Exercise-induced increase in muscle insulin sensitivity

Targeting thermogenesis and related pathways in anti-obesity drug discovery

The health consequences of the obesity epidemic are a huge burden on patients and society. Yet it remains an unmet therapeutic need. Lifestyle or behaviour modification, although desirable, seems to benefit only a few and bariatric surgery is not an option for all and not without risks. Nevertheless, bariatric surgery is currently the gold standard in terms of weight loss therapy and any weight loss agent will be in combination with management of lifestyle modification. Sadly, there is a poor history for the pharmacological treatment of obesity and repeated safety concerns have attracted intense regulatory scrutiny. Indeed, recent market withdrawals leave us with just one agent approved for the long term treatment of obesity and that is only mildly efficacious in terms of weight loss, although it is beneficial in terms of metabolic health. There are two broad pharmacological approaches that can be applied in obesity drug discovery: reduce intake (or absorption) or increase expenditure (thermogenesis) of calories. In this review we will look at the latter approach. We will cover regulatory requirements and the rationale for this approach. We believe that post-obese subjects display abnormal metabolic responses to weight loss that almost inevitably leads to weight regain. We will then explore a number of approaches that potentially increase thermogenesis in humans. The challenge we have is in accumulating enough human data to validate this approach using drugs.

Prolonged exercise-induced stimulation of skeletal muscle glucose uptake is due to sustained increases in tissue perfusion and fractional glucose extraction

CONTEXT

The mechanisms behind the positive effects of physical activity on glucose metabolism in skeletal muscle and the time course of the effects need to be more elucidated.

OBJECTIVE

The aim was to examine the prolonged effects of an acute bout of one-legged exercise on local skeletal muscle glucose utilization and tissue perfusion.

DESIGN AND SETTING

Interstitial glucose concentration, local tissue perfusion, glucose uptake, and effects of insulin infusion were studied 12 h after an acute bout of exercise and without prior exercise.

PARTICIPANTS

Ten healthy subjects, five women and five men, participated in the study.

INTERVENTION

Microdialysis measurements, (133)Xe clearance, and a 2-h hyperinsulinemic euglycemic clamp were performed on two occasions.

MAIN OUTCOME MEASURES

We measured interstitial glucose concentration and tissue perfusion in the quadriceps femoris muscle of both legs.

RESULTS

Tissue perfusion (3.3 ± 0.6 ml × 100 g(-1) × min(-1) vs. 1.4 ± 0.2 ml × 100 g(-1) × min(-1); P = 0.007) and basal glucose uptake (2.3 ± 0.5 μmol × 100 g(-1) × min(-1) vs. 0.9 ± 0.2 μmol × 100 g(-1) × min(-1); P = 0.006) were increased in the leg that had exercised compared to the resting leg; the findings in the resting leg were comparable to those in the control experiment without prior exercise. The relative effect of insulin on fractional skeletal muscle glucose uptake was the same in all experimental settings, and insulin did not affect tissue perfusion.

CONCLUSIONS

The prolonged stimulatory effect of physical exercise on skeletal muscle glucose uptake was mediated via vascular effects combined with an increase in basal glucose transport independent of enhancement of insulin responses.

Upright water-based exercise to improve cardiovascular and metabolic health: a qualitative review

Research regarding the benefits of exercise for cardiovascular and metabolic health is extensive and well-documented. However, weight-bearing exercise may not be suitable for individuals with orthopaedic or musculoskeletal limitations, excess adiposity or other medical conditions. Water-based exercise may provide an attractive alternative to land-based exercise for achieving improved health and fitness in these populations. Although swimming is a popular form of water-based exercise it requires specific skills and is often undertaken at intensities that may not be safely prescribed in patient populations. Therefore upright, water-based exercise has been suggested as a viable water-based alternative. However, surprisingly little is known about the effects of upright water-based exercise on improvements in cardiovascular and metabolic health. Limited evidence from water-based studies indicate that regular deep or shallow water exercise can exert beneficial effects on cardiorespiratory fitness, strength, and body fat distribution. However, the impacts of water-based exercise on lipid profile, bodyweight, and carbohydrate metabolism are still unclear. Further studies are warranted to establish the effects of non-swimming, water-based exercise on cardiometabolic risks in humans.

Management of hypertension and diabetes in obesity: non-pharmacological measures

Obesity has become a global epidemic over the past few decades because of unhealthy dietary habits and reduced physical activity. Hypertension and diabetes are quite common among obese individuals and there is a linear relationship between the degree of obesity and these diseases. Lifestyle interventions like dietary modifications and regular exercise are still important and safe first-line measures for treatment. Recently, bariatric surgery has emerged as an important and very effective treatment option for obese individuals especially in those with comorbidities like hypertension and diabetes. Though there are few effective drugs for the management of obesity, their efficacy is only modest, and they should always be combined with lifestyle interventions for optimal benefit. In this paper we aim to outline the non-pharmacological measures for the management of hypertension and diabetes in obesity.

Lipid profiling identifies a triacylglycerol signature of insulin resistance and improves diabetes prediction in humans

Dyslipidemia is an independent risk factor for type 2 diabetes, although exactly which of the many plasma lipids contribute to this remains unclear. We therefore investigated whether lipid profiling can inform diabetes prediction by performing liquid chromatography/mass spectrometry-based lipid profiling in 189 individuals who developed type 2 diabetes and 189 matched disease-free individuals, with over 12 years of follow up in the Framingham Heart Study. We found that lipids of lower carbon number and double bond content were associated with an increased risk of diabetes, whereas lipids of higher carbon number and double bond content were associated with decreased risk. This pattern was strongest for triacylglycerols (TAGs) and persisted after multivariable adjustment for age, sex, BMI, fasting glucose, fasting insulin, total triglycerides, and HDL cholesterol. A combination of 2 TAGs further improved diabetes prediction. To explore potential mechanisms that modulate the distribution of plasma lipids, we performed lipid profiling during oral glucose tolerance testing, pharmacologic interventions, and acute exercise testing. Levels of TAGs associated with increased risk for diabetes decreased in response to insulin action and were elevated in the setting of insulin resistance. Conversely, levels of TAGs associated with decreased diabetes risk rose in response to insulin and were poorly correlated with insulin resistance. These studies identify a relationship between lipid acyl chain content and diabetes risk and demonstrate how lipid profiling could aid in clinical risk assessment.

Uncomplicated resistance training and health-related outcomes: evidence for a public health mandate

Compared to aerobic training (AT), resistance training (RT) has received far less attention as a prescription for general health. However, RT is as effective as AT in lowering risk for cardiovascular disease, diabetes, and other diseases. There is a clear ability of RT, in contrast to AT, to promote gains, maintenance, or slow loss of skeletal muscle mass/strength. Thus, as an antisarcopenic exercise treatment, RT is of greater benefit than AT; given the aging of our population, this is of primary importance. In our view, a substantial barrier to greater adoption of RT is the incorrectly perceived importance of variables such as external load, intensity, and volume, leading to complex, difficult-to-follow regimes. We propose a more feasible and easier-to-adhere-to paradigm for RT that could affect how RT is viewed and adopted as a prescription for public health.

Acute hypoxia and exercise improve insulin sensitivity (S(I) (2*)) in individuals with type 2 diabetes

BACKGROUND

hypoxia has been shown to increase glucose uptake in skeletal muscle using the contraction-stimulated pathway, independent of the actions of insulin. Yet, the same stress has also been linked with causing insulin resistance and hyperglycaemia. The aim of this study was to examine the effects of acute hypoxia with and without exercise on insulin sensitivity (S(I)(2*) in individuals with type 2 diabetes.

METHODS

eight type 2 diabetic patients completed 60 min of the following: (1) normoxic rest; (2) hypoxic rest [O(2) = 14.6 (0.4)%]; (3) normoxic exercise and (4) hypoxic exercise [O(2) = 14.6 (0.4)%]. Exercise trials were set at 90% of lactate threshold. Each condition was followed by a labelled intravenous glucose tolerance test to provide estimations of insulin sensitivity (S(I)(2*) and β-cell function.

RESULTS

Two-compartmental analysis showed that insulin sensitivity (S(I)(2*) was higher following hypoxic rest compared with normoxic rest (p = 0.047). Insulin sensitivity (S(I)(2*) was also higher following hypoxic exercise [4.37 (0.48) × 10(-4) /min (µU/mL)] compared with normoxic exercise [3.24 (0.51) × 10(-4) /min (µU/mL)] (p = 0.048). Acute insulin response to glucose was reduced following hypoxic rest versus normoxic rest (p = 0.014).

CONCLUSIONS

this study demonstrated that (1) hypoxic-induced improvements in glucose tolerance in the 4 h following exposure can be attributed to improvements in peripheral insulin sensitivity (S( I)(2*) and (2) exercise and hypoxia have an additive effect on insulin sensitivity (S(I)(2*) in type 2 diabetic patients. Acute hypoxia may therefore improve short-term glycaemic control in individuals with type 2 diabetes. The application of these findings in the clinic will require further investigation.

Strategies for reducing body fat mass: effects of liposuction and exercise on cardiovascular risk factors and adiposity

Liposuction is the most popular aesthetic surgery performed in Brazil and worldwide. Evidence showing that adipose tissue is a metabolically active tissue has led to the suggestion that liposuction could be a viable method for improving metabolic profile through the immediate loss of adipose tissue. However, the immediate liposuction-induced increase in the proportion of visceral to subcutaneous adipose tissue could be detrimental to metabolism, because a high proportion of visceral to subcutaneous adipose tissue is associated with risk factors for cardiovascular disease. The results of studies investigating the effects of liposuction on the metabolic profile are inconsistent, however, with most studies reporting either no change or improvements in one or more cardiovascular risk factors. In addition, animal studies have demonstrated a compensatory growth of intact adipose tissue in response to lipectomy, although studies with humans have reported inconsistent results. Exercise training improves insulin sensitivity, inflammatory balance, lipid oxidation, and adipose tissue distribution; increases or preserves the fat-free mass; and increases total energy expenditure. Thus, liposuction and exercise appear to directly affect metabolism in similar ways, which suggests a possible interaction between these two strategies. To our knowledge, no studies have reported the associated effects of liposuction and exercise in humans. Nonetheless, one could suggest that exercise training associated with liposuction could attenuate or even block the possible compensatory fat deposition in intact depots or regrowth of the fat mass and exert an additive or even a synergistic effect to liposuction on improving insulin sensitivity and the inflammatory balance, resulting in an improvement of cardiovascular risk factors. Consequently, one could suggest that liposuction and exercise appear to be safe and effective strategies for either the treatment of metabolic disorders or aesthetic purposes.

Thermogenesis and related metabolic targets in anti-diabetic therapy

Exercise, together with a low-energy diet, is the first-line treatment for type 2 diabetes type 2 diabetes . Exercise improves insulin sensitivity insulin sensitivity by increasing the number or function of muscle mitochondria mitochondria and the capacity for aerobic metabolism, all of which are low in many insulin-resistant subjects. Cannabinoid 1-receptor antagonists and β-adrenoceptor agonists improve insulin sensitivity in humans and promote fat oxidation in rodents independently of reduced food intake. Current drugs for the treatment of diabetes are not, however, noted for their ability to increase fat oxidation, although the thiazolidinediones increase the capacity for fat oxidation in skeletal muscle, whilst paradoxically increasing weight gain.There are a number of targets for anti-diabetic drugs that may improve insulin sensitivity insulin sensitivity by increasing the capacity for fat oxidation. Their mechanisms of action are linked, notably through AMP-activated protein kinase, adiponectin, and the sympathetic nervous system. If ligands for these targets have obvious acute thermogenic activity, it is often because they increase sympathetic activity. This promotes fuel mobilisation, as well as fuel oxidation. When thermogenesis thermogenesis is not obvious, researchers often argue that it has occurred by using the inappropriate device of treating animals for days or weeks until there is weight (mainly fat) loss and then expressing energy expenditure energy expenditure relative to body weight. In reality, thermogenesis may have occurred, but it is too small to detect, and this device distracts us from really appreciating why insulin sensitivity has improved. This is that by increasing fatty acid oxidation fatty acid oxidation more than fatty acid supply, drugs lower the concentrations of fatty acid metabolites that cause insulin resistance. Insulin sensitivity improves long before any anti-obesity effect can be detected.

Aging, resistance training, and diabetes prevention

With the aging of the baby-boom generation and increases in life expectancy, the American population is growing older. Aging is associated with adverse changes in glucose tolerance and increased risk of diabetes; the increasing prevalence of diabetes among older adults suggests a clear need for effective diabetes prevention approaches for this population. The purpose of paper is to review what is known about changes in glucose tolerance with advancing age and the potential utility of resistance training (RT) as an intervention to prevent diabetes among middle-aged and older adults. Age-related factors contributing to glucose intolerance, which may be improved with RT, include improvements in insulin signaling defects, reductions in tumor necrosis factor-α, increases in adiponectin and insulin-like growth factor-1 concentrations, and reductions in total and abdominal visceral fat. Current RT recommendations and future areas for investigation are presented.

Physical activity as the main therapeutic tool for metabolic syndrome in childhood

Physical activity (PA) and diet directly influence obesity and metabolic syndrome (MS) as important determinants of body composition. Understanding how PA relates to MS in youth is of great importance, and could offer a common strategy for clinical and public health approaches to control this condition. The underlying disorder of MS is a condition of insulin resistance, and a strong relationship between PA level and insulin sensitivity is clearly ascertained. The type, duration, frequency and intensity of PA affect fuel metabolism, in particular carbohydrate and lipid oxidation. The possible modulation of metabolism because of increased fat oxidation by PA is the basis for both prevention and restoration of insulin resistance and MS in obese children. In daily clinical practice, diet followed by pharmacologic treatment are usually the approaches taken, whereas PA is often considered just a suggestion. Although diet and PA have different effects on body composition, with both contributing to fat loss, only PA increases muscle mass and thus has a direct effect on metabolic function, expressed by changes in cardiovascular risk factors. Therefore, it is important to remember their complementary but different targets in daily clinical practice, such as body weight control for diet and metabolic health for PA. In this review, we have summarized the literature on the relationship between PA and MS in pediatrics. Then, we have analyzed the possibility of using PA for MS treatment, as an alternative to drugs, by discussing the results of intervention studies, reasons for low compliance to PA, related benefits, adherence difficulties and costs. Finally, we have tried to suggest recommendations for a multiple-step PA strategy in children and adolescents at risk for MS, by considering PA as the 'key' player in treatment.

A comparison of the effects of swimming and walking on body weight, fat distribution, lipids, glucose, and insulin in older women--the Sedentary Women Exercise Adherence Trial 2

All types of aerobic exercise are assumed to affect cardiovascular risk similarly. There are few studies of swimming, but complex responses to water-based exercise suggest its potential for differential effects. The aim of the study was to compare the effects of swimming and walking on fitness, body weight, lipids, glucose, and insulin in older women. Sedentary women aged 50 to 70 years (N = 116), randomly assigned to swimming or walking plus usual care or a behavioral intervention, completed 3 sessions per week of moderate-intensity exercise, supervised for 6 months then unsupervised for 6 months. After 6 months, 1.6-km walk time decreased in walkers and swimmers, with greater improvement in walkers (1.0 vs 0.6 minute, P = .001). In swimmers, but not walkers, distance swum in 12 minutes increased (78.1 vs -2.2 m, P = .021). Waist and hip circumferences (80.8 vs 83.1 cm and 101.8 vs 102.4 cm; P = .023 and P = .042, respectively) and insulin area under the curve (oral glucose tolerance test) (5128 vs 5623 μU/[L 120 min], P < .05) were lower with swimming. Lipids did not differ between groups. At 12 months, fitness was maintained. Relative to walking, swimming reduced body weight by (1.1 kg, P = .039) and resulted in lower total and low-density lipoprotein cholesterol (0.3 and 0.2 mmol/L; P = .040 and P = .049, respectively). The magnitude of the difference in the reduction of insulin area under the curve between swimming and walking was greater at 12 months; however, the significance was attenuated (4677 vs 5240 μU/[L 120 min], P = .052). Compared with walking, swimming improved body weight, body fat distribution, and insulin in the short term and, in the longer term, body weight and lipid measures. These findings suggest that the type of exercise can influence health benefits.

{beta}-Hydroxybutyrate inhibits insulin-mediated glucose transport in mouse oxidative muscle

Blood ketone body levels increase during starvation and untreated diabetes. Here we tested the hypothesis that ketone bodies directly inhibit insulin action in skeletal muscle. We investigated the effect of d,l-beta-hydroxybutyrate (BOH; the major ketone body in vivo) on insulin-mediated glucose uptake (2-deoxyglucose) in isolated mouse soleus (oxidative) and extensor digitorum longus (EDL; glycolytic) muscle. BOH inhibited insulin-mediated glucose uptake in soleus (but not in EDL) muscle in a time- and concentration-dependent manner. Following 19.5 h of exposure to 5 mM BOH, insulin-mediated (20 mU/ml) glucose uptake was inhibited by approximately 90% (substantial inhibition was also observed in 3-O-methylglucose transport). The inhibitory effect of BOH was reproduced with d- but not l-BOH. BOH did not significantly affect hypoxia- or AICAR-mediated (activates AMP-dependent protein kinase) glucose uptake. The BOH effect did not require the presence/utilization of glucose since it was also seen when glucose in the medium was substituted with pyruvate. To determine whether the BOH effect was mediated by oxidative stress, an exogenous antioxidant (1 mM tempol) was used; however, tempol did not reverse the BOH effect on insulin action. BOH did not alter the levels of total tissue GLUT4 protein or insulin-mediated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 but blocked insulin-mediated phosphorylation of protein kinase B by approximately 50%. These data demonstrate that BOH inhibits insulin-mediated glucose transport in oxidative muscle by inhibiting insulin signaling. Thus ketone bodies may be potent diabetogenic agents in vivo.

A randomized clinical trial of home-based exercise combined with a slight caloric restriction on obesity prevention among women

OBJECTIVE

The study investigated the effectiveness of home-based exercise combined with a slight caloric restriction on weight change during 12 months in non-obese women.

METHODS

A randomized clinical trial with a factorial design was conducted from 2003 to 2005. Two hundred three middle-aged women (Rio de Janeiro/Brazil), 25-45 years, were randomly assigned to one of two groups: control (CG) and home-based exercise (HB). The HB group received a booklet on aerobic exercise that could be practiced at home (3 times/week-40 min/session), in low-moderate intensity, during 12 months. Both groups received dietary counseling aimed at a slight energy restriction of 100-300 calories per day.

RESULTS

The HB experienced a greater weight loss in the first 6 months (-1.4 vs. -0.8 kg; p=0.04), but after 12 months there was no differences between groups (-1.1 vs. -1.0; p=0.20). Of the serum biochemical markers, HDL cholesterol showed major change, with an increase at month 12 of 18.3mg/dl in the HB compared to 9.5 in the CG (p<0.01).

CONCLUSION

Home-based exercise promoted greater weight reduction during the first 6 months after which no further benefits are observed. Continuous favorable changes in HDL cholesterol after 1 year suggest that home-based exercise promote health benefits.

Peroxisome proliferator-activated receptor {gamma} coactivator 1{alpha} (PGC-1{alpha}) promotes skeletal muscle lipid refueling in vivo by activating de novo lipogenesis and the pentose phosphate pathway

Exercise induces a pleiotropic adaptive response in skeletal muscle, largely through peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). PGC-1α enhances lipid oxidation and thereby provides energy for sustained muscle contraction. Its potential implication in promoting muscle refueling remains unresolved, however. Here, we investigated a possible role of elevated PGC-1α levels in skeletal muscle lipogenesis in vivo and the molecular mechanisms that underlie PGC-1α-mediated de novo lipogenesis. To this end, we studied transgenic mice with physiological overexpression of PGC-1α and human muscle biopsies pre- and post-exercise. We demonstrate that PGC-1α enhances lipogenesis in skeletal muscle through liver X receptor α-dependent activation of the fatty acid synthase (FAS) promoter and by increasing FAS activity. Using chromatin immunoprecipitation, we establish a direct interaction between PGC-1α and the liver X receptor-responsive element in the FAS promoter. Moreover, we show for the first time that increased glucose uptake and activation of the pentose phosphate pathway provide substrates for RNA synthesis and cofactors for de novo lipogenesis. Similarly, we observed increased lipogenesis and lipid levels in human muscle biopsies that were obtained post-exercise. Our findings suggest that PGC-1α coordinates lipogenesis, intramyocellular lipid accumulation, and substrate oxidation in exercised skeletal muscle in vivo.

Toward a comprehensive neurobiology of IGF-I

Insulin-like growth factor I (IGF-I) belongs to an ancient family of hormones already present in early invertebrates. The insulin family is well characterized in mammals, although new members have been described recently. Since its characterization over 50 years ago, IGF-I has been considered a peptide mostly involved in the control of body growth and tissue remodeling. Currently, its most prominent recognized role is as a quasi-universal cytoprotectant. This role connects IGF-I with regulation of lifespan and with cancer, two areas of very active research in relation to this peptide. In the brain, IGF-I was formerly considered a neurotrophic factor involved in brain growth, as many other neurotrophic factors. Other aspects of the neurobiology of IGF-I are gradually emerging and suggest that this growth factor has a prominent role in brain function as a whole. During development IGF-I is abundantly expressed in many areas, whereas once the brain is formed its expression is restricted to a few regions and in very low quantities. However, the adult brain appears to have an external input from serum IGF-I, where this anabolic peptide is abundant. Thus, serum IGF-I has been proven to be an important modulator of brain activity, including higher functions such as cognition. Many of these functions can be ascribed to its tissue-remodeling activity as IGF-I modulates adult neurogenesis and angiogenesis. Other activities are cytoprotective; indeed, IGF-I can be considered a key neuroprotective peptide. Still others pertain to the functional characteristics of brain cells, such as cell excitability. Through modulation of membrane channels and neurotransmission, IGF-I impinges directly on neuronal plasticity, the cellular substrate of cognition. However, to fully understand the role of IGF-I in the brain, we have to sum the actions of locally produced IGF-I to those of serum IGF-I, and this is still pending. Thus, an integrated view of the role played by IGF-I in the brain is not yet possible. An operational approach to overcome this limitation would be to consider IGF-I as a signal coupling environmental influences on body metabolism with brain function. Or in a more colloquial way, we may say that IGF-I links body "fitness" with brain fitness, providing a mechanism to the roman saying "mens sana in corpore sano."

Electrically induced contraction of C2C12 myotubes cultured on a porous membrane-based substrate with muscle tissue-like stiffness

A porous membrane-based cell culture device was developed to electrically stimulate a confluent monolayer of C2C12 myotubes. The device's cell culture substrate is a microporous alumina membrane-modified by attaching an atelocollagen membrane on the upperside and a hole-spotted poly(dimethylsiloxane) (PDMS) film on the underside. When electric current is generated between the device's Pt ring electrodes--one of which is placed above the cells and the other below the PDMS layer--the focused current at the PDMS hole can electrically stimulate the cells. C2C12 myoblasts were cultured on the substrate and differentiated into myotubes. When the electrical pulses were applied, myotubes started to contract slightly in and near the hole, and that the continuous stimulation increased both the number of stimuli-responding myotubes and the magnitude of the contraction considerably owing to the underlying atelocollagen membrane with muscle tissue-like stiffness. Also, the generation of contractile myotubes on a wider region of the membrane substrate was possible by applying the electrical pulses through the array of holes in the PDMS film. Using the present system, the glucose uptake by contractile myotubes was examined with fluorescence-labeled glucose, 2-NBDG, which displayed a positive correlation between the contractile activity of myotubes and the uptake of 2-NBDG.

Short-term sprint interval training increases insulin sensitivity in healthy adults but does not affect the thermogenic response to beta-adrenergic stimulation

Sprint interval training (SIT) and traditional endurance training elicit similar physiological adaptations. From the perspective of metabolic function, superior glucose regulation is a common characteristic of endurance-trained adults. Accordingly, we have investigated the hypothesis that short-term SIT will increase insulin sensitivity in sedentary/recreationally active humans. Thirty one healthy adults were randomly assigned to one of three conditions: (1) SIT (n = 12): six sessions of repeated (4-7) 30 s bouts of very high-intensity cycle ergometer exercise over 14 days; (2) sedentary control (n = 10); (3) single-bout SIT (n = 9): one session of 4 x 30 s cycle ergometer sprints. Insulin sensitivity was determined (hyperinsulinaemic euglycaemic clamp) prior to and 72 h following each intervention. Compared with baseline, and sedentary and single-bout controls, SIT increased insulin sensitivity (glucose infusion rate: 6.3 +/- 0.6 vs. 8.0 +/- 0.8 mg kg(1) min(1); mean +/- s.e.m.; P = 0.04). In a separate study, we investigated the effect of SIT on the thermogenic response to beta-adrenergic receptor (beta-AR) stimulation, an important determinant of energy balance. Compared with baseline, and sedentary and single-bout control groups, SIT did not affect resting energy expenditure (EE: ventilated hood technique; 6274 +/- 226 vs. 6079 +/- 297 kJ day(1); P = 0.51) or the thermogenic response to isoproterenol (6, 12 and 24 ng (kg fat-free mass)(1) min(1): %EE 11 +/- 2, 14 +/- 3, 23 +/- 2 vs. 11 +/- 1, 16 +/- 2, 25 +/- 3; P = 0.79). Combined data from both studies revealed no effect of SIT on fasted circulating concentrations of glucose, insulin, adiponectin, pigment epithelial-derived factor, non-esterified fatty acids or noradrenaline (all P > 0.05). Sixteen minutes of high-intensity exercise over 14 days augments insulin sensitivity but does not affect the thermogenic response to beta-AR stimulation.

Short-term sprint interval training increases insulin sensitivity in healthy adults but does not affect the thermogenic response to beta-adrenergic stimulation

Sprint interval training (SIT) and traditional endurance training elicit similar physiological adaptations. From the perspective of metabolic function, superior glucose regulation is a common characteristic of endurance-trained adults. Accordingly, we have investigated the hypothesis that short-term SIT will increase insulin sensitivity in sedentary/recreationally active humans. Thirty one healthy adults were randomly assigned to one of three conditions: (1) SIT (n = 12): six sessions of repeated (4-7) 30 s bouts of very high-intensity cycle ergometer exercise over 14 days; (2) sedentary control (n = 10); (3) single-bout SIT (n = 9): one session of 4 x 30 s cycle ergometer sprints. Insulin sensitivity was determined (hyperinsulinaemic euglycaemic clamp) prior to and 72 h following each intervention. Compared with baseline, and sedentary and single-bout controls, SIT increased insulin sensitivity (glucose infusion rate: 6.3 +/- 0.6 vs. 8.0 +/- 0.8 mg kg(1) min(1); mean +/- s.e.m.; P = 0.04). In a separate study, we investigated the effect of SIT on the thermogenic response to beta-adrenergic receptor (beta-AR) stimulation, an important determinant of energy balance. Compared with baseline, and sedentary and single-bout control groups, SIT did not affect resting energy expenditure (EE: ventilated hood technique; 6274 +/- 226 vs. 6079 +/- 297 kJ day(1); P = 0.51) or the thermogenic response to isoproterenol (6, 12 and 24 ng (kg fat-free mass)(1) min(1): %EE 11 +/- 2, 14 +/- 3, 23 +/- 2 vs. 11 +/- 1, 16 +/- 2, 25 +/- 3; P = 0.79). Combined data from both studies revealed no effect of SIT on fasted circulating concentrations of glucose, insulin, adiponectin, pigment epithelial-derived factor, non-esterified fatty acids or noradrenaline (all P > 0.05). Sixteen minutes of high-intensity exercise over 14 days augments insulin sensitivity but does not affect the thermogenic response to beta-AR stimulation.

Micropatterning contractile C2C12 myotubes embedded in a fibrin gel

Contractile C(2)C(12) myotube line patterns embedded in a fibrin gel have been developed to afford a physiologically relevant and stable bioassay system. The C(2)C(12) myotube/fibrin gel system was prepared by transferring a myotube monolayer from a glass substrate to a fibrin gel while retaining the original line patterns of myotubes. To endow the myotubes with contractile activity, a series of electrical pulses was applied through a pair of carbon electrodes placed at either side of a fibrin gel separately. The frequency and magnitude of myotube contraction were functions of the pulse frequency and duration, respectively. We found that the myotubes supported by an elastic fibrin gel maintained their line patterns and contractile activities for a longer period of time (1 week) than myotubes adhered on a conventional culture dish.

Blood glucose regulation during prolonged, submaximal, continuous exercise: a guide for clinicians

Management of many chronic diseases now includes regular exercise as part of a viable treatment plan. Exercise in the form of prolonged, submaximal, continuous exercise (SUBEX; i.e., approximately 30 min to 1 h, approximately 40-70% of maximal oxygen uptake) is often prescribed due to its relatively low risk, the willingness of patients to undertake, its efficacy, its affordability, and its ease of prescription. Specifically, patients who are insulin resistant or that have type 2 diabetes mellitus may benefit from regular exercise of this type. During this type of exercise, muscles dramatically increase glucose uptake as the liver increases both glycogenolysis and gluco-neogenesis. While a redundancy of mechanisms is at work to maintain blood glucose concentration ([glucose]) during this type of exercise, the major regulator of blood glucose is the insulin/glucagon response. At exercise onset, blood [glucose] transiently rises before beginning to decline after approximately 30 min, causing a subsequent decline in blood [insulin] and rise in blood glucagon. This leads to many downstream effects, including an increase in glucose output from the liver to maintain adequate glucose in the blood to fuel both the muscles and the brain. Finally, when analyzing blood [glucose], consideration should be given to nutritional status (postabsorptive versus postprandial) as well as both what the analyzer measures and the type of sample used (plasma versus whole blood). In view of both prescribing exercise to patients as well as designing studies that perturb glucose homeostasis, it is imperative that clinicians and researchers alike understand the controls of blood glucose homeostasis during SUBEX.

Short-term AMP-regulated protein kinase activation enhances insulin-sensitive fatty acid uptake and increases the effects of insulin on fatty acid oxidation in L6 muscle cells

Evidence shows that exercise increases insulin-sensitive glucose uptake and that exercise-induced AMP-regulated protein kinase (AMPK) activation is a likely candidate to mediate this metabolic adaptation. The purpose of this study was to determine whether repeated AMPK activation can similarly enhance insulin-sensitive fatty acid (FA) metabolism. L6 myotubes were incubated under the following conditions: repeated plus acute 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) treatment (RAA; 1 mmol/L AICAR for 5 h/d for 5 days plus 1 mmol/L AICAR for 60 min on day 6), repeated AICAR (RA; 1 mmol/L AICAR for 5 h/d for five days) or acute AICAR (AA; 1 mmol/L AICAR for 60 min) and were compared with control cells that were not treated with AICAR. On day six, cells from each group were incubated with or without 100 nmol/L insulin. AICAR treatment and insulin stimulation independently increased (P < 0.05) palmitate uptake in all groups. RAA potentiated the insulin-induced increase in palmitate uptake by 97% (P < 0.05) as compared with control cells. RA and AA treatments prevented the insulin-induced decrease in palmitate oxidation, while RAA treatment restored the sensitivity of the cells to insulin action on palmitate oxidation. Total peroxisome proliferator-activated receptor-gamma co-activator-1 alpha, atypical protein kinase C-zeta, cytochrome C and CD36 protein content was increased (P < 0.05) by RA treatment, but unaffected by insulin. These results indicate that repeated AMPK activation induces improvements in insulin-sensitive FA uptake and oxidation and that this occurs partly via changes in the expression of proteins linked to insulin signaling and FA uptake and oxidation capacity.

Physical activity and cardiovascular disease in Japan: the Jichi Medical School Cohort Study

Background

Many studies have reported an association between physical activity and cardiovascular disease (CVD); however, the effect of physical activity remains controversial. Few such studies have been conducted in Japan. Therefore, we examined the relationship between physical activity and death from CVD using prospective data from a Japanese population.

Methods

From a prospective cohort study that comprised 12 490 participants, data from 9810 were analyzed. From April 1992 through July 1995, a baseline survey was conducted in 12 communities in Japan. The participants were followed up until December 2005. Physical activity was assessed using the physical activity index (PAI). PAI scores were grouped in quartiles: Q1 was the lowest PAI quartile and Q4 was the highest. Hazard ratios (HRs) for death from CVD, stroke, and myocardial infarction (MI) were calculated for all PAI quartiles.

Results

The mean follow-up period was 11.9 years, during which time 194 participants died of CVD. With Q1 as the reference, the HRs for death from CVD in Q2, Q3, and Q4, were 0.62 (95% confidence interval, 0.40–0.98), 0.53 (0.31–0.88), and 0.40 (0.22–0.73), respectively, in men, and 0.71 (0.38–1.32), 0.52 (0.26–1.04), and 0.48 (0.22–1.05), respectively, in women. The HRs for death from CVD subtypes were similar but not statistically significant.

Conclusions

Among a Japanese population, physical activity was associated with a decreased risk of death from CVD. However, more evidence is needed to elucidate the relationships between physical activity and CVD subtypes.

Effects of long-term calorie restriction and endurance exercise on glucose tolerance, insulin action, and adipokine production

Calorie restriction (CR) slows aging and is thought to improve insulin sensitivity in laboratory animals. In contrast, decreased insulin signaling and/or mild insulin resistance paradoxically extends maximal lifespan in various genetic animal models of longevity. Nothing is known regarding the long-term effects of CR on glucose tolerance and insulin action in lean healthy humans. In this study we evaluated body composition, glucose, and insulin responses to an oral glucose tolerance test and serum adipokines levels in 28 volunteers, who had been eating a CR diet for an average of 6.9 +/- 5.5 years, (mean age 53.0 +/- 11 years), in 28 age-, sex-, and body fat-matched endurance runners (EX), and 28 age- and sex-matched sedentary controls eating Western diets (WD). We found that the CR and EX volunteers were significantly leaner than the WD volunteers. Insulin sensitivity, determined according to the HOMA-IR and the Matsuda and DeFronzo insulin sensitivity indexes, was significantly higher in the CR and EX groups than in the WD group (P = 0.001). Nonetheless, despite high serum adiponectin and low inflammation, approximately 40% of CR individuals exhibited an exaggerated hyperglycemic response to a glucose load. This impaired glucose tolerance is associated with lower circulating levels of IGF-1, total testosterone, and triiodothyronine, which are typical adaptations to life-extending CR in rodents.

Acute altitude-induced hypoxia suppresses plasma glucose and leptin in healthy humans

To examine the effects of acute altitude-induced hypoxia on the hormonal and metabolic response to ingested glucose, 8 young, healthy subjects (5 men and 3 women; age, 26 +/- 2 years; body mass index, 23.1 +/- 1.0 kg/m(2)) performed 2 randomized trials in a hypobaric chamber where a 75-g glucose solution was ingested under simulated altitude (ALT, 4300 m) or ambient (AMB, 362 m) conditions. Plasma glucose, insulin, C-peptide, epinephrine, leptin, and lactate concentrations were measured at baseline and 30, 60, 90, and 120 minutes after glucose ingestion during both trials. Compared with AMB, the plasma glucose response to glucose ingestion was reduced during the ALT trial (P = .04). There were no differences in the insulin and C-peptide responses between trials or in insulin sensitivity based on the homeostasis model assessment of insulin resistance. Epinephrine and lactate were both elevated during the ALT trial (P < .05), whereas the plasma leptin response was reduced compared with AMB (P < .05). The data suggest that the plasma glucose response is suppressed at ALT, but this is not due to insulin per se because insulin and C-peptide levels were similar for both trials. Elevated plasma epinephrine and lactate during ALT are indicative of increased glycogenolysis, which may have masked the magnitude of the reduced glucose response. We conclude that, during acute altitude exposure, there is a rapid metabolic response that is accompanied by a shift in the hormonal milieu that appears to favor increased glucose utilization.

Enhanced insulin sensitivity after acute exercise is not associated with changes in high-molecular weight adiponectin concentration in plasma

BACKGROUND AND OBJECTIVE

The effect of exercise on the plasma concentration of high-molecular weight (HMW) adiponectin (i.e. the biologically active form of circulating adiponectin) and the possible role of HMW adiponectin in mediating the exercise-induced enhancement of insulin action are not known. The aim of this study was to evaluate the relationship between the post-exercise increase in insulin sensitivity and plasma HMW adiponectin concentration.

DESIGN AND METHODS

We measured total and HMW adiponectin concentrations in plasma using an ELISA kit, and insulin sensitivity using the updated homeostasis model assessment of insulin sensitivity (HOMA2-IS) score in the basal, overnight fasted state, once approximately 12 h after a single bout of moderate-intensity endurance exercise and once after an equivalent period of rest, in 27 healthy men and women (age: 29+/-1 years and body mass index: 24.7+/-0.8 kg/m(2)).

RESULTS

The HOMA2-IS score was 18+/-7% greater after exercise than after rest (229+/-20 and 196+/-17 respectively; P=0.006), whereas the concentrations of total adiponectin (7.8+/-0.5 and 7.7+/-0.5 mg/l respectively; P=0.597) and HMW adiponectin (3.0+/-0.3 and 3.0+/-0.3 mg/l respectively; P=0.625) were not different. The exercise-induced change in HOMA2-IS score was not related to changes in total and HMW adiponectin concentrations (P>0.3).

CONCLUSIONS

Changes in HMW adiponectin concentration are not involved in the acute exercise-induced enhancement of insulin action.

Effects of calcium supplementation on glucose and insulin levels of athletes at rest and after exercise

This study was performed to determine how the calcium supplementation for a 4-week period affects the glucose and insulin levels at rest and at exhaustion in athletes. This is a 4-week study performed on 30 healthy subjects varying between 18 and 22 ages. Subjects were separated into three groups: first group (group supplemented with calcium, sedentary group), second group (calcium supplementations + exercise group), and third group (training group). Glucose and insulin parameters of the groups were measured four times, at rest and exhaustion in the beginning of the research and at rest and exhaustion after the end of 4 weeks application period. Exhaustion measurements both before and after the supplementations significantly decreased in compared to rest measurements in terms of insulin (p < 0.05). Significant difference was not determined in the glucose values of groups. In terms of glucose, values increased in all of the three groups occurred with exercise both before and after the supplementation by exercise and exhaustion (p < 0.05). The results of our study indicate that calcium gluconate supplementations for 4 weeks in sedentary subjects and athletes did not significantly affect plasma insulin levels at rest and exhaustion. However, glucose levels were affected by calcium supplementation and exhausting exercise in athletes.

Association between physical activity and insulin resistance in Iranian adults: National Surveillance of Risk Factors of Non-Communicable Diseases (SuRFNCD-2007)

BACKGROUND

Insulin resistance is an underlying mechanism of metabolic syndrome. We attempted to determine the association between physical activity and insulin resistance in Iranian adults.

METHODS

The data of the third national Surveillance of Risk Factors of Non-Communicable Diseases (SuRFNCD-2007) in Iran were used. We ran the Global Physical Activity Questionnaire (GPAQ) over a nationally representative sample of 3101 adults. Total physical activity (TPA) was calculated using metabolic equivalents (MET) for intensity of physical activities. Insulin resistance was measured by the homeostasis model assessment of insulin resistance (HOMA-IR).

RESULTS

When physical activity was classified into high, moderate, and low categories, HOMA-IR values significantly increased from the high category to the moderate and low categories (p<0.01). After adjustment for age, area of residence, smoking, and body mass index (BMI), TPA (r=-0.26, p<0.01 in males and r=-0.21, p<0.01 in females), duration of vigorous-intensity activity (r=-0.28, p<0.01 in males and r=-0.18, p=0.01 in females), duration of moderate-intensity activity (r=-0.16, p=0.01 in males and r=-0.17, p<0.01 in females), and the time spent on sedentary behaviors (r=0.16, p=0.01 in males and r=-0.22, p<0.01 in females) were significantly correlated to HOMA-IR. The prevalence of physical inactivity increased linearly with increasing HOMA-IR quintiles.

CONCLUSIONS

Our findings indicate a significant relationship between physical inactivity and insulin resistance. For communities in a transition phase of lifestyle, encouraging physical activity may help prevent insulin resistance and its adverse consequences.

Relationship between Sirt1 expression and mitochondrial proteins during conditions of chronic muscle use and disuse

Sirt1 is a NAD(+)-dependent histone deacetylase that interacts with the regulatory protein of mitochondrial biogenesis PGC-1alpha and is sensitive to metabolic alterations. We assessed whether a strict relationship between the expression of Sirt1, mitochondrial proteins, and PGC-1alpha existed across tissues possessing a wide range of oxidative capabilities, as well as in skeletal muscle subject to chronic use (voluntary wheel running or electrical stimulation for 7 days, 10 Hz; 3 h/day) or disuse (denervation for up to 21 days) in which organelle biogenesis is altered. PGC-1alpha levels were not closely associated with the expression of Sirt1, measured using immunoblotting or via enzymatic deacetylase activity. The mitochondrial protein cytochrome c increased by 70-90% in soleus and plantaris muscles of running animals, whereas Sirt1 activity remained unchanged. In chronically stimulated muscle, cytochrome c was increased by 30% compared with nonstimulated muscle, whereas Sirt1 activity was increased modestly by 20-25%. In contrast, in denervated muscle, these markers of mitochondrial content were decreased by 30-50% compared with the control muscle, whereas Sirt1 activity was increased by 75-80%. Our data suggest that Sirt1 and PGC-1alpha expression are independently regulated and that, although Sirt1 activity may be involved in mitochondrial biogenesis, its expression is not closely correlated to changes in mitochondrial proteins during conditions of chronic muscle use and disuse.

Large-for-gestational-age infants of type 1 diabetic mothers: an effect of preprandial hyperglycemia?

OBJECTIVE

To determine how the frequency, timing and magnitude of hyperglycemia are associated with large-for-gestational-age (LGA) infants in pregnancies complicated by type 1 diabetes.

METHODS

Charts from pregnant women with type 1 diabetes (n = 70) were reviewed. Indices of maternal glycemic control were determined for seven gestational periods (weeks 7-10, 11-15, 16-19, 20-24, 25-28, 29-32 and 33-38) and compared between women who delivered LGA infants and appropriate-for-gestational-age (AGA) infants.

RESULTS

Of the 70 pregnancies, 57% of the infants were LGA (4.3 +/- 0.4 kg) and 43% were AGA (3.2 +/- 0.4 kg). Total maternal weight gain and rate of weight gain were significantly higher in mothers with LGA infants. The glycemic variables associated with an LGA infant were percentage of preprandial values above target for weeks 11-15, 25-28 and 29-32, and percentage of all values above target for weeks 33-38. For the entire pregnancy, the strongest predictors of an LGA infant were percentage of preprandial blood glucose values above target during weeks 29-32 and maternal weight gain.

CONCLUSIONS

In pregnant women with type 1 diabetes, frequent episodes of preprandial hyperglycemia in the third trimester significantly impact the development of LGA infants.

Acute exercise and impaired glucose tolerance in obese humans

BACKGROUND

Individuals with impaired glucose tolerance (IGT) have a greater risk of developing diabetes and cardiovascular disease compared with those with normal glycemic control. The aim of this study was to examine the effects of acute aerobic exercise on glycemia, regional arterial stiffness, and oxidative stress in obese subjects with IGT.

DESIGN

Twelve obese subjects (7 men and 5 women; 48.0±9.4 years; body mass index 32.4±7.0kg/m(2)) with IGT participated in a 30-minute bout of walking at 65% of maximum predicted heart rate. Pulse wave velocity (PWV, for determination of arterial stiffness) and blood pressure were examined before and after exercise, whereas venous blood samples were drawn for the determination of glucose, blood lipids, and indices of oxidative stress and inflammation (lipid hydroperoxides; superoxide dismutase; high-sensitivity C-reactive protein).

RESULTS

After exercise PWV (9.1±1.2m/s vs. 8.6±1.0m/s), glucose (5.7±0.6 mmol·L(-1) vs. 5.4±0.6 mmol·L(-1)), and diastolic blood pressure (94±14mm Hg vs. 86±13mm Hg) decreased, respectively (P < .05). A correlation was observed between PWV and glucose (r=0.544, P < .05). There were no changes in lipid hydroperoxides, superoxide dismutase, high-sensitivity C-reactive protein, or blood lipids (P > .05).

CONCLUSIONS

These findings suggest that acute aerobic exercise can reduce regional arterial stiffness in obese subjects with IGT by possibly improving glucose metabolism, independent of changes in oxidative stress.

Discipline-specific insulin sensitivity in athletes

OBJECTIVE

Weight status and abnormal liver function are the two factors that influence whole-body insulin sensitivity. The main goal of the study was to compare insulin sensitivity in athletes (n=757) and physically active controls (n=670) in relation to the two factors.

METHODS

Homeostatic metabolic assessment for insulin resistance (HOMA-IR), weight status, and abnormal liver function (alanine aminotransferase and aspartate aminotransferase) were determined from 33 sports disciplines under morning fasted condition. This study was initiated in autumn 2006 and repeated in autumn 2007 (n=1508) to ensure consistency of all observations.

RESULTS

In general, HOMA-IR and blood pressure levels in athletes were significantly greater than those in physically active controls but varied widely with sport disciplines. Rowing and short-distance track athletes had significantly lower HOMA-IR values and archery and field-throwing athletes had significantly higher values than the control group. Intriguingly, athletes from 22 sports disciplines displayed significantly greater body mass index values above control values. Multiple regression analysis showed that, for non-athlete controls, body mass index was the only factor that contributed to the variations in HOMA-IR. For athletes, body mass index and alanine aminotransferase independently contributed to the variation of HOMA-IR.

CONCLUSION

This is the first report documenting HOMA-IR values in athletes from a broad range of sport disciplines. Weight status and abnormal liver function levels appear to be the major contributors predicting insulin sensitivity for the physically active population.

Effects of 7 days of exercise training on insulin sensitivity and responsiveness in type 2 diabetes mellitus

The objectives of this study were to determine whether 1) the improvement in insulin action induced by short-term exercise training in patients with type 2 diabetes is due to an improvement in insulin sensitivity, an improvement in insulin responsiveness, or a combination of improved insulin sensitivity and responsiveness and 2) short-term exercise training results in improved suppression of hepatic glucose production by insulin. Fourteen obese patients with type 2 diabetes, age 64 +/- 2 yr, underwent a two-stage hyperinsulinemic euglycemic clamp procedure, first stage 40 mU.m(-2).min(-1) insulin infusion, second stage 1,000 mU.m(-2).min(-1) insulin infusion, together with a [3-(3)H]glucose infusion, before and after 7 days of exercise. The training consisted of 30 min of cycling and 30 min of treadmill walking at approximately 70% of maximal aerobic capacity daily for 7 days. The exercise program resulted in improvements in insulin action in the absence of weight loss. Glucose disposal rates during the euglycemic clamp were significantly increased at both hyperinsulinemic stages after training (40 mU: 1.84 +/- 0.32 to 2.67 +/- 0.37 mg.kg(-1).min(-1), P < 0.0001; 1,000 mU: 7.57 +/- 0.61 to 8.84 +/- 0.56 mg.kg(-1).min(-1), P = 0.008). Hepatic glucose production, both in the basal state (3.17 +/- 0.43 vs. 2.54 +/- 0.26 mg.kg(-1).min(-1), P = 0.05) and during the 40-mU clamp stage (1.15 +/- 0.41 vs. 0.46 +/- 0.20 mg.kg(-1).min(-1), P = 0.03), was significantly reduced after training. One week of vigorous exercise training can induce significant improvements in insulin action in type 2 diabetes. These improvements include increased peripheral insulin sensitivity and responsiveness as well as enhanced suppression of hepatic glucose production.

Increased AS160 phosphorylation, but not TBC1D1 phosphorylation, with increased postexercise insulin sensitivity in rat skeletal muscle

A single exercise bout can increase insulin-independent glucose transport immediately postexercise and insulin-dependent glucose transport (GT) for several hours postexercise. Akt substrate of 160 kDa (AS160) and TBC1D1 are paralog Rab GTPase-activating proteins that have been proposed to contribute to these exercise effects. Previous research demonstrated greater AS160 and Akt threonine phosphorylation in rat skeletal muscle at 3-4 h postexercise concomitant with enhanced insulin-stimulated GT. To further probe whether these signaling events or TBC1D1 phosphorylation were important for the enhanced postexercise insulin-stimulated GT, male Wistar rats were studied using four experimental protocols (2-h swim exercise, differing with regard to timing of muscle sampling and whether food was provided postexercise) that were known to vary in their influence of insulin-independent and insulin-dependent GT postexercise. The results indicated that, in isolated rat epitrochlearis muscle, 1) elevated phosphorylation of AS160 (measured using anti-phospho-Akt substrate, PAS-AS160, and phosphospecific anti-Thr(642)-AS160, pThr(642)-AS160) consistently tracked with elevated insulin-stimulated GT; 2) PAS-TBC1D1 was not different from sedentary values at 3 or 27 h postexercise, when insulin sensitivity was increased; 3) insulin-stimulated Akt activity was not increased postexercise in muscles with increased insulin sensitivity; 4) PAS-TBC1D1 was increased immediately postexercise, when insulin-independent GT was elevated, and reversed at 3 and 27 h postexercise, when insulin-independent GT was also reversed; and 5) there was no significant effect of exercise or insulin on total abundance of AS160, TBC1D1, Akt, or GLUT4 protein with any of the protocols. The results are consistent with increased AS160 phosphorylation (PAS-AS160 or pThr(642)-AS160) but not increased PAS-TBC1D1 or Akt activity, which is important for increased postexercise insulin-stimulated GT in rat skeletal muscle. They also support the idea that increased TBC1D1 phosphorylation may play a role in the insulin-independent increase in GT postexercise.

Long-term physical training increases liver IGF-I in diabetic rats

Diabetes reduces the serum levels of insulin-like growth factor-I (IGF-I) and physical training may prevent this reduction. Almost all circulating IGF-I is produced and secreted by the liver. To examine the influence of moderate physical training on liver IGF-1 levels in diabetes, male Wistar rats were given a single dose of alloxan (30 mg/kg b.w.) to induce diabetes and then randomly allocated to sedentary or trained groups. The training protocol consisted of a 1h swimming session/day, five days/week for eight weeks with a load corresponding to 5% of the body weight. These two groups were compared with sedentary or trained non-diabetic rats (controls). A subcutaneous insulin tolerance test (ITT) was performed at the 6th week of experiment. At the end of the training period, the rats in all groups were sacrificed and blood was collected for the quantification of hematocrit and serum glucose, insulin, triglycerides, albumin, GH and IGF-1. Skeletal muscle and hepatic glycogen levels and hepatic triglyceride, protein, DNA and IGF-I concentrations were also determined. Diabetes reduced the serum insulin, GH and IGF-I concentrations, and the hepatic protein/DNA ratio and IGF-I concentrations, but increased serum glucose and triglyceride levels. Serum glucose removal during ITT was increased in the trained diabetic animals compared to sedentary control. Physical training reduced the serum glucose and triglyceride levels but increased the muscle glycogen content and restored the hepatic protein/DNA ratio and serum and hepatic IGF-I in diabetic rats. In conclusion, long-term chronic exercise improved the metabolic state and attenuated the reduction in serum and hepatic IGF-I concentrations caused by diabetes.

Effects of moderate-severe exercise on blood glucose in Type 1 diabetic adolescents treated with insulin pump or glargine insulin

BACKGROUND

Few papers focus on exercise-related blood glucose (BG) in patients on continuous sc insulin infusion (CSII) or multiple daily injections (MDI) with glargine.

AIM

The main objective was to evaluate the degree of glycemic control in Type 1 diabetes mellitus adolescents on CSII doing physical activity with pump switched on or off. These findings were also compared with a small group of patients on MDI with glargine.

SUBJECTS AND METHODS

Eight patients on CSII (basal rate continued or turned off in alternating sessions) and 5 on MDI joined 4 sessions of moderate-severe exercise.

RESULTS

Post-exercise BG significantly increased with the pump off and was unchanged/decreased with the pump on and MDI groups vs baseline. The hypoglycemia rate was not different among the 3 groups at any time. Pump on: hypoglycemias more frequent both at bedtime (p=0.031) and at awakening (p<0.001) than before dinner and at awakening than at bed-time (p=0.044). Pump off: hypoglycemias more frequent both at bed-time (p=0.010) and at awakening (p=0.031) than before dinner. MDI: no differences.

CONCLUSIONS

Glargine is safe and reducing the pre-lunch insulin is unnecessary. Subjects on insulin pump should not stop the basal rate. If they stop the pump, some actions are advisable: pre-exercise insulin bolus, pre-sleeping snack rich in carbohydrates, slight reduction of the overnight basal rate. On the other hand, if the basal rate is unmodified, the ingestion of sugary drinks during the exercise, the reduction of the overnight basal rate, a reduction of the pre-dinner insulin bolus and/or a pre-sleeping snack should be considered.

Objectively measured moderate- and vigorous-intensity physical activity but not sedentary time predicts insulin resistance in high-risk individuals

OBJECTIVE

Low levels of physical activity appear to be associated with insulin resistance. However, the detailed associations of these complex relationships remain elusive. We examined the prospective associations between self-reported TV viewing time, objectively measured time spent sedentary, at light-intensity activity, and at moderate- and vigorous-intensity physical activity (MVPA) with insulin resistance.

RESEARCH DESIGN AND METHODS

In 192 individuals (81 men and 111 women) with a family history of type 2 diabetes, we measured physical activity and anthropometric and metabolic variables at baseline and after 1 year of follow-up in the ProActive UK trial. Physical activity was measured objectively by accelerometry. Insulin resistance was expressed as fasting insulin and the homeostasis model assessment score (HOMA-IR).

RESULTS

Baseline MVPA was a significant predictor of fasting insulin at follow-up (beta = -0.004 [95% CI -0.007 to -0.0001], P = 0.022), and the association approached significance for HOMA-IR (beta = -0.003 [-0.007 to 0.000002], P = 0.052), independent of time spent sedentary, at light-intensity activity, sex, age, smoking status, waist circumference, and self-reported TV viewing. Time spent sedentary and at light-intensity activity were not significantly associated with insulin resistance. The change in MVPA between baseline and follow-up was inversely related to fasting insulin (beta = -0.003 [-0.007 to -0.0003], P = 0.032) and the HOMA-IR score (beta = -0.004 [-0.008 to -0.001], P = 0.015) at follow-up, after adjustment for baseline phenotype in addition to the same confounders as above.

CONCLUSIONS

These results highlight the importance of promoting moderate-intensity activity such as brisk walking for improving insulin sensitivity and possibly other metabolic risk factors to prevent type 2 diabetes.

Muscle-specific overexpression of heparin-binding epidermal growth factor-like growth factor increases peripheral glucose disposal and insulin sensitivity

Physical exercise ameliorates metabolic disorders such as type 2 diabetes mellitus and obesity, but the molecular basis of these effects remains elusive. In the present study, we found that exercise up-regulates heparin-binding epidermal growth factor-like growth factor (HB-EGF) in skeletal muscle. To address the metabolic consequences of such gain of HB-EGF function, we generated mice that overexpress this protein specifically in muscle. The transgenic animals exhibited a higher respiratory quotient than did wild-type mice during indirect calorimetry, indicative of their selective use of carbohydrate rather than fat as an energy substrate. They also showed substantial increases in glucose tolerance, insulin sensitivity, and glucose uptake by skeletal muscle. These changes were accompanied by increased kinase activity of Akt in skeletal muscle and consequent inhibition of Forkhead box O1-dependent expression of the pyruvate dehydrogenase kinase 4 gene. Furthermore, mice with a high level of transgene expression were largely protected from obesity, hepatic steatosis, and insulin resistance, even when maintained on a high-fat diet. Our results suggest that HB-EGF produced by contracting muscle acts as an insulin sensitizer that facilitates peripheral glucose disposal.

Cerebellar neurons possess a vesicular compartment structurally and functionally similar to Glut4-storage vesicles from peripheral insulin-sensitive tissues

The insulin-sensitive isoform of the glucose transporting protein, Glut4, is expressed in fat as well as in skeletal and cardiac muscle and is responsible for the effect of insulin on blood glucose clearance. Recent studies have revealed that Glut4 is also expressed in the brain, although the intracellular compartmentalization and regulation of Glut4 in neurons remains unknown. Using sucrose gradient centrifugation, immunoadsorption and immunofluorescence staining, we have shown that Glut4 in the cerebellum is localized in intracellular vesicles that have the sedimentation coefficient, the buoyant density, and the protein composition similar to the insulin-responsive Glut4-storage vesicles from fat and skeletal muscle cells. In cultured cerebellar neurons, insulin stimulates glucose uptake and causes translocation of Glut4 to the cell surface. Using 18FDG (18fluoro-2-deoxyglucose) positron emission tomography, we found that physical exercise acutely increases glucose uptake in the cerebellum in vivo. Prolonged physical exercise increases expression of the Glut4 protein in the cerebellum. Our results suggest that neurons have a novel type of translocation-competent vesicular compartment which is regulated by insulin and physical exercise similar to Glut4-storage vesicles in peripheral insulin target tissues.

Effect of acute high-intensity intermittent swimming on post-exercise insulin responsiveness in epitrochlearis muscle of fed rats

Maximally insulin-stimulated glucose uptake in skeletal muscle, ie, insulin responsiveness, is reduced in fed animals as compared with fasted animals; but acute prior endurance exercise improves insulin responsiveness in the muscles of fed rats. The effect of acute prior sprint interval exercise on insulin responsiveness in the muscles of fed animals has not been clarified, and we therefore compared the effect of short high-intensity swimming as a model of sprint interval exercise on insulin responsiveness in the muscles of fed rats with the effect of prolonged low-intensity swimming as a model of endurance exercise. The fed rats were subjected to an acute bout of high-intensity intermittent swimming (HIS) or low-intensity continuous swimming (LIS). The HIS rats swam for eight 20-second periods with a weight equal to 18% of their body weight. The LIS rats swam with no load for 3 hours. HIS increased (P < .05) the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) Thr(172) and that of its downstream target acetyl-CoA carboxylase (ACC) Ser(79) 12.6- and 3.1-fold, respectively, whereas LIS increased them 3.8- and 1.9-fold, respectively, immediately after exercise compared with rested muscle. HIS and LIS increased the insulin responsiveness of 2-deoxyglucose uptake measured 4 hours after exercise by 39% and 41%, respectively, compared with rested muscles. These results show that very short (160 seconds) HIS exercise with greater AMPK activation increases the responsiveness of glucose uptake to insulin in the muscles of fed rats to a similar level observed after prolonged (3 hours) LIS exercise with lower AMPK activation. Therefore, it is suggested that an acute bout of sprint interval exercise that activates AMPK to a sufficiently high level can increase post-exercise insulin responsiveness on muscle glucose uptake irrespective of very short exercise duration.

The relationship of serum osteocalcin concentration to insulin secretion, sensitivity, and disposal with hypocaloric diet and resistance training

CONTEXT

Bone has recently been described as exhibiting properties of an endocrine organ by producing osteocalcin that increases insulin sensitivity and secretion in animal models.

OBJECTIVE AND DESIGN

We aimed to evaluate circulating osteocalcin in association with insulin sensitivity and insulin secretion in three different studies in nondiabetic subjects: one cross-sectional study in 149 men (using minimal model), and two longitudinal studies in two independent groups (one formed by 26 women, and the other by 9 men and 11 women), after a mean of 7.3 and 16.8% weight loss, and after a mean of 8.7% weight loss plus regular exercise.

RESULTS

In the cross-sectional study, circulating osteocalcin was associated with insulin sensitivity, mainly in lean subjects, and with insulin secretion (only in lean subjects). A mean of 16.8%, but not 7.3% weight loss, led to significant increases in circulating osteocalcin. However, a mean of 8.7% weight loss plus regular exercise led to the more pronounced effects on the serum osteocalcin concentration, which increased in parallel to reduced visceral fat mass, unchanged thigh muscle mass, and increased leg strength and force. The postintervention serum levels of osteocalcin were associated with both insulin sensitivity (r = 0.49; P = 0.03) and fasting triglycerides (r = -0.54; P = 0.01). The change in visceral fat was the parameter that best predicted the change in serum osteocalcin, once age, body mass index, and insulin sensitivity changes were controlled for (P = 0.002).

CONCLUSION

Circulating osteocalcin could mediate the role of bone as an endocrine organ in humans.

The metabolic syndrome

The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.

Acute regulation of metabolic genes and insulin receptor substrates in the liver of mice by one single bout of treadmill exercise

Acute exercise performance represents a major metabolic challenge for the skeletal muscle, but also for the liver as the most important source of energy. However the molecular adaptation of the liver to one single bout of exercise is largely unknown. C57BL/6 mice performed a 60 min treadmill run at high aerobic intensity. Liver, soleus and white gastrocnemius muscle were removed immediately after exercise. The single bout of exercise resulted in a very rapid and pronounced induction of hepatic metabolic enzymes and regulators of metabolism or transcription: glucose-6-phosphatase (G6Pase; 3-fold), pyruvate dehydrogenase kinase-4 (PDK4; 4.8-fold), angiopoietin-like 4 (2.1-fold), insulin receptor substrate (IRS)-2 (5.1-fold), peroxisome proliferator activated receptor-gamma coactivator 1alpha (PGC-1alpha; 3-fold). In soleus and white gastrocnemius muscle the up-regulation of IRS-2 and PDK4 was less pronounced compared with the liver and no significant induction of PGC-1alpha could be detected at this early time point. Activation of AMPK was found in both liver and white gastrocnemius muscle as phosphorylation of Thr-172. The induction of endogenous insulin secretion by a glucose load directly after the exercise bout resulted in a significantly higher PKB/Akt phosphorylation in the liver of exercised mice. The markedly enhanced IRS-2 protein amount, and presumably reduced serine/threonine phosphorylation of the IRS proteins induced by the acute exercise could be responsible for this enhanced action of insulin. In conclusion, acute exercise induced a rapid and pronounced transcriptional adaptation in the liver, and regulated hepatic IRS proteins leading to improved cellular insulin signal transduction.

Skeletal muscle insulin resistance: roles of fatty acid metabolism and exercise

The purpose of this review is to provide information about the role of exercise in the prevention of skeletal muscle insulin resistance, that is, the inability of insulin to properly cause glucose uptake into skeletal muscle. Insulin resistance is associated with high levels of stored lipids in skeletal muscle cells. Aerobic exercise training decreases the amounts of these lipid products and increases the lipid oxidative capacity of muscle cells. Thus, aerobic exercise training may prevent insulin resistance by correcting a mismatch between fatty acid uptake and fatty acid oxidation in skeletal muscle. Additionally, a single session of aerobic exercise increases glucose uptake by muscle during exercise, increases the ability of insulin to promote glucose uptake, and increases glycogen accumulation after exercise, all of which are important to blood glucose control. There also is some indication that resistance exercise may be effective in preventing insulin resistance. The information provided is intended to help clinicians understand and explain the roles of exercise in reducing insulin resistance.

Contractile C2C12 myotube model for studying exercise-inducible responses in skeletal muscle

Adequate exercise leads to a vast variety of physiological changes in skeletal muscle as well as other tissues/organs and is also responsible for maintaining healthy muscle displaying enhanced insulin-responsive glucose uptake via GLUT4 translocation. We generated highly developed contractile C(2)C(12) myotubes by manipulating intracellular Ca(2+) transients with electric pulse stimulation (EPS) that is endowed with properties similar to those of in vivo skeletal muscle in terms of 1) excitation-induced contractile activity as a result of de novo sarcomere formation, 2) activation of both the AMP kinase and stress-activated MAP kinase cascades, and 3) improved insulin responsiveness as assessed by GLUT4 recycling. Tbc1d1, a Rab-GAP implicated in exercise-induced GLUT4 translocation in skeletal muscle, also appeared to be phosphorylated on Ser(231) after EPS-induced contraction. In addition, a switch in myosin heavy-chain (MHC) expression from "fast type" to "slow type" was observed in the C(2)C(12) myotubes endowed with EPS-induced repetitive contractility. Taking advantage of these highly developed contractile C(2)C(12) myotubes, we identified myotube-derived factors responsive to EPS-evoked contraction, including the CXC chemokines CXCL1/KC and CXCL5/LIX, as well as IL-6, previously reported to be upregulated in contracting muscles in vivo. Importantly, animal treadmill experiments revealed that exercise significantly increased systemic levels of CXCL1/KC, perhaps derived from contracting muscle. Taken together, these results confirm that we have established a specialized muscle cell culture model allowing contraction-inducible cellular responses to be explored. Utilizing this model, we identified contraction-inducible myokines potentially linked to the metabolic alterations, immune responses, and angiogenesis induced by exercise.

Physical activity and insulin sensitivity: the RISC study

OBJECTIVE

Physical activity is a modifiable risk factor for type 2 diabetes, partly through its action on insulin sensitivity. We report the relation between insulin sensitivity and physical activity measured by accelerometry.

RESEARCH DESIGN AND METHODS

This is a cross-sectional study of 346 men and 455 women, aged 30-60 years, without cardiovascular disease and not treated by drugs for diabetes, hypertension, dyslipidemia, or obesity. Participants were recruited in 18 clinical centers from 13 European countries. Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. Physical activity was recorded by accelerometry for a median of 6 days. We studied the relationship of insulin sensitivity with total activity (in counts per minute), percent of time spent sedentary, percent of time in light activity, and activity intensity (whether the participant recorded some vigorous or some moderate activity).

RESULTS

In both men and women, total activity was associated with insulin sensitivity (P < 0.0001). Time spent sedentary, in light activity, and activity intensity was also associated with insulin sensitivity (P < 0.0004/0.01, 0.002/0.03, and 0.02/0.004, respectively, for men/women) but lost significance once adjusted for total activity. Adjustment for confounders such as adiposity attenuated the relationship with total activity; there were no interactions with confounders. Even in the 25% most sedentary individuals, total activity was significantly associated with better insulin sensitivity (P < 0.0001).

CONCLUSIONS

Accumulated daily physical activity is a major determinant of insulin sensitivity. Time spent sedentary, time spent in light-activity, and bouts of moderate or vigorous activity did not impact insulin sensitivity independently of total activity.