Anti-α-glucosidase and Anti-dipeptidyl Peptidase-IV Activities of Extracts and Purified Compounds from Vitis thunbergii var. taiwaniana

Natural hypoglycaemic bioactives: Newer avenues and newer possibilities

The incidences of endocrine and metabolic disorders like diabetes have increased worldwide. Several proposed molecular pathways mechanisms for the management of diabetes have been identified, but glycaemic control is still a challenging task in the drug discovery process. Most of the drug discovery processes lead to numerous scaffolds that are prominent in natural products. The review deals with the natural bioactives as an α-amylase inhibitors, α-glucosidase inhibitors, protein tyrosine phosphatase-1B inhibitors, dipeptidyl peptidase-IV inhibitors, G-protein coupled receptors-40 agonists, PPAR-γ agonists and the activators of 5'-adenosine monophosphate-activated protein kinase and glucokinase. So, in this review, we focused on the hypoglycaemic bioactives, which will assist scientific developers, traditional medicinal practitioners, and readers to discover some potent antidiabetic molecules. Strategies like chemometric approaches, scaffold hopping, and total synthesis of natural products by group modification or ring opening/closing mechanism could be useful for the development of novel hit/lead antidiabetic molecules. The study concludes that each phyto molecule inherits a potential to get explored by repurposing techniques for various antidiabetic targets and offer an alternative antidiabetic therapeutic medicinal potential.

Polysaccharides from Seedless Chestnut Rose (Rosa sterilis) Fruits: Insights into Innovative Drying Technologies and Their Structural Characteristics, Antioxidant, Antiglycation, and α-Glucosidase Inhibitory Activities

The selection of an optimal drying method is essential for extending the shelf life and enhancing the quality of Rosa sterilis fruits. This study investigated the effects of both innovative (microwave vacuum drying and infrared drying) and traditional (freeze-drying and hot air drying) techniques on the structural characteristics and bioactivities of polysaccharides from R. sterilis fruits (RSPs). Four different RSPs were obtained from fruits dried using these methods. Results demonstrated that the structural characteristics and bioactivities of RSPs varied significantly with the drying method. Notable differences were observed in extraction yield, total sugar, uronic acid content, monosaccharide molar ratios, molecular weight distribution, particle size, thermal stability, and microstructures of RSPs. Despite these variations, the types of constituent monosaccharides and major glycosidic linkages remained consistent across all methods. Notably, RSPs obtained via microwave vacuum drying (RSPs-MVD) showed a higher uronic acid content and lower molecular weight, and exhibited stronger in vitro antioxidant, α-glucosidase inhibitory, and antiglycation activities. These findings suggest that microwave vacuum drying is an effective pre-drying technique for extracting RSPs, making them suitable as bioactive ingredients in functional foods and pharmaceuticals for managing diabetes mellitus and its complications.

Effects of Different Drying Methods on the Structural Characteristics and Multiple Bioactivities of Rosa roxburghii Tratt Fruit Polysaccharides

Drying conditions significantly impact the compositions and microstructures of polysaccharides, leading to various effects on their chemical characteristics and bioactivities. The objective of this study was to investigate how different industrial drying techniques, i.e., hot air drying, infrared drying, microwave vacuum drying, and freeze drying, affect the structural properties and biological activities of polysaccharides extracted from Rosa roxburghii Tratt fruit (RRTP). Results revealed that these drying methods significantly altered the extraction yield, molecular weights, monosaccharide ratios, contents of uronic acid and total sugars, gelling properties, particle sizes, thermal stability, and microstructures of RRTPs. However, the monosaccharide composition and functional groups of polysaccharides remained consistent across the different drying techniques. Biological activity assays demonstrated that RRTPs, particularly those processed through microwave vacuum drying (MVD-RRTP), exhibited excellent anti-linoleic acid oxidation, robust anti-glycosylation effects, and significant α-glucosidase inhibition in vitro. The outcomes of this research demonstrate that microwave vacuum drying serves as an effective pre-extraction drying method for RRTPs, enhancing their biological activities. This technique is particularly advantageous for preparing RRTPs intended for use in functional foods and pharmaceuticals, optimizing their health-promoting properties for industrial applications.

Ultrasonic-Assisted Decoloration of Polysaccharides from Seedless Chestnut Rose (Rosa sterilis) Fruit: Insight into the Impact of Different Macroporous Resins on Its Structural Characterization and In Vitro Hypoglycemic Activity

Pigments within polysaccharides pose significant challenges when analyzing their structural characteristics and evaluating their biological activities, making decolorization a crucial step in purifying these biomolecules. In this research, a novel approach using ultrasound-assisted static adsorption with macroporous resins was employed to decolorize polysaccharides extracted from seedless chestnut rose (Rosa sterilis S. D. Shi) fruit (RSP). Among the fourteen tested resins, AB-8, D101, D4020, HPD100, and S8 were identified as the most effective, demonstrating superior decoloration efficiency and polysaccharide recovery. Further examinations of RSPs treated with these five resins revealed distinct effects on their uronic acid levels, monosaccharide makeup, molecular weight, surface structure, and hypoglycemic properties. The RSP treated with HPD100 resin stood out for having the highest uronic acid content, smallest particle size, and lowest molecular weight, leading to the most notable inhibition of α-glucosidase activity through a mixed inhibition model. The application of HPD100 resin in the decolorization process not only potentially preserved the macromolecular structure of RSP but also enhanced its hypoglycemic efficacy. These findings provide a solid theoretical basis for further exploring RSP as a component of functional foods, underscoring the effectiveness of the ultrasound-assisted resin adsorption method in polysaccharide purification.

Comparative Study on the Impact of Different Extraction Technologies on Structural Characteristics, Physicochemical Properties, and Biological Activities of Polysaccharides from Seedless Chestnut Rose (Rosa sterilis) Fruit

Seedless chestnut rose (Rosa sterilis S. D. Shi, RS) is a fresh type of R. roxburghii Tratt with copious functional components in its fruit. Polysaccharides are recognized as one of the vital bioactive compounds in RS fruits, but their antioxidant and hypoglycemic properties have not been extensively explored. Hence, in this study, accelerated solvent extraction (RSP-W), citric acid (RSP-C), 5% sodium hydroxide/0.05% sodium borohydride (RSP-A), and 0.9% sodium chloride (RSP-S) solution extraction were individually utilized to obtain RS fruit polysaccharides. The physicochemical properties, structural characteristics, and biological activities were then compared. Results indicated that extraction methods had significant influences on the extraction yield, uronic acid content, monosaccharide composition, molecular weight, particle size, thermal stability, triple-helical structure, and surface morphology of RSPs apart from the major linkage bands and crystalline characteristics. The bioactivity tests showed that the RSP-S, which had the greatest amount of uronic acid and a comparatively lower molecular weight, exhibited more potent antioxidant and α-glucosidase inhibitory property. Furthermore, all RSPs inhibited α-glucosidase through a mixed-type manner and quenched their fluorescence predominantly via a static quenching mechanism, with RSP-S showing the highest binding efficiency. Our findings provide a theoretical basis for utilizing RSPs as functional ingredients in food industries.

The In Vitro Inhibitory Activity of Pacaya Palm Rachis versus Dipeptidyl Peptidase-IV, Angiotensin-Converting Enzyme, α-Glucosidase and α-Amylase

The pacaya palm (Chamaedorea tepejilote Liebm) is an important food that is commonly consumed in Mexico and Central America due to its nutritive value. It is also used as a nutraceutical food against some chronic diseases, such as hypertension and hyperglycemia. However, few reports have indicated its possible potential. For this reason, the goal of this research was to evaluate the effects of the enzymatic activity of the pacaya palm inflorescence rachis on both hypertension and hyperglycemia and the effects of thermal treatments on the enzymatic activity. The enzymatic inhibition of ACE (angiotensin-converting enzyme), DPP-IV (dipeptidyl peptidase-IV), α-glucosidase and α-amylase were evaluated, all with powder extracts of pacaya palm inflorescences rachis. The results indicated that thermally treated rachis showed increased enzymatic inhibitory activity against α-amylase and DPP-IV. However, all rachis, both with and without thermal treatment, showed low- or no enzymatic activity against α-glucosidase and ACE. Apparently, the mechanism of action of the antidiabetic effect of rachis is mediated by the inhibition of α-amylase and DPP-IV and does not contribute with a significant effect on enzymes involved in the hypertension mechanism. Finally, the properties of the extract were modified via the extraction method and the temperature tested.

Inhibitory effects of selected cannabinoids against dipeptidyl peptidase IV, an enzyme linked to type 2 diabetes

Ethnopharmacological relevance

In recent times the decriminalisation of cannabis globally has increased its use as an alternative medication. Where it has been used in modern medicinal practises since the 1800s, there is limited scientific investigation to understand the biological activities of this plant.

Aim of the study

Dipeptidyl peptidase IV (DPP-IV) plays a key role in regulating glucose homeostasis, and inhibition of this enzyme has been used as a therapeutic approach to treat type 2 diabetes. However, some of the synthetic inhibitors for this enzyme available on the market may cause undesirable side effects. Therefore, it is important to identify new inhibitors of DPP-IV and to understand their interaction with this enzyme.

Methods

In this study, four cannabinoids (cannabidiol, cannabigerol, cannabinol and Δ9-tetrahydrocannabinol) were evaluated for their inhibitory effects against recombinant human DPP-IV and their potential inhibition mechanism was explored using both in vitro and in silico approaches.

Results

All four cannabinoids resulted in a dose-dependent response with IC50 values of between 4.0 and 6.9 μg/mL. Kinetic analysis revealed a mixed mode of inhibition. CD spectra indicated that binding of cannabinoids results in structural and conformational changes in the secondary structure of the enzyme. These findings were supported by molecular docking studies which revealed best docking scores at both active and allosteric sites for all tested inhibitors. Furthermore, molecular dynamics simulations showed that cannabinoids formed a stable complex with DPP-IV protein via hydrogen bonds at an allosteric site, suggesting that cannabinoids act by either inducing conformational changes or blocking the active site of the enzyme.

Conclusion

These results demonstrated that cannabinoids may modulate DPP-IV activity and thereby potentially assist in improving glycaemic regulation in type 2 diabetes.

Therapeutic application of natural compounds for skeletal muscle-associated metabolic disorders: A review on diabetes perspective

Skeletal muscle (SM) plays a vital role in energy and glucose metabolism by regulating insulin sensitivity, glucose uptake, and blood glucose homeostasis. Impaired SM metabolism is strongly linked to several diseases, particularly type 2 diabetes (T2D). Insulin resistance in SM may result from the impaired activities of insulin receptor tyrosine kinase, insulin receptor substrate 1, phosphoinositide 3-kinase, and AKT pathways. This review briefly discusses SM myogenesis and the critical roles that SM plays in insulin resistance and T2D. The pharmacological targets of T2D which are associated with SM metabolism, such as DPP4, PTB1B, SGLT, PPARγ, and GLP-1R, and their potential modulators/inhibitors, especially natural compounds, are discussed in detail. This review highlights the significance of SM in metabolic disorders and the therapeutic potential of natural compounds in targeting SM-associated T2D targets. It may provide novel insights for the future development of anti-diabetic drug therapies. We believe that scientists working on T2D therapies will benefit from this review by enhancing their knowledge and updating their understanding of the subject.

Caffeic Acid in Spent Coffee Grounds as a Dual Inhibitor for MMP-9 and DPP-4 Enzymes

Type 2 diabetes mellitus and diabetic foot ulcers remain serious worldwide health problems. Caffeic acid is one of the natural products that has been experimentally proven to have diverse pharmacological properties. This study aimed to assess the inhibitory activity of caffeic acid and ethanolic extract of spent coffee grounds targeting DPP-4 and MMP-9 enzymes and evaluate the molecular interactions through 50-ns molecular dynamics simulations. This study also introduced our new version of PyPLIF HIPPOS, PyPLIF HIPPOS 0.2.0, which allowed us to identify protein-ligand interaction fingerprints and interaction hotspots resulting from molecular dynamics simulations. Our findings revealed that caffeic acid inhibited the DPP-4 and MMP-9 activity with an IC50 of 158.19 ± 11.30 µM and 88.99 ± 3.35 µM while ethanolic extract of spent coffee grounds exhibited an IC50 of 227.87 ± 23.80 µg/100 µL and 81.24 ± 6.46 µg/100 µL, respectively. Molecular dynamics simulations showed that caffeic acid interacted in the plausible allosteric sites of DPP-4 and in the active site of MMP-9. PyPLIF HIPPOS 0.2.0 identified amino acid residues interacting more than 10% throughout the simulation, which were Lys463 and Trp62 in the plausible allosteric site of DPP-4 and His226 in the active site of MMP-9.

Vitisin B, a resveratrol tetramer from Vitis thunbergii var. taiwaniana, ameliorates impaired glucose regulations in nicotinamide/streptozotocin-induced type 2 diabetic mice

Background and aim

In Taiwan, Vitis thunbergii var. taiwaniana (VTT) is used in traditional medicine and as a local tea. VTT rich in resveratrol and resveratrol oligomers have been reported to exhibit anti-obesity and anti-hypertensive activities in animal models; however, no studies have investigated type 2 diabetes mellitus (T2DM) treatments. This study aimed to investigate the anti-T2DM effects of resveratrol tetramers isolated from the VTT in nicotinamide/streptozotocin (STZ)-induced Institute of Cancer Research (ICR) mice.

Experimental procedure

The oral glucose tolerance test (OGTT) was used to imitate postprandial blood glucose (BG) regulations in mice by pre-treatment with VTT extracts, resveratrol tetramers of vitisin A, vitisin B, and hopeaphenol 30 min before glucose loads. Vitisin B (50 mg/kg) was administered to treat T2DM-ICR mice once daily for 28 days to investigate its hypoglycemic activity.

Results and conclusion

Mice pre-treated with VTT-S-95EE, or vitisin B (100 mg/kg) 30-min before glucose loading showed significant reductions (P < 0.001) in the area under the curve at 120-min (BG-AUC0-120) than those without pre-treatment with VTT-S-95 E E or vitisin B. Vitisin B-treated T2DM mice showed hypoglycemic activities via a reduction in plasma dipeptidyl peptidase (DPP)-IV activities to maintain insulin actions and differed significantly than those of untreated T2DM mice (P < 0.05), and also reduced BG-AUC0-120 and insulin-AUC0-120 in the OGTT.These in vivo results showed that VTT containing vitisin B would be beneficial for developing nutraceuticals and/or functional foods for glycemic control in patients with T2DM, which should be investigated further.

The flavonoid profiles in the pulp of different pomelo (Citrus grandis L. Osbeck) and grapefruit (Citrus paradisi Mcfad) cultivars and their in vitro bioactivity

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Fourteen flavonoid compounds were detected in pomelo and grapefruit pulp.

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The flavonoid profiles in pomelo and grapefruit pulp had varietal difference.

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Flavonoids of pomelo and grapefruit showed strong cellular antioxidant activity.

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Flavonoids of pomelo and grapefruit are good inhibitors of pancreatic lipase.

Previous results indicated that the flavonoid profiles might have varietal differences in pomelo, but detailed information is unknown. We previously isolated 4 new flavonoids, cigranoside C, D, E, F, in Citrus grandis Shatianyu pulp. However, their distribution in different pomelo cultivars remains to be explored. Therefore, the flavonoid profiles and in vitro bioactivity of the pulp from 5 pomelo and 1 grapefruit cultivars commonly consumed in China were investigated. Fourteen flavonoids were identified, cigranoside C, D, E were detected in these pomelo and grapefruit. Naringin and cigranoside C were the major flavonoids in grapefruit, Guanximiyu-W, Guanximiyu-R and Liangpingyu, while melitidin and rhoifolin was the predominant flavonoid in Shatianyu and Yuhuanyu, respectively. Pomelo and grapefruit showed strong antioxidant activity, and were potent inhibitors of pancreatic lipase with IC₅₀ values of 11.4–72.6 mg fruit/mL except Shatianyu. Thus, pomelo and grapefruit are natural antioxidants and possess anti-obesity potential.

Supplementation with Vitis vinifera Jingzaojing Leaf and Shoot Extract Improves Exercise Endurance in Mice

Switching myofibers from the fast-glycolytic type to the slow-oxidative type is associated with an alleviation of the symptoms associated with various cardiometabolic diseases. This study investigates the effect of Vitis vinifera Jingzaojing leaf and shoot extract (JLSE), which is rich in phenolic compounds, on the regulation of skeletal muscle fiber-type switching, as well as the associated underlying mechanism. Male C57BL/6N mice were supplemented orally with vehicle or JLSE (300 mg/kg) and subjected to treadmill exercise training. After four weeks, mice in the JLSE-supplemented group showed significantly improved exercise endurance and mitochondrial oxidative capacity. JLSE supplementation increased the expression of sirtuin 6 and decreased Sox6 expression, thereby elevating the number of mitochondria and encouraging fast-to-slow myofiber switching. The results of our experiments suggest that JLSE supplementation reprograms myofiber composition to favor the slow oxidative type, ultimately enhancing exercise endurance.

Mechanistic insights into the inhibitory activities of chemical constituents from the fruits of Terminalia boivinii on α-glucosidase

Regulation of key digestive enzymes is currently considered an effective remedy for diabetes mellitus. In this study, bioactive constituents were purified from Terminalia boivinii fruits and identified by 1 H NMR, 13 C NMR and EI-MS. In vitro and in silico methods were used to evaluate α-glucosidase, α-amylase, and lipase inhibition activities. Compounds 1 , 2 , and 4-7 with IC50 values between 89 and 445 µM showed stronger α-glucosidase inhibitory activities than the antihyperglycemic drug acarbose (IC 50 =1463.0 ± 29.5 µM). However, the compounds showed lower inhibitory effects against α-amylase and lipase with IC 50 values above 500 µM than acarbose (IC 50 = 16.7 ± 3.5 µM) and ursolic acid (IC 50 = 89.5 ± 5.6 µM), respectively. Lineweaver-Burk plots showed that compounds 1 , 2 , and 7 were non-competitive inhibitors, compounds 4 and 5 were competitive inhibitors and compound 6 was a mixed-type inhibitor. Fluorescence spectroscopic data showed that the compounds altered the microenvironment and conformation of α-glucosidase. Computer simulations indicated that the compounds and enzyme interacted primarily through hydrogen bonding. The findings indicated that the compounds were inhibitors of α-glucosidase and provided significant structural basis for understanding the binding activity of the compounds with α-glucosidase.

Metabolic Profiling for Evaluating the Dipeptidyl Peptidase-IV Inhibitory Potency of Diverse Green Tea Cultivars and Determining Bioactivity-Related Ingredients and Combinations

There are numerous cultivars of tea (Camellia sinensis L.), but the differences in their anti-hyperglycemic-related effects are largely unknown. The inhibition of the dipeptidyl peptidase (DPP)-IV enzyme plays an essential role in controlling hyperglycemia in diabetes by blocking the degradation of incretin hormones, which is necessary for insulin secretion. In this study, we examined the DPP-IV inhibitory activity of leaf extracts from diverse Japanese green tea cultivars. The inhibitory rates differed among tea extracts. Metabolic profiling (MP), using liquid chromatography-mass spectrometry, of all cultivars revealed compositional differences among cultivars according to their DPP-IV inhibitory capacity. Epigallocatechin-3-O-(3-O-methyl)gallate, kaempferol-3-O-rutinoside, myricetin-3-O-glucoside/galactoside, and theogallin were newly identified as DPP-IV inhibitors. The bioactivity of a tea extract was potentiated by adding these ingredients in combination. Our results show that MP is a useful approach for evaluating the DPP-IV inhibitory potency of green tea and for determining bioactivity-related ingredients and combinations.

Phenolic profiles and bioactivities of different milling fractions of rice bran from black rice

Phytochemicals are unevenly distributed in grain kernels and concentrated in bran fractions. However, their specific distribution in the grain bran, especially colored grains, is not clarified. This study divided rice bran from black rice into five fractions by stepwise milling to obtain BF1(outermost layer) to BF5 (the innermost layer). Each fraction accounted for approximately 2% of the whole kernel. The total content of phenolics (TPC), flavonoids (TFC), and anthocyanins (TAC) of five fractions significantly decreased from BF1 to BF5. The TPC, TFC and TAC of BF1 contribute 25.7%, 28.2%, 28.4% to the total of five fractions, respectively. HPLC analysis showed that the contents of most anthocyanin and phenolic acids compounds decreased from BF1 to BF5. Together with α-glucosidase and α-amylase inhibitory activities of BF1, the antioxidant activity was higher than those of other fractions. These results can guide the moderate processing of black rice and the utilization of its bran.

Exploration of Dipeptidyl Peptidase-IV (DPP-IV) Inhibitory Peptides from Silkworm Pupae (Bombyx mori) Proteins Based on In Silico and In Vitro Assessments

This study aimed at exploring dipeptidyl peptidase-IV (DPP-IV) inhibitory peptides from silkworm pupae proteins by in silico analysis and in vitro assessments. In silico analysis of 274 silkworm pupae proteomes indicated that DPP-IV inhibitory peptides can be released from silkworm pupae proteins. In vitro assessments revealed that pepsin and bromelain led to better production of DPP-IV inhibitory peptides from silkworm pupae protein. Notably, peptide fractions (<1 kDa) from pepsin- and bromelain-treated hydrolysates exhibited more potent DPP-IV inhibitory activities. Two novel DPP-IV inhibitory peptides (Leu-Pro-Pro-Glu-His-Asp-Trp-Arg and Leu-Pro-Ala-Val-Thr-Ile-Arg) were identified by LC-MS/MS with IC₅₀ values of 261.17 and 192.47 μM, respectively. Enzyme kinetics data demonstrated that these two peptides displayed a mixed-type DPP-IV inhibition mode, which was further validated by molecular docking data. Overall, in silico analysis combined with in vitro assessments can serve as an effective and rapid approach for discovery of DPP-IV peptides from silkworm pupae proteins.

Vitisin A, a Resveratrol Tetramer, Improves Scopolamine-Induced Impaired Learning and Memory Functions in Amnesiac ICR Mice

Resveratrol has been reported to exhibit neuroprotective activities in vitro and in vivo. However, little is known about resveratrol tetramers of hopeaphenol, vitisin A, and vitisin B with the same molecular mass in the improvement of degenerative disorders. In this study, two 95% ethanol extracts (95EE) from stem parts of Vitis thunbergii Sieb. & Zucc. (VT-95EE) and from the root (R) parts of Vitis thunbergii var. taiwaniana (VTT-R-95EE) showed comparable acetylcholinesterase (AChE) inhibitory activities. It was found that VT-95EE and VTT-R-95EE showed different distribution patterns of identified resveratrol and resveratrol tetramers of hopeaphenol, vitisin A, and vitisin B based on the analyses of HPLC chromatographic profiles. The hopeaphenol, vitisin A, and vitisin B, showed AChE and monoamine oxidase-B inhibitions in a dose-dependent manner, among which vitisin B and vitisin A exhibited much better activities than those of resveratrol, and had neuroprotective activities against methylglyoxal-induced SH-SY5Y cell deaths. The scopolamine-induced amnesiac ICR mice treated with VT-95EE and its ethyl acetate-partitioned fraction (VT-95EE-EA) at doses of 200 and 400 mg/kg, or vitisin A at a dose of 40 mg/kg, but not vitisin B (40 mg/kg), were shown significantly to improve the impaired learning behaviors by passive avoidance tests compared to those in the control without drug treatments (p < 0.05). Compared to mice in the control group, the brain extracts in the vitisin A-treated mice or donepezil-treated mice showed significant reductions in AChE activities and malondialdehyde levels (p < 0.05), and elevated the reduced protein expressions of brain-derived neurotrophic factor (BDNF) and BDNF receptor, tropomyosin receptor kinase B (TrkB). These results revealed that vitisin A was the active constituent in the VT-95EE and VTT-95EE, and the VT medicinal plant and that the endemic variety of VTT has potential in developing functional foods for an unmet medical need for neurodegenerative disorders.

The Natural Stilbenoid (-)-Hopeaphenol Inhibits Cellular Entry of SARS-CoV-2 USA-WA1/2020, B.1.1.7, and B.1.351 Variants

Antivirals are urgently needed to combat the global SARS-CoV-2/COVID-19 pandemic, supplement existing vaccine efforts, and target emerging SARS-CoV-2 variants of concern. Small molecules that interfere with binding of the viral spike receptor binding domain (RBD) to the host angiotensin-converting enzyme II (ACE2) receptor may be effective inhibitors of SARS-CoV-2 cell entry. Here, we screened 512 pure compounds derived from natural products using a high-throughput RBD/ACE2 binding assay and identified (-)-hopeaphenol, a resveratrol tetramer, in addition to vatalbinoside A and vaticanol B, as potent and selective inhibitors of RBD/ACE2 binding and viral entry. For example, (-)-hopeaphenol disrupted RBD/ACE2 binding with a 50% inhibitory concentration (IC50) of 0.11 μM, in contrast to an IC50 of 28.3 μM against the unrelated host ligand/receptor binding pair PD-1/PD-L1 (selectivity index, 257.3). When assessed against the USA-WA1/2020 variant, (-)-hopeaphenol also inhibited entry of a VSVΔG-GFP reporter pseudovirus expressing SARS-CoV-2 spike into ACE2-expressing Vero-E6 cells and in vitro replication of infectious virus in cytopathic effect and yield reduction assays (50% effective concentrations [EC50s], 10.2 to 23.4 μM) without cytotoxicity and approaching the activities of the control antiviral remdesivir (EC50s, 1.0 to 7.3 μM). Notably, (-)-hopeaphenol also inhibited two emerging variants of concern, B.1.1.7/Alpha and B.1.351/Beta in both viral and spike-containing pseudovirus assays with similar or improved activities over the USA-WA1/2020 variant. These results identify (-)-hopeaphenol and related stilbenoid analogues as potent and selective inhibitors of viral entry across multiple SARS-CoV-2 variants of concern.

A Comprehensive Review and Perspective on Natural Sources as Dipeptidyl Peptidase-4 Inhibitors for Management of Diabetes

Type 2 diabetes mellitus (T2DM) is an increasing global public health problem, and its prevalence is expected to rise in coming decades. Dipeptidyl peptidase-4 (DPP-4) is a therapeutic target for the management of T2DM, and its inhibitors prevent the degradation of glucose-dependent insulinotropic peptide and glucagon-like peptide 1, and thus, maintain their endogenous levels and lower blood glucose levels. Various medicinal plant extracts and isolated bioactive compounds exhibit DPP-4 inhibitory activity. In this review, we discussed different natural sources that have been shown to have anti-diabetic efficacy with a particular emphasis on DPP-4 inhibition. Furthermore, the effect of DPP-4 inhibition on pancreatic beta cell function, skeletal muscle function, and the glucose-lowering mechanisms were also discussed. We believe that scientists looking for novel compounds with therapeutic promise against T2DM will be able to develop antidiabetic drugs using these natural sources.

The perceptions of natural compounds against dipeptidyl peptidase 4 in diabetes: from in silico to in vivo

Dipeptidyl peptidase IV (DPP-4), an incretin glucagon-like peptide-1 (GLP-1) degrading enzyme, contains two forms and it can exert various physiological functions particular in controlling blood glucose through the action of GLP-1. In diabetic use, the DPP-4 inhibitor can block the DDP-4 to attenuate GLP-1 degradation and prolong GLP-1 its action and sensitize insulin activity for the purpose of lowering blood glucose. Nonetheless the adverse effects of DPP-4 inhibitors severely hinder their clinical applications, and notably there is a clinical demand for novel DPP-4 inhibitors from various sources including chemical synthesis, herbs, and plants with fewer side effects. In this review, we highlight various strategies, namely computational biology (in silico), in vitro enzymatic and cell assays, and in vivo animal tests, for seeking natural DPP-4 inhibitors from botanic sources including herbs and plants. The pros and cons of all approaches for new inhibitor candidates or hits will be under discussion.

Polyalthia Clerodane Diterpene Potentiates Hypoglycemia via Inhibition of Dipeptidyl Peptidase 4

Serine protease dipeptidyl peptidase 4 (DPP-4) is involved in self/non-self-recognition and insulin sensitivity. DPP-4 inhibitors are conventional choices for diabetic treatment; however, side effects such as headache, bronchus infection, and nasopharyngitis might affect the daily lives of diabetic patients. Notably, natural compounds are believed to have a similar efficacy with lower adverse effects. This study aimed to validate the DPP-4 inhibitory activity of clerodane diterpene 16-hydroxycleroda-3,13-dien-15,16-olide (HCD) from Polyalthia longifolia, rutin, quercetin, and berberine, previously selected through molecular docking. The inhibitory potency of natural DPP-4 candidates was further determined by enzymatic, in vitro Caco-2, and ERK/PKA activation in myocyte and pancreatic cells. The hypoglycemic efficacy of the natural compounds was consecutively analyzed by single-dose and multiple-dose administration in diet-induced obese diabetic mice. All the natural-compounds could directly inhibit DPP-4 activity in enzymatic assay and Caco-2 inhibition assay, and HCD showed the highest inhibition of the compounds. HCD down-regulated LPS-induced ERK phosphorylation in myocyte but blocked GLP-1 induced PKA expression. For in vivo tests, HCD showed hypoglycemic efficacy only in single-dose administration. After 28-days administration, HCD exhibited hypolipidemic and hepatoprotective efficacy. These results revealed that HCD performed potential antidiabetic activity via inhibition of single-dose and long-term administrations, and could be a new prospective anti-diabetic drug candidate.

Structural characterization of a novel acidic polysaccharide from Rosa roxburghii Tratt fruit and its α-glucosidase inhibitory activity

An acidic polysaccharide (RTFP-3) extracted from Rosa roxburghii Tratt fruit can inhibit the activity of α-glucosidase.

Hot-Water Extracts from Roots of Vitis thunbergii var. taiwaniana and Identified ε-Viniferin Improve Obesity in High-Fat Diet-Induced Mice

In this study, hot-water extracts (HW) from roots of Vitis thunbergii var. taiwaniana (VTT-R) were shown to lower levels of lipid accumulation significantly (P < 0.01 or 0.001) compared to the control in 3T3-L1 adipocytes. The VTT-R-HW (40 mg/kg) interventions concurrent with a high-fat (HF) diet in C57BL/6 mice over a 5 eek period were shown to reduce body weights significantly (P < 0.05) compared to those of mice fed a HF diet under the same food-intake regimen. The (+)-ε-viniferin isolated from VTT-R-HW was shown to reduce the size of lipid deposits significantly compared to the control (P < 0.05 or 0.001) in 3T3-L1 adipocytes, and dose-dependent 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitions showed that the 50% inhibitory concentration was calculated to be 96 μM. The two-stage (+)-ε-viniferin interventions (10 mg/kg, day 1 to day 38; 25 mg/kg, day 39 to day 58) were shown to lower mice body weights significantly (P < 0.05 or 0.001), the weight ratio of mesenteric fat, blood glucose, total cholesterol, and low-density lipoprotein compared to that of the HF group under the same food-intake regimen but without concurrent VTT-R-HW interventions. It might be possible to use VTT-R-HW or (+)-ε-viniferin as an ingredient in the development of functional foods for weight management, and this will need to be investigated further.

Flavanol concentrations do not predict dipeptidyl peptidase-IV inhibitory activities of four cocoas with different processing histories

Cocoa and its constituent bioactives (particularly flavanols) have reported anti-diabetic and anti-obesity activities. One potential mechanism of action is inhibition of dipeptidyl peptidase-IV (DPP4), the enzyme that inactivates incretin hormones such as glucagon-like peptide-1 and gastric inhibitory peptide. The objective of this study was to determine the DPP4 inhibitory activities of cocoas with different processing histories, and identify processing factors and bioactive compounds that predict DPP4 inhibition. IC₂₅ values (μg mL^-1) were 4.82 for Diprotin A (positive control), 2135 for fermented bean extract, 1585 for unfermented bean extract, 2871 for unfermented liquor extract, and 1076 for fermented liquor extract This suggests mild inhibitory activity. Surprisingly, protein binding activity, total polyphenol, total flavanol, individual flavanol and complex fermentation/roasting product levels were all positively correlated to IC₂₅ concentrations (greater levels correspond to less potent inhibition). For the representative samples studied, fermentation appeared to improve inhibition. This study suggests that cocoa may possess mild DPP4 inhibitory activity, and that processing steps such as fermentation may actually enhance activity. Furthermore, this activity and the variation between samples were not easily explainable by traditional putative bioactives in cocoa. The compounds driving this activity, and the associated mechanism(s) by which this inhibition occurs, remain to be elucidated.

Isolation of rugosin A, B and related compounds as dipeptidyl peptidase-IV inhibitors from rose bud extract powder

Dipeptidyl peptidase-IV (DPP-IV) is a protease responsible for the degradation of the incretin hormone. A number of DPP-IV inhibitors have been approved for use in the treatment of type 2 diabetes. While these inhibitors are effective for this treatment, methods for the prevention of this disease are also required as diabetes patient numbers are currently increasing rapidly worldwide. We screened the DPP-IV inhibitory activities of edible plant extracts with the intention of using these extracts in a functional food supplement for the prevention of diabetes. Rose (Rosa gallica) bud extract powder was a promising material with high inhibitory activity. In this study, seven ellagitannins were isolated as active compounds through activity-guided fractionations, and their DPP-IV inhibitory activities were measured. Among them, rugosin A and B showed the highest inhibitory activities and rugosin B was shown as the major contributing compound in rose bud extract powder.

Synthesized Peptides from Yam Dioscorin Hydrolysis in Silico Exhibit Dipeptidyl Peptidase-IV Inhibitory Activities and Oral Glucose Tolerance Improvements in Normal Mice

RRDY, RL, and DPF were the top 3 of 21 peptides for inhibitions against dipeptidyl peptidase-IV (DPP-IV) from the pepsin hydrolysis of yam dioscorin in silico and were further investigated in a proof-of-concept study in normal ICR mice for regulating glucose metabolism by the oral glucose tolerance test (OGTT). The sample or sitagliptin (positive control) was orally administered by a feeding gauge; 30 min later, the glucose loads (2.5 g/kg) were performed. RRDY, yam dioscorin, or sitagliptin preload, but not DPF, lowered the area under the curve (AUC0-120) of blood glucose and DPP-IV activity and elevated the AUC0-120 of blood insulin, which showed significant differences compared to control (P < 0.05 or 0.001). These results suggested that RRDY and yam dioscorin might be beneficial in glycemic control in normal mice and need further investigations in diabetic animal models.

Grape powder attenuates the negative effects of GLP-1 receptor antagonism by exendin-3 (9–39) in a normoglycemic mouse model

Acute oral administration of grape powder attenuates the hyperglycemic effects of GLP-1 receptor antagonism in rats.

Comparison of antidiabetic potential of (+) and (−)-hopeaphenol, a pair of enantiomers isolated from Ampelocissus indica (L.) and Vateria indica Linn., with respect to inhibition of digestive enzymes and induction of glucose uptake in L6 myotubes

The remarkable α-glucosidase inhibition exhibited by the acetone extract of the rhizome of Ampelocissus indica (L.) and stem bark of Vateria indica Linn. (IC₅₀ 23.2 and 1.47 μg mL⁻¹) encouraged us to isolate the phytochemicals from these plants.

Vitis thunbergii var. taiwaniana Extracts and Purified Compounds Ameliorate Obesity in High-Fat Diet-Induced Obese Mice

The increasing prevalence of obesity continues to gain more attention worldwide. In this study, diet-induced obese mice were used to evaluate the antiobesity effects of extracts, fractions, and purified compounds from Vitis thunbergii var. taiwaniana (VTT). The C57BL/6J mice were fed a 5-week high-fat diet (HF) concurrently with ethanol extracts (Et-ext, 80 mg/kg) from roots (R), stems (S), and leaves (L) by oral gavage daily. Only R-Et-ext interventions showed significant weight reduction in mice compared with those in the HF group; however, mouse plasma contents of total cholesterols (TC), total triglycerides (TG) and low-density lipoproteins (LDL) of all three Et-ext intervened groups showed significant reductions compared with those in the HF group. Furthermore, intervention with the ethyl acetate-partitioned fraction (EA-fra, 60 mg/kg) from R-Et-ext but not the n-butanol-partitioned fraction or water fraction from R-Et-ext showed significant weight reduction in mice compared with those in the HF group. The same molecular weights of three resveratrol tetramers, (+)-hopeaphenol, (+)-vitisin A, and (-)-vitisin B, were isolated from the EA-fra of VTT-R. The (+)-vitisin A and fenofibrate (25 mg/kg) but not the (+)-hopeaphenol and (-)-vitisin B interventions showed significant weight reduction in mice compared with those in the HF group. The total feed intake among the HF groups with or without interventions showed no significant differences. The mouse plasma contents of TC, TG, LDL, free fatty acid, and plasma lipase activity of the three resveratrol tetramer-intervened groups showed reductions in the mice compared with those in the HF group. It was proposed that the lipase inhibitory activities of VTT extracts and purified resveratrol tetramers might contribute in part to the antiobesity effect, and these results suggested that VTT may be developed as functional food for achieving antiobesity objectives and requires further investigation.