Probing the interaction between 3 flavonoids and pancreatic lipase by methods of fluorescence spectroscopy and enzymatic kinetics

Design, synthesis, biological evaluation and molecular docking of alkoxyaurones as potent pancreatic lipase inhibitors

Aurones are a minor subgroup of flavonoids. Unlike other subgroups such as chalcones, flavones, and isoflavones, aurones have not been extensively explored as pancreatic lipase inhibitors. In this work, we studied the pancreatic lipase inhibitory potency of synthetic aurone derivatives. Thirty-six compounds belonging to four series (4,6-dihydroxyaurone, 6-hydroxyaurone, 4,6-dialkoxyaurone, and 6-alkoxyaurone) were designed and synthesized. Their in vitro inhibitory activities were determined by spectrophotometric assay in comparison with quercetin and orlistat. Alkoxyaurone derivatives with long-chain (6-10 carbons) alkoxy substituents showed greater potency. Of them, 4,6-dialkoxyaurone 8 displayed the highest activity against pancreatic lipase (IC50 of 1.945 ± 0.520 µM) relative to quercetin (IC50 of 86.98 ± 3.859 µM) and orlistat (IC50 of 0.0334 ± 0.0015 µM). Fluorescence quenching measurement confirmed the affinity of alkoxyaurone derivatives to pancreatic lipase. Kinetic study showed that 8 inhibited lipase through a competitive mechanism (Ki of 1.288 ± 0.282 µM). Molecular docking results clarified the role of long-chain substituents on ring A in interacting with the hydrophobic pockets and pushing the inhibitor molecule closer to the catalytic triad. The findings in this study may contribute to the development of better pancreatic lipase inhibitors with aurone structure.

Antioxidant Properties of Kombucha Made with Tartary Buckwheat Tea and Burdock Tea

Kombucha is a beverage fermented by SCOBY, which is a symbiotic culture of bacteria and yeast. Recently, kombucha has received significant attention due to its health benefits, which include antioxidant and anti-obesity effects. In this study, we investigated the characteristics of kombucha made with Tartary buckwheat and burdock, both known for their high polyphenols content. First, the total polyphenol content and antioxidant activity were measured by 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assays, which revealed a polyphenol content of 180 ug/mL in Tartary buckwheat kombucha and a high radical scavenging ability of over 90% in both kombucha preparations. Analysis of the changes in the organic acid content during fermentation revealed increases in various organic acid contents, such as glucuronic acid, lactic acid, and acetic acid. Glucuronic acid, especially, which has many functional properties in health, was found to be produced at a concentration of 4.03 g/L in Tartary buckwheat kombucha. Pancreatic lipase inhibitory ability analysis revealed inhibitory effects of 40.47% and 57.68% for Tartary buckwheat and burdock kombucha, respectively. The results of this study confirmed the antioxidant and anti-obesity effects of kombucha made from Tartary buckwheat and burdock, indicating the potential value of these ingredients as functional kombucha ingredients.

Methodologies for Assessing Pancreatic Lipase Catalytic Activity: A Review

Obesity is a disease of epidemic proportions with a concerning increasing trend. Regarded as one of the main sources of energy, lipids can also represent a big part of an unnecessary intake of calories and be, therefore, directly related to the problem of obesity. Pancreatic lipase is an enzyme that is essential in the absorption and digestion of dietary fats and has been explored as an alternative for the reduction of fat absorption and consequent weigh loss.Literature describes a great variability of methodologies and experimental conditions used in research to evaluate the in vitro inhibitory activity of compounds against pancreatic lipase. However, in an attempt to choose the best approach, it is necessary to know all the reaction conditions and understand how these can affect the enzymatic assay.The objective of this review is to understand and summarize the methodologies and respective experimental conditions that are mainly used to evaluate pancreatic lipase catalytic activity.156 studies were included in this work and a detailed description of the most commonly used UV/Vis spectrophotometric and fluorimetric instrumental techniques are presented, including a discussion regarding the differences found in the parameters used in both techniques, namely enzyme, substrate, buffer solutions, kinetics conditions, temperature and pH.This works shows that both UV/Vis spectrophotometry and fluorimetry are useful instrumental techniques for the evaluation of pancreatic lipase catalytic activity, presenting several advantages and limitations, which make the choice of parameters and experimental conditions a crucial decision to obtain the most reliable results.

In vitro anti-obesity activity by pancreatic lipase inhibition - Simple HPLC approach using EVOO as natural substrate

BACKGROUND

Pancreatic lipase (PL) is a key lipolytic enzyme in humans for the digestion and absorption of dietary fats. Thereby, PL is a well-recognized target in the management of obesity and its inhibition attracts the interest of researchers globally. The screening of new natural PL inhibitors as alternative strategy to the synthesis of chemical ones represents nowadays a hot topic in research. The main challenge in this matter is the lack of a universal analytical method allowing the monitoring of PL activity and the reliable quantification of lipid digestion products.

RESULTS

The (normal phase)-high-performance liquid chromatography-evaporative light scattering detector [(NP)-HPLC-ELSD] method proposed in this work represents a direct and rapid strategy to simultaneously quantify the products obtained from in vitro PL digestion. As one of the main novelties, the triacylglycerol (TAG) fraction from extra-virgin olive oil was selected as natural substrate. The PL activity was measured by monitoring the levels of remaining TAGs and formed free fatty acids (FFAs), using Orlistat as known inhibitor. The method validation confirmed the adequacy of the analytical method for quantitative purposes, showing high recovery percentage values (between 99% and 103%) and low relative standard deviation (RSD%) values (between 2% and 7%) for triolein and oleic acid standard solutions, as well as appreciably low limit of detection (LOD) and limit of quantification (LOQ) values (respectively 58 and 177 ng mL-1 for triolein; 198 and 602 ng mL-1 for oleic acid). Finally, the developed HPLC-ELSD method was successfully applied to evaluate the inhibitory effect of a polyphenolic extract obtained from apple pomace. The results showed a comparable inhibition degree between a 4.0 mg mL-1 apple pomace solution and a 1.0 μg mL-1 Orlistat solution.

CONCLUSION

The proposed innovative method reveals highly sensitive and simple to follow the fate of PL digestion, thus opening the way to further investigations in the research of new potentially anti-obesity compounds. © 2022 Society of Chemical Industry.

Exploring the binding effects and inhibiting mechanism of hyperoside to lipase using multi-spectroscopic approaches, isothermal titration calorimetry, inhibition kinetics and molecular dynamics

Hyperoside (HYP) is a flavonoid with various physiological activities. The present study examined the interaction mechanism between HYP and lipase using multi-spectrum and computer-aided techniques. Results demonstrated that the force type of HYP on lipase was mainly hydrogen bond, hydrophobic interaction force, and van der Waals force, and HYP had an excellent binding affinity with lipase at 1.576 × 10⁵ M^-1. HYP dose-dependently inhibited lipase in the inhibition experiment, and its IC₅₀ value was 1.92 × 10^-3 M. Moreover, the results suggested that HYP could inhibit the activity by binding to essential groups. Conformational studies indicated that the conformation and microenvironment of lipase were slightly changed after the addition of HYP. Computational simulations further confirmed the structural relationships of HYP to lipase. The interaction between HYP and lipase can provide ideas for the development of functional foods related to weight loss. The results of this study help comprehend the pathological significance of HYP in biological systems, as well as its mechanism.

Design and Synthesis of Echitamine-inspired Hybrid Analogues Containing Thiazolidinediones as Potential Pancreatic Lipase Inhibitors

Background:

Obesity is a multifactorial metabolic disease characterised by excessive accumulation of triglycerides. The prevalence and morbidity rates associated with obesity are increasing tremendously, posing a significant risk to society. Pancreatic lipase (PL) is a key enzyme responsible for the digestion of dietary triglycerides; hence its inhibition is considered an attractive target in obesity.

Methods:

In this present work, a new series of echitamine-inspired indole-based thiazolidinedione hybrid analogues were designed, synthesized, and evaluated for their in vitro PL inhibitory potential. The nature of inhibition has been identified by enzyme kinetic analysis, whereas in silico molecular modelling tools (molecular docking and dynamic studies) were used for the identification of the mode of action at the catalytic site of PL (PDB ID: 1LPB). Fluorescence quenching was used for the identification of the interaction between the potent analogues with PL.

Results:

The condensation reaction of substituted indole derivatives with TZD in the presence of aqueous KOH resulted in the formation of the titled analogues. Analogues 7k and 7p displayed a potential PL inhibitory activity (IC50 = 11.36 and 11.87 μM, respectively). A competitive mode of PL inhibition was revealed in the enzyme kinetic analysis. A static quenching mechanism was exhibited by the screened agents on PL. The obtained MolDock scores were aligned with the in vitro PL inhibitory activity (Pearson’s r - 0.7575, p<0.05). Moreover, the PL-ligand complexes were stable in the dynamic conditions.

Conclusion:

Analogue 7k exerted the potential activity, and further studies might result in novel lead molecules.

In Vitro and In Silico Study of the α-Glucosidase and Lipase Inhibitory Activities of Chemical Constituents from Piper cumanense (Piperaceae) and Synthetic Analogs

Digestive enzymes are currently considered important therapeutic targets for the treatment of obesity and some associated metabolic diseases, such as type 2 diabetes. Piper cumanense is a species characterized by the presence of bioactive constituents, particularly prenylated benzoic acid derivatives. In this study, the inhibitory potential of chemical constituents from P. cumanense and some synthesized compounds was determined on digestive enzymes (pancreatic lipase (PL) and α-glucosidase (AG)). The methodology included isolating and identifying secondary metabolites from P. cumanense, synthesizing some analogs, and a molecular docking study. The chemical study allowed the isolation of four prenylated benzoic acid derivatives (1–4). Four analogs (5–8) were synthesized. Seven compounds were found to significantly inhibit the catalytic activity of PL with IC₅₀ values between 28.32 and 55.8 µM. On the other hand, only two compounds (6 and 7) were active as inhibitors of AG with IC₅₀ values lower than 155 µM, standing out as the potential multitarget of these chromane compounds. Enzyme kinetics and molecular docking studies showed that the bioactive compounds mainly interact with amino acids other than those of the catalytic site in both PL and AG. This work constitutes the first report on the antidiabetic and antiobesity potential of substances derived from P. cumanense.

Inhibition of the in vitro Activities of α-Amylase and Pancreatic Lipase by Aqueous Extracts of Amaranthus viridis, Solanum macrocarpon and Telfairia occidentalis Leaves

Inhibition of digestive enzymes such as α-amylase and pancreatic lipase (PL) is a promising therapeutic strategy for the treatment and management of chronic health conditions such as diabetes and obesity. Therefore, the aim of this work was to determine the enzyme inhibitory activity of polyphenol-rich aqueous extracts of Amaranthus viridis (AV), Solanum macrocarpon (SM) and Telfairia occidentalis (TO) leaves, which were harvested from plants produced using multiple urea fertilizer doses (0-80 kg N/ha). Fertilizer application was applied at two time points (at planting or 2 weeks after seedling emergence). Leaf extracts were obtained using aqueous extraction (1:20, leaves:water) for 4 h at 60°C followed by centrifugation and freeze-drying of the supernatant. Results showed that the extracts inhibited α-amylase, and pancreatic lipase dose-dependently with TO extracts having significantly (p < 0.05) higher inhibitory activities for both enzymes. Fluorescence intensity and circular dichroism spectra in the presence and absence of leaf extracts indicate significant changes to the enzyme protein secondary and tertiary conformations. We conclude that the leaf extracts, especially from TO are potential agents for reducing calorie intake as a preventive or treatment tool against chronic diseases such as diabetes and obesity.

Comparison of quercetin and rutin inhibitory influence on Tartary buckwheat starch digestion in vitro and their differences in binding sites with the digestive enzyme

Inhibitory effects of flavonoids on starch digestibility were well known, but the structural mechanism was not clear. This study was focused on the diverse effect of quercetin and rutin on digestibility of Tartary buckwheat starch. Results showed that quercetin and rutin reduced the starch digestion by altering starch structure in bound forms and inhibiting digestive enzyme activity in free forms simultaneously, and quercetin showed a stronger effect than rutin. Molecular docking and saturation transfer difference-nuclear magnetic resonance (STD-NMR) revealed different binding site of rutin from quercetin was due to its hydroxyl and hydrogen on the glycoside structure. Rutin interacted with enzymes mainly by CH and OH on the glycoside structure which induced steric hindrance and restricted the inhibitory effect of quercetin fraction. The glycoside structure weakened inhibition of rutin on digestive enzymes in free forms rather than influence its anti-digestive effects in bound forms with starch.

Encapsulation of lipophilic polyphenols in plant-based nanoemulsions: impact of carrier oil on lipid digestion and curcumin, resveratrol and quercetin bioaccessibility

Lipophilic polyphenol compounds (LPCs) are claimed to exhibit a broad spectrum of biological activities that may improve human health and wellbeing, including antioxidant, anti-inflammatory, and anti-cancer properties. Nanoemulsion-based delivery systems have been developed to encapsulate LPCs so as to increase their food matrix compatibility, physicochemical stability, and bioavailability. LPCs vary in their structural features, including the number and position of phenolic hydroxyl, ketone, and aliphatic groups, which results in different molecular, physicochemical, and gastrointestinal properties. In this study, we examined the impact of plant-based carrier oils (coconut, sunflower, and flaxseed oils) and LPC type (curcumin, resveratrol, and quercetin) on the in vitro gastrointestinal fate of polyphenols loaded into quillaja saponin-stabilized nanoemulsions. Coconut oil contains high levels of medium-chain saturated fatty acids (MC-SFAs), sunflower oil contains high levels of long-chain monounsaturated fatty acids (LC-MUFAs), and flaxseed oil contains high levels of long-chain polyunsaturated fatty acids (LC-PUFAs). The encapsulation efficiency and gastrointestinal stability of the LPCs were slightly lower in the MC than the LC oils. Differences in the gastrointestinal stability of the three LPCs were linked to differences in their oil-water partition coefficients. Some of the LPCs inhibited lipid digestion for certain oil types. In particular, resveratrol retarded the digestion of all three oils, but it still had the highest GIT stability and bioaccessibility. This study provides valuable information about the gastrointestinal fate of LPC-loaded nanoemulsions and highlights important differences in the behavior of LPCs with different characteristics. This knowledge may facilitate the design of more effective plant-based delivery systems for bioactive lipophilic polyphenols.

Polyphenol bioaccessibility and antioxidant properties of in vitro digested spray-dried thermally-treated skimmed goat milk enriched with pollen

The aim of research was to determine polyphenols bioaccessibility and antioxidant properties of thermally-treated skimmed goat milk enriched with sunflower bee-collected pollen through in vitro digestion. HPLC analysis confirmed that pollen-enriched milk contained flavonols as the main phenolic fraction (80.7-76.2%) followed by phenolic acids (14.2-17.4%). Among individual compounds quercetin-3-O-glucoside (155.1-197.2 μg/L) and p-coumaric acid (29.5-30.7 μg/L) were the main quantified flavonols and phenolic acids, respectively. After digestion of milk/pollen sample, total polyphenols recovery was 30.71% with higher phenolic acids recovery (40.1%) compared to flavonols (28.3%) indicating strong interactions between caprine milk casein micelles and pollen polyphenols. Applied antioxidant assays (phosphomolybdenum, ABTS•⁺scavenging activity and ferrous-ion-chelating capacity) have confirmed complexity of prepared product- it had high ability to quench ABTS•⁺ radicals and to form chelating complexes with Fe²⁺ ions. Digestion provoked 20% reduction in total antioxidant capacity compared to the initial sample. TTSG milk/pollen powder could be good functional ingredient.

Design, synthesis, in silico molecular modelling studies and biological evaluation of novel indole-thiazolidinedione hybrid analogues as potential pancreatic lipase inhibitors

A series of thiazolidinedione-indole hybrids are designed and synthesized as a potential inhibitor for pancreatic lipase (PL).

Mechanisms of action for the anti-obesogenic activities of phytochemicals

The prevalence of obesity is increasing rapidly globally and has recently reached pandemic proportions. It is a multifactorial disorder linked to a number of non-communicable diseases such as type-2 diabetes, cardiovascular disease, and cancer. Over-nutrition and a sedentary lifestyle are considered the most significant causes of obesity; a healthy lifestyle and behavioural interventions are the most powerful ways to achieve successful weight loss, but to maintain this in the long term can prove difficult for many individuals, without medical intervention. Various pharmacological anti-obesogenic drugs have been tested and marketed in the past and have been moderately successful in the management of obesity, but their adverse effects on human health often outweigh the benefits. Natural products from plants, either in the form of crude extracts or purified phytochemicals, have been shown to have anti-obesogenic properties and are generally considered as nontoxic and cost-effective compared to synthetic alternatives. These plant products combat obesity by targeting the various pathways and/or regulatory functions intricately linked to obesity. Their mechanisms of action include inhibition of pancreatic lipase activities, an increase in energy expenditure, appetite regulation, lipolytic effects, and inhibition of white adipose tissue development. In this review, we discuss the distinct anti-obesogenic properties of recently reported plant extracts and specific bioactive compounds, along with their molecular mechanisms of action. This review will provide a common platform for understanding the different causes of obesity and the possible approaches to using plant products in tackling this worldwide health issue.

Gustavia gracillima Miers. flowers effects on enzymatic targets underlying metabolic disorders and characterization of its polyphenolic content by HPLC-DAD-ESI/MSn

Notwithstanding Gustavia gracillima Miers widespread distribution in neotropical regions, its chemical profile and biological properties remain uninvestigated. A methanol extract obtained from the flowers was characterized through HPLC-DAD-ESI/MSⁿ, nine ellagic acid derivatives and twelve kaempferol 3-O-glycosides being identified and quantitated for the first time at the species and genus. Preliminary cytotoxicity screening did not reveal noticeable effects upon gastrointestinal representative cell lines (AGS, Caco-2 and Hep G2), which further prompted us to evaluate the impact in a series of targets involved in metabolic disorders and associated complications. Despite of the moderate inhibition towards 5-lipoxygense activity, G. gracillima methanol extract displayed significant effects on carbohydrates-hydrolysing enzymes. In contrast with the antidiabetic reference drug acarbose, the extract was able to selectively inhibit yeast α-glucosidase activity (IC₅₀ = 4.72 µg/mL), with negligible inhibitory effects upon α-amylase. Kinetic studies pointed to a model of mixed inhibition with a great binding activity, characterized by an inhibitory constant of 2.91 µg/mL. The notable inhibitory activity was also confirmed in α-glucosidase homogenates isolated from human intestinal cells (IC₅₀ = 34.03 µg/mL). Moreover, the extract obtained from the flowers of G. gracillima displayed significant aldose reductase inhibition (IC₅₀ = 61.88 µg/mL), as well as O₂^- and NO scavenging properties. A moderate inhibitory effect was also recorded against pancreatic lipase (IC₅₀ = 362.17 µg/mL) through a mixed inhibition mode. Recorded data supports the potential incorporation of G. gracillima flowers on antidiabetic herbal formulations and/or supplements, with not only straight action on carbohydrates digestion, but also direct interference with targets involved on subsequent diabetes events, such as triglycerides metabolism, inflammation and radical-mediated stress.

Inhibition of glutathione and s-allyl glutathione on pancreatic lipase: Analysis through in vitro kinetics, fluorescence spectroscopy and in silico docking

Inhibition of pancreatic lipase (PL) is considered one of the important therapeutic interventions against obesity. In the present study, the inhibition of porcine (mammalian) PL (PPL) by two tripeptides glutathione (GSH) and s-allyl glutathione (SAG) was studied. In vitro kinetic analysis was done to determine the inhibition of GSH and SAG against PPL. The binding of GSH and SAG with PPL was elucidated by fluorescence spectroscopy analysis. Docking and molecular dynamics (MD) simulation analysis was carried out to understand the intermolecular interaction between both GSH and SAG with PPL as well as human PL (HPL). Both GSH and SAG inhibited PPL in mixed non-competitive manner. The IC₅₀ value for GSH and SAG against PPL was found to be 2.97 and 6.4 mM, respectively. Both GSH and SAG quenched the intrinsic fluorescence of PPL through static quenching that is through forming complex with the PPL. SAG and GSH interacted with amino acids involved in catalysis of both PPL and HPL. MD simulation showed interactions of SAG and GSH with both PPL and HPL were stable. These results would lead to the further studies and application of GSH and SAG against obesity through inhibition of PL.

Antioxidant and pancreatic lipase inhibitory effects of flavonoids from different citrus peel extracts: An in vitro study

Obesity and oxidative damage are two important risk factors associated closely with metabolic syndrome. Utilization of functional food ingredients is considered as a feasible way to tackle these challenges. In the present study, eight representative species of citrus peel extracts (CPEs) were evaluated and compared for their flavonoid profiles, antioxidant activities, and pancreatic lipase (PL) inhibitory capacities and mechanisms. Results indicated that hesperidin, naringin, neohesperidin, narirutin and eriocitrin were the five major flavonoids in CPEs, among which hesperidin was the main active PL inhibitor. Moreover, hesperidin could interact with PL by hydrogen bonds and van der Waals forces, and the interaction would not obviously change the secondary structure of PL. Overall, ponkan peel extract, having the strongest overall antioxidant activity, the highest content of hesperidin and total phenolic compounds among all tested CPEs, is a promising natural ingredient to scavenge free radicals and manage obesity.

Enzyme-assisted modification of flavonoids from Matricaria chamomilla: antioxidant activity and inhibitory effect on digestive enzymes

Matricaria chamomilla L. contains antioxidant flavonoids that can have their bioactivity enhanced by enzymatic hydrolysis of specific glycosyl groups. This study implements an untargeted metabolomics approach based on ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole time-of-flight mass spectrometry technique operating in MS^E mode (UPLC-QTOF-MS^E) and spectrophotometric analysis of chamomile aqueous infusions, before and after hydrolysis by hesperidinase and β-galactosidase. Several phenolic compounds were altered in the enzymatically treated infusion, with the majority being flavonoid derivatives of apigenin, esculetin, and quercetin. Although enzymatically modifying the infusion only led to a small increase in antioxidant activity (DPPH• method), its inhibitory effect on pancreatic lipase was of particular interest. The enzymatically treated infusion exhibited a greater inhibitory effect (EC₅₀ of 35.6 µM) than unmodified infusion and kinetic analysis suggested mixed inhibition of pancreatic lipase. These results are of great relevance due to the potential of enzymatically treated functional foods in human health.

An assessment of the interaction for three Chrysanthemum indicum flavonoids and α-amylase by surface plasmon resonance

This study evaluated the interaction of Chrysanthemum indicum (CI) flavonoids (luteolin, acacetin, and buddleoside) with α-amylase. Surface plasmon resonance (SPR) assay showed their equilibrium dissociation constants (KD ) are 1.9695 ± 0.12, 2.9240 ± 0.20, and 3.2966 ± 0.08 mM at pH 6.0, respectively. Furthermore, their binding affinities were influenced by KCl, MgCl2, and CaCl2. Enzymatic kinetic studies revealed that three flavonoids exhibited noncompetitive α-amylase inhibitory activity. The inhibitory sequence is luteolin > acacetin > buddleoside, which was in accordance with the results of binding affinity from SPR. 1,1-diphenyl-2-picryl hydrazyl radical assay demonstrated that antioxidant activities of three flavonoids were inhibited significantly with α-amylase. Meanwhile, the study reveals that hydroxyl on C'-4, C'-5, and C-7 of flavonoids play an important role on the interaction of three flavonoids with α-amylase. Also, SPR could be used as sensor for rapid screening inhibitors of α-amylase and provide useful information for the application of C. indicum flavonoids in food and pharmaceutical area.

Binding characteristics of polyphenols as milk plasmin inhibitors

BACKGROUND

The potential use of polyphenols to improve the functional characteristics of dairy products has gained much attention. However, the effects of the polyphenols on naturally occurring enzymes in milk have not been studied extensively. Excess plasmin activity in dairy products might result in several quality defects. The objective of this study was to assess the ability of polyphenols to inhibit plasmin in milk using a molecular and kinetic approach.

RESULTS

Epicatechin gallate (ECG), epigallocatechin gallate (EGCG), quercetin (QUER), and myricetin (MYR) caused a significant decrease in plasmin activity by 60, 86, 65, and 90%, respectively. The inhibition rates were alleviated in the presence of milk proteins. EGCG, QUER, and MYR, exhibited noncompetitive inhibition against plasmin, whereas ECG caused a mixed-type inhibition. A decrease in the random structure of plasmin upon the complex formation with ECG, EGCG, QUER, and MYR was found. The other phenolics that were evaluated did not cause any significant changes in plasmin conformation. The observed inhibitory phenolic-plasmin interactions were dominated by H-bonds and electrostatic attractions. Green tea extract (GTE) rich in catechins also inhibited plasmin activity in the milk.

CONCLUSION

Significant changes in the secondary structure of plasmin upon binding of ECG, EGCG, QUER, and MYR led to diminished plasmin activity both in the absence and presence of milk proteins. These flavonoids with promising plasmin inhibitory potential could be used in new dairy formulations leading to controlled undesired consequences of plasmin activity. © 2019 Society of Chemical Industry.

Inhibition of CpLIP2 Lipase Hydrolytic Activity by Four Flavonols (Galangin, Kaempferol, Quercetin, Myricetin) Compared to Orlistat and Their Binding Mechanisms Studied by Quenching of Fluorescence

The inhibition of recombinant CpLIP2 lipase/acyltransferase from Candida parapsiolosis was considered a key model for novel antifungal drug discovery and a potential therapeutic target for candidiasis. Lipases have identified recently as potent virulence factors in C. parapsilosis and some other yeasts. The inhibition effects of orlistat and four flavonols (galangin, kaempferol, quercetin and myricetin) characterized by an increasing degree of hydroxylation in B-ring, were investigated using ethyl oleate hydrolysis as the model reaction. Orlistat and kaempferol (14 µM) strongly inhibited CpLIP2 catalytic activity within 1 min of pre-incubation, by 90% and 80%, respectively. The relative potency of flavonols as inhibitors was: kaempferol > quercetin > myricetin > galangin. The results suggested that orlistat bound to the catalytic site while kaempferol interacted with W294 on the protein lid. A static mechanism of interactions between flavonols and CpLIP2 lipase was confirmed by fluorescence quenching analyses, indicating that the interactions were mainly driven by hydrophobic bonds and electrostatic forces. From the Lehrer equation, fractions of tryptophan accessibility to the quencher were evaluated, and a relationship with the calculated number of binding sites was suggested.

Inhibition of α-amylase by flavonoids: Structure activity relationship (SAR)

Flavonoids are recognized to regulate animals' food digestion processes trough interaction with digestive enzymes. The binding capacity of hesperetin (HES), luteolin (LUT), quercetin (QUE), catechin (CAT) and rutin (RUT) with pancreatic α-amylase were evaluated, using UV-Vis spectroscopy, fluorescence and molecular docking. Using p-nitrophenyl-α-d-maltopentoside (pNPG5) as substrate analog, LUT showed the best inhibitory capacity, even better than that of the positive control, acarbose (ACA). A mixed-type inhibition was observed for HES, LUT and QUE, a competitive-type for ACA, while no inhibition was observed with CAT and RUT. In agreement with kinetic results, α-amylase presented a higher affinity for LUT, when analyzed by fluorescence quenching. The binding of flavonoids to amylase followed a static mechanism, where the binding of one flavonoid per enzyme molecule was observed. Docking analysis showed that flavonoids bound near to enzyme active site, while ACA bound in another site behind the catalytic triad. Extrinsic fluorescence analysis, together with docking analysis pointed out that hydrophobic interactions regulated the flavonoid-α-amylase interactions. The present study provides evidence to understand the relationship of flavonoids structure with their inhibition mechanism.

Antiobesity and antihyperglycaemic effects of Adiantum capillus-veneris extracts: in vitro and in vivo evaluations

CONTEXT

Adiantum capillus-veneris L. (Adiantaceae) hypocholesterolemic activity is therapeutically praised.

OBJECTIVES

Pharmacological modulation of pancreatic triacylglycerol lipase (PL) and α-amylase/α-glucosidase by A. capillus-veneris are evaluated.

MATERIALS AND METHODS

Using positive controls (acarbose, orlistat, guar gum, atorvastatin, glipizide and metformin) as appropriate, crude aqueous extracts (AEs) of A. capillus-veneris aerial parts were tested via a combination of in vitro enzymatic (0.24-100 mg/mL), acute in vivo carbohydrate tolerance tests (125, 250 or 500 mg/kg body weight [b.wt]) and chronic in vivo studies (500 mg/kg b.wt) in high cholesterol diet (HCD) fed Wistar rats.

RESULTS

Like acarbose, A. capillus-veneris as well as chlorogenic acid, with respective IC₅₀ values (mg/mL) of 0.8 ± 0.0 and 0.2 ± 0.0, were identified as in vitro potent dual inhibitors of α-amylase/α-glucosidase. Unlike guar gum, A. capillus-veneris had no glucose diffusion hindrance capacity. Equivalent to orlistat, A. capillus-veneris and its phytoconstituents inhibited PL in vitro with an ascending order of PL- IC₅₀ values (μg/mL): ferulic acid; 0.48 ± 0.06 < ellagic acid; 13.53 ± 1.83 < chlorogenic acid; 38.4 ± 2.8 < A. capillus-veneris; 1600 ± 100. Incomparable to acarbose or metformin and glipizide, A. capillus-veneris (125, 250 and 500 mg/kg b.wt) lacked antihyperglycaemic efficacies in acute starch- or glucose-evoked postprandial hyperglycaemia increments in normoglycaemic overnight fasting rats. Superior to atorvastatin; A. capillus-veneris exerted significant antiobesity (p < 0.001) with marked triacylglycerol-reducing capacities (p < 0.001) in comparison to rats fed with HCD for 10 weeks.

DISCUSSION AND CONCLUSION

A. capillus-veneris, modulating pancreatic digestive enzymes, may be advocated as a combinatorial diabesity prevention/phytotherapy agent.

Berberine Inhibited the Proliferation of Cancer Cells by Suppressing the Activity of Tumor Pyruvate Kinase M2

Berberine, an isoquinoline alkaloid extracted from coptis, exerts anti-proliferation and anticancer properties. Pyruvate kinase M2 (PKM2) is a key enzyme of aerobic glycolysis and considered as the potential anticancer target. However, the inhibition effects and interaction action between Berberine and PKM2 is not well known. In this study, berberine showed antitumor activity of HCT-116 and HeLa cells with the suppression of cell proliferation. Moreover, berberine inhibited the enzyme activity of PKM2 in cancer cells, but had no impact on PKM2 expression. Further research showed that the interaction between berberine and PKM2 was dynamic fluorescence quenching and the main intermolecular force was hydrogen bonding. These findings revealed that berberine may serve as a therapeutic drug for cancer chemotherapy.

Polyphenolic Compounds and Digestive Enzymes: In Vitro Non-Covalent Interactions

The digestive enzymes–polyphenolic compounds (PCs) interactions behind the inhibition of these enzymes have not been completely studied. The existing studies have mainly analyzed polyphenolic extracts and reported inhibition percentages of catalytic activities determined by UV-Vis spectroscopy techniques. Recently, pure PCs and new methods such as isothermal titration calorimetry and circular dichroism have been applied to describe these interactions. The present review focuses on PCs structural characteristics behind the inhibition of digestive enzymes, and progress of the used methods. Some characteristics such as molecular weight, number and position of substitution, and glycosylation of flavonoids seem to be related to the inhibitory effect of PCs; also, this effect seems to be different for carbohydrate-hydrolyzing enzymes and proteases. The digestive enzyme–PCs molecular interactions have shown that non-covalent binding, mostly by van der Waals forces, hydrogen binding, hydrophobic binding, and other electrostatic forces regulate them. These interactions were mainly associated to non-competitive type inhibitions of the enzymatic activities. The present review emphasizes on the digestive enzymes such as α-glycosidase (AG), α-amylase (PA), lipase (PL), pepsin (PE), trypsin (TP), and chymotrypsin (CT). Existing studies conducted in vitro allow one to elucidate the characteristics of the structure–function relationships, where differences between the structures of PCs might be the reason for different in vivo effects.

Investigation of the interaction for three Citrus flavonoids and α-amylase by surface plasmon resonance

Flavonoids, a class of natural drugs with broad biological activity, exhibit inhibitory effect on α-amylase. Citrus peel is a good source of flavonoids. The real-time interactions between three Citrus flavonoids (naringin, neohesperidin, hesperidin) and α-amylase were investigated by surface plasmon resonance biosensor, and were compared with the α-amylase inhibitors, acarbose. These results showed the binding affinities of naringin, neohesperidin and hesperidin with α-amylase reach the highest at pH6 with K_D values of 2.27±0.18mM, 3.09±0.20mM and 3.51±0.09mM, and can be reinforced with 0.2M NaCl and 0.1M CaCl₂, respectively. The results of 1, 1-diphenyl-2-picryl hydrazyl radical assay indicate that the antioxidant activities of naringin, neohesperidin and hesperidin are significantly inhibited by interacting with α-amylase, and the inhibition percentage are 47.61±0.034%, 22.81±0.037% and 21.01±0.051%, respectively. Additionally, it is found that both the number and the position of hydroxyl group play an important role in the interaction of three Citrus flavonoids and α-amylase. These results provide useful information for rapid screening inhibitors of α-amylase from plant-based food.

Chemical composition and health effects of Tartary buckwheat

Tartary buckwheat (Fagopyrum tataricum) contains a range of nutrients including bioactive carbohydrates and proteins, polyphenols, phytosterols, vitamins, carotenoids, and minerals. The unique composition of Tartary buckwheat contributes to their various health benefits such as anti-oxidative, anti-cancer, anti-hypertension, anti-diabetic, cholesterol-lowering, and cognition-improving. Compared with the more widely cultivated and utilised common buckwheat (F. esculentum), Tartary buckwheat tends to contain higher amounts of certain bioactive components such as rutin, therefore, showing higher efficiency in preventing/treating various disorders. This review summarises the current knowledge of the chemical composition of Tartary buckwheat, and their bio-functions as studied by both in vitro and in vivo models. Tartary buckwheat can be further developed as a sustainable crop for functional food production to improve human health.

Synergistic interactions of apigenin, naringin, quercetin and emodin on inhibition of 3T3-L1 preadipocyte differentiation and pancreas lipase activity

The interactions of four natural compounds including apigenin, naringin, emodin and quercetin were investigated on inhibiting 3T3-L1 preadipocyte differentiation and pancreas lipase activity. Oil Red O staining was conducted to visualise and quantify lipid accumulation. The difference between experimental and calculated results was utilised for determining the interaction types. Interestingly, emodin synergistically interacted with the other three compounds, and the combination of emodin and apigenin exhibited the strongest synergistic effect in both differentiation and pancreas lipase assays. Results implied that the combination of apigenin and emodin may be regarded as a promising complementary therapy for management of overweight or obesity.

Flavonoids from tartary buckwheat induce G2/M cell cycle arrest and apoptosis in human hepatoma HepG2 cells

The cytotoxicity and antioxidant activity on human hepatoma cell line HepG2 of three flavonoids homogenous compounds from tartary buckwheat seeds and bran, namely quercetin, isoquercetin, and rutin, were investigated. The total antioxidant competency detection results indicated that the antioxidant capacity of quercetin was the strongest in a biological response system. A [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay showed that quercetin exhibited the strongest cytotoxic effects against the HepG2 cell line. Flow cytometric analysis indicated that quercetin significantly increased the production of reactive oxygen species, and led to the G2/M phase arrest accompanied by an increase of apoptotic cell death after 48 h of incubation. Quercetin-induced cell apoptosis was shown to involve p53 and p21 up-regulation, Cyclin D1, Cdk2, and Cdk7 down-regulation. These results suggested that the induction of G2/M arrest, apoptosis, and cell death by quercetin may associate with increased expression of p53 and p21, decrease of Cyclin D1, Cdk2, and Cdk7 levels, and generation of reactive oxygen species in cells. This study will help to better understand and fully utilize medicinal resources of plant flavonoids.

In vitro Inhibitory Effects of Limonium contortirameum and L. virgatum Extracts from Sardinia on α-Amylase, α-Glucosidase and Pancreatic Lipase

Pancreatic triacylglycerol lipase (PL), α-amylase and α-glucosidase are interesting pharmacological targets for the management of dyslipidemia, atherosclerosis, and obesity-diabetes. Limonium spp (Plumbaginaceae) are endemic to Sardinia, Italy. Comparable with acarbose, aqueous extracts (AE) of L. contortirameum and L. virgatum, and their phytoconstituent gallic acid concentration gradients (mg/mL) were identified as in vitro potent ( p<0.001, n=3) and efficacious dual inhibitors of α-amylase and α-glucosidase with respective IC50 (mg/mL) values of 0.6 ± 0.1, 1.2 ± 0.1 and 0.15 ± 0.02. Equivalent to orlistat (PL IC50 of 0.114 ± 0.004 μg/mL), L. contortirameum, L. virgatum AE and their phytoprinciple gallic acid inhibited PL substantially ( p<0.001, n=3) in a dose-dependent manner in vitro with PL- IC50 (μg/mL) of 920.4 ± 105.2, 593.1 ± 56.8 and 8.4 ± 0.9, respectively. LC-MS analysis of extracts revealed the presence of several phenolic compounds in their aglycon and glycoside forms. These are catechins, flavones, epigallocatechins and flavonols. Flavonoid- and polyphenol-rich L contortirameum and L. virgatum, modulating gastrointestinal carbohydrate and lipid digestion and absorption, may be advocated as candidates for obesity-diabetes prevention and phytotherapy.

Optimization of the preparation of fish protein anti-obesity hydrolysates using response surface methodology

The enzymatic condition for producing the anti-obesity hydrolysates from fish water-soluble protein was optimized with the aid of response surface methodology, which also derived a statistical model for experimental validation. Compared with neutral protease, papain and protamex, the porcine pancreas lipase inhibitory rate of hydrolysates from fish water-soluble protein was higher with alkaline protease. Results showed that the model terms were significant, the terms of lack of fit were not significant, and the optimal conditions for the hydrolysis by alkaline protease were initial pH 11, temperature 39 °C, enzyme dosage 122 U/mL and 10 h of hydrolysis time. Under these conditions, the porcine pancreas lipase and the α-amylase inhibitory rate could reach 53.04% ± 1.32% and 20.03 ± 0.89%, while predicted value were 54.63% ± 1.75%, 21.22% ± 0.70%, respectively. In addition, Lineweaver-Burk plots showed noncompetitive inhibition. The K_i value calculated was 84.13 mg/mL. These results demonstrated that fish water-soluble protein could be used for obtaining anti-obesity hydrolysates.