Dietary 5,6,7-Trihydroxy-flavonoid Aglycones and 1-Deoxynojirimycin Synergistically Inhibit the Recombinant Maltase-Glucoamylase Subunit of α-Glucosidase and Lower Postprandial Blood Glucose

Chemical Epigenetic Regulation Secondary Metabolites Derived from Aspergillus sydowii DL1045 with Inhibitory Activities for Protein Tyrosine Phosphatases

Protein tyrosine phosphatases (PTPs) are ubiquitous in living organisms and are promising drug targets for cancer, diabetes/obesity, and autoimmune disorders. In this study, a histone deacetylase inhibitor called suberoylanilide hydroxamic acid (SAHA) was added to a culture of marine fungi (Aspergillus sydowii DL1045) to identify potential drug candidates related to PTP inhibition. Then, the profile of the induced metabolites was characterized using an integrated metabolomics strategy. In total, 46% of the total SMs were regulated secondary metabolites (SMs), among which 20 newly biosynthesized metabolites (10% of the total SMs) were identified only in chemical epigenetic regulation (CER) broth. One was identified as a novel compound, and fourteen compounds were identified from Aspergillus sydowii first. SAHA derivatives were also biotransformed by A. sydowii DL1045, and five of these derivatives were identified. Based on the bioassay, some of the newly synthesized metabolites exhibited inhibitory effects on PTPs. The novel compound sydowimide A (A11) inhibited Src homology region 2 domain-containing phosphatase-1 (SHP1), T-cell protein tyrosine phosphatase (TCPTP) and leukocyte common antigen (CD45), with IC50 values of 1.5, 2.4 and 18.83 μM, respectively. Diorcinol (A3) displayed the strongest inhibitory effect on SHP1, with an IC50 value of 0.96 μM. The structure-activity relationship analysis and docking studies of A3 analogs indicated that the substitution of the carboxyl group reduced the activity of A3. Research has demonstrated that CER positively impacts changes in the secondary metabolic patterns of A. sydowii DL1045. The compounds produced through this approach will provide valuable insights for the creation and advancement of novel drug candidates related to PTP inhibition.

Shiitake polysaccharides acted as a non-competitive inhibitor to α-glucosidase and inhibited glucose transport of digested starch from Caco-2 cells monolayer

The inhibition mechanism of shitake mushroom polysaccharides (Lentinula edodes polysaccharides, LEP) against α-glucosidase was studied by enzyme kinetic assay, fluorescence quenching and molecular docking. The effect of LEP on glucose transport of digested starch was investigated via an in vitro digestion/Caco-2 transwell model. LEP exhibited a stronger inhibiting effect (IC50 = 0.66 mg/mL) than acarbose and presented a non-competitive inhibition mechanism. The interaction between LEP and α-glucosidase primarily involved electrostatic interaction and hydrogen bonding. Molecular docking modelling showed that the four structures of LEP were bound to the allosteric tunnel or adjacent pocket of α-glucosidase via electrostatic force and hydrogen bonds. The (1 → 6)-linkages in LEP structures favoured its binding affinity to the α-glucosidase. The α-glucosidase inhibiting activity of LEP was also found to emanate from the reduction in glucose transport of digested starch as deducted from the in vitro digestion/Caco-2 transwell data. The release of glucose from digested starch cooked with LEP was significantly reduced (33.7%) compared to the digested starch without LEP. The findings from the current study suggest that LEP could be a promising ingredient to inhibit α-glucosidase activity as well as control the level of postprandial blood glucose when incorporated into starchy foods.

The Effects of 1-Deoxynojirimycin from Mulberry on Oxidative Stress and Inflammation in Laying Hens and the Direct Effects on Intestine Epithelium Cells In Vitro

The intestine is highly vulnerable to various factors and has been proposed as a promising determinant for poultry health. Phytogenic or plant-derived feed additives can be used to help improve intestinal health. In this study, we aimed to investigate the effects of DNJ on the antioxidative parameters, including malondialdehyde (MDA), total superoxide dismutase (T-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and inflammatory cytokines (IL-6, IL-1β, and TNF-α), in plasma and intestinal tissues using layers supplemented with or without the DNJ extract of mulberry leaves (DNJ-E) via the ELISA method. A total of 192 healthy Hy-Line Brown layers, aged 47 weeks old, were used to conduct a 56-day study. All hens were randomly separated into four groups as follows: a basal diet containing 0 mg/kg DNJ-E(CON), 50 mg/kg, 100 mg/kg, and 150 mg/kg DNJ-E. Furthermore, the potential mechanism by which DNJ influences intestinal function was also investigated in in vitro cultured intestinal epithelium cells (IEC) with quantification methods including the use of a cell counting kit-8 (CCK8), ELISA, qRT-PCR, and ROS detection. The results showed that CAT in plasma significantly increased following 50 mg/kg DNJ-E supplementation. Moreover, 50 mg/kg DNJ-E supplementation was associated with increases in T-SOD in the jejunum and ileum. However, there was no significant difference in inflammatory cytokines between groups in in vivo experiments. Subsequent in vitro IEC studies revealed that cell viability increased significantly following 5 µM and 10 µM DNJ treatments while decreasing significantly following 20 µM DNJ treatment. Antioxidative parameters improved at 5 µM and 10 µM DNJ concentrations. However, there were no ameliorative effects on antioxidant parameters observed under 20 µM DNJ treatment. The expression levels of Nrf2 mRNA increased significantly under DNJ treatment. DNJ treatment was associated with significant changes in the expression of genes of inflammatory cytokines. In conclusion, our study revealed that DNJ could improve oxidative stress and inflammation responses in the chicken intestine. These findings provide a theoretical reference for the development of functional feed additives that regulate intestinal health and lay the foundation for systematically revealing the mechanism of DNJ.

Research Progress of α-Glucosidase Inhibitors Produced by Microorganisms and Their Applications

Based on the easy cultivation of microorganisms and their short cycle time, research on α-glucosidase inhibitors (α-GIs) of microbial origin is receiving extensive attention. Raw materials used in food production, such as cereals, dairy products, fruits, and vegetables, contain various bioactive components, like flavonoids, polyphenols, and alkaloids. Fermentation with specific bacterial strains enhances the nutritional value of these raw materials and enables the creation of hypoglycemic products rich in diverse active ingredients. Additionally, conventional food processing often results in significant byproduct generation, causing resource wastage and environmental issues. However, using bacterial strains to ferment these byproducts into α-GIs presents an innovative solution. This review describes the microbial-derived α-GIs that have been identified. Moreover, the production of α-GIs using industrial food raw materials and processing byproducts as a medium in fermentation is summarized. It is worth analyzing the selection of strains and raw materials, the separation and identification of key compounds, and fermentation broth research methods. Notably, the innovative ideas in this field are described as well. This review will provide theoretical guidance for the development of microbial-derived hypoglycemic foods.

Studies on the inhibition of α-glucosidase by biflavonoids and their interaction mechanisms

Biflavonoids are a kind of polyphenol compounds with numerous biological functions. However, the potential inhibitory activities of biflavonoids on α-glucosidase are yet unknown. Here, the inhibitory effects of two biflavonoids (amentoflavone and hinokiflavone) on α-glucosidase and their interaction mechanisms were explored using multispectral approaches and molecular docking. The results showed that the inhibitory activities of biflavonoids were much better compared with monoflavonoid (apigenin) and acarbose, and the order of inhibition ability was hinokiflavone > amentoflavone > apigenin > acarbose. These flavonoids were noncompetitive inhibitors of α-glucosidase and showed synergistic inhibition effects with acarbose. Additionally, they could statically quench the intrinsic fluorescence of α-glucosidase, and form the non-covalent complexes with enzyme primarily through hydrogen bonds and van der Waals forces. The binding of flavonoids changed the conformational structure of α-glucosidase, therefore impairing the enzyme activity. The findings suggested that biflavonoids could be considered as potential hypoglycemic functional foods in diabetes therapy.

Evaluation of mulberry leaves’ hypoglycemic properties and hypoglycemic mechanisms

The effectiveness of herbal medicine in treating diabetes has grown in recent years, but the precise mechanism by which it does so is still unclear to both medical professionals and diabetics. In traditional Chinese medicine, mulberry leaf is used to treat inflammation, colds, and antiviral illnesses. Mulberry leaves are one of the herbs with many medicinal applications, and as mulberry leaf study grows, there is mounting evidence that these leaves also have potent anti-diabetic properties. The direct role of mulberry leaf as a natural remedy in the treatment of diabetes has been proven in several studies and clinical trials. However, because mulberry leaf is a more potent remedy for diabetes, a deeper understanding of how it works is required. The bioactive compounds flavonoids, alkaloids, polysaccharides, polyphenols, volatile oils, sterols, amino acids, and a variety of inorganic trace elements and vitamins, among others, have been found to be abundant in mulberry leaves. Among these compounds, flavonoids, alkaloids, polysaccharides, and polyphenols have a stronger link to diabetes. Of course, trace minerals and vitamins also contribute to blood sugar regulation. Inhibiting alpha glucosidase activity in the intestine, regulating lipid metabolism in the body, protecting pancreatic -cells, lowering insulin resistance, accelerating glucose uptake by target tissues, and improving oxidative stress levels in the body are some of the main therapeutic properties mentioned above. These mechanisms can effectively regulate blood glucose levels. The therapeutic effects of the bioactive compounds found in mulberry leaves on diabetes mellitus and their associated molecular mechanisms are the main topics of this paper’s overview of the state of the art in mulberry leaf research for the treatment of diabetes mellitus.

Identification of a novel α-glucosidase inhibitor from Melastoma dodecandrum Lour. fruits and its effect on regulating postprandial blood glucose

Melastoma dodecandrum Lour. (MDL) extracts have shown potent α-glucosidase inhibitory activity, suggesting MDL might be a good source of α-glucosidase inhibitors. The aim of the study was to identify compounds in MDL extracts with α-glucosidase inhibitory activities and evaluate their effect on postprandial blood glucose as well as elucidating the underlying mechanisms of inhibition. A total of 34 polyphenols were identified in MDL fruits, among which 10 anthocyanins and three proanthocyanidin derivatives were discovered for the first time. Dosing mice with MDL extracts (100 mg/kg body weight, by gavage) was associated with a significantly decrease in postprandial blood glucose concentrations after oral administration of maltose. The most potent α-glucosidase inhibitor was identified as casuarictin (IC₅₀ of 0.21 μg/mL). Casuarictin bound competitively to α-glucosidase, occupying not only the catalytic site but also forming strong hydrogen bonds with α-glucosidase residues. Therefore, casuarictin derived from MDL fruits might be used as novel α-glucosidase inhibitor in functional foods or other dietary products.

Metabolomic Strategy to Characterize the Profile of Secondary Metabolites in Aspergillus aculeatus DL1011 Regulated by Chemical Epigenetic Agents

Chemical epigenetic regulation (CER) is an effective method to activate the silent pathway of fungal secondary metabolite synthesis. However, conventional methods for CER study are laborious and time-consuming. In the meantime, the overall profile of the secondary metabolites in the fungi treated by the CER reagent is not well characterized. In this study, suberohydroxamic acid (SBHA), a histone deacetylase inhibitor, was added to a culture of Aspergillus aculeatus DL1011 and a new strategy based on LC-MS/MS analysis integrated with various metabolomic tools (MetaboAnalyst, MS-DIAL, SIRIUS and GNPS) was developed to characterize the profile of induced metabolites. As a result, 13.6%, 29.5% and 27.2% of metabolites were identified as newly biosynthesized, increasing and decreasing in abundance by CER, respectively. The structures of the 18 newly induced secondary metabolites were further identified by the new strategy to demonstrate that 72.2% of them (1 novel compound and 12 known compounds) were first discovered in A. aculeatus upon SBHA treatment. The accuracy of the new approach was confirmed by purification and NMR data analysis of major newly biosynthesized secondary metabolites. The bioassay showed that the newly biosynthesized compounds, roseopurpurin analogues, showed selective activities against DPPH scavenging, cytotoxicity and SHP1 inhibition. Our research demonstrated that CER was beneficial for changing the secondary metabolic profile of fungi and was an effective means of increasing the diversity of active metabolites. Our work also supplied a metabolomic strategy to characterize the profile changes and determine the newly induced compounds in the secondary metabolites of fungi treated with the chemical epigenetic regulator.

Synthesis of activity evaluation of flavonoid derivatives as ɑ-glucosidase inhibitors

Six flavonoid derivatives were synthesized and tested for anti-α-glucosidase activities. All derivatives were confirmed using NMR and HRMS and exhibited excellent inhibitory effects on α-glucosidase. Derivative four exhibited the highest anti-α-glucosidase activity (IC50: 15.71 ± 0.21 μM). Structure-activity relationship results showed that bromine group would be the most beneficial group to anti-α-glucosidase activity. Inhibitory mechnism and inhibition kinetics results showed derivative four was a reversible and mixed-type inhibitor. Molecular docking revealed that derivative four was tightly bind to the amino acid residues of active pocket of α-glucosidase and formed hydrogen bond, π-π stacking, and Pi-Donor hydrogen with α-glucosidase. Moreover, the physicochemical parameters of all derivatives were assessed using SwissADME software. This results also showed that the hybridization of flavonoid and phenylpropionic acid would be a useful strategy for the development of α-glucosidase inhibitors.

Effect of 1-Deoxynojirimycin on insulin resistance in prediabetic mice based on next-generation sequencing and intestinal microbiota study

ETHNOPHARMACOLOGICAL RELEVANCE

1-Deoxynojirimycin (DNJ), the major alkaloid in Morus alba L., is the main effective constituent in "Mulberry twig Alkaloids Tablets" launched in China in 2020. Prediabetes, characterized by insulin resistance, is regarded as the key period for reversing Type 2 diabetes mellitus (T2DM) through lifestyle intervention and glucose-lowering drugs. Besides the excellent activity as an α-glucosidase inhibitor, DNJ also improves insulin sensitivity in T2DM murine models, yet the mechanism is still unclear. Besides, the pharmaceutical effect of DNJ on prediabetes is also undocumented.

AIM OF THE STUDY

The aim of this study was to investigate the pharmaceutical effect of DNJ on high-fat and streptozotocin (STZ)-induced prediabetes mice, and to elucidate the mechanism of insulin resistance ameliorated by DNJ.

MATERIALS AND METHODS

Oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) were performed to detect blood glucose level and insulin sensitivity in mice. The levels of circulating lipopolysaccharide (LPS), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) in the plasma of mice were measured by limulus reagent and enzyme-linked immunosorbent assay (ELISA), respectively. Next-generation sequencing (NGS) and intestinal microbiota sequencing were used to screen the alterations in the transcriptome of liver tissues and to assess the differences in intestinal flora composition, respectively. Expression of cytokine signaling pathway inhibitor 3 (SOCS3), insulin receptor substrate (IRS1), p-IRS1 (Tyr896), occludin, and toll like receptor 4 (TLR4)/NF-κB signaling pathway were confirmed by western blotting.

RESULTS

Our study revealed that DNJ decreased the blood glucose level and improve insulin sensitivity in prediabetic mice. DNJ significantly reduced the relative risk of T2DM in prediabetic mice by approximately 83.7%. Mechanistically, DNJ treatment suppressed the circulating levels of LPS, IL-6, and TNF-α in plasma and decreased the inflammatory infiltration in liver and colon tissues. DNJ-treatment increased the abundance of Akkermansia, Bifidobacterium, and Lactobacillus, and decreased the abundance of Enterococcaceae and Lachnospiraceae. Moreover, DNJ suppressed the expression of SOCS3 and the activity of TLR4/NF-κB signaling pathway, meanwhile improving the expression of occludin and the ratio of p-IRS1 (Tyr896)/IRS1.

CONCLUSIONS

DNJ effectively ameliorates glucose and lipid metabolism in prediabetic mice, and decreased the relative risk of progression into T2DM from prediabetes. The suppressed immune responses play essential roles in the improvement of insulin resistance by DNJ treatment. In conclusion, DNJ from Morus alba L. is a promising alternative agent in T2DM prevention.

Influence of Sargassum pallidum and the synergistic interaction mechanism of 6-gingerol and poricoic acid A on inhibiting ovalbumin glycation

This study aimed to investigate the antiglycation capacity of Sargassum pallidum extract on ovalbumin (OVA) glycation, and the interaction mechanism of its active compounds, including 6-gingerol (6G) and poricoic acid A (PA). The results showed that Sargassum pallidum extract, PA and 6G had excellent suppression on the formation of fructosamine, 5-hydroxymethylfurfural (5-HMF), acrylamide and advanced glycation end products (AGEs), which was higher than aminoguanidine (AG). The combination of PA and 6G showed good synergistic effect on inhibiting the formation of AGEs. PA exhibited the strongest inhibition activity for protein glycation products, and the content of 5-HMF and acrylamide decreased from 277.44 and 10.60 μg mL-1 to 208.37 and 5.46 μg mL-1, respectively, at 30.08 × 10-5 M compared with the control group. 6G and PA quenched the fluorescence of OVA with a static mechanism, and enhanced the hydrophilic microenvironment of the tyrosine (Tyr) and tryptophan (Trp) residues. The binding of 6G and PA with OVA was spontaneous and driven by hydrogen bonds and van der Waals interactions. Molecular docking indicated that 6G and PA entered the hydrophobic cavity of OVA, and formed hydrogen bonds with Ser103, Leu101 and Thr 91. These findings suggested that Sargassum pallidum extract, PA and 6G have great potential as antiglycation inhibitors to treat diabetes complications in healthy food.