Biochemical and Molecular Mechanisms of Glucose Uptake Stimulated by Physical Exercise in Insulin Resistance State: Role of Inflammation / Mecanismos Bioquímicos e Moleculares da Captação da Glicose Estimulada pelo Exercício Físico no Estado de Resistência à Insulina: Papel da Inflamação

Abstract Obesity associated with systemic inflammation induces insulin resistance (IR), with consequent chronic hyperglycemia. A series of reactions are involved in this process, including increased release of proinflammatory cytokines, and activation of c-Jun N-terminal kinase (JNK), nuclear factor-kappa B (NF-κB) and toll-like receptor 4 (TLR4) receptors. Among the therapeutic tools available nowadays, physical exercise (PE) has a known hypoglycemic effect explained by complex molecular mechanisms, including an increase in insulin receptor phosphorylation, in AMP-activated protein kinase (AMPK) activity, in the Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) pathway, with subsequent activation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), Rac1, TBC1 domain family member 1 and 4 (TBC1D1 and TBC1D4), in addition to a variety of signaling molecules, such as GTPases, Rab and soluble N-ethylmaleimide-sensitive factor attached protein receptor (SNARE) proteins. These pathways promote greater translocation of GLUT4 and consequent glucose uptake by the skeletal muscle. Phosphoinositide-dependent kinase (PDK), atypical protein kinase C (aPKC) and some of its isoforms, such as PKC-iota/lambda also seem to play a fundamental role in the transport of glucose. In this sense, the association between autophagy and exercise has also demonstrated a relevant role in the uptake of muscle glucose. Insulin, in turn, uses a phosphoinositide 3-kinase (PI3K)-dependent mechanism, while exercise signal may be triggered by the release of calcium from the sarcoplasmic reticulum. The objective of this review is to describe the main molecular mechanisms of IR and the relationship between PE and glucose uptake.

Resumo A obesidade associada à inflamação sistêmica induz resistência à insulina (RI), com consequente hiperglicemia crônica. Este processo envolve o aumento na liberação de citocinas pró-inflamatórias, ativação da enzima c-Jun N-terminal cinase (JNK), do fator nuclear kappa-B (NF-κB) e dos receptores do tipo Toll 4 (TLR4). Dentre as ferramentas terapêuticas disponíveis, o exercício físico (EF) tem efeito hipoglicemiante conhecido, explicado por mecanismos moleculares complexos. Dentre eles, ocorre aumento na fosforilação do receptor da insulina, na atividade da proteína quinase ativada por AMP (AMPK), na via da proteína cinase cinase dependente de Ca+2/calmodulina (CaMKK), com posterior ativação do coativador-1α do receptor ativado por proliferador do peroxissoma (PGC-1α), proteínas Rac1, TBC1 membro das famílias de domínio 1 e 4 (TBC1D1 e TBC1D4), além de uma variedade de moléculas de sinalização, como as proteínas GTPases, Rab e proteína solúvel de fusão sensível a N-etil-maleimida (SNARE); estas vias promovem maior translocação de transportador de glicose do tipo 4 (GLUT4) e consequente captação de glicose pelo músculo esquelético. A cinase fosfatidilinositol-dependente (PDK), proteína quinase C atípica (aPKC) e algumas das suas isoformas, como a PKC-iota/lambda também parecem desempenhar papel fundamental no transporte de glicose. Nesse sentido, a associação entre autofagia e EF também tem demonstrado papel relevante na captação de glicose muscular. A insulina, por sua vez, utiliza um mecanismo dependente da fosfatidilinositol-3-quinase (PI3K), enquanto que o sinal do EF pode ter início mediante liberação de cálcio pelo retículo sarcoplasmático e concomitante ativação da AMPK. O objetivo desta revisão é descrever os principais mecanismos moleculares da RI e da relação entre o EF e a captação de glicose.

Avaliação do mecanismo epigenético por metilação do DNA e da expressão de GLUT4 em tecido muscular esquelético de ratos adultos, proles de ratas com doença periodontal / Evaluation of the epigenetic mechanism by DNA methylation and GLUT4 expression in skeletal muscle tissue of adult rats, prole of rats with periodontal disease

Atualmente, está bem estabelecido que o ambiente fetal está ligado à saúde materna, e estímulos ou agressões anormais durante a vida intra-uterina podem resultar em mudanças na fisiologia e metabolismo da prole, aumentando o risco de doenças na vida adulta. Tal fenômeno é conhecido como programação fetal. Alterações na metilação do DNA e expressão gênica são consideradas mecanismos moleculares responsáveis por esta programação. Estudos anteriores demonstraram que a doença periodontal (DP) materna promove resistência insulínica, aumento nas concentrações plasmáticas de citocinas, redução do conteúdo de GLUT4 e do seu índice de translocação para membrana plasmática em sua prole adulta. E citocinas, como por exemplo, o TNF-α, têm sido relacionadas com a redução da expressão de GLUT4 por meio da ativação do fator de transcrição nuclear κappa B (NF-κB). Além disso, esta citocina pode estimular algumas serinas quinases, incluindo IκB quinase (IKK), c-Jun amino-terminal kinase (JNK) e quinases reguladas por sinais extracelulares (ERKs) que estão envolvidas na resistência insulínica. Tais achados evidenciam a necessidade de realizar mais estudos para verificar os mecanismos envolvidos nestas alterações. Portanto, os objetivos do presente estudo foram avaliar em ratos adultos, proles de ratas com DP: 1) massa corpórea ao longo de 75 dias de idade; 2) glicemia e insulinemia; 3) expressão do RNAm da proteína transportadora de glicose GLUT4 e do IRS1 em muscular esquelético gastrocnêmio (MG); 4) o grau de metilação do DNA na região promotora do gene do GLUT4 em MG; 5) fosforilação das proteínas JNK, IKKα/ß, ERK 1/2, NF-κBp65 e NF-κBp50 e seus conteúdos totais em MG; 6) conteúdo total de TNF-α em MG. As ratas foram divididas em dois grupos: 1) com doença periodontal (DP), no qual esta doença foi induzida por meio de ligadura com fio de seda ao redor do 1º molar inferior; 2) ratas controle (CN). Após 7 dias da colocação da ligadura, as ratas de ambos os grupos foram colocadas para acasalamento, verificou-se diariamente, por esfregaço vaginal, o dia da copulação. As ratas prenhas foram separadas em caixas individuais. Quando os filhotes machos destas ratas completaram 75 dias, realizaram-se os experimentos: 1) glicemia e insulinemia; 2) expressão do RNAm do GLUT4 e do IRS1 em MG; 3) o grau de metilação do DNA na região promotora do gene do GLUT4 em MG; 4) fosforilação das proteínas JNK, IKKα/ß, ERK 1/2, NF-κBp65 e NF-κBp50 e seus conteúdos totais em MG; 5) conteúdo total de TNF-α em MG. Os resultados demonstraram que a doença periodontal materna promove na sua prole adulta baixo peso ao nascimento (BPN), resistência insulínica, aumento do conteúdo total de TNF-α em MG, aumento do grau de fosforilação de IKKα/ß, ERK 1/2, NF-κBp65 (grau de fosforilação e conteúdo) e NF-κBp50 em MG, diminuição na expressão gênica da proteína transportadora de glicose GLUT4 e aumento na expressão gênica do IRS1; porém não promove nessa prole alteração no grau de metilação do DNA na região promotora do gene do GLUT4, e no grau de fosforilação da proteína JNK em MG. Portanto, este estudo é de fundamental importância para o entendimento de alguns dos mecanismos envolvidos na relação entre a doença periodontal materna e resistência à insulina na prole adulta. Além disso, mostra que a saúde bucal materna ideal pode ajudar a prevenir doenças futuras na prole adulta(AU)

It is well established that the fetal environment is linked to maternal health, and abnormal stimuli or aggressions during intrauterine life can result in changes in the physiology and metabolism of offspring, increasing the risk of disease in adult life, this phenomenon is known as fetal programming. Changes in DNA methylation and gene expression are considered molecular mechanisms responsible for this programming. Previous studies have demonstrated that maternal periodontal disease (PD) promotes insulin resistance, increased plasma concentrations of cytokines, reduced GLUT4 content and its plasma membrane translocation index in its adult offspring. And cytokines, such as TNF-α, have been linked to reduced GLUT4 expression through the activation of nuclear transcription factor kappa B (NF-κB). In addition, this cytokine can stimulate some serine kinases including IκB kinase (IKK), c-Jun amino-terminal kinase (JNK) and extracellular signal­regulated kinases (ERKs) that are involved in insulin resistance. These findings evidenced the need for further studies to verify the mechanisms involved in these changes. Therefore, the objectives of the present study were to evaluate in adult rats, offspring of rats with PD: 1) birth weight and during the 75 days of age; 2) glycemia and insulinemia; 3) GLUT4 and IRS1 mRNA expression in skeletal muscle gastrocnemius (MG); 4) the degree of DNA methylation in the promoter region of the GLUT4 gene in MG; 5) phosphorylation of JNK, IKKα/ß, ERK 1/2, NF-κBp65 and NF-κBp50 proteins and their total contents in MG; 6) TNF-α content in MG. Female Wistar rats were distributed into a control group and an experimental periodontal disease group, in which the disease is induced by ligation with silk thread around the 1st molar. Seven days after ligature placement, animals from both groups mated and daily vaginal smears were taken to verify the presence of sperm. Pregnant rats were kept in individual cages. The body weights of the offspring were measured once weekly from birth until 75 days of age. When male offspring of these rats completed 75 days, the experiments were performed: 1) glycemia and insulinemia; 2) GLUT4 and IRS1 mRNA expression in skeletal muscle gastrocnemius (MG); 3) the degree of DNA methylation in the promoter region of the GLUT4 gene in MG; 4) phosphorylation of JNK, IKKα/ß, ERK 1/2, NF-κBp65 and NF-κBp50 proteins and their total contents in MG; 5) TNF-α content in MG. The results demonstrated that maternal periodontal disease promotes in its adult offspring low birth weight (LBW), insulin resistance, increased TNF-α content in MG, increased IKKα/ß, ERK 1/2, NF-κBp65 (phosphorylation status and content) and NF-κBp50 phosphorylation status in the MG, decrease in gene expression of GLUT4 and increase in IRS1 gene expression; but does not promote in this progeny change in the degree of DNA methylation in the promoter region of the GLUT4 gene, and JNK phosphorylation status in MG. Therefore, this study is of fundamental importance for the understanding of some of the mechanisms involved in the relationship between maternal periodontal disease and insulin resistance in adult offspring. In addition, it shows that ideal maternal oral health can help prevent future illnesses in adult offspring(AU)

Xiao Ke Qing improves glycometabolism and ameliorates insulin resistance by regulating the PI3K/Akt pathway in KKAy mice / 医学前沿

Xiao Ke Qing (XKQ) granule has been clinically used to treat type 2 diabetes mellitus (T2DM) for 10 years in Chinese traditional medication. However, its mechanisms against hyperglycemia remain poorly understood. This study aims to investigate XKQ mechanisms on diabetes and diabetic liver disease by using the KKAy mice model. Our results indicate that XKQ can significantly reduce food and water intake. XKQ treatment also remarkably decreases both the fasting blood glucose and blood glucose in the oral glucose tolerance test. Additionally, XKQ can significantly decrease the serum alanine aminotransferase level and liver index and can alleviate the fat degeneration in liver tissues. Moreover, XKQ can ameliorate insulin resistance and upregulate the expression of IRS-1, PI3K (p85), p-Akt, and GLUT4 in the skeletal muscle of KKAy mice. XKQ is an effective drug for T2DM by ameliorating insulin resistance and regulating the PI3K/Akt signaling pathway in the skeletal muscle.

High Estradiol Differentially Affects the Expression of the Glucose Transporter Type 4 in Pelvic Floor Muscles of Rats / 대한배뇨장애요실금학회지

PURPOSE: To characterize the relationship between serum estradiol levels and the expression of glucose transporter type 4 (Glut4) in the pubococcygeus and iliococcygeus muscles in female rats. METHODS: The muscles were excised from virgin rats during the metestrus and proestrus stages of the estrous cycle, and from sham and ovariectomized rats implanted with empty or estradiol benzoate–filled capsules. The expression of estrogen receptors (ERs) was inspected in the muscles at metestrus and proestrus. Relative Glut4 expression, glycogen content, and serum glucose levels were measured. Appropriate statistical tests were done to identify significant differences (P≤0.05). RESULTS: The pubococcygeus and iliococcygeus muscles expressed ERα and ERβ. Glut4 expression and glycogen content in the pubococcygeus muscle were higher at proestrus than at metestrus. No significant changes were observed in the iliococcygeus muscle. In ovariectomized rats, the administration of estradiol benzoate increased Glut4 expression and glycogen content in the pubococcygeus muscle alone. CONCLUSIONS: High serum estradiol levels increased Glut4 expression and glycogen content in the pubococcygeus muscle, but not in the iliococcygeus muscle.

Beetle (Ulomoides dermestoides) fat improves diabetes: effect on liver and pancreatic architecture and on PPARgamma expression

Ulomoides dermestoides is a beetle traditionally consumed to treat diabetes. In this study, we performed a composition analysis of U. dermestoides to obtain the principal fractions, which were used to assess the effect on glycemia, liver and pancreatic architecture, and PPARγ and GLUT4 expression. Normal mice and alloxan-induced diabetic mice were administered fractions of chitin, protein or fat, and the acute hypoglycemic effect was evaluated. A subacute study involving daily administration of these fractions to diabetic mice was also performed over 30 days, after which the liver and pancreas were processed by conventional histological techniques and stained with hematoxylin and eosin to evaluate morphological changes. The most active fraction, the fat fraction, was analyzed by gas chromatography-mass spectrometry (GC-MS), and PPARγ and GLUT4 mRNA expressions were determined in 3T3-L1 adipocytes. The protein and fat fractions exhibited hypoglycemic effects in the acute as well as in the 30-day study. Only the fat fraction led to elevated insulin levels and reduced glycemia, as well as lower intake of water and food. In the liver, we observed recovery of close hepatic cords in the central lobule vein following treatment with the fat fraction, while in the pancreas there was an increased density and percentage of islets and number of cells per islet, suggesting cellular regeneration. The GC-MS analysis of fat revealed three fatty acids as the major components. Finally, increased expression of PPARγ and GLUT4 was observed in 3T3-L1 adipocytes, indicating an antidiabetic effect.

Pear pomace ethanol extract improves insulin resistance through enhancement of insulin signaling pathway without lipid accumulation

BACKGROUND/OBJECTIVES: The anti-diabetic activity of pear through inhibition of α-glucosidase has been demonstrated. However, little has been reported about the effect of pear on insulin signaling pathway in obesity. The aims of this study are to establish pear pomace 50% ethanol extract (PPE)-induced improvement of insulin sensitivity and characterize its action mechanism in 3T3-L1 cells and high-fat diet (HFD)-fed C57BL/6 mice. MATERIALS/METHODS: Lipid accumulation, monocyte chemoattractant protein-1 (MCP-1) secretion and glucose uptake were measure in 3T3-L1 cells. Mice were fed HFD (60% kcal from fat) and orally ingested PPE once daily for 8 weeks and body weight, homeostasis model assessment of insulin resistance (HOMA-IR), and serum lipids were measured. The expression of proteins involved in insulin signaling pathway was evaluated by western blot assay in 3T3-L1 cells and adipose tissue of mice. RESULTS: In 3T3-L1 cells, without affecting cell viability and lipid accumulation, PPE inhibited MCP-1 secretion, improved glucose uptake, and increased protein expression of phosphorylated insulin receptor substrate 1 [p-IRS-1, (Tyr⁶³²)], p-Akt, and glucose transporter type 4 (GLUT4). Additionally, in HFD-fed mice, PPE reduced body weight, HOMA-IR, and serum lipids including triglyceride and LDL-cholesterol. Furthermore, in adipose tissue, PPE up-regulated GLUT4 expression and expression ratio of p-IRS-1 (Tyr⁶³²)/IRS, whereas, down-regulated p-IRS-1 (Ser³⁰⁷)/IRS. CONCLUSIONS: Our results collectively show that PPE improves glucose uptake in 3T3-L1 cells and insulin sensitivity in mice fed a HFD through stimulation of the insulin signaling pathway. Furthermore, PPE-induced improvement of insulin sensitivity was not accompanied with lipid accumulation.

Relationships of glucose transporter 4 with cognitive changes induced by high fat diet and glucose metabolism in hippocampus / 生理学报

The hippocampus not only plays a role in appetite and energy balance, but also is particularly important in learning and memory. Figuring out the relationships of hippocampal glucose transporter 4 (GLUT4) with hippocampal glucose metabolism and hippocampus-dependent cognitive function is very important to clearly understand the pathophysiological basis of nutritional obesity and diabetes-related diseases, and treat obesity and cognitive dysfunction. Therefore, this study reviewed recent researches conducted on hippocampal GLUT4, hippocampal glucose metabolism, and hippocampus-dependent cognitive function. In this review, we mainly discussed: (1) The structure of GLUT4 and the distribution and function of GLUT4 in the hippocampus; (2) The translocation of GLUT4 in the hippocampus; (3) The relationships of the PI3K-Akt-GLUT4 signaling pathway with the high fat diet-induced changes of cognitive function and the glucose metabolism in the hippocampus; (4) The associations of the PI3K-Akt-GLUT4 signaling pathway with the diabetes-related cognitive dysfunction in the hippocampus; (5) The potential mechanisms of cognitive dysfunction induced by glucose metabolic disorder.

Evaluation of fish oil-rich in MUFAs for anti-diabetic and anti-inflammation potential in experimental type 2 diabetic rats

The advantages of monounsaturated fatty acids (MUFAs) on insulin resistance and type 2 diabetes mellitus (T2DM) have been well established. However, the molecular mechanisms of the anti-diabetic action of MUFAs remain unclear. This study examined the anti-hyperglycemic effect and explored the molecular mechanisms involved in the actions of fish oil- rich in MUFAs that had been acquired from hybrid catfish (Pangasius larnaudii×Pangasianodon hypophthalmus) among experimental type 2 diabetic rats. Diabetic rats that were fed with fish oil (500 and 1,000 mg/kg BW) for 12 weeks significantly reduced the fasting plasma glucose levels without increasing the plasma insulin levels. The diminishing levels of plasma lipids and the muscle triglyceride accumulation as well as the plasma leptin levels were identified in T2DM rats, which had been administrated with fish oil. Notably, the plasma adiponectin levels increased among these rats. The fish oil supplementation also improved glucose tolerance, insulin sensitivity and pancreatic histological changes. Moreover, the supplementation of fish oil improved insulin signaling (p-Akt(Ser473) and p-PKC-ζ/λ(Thr410/403)), p-AMPK(Thr172) and membrane GLUT4 protein expressions, whereas the protein expressions of pro-inflammatory cytokines (TNF-α and nuclear NF-κB) as well as p-PKC-θ(Thr538) were down regulated in the skeletal muscle. These data indicate that the effects of fish oil-rich in MUFAs in these T2DM rats were partly due to the attenuation of insulin resistance and an improvement in the adipokine imbalance. The mechanisms of the anti-hyperglycemic effect are involved in the improvement of insulin signaling, AMPK activation, GLUT4 translocation and suppression of pro-inflammatory cytokine protein expressions.

Potential role of marine algae extract on 3T3-L1 cell proliferation and differentiation: an in vitro approach

BACKGROUND: From ancient times, marine algae have emerged as alternative medicine and foods, contains the rich source of natural products like proteins, vitamins, and secondary metabolites, especially Chlorella vulgaris (C. vulgaris) contains numerous anti-inflammatory, antioxidants and wound healing substances. Type 2 diabetes mellitus is closely associated with adipogenesis and their factors. Hence, we aimed to investigate the chemical constituents and adipo-genic modulatory properties of C. vulgaris in 3T3-L1 pre-adipocytes. RESULTS: We analysed chemical constituents in ethanolic extract of C. vulgaris (EECV) by LC-MS. Results revealed that the EECV contains few triterpenoids and saponin compounds. Further, the effect of EECV on lipid accumulation along with genes and proteins expressions which are associated with adipogenesis and lipogenesis were evaluated using oil red O staining, qPCR and western blot techniques. The data indicated that that EECV treatment increased differentiation and lipid accumulation in 3T3-L1 cells, which indicates positive regulation of adipogenic and lipogenic activity. These increases were associated with up-regulation of PPAR-γ2, C/EBP-α, adiponectin, FAS, and leptin mRNA and protein expressions. Also, EECV treatments increased the concentration of glycerol releases as compared with control cells. Troglitazone is a PPAR-γ agonist that stimulates the PPAR-y2, adiponectin, and GLUT-4 expressions. Similarly, EECV treatments significantly upregulated PPAR-γ, adiponectin, GLUT-4 expressions and glucose utilization. Further, EECV treatment decreased AMPK-α expression as compared with control and metformin treated cells. CONCLUSION: The present research findings confirmed that the EECV effectively modulates the lipid accumulation and differentiation in 3T3-L1 cells through AMPK-α mediated signalling pathway.

Exercise improved lipid metabolism and insulin sensitivity in rats fed a high-fat diet by regulating glucose transporter 4 (GLUT4) and musclin expression

This study aimed to evaluate the effects of exercise training on triglyceride deposition and the expression of musclin and glucose transporter 4 (GLUT4) in a rat model of insulin resistance. Thirty male Sprague-Dawley rats (8 weeks old, weight 160±10 g) were fed a high-fat diet (40% calories from fat) and randomly divided into high-fat control group and swimming intervention group. Rats fed with standard food served as normal control. We found that 8-week swimming intervention significantly decreased body weight (from 516.23±46.27 to 455.43±32.55 g) and visceral fat content (from 39.36±2.50 to 33.02±2.24 g) but increased insulin sensitivity index of the rats fed with a high-fat diet. Moreover, swimming intervention improved serum levels of TG (from 1.40±0.83 to 0.58±0.26 mmol/L) and free fatty acids (from 837.80±164.25 to 556.38±144.77 μEq/L) as well as muscle triglycerides deposition (from 0.55±0.06 to 0.45±0.02 mmol/g) in rats fed a high-fat diet. Compared with rats fed a standard food, musclin expression was significantly elevated, while GLUT4 expression was decreased in the muscles of rats fed a high-fat diet. In sharp contrast, swimming intervention significantly reduced the expression of musclin and increased the expression of GLUT4 in the muscles of rats fed a high-fat diet. In conclusion, increased musclin expression may be associated with insulin resistance in skeletal muscle, and exercise training improves lipid metabolism and insulin sensitivity probably by upregulating GLUT4 and downregulating musclin.

Caveolin-1 and glucose transporter 4 involved in the regulation of glucose-deprivation stress in PC12 cells / 生理学报

Recent evidence suggests that caveolin-1 (Cav-1), the major protein constituent of caveolae, plays a prominent role in neuronal nutritional availability with cellular fate regulation besides in several cellular processes such as cholesterol homeostasis, regulation of signal transduction, integrin signaling and cell growth. Here, we aimed to investigate the function of Cav-1 and glucose transporter 4 (GLUT4) upon glucose deprivation (GD) in PC12 cells. The results demonstrated firstly that both Cav-1 and GLUT4 were up-regulated by glucose withdrawal in PC12 cells by using Western blot and laser confocal technology. Also, we found that the cell death rate, mitochondrial membrane potential (MMP) and intracellular free Ca(2+) concentration ([Ca(2+)]i) were also respectively changed followed the GD stress tested by CCK8 and flow cytometry. After knocking down of Cav-1 in the cells by siRNA, the level of [Ca(2+)]i was increased, and MMP was reduced further in GD-treated PC12 cells. Knockdown of Cav-1 or methylated-β-Cyclodextrin (M-β-CD) treatment inhibited the expression of GLUT4 protein upon GD. Additionally, we found that GLUT4 could translocate from cytoplasm to cell membrane upon GD. These findings might suggest a neuroprotective role for Cav-1, through coordination of GLUT4 in GD.

Methanolic extract of Momordica cymbalaria enhances glucose uptake in L6 myotubes in vitro by up-regulating PPAR-γ and GLUT-4 / 中国天然药物

The present study was undertaken to evaluate the influence of the methanolic fruit extract of Momordica cymbalaria (MFMC) on PPARγ (Peroxisome Proliferator Activated Receptor gamma) and GLUT-4 (Glucose transporter-4) with respect to glucose transport. Various concentrations of MFMC ranging from 62.5 to 500 μg·mL(-1) were evaluated for glucose uptake activity in vitro using L6 myotubes, rosiglitazone was used as a reference standard. The MFMC showed significant and dose-dependent increase in glucose uptake at the tested concentrations, further, the glucose uptake activity of MFMC (500 μg·mL(-1)) was comparable with rosigilitazone. Furthermore, MFMC has shown up-regulation of GLUT-4 and PPARγ gene expressions in L6 myotubes. In addition, the MFMC when incubated along with cycloheximide (CHX), which is a protein synthesis inhibitor, has shown complete blockade of glucose uptake. This indicates that new protein synthesis is required for increased GLUT-4 translocation. In conclusion, these findings suggest that MFMC is enhancing the glucose uptake significantly and dose dependently through the enhanced expression of PPARγ and GLUT-4 in vitro.

Modified Si-Miao-San inhibits inflammation and promotes glucose disposal in adipocytes through regulation of AMP-kinase / 中国天然药物

Modified Si-Miao-San (mSMS) is composed of Rhizoma Coptidis, Cortex Phellodendri, Rhizoma Coptidis Semen Coicis and Atractylodes Rhizome. The prescription is used for the management of diabetes and insulin resistance in the clinic. This study aims to investigate its regulation of glucose disposal in adipocytes. Differentiated 3T3-L1 adipocytes were stimulated with conditioned medium derived from activated macrophages to induce insulin resistance and observed the effects of Mac-CM on insulin-mediated glucose uptake along the insulin receptor substrate-1/PI3K/Akt signaling pathway. Moreover, its regulation of AMPK phosphorylation was also investigated. mSMS enhanced AMPK phosphorylation and promoted basal glucose uptake in adipocytes; mSMS inhibited NF-κB activation by reducing P65 phosphorylation and improved insulin-stimulated IRS-1 tyrosine and Akt phosphorylation, leading to the restoration of insulin-mediated glucose uptake when cells were exposed to inflammatory stimulation. These beneficial effects were diminished in the presence of the AMPK inhibitor compound C. mSMS positively regulated AMPK activity, and this action contributed to improving insulin PI3K signaling by the beneficial regulation of IRS-1 function through inhibition of inflammation in adipocytes.

Effects of chronic intermittent hypoxia on glucose transporter 4 expression in rat skeletal muscles / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the effect of chronic intermittent hypoxia-induced inflammatory cytokines and reoxygenation on glucose transporter 4 (GLUT-4) expression in rat skeletal muscles.</p><p><b>METHODS</b>Twenty-four male Sprague-Dawley rats were randomly assigned to blank control group, chronic intermittent hypoxia (CIH) group, and reoxygenation group. At the end of the experiment, fasting blood glucose (FBG), fasting blood insulin (FINS) and serum inflammatory cytokine levels were measured with glucose oxidase-peroxidase, insulin radioimmunoassay and ELISA, respectively. Homeostasis model assessment (IRI) was used to evaluate insulin resistance in the rats, and GLUT-4 protein expression in the skeletal muscles was measured with Western blotting.</p><p><b>RESULTS</b>Compared with the blank control group, CIH resulted in significantly increased fasting blood glucose, blood insulin levels and insulin resistance index (IRI) (P<0.05); fasting blood glucose was significantly elevated in reoxygenation group (P<0.05). Inflammatory cytokines levels (IL-6 and TNF-α) were significantly higher in CIH group than in the blank control and reoxygenation groups (P<0.05), and were higher in reoxygenation group than in the blank control group. GLUT-4 expression in the skeletal muscles was significantly reduced after CIH (P<0.05) but increased after subsequent reoxygenation (P<0.05).</p><p><b>CONCLUSION</b>CIH can cause increased release of inflammatory cytokines to lower GLUT-4 protein expression in the skeletal muscles, which contributes to insulin resistance in adult rats.</p>

Association of glucose transporter 4 gene polymorphism with hypoxia caused by obstructive sleep apnea syndrome and with related inflammatory factors / 中国医学科学院学报

<p><b>OBJECTIVE</b>To investigate the relationship between genetic polymorphisms of glucose transporter 4 (GLUT4) and hypoxia caused by obstructive sleep apnea syndrome (OSAS) as well as with related inflammatory factors.</p><p><b>METHODS</b>Consecutive hypertension patients diagnosed at the People's Hospital of Xinjiang Uygur Autonomous Region were selected from January to December 2010. A total of 859 subjects with possible OSAS base on their histories and physical examination findings udner went the polysomnography and inflammatory factor determination, of whom 616 (72%) were diagnosed with moderate and severe hypoxia with OSAS (case group) and 243 (28%) without hypoxia or OASA (control group). Ninty-six patients from the case group underwent DNA sequencing at the functional domain of GLUT4 gene to screen for representative mutations. TaqMan PCR was used to genotyping then analyzed the relationship between locis of GLUT4 and hypoxia.</p><p><b>RESULTS</b>GLUT4 genome sequencing was performed in 96 severe OSAS patients and 4 mutated sites were found, among which 3 mutated sites (rs5415, rs4517, and rs5435) were selected according to the principle of linkage disequilibrium (r² > 0.8) and minimum gene allele frequency > 5%. All of single nucleotide polymorphisms (SNP) satisfied Hardy-Weinberg equilibrium (P>0.05). A significant association of GLUT4 SNP rs5417 allele carried in control subjects, compared with moderate and severe hypoxia in OSAS patients (P<0.05); AA+AC genotype relative to CC with low oxygen levels in subjects significantly reduced. The difference existed in overweight and obese patients, as well as in those aged more than 50 years (P<0.05). AA was still an independent protective factor for hypoxia caused by OSAS (OR=0.385, 95%CI = 0.210-0.704, P=0.002). Male (OR=1.635, 95% CI=1.037-2.577, P=0.034) and total cholesterol (OR=1.600, 95% CI=1.287-1.987, P<0.001) were independent risk factors associated with hypoxia. Normal weight(OR=0.059, 95% CI=0.037-0.094, P<0.001) and high density lipoprotein cholesterol (OR=0.337, 95% CI=0.171-0.666, P=0.002)were independent protective factors for hypoxia. The levels of monocyte chemoattractant protein-1 and C-reaction protein above CC were significantly higher than AA+AC (P<0.05).</p><p><b>CONCLUSION</b>Hypoxia caused by OSAS is associated with GLUT4 gene SNP rs5417.</p>

[Combined effect of aerobic training and Pistacia athlantica extract on GLUT-4 protein expression and muscle glycogen in diabetic rats]

The effects of exercise training on GLUT4 protein expression have been examined in several studies whereas those of aerobic training along with the use of plant extracts on muscle GLUT4 protein expression are unknown. The aim of the present study was to investigate the effects of aerobic training and Pistacia athlantica extract on GLUT4 protein expression and glycogen level in the gastrocnemius muscle of diabetic rats. Forty-male Wistar rats were randomly divided into five groups: Healthy control, diabetic control, diabetic+ aerobic training, diabetic+extract and diabetic+ aerobic training+ extract. The program included six weeks of aerobic training on the treadmill. Forty eight hours after last session of training and consumption the extract, the rats were anesthetized and gastrocnemius muscle was isolated for measurement of glycogen levels and GLUT4 protein expression. Data was analyzed by using one-way ANOVA test [P<0.05]. GLUT4 protein expression and glycogen levels in gastrocnemius muscle in diabetic+ aerobic training+ extract group were significantly higher than in the diabetic control group [P values 0.001, 0.02 respectively], whereas these variables in the aerobic training and the Pistacia athlantica extract perse groups did not change compared to the diabetic control group. It seems that Pistacia athlantica extract along with specific exercises, compared to utilization of each of strategies perse, are more effective in increasing glucose transporter proteins and possibly improving insulin function

The synergistic effect of FGF-21 and insulin on regulating glucose metabolism and its mechanism / 药学学报

Previous studies proposed that the synergistic effect of fibroblast growth factor-21 (FGF-21) and insulin may be due to the improvement of insulin sensitivity by FGF-21. However, there is no experimental evidence to support this. This study was designed to elucidate the mechanism of synergistic effect of FGF-21 and insulin in the regulation of glucose metabolism. The synergistic effect of FGF-21 and insulin on regulating glucose metabolism was demonstrated by investigating the glucose absorption rate by insulin resistance HepG2 cell model and the blood glucose chances in type 2 diabetic db/db mice after treatments with different concentrations of FGF-21 or/and insulin; The synergistic metabolism was revealed through detecting GLUT1 and GLUT4 transcription levels in the liver by real-time PCR method. The experimental results showed that FGF-21 and insulin have a synergistic effect on the regulation of glucose metabolism. The results of real-time PCR showed that the effective dose of FGF-21 could up-regulate the transcription level of GLUT1 in a dose-dependent manner, but had no effect on the transcription level of GLUT4. Insulin (4 u) alone could up-regulate the transcription level of GLUT4, yet had no effect on that of GLUT1. Ineffective dose 0.1 mg kg(-1) FGF-21 alone could not change the transcription level of GLUT1 or GLUT4. However, when the ineffective dose 0.1 mg x kg(-1) FGF-21 was used in combination with insulin (4 u) significantly increased the transcription levels of both GLUT1 and GLUT4, the transcription level of GLUT1 was similar to that treated with 5 time concentration of FGF-21 alone; the transcription level of GLUT4 is higher than that treated with insulin (4 u) alone. In summary, in the presence of FGF-21, insulin increases the sensitivity of FGF-21 through enhancing GLUT1 transcription. Vice versa, FGF-21 increases the sensitivity of insulin by stimulating GLUT4 transcription in the presence of insulin. FGF-21 and insulin exert a synergistic effect on glucose metabolism through mutual sensitization.

Decrease in myostatin by ladder-climbing training is associated with insulin resistance in diet-induced obese rats / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Suppression of myostatin (MSTN) has been associated with skeletal muscle atrophy and insulin resistance (IR). However, few studies link MSTN suppression by ladder-climbing training (LCT) and IR. Therefore, we intended to identify the correlation with IR between LCT and to analyze the signaling pathways through which MSTN suppression by LCT regulates IR.</p><p><b>METHODS</b>The rats were randomly assigned to two types of diet: normal pellet diet (NPD, n = 8) and high-fat diet (HFD, n = 16). After 8 weeks, the HFD rats were randomly re-assigned to two groups (n = 8 for each group): HFD sedentary (HFD-S) and high-fat diet ladder-climbing training (HFD-LCT). HFD-LCT rats were assigned to LCT for 8 weeks. Western blotting, immunohistochemistry and enzyme assays were used to measure expression levels and activities of MSTN, GLUT4, PI3K, Akt and Akt-activated targets (mTOR, FoxO1 and GSK-3β).</p><p><b>RESULTS</b>The LCT significantly improved IR and whole-body insulin sensitivity in HDF-fed rats. MSTN protein levels decreased in matching serum (42%, P = 0.007) and muscle samples (25%, P = 0.035) and its receptor mRNA expression also decreased (16%, P = 0.041) from obese rats after LCT. But the mRNA expression of insulin receptor had no obvious changes in LCT group compared with NPD and HFD-S groups (P = 0.074). The ladder-climbing training significantly enhanced PI3K activity (1.7-fold, P = 0.024) and Akt phosphorylation (83.3%, P = 0.022) in HFD-fed rats, significantly increased GLUT4 protein expression (84.5%, P = 0.036), enhanced phosphorylation of mTOR (4.8-fold, P < 0.001) and inhibited phosphorylation of FoxO1 (57.7%, P = 0.020), but did not affect the phosphorylation of GSK-3β.</p><p><b>CONCLUSIONS</b>The LCT significantly reduced IR in diet-induced obese rats. MSTN may play an important role in regulating IR and fat accumulation by LCT via PI3K/Akt/mTOR and PI3K/Akt/FoxO1 signaling pathway in HFD-fed rats.</p>

The role of arecoline on hepatic insulin resistance in type 2 diabetes rats / 中国应用生理学杂志

<p><b>OBJECTIVE</b>To explore the effects of arecoline on hepatic insulin resistance in type 2 diabetes rats and to elucidate its possible mechanism.</p><p><b>METHODS</b>Forty five Wistar rats were fed with high fructose diet for 12 weeks to induce type 2 diabetic rat model. rats were randomly divided into 5 groups (n = 8): control group, model group and model group were treated with different dose (0, 0.5, 1, 5 mg/kg) of arecoline. After 4 weeks, the fasting blood glucose, blood lipid and insulin level measured , mRNA expression of liver constitutive androstane receptor (CAR), pregnane X receptor (PXR), glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were detected by reverse transcription polymerase chain reaction (RT-PCR), the protein expression of p-AKT and glucose transporter4 (GLUT4) were detected by Western blot.</p><p><b>RESULTS</b>1.5 mg/kg arecoline could significantly decrease the level of fasting blood glucose, blood lipid, blood insulin level and liver G6Pase, PEPCK, IL-6, TNF-alpha mRNA level in type 2 diabetes rats. 1.5 mg/kg arecoline also could significantly increase CAR, PXR mRNA level and p-AKT and GLUT4 protein expression.</p><p><b>CONCLUSION</b>Arecoline improved hepatic insulin resistance in type 2 diabetes rats by increasing the mRNA levels of CAR and PXR leading to the creased glucose metabolism and inflammation related genes expression.</p>

Glycyrrhizin ameliorates insulin resistance, hyperglycemia, dyslipidemia and oxidative stress in fructose-induced metabolic syndrome-X in rat model.

This study investigates if glycyrrhizin, a constituent of licorice (Glycyrrhiza glabra) root, is able to treat the complications (insulin resistance, hyperglycemia, dyslipidemia and oxidative stress) of metabolic syndrome. Metabolic syndrome was induced in rats by feeding a fructose-enriched (60%) diet for six weeks, after which single dose of glycyrrhizin (50 mg/kg body weight) was administered intraperitoneally. Different biochemical parameters from blood were estimated during three weeks after treatment. Then the rats were sacrificed to collect skeletal muscle tissue. Glycyrrhizin reduced the enhanced levels of blood glucose, insulin and lipids in metabolic syndrome group. Increased advanced glycation end products of hemoglobin, glycohemoglobin, hemoglobin-mediated iron release and iron-mediated free radical reactions (arachidonic acid and deoxyribose degradation) in metabolic syndrome were inhibited by glycyrrhizin treatment. Reduced activities of enzymatic antioxidants (superoxide dismutase and catalase) and elevated oxidative stress markers (malonaldehyde, fructosamine, hemoglobin carbonyl content and DNA damage) in metabolic syndrome were reversed to almost normal levels by glycyrrhizin. The decreased levels of peroxisome proliferator activated receptor (PPAR) and glucose transporter 4 (GLUT4) proteins in skeletal muscle of metabolic syndrome group were elevated by glycyrrhizin, indicating improved fatty acid oxidation and glucose homeostasis.