Combined use of high-resolution α-glucosidase inhibition profiling and high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy for investigation of antidiabetic principles in crude plant extracts

The phytochemistry and pharmacology of three Rheum species: A comprehensive review with future perspectives

BACKGROUND

Rheum palmatum, R. tanguticum, and R. officinale, integral species of the genus Rheum, are widely used across global temperate and subtropical regions. These species are incorporated in functional foods, medicines, and cosmetics, recognized for their substantial bioactive components.

PURPOSE

This review aims to synthesize developments from 2014 to 2023 concerning the botanical characteristics, ethnopharmacology, nutritional values, chemical compositions, pharmacological activities, mechanisms of action, and toxicity of these species.

METHODS

Data on the three Rheum species were gathered from a comprehensive review of peer-reviewed articles, patents, and clinical trials accessed through PubMed, Google Scholar, Web of Science, and CNKI.

RESULTS

The aerial parts are nutritionally rich, providing essential amino acids, fatty acids, and minerals, suitable for use as health foods or supplements. Studies have identified 143 chemical compounds, including anthraquinones, anthrones, flavonoids, and chromones, which contribute to their broad pharmacological properties such as laxative, anti-diarrheal, neuroprotective, hepatoprotective, cardiovascular, antidiabetic, antitumor, anti-inflammatory, antiviral, and antibacterial effects. Notably, the materials science approach has enhanced understanding of their medicinal capabilities through the evaluation of bioactive compounds in different therapeutic contexts.

CONCLUSION

As medicinal and economically significant herb species, Rheum species provide both edible aerial parts and medicinal underground components that offer substantial health benefits. These characteristics present new opportunities for developing nutritional ingredients and therapeutic products, bolstering the food and pharmaceutical industries.

Application of two-dimensional reversed phase countercurrent chromatography × high-performance liquid chromatography to bioactivity-guided screening and isolation of α-glucosidase inhibitors from Rheum palmatum L

In the present work, comprehensive two-dimensional reversed-phase countercurrent chromatography × reversed-phase liquid chromatography combined (2D RPCCC × RPLC) with 2D microfraction bioactive evaluation was employed to screen and isolate α-glucosidase inhibitors from Rheum palmatum L. Countercurrent chromatography was employed to improve 2D analysis and preparative separation. A selected biphasic solvent system composed of petroleum ether/ethyl acetate/methanol/water with gradient elution mode was used for the first dimension RPCCC separation (1D RPCCC). Solid-phase extraction was applied to eliminate interfering polar compounds before the second dimension analysis (2D RPLC). 76 components were shown in 2D contour plot in UV 280 nm. 11 Candidates were separated by a scaled-up CCC and identified by 1H NMR and 13C NMR, including anthraquinones, flavonoids, stilbenes, phenols, and glucoside derivatives. In addition, it was found that two components, resveratrol-4'-O-(6″-galloyl)glucoside (36) and lyciumaside (43) were identified as natural α-glucosidase inhibitors in Rheum palmatum L. for the first time.

The genus Scorzonera L. (Asteraceae): A comprehensive review on traditional uses, phytochemistry, pharmacology, toxicology, chemotaxonomy, and other applications

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Scorzonera L. comprises of approximately 175 species, which are mainly distributed in temperate and arid regions of Central Europe, Central Asia, and Africa. Twenty-nine Scorzonera traditional ethnomedicines have been used for treating colds and fevers, pulmonary diseases, asthma, dyspepsia, malignant stomach neoplasia, liver disorder, jaundice, kidney diseases, mastitis, women's vaginitis, herpes zoster, poisonous ulcers, rheumatic pain, diabetic, atherosclerosis, headache, hypertension, dysentery, pregnant vomiting, snakebites, etc. AIM OF THE REVIEW: This review aims to systematically evaluate the genus Scorzonera over its ethnomedicinal uses, phytochemistry, pharmacology, and toxicology, discuss the relationship between traditional uses, phytochemistry and pharmacological properties, and put forward some suggestions to promote further development and utilization of Scorzonera.

MATERIALS AND METHODS

This review is based on published scientific research works obtained from the following databases: Elsevier, Web of Science, PubMed, Springer, Wiley, Taylor & Francis, Google Scholar, CNKI, Baidu Scholar, ResearchGate, and others (the Flora of China, 1997 edition; Chinese herbal books, PhD dissertation and Master thesis in Chinese).

RESULTS

The genus 81 Scorzonera plants have been studied for their traditional usage, phytochemistry, and pharmacology. Altogether 421 chemical constituents are isolated from the 54 species of Scorzonera, which include sesquiterpenoids, monoterpenes, diterpenes, triterpenoids, steroids, quinic acid derivatives, flavonoids, cumarinoids, lignanoids, phenylpropanoids, stilbene derivatives, benzylphthalides, kava lactones, phenolics, aliphatic acids, phthalic acids, alkanes, vitamins, sugars, alkaloids, and other constitutes. Besides those listed above, there are also volatile oils, polysaccharides, tannins, amino acids, enzymes, and inorganic elements. The extracts and compounds extracted from 55 Scorzonera species exhibit extensive pharmacological activities, such as anti-inflammatory, antinociceptive, wound healing, anti-cancer, hepatoprotective, anti-microbial, anti-ulcerogenic, antidiarrheal, antidiabetic, hypolipidemic, antioxidant, repairing cerebral ischemia, antidepressant, immunomodulatory activities, enzyme inhibitory effects, etc. Clinical applications strongly indicate that certain species are effective in treating herpes zoster and pregnancy resistance. Certain species are studied over applicationssuch as pharmacokinetic and histological distribution, and toxicity, the product extraction process, quick-freezing processing technology, synthesized metabolites, etc. Chemotaxonomy is also discussed on Scorzonera.

CONCLUSION

This review provides information on traditional usage, phytochemistry, pharmacology, toxicology, chemotaxonomy, other applications aspects, and future prospects of the genus Scorzonera. However, only around one third of Scorzonera species have been studied so far. This review may be used as the basis for future endeavors, including further biological and chemical investigations, and efforts of seeking more applications.

Towards non-target proactive food safety: identification of active compounds in convenience tomato products by ten-dimensional hyphenation with integrated simulated gastrointestinal digestion

Current strategies for non-target food screening focus mainly on known hazardous chemicals (adulterants, residues, contaminants, packaging migrants, etc.) instead of bioactive constituents in general and exclude the biological effect detection. To widen the perspective, a more proactive non-target effect-directed strategy is introduced to complement food safety in order to detect not only known but also unknown bioactive compounds. The developed 10-dimensional hyphenation included on-surface digestion (1D), planar chromatographic separation (2D), visualization using white light (3D), UV light (4D), fluorescence light (5D), effect-directed assay analysis (6D), heart-cut zone elution to an orthogonal reversed phase column chromatography including online desalting (7D) with subsequent diode array detection (8D), high-resolution mass spectrometry (9D), and fragmentation (10D). Metabolism, i.e., intestinal digestion of each sample, was simulated and integrated on the same adsorbent surface to study any changes in the compound profiles. As proof of principle, nine convenience tomato products and a freshly prepared tomato soup were screened via five different planar assays in a non-targeted mode. Non-digested and digested samples were compared side by side. In their effect-directed profiles, 14 bioactive compounds from classes of lipids, plant hormones, spices, and pesticides were identified. In particular, bioactive compounds coming from the lipid class were increased by gastrointestinal digestion, while spices and pesticides remained unaffected. With regard to food safety, the determination of the two dinitrophenol herbicides dinoterb and dinoseb in highly processed tomato products should be given special attention. The hyphenation covered a broad analyte spectrum and showed robust and reliable results.

Metabolites of Geum aleppicum and Sibbaldianthe bifurca: Diversity and α-Glucosidase Inhibitory Potential

α-Glucosidase inhibitors are essential in the treatment of diabetes mellitus. Plant-derived drugs are promising sources of new compounds with glucosidase-inhibiting ability. The Geum aleppicum Jacq. and Sibbaldianthe bifurca (L.) Kurtto & T.Erikss. herbs are used in many traditional medical systems to treat diabetes. In this study, metabolites of the G. aleppicum and S. bifurca herbs in active growth, flowering, and fruiting stages were investigated using high-performance liquid chromatography with photodiode array and electrospray ionization triple quadrupole mass spectrometric detection (HPLC-PDA-ESI-tQ-MS/MS). In total, 29 compounds in G. aleppicum and 41 components in S. bifurca were identified including carbohydrates, organic acids, benzoic and ellagic acid derivatives, ellagitannins, flavonoids, and triterpenoids. Gemin A, miquelianin, niga-ichigoside F1, and 3,4-dihydroxybenzoic acid 4-O-glucoside were the dominant compounds in the G. aleppicum herb, while guaiaverin, miquelianin, tellimagrandin II₂, casuarictin, and glucose were prevailing compounds in the S. bifurca herb. On the basis of HPLC activity-based profiling of the G. aleppicum herb extract, the most pronounced inhibition of α-glucosidase was observed for gemin A and quercetin-3-O-glucuronide. The latter compound and quercetin-3-O-arabinoside demonstrated maximal inhibition of α-glucosidase in the S. bifurca herb extract. The obtained results confirm the prospects of using these plant compounds as possible sources of hypoglycemic nutraceuticals.

Magnetic metal-organic frameworks immobilized enzyme-based nano-biocatalytic systems for sustainable biotechnology

Nanobiocatalysts, in which enzyme molecules are integrated into/onto multifunctional materials, such as metal-organic frameworks (MOFs), have been fascinating and appeared as a new interface of nanobiocatalysis with multi-oriented applications. Among various nano-support matrices, functionalized MOFs with magnetic attributes have gained supreme interest as versatile nano-biocatalytic systems for organic bio-transformations. From the design (fabrication) to deployment (application), magnetic MOFs have manifested notable efficacy in manipulating the enzyme microenvironment for robust biocatalysis and thus assure requisite applications in several areas of enzyme engineering at large and nano-biocatalytic transformations, in particular. Magnetic MOFs-linked enzyme-based nano-biocatalytic systems offer chemo-regio- and stereo-selectivities, specificities, and resistivities under fine-tuned enzyme microenvironments. Considering the current sustainable bioprocesses demands and green chemistry needs, we reviewed synthesis chemistry and application prospects of magnetic MOFs-immobilized enzyme-based nano-biocatalytic systems for exploitability in different industrial and biotechnological sectors. More specifically, following a thorough introductory background, the first half of the review discusses various approaches to effectively developed magnetic MOFs. The second half mainly focuses on MOFs-assisted biocatalytic transformation applications, including biodegradation of phenolic compounds, removal of endocrine disrupting compounds, dye decolorization, green biosynthesis of sweeteners, biodiesel production, detection of herbicides and screening of ligands and inhibitors.

Therapeutic Uses and Pharmacological Properties of Shallot (Allium ascalonicum): A Systematic Review

Background

Shallot (Allium ascalonicum L.) is a traditional plant species used throughout the world both for culinary purposes and as a folk remedy. To date (i.e., April 2022), there is no report on the main pharmacological activities exerted by shallot preparations and/or extracts.

Scope and Approach

The aim of this study was to comprehensively review the pharmacological activities exerted by shallot, with rigorous inclusion and exclusion criteria based on the scientific rigor of studies. Prisma guidelines were followed to perform the literature search.

Key Findings and Conclusions

The literature search yielded 2,410 articles of which 116 passed the required rigorous criteria for inclusion in this review. The extracts exert a potent antioxidant activity both in vitro and in vivo, as well as a strong inhibitory capacity on various pathogens with relevant implications for public health. Moreover, shallot can be used as adjuvant therapy in cardiovascular diseases, diabetes, cancer prevention, and other non-communicable diseases associated with inflammatory and oxidative pathways. Future studies investigating the chemical composition of this species, as well as the molecular mechanisms involved in the empirically observed pharmacological actions are required.

Combining Activity Profiling with Advanced Annotation to Accelerate the Discovery of Natural Products Targeting Oncogenic Signaling in Melanoma

The discovery of bioactive natural products remains a time-consuming and challenging task. The ability to link high-confidence metabolite annotations in crude extracts with activity would be highly beneficial to the drug discovery process. To address this challenge, HPLC-based activity profiling and advanced UHPLC-HRMS/MS metabolite profiling for annotation were combined to leverage the information obtained from both approaches on a crude extract scaled down to the submilligram level. This strategy was applied to a subset of an extract library screening aiming to identify natural products inhibiting oncogenic signaling in melanoma. Advanced annotation and data organization enabled the identification of compounds that were likely responsible for the activity in the extracts. These compounds belonged to two different natural product scaffolds, namely, brevipolides from a Hyptis brevipes extract and methoxylated flavonoids identified in three different extracts of Hyptis and Artemisia spp. Targeted isolation of these prioritized compounds led to five brevipolides and seven methoxylated flavonoids. Brevipolide A (1) and 6-methoxytricin (9) were the most potent compounds from each chemical class and displayed AKT activity inhibition with an IC₅₀ of 17.6 ± 1.6 and 4.9 ± 0.2 μM, respectively.

Evidence that Indo-Pacific bottlenose dolphins self-medicate with invertebrates in coral reefs

Indo-Pacific bottlenose dolphins (Tursiops aduncus) have been observed queueing up in natural environments to rub particular body parts against selected corals (Rumphella aggregata, Sarcophyton sp.) and sponges (Ircinia sp.) in the Egyptian Northern Red Sea. It was hypothesized that the presence of bioactive metabolites accounts for this selective rubbing behavior. The three invertebrates preferentially accessed by the dolphins, collected and analyzed by hyphenated high-performance thin-layer chromatography contained seventeen active metabolites, providing evidence of potential self-medication. Repeated rubbing allows these active metabolites to come into contact with the skin of the dolphins, which in turn could help them achieve skin homeostasis and be useful for prophylaxis or auxiliary treatment against microbial infections. This interdisciplinary research in behavior, separation science, and effect-directed analysis highlighted the importance of particular invertebrates in coral reefs, the urgent need to protect coral reefs for dolphins and other species, and calls for further vertebrate-invertebrate interaction studies.

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Dolphins rubbed body parts against specifically selected corals and sponges

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Behavioral studies were linked with hyphenated bioanalytical technique

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Vertebrate-invertebrate interaction in coral reefs may serve self-medication

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Molecular formulae were assigned to known and unknown bioactive molecules

Is Our Natural Food Our Homeostasis? Array of a Thousand Effect-Directed Profiles of 68 Herbs and Spices

The beneficial effects of plant-rich diets and traditional medicines are increasingly recognized in the treatment of civilization diseases due to the abundance and diversity of bioactive substances therein. However, the important active portion of natural food or plant-based medicine is presently not under control. Hence, a paradigm shift from quality control based on marker compounds to effect-directed profiling is postulated. We investigated 68 powdered plant extracts (botanicals) which are added to food products in food industry. Among them are many plants that are used as traditional medicines, herbs and spices. A generic strategy was developed to evaluate the bioactivity profile of each botanical as completely as possible and to straightforwardly assign the most potent bioactive compounds. It is an 8-dimensional hyphenation of normal-phase high-performance thin-layer chromatography with multi-imaging by ultraviolet, visible and fluorescence light detection as well as effect-directed assay and heart-cut of the bioactive zone to orthogonal reversed-phase high-performance liquid chromato-graphy-photodiode array detection-heated electrospray ionization mass spectrometry. In the non-target, effect-directed screening via 16 different on-surface assays, we tentatively assigned more than 60 important bioactive compounds in the studied botanicals. These were antibacterials, estrogens, antiestrogens, androgens, and antiandrogens, as well as acetylcholinesterase, butyrylcholinesterase, α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase inhibitors, which were on-surface heart-cut eluted from the bioautogram or enzyme inhibition autogram to the next dimension for further targeted characterization. This biological-physicochemical hyphenation is able to detect and control active mechanisms of traditional medicines or botanicals as well as the essentials of plant-based food. The array of 1,292 profiles (68 samples × 19 detections) showed the versatile bioactivity potential of natural food. It reveals how efficiently and powerful our natural food contributes to our homeostasis.

Antioxidant and antihyperglycemic activities of Scorzonera cinerea radical leaves in streptozocin-induced diabetic rats

Scorzonera species are used for treating various diseases. They are consumed raw, especially in the spring, and have nutritious and dietetic values. This study evaluated the antidiabetic and antioxidant effects of ethanolic extracts of Scorzonera cinerea (Sc) radical leaves in diabetes mellitus. Five random groups of Wistar rats (n = 8) were created - control, diabetic, acarbose, Sc-Dried, and Sc-Frozen. Phenolic profiles of extracts were determined by HPLC. Free radical scavenging capacity was measured using DPPH and ABTS tests. The inhibitory effects of Sc extracts on α-glucosidase and α-amylase activities were also evaluated. Moreover, superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) activities, glutathione (GSH) concentration, malondialdehyde (MDA), total antioxidant status (TAS) and total oxidant status (TOS) were analyzed in the liver tissues. While dried Scorzonera extract was more effective in α-amylase inhibitory activity, frozen Scorzonera extract was more effective in α-glucosidase inhibitory activity. Sc-Dried and Sc-Frozen extracts lowered blood glucose and HbA_1c levels, they also increased insulin. Although liver MDA and TOS were significantly increased in the diabetic group, their values were significantly lower in the Sc-Dried- and Sc-Frozen-treated groups. GSH, TAS, and anti-oxidant enzyme activities decreased in the diabetic group, but Sc-Dried and Sc-Frozen supplements significantly enhanced liver antioxidant values. In conclusion, S. cinerea treatment exerts potential hypoglycemic and antioxidant effects in diabetes. Thus, it can be considered as a candidate dietary supplement for health benefits in diabetes.

Identification of α-Glucosidase Inhibitors from Leaf Extract of Pepper (Capsicum spp.) through Metabolomic Analysis

Metabolomics and in vitro α-glucosidase inhibitory (AGI) activities of pepper leaves were used to identify bioactive compounds and select genotypes for the management of type 2 diabetes mellitus (T2DM). Targeted metabolite analysis using UPLC-DAD-QToF-MS was employed and identified compounds that belong to flavone and hydroxycinnamic acid derivatives from extracts of pepper leaves. A total of 21 metabolites were detected from 155 samples and identified based on MS fragmentations, retention time, UV absorbance, and previous reports. Apigenin-O-(malonyl) hexoside, luteolin-O-(malonyl) hexoside, and chrysoeriol-O-(malonyl) hexoside were identified for the first time from pepper leaves. Pepper genotypes showed a huge variation in their inhibitory activity against α-glucosidase enzyme(AGE) ranging from 17% to 79%. Genotype GP38 with inhibitory activity of 79% was found to be more potent than the positive control acarbose (70.8%.). Orthogonal partial least square (OPLS) analyses were conducted for the prediction of the AGI activities of pepper leaves based on their metabolite composition. Compounds that contributed the most to the bioactivity prediction model (VIP >1.5), showed a strong inhibitory potency. Caffeoyl-putrescine was found to show a stronger inhibitory potency (IC₅₀ = 145 µM) compared to acarbose (IC₅₀ = 197 µM). The chemometric procedure combined with high-throughput AGI screening was effective in selecting polyphenols of pepper leaf for T2DM management.

α-glucosidase immobilization on magnetic core-shell metal-organic frameworks for inhibitor screening from traditional Chinese medicines

In this work, a simple and rapid screening strategy was developed combining capillary electrophoresis analysis with enzymatic assay based on immobilized α-glucosidase. For α-glucosidase immobilization, magnetic core-shell metal-organic frameworks composite (Fe₃O₄@CS@ZIF-8) was fabricated by a step-by-step assembly method, and α-glucosidase was in situ encapsulated in crystal lattice of ZIF-8. The composite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. After immobilization, α-glucosidase exhibited enhanced tolerance to temperature and pH, and its reusability was greatly improved with 74 % of initial enzyme activity after being recycled 10 times. The Michaelis-Menten constant of immobilized enzyme was calculated to be 0.47 mM and its inhibition constant and IC₅₀ for acarbose were 0.57 μM and 0.18 μM, respectively. The immobilized enzyme was subsequently applied to inhibitor screening from 14 TCMs, and Rhei Radix et Rhizoma was screened out. Among the commercially available 10 components presented in Rhei Radix et Rhizoma, gallic acid, (+)-catechin and epicatechin exhibited the strongest inhibitory effect on α-glucosidase. Their binding sites and modes with α-glucosidase were simulated via molecular docking to further verify the inhibition screening assay results. The positive results indicated that the Fe₃O₄@CS@ZIF-8-based screening strategy may provide a new avenue for discovering enzyme inhibitors from TCMs.

Antioxidant and Antidiabetic Activity of Proanthocyanidins from Fagopyrum dibotrys

Proanthocyanidins are natural glycosidase inhibitors with excellent antioxidant activity. This study aims to search for a new source of proanthocyanidins for the prevention and treatment of type 2 diabetes with higher content and better activity and get their structure elucidated. First, the total proanthocyanidins contents (TOPCs), antioxidant activity, antidiabetic activity of seven common Polygonaceae plants were analyzed and compared. Then proanthocyanidins from the rhizome of Fagopyrum dibotrys were purified, and the detailed structure was comprehensively analyzed by ultraviolet visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR), reversed-phase high-performance liquid chromatography-electrospray mass spectrometry (RP-HPLC-ESI-MS), and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). The rhizome of F. dibotrys showed the highest TOPCs, the strongest antioxidant, and antidiabetic activities; the TOPCs, antioxidant and antidiabetic activities were all very significantly positively correlated. Proanthocyanidins purified from the rhizome of F. dibotrys showed better antidiabetic activity than grape seed proanthocyanidins (GsPs). Seventy-two proanthocyanidins from trimer to undecamer with a mean degree of polymerization (mDP) of about 5.02 ± 0.21 were identified with catechin and epicatechin as the dominant monomers. Conclusion: Proanthocyanidins are the main antioxidant and antidiabetic active substances of F. dibotrys and are expected to be developed into potential antioxidant and hypoglycemic products.

Eight different bioactivity profiles of 40 cinnamons by multi-imaging planar chromatography hyphenated with effect-directed assays and high-resolution mass spectrometry

Spices contain plenty of bioactive compounds, used to valorize foods. However, product quality may be affected by contaminations and adulterations along the global production chain. A newly developed multi-imaging in combination with bioactivity screening directly pointed to individual multi-potent compounds. For cinnamon as prominent example, the multi-imaging results provided a wealth of new information on their effects and clearly visualized the valorizing potential of cinnamon to foods. The separation focus was in the mid-polar to apolar range. Eight effect-directed assays (EDA, i.e. one radical scavenging, two biological and five biochemical assays) were performed in situ the high-performance thin-layer chromatography (HPTLC) adsorbent. Several multi-potent compound zones were revealed and further characterized by high-resolution mass spectrometry (HRMS), highlighting the bioactive potential of cinnamaldehyde, cinnamic acid, benzoic acid, coumarin, linoleic acid, oleic acid, stearic acid, palmitic acid, caproic acid, and linalool oxide. This HPTLC-UV/Vis/FLD-EDA-HRMS profiling provided comprehensive information on product quality and safety.

Ethnobotanical Uses, Phytochemistry and Pharmacology of Different Rheum Species (Polygonaceae): A Review

Today, there is an increased tendency to use herbal remedies. Rhubarb refers to several species of the genus Rheum L. in the Polygonaceae family. This species-rich genus is mainly distributed in Asian countries. Several medicinal effects have been attributed to the Rheum spp. in the traditional and modern medicine such as healing lungs, liver, kidney, womb and bladder diseases, cancer, diabetes, insect bites, relapsing fevers, diarrhea and constipation. Various in vitro, in vivo and clinical studies have investigated the therapeutic effect of extracts, fractions and pure compounds isolated from different species of this genus. Considering the positive findings, several pharmaceutical formulations containing rhubarb extract like capsules, drops, mouthwashes and different topical formulations are now present in the market. However, there are other traditional therapeutic effects of rhubarb that have not been studied yet and it is of great importance to perform confirmatory experiments or clinical investigations. The current review summarizes general information regarding botany, phytochemistry, ethnobotany and pharmacological aspects of Rheum spp. It is hoped that the present review could motivate subsequent research on the other medicinal properties of these plants that have been neglected until today.

Unraveling the complexity of complex mixtures by combining high-resolution pharmacological, analytical and spectroscopic techniques: antidiabetic constituents in Chinese medicinal plants

Medicinal plants have been widely used as (poly)pharmacological remedies and constitute a rich source for antidiabetic drug discovery. In the present study, forty medicinal plant samples collected in China were tested for inhibitory activity against α-glucosidase, α-amylase, and protein-tyrosine phosphatase 1B (PTP1B). Crude ethyl acetate extracts of Dioscorea bulbifera L., Boehmeria nivea Gaudich, Tinospora sagittata Gagnep. and Persicaria bistorta (L.) Samp. showed dual inhibitory activity towards α-glucosidase and PTP1B, and were chosen for further investigation. Subsequent dual high-resolution α-glucosidase/PTP1B profiling or triple high-resolution α-glucosidase/α-amylase/PTP1B profiling combined with HPLC-HRMS and NMR spectroscopy led to the identification of 28 metabolites with one or more bioactivities. Among these, three new phenanthrenes were identified from D. bulbifera, including one new biphenanthrene (10) exhibiting promising dual inhibitory activity towards α-glucosidase and PTP1B with IC50 values of 2.08 ± 0.19 and 3.36 ± 0.25 μM, respectively. Two triterpenoids and one fatty acid from B. nivea and T. sagittata as well as some commercially available fatty acids showed strong PTP1B inhibitory activity with IC50 values in the range of 4.89 ± 0.38 to 53.77 ± 4.20 μM.

Metabolomics in the Context of Plant Natural Products Research: From Sample Preparation to Metabolite Analysis

Plant-derived natural products have long been considered a valuable source of lead compounds for drug development. Natural extracts are usually composed of hundreds to thousands of metabolites, whereby the bioactivity of natural extracts can be represented by synergism between several metabolites. However, isolating every single compound from a natural extract is not always possible due to the complex chemistry and presence of most secondary metabolites at very low levels. Metabolomics has emerged in recent years as an indispensable tool for the analysis of thousands of metabolites from crude natural extracts, leading to a paradigm shift in natural products drug research. Analytical methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) are used to comprehensively annotate the constituents of plant natural products for screening, drug discovery as well as for quality control purposes such as those required for phytomedicine. In this review, the current advancements in plant sample preparation, sample measurements, and data analysis are presented alongside a few case studies of the successful applications of these processes in plant natural product drug discovery.

Emerging strategies for the activity assay and inhibitor screening of alpha-glucosidase

The high incidence of diabetes mellitus has caused widespread concern around the world, and has quickly become one of the most prevalent and costly chronic diseases.

Identification of Bioactive Phytochemicals in Mulberries

Mulberries are consumed either freshly or as processed fruits and are traditionally used to tackle several diseases, especially type II diabetes. Here, we investigated the metabolite compositions of ripe fruits of both white (Morus alba) and black (Morus nigra) mulberries, using reversed-phase HPLC coupled to high resolution mass spectrometry (LC-MS), and related these to their in vitro antioxidant and α-glucosidase inhibitory activities. Based on accurate masses, fragmentation data, UV/Vis light absorbance spectra and retention times, 35 metabolites, mainly comprising phenolic compounds and amino sugar acids, were identified. While the antioxidant activity was highest in M. nigra, the α-glucosidase inhibitory activities were similar between species. Both bioactivities were mostly resistant to in vitro gastrointestinal digestion. To identify the bioactive compounds, we combined LC-MS with 96-well-format fractionation followed by testing the individual fractions for α-glucosidase inhibition, while compounds responsible for the antioxidant activity were identified using HPLC with an online antioxidant detection system. We thus determined iminosugars and phenolic compounds in both M. alba and M. nigra, and anthocyanins in M. nigra as being the key α-glucosidase inhibitors, while anthocyanins in M. nigra and both phenylpropanoids and flavonols in M. alba were identified as key antioxidants in their ripe berries.

Alpha Glucosidase Inhibitory Activities of Plants with Focus on Common Vegetables

Type-2 diabetes mellitus is one of the most prevalent metabolic diseases in the world, and is characterized by hyperglycemia (i.e., high levels of glucose in the blood). Alpha-glucosidases are enzymes in the digestive tract that hydrolyze carbohydrates into glucose. One strategy that has been developed to treat type-2 diabetes is inhibition of the activity of alpha-glucosidases using synthetic drugs. However, these inhibitors are usually associated with gastrointestinal side effects. Therefore, the development of inhibitors from natural products offers an alternative option for the control of hyperglycemia. In recent years, various studies have been conducted to identify alpha-glucosidases inhibitors from natural sources such as plants, and many candidates have transpired to be secondary metabolites including alkaloids, flavonoids, phenols, and terpenoids. In this review, we focus on the alpha-glucosidases inhibitors found in common vegetable crops and the major classes of phytochemicals responsible for the inhibitory activity, and also as potential/natural drug candidates for the treatment of type-2 diabetes mellitus. In addition, possible breeding strategies for production of improved vegetable crops with higher content of the inhibitors are also described.

Untargeted Metabolomics Toward Systematic Characterization of Antioxidant Compounds in Betulaceae Family Plant Extracts

Plant species have traditionally been revered for their unparalleled pharmacognostic applications. We outline a non-iterative multi-parallel metabolomic-cum-bioassay-guided methodology toward the functional characterization of ethanol extracts from the Betulaceae family plants (n = 10). We performed mass spectrometry (MS)-based multivariate analyses and bioassay-guided (ABTS antioxidant activity and cytoprotective effects against H₂O₂-induced cell damage) analyses of SPE fractions. A clearly distinct metabolomic pattern coupled with significantly higher bioactivities was observed for 40% methanol SPE eluate. Further, the 40% SPE eluate was subjected to preparative high-performance liquid chromatography (prep-HPLC) analysis, yielding 72 sub-fractions (1 min⁻¹), with the highest antioxidant activities observed for the 15 min and 31 min sub-fractions. We simultaneously performed hyphenated-MS-based metabolite characterization of bioactive components for both the 40% methanol SPE fraction and its prep-HPLC sub-fraction (15 min and 31 min). Altogether, 19 candidate metabolites were mainly observed to contribute toward the observed bioactivities. In particular, ethyl gallate was mainly observed to affect the antioxidant activities of SPE and prep-HPLC fractions of Alnus firma extracts. We propose an integrated metabolomic-cum-bioassay-guided approach for the expeditious selection and characterization of discriminant metabolites with desired phenotypes or bioactivities.

Piceatannol alleviates inflammation and oxidative stress via modulation of the Nrf2/HO-1 and NF-κB pathways in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is one of the leading causes of morbidity and mortality in diabetic patients. Piceatannol (PIC) has protective effects against cardiovascular disease; however, it remains unknown whether it also protects against DCM. A Cell Counting Kit-8 (CCK-8) assay was used to evaluate the effects of PIC on the viability of high glucose (HG)-induced H9C2 cells. Protein expression and mRNA levels were detected by western blotting and real-time polymerase chain reaction (RT-PCR), respectively. In vivo, physical and biochemical analyses, together with transthoracic echocardiography and hemodynamic measurements, were used to detect the effects of PIC treatment on cardiac function in DCM rats. Reactive oxygen species production was determined using an ELISA kit, and inflammatory cytokines were detected by RT-PCR. Pathological changes were assessed by hematoxylin-eosin staining, immunohistochemical staining, and TUNEL staining. According to the results, PIC treatment improved cell viability and inhibited cell apoptosis in HG-induced H9C2 cardiac myoblasts. In addition, PIC not only attenuated the over-production of interleukin-6 (IL-6) (P < 0.05) and tumor necrosis factor alpha (TNF-α) (P < 0.05), but also improved the expression of nuclear factor E2-related factor 2 (Nrf2) (P < 0.05) and heme oxygenase-1 (HO-1) (P < 0.01). Importantly, knockdown of Nrf2 suppressed PIC-mediated activation of the Nrf2/HO-1 pathway and abolished its anti-inflammatory effects. In vivo, oral administration of PIC suppressed STZ-induced inflammation, oxidative stress hypertrophy, fibrosis(myocardial collagen volume fraction in 5 mg/kg and 10 mg/kg PIC group was decreased 25.83% and 55.61% compared with the DM group), and apoptosis(Caspase-3 level in 5 mg/kg and 10 mg/kg PIC group was decreased 13.21% and 33.91% compared with the DM group), thereby relieving cardiac dysfunction and improving both fibrosis and pathological changes in cardiac tissues of diabetic rats. These findings define for the first time that the effects of PIC against DCM can be attributed to its role in inflammation and oxidative stress inhibition.

Combined magnetic ligand fishing and high-resolution inhibition profiling for identification of α-glucosidase inhibitory ligands: A new screening approach based on complementary inhibition and affinity profiles

Plants are well-recognized sources of inhibitors for α-glucosidase - a key target enzyme for management of type 2 diabetes. Recently, two advanced bioactivity-profiling techniques, i.e., ligand fishing and high-resolution inhibition profiling, have shown great promises for accelerating identification of α-glucosidase inhibitors from complex plant extracts. Non-specific affinities and non-specific inhibitions are major sources of false positive hits from ligand fishing and high-resolution inhibition profiling, respectively. In an attempt to minimize such false positive hits, we describe a new screening approach based on ligand fishing and high-resolution inhibition profiling for detection of high-affinity ligands and assessment of inhibitory activity, respectively. The complementary nature of ligand fishing and high-resolution inhibition profiling was explored to identify α-glucosidase inhibitory ligands from a complex mixture, and proof-of-concept was demonstrated with crude ethyl acetate extract of Ginkgo biloba. In addition to magnetic beads with a 3-carbon aliphatic linker, α-glucosidase was immobilized on magnetic beads with a 21-carbon aliphatic linker; and the two different types of magnetic beads were compared for their hydrolytic activity and fishing efficiency.

Identification of α-Glucosidase Inhibitors in Machilus litseifolia by Combined Use of High-Resolution α-Glucosidase Inhibition Profiling and HPLC-PDA-HRMS-SPE-NMR

Type 2 diabetes is a chronic multifactorial disease affecting more than 425 million people worldwide, and new selective α-glucosidase inhibitors with fewer side effects are urgently needed. In this study, a crude ethyl acetate extract of Machilus litseifolia was fractionated by solid-phase extraction using C₁₈ cartridges to give a fraction enriched in α-glucosidase inhibitors. Subsequent microfractionation and bioassaying of the eluate by high-performance liquid chromatography (HPLC) using a complementary pentafluorophenyl column allowed construction of a high-resolution α-glucosidase inhibition profile (biochromatogram). This was used to target high-performance liquid chromatography-photodiode array detection-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-PDA-HRMS-SPE-NMR) analysis toward α-glucosidase inhibitors. This led to the identification of 13 dicoumaroylated flavonol rhamnosides, of which seven (8, 10, 12a, 12b, 16, 17, and 18) are reported for the first time, and two lignans, of which one (5) is reported for the first time. IC₅₀ values of isolated compounds toward α-glucosidase range from 5.9 to 35.3 μM, which is 8 to 91 times lower than the IC₅₀ value of 266 μM measured for the reference compound acarbose.

High-Resolution PTP1B Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of PTP1B Inhibitors from Miconia albicans

Protein tyrosine phosphatase 1B (PTP1B) is an intracellular enzyme responsible for deactivation of the insulin receptor, and consequently acts as a negative regulator of insulin signal transduction. In recent years, PTP1B has become an important target for controlling insulin resistance and type 2 diabetes. In the present study, the ethyl acetate extract of leaves of Miconia albicans (IC₅₀ = 4.92 µg/mL) was assessed by high-resolution PTP1B inhibition profiling combined with HPLC-HRMS-SPE-NMR for identification of antidiabetic compounds. This disclosed eleven PTP1B inhibitors, including five polyphenolics: 1-O-(E)-caffeoyl-4,6-di-O-galloyl-β-d-glucopyranose (2), myricetin 3-O-α-l-rhamnopyranoside (3), quercetin 3-O-(2″-galloyl)-α-l-rhamnopyranoside (5), mearnsetin 3-O-α-l-rhamnopyranoside (6), and kaempferol 3-O-α-l-arabinopyranoside (8) as well as eight triterpenoids: maslinic acid (13), 3-epi-sumaresinolic acid (14), sumaresinolic acid (15), 3-O-cis-p-coumaroyl maslinic acid (16), 3-O-trans-p-coumaroyl maslinic acid (17), 3-O-trans-p-coumaroyl 2α-hydroxydulcioic acid (18), oleanolic acid (19), and ursolic acid (20). These results support the use of M. albicans as a traditional medicine with antidiabetic properties and its potential as a source of PTP1B inhibitors.

Quadruple high-resolution α-glucosidase/α-amylase/PTP1B/radical scavenging profiling combined with high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy for identification of antidiabetic constituents in crude root bark of Morus alba L

In this paper, quadruple high-resolution α-glucosidase/α-amylase/PTP1B/radical scavenging profiling combined with HPLC-HRMS-SPE-NMR were used for studying the polypharmacological properties of crude root bark extract of Morus alba L. This species is used as an anti-diabetic principle in many traditional treatment systems around the world, and the crude ethyl acetate extract of M. alba root bark was found to inhibit α-glucosidase, α-amylase and protein-tyrosine phosphatase 1B (PTP1B) with IC₅₀ values of 1.70 ± 0.72, 5.16 ± 0.69, and 5.07 ± 0.68 μg/mL as well as showing radical scavenging activity equaling a TEAC value of (3.82 ± 0.14) × 10⁴ mM per gram extract. Subsequent investigation of the crude extract using quadruple high-resolution α-glucosidase/α-amylase/PTP1B/radical scavenging profiling provided a quadruple biochromatogram that allowed direct correlation of the HPLC peaks with one or more of the tested bioactivities. This was used to target subsequent HPLC-HRMS-SPE-NMR analysis towards peaks representing bioactive analytes, and led to identification of a new Diels-Alder adduct named Moracenin E as well as a series of Diels-Alder adducts and isoprenylated flavonoids as potent α-glucosidase and α-amylase inhibitors with IC₅₀ values in the range of 0.60-27.15 μM and 1.22-69.38 μM, respectively. In addition, these compounds and two 2-arylbenzofurans were found to be potent PTP1B inhibitors with IC₅₀ values ranging from 4.04 to 21.67 μM. The high-resolution radical scavenging profile also revealed that almost all of the compounds possess radical scavenging activity. In conclusion the quadruple high-resolution profiling method presented here allowed a detailed profiling of individual constituents in crude root bark extract of M. alba, and the method provides a general tool for detailed mapping of bioactive constituents in polypharmacological herbal remedies.

High-Resolution Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of PTP1B Inhibitors from Vietnamese Plants

Protein tyrosine phosphatase 1B (PTP1B) plays a key role as a negative regulator in insulin signal transduction by deactivating the insulin receptor. Thus, PTP1B inhibition has emerged as a potential therapeutic strategy for curing insulin resistance. In this study, 40 extracts from 18 different plant species were investigated for PTP1B inhibitory activity in vitro. The most promising one, the EtOAc extract of Ficus racemosa, was investigated by high-resolution PTP1B inhibition profiling combined with HPLC-HRMS-SPE-NMR analysis. This led to the identification of isoderrone (1), derrone (2), alpinumisoflavone (3) and mucusisoflavone B (4) as PTP1B inhibitors. IC₅₀ of these compounds were 22.7 ± 1.7, 12.6 ± 1.6, 21.2 ± 3.8 and 2.5 ± 0.2 µM, respectively. Kinetics analysis revealed that these compounds inhibited PTP1B non-competitively with K_i values of 21.3 ± 2.8, 7.9 ± 1.9, 14.3 ± 2.0, and 3.0 ± 0.5 µM, respectively. These findings support the important role of F. racemosa as a novel source of new drugs and/or as a herbal remedy for treatment of type 2 diabetes.

Characterization of Antileishmanial Compounds from Lawsonia inermis L. Leaves Using Semi-High Resolution Antileishmanial Profiling Combined with HPLC-HRMS-SPE-NMR

This work describes an analytical platform based on semi-high-resolution antileishmanial profiling combined with hyphenation of high-performance liquid chromatography – high-resolution mass spectrometry – solid-phase extraction – nuclear magnetic resonance spectroscopy, i.e., semiHR-antileishmanial assay/HPLC-HRMS-SPE-NMR. The platform enables fast pinpointing of HPLC peaks representing Leishmania tropica inhibitors in complex matrices, with subsequent structural identification of targeted inhibitors. Active analytes were cumulatively trapped on SPE cartridges and the structures elucidated by analysis of NMR spectra obtained in the HPLC-HRMS-SPE-NMR mode. This led to the identification of six known compounds 2,4,6-trihydroxyacetophenone-2-O-β-D-glucopyranoside (1), lalioside (2), luteolin-4′-O-β-D-glucopyranoside (3), apigenin-4′-O-β-D-glucopyranoside (4), luteolin (5), and apigenin (6). IC₅₀ of the active compounds were determined with luteolin being the most potent inhibitor with an IC₅₀ value of 4.15 μg/ml. The platform proved to be an efficient method for the identification of L. tropica inhibitors.

Grape skin phenolics as inhibitors of mammalian α-glucosidase and α-amylase--effect of food matrix and processing on efficacy

Type-2 diabetes is continuously increasing worldwide. Hence, there is a need to develop functional foods that efficiently alleviate damage due to hyperglycaemia complications while meeting the criteria for a sustainable food processing technology. Inhibition of mammalian α-amylase and α-glucosidase was studied for white grape skin samples recovered from wineries and found to be higher than that of the drug acarbose. In white grape skins, quercetin and kaempferol derivatives, analysed by UPLC-DAD-MS, and the oligomeric series of catechin/epicatechin units and their gallic acid ester derivatives up to nonamers, analysed by MALDI-TOF-MS were identified. White grape skin was then used for enrichment of a tomato puree (3%) and a flat bread (10%). White grape skin phenolics were found in the extract obtained from the enriched foods, except for the higher mass proanthocyanidin oligomers, mainly due to their binding to the matrix and to a lesser extent to heat degradation. Proanthocyanidin solubility was lower in bread, most probably due to formation of binary proanthocyanin/protein complexes, than in tomato puree where possible formation of ternary proanthocyanidin/protein/pectin complexes can enhance solubility. Enzyme inhibition by the enriched foods was significantly higher than for unfortified foods. Hence, this in vitro approach provided a platform to study potential dietary agents to alleviate hyperglycaemia damage and suggested that grape skin phenolics could be effective even if the higher mass proanthocyanidins are bound to the food matrix.

Screening for potential α-glucosidase and α-amylase inhibitory constituents from selected Vietnamese plants used to treat type 2 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

The 18 plant species investigated in this study have been used as herbal antidiabetic remedies in Vietnamese traditional medicines. This study aimed to evaluate their ability to inhibit α-glucosidase and α-amylase, two key enzymes involved in serum glucose regulation.

MATERIALS AND METHODS

Chloroform, ethanol and water extracts of 18 plants were screened for α-glucosidase and α-amylase inhibitory activity. Analytical-scale HPLC was subsequently used to investigate the most active extracts, where samples with low level of tannins were identified and fractionated into 96-well microplates, followed by α-glucosidase and α-amylase assessment of each well. High-resolution α-glucosidase and α-amylase inhibition profiles constructed from these assays allowed identification of HPLC peaks correlated with α-glucosidase and α-amylase inhibitory activity. The active constituents were subsequently isolated using preparative-scale HPLC and their structure was elucidated by HR-ESIMS and NMR.

RESULTS

Ethanol extracts of Nepenthes mirabilis, Phyllanthus urinaria, and Kandelia candel significantly inhibited α-glucosidase with IC50 values of 32.7±6.3, 39.7±9.7, and 35.4±13.9μg/mL, respectively. Water extracts of N. mirabilis, Phyllanthus amarus, P. urinaria, Lagerstroemia speciosa, Syzygium cumini, Rhizophora mucronata, and K. candel showed IC50 values of 3.3±0.8, 34.9±1.5, 14.6±4.6, 5.4±0.5, 20.9±1.8, 3.3±0.6, and 4.0±0.8μg/mL, respectively. In the α-amylase inhibition assay, ethanol extracts of K. candel and Ficus racemosa showed IC50 of 7.6±0.9 and 46.7±23.6μg/mL, respectively. Showing low tannin constituents as seen from HPLC profiles, P. amarus and P. urinaria water extracts and F. racemosa ethanol extract were subjected to microfractionation. Only high-resolution α-glucosidase inhibition profiles of P. amarus and P. urinaria water extracts showed several active compounds, which were isolated and identified as corilagin (1), repandusinic acid A (2), and mallotinin (3). IC50 of these compounds were 1.70±0.03, 6.10±0.10, and 3.76±0.15μM, respectively. Kinetics analysis revealed that 1 displayed a mixed type mode of inhibition with Ki and Ki' values of 2.37±0.90 and 2.61±0.61μM, respectively, whereas 2 and 3 competitively inhibited α-glucosidase with Ki values of 4.01±0.47 and 0.65±0.11μM, respectively.

CONCLUSION

Corilagin (1), repandusinic acid A (2), and mallotinin (3) were potent α-glucosidase inhibitors contributing significantly to the inhibitory effect observed for the water extracts of P. amarus and P. urinaria.

High-Resolution α-Glucosidase Inhibition Profiling Combined with HPLC-HRMS-SPE-NMR for Identification of Antidiabetic Compounds in Eremanthus crotonoides (Asteraceae)

α-Glucosidase inhibitors decrease the cleavage- and absorption rate of monosaccharides from complex dietary carbohydrates, and represent therefore an important class of drugs for management of type 2 diabetes. In this study, a defatted ethyl acetate extract of Eremanthus crotonoides leaves with an inhibitory concentration (IC₅₀) of 34.5 μg/mL towards α-glucosidase was investigated by high-resolution α-glucosidase inhibition profiling combined with HPLC-HRMS-SPE-NMR. This led to identification of six α-glucosidase inhibitors, namely quercetin (16), trans-tiliroside (17), luteolin (19), quercetin-3-methyl ether (20), 3,5-di-O-caffeoylquinic acid n-butyl ester (26) and 4,5-di-O-caffeoylquinic acid n-butyl ester (29). In addition, nineteen other metabolites were identified. The most active compounds were the two regioisomeric di-O-caffeoylquinic acid derivatives 26 and 29, with IC₅₀ values of 5.93 and 5.20 μM, respectively. This is the first report of the α-glucosidase inhibitory activity of compounds 20, 26, and 29, and the findings support the important role of Eremanthus species as novel sources of new drugs and/or herbal remedies for treatment of type 2 diabetes.

Edible seaweed as future functional food: Identification of α-glucosidase inhibitors by combined use of high-resolution α-glucosidase inhibition profiling and HPLC-HRMS-SPE-NMR

Crude chloroform, ethanol and acetone extracts of nineteen seaweed species were screened for their antioxidant and α-glucosidase inhibitory activity. Samples showing more than 60% α-glucosidase inhibitory activity, at a concentration of 1 mg/ml, were furthermore investigated using high-resolution α-glucosidase inhibition profiling combined with high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HR-bioassay/HPLC-HRMS-SPE-NMR). The results showed Ascophyllum nodosum and Fucus vesicolosus to be rich in antioxidants, equaling a Trolox equivalent antioxidant capacity of 135 and 108 mM Troloxmg(-1) extract, respectively. HR-bioassay/HPLC-HRMS-SPE-NMR showed the α-glucosidase inhibitory activity of A. nodosum, F. vesoculosus, Laminaria digitata, Laminaria japonica and Undaria pinnatifida to be caused by phlorotannins as well as fatty acids - with oleic acid, linoleic acid and eicosapentaenoic acid being the most potent with IC50 values of 0.069, 0.075 and 0.10 mM, respectively, and showing a mixed-type inhibition mode.

Selective separation and identification of metabolite groups of Polygonum cuspidatum extract in rat plasma using dispersion solid-phase extraction by magnetic molecularly imprinted polymers coupled with LC/Q-TOF-MS

In this work, magnetic molecularly imprinted polymers (MMIPs) were successfully prepared for specific recognition and selective enrichment of metabolite groups of Polygonum cuspidatum extract in rat plasma.

Phenolic group on A-ring is key for dracoflavan B as a selective noncompetitive inhibitor of α-amylase

A high throughput assay was applied to guide the isolation of a new pancreatic α-amylase inhibitor, dracoflavan B, from the dragon's blood resin from Daemonorops draco. Applying C18 column, we successfully isolated both diastereomers and their structures verified by (1)H NMR spectra in comparison with the literature values. Their activity in inhibition of pancreatic α-amylase with comparable IC50 values of 23μM (A type) and 27μM (B type) that are similar to that of acarbose. Dracoflavan B shows much weaker activity in inhibiting bacterial α-amylase and no activity towards fungal α-amylase. Moreover, both isomers show no inhibitory activity towards mammalian α-glucosidase. Kinetic analysis revealed that using starch as the substrate, dracoflavan B was a non-competitive α-amylase inhibitor with a Ki value of 11.7μM. Lack of α-amylase inhibition for proanthocyanidin A2 dimer demonstrated that dracoflavan B hydrophobic nature of the B, A', C' and B' rings are important for its α-amylase inhibition. In addition, selective chemical modification studies revealed that the phenolic group is also vital to dracoflavan B for its pancreatic α-amylase inhibition activity. Without the A ring phenolic hydrogen bond donor, the derivatives of dracoflavan B showed detrimental α-amylase inhibition. On the contrary, galloylation on the A ring phenolic OH group enhanced the activity as shown by the low IC50 (12μM) against α-amylase which is 56% more potent as compared to dracoflavan B.