Muscle damage impairs insulin stimulation of IRS-1, PI 3-kinase, and Akt-kinase in human skeletal muscle

Biological Roles of Selected microRNAs in Glucose Metabolism as a Candidate Biomarker for Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is a medical disorder characterized by high blood sugar levels resulting from a lack of insulin caused by impaired activity of 𝛽-cells and/or the inability of insulin to efficiently transport glucose from the bloodstream into cells, a condition referred to as insulin resistance. This occurs not only in insulin-sensitive tissues such as muscles, adipose tissue, and the liver, but also in the gastrointestinal tract, which may be caused by a defect in the insulin signaling pathway. MicroRNAs (miRNAs) are RNA molecules that do not code for proteins and play a role in multiple pathways. Several studies have suggested that specific miRNAs could potentially be used as biomarkers for diagnosing diabetes. These miRNAs regulate the formation of pancreatic islets, the differentiation of β-cells, the secretion of insulin, and the control of glucose metabolism. miRNA-mediated pathways are associated with human genetic illnesses resulting from mutations in the maturation process of miRNAs. The changes in miRNAs impact their ability to bind to mRNA targets, hence modifying gene expression. This review provides a concise overview of the latest studies investigating the correlation between miRNA expression and the regulation of glucose levels in cases of β-cell malfunction and insulin resistance.

Association between periodontitis and physical fitness in law enforcement workers

OBJECTIVES

Oral and periodontal health have been linked to systemic health, cardiovascular disease and inflammation markers. Physical fitness has been linked to increased inflammatory response, but only few studies have investigated the association between oral health with physical activity. The aim of this study was to evaluate the association between oral and periodontal health status and physical fitness in British law enforcement workers.

METHODS

89 subjects were recruited between November and December 2019. Cardiopulmonary fitness was measured by Maximal Oxygen Uptake (VO2max) (ml/kg/min) and Maximum Load (Loadmax) (W) generated at the end of the Bruce incremental treadmill test; physical activity levels through accelerometers; functional strength tests by Countermovement Jump (CMJ) Power (W) and Height (cm) average. Oral variables included percentage of sites with PPD > 4 mm (% PPD > 4), full-mouth bleeding score (FMBS) and Decayed, Missing, and Filled Teeth (DMFT) index. Linear regression models were adjusted for age, gender and fat %.

RESULTS

Mean age was 41.5 years (range 23-61; 71.9% male). Higher % PPD > 4 was consistently correlated with lower Loadmax (-4.96; p = 0.092), CMJ Height average (-0.39; p = 0.064), and press-ups in 60 s (-0.85; p = 0.052) though the associations were not statistically significant. FMBS was associated with the % of a day spent in sedentary (0.78; p = 0.030) and light activities (-0.75; p = 0.022).

CONCLUSIONS

Periodontitis may be negatively associated with certain components of physical performance.

CLINICAL RELEVANCE

Oral health status may be associated with physical fitness and functional strength.

Glycaemic Effects of a 156-km Ultra-trail Race in Athletes: An Observational Field Study

BACKGROUND

Ultra-trail running races pose appreciable physiological challenges, particularly for glucose metabolism. Previous studies that yielded divergent results only measured glycaemia at isolated times.

OBJECTIVES

We aimed to explore the impact of an ultra-endurance race on continuously measured glycaemia and to understand potential physiological mechanisms, as well as the consequences for performance and behavioural alertness.

METHODS

Fifty-five athletes (78% men, 43.7 ± 9.6 years) ran a 156-km ultra-trail race (six 26-km laps, total elevation 6000 m). Participants wore a masked continuous glucose monitoring sensor from the day before the race until 10 days post-race. Blood was taken at rest, during refuelling stops after each lap, and after 24-h recovery. Running intensity (% heart rate reserve), performance (lap times), psychological stress, and behavioural alertness were explored. Linear mixed models and logistic regressions were carried out.

RESULTS

No higher risk of hypo- or hyperglycaemia was observed during the exercise phases of the race (i.e. excluding stops for scientific measurements and refuelling) compared with resting values. Laps comprising a greater proportion of time spent at maximal aerobic intensity were nevertheless associated with more time > 180 mg/dL (P = 0.021). A major risk of hyperglycaemia appeared during the 48-h post-race period compared with pre-race (P < 0.05), with 31.9% of the participants spending time with values > 180 mg/dL during recovery versus 5.5% during resting. Changes in circulating insulin, cortisol, and free fatty acids followed profiles comparable with those usually observed during traditional aerobic exercise. However, creatine phosphokinase, and to a lesser extent lactate dehydrogenase, increased exponentially during the race (P < 0.001) and remained high at 24-h post-race (P < 0.001; respectively 43.6 and 1.8 times higher vs. resting). Glycaemic metrics did not influence physical performance or behavioural alertness.

CONCLUSION

Ultra-endurance athletes were exposed to hyperglycaemia during the 48-h post-race period, possibly linked to muscle damage and inflammation. Strategies to mitigate muscle damage or subsequent inflammation before or after ultra-trail races could limit recovery hyperglycaemia and hence its related adverse health consequences.

TRIAL REGISTRATION NUMBER

NCT05538442 2022-09-21 retrospectively registered.

Stevia (Stevia rebaudiana) extract ameliorates insulin resistance by regulating mitochondrial function and oxidative stress in the skeletal muscle of db/db mice

BACKGROUND

Type 2 diabetes mellitus (T2DM), a growing health problem worldwide, is a metabolic disorder characterized by hyperglycemia due to insulin resistance and defective insulin secretion by pancreatic β-cells. The skeletal muscle is a central organ that consumes most of the insulin-stimulated glucose in the body, and insulin resistance can damage muscles in T2DM. Based on a strong correlation between diabetes and muscles, we investigated the effects of stevia extract (SE) and stevioside (SV) on the skeletal muscle of diabetic db/db mice.

METHODS

The mice were administered saline, metformin  (200 mg/kg/day), SE (200 and 500 mg/kg/day), and SV (40 mg/kg/day) for 35 days. During administration, we checked the levels of fasting blood glucose twice a week and conducted the oral glucose tolerance test (OGTT) and insulin tolerance test (ITT). After administration, we analyzed serum biochemical parameters, triglyceride (TG), total cholesterol (TC), insulin and antioxidant enzymes, and the cross-sectional area of skeletal muscle fibers of db/db mice. Western blots were conducted using the skeletal muscle of mice to examine the effect of SE and SV on protein expression of insulin signaling, mitochondrial function, and oxidative stress.

RESULTS

SE and SV administration lowered the levels of fasting blood glucose, OGTT, and ITT in db/db mice. The administration also decreased serum levels of TG, TC, and insulin while increasing those of superoxide dismutase (SOD) and glutathione peroxidase (GPx). Interestingly, muscle fiber size was significantly increased in db/db mice treated with SE500 and SV. In the skeletal muscle of db/db mice, SE and SV administration activated insulin signaling by increasing the protein expression of insulin receptor substrate, Akt, and glucose transporter type 4. Furthermore, SE500 administration markedly increased the protein expression of AMP-activated protein kinase-α, sirtuin-1, and peroxisome proliferator-activated receptor-γ coactivator-1α. SV administration significantly reduced oxidative stress by down-regulating the protein expression of 4-hydroxynonenal, heme oxygenase-1, SOD, and GPx. In addition, SE500 and SV administration suppressed the expression of apoptosis-related proteins in the skeletal muscle of db/db mice.

CONCLUSION

SE and SV administration attenuated hyperglycemia in diabetic mice. Moreover, the administration ameliorated insulin resistance by regulating mitochondrial function and oxidative stress, increasing muscle fiber size. Overall, this study suggests that SE and SV administration may serve as a potential strategy for the treatment of diabetic muscles.

Sorting nexins: role in the regulation of blood pressure

Sorting nexins (SNXs) are a family of proteins that regulate cellular cargo sorting and trafficking, maintain intracellular protein homeostasis, and participate in intracellular signaling. SNXs are also important in the regulation of blood pressure via several mechanisms. Aberrant expression and dysfunction of SNXs participate in the dysregulation of blood pressure. Genetic studies show a correlation between SNX gene variants and the response to antihypertensive drugs. In this review, we summarize the progress in SNX-mediated regulation of blood pressure, discuss the potential role of SNXs in the pathophysiology and treatment of hypertension, and propose novel strategies for the medical therapy of hypertension.

Muscle damaging eccentric exercise attenuates disuse-induced declines in daily myofibrillar protein synthesis and transiently prevents muscle atrophy in healthy men

Short-term disuse leads to muscle loss driven by lowered daily myofibrillar protein synthesis (MyoPS). However, disuse commonly results from muscle damage, and its influence on muscle deconditioning during disuse is unknown. Twenty-one males [20 ± 1 yr, BMI = 24 ± 1 kg·m^-2 (± SE)] underwent 7 days of unilateral leg immobilization immediately preceded by 300 bilateral, maximal, muscle-damaging eccentric quadriceps contractions (DAM; subjects n = 10) or no exercise (CON; subjects n = 11). Participants ingested deuterated water and underwent temporal bilateral thigh MRI scans and vastus lateralis muscle biopsies of immobilized (IMM) and nonimmobilized (N-IMM) legs. N-IMM quadriceps muscle volume remained unchanged throughout both groups. IMM quadriceps muscle volume declined after 2 days by 1.7 ± 0.5% in CON (P = 0.031; and by 1.3 ± 0.6% when corrected to N-IMM; P = 0.06) but did not change in DAM, and declined equivalently in CON [by 6.4 ± 1.1% (5.0 ± 1.6% when corrected to N-IMM)] and DAM [by 2.6 ± 1.8% (4.0 ± 1.9% when corrected to N-IMM)] after 7 days. Immobilization began to decrease MyoPS compared with N-IMM in both groups after 2 days (P = 0.109), albeit with higher MyoPS rates in DAM compared with CON (P = 0.035). Frank suppression of MyoPS was observed between days 2 and 7 in CON (IMM = 1.04 ± 0.12, N-IMM = 1.86 ± 0.10%·day^-1; P = 0.002) but not DAM (IMM = 1.49 ± 0.29, N-IMM = 1.90 ± 0.30%·day^-1; P > 0.05). Declines in MyoPS and quadriceps volume after 7 days correlated positively in CON (r² = 0.403; P = 0.035) but negatively in DAM (r² = 0.483; P = 0.037). Quadriceps strength declined following immobilization in both groups, but to a greater extent in DAM. Prior muscle-damaging eccentric exercise increases MyoPS and prevents loss of quadriceps muscle volume after 2 (but not 7) days of disuse.NEW & NOTEWORTHY We investigated the impact of prior muscle-damaging eccentric exercise on disuse-induced muscle deconditioning. Two and 7 days of muscle disuse per se lowered quadriceps muscle volume in association with lowered daily myofibrillar protein synthesis (MyoPS). Prior eccentric exercise prevented the decline in muscle volume after 2 days and attenuated the decline in MyoPS after 2 and 7 days. These data indicate eccentric exercise increases MyoPS and transiently prevents quadriceps muscle atrophy during muscle disuse.

Reducing NF-κB Signaling Nutritionally is Associated with Expedited Recovery of Skeletal Muscle Function After Damage

CONTEXT

The early events regulating the remodeling program following skeletal muscle damage are poorly understood.

OBJECTIVE

The objective of this study was to determine the association between myofibrillar protein synthesis (myoPS) and nuclear factor-kappa B (NF-κB) signaling by nutritionally accelerating the recovery of muscle function following damage.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Healthy males and females consumed daily postexercise and prebed protein-polyphenol (PP; n = 9; 4 females) or isocaloric maltodextrin placebo (PLA; n = 9; 3 females) drinks (parallel design) 6 days before and 3 days after 300 unilateral eccentric contractions of the quadriceps during complete dietary control.

MAIN OUTCOME MEASURES

Muscle function was assessed daily, and skeletal muscle biopsies were taken after 24, 27, and 36 hours for measurements of myoPS rates using deuterated water, and gene ontology and NF-κB signaling analysis using a quantitative reverse transcription PCR (RT-qPCR) gene array.

RESULTS

Eccentric contractions impaired muscle function for 48 hours in PLA intervention, but just for 24 hours in PP intervention (P = 0.047). Eccentric quadricep contractions increased myoPS compared with the control leg during postexercise (24-27 hours; 0.14 ± 0.01 vs 0.11 ± 0.01%·h-1, respectively; P = 0.075) and overnight periods (27-36 hours; 0.10 ± 0.01 vs 0.07 ± 0.01%·h-1, respectively; P = 0.020), but was not further increased by PP drinks (P > 0.05). Protein-polyphenol drinks decreased postexercise and overnight muscle IL1R1 (PLA = 2.8 ± 0.4, PP = 1.1 ± 0.4 and PLA = 1.9 ± 0.4, PP = 0.3 ± 0.4 log2 fold-change, respectively) and IL1RL1 (PLA = 4.9 ± 0.7, PP = 1.6 ± 0.8 and PLA = 3.7 ± 0.6, PP = 0.7 ± 0.7 log2 fold-change, respectively) messenger RNA expression (P < 0.05) and downstream NF-κB signaling compared with PLA.

CONCLUSION

Protein-polyphenol drink ingestion likely accelerates recovery of muscle function by attenuating inflammatory NF-κB transcriptional signaling, possibly to reduce aberrant tissue degradation rather than increase myoPS rates.

Recent Advances in Panax ginseng C.A. Meyer as a Herb for Anti-Fatigue: An Effects and Mechanisms Review

As an ancient Chinese herbal medicine, Panax ginseng C.A. Meyer (P. ginseng) has been used both as food and medicine for nutrient supplements and treatment of human diseases in China for years. Fatigue, as a complex and multi-cause symptom, harms life from all sides. Millions worldwide suffer from fatigue, mainly caused by physical labor, mental stress, and chronic diseases. Multiple medicines, especially P. ginseng, were used for many patients or sub-healthy people who suffer from fatigue as a treatment or healthcare product. This review covers the extract and major components of P. ginseng with the function of anti-fatigue and summarizes the anti-fatigue effect of P. ginseng for different types of fatigue in animal models and clinical studies. In addition, the anti-fatigue mechanism of P. ginseng associated with enhancing energy metabolism, antioxidant and anti-inflammatory activity is discussed.

Enhanced skeletal muscle glycogen repletion after endurance exercise is associated with higher plasma insulin and skeletal muscle hexokinase 2 protein levels in mice: comparison of level running and downhill running model

To identify factors that influence post-exercise muscle glycogen repletion, we compared the glycogen recovery after level running with downhill running, an experimental model of impaired post-exercise glycogen recovery. Male Institute of Cancer Research (ICR) mice performed endurance level running (no inclination) or downhill running (-5° inclination) on a treadmill. In Experiment 1, to determine whether these two types of exercise resulted in different post-exercise glycogen repletion patterns, tissues were harvested immediately post-exercise or 2 days post-exercise. Compared to the control (sedentary) group, level running induced significant glycogen supercompensation in the soleus muscle at 2 days post-exercise (p = 0.002). Downhill running did not induce glycogen supercompensation. In Experiment 2, mice were orally administered glucose 1 day post-exercise; this induced glycogen supercompensation in soleus and plantaris muscle only in the level running group (soleus: p = 0.005, plantaris: p = 0.003). There were significant positive main effects of level running compared to downhill running on the plasma insulin (p = 0.017) and C-peptide concentration (p = 0.011). There was no difference in the glucose transporter 4 level or the phosphorylated states of proteins related to insulin signaling and metabolism in skeletal muscle. The level running group showed significantly higher hexokinase 2 (HK2) protein content in both soleus (p = 0.046) and plantaris muscles (p =0.044) at 1 day after exercise compared to the downhill running group. Our findings suggest that post-exercise skeletal muscle glycogen repletion might be partly influenced by plasma insulin and skeletal muscle HK2 protein levels.

Placental Regulation of Energy Homeostasis During Human Pregnancy

Successful pregnancies rely on sufficient energy and nutrient supply, which require the mother to metabolically adapt to support fetal needs. The placenta has a critical role in this process, as this specialized organ produces hormones and peptides that regulate fetal and maternal metabolism. The ability for the mother to metabolically adapt to support the fetus depends on maternal prepregnancy health. Two-thirds of pregnancies in the United States involve obese or overweight women at the time of conception. This poses significant risks for the infant and mother by disrupting metabolic changes that would normally occur during pregnancy. Despite well characterized functions of placental hormones, there is scarce knowledge surrounding placental endocrine regulation of maternal metabolic trends in pathological pregnancies. In this review, we discuss current efforts to close this gap of knowledge and highlight areas where more research is needed. As the intrauterine environment predetermines the health and wellbeing of the offspring in later life, adequate metabolic control is essential for a successful pregnancy outcome. Understanding how placental hormones contribute to aberrant metabolic adaptations in pathological pregnancies may unveil disease mechanisms and provide methods for better identification and treatment. Studies discussed in this review were identified through PubMed searches between the years of 1966 to the present. We investigated studies of normal pregnancy and metabolic disorders in pregnancy that focused on energy requirements during pregnancy, endocrine regulation of glucose metabolism and insulin resistance, cholesterol and lipid metabolism, and placental hormone regulation.

Health Benefits of Lactic Acid Bacteria (LAB) Fermentates

Consuming fermented foods has been reported to result in improvements in a range of health parameters. These positive effects can be exerted by a combination of the live microorganisms that the fermented foods contain, as well as the bioactive components released into the foods as by-products of the fermentation process. In many instances, and particularly in dairy fermented foods, the microorganisms involved in the fermentation process belong to the lactic acid group of bacteria (LAB). An alternative approach to making some of the health benefits that have been attributed to fermented foods available is through the production of ‘fermentates’. The term ‘fermentate’ generally relates to a powdered preparation, derived from a fermented product and which can contain the fermenting microorganisms, components of these microorganisms, culture supernatants, fermented substrates, and a range of metabolites and bioactive components with potential health benefits. Here, we provide a brief overview of a selection of in vitro and in vivo studies and patents exclusively reporting the health benefits of LAB ‘fermentates’. Typically, in such studies, the potential health benefits have been attributed to the bioactive metabolites present in the crude fermentates and/or culture supernatants rather than the direct effects of the LAB strain(s) involved.

Glycaemic stability of a cyclist with Type 1 diabetes: 4011 km in 20 days on a ketogenic diet

BACKGROUND

Maintaining glycaemic control during exercise presents a significant challenge for people living with Type 1 diabetes. Significant glycaemic variability has been observed in athletes with Type 1 diabetes in competitive contexts. While very-low-carbohydrate ketogenic diets have been shown to minimize glycaemic excursions, no published data have examined if this translates to exercise.

CASE REPORT

We report the case of a 37-year-old man with Type 1 diabetes who successfully undertook a 4011 km cycle across Australia over 20 consecutive days whilst consuming a very-low-carbohydrate ketogenic diet. Continuous glucose monitoring data capture was 98.4% for the ride duration and showed remarkable glycaemic stability, with a standard deviation of 2.1 mmol/l (average interstitial glucose 6.1 mmol/l) and 80.4% of time spent within a range of 3.9-10 mmol/l. Interstitial glucose was <3 mmol/l for 2.1% of this time, with only a single episode of symptomatic hypoglycaemia prompting brief interruption of exercise for carbohydrate administration.

CONCLUSION

This case demonstrates the viability of a very-low-carbohydrate ketogenic diet in an individual with Type 1 diabetes undertaking exercise. While the effect of a very-low-carbohydrate ketogenic diet is yet to be examined more broadly in athletes with Type 1 diabetes, the glycaemic stability observed suggests that fat adaptation may attenuate glycaemic swings and reduce reliance on carbohydrate consumption during exercise for maintaining euglycaemia.

Early effects of eccentric contractions on muscle glucose uptake

Muscle-damaging eccentric exercise impairs muscle glucose uptake several hours to days after exercise. Little, however, is known about the acute effects of eccentric exercise on contraction- and insulin-induced glucose uptake. This study compares glucose uptake rates in the first hours following eccentric, concentric, and isometric contractions with and without insulin present. Isolated rat extensor digitorum longus muscles were exposed to either an eccentric, concentric, or isometric contraction protocol, and muscle contractions were induced by electric stimulation that was identical between contraction protocols. In eccentric and concentric modes, length changes of 0.6 or 1.2 mm were used during contractions. Both contraction- and insulin-induced glucose uptake were assessed immediately and 2 h after contractions. Glucose uptake increased significantly following all modes of contraction and was higher after eccentric contractions with a stretch of 1.2 mm compared with the remaining contraction groups when assessed immediately after contractions [eccentric (1.2 mm) > eccentric (0.6 mm), concentric (1.2 mm), concentric (0.6 mm), isometric > rest; P < 0.05]. After 2 h, contraction-induced glucose uptake was still higher than noncontracting levels, but with no difference between contraction modes. The presence of insulin increased glucose uptake markedly, but this response was blunted by, respectively, 39–51% and 29–36% ( P < 0.05) immediately and 2 h after eccentric contractions stretched 1.2 mm compared with concentric and isometric contractions. The contrasting early effects of eccentric contractions on contraction- and insulin-induced glucose uptake suggest that glucose uptake is impaired acutely following eccentric exercise because of reduced insulin responsiveness.

NEW & NOTEWORTHY This study shows that, in isolated rat muscle, muscle-damaging eccentric contractions result in a transient increase in contraction-induced glucose uptake compared with isometric and concentric contractions induced by identical muscle activation protocols. Furthermore, our results demonstrate that, in contrast, the insulin-stimulated glucose uptake is impaired immediately following muscle-damaging eccentric contractions.

Effect of downhill walking on next-day muscle damage and glucose metabolism in healthy young subjects

This study aimed to investigate the effect of downhill walking on muscle damage and glucose metabolism in healthy subjects. All ten healthy young men and women (age, 24.0 ± 1.4 years) performed rest, uphill walking, and downhill walking trials. In the exercise trials, uphill (+ 5%) or downhill (- 5%) treadmill walking was performed at 6 km/h for 30 min. On the next day, muscle soreness was significantly higher in the downhill trial than in the uphill trial (P < 0.01). Respiratory metabolic performance did not differ between trials. However, carbohydrate oxidation was negatively correlated with plasma creatine kinase (r = - 0.41) and muscle soreness (r = - 0.47). Fasting blood glucose was significantly lower in the uphill trial than in the rest trial (P < 0.01) but not in the downhill trial. These observations suggest that downhill but not uphill walking causes mild delayed-onset muscle damage, which did not cause marked impairment in glucose metabolism. However, higher muscle damage responders might exhibit lower glucose metabolism.

Implications of Impaired Endurance Performance following Single Bouts of Resistance Training: An Alternate Concurrent Training Perspective

A single bout of resistance training induces residual fatigue, which may impair performance during subsequent endurance training if inadequate recovery is allowed. From a concurrent training standpoint, such carry-over effects of fatigue from a resistance training session may impair the quality of a subsequent endurance training session for several hours to days with inadequate recovery. The proposed mechanisms of this phenomenon include: (1) impaired neural recruitment patterns; (2) reduced movement efficiency due to alteration in kinematics during endurance exercise and increased energy expenditure; (3) increased muscle soreness; and (4) reduced muscle glycogen. If endurance training quality is consistently compromised during the course of a specific concurrent training program, optimal endurance development may be limited. Whilst the link between acute responses of training and subsequent training adaptation has not been fully established, there is some evidence suggesting that cumulative effects of fatigue may contribute to limiting optimal endurance development. Thus, the current review will (1) explore cross-sectional studies that have reported impaired endurance performance following a single, or multiple bouts, of resistance training; (2) identify the potential impact of fatigue on chronic endurance development; (3) describe the implications of fatigue on the quality of endurance training sessions during concurrent training, and (4) explain the mechanisms contributing to resistance training-induced attenuation on endurance performance from neurological, biomechanical and metabolic standpoints. Increasing the awareness of resistance training-induced fatigue may encourage coaches to consider modulating concurrent training variables (e.g., order of training mode, between-mode recovery period, training intensity, etc.) to limit the carry-over effects of fatigue from resistance to endurance training sessions.

Cardiovascular Effects and Benefits of Exercise

It is widely accepted that regular physical activity is beneficial for cardiovascular health. Frequent exercise is robustly associated with a decrease in cardiovascular mortality as well as the risk of developing cardiovascular disease. Physically active individuals have lower blood pressure, higher insulin sensitivity, and a more favorable plasma lipoprotein profile. Animal models of exercise show that repeated physical activity suppresses atherogenesis and increases the availability of vasodilatory mediators such as nitric oxide. Exercise has also been found to have beneficial effects on the heart. Acutely, exercise increases cardiac output and blood pressure, but individuals adapted to exercise show lower resting heart rate and cardiac hypertrophy. Both cardiac and vascular changes have been linked to a variety of changes in tissue metabolism and signaling, although our understanding of the contribution of the underlying mechanisms remains incomplete. Even though moderate levels of exercise have been found to be consistently associated with a reduction in cardiovascular disease risk, there is evidence to suggest that continuously high levels of exercise (e.g., marathon running) could have detrimental effects on cardiovascular health. Nevertheless, a specific dose response relationship between the extent and duration of exercise and the reduction in cardiovascular disease risk and mortality remains unclear. Further studies are needed to identify the mechanisms that impart cardiovascular benefits of exercise in order to develop more effective exercise regimens, test the interaction of exercise with diet, and develop pharmacological interventions for those unwilling or unable to exercise.

Drosophila muscles regulate the immune response against wasp infection via carbohydrate metabolism

We recently found that JAK/STAT signaling in skeletal muscles is important for the immune response of Drosophila larvae against wasp infection, but it was not clear how muscles could affect the immune response. Here we show that insulin signaling is required in muscles, but not in fat body or hemocytes, during larval development for an efficient encapsulation response and for the formation of lamellocytes. This effect requires TOR signaling. We show that muscle tissue affects the immune response by acting as a master regulator of carbohydrate metabolism in the infected animal, via JAK/STAT and insulin signaling in the muscles, and that there is indirect positive feedback between JAK/STAT and insulin signaling in the muscles. Specifically, stimulation of JAK/STAT signaling in the muscles can rescue the deficient immune response when insulin signaling is suppressed. Our results shed new light on the interaction between metabolism, immunity, and tissue communication.

How much variance in insulin resistance is explained by obesity?

Background: Obesity is believed to be the major cause of insulin resistance, although many other obesity-independent signals are shown to affect insulin sensitivity.Aim: We address the degree to which variation in insulin resistance is explained by morphometric and biochemical measures of obesity.Methods: PubMed and Google Scholar were searched for epidemiological studies published between 1994 and 2015 that report correlations between at least one measure of obesity and that of insulin resistance.Results: A total of 63 studies satisfied inclusion criteria. Frequency distribution of coefficients of determination between morphometric measures of obesity and insulin resistance was skewed with the mode being less than 10%, class and median being 17.3%. Plasma leptin concentration, but not plasma non-esterified fatty acid level, was better correlated with insulin resistance, the median variance explained being 33.29%. Morphometric measures alone had a median variance explained of 16%. Ethnicity explained part of the variance across studies with the correlation being significantly poorer in Asians.Conclusion: The extremely limited predictive power of morphometric and biochemical measures of obesity suggests that more research needs to focus on the obesity-independent signals that affect insulin sensitivity as well as leptin expression.

Glycemic Control and Muscle Damage in 3 Athletes With Type 1 Diabetes During a Successful Performance in a Relay Ultramarathon: A Case Report

Ultramarathon races are fairly demanding and impose substantial physiological stress on healthy athletes. These competitions may thus be considerably more challenging for individuals with diabetes. This case study aims to describe glycemic control, muscle damage, inflammation, and renal function in 3 athletes with type 1 diabetes during a successful performance in a relay ultramarathon. The team completed the race in 29 hours and 28 minutes, earning third place. The total distance covered by each athlete was 68.7, 84.5, and 65.1 km. Most blood glucose levels showed that athletes were in a zone where it was safe to exercise (90-250 mg/dL or 5.0-13.9 mmol/L). Creatine kinase, lactate dehydrogenase, and aspartate aminotransferase serum levels increased 1.2- to 50.7-fold prerace to postrace, and were higher than the reference ranges for all the athletes postrace. Blood leukocytes, neutrophils, and serum C-reactive protein (CRP) increased 1.6- to 52-fold prerace to postrace and were higher than the reference ranges for 2 athletes after the race. Serum creatinine increased 1.2-fold prerace to postrace for all the athletes but did not meet the risk criteria for acute kidney injury. In conclusion, our main findings show evidence of satisfactory glycemic control in athletes with type 1 diabetes during a relay ultramarathon. Moreover, elevation of muscle damage and inflammatory biomarkers occurred without affecting renal function and challenging the maintenance of blood glucose among athletes. These findings are novel and provide an initial understanding of the physiological responses in athletes with type 1 diabetes during ultramarathon races.

Acute effects of concentric and eccentric exercise matched for energy expenditure on glucose metabolism in healthy females: a randomized crossover trial

Background

Single bouts of muscle damaging eccentric exercise (EE) affect glucose metabolism negatively while single bouts of concentric (CE) and not muscle damaging eccentric exercise have positive acute short-term effects on glucose metabolism. It has been proposed that long-term endurance EE might be more effective in improving glucose metabolism than long-term CE when adjusted for energy expenditure. This would imply that adaptations of glucose metabolism are dependent on the type of exercise. Interleukin-6 (IL-6) released from the exercising muscles may be involved in and could therefore explain acute adaptations on glucose metabolism. The aim of the study was to investigate the effects of a single bout of CE and a single bout of EE inducing no or just mild muscle damage, matched for energy expenditure, on glucose metabolism.

Methods

7 healthy but sedentary female participants (age 20.7 ± 2.9 years; BMI 22.45 ± 1.66 kg m⁻²; VO₂peak 39.0 ± 4.5 ml kg⁻¹ min⁻¹) took part in a randomized cross over trial consisting of 1 h uphill (CE) respectively downhill (EE) walking on a treadmill. Venous blood samples were drawn before, directly after and 24 h after exercise. An oral glucose tolerance test (OGTT) was performed before and 24 h after exercise.

Results

CE and EE lead to comparable changes of glucose tolerance (area under the curve of the OGTT) (−16.0 ± 25.81 vs. −6.3 ± 45.26 mg dl⁻¹ h⁻¹, p = 1.000) and HOMA insulin resistance (−0.16 ± 1.53 vs. −0.08 ± 0.75, p = 0.753). Compared to baseline, IL-6 concentration increased significantly immediately after EE (1.07 ± 0.67 vs. 1.32 ± 0.60 pg ml⁻¹, p = 0.028) and tended to increase immediately after CE (0.75 ± 0.29 vs. 1.03 ± 0.21 pg ml⁻¹, p = 0.058). TNF-α concentration decreased significantly immediately after EE (1.47 ± 0.19 vs. 1.06 ± 0.29 pg ml⁻¹, p = 0.046) but not after CE (1.27 ± 0.43 vs. 1.24 ± 0.43 pg ml⁻¹, p = 0.686) compared to baseline.

Conclusions

Acute effects of a single bout of exercise inducing no or just mild muscle damage on glucose tolerance and insulin resistance seem to be primarily energy expenditure dependent whereas acute anti-inflammatory activity induced by a single bout of exercise appears to be rather exercise type dependent.

Trial registration: NCT01890876, clinicaltrials.gov, https://clinicaltrials.gov/.

Concentric and eccentric exercise, glycemic responses to a postexercise meal, and inflammation in women with high versus low waist circumference

Carbohydrate ingestion and level of concentric versus eccentric muscle activity may alter exercise-induced health benefits for individuals who have high waist circumference as a metabolic risk factor. The purpose of this study was to determine whether metabolic and inflammation responses to an exercise recovery meal differ between women with lower (Lo-WC, <80 cm) compared with higher (Hi-WC) waist circumference when the exercise is primarily concentric (uphill walking; UPHILL) versus primarily eccentric (downhill walking; DOWNHILL). Recreationally active women (age, 18-39 years; body mass index, 19-35.4 m·kg^-2; Lo-WC, n = 13; Hi-WC, n = 10) completed UPHILL, DOWNHILL, and resting (CONTROL) conditions followed 30 min later by a mixed meal tolerance test (MMTT) with carbohydrates to protein ratio of 4:1, and blood glucose, insulin, and inflammation markers were compared across conditions. Compared with Lo-WC, the Hi-WC group had higher (p < 0.05) (i) insulin during the MMTT in CONTROL (mean ± SE; 48.5 ± 8.2 vs 22.9 ± 2.8 pmol·L^-1), (ii) baseline (0.7 ± 0.4 vs 2.0 ± 1.7 pg·mL^-1) interleukin-6 (IL-6), and (iii) IL-6 responses 8 h after UPHILL and CONTROL. Both groups had (i) increases in IL-6 at 0 h after UPHILL and at 8 h after DOWNHILL, and (ii) lower glycemic responses in UPHILL. Women with Hi-WC had higher IL-6 at rest and delayed increases in IL-6 after a high-carbohydrate meal in all conditions. This is consistent with an inflammation response to the meal and or uphill walking exercise. However, both concentrically and eccentrically biased exercises offered benefits to insulin responses to a high carbohydrate meal for Hi-WC.

Acute effects of concentric and eccentric exercise on glucose metabolism and interleukin-6 concentration in healthy males

Acute muscle-damaging eccentric exercise (EE) negatively affects glucose metabolism. On the other hand, long-term eccentric endurance exercise seems to result in equal or superior positive effects on glucose metabolism compared to concentric endurance exercise. However, it is not known if acute non-muscle-damaging EE will have the same positive effects on glucose metabolism as acute concentric exercise (CE). Interleukin-6 (IL-6) released from the exercising muscles may be involved in the acute adaptations of glucose metabolism after CE and non-muscle-damaging EE. The aim of this study was to assess acute effects of uphill walking (CE) and non-muscle-damaging downhill walking (EE) on glucose metabolism and IL-6 secretion. Seven sedentary non-smoking, healthy males participated in a crossover trial consisting of a 1 h uphill (CE) and a 1 h downhill (EE) walking block on a treadmill. Venous blood samples were drawn before (pre), directly after (acute) and 24 h after (post) exercise. An oral glucose tolerance test (OGTT) was performed before and 24 h after exercise. Glucose tolerance after 1 and 2 hours significantly improved 24 hours after CE (-10.12±3.22%: P=0.039; -13.40±8.24%: P=0.028). After EE only the 1-hour value was improved (-5.03±5.48%: P=0.043). Acute IL-6 concentration rose significantly after CE but not after EE. We conclude that both a single bout of CE and a single bout of non-muscle-damaging EE elicit positive changes in glucose tolerance even in young, healthy subjects. Our experiment indicates that the overall metabolic cost is a major trigger for acute adaptations of glucose tolerance after exercise, but only the IL-6 production during EE was closely related to changes in glycaemic control.

Positive effect of IGF-1 injection on gastrocnemius of rat during distraction osteogenesis

Distraction osteogenesis (DO) is used to form new bone between bone segments to lengthen the callus. Skeletal muscles frequently fail to adapt to distraction, which causes complications. Insulin-like growth factor-1 (IGF-1) has been implicated as a central regulator of muscle repair. We hypothesized that IGF-1 injection could reduce muscle complications in DO. A total of 102 Sprague-Dawley rats received DO or did not were randomly assigned into saline, IGF-1 and normal groups. On the day before the distraction, the rats in the IGF-1 group were injected with IGF-1. The gastrocnemius muscles of the rats were harvested at the 0, 1st, 4th, 7th, and 10th days of distraction. The weight of the muscles, cross-sectional area (CSA) of the muscle fibers, collagen volume fraction (CVF), maximum limit load (MLL), maximum contraction forces, and gene expression of Akt, MyoD, myogenin, myostatin, and collagen I were analyzed. The results indicated that IGF-1 injection had increased the weights, CSA of the muscle fibers, MLL and force generation of the gastrocnemius. Also, Akt, MyoD, and myogenin were upregulated, and myostatin was downregulated in the IGF-1 group. Injection of IGF-1 could attenuate the gastrocnemius atrophy, prevent fibrosis, increase MLL, and regulate the related mRNA.

Endocrine alterations from concentric vs. eccentric muscle actions: a brief review

Resistance exercise has a positive effect on many tissues, including heart, bone, skeletal muscle, and nervous tissue. Eccentric muscle actions offer a unique and a potentially beneficial form of exercise for maintaining and improving health. During resistance exercise, the effects of gravity, and mechanical properties of the sarcomere and connective tissue in skeletal muscle allow a greater muscle load during an eccentric (lengthening) muscle contraction than a concentric (shortening) muscle contraction. Consequently, older patients, patients with muscle or limb movement limitations or injuries, as well as cancer patients may be able to benefit from isolated eccentric muscle actions. There are specific physiological responses to eccentric muscle contractions. This review will describe the effects of different eccentric muscle contraction protocols on endocrine responses that could have positive effects on different tissues and recommend direction for future research.

Eccentric exercise leads to performance decrease and insulin signaling impairment

PURPOSE

This study aimed to evaluate the effects of an overtraining (OT) protocol based on eccentric exercise (EE) sessions on the insulin and inflammatory signaling pathways in the skeletal muscles of Swiss mice.

METHODS

Rodents were divided into control (C; sedentary mice), trained (TR; performed the aerobic training protocol), and overtrained (OTR; performed the OT protocol). The incremental load test and exhaustive test were used to measure performances before and after exercise protocols. Twenty-four hours after the exhaustive test performed at the end of week 8, the extensor digitorum longus (EDL) and soleus muscles were removed for subsequent protein analysis by immunoblotting.

RESULTS

The phosphorylation of insulin receptor beta (pIRbeta; Tyr1146) diminished for EDL and soleus muscles in OTR compared with C. The phosphorylation of insulin receptor substrate 1 (pIRS-1; Ser307) increased for EDL and soleus muscles in OTR compared with C and TR. The phosphorylation of protein kinase B (pAkt; Ser473) diminished for EDL and soleus muscles in OTR compared with C and TR. The phosphorylation of IκB kinase alpha and beta (pIKKalpha/beta; Ser176/180), stress-activated protein kinases/Jun amino-terminal kinases (pSAPK/JNK; Thr183/Tyr185), and the protein levels of suppressor of cytokine signaling 3 (SOCS3) increased for EDL and soleus muscles in OTR compared with C and TR.

CONCLUSION

In summary, the current used OT protocol based on eccentric exercise sessions impaired the insulin signaling pathway with concomitant increases of IKK, SAPK/JNK, and SOCS3 protein levels.

Influence of miRNA in insulin signaling pathway and insulin resistance: micro-molecules with a major role in type-2 diabetes

The prevalence of type-2 diabetes (T2D) is increasing significantly throughout the globe since the last decade. This heterogeneous and multifactorial disease, also known as insulin resistance, is caused by the disruption of the insulin signaling pathway. In this review, we discuss the existence of various miRNAs involved in regulating the main protein cascades in the insulin signaling pathway that affect insulin resistance. The influence of miRNAs (miR-7, miR-124a, miR-9, miR-96, miR-15a/b, miR-34a, miR-195, miR-376, miR-103, miR-107, and miR-146) in insulin secretion and beta (β) cell development has been well discussed. Here, we highlight the role of miRNAs in different significant protein cascades within the insulin signaling pathway such as miR-320, miR-383, miR-181b with IGF-1, and its receptor (IGF1R); miR-128a, miR-96, miR-126 with insulin receptor substrate (IRS) proteins; miR-29, miR-384-5p, miR-1 with phosphatidylinositol 3-kinase (PI3K); miR-143, miR-145, miR-29, miR-383, miR-33a/b miR-21 with AKT/protein kinase B (PKB) and miR-133a/b, miR-223, miR-143 with glucose transporter 4 (GLUT4). Insulin resistance, obesity, and hyperlipidemia (high lipid levels in the blood) have a strong connection with T2D and several miRNAs influence these clinical outcomes such as miR-143, miR-103, and miR-107, miR-29a, and miR-27b. We also corroborate from previous evidence how these interactions are related to insulin resistance and T2D. The insights highlighted in this review will provide a better understanding on the impact of miRNA in the insulin signaling pathway and insulin resistance-associated diagnostics and therapeutics for T2D.

Hind limb ischemia-reperfusion injury in diet-induced obese mice

BACKGROUND

Obesity is a major risk factor for the development of diabetes. Limb ischemia-reperfusion injury (IR) is a common clinical problem in diabetics who have compromised lower extremity perfusion. This study compared the histologic, metabolic, and functional outcomes after hind limb IR in diet-induced obese (DIO) and non-diabetic (ND) mice during the acute and the regenerative phases of IR.

METHODS

DIO and ND mice were subjected to 1.5 h unilateral hind limb ischemia followed by 1- or 28-d IR. Muscle morphology, metabolic, and genomic stress were evaluated at days 1 and 28 IR; Acute inflammation and thrombosis were only measured at day-1 IR. At day 28, IR, skeletal muscle contractility, and maturation were also assessed.

RESULTS

At day-1 IR, similar levels of acute muscle fiber necrosis were seen in both groups. DIO mice demonstrated substantially greater inflammatory, prothrombotic, and genomic stress responses, which were also associated with a greater reduction in energy substrates and Akt phosphorylation. At 28d, there was no difference in the peak forces generated in the hind limbs for the two groups. DIO mice had reduced fatigue resistance compared with ND and larger areas of fat accumulation although there was no significant difference in muscle fiber maturation.

CONCLUSIONS

DIO mice had an exacerbated acute response to IR with enhanced metabolic deficit, fat accumulation, and defective functional recovery during the regenerative phase of IR. These changes in fatigue resistance reflect compromised functional recovery after IR injury and have relevance for the functional recovery of patients with metabolic syndrome and insulin resistance.

Periexercise coingestion of branched-chain amino acids and carbohydrate in men does not preferentially augment resistance exercise-induced increases in phosphatidylinositol 3 kinase/protein kinase B-mammalian target of rapamycin pathway markers indicative of muscle protein synthesis

The effects of a single bout of resistance exercise (RE) in conjunction with periexercise branched-chain amino acid (BCAA) and carbohydrate (CHO) ingestion on skeletal muscle signaling markers indicative of muscle protein synthesis were determined. It was hypothesized that CHO + BCAA would elicit a more profound effect on these signaling markers compared with CHO. Twenty-seven males were randomly assigned to CHO, CHO + BCAA, or placebo (PLC) groups. Four sets of leg presses and leg extensions were performed at 80% 1 repetition maximum. Supplements were ingested 30 minutes and immediately before and after RE. Venous blood and muscle biopsy samples were obtained immediately before supplement ingestion and 0.5, 2, and 6 hours after RE. Serum insulin and glucose and phosphorylated levels of muscle insulin receptor substrate 1 (IRS-1), protein kinase B, mammalian target of rapamycin, phosphorylated 70S6 kinase, and 4E binding protein 1 were assessed. Data were analyzed by 2-way repeated-measures analysis of variance. Significant group × time interactions were observed for glucose and insulin (P < .05) showing that CHO and CHO + BCAA were significantly greater than PLC. Significant time main effects were observed for IRS-1 (P = .001), protein kinase B (P = .031), mammalian target of rapamycin (P = .003), and phosphorylated 70S6 kinase (P = .001). Carbohydrate and CHO + BCAA supplementation significantly increased IRS-1 compared with PLC (P = .002). However, periexercise coingestion of CHO and BCAA did not augment RE-induced increases in skeletal muscle signaling markers indicative of muscle protein synthesis when compared with CHO.

Role of oxidative stress in impaired insulin signaling associated with exercise-induced muscle damage

Skeletal muscle is a major tissue that utilizes blood glucose. A single bout of exercise improves glucose uptake in skeletal muscle through insulin-dependent and insulin-independent signal transduction mechanisms. However, glucose utilization is decreased in muscle damage induced by acute, unaccustomed, or eccentric exercise. The decrease in glucose utilization is caused by decreased insulin-stimulated glucose uptake in damaged muscles with inhibition of the membrane translocation of glucose transporter 4 through phosphatidyl 3-kinase/Akt signaling. In addition to inflammatory cytokines, reactive oxygen species including 4-hydroxy-2-nonenal and peroxynitrate can induce degradation or inactivation of signaling proteins through posttranslational modification, thereby resulting in a disturbance in insulin signal transduction. In contrast, treatment with factors that attenuate oxidative stress in damaged muscle suppresses the impairment of insulin sensitivity. Muscle-damaging exercise may thus lead to decreased endurance capacity and muscle fatigue in exercise, and it may decrease the efficiency of exercise therapy for metabolic improvement.

Helpful or harmful? Potential effects of exercise on select inflammatory conditions

Inflammation has been characterized as a double-edged sword, requiring a balance between health as maintained by regular exercise and activities that would exacerbate inflammatory diseases. The influence of exercise on inflammation is complex and has been widely studied in both healthy patient populations as well as populations of patients with many inflammatory and/or autoimmune rheumatic diseases. Inflammatory markers can be affected by the type of exercise and muscle contraction, as well as the intensity, duration, and consistency of the exercise sessions. Because of these potentially important effects, many members of the general public, as well as some clinicians, believe that exercise could exacerbate symptoms and accelerate the progression of such conditions. The effects of different types of exercise have been studied among patients with inflammatory conditions such as ankylosing spondylitis, systemic lupus erythematosus, rheumatoid arthritis, osteoarthritis, fibromyalgia, and idiopathic inflammatory myopathies, as well as congestive heart failure, type 2 diabetes mellitus, and metabolic syndrome, which are considered low-grade systemic inflammatory diseases. This review will help exercise professionals and clinicians understand the effects of exercise on inflammatory markers, as well as offer effective treatment options and recommendations for patients exercising with rheumatic or inflammatory conditions.

Heat shock transcription factor 1-deficiency attenuates overloading-associated hypertrophy of mouse soleus muscle

Hypertrophic stimuli, such as mechanical stress and overloading, induce stress response, which is mediated by heat shock transcription factor 1 (HSF1), and up-regulate heat shock proteins (HSPs) in mammalian skeletal muscles. Therefore, HSF1-associated stress response may play a key role in loading-associated skeletal muscle hypertrophy. The purpose of this study was to investigate the effects of HSF1-deficiency on skeletal muscle hypertrophy caused by overloading. Functional overloading on the left soleus was performed by cutting the distal tendons of gastrocnemius and plantaris muscles for 4 weeks. The right muscle served as the control. Soleus muscles from both hindlimbs were dissected 2 and 4 weeks after the operation. Hypertrophy of soleus muscle in HSF1-null mice was partially inhibited, compared with that in wild-type (C57BL/6J) mice. Absence of HSF1 partially attenuated the increase of muscle wet weight and fiber cross-sectional area of overloaded soleus muscle. Population of Pax7-positive muscle satellite cells in HSF1-null mice was significantly less than that in wild-type mice following 2 weeks of overloading (p<0.05). Significant up-regulations of interleukin (IL)-1β and tumor necrosis factor mRNAs were observed in HSF1-null, but not in wild-type, mice following 2 weeks of overloading. Overloading-related increases of IL-6 and AFT3 mRNA expressions seen after 2 weeks of overloading tended to decrease after 4 weeks in both types of mice. In HSF1-null mice, however, the significant overloading-related increase in the expression of IL-6, not ATF3, mRNA was noted even at 4th week. Inhibition of muscle hypertrophy might be attributed to the greater and prolonged enhancement of IL-6 expression. HSF1 and/or HSF1-mediated stress response may, in part, play a key role in loading-induced skeletal muscle hypertrophy.

A single bout of downhill running transiently increases HOMA-IR without altering adipokine response in healthy adult women

PURPOSE

Eccentric exercise-induced muscle damage may cause marked alterations in insulin sensitivity. However, it is not entirely known whether such alterations are also related to changes in adipokine levels. The aim of this study was to investigate the effects of muscle damage due to downhill running on inflammation, insulin sensitivity and selected adipokines related to insulin regulation (adiponectin, visfatin, resistin).

METHODS

Data were collected from 12 healthy adult women. Each subject participated in two trials, 4 weeks apart. The first trial was reserved for resting measurements only (control trial), while the second trial involved a 45-min exercise (-15 % slope, ~60 % of VO2max) intervention (exercise trial). Insulin sensitivity (HOMA), creatine kinase activity (CK), delayed onset muscle soreness (DOMS), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), glucose, insulin, adiponectin, resistin, and visfatin were assessed pre-exercise and 1, 2, 3, and 4 days post-exercise and during the same time points in the control trial.

RESULTS

Analyses revealed that CK, DOMS, TNF-α, IL-6, insulin and HOMA significantly increased (p < 0.05) throughout recovery (days 1-4). Adiponectin and visfatin remained unchanged, while resistin significantly increased (p < 0.05) only 2 days post-exercise. Visfatin was negatively correlated with HOMA at days 1 and 4 of recovery.

CONCLUSION

Although muscle damage due to downhill running caused a decline of insulin sensitivity, this response was not associated with the changes in adipokine levels.

Age attenuates leucine oxidation after eccentric exercise

Aging may alter protein metabolism during periods of metabolic and physiologic challenge. The purpose of this study was to assess the effects of age on whole-body amino acid turnover in response to eccentric exercise and hyperglycemia-induced hyperinsulinemia. 16 healthy men were divided into young (N=8) and older (N=8) groups. Protein metabolism was assessed using a [1-13C]-leucine isotopic tracer approach. Measures were obtained under fasted basal conditions and during 3-h hyperglycemic clamps that were performed without (control) and 48 h after eccentric exercise. Exercise reduced leucine oxidation in the younger men (P<0.05), but not in older men. Insulin sensitivity was inversely correlated with leucine oxidation (P<0.05), and was lower in older men (P<0.05). Healthy aging is associated with an impaired capacity to adjust protein oxidation in response to eccentric exercise. The decreased efficiency of protein utilization in older men may contribute to impaired maintenance, growth, and repair of body tissues with advancing age.

Fermented milk improves glucose metabolism in exercise-induced muscle damage in young healthy men

Background

This study investigated the effect of fermented milk supplementation on glucose metabolism associated with muscle damage after acute exercise in humans.

Methods

Eighteen healthy young men participated in each of the three trials of the study: rest, exercise with placebo, and exercise with fermented milk. In the exercise trials, subjects carried out resistance exercise consisting of five sets of leg and bench presses at 70–100% 12 repetition maximum. Examination beverage (fermented milk or placebo) was taken before and after exercise in double-blind method. On the following day, we conducted an analysis of respiratory metabolic performance, blood collection, and evaluation of muscle soreness.

Results

Muscle soreness was significantly suppressed by the consumption of fermented milk compared with placebo (placebo, 14.2 ± 1.2 score vs. fermented milk, 12.6 ± 1.1 score, p < 0.05). Serum creatine phosphokinase was significantly increased by exercise, but this increase showed a tendency of suppression after the consumption of fermented milk. Exercise significantly decreased the respiratory quotient (rest, 0.88 ± 0.01 vs. placebo, 0.84 ± 0.02, p < 0.05), although this decrease was negated by the consumption of fermented milk (0.88 ± 0.01, p < 0.05). Furthermore, exercise significantly reduced the absorption capacity of serum oxygen radical (rest, 6.9 ± 0.4 μmol TE/g vs. placebo, 6.0 ± 0.3 μmol TE/g, p < 0.05), although this reduction was not observed with the consumption of fermented milk (6.2 ± 0.3 μmol TE/g).

Conclusion

These results suggest that fermented milk supplementation improves glucose metabolism and alleviates the effects of muscle soreness after high-intensity exercise, possibly associated with the regulation of antioxidant capacity.

Potential mechanisms of exercise in gestational diabetes

Gestational diabetes mellitus (GDM) is defined as glucose intolerance first diagnosed during pregnancy. This condition shares same array of underlying abnormalities as occurs in diabetes outside of pregnancy, for example, genetic and environmental causes. However, the role of a sedentary lifestyle and/or excess energy intake is more prominent in GDM. Physically active women are less likely to develop GDM and other pregnancy-related diseases. Weight gain in pregnancy causes increased release of adipokines from adipose tissue; many adipokines increase oxidative stress and insulin resistance. Increased intramyocellular lipids also increase cellular oxidative stress with subsequent generation of reactive oxygen species. A well-planned program of exercise is an important component of a healthy lifestyle and, in spite of old myths, is also recommended during pregnancy. This paper briefly reviews the role of adipokines in gestational diabetes and attempts to shed some light on the mechanisms by which exercise can be beneficial as an adjuvant therapy in GDM. In this regard, we discuss the mechanisms by which exercise increases insulin sensitivity, changes adipokine profile levels, and boosts antioxidant mechanisms.

Diabetic status of patients with leprosy in Kuwait

OBJECTIVE

The aim of this study was to screen for diabetes mellitus in leprosy patients to elucidate whether leprosy infection may play a role in the pathogenesis of diabetes mellitus in this population.

SUBJECTS AND METHODS

Thirty patients of different ages and of both sexes with various types of leprosy were included in this study. In addition, 15 healthy individuals of comparable age and sex who had no family history of diabetes mellitus were identified as controls. In both groups, determinations of fasting and postprandial blood sugar, an oral glucose tolerance test (OGTT), measures of fasting serum insulin and pro-inflammatory cytokine tumor necrosis factor alpha (TNFα), as well as calculations using the Homeostasis Model Assessment for Insulin Resistance (HOMA-IR), were carried out.

RESULT

Approximately 13.3% of the leprosy patients were diabetic, and 37.7% were in pre-diabetic. The highest incidences of diabetes and pre-diabetes were in lepromatous leprosy (10% and 20%, respectively); a lower incidence of pre-diabetes (6.6%) was observed in tuberculoid leprosy; and the lowest incidence of diabetes (0.0%) was noted in borderline leprosy patients. Although normal healthy persons were not diabetic (0%), 20% were pre-diabetic.

CONCLUSION

This study revealed that the incidence of diabetes was higher in the leprosy patients than in the control group. As a result, we recommend that all leprosy patients should be screened for diabetes.

Renewed avenues through exercise muscle contractility and inflammatory status

Physical inactivity leads to the accumulation of visceral fat and, consequently, to the activation of a network of inflammatory pathways which may promote development of insulin resistance, atherosclerosis, neurodegeneration, and tumour growth. These conditions belong to the "diseasome of physical inactivity". In contrast, the protective effect of regular exercise against diseases associated with chronic inflammation may to some extent be ascribed to an anti-inflammatory effect. The so called "acute exercise threshold", the complex mixture of several variables involved in exercise, such as type, volume, frequency, and intensity range is capable of inducing positive physiological adaptations and has been specifically addressed in the recent literature. The major concern is related to the level of the threshold: "exercise training shifts from a therapeutic adaptive intervention to one with potential pathological consequences". Nonetheless, if the mechanical stimulus is too weak to disrupt cellular homeostasis, training adaptations will not occur. Answering these questions could present practical applications, especially during inflammatory diseases associated with detrimental muscle effects and could theoretically constitute a "new" therapeutic approach to treat/improve an inflammatory state. This paper aims to describe specific data from the literature regarding the effects of exercise on inflammatory diseases in order to promote a more sophisticated perspective on the anti-inflammatory effects of exercise.

Effects of Panax ginseng Supplementation on Muscle Damage and Inflammation after Uphill Treadmill Running in Humans

The purpose of this investigation was to determine whether Panax ginseng extract intake would influence exercise-induced muscle damage and inflammation responses. Eighteen male college students were randomly assigned to either an RG intake group (RG, n = 9) or a placebo group (P, n = 9). All subjects performed a high-intensity uphill treadmill running task (two rounds of 45 min at 10 km/h speed with a 15 degree uphill slope separated by 5 min of rest). The RG group ingested 20 g/day of Korean red ginseng extract (mixed with 200 ml of water) three times/day for seven days prior to performing the uphill treadmill exercise test and for four days after the treadmill test, while the P group ingested 200 ml of water containing Agastachis Herba on the same schedule. Plasma creatine kinase activity (CK) and interlukin-6 (IL-6) levels were measured at pre-exercise and 24, 48, 72, and 96 h post-exercise; the IL-6 level was also measured at 1 and 2 h post-exercise. To evaluate insulin sensitivity, the oral glucose tolerance test (OGTT) was performed 24 h post-exercise. Plasma CK level in RG was significantly lower than that in P 72 h post-exercise (p < 0.05), and IL-6 level was significantly decreased in RG during the 2 h and 3 h recovery period compared to that of P (p < 0.05). Plasma glucose and insulin responses in RG were significantly reduced compared to those of P (p < 0.05). The results of this study suggest that RG supplementation could reduce exercise-induced muscle damage and inflammatory responses, resulting in improvements in insulin sensitivity.

Carbohydrates for Physical Activity

Intake of carbohydrates above the dietary guidelines to support performance of physical activity is common but may be unnecessary and counterproductive. Sports nutrition guidelines have not been designed to incorporate characteristics that may make high carbohydrate consumption a source of metabolic stress that may increase oxidative stress, inflammation, and lipogenesis. This metabolic stress is linked to the physiology underlying the development of insulin resistance, type 2 diabetes mellitus, and cardiovascular diseases. This review describes research-based evidence to aid in bridging the gap between dietary guidelines for overall health and those to support physical activity. Characteristics that increase the likelihood of metabolic stress resulting from carbohydrate intake include overweight and obesity, central/visceral adiposity, older age, sedentary lifestyle, and caloric state. Carbohydrate-based foods that provide the most health benefits are whole grains, beans and legumes, fruits, and vegetables. Carbohydrate-based foods that most readily elicit metabolic stress are those with added sugars and refined grains or that have a high glycemic index. A checklist that incorporates both the number of these characteristics and prevailing guidelines for nutrition and physical activity is presented. This may be useful in determining whether additional carbohydrates are needed to support the physical activity level of the individual.

Exercise-induced muscle damage impairs insulin signaling pathway associated with IRS-1 oxidative modification

Strenuous exercise induces delayed-onset muscle damage including oxidative damage of cellular components. Oxidative stress to muscle cells impairs glucose uptake via disturbance of insulin signaling pathway. We investigated glucose uptake and insulin signaling in relation to oxidative protein modification in muscle after acute strenuous exercise. ICR mice were divided into sedentary and exercise groups. Mice in the exercise group performed downhill running exercise at 30 m/min for 30 min. At 24 hr after exercise, metabolic performance and insulin-signaling proteins in muscle tissues were examined. In whole body indirect calorimetry, carbohydrate utilization was decreased in the exercised mice along with reduction of the respiratory exchange ratio compared to the rested control mice. Insulin-stimulated uptake of 2-deoxy-[(3)H]glucose in damaged muscle was decreased after acute exercise. Tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and phosphatidyl-3-kinase/Akt signaling were impaired by exercise, leading to inhibition of the membrane translocation of glucose transporter 4. We also found that acute exercise caused 4-hydroxy-nonenal modification of IRS-1 along with elevation of oxidative stress in muscle tissue. Impairment of insulin-induced glucose uptake into damaged muscle after strenuous exercise would be related to disturbance of insulin signal transduction by oxidative modification of IRS-1.

Wnt7a-Fzd7 signalling directly activates the Akt/mTOR anabolic growth pathway in skeletal muscle

Wnt7a signals through its receptor Fzd7 to activate the planar-cell-polarity pathway and drive the symmetric expansion of satellite stem cells resulting in enhanced repair of skeletal muscle. In differentiated myofibres, we observed that Wnt7a binding to Fzd7 directly activates the Akt/mTOR growth pathway thereby inducing myofibre hypertrophy. Notably, the Fzd7 receptor complex was associated with Gαs and PI3kinase and these components were required for Wnt7a to activate the Akt/mTOR growth pathway in myotubes. Wnt7a/Fzd7 activation of this pathway was completely independent of IGF-receptor activation. Together, these experiments demonstrate that Wnt7a/Fzd7 activates distinct pathways at different developmental stages during myogenic lineage progression, and together identify a novel non-canonical anabolic signalling pathway for Wnt7a and its receptor Fzd7 in skeletal muscle.

Current understanding of increased insulin sensitivity after exercise - emerging candidates

Exercise counteracts insulin resistance and improves glucose homeostasis in many ways. Apart from increasing muscle glucose uptake quickly, exercise also clearly increases muscle insulin sensitivity in the post-exercise period. This review will focus on the mechanisms responsible for this increased insulin sensitivity. It is believed that increased sarcolemmal content of the glucose transporter GLUT4 can explain the phenomenon to some extent. Surprisingly no improvement in the proximal insulin signalling pathway is observed at the level of the insulin receptor, IRS1, PI3K or Akt. Recently more distal signalling component in the insulin signalling pathway such as aPKC, Rac1, TBC1D4 and TBC1D1 have been described. These are all affected by both insulin and exercise which means that they are likely converging points in promoting GLUT4 translocation and therefore possible candidates for regulating insulin sensitivity after exercise. Whereas TBC1D1 does not appear to regulate insulin sensitivity after exercise, correlative evidence in contrast suggests TBC1D4 to be a relevant candidate. Little is known about aPKC and Rac1 in relation to insulin sensitivity after exercise. Besides mechanisms involved in signalling to GLUT4 translocation, factors influencing the trans-sarcolemmal glucose concentration gradient might also be important. With regard to the interstitial glucose concentration microvascular perfusion is particular relevant as correlative evidence supports a connection between insulin sensitivity and microvascular perfusion. Thus, there are new candidates at several levels which collectively might explain the phenomenon.

p38 mitogen-activated protein kinase-dependent transactivation of ErbB receptor family: a novel common mechanism for stress-induced IRS-1 serine phosphorylation and insulin resistance

OBJECTIVE

Stress stimuli such as tumor necrosis factor (TNF) have been shown to induce insulin receptor substrate (IRS)-1 serine phosphorylation and insulin resistance by transactivation of ErbB receptors. We aimed at elucidating the potential role of p38 mitogen-activated protein kinase (p38MAPK) in mediating stress-induced ErbB receptors activation.

RESEARCH DESIGN AND METHODS

p38MAPK effect on ErbBs transactivation and insulin signaling was assessed in Fao or HepG2 cells, exposed to stress stimuli, and on metabolic parameters in ob/ob and C57/BL6 mice.

RESULTS

High-fat diet-fed mice and ob/ob mice exhibited elevated hepatic p38MAPK activation associated with glucose intolerance and hyperinsulinemia. Liver expression of dominant-negative (DN)-p38MAPKα in ob/ob mice reduced fasting insulin levels and improved glucose tolerance, whereas C57/BL6 mice overexpressing wild-type p38MAPKα exhibited enhanced IRS-1 serine phosphorylation and reduced insulin-stimulated IRS-1 tyrosine phosphorylation. Fao or HepG2 cells exposed to TNF, anisomycin, or sphingomyelinase demonstrated rapid transactivation of ErbB receptors leading to PI3-kinase/Akt activation and IRS-1 serine phosphorylation. p38MAPK inhibition either by SB203580, by small interfering RNA, or by DN-p38MAPKα decreased ErbB receptors transactivation and IRS-1 serine phosphorylation and partially restored insulin-stimulated IRS-1 tyrosine phosphorylation. When cells were incubated with specific ErbB receptors antagonists or in cells lacking ErbB receptors, anisomycin- and TNF-induced IRS-1 serine phosphorylation was attenuated, despite intact p38MAPK activation. The stress-induced p38MAPK activation leading to ErbB receptors transactivation was associated with intracellular reactive oxygen species generation and was attenuated by treatment with antioxidants.

CONCLUSIONS

Hepatic p38MAPK is activated following various stress stimuli. This event is upstream to ErbB receptors transactivation and plays an important role in stress-induced IRS-1 serine phosphorylation and insulin resistance.

Landscape mapping of functional proteins in insulin signal transduction and insulin resistance: a network-based protein-protein interaction analysis

The type 2 diabetes has increased rapidly in recent years throughout the world. The insulin signal transduction mechanism gets disrupted sometimes and it's known as insulin-resistance. It is one of the primary causes associated with type-2 diabetes. The signaling mechanisms involved several proteins that include 7 major functional proteins such as INS, INSR, IRS1, IRS2, PIK3CA, Akt2, and GLUT4. Using these 7 principal proteins, multiple sequences alignment has been created. The scores between sequences also have been developed. We have constructed a phylogenetic tree and modified it with node and distance. Besides, we have generated sequence logos and ultimately developed the protein-protein interaction network. The small insulin signal transduction protein arrangement shows complex network between the functional proteins.

Influence of macronutrient intake and anthropometric characteristics on plasma insulin after eccentric exercise

To increase understanding of the interaction between macronutrients and insulin resistance (IR), this study sought to determine the influence of macronutrient intake and anthropometric differences on IR and inflammation responses to eccentric resistance exercise. Men and women (n = 12, 19-36 years old) participated in a crossover study and completed 6 sets of 10 unilateral maximal eccentric contractions of the elbow flexors and extensors followed by controlled diet conditions for the first 8 hours postexercise of carbohydrate/fat/protein proportions of either 75%/15%/10% (CHO) or 6%/70%/24% (FAT/PRO). Fasting glucose, insulin, homeostatic model assessment (HOMA) variables, and interleukin (IL)-1β were measured preexercise and 23 hours postexercise (additional measures of glucose and insulin 1 hour after meals consumed 0.5, 3, and 7 hours postexercise). Insulin increased more (P < .01) in the CHO compared with the FAT/PRO condition at 1.5, 4, and 8 hours postexercise. Insulin, HOMA-IR, and HOMA-β-cell function increased 23 hours postexercise in both conditions, whereas IL-1β increased 23 hours postexercise only in the CHO condition. Magnitude of change (Δ) for these variables associated positively with body mass index (BMI) and waist to hip ratio (WHR) in the CHO and inversely in the FAT/PRO condition; that is, r = 0.53 (P = .10) and r = -0.82 (P < .01) for BMI vs Δ insulin in CHO and FAT/PRO conditions, respectively. The Δ IL-1β associated with BMI (r = 0.62, P < .05) and WHR (r = 0.84, P < .01) in the CHO condition. The CHO enhanced IR and inflammation as BMI and WHR increased, whereas fat and protein enhanced IR as BMI and WHR decreased. Thus, BMI and WHR may need to be taken into account in the development of nutritional strategies to prevent IR.

Effects of eccentric exercise-induced muscle damage on intramyocellular lipid concentration and high energy phosphates

Eccentric exercise is known to cause changes to the ultrastructure of skeletal muscle and, in turn, may alter the ability of the muscle to store and utilise intracellular substrates such as intramyocellular lipid (IMCL). The purpose of this study was to test the hypothesis that exercise-induced muscle damage (EIMD) results in IMCL accumulation. Six males (31 ± 6 years; mean ± SD, and 72.3 ± 9.7 kg body mass) performed 300 unilateral, maximal, isokinetic, eccentric contractions (Ecc) (30° s(-1)) of the quadriceps on an isokinetic dynamometer, followed immediately by an equal amount of work by the contralateral leg but with concentric action (Con). Phosphate compounds and IMCL content of the vastus lateralis of both legs were measured using (31)P and (1)H magnetic resonance spectroscopy. IMCL content was higher in Ecc than Con 24 h post but the reverse was evident 48 h post-exercise (P = 0.046). A significant time × trial interaction for resting [P(i)] (P = 0.045), showed increases in Ecc across time but no change in Con. A significant main effect of trial (P = 0.002) was apparent indicating the Ecc leg had marked metabolic dysfunction. The P(i)/PCr ratio showed a significant effect of trial (P = 0.001) with an increase evident in Ecc leg, primarily due to increases in [P(i)]. The present study highlights changes in IMCL content of skeletal muscle following EIMD.