Voluntary exercise training enhances glucose transport in muscle stimulated by insulin-like growth factor I

Detection of synthetic analogues of insulin-like growth factor 1 in different biological fluids by liquid chromatography quadrupole time-of-flight mass spectrometry: comparison of different immunoaffinity protocols

Insulin-like growth factor 1 analogues are prohibited in sport for their ability to enhance athletic performance in several sport disciplines. Their detection presents several analytical challenges, mainly due to the minimum required performance limits fixed by the World Anti-Doping Agency. Here, we are presenting analytical workflows to detect IGF-1 and its analogues in different biological matrices. Several off-line immunocapture techniques and protocols were comparatively evaluated. Separation and detection were performed by using standard flow reverse-phase liquid chromatography coupled to a time-of-flight mass spectrometer. The best recoveries were obtained using magnetic beads or pipette tips functionalized with protein A. The analytical workflows were fully validated for qualitative determinations: all the target analytes were clearly distinguishable from the interference of the matrices, with limits of detection and identification in the range of 0.05-0.30 ng/mL in urine and 0.5-2.0 ng/mL in serum/plasma. The extraction efficiency proved to be repeatable (CV% < 10) with recoveries higher than 50%. Intra- and inter-day precision were found to be smaller than 10 and 15%, respectively. The method was successfully applied to the analysis of authentic matrix samples containing the target peptides at the minimum required performance limits, proving that the method developed can be successfully applied to detect and identify IGF-1 analogues for doping control purposes in all the matrices selected. The analytical workflow developed here to detect the target peptides in different matrices can be readily implemented in anti-doping laboratories and has the potential to be adapted for the simultaneous analysis of different similarly sized peptide hormones of doping relevance.

Detection of LongR3 -IGF-I, Des(1-3)-IGF-I, and R3 -IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes

Insulin-like growth factor-I (IGF-I) and its analogs LongR³ -IGF-I, Des(1-3)-IGF-I, and R³ -IGF-I are prohibited substances in sport. Although they were never approved for use in humans, they are readily available as black market products for bodybuilding and can be used to enhance physical performance. This study's aims were to validate a fast and sensitive detection method for IGF-I analogs and to evaluate their detectability after intramuscular administration in rats. The sample preparation consisted of an immunopurification on MSIA™ microcolumns using a polyclonal anti-human-IGF-I antibody. The target substances were then directly analyzed by nano-liquid chromatography coupled with high-resolution mass spectrometry. Abundant signs of lower quality, oxidized peptide forms were found in black market products, justifying the need to monitor at least both the native and mono-oxidized forms. The analytical performance of this method (linearity, carry over, detection limits, precision, specificity, recovery, and matrix effect) was studied by spiking the analogs into human serum. Following a single intramuscular administration (100 μg/kg) in rats, detection was evaluated up to 36 h after injection. While unchanged Des(1-3)-IGF-I and R³ -IGF-I were detected until 24 h after administration, LongR³ -IGF-I disappeared rapidly after 4 h. Des(1)-LongR³ -IGF-I, a new N-terminal Long-R³ -IGF-I degradation product, was detected in addition to Des(1-10)-LongR³ -IGF-I and Des(1-11)-LongR^3- IGF-I: the latter was detected up to 16 h. The same products were found after in vitro incubation of the analogs in human whole blood, suggesting that observations in rats may be extrapolated to humans and that the validated method may be applicable to antidoping testing.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Application of Chronic Stimulation to Study Contractile Activity-induced Rat Skeletal Muscle Phenotypic Adaptations

Skeletal muscle is a highly adaptable tissue, as its biochemical and physiological properties are greatly altered in response to chronic exercise. To investigate the underlying mechanisms that bring about various muscle adaptations, a number of exercise protocols such as treadmill, wheel running, and swimming exercise have been used in the animal studies. However, these exercise models require a long period of time to achieve muscle adaptations, which may be also regulated by humoral or neurological factors, thus limiting their applications in studying the muscle-specific contraction-induced adaptations. Indirect low frequency stimulation (10 Hz) to induce chronic contractile activity (CCA) has been used as an alternative model for exercise training, as it can successfully lead to muscle mitochondrial adaptations within 7 days, independent of systemic factors. This paper details the surgical techniques required to apply the treatment of CCA to the skeletal muscle of rats, for widespread application in future studies.

Endurance training-induced changes in the GH-IGF-I axis influence maximal muscle strength in previously untrained men

OBJECTIVE

In this study we have determined the effects of 20weeks of endurance running training on the GH-IGF-I axis changes in the context of the skeletal muscle performance and physical capacity level.

DESIGN

Before and after the endurance training program a maximal incremental exercise tests, a 1500m race and a muscle strength measurements were performed and the blood samples were taken to determine both resting as well as end-exercise serum growth hormone (GH), insulin-like growth hormone-I (IGF-I), insulin-like growth hormone binding protein-3 (IGFBP-3) and plasma interleukin-6 (IL-6) concentrations.

RESULTS

20weeks of endurance running training improved power output generated at the end of the maximal incremental test by 24% (P<0.012), 1500m running time by 13% (P<0.012) and maximal muscle strength by 9% (P<0.02). End-exercise IGF-I/IGFBP-3 ratio was decreased by 22% after the training (P<0.04) and the magnitude of IGF-I/IGFBP-3 ratio decrease (ΔIGF-I/IGFBP-3_ex) was 2.3 times higher after the training (P<0.04). The magnitude of the exercise-induced changes in IGFBP-3 concentration was also significantly higher (P<0.04) and there was a trend toward lower end-exercise IGF-I concentration (P=0.08) after the training. These changes were accompanied by a significantly higher (30%) end-exercise IL-6 concentration (P<0.01) as well as by a 3.4 times higher magnitude of IL-6 increase (P<0.02) after the training. Moreover, there were strong positive correlations between changes in resting serum IGF-I concentration (ΔIGF-I_res) and IGF-I/IGFBP-3 ratio (ΔIGF-I/IGFBP-3_res) and changes in muscle strength (ΔMVC) (r=0.95, P=0.0003 and r=0.90, P=0.002, respectively).

CONCLUSIONS

The training-induced changes in the components of the GH-IGF-I axis may have additive effects on skeletal muscle performance and physical capacity improvement.

From physical inactivity to immobilization: Dissecting the role of oxidative stress in skeletal muscle insulin resistance and atrophy

In the literature, the terms physical inactivity and immobilization are largely used as synonyms. The present review emphasizes the need to establish a clear distinction between these two situations. Physical inactivity is a behavior characterized by a lack of physical activity, whereas immobilization is a deprivation of movement for medical purpose. In agreement with these definitions, appropriate models exist to study either physical inactivity or immobilization, leading thereby to distinct conclusions. In this review, we examine the involvement of oxidative stress in skeletal muscle insulin resistance and atrophy induced by, respectively, physical inactivity and immobilization. A large body of evidence demonstrates that immobilization-induced atrophy depends on the chronic overproduction of reactive oxygen and nitrogen species (RONS). On the other hand, the involvement of RONS in physical inactivity-induced insulin resistance has not been investigated. This observation outlines the need to elucidate the mechanism by which physical inactivity promotes insulin resistance.

Additive effect of diets and training on total insulin-like growth factor-1 (IGF-1) in rats

OBJECTIVES

Although it is known that circulating levels of insulin-like growth factor-1 (IGF-1) are influenced by both physical exercise and dietary intake separately, there is little information regarding the additive effect of diets and training on IGF-1 regulation. To test this, we examined the combined effect of 30 days of two different diets (high-protein and high-carbohydrate) and exercise training on total IGF-1.

MATERIALS AND METHODS

The study was carried out with four groups of rats; the sedentary group with standard diet (SS) (control group), standard diet with exercise (SE), high-protein diet with exercise (PE) and high-carbohydrate diet with exercise (CE). Serum IGF-1, insulin, corticosterone were analyzed.

RESULTS

IGF-1 concentrations were decreased by exercise training (p<0.001) and only with protein diet (p<0.05). Physical training, with and without diet, decreased body weight and food intake (p<0.01) and increased corticosterone levels (p<0.05). Carbohydrate diet did not cause major hormonal and metabolic alterations.

CONCLUSION

The main result of this study was the decreased levels of IGF-1 in spite of high-protein diet, which is known to enhance IGF-1 secretion, and the little changes with carbohydrate diet. This may be related to the negative energy balance as a result of the catabolic state induced by exercise training and decreased calorie intake in protein diet. Thus, it can be concluded that the caloric restriction, regardless of dietary composition, decreased IGF-1 secretion.

Improvement of insulin sensitivity by antagonism of the renin-angiotensin system

The reduced capacity of insulin to stimulate glucose transport into skeletal muscle, termed insulin resistance, is a primary defect leading to the development of prediabetes and overt type 2 diabetes. Although the etiology of this skeletal muscle insulin resistance is multifactorial, there is accumulating evidence that one contributor is overactivity of the renin-angiotensin system (RAS). Angiotensin II (ANG II) produced from this system can act on ANG II type 1 receptors both in the vascular endothelium and in myocytes, with an enhancement of the intracellular production of reactive oxygen species (ROS). Evidence from animal model and cultured skeletal muscle cell line studies indicates ANG II can induce insulin resistance. Chronic ANG II infusion into an insulin-sensitive rat produces a markedly insulin-resistant state that is associated with a negative impact of ROS on the skeletal muscle glucose transport system. ANG II treatment of L6 myocytes causes impaired insulin receptor substrate (IRS)-1-dependent insulin signaling that is accompanied by augmentation of NADPH oxidase-mediated ROS production. Further critical evidence has been obtained from the TG(mREN2)27 rat, a model of RAS overactivity and insulin resistance. The TG(mREN2)27 rat displays whole body and skeletal muscle insulin resistance that is associated with local oxidative stress and a significant reduction in the functionality of the insulin receptor (IR)/IRS-1-dependent insulin signaling. Treatment with a selective ANG II type 1 receptor antagonist leads to improvements in whole body insulin sensitivity, enhanced insulin-stimulated glucose transport in muscle, and reduced local oxidative stress. In addition, exercise training of TG(mREN2)27 rats enhances whole body and skeletal muscle insulin action. However, these metabolic improvements elicited by antagonism of ANG II action or exercise training are independent of upregulation of IR/IRS-1-dependent signaling. Collectively, these findings support targeting the RAS in the design of interventions to improve metabolic and cardiovascular function in conditions of insulin resistance associated with prediabetes and type 2 diabetes.

The influence of bovine colostrum supplementation on exercise performance in highly trained cyclists

PURPOSE

The aim of this experiment was to investigate the influence of low dose bovine colostrum supplementation on exercise performance in cyclists over a 10 week period that included 5 days of high intensity training (HIT).

METHODS

Over 7 days of preliminary testing, 29 highly trained male road cyclists completed a VO(2max) test (in which their ventilatory threshold was estimated), a time to fatigue test at 110% of ventilatory threshold, and a 40 km time trial (TT40). Cyclists were then assigned to either a supplement (n = 14, 10 g/day bovine colostrum protein concentrate (CPC)) or a placebo group (n = 15, 10 g/day whey protein) and resumed their normal training. Following 5 weeks of supplementation, the cyclists returned to the laboratory to complete a second series of performance testing (week 7). They then underwent five consecutive days of HIT (week 8) followed by a further series of performance tests (week 9).

RESULTS

The influence of bovine CPC on TT40 performance during normal training was unclear (week 7: 1+/-3.1%, week 9: 0.1+/-2.1%; mean+/-90% confidence limits). However, at the end of the HIT period, bovine CPC supplementation, compared to the placebo, elicited a 1.9+/-2.2% improvement from baseline in TT40 performance and a 2.3+/-6.0% increase in time trial intensity (% VO(2max)), and maintained TT40 heart rate (2.5+/-3.7%). In addition, bovine CPC supplementation prevented a decrease in ventilatory threshold following the HIT period (4.6+/-4.6%).

CONCLUSION

Low dose bovine CPC supplementation elicited improvements in TT40 performance during an HIT period and maintained ventilatory threshold following five consecutive days of HIT.

Training effects in mice after long-term voluntary exercise

BACKGROUND

Mice are an important animal model in exercise studies on the immune system, cancer, and aging. There is limited research about the training effects of long-term voluntary exercise in this species.

PURPOSE

To describe the training effects in mice given long-term aerobic voluntary exercise.

METHODS

Female C57BL/6 mice were randomly assigned to 1) individual cages with in-cage running wheels with 24-h access (WR; N = 31), or 2) individual cages without running wheels for 16 wk (NR; N = 20). Run-to-exhaustion (RTE) times, VO2peak, speed at VO2peak, and citrate synthase (CS), succinate dehydrogenase (SDH), and phosphofructokinase (PFK) activity in the soleus, plantaris, and red and white gastrocnemius were assessed.

RESULTS

Final body weight and speed at VO2peak did not differ by training condition. WR mice had significantly longer RTE times (P < 0.001) and higher VO2peak (P < 0.05) compared with NR mice. Higher CS and SDH activities were found in WR compared with NR mice for soleus (P < 0.01), red gastrocnemius (P < 0.01), and plantaris (P < 0.01) muscles. PFK activity was higher in WR mice in white gastrocnemius compared with NR mice (P < 0.01).

CONCLUSIONS

Voluntary running wheel activity for 16 wk in female C57BL/6 mice resulted in longer run times to exhaustion, higher VO2peak, and higher SDH and CS activities in oxidative muscles. These findings suggest that wheel running in female C57BL/6 mice: 1) produces a measurable aerobic training effect and 2) is an effective exercise modality for long-term training studies.

Whole-body insulin resistance in the absence of obesity in FVB mice with overexpression of Dgat1 in adipose tissue

Insulin resistance is often associated with obesity. We tested whether augmentation of triglyceride synthesis in adipose tissue by transgenic overexpression of the diacylglycerol aclytransferase-1 (Dgat1) gene causes obesity and/or alters insulin sensitivity. Male FVB mice expressing the aP2-Dgat1 had threefold more Dgat1 mRNA and twofold greater DGAT activity levels in adipose tissue. After 30 weeks of age, these mice had hyperglycemia, hyperinsulinemia, and glucose intolerance on a high-fat diet but were not more obese than wild-type littermates. Compared with control littermates, Dgat1 transgenic mice were both insulin and leptin resistant and had markedly elevated plasma free fatty acid levels. Adipocytes from Dgat1 transgenic mice displayed increased basal and isoproterenol-stimulated lipolysis rates and decreased gene expression for fatty acid uptake. Muscle triglyceride content was unaffected, but liver mass and triglyceride content were increased by 20 and 300%, respectively. Hepatic insulin signaling was suppressed, as evidenced by decreased phosphorylation of insulin receptor-beta (Tyr(1,131)/Tyr(1,146)) and protein kinase B (Ser473). Gene expression data suggest that the gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were upregulated. Thus, adipose overexpression of Dgat1 gene in FVB mice leads to diet-inducible insulin resistance, which is secondary to redistribution of fat from adipose tissue to the liver in the absence of obesity.

Sustained rise in triacylglycerol synthesis and increased epididymal fat mass when rats cease voluntary wheel running

Four-week-old, Fischer-Brown Norway F1-generation male rats were given access to voluntary running wheels for 21 days, and then the wheels were locked for 5 (WL5), 10 (WL10), 29 (WL29), or 53 (WL53) hours. Two other groups (SED5 and SED10) had no access to voluntary running wheels and were killed at the same time as WL5 and WL10, respectively. Absolute and relative epididymal fat mass, mean cell volume, and amount of lipid per cell increased in WL53 relative to all other groups, with no change in cell number. C/EBPalpha protein levels in epididymal fat were 30% greater in SED5 than in WL5. The rate of triacylglycerol synthesis in epididymal fat was 4.2-fold greater in SED5 than in WL5, increased 14-fold between WLS and WL10, and was 79% lower in SED10 than in WL10. Triacylglycerol synthesis remained at this elevated level (at least 3.5-fold greater than SED5) through WL53. Thus, the rapid increase in epididymal fat mass with the cessation of voluntary wheel running is associated with a prolonged overshoot in epididymal fat triacylglycerol synthesis. Moreover, rats without running wheels had a 9.4% lower body mass after 21 days than those with running wheels. The individual mass of seven different muscles from the hindlimb, upper forelimb, and back were each lower in animals without running wheels, suggesting that physical activity in rapidly growing rats may be requisite for optimal muscle development.

Alterations in insulin receptor signalling in the rat epitrochlearis muscle upon cessation of voluntary exercise

The major purpose of this study was to elucidate mechanisms by which decreasing enhanced physical activity induces decreased insulin sensitivity in skeletal muscle. Rats with access to voluntary running wheels for 3 weeks had their wheels locked for 5 h (WL5), 29 h (WL29), or 53 h (WL53); a separate group of rats never had wheel access (sedentary, SED). Relative to WL5, submaximal insulin-stimulated 2-deoxyglucose uptake into the epitrochlearis muscle was lower in WL53 and SED. Insulin binding, insulin receptor beta-subunit (IRbeta) protein level, submaximal insulin-stimulated IRbeta tyrosine phosphorylation, and glucose transporter-4 protein level were each lower in both WL53 and SED than in WL5 and WL29. Akt/protein kinase B Ser(473) phosphorylation was lower in WL53 and SED than in WL5. Protein levels of protein tyrosine phosphatase-1B, Src homology phosphatase-2, and protein kinase C- did not vary among groups. The amount of protein tyrosine phosphatase-1B, Src homology phosphatase-2, and protein kinase C- associated with IRbeta in insulin-stimulated muscle also did not differ among the four groups. The mean of SED and WL53 had a significantly higher IRbeta-associated protein tyrosine phosphatase-1B than the mean of WL5 and WL29. The enclosure of multiple changes (decreases in insulin binding, IRbeta protein, IRbeta tyrosine phosphorylation, and glucose transporter-4 protein) in the epitrochlearis muscle within the 29th to 53rd hour after cessation of voluntary wheel running raises the possibility that a single regulatory event could be responsible for the coordinated decrease.

Age-related differences in the des IGF-I-mediated activation of Akt-1 and p70 S6K in mouse skeletal muscle

The ability of des IGF-I to activate Akt-1 and p70 S6K in skeletal muscle with or without acute endurance exercise was examined in young and old mice. Mice were sacrificed 12 h after a moderate intensity treadmill run following an interperitoneal injection of des-IGF-I or saline. Blood and skeletal muscle were collected and IGF-I receptor, Akt-1 and p70 S6K protein contents and their phosphorylation status were determined. Injection of des IGF-I similarly decreased plasma glucose concentration in both young (P<0.01) and old mice (P<0.01) whereas plasma insulin and total IGF-I levels of young and old mice were not significantly changed by des IGF-I. Total IGF-I receptor protein and IGF-1 receptor phosphorylation were lower in aged mice (P<0.05). Basal phosphorylation of Akt-1 was lower in aged skeletal muscle (P<0.01) and this was not caused by changes in Akt-1 protein. In both young (P<0.01) and aged (P<0.05) mice, des IGF-I significantly increased the phosphorylation of Akt-1 at Ser 473. However, a des IGF-I-mediated increase in the p70 S6K phosphorylation (P<0.01) was only seen in young mice. Prior exercise decreased the total plasma IGF-I level in the presence of des IGF-I in aged mice. Des IGF-I-mediated Akt-1 and p70 S6K phosphorylation was not changed by exercise in either young or old mice. It is concluded that there was an aging-related resistance at the p70 S6K level in mouse skeletal muscle that could not be restored by prior exercise and this resistance is associated with lower IGF-I receptor number and Akt-1 phosphorylation in the aged skeletal muscle.

Genetic selection of mice for high voluntary wheel running: effect on skeletal muscle glucose uptake

Effects of genetic selection for high wheel-running activity (17th generation) and access to running wheels on skeletal muscle glucose uptake were studied in mice with the following treatments for 8 wk: 1) access to unlocked wheels; 2) same as 1, but wheels locked 48 h before glucose uptake measurement; or 3) wheels always locked. Selected mice ran more than random-bred (nonselected) mice (8-wk mean +/- SE = 8,243 +/- 711 vs. 3,719 +/- 233 revolutions/day). Body weight was 5-13% lower for selected vs. nonselected groups. Fat pad/body weight was ~40% lower for selected vs. nonselected and unlocked vs. locked groups. Insulin-stimulated glucose uptake and fat pad/body weight were inversely correlated for isolated soleus (r = -0.333; P < 0.005) but not extensor digitorum longus (EDL) or epitrochlearis muscles. Insulin-stimulated glucose uptake was higher in EDL (P < 0.02) for selected vs. nonselected mice. Glucose uptake did not differ by wheel group, and amount of running did not correlate with glucose uptake for any muscle. Wheel running by mice did not enhance subsequent glucose uptake by isolated muscles.

Correlations of growth hormone (GH) and insulin-like growth factor I (IGF-I): effects of exercise and abuse by athletes

The importance of hormones on body metabolism when physical exercise is carried out has been established for a long time. Growth hormone (GH) is crucial in energy metabolism as well as in body anabolism. Recent studies have increased our knowledge of GH's mechanisms of action. In particular, insulin-like growth factor I (IGF-I), the main hormone mediating the principal GH effects and other protein structures (i.e. the binding proteins related to these two hormones), has been recognized as playing a crucial role. The biochemical aspects relating to the molecules of the GH/IGF-I axis have been described here. Furthermore, the belief that GH and IGF-I enhance performance has induced an 'abuse' of GH (and possibly of IGF-I) by competitive sports athletes and amateurs. The present study outlines the best methods available to uncover abuse, as well as a series of potential research projects to recognize doping. The review also underlines the principal variables measurable in the laboratory and summarizes published reference ranges of these parameters. These biochemical and laboratory profiles describe principal experimental approaches, with the hope that this will stimulate new ideas on the subject of detecting doping practices.

Serum levels of total and free IGF-I and IGFBP-3 are increased and maintained in long-term training

The goals of this study were to determine whether the long-term training regimens experienced by competitive collegiate swimmers would result in altered levels of total and free serum insulin-like growth factor I (IGF-I) as well as IGF-binding proteins (BP) IGFBP-1 and -3. Two male (Teams 1M and 2M) and one female (Team 2F) teams were studied at the start of training, after 2 mo of training, after 4 mo (2-4 mo had the highest volume of training), after 5 mo (near the end of tapering; only for Team 1M), and several days after training was over. For Team 1M, total IGF-I concentrations were increased by 76% after 4 mo and were subsequently maintained at this level. Total IGF-I responses were more variable for Teams 2F and 2M. Free IGF-I levels were increased nearly twofold for all teams at 2 mo and were maintained or increased further with subsequent training. Only the levels of free IGF-I for Team 1M returned to pretraining values after training had ended. Training had little effect on IGFBP-1 levels. For all teams, serum IGFBP-3 was elevated by 4 mo of training (for Team 2F it was increased at 2 mo) by 30-97% and remained at these higher levels thereafter. The ratio of total IGF-I to IGFBP-3 was not increased by training in any group. These data indicate that serum levels of total and free IGF-I and total IGFBP-3 can be increased with intense training and maintained with reduced training (tapering). The findings show that changes in free IGF-I levels are not accounted for by alterations in the total IGF-I/IGFBP-3 complex or in IGFBP-3 levels and indicate that there are other important determinants of free IGF-I.