Neferine Promotes GLUT4 Expression and Fusion With the Plasma Membrane to Induce Glucose Uptake in L6 Cells

Biologically active isoquinoline alkaloids covering 2019-2022

Isoquinoline alkaloids are an important class of natural products that are abundant in the plant kingdom and exhibit a wide range of structural diversity and biological activities. With the deepening of research in recent years, more and more isoquinoline alkaloids have been isolated and identified and proved to contain a variety of biological activities and pharmacological effects. In this review, we introduce the research progress of isoquinoline alkaloids from 2019 to 2022, mainly in the part of biological activities, including antitumor, antimicrobial, antidiabetic, antiviral, anti-inflammatory, antioxidant, neuroprotective, hepatoprotective, analgesic, and other activities. This study provides a clear direction for the rational development and utilization of isoquinoline alkaloids, suggesting that these alkaloids have great potential in the field of drug research.

Glucose Uptake Is Increased by Estradiol Dipropionate in L6 Skeletal Muscle Cells

GLUT4 is an important glucose transporter, which is closely related to insulin resistance and type 2 diabetes. In this study, we investigated the mechanism of Estradiol Dipropionate (EDP) on uptake of glucose in L6 skeletal muscle cells. In our study, we confirmed that EDP promoted uptake of glucose in L6 skeletal muscle cells in both normal and insulin resistant models. Western blot indicated that EDP accelerated GLUT4 expression and significantly activated AMPK and PKC phosphorylation; the expression of GLUT4 was significantly inhibited by AMPK inhibitor compound C and PKC inhibitor Gö6983, but not by Wortmannin (Akt inhibitor). Meanwhile, EDP boosted GLUT4 expression, and also increased intracellular Ca²⁺ levels. In the presence of 2 mM, 0 mM extracellular Ca²⁺ and 0 mM extracellular Ca²⁺ + BAPTA-AM, the involvement of intracellular Ca²⁺ levels contribute to EDP-induced GLUT4 expression and fusion with plasma membrane. Therefore, this study investigated whether EDP promoted GLUT4 expression through AMPK and PKC signaling pathways, thereby enhancing GLUT4 uptake of glucose and fusion into plasma membrane in L6 skeletal muscle cells. In addition, both EDP induced GLUT4 translocation and uptake of glucose were Ca²⁺ dependent. These findings suggested that EDP may be potential drug for the treatment of type 2 diabetes.

Andrographolide Promotes Uptake of Glucose and GLUT4 Transport through the PKC Pathway in L6 Cells

Glucose transporter 4 (GLUT4) is a membrane protein that regulates blood glucose balance and is closely related to type 2 diabetes. Andrographolide (AND) is a diterpene lactone extracted from herbal medicine Andrographis paniculata, which has a variety of biological activities. In this study, the antidiabetic effect of AND in L6 cells and its mechanism were investigated. The uptake of glucose of L6 cells was detected by a glucose assay kit. The expression of GLUT4 and phosphorylation of protein kinase B (PKB/Akt), AMP-dependent protein kinase (AMPK), and protein kinase C (PKC) were detected by Western blot. At the same time, the intracellular Ca2+ levels and GLUT4 translocation in myc-GLUT4-mOrange-L6 cells were detected by confocal laser scanning microscopy. The results showed that AND enhanced the uptake of glucose, GLUT4 expression and fusion with plasma membrane in L6 cells. Meanwhile, AND also significantly activated the phosphorylation of AMPK and PKC and increased the concentration of intracellular Ca2+. AND-induced GLUT4 expression was significantly inhibited by a PKC inhibitor (Gö6983). In addition, in the case of 0 mM extracellular Ca2+ and 0 mM extracellular Ca2+ + 10 μM BAPTA-AM (intracellular Ca2+ chelator), AND induced the translocation of GLUT4, and the uptake of glucose was significantly inhibited. Therefore, we concluded that AND promoted the expression of GLUT4 and its fusion with plasma membrane in L6 cells through PKC pathways in a Ca2+—dependent manner, thereby increasing the uptake of glucose.

New Aclyphloroglucinols and geranyl-α-pyrones from Hypericum hengshanense

Hypericum hengshanense is a previously uninvestigated endemic plant species of China. Three new aclyphloroglucinols, hengshanols A-C (1-3), and two new geranyl-α-pyrones, hengshanpyol D and E (4 and 5), together with three known compounds were isolated from the aerial parts of H. hengshanense. The structure of these compounds were elucidated by NMR, MS, optical rotation, and ECD data. All compounds were isolated from H. hengshanense for the first time. Among them, compounds 2-4 may have anti-laryngeal cancer activity. Compounds isolated were tested for glucose uptake in L6 cells, and compound 4 showed the most potent glucose uptake with 1.62-fold enhancement.

Capsaicin and Zinc Promote Glucose Uptake in C2C12 Skeletal Muscle Cells through a Common Calcium Signalling Pathway

Capsaicin and zinc have recently been highlighted as potential treatments for glucose metabolism disorders; however, the effect of these two natural compounds on signalling pathways involved in glucose metabolism is still uncertain. In this study, we assessed the capsaicin- or zinc- induced activation of signalling molecules including calcium/calmodulin-dependent protein kinase 2 (CAMKK2), cAMP-response element-binding protein (CREB), and target of rapamycin kinase complex 1 (TORC1). Moreover, the expression status of genes associated with the control of glucose metabolism was measured in treated cells. The activation of cell signalling proteins was then evaluated in capsaicin- or zinc treated cells in the presence or absence of cell-permeant calcium chelator (BAPTA-AM) and the CAMKK inhibitor (STO-609). Finally, capsaicin- and zinc-induced glucose uptake was measured in the cells pre-treated with or without BAPTA-AM. Our results indicate that calcium flux induced by capsaicin or zinc led to activation of calcium signalling molecules and promoting glucose uptake in skeletal muscle cells. Pharmacological inhibition of CAMKK diminished activation of signalling molecules. Moreover, we observed an increase in intracellular cAMP levels in the cells after treatment with capsaicin and zinc. Our data show that capsaicin and zinc mediate glucose uptake in C2C12 skeletal muscle cells through the activation of calcium signalling.

Four new polycyclic polyprenylated acylphloroglucinols from Hypericum wilsonii and their glucose uptake bioactivities

Wilsonglucinols H-K (1-4), four new polycyclic polyprenylated acylphloroglucinols (PPAPs), and eight known compounds (5-12) were isolated and identified from the aerial parts of Hypericum wilsonii. Their planner structures were confirmed via extensive NMR and HRESIMS data analysis. The absolute configurations of the new compounds were mainly determined by NMR calculation and electronic circular dichroism (ECD) calculation. Compounds 1, 6, 8, and 10 showed glucose uptake activities at 30 μg/mL, in which compound 6 showed the strongest effect and increased the glucose uptake by 2.73 folds.

Stevioside Attenuates Insulin Resistance in Skeletal Muscle by Facilitating IR/IRS-1/Akt/GLUT 4 Signaling Pathways: An In Vivo and In Silico Approach

Type-2 diabetes mellitus (T2DM), the leading global health burden of this century majorly develops due to obesity and hyperglycemia-induced oxidative stress in skeletal muscles. Hence, developing novel drugs that ameliorate these pathological events is an immediate priority. The study was designed to analyze the possible role of Stevioside, a characteristic sugar from leaves of Stevia rebaudiana (Bertoni) on insulin signaling molecules in gastrocnemius muscle of obesity and hyperglycemia-induced T2DM rats. Adult male Wistar rats rendered diabetic by administration of high fat diet (HFD) and sucrose for 60 days were orally administered with SIT (20 mg/kg/day) for 45 days. Various parameters were estimated including fasting blood glucose (FBG), serum lipid profile, oxidative stress markers, antioxidant enzymes and expression of insulin signaling molecules in diabetic gastrocnemius muscle. Stevioside treatment improved glucose and insulin tolerances in diabetic rats and restored their elevated levels of FBG, serum insulin and lipid profile to normalcy. In diabetic gastrocnemius muscles, Setvioside normalized the altered levels of lipid peroxidase (LPO), hydrogen peroxide (H₂O₂) and hydroxyl radical (OH*), antioxidant enzymes (CAT, SOD, GPx and GSH) and molecules of insulin signaling including insulin receptor (IR), insulin receptor substrate-1 (IRS-1) and Akt mRNA levels. Furthermore, Stevioside enhanced glucose uptake (GU) and oxidation in diabetic muscles by augmenting glucose transporter 4 (GLUT 4) synthesis very effectively in a similar way to metformin. Results of molecular docking analysis evidenced the higher binding affinity with IRS-1 and GLUT 4. Stevioside effectively inhibits oxidative stress and promotes glucose uptake in diabetic gastrocnemius muscles by activating IR/IRS-1/Akt/GLUT 4 pathway. The results of the in silico investigation matched those of the in vivo study. Hence, Stevioside could be considered as a promising phytomedicine to treat T2DM.

Alkaloids from lotus (Nelumbo nucifera): recent advances in biosynthesis, pharmacokinetics, bioactivity, safety, and industrial applications

Different parts of lotus (Nelumbo nucifera Gaertn.) including the seeds, rhizomes, leaves, and flowers, are used for medicinal purposes with health promoting and illness preventing benefits. The presence of active chemicals such as alkaloids, phenolic acids, flavonoids, and terpenoids (particularly alkaloids) may account for this plant's pharmacological effects. In this review, we provide a comprehensive overview and summarize up-to-date research on the biosynthesis, pharmacokinetics, and bioactivity of lotus alkaloids as well as their safety. Moreover, the potential uses of lotus alkaloids in the food, pharmaceutical, and cosmetic sectors are explored. Current evidence shows that alkaloids, mainly consisting of aporphines, 1-benzylisoquinolines, and bisbenzylisoquinolines, are present in different parts of lotus. The bioavailability of these alkaloids is relatively low in vivo but can be enhanced by technological modification using nanoliposomes, liposomes, microcapsules, and emulsions. Available data highlights their therapeutic and preventive effects on obesity, diabetes, neurodegeneration, cancer, cardiovascular disease, etc. Additionally, industrial applications of lotus alkaloids include their use as food, medical, and cosmetic ingredients in tea, other beverages, and healthcare products; as lipid-lowering, anticancer, and antipsychotic drugs; and in facial masks, toothpastes, and shower gels. However, their clinical efficacy and safety remains unclear; hence, larger and longer human trials are needed to achieve their safe and effective use with minimal side effects.

An updated review on pharmacological properties of neferine-A bisbenzylisoquinoline alkaloid from Nelumbo nucifera

Phytochemicals have recently received a lot of recognition for their pharmacological activities such as anticancer, chemopreventive, and cardioprotective properties. In traditional Indian and Chinese medicine, parts of lotus (Nelumbo nucifera) such as lotus seeds, fruits, stamens, and leaves are used for treating various diseases. Neferine is a bisbenzylisoquinoline alkaloid, a major component from the seed embryos of N. nucifera. Neferine is effective in the treatment of high fevers and hyposomnia, as well as arrhythmia, platelet aggregation, occlusion, and obesity. Neferine has been found to have a variety of therapeutic effects such as anti-inflammatory, anti-oxidant, anti-hypertensive, anti-arrhythmic, anti-platelet, anti-thrombotic, anti-amnesic, and negative inotropic. Neferine also exhibited anti-anxiety effects, anti-cancerous, and chemosensitize to other anticancer drugs like doxorubicin, cisplatin, and taxol. Induction of apoptosis, autophagy, and cell cycle arrest are the key pathways that underlying the anticancer activity of neferine. Therefore, the present review summarizes the neferine biosynthesis, pharmacokinetics, and its effects in myocardium, cancer, chemosensitizing to cancer drug, central nervous system, diabetes, inflammation, and kidney diseases. PRACTICAL APPLICATIONS: Natural phytochemical is gaining medicinal importance for a variety of diseases like including cancer, neurodegenerative disorder, diabetes, and inflammation. Alkaloids and flavonoids, which are abundantly present in Nelumbo nucifera have many therapeutic applications. Neferine, a bisbenzylisoquinoline alkaloid from N. nucifera has many pharmacological properties. This present review was an attempt to compile an updated pharmacological action of neferine in different disease models in vitro and in vivo, as well as to summarize all the collective evidence on the therapeutic potential of neferine.

Identification of C21 Steroidal Glycosides from Gymnema sylvestre (Retz.) and Evaluation of Their Glucose Uptake Activities

Gymnema sylvestre (Retz.) Schult is a multi-purpose traditional medicine that has long been used for the treatment of various diseases. To discover the potential bioactive composition of G. sylvestre, a chemical investigation was thus performed. In this research, four new C₂₁ steroidal glycosides sylvepregosides A-D (1–4) were isolated along with four known compounds, gymnepregoside H (5), deacetylkidjoladinin (6), gymnepregoside G (7) and gymnepregoside I (8), from the ethyl acetate fraction of G. sylvestre. The structures of the new compounds were established by extensive 1D and 2D nuclear magnetic resonance (NMR) spectra with mass spectroscopy data. Compounds 1–6 promoted glucose uptake by the range of 1.10- to 2.37-fold, respectively. Compound 1 showed the most potent glucose uptake, with 1.37-fold enhancement. Further study showed that compounds 1 and 5 could promote GLUT-4 fusion with the plasma membrane in L6 cells. The result attained in this study indicated that the separation and characterization of these compounds play an important role in the research and development of new anti-diabetic drugs and pharmaceutical industry.

Plants Secondary Metabolites as Blood Glucose-Lowering Molecules

Recently, significant advances in modern medicine and therapeutic agents have been achieved. However, the search for effective antidiabetic drugs is continuous and challenging. Over the past decades, there has been an increasing body of literature related to the effects of secondary metabolites from botanical sources on diabetes. Plants-derived metabolites including alkaloids, phenols, anthocyanins, flavonoids, stilbenoids, saponins, tannins, polysaccharides, coumarins, and terpenes can target cellular and molecular mechanisms involved in carbohydrate metabolism. In addition, they can grant protection to pancreatic beta cells from damage, repairing abnormal insulin signaling, minimizing oxidative stress and inflammation, activating AMP-activated protein kinase (AMPK), and inhibiting carbohydrate digestion and absorption. Studies have highlighted many bioactive naturally occurring plants' secondary metabolites as candidates against diabetes. This review summarizes the current knowledge compiled from the latest studies published during the past decade on the mechanism-based action of plants-derived secondary metabolites that can target various metabolic pathways in humans against diabetes. It is worth mentioning that the compiled data in this review will provide a guide for researchers in the field, to develop candidates into environment-friendly effective, yet safe antidiabetics.

Davidones F and G, Two Novel Flavonoids from Sophora davidii (Franch.) Skeels

An unprecedented novel flavanone davidone F (1) with a seven-membered ring side chain, and a novel flavanonol davidone G (2), along with 11 known flavonoids, were isolated from the ethyl acetate fraction of Sophora davidii (Franch.) Skeels. Their planar structures were established by UV, IR, HRESIMS, 1D and 2D NMR data. The relative configurations of 1 and 2 were determined by calculation of NMR chemical shift values, the absolute configuration of 1 and 2 were assigned by comparing their experimental and calculated electronic circular dichroism (ECD) spectra. Moreover, compounds 1–13 were screened for the translocation activity of glucose transporter 4 (GLUT-4), and the fluorescence intensity was increased to the range of 1.56 and 2.79 folds. Compounds 1 and 2 showed moderate GLUT-4 translocation activity with 1.64 and 1.79 folds enhancement, respectively, at a concentration of 20 μg/mL.

Vitamin D Levels and the Risk of Posttransplant Diabetes Mellitus After Kidney Transplantation

Introduction:

Given the burden of posttransplant diabetes mellitus and the high prevalence of low vitamin D levels in kidney transplant recipients, it is reasonable to consider vitamin D as a novel and potentially modifiable risk factor in this patient population.

Research question:

To determine the association between 25- hydroxyvitamin D (25(OH)D) level and posttransplant diabetes among kidney transplant recipients. Design: In a multi-center cohort study of 442 patients who received a kidney transplant between January 1, 2005 and December 31, 2010, serum samples within one-year before transplant were analyzed for 25(OH)D levels. The association between 25(OH)D and posttransplant diabetes were examined in Cox proportional hazard models.

Results:

The median 25(OH)D level was 66 nmol/L. The cumulative probability of diabetes at 12-months by quartiles of 25(OH)D (< 42, 42 to 64.9, 65 to 94.9, and > 95 nmol/L) were 23.4%, 26.9%, 21.4%, and 15.6%, respectively. Compared to the highest 25(OH)D quartile, hazard ratios (95% CI) for the risk were 1.85 (1.03, 3.32), 2.01 (1.12, 3.60), 1.77 (0.96, 3.25) across the first to third quartiles, respectively. The associations were accentuated in a model restricted to patients on tacrolimus. When modeled as a continuous variable, 25(OH)D levels were significantly associated with a higher risk of diabetes (hazard ratio 1.06, 95% CI: 1.01, 1.13 per 10 nmol/L decrease).

Discussion:

Serum 25(OH)D was an independent predictor of posttransplant diabetes in kidney transplant recipients. These results may inform the design of trials using vitamin D to reduce the risk in kidney transplant recipients.

Cassia Abbreviata Enhances Glucose Uptake and Glucose Transporter 4 Translocation in C2C12 Mouse Skeletal Muscle Cells

Background.

This study aim at assessing C. abbreviata aqueous extracts for its potential to exhibit anti-diabetic activity in skeletal muscle cells. In addition to the toxicological and glucose absorption studies, the action of C. abbreviata extracts on some major genes involved in the insulin signaling pathway was established.

Methods.

The in vitro cytotoxic effects C. abbreviata was evaluated on muscle cells using the MTT assay and the in vitro glucose uptake assay conducted using a modified glucose oxidase method described by Van de Venter et al. (2008). The amount of GLUT-4 on cell surfaces was estimated quantitatively using the flow cytometry technique. Real time quantitative PCR (RT-qPCR) was used to determine the expression of GLUT-4, IRS-1, PI3 K, Akt1, Akt2, PPAR-γ.

Results.

Cytotoxicity tests revealed that all extracts tested at various concentrations were non-toxic (LC₅₀ > 5000). Aqueous extracts of leaves, bark and seeds resulted in a dose-dependent increase in glucose absorption by cells, after 1 h, 3 h and 6 h incubation period. Extracts of all three plant parts had the best effect after 3 h incubation, with the leaf extract showing the best activity across time (Glucose uptake of 29%, 56% and 42% higher than untreated control cells after treatment with 1 mg/ml extract at 1 h, 3 h and 6 h, respectively). All extracts, with the exception 500 µg/ml seed extract, induced a two-fold increase in GLUT-4 translocation while marginally inducing GLUT-10 translocation in the muscle cells. The indirect immunofluorescence confirmed that GLUT-4 translocation indeed occurred. There was an increased expression of GLUT-4, IRS1 and PI3 K in cells treated with insulin and bark extract as determined by the RT-qPCR.

Conclusion.

The study reveals that glucose uptake involves GLUT-4 translocation through a mechanism that is likely to involve the upstream effectors of the PI3-K/Akt pathway.

Antidiabetic effect of a flavonoid-rich extract from Sophora alopecuroides L. in HFD- and STZ- induced diabetic mice through PKC/GLUT4 pathway and regulating PPARα and PPARγ expression

HEADINGS ETHNOPHARMACOLOGICAL RELEVANCE

Sophora alopecuroides L. is a traditional ethnopharmacological plant, which is widely used in traditional Chinese medicine and Mongolian and Uighur medicine to ameliorate "thirst disease".

AIM OF THE STUDY

This study aimed to investigate the antidiabetic activities and mechanisms of a flavonoid-rich extract from Sophora alopecuroides L. (SA-FRE) both in vivo and vitro.

MATERIALS AND METHODS

The main six chemical constituents of SA-FRE were elucidated based on an off-line semi-preparative liquid chromatography nuclear magnetic resonance (LC-NMR) protocol. Myc-GLUT4-mOrange-L6 cell models and mouse model with diabetes induced by high-fat diet combined with STZ injection were respectively adopted to investigate the antidiabetic effects of SA-FRE both in vitro and vivo.

RESULTS

In vivo, 4-week treatment of SA-FRE ameliorated hyperglycemia, dyslipidemia, and insulin resistance in diabetic mice. Mechanically, SA-FRE regulated PPARα and PPARγ expression in white adipose tissue (WAT) and liver, thereby ameliorating dyslipidemia. Moreover, SA-FRE increased the phosphorylation of PKC and further stimulated the GLUT4 expression in WAT and skeletal muscle, thus increasing the glucose utilization in vivo. In vitro, 50 μg/mL SA-FRE increased GLUT4 translocation to about 1.91-fold and glucose uptake to 1.82-fold in L6-myotubes. SA-FRE treatment increased the GLUT4 expression at both gene and protein levels. Furthermore, only Gö6983, a PKC inhibitor, reversed the SA-FRE-induced GLUT4 translocation and expression at the gene and protein levels.

CONCLUSIONS

Generally, SA-FRE ameliorated hyperglycemia, dyslipidemia, and insulin resistance partly through activating PKC/GLUT4 pathway and regulating PPARα and PPARγ expression.

Chemical Constituents from Roots of Sophora davidii (Franch.) Skeels and Their Glucose Transporter 4 Translocation Activities

Sophora davidii (Franch.) Skeels is a multi-purpose traditional medicine that has long been used for the treatment of various diseases. To discover the potential bioactive composition of S. davidii, a chemical investigation was thus performed. In this research, two new stilbene oligomers, Davidiol E–F (1–2), one new 4-aryl-substituted isoflavan Davidinin A (3), and one new 2-arylbenzofuran dimer, Shandougenine C (4), as well as six known compounds (5–10) were obtained from the ethyl acetate fraction of Sophora davidii (Franch.) Skeels. The structures of new compounds were established by extensive 1D and 2D nuclear magnetic resonance (NMR) spectra with mass spectroscopy data. The absolute configuration of 1–3 was assigned by comparing its experimental and calculated electronic circular dichroism (ECD) spectra. Compounds 1–10 promoted glucose transporter 4 (GLUT-4) translocations by the range of 1.28–2.60 folds, respectively. Compound 9 showed the most potent glucose transporter 4 translocations with 1.60 fold enhancement. The result attained in this study indicated that the separation and characterization of these compounds plays an important role in the research and development of new anti-diabetic drugs and pharmaceutical industry.

Red rice koji extract alleviates hyperglycemia by increasing glucose uptake and glucose transporter type 4 levels in skeletal muscle in two diabetic mouse models

Background

Red rice koji (RRK), prepared by growing Monascus species on steamed rice, has been reported to lower blood glucose levels in diabetic animal models. However, the action mechanism is not yet completely understood.

Objective

The objective of this study was to examine the mechanism underlying the hypoglycemic action of RRK extract in two diabetic animal models: the insulin-deficiency mice, where the insulin deficiency was induced by streptozotocin (STZ), and insulin-resistance mice, where the insulin resistance was induced by a high-fat diet (HFD).

Design

Low (12.5 mg/kg body weight [BW]) and high (50.0 mg/kg BW) doses of RRK extract were orally administered to the mice for 10 successive days (0.25 mL/day/mouse). The protein expression levels of glucose transporter type 4 (GLUT4) in the skeletal muscle and glucose transporter type 2 (GLUT2) in the liver were measured. Blood glucose (BG) levels of STZ-treated mice in insulin tolerance test (ITT) and BG and insulin levels of HFD-fed mice in intraperitoneal glucose tolerance test (IPGTT) were investigated.

Results

In the STZ-treated mice, oral administration of RRK extract lowered BG levels and food intake but increased plasma 1,5-anhydroglucitol level. Moreover, the RRK extract lowered the BG levels of STZ-treated mice as measured by ITT. In the HFD-fed mice, we confirmed that the orally administered RRK extract lowered the BG and the homeostasis model assessment index for insulin resistance. Furthermore, the RRK extract lowered the BG and insulin levels of HFD-fed mice in IPGTT. Regarding the protein levels of GLUT, the orally administered RRK extract increased the GLUT4 level in the skeletal muscle; however, the RRK extract did not alter the GLUT2 level in the liver of either the STZ-treated or the HFD-fed mice.

Discussion

Our study demonstrates that RRK extract can improve impaired glucose tolerance in mouse models of diabetes by enhancing GLUT4 expression in skeletal muscle.

Conclusion

These results suggest that RRK extract could potentially be a functional food for the treatment of diabetes mellitus.

New flavonoids from the roots of Sophora davidii (Franch.) Skeels and their glucose transporter 4 translocation activities

Five new flavanones, davidones A-E (1-5), one new isoflavonoid, cyclolicoisoflavones A₃ (8), together with seven known compounds were isolated from the petroleum ether and the ethyl acetate fractions of the roots of Sophora davidii (Franch.) Skeels. The structures of new compounds were established by 1D and 2D NMR and MS data. The absolute configuration of 1-5 was assigned by NMR calculations and comparing its experimental and calculated ECD spectra. Flavanones were the main active principles responsible for the glucose transporter 4 (GLUT-4) translocation activities of SD-PE and SD-EtOAc. Compounds 1-7 and acacetin (12) promoted GLUT-4 translocation by the range of 1.35-3.00 folds, respectively.

Anti-Obesity and Antidiabetic Effects of Nelumbinis Semen Powder in High-Fat Diet-Induced Obese C57BL/6 Mice

Nelumbinis Semen (NS, the seeds of Nelumbo nucifera) extract is a traditional Korean medicine with anti-oxidant activity. The present study examined the anti-obesity and antidiabetic effects of NS powder in high-fat diet (HFD)-induced obese C57BL/6 mice. Mice (n = 8/group) were fed a normal diet (CON), HFD, HFD containing 5% NS powder (HFD-NS5%), or HFD containing 10% NS powder (HFD-NS10%) for 12 weeks. Food intake was relatively higher in groups HFD-NS5% and HFD-NS10%, while the food efficiency ratio was highest in group HFD (p < 0.05). HFD-NS5% reduced the body weight (-39.1%) and fat weight (-26.6%), including epididymal fat and perirenal fat, and lowered the serum triglyceride levels (-20.6%) compared with HFD. Groups HFD-NS5% and HFD-NS10% showed hepatoprotective properties, reducing the serum ALT levels (p < 0.05) and fat globules (size and number) in the liver compared with group HFD. HFD-NS5% and HFD-NS10% regulated the blood glucose, improved the glucose intolerance, and showed a 12.5% and 15.0% reduction in the area under the curve (AUC) of intraperitoneal glucose tolerance test (IPGTT), and a 26.8% and 47.3% improvement in homeostatic model assessment insulin resistance (HOMA-IR), respectively, compared with HFD (p < 0.05). Regarding the expressions of genes related to anti-obesity and antidiabetes, there was a 1.7- and 1.3-fold increase in PPAR-α protein expression, 1.4- and 1.6-fold increase in PPAR-γ protein expression, and 0.7- and 0.6-fold decrease in TNF-α protein expression, respectively, following HFD-NS5% and HFD-NS10% treatments, compared with HFD, and GLUT4 protein expression increased relative to CON (p < 0.05). These results comprehensively provide the fundamental data for NS powder's functional and health-promoting benefits associated with anti-obesity and antidiabetes.

The Molecular Mechanisms Underlying Mitochondria-Associated Endoplasmic Reticulum Membrane-Induced Insulin Resistance

Mitochondria and the endoplasmic reticulum (ER) are connected at multiple sites via what are known as mitochondria-associated ER membranes (MAMs). These associations are known to play an important role in maintaining cellular homeostasis. Impaired MAM signaling has wide-ranging effects in many diseases, such as obesity, diabetes, and neurodegenerative disorders. Accumulating evidence has suggested that MAMs influence insulin signaling through different pathways, including those associated with Ca²⁺ signaling, lipid metabolism, mitochondrial function, ER stress responses, and inflammation. Altered MAM signaling is a common feature of insulin resistance in different tissues, including the liver, muscle, and even the brain. In the liver, MAMs are key glucose-sensing regulators and have been proposed to be a hub for insulin signaling. Impaired MAM integrity has been reported to disrupt hepatic responses to changes in glucose availability during nutritional transition and to induce hepatic insulin resistance. Meanwhile, these effects can be rescued by the reinforcement of MAM interactions. In contrast, several studies have proposed that enhanced ER-mitochondria connections are detrimental to hepatic insulin signaling and can lead to mitochondrial dysfunction. Thus, given these contradictory results, the role played by the MAM in the regulation of hepatic insulin signaling remains elusive. Similarly, in skeletal muscle, enhanced MAM formation may be beneficial in the early stage of diabetes, whereas continuous MAM enhancement aggravates insulin resistance. Furthermore, recent studies have suggested that ER stress may be the primary pathway through which MAMs induce brain insulin resistance, especially in the hypothalamus. This review will discuss the possible mechanisms underlying MAM-associated insulin resistance as well as the therapeutic potential of targeting the MAM in the treatment of type 2 diabetes.