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

1-Deoxynojirimycin attenuates pathological markers of Alzheimer's disease in the in vitro model of neuronal insulin resistance

Insulin resistance, the hallmark of type 2 diabetes mellitus (T2DM), has emerged as a pathological feature in Alzheimer's disease (AD). Given the shared role of insulin resistance in T2DM and AD, repurposing peripheral insulin sensitizers is a promising strategy to preserve neuronal insulin sensitivity and prevent AD. 1-Deoxynojirimycin (DNJ), a bioactive iminosugar, exhibited insulin-sensitizing effects in metabolic tissues and was detected in brain tissue post-oral intake. However, its impact on brain and neuronal insulin signaling has not been described. Here, we investigated the effect of DNJ treatment on insulin signaling and AD markers in insulin-resistant human SK-N-SH neuroblastoma, a cellular model of neuronal insulin resistance. Our findings show that DNJ increased the expression of insulin signaling genes and the phosphorylation status of key molecules implicated in insulin resistance (Y1146-pIRβ, S473-pAKT, S9-GSK3B) while also elevating the expression of glucose transporters Glut3 and Glut4, resulting in higher glucose uptake upon insulin stimuli. DNJ appeared to mitigate the insulin resistance-driven increase in phosphorylated tau and Aβ1-42 levels by promoting insulin-induced phosphorylation of GSK3B (a major tau kinase) and enhancing mRNA expression of the insulin-degrading enzyme (IDE) pivotal for insulin and Aβ clearance. Overall, our study unveils probable mechanisms underlying the potential benefits of DNJ for AD, wherein DNJ attenuates tau and amyloid pathologies by reversing neuronal insulin resistance. This provides a scientific basis for expanding the use of DNJ-containing products for neuroprotective purposes and prompts further research into compounds with similar mechanisms of action.

Effect of Akkermansia muciniphila on pancreatic islet β-cell function in rats with prediabetes mellitus induced by a high-fat diet

Prediabetes is an important stage in the development of diabetes. It is necessary to find a safe, effective and sustainable way to delay and reverse the progression of prediabetes. Akkermansia muciniphila (A. muciniphila) is one of the key bacteria associated with glucose metabolism. Recent studies mainly focus on the effect of A. muciniphila on obesity and insulin resistance, but there is no research on the effect of A. muciniphila on pancreatic β-cell function and its mechanism in prediabetes. In this study, we investigated the effects of A. muciniphila on β-cell function, apoptosis and differentiation, as well as its effects on the gut microbiome, intestinal barrier, metaflammation and the expression of Toll-like receptors (TLRs) in a high-fat diet (HFD)-induced prediabetic rat model. The effect of A. muciniphila was compared with dietary intervention. The results showed both A. muciniphila treatment and dietary intervention can reduce metaflammation by repairing the intestinal barrier in rats with prediabetes induced by an HFD and improve β-cell secretory function, apoptosis and differentiation through signaling pathways mediated by TLR2 and TLR4. Additionally, A. muciniphila can further elevate β-cell secretion, attenuate apoptosis and improve differentiation and the TLR signaling pathway on the basis of diet.

Mulberry (Morus alba L.) leaf water extract attenuates type 2 diabetes mellitus by regulating gut microbiota dysbiosis, lipopolysaccharide elevation and endocannabinoid system disorder

ETHNOPHARMACOLOGICAL RELEVANCE

Mulberry (Morus alba L.) leaf is a well-known herbal medicine and has been used to treat diabetes in China for thousands of years. Our previous studies have proven mulberry leaf water extract (MLWE) could improve type 2 diabetes mellitus (T2D). However, it is still unclear whether MLWE could mitigate T2D by regulating gut microbiota dysbiosis and thereof improve intestinal permeability and metabolic dysfunction through modulation of lipopolysaccharide (LPS) and endocannabinoid system (eCBs).

AIM OF STUDY

This study aims to explore the potential mechanism of MLWE on the regulation of metabolic function disorder of T2D mice from the aspects of gut microbiota, LPS and eCBs.

MATERIALS AND METHODS

Gut microbiota was analyzed by high-throughput 16S rRNA gene sequencing. LPS, N-arachidonoylethanolamine (AEA) and 2-ararchidonylglycerol (2-AG) contents in blood were determined by kits or liquid phase chromatography coupled with triple quadrupole tandem mass spectrometry, respectively. The receptors, enzymes or tight junction protein related to eCBs or gut barrier were detected by RT-PCR or Western blot, respectively.

RESULTS

MLWE reduced the serum levels of AEA, 2-AG and LPS, decreased the expressions of N-acylphophatidylethanolamine phospholipase D, diacylglycerol lipase-α and cyclooxygenase 2, and increased the expressions of fatty acid amide hydrolase (FAAH), N-acylethanolamine-hydrolyzing acid amidase (NAAA), alpha/beta hydrolases domain 6/12 in the liver and ileum and occludin, monoacylglycerol lipase and cannabinoid receptor 1 in the ileum of T2D mice. Furthermore, MLWE could change the abundances of the genera including Acetatifactor, Anaerovorax, Bilophila, Colidextribacter, Dubosiella, Gastranaerophilales, Lachnospiraceae_NK4A136_group, Oscillibacter and Rikenella related to LPS, AEA and/or 2-AG. Moreover, obvious improvement of MLWE treatment on serum AEA level, ileum occludin expression, and liver FAAH and NAAA expression could be observed in germ-free-mimic T2D mice.

CONCLUSION

MLWE could ameliorate intestinal permeability, inflammation, and glucose and lipid metabolism imbalance of T2D by regulating gut microbiota, LPS and eCBs.

Edible traditional Chinese medicines improve type 2 diabetes by modulating gut microbiotal metabolites

Type 2 diabetes mellitus (T2DM) is a metabolic disorder with intricate pathogenic mechanisms. Despite the availability of various oral medications for controlling the condition, reports of poor glycemic control in type 2 diabetes persist, possibly involving unknown pathogenic mechanisms. In recent years, the gut microbiota have emerged as a highly promising target for T2DM treatment, with the metabolites produced by gut microbiota serving as crucial intermediaries connecting gut microbiota and strongly related to T2DM. Increasingly, traditional Chinese medicine is being considered to target the gut microbiota for T2DM treatment, and many of them are edible. In studies conducted on animal models, edible traditional Chinese medicine have been shown to primarily alter three significant gut microbiotal metabolites: short-chain fatty acids, bile acids, and branched-chain amino acids. These metabolites play crucial roles in alleviating T2DM by improving glucose metabolism and reducing inflammation. This review primarily summarizes twelve edible traditional Chinese medicines that improve T2DM by modulating the aforementioned three gut microbiotal metabolites, along with potential underlying molecular mechanisms, and also incorporation of edible traditional Chinese medicines into the diets of T2DM patients and combined use with probiotics for treating T2DM are discussed.

Protein engineering of transaminase facilitating enzyme cascade reaction for the biosynthesis of azasugars

Azasugars, such as 1-deoxynojirimycin (1-DNJ), exhibit unique physiological functions and hold promising applications in medicine and health fields. However, the biosynthesis of 1-DNJ is hindered by the low activity and thermostability of the transaminase. In this study, the transaminase from Mycobacterium vanbaalenii (MvTA) with activity toward d-fructose was engineered through semi-rational design and high-throughput screening method. The final mutant M9-1 demonstrated a remarkable 31.2-fold increase in specific activity and an impressive 200-fold improvement in thermostability compared to the wild-type enzyme. Molecular dynamics (MD) simulations revealed that the mutation sites of H69R and K145R in M9-1 played crucial roles in the binding of the amino acceptor and donor, leading to the stable conformation of substrates within the active pocket. An enzyme cascade reaction was developed using M9-1 and the dehydrogenase from Paenibacillus polymyxa (GutB1) for the production of mannojirimycin (MJ), which provided a new idea for the in vitro biosynthesis of 1-DNJ.

Dietary tangeretin improved antibiotic-associated diarrhea in mice by enhancing the intestinal barrier function, regulating the gut microbiota, and metabolic homeostasis

Antibiotic-associated diarrhea is mediated by antibiotic treatment and is usually caused by the disruption of the intestinal barrier, gut microbiota, and metabolic balance. To identify a dietary strategy that can mitigate the side effects of antibiotics, this study investigated the effect of tangeretin on antibiotic-associated diarrhea in C57BL/6 mice. The results revealed that dietary tangeretin significantly ameliorated symptoms of antibiotic-associated diarrhea, as evidenced by the decreased diarrhea status scores, the reduced fecal water content, the decreased caecum/body weight ratio, and the alleviated colonic tissue damage. Dietary tangeretin also exhibited a protective effect on the intestinal barrier function by upregulating the mRNA and protein expression of claudin-1 and ZO-1. Furthermore, analysis of the gut microbiota using 16S rRNA gene sequencing indicated that dietary tangeretin modulated the gut microbiota of mice with antibiotic-associated diarrhea via increasing the gut microbiota diversity and the abundance of beneficial bacteria, e.g., Lactobacillaceae and Ruminococcaceae, and decreasing the abundance of harmful bacteria, e.g., Enterococcus and Terrisporobacter. Additionally, dietary tangeretin restored the levels of short-chain fatty acids and modulated metabolic pathways by enriching purine metabolism, bile acid metabolism, ABC transporters, and choline metabolism in cancer. Collectively, these findings provide a solid scientific basis for the rational use of tangeretin as a preventive and therapeutic agent for antibiotic-associated diarrhea.

Combinational application of the natural products 1-deoxynojirimycin and morin ameliorates insulin resistance and lipid accumulation in prediabetic mice

BACKGROUND

Prediabetes, a stage characterized by chronic inflammation, obesity and insulin resistance. Morin and 1-deoxynojirimycin (DNJ) are natural flavonoids and alkaloids extracted from Morus nigra L., exhibiting anti-hyperglycemic efficacy. However, the benefits of DNJ are shadowed by the adverse events, and the mechanism of morin in anti-diabetes remains under investigation.

PURPOSE

In this study, the combinational efficacy and mechanisms of DNJ and morin in ameliorating insulin resistance and pre-diabetes were investigated.

METHODS

The mice model with prediabetes and Alpha mouse liver-12 (AML-12) cell model with insulin resistance were established. The anti-prediabetic efficacy of the drug combination was determined via analyzing the blood glucose, lipid profiles and inflammatory factors. The application of network pharmacology provided guidance for the research mechanism.

RESULTS

In our study, the intervention of morin ameliorated the insulin resistance via activating the Peroxisome proliferator-activated receptor γ (PPARγ). However, PPARγ activation leaded to the lipid accumulation in prediabetic mice. The combination of 5 mg/kg dose of DNJ and 25 mg/kg morin effectively hindered the progression of T2DM by 87.56%, which was achieved via inhibition of Suppressors of cytokine signaling 3 (SOCS3) and promotion of PPARγ as well as SOCS2 expression. Furthermore, this treatment exhibited notable capabilities in combating dyslipidemia and adipogenesis, achieved by suppressing the Cluster of differentiation 36/ Sterol-regulatory element binding proteins-1/ Fatty acid synthetase (CD36/Serbp1/Fas) signaling.

CONCLUSION

This research confirmed that the drug combination of DNJ and morin in ameliorating insulin resistance and lipid accumulation, and revealed the potential mechanisms. In summary, the combination of DNJ and morin is an underlying alternative pharmaceutical composition in T2DM prevention.

Total Astragalus saponins can reverse type 2 diabetes mellitus-related intestinal dysbiosis and hepatic insulin resistance in vivo

Objective

Intestinal flora homeostasis in rats with type 2 diabetes mellitus (T2DM) was evaluated to explore the effects of total Astragalus saponins (TAS) on hepatic insulin resistance (IR).

Methods

Six-week-old male Sprague-Dawley rats were fed high-fat and high-sugar diet for 4 weeks and intraperitoneally injected with streptozotocin to induce T2DM, and they were then randomly divided into control, model, metformin, and TAS groups. Stool, serum, colon, and liver samples were collected after 8 weeks of drug administration for relevant analyses.

Results

TAS reduced fasting blood glucose, 2-hour postprandial blood glucose, area under the curve of oral glucose tolerance test, glycated serum protein, homeostasis model assessment of insulin resistance, total cholesterol, triglyceride, and low-density lipoprotein cholesterol levels in T2DM rats but increased insulin, C-peptide, and high-density lipoprotein cholesterol levels. Moreover, TAS improved the morphology and structure of liver and colon tissues and improved the composition of the intestinal microbiome and bacterial community structure at different taxonomic levels. In addition, TAS increased the protein expression of hepatic IRS-1, PI3K, PDK1, and p-AKT and decreased the protein expression of p-GSK-3β. Meanwhile, TAS increased the mRNA expression of liver PDK1, PI3K, and GS and decreased the mRNA expression of GSK-3β.

Conclusion

TAS can ameliorate T2DM-related abnormal glucose and blood lipid metabolism, intestinal dysbiosis, and IR.

Effects and Mechanistic Role of Mulberry Leaves in Treating Diabetes and its Complications

Diabetes mellitus (DM) has become a surge burden worldwide owing to its high prevalence and range of associated complications such as coronary artery disease, blindness, stroke, and renal failure. Accordingly, the treatment and management of DM have become a research hotspot. Mulberry leaves (Morus alba L.) have been used in Traditional Chinese Medicine for a long time, with the first record of its use published in Shennong Bencao Jing (Shennong's Classic of Materia Medica). Mulberry leaves (MLs) are considered highly valuable medicinal food homologs that contain polysaccharides, flavonoids, alkaloids, and other bioactive substances. Modern pharmacological studies have shown that MLs have multiple bioactive effects, including hypolipidemic, hypoglycemic, antioxidation, and anti-inflammatory properties, with the ability to protect islet [Formula: see text]-cells, alleviate insulin resistance, and regulate intestinal flora. However, the pharmacological mechanisms of MLs in DM have not been fully elucidated. In this review, we summarize the botanical characterization, traditional use, chemical constituents, pharmacokinetics, and toxicology of MLs, and highlight the mechanisms involved in treating DM and its complications. This review can provide a valuable reference for the further development and utilization of MLs in the prevention and treatment of DM.

Dendrobium officinale Polysaccharide Prevents Diabetes via the Regulation of Gut Microbiota in Prediabetic Mice

Dendrobium officinale polysaccharide (DOP), which serves as a prebiotic, exhibits a variety of biological activities, including hypoglycemic activities. However, the effects of DOP on diabetes prevention and its hypoglycemic mechanisms are still unclear. In this study, the effects of DOP treatment on the prediabetic mice model were studied and the mechanism was investigated. The results showed that 200 mg/kg/d of DOP reduced the relative risk of type 2 diabetes mellitus (T2DM) from prediabetes by 63.7%. Meanwhile, DOP decreased the level of LPS and inhibited the expression of TLR4 by regulating the composition of the gut microbiota, consequently relieving the inflammation and alleviating insulin resistance. In addition, DOP increased the abundance of SCFA (short chain fatty acid)-producing bacteria in the intestine, increased the levels of intestinal SCFAs, promoted the expression of short-chain fatty acid receptors FFAR2/FFAR3, and increased the secretion of the intestinal hormones GLP-1 and PYY, which helped to repair islet damage, suppress appetite, and improve insulin resistance. Our results suggested that DOP is a promising functional food supplement for the prevention of T2DM.

The linkage of gut microbiota and the property theory of traditional Chinese medicine (TCM): Cold-natured and sweet-flavored TCMs as an example

ETHNOPHARMACOLOGICAL RELEVANCE

The property theory of traditional Chinese medicine (TCM) is a unique medical theory based on an extensive clinical practice for thousands of years, which guides TCM doctors choosing proper medicines to treat specific diseases. The nature and flavor of TCM are a high generalization of drug's characteristics according to the property theory. Despite intensive investigations, the modern interpretation of TCM property theory still confronts several challenges, which greatly hampers the elucidation of TCM's mechanisms as well as its application. Compelling evidence has proved that gut microbiota may be a potential indicator for TCM's efficacy and mechanism. Nevertheless, at present, the relationship between the gut microbiota and the nature and flavor of TCM has not been fully elucidated.

AIM OF THE STUDY

To fill the gap in this field, we developed a comprehensive study to investigate the relationship between gut microbial community and TCM's property.

MATERIALS AND METHODS

We searched "PubMed" and "China National Knowledge Infrastructure (CNKI)" with the key word "gut microbiota", and screened the published articles related to TCM. In this review, we mainly applied cold-natured and sweet-flavored TCMs as an example to explore the modulation of cold-natured and sweet-flavored TCMs on gut microbiota, and identify the potential relationship between the alterations of gut microbiota and TCM's efficacy.

RESULTS

We found cold-natured and sweet-flavored TCMs possess several pharmacological activities and generally enrich beneficial bacteria like Akkermansia, Bacteroides, Lactobacillus and Bifidobacterium, which is in good accordance with their pharmacological effects. Simultaneously, these TCMs reduce the relative abundance of some harmful bacteria belonging to Firmicutes (Streptpcoccus, Enterococcus, Turicibacter, Anaerostipes and Oscillibacter) and Proteobacteria (Helicobacter, Enterobacter, Sutterella, Klebsiella, Desulfovibrio, Escherichia coli and Campylobacter jejuni). These results indicate that there are some intrinsic correlations between gut microbiota and the property of TCM, and gut microbiota may serve as a potential indicator to reflect the property of TCM.

CONCLUSIONS

This pilot but comprehensive review provides an interesting proposal that the ancient theory of TCM property may be interpreted by the modern biological findings in gut microbiome.

Gut microbiome dysregulation drives bone damage in broiler tibial dyschondroplasia by disrupting glucose homeostasis

Tibial dyschondroplasia (TD) with multiple incentives is a metabolic skeletal disease that occurs in fast-growing broilers. Perturbations in the gut microbiota (GM) have been shown to affect bone homoeostasis, but the mechanisms by which GM modulates bone metabolism in TD broilers remain unknown. Here, using a broiler model of TD, we noted elevated blood glucose (GLU) levels in TD broilers, accompanied by alterations in the pancreatic structure and secretory function and damaged intestinal barrier function. Importantly, faecal microbiota transplantation (FMT) of gut microbes from normal donors rehabilitated the GM and decreased the elevated GLU levels in TD broilers. A high GLU level is a predisposing factor to bone disease, suggesting that GM dysbiosis-mediated hyperglycaemia might be involved in bone regulation. 16S rRNA gene sequencing and short-chain fatty acid analysis revealed that the significantly increased level of the metabolite butyric acid derived from the genera Blautia and Coprococcus regulated GLU levels in TD broilers by binding to GPR109A in the pancreas. Tibial studies showed reduced expression of vascular regulatory factors (including PI3K, AKT and VEFGA) based on transcriptomics analysis and reduced vascular distribution, contributing to nonvascularization of cartilage in the proximal tibial growth plate of TD broilers with elevated GLU levels. Additionally, treatment with the total flavonoids from Rhizoma drynariae further validated the improvement in bone homoeostasis in TD broilers by regulating GLU levels through the regulation of GM to subsequently improve intestinal and pancreatic function. These findings clarify the critical role of GM-mediated changes in GLU levels via the gut-pancreas axis in bone homoeostasis in TD chickens.

Ameliorating Effect of the Total Flavonoids of Morus nigra L. on Prediabetic Mice Based on Regulation of Inflammation and Insulin Sensitization

Prediabetes is a critical stage characterized by insulin resistance. Morus nigra L., an edible plant, is widely used in food and nutritive supplements and exhibits various pharmacological activities; however, its therapeutic effects and mechanisms on prediabetes have rarely been reported. In this research, the major components of total flavonoids of M. nigra L. (TFM) were identified, and TFM treatment was found to reduce prediabetes progressing to type 2 diabetes mellitus (T2DM) from 93.75 to 18.75%. The microbiota and next-generation sequencing combined with western blotting in vivo and in vitro demonstrated that TFM and its components ameliorated insulin resistance mediated by the suppressor of cytokine signaling and protein tyrosine phosphatase 1B, which benefited by maintaining intestinal homeostasis and restraining plasma levels of inflammatory factors. This study confirmed the T2DM prevention effect of TFM and revealed the underlying mechanism, setting the stage for the design of functional foods for diabetes prevention.

Rapid Screening of Nonalkaloid α-Glucosidase Inhibitors from a Mulberry Twig Extract Using Enzyme-Functionalized Magnetic Nanoparticles Coupled with UPLC-MS/MS

Mulberry twigs are an important source of α-glucosidase inhibitors. To date, research studies on α-glucosidase in mulberry twigs have mainly focused on alkaloids such as 1-deoxynojirimycin (DNJ). Preliminary studies have shown that there may be more active nonalkaloid α-glucosidase inhibitors in mulberry twigs. In this study, we immobilized α-glucosidase on Fe₃O₄@SiO₂ for the first time and rapidly screened four nonalkaloid α-glucosidase inhibitors (kuwanon G, kuwanon C, kuwanon H, and morusin) using ligand fishing technology with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) from the mulberry twig extract of Jialing 20, the excellent artificial triploid variety of mulberry cultivated extensively in Southwest China. The half maximal inhibitory concentrations (IC₅₀) of kuwanon H and kuwanon G were 2.82 ± 0.68 and 2.83 ± 0.31 μM, respectively, with better inhibition activity than that of DNJ (with an IC₅₀ of 7.04 ± 0.82 μM). Meanwhile, the molecular docking results showed that the action sites of these two isopentenyl flavonoids on α-glucosidase were different from that of DNJ. In brief, this work is beneficial to discovering new α-glucosidase inhibitors from mulberry twigs quickly and accurately and provides a theoretical basis for the mulberry twig extract as a functional food or a natural hypoglycemic drug source, as well as a reference for directional breeding of mulberry, which greatly improves the exploitation and utilization value of mulberry twigs as an agricultural byproduct in the fields of agricultural production, functional food, and natural medicine.

Preclinical Studies of Natural Products Targeting the Gut Microbiota: Beneficial Effects on Diabetes

Diabetes mellitus (DM) is a serious metabolic disease characterized by persistent hyperglycemia, with a continuously increasing morbidity and mortality. Although traditional treatments including insulin and oral hypoglycemic drugs maintain blood glucose levels within the normal range to a certain extent, there is an urgent need to develop new drugs that can effectively improve glucose metabolism and diabetes-related complications. Notably, accumulated evidence implicates that the gut microbiota is unbalanced in DM individuals and is involved in the physiological and pathological processes of this metabolic disease. In this review, we introduce the molecular mechanisms by which the gut microbiota contributes to the development of DM. Furthermore, we summarize the preclinical studies of bioactive natural products that exert antidiabetic effects by modulating the gut microbiota, aiming to expand the novel therapeutic strategies for DM prevention and management.

Recent Advances in the Treatment of Insulin Resistance Targeting Molecular and Metabolic Pathways: Fighting a Losing Battle?

Diabetes Mellitus (DM) is amongst the most notable causes of years of life lost worldwide and its prevalence increases perpetually. The disease is characterized as multisystemic dysfunctions attributed to hyperglycemia resulting directly from insulin resistance (IR), inadequate insulin secretion, or enormous glucagon secretion. Insulin is a highly anabolic peptide hormone that regulates blood glucose levels by hastening cellular glucose uptake as well as controlling carbohydrate, protein, and lipid metabolism. In the course of Type 2 Diabetes Mellitus (T2DM), which accounts for nearly 90% of all cases of diabetes, the insulin response is inadequate, and this condition is defined as Insulin Resistance. IR sequela include, but are not limited to, hyperglycemia, cardiovascular system impairment, chronic inflammation, disbalance in oxidative stress status, and metabolic syndrome occurrence. Despite the substantial progress in understanding the molecular and metabolic pathways accounting for injurious effects of IR towards multiple body organs, IR still is recognized as a ferocious enigma. The number of widely available therapeutic approaches is growing, however, the demand for precise, safe, and effective therapy is also increasing. A literature search was carried out using the MEDLINE/PubMed, Google Scholar, SCOPUS and Clinical Trials Registry databases with a combination of keywords and MeSH terms, and papers published from February 2021 to March 2022 were selected as recently published papers. This review paper aims to provide critical, concise, but comprehensive insights into the advances in the treatment of IR that were achieved in the last months.