Preparation of a Novel Oat ß-Glucan-Chromium(III) Complex and Its Hypoglycemic Effect and Mechanism.

This study synthesized a novel oat ß-glucan (OBG)-Cr(III) complex (OBG-Cr(III)) and explored its structure, inhibitory effects on α-amylase and α-glucosidase, and hypoglycemic activities and mechanism in vitro using an insulin-resistant HepG2 (IR-HepG2) cell model. The Cr(III) content in the complex was found to be 10.87%. The molecular weight of OBG-Cr(III) was determined to be 7.736 × 104 Da with chromium ions binding to the hydroxyl groups of OBG. This binding resulted in the increased asymmetry and altered spatial conformation of the complex along with significant changes in morphology and crystallinity. Our findings demonstrated that OBG-Cr(III) exhibited inhibitory effects on α-amylase and α-glucosidase. Furthermore, OBG-Cr(III) enhanced the insulin sensitivity of IR-HepG2 cells, promoting glucose uptake and metabolism more efficiently than OBG alone. The underlying mechanism of its hypoglycemic effect involved the modulation of the c-Cbl/PI3K/AKT/GLUT4 signaling pathway, as revealed by Western blot analysis. This research not only broadened the applications of OBG but also positioned OBG-Cr(III) as a promising Cr(III) supplement with enhanced hypoglycemic benefits.

Evaluation of skeletal muscle function in male rats with doxorubicin-induced myopathy following various exercise techniques: the significant role of glucose transporter 4.

A common anthracycline antibiotic used to treat cancer patients is doxorubicin (DOX). One of the effects of DOX therapy is skeletal muscle fatigue. Our goal in this research was to study the beneficial effect of exercise on DOX-induced damaged muscle fibers and compare the effect of different exercise strategies (prophylactic, post- toxicity and combined) on DOX toxicity. Five groups were created from 40 male rats: group I, control group; group II, DOX was administered intraperitoneally for 2 weeks over 6 equal injections (each 2.5 mg/kg); group III, rats trained for 3 weeks before DOX; group IV, rats trained for 8 weeks after DOX; and group V, rats were trained for 3 weeks before DOX followed by 8 weeks after. Measures of oxidative damage (H2O2, catalase), inflammation (TNF-α), and glucose transporter 4 (GLUT4) expression on skeletal muscle were assessed. Also, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) was estimated. Skeletal performance was evaluated by contraction time (CT), half relaxation time (1/2 RT), and force-frequency relationship by the end of this research. The current study demonstrated a detrimental effect of DOX on skeletal performance as evidenced by a significant increase in CT and 1/2 RT compared to control; in addition, H2O2, TNF-α, and HOMA-IR were significantly increased with a significant decrease in GLUT4 expression and catalase activity. Combined exercise therapy showed a remarkable improvement in skeletal muscle performance, compared to DOX, CT, and 1/2 RT which were significantly decreased; H2O2 and TNF-α were significantly decreased unlike catalase antioxidant activity that significantly increased; in addition, skeletal muscle glucose metabolism was significantly improved as GLUT4 expression significantly increased and HOMA-IR was significantly decreased. Exercise therapy showed significant improvement in all measured parameters relative to DOX. However, combined exercise therapy showed the best improvement relative to both pre-exercise and post-exercise groups.

Two Prenylated Chalcones, 4-Hydroxyderricin, and Xanthoangelol Prevent Postprandial Hyperglycemia by Promoting GLUT4 Translocation via the LKB1/AMPK Signaling Pathway in Skeletal Muscle Cells.

SCOPE: Stimulation of glucose uptake in the skeletal muscle is crucial for the prevention of postprandial hyperglycemia. Insulin and certain polyphenols enhance glucose uptake through the translocation of glucose transporter 4 (GLUT4) in the skeletal muscle. The previous study reports that prenylated chalcones, 4-hydroxyderricin (4-HD), and xanthoangelol (XAG) promote glucose uptake and GLUT4 translocation in L6 myotubes, but their underlying molecular mechanism remains unclear. This study investigates the mechanism in L6 myotubes and confirms antihyperglycemia by 4-HD and XAG. METHODS AND RESULTS: In L6 myotubes, 4-HD and XAG promote glucose uptake and GLUT4 translocation through the activation of adenosine monophosphate-activated protein kinase (AMPK) and liver kinase B1 (LKB1) signaling pathway without activating phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) and Janus kinases (JAKs)/signal transducers and activators of transcriptions (STATs) pathways. Moreover, Compound C, an AMPK-specific inhibitor, as well as siRNA targeting AMPK and LKB1 completely canceled 4-HD and XAG-increased glucose uptake. Consistently, oral administration of 4-HD and XAG to male ICR mice suppresses acute hyperglycemia in an oral glucose tolerance test. CONCLUSION: In conclusion, LKB1/AMPK pathway and subsequent GLUT4 translocation in skeletal muscle cells are involved in Ashitaba chalcone-suppressed acute hyperglycemia.

The P2Y2 receptor mediates terminal adipocyte differentiation and insulin resistance: Evidence for a dual G-protein coupling mode.

Several P2Y nucleotide receptors have been shown to be involved in the early stage of adipocyte differentiation in vitro and insulin resistance in obese mice; however, the exact receptor subtype(s) and its underlying molecular mechanism in relevant human cells are unclear. Here, using human primary visceral preadipocytes as a model, we found that during preadipocyte-to-mature adipocyte differentiation, the P2Y2 nucleotide receptor (P2Y2R) was the most upregulated subtype among the eight known P2Y receptors and the only one further dramatically upregulated after inflammatory TNFα treatment. Functional studies indicated that the P2Y2R induced intracellular Ca2+, ERK1/2, and JNK signaling but not the p38 pathway. In addition, stimulation of the P2Y2R suppressed basal and insulin-induced phosphorylation of AKT, accompanied by decreased GLUT4 membrane translocation and glucose uptake in mature adipocytes, suggesting a role of P2Y2R in insulin resistance. Mechanistically, we found that activation of P2Y2R did not increase lipolysis but suppressed PIP3 generation. Interestingly, activation of P2Y2R triggered Gi-protein coupling, and pertussis toxin pretreatment largely inhibited P2Y2R-mediated ERK1/2 signaling and cAMP suppression. Further, treatment of the cells with AR-C 118925XX, a selective P2Y2R antagonist, significantly inhibited adipogenesis, and P2Y2R knockout decreased mouse body weight gain with smaller eWAT mass infiltrated with fewer macrophages as compared to WT mice in response to a Western diet. Thus, we revealed that terminal adipocyte differentiation and inflammation selectively upregulate P2Y2R expression and that P2Y2R mediates insulin resistance by suppressing the AKT signaling pathway, highlighting P2Y2R as a potential new drug target to combat obesity and type-2 diabetes.

Akt may associate with insulin-responsive vesicles via interaction with sortilin.

Insulin-responsive vesicles (IRVs) deliver the glucose transporter Glut4 to the plasma membrane in response to activation of the insulin signaling cascade: insulin receptor-IRS-PI3 kinase-Akt-TBC1D4-Rab10. Previous studies have shown that Akt, TBC1D4, and Rab10 are compartmentalized on the IRVs. Although functionally significant, the mechanism of Akt association with the IRVs remains unknown. Using pull-down assays, immunofluorescence microscopy, and cross-linking, we have found that Akt may be recruited to the IRVs via the interaction with the juxtamembrane domain of the cytoplasmic C terminus of sortilin, a major IRV protein. Overexpression of full-length sortilin increases insulin-stimulated phosphorylation of TBC1D4 and glucose uptake in adipocytes, while overexpression of the cytoplasmic tail of sortilin has the opposite effect. Our findings demonstrate that the IRVs represent both a scaffold and a target of insulin signaling.

AS160 expression, but not AS160 Serine-588, Threonine-642, and Serine-704 phosphorylation, is essential for elevated insulin-stimulated glucose uptake by skeletal muscle from female rats after acute exercise.

One exercise session can increase subsequent insulin-stimulated glucose uptake (ISGU) by skeletal muscle in both sexes. We recently found that muscle expression and phosphorylation of key sites of Akt substrate of 160 kDa (AS160; also called TBC1D4) are essential for the full-exercise effect on postexercise-ISGU (PEX-ISGU) in male rats. In striking contrast, AS160's role in increased PEX-ISGU has not been rigorously tested in females. Our rationale was to address this major knowledge gap. Wild-type (WT) and AS160-knockout (KO) rats were either sedentary or acutely exercised. Adeno-associated virus (AAV) vectors were engineered to express either WT-AS160 or AS160 mutated on key serine and threonine residues (Ser588, Thr642, and Ser704) to alanine to prevent their phosphorylation. AAV vectors were delivered to the muscle of AS160-KO rats to determine if WT-AS160 or phosphorylation-inactivated AS160 would influence PEX-ISGU. AS160-KO rats have lower skeletal muscle abundance of the GLUT4 glucose transporter protein. This GLUT4 deficit was rescued using AAV delivery of GLUT4 to determine if eliminating muscle GLUT4 deficiency would normalize PEX-ISGU. The novel results were as follows: (1) AS160 expression was required for greater PEX-ISGU; (2) rescuing muscle AS160 expression in AS160-KO rats restored elevated PEX-ISGU; (3) AS160's essential role for the postexercise increase in ISGU was not attributable to reduced muscle GLUT4 content; and (4) AS160 phosphorylation on Ser588, Thr642, and Ser704 was not essential for greater PEX-ISGU. In conclusion, these novel findings revealed that three phosphosites widely proposed to influence PEX-ISGU are not required for this important outcome in female rats.

Mung bean peptides promote glucose uptake via Jak2 activation in L6 myotubes.

Mung beans are among the important edible legumes cultivated in Asia, Southern Europe, and Northern America. Mung beans contain 20-30% proteins with high digestibility and possess biological activities, but detailed health beneficial functions are not fully understood yet. In this study, we report the isolation and identification of active peptides from mung beans which promote glucose uptake and elucidate their mechanism in L6 myotubes. HTL, FLSSTEAQQSY, and TLVNPDGRDSY were isolated and identified as active peptides. These peptides promoted the translocation of glucose transporter 4 (GLUT4) to the plasma membrane. The tripeptide HTL promoted glucose uptake through the activation of adenosine monophosphate-activated protein kinase, while the oligopeptides FLSSTEAQQSY and TLVNPDGRDSY through the activation of the PI3K/Akt pathway. Furthermore, these peptides promoted the phosphorylation of Jak2 via interaction with the leptin receptor. Thus, mung bean is a promising functional food for the prevention of hyperglycemia and type 2 diabetes through promoting glucose uptake accompanied by JAK2 activation in the muscle cells.

The SWGEDWGEIW from Soybean Peptides Reduces Insulin Resistance in 3T3-L1 Adipocytes by Activating p-Akt/GLUT4 Signaling Pathway.

Diabetes mellitus, a group of metabolic disorders characterized by persistent hyperglycemia, affects millions of people worldwide and is on the rise. Dietary proteins, from a wide range of food sources, are rich in bioactive peptides with anti-diabetic properties. Notably, the protective mechanism of the single peptide SWGEDWGEIW (TSP) from soybean peptides (SBPs) on insulin resistance of adipocytes in an inflammatory state was investigated by detecting the lipolysis and glucose absorption and utilization of adipocytes. The results showed that different concentrations of TSP (5, 10, 20 µg/mL) intervention can reduce 3T3-L1 adipocytes' insulin resistance induced by inflammatory factors in a dose-dependent manner and increase glucose utilization by 34.2 ± 4.6%, 74.5 ± 5.2%, and 86.7 ± 6.1%, respectively. Thus, TSP can significantly alleviate the lipolysis of adipocytes caused by inflammatory factors. Further mechanism analysis found that inflammatory factors significantly reduced the phosphorylation (p-Akt) of Akt, two critical proteins of glucose metabolism in adipocytes, and the expression of GLUT4 protein downstream, resulting in impaired glucose utilization, while TSP intervention significantly increased the expression of these two proteins. After pretreatment of adipocytes with PI3K inhibitor (LY294002), TSP failed to reduce the inhibition of p-Akt and GLUT4 expression in adipocytes. Meanwhile, the corresponding significant decrease in glucose absorption and the increase in the fat decomposition of adipocytes indicated that TSP reduced 3T3-L1 adipocytes' insulin resistance by specifically activating the p-Akt/GLUT4 signal pathway. Therefore, TSP has the potential to prevent obesity-induced adipose inflammation and insulin resistance.

Tilorone increases glucose uptake in vivo and in skeletal muscle cells by enhancing Akt2/AS160 signaling and glucose transporter levels.

Skeletal muscle plays a major role in whole-body glucose metabolism. Insulin resistance in skeletal muscle is characterized by decreased insulin-stimulated glucose uptake resulting from impaired intracellular trafficking and decreased glucose transporter 4 (GLUT4) expression. In this study, we illustrated that tilorone, a low-molecular-weight antiviral agent, improves glucose uptake in vitro and in vivo. Tilorone increased bone morphogenetic protein (BMP) signaling in C2C12 myoblasts, the transcription of multiple BMPs (BMP2, BMP4, BMP7, and BMP14), Smad4 expression, and the phosphorylation of BMP-mediated Smad1/5/8. The activation of Akt2/AS160 (TBC1D4) signaling, the critical regulator of GLUT4 translocation, was also increased, as well as the levels of GLUT4 and GLUT1, leading to enhanced uptake of the radioactively labeled glucose analog 18 F-fluoro-2-deoxyglucose (18 FDG). However, this excess glucose content did not result in increased ATP formation by mitochondrial respiration; both basal and ATP-linked respiration were diminished, thereby contributing to the induction of AMPK. In differentiated myotubes, AS160 phosphorylation and 18 FDG uptake also increased. Moreover, tilorone administration further increased insulin-stimulated phosphorylation of Akt2 and glucose uptake of myotubes indicating an insulin-sensitizing effect. Importantly, during in vivo experiments, the systemic administration of tilorone resulted in increased 18 FDG uptake of skeletal muscle, liver, and adipose tissue in C57BL/6 mice. Our results provide new perspectives for the treatment of type 2 diabetes, which has a limited number of treatments that regulate protein expression or translocation.

GLUT4 mediates the protective function of gastrodin against pressure overload-induced cardiac hypertrophy.

Gastrodia elata exhibits extensive pharmacological activity; its extract gastrodin (GAS) has been used clinically to treat cardiovascular diseases. In the present study, we examined the effect of GAS in a mice model of pathological cardiac hypertrophy, which was induced using transverse aortic constriction (TAC). Male C57BL/6 J mice underwent either TAC or sham surgery. GAS was administered post-surgically for 6 weeks and significantly improved the deterioration of cardiac contractile function caused by pressure overload, cardiac hypertrophy, and fibrosis in mice. Treatment with GAS for 6 weeks upregulated myosin heavy chain α and down-regulated myosin heavy chain ß and atrial natriuretic peptide, while insulin increased the effects of GAS against cardiac hypertrophy. In vitro studies showed that GAS could also protect phenylephrine-induced cardiomyocyte hypertrophy, and these effects were attenuated by BAY-876, and increased by insulin. Taken together, our results suggest that the anti-hypertrophic effect of gastrodin depends on its entry into cardiomyocytes through GLUT4.

A role for ß-catenin in diet-induced skeletal muscle insulin resistance.

A central characteristic of insulin resistance is the impaired ability for insulin to stimulate glucose uptake into skeletal muscle. While insulin resistance can occur distal to the canonical insulin receptor-PI3k-Akt signaling pathway, the signaling intermediates involved in the dysfunction are yet to be fully elucidated. ß-catenin is an emerging distal regulator of skeletal muscle and adipocyte insulin-stimulated GLUT4 trafficking. Here, we investigate its role in skeletal muscle insulin resistance. Short-term (5-week) high-fat diet (HFD) decreased skeletal muscle ß-catenin protein expression 27% (p = 0.03), and perturbed insulin-stimulated ß-cateninS552 phosphorylation 21% (p = 0.009) without affecting insulin-stimulated Akt phosphorylation relative to chow-fed controls. Under chow conditions, mice with muscle-specific ß-catenin deletion had impaired insulin responsiveness, whereas under HFD, both mice exhibited similar levels of insulin resistance (interaction effect of genotype × diet p < 0.05). Treatment of L6-GLUT4-myc myocytes with palmitate lower ß-catenin protein expression by 75% (p = 0.02), and attenuated insulin-stimulated ß-catenin phosphorylationS552 and actin remodeling (interaction effect of insulin × palmitate p < 0.05). Finally, ß-cateninS552 phosphorylation was 45% lower in muscle biopsies from men with type 2 diabetes while total ß-catenin expression was unchanged. These findings suggest that ß-catenin dysfunction is associated with the development of insulin resistance.

Akt substrate of 160 kDa is essential for the calorie restriction-induced increase in insulin-stimulated glucose uptake by skeletal muscle of female rats.

We evaluated effects of calorie restriction (CR; consuming 65% of ad libitum (AL) intake) for 8 weeks on female wildtype (WT) and Akt substrate of 160 kDa knockout (AS160-KO) rats. Insulin-stimulated glucose uptake (ISGU) was determined in isolated epitrochlearis muscles incubated with 0, 50, 100, or 500 µU/mL insulin. Phosphorylation of key insulin signaling proteins that control ISGU (Akt and AS160) was assessed by immunoblotting (Akt phosphorylation on Threonine-308, pAktThr308 and Serine-473, pAktSer473; AS160 phosphorylation on Serine-588, pAS160Ser588, and Threonine-642, pAS160Thr642). Abundance of proteins that regulate ISGU (GLUT4 glucose transporter protein and hexokinase II) was also determined by immunoblotting. The major results were as follows: (i) WT-CR versus WT-AL rats had greater ISGU with 100 and 500 µU/mL insulin; (ii) CR versus WT-AL rats had greater GLUT4 protein abundance; (iii) WT-CR versus WT-AL rats had greater pAktThr308 with 500 µU/mL insulin; (iv) WT-CR versus WT-AL rats did not differ for pAktSer473, pAS160Ser588, or pAS160Thr642 at any insulin concentration; (v) AS160-KO versus WT rats with each diet had lower ISGU at each insulin concentration, but not lower pAkt on either phosphosite; (vi) AS160-KO versus WT rats had lower muscle GLUT4 abundance regardless of diet; and (vii) AS160-KO-CR versus AS160-KO-AL rats did not differ for ISGU, GLUT4 abundance, pAkt on either phosphosite, or pAS160 on either phosphosite. These novel results demonstrated that AS160 expression, but not greater pAS160 on key phosphosites, was essential for the CR-induced increases in muscle ISGU and GLUT4 abundance of female rats.

CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells.

The cellular repressor of adenovirus early region 1A-stimulated gene 1 (CREG1) is a secreted glycoprotein involved in cell differentiation and energy metabolism. It also binds to insulin-like growth factor 2 receptor (IGF2R), a protein implicated in muscle regeneration. However, whether CREG1 regulates the regeneration and metabolism of skeletal muscles via IGF2R remains unclear. This study investigates the role of CREG1 in skeletal muscle regeneration and glucose uptake in C2C12 myotubes and a cardiotoxin (CTX)-induced mouse skeletal muscle regeneration model. CTX-treated skeletal muscle showed significantly higher levels of IGF2R, CREG1, phospho-AMPKα Thr172, and GLUT4 proteins. Similarly, treatment of myotubes with CREG1 also stimulated AMPKα phosphorylation and GLUT4 expression. CREG1-induced AMPKα phosphorylation and 2DG uptake in myotubes were suppressed by IGF2R knockdown and Compound C, an AMPK inhibitor. These results suggest that CREG1 stimulates glucose uptake in skeletal muscles partially through AMPK activation. Hence, CREG1 plays an essential role in muscle regeneration by affecting glucose metabolism in skeletal muscles.

Kaempferol 3-O-rutinoside from Antidesma acidum Retz. Stimulates glucose uptake through SIRT1 induction followed by GLUT4 translocation in skeletal muscle L6 cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Antidesma acidum Retz, a perennial herb is known for its anti-diabetic potential among the traditional health care providers of the tribal communities of Manipur, India. Scientific validation of the ancient knowledge on traditional use of this plant with the help of modern tools and techniques can promote further research and its use in health care. AIM OF THE STUDY: Type 2 Diabetes (T2D) is a complex metabolic disorder and linked with hyperglycemia occurring from insufficiency in insulin secretion, action, or both. The aim of this study was to scientifically validate the traditional myth behind the uses of this plant material against diabetes. More specifically, it was aimed to determine the effect of methanolic extract of A. acidum leaves and/or any of its bioactive phytochemical(s), in enhancing insulin sensitization and subsequently stimulating the insulin signaling cascade of glucose metabolism. MATERIALS AND METHODS: Methanol was used for extraction from the leaf powder of A. acidum followed by bioactivity guided fractionation and isolation of most active component. Biological evaluation was performed to determine the glucose uptake ability against insulin resistance in skeletal muscle (L6) cells. To understand the detailed mechanism of actions of the purified compound, several molecular biology and structural biology experiments such as Western blot, siRNA transfection assay and molecular docking study were performed. RESULTS AND DISCUSSION: Bioactivity guided isolation of pure compound and spectral data analysis led us to identify the active component as Kaempferol 3-O-rutinoside (KOR) for the first time from the leaf of A. acidum. Over expression of NAD-dependent histone deacetylase, Sirtuin 1 (SIRT1) was observed following KOR treatment. SIRT1 plays an important role in the metabolic pathway and over expression of SIRT implies that it involves in insulin signaling directly or indirectly. Molecular docking and simulation study showed the strong involvement between KOR and SIRT1.Treatment with KOR resulted in significant over expression of SIRT1followed by upregulation of insulin-dependent p-IRS, AKT and AMPK signaling molecules, and stimulation of the GLUT4 translocation, which ultimately enhanced the glucose uptake in sodium palmitate-treated insulin resistant L6 myotubes. Further, the effect of KOR on IRS1, AKT and AMPK phosphorylation, GLUT4 translocation, and glucose uptake was attenuated in SIRT1-knockdown myotubes. CONCLUSION: Overall, the results of this study suggest that Kaempferol 3-O-rutinoside is the active component presents in the leaf of A. acidum which increases glucose consumption by inducing SIRT1 activation and consequently improves insulin sensitization. These results may find future applications in drug discovery research against T2DM.

A ~24 kDa protein isolated from protein isolates of Hawaijar, popular fermented soy food of North-East India exhibited promising antidiabetic potential via stimulating PI3K/AKT/GLUT4 signaling pathway of muscle glucose metabolism.

The present study investigated the antidiabetic potential of protein isolates from Hawaijar (HPI), a popular fermented soybean food of North-East India. Treatment with HPI significantly upregulated glucose uptake, glucose utilization, glucose-6-phosphate, and stimulated PI3K/AKT/GLUT4 pathway in high-glucose (HG)-treated myotubes. Signal silencing studies demonstrated that knockdown of insulin-dependent signaling molecule (IR) but not insulin-independent signaling molecule (AMPK) significantly inhibited HPI-induced activation of PI3K/AKT/GLUT4 pathway and glucose uptake in HG-treated myotubes. SDS-PAGE and immunoblotting analyses of HPI showed the reduction and/or absence of various subunits of 7S and 11S globulin protein and appearance of new proteins compared to respective non-fermented soy protein isolates. Using various chromatographic techniques, the present study further isolated a single protein (ISP, ~24 kDa) from HPI as one of the bioactive principles with promising glucose utilization potential via stimulating PI3K/AKT/GLUT4 pathway in HG-treated cells. ISP treatment along with insulin significantly stimulated PI3K/AKT/GLUT4 pathway and glucose uptake compared to either insulin or ISP alone treated cells against HG exposure suggesting the insulin sensitizing effect of ISP. Furthermore, ISP supplementation significantly reduced metabolic markers linked with diabetes in high-fructose high-fat diet-fed animal model of type 2 diabetes. This study demonstrated a novel molecular mechanism underlying the promising antidiabetic potential of HPI.

Queueing theory model of mTOR complexes' impact on Akt-mediated adipocytes response to insulin.

A queueing theory based model of mTOR complexes impact on Akt-mediated cell response to insulin is presented in this paper. The model includes several aspects including the effect of insulin on the transport of glucose from the blood into the adipocytes with the participation of GLUT4, and the role of the GAPDH enzyme as a regulator of mTORC1 activity. A genetic algorithm was used to optimize the model parameters. It can be observed that mTORC1 activity is related to the amount of GLUT4 involved in glucose transport. The results show the relationship between the amount of GAPDH in the cell and mTORC1 activity. Moreover, obtained results suggest that mTORC1 inhibitors may be an effective agent in the fight against type 2 diabetes. However, these results are based on theoretical knowledge and appropriate experimental tests should be performed before making firm conclusions.

BPA exposure in L6 myotubes increased basal glucose metabolism in an estrogen receptor-dependent manner but induced insulin resistance.

Exposure to bisphenol A (BPA) is associated with insulin resistance and type 2 diabetes (T2D). Since muscle insulin resistance is the primary defect in T2D, we aimed to determine whether BPA alters glucose metabolism in L6 muscle cells. L6 or L6-GLUT4-myc cells were exposed to 1-104 nM BPA or the vehicle (0.1% DMSO) for 7 days. BPA at 103-104 nM significantly decreased the levels of the muscle differentiation markers troponin- T and myosin heavy chain 3. Insulin-stimulated phosphorylation of Akt and GSK3, insulin-stimulated glucose uptake, and insulin-stimulated GLUT4 translocation were significantly decreased with 103-104 nM BPA. Basal glucose uptake and glycolysis (extracellular acidification rates measured by Seahorse XFe96) were increased with 103-104 nM BPA. Levels of ROS detoxifying enzymes were increased with BPA >10 nM, while catalase activity was increased with 103-104 nM BPA. However, BPA did not induce oxidative stress (measured by protein carbonylation and lipid peroxidation) nor mitochondrial dysfunction. The effects of BPA on basal glucose uptake and catalase activity, but not on insulin sensitivity, were restored when estrogen receptors (ERs) were inhibited with ICI. These findings suggest that high concentrations of BPA increase muscle glucose uptake through the ERs but induce insulin resistance through another pathway.

Quercetin ameliorated insulin resistance via regulating METTL3-mediated N6-methyladenosine modification of PRKD2 mRNA in skeletal muscle and C2C12 myocyte cell line.

BACKGROUND AND AIMS: N6-Methyladenosine (m6A) modification is involved in many pathological processes, including insulin resistance (IR). Quercetin (Que), a bioactive compound with strong antioxidant activity, has potential therapeutic effects on IR-related metabolic diseases. The aim of this study is to investigate the roles of m6A and Que in hyperinsulinemia. METHODS AND RESULTS: Male C57Bl/6 mice received a high-fat diet (HFD) for 8 weeks to establish an IR model. Que treatment reduced the body weight, blood glucose, plasma triglycerides (TG) and serum insulin, ameliorated IR, and decreased oxidative stress in HFD-fed mice. Cellular IR model was established in C2C12 cells by palmitic acid (PA) stimulation, and a noncytotoxic dose of Que was found to promote glucose uptake and inhibit oxidative stress. Moreover, methyltransferase-like 3 (METTL3) and serine-threonine kinase protein kinase D2 (PRKD2) was downregulated in skeletal muscle of HFD-fed mouse and in PA-induced C2C12 cells. The online bioinformatic tool SRAMP revealed that there were multiple m6A modification sites in the PRKD2 mRNA sequence. Downregulation of METTL3 enhanced PRKD2 expression by reducing m6A level and promoting mRNA stability in PRKD2 mRNA transcript. Que decreased m6A, METTL3, and phosphorylated insulin receptor substrate 1 (p-IRS1) levels, increased the protein expression of PRKD2, glucose transporter type 4 (GLUT4) and p-AKT, promoted glucose uptake, and reduced oxidative stress in PA-induced C2C12 cells. Moreover, METTL3 overexpression or PRKD2 silence reversed the inhibitory effects of Que on the levels of MDA and p-IRS1 and the promotive effects on glucose uptake, superoxide dismutase (SOD), GSH and GLUT4 and p-AKT levels. CONCLUSION: Que promoted glucose uptake, repressed oxidative stress and improved IR through METTL3-mediated m6A of PRKD2 mRNA.

Autocrine FGF1 signaling promotes glucose uptake in adipocytes.

Fibroblast growth factor 1 (FGF1) is an autocrine growth factor released from adipose tissue during over-nutrition or fasting to feeding transition. While local actions underlie the majority of FGF1's anti-diabetic functions, the molecular mechanisms downstream of adipose FGF receptor signaling are unclear. We investigated the effects of FGF1 on glucose uptake and its underlying mechanism in murine 3T3-L1 adipocytes and in ex vivo adipose explants from mice. FGF1 increased glucose uptake in 3T3-L1 adipocytes and epididymal WAT (eWAT) and inguinal WAT (iWAT). Conversely, glucose uptake was reduced in eWAT and iWAT of FGF1 knockout mice. We show that FGF1 acutely increased adipocyte glucose uptake via activation of the insulin-sensitive glucose transporter GLUT4, involving dynamic crosstalk between the MEK1/2 and Akt signaling proteins. Prolonged exposure to FGF1 stimulated adipocyte glucose uptake by MEK1/2-dependent transcription of the basal glucose transporter GLUT1. We have thus identified an alternative pathway to stimulate glucose uptake in adipocytes, independent from insulin, which could open new avenues for treating patients with type 2 diabetes.

A popular fermented soybean food of Northeast India exerted promising antihyperglycemic potential via stimulating PI3K/AKT/AMPK/GLUT4 signaling pathways and regulating muscle glucose metabolism in type 2 diabetes.

This study examined the antidiabetic efficacy of popular fermented soybean foods (FSF) of Northeast (NE) India. Results showed that among different FSF, aqueous extract of Hawaijar (AEH), a traditional FSF of Manipur, NE India, significantly augmented glucose utilization in cultured myotubes treated with high glucose (HG, 25 mM). Furthermore, AEH also upregulated glucose uptake, glucose-6-phosphate level, and phopho-PI3K/phospho-AKT/phospho-AMPK/GLUT4 protein expression in HG-treated myotubes. In vivo studies demonstrated that AEH supplementation (50, 100, or 200 mg/kg body weight/day, oral gavaging, 16 weeks) reduced body weight, fasting blood glucose, glycated hemoglobin, insulin resistance, and glucose intolerance in rats fed with high-fat diet (HFD). AEH supplementation stimulated phopho-PI3K/phospho-AKT/phospho-AMPK/GLUT4 signaling cascades involved in glucose metabolism of muscle tissues in diabetic rats. Chemical profiling of AEH (SDS-PAGE, immunoblotting, and HRMS) suggests the possible role of bioactive proteins/peptides and isoflavones underlying the antihyperglycemic potential AEH. Results from this study will be helpful for developing food-based prophylactics/therapeutics in managing hyperglycemia. PRACTICAL APPLICATIONS: Fermented soybean foods are gaining acceptance due to multiple health benefits. This study for the first time reports the antidiabetic potential of Hawaijar, an indigenous fermented soybean food of North-East India. Higher abundance of bioactive compounds (isoflavones and proteins/peptides) in Hawaijar may be responsible for the alleviation of impaired glucose metabolism associated with diabetes. The findings may be helpful for the development of a novel therapeutic to achieve better control of hyperglycemia and improve the lives of the patient population with diabetes.