Alpha-glucosidase Inhibitory Effects of Flavonoids, Phenolic Acids and Iridoids Isolated From Vinca soneri: In vitro and in silico Perspectives.

Various Vinca species have been traditionally used for their antihypertensive, sedative, and hemostatic properties, as well as for treating diabetes. In this study, some flavonoids, phenolic acids and iridoids were isolated from an endemic Vinca species, Vinca soneri for the first time. α-Glucosidase inhibitory effects of the isolates were tested and kaempferol-3-O-α-rhamnopyranosyl (1→6) ß-galactopyranoside (1) was found to be the most active one with an IC50 value of 285.73 ± 7.35 µM. Enzyme kinetic assay revealed that it inhibited α-glucosidase in competitive manner. Molecular geometry of 1 was predicted and Frontier molecular orbital analysis was performed using Density Functional Theory (DFT) calculations. Molecular docking and MM-GBSA calculations predicted good fit for 1 in the enzyme active site and key interactions with the catalytic residues. As a result, current study identifies 1 as a promising competitive α-glucosidase inhibitor to be developed as a potential antidiabetic drug candidate.

In Vitro and in Silico Investigation of DNA Interaction, Topoisomerase I and II Inhibitory Properties of Polydatin.

Polydatin or piceid, is the 3-O-glucoside of resveratrol and is found abundantly in grapes, peanuts, wine, beer, and cacao products. Although anticancer activity of polydatin was reported before, and potential antiproliferative mechanisms of polydatin have been proposed, its direct effects on DNA and inhibitory potential against topoisomerase enzymes have remained unknown. In this study we aimed to reveal the link between polydatin's effects on DNA and DNA-topoisomerases and its antiproliferative promise. For this purpose, we evaluated the effects of polydatin on DNA and DNA topoisomerase using in vitro and in silico techniques. Polydatin was found to protect DNA against Fenton reaction-induced damage while not showing any hydrolytic nuclease effect. Further, polydatin inhibited topoisomerase II but not topoisomerase I. According to molecular docking studies, polydatin preferably showed minor groove binding to DNA where the stilbene moiety was important for binding to the DNA-topoisomerase II complex. As a result, topoisomerase II inhibition might be another anticancer mechanism of polydatin.

Multiple biological effects of secondary metabolites of Ziziphus jujuba: isolation and mechanistic insights through in vitro and in silico studies.

In this study, we tested tyrosinase and α-glucosidase effects of different extracts of Ziziphus jujuba fruits. The n-BuOH subextract inhibited both tyrosinase and α-glucosidase (IC50 = 18.82 ± 1.13 and 25.03 ± 0.77 µg/mL, respectively) better than the positive controls kojic acid and acarbose (IC50 = 58.26 ± 0.25 and 46.10 ± 2.3 µg/mL, respectively). Thus, the n-BuOH extract was selected for further phytochemical studies. Indole-3-lactic acid methylester, catechin, magnoflorine, kaempferol 3-O-α-rhamnopyranosyl-(1 → 6)-ß-galactopyranoside, quercetin 3-O-α-rhamnopyranosyl-(1 → 6)-ß-galactopyranoside, and procyanidin B4 were isolated from the extract. We tested α-glucosidase and tyrosinase inhibitory effects, as well as DNA nuclease effects of the isolated compounds. Procyanidin B4 exhibited the best activity against both tyrosinase and α-glucosidase (IC50 = 60.25 ± 0.88 and 170.18 ± 5.60 µg/mL, respectively). The isolates did not show any nuclease effect at increasing concentrations. Molecular docking studies provided insights into inhibition mechanisms of the isolates against tyrosinase and α-glucosidase at the molecular level. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00217-021-03946-0.

Flavonoids as tyrosinase inhibitors in in silico and in vitro models: basic framework of SAR using a statistical modelling approach.

Flavonoids are widely distributed in plants and constitute the most common polyphenolic phytoconstituents in the human diet. In this study, the in vitro inhibitory activity of 44 different flavonoids (1-44) against mushroom tyrosinase was studied, and an in silico study and type of inhibition for the most active compounds were evaluated too. Tyrosinase inhibitors block melanogenesis and take part in melanin production or distribution leading to pigmentation diseases. The in vitro study showed that quercetin was a competitive inhibitor (IC50=44.38 ± 0.13 µM) and achieved higher antityrosinase activity than the control inhibitor kojic acid. The in silico results highlight the importance of the flavonoid core with a hydroxyl at C7 as a strong contributor of interference with tyrosinase activity. According to the developed statistical model, the activity of molecules depends on hydroxylation at C3 and methylation at C8, C7, and C3 in the benzo-γ-pyrane ring of the flavonoids.

Immunomodulatory properties of triterpenes.

The immune system is one of the main defence mechanisms of the human body. Inadequacy of this system or immunodeficiency results in increased risk of infections and tumours, whereas over-activation of the immune system causes allergic or autoimmune disorders. A well-balanced immune system is important for protection and for alleviation of these diseases. There is a growing interest to maintain a well-balanced immune system, especially after the Covid-19 pandemic. Many biological extracts, as well as natural products, have become popular due to their wide array of immunomodulatory effects and influence on the immune system. Triterpenes, one of the secondary metabolite groups of medicinal plants, exhibit immunomodulatory properties by various mechanisms. Different triterpenes, including components of commonly consumed plants, can promote some protection and alleviation of disease symptoms linked with immune responses and thus enhance overall well-being. This review aims to highlight the efficacy of triterpenes in light of the available literature evidence regarding the immunomodulatory properties of triterpenes. We have reviewed widely investigated immunomodulatory triterpenes; oleanolic acid, glycyrrhizin, glycyrrhetinic acid, pristimerin, ursolic acid, boswellic acid, celastrol, lupeol, betulin, betulinic acid, ganoderic acid, cucumarioside, and astragalosides which have important immunoregulatory properties. In spite of many preclinical and clinical trials were conducted on triterpenes related to their immunoregulatory actions, current studies have several limitations. Therefore, especially more clinical studies with optimal design is essential.

In vitro and in silico assessment of DNA interaction, topoisomerase I and II inhibition properties of chrysosplenetin.

Chrysosplenetin is a methoxyflavone with reported anti-cancer effect. We tested its cytotoxic effect on the MCF-7 breast cancer cell line, and determined its effect on DNA intercalation and on the activity of topoisomerases I and II. The compound inhibited proliferation MCF-7 with an IC50 value of 0.29 µM. Chrysosplenetin did not initiate plasmid DNA cleavage but, in a concentration-dependent manner, protected plasmid DNA against damage induced by Fenton reagents. Furthermore, it possessed dual Topoisomerase I and II inhibitory properties. Especially, it inhibited topoisomerase II by 83-96% between the range 12.5-100 µM. In the light of these experimental findings, molecular docking studies were performed to understand binding mode, interactions and affinity of chrysosplenetin with DNA, and with topoisomerases I and II. These studies showed that of 4-chromone core and the hydroxyl and methoxy groups important for both intercalation with DNA and topoisomerase I and II inhibition.

Flavones as tyrosinase inhibitors: kinetic studies in vitro and in silico.

INTRODUCTION: Tyrosinase is a multifunctional copper-containing oxidase enzyme that catalyses the first steps in the formation of melanin pigments. Identification of tyrosinase inhibitors is of value for applications in cosmetics, medicine and agriculture. OBJECTIVE: To develop an analytical method that allows identification of drug-like natural products that can be further developed as tyrosinase inhibitors. Results of in vitro and in silico studies will be compared in order to gain a deeper insight into the mechanism of action of enzyme inhibition. METHOD: Using an in vitro assay we tested tyrosinase inhibitor effects of five structurally related flavones, i.e. luteolin (1), eupafolin (2), genkwanin (3), nobiletin (4), and chrysosplenetin (5). The strongest inhibitors were further investigated in silico, using enzyme docking simulations. RESULTS: All compounds tested showed modest tyrosinase inhibitory effect compared to the positive control, kojic acid. The polymethoxy flavones 4 and 5 exhibited the strongest tyrosinase inhibitory effect with the half maximal inhibitory concentration (IC50 ) values of 131.92 ± 1.75 µM and 99.87 ± 2.38 µM respectively. According to kinetic analysis 2, 4 and 5 were competitive inhibitors, whereas 1 and 3 were non-competitive inhibitors of tyrosinase. Docking studies indicated that methoxy groups on 4 and 5 caused steric hindrance which prevented alternative binding modes in the tyrosinase; the methoxy groups on the B-ring of these flavones faced the catalytic site in the enzyme. CONCLUSIONS: The docking simulations nicely complemented the in vitro kinetic studies, opening the way for the development of predictive models for use in drug design.

ReishiMax inhibits mTORC1/2 by activating AMPK and inhibiting IGFR/PI3K/Rheb in tumor cells.

Ganoderma lucidum (G. lucidum) extracts, as dietary supplements, have been found to exert potent anticancer activity, which is attributed to the presence of polysaccharides and triterpenes. However, the molecular mechanism underlying the anticancer action of G. lucidum extracts remains to be investigated. Here, we show that ReishiMax GLp, containing G. lucidum polysaccharides and triterpenes (GLPT), inhibited cell proliferation and induced cell death in human lung cancer cells (A549 and A427) and simultaneously suppressed the signaling pathways of mammalian target of rapamycin complexes 1 and 2 (mTORC1 and mTORC2), respectively. Mechanistically, GLPT downregulated the phosphorylation and protein levels of insulin-like growth factor 1 receptor (IGFR) and phosphoinositide 3-kinase (PI3K) as well as the protein level of RAS homolog enriched in brain (Rheb). In addition, GLPT also activated the AMP-activated protein kinase (AMPK) network. This was evidenced by observations that GLPT increased the phosphorylation of AMPKα (T172) and its substrates tuberous sclerosis complex 2 (TSC2, S1387) and regulatory-associated protein of mTOR (raptor, S792). Ectopic expression of dominant-negative AMPKα partially mitigated the inhibitory effect of GLPT on mTORC1, indicating that GLPT inhibits mTORC1 partly by activating AMPK. The results suggest that G. lucidum extracts exert anticancer action at least partly by suppressing mTORC1/2 signaling via activation of AMPK and inhibition of IGFR/PI3K/Rheb in tumor cells.

Tyrosinase inhibitory effects of Vinca major and its secondary metabolites: Enzyme kinetics and in silico inhibition model of the metabolites validated by pharmacophore modelling.

In the present study, we aimed to identify the tyrosinase enzyme inhibitory potential of Vinca major L. extract and its secondary metabolites. The extract possessed remarkable tyrosinase enzyme inhibitory effect with IC50 value of 20.39 ±â€¯0.44 µg/mL compared to the positive control, kojic acid (IC50 8.56 ±â€¯0.17 µg/mL). Compounds 1 and 5 were the most potent isolates with IC50 values of 32.41 ±â€¯0.99 and 31.34 ±â€¯0.75 µM, they were more potent than kojic acid (IC50: 60.25 ±â€¯0.54 µM). Compound 2 also exhibited remarkable tyrosinase inhibition with an IC50 value of 64.51 ±â€¯1.29 µM. An enzyme kinetics analysis revealed that 1 was a mixed-type, 2 and 5 were noncompetitive inhibitors. Using molecular docking, we predicted binding affinity and interactions of the compounds, which were in good alignment with a pharmacophore hypothesis generated out of a number of known tyrosinase inhibitors. The modelling studies underlined crucial interactions with the copper ions and residues around them such as Asn260, His263, and Met280.

Tyrosinase and α-glucosidase inhibitory potential of compounds isolated from Quercus coccifera bark: In vitro and in silico perspectives.

Bark of Quercus coccifera is widely used in folk medicine. We tested tyrosinase and α-glucosidase inhibitory effects of Q. coccifera bark extract and isolated compounds from it. The extract inhibited tyrosinase with an IC50 value of 75.13 ±â€¯0.44 µg/mL. Among the isolated compounds, polydatin (6) showed potent tyrosinase inhibition compared to the positive control, kojic acid, with an IC50 value of 4.05 ±â€¯0.30 µg/mL. The Q. coccifera extract also inhibited α-glucosidase significantly with an IC50 value of 3.26 ±â€¯0.08 µg/mL. (-)-8-Chlorocatechin (5) was the most potent isolate, also more potent than the positive control, acarbose, with an IC50 value of 43.60 ±â€¯0.67 µg/mL. According to the kinetic analysis, 6 was a noncompetitive and 5 was a competitive inhibitor of tyrosinase, and 5 was a noncompetitive α-glucosidase inhibitor. In the light of these findings, we performed in silico molecular docking studies for 5 and 6 with QM/MM optimizations to predict their tyrosinase inhibition mechanisms at molecular level and search for correlations with the in vitro results. We found that the ionized form of 5 (5i) showed higher affinity and more stable binding to tyrosinase catalytic site than its neutral form, while 6 bound to the predicted allosteric sites of the enzyme better than the catalytic site.

α-Glucosidase inhibitory effects of polyphenols from Geranium asphodeloides: Inhibition kinetics and mechanistic insights through in vitro and in silico studies.

Some Geranium species have been used to treat diabetes. To evaluate the scientific basis of this ethnopharmacological use, we aimed to isolate potent α-glucosidase inhibitory metabolites of Geranium asphodeloides Burm. through in vitro bioactivity-guided fractionation. All the tested extracts showed high α-glucosidase inhibitory effect compared to acarbose. Among the tested extracts, the ethyl acetate subextract showed the highest activity with an IC50 value of 0.85 ±â€¯0.01 µM. A hydrolysable tannin, 1,2,4-tri-O-galloyl-ß-d-glucopyranose (1), and five flavonoid glycosides, kaempferol-3-O-α-rhamnopyranoside (2), kaempferol-3-O-α-arabinofuranoside (3), quercetin-3-O-ß-glucopyranoside (4), quercetin-3-O-α-rhamnopyranoside (5), and quercetin-3-O-α-rhamnofuranoside (6), were isolated from the ethyl acetate subextract. Their structures were identified by 1D- and 2D-NMR experiments. 1 exhibited the highest α-glucosidase inhibitory effect, approximately 61 times more potent than positive control, acarbose, with an IC50 value of 0.95 ±â€¯0.07 µM. Also, 2 was more potent than acarbose. An enzyme kinetics analysis revealed that compounds 2, 3 and 4 were competitive, whereas 1 and 6 uncompetitive inhibitors. Molecular docking studies were performed to get insights into inhibition mechanisms of the isolated compounds in the light of the enzyme kinetic studies using various binding sites of the enzyme model.

Tyrosinase inhibition by some flavonoids: Inhibitory activity, mechanism by in vitro and in silico studies.

Flavonoids are main polyphenolic groups widely distributed to fruits, vegetables and beverages we consumed daily. They exhibit many biological effects. We tested tyrosinase inhibitor potential of structurally related (1-9) flavonoids and found that all the tested materials possessed tyrosinase inhibitory effect compared to the positive control, kojic acid. 2 exhibited the strongest tyrosinase inhibitory effect with an IC50 value of 40.94 ±â€¯0.78 µM in a competitive manner. According to kinetic analysis 1, 4 and 7 were found to be competitive inhibitors, 3, 5, and 6 noncompetitive inhibitors of tyrosinase. According to the docking studies, A and C ring of the flavonoid structure, hydroxyl substituent at the 7th position, and hydroxyl substituents at para or para and meta position of ring B play key role for competitive inhibition of the enzyme.

Tyrosinase inhibition by a rare neolignan: Inhibition kinetics and mechanistic insights through in vitro and in silico studies.

Neolignans are a large group of polyphenols found in plants and exhibit a wide range of bioactivities including cytotoxicity, apoptosis inducer, antimalarial and antifungal effects, acetylcholinesterase, tyrosinase, and α-glucosidase inhibition. In this study we tested acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), tyrosinase, and α-glucosidase inhibitory effects of a rare neolignan, (-)-4-O-methyldehydrodiconiferyl alcohol 9'-O-ß-glucopyranoside (1) in search for its new pharmaceutical effects. This compound exhibited good tyrosinase inhibition with an IC50 value of 44.62 ±â€¯3.99 µg/mL. Enzyme kinetics and molecular modelling studies were performed to provide insights into its tyrosinase inhibition mechanism.

Discovery of potent α-glucosidase inhibitor flavonols: Insights into mechanism of action through inhibition kinetics and docking simulations.

Beside other pharmaceutical benefits, flavonoids are known for their potent α-glucosidase inhibition. In the present study, we investigated α-glucosidase inhibitory effects of structurally related 11 flavonols, among which quercetin-3-O-(3″-O-galloyl)-ß-galactopyranoside (8) and quercetin 3-O-(6″-O-galloyl)-ß-glucopyranoside (9) showed significant inhibition compared to the positive control, acarbose, with IC50 values of 0.97 ±â€¯0.02 and 1.35 ±â€¯0.06 µM, respectively. It was found that while sugar substitution to C3-OH of C ring reduced the α-glucosidase inhibitory effect, galloyl substitution to these sugar units increased it. An enzyme kinetics analysis revealed that 7 was competitive, whereas 1, 2, 8, and 9 were uncompetitive inhibitors. In the light of these findings, we performed molecular docking studies to predict their inhibition mechanisms at atomic level.

Potential of Potentilla inclinata and its polyphenolic compounds in α-glucosidase inhibition: Kinetics and interaction mechanism merged with docking simulations.

In the present study we aimed to identify the α-glucosidase enzyme inhibitory potential of Potentilla inclinata Vill. MeOH and n-BuOH extracts which possessed remarkable α-glucosidase enzyme inhibitory effects with IC50 values of 1.06±0.02 and 0.93±0.01µg/ml respectively, compared to that of acarbose (IC50 31.92±0.17). Thus, BuOH extract was chosen for further phytochemical investigations. A phenolic acid, six flavonol glycosides, and two hydrolysable tannins were isolated from the most active n-BuOH extract of the title plant. Structures of the isolated compounds were elucidated by 1D- and 2D-NMR experiments. All the compounds exhibited remarkable α-glucosidase inhibitory activity compared to the positive control, acarbose. Rutin (2) showed the highest activity with an IC50 value of 26.31±0.02µg/ml. An enzyme kinetics analysis revealed that compounds 5 and 7 were competitive, 4 and 6 noncompetitive, and 3 was uncompetitive inhibitors of α-glucosidase enzyme. Molecular docking studies were performed to get insights into inhibition mechanisms of the isolates considering their inhibition type using various binding sites of the enzyme model we previously reported.

Ganoderma lucidum Polysaccharides as An Anti-cancer Agent.

The mushroom Ganoderma lucidum (G. lucidum) has been used for centuries in Asian countries to treat various diseases and to promote health and longevity. Clinical studies have shown beneficial effects of G. lucidum as an alternative adjuvant therapy in cancer patients without obvious toxicity. G. lucidum polysaccharides (GLP) is the main bioactive component in the water soluble extracts of this mushroom. Evidence from in vitro and in vivo studies has demonstrated that GLP possesses potential anticancer activity through immunomodulatory, anti-proliferative, pro-apoptotic, anti-metastatic and anti-angiogenic effects. Here, we briefly summarize these anticancer effects of GLP and the underlying mechanisms.

α-Glucosidase inhibitory effect of Potentilla astracanica and some isoflavones: Inhibition kinetics and mechanistic insights through in vitro and in silico studies.

α-Glucosidase enzyme inhibitors are clinically used for the treatment of Type 2 diabetes mellitus. We tested α-glucosidase inhibitory effects of Potentilla astracanica Jacq. extracts (1, 2), two compounds isolated from these extracts, prunetin 5-O-ß-glucopyranoside (3) and genistein 5-O-ß-glucopyranoside (4), and their aglycon forms (5 and 6). All the tested materials possessed remarkable α-glucosidase inhibitor activity compared to the positive control, acarbose. Genistein (6) showed the highest activity with an IC50 value of 1.47 (±0.11) µg/ml. An enzyme kinetics analysis revealed that 3 and 6 were uncompetitive, 5 was noncompetitive, and 4 was competitive inhibitors. Using molecular modeling techniques we tried to provide insight into molecular mechanisms of their activity and how allosteric binding of 6 affected binding interactions between the agonist (maltose) and the enzyme.

Phytochemical Content, Antioxidant and Cytotoxic Activities of Sedum spurium.

Sedum L. species are used for their hemostatic, antidiarrheal, antifungal, diuretic and wound healing properties, and there is growing interest in these species because of their usage in folk medicine. DPPH, SO, NO, and ABTS radical scavenging activities and protective effects against H(2)(02) induced cytotoxicity, as well as cytotoxic activities against the Hep-2 cell line of various extracts from Sedum spurium Bieb. were investigated. Besides, the total phenol, flavonoid, and flavonol contents of the extracts were determined to clarify their biological and phytochemical properties. Chromatographic studies on the most active extract led to the isolation of the major compound, identified as 2-methyl-erythritol by (1)H and (13)C NMR techniques. The EtOAc extract is found to be the most active extract in all tests. However, major compound of EtOAc extract did not possess tested activities. The EtOAC extract of S. spurium could be effective to improve antihemolytic defences of erythrocytes, and radical scavenging potential of the antioxidant mechanism. The extracts should be investigated in detail for their cytotoxic activities because of their possible pro-oxidant effects at high concentrations.