Intracellular mechanisms underlying increases in glucose uptake in response to insulin or exercise in skeletal muscle

Extract of Phyllanthus emblica L. fruit stimulates basal glucose uptake and ameliorates palmitate-induced insulin resistance through AMPK activation in C2C12 myotubes

BACKGROUND

The fruit of Phyllanthus emblica L., a traditional medicine in China and India, is used to treat diabetes mellitus. Its water extract (WEPE) has demonstrated hypoglycemic effects in diabetic rats, but its mechanisms on glucose utilization and insulin resistance in skeletal muscle remain unclear. Therefore, this study aims to investigate the effects and underlying mechanisms of WEPE on glucose utilization and insulin resistance using C2C12 myotubes.

METHODS

Effects of WEPE on glucose uptake, GLUT4 translocation, and AMPK and AKT phosphorylation were investigated in C2C12 myotubes and palmitate-treated myotubes. An AMPK inhibitor and siRNA were used to explore the mechanisms of WEPE. Glucose uptake was determined using a 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-2-deoxyglucose (2-NBDG) uptake assay, and protein expression and GLUT4 translocation were assessed via western blotting.

RESULTS

In normal myotubes, WEPE significantly stimulated glucose uptake and GLUT4 translocation to the plasma membrane at concentrations of 125 and 250 µg/mL. This was accompanied by an increase in the phosphorylation of AMPK and its downstream targets. However, both compound C and AMPK siRNA blocked the WEPE-induced GLUT4 translocation and glucose uptake. Moreover, pretreatment with STO-609, a calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor, inhibited WEPE-induced AMPK phosphorylation and attenuated the WEPE-stimulated glucose uptake and GLUT4 translocation. In myotubes treated with palmitate, WEPE prevented palmitate-induced insulin resistance by enhancing insulin-mediated glucose uptake and AKT phosphorylation. It also restored the insulin-mediated translocation of GLUT4 from cytoplasm to membrane. However, these effects of WEPE on glucose uptake and GLUT4 translocation were blocked by pretreatment with compound C.

CONCLUSIONS

WEPE significantly stimulated basal glucose uptake though CaMKKβ/AMPK pathway and markedly ameliorated palmitate-induced insulin resistance by activating the AMPK pathway in C2C12 myotubes.

Optimization of Extraction and Purification of Flavonoids from Stigmaless Floral Residues of Crocus sativus L. and Their Stimulatory Effect on Glucose Uptake In Vitro

Saffron, the dried stigma of Crocus sativus L., is a renowned spice and medicinal herb. During its production, a significant amount of floral residues, rich in bioactive compounds, are discarded as agricultural by-products. This study presents a novel approach to the sustainable utilization of these stigmaless floral residues (FRC) by optimizing the extraction and purification of their flavonoids, analyzing their chemical composition, and evaluating their effect on glucose uptake. The extraction of flavonoids from FRC was optimized using single-factor experiments and response surface methodology. The optimal conditions for extraction were an ethanol concentration of 67.7%, a temperature of 67.6 °C, a solid-to-liquid ratio of 1:30, an extraction time of 3 h, and two extractions. The crude extract obtained was then purified using macroporous resin HPD100, selected after comparing the adsorption and desorption characteristics of six different resins. The optimal purification parameters were an adsorption concentration of 40 mg/mL, a loading volume of 7 bed volumes (BV) at a flow rate of 3 BV/h, and 80% ethanol as the eluent with a volume of 4 BV. The resulting flavonoid-enriched extract (FFRC) had an experimental yield of 8.67% ± 0.01 and a flavonoid content of 128.30 ± 4.64 mg/g. The main flavonoids in FFRC were identified as kaempferol glycosides, isorhamnetin glycosides, and quercetin glycosides. Moreover, FFRC significantly stimulated glucose consumption and uptake in C2C12 myotubes, suggesting its potential utility as a natural hypoglycemic agent. This study contributes to the sustainable and value-added utilization of agricultural resources by providing data for the exploitation and application of flavonoids from saffron by-products.

The Lipophilic Extract from Ginkgo biloba L. Leaves Promotes Glucose Uptake and Alleviates Palmitate-Induced Insulin Resistance in C2C12 Myotubes

Ginkgo biloba L. (ginkgo) is a widely used medicinal plant around the world. Its leaves, which have been used as a traditional Chinese medicine, are rich in various bioactive components. However, most of the research and applications of ginkgo leaves have focused on terpene trilactones and flavonol glycosides, thereby overlooking the other active components. In this study, a lipophilic extract (GL) was isolated from ginkgo leaves. This extract is abundant in lipids and lipid-like molecules. Then, its effect and potential mechanism on glucose uptake and insulin resistance in C2C12 myotubes were investigated. The results showed that GL significantly enhanced the translocation of GLUT4 to the plasma membrane, which subsequently promoted glucose uptake. Meanwhile, it increased the phosphorylation of AMP-activated protein kinase (AMPK) and its downstream targets. Both knockdown of AMPK with siRNA and inhibition with AMPK inhibitor compound C reversed these effects. Additionally, GL ameliorated palmitate-induced insulin resistance by enhancing insulin-stimulated glucose uptake, increasing the phosphorylation of protein kinase B (PKB/AKT), and restoring the translocation of GLUT4 from the cytoplasm to the membrane. However, pretreatment with compound C abolished these beneficial effects of GL. In conclusion, GL enhances basal glucose uptake in C2C12 myotubes and improves insulin sensitivity in palmitate-induced insulin resistant myotubes through the AMPK pathway.

The Effect of Lower Limb Combined Neuromuscular Electrical Stimulation on Skeletal Muscle Signaling for Glucose Utilization, Myofiber Distribution, and Metabolic Function after Spinal Cord Injury

Maintaining healthy myofiber type and metabolic function early after spinal cord injury (SCI) may prevent chronic metabolic disorders. This study compares the effects of a 2-5 week combined (aerobic + resistance) neuromuscular electrical stimulation (Comb-NMES) regimen versus a sham control treatment on muscle protein signaling for glucose uptake, myofiber type distribution, and metabolic function. Twenty participants (31 ± 9 years of age) with an SCI (C4-L1, AIS level A-C) within 14 days of the SCI were randomly assigned to control (N = 8) or Comb-NMES (N = 12). Sessions were given three times per week. Fasting blood samples and vastus lateralis muscle biopsies were collected 24-48 h before or after the last session. Western blots were performed to quantify proteins, immunohistochemical analyses determined muscle myofiber distribution, and enzymatic assays were performed to measure serum glucose, insulin, and lipids. Our main findings include a decrease in fasting glucose (p < 0.05) and LDL-C (p < 0.05) levels, an upregulation of CamKII and Hexokinase (p < 0.05), and an increase in type I (+9%) and a decrease in type IIx (-36%) myofiber distribution in response to Comb-NMES. Our findings suggest that maintaining healthy myofiber type and metabolic function may be achieved via early utilization of Comb-NMES.

Organ-specific fuel rewiring in acute and chronic hypoxia redistributes glucose and fatty acid metabolism

Oxygen deprivation can be detrimental. However, chronic hypoxia is also associated with decreased incidence of metabolic syndrome and cardiovascular disease in high-altitude populations. Previously, hypoxic fuel rewiring has primarily been studied in immortalized cells. Here, we describe how systemic hypoxia rewires fuel metabolism to optimize whole-body adaptation. Acclimatization to hypoxia coincided with dramatically lower blood glucose and adiposity. Using in vivo fuel uptake and flux measurements, we found that organs partitioned fuels differently during hypoxia adaption. Acutely, most organs increased glucose uptake and suppressed aerobic glucose oxidation, consistent with previous in vitro investigations. In contrast, brown adipose tissue and skeletal muscle became "glucose savers," suppressing glucose uptake by 3-5-fold. Interestingly, chronic hypoxia produced distinct patterns: the heart relied increasingly on glucose oxidation, and unexpectedly, the brain, kidney, and liver increased fatty acid uptake and oxidation. Hypoxia-induced metabolic plasticity carries therapeutic implications for chronic metabolic diseases and acute hypoxic injuries.

The role of exercise in obesity-related cancers: Current evidence and biological mechanisms

Cancer ranks among the five leading causes of death in almost all countries and has important repercussions for individual and public health, the healthcare system, and society in general. Obesity increases the incidence of many types of cancer, but growing evidence suggests that physical activity may decrease risk for developing a variety of obesity-related cancer types, and, in some cases, may improve cancer prognosis and mortality rates. This review summarizes recent evidence on the effect of physical activity on obesity-related cancer prevention and survival. For some cancers, including breast, colorectal, and endometrial cancer, there is strong evidence for a preventative effect of exercise, but for many others, including gallbladder and kidney cancer, and multiple myeloma, evidence is inconsistent or largely lacking. Though many potential mechanisms have been proposed to explain the onco-protective effect of exercise, including improved insulin sensitivity, alterations in sex hormone availability, improved immune function and inflammation, myokine secretion, and modulation of intracellular signaling at the level of AMP kinase, the exact mechanism(s) of action within each cancer subtype remains poorly defined. Overall, a deeper understanding of how exercise can help against cancer and of the exercise parameters that can be altered to optimize exercise prescription is necessary and should be the subject of future investigation.

Nutritional and Exercise-Focused Lifestyle Interventions and Glycemic Control in Women with Diabetes in Pregnancy: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

Diabetes disrupts one in six pregnancies, bestowing immediate and long-term health risks to mother and child. Diet and exercise are commonly prescribed to control dysglycemia, but their effectiveness across sub-populations and types of diabetes (type-1; type-2; or gestational diabetes mellitus, GDM) is uncertain. Therefore, a systematic review and meta-analysis on the effect of diet and/or exercise on glycemia in pregnant women with diabetes was conducted. Random effects models were used to evaluate effect sizes across studies and anticipated confounders (e.g., age, ethnicity, BMI). Of the 4845 records retrieved, 26 studies (8 nutritional supplements, 12 dietary, and 6 exercise interventions) were included. All studies were conducted in patients with GDM. Overall, supplement- and exercise-based interventions reduced fasting glucose (−0.30 mmol/L; 95% CI = −0.55, −0.06; p = 0.02; and 0.10 mmol/L; 95% CI = −0.20, −0.01; p = 0.04); and supplement- and diet-based interventions reduced HOMA-IR (−0.40; 95% CI = −0.58, −0.22; p < 0.001; and −1.15; 95% CI = −2.12, −0.17; p = 0.02). Subgroup analysis by confounders only confirmed marginal changed effect sizes. Our results suggest a favorable role of certain nutritional supplements, diet, and exercise practices on glycemia in women with GDM and underline a lack of evidence in ~20% of other diabetes-related pregnancies (i.e., women with pre-existing diabetes).

Insights into the development of insulin resistance: Unraveling the interaction of physical inactivity, lipid metabolism and mitochondrial biology

While impairments in peripheral tissue insulin signalling have a well-characterized role in the development of insulin resistance and type 2 diabetes (T2D), the specific mechanisms that contribute to these impairments remain debatable. Nonetheless, a prominent hypothesis implicates the presence of a high-lipid environment, resulting in both reactive lipid accumulation and increased mitochondrial reactive oxygen species (ROS) production in the induction of peripheral tissue insulin resistance. While the etiology of insulin resistance in a high lipid environment is rapid and well documented, physical inactivity promotes insulin resistance in the absence of redox stress/lipid-mediated mechanisms, suggesting alternative mechanisms-of-action. One possible mechanism is a reduction in protein synthesis and the resultant decrease in key metabolic proteins, including canonical insulin signaling and mitochondrial proteins. While reductions in mitochondrial content associated with physical inactivity are not required for the induction of insulin resistance, this could predispose individuals to the detrimental effects of a high-lipid environment. Conversely, exercise-training induced mitochondrial biogenesis has been implicated in the protective effects of exercise. Given mitochondrial biology may represent a point of convergence linking impaired insulin sensitivity in both scenarios of chronic overfeeding and physical inactivity, this review aims to describe the interaction between mitochondrial biology, physical (in)activity and lipid metabolism within the context of insulin signalling.

The Impact of Exercise Training Intensity on Physiological Adaptations and Insulin Resistance in Women with Abdominal Obesity

Abdominal obesity has emerged globally as a major public health issue due to its high prevalence and morbidity. The benefits of physical exercise among the obese population are well documented. However, the optimal exercise intensity for reducing body fat and preventing insulin resistance and metabolic disorders is still under debate. This study aimed to examine the effects of three different intensities of combined endurance and strength training programs on anthropometric variables, physiological and muscular adaptations, and insulin sensitivity. Forty-three obese young women (age 26.4 ± 4.7 years, BMI 33.1 ± 2.5 kg/m2) were randomly assigned to one of four groups: a control group (G0), a moderate-intensity training group (G50, exercising brisk walking at 50% heart rate reserve HRR), a high-intensity training group (G75, exercise jogging at 75% HRR), and an alternated-intensity training group (G50/75, exercise brisk-walking/jogging at 50−75% HRR) with additional strength training once a week for each group. Body composition, waist circumference (WC), fasting blood glucose, insulin sensitivity and resistance (Homa-IR), resting heart rate (RHR), 6-min walk distance (6MWD), 1-repetition maximum (1-RM), and time to exhaustion (TTE) at 45% and 75% maximal voluntary contraction (MVC) for both the flexor and extensor muscle groups of the knees, were recorded before and after three months of exercise training. All training groups showed significant decreases in body mass, BMI, total body fat, body fat percentage, WC, abdominal and visceral mass (p < 0.001), with a greater reduction of body mass and BMI in G75 (p < 0.05). Lean mass increased significantly only in G50/75 (p < 0.05). The insulin sensitivity and Homa-IR decreased in the three training groups (p < 0.01), with greater enhanced resistance in G50 compared to G75 and G50/75 (p < 0.05). In contrast, there were no pre-post changes in all groups for fasting blood glucose (p > 0.05). 1-RM and TTE of the knee flexor and extensor muscles were improved in the three groups (p < 0.01), with greater improvement in G50/75 for 1RM and G75 in most of the TTE parameters (p < 0.05). RHR decreased and 6MWD increased significantly in the three training groups (p < 0.01), with greater 6MWD improvement in G75 (p < 0.05). In conclusion, the three training intensities seem to generate benefits in terms of body composition, physiological and muscular adaptations, and insulin resistance. High training intensity resulted in greater improvements in body mass, BMI, and endurance and strength, whereas moderate training intensity resulted in greater improvements of insulin resistance and homo-IR. Following alternate-intensity training, greater improvements were observed in lean mass and maximal strength performance.

Acute Low Force Electrically Induced Exercise Modulates Post Prandial Glycemic Markers in People with Spinal Cord Injury

Regular exercise involves daily muscle contractions helping metabolize up to 70% of daily ingested glucose. Skeletal muscle increases glucose uptake through two distinct pathways: insulin signaling pathway and muscle contraction mediated AMPK pathway. People with paralysis are unable to contract their muscles which atrophy, transform into insulin resistant glycolytic muscle, and develop osteoporosis. Our goal is to determine if low force electrically induced exercise (LFE) will modulate the post prandial insulin and glucose response in people with and without spinal cord injury (SCI). 18 people with SCI and 23 without SCI (Non-SCI) participated in an assessment of metabolic biomarkers during passive sitting (CTL) and a bout of LFE delivered to the quadriceps/hamstring muscle groups after a glucose challenge. Baseline fasting insulin (p = 0.003) and lactate (p = 0.033) levels were higher in people with SCI, but glucose levels (p = 0.888) were similar compared to the non-SCI population. After 1-h of muscle contractions using LFE, heart rate increased (p < 0.001), capillary glucose decreased (p = 0.004), insulin decreased (p < 0.001), and lactate increased (p = 0.001) in the SCI population. These findings support that LFE attenuates certain metabolic blood biomarkers during a glucose challenge and may offer a lifestyle strategy to regulate metabolic responses after eating among people with SCI.

Advances in FGFs for diabetes care applications

BACKGROUND

Diabetes mellitus (DM) is an endocrine and metabolic disease caused by a variety of pathogenic factors, including genetic factors, environmental factors and behavior. In recent decades, the number of cases and the prevalence of diabetes have steadily increased, and it has become one of the most threatening diseases to human health in the world. Currently, insulin is the most effective and direct way to control hyperglycemia for diabetes treatment at a low cost. However, hypoglycemia is often a common complication of insulin treatment. Moreover, with the extension of treatment time, insulin resistance, considered the typical adverse symptom, can appear. Therefore, it is urgent to develop new targets and more effective and safer drugs for diabetes treatment to avoid adverse reactions and the insulin tolerance of traditional hypoglycemic drugs.

SCOPE OF REVIEW

In recent years, it has been found that some fibroblast growth factors (FGFs), including FGF1, FGF19 and FGF21, can safely and effectively reduce hyperglycemia and have the potential to be developed as new drugs for the treatment of diabetes. FGF23 is also closely related to diabetes and its complications, which provides a new approach for regulating blood glucose and solving the problem of insulin tolerance.

MAJOR CONCLUSIONS

This article reviews the research progress on the physiology and pharmacology of fibroblast growth factor in the treatment of diabetes. We focus on the application of FGFs in diabetes care and prevention.

Effect of anaerobic resistance training on gastric emptying of solids, nutritional parameters and food behavior in the rats treated with dexamethasone

Dexamethasone (Dexa) is a potent glucocorticoid that can trigger side effects, such as neuromuscular, cardiovascular, and gastric motility disorders. Exercise can ameliorate gastrointestinal disorders. However, it is not clear whether exercise can modulate the side effects of using Dexa on gastric motility. To investigate the role of anaerobic resistance training (ART) on gastric motility and feeding behavior of rats treated with dexamethasone, rats were divided into three groups: control (Ctrl), dexamethasone (Dexa), and anaerobic resistance training + dexamethasone (ARTDexa). Anaerobic resistance training (ART) consisted of climbing a vertical ladder 5 days/week (with intensity of 50% to 100% of the maximum overload/8 weeks). At the end of the ART or control period, the rats received Dexa (1 mg/kg i.p) for 10 consecutive days. In the end, we evaluated anthropometric parameters and feeding behavior, heart rate, gastric emptying, and lipid profile in all groups. We observed significant decrease (p < 0.05) in body weight and food intake in the Dexa and ARTDexa groups compared to the control. Dexa promoted significant tachycardia (p < 0.05) and a decrease (p < 0.05) in the r-r' interval. The ART significantly prevented (p < 0.05) cardiovascular effects. Dexa induced a decrease (p < 0.05) in gastric emptying compared to the control group. On the other hand, ART significantly prevented (p < 0.05) the decrease in gastric emptying compared to Dexa. The chronic use of Dexa caused tachycardia, decreased food intake, and decreased gastric emptying. The ART modulated cardiovascular parameters, improving tachycardia. In addition, this exercise prevented gastric dysmotility induced by dexamethasone.

Beta-klotho in type 2 diabetes mellitus: From pathophysiology to therapeutic strategies

Type 2 diabetes mellitus (T2DM) has become a global health problem with no cure. Despite lifestyle modifications and various pharmaceutical options, the achievement of stable and durable glucose control along with effective prevention of T2DM-related cardiovascular complications remains a challenging task in clinical management. With its selective high abundance in metabolic tissues (adipose tissue, liver, and pancreas), β-Klotho is the essential component of fibroblast growth factor (FGF) receptor complexes. It is essential for high-affinity binding of endocrine FGF19 and FGF21 to evoke the signaling cascade actively involved in homeostatic maintenance of glucose metabolism and energy expenditure. In this Review, we discuss the biological function of β-Klotho in the regulation of glucose metabolism and offer mechanistic insights into its involvement in the pathophysiology of T2DM. We review our current understanding of the endocrine axis comprised of β-Klotho and FGFs (FGF19 and FGF21) and its regulatory effects on glucose metabolism under physiological and T2DM conditions. We also highlight advances in the development and preclinical validation of pharmacological compounds that target β-Klotho and/or the β-Klotho-FGFRs complex for the treatment of T2DM. Given the remarkable advances in this field, we also discuss outstanding research questions and the many challenges in the clinical development of β-Klotho-based therapies.

Effects of exercise on cellular and tissue aging

The natural aging process is carried out by a progressive loss of homeostasis leading to a functional decline in cells and tissues. The accumulation of these changes stem from a multifactorial process on which both external (environmental and social) and internal (genetic and biological) risk factors contribute to the development of adult chronic diseases, including type 2 diabetes mellitus (T2D). Strategies that can slow cellular aging include changes in diet, lifestyle and drugs that modulate intracellular signaling. Exercise is a promising lifestyle intervention that has shown antiaging effects by extending lifespan and healthspan through decreasing the nine hallmarks of aging and age-associated inflammation. Herein, we review the effects of exercise to attenuate aging from a clinical to a cellular level, listing its effects upon various tissues and systems as well as its capacity to reverse many of the hallmarks of aging. Additionally, we suggest AMPK as a central regulator of the cellular effects of exercise due to its integrative effects in different tissues. These concepts are especially relevant in the setting of T2D, where cellular aging is accelerated and exercise can counteract these effects through the reviewed antiaging mechanisms.

Decreased muscle-derived musclin by chronic resistance exercise is associated with improved insulin resistance in rats with type 2 diabetes

Chronic resistance exercise induces improved hyperglycemia in patients with type 2 diabetes mellitus. Musclin, a muscle‐derived secretory factor, is involved in the induction of insulin resistance via the downregulation of the glucose transporter‐4 (GLUT‐4) signaling pathway in skeletal muscles. However, whether musclin affects the mechanism of resistance exercise remains unclear. This study aimed to clarify whether decreased muscle‐derived musclin secretion in chronic resistance exercise is involved in the improvement of insulin resistance via the GLUT‐4 signaling pathway in rats with type 2 diabetes. Male, 20‐week‐old, Otsuka Long‐Evans Tokushima Fatty (OLETF) rats, a type 2 diabetes model, were randomly divided into two groups: sedentary control (OLETF‐Con) and chronic resistance exercise (OLETF‐RT; climbing a ladder three times a week on alternate days for 8 weeks), whereas Long‐Evans Tokushima Otsuka rats were used as the nondiabetic sedentary control group. OLETF‐Con rats showed increased fasting glucose levels, decreased insulin sensitivity index (QUICKI), muscle GLUT‐4 translocation, and protein kinase B (Akt) phosphorylation, and concomitantly increased muscle musclin expression. In contrast, OLETF‐RT rats significantly reduced muscle musclin expression, improved hyperglycemia, and QUICKI through an accelerated muscle GLUT‐4/Akt signaling pathway. Moreover, chronic resistance exercise‐induced reduction of muscle musclin was correlated with changes in fasting glucose, QUICKI, GLUT‐4 translocation, and Akt phosphorylation. These findings suggest that the reduction in muscle‐derived musclin production by chronic resistance exercise may be involved in improved insulin resistance in rats with type 2 diabetes.

Modulation of Insulin Sensitivity by Exercise Training: Implications for Cardiovascular Prevention

The beneficial effects of physical activity on the cardiovascular system nowadays have achieved the relevance of clinical evidence. In fact, several studies have documented the benefits of exercise training in the prevention of the cardiovascular risk. Abnormalities of insulin signaling transduction account for the impairment of insulin sensitivity and development of insulin resistance, which, in turn, is responsible for the enhancement of cardiovascular risk. Insulin sensitivity is related to the degree of physical activity, and physical training has been shown to ameliorate insulin action in insulin-resistant subjects. This effect is mediated by the improvement of the molecular abnormalities that are responsible of the insulin resistance, contributing in this way to restore the physiological insulin sensitivity. However, it should be underlined that mechanisms that account for this phenomenon are extremely complex and still unclear. Further studies are required to better clarify the molecular basis of the exercise-evoked improvement of insulin signal.

Pathophysiology of exercise-induced muscle damage and its structural, functional, metabolic, and clinical consequences

Extreme or unaccustomed eccentric exercise can cause exercise-induced muscle damage, characterized by structural changes involving sarcomere, cytoskeletal, and membrane damage, with an increased permeability of sarcolemma for proteins. From a functional point of view, disrupted force transmission, altered calcium homeostasis, disruption of excitation-contraction coupling, as well as metabolic changes bring about loss of strength. Importantly, the trauma also invokes an inflammatory response and clinically presents itself by swelling, decreased range of motion, increased passive tension, soreness, and a transient decrease in insulin sensitivity. While being damaging and influencing heavily the ability to perform repeated bouts of exercise, changes produced by exercise-induced muscle damage seem to play a crucial role in myofibrillar adaptation. Additionally, eccentric exercise yields greater hypertrophy than isometric or concentric contractions and requires less in terms of metabolic energy and cardiovascular stress, making it especially suitable for the elderly and people with chronic diseases. This review focuses on our current knowledge of the mechanisms underlying exercise-induced muscle damage, their dependence on genetic background, as well as their consequences at the structural, functional, metabolic, and clinical level. A comprehensive understanding of these is a prerequisite for proper inclusion of eccentric training in health promotion, rehabilitation, and performance enhancement.

Ethanolic extract and ethyl acetate fraction of Coutoubea spicata attenuate hyperglycemia, oxidative stress, and muscle damage in alloxan-induced diabetic rats subjected to resistance exercise training program

Gentianaceae family (such as Coutoubea spicata) contains iridoids and flavonoids with antidiabetic properties. However, there is no information available about the antidiabetic effects of C. spicata when combined with resistance exercise training (RET). This study evaluated the effects of the ethanolic extract (EE) and ethyl acetate fraction (EAF) of C. spicata on biochemical markers, muscle damage, and oxidative stress in diabetic rats submitted to RET. Alloxan-induced diabetic rats were distributed into 4 groups (each group, n = 8) treated with distilled water (TD), EE, EAF, or metformin and submitted to RET. Two groups without the disease (each group, n = 8) (sedentary control and trained control), as well as a sedentary diabetic group (n = 8) were included. Body weight and glycemia were evaluated weekly. After 30 days, lipid/lipoprotein profile, aspartate aminotransferase, alanine aminotransferase, muscle damage ((creatine kinase (CK) and lactate dehydrogenase (LDH)), and oxidative stress (malondialdehyde (MDA), sulfhydryl groups (SH), and ferric reducing antioxidant power) were evaluated. MDA and SH for pancreas, liver, heart, and muscle were evaluated. C. spicata extract and fraction combined with RET recovered body weight and reduced glycemia, muscle damage (CK: 36.83% and 21.45%; LDH: 49.83% and 68.55%), and low-density lipoprotein cholesterol (70.63%; 59.18%) and improved redox status (MDA: 50.33%, 39.74%; and SH: 53.97%; 76.41%), respectively, when compared with the TD group. C. spicata plus RET promoted anti-hyperglycemic, lipid-reducing, and antioxidant effects in diabetic rats. Novelty C. spicata presents anti-hyperglycemic and lipid-lowering effects potentiated by RET. C. spicata reduces muscle injury and increases antioxidant defense.

Comparative study of testosterone and vitamin D analogue, elocalcitol, on insulin-controlled signal transduction pathway regulation in human skeletal muscle cells

PURPOSE

Skeletal muscle (Skm) plays a key role in regulating energetic metabolism through glucose homeostasis. Several hormones such as Testosterone (T) and Vitamin D (VD) have been shown to affect energy-dependent cell trafficking by determining Insulin (I)-like effects.

AIM

To elucidate possible hormone-related differences on muscular metabolic control, we analyzed and compared the effects of T and elocalcitol (elo), a VD analogue, on the activation of energy-dependent cell trafficking, metabolism-related-signal transduction pathways and transcription of gene downstream targets.

METHODS

Human fetal skeletal muscle cells (Hfsmc) treated with T or elo were analyzed for GLUT4 localization, phosphorylation/activation status of AKT, ERK1/2, IRS-1 signaling and c-MYC protein expression.

RESULTS

T, similar to elo, induced GLUT4 protein translocation likely in lipid raft microdomains. While both T and elo induced a rapid IRS-1 phosphorylation, the following dynamic in phosphorylation/activation of AKT and ERK1/2 signaling was different. Moreover, T but not elo increased c-MYC protein expression.

CONCLUSIONS

All together, our evidence indicates that whether both T and elo are able to affect upstream I-like pathway, they differently determine downstream effects in I-dependent cascade, suggesting diverse physiological roles in mediating I-like response in human skeletal muscle.

Dietary and exercise interventions and glycemic control and maternal and newborn outcomes in women diagnosed with gestational diabetes: Systematic review

Gestational diabetes mellitus (GDM) is one of the most common complication of pregnancy and can lead to significant perinatal mortalities as well as long term risk of comorbidities for both mother and her offspring. This systematic review aimed to explore whether combined diet and exercise interventions are associated with improved glycemic control and/or improved maternal and newborn outcomes in women with GDM when compared to dietary interventions. A search on combined diet and exercise interventions during pregnancy in women with GDM was performed in 3 electronic databases: PubMed (NCBI), ScienceDierct, and the Cochrane Library. Evaluated outcomes were fasting blood glucose levels, postprandial blood glucose levels, glycated hemoglobin percentages, total weight gain during pregnancy, proportion of caesarean delivery, proportion of patients needing insulin, neonatal birth weight, proportion of macrosomia, neonatal hypoglycemia, and preterm birth. This systematic review identified eight randomized, controlled trials involving 592 pregnant women and 350 infants. The risk of bias of the included trials ranged from high to low. The combined diet and exercise interventions reduced fasting and postprandial blood glucose levels when compared to dietary interventions. No significant differences were reported in the selected trials regarding total weight gain during pregnancy, cesarean section, neonatal birth weight, macrosomia, neonatal hypoglycemia, and preterm birth between diet plus exercise and diet groups. The combination of diet and exercise interventions help to control postprandial blood glucose concentration in women diagnosed with GDM, but did not change either maternal or newborn outcomes. REGISTRATION: PROSPERO CRD42018109896.

Mitochondrial (Dys)function and Insulin Resistance: From Pathophysiological Molecular Mechanisms to the Impact of Diet

Mitochondrial dysfunction has been implicated in the pathogenesis of insulin resistance, the hallmark of type 2 diabetes mellitus (T2DM). However, the cause-effect relationship remains to be fully elucidated. Compelling evidence suggests that boosting mitochondrial function may represent a valuable therapeutic tool to improve insulin sensitivity. Mitochondria are highly dynamic organelles, which adapt to short- and long-term metabolic perturbations by undergoing fusion and fission cycles, spatial rearrangement of the electron transport chain complexes into supercomplexes and biogenesis governed by peroxisome proliferator-activated receptor γ co-activator 1α (PGC 1α). However, these processes appear to be dysregulated in type 2 diabetic individuals. Herein, we describe the mechanistic link between mitochondrial dysfunction and insulin resistance in skeletal muscle alongside the intracellular pathways orchestrating mitochondrial bioenergetics. We then review current evidence on nutritional tools, including fatty acids, amino acids, caloric restriction and food bioactive derivatives, which may enhance insulin sensitivity by therapeutically targeting mitochondrial function and biogenesis.

GLUT1 is associated with sphingolipid-organized, cholesterol-independent domains in L929 mouse fibroblast cells

Glucose is a preferred metabolite in most mammalian cells, and proper regulation of uptake is critical for organism homeostasis. The glucose transporter 1 (GLUT1) is responsible for glucose uptake in a wide variety of cells and appears to be regulated in a tissue specific manner. Therefore, a better understanding of GLUT1 regulation within its various cellular environments is essential for developing therapeutic strategies to treat disorders associated with glucose homeostasis. Previous findings suggest that plasma membrane subdomains called lipid rafts may play a role in regulation of GLUT1 uptake activity. While studying this phenomenon in L929 mouse fibroblast cells, we observed that GLUT1 associates with a low density lipid microdomain distinct from traditionally-defined lipid rafts. These structures are not altered by cholesterol removal with methyl-β-cyclodextrin and lack resistance to cold Triton X-100 extraction. Our data indicate that the GLUT1-containing membrane microdomains in L929 cells, as well as GLUT1's basal activity, are instead sphingolipid-dependent, being sensitive to both myriocin and sphingomyelinase treatment. These microdomains appear to be organized primarily by their lipid composition, as disruption of the actin cytoskeleton or microtubules does not alter the association of GLUT1 with them. Furthermore, the association of GLUT1 with these microdomains appears not to require palmitoylation or glycosylation, as pharmacologic inhibition of these processes had no impact on GLUT1 density in membrane fractions. Importantly, we find no evidence that GLUT1 is actively translocated into or out of low density membrane fractions in response to acute activation in L929 cell.

How diet, physical activity and psychosocial well-being interact in women with gestational diabetes mellitus: an integrative review

Background

Gestational Diabetes Mellitus (GDM) is associated with future cardio-metabolic risks for the mother and her child. In addition, one-third of women with recent GDM develop postpartum depression. Given these adverse impacts of GDM on the health of the mother and her offspring, it is important to intervene on modifiable factors, such as diet, physical activity, and psychosocial well-being. This integrative review therefore explored evidence on how these modifiable factors interact in women with GDM and their offspring, and how effective combined interventions are on reducing adverse impacts of GDM.

Methods

A comprehensive search strategy included carefully selected terms that corresponded to the domains of interest (diet, physical activity and psychosocial well-being). The databases searched for articles published between 1980 and February 2018 were: CINAHL, PsycINFO, Embase, Pubmed and Cochrane. Studies that were included in this review were either observational or intervention studies that included at least two domains of interest. Articles had to at least report data on maternal outcomes of women with GDM.

Results

The search strategies identified 14′419 citations after excluding duplicates. After screening titles and then abstracts, 114 articles were selected for detailed evaluation of their full text, and 16 were included in this review: two observational and 14 intervention studies. Results from observational studies showed that psychosocial well-being (social support and self-efficacy) were positively associated with physical activity and dietary choice. Intervention studies always included diet and physical activity interventions, although none integrated psychosocial well-being in the intervention. These lifestyle interventions mostly led to increased physical activity, improved diet and lower stress perception. Many of these lifestyle interventions also reduced BMI and postpartum diabetes status, improved metabolic outcomes and reduced the risk of preterm deliveries and low birth weight.

Conclusion

This integrative review showed that psychosocial well-being interacted with diet as well as with physical activity in women with GDM. We recommend that future studies consider integrating psychosocial well-being in their intervention, as observational studies demonstrated that social support and self-efficacy helped with adopting a healthy lifestyle following GDM diagnosis.

Electronic supplementary material

The online version of this article (10.1186/s12884-019-2185-y) contains supplementary material, which is available to authorized users.

Effect of combination of chlorella intake and aerobic exercise training on glycemic control in type 2 diabetic rats

OBJECTIVES

Chlorella is a type of unicellular green algae that contains various nutrients. Habitual exercise and chlorella treatment can improve insulin resistance in obese or diabetic animal models. However, the additive effects of combined chlorella intake and aerobic exercise training remain unclear. The aim of this study was to investigate whether a combination of chlorella intake and aerobic exercise training would produce greater effects on improving glycemic control in rats with type 2 diabetes.

METHODS

Twenty-wk-old male rats with type 2 diabetes (Otsuka Long-Evans Tokushima Fatty [OLETF] rats) were randomly divided into four groups: sedentary control, aerobic exercise training (treadmill running for 1 h, 25m/min, 5 d/wk), chlorella intake (0.5% chlorella powder in normal diet), or combination of aerobic exercise training and chlorella intake for 8 wk (n = 7 per group).

RESULTS

Chlorella intake and aerobic exercise training significantly decreased fasting blood glucose, insulin levels, and total glucose area under the curve during the oral glucose tolerance test and increased the insulin sensitivity index concomitant with muscle phosphatidylinositol-3 kinase (PI3K) activity, protein kinase B (Akt) phosphorylation, and glucose transporter 4 (GLUT4) translocation levels. Furthermore, a combination of chlorella intake and aerobic exercise training significantly further improved these effects compared with aerobic exercise training or chlorella intake alone.

CONCLUSIONS

These results suggested that chlorella intake combined with aerobic exercise training had more pronounced effects on the improvement of glycemic control via further activation of muscle PI3K/Akt/GLUT4 signaling in rats with type 2 diabetes.

Prenatal exercise for the prevention of gestational diabetes mellitus and hypertensive disorders of pregnancy: a systematic review and meta-analysis

Objective

Gestational diabetes mellitus (GDM), gestational hypertension (GH) and pre-eclampsia (PE) are associated with short and long-term health issues for mother and child; prevention of these complications is critically important. This study aimed to perform a systematic review and meta-analysis of the relationships between prenatal exercise and GDM, GH and PE.

Design

Systematic review with random effects meta-analysis and meta-regression.

Data sources

Online databases were searched up to 6 January 2017.

Study eligibility criteria

Studies of all designs were included (except case studies) if published in English, Spanish or French, and contained information on the Population (pregnant women without contraindication to exercise), Intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone [“exercise-only”] or in combination with other intervention components [e.g., dietary; “exercise + co-intervention”]), Comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and Outcomes (GDM, GH, PE).

Results

A total of 106 studies (n=273 182) were included. ‘Moderate’ to ‘high’-quality evidence from randomised controlled trials revealed that exercise-only interventions, but not exercise+cointerventions, reduced odds of GDM (n=6934; OR 0.62, 95% CI 0.52 to 0.75), GH (n=5316; OR 0.61, 95% CI 0.43 to 0.85) and PE (n=3322; OR 0.59, 95% CI 0.37 to 0.9) compared with no exercise. To achieve at least a 25% reduction in the odds of developing GDM, PE and GH, pregnant women need to accumulate at least 600 MET-min/week of moderate-intensity exercise (eg, 140 min of brisk walking, water aerobics, stationary cycling or resistance training).

Summary/conclusions

In conclusion, exercise-only interventions were effective at lowering the odds of developing GDM, GH and PE.

Exercise improves glucose uptake in murine myotubes through the AMPKα2-mediated induction of Sestrins

Exercise training increases insulin sensitivity. Over the past decades, considerable progress has been made in understanding the molecular basis for this important effect of physical exercise. However, the underlying mechanism is still not fully described. Recent studies have revealed that the stress responsive protein family Sestrins (SESNs) may play an important role in improving insulin sensitivity of skeletal muscle under exercise training. In this study, we aim to better understand the relationship between SESNs and AMPK in response to exercise training and the possible mechanism by which SESNs mediate glucose metabolism. We used wild type, AMPKα2^+/- and AMPKα2^-/- C57BL/6 mice to reveal the pathway by which 6 weeks of exercise training induced SESNs. We explored the mechanism through which SESNs regulated glucose metabolism in vitro by overexpressing or inhibiting SESNs, and inhibiting AMPK or autophagy in myotubes. We found that a 6-week exercise training regime improved oxidative metabolism, activated the insulin signaling pathway and increased the level of SESN2 and SESN3 in an AMPKα2-dependent manner. Overexpression of SESN3 or SESN2 and SESN3 together increased glucose uptake, activated the insulin signaling pathway, and promoted GLUT4 translocation in myotubes. Although inhibition of SESNs had no effect on glucose uptake, SESNs could reverse reduced glucose uptake following autophagy inhibition, and may be downstream effectors of AMPK responses in myotubes. Taken together our data show that SESNs are induced by AMPKα2 after exercise training, and SESNs, specifically SESN3, play a key role in exercise training-mediated glucose metabolism in skeletal muscle.

Soybean-Hop Alleviates Estrogen Deficiency-Related Bone Loss and Metabolic Dysfunction in Ovariectomized Rats Fed a High-Fat Diet

Soybeans and hops have been traditionally used as a natural estrogen replacement therapy and their major active ingredients, isoflavones and prenylflavanones, are known to have estrogenic/antiestrogenic effects depending on the target organ. However, their potential benefits are still subject to controversies. The present study investigated the dual effect of soy isoflavones plus hop prenylflavanones (Soy-Hop) on bone loss and metabolic dysfunction under estrogen deficient condition. Rats were sham-operated (n = 10) or ovariectomized (OVX; n = 40) and then fed a high-fat diet (HFD) to develop hyperlipidemia in OVX rats within the experimental period of 8 weeks. The OVX/HFD rats were assigned to four groups to receive different doses of Soy-Hop (0, 30, 100, and 300 mg/kg) by oral gavage for 8 weeks. High-dose Soy-Hop significantly suppressed OVX/HFD-induced increases in food intake, body weight gain, fat mass, and circulating levels of leptin, adiponectin, LDL-cholesterol, total cholesterol, triglycerides, glucose, and insulin. High-dose Soy-Hop also attenuated OVX/HFD-induced elevation of osteocalcin, alkaline phosphatase, and CTX in plasma and RANKL/OPG gene expression ratio in femur. These findings were confirmed visually by confocal analysis of GLUT4 translocation in soleus muscle cells and micro-computed tomography scanning of the distal femoral epiphysis, respectively. These results suggest that Soy-Hop may have potential to ameliorate estrogen deficiency-related alterations in both metabolism and bone quality, at least in part, by hormonal factors secreted by adipocytes.

Exercise training prevents skeletal muscle plasma membrane cholesterol accumulation, cortical actin filament loss, and insulin resistance in C57BL/6J mice fed a western-style high-fat diet

Insulin action and glucose disposal are enhanced by exercise, yet the mechanisms involved remain imperfectly understood. While the causes of skeletal muscle insulin resistance also remain poorly understood, new evidence suggest excess plasma membrane (PM) cholesterol may contribute by damaging the cortical filamentous actin (F-actin) structure essential for GLUT4 glucose transporter redistribution to the PM upon insulin stimulation. Here, we investigated whether PM cholesterol toxicity was mitigated by exercise. Male C57BL/6J mice were placed on low-fat (LF, 10% kCal) or high-fat (HF, 45% kCal) diets for a total of 8 weeks. During the last 3 weeks of this LF/HF diet intervention, all mice were familiarized with a treadmill for 1 week and then either sham-exercised (0 m/min, 10% grade, 50 min) or exercised (13.5 m/min, 10% grade, 50 min) daily for 2 weeks. HF-feeding induced a significant gain in body mass by 3 weeks. Sham or chronic exercise did not affect food consumption, water intake, or body mass gain. Prior to sham and chronic exercise, "pre-intervention" glucose tolerance tests were performed on all animals and demonstrated that HF-fed mice were glucose intolerant. While sham exercise did not affect glucose tolerance in the LF or HF mice, exercised mice showed an improvement in glucose tolerance. Muscle from sham-exercised HF-fed mice showed a significant increase in PM cholesterol, loss of cortical F-actin, and decrease in insulin-stimulated glucose transport compared to sham-exercised LF-fed mice. These HF-fed skeletal muscle membrane/cytoskeletal abnormalities and insulin resistance were improved in exercised mice. These data reveal a new therapeutic aspect of exercise being regulation of skeletal muscle PM cholesterol homeostasis. Further studies on this mechanism of insulin resistance and the benefits of exercise on its prevention are needed.

Effects of weekly supervised exercise or physical activity counseling on fasting blood glucose in women diagnosed with gestational diabetes mellitus: A systematic review and meta-analysis of randomized trials

BACKGROUND

Exercise is an important part of gestational diabetes mellitus (GDM) lifestyle management. However, no meta-analysis has analyzed the effects of exercise programs on fasting blood glucose (FBG) in women with GDM. A systematic review with meta-analysis was performed to evaluate the effects of weekly supervised exercise (EXE) or physical activity counseling (PA) in women with GDM compared with usual prenatal care (UPN) on glycemic control.

METHODS

Eligible trials were identified from Medline, EMBASE, Web of Science, Scopus and SportDiscus up to December 2016. Data were retrieved from randomized controlled trials comparing UPN with UPN plus weekly supervised (at least once a week) prenatal exercise or PA counseling for which FBG values before and after intervention were available. Random-effects meta-analysis was performed for mean difference in FBG after exercise intervention.

RESULTS

The search yielded 781 publications, of which 82 were assessed for eligibility and eight were included in the meta-analysis. The overall effect on absolute FBG concentrations was not significant (P = 0.11) compared with UPN. However, PA versus UPN showed a significant reduction in absolute FBG concentrations (weighted mean difference -3.88 mg/dL; 95% confidence interval -7.33, -0.42 mg/dL; I ² 48%; P _{heterogeneity}  < 0.15).

CONCLUSIONS

Physical activity counseling in women with GDM showed a significant effect compared with UPN on FBG concentrations, possibly due to a longer follow-up time compared with the EXE groups. This result highlights the importance of an early intervention that lasts to delivery for best practice of GDM management.

Leisure Time Physical Activity and Gestational Diabetes Mellitus in the Omega Study

PURPOSE

Findings of studies investigating associations of leisure time physical activity (LTPA) with gestational diabetes mellitus (GDM) risk have been inconsistent. We investigated associations of LTPA with GDM and whether these associations differ by prepregnancy overweight/obese status or gestational weight gain category.

METHODS

Participants (N = 3209) of the Omega study, a pregnancy cohort study in Washington State (1996-2008), reported LTPA duration (h·wk) and energy expenditure (MET·h·wk) in the year before pregnancy and in early pregnancy. Diagnoses of GDM were abstracted from medical records. Poisson regression models were used to determine relative risks of GDM across tertiles of prepregnancy or early pregnancy LTPA duration and energy expenditure. Stratified analyses and interaction terms were used to assess effect modification by prepregnancy overweight/obese status (BMI ≥25 kg·m) or gestational weight gain category (adequate or excessive).

RESULTS

Each tertile increase in prepregnancy LTPA duration or energy expenditure was associated with 15% (95% CI = 0.72-1.00) and 19% (95% CI = 0.69-0.96) lower risk of GDM, respectively. Each tertile increase in early pregnancy LTPA duration or energy expenditure was associated with 16% (95% CI = 0.72-0.97) and 17% (95% CI = 0.72-0.95) lower risk of GDM, respectively. LTPA during both prepregnancy and early pregnancy was associated with a 46% reduced risk of GDM (95% CI = 0.32-0.89) compared with inactivity during both periods. LTPA-GDM associations were similar by prepregnancy BMI and gestational weight gain.

CONCLUSION

Our results support a role for the promotion of physical activity before and during pregnancy in the prevention of GDM.

Healthy Lifestyle During Early Pregnancy and Risk of Gestational Diabetes Mellitus

Previous studies have found associations between individual healthy behaviors and reduced risk of gestational diabetes mellitus (GDM); however, the association of composite healthy lifestyle during pregnancy with GDM has not been examined. Participants in the Omega Study (n = 3,005), a pregnancy cohort study conducted in Washington State (1996-2008), reported information on diet, physical activity, smoking, and stress during early pregnancy. Lifestyle components were dichotomized into healthy/unhealthy and then combined into a total lifestyle score (range, 0-4). Regression models were used to determine relative risk of GDM (n = 140 cases) in relation to healthy lifestyle. Twenty percent of participants had a healthy diet, 66% were physically active, 95% were nonsmokers, and 55% had low stress. Each 1-point increase in lifestyle score was associated with a 21% lower risk of GDM (95% confidence interval: 0.65, 0.96) after adjustment for age, race, and nulliparity. Adjustment for prepregnancy body mass index, prepregnancy physical activity, and prepregnancy smoking attenuated the associations slightly. Associations were similar in normal-weight and overweight/obese women. In this study, a composite measure of healthy lifestyle during early pregnancy was associated with substantially lower GDM risk. Public health messaging and interventions promoting multiple aspects of a healthy lifestyle during early pregnancy should be considered for GDM prevention.

Metabolic responses to exercise on land and in water following glucose ingestion

Although aerobic exercise after a meal decreases postprandial blood glucose, the differences in glucose response between land and aquatic exercise are unclear. Thus, we examined the effect of different modes of exercise with same energy expenditure following glucose ingestion on carbohydrate metabolism. Ten healthy sedentary men (age, 22 ± 1 years) participated in this study. All subjects performed each of three exercise modes (cycling, walking and aquatic exercise) for 30 min after ingestion of a 75-g glucose solution with 1-2 weeks between trials. The exercise intensity was set at 40% of the maximum oxygen uptake that occurred during cycling. The velocity during walking and the target heart rate during aquatic exercise were predetermined in a pretest. The plasma glucose concentration at 30 min after exercise was significantly lower with aquatic exercise compared to that with cycling and walking (P<0·05). However, there were no significant differences among the three exercise modes in respiratory exchange ratio. On the other hand, serum free fatty acid concentration with aquatic exercise was significantly higher at 120 min after exercise compared with that after walking (P<0·05). These results suggest that aquatic exercise reduces postprandial blood glucose compared with both cycling and walking with the same energy expenditure. Aquatic exercise shows potential as an exercise prescription to prevent postprandial hyperglycaemia.

Adrenoceptors promote glucose uptake into adipocytes and muscle by an insulin-independent signaling pathway involving mechanistic target of rapamycin complex 2

Uptake of glucose into skeletal muscle and adipose tissue plays a vital role in metabolism and energy balance. Insulin released from β-islet cells of the pancreas promotes glucose uptake in these target tissues by stimulating translocation of GLUT4 transporters to the cell surface. This process is complex, involving signaling proteins including the mechanistic (or mammalian) target of rapamycin (mTOR) and Akt that intersect with multiple pathways controlling cell survival, growth and proliferation. mTOR exists in two forms, mTOR complex 1 (mTORC1), and mTOR complex 2 (mTORC2). mTORC1 has been intensively studied, acting as a key regulator of protein and lipid synthesis that integrates cellular nutrient availability and energy balance. Studies on mTORC2 have focused largely on its capacity to activate Akt by phosphorylation at Ser473, however recent findings demonstrate a novel role for mTORC2 in cellular glucose uptake. For example, agonists acting at β₂-adrenoceptors (ARs) in skeletal muscle or β₃-ARs in brown adipose tissue increase glucose uptake in vitro and in vivo via mechanisms dependent on mTORC2 but not Akt. In this review, we will focus on the signaling pathways downstream of β-ARs that promote glucose uptake in skeletal muscle and brown adipocytes, and will highlight how the insulin and adrenergic pathways converge and interact in these cells. The identification of insulin-independent mechanisms that promote glucose uptake should facilitate novel treatment strategies for metabolic disease.

Testosterone stimulates glucose uptake and GLUT4 translocation through LKB1/AMPK signaling in 3T3-L1 adipocytes

Decreases in serum testosterone concentrations in aging men are associated with metabolic disorders. Testosterone has been reported to increase GLUT4-dependent glucose uptake in skeletal muscle cells and cardiomyocytes. However, studies on glucose uptake occurring in response to testosterone stimulation in adipocytes are currently not available. This study was designed to determine the effects of testosterone on glucose uptake in adipocytes. Glucose uptake was assessed with 2-[(3)H] deoxyglucose in 3T3-L1 adipocytes. GLUT4 translocation was evaluated in plasma membrane (PM) sheets and PM fractions by immunofluorescence and immunoblotting, respectively. Activation of GLUT4 translocation-related protein kinases, including Akt, AMPK, LKB1, CaMKI, CaMKII, and Cbl was followed by immunoblotting. Expression levels of androgen receptor (AR) mRNA and AR translocation to the PM were assessed by real-time RT-PCR and immunoblotting, respectively. The results showed that both high-dose (100 nM) testosterone and testosterone-BSA increased glucose uptake and GLUT4 translocation to the PM, independently of the intracellular AR. Testosterone and testosterone-BSA stimulated the phosphorylation of AMPK, LKB1, and CaMKII. The knockdown of LKB1 by siRNA attenuated testosterone- and testosterone-BSA-stimulated AMPK phosphorylation and glucose uptake. These results indicate that high-dose testosterone and testosterone-BSA increase GLUT4-dependent glucose uptake in 3T3-L1 adipocytes by inducing the LKB1/AMPK signaling pathway.

Metabolic, anabolic, and mitogenic insulin responses: A tissue-specific perspective for insulin receptor activators

Insulin acts as the major regulator of the fasting-to-fed metabolic transition by altering substrate metabolism, promoting energy storage, and helping activate protein synthesis. In addition to its glucoregulatory and other metabolic properties, insulin can also act as a growth factor. The metabolic and mitogenic responses to insulin are regulated by divergent post-receptor signaling mechanisms downstream from the activated insulin receptor (IR). However, the anabolic and growth-promoting properties of insulin require tissue-specific inter-relationships between the two pathways, and the nature and scope of insulin-regulated processes vary greatly across tissues. Understanding the nuances of this interplay between metabolic and growth-regulating properties of insulin would have important implications for development of novel insulin and IR modulator therapies that stimulate insulin receptor activation in both pathway- and tissue-specific manners. This review will provide a unique perspective focusing on the roles of "metabolic" and "mitogenic" actions of insulin signaling in various tissues, and how these networks should be considered when evaluating selective pharmacologic approaches to prevent or treat metabolic disease.

Physical activity interventions in pregnancy and risk of gestational diabetes mellitus: a systematic review and meta-analysis

OBJECTIVE

Gestational diabetes mellitus (GDM) is a common complication of pregnancy associated with an increased incidence of pregnancy complications, adverse pregnancy outcomes, and maternal and fetal risks of chronic health conditions later in life. Physical activity has been proposed to reduce the risk of GDM and is supported by observational studies, but experimental research assessing its effectiveness is limited and conflicting. We aimed to use meta-analysis to synthesize existing randomized controlled studies of physical activity and GDM.

DATA SOURCES

We searched MEDLINE, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov for eligible studies.

METHODS OF STUDY SELECTION

The following combination of keywords was used: (pregnant or pregnancy or gestation or gestate or gestational or maternity or maternal or prenatal) AND (exercise or locomotion or activity or training or sports) AND (diabetes or insulin sensitivity or glucose tolerance) AND (random* or trial). Eligibility was restricted to studies that randomized participants to an exercise-only-based intervention (ie, separate from dietary interventions) and presented data regarding GDM risk. Two authors performed the database search, assessment of eligibility, and abstraction of data from included studies, and a third resolved any discrepancies. A total of 469 studies was retrieved, of which 10 met inclusion criteria and could be used for analysis (3,401 participants).

TABULATION, INTEGRATION, AND RESULTS

Fixed-effects models were used to estimate summary relative risk (RR) and 95% confidence interval (CI) and I to assess heterogeneity. There was a 28% reduced risk (95% CI 9-42%) in the intervention group compared with the control group (RR 0.72, P=.005). Heterogeneity was low (I=12%) and nonsignificant (P=.33).

CONCLUSION

The results from this meta-analysis suggest that physical activity in pregnancy provides a slight protective effect against the development of GDM. Studies evaluating type, timing, duration, and compliance of physical activity regimens are warranted to best inform obstetric guidelines.

AMPK binds to Sestrins and mediates the effect of exercise to increase insulin-sensitivity through autophagy

OBJECTIVE

Exercise has beneficial effects on human health, including protection against metabolic disorders such as diabetes. However, the cellular mechanisms underlying the metabolic effects of exercise are not completely understood. We know that autophagy plays an important role in maintaining cellular homeostasis. In this study, we aimed to better understand the metabolic effects of autophagy in skeletal muscle and the role of Sestrins/AMPK in mediating the beneficial effects of physical exercise through autophagy.

MATERIAL/METHODS

We used wild type and AMPKα2(-/-) C57BL/6 mice as animal models to elucidate the role of AMPK in autophagy activation and the metabolism-promoting effects of acute and regular exercise. C2C12 myotubes were used to study the metabolic effects of autophagy in vitro.

RESULTS

Autophagy promotes glucose uptake in skeletal muscle. A single bout of exercise increased the activity of autophagy in the skeletal muscle of wild type mice but not of AMPKα2(-/-) mice. This difference was associated with increased amounts of both Sestrin2 and Sestrin3 coimmunoprecipitated with AMPKα2. Long-term physical exercise significantly increased the basal level of muscle autophagy and protein expression of Sestrin2 and Sestrin3 in both normal chow and high-fat diet-fed mice.

CONCLUSION

We believe that exercise-induced AMPK and Sestrins interaction may be involved in the beneficial metabolic effects of exercise by activating autophagy. This interaction provides a molecular mechanism that is a potential target in metabolic syndromes.

Two chalcones, 4-hydroxyderricin and xanthoangelol, stimulate GLUT4-dependent glucose uptake through the LKB1/AMP-activated protein kinase signaling pathway in 3T3-L1 adipocytes

4-Hydroxyderricin (4HD) and xanthoangelol (XAG) are major components of n-hexane/ethyl acetate (5:1) extract of the yellow-colored stem juice of Angelica keiskei. 4-Hydroxyderricin and XAG have been reported to increase glucose transporter 4 (GLUT4)-dependent glucose uptake in 3T3-L1 adipocytes, but the detailed mechanism of this phenomenon remains unknown. This present study was aimed at clarifying the detailed mechanism by which 4HD and XAG increase GLUT4-dependent glucose uptake in 3T3-L1 adipocytes. Both 4HD and XAG increased glucose uptake and GLUT4 translocation to the plasma membrane. 4-Hydroxyderricin and XAG also stimulated the phosphorylation of 5' adenosine monophosphate-activated protein kinase (AMPK) and its downstream target acetyl-CoA carboxylase. In addition, phosphorylation of liver kinase B1 (LKB1), which acts upstream of AMPK, was also increased by 4HD and XAG treatment. Small interfering RNA knockdown of LKB1 attenuated 4HD- and XAG-stimulated AMPK phosphorylation and suppressed glucose uptake. These findings demonstrate that 4HD and XAG can increase GLUT4-dependent glucose uptake through the LKB1/AMPK signaling pathway in 3T3-L1 adipocytes.

Ursolic acid improves lipid and glucose metabolism in high-fat-fed C57BL/6J mice by activating peroxisome proliferator-activated receptor alpha and hepatic autophagy

SCOPE

This study investigated metabolic effects of ursolic acid (UA), a peroxisome proliferation-activated receptor (PPAR)-α activator, in vivo.

METHODS AND RESULTS

High-fat diet (HFD)-fed C57BL/6J mice were orally administered UA (50 or 200 mg/kg body weight) for 8 wk. UA reduced liver and adipose tissue mass, adipocyte size, and plasma leptin concentrations, plasma triglyceride and low-density-lipoprotein cholesterol concentrations, while it elevated the high-density-lipoprotein cholesterol and adiponectin concentrations significantly compared with controls. UA induced the expression of PPARα and its responsive genes involved in fatty acid uptake and β-oxidation in the livers, whereas genes involved in lipogenesis, including sterol regulatory element-binding proteins-1c, were downregulated. UA administration improved glucose tolerance and insulin sensitivity significantly compared with the HFD-fed control livers. UA administration also activated hepatic autophagy as assessed by the expression of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II and other key proteins in the autophagy pathway.

CONCLUSION

Our findings suggest that UA ameliorates lipid and glucose metabolism in HFD-fed mice primarily by the activation of PPARα and induction of the hepatic autophagy pathway. Thus, intake of UA in the diet or in an isolated form may ameliorate lipid and glucose metabolism.

A pregnancy lifestyle intervention to prevent gestational diabetes risk factors in overweight Hispanic women: a feasibility randomized controlled trial

AIMS

To pilot the feasibility of a prenatal lifestyle intervention to modify physical activity and diet among pregnant overweight and obese Hispanic women, with the aim of reducing risk factors for gestational diabetes mellitus.

METHODS

Women were randomized either to a lifestyle intervention (n = 33, 48.5%), consisting of a culturally and linguistically modified, motivationally targeted, individually tailored 6-month prenatal programme, or to standard care (n = 35, 51.5%). Bilingual and bicultural health educators encouraged women to achieve guidelines for physical activity, decrease saturated fat and increase dietary fibre. Outcomes included gestational weight gain, infant birth weight and biomarkers associated with insulin resistance.

RESULTS

Patient retention up to delivery was 97% in both study groups. The lifestyle intervention attenuated the pregnancy-associated decline in moderate-intensity physical activity, but differences between groups were not significant (mean ± se -23.4 ± 16.6 vs -27.0 ± 16.2 metabolic equivalent of task h/week; P = 0.88). Vigorous-intensity activity increased during the course of pregnancy in the lifestyle intervention group (mean ± se 1.6 ± 0.8 metabolic equivalent of task h/week) and declined in the standard care group (-0.8 ± 0.8 metabolic equivalent of task h/week; P = 0.04). The lifestyle intervention group also had slightly lower gestational weight gain and infant birth weights compared with the standard care group; however, these differences were not statistically significant. There were no statistically significant differences in biomarkers of insulin resistance between groups.

CONCLUSIONS

Findings suggest that a motivationally matched lifestyle intervention is feasible and may help attenuate pregnancy-related decreases in vigorous physical activity in a population of overweight and obese Hispanic women. The intervention protocol can readily be translated into clinical practice in underserved and minority populations.

The inhibition effects of insulin on BMP2-induced muscle heterotopic ossification

Bone morphogenetic proteins (BMPs) play an important role in regulating osteoblastic differentiation and bone formation. But the diffuse of BMPs into muscle tissues around bone injury sites often leads to heterotopic ossification, which has been regarded as one of major side-effects of BMP implementation in bone defect patients. It raises great demands for exploring effective methods that preventing BMP-induced heterotopic ossification while not interrupting the osteoinductive activity of BMPs for in situ bone defect repair. Here we found insulin, a positive regulator for bone regeneration, inhibited BMP2-induced muscle heterotopic ossification by suppressing the expression of bone transcription factor Osterix. By analyzing downstream molecules of insulin pathway, we found AKT/mTOR/GSK3 signaling was responsible for the inhibition of insulin on BMP2-induced ossification, and GSK3 inhibitor SB216763 attenuated BMP2-induced muscle heterotopic ossification. The data might shed light on developing effective clinical therapy for inhibiting muscle heterotopic ossification when BMPs were used bone defect repair.

Diabetes-ameliorating effects of fermented red ginseng and causal effects on hormonal interactions: testing the hypothesis by multiple group path analysis

Although diagnostic criteria for metabolic syndrome (MtS) vary among various health professionals and organizations, blood glucose dysregulation and insulin resistance are common to all definitions. Red ginseng is beneficial for glucose regulation and insulin sensitivity but the mechanism is not yet elucidated. Ginsenosides Rh1 and Rg3 act as ligands of the estrogen receptor, and Rh2 and compound K act as ligands of the glucocorticoid receptors, which may influence the diabetes markers. The objective of this study was to test the hypothesis that there are significant causal relationships among diabetes-related markers and several hormones, and assess whether or not the consumption of fermented red ginseng (FRG) influences these causal relationships by multiple group path analysis and conventional statistical analyses. The 93 postmenopausal women were randomly divided into two groups for a double-blind trial. FRG powder and placebo were provided for 2 weeks. The data were analyzed by multiple group path analysis and the mean between groups were compared. The model's goodness of fit was excellent, with a root mean square error of approximation of 0.00, and comparative fit index of 1.00. The FRG group exhibited significantly increased levels of dehydroepiandrosterone sulfate (DHEAS), growth hormone (GH), and estradiol (E2), and they exhibited decreased levels of glycosylated hemoglobin (HbA1c), insulin, and homeostatic model assessment of insulin resistance. With regard to the hypothesis, the blood glucose lowering effects of FRG were due to the negative effects of aldosterone and increased GH, which was associated with DHEAS and E2. Even though the differences of variables between both groups were small, the total effects of these variables may indicate beneficial changes for the prevention of diabetes in healthy postmenopausal women.

Pectinase-Processed Ginseng Radix (GINST) Ameliorates Hyperglycemia and Hyperlipidemia in High Fat Diet-Fed ICR Mice

To develop a ginseng product possessing an efficacy for diabetes, ginseng radix ethanol extract was treated with pectinase and obtained the GINST. In the present study, we evaluate the beneficial effect of GINST on high fat diet (HFD)-induced hyper-glycemia and hyperlipidemia and action mechanism(s) in ICR mice. The mice were randomly divided into five groups: regular diet group (RD), high fat diet group (HFD), HFD plus GINST at 75 mg/kg (GINST75), 150 mg/kg (GINST150), and 300 mg/kg (GINST300). Oral glucose tolerance test reveals that GINST improves the glucose tolerance after glucose challenge. Fasting plasma glucose and insulin levels were decreased by 4.3% and 4.2% in GINST75, 10.9% and 20.0% in GINST150, and 19.6% and 20.9% in GINST300 compared to those in HFD control group. Insulin resistance indices were also markedly decreased by 8.2% in GINST75, 28.7% in GINST150, and 36.4% in GINST300, compared to the HFD control group. Plasma triglyceride, total cholesterol and non-esterified fatty acid levels in the GINST300 group were decreased by 13.5%, 22.7% and 24.1%, respectively, compared to those in HFD control group. Enlarged adipocytes of HFD control group were markedly decreased in GINST-treated groups, and shrunken islets of HFD control mice were brought back to near normal shape in GINST300 group. Furthermore, GINST enhanced phosphorylation of AMP-activated protein kinase (AMPK) and glucose transporter 4 (GLUT4). In summary, GINST prevents HFD-induced hyperglycemia and hyperlipidemia through reducing insulin resistance via activating AMPK-GLUT4 pathways, and could be a potential therapeutic agent for type 2 diabetes.

The important role of physical activity in the prevention and management of gestational diabetes mellitus

The actual pathophysiology behind gestational diabetes mellitus (GDM) is still unclear, but a deterioration in insulin resistance beyond that induced by pregnancy, combined with beta cell dysfunction, plays a key role. Interventions that help improve glucose tolerance by attenuating pregnancy-induced insulin resistance or achieve glycaemic control may therefore help in preventing and managing GDM. In non-pregnant populations, physical activity has been associated with an improvement in glucose homeostasis and insulin sensitivity and a risk reduction for type 2 diabetes mellitus (T2DM) and is a cornerstone for T2DM treatment. However, there is still controversy regarding the benefits of physical activity in preventing and managing GDM. The objective of this review is therefore to provide a comprehensive overview of the effect of prenatal physical activity-based interventions on (1) glucose tolerance, insulin sensitivity and GDM prevention and (2) glycaemic control and insulin use in GDM women. On the basis of the available literature, there is a lack of consistent evidence regarding the benefits of physical activity on improving glucose tolerance and insulin sensitivity and preventing GDM. However, it appears that physical activity may help to achieve good glycaemic control and limit insulin use in GDM women. Compliance appears to be a major problem in physical activity-based intervention studies aimed at GDM prevention. Rigorous scientific research is still required to make an informed decision about the role of physical activity in the prevention and management of GDM and to develop evidence-based physical activity guidelines for GDM prevention and management.

Skeletal muscle signaling associated with impaired glucose tolerance in spinal cord-injured men and the effects of contractile activity

The mechanisms underlying poor glucose tolerance in persons with spinal cord injury (SCI), along with its improvement after several weeks of neuromuscular electrical stimulation-induced resistance exercise (NMES-RE) training, remain unclear, but presumably involve the affected skeletal musculature. We, therefore, investigated skeletal muscle signaling pathways associated with glucose transporter 4 (GLUT-4) translocation at rest and shortly after a single bout of NMES-RE in SCI (n = 12) vs. able-bodied (AB, n = 12) men. Subjects completed an oral glucose tolerance test during visit 1 and ≈90 NMES-RE isometric contractions of the quadriceps during visit 2. Muscle biopsies were collected before, and 10 and 60 min after, NMES-RE. We assessed transcript levels of GLUT-4 by quantitative PCR and protein levels of GLUT-4 and phosphorylated- and total AMP-activated protein kinase (AMPK)-α, CaMKII, Akt, and AS160 by immunoblotting. Impaired glucose tolerance in SCI was confirmed by higher (P < 0.05) plasma glucose concentrations than AB at all time points after glucose ingestion, despite equivalent insulin responses to the glucose load. GLUT-4 protein content was lower (P < 0.05) in SCI vs. AB at baseline. Main group effects revealed higher phosphorylation in SCI of AMPK-α, CaMKII, and Akt (P < 0.05), and Akt phosphorylation increased robustly (P < 0.05) following NMES-RE in SCI only. In SCI, low skeletal muscle GLUT-4 protein concentration may, in part, explain poor glucose tolerance, whereas heightened phosphorylation of relevant signaling proteins (AMPK-α, CaMKII) suggests a compensatory effort. Finally, it is encouraging to find (based on Akt) that SCI muscle remains both sensitive and responsive to mechanical loading (NMES-RE) even ≈22 yr after injury.

Effects of electrical microstimulation of peripheral sympathetic nervous fascicle on glucose uptake in rats

Artificial pancreas systems control insulin-mediated glucose uptake. Although these systems are widely used in the clinical setting, they are still fraught with structural and biological problems. The non-insulin mediated glucose uptake (NIMGU) mechanism could be an alternative candidate as a target system for the artificial control of peripheral glucose uptake. Although the sympathetic nervous system is known to be one of the regulators of NIMGU, the effects of peripheral sympathetic activation on glucose uptake have not been well documented. We electrically stimulated a sympathetic nerve fascicle to clarify the possibility of controlling peripheral glucose uptake. A sympathetic signal was microneurographically obtained in the unilateral sciatic nerve in normal (NRML), insulin-resistant high-fat-fed (HFF), and streptozotocin-induced insulin-depleted (STZ) rats, and electrical stimulation was applied via the microelectrode (microstimulation). The microstimulation was also applied to sites other than the sympathetic fascicles in an additional group of normal rats (NSYMP group). The stimulation applied to the sympathetic fibers resulted in an immediate and transient decrease of blood glucose (BG) in the NRML, HFF, and STZ groups, with little change in the plasma insulin. The change in BG level seemed to depend on the basal BG level (NRML < HFF < STZ). In contrast, no reduction in BG was observed in the NSYMP group. These results suggest that microstimulation in the peripheral sympathetic fascicle could enhance glucose uptake in peripheral tissues-independently of insulin function-and show an alternative possibility for controlling glucose uptake.

High oxidative capacity due to chronic exercise training attenuates lipid-induced insulin resistance

Fat accumulation in skeletal muscle combined with low mitochondrial oxidative capacity is associated with insulin resistance (IR). Endurance-trained athletes, characterized by a high oxidative capacity, have elevated intramyocellular lipids, yet are highly insulin sensitive. We tested the hypothesis that a high oxidative capacity could attenuate lipid-induced IR. Nine endurance-trained (age = 23.4 ± 0.9 years; BMI = 21.2 ± 0.6 kg/m(2)) and 10 untrained subjects (age = 21.9 ± 0.9 years; BMI = 22.8 ± 0.6 kg/m(2)) were included and underwent a clamp with either infusion of glycerol or intralipid. Muscle biopsies were taken to perform high-resolution respirometry and protein phosphorylation/expression. Trained subjects had ~32% higher mitochondrial capacity and ~22% higher insulin sensitivity (P < 0.05 for both). Lipid infusion reduced insulin-stimulated glucose uptake by 63% in untrained subjects (P < 0.05), whereas this effect was blunted in trained subjects (29%, P < 0.05). In untrained subjects, lipid infusion reduced oxidative and nonoxidative glucose disposal (NOGD), whereas trained subjects were completely protected against lipid-induced reduction in NOGD, supported by dephosphorylation of glycogen synthase. We conclude that chronic exercise training attenuates lipid-induced IR and specifically attenuates the lipid-induced reduction in NOGD. Signaling data support the notion that high glucose uptake in trained subjects is maintained by shuttling glucose toward storage as glycogen.

Physical exercise and pancreatic islets: acute and chronic actions on insulin secretion

Diabetes mellitus (DM) is a great public health problem, which attacks part of the world population, being characterized by an imbalance in body glucose homeostasis. Physical exercise is pointed as a protective agent and is also recommended to people with DM. As pancreatic islets present an important role in glucose homeostasis, we aim to study the role of physical exercise (chronic adaptations and acute responses) in pancreatic islets functionality in Wistar male rats. First, animals were divided into two groups: sedentary (S) and aerobic trained (T). At the end of 8 weeks, half of them (S and T) were submitted to an acute exercise session (exercise until exhaustion), being subdivided as acute sedentary (AS) and acute trained (AT). After the experimental period, periepididymal, retroperitoneal and subcutaneous fat pads, blood, soleus muscle and pancreatic islets were collected and prepared for further analysis. From the pancreatic islets, total insulin content, insulin secretion stimulated by glucose, leucine, arginine and carbachol were analyzed. Our results pointed that body adiposity and glucose homeostasis improved with chronic physical exercise. In addition, total insulin content was reduced in group AT, insulin secretion stimulated by glucose was reduced in trained groups (T and AT) and insulin secretion stimulated by carbachol was increased in group AT. There were no significant differences in insulin secretion stimulated by arginine and leucine. We identified a possible modulating action on insulin secretion, probably related to the association of chronic adaptation with an acute response on cholinergic activity in pancreatic islets.