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Regular endurance exercise promotes metabolic and oxidative changes in skeletal muscle. Overexpression of interleukin-15 (IL-15) in mice exerts similar metabolic changes in muscle as seen with endurance exercise. Muscular IL-15 production has been shown to increase in mice after weeks of regular endurance running. With the present study we aimed to determine if muscular IL-15 production would increase in human male subjects following 12 weeks of endurance training. In two different studies we obtained plasma and muscle biopsies from young healthy subjects performing: (1) 12 weeks of ergometer cycling exercise five times per week with plasma and biopsies before and after the intervention, and (2) 3 h of ergometer cycling exercise with plasma and biopsies before and after the exercise bout and well into recovery. We measured changes in plasma IL-15, muscle IL-15 mRNA and IL-15 protein. Twelve weeks of regular endurance training induced a 40% increase in basal skeletal muscle IL-15 protein content (p < 0.01), but with no changes in either muscle IL-15 mRNA or plasma IL-15 levels. However, an acute bout of 3-h exercise did not show significant changes in muscle IL-15 or plasma IL-15 levels. The induction of muscle IL-15 protein in humans following a regular training period supports previous findings in mice and emphasizes the hypothesis of IL-15 taking part in skeletal muscle adaptation during training.

Soluble CD163 (sCD163) was recently identified as a strong risk marker for developing type 2 diabetes. We hypothesised that sCD163 independently associates with insulin resistance. This cross-sectional study includes 234 participants: 96 with type 2 diabetes, 34 with impaired glucose tolerance (IGT) and 104 with normal glucose tolerance (NGT), matched for sex and BMI. Glucose-lowering medication was paused for 1 week before plasma samples were obtained for determination of sCD163 and other inflammatory and metabolic variables. Insulin resistance was estimated by homeostasis model assessment of insulin resistance (HOMA-IR). Concentrations of sCD163 were 1.95 mg/l (0.63–6.97) in individuals with type 2 diabetes, 1.64 mg/l (0.58–4.19) in those with IGT, and 1.48 mg/l (0.48–4.11) (median [range]) in those with NGT (p

Vitamin C and E supplementation has been shown to attenuate the acute exercise-induced increase in plasma interleukin-6 (IL-6) concentration. Here, we studied the effect of antioxidant vitamins on the regulation of IL-6 expression in muscle and the circulation in response to acute exercise before and after high-intensity endurance exercise training. Twenty-one young healthy men were allocated into either a vitamin (VT; vitamin C and E, n = 11) or a placebo (PL, n = 10) group. A 1-h acute bicycling exercise trial at 65% of maximal power output was performed before and after 12 wk of progressive endurance exercise training. In response to training, the acute exercise-induced IL-6 response was attenuated in PL ( P < 0.02), but not in VT ( P = 0.82). However, no clear difference between groups was observed (group × training: P = 0.13). Endurance exercise training also attenuated the acute exercise-induced increase in muscle-IL-6 mRNA in both groups. Oxidative stress, assessed by plasma protein carbonyls concentration, was overall higher in the VT compared with the PL group (group effect: P < 0.005). This was accompanied by a general increase in skeletal muscle mRNA expression of antioxidative enzymes, including catalase, copper-zinc superoxide dismutase, and glutathione peroxidase 1 mRNA expression in the VT group. However, skeletal muscle protein content of catalase, copper-zinc superoxide dismutase, or glutathione peroxidase 1 was not affected by training or supplementation. In conclusion, our results indicate that, although vitamin C and E supplementation may attenuate exercise-induced increases in plasma IL-6 there is no clear additive effect when combined with endurance training.

OBJECTIVE—YKL-40 is produced by macrophages, and plasma YKL-40 is elevated in patients with diseases characterized by inflammation. In the present study, YKL-40 was examined in relation to obesity, inflammation, and type 2 diabetes. RESEARCH DESIGN AND METHODS—Plasma YKL-40 and adipose tissue YKL-40 mRNA levels were investigated in 199 subjects who were divided into four groups depending on the presence or absence of type 2 diabetes and obesity. In addition, plasma YKL-40 was examined in healthy subjects during a hyperglycemic clamp, in which the plasma glucose level was kept at 15 mmol/l for 3 h, and during a hyperinsulinemic-euglycemic clamp. RESULTS—Patients with type 2 diabetes had higher plasma YKL-40 (76.7 vs. 45.1 ng/ml, P = 0.0001) but not higher expression in adipose tissue YKL-40 mRNA (1.20 vs. 0.98, P = 0.2) compared with subjects with a normal glucose tolerance. Within the groups with normal glucose tolerance and type 2 diabetes, obesity subgroups showed no difference with respect to either plasma YKL-40 or adipose tissue YKL-40 mRNA levels. Multivariate regression analysis showed that plasma YKL-40 was associated with fasting plasma glucose (β = 0.5, P = 0.0014) and plasma interleukin (IL)-6 (β = 0.2, P = 0.0303). Plasma YKL-40 was not related to parameters of obesity. There were no changes in plasma YKL-40 in healthy subjects during either hyperglycemic or hyperinsulinemic-euglycemic clamps. CONCLUSIONS—Plasma YKL-40 was identified as an obesity-independent marker of type 2 diabetes related to fasting plasma glucose and plasma IL-6 levels.

Objective: IL-15 decreases lipid deposition in preadipocytes and decreases the mass of white adipose tissue in rats, indicating that IL-15 may take part in regulating this tissue. IL-15 is expressed in human skeletal muscle and skeletal muscle may be a source of plasma IL-15 and in this way regulate adipose tissue mass.Design: The relation between skeletal muscle IL-15 mRNA expression, plasma IL-15, and adipose tissue mass was studied in 199 humans divided into four groups on the basis of obesity and type 2 diabetes. Furthermore, using a DNA electrotransfer model, we assessed the effect of IL-15 overexpression in skeletal muscle of mice.Results: In humans, multiple regression analysis showed a negative association between plasma IL-15 and total fat mass (P < 0.05), trunk fat mass (P < 0.01), and percent fat mass (P < 0.05), independent of type 2 diabetes. Negative associations were also found between muscle IL-15 mRNA and obesity parameters. IL-15 overexpression in skeletal muscle of mice reduced trunk fat mass but not sc fat mass.Conclusions: Our results indicate that IL-15 may be a regulator of trunk fat mass.

Skeletal muscle has been identified as a secretory organ. We hypothesized that IL-6, a cytokine secreted from skeletal muscle during exercise, could induce production of other secreted factors in skeletal muscle. IL-6 was infused for 3 h into healthy young males (n = 7) and muscle biopsies obtained at time points 0, 3 and 6 h in these individuals and in resting controls. Affymetrix microarray analysis of gene expression changes in skeletal muscle biopsies identified a small set of genes changed by IL-6 infusion. RT-PCR validation confirmed that S100A8 and S100A9 mRNA were up-regulated 3-fold in skeletal muscle following IL-6 infusion compared to controls. Furthermore, S100A8 and S100A9 mRNA levels were up-regulated 5-fold in human skeletal muscle following cycle ergometer exercise for 3 h at approximately 60% of in young healthy males (n = 8). S100A8 and S100A9 form calprotectin, which is known as an acute phase reactant. Plasma calprotectin increased 5-fold following acute cycle ergometer exercise in humans, but not following IL-6 infusion. To identify the source of calprotectin, healthy males (n = 7) performed two-legged dynamic knee extensor exercise for 3 h with a work load of approximately 50% of peak power output and arterial-femoral venous differences were obtained. Arterial plasma concentrations for calprotectin increased 2-fold compared to rest and there was a net release of calprotectin from the working muscle. In conclusion, IL-6 infusion and muscle contractions induce expression of S100A8 and S100A9 in skeletal muscle. However, IL-6 alone is not a sufficient stimulus to facilitate release of calprotectin from skeletal muscle.

IL-6 is a key modulator of immune function and suggested to be involved in skeletal muscle wasting as seen in sepsis.Our objective was to determine the role of IL-6 in human in vivo systemic and skeletal muscle amino acid metabolism and protein turnover.There were 12 healthy men infused for 3 h with saline (saline, n = 6) or recombinant human IL (rhIL)-6 (n = 6). Systemic and muscle protein turnover was determined with a combination of tracer dilution methodology, primed constant infusion of L-[ring-(2)H(5)]phenylalanine, and femoral arterial-venous blood differences and m. vastus lateralis biopsies after 2-h basal, 3-h infusion, and 3 h after infusion.The IL-6 concentration after 30-min infusion was approximately 4 (saline) and 140 pg/ml (rhIL-6). Three-hour rhIL-6 infusion caused an approximate 50% decrease in muscle protein turnover, albeit synthesis was more suppressed than breakdown, causing a small increase in net muscle protein breakdown. Furthermore, rhIL-6 decreased arterial amino acid concentration with 20-40%, despite the increase net release from muscle.We demonstrated that IL-6 profoundly alters amino acid turnover. A substantial decrease in plasma amino acids was observed with a concomitant 50% decrease in muscle protein turnover, however, modest increase in net muscle degradation. We hypothesize that the profound reduction in muscle protein turnover and modest increase in net degradation are primarily caused by the reduced plasma amino acid availability and not directly mediated by IL-6.

Low-grade systemic inflammation is a feature of most lifestyle-related chronic diseases. Enhanced TNF-alpha concentrations have been implicated in the development of hyperlipidemia.We hypothesized that an acute elevation of TNF-alpha in plasma would cause an increase in lipolysis, increasing circulatory free fatty acid (FFA) levels.Using a randomized controlled, crossover design, healthy young male individuals (n = 10) received recombinant human (rh) TNF-alpha (700 ng/m(-2).h(-1)) for 4 h, and energy metabolism was evaluated using a combination of tracer dilution methodology and arterial-venous differences over the leg.Plasma TNF-alpha levels increased from 0.7 +/- 0.04 to 16.7 +/- 1.8 pg/ml, and plasma IL-6 increased from 1.0 +/- 0.2 to 9.2 +/- 1.0 pg/ml (P0.05) after 4-h rhTNF-alpha infusion. Here, we demonstrate that 4-h rhTNF-alpha infusion increases whole body lipolysis by 40% (P0.05) with a concomitant increase in FFA clearance, with no changes in skeletal muscle FFA uptake, release, or oxidation. Of note, systemic glucose turnover and lactate and catecholamine levels were unaffected by rhTNF-alpha infusion.This study demonstrates that a relatively low dose of rhTNF-alpha induces systemic lipolysis and that the skeletal muscle fat metabolism is unaffected.

During the past 20 yr, it has been well documented that exercise has a profound effect on the immune system. With the discovery that exercise provokes an increase in a number of cytokines, a possible link between skeletal muscle contractile activity and immune changes was established. For most of the last century, researchers sought a link between muscle contraction and humoral changes in the form of an “exercise factor,” which could mediate some of the exercise-induced metabolic changes in other organs such as the liver and the adipose tissue. We suggest that cytokines and other peptides that are produced, expressed, and released by muscle fibers and exert either paracrine or endocrine effects should be classified as “myokines.” Since the discovery of interleukin (IL)-6 release from contracting skeletal muscle, evidence has accumulated that supports an effect of IL-6 on metabolism. We suggested that muscle-derived IL-6 fulfils the criteria of an exercise factor and that such classes of cytokines should be named “myokines.” Interestingly, recent research demonstrates that skeletal muscles can produce and express cytokines belonging to distinctly different families. Thus skeletal muscle has the capacity to express several myokines. To date the list includes IL-6, IL-8, and IL-15, and contractile activity plays a role in regulating the expression of these cytokines in skeletal muscle. The present review focuses on muscle-derived cytokines, their regulation by exercise, and their possible roles in metabolism and skeletal muscle function and it discusses which cytokines should be classified as true myokines.

To discuss recent findings with regard to the regulation of muscle-derived interleukin-6 as well as the possible physiological and metabolic roles of interleukin-6 in response to exercise.Contraction-induced transcription and release of interleukin-6 is primarily regulated by an altered intramuscular milieu in response to exercise. Accordingly, changes in calcium homeostasis, impaired glucose availability and increased formation of reactive oxygen species are all associated with exercise and capable of activating transcription factors known to regulate interleukin-6 synthesis. Acute interleukin-6 administration to humans increases lipolysis, fat oxidation and insulin-mediated glucose disposal. Adenosine monophosphate-activated protein kinase activation by interleukin-6 appears to play an important role in modulating some of these metabolic effects. Interleukin-6 facilitates an antiinflammatory milieu and may exert some of its biological effects via inhibition of the proinflammatory cytokine tumor necrosis factor-alpha.The discovery of contracting muscle as a cytokine-producing organ opens a new paradigm: skeletal muscle is an endocrine organ that in response to contractions produces and releases 'myokines', which subsequently can modulate the metabolic and immunological response to exercise in several tissues. In our view, interleukin-6 may be one of several myokines.

It is not clear how contracting skeletal muscles mediate the numerous and diverse metabolic and physiological effects that are beneficial for health. Researchers have searched for a muscle-contraction-induced factor - an 'exercise factor' - that mediates some of the exercise effects in other tissues such as the liver and adipose tissue. In our search for such a factor, we encountered the cytokine interleukin (IL)-6, which is produced by contracting muscles and released into the blood. We propose that muscle-derived IL-6 meets the criteria of an exercise factor and that such classes of cytokine should be named 'myokines'. The discovery of contracting muscle as a cytokine-producing organ creates a new paradigm: skeletal muscle as an endocrine organ. By contracting, it stimulates the production and release of myokines that can influence metabolism in tissue and organs. Newly identified myokines and their receptors could serve as targets in the treatment of metabolic disorders and other diseases.

Decreased levels of brain-derived neurotrophic factor (BDNF) have been implicated in the pathogenesis of Alzheimer’s disease and depression. These disorders are associated with type 2 diabetes, and animal models suggest that BDNF plays a role in insulin resistance. We therefore explored whether BDNF plays a role in human glucose metabolism. We included (Study 1) 233 humans divided into four groups depending on presence or absence of type 2 diabetes and presence or absence of obesity; and (Study 2) seven healthy volunteers who underwent both a hyperglycaemic and a hyperinsulinaemic–euglycaemic clamp. Plasma levels of BDNF in Study 1 were decreased in humans with type 2 diabetes independently of obesity. Plasma BDNF was inversely associated with fasting plasma glucose, but not with insulin. No association was found between the BDNF G196A (Val66Met) polymorphism and diabetes or obesity. In Study 2 an output of BDNF from the human brain was detected at basal conditions. This output was inhibited when blood glucose levels were elevated. In contrast, when plasma insulin was increased while maintaining normal blood glucose, the cerebral output of BDNF was not inhibited, indicating that high levels of glucose, but not insulin, inhibit the output of BDNF from the human brain. Low levels of BDNF accompany impaired glucose metabolism. Decreased BDNF may be a pathogenetic factor involved not only in dementia and depression, but also in type 2 diabetes, potentially explaining the clustering of these conditions in epidemiological studies.

The present study examined the role of the cytokine IL-6 in the regulation of fatty acid metabolism during exercise in humans. Six well-trained males completed three trials of 120 min of cycle ergometry at 70% peak O2 consumption (V̇o2 peak; MOD) and 40% V̇o2 peak with (LOW + IL-6) and without (LOW) infusion of recombinant human (rh)IL-6. The dose of rhIL-6 during LOW + IL-6 elicited IL-6 concentration similar to those during MOD but without altering the circulating hormonal milieu seen in MOD. Palmitate rate of appearance (Ra), rate of disappearance (Rd), and oxidation were measured by means of a constant infusion of [U-13C]palmitate (0.015 μmol·kg−1·min−1, prime NaHCO3, 1 μmol/kg). Palmitate Ra, Rd, and oxidation were not affected by rhIL-6 infusion, remaining similar to LOW at all times. Palmitate Ra and oxidation were significantly greater in the MOD trial ( P < 0.05) compared with the LOW + IL-6 and LOW trials. Our data show that a low dose of rhIL-6, administered during low-intensity exercise without altering the hormonal milieu, does not alter fatty acid metabolism. These data suggest that the increase in fatty acid utilization seen during exercise at moderate compared with low intensity is not mediated via alterations in plasma IL-6.

The mechanisms that mediate the tightly controlled production and clearance of glucose during muscular work are unclear, and it has been suggested that an unidentified “work factor” exists that influences the contraction-induced increase in endogenous glucose production (EGP). The cytokine interleukin (IL)-6 is released from skeletal muscle during contraction. Here we show that IL-6 contributes to the contraction-induced increase in EGP. Six men performed 2 h of bicycle exercise on three separate occasions, at a relatively high intensity (HI) or at a low intensity with (LO + IL-6) or without (LO) an infusion of recombinant human IL-6 that matched the circulating concentration of IL-6 seen in HI exercise. The stable isotope 6,6 2H2 glucose was infused to calculate EGP (rate of glucose appearance [Ra]), whole-body glucose disposal (rate of glucose disappearance [Rd]), and metabolic clearance rate (MCR) of glucose. Glucose Ra, Rd, and MCR were higher (P < 0.05) at HI than at LO. Throughout exercise at LO + IL-6, glucose Ra and Rd were higher (P < 0.05) than LO, even though the exercise intensity was identical. In addition, MCR was higher (P < 0.05) at LO + IL-6 than at LO at 90 min. Insulin, glucagon, epinephrine, norepinephrine, cortisol, and growth hormone were identical when comparing LO + IL-6 with LO. These data suggest that IL-6 influences glucose homeostasis during exercise. Our results provide potential new insights into factors that mediate glucose production and disposal and implicates IL-6 in the so-called “work factor.”

Contracting human skeletal muscle is a major contributor to the exercise-induced increase of plasma interleukin-6 (IL-6). Although antioxidants have been shown to attenuate the exercise-induced increase of plasma IL-6, it is unknown whether antioxidants inhibit transcription, translation or translocation of IL-6 within contracting human skeletal muscle. Using a single-blind placebo-controlled design with randomization, young healthy men received an oral supplementation with either a combination of ascorbic acid (500 mg day(-1)) and RRR-alpha-tocopherol (400 i.u. day(-1)) (Treatment, n= 7), or placebo (Control, n= 7). After 28 days of supplementation, the subjects performed 3 h of dynamic two-legged knee-extensor exercise at 50% of their individual maximal power output. Muscle biopsies from vastus lateralis were obtained at rest (0 h), immediately post exercise (3 h) and after 3 h of recovery (6 h). Leg blood flow was measured using Doppler ultrasonography. Plasma IL-6 concentration was measured in blood sampled from the femoral artery and vein. The net release of IL-6 was calculated using Fick's principle. Plasma vitamin C and E concentrations were elevated in Treatment compared to Control. Plasma 8-iso-prostaglandin F(2alpha), a marker of lipid peroxidation, increased in response to exercise in Control, but not in Treatment. In both Control and Treatment, skeletal muscle IL-6 mRNA and protein levels increased between 0 and 3 h. In contrast, the net release of IL-6 from the leg, which increased during exercise with a peak at 3.5 h in Control, was completely blunted during exercise in Treatment. The arterial plasma IL-6 concentration from 3 to 4 h, when the arterial IL-6 levels peaked in both groups, was approximately 50% lower in the Treatment group compared to Control (Treatment versus Control: 7.9 pg ml(-1), 95% confidence interval (CI) 6.0-10.7 pg ml(-1), versus 19.7 pg ml(-1), CI 13.8-29.4 pg ml(-1), at 3.5 h, P < 0.05 between groups). Moreover, plasma interleukin-1 receptor antagonist (IL-1ra), C-reactive protein and cortisol levels all increased after the exercise in Control, but not in Treatment. In conclusion, our results show that supplementation with vitamins C and E attenuated the systemic IL-6 response to exercise primarily via inhibition of the IL-6 protein release from the contracting skeletal muscle per se.

Interleukin-6 (IL-6) is a cytokine with immuno-regulatory functions. However, contracting skeletal muscle expresses and subsequently releases IL-6 in high amounts, and recent evidence in IL-6 deficient mice suggests a role of IL-6 in metabolism. Since IL-6 mRNA levels also increase in abdominal adipose tissue in response to exercise, we wanted to examine the possible existence of a positive feedback mechanism between muscle and adipose tissue. We obtained biopsies from human skeletal muscle and abdominal subcutaneous adipose tissue in relation to either 3 h of bicycle exercise or recombinant human IL-6 infusion (rhIL-6) or saline infusion. In muscle, IL-6 mRNA increased (p

The purpose of the present study was to test the hypothesis that a transient increase in plasma IL-6 induces an anti-inflammatory environment in humans. Therefore, young healthy volunteers received a low dose of recombinant human (rh)IL-6 or saline for 3 h. Plasma IL-6 levels during rhIL-6 infusion were approximately 140 pg/ml, corresponding to the levels obtained during strenuous exercise. The infusion of rhIL-6 did not induce enhanced levels of the proinflammatory cytokine TNF-alpha but enhanced the plasma levels of the two anti-inflammatory cytokines IL-1 receptor agonist (IL-1ra) and IL-10 compared with saline infusion. In addition, C-reactive protein increased 3 h post-rhIL-6 infusion and was further elevated 16 h later compared with saline infusion. rhIL-6 induced increased levels of plasma cortisol and, consequently, an increase in circulating neutrophils and a decrease in the lymphocyte number without effects on plasma epinephrine, body temperature, mean arterial pressure, or heart rate. In conclusion, this study demonstrates that physiological concentrations of IL-6 induce an anti-inflammatory rather than an inflammatory response in humans and that IL-6, independently of TNF-alpha, enhances the levels not only of IL-1ra but also of IL-10. Furthermore, IL-6 induces an increase in cortisol and, consequently, in neutrocytosis and late lymphopenia to the same magnitude and with the same kinetics as during exercise, suggesting that muscle-derived IL-6 has a central role in exercise-induced leukocyte trafficking.

The cytokine interleukin (IL)-6 has recently been linked with type 2 diabetes mellitus and has been suggested to affect glucose metabolism. To determine whether acute IL-6 administration affects whole-body glucose kinetics or muscle glucose uptake, 18 healthy young men were assigned to one of three groups receiving a high dose of recombinant human IL-6 (HiIL-6; n = 6), a low dose of IL-6 (LoIL-6; n = 6) or saline (Con; n = 6) infused into one femoral artery for 3 h. The stable isotope [6,6-2H2] glucose was infused into a forearm vein throughout the 3 h infusion period and for a further 3 h after the cessation of infusion (recovery) to determine endogenous glucose production and whole-body glucose disposal. Infusion with HiIL-6 and LoIL-6 resulted in a marked (P < 0.05) increase in systemic IL-6 concentration throughout the 3 h of infusion (mean arterial plasma [IL-6]s of 319 and 143 pg ml−1 for HiIL-6 and LoIL-6, respectively), followed by a rapid decline (P < 0.05) during the recovery period. Subjects experienced clinical symptoms such as shivering and discomfort during HiIL-6 administration, but were asymptomatic during LoIL-6 administration. In addition, only HiIL-6 elevated (P < 0.05) plasma adrenaline (epinephrine). IL-6 infusion, irrespective of dose, did not result in any changes to endogenous glucose production, whole-body glucose disposal or leg- glucose uptake. These data demonstrate that acute IL-6 administration does not impair whole-body glucose disposal, net leg-glucose uptake, or increase endogenous glucose production at rest in healthy young humans.

Type 2 diabetes is characterized by increased insulin resistance and impaired insulin secretion. Type 2 diabetes is also associated with low-grade inflammation and increased levels of proinflammatory cytokines such as TNF-α. TNF-αhas been shown to impair peripheral insulin signalingin vitroandin vivo. However, it is unclear whether TNF-αmay also affect endogenous glucose production (EGP) during fasting and glucose-stimulated insulin secretion (GSIS)in vivo. We hypothesized that low-dose TNF-αwould increase EGP and attenuate GSIS. Recombinant human TNF-αor placebo was infused in healthy, nondiabetic young men (n=10) during a 4-hour basal period followed by an intravenous glucose tolerance test (IVGTT). TNF-αlowered insulin levels by 12% during the basal period (P<0.05). In response to the IVGTT, insulin levels increased markedly in both trials, but there was no difference between trials. Compared to placebo, TNF-αdid not affect EGP during the basal period. Our results indicate that TNF-αacutely lowers basal plasma insulin levels but does not impair GSIS. The mechanisms behind this are unknown but we suggest that it may be due to TNF-αincreasing clearance of insulin from plasma without impairing beta-cell function or hepatic insulin sensitivity.

Obesity and type 2 diabetes are associated with chronically elevated systemic levels of IL-6, a pro-inflammatory cytokine with a role in skeletal muscle metabolism that signals through the IL-6 receptor (IL-6Rα). We hypothesized that skeletal muscle in obesity-associated type 2 diabetes develops a resistance to IL-6. By utilizing western blot analysis, we demonstrate that IL-6Rα protein was down regulated in skeletal muscle biopsies from obese persons with and without type 2 diabetes. To further investigate the status of IL-6 signaling in skeletal muscle in obesity-associated type 2 diabetes, we isolated satellite cells from skeletal muscle of people that were healthy (He), obese (Ob) or were obese and had type 2 diabetes (DM), and differentiated them in vitro into myocytes. Down-regulation of IL-6Rα was conserved in Ob myocytes. In addition, acute IL-6 administration for 30, 60 and 120 minutes, resulted in a down-regulation of IL-6Rα protein in Ob myocytes compared to both He myocytes (P

ObjectiveMyostatin is a secreted growth factor expressed in skeletal muscle tissue, which negatively regulates skeletal muscle mass. Recent animal studies suggest a role for myostatin in insulin resistance. We evaluated the possible metabolic role of myostatin in patients with type 2 diabetes and healthy controls.Design76 patients with type 2 diabetes and 92 control subjects were included in the study. They were matched for age, gender and BMI. Plasma samples and biopsies from the vastus lateralis muscle were obtained to assess plasma myostatin and expression of myostatin in skeletal muscle.ResultsPatients with type 2 diabetes had higher fasting glucose (8.9 versus 5.1 mmol/L, PConclusionsThis study supports the idea that myostatin may have a negative effect on metabolism. However, the metabolic effect of myostatin appears to be overruled by other factors in patients with type 2 diabetes.

To determine whether the cytokine interleukin (IL)-6 induces heat shock protein (HSP) 72 gene expression in skeletal muscle, 18 healthy, young men had either a high dose of IL-6 (HiIL-6; n=6), low dose IL-6 (LoIL-6; n=6), or saline (CON; n=6) infused into one femoral artery for 3h. Muscle biopsies were obtained from the vastus lateralis of the infusion limb and samples were analyzed for HSP72 mRNA. In addition, blood samples were collected from the femoral vein of the infusion limb and analyzed for plasma IL-6. In CON, femoral vein IL-6 concentration remained at basal levels throughout the experiment but in both HiIL-6 and LoIL-6, femoral vein IL-6 concentrations were markedly elevated (P

Background: There is a considerable commercial market, especially within the sports community, claiming the need for antioxidant supplementation. One argument for antioxidant supplementation in sports is that physical exercise is associated with increased reactive oxygen and nitrogen species (RONS) production, which may cause cell damage. However, RONS production may also activate redox-sensitive signaling pathways and transcription factors, which subsequently, may promote training adaptation. Purpose: Our aim was to investigate the effects of combined vitamin C and E supplementation to healthy individuals on different measures of exercise performance after endurance training. Methods: Using a double-blinded placebo-controlled design, moderately trained young men received either oral supplementation with vitamins C and E (n = 11) or placebo (n = 10) before and during 12 wk of supervised, strenuous bicycle exercise training of a frequency of 5 d[middle dot]wk-1. Muscle biopsies were obtained before and after training. Results: After the training period, maximal oxygen consumption, maximal power output, and workload at lactate threshold increased markedly (P < 0.01) in both groups. Also, glycogen concentration, citrate synthase, and [beta]-hydroxyacyl-CoA dehydrogenase activity in the muscle were significantly higher in response to training (P < 0.01) in both groups. However, there were no differences between the two groups concerning any of the physiological and metabolic variables measured. Conclusions: Our results suggest that administration of vitamins C and E to individuals with no previous vitamin deficiencies has no effect on physical adaptations to strenuous endurance training.

The heat shock proteins (HSP) are a family of highly conserved proteins with critical roles in maintaining cellular homeostasis and in protecting the cell from chronically and acutely stressful conditions. An increased expression of Hsp72 in skeletal muscle appears to be a part of the normal exercise response as well as training adaptation. Regular exercise offers protection against a number of chronic diseases, including type 2 diabetes and the basal expression of Hsp72 mRNA is suppressed in skeletal muscle of patients with type 2 diabetes. Moreover, mechanistic studies show that muscular Hsp72 protects against obesity-induced peripheral insulin resistance. Physical activity provokes an increased production of reactive oxygen species (ROS) and ROS is an inducer of Hsp72. The mechanisms whereby exercise and ROS regulate muscular Hsp72 expression are discussed. Anti-oxidant treatment with the vitamin E isoform γ-tochoferol is a potent inhibitor of exercise-induced expression of muscular Hsp72. This fact may contribute to explain the findings from large clinical studies that antioxidant supplementation may have detrimental effects on morbidity and mortality

BackgroundThe two inflammatory molecules, S100A8 and S100A9, form a heterodimer, calprotectin. Plasma calprotectin levels are elevated in various inflammatory disorders. We hypothesized that plasma calprotectin levels would be increased in subjects with low-grade systemic inflammation i.e. either obese subjects or subjects with type 2 diabetes.Methodology/principal findingsPlasma calprotectin and skeletal muscle S100A8 mRNA levels were measured in a cohort consisting of 199 subjects divided into four groups depending on presence or absence of type 2 diabetes (T2D), and presence or absence of obesity. There was a significant interaction between obesity and T2D (p = 0.012). Plasma calprotectin was increased in obese relative to non-obese controls (pConclusions/significancePlasma calprotectin is a marker of obesity in individuals without type 2 diabetes.

Glucose ingestion during exercise attenuates activation of metabolic enzymes and expression of important transport proteins. In light of this, we hypothesized that glucose ingestion during training would result in 1) an attenuation of the increase in fatty acid uptake and oxidation during exercise, 2) lower citrate synthase (CS) and β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity and glycogen content in skeletal muscle, and 3) attenuated endurance performance enhancement in the trained state. To investigate this we studied nine male subjects who performed 10 wk of one-legged knee extensor training. They trained one leg while ingesting a 6% glucose solution (Glc) and ingested a sweetened placebo while training the other leg (Plc). The subjects trained their respective legs 2 h at a time on alternate days 5 days a week. Endurance training increased peak power (Pmax) and time to fatigue at 70% of Pmax ∼14% and ∼30%, respectively. CS and β-HAD activity increased and glycogen content was greater after training, but there were no differences between Glc and Plc. After training the rate of oxidation of palmitate (Rox) and the % of rate of disappearance that was oxidized (%Rdox) changed. %Rdox was on average 16.4% greater during exercise after training whereas, after exercise %Rdox was 30.4% lower. Rox followed the same pattern. However, none of these parameters were different between Glc and Plc. We conclude that glucose ingestion during training does not alter training adaptation related to substrate metabolism, mitochondrial enzyme activity, glycogen content, or performance.

Aim: It was recently reported that serum retinol-binding protein (RBP), also known as retinol-binding protein 4 (RBP4), was positively associated with systemic insulin resistance. We hypothesized that an imbalance between RBP and retinol might be the underlying cause for this association. Methods: We studied the ratio between RBP and retinol in 233 humans divided into groups depending on normal glucose tolerance (NGT), impaired glucose tolerance (IGT), type 2 diabetes (T2DM) and presence or absence of obesity. Results: Plasma RBP and retinol levels were lower in patients with T2DM than in individuals with NGT (p

Skeletal muscle wasting has been associated with elevations in circulating inflammatory cytokines, in particular TNF-alpha.In this study, we investigated whether TNF-alpha affects human systemic and skeletal muscle protein turnover via a 4-h recombinant human (rh) TNF-alpha infusion. We hypothesize that TNF-alpha increases human muscle protein breakdown and/or inhibits synthesis.Using a randomized, controlled, crossover design, postabsorptive healthy young males (n = 8) were studied 2 h under basal conditions followed by a 4-h infusion of either rhTNF-alpha (700 ng . m(-2) . h(-1)) or 20% human albumin (control), which was the vehicle of rhTNF-alpha. Systemic and skeletal muscle protein turnover was estimated by a combination of tracer dilution methodology (primed continuous infusion of l-[ring-(2)H(5)]phenylalanine and l-[(15)N-leucine], with prime of l-[ring-(2)H(4)]tyrosine) and femoral arterial-venous differences over the leg and muscle biopsies.Plasma TNF-alpha concentration rapidly increased from basal levels of approximately 0.7 to 17 pg . ml(-1) with rhTNF-alpha infusion. Whole body protein synthesis, breakdown, and net degradation were similar after the basal and infusion period of the control and rhTNF-alpha trials. Skeletal muscle, musculus vastus lateralis, protein fractional synthetic rate was not different over 4 h of control or rhTNF-alpha (rate of incorporation of (15)N-leucine). Muscle protein turnover determined with the phenylalanine three-compartment model showed similar muscle synthesis, breakdown, and net muscle degradation after 2-h basal and after 4-h control or rhTNF-alpha infusion.This study is the first to show in humans that TNF-alpha does not affect systemic and skeletal muscle protein turnover, when acutely elevated for 4 h to moderate levels not causing adverse effects.

OBJECTIVE—YKL-40 is produced by macrophages, and plasma YKL-40 is elevated in patients with diseases characterized by inflammation. In the present study, YKL-40 was examined in relation to obesity, inflammation, and type 2 diabetes. RESEARCH DESIGN AND METHODS—Plasma YKL-40 and adipose tissue YKL-40 mRNA levels were investigated in 199 subjects who were divided into four groups depending on the presence or absence of type 2 diabetes and obesity. In addition, plasma YKL-40 was examined in healthy subjects during a hyperglycemic clamp, in which the plasma glucose level was kept at 15 mmol/l for 3 h, and during a hyperinsulinemic-euglycemic clamp. RESULTS—Patients with type 2 diabetes had higher plasma YKL-40 (76.7 vs. 45.1 ng/ml, P = 0.0001) but not higher expression in adipose tissue YKL-40 mRNA (1.20 vs. 0.98, P = 0.2) compared with subjects with a normal glucose tolerance. Within the groups with normal glucose tolerance and type 2 diabetes, obesity subgroups showed no difference with respect to either plasma YKL-40 or adipose tissue YKL-40 mRNA levels. Multivariate regression analysis showed that plasma YKL-40 was associated with fasting plasma glucose (β = 0.5, P = 0.0014) and plasma interleukin (IL)-6 (β = 0.2, P = 0.0303). Plasma YKL-40 was not related to parameters of obesity. There were no changes in plasma YKL-40 in healthy subjects during either hyperglycemic or hyperinsulinemic-euglycemic clamps. CONCLUSIONS—Plasma YKL-40 was identified as an obesity-independent marker of type 2 diabetes related to fasting plasma glucose and plasma IL-6 levels.

FSP27 (fat-specific protein 27) is a member of the cell death-inducing DNA fragmentation factor-alpha-like effector (CIDE) family. Although Cidea and Cideb were initially characterized as activators of apoptosis, recent studies have demonstrated important metabolic roles for these proteins. In this study, we investigated the function of another member of this family, FSP27 (Cidec), in apoptosis and adipocyte metabolism. Although overexpression of FSP27 is sufficient to increase apoptosis of 293T and 3T3-L1 cells, more physiological levels of expression stimulate spontaneous lipid accumulation in several cell types without induction of adipocyte genes. Increased triacylglycerol is likely due to decreased beta-oxidation of nonesterified fatty acids. Altered flux of fatty acids into triacylglycerol may be a direct effect of FSP27 function, which is localized to lipid droplets in 293T cells and 3T3-L1 adipocytes. Stable knockdown of FSP27 during adipogenesis of 3T3-L1 cells substantially decreases lipid droplet size, increases mitochondrial and lipid droplet number, and modestly increases glucose uptake and lipolysis. Expression of FSP27 in subcutaneous adipose tissue of a human diabetes cohort decreases with total fat mass but is not associated with measures of insulin resistance (e.g. homeostasis model assessment). Together, these data indicate that FSP27 binds to lipid droplets and regulates their enlargement.

We hypothesized that the peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1) family of transcriptional coactivators (PGC-1alpha, PGC-1beta, and PRC) is differentially regulated by training once daily vs. training twice daily every second day and that this difference might be observed in the acute response to endurance exercise. Furthermore, we hypothesized that expression levels of the PGC-1 family differ with muscular fiber-type composition. Thus, before and after 10 wk of knee extensor endurance training, training one leg once daily and the other leg twice daily every second day, keeping the total amount of training for the legs equal, skeletal muscle mRNA expression levels of PGC-1alpha, PGC-1beta, and PRC were determined in young healthy men (n = 7) in response to 3 h of acute exercise. No significant difference was found between the two legs, suggesting that regulation of the PGC-1 family is independent of training protocol. Training decreased PGC-1beta in both legs, whereas PGC-1alpha was increased, but not significantly, in the leg training once daily. PRC did not change with training. Both PGC-1alpha and PRC were increased by acute exercise both before and after endurance training, whereas PGC-1beta did not change. The mRNA levels of the PGC-1 family were examined in different types of human skeletal muscle (triceps, soleus, and vastus lateralis; n = 7). Only the expression level of PGC-1beta differed and correlated inversely with percentage of type I fibers. In conclusion, there was no difference between training protocols on the acute exercise and training response of the PGC-1 family. However, training caused a decrease in PGC-1beta mRNA levels.