anticancer agents and improvement of their bioavailability by liposomes

Phenolic compounds, widespread in plants, are a necessary part of the human regimen due to their antioxidant and pro-oxidative properties. Naturally, phenolics structurally range from a very simple phenolic molecule moiety to an intricate polymer. For decades, phenolic compounds have gained pronounced attention because of their protective effects against degenerative disorders such as inflammation, diabetes and cancer. Physico-chemical properties (eg, solubility) restricted their bioactivity and also limited their usage as nutraceutical ingredients. However, encapsulation technology like liposomal formulations has been developed for the delivery of phenolic compounds without affecting their original aesthetic and organoleptic property. Hence, this review outlines the antioxidant and pro-oxidative properties of phenolic compounds and focuses on biological activity reports of flavonoids and phenolic acids as antidiabetic, anti-inflammatory and anticancer agents. Also, the delivery applications of phenolic compounds as liposomes are discussed with few examples.

Traditional use, phytochemistry, toxicology, and pharmacology of Origanum majorana L

ETHNOPHARMACOLOGICAL RELEVANCE

Origanum majorana L., is an aromatic and medicinal plant distributed in different parts of Mediterranean countries. This species is widely used in traditional medicine for the treatment of many diseases such as allergies, hypertension, respiratory infections, diabetes, stomach pain, and intestinal antispasmodic.

AIM OF THE REVIEW

This work reports previous studies on O. majorana concerning its taxonomy, botanical description, geographical distribution, traditional use, bioactive compounds, toxicology, and biological effects.

MATERIALS AND METHODS

Different scientific data bases such as Web of Science, Scopus, Wiley Online, SciFinder, Google Scholar, PubMed, ScienceDirect, and SpringerLink were consulted to collect data about O. majorana. The presented data emphasis bioactive compounds, traditional uses, toxicological investigations, and biological activities of O. majorana.

RESULTS

The findings of this work marked an important correlation between the traditional use of O. majorana as an anti-allergic, antihypertensive, anti-diabetic agent, and its biological effects. Indeed, pharmacological investigations showed that essential oils and extracts from O. majorana exhibit different biological properties, particularly; antibacterial, antifungal, antioxidant, antiparasitic, antidiabetic, anticancer, nephrotoxicity protective, anti-inflammatory, analgesic and anti-pyretic, hepatoprotective, and antimutagenic effects. Toxicological evaluation confirmed the safety and innocuity of this species and supported its medicinal uses. Several bioactive compounds belonging to different chemical family such as terpenoids, flavonoids, and phenolic acids were also identified in O. majorana.

CONCLUSIONS

The results suggest that the pharmacological properties of O. majorana confirm its traditional uses. Indeed, O. majorana essential oils showed remarkable antimicrobial, antioxidant, anticancer, anti-inflammatory, antimutagenic, nephroprotective, and hepatoprotective activities. However, further investigations regarding the evaluation of molecular mechanisms of identified compounds against human cancer cell lines, inflammatory process, and microbial infections are needed to validate pharmacodynamic targets. The toxicological investigation of O. Majorana confirmed its safety and therefore encouraged pharmacokinetic evaluation tests to validate its bioavailability.

Ligand compatibility of salacinol-type α-glucosidase inhibitors toward the GH31 family

We show that salacinol-type α-glucosidase inhibitors are ligand-compatible with the GH 31 family. Salacinol and its 3′-O-benzylated analogs inhibit human lysosomal α-glucosidase at submicromolar levels. Simple structure-activity relationship studies reveal that the salacinol side-chain stereochemistry significantly influences binding to GH31 α-glucosidases.

Salacinol-type α-glucosidase inhibitors are ligand-compatible with the GH 31 family. Salacinol and its 3′-O-benzylated analogs inhibit human lysosomal α-glucosidase at submicromolar levels.

Evaluation of the Antidiabetic and Insulin Releasing Effects of A. squamosa, Including Isolation and Characterization of Active Phytochemicals

Annona squamosa is generally referred to as a 'custard apple'. Antidiabetic actions of hot water extract of Annona squamosa (HWAS) leaves together with isolation of active insulinotropic compounds were studied. Insulin release, membrane potential and intracellular Ca2+ were determined using BRIN-BD11 cells and isolated mouse islets. 3T3L1 adipocytes and in vitro models were used to determine cellular glucose uptake, insulin action, starch digestion, glucose diffusion, DPP-IV activity and glycation. Glucose intolerant high-fat fed rats were used for in vivo studies. Active compounds were isolated and characterized by HPLC, LCMS and NMR. HWAS stimulated insulin release from clonal β-cells and mouse islets. Using fluorescent indicator dyes and modulators of insulin secretion, effects could be attributed to depolarization of β-cells and influx of Ca2+. Secretion was stimulated by isobutylmethylxanthine (IBMX), tolbutamide or 30 mM KCl, indicating additional non-KATP dependent pathways. Extract stimulated cellular glucose uptake and insulin action and inhibited starch digestion, protein glycation, DPP-IV enzyme activity and glucose diffusion. Oral HWAS improved glucose tolerance and plasma insulin in high-fat fed obese rats. Treatment for 9 days with HWAS (250 mg/5 mL/kg), partially normalised energy intake, body weight, pancreatic insulin content, and both islet size and beta cell mass. This was associated with improved oral glucose tolerance, increased plasma insulin and inhibition of plasma DPP-IV activity. Isolated insulinotropic compounds, including rutin (C27H30O16), recapitulated the positive actions of HWAS on beta cells and in vivo glucose tolerance and plasma insulin responses. Annona squamosa is attractive as a dietary adjunct in treatment of T2DM and as a source of potential antidiabetic agents including rutin.

Investigation of Anthocyanidins and Anthocyanins for Targeting α-Glucosidase in Diabetes Mellitus

Anthocyanidins are bioactive compounds found mostly in colored plants and fruits. Consumption of anthocyanidin-rich foods has been shown to reduce the risk of diabetes. However, limited information is available regarding the inhibitory effect and interactions of anthocyanidins on α-glucosidase, the key enzyme that controls diabetes through degrading carbohydrate. Therefore, we used computational docking analysis to investigate the degree and type of inhibition by α-glucosidase, and the structural interactions of enzyme-selected anthocyanidins. The results suggested that anthocyanidins exhibit half maximal inhibitory concentration of 4∼55 μM; the strongest and weakest α-glucosidase inhibitors were delphinidin and malvidin, respectively. Indeed, delphinidin inhibits α-glucosidase in a mixed type, close to non-competitive manner with an inhibitory constant of 78 nM. Addition of a glycoside (glucoside or galactoside) at C3 on the C ring of delphinidin significantly decreased inhibitory activity, and addition of glycosides at C3 on the C ring and C5 on the A ring of delphinidin prevented all inhibitory activity. Molecular docking and free binding energy accurately confirmed the mode of inhibition determined by enzyme kinetics. These data will inform the use of alternative sources of anthocyanidins in functional foods and dietary supplements for prevention of diabetes. The results provide useful information for evaluating possible molecular models using anthocyanins/anthocyanidins as templates and α-glucosidase as the key enzyme in management of diabetes.

Validation of Antidiabetic Potential of Gymnocarpos decandrus Forssk

Gymnocarpos decandrus Forssk. is a well-known grazing wild plant. This study targets scientific validation of its claimed antidiabetic activity and exploring its bioactive metabolites. Chromatographic purification of G. decandrus ethanol extract (GDEE) allowed isolation of vitexin (C1), protocatechuic acid (C2) and quercetin (C3). HPLC-PDA-MS/MS enabled identification of nineteen metabolites; 13 flavonoids, 5 saponins, and 1 phenolic acid in G. decandrus and four in the genus Gymnocarpos for the first time. The antidiabetic potential was evaluated via testing the Coxsackie B4 virus and α-glucosidase inhibitory potentials. C3 exhibited its potent antiviral activity through blocking of the virus attachment (96.28%, SI 4.41) and virus inactivation before adsorption (91.47%, SI 4.78). GDEE and C1-C3 showed dose dependent α-glucosidase inhibitory activity with IC₅₀ of 733.9, 293.3, 118.1 and 69.1 µg/mL, respectively. Our study represents the sole complete map for G. decandrus secondary metabolites and presents it as promising drug for diabetes management.

Evaluation of the Anti-Diabetic Activity of Some Common Herbs and Spices: Providing New Insights with Inverse Virtual Screening

Culinary herbs and spices are widely used as a traditional medicine in the treatment of diabetes and its complications, and there are several scientific studies in the literature supporting the use of these medicinal plants. However, there is often a lack of knowledge on the bioactive compounds of these herbs and spices and their mechanisms of action. The aim of this study was to use inverse virtual screening to provide insights into the bioactive compounds of common herbs and spices, and their potential molecular mechanisms of action in the treatment of diabetes. In this study, a library of over 2300 compounds derived from 30 common herbs and spices were screened in silico with the DIA-DB web server against 18 known diabetes drug targets. Over 900 compounds from the herbs and spices library were observed to have potential anti-diabetic activity and liquorice, hops, fennel, rosemary, and fenugreek were observed to be particularly enriched with potential anti-diabetic compounds. A large percentage of the compounds were observed to be potential polypharmacological agents regulating three or more anti-diabetic drug targets and included compounds such as achillin B from yarrow, asparasaponin I from fenugreek, bisdemethoxycurcumin from turmeric, carlinoside from lemongrass, cinnamtannin B1 from cinnamon, crocin from saffron and glabridin from liquorice. The major targets identified for the herbs and spices compounds were dipeptidyl peptidase-4 (DPP4), intestinal maltase-glucoamylase (MGAM), liver receptor homolog-1 (NR5A2), pancreatic alpha-amylase (AM2A), peroxisome proliferator-activated receptor alpha (PPARA), protein tyrosine phosphatase non-receptor type 9 (PTPN9), and retinol binding protein-4 (RBP4) with over 250 compounds observed to be potential inhibitors of these particular protein targets. Only bay leaves, liquorice and thyme were found to contain compounds that could potentially regulate all 18 protein targets followed by black pepper, cumin, dill, hops and marjoram with 17 protein targets. In most cases more than one compound within a given plant could potentially regulate a particular protein target. It was observed that through this multi-compound-multi target regulation of these specific protein targets that the major anti-diabetic effects of reduced hyperglycemia and hyperlipidemia of the herbs and spices could be explained. The results of this study, taken together with the known scientific literature, indicated that the anti-diabetic potential of common culinary herbs and spices was the result of the collective action of more than one bioactive compound regulating and restoring several dysregulated and interconnected diabetic biological processes.

Verification of the anti-inflammatory activity of the polyphenolic-rich fraction of Araucaria bidwillii Hook. using phytohaemagglutinin-stimulated human peripheral blood mononuclear cells and virtual screening

ETHNOPHARMACOLOGICAL RELEVANCE

Araucaria bidwillii Hook., the bunya pine, is an evergreen plant belonging to family Araucariaceae. Traditionally, its leaves and oleoresins have been used as herbal remedies to alleviate pain and inflammation. Based upon the frequent adverse effects accompanying synthetic anti-inflammatory drugs, this study will assess the anti-inflammatory activity of both the total methanol extract and the polyphenolic-rich fraction of A. bidwillii leaves.

MATERIALS AND METHODS

The anti-inflammatory activity was assessed in vitro using phytohaemagglutinin-stimulated human peripheral blood mononuclear cells (PBMCs). Isolation of the major compounds was conducted using various chromatographic techniques. Molecular modelling studies are performed on tumor necrosis factor-α (TNF-α), cyclooxygenase-II (COX-II) and 5-lipooxygenase (5-LOX).

RESULTS

Both the total methanol extract of Araucaria bidwillii leaves and its fraction revealed a dose-dependent manner in lowering the levels of IL-1β, IL-6 and TNF-α with an equivalent activity to that of indomethacin. In addition, the phytochemical investigation of the polyphenolic-rich fraction results in identification of agathisflavone-4',7''-dimethyl ether (1), 7-O-methyl-6-hydroxyapigenin (2) and 4',4'-di-O-methylamentoflavone (3) as the main components. In silico molecular modelling showed that agathisflavone-4',7''-dimethyl ether (1) exhibited the fittest binding in TNF-α active sites, while 7-O-methyl-6-hydroxyapigenin (2) showed the highest inhibition in COX-II whereas 4',4'-di-O-methylamentoflavone (3) is the most potent 5-LOX inhibitor.

CONCLUSION

Thus, the leaves of Araucaria bidwillii could afford a potent anti-inflammatory agent that effectively ameliorates inflammation and its related hazards. This in turn consolidates the fact of using the leaves of Araucaria bidwillii to sooth inflammation in traditional medicine.

Anti-Inflammatory and Antioxidant Activities from the Basolateral Fraction of Caco-2 Cells Exposed to a Rosmarinic Acid Enriched Extract

The potential use of Origanum majorana L. as a source of bioavailable phenolic compounds, specifically rosmarinic acid (RA), has been evaluated. Phenolic bioavailability was tested using an in vitro digestion process followed by a Caco-2 cellular model of intestinal absorption. The high-performance liquid chromatography-photodiode array detector-tandem mass spectrometry (HPLC-PAD-MS/MS) analysis showed the main components in the extract were 6-hydroxyluteolin-7-O-glucoside and rosmarinic acid, followed by luteolin-O-glucoside. After digestion process, the amount of total phenolic compounds (TPC) only decreased slightly, although a remarkable reduction in RA (near 50%) was detected. Bioavailable fraction contained 7.37 ± 1.39 mg/L digested extract of RA with small quantities of lithospermic acid and diosmin and presented an important antioxidant activity (0.89 ± 0.09 mmol Trolox/L digested extract). Besides, this bioavailable fraction produced a significant inhibition in TNF-α, IL-1β, and IL-6 secretion, using a human THP-1 macrophages model. Therefore, RA content in the basolateral compartment could play an important role in the antioxidant and anti-inflammatory activities found.

Antioxidant and Antidiabetic Effects of Flavonoids: A Structure-Activity Relationship Based Study

The best described pharmacological property of flavonoids is their capacity to act as potent antioxidant that has been reported to play an important role in the alleviation of diabetes mellitus. Flavonoids biochemical properties are structure dependent; however, they are yet to be thoroughly understood. Hence, the main aim of this work was to investigate the antioxidant and antidiabetic properties of some structurally related flavonoids to identify key positions responsible, their correlation, and the effect of methylation and acetylation on the same properties. Antioxidant potential was evaluated through dot blot, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, ABTS⁺ radical scavenging, ferric reducing antioxidant power (FRAP), and xanthine oxidase inhibitory (XOI) assays. Antidiabetic effect was investigated through α-glucosidase and dipeptidyl peptidase-4 (DPP-4) assays. Results showed that the total number and the configuration of hydroxyl groups played an important role in regulating antioxidant and antidiabetic properties in scavenging DPPH radical, ABTS⁺ radical, and FRAP assays and improved both α-glucosidase and DPP-4 activities. Presence of C-2-C-3 double bond and C-4 ketonic group are two essential structural features in the bioactivity of flavonoids especially for antidiabetic property. Methylation and acetylation of hydroxyl groups were found to diminish the in vitro antioxidant and antidiabetic properties of the flavonoids.

Antidiabetic plant-derived nutraceuticals: a critical review

Diabetes mellitus (DM) is one of the major health problems in the world, especially amongst the urban population. Chemically synthesized drugs used to decrease the ill effects of DM and its secondary complications cause adverse side effects, viz., weight gain, gastrointestinal disturbances, and heart failure. Currently, various other approaches, viz., diet control, physical exercise and use of antidiabetic plant-derived molecules/foods are advocated to manage DM, as they are economical with fewer or no side effects. This review mainly focuses on antidiabetic plants, chemically characterized plant molecules and plant-based foods in the treatment of DM. Very little science-based evidence is available on the mechanism of action of plant-derived food molecules on the DM targets. Critical DM targets include α-amylase, α-glucosidase, DPP-IV, aldose reductase, PPAR-γ, AMP kinase and GLUT4. In-depth studies carried out on a few of those targets with specific mechanisms of action are addressed in this review. This review may help future researchers in identifying a right plant molecule to treat DM or to develop food formulations for DM management.

Dietary flavonoid aglycones and their glycosides: Which show better biological significance?

The dietary flavonoids, especially their glycosides, are the most vital phytochemicals in diets and are of great general interest due to their diverse bioactivity. The natural flavonoids almost all exist as their O-glycoside or C-glycoside forms in plants. In this review, we summarized the existing knowledge on the different biological benefits and pharmacokinetic behaviors between flavonoid aglycones and their glycosides. Due to various conclusions from different flavonoid types and health/disease conditions, it is very difficult to draw general or universally applicable comments regarding the impact of glycosylation on the biological benefits of flavonoids. It seems as though O-glycosylation generally reduces the bioactivity of these compounds - this has been observed for diverse properties including antioxidant activity, antidiabetes activity, anti-inflammation activity, antibacterial, antifungal activity, antitumor activity, anticoagulant activity, antiplatelet activity, antidegranulating activity, antitrypanosomal activity, influenza virus neuraminidase inhibition, aldehyde oxidase inhibition, immunomodulatory, and antitubercular activity. However, O-glycosylation can enhance certain types of biological benefits including anti-HIV activity, tyrosinase inhibition, antirotavirus activity, antistress activity, antiobesity activity, anticholinesterase potential, antiadipogenic activity, and antiallergic activity. However, there is a lack of data for most flavonoids, and their structures vary widely. There is also a profound lack of data on the impact of C-glycosylation on flavonoid biological benefits, although it has been demonstrated that in at least some cases C-glycosylation has positive effects on properties that may be useful in human healthcare such as antioxidant and antidiabetes activity. Furthermore, there is a lack of in vivo data that would make it possible to make broad generalizations concerning the influence of glycosylation on the benefits of flavonoids for human health. It is possible that the effects of glycosylation on flavonoid bioactivity in vitro may differ from that seen in vivo. With in vivo (oral) treatment, flavonoid glycosides showed similar or even higher antidiabetes, anti-inflammatory, antidegranulating, antistress, and antiallergic activity than their flavonoid aglycones. Flavonoid glycosides keep higher plasma levels and have a longer mean residence time than those of aglycones. We should pay more attention to in vivo benefits of flavonoid glycosides, especially C-glycosides.

Selected novel 5'-amino-2'-hydroxy-1, 3-diaryl-2-propen-1-ones arrest cell cycle of HCT-116 in G0/G1 phase

A series of 5'-amino-2'-hydroxy-1,3-diaryl-2-propen-1-ones (AC1-AC15) were synthesized by Claisen-Schmidt condensation of 5'-acetamido-2'-hydroxy acetophenone with various substituted aromatic aldehydes. The synthesized compounds were characterized by FTIR, ¹H NMR and mass spectrometry and evaluated for their selective cytotoxicity using MTT assay on two cancer cell lines namely breast cancer cell line (MCF-7), colon cancer cell line (HCT-116) and one normal kidney epithelial cell line (Vero). Among the tested compounds, AC-10 showed maximum cytotoxic effect on MCF-7 cell line with IC₅₀ value 74.7 ± 3.5 µM. On HCT-116 cells, AC-13 exhibited maximum cytotoxicity with IC₅₀ value 42.1 ± 4.0 µM followed by AC-14 and AC-10 with IC₅₀ values 62 ± 2.3 µM and 95.4 ± 1.7 µM respectively. All tested compounds were found to be safe on Vero cell line with IC₅₀ value more than 200 µM. Based on their highest efficacy on HCT-116, AC-10, AC-13 and AC-14 were selected for mechanistic study on this cell line by evaluating changes nucleomorphological characteristics using acridine orange-ethidium bromide (AOEB) dual stain and by analyzing cell cycle with flow cytometry using propidium iodide stain. In AOEB staining, all three tested compounds showed significant (p < 0.05) increase in percentage apoptotic nuclei compared to control cells, with highest increase in apoptotic nuclei by AC-13 treatment (31 %). Flow cytometric studies showed cell cycle arrest by AC-10 and AC-14 treatment in G₀/G₁ phase and by AC-13 in G₀/G₁ and G₂/M phase. The study reflected the potential of AC-10, AC-13 and AC-14 to be the lead molecules for further optimization.

Bioactive diterpenoids and flavonoids from the aerial parts of Scoparia dulcis

Six new diterpenoids, 4-epi-7α-O-acetylscoparic acid A (1), 7α-hydroxyscopadiol (2), 7α-O-acetyl-8,17β-epoxyscoparic acid A (3), neo-dulcinol (4), dulcinodal-13-one (5), and 4-epi-7α-hydroxydulcinodal-13-one (6), and a new flavonoid, dillenetin 3-O-(6″-O-p-coumaroyl)-β-D-glucopyranoside (10), along with 12 known compounds, were isolated from the aerial parts of Scoparia dulcis. The 7S absolute configuration of the new diterpenoids 1-4 and 6 was deduced by comparing their NOESY spectra with that of a known compound, (7S)-4-epi-7-hydroxyscoparic acid A (7), which was determined by the modified Mosher's method. The flavonoids scutellarein (11), hispidulin (12), apigenin (15), and luteolin (16) and the terpenoids 4-epi-scopadulcic acid B (9) and betulinic acid (19) showed more potent α-glucosidase inhibitory effects (with IC50 values in the range 13.7-132.5 μM) than the positive control, acarbose. In addition, compounds 1, 11, 12, 15, 16, and acerosin (17) exhibited peroxisome proliferator-activated receptor gamma (PPAR-γ) agonistic activity, with EC50 values ranging from 0.9 to 24.9 μM.

WITHDRAWN: Flavonoid glycosylation and biological benefits

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Advance in dietary polyphenols as α-glucosidases inhibitors: a review on structure-activity relationship aspect

The dietary polyphenols as α-glucosidases inhibitors have attracted great interest among researchers. The aim of this review is to give an overview of the research reports on the structure-activity relationship of dietary polyphenols inhibiting α-glucosidases. The molecular structures that influence the inhibition are the following: (1) The hydroxylation and galloylation of flavonoids including catechins improve the inhibitory activity. (2) The glycosylation of hyroxyl group and hydrogenation of the C2=C3 double bond on flavonoids weaken the inhibition. (3) However, cyaniding glycosides show higher inhibition against than cyanidin. Proanthocyanidins oligomers exhibit a stronger inhibitory activity than their polymers. (4) The hydroxylation on B ring and the glycosylation of stilbenes reduce the inhibitory activity. (5) Caffeoylquinic acids display strong inhibition against α-glucosidases. However, hydroxycinnamic acid, ferulic acid, and gallic acid hardly inhibited α-glucosidases. (6) The coupled galloyl structures attached to C-3 and C-6 of the 4C(1) glucose core of ellagitanin gave basic inhibitory activity. (7) The mono-glycosylation of chalcones slightly lowers the inhibition. However, the diglycosylation of chalcones significantly decreased the activity.

Inhibition of Advanced Glycation End-Product Formation by Origanum majorana L. In Vitro and in Streptozotocin-Induced Diabetic Rats

The development of AGE inhibitors is considered to have therapeutic potential in patients with diabetes diseases. The aim of the present study was investigate the effect of methanolic extract of the leaves of Origanum majorana (OM) used as spice in many countries on AGEs formation. In vitro studies indicated a significant inhibitory effects on the formation of AGEs. Their antiglycation activities were not only brought about by their antioxidant activities but also related to their trapping abilities of reactive carbonyl species such as methylglyoxal, an intermediate reactive carbonyl of AGE formation. The results demonstrate that OM have significant effects on in vitro AGE formation, and the glycation inhibitory activity was more effectively than those obtained using as standard antiglycation agent aminoguanidine. OM is a potent agent for protecting LDL against oxidation and glycation. Treatment of streptozotocin-diabetic mice with OM and glibenclamide for 28 days had beneficial effects on renal metabolic abnormalities including glucose level and AGEs formation. Diabetic mice showed increase in tail tendon collagen, glycated collagen linked fluorescence and reduction in pepsin digestion. Treatment with OM improved these parameters when compared to diabetic control and glibenclamide.

α-glucosidase inhibitors from plants: A natural approach to treat diabetes

Diabetes is a common metabolic disease characterized by abnormally high plasma glucose levels, leading to major complications, such as diabetic neuropathy, retinopathy, and cardiovascular diseases. One of the effective managements of diabetes mellitus, in particular, non-insulin-dependent diabetes mellitus (NIDDM) to decrease postprandial hyperglycemia, is to retard the absorption of glucose by inhibition of carbohydrate hydrolyzing enzymes, such as α-glucosidase and α-amylase, in the digestive organs. α-Glucosidase is the key enzyme catalyzing the final step in the digestive process of carbohydrates. Hence, α-glucosidase inhibitors can retard the liberation of d-glucose from dietary complex carbohydrates and delay glucose absorption, resulting in reduced postprandial plasma glucose levels and suppression of postprandial hyperglycemia. In recent years, many efforts have been made to identify effective α-glucosidase inhibitors from natural sources in order to develop a physiologic functional food or lead compounds for use against diabetes. Many α-glucosidase inhibitors that are phytoconstituents, such as flavonoids, alkaloids, terpenoids,anthocyanins, glycosides, phenolic compounds, and so on, have been isolated from plants. In the present review, we focus on the constituents isolated from different plants having α-glucosidase inhibitory potency along with IC50 values.

The effects of corni fructus extract and its fractions against α-glucosidase inhibitory activities in vitro and sucrose tolerance in normal rats

Corni fructus (Cornus officinalis Sieb. et Zucc.) is a traditional medicine exerting multifaceted protective effects against diabetes and its complications. In this study, to further identify the physiological effects of corni fructus against diabetes and its complications, we investigated α-glucosidase inhibitory activities in vitro and employed the sucrose tolerance test as an indicator of the control of the postprandial blood glucose level. In vitro assays showed that corni fructus extract has a higher inhibitory activity than its major components. Then, corni fructus extract was fractionated again to screen the fractions showing a strong inhibitory activity against α-glucosidase. Of the tested fractions, five showed a rate of α-glucosidase inhibition of over 80%. Next, the four abundant fractions were evaluated their IC(50) values, as well as the inhibition mode in vitro and plasma glucose level after sucrose loading in normal Wistar rats. As a result, the IC(50) values of these fractions were between 1.1-2.1 μg/ml. Among the four fractions, three showed mixed inhibition, while one (Fr. 4-9) showed the competition-independent inhibition of α-glucosidase. In addition, Fr. 4S-1 significantly inhibited the rise in the plasma glucose levels at a dose of 20 mg/kg body weight after sucrose loading. These results indicate that Fr. 4S-1 from corni fructus has a potential to control postprandial hyperglycemia by α-glucosidase inhibition.

Methyl caffeate as an alpha-glucosidase inhibitor from Solanum torvum fruits and the activity of related compounds

In screening experiments for rat intestinal alpha-glucosidase (sucrase and maltase) inhibitors in 325 plants cultivated in Japan's southern island, of Tanegashima, marked inhibition against both sucrase and maltase was found in the extract of the fruit of Solanum torvum. Enzyme-assay guided fractionation of the extract led to the isolation of methyl caffeate (1) as a rat intestinal sucrase and maltase inhibitor. We examined 13 caffeoyl derivatives for sucrase- and maltase-inhibitory activities. The results showed that methyl caffeate (1) had a most favorable structure for both sucrase and maltase inhibition, except for a higher activity of methyl 3,4,5-trihydroxycinnamate (14) against sucrase. Its moderate inhibitory action against alpha-glucosidase provides a prospect for antidiabetic usage of S. torvum fruit.

Combined effect of total alkaloids from Feculae Bombycis and natural flavonoids on diabetes

Both total alkaloids from Feculae Bombycis (TAFB) and natural flavonoids can inhibit α-glucosidase activity to depress the glucose level in blood. To investigate the cooperative effect of TAFB and flavonoids on blood glucose, we have studied their combined function compared with individual ingredients on enzymology, in-vitro and in-vivo. In the enzymological assay, the combination of TAFB and flavonoids showed more effective inhibition, compared with either TAFB or flavonoids alone, to α-glucosidase activity. In the everted intestine model in-vitro, the combined inhibition of starch hydrolysation and glucose transference to blood was much stronger than with separate components. In short-term studies with normal and experimentally-induced diabetic mice in-vivo, the combination of TAFB and flavonoids also had a stronger suppressive effect on the postprandial elevation in blood glucose after oral administration. In long-term treatment to diabetic mice in-vivo, the compound prescription could depress not only the fasting blood glucose, but also the fasting blood total cholesterol. These results demonstrated that TAFB and flavonoids could inhibit α-glucosidase activity cooperatively, which would successfully depress blood glucose level in the therapy of diabetes.

Terminalia bellirica stimulates the secretion and action of insulin and inhibits starch digestion and protein glycation in vitro

Traditional plant treatments have been used throughout the world for the therapy of diabetes mellitus. The aim of the present study was to investigate the efficacy and mode of action of Terminalia bellirica used traditionally for the treatment of diabetes in India. T. bellirica aqueous extract stimulated basal insulin output and potentiated glucose-stimulated insulin secretion concentration-dependently in the clonal pancreatic β-cell line, BRIN-BD11 (P < 0·001). The insulin-secretory activity of the plant extract was abolished in the absence of extracellular Ca2+ and by inhibitors of cellular Ca2+ uptake, diazoxide and verapamil (P < 0·001; n 8). Furthermore, the extract did not increase insulin secretion in depolarised cells and did not further augment insulin secretion triggered by tolbutamide or glibenclamide. T. bellirica extract also displayed insulin-mimetic activity and enhanced insulin-stimulated glucose uptake in 3T3-L1 adipocytes by 300 %. At higher concentrations, the extract also produced a 10–50 % (P < 0·001) decrease in starch digestion in vitro and inhibited protein glycation (P < 0·001). The present study has revealed that components in T. bellirica extract stimulate insulin secretion, enhance insulin action and inhibit both protein glycation and starch digestion. The former actions are dependent on the active principle(s) in the plant being absorbed intact. Future work assessing the use of T. bellirica as a dietary adjunct or as a source of active anti-diabetic agents may provide new opportunities for the treatment of diabetes.

Flavonol Caffeoylglycosides as alpha-Glucosidase Inhibitors from Spiraea cantoniensis Flower

In the screening experiments for rat intestinal alpha-glucosidase inhibitors in 218 plants cultivated in the Japanese temperate region, potent maltase-inhibiting activity was found in the extract of flowers of Spiraea cantoniensis. The enzyme assay guided fractionation of the extract led to the isolation of three flavonol caffeoylglycosides, quercetin 3- O-(6- O-caffeoyl)-beta-galactoside ( 1), kaempferol 3- O-(6- O-caffeoyl)-beta-galactoside ( 2), and kaempferol 3- O-(6- O-caffeoyl)-beta-glucoside ( 3), as rat intestinal maltase inhibitors. This is the first report on the alpha-glucosidase-inhibitory activity of those flavonol caffeoylglycosides. Comparison in the activity of the isolates indicated the importance of caffeoyl substructures in the molecule for the alpha-glucosidase-inhibiting activity. The relatively high contents of the active isolates in the plant suggest that S. cantoniensis could be physiologically useful for treatment of diabetes.

Asparagus adscendens(Shweta musali) stimulates insulin secretion, insulin action and inhibits starch digestion

Diabetes mellitus is a complex metabolic disease characterised by glucose overproduction and under-utilisation. As the incidence of diabetes expands rapidly across the globe there is an urgent need to expand the range of effective treatments. Higher plants such asAsparagus adscendensprovide therapeutic opportunities and a rich source of potential antidiabetic agents. In the present study an aqueous extract ofAsparagus adscendenswas shown to induce a significant non-toxic 19–248% increase in glucose-dependent insulinotropic actions (P<0·001) in the clonal pancreatic β cell line, BRIN-BD11. In addition, the extract produced an 81% (P<0·0001) increase in glucose uptake in 3T3-L1 adipocytes.Asparagus adscendensalso produced a 21% (P<0·001) decrease in starch digestionin vitro. The present study has revealed the presence of insulinotropic, insulin-enhancing activity and inhibitory effects on starch digestion inAsparagus adscendens. The former actions are dependent on the active principle(s) in the plant being absorbed intact. Future work assessing its use as a dietary adjunct or as a source of active components may provide new opportunities for the treatment of diabetes

Inhibitory effects of 5,6,7-trihydroxyflavones on tyrosinase

Baicalein (1), 6-hydroxyapigenin (6), 6-hydroxygalangin (13) and 6-hydroxy-kaempferol (14), which are naturally occurring flavonoids from a set of 14 hydroxy-flavones tested, exhibited high inhibitory effects on tyrosinase with respect to L-DOPA, while each of the 5,6,7-trihydroxyflavones 1, 6, 13 or 14 acted as a cofactor to monophenolase. Moreover, 6-hydroxykaempferol (14) showed the highest activity and was a competitive inhibitor of tyrosinase compared to L-DOPA. 5,6,7-Trihydroxyflavones 1, 6, 13 or 14 showed also high antioxidant activities. Hence, we conclude that the 5,6,7-trihydroxy-flavones are useful as good depigmentation agents with inhibitory effects in addition to their antioxidant properties.

Protective effect of volatile oil, alcoholic and aqueous extracts of Origanum majorana on lead acetate toxicity in mice

Natural dietary antioxidants are extensively studied for their ability to protect cells from miscellaneous damages. Origanum majorana L., Lamiaceae, is a potent antioxidant. The effect of administration of O. majorana (volatile oil, alcoholic and aqueous extracts) on oral administration of lead acetate in the diet of mice at concentration 0.5% (W/W) for one month were studied by measuring serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), urea and creatinine, histopathological changes of the liver and kidney and genotoxicity including, rate of micronucleus and chromosomal aberrations in bone marrow cells. Mice were treated with the 3 different forms of O. majorana, one month before and maintained with lead acetate administration. The 3 forms of O. majorana induced a significant decrease in serum activities of transaminases (AST & ALT), ALP, urea and creatinine and improved the liver and kidney histology in comparison with lead acetate treated group. Alcoholic extracts of O. majorana significantly reduced the rate of micronucleus, number of aberrant cells and different kinds of chromosomal aberrations. Volatile oil extract significantly reduced the rate of micronucleus and chromosomal fragments. Aqueous extract and volatile oil also of O. majorana significantly reduced number of gaps, ring chromosome and stickiness. It could be concluded that O. majorana plays an important role in ameliorating liver and kidney functions and genotoxicity induced by lead toxicity.

Use of the pig caecum model to mimic the human intestinal metabolism of hispidulin and related compounds

Up to now, the metabolism of hispidulin (5,7,4'-trihydroxy-6-methoxyflavone), a potent ligand of the central human benzodiazepine receptor, has not been investigated. To elucidate the metabolism of hispidulin in the large intestine, its biotransformation by the pig caecal microflora was studied. In addition, the efficiency of the pig caecal microflora to degrade galangin (3,5,7-trihydroxyflavone), kaempferol (3,5,7,4'-tetrahydroxyflavone), apigenin (5,7,4'-trihydroxyflavone), and luteolin (5,7,3',4'-tetrahydroxyflavone) was investigated. Identification of the formed metabolites was performed by high-performance liquid chromatography (HPLC)-diode array detection, HPLC-electrospray ionization-tandem mass spectrometry, and high-resolution gas chromatography-mass spectrometry. The caecal microflora transformed hispidulin to scutellarein (5,6,7,4'-tetrahydroxyflavone), an effective alpha-glucosidase inhibitor, and 3-(4-hydroxyphenyl)-propionic acid; galangin to phenylacetic acid and phloroglucinol; kaempferol to 4-hydroxyphenylacetic acid, phloroglucinol, and 4-methylphenol; apigenin to 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid, and luteolin to 3-(3-hydroxyphenyl)-propionic acid, respectively. To elucidate to what extent different hydroxylation patterns on the B-ring influence the degradation degree of flavonoids, the conversions of galangin and kaempferol as well as that of apigenin and luteolin were compared with those of quercetin (3,5,7,3',4'-pentahydroxyflavone) and chrysin (5,7-dihydroxyflavone), respectively. Regardless of the flavonoid subclass, the presence of a hydroxy group at the 4'-position seems to be a prerequisite for fast breakdown. An additional hydroxy group at the B-ring did not affect the degradation degree.

Inhibition of .ALPHA.-Glucosidase and .ALPHA.-Amylase by Flavonoids

The inhibitory activity of six groups of flavonoids against yeast and rat small intestinal alpha-glucosidases and porcine pancreatic alpha-amylase was compared, and chemical structures of flavonoids responsible for the inhibitory activity were evaluated. Yeast alpha-glucosidase was potently inhibited by the anthocyanidin, isoflavone and flavonol groups with the IC50 values less than 15 microM. The following structures enhanced the inhibitory activity: the unsaturated C ring, 3-OH, 4-CO, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring. Rat small intestinal alpha-glucosidase was weakly inhibited by many flavonoids, and slightly by the anthocyanidin and isoflavone groups. 3-OH and the hydroxyl substitution on the B ring increased the inhibitory activity. In porcine pancreatic alpha-amylase, luteolin, myricetin and quercetin were potent inhibitors with the IC50 values less than 500 microM. The 2,3-double bond, 5-OH, the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring enhanced the inhibitory activity, while 3-OH reduced it.

Acylated flavonoids and phenol glycosides from Veronica thymoides subsp. pseudocinerea

A new acylated flavone glucoside, 3'-hydroxyscutellarein 7-O-(6''-O-protocatechuoyl)-beta-glucopyranoside (1), and a new phenol glucoside, 3,5-dihydroxyphenethyl alcohol 3-O-beta-glucopyranoside (6) were isolated from Veronica thymoides subsp. pseudocinerea together with seven known flavone, phenol and lignan glycosides; 3'-hydroxyscutellarein 7-O-(6''-O-trans-feruloyl)-beta-glucopyranoside (2), 3'-hydroxy, 6-O-methylscutellarein 7-O-beta-glucopyranoside (3), luteolin 7-O-beta-glucopyranoside (4), isoscutellarein 7-O-(6'''-O-acetyl)-beta-allopyranosyl (1''' --> 2'')-beta-glucopyranoside (5), 3,4-dihydroxyphenethyl alcohol 8-O-beta-glucopyranoside (7), benzyl alcohol 7-O-beta-xylopyranosyl (1" --> 2')-beta-glucopyranoside (8), and (+)-syringaresinol 4'-O-beta-glucopyranoside (9). Compounds 2, 3 and 7-9 were reported for the first time in the genus Veronica. The structures of the isolates were determined by means of spectroscopic (UV, IR, 1D and 2D NMR, HR ESI-MS) methods. Isolated compounds (1-7) exhibited potent radical scavenging activity against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.