α-Glucosidase inhibition action of major flavonoids identified from Hypericum attenuatum Choisy and their synergistic effects

Two New α-Glucosidase Inhibitors from Haplophyllum tuberculatum: Inhibition Kinetics and Mechanistic Insights Through in Vitro and in Silico Approaches

Diabetes is a multifactorial global health disorder marked by unusually high plasma glucose levels, which can lead to serious consequences including diabetic neuropathy, kidney damage, retinopathy, and cardiovascular disease. One effective therapy approach for reducing hyperglycemia associated with type 2 diabetes is to target α-glucosidase, enzymes that catalyze starch breakdown in the intestine. In the current study, two new (1, 2) and nine known (3-11) compounds were isolated from the rutaceous plant Haplophyllum tuberculatum and characterized by extensive nuclear magnetic resonance spectroscopic techniques and high-resolution electrospray ionization mass spectrometry. After structural elucidation, nine compounds were evaluated for their ability to inhibit α-glucosidase, a target for the treatment of type-2 diabetes. Among them, three compounds (7, 5, and 2) exhibited notable inhibition with half-maximal inhibitory concentration (IC50) values of 3.42 ± 0.12, 5.79 ± 0.28, and 6.75 ± 1.18 µM, respectively, while the remaining six compounds (1, 3, 4, 6, 8, and 9) had a moderate activity with IC50 values ranging from 12.14 ± 0.35 to 24.60 ± 0.57 µM, compared to the standard drug acarbose (IC50 = 875.75 ± 1.24 µM). A kinetic study of compounds 5 and 7 exhibited the competitive type of inhibition with Ki values of 4.82 ± 0.0036 and 3.92 ± 0.0062 µM, respectively. Furthermore, a structure-based prediction of the compounds' binding mode suggested that these inhibitors fitted exceptionally well within the active site of the target enzyme, α-glucosidase, forming multiple hydrogen and hydrophobic interactions with its active site residues. In conclusion, compounds with potent α-glucosidase inhibitory activity are abundant in nature and can be explored and further developed for treating diabetes mellitus.

Functional Food Potential of Chrysanthemum morifolium, Perilla frutescens, and Sophora japonica in Managing Hyperuricemia through Dual Enzyme Inhibition

Amid growing concerns regarding gout and hyperuricemia associated with high-protein and purine-rich diets, the need for effective prevention and management strategies with minimal side effects has become increasingly critical. This study evaluates the potential of three commonly consumed plant-based functional foods, Chrysanthemum morifolium, Perilla frutescens, and Sophora japonica, inhibiting xanthine oxidase (XO) and adenosine deaminase (ADA), key enzymes in uric acid metabolism. Results from hyperuricemia model mice indicate that this blend significantly reduces serum uric acid levels, mirroring the efficacy of conventional prevention and management strategies such as allopurinol but with fewer adverse effects. Liquid chromatography-mass spectrometry (LC-MS) analysis confirms that flavonoids are the primary bioactive agents, exhibiting a strong affinity for XO. These findings highlight the viability of integrating plant-based functional foods into comprehensive gout management strategies, underscoring their role in enhancing patient health through dietary innovation.

Antidiabetic Activity, Phytochemical Analysis, and Acute Oral Toxicity Test of Combined Ethanolic Extract of Syzygium polyanthum and Muntingia calabura Leaves

Syzygium polyanthum is known for its capacity to regulate blood glucose levels in individuals with diabetes, while Muntingia calabura leaves have a traditional history as an alternative therapy due to their antidiabetic compounds. The combination of these two plants is expected to yield more optimized antidiabetic agents. This study aims to assess the antidiabetic activity of the combined ethanolic extract of S. polyanthum and M. calabura leaves by measuring the in vitro inhibition of the α-glucosidase enzyme and the blood glucose level in streptozotocin-induced rats and to determine the phytochemical contents of total phenolics, total flavonoids, and quercetine as marker compounds. Acute oral toxicity test was also evaluated. Both plants were extracted by maceration using 96% ethanol. Various combinations of S. polyanthum and M. calabura leaves extracts (1 : 1, 2 : 1, 3 : 1, 1 : 3, and 1 : 2) were prepared. The in vitro test, along with the total phenolic and total flavonoid content, were measured by using UV-Vis spectrophotometry, while quercetine levels were quantified through high-performance liquid chromatography (HPLC). The in vivo and acute toxicity tests were performed on rats as an animal model. The findings demonstrated that the 1 : 1 combination of S. polyanthum and M. calabura leaves ethanolic extract displayed the highest enzyme inhibitory activity with IC50 value of 36.43 µg/mL. Moreover, the combination index (CI) was found <1 that indicates the synergism effect. This combination also decreases the blood glucose level in rats after 28 days of treatments without significant difference with positive control glibenclamide (p > 0.005), and it had medium lethal doses (LD50) higher than 2000 mg/kg BW. Phytochemical analysis showed that the levels of total phenolics, total flavonoids, and quercetine were 30.81% w/w, 1.37% w/w, and 3.25 mg/g, respectively. These findings suggest the potential of combined ethanolic extracts of S. polyanthum and M. calabura leaves (1 : 1) as raw materials for herbal antidiabetic medication.

Persimmon leaf polyphenols as potential ingredients for modulating starch digestibility: Effect of starch-polyphenol interaction

The interaction mode between persimmon leaf polyphenols (PLP) and corn starch with different amylose content and its effect on starch digestibility was studied. Results of iodine binding test, TGA, and DSC revealed that PLP interacted with starch and reduced the iodine binding capacity and thermal stability of starch. High amylopectin corn starch (HAPS) interacted with PLP mainly via hydrogen bonds, since the FT-IR of HAPS-PLP complex showed higher intensity at 3400 cm-1 and an obvious shift of 21 cm-1 to shorter wavelength, and the chemical shifts of protons in 1H NMR and the shift of C-6 peak in 13C NMR of HAPS moved to low field with the addition of PLP. Results of 1H NMR also showed the preferential formation of hydrogen bonds between PLP and OH-3 of HAPS. Different from HAPS, PLP formed V-type inclusion complex with high amylose corn starch (HAS) because XRD of HAS-PLP complex showed characteristic feature peaks of V-type inclusion complex and C-1 signal in 13C NMR of PLP-complexed HAS shifted to low field. Interaction with PLP reduced starch digestibility and HAS-PLP complex resulted in more resistant starch production than HAPS-PLP complex. To complex PLP with starch might be a potential way to prepare functional starch with slower digestion.

Flavonoids as dual-target inhibitors against α-glucosidase and α-amylase: a systematic review of in vitro studies

Diabetes mellitus remains a major global health issue, and great attention is directed at natural therapeutics. This systematic review aimed to assess the potential of flavonoids as antidiabetic agents by investigating their inhibitory effects on α-glucosidase and α-amylase, two key enzymes involved in starch digestion. Six scientific databases (PubMed, Virtual Health Library, EMBASE, SCOPUS, Web of Science, and WHO Global Index Medicus) were searched until August 21, 2022, for in vitro studies reporting IC50 values of purified flavonoids on α-amylase and α-glucosidase, along with corresponding data for acarbose as a positive control. A total of 339 eligible articles were analyzed, resulting in the retrieval of 1643 flavonoid structures. These structures were rigorously standardized and curated, yielding 974 unique compounds, among which 177 flavonoids exhibited inhibition of both α-glucosidase and α-amylase are presented. Quality assessment utilizing a modified CONSORT checklist and structure-activity relationship (SAR) analysis were performed, revealing crucial features for the simultaneous inhibition of flavonoids against both enzymes. Moreover, the review also addressed several limitations in the current research landscape and proposed potential solutions. The curated datasets are available online at https://github.com/MedChemUMP/FDIGA .

Flavonoid Constituents and Alpha-Glucosidase Inhibition of Solanum stramonifolium Jacq. Inflorescence with In Vitro and In Silico Studies

Solanum stramonifolium Jacq. (Solanaceae) is widely found in South East Asia. In Thailand, it is used as vegetable and as a component in traditional recipes. The results of an alpha-glucosidase inhibitory screening test found that the crude extract of S. stramonifolium inflorescence exhibited the potential effect with IC₅₀ 81.27 μg/mL. The separation was performed by the increasing solvent polarity method. The ethyl acetate, ethanol, and water extracts of S. stramonifolium inflorescence showed the synergistic effect together with acarbose standard. The phytochemical investigation of these extracts was conducted by chromatographic and spectroscopic techniques. Six flavonoid compounds, myricetin 3, 4', 5', 7-tetramethyl ether (1), combretol (2), kaempferol (3), kaempferol 7-O-glucopyranoside (4), 5-hydroxy 3-7-4'-5'-tetramethoxyflavone-3'-O-glucopyranoside (5), and a mixture (6) of isorhamnetin 3-O-glucopyranoside (6a) and astragalin (6b) were isolated. This discovery is the first report of flavonoid-glycoside 5. Moreover, the selected flavonoids, kaempferol and astragalin, were representatives to explore the mechanism of action. Both of them performed mixed-type inhibition. The molecular docking gave a better understanding of flavonoid compounds' ability to inhibit the alpha-glucosidase enzyme.

Hypericum Genus as a Natural Source for Biologically Active Compounds

Hypericum L. genus plants are distributed worldwide, with numerous species identified throughout all continents, except Antarctica. These plant species are currently used in various systems of traditional medicine to treat mild depression, wounds and burns, diarrhea, pain, fevers, and their secondary metabolites previously shown, and the in vitro and/or in vivo cytotoxic, antimicrobial, anti-inflammatory, antioxidant, antihyperglycemic, and hepatoprotective activities, as well as the acetylcholinesterase and monoamine oxidase inhibitory activities. We conducted a systematic bibliographic search according to the Cochrane Collaboration guidelines to answer the question: "What is known about plants of Hypericum genus as a source of natural products with potential clinical biological activity?" We documented 414 different natural products with confirmed in vitro/in vivo biological activities, and 58 different Hypericum plant species as sources for these natural products. Phloroglucinols, acylphloroglucinols, xanthones, and benzophenones were the main chemical classes identified. The selective cytotoxicity against tumor cells, cell protection, anti-inflammatory, antimicrobial, antidepressant, anti-Alzheimer's, and adipogenesis-inhibition biological activities are described. Acylphloroglucinols were the most frequent compounds with anticancer and cell-protection mechanisms. To date, no work has been published with a full descriptive list directly relating secondary metabolites to their species of origin, plant parts used, extraction methodologies, mechanisms of action, and biological activities.