Source and kinetics of interleukin-6 in humans during exercise demonstrated by a minimally invasive model.

The objective of this study was to use a novel and non-invasive model to explore whether: (1) exercise-induced increases in systemic levels of interleukin-6 (IL-6) and other cytokines can be ascribed to local production in working muscle; and (2) how acute release of retained blood from an exercised limb impacts on metabolites in the systemic circulation. On two experimental days, at least 3 weeks apart, six healthy moderately trained male subjects performed one-legged knee-extensor exercise for 2 h at 60% of their maximal workload. On one occasion venous outflow from the exercised leg was inhibited for 18 min by inflating a cuff around the thigh as proximally as possible immediately following exercise. On the control occasion venous outflow was not inhibited. Venous blood samples were collected from an arm vein at 2-min intervals after exercise. During inhibition of venous outflow from the exercised leg systemic plasma levels of IL-6 decreased within minutes to near pre-exercise levels, whereas plasma glucose levels increased to higher levels than without the cuff. After release of the cuff, systemic levels of IL-6 increased rapidly to match levels on the control occasion. On release of the cuff, plasma levels of free fatty acids (FFAs) declined more than without the cuff. In conclusion, the observed increase in systemic IL-6 plasma concentrations during exercise can be attributed to release from the working limb. Other potential sources of IL-6 outside the working limb do not contribute significantly to the increase in plasma IL-6 levels during exercise.

European multicentre study in children born small for gestational age with persistent short stature: comparison of continuous and discontinuous growth hormone treatment regimens.

BACKGROUND: The most effective growth hormone (GH) treatment regimen for increasing height in short children born small for gestational age (SGA) has not been well defined. METHODS: Short SGA children (n = 151, age 3-8 years, height less than -2.5 standard deviation scores) were randomised to receive low-dose GH for 2 years (0.033/0.033 mg/kg/day, n = 51), high-dose GH for 1 year and then no treatment for 1 year (0.100/0 mg/kg/day, n = 51) or were untreated for 1 year then received mid-dose GH for 1 year (0/0.067 mg/kg/day, n = 47). Height, bone age and adverse events were determined at check-ups every 3 months. RESULTS: The mean +/- SD additional height gain with GH after 1 year, relative to untreated controls, was higher with discontinuous high-dose than with continuous low-dose GH (6.5 +/- 0.2 vs. 3.3 +/- 0.2 cm). After 2 years, the additional height gain was similar between high- and low-dose GH groups (between-group treatment difference = 0.2, 95% CI = -0.8 to 1.2 cm, p = 0.702). Patients treated exclusively in the last year had a similar height gain to those in the other treatment groups (p = 0.604). CONCLUSIONS: In short SGA children, continuous low-dose and discontinuous high-dose GH regimens were associated with similar height gain. Treatment with mid-dose GH for 1 year also led to a similar improvement in growth.

Effects of glepaglutide, a novel long-acting glucagon-like peptide-2 analogue, on markers of liver status in patients with short bowel syndrome: findings from a randomised phase 2 trial.

BACKGROUND: With the introduction of glucagon-like peptide-2 (GLP-2) in the treatment of short bowel syndrome (SBS), there is emerging evidence that GLP-2 may play a role in the restoration of the disturbed homeostatic feedback in the gut-liver axis and may ameliorate SBS-associated liver damage. We have previously presented that daily subcutaneous injections with 1 and 10 mg of glepaglutide improved intestinal function in patients with SBS. As exploratory endpoints, we here assessed the effect of glepaglutide on liver function. METHODS: Liver tests, transient elastography (TE) with controlled attenuation parameter (CAP), indocyanine green (ICG) kinetics, soluble CD163 (sCD163), soluble mannose receptor (sMR), and lipopolysaccharide binding protein (LBP) were assessed in 18 patients with SBS in a randomised, cross-over, dose-finding phase 2 trial before and after three weeks of treatment with glepaglutide. This trial is completed and registered at ClinicalTrials.gov: NCT02690025. FINDINGS: Between Feb 2016 and Jan 2017, 22 patients with SBS were screened. Of these, 18 patients were randomised and treated with glepaglutide; 16 patients completed the trial. Treatment with glepaglutide was associated with increase in TE and ICG-elimination. In the 10 mg dose group, glepaglutide increased sCD163 by 0·44 mg/mL (P = 0·0498), and alkaline phosphatase (ALP) decreased in the 1 mg dose group by 33 U/L (P = 0·032). CAP, sMR, LBP, liver transaminases, and INR were not affected. INTERPRETATION: Glepaglutide may improve hepatic excretory function, but at the same time activate resident liver macrophages and increase liver stiffness. The excretory and the stiffness findings may to some extent relate to increased splanchnic blood flow which would not influence the marker of macrophage activation. Thus, glepaglutide exerted diverse effects on liver status that call for attention in future studies. FUNDING: Zealand Pharma.

Glepaglutide, a novel long-acting glucagon-like peptide-2 analogue, for patients with short bowel syndrome: a randomised phase 2 trial.

BACKGROUND: Patients with short bowel syndrome might have impaired postprandial endogenous glucagon-like peptide-2 (GLP-2) secretion, which is required for optimal intestinal adaptation. We aimed to assess the therapeutic potential of glepaglutide, a novel long-acting GLP-2 analogue, for reducing faecal output and increasing intestinal absorption in patients with short bowel syndrome. METHODS: In this single-centre, double-blind, crossover, randomised phase 2 trial, adults (aged ≥18 to ≤90 years) with short bowel syndrome and with a faecal wet weight output of 1500 g/day or more were randomly assigned to receive one of six dose sequences of glepaglutide (10 mg, 1 mg; 10 mg, 0·1 mg; 1 mg, 10 mg; 1 mg, 0·1 mg; 0·1 mg, 10 mg; or 0·1 mg, 1 mg). Patients received daily subcutaneous injections of the first assigned dose of glepaglutide for 3 weeks, followed by a washout period of 4-8 weeks, and then the second dose of glepaglutide for 3 weeks. An unmasked statistician generated the randomisation list, and the trial investigator enrolled patients and assigned them their patient numbers. Trial investigators, patients, and other care providers were masked throughout the trial. The primary endpoint was the absolute change from baseline in faecal wet weight output, measured separately over the two treatment periods. Metabolic balance studies were done before and after each treatment period to assess the primary endpoint. Per-protocol analysis was used to assess the efficacy. Safety analysis was by intention to treat. This trial is registered at ClinicalTrials.gov, number NCT02690025, and has completed. FINDINGS: Of the 22 patients screened between Feb 5, 2016, and Jan 25, 2017, 18 patients were randomly assigned and treated with glepaglutide; 16 patients completed the trial. Treatment with 1 mg and 10 mg glepaglutide changed the adjusted mean faecal output by -592 g/day (95% CI -913 to -272; p=0·002) and -833 g/day (-1152 to -515; p=0·0002) from baseline, respectively. No changes were observed with 0·1 mg glepaglutide. Of the 18 patients who were randomly assigned to treatment, common treatment-related adverse events were stoma complications (13 [72%] patients), injection site reactions (11 [61%]), peripheral oedema (ten [56%]), nausea and abdominal pain (eight [44%] each), polyuria and fatigue (six [33%] each), abdominal distention, vomiting, and dizziness (five [28%] each); and cough and decreased appetite (four [22%] each). Related or possibly related serious adverse events were reported in two patients in the 0·1 mg dose group and two patients in the 10 mg dose group. These events included abdominal pain, stoma obstruction, catheter-related sepsis, and infection of unknown origin. No patients died during the trial. INTERPRETATION: Glepaglutide was well tolerated, and was associated with improved intestinal absorption in patients with short bowel syndrome with 1 mg and 10 mg glepaglutide, but not with 0·1 mg glepaglutide. Larger phase 3 clinical trials of longer durations have been initiated to fully assess the safety and efficacy of glepaglutide. FUNDING: Zealand Pharma.

Interleukin-6 markedly decreases skeletal muscle protein turnover and increases nonmuscle amino acid utilization in healthy individuals.

CONTEXT: IL-6 is a key modulator of immune function and suggested to be involved in skeletal muscle wasting as seen in sepsis. OBJECTIVE: Our objective was to determine the role of IL-6 in human in vivo systemic and skeletal muscle amino acid metabolism and protein turnover. SUBJECTS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Nitric oxide production is a proximal signaling event controlling exercise-induced mRNA expression in human skeletal muscle.

Previous studies have described the magnitude and time course by which several genes are regulated within exercising skeletal muscle. These include interleukin-6 (IL-6), interleukin-8 (IL-8), heme oxygenase-1 (HO-1), and heat shock protein-72 (HSP72), which are involved in secondary signaling and preservation of intracellular environment. However, the primary signaling mechanisms coupling contraction to transcription are unknown. We hypothesized that exercise-induced nitric oxide (NO) production is an important signaling event for IL-6, IL-8, HO-1, and HSP72 expression in muscle. Twenty healthy males participated in the study. By real-time PCR, mRNA levels for 11 genes were determined in thigh muscle biopsies obtained 1) before and after 2 h knee extensor exercise without (control) and with concomitant NO synthase inhibition (nitro-L-arginine methyl ester, L-NAME, 5 mg x kg(-1)); or 2) before and after 2 h femoral artery infusion of the NO donor nitroglycerin (NTG, 1.5 microg x kg(-1) x min(-1)). L-NAME caused marked reductions in exercise-induced expression of 4 of 11 mRNAs including IL-6, IL-8, and HO-1. IL-6 protein release from the study leg to the circulation increased in the control but not in the L-NAME trial. NTG infusion significantly augmented expression of the mRNAs attenuated by L-NAME. These findings advance the novel concept that NO production contributes to regulation of gene expression in muscle during exercise. Subsequently, we sought evidence for involvement of AMP-activated kinase or nuclear factor kappa B, but found none.

Danegaptide for primary percutaneous coronary intervention in acute myocardial infarction patients: a phase 2 randomised clinical trial.

OBJECTIVES: Reperfusion immediately after reopening of the infarct-related artery in ST-segment elevation myocardial infarction (STEMI) may cause myocardial damage in addition to the ischaemic insult (reperfusion injury). The gap junction modulating peptide danegaptide has in animal models reduced this injury. We evaluated the effect of danegaptide on myocardial salvage in patients with STEMI. METHODS: In addition to primary percutaneous coronary intervention in STEMI patients with thrombolysis in myocardial infarction flow 0-1, single vessel disease and ischaemia time less than 6 hours, we tested, in a clinical proof-of-concept study, the therapeutic potential of danegaptide at two-dose levels. Primary outcome was myocardial salvage evaluated by cardiac MRI after 3 months. RESULTS: From November 2013 to August 2015, a total of 585 patients were randomly enrolled in the trial. Imaging criteria were fulfilled for 79 (high dose), 80 (low dose) and 84 (placebo) patients eligible for the per-protocol analysis. Danegaptide did not affect the myocardial salvage index (danegaptide high (63.9±14.9), danegaptide low (65.6±15.6) and control (66.7±11.7), P=0.40), final infarct size (danegaptide high (19.6±11.4 g), danegaptide low (18.6±9.6 g) and control (21.4±15.0 g), P=0.88) or left ventricular ejection fraction (danegaptide high (53.9%±9.5%), danegaptide low (52.7%±10.3%) and control (52.1%±10.9%), P=0.64). There was no difference between groups with regard to clinical outcome. CONCLUSIONS: Administration of danegaptide to patients with STEMI did not improve myocardial salvage. TRIAL REGISTRATION NUMBER: NCT01977755; Pre-results.

Interleukin-6 receptor expression in contracting human skeletal muscle: regulating role of IL-6.

Contracting muscle fibers produce and release IL-6, and plasma levels of this cytokine are markedly elevated in response to physical exercise. We recently showed autocrine regulation of IL-6 in human skeletal muscle in vivo and hypothesized that this may involve up-regulation of the IL-6 receptor. Therefore, we investigated IL-6 receptor regulation in response to exercise and IL-6 infusion in humans. Furthermore, using IL-6-deficient mice, we investigated the role of IL-6 in the IL-6 receptor response to exercise. Human skeletal muscle biopsies were obtained in relation to: 3 h of bicycle exercise and rest (n=6+5), or recombinant human IL-6 infusion (rhIL-6) or saline infusion (n=6+6). We further obtained skeletal muscle samples from IL-6 knockout (KO) mice and wild-type C57/BL-6 mice in response to a 1-h bout of exercise. In exercising human skeletal muscle, IL-6 receptor mRNA increased sixfold with a peak at 6 h postexercise. Detection of the IL-6 receptor protein by immunohistochemistry revealed a pronounced staining following exercise that was primarily located at the cell membrane of the muscle fibers, whereas muscle gp130 expression and plasma levels of soluble IL-6 receptor were unaffected. Infusion of rhIL-6 to humans had no effect on the mRNA level of the IL-6 receptor, whereas there was an increase at the protein level. IL-6 receptor mRNA increased similarly in muscle of both IL-6 KO mice and wild-type mice in response to exercise. In conclusion, exercise increases IL-6 receptor production in human skeletal muscle. This effect is most prominent 6 h after the end of the exercise bout, suggesting a postexercise-sensitizing mechanism to IL-6 when plasma IL-6 is concomitantly low. Exercise-induced increases in IL-6 receptor mRNA most likely occurs via an IL-6 independent mechanism as shown in IL-6 KO mice and the human rhIL-6 infusion study, whereas IL-6 receptor protein levels are responsive to elevated plasma IL-6 levels.

Muscle and blood metabolites during a soccer game: implications for sprint performance.

PURPOSE: To examine muscle and blood metabolites during soccer match play and relate it to possible changes in sprint performance. METHODS: Thirty-one Danish fourth division players took part in three friendly games. Blood samples were collected frequently during the game, and muscle biopsies were taken before and after the game as well as immediately after an intense period in each half. The players performed five 30-m sprints interspersed by 25-s recovery periods before the game and immediately after each half (N=11) or after an intense exercise period in each half (N=20). RESULTS: Muscle lactate was 15.9+/-1.9 and 16.9+/-2.3 mmol.kg d.w. during the first and second halves, respectively, with blood lactate being 6.0+/-0.4 and 5.0+/-0.4 mM, respectively. Muscle lactate was not correlated with blood lactate (r=0.06-0.25, P>0.05). Muscle glycogen decreased (P<0.05) from 449+/-23 to 255+/-22 mmol.kg d.w. during the game, with 47+/-7% of the muscle fibers being completely or almost empty of glycogen after the game. Blood glucose remained elevated during the game, whereas plasma FFA increased (P<0.05) from 0.45+/-0.05 to 1.37+/-0.23 mM. Mean sprint time was unaltered after the first half, but longer (P<0.05) after the game (2.8+/-0.7%) as well as after intense periods in the first (1.6+/-0.6%) and second halves (3.6+/-0.5%). The decline in sprint performance during the game was not correlated with muscle lactate, muscle pH, or total glycogen content. CONCLUSION: Sprint performance is reduced both temporarily during a game and at the end of a soccer game. The latter finding may be explained by low glycogen levels in individual muscle fibers. Blood lactate is a poor indicator of muscle lactate during soccer match play.

Leptin gene expression and systemic levels in healthy men: effect of exercise, carbohydrate, interleukin-6, and epinephrine.

Leptin, an adipose tissue-derived cytokine, is correlated with adipose mass as obese persons have increased levels of leptin that decrease with weight loss. Previous studies demonstrate that high-energy-expenditure exercise decreases circulating leptin levels, whereas low-energy-expenditure exercise has no effect. We aimed to test the hypothesis that acute exercise reduced leptin mRNA levels in human adipose tissue and that this effect would be ameliorated by carbohydrate supplementation. Because exercise markedly increases circulating IL-6 and epinephrine, we investigated whether the changes in leptin seen with acute exercise could be mediated by IL-6 or epinephrine infusion. Abdominal subcutaneous adipose tissue mRNA and plasma levels of leptin were measured in healthy men in response to 3-h ergometer exercise with or without carbohydrate (CHO) ingestion (n = 8) and in response to infusion with recombinant human (rh)IL-6 (n = 11) or epinephrine (n = 8) or saline. Plasma leptin declined in response to exercise (P < 0.05) compared with rest, whereas mRNA expression in adipose tissue was unaffected. The exercise-induced decrease in plasma leptin was attenuated by CHO ingestion (P < 0.001). A 3-h epinephrine infusion decreased plasma leptin (P < 0.001) to the same level seen with 3 h of exercise, whereas leptin levels were unaffected by rhIL-6 infusion. In conclusion, both acute exercise and epinephrine infusion decreased plasma leptin to a similar extent, whereas there was no effect with rhIL-6 infusion. Acute exercise solely affected leptin plasma levels, as mRNA levels were unchanged. The exercise-induced decrease in circulating leptin was counteracted by CHO ingestion, suggesting a posttranscriptional regulatory mechanism of leptin involving substrate availability.

Effect of exercise, training, and glycogen availability on IL-6 receptor expression in human skeletal muscle.

The cytokine interleukin-6 (IL-6) exerts it actions via the IL-6 receptor (IL-6R) in conjunction with the ubiquitously expressed gp130 receptor. IL-6 is tightly regulated in response to exercise, being affected by factors such as exercise intensity and duration, as well as energy availability. Although the IL-6 response to exercise has been extensively studied, little is known about the regulation of the IL-6R response. In the present study, we aimed to investigate the effect of exercise, training, and glycogen availability, factors known to affect IL-6, on the regulation of gene expression of the IL-6R in human skeletal muscle. Human subjects performed either 10 wk of training with an acute exercise bout before and after the training period, or a low-glycogen vs. normal-glycogen acute exercise trial. The IL-6R mRNA response was evaluated in both trials. In response to acute exercise, an increase in IL-6R mRNA levels was observed. Neither training nor intramuscular glycogen levels had an effect on the IL-6R mRNA response to exercise. However, after 10 wk of training, the skeletal muscle expressed a higher mRNA level of IL-6R compared with before training. The present study demonstrated that the IL-6R gene expression levels in skeletal muscle are increased in response to acute exercise, a response that is very well conserved, being affected by neither training status nor intramuscular glycogen levels, as opposed to IL-6. However, after the training period, IL-6R mRNA production was increased in skeletal muscle, suggesting a sensitization of skeletal muscle to IL-6 at rest.

Interleukin-6 stimulates lipolysis and fat oxidation in humans.

Although IL-6 is a key modulator of immune function, it also plays a role in regulating substrate metabolism. To determine whether IL-6 affects lipid metabolism, 18 healthy men were infused for 3 h with saline (Con; n = 6) or a high dose (High-rhIL6; n = 6) or a low dose (Low-rhIL6; n = 6) of recombinant human IL-6 (rhIL-6). The IL-6 concentration during Con, Low-rhIL6, and High-rhIL6 was at a steady state after 30 min of infusion at approximately 4, 140, and 320 pg/ml, respectively. Either dose of rhIL-6 was associated with a similar increase in fatty acid (FA) concentration and endogenous FA rate of appearance (R(a)) from 90 min after the start of the infusion. The FA concentration and FA R(a) continued to increase until the cessation of rhIL-6 infusion, reaching levels approximately 50% greater than Con values. The elevated levels reached at the end of rhIL-6 infusion persisted at least 3 h postinfusion. Triacylglycerol concentrations were unchanged during rhIL-6 infusion, whereas whole body fat oxidation increased after the second hour of rhIL-6 infusion. Of note, during Low-rhIL6, the induced elevation in FA concentration and FA R(a) occurred in the absence of any change in adrenaline, insulin, or glucagon, and no adverse side effects were observed. In conclusion, the data identify IL-6 as a potent modulator of fat metabolism in humans, increasing fat oxidation and FA reesterification without causing hypertriacylglyceridemia.

Glucose ingestion attenuates the exercise-induced increase in circulating heat shock protein 72 and heat shock protein 60 in humans.

Heat shock protein (Hsp) 72 is a cytosolic stress protein that is highly inducible by several factors including exercise. Hsp60 is primarily mitochondrial in cellular location, plays a key role in the intracellular protein translocation and cytoprotection, is increased in skeletal muscle by exercise, and is found in the peripheral circulation of healthy humans. Glucose deprivation increases Hsp72 in cultured cells, whereas reduced glycogen availability elevates Hsp72 in contracting human skeletal muscle. To determine whether maintained blood glucose during exercise attenuates the exercise-induced increase in intramuscular and circulating Hsp72 and Hsp60, 6 males performed 120 minutes of semirecumbent cycling at approximately 65% maximal oxygen uptake on 2 occasions while ingesting either a 6.4% glucose (GLU) or sweet placebo (CON) beverage throughout exercise. Muscle biopsies, obtained before and immediately after exercise, were analyzed for Hsp72 and Hsp60 protein expression. Blood samples were simultaneously obtained from a brachial artery, a femoral vein, and the hepatic vein before and during exercise for the analysis of serum Hsp72 and Hsp60. Leg and hepatosplanchnic blood flow were measured to determine Hsp72-Hsp60 flux across these tissue beds. Neither exercise nor glucose ingestion affected the Hsp72 or Hsp60 protein expression in, or their release from, contracting skeletal muscle. Arterial serum Hsp72 increased (P < 0.05) throughout exercise in both trials but was attenuated (P < 0.05) in GLU. This may have been in part because of the increased (P < 0.05) hepatosplanchnic Hsp72 release in CON, being totally abolished (P < 0.05) in GLU. Serum Hsp60 increased (P < 0.05) after 60 minutes of exercise in CON before returning to resting levels at 120 minutes. In contrast, no exercise-induced increase in serum Hsp60 was observed in GLU. We detected neither hepatosplanchnic nor contracting limb Hsp60 release in either trial. In conclusion, maintaining glucose availability during exercise attenuates the circulating Hsp response in healthy humans.

Skeletal muscle interleukin-6 and tumor necrosis factor-alpha release in healthy subjects and patients with type 2 diabetes at rest and during exercise.

To examine the influence of type 2 diabetes on cytokine release from the leg at rest and during exercise, 9 male type 2 diabetics (D) and 8 age-, gender-, Vo2peak-, weight- and body mass index (BMI)-matched control subjects (C) were studied before and after 25 minutes of supine bicycle exercise at 60% Vo2peak. Blood samples were obtained from a femoral artery and vein from 1 limb, and plasma was analyzed for glucose and the cytokines, interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha. Leg blood flow (LBF) was measured by thermodilution in the femoral vein, and net leg IL-6, TNF-alpha, and glucose balance were calculated as the product of LBF and femoral arteriovenous (fa-v) glucose, IL-6, and TNF-alpha difference. Arterial plasma glucose and IL-6 were higher (P<.05) at rest in D compared with C, but there were no differences in arterial TNF-alpha concentrations at rest when comparing groups. Despite measurable arterial levels of both IL-6 and TNF-alpha in both groups at rest, there was not net leg release of either cytokine at rest. Exercise increased (P<.05) IL-6 release and glucose uptake in both D and C, and contracting leg glucose uptake was similar when comparing D with C. While not significant, there was a trend (P=.1) for augmented exercise-induced IL-6 release in D compared with C. In contrast, exercise did not result in TNF-alpha release in either D or C. These data demonstrate that basal circulating TNF-alpha is not elevated in patients with type 2 diabetes when matched for BMI with control subjects. The results also suggest that neither type 2 diabetic nor healthy skeletal muscle releases these cytokines at rest, indicating that organs other than skeletal muscle contribute to the elevated basal IL-6 in type 2 diabetics. In contrast with IL-6, exercise does not result in the release of TNF-alpha from the contracting limbs of either healthy subjects or patients with type 2 diabetes.

The role of IL-6 in exercise-induced immune changes and metabolism.

Cytokines such as interleukin (IL)-6 are proteins, which were originally discovered within the immune system. Recent studies, however, demonstrate that IL-6 is produced by, and released from contracting skeletal muscles during exercise. This release occurs in the absence of muscle damage and is related to both contraction per se and low muscle glycogen. IL-6 seems to work as an energy sensor within the muscle cells. Other organs also release IL-6 during exercise; however, muscle-derived IL-6 seems to play an important role in signalling between the muscles and other organs in order to maintain energy supply. IL-6 can enhance lipolysis in humans and might play a role in glucose metabolism. In addition, muscle-derived IL-6 is likely to initiate many of the exercise associated immune changes, as IL-6 can increase plasma levels of the cytokines IL-1 ra and IL-10, together with cortisol and blood neurtrophils. Also, the observed shift towards Th2 lymphocyte dominance during exercise may be mediated by IL-6. Because carbohydrate ingestion during exercise has been demonstrated to blunt the IL-6 and hormonal response, it might also blunt other beneficial adaptations. This review discusses the possible beneficial biological role of high plasma levels of IL-6 during exercise.

Does the aging skeletal muscle maintain its endocrine function?

Contracting skeletal muscles produce and release the cytokine interleukin (IL)-6 and this release is augmented by the presence of low muscle glycogen. Since muscle metabolism in elderly subjects relies on glycogen more than younger subjects, it is possible that aging is associated with an altered production of muscle-derived IL-6 during exercise. To test the relation between aging and muscle-derived IL-6, seven healthy elderly males, mean age 70+/-1 (SEM) yr and six healthy young males, mean age 26+/-2 (SEM) yr performed three hours of dynamic knee-extensor exercise at 50% of maximal work load (Wmax). IL-6 mRNA and glycogen in muscles were analysed and the IL-6 release were estimated before, during and after the exercise. Although the absolute work load in the elderly was less than half of that in the young, 41.1+/-3.1 W and 92.5+/-4.0 W, respectively, the muscle glycogen utilization after three hours of exercise did not differ between groups, 238.7+/-52.4 and 245.2+/-74.0 mmol/kg muscle in elderly and young, respectively. This could explain that the IL-6 release and the IL-6 mRNA amplification increased during exercise with no difference between groups, two-way ANOVA-P = 0.50 and 0.45, respectively. In conclusion, elderly healthy people maintain the capacity to produce and release IL-6 in response to dynamic exercise, with no difference compared to young individuals furthermore, glycogen utilization expressed in changes of glycogen related to muscle mass was equal in elderly and young subject at 50 % of Wmax.

Exercise and hypoxia: effects on leukocytes and interleukin-6-shared mechanisms?

Stress-induced immunological reactions to exercise have stimulated much research into stress immunology and neuroimmunology. It has been suggested that exercise can be employed as a model of temporary immunosuppression, which occurs during physical stress, such as hypoxia. Acute exercise and acute hypoxia mediate in principle identical effects on circulating lymphocyte and neutrophil numbers. Thus, during exercise and hypoxia, lymphocytes are recruited to the blood. After the stress, the number of lymphocytes declines after the stress, whereas the neutrophil number continues to increase. When exercise is performed during hypoxia, the exercise-induced immune changes are pronounced. There is some evidence that the exercise- and hypoxia-induced changes in leukocyte subpopulations are mediated by neuroendocrinological factors such as catecholamines, growth hormone, and cortisol. In contrast, although exercise, as well as hypoxia, is associated with increased plasma levels of IL-6, the mechanisms are not likely to be the same. Thus, during exercise, contracting skeletal muscles are the main source of IL-6 production, whereas the source of IL-6 during hypoxia has not been demonstrated. The increased level of adrenaline contributes to the enormous increase in plasma IL-6 only to a minor degree during strenuous exercise. However, the only modest increase in IL-6 during hypoxia may be linked to hormonal changes, whereas the prolonged increase in IL-6 during chronic hypoxia is likely to be multifactorial.

Metabolic impact of growth hormone treatment in short children born small for gestational age.

BACKGROUND: Growth hormone (GH) treatment in short children born small for gestational age (SGA) may result in metabolic changes with potential long-term effects. METHODS: 149 short SGA children (mean birth weight 2.0 ± 0.6 kg, age 5.5 ± 1.5 years, height standard deviation score (SDS) -3.1 ± 0.6) were randomised to: low-dose GH therapy (0.033 mg/kg/day) for 2 years; high-dose GH therapy (0.100 mg/kg/day) for 1 year, or mid-dose GH therapy (0.067 mg/kg/day) for 1 year. Leptin, ghrelin, insulin-like growth factor-I (IGF-I), IGF binding protein-1 (IGFBP-1), lipids, fasting blood glucose and fasting insulin were assessed at baseline, 12 and 24 months. RESULTS: After 1 year of active treatment, GH significantly reduced serum ghrelin and increased IGF-I SDS and insulin levels. Regression analysis showed an inverse correlation between ghrelin and IGF-I SDS (p < 0.001). Leptin and IGFBP-1 also declined (both p < 0.05). Changes in insulin levels reversed upon discontinuation. Improvements in lipid profile were nonsignificant and fasting blood glucose levels remained within the normal range. CONCLUSION: In short SGA children, ghrelin and leptin reductions associated with GH treatment may occur through a negative feedback loop of the GH-IGF-I axis. Consequently, via ghrelin and leptin suppression, GH treatment may modify food intake and body composition and potentially improve long-term metabolic outcomes.