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Irisin in response to acute and chronic whole-body vibration exercise in humans
M ET ABOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
Available online at www.sciencedirect.com
Metabolism www.metabolismjournal.com
Brief Report
Irisin in response to acute and chronic whole-body vibration exercise in humans☆,☆☆ Joo Young Huh a,⁎, 1 , Vassilis Mougios b, 1 , Athanasios Skraparlis b , Athanasios Kabasakalis b , Christos S. Mantzoros a a b
Section of Endocrinology, Boston VA Healthcare System, Harvard Medical School, Boston, MA School of Physical Education and Sports Science, Aristotle University of Thessaloniki, Thessaloniki, Greece
A R T I C LE I N FO Article history:
AB S T R A C T Objective. Irisin is a recently identified myokine, suggested to mediate the beneficial
Received 7 March 2014
effects of exercise by inducing browning of white adipocytes and thus increasing energy
Accepted 2 April 2014
expenditure. In humans, the regulation of irisin by exercise is not completely understood. We investigated the effect of acute and chronic whole-body vibration exercise, a moderate-
Keywords:
intensity exercise that resembles shivering, on circulating irisin levels in young
Irisin
healthy subjects. Materials/Methods. Healthy untrained females participated in a 6-week program of whole-
FNDC5 Whole body vibration exercise
body vibration exercise training. Blood was drawn before and immediately after an acute
Myokine
bout of exercise at baseline (week 0) and after 6 weeks of training. Results. The resting irisin levels were not different at baseline (week 0) and after 6 weeks of training. At both 0 and 6 weeks of training, an acute bout of vibration exercise significantly elevated circulating irisin levels by 9.5% and 18.1%, respectively (p = 0.05 for the percent change of irisin levels). Conclusions. Acute bouts of whole-body vibration exercise are effective in increasing circulating irisin levels but chronic training does not change levels of baseline irisin levels in humans. © 2014 Elsevier Inc. All rights reserved.
1.
Introduction
Irisin, a recently discovered myokine, is suggested to mediate beneficial effects of exercise by inducing browning in adipose tissue [1]. In mice, overexpression of irisin precursor, fibro-
nectin type III domain-containing protein 5 (FNDC5), resulted in mitigation of diet-induced insulin resistance [1]. Irisin has also been shown to be related to various physiological and pathophysiological conditions in mice and humans [2–9]. Therefore, irisin is an attractive target for the treatment of
Abbreviations: FNDC5, fibronectin type III domain-containing protein 5; WBV, whole body vibration exercise; IGF1, insulin-like growth factor 1; IGFBP3, insulin-like growth factor binding protein 3; IL-6, interleukin-6. ☆ Grant Support: Award from the Clinical Science Research and Development Service of the VA Office of Research and Development. ☆☆ Disclosure statement: The authors have nothing to disclose. ⁎ Corresponding author at: Harvard Medical School, Boston, MA 02215, USA. Tel.: +1 617 667 2839; fax: + 1 617 667 2896. E-mail address: [email protected] (J.Y. Huh). 1 The authors have contributed equally to this work. http://dx.doi.org/10.1016/j.metabol.2014.04.001 0026-0495/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
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ME TA BOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
obesity and related metabolic disorders [10,11]. We have previously shown that acute bout of high-intensity exercise can induce irisin secretion in humans [12]. Although prior studies have failed to observe increased irisin levels in response to chronic, habitual exercise [13–15], several others have confirmed the increased circulating irisin in response to acute bouts of exercise, mainly employing treadmill or bicycle exercise [14–17]. It remains to be clarified whether other types of exercise can increase irisin acutely or after a period of training, and whether the increased irisin would be a result of cleavage of extracellular part of FNDC5 and/or release of intracellular irisin into the circulation, for example, by muscle damage. Here, we examine the effect of whole body vibration exercise (WBV) on circulating irisin levels. WBV is a moderateintensity exercise employing low amplitude and low frequency mechanical stimulation to improve muscle capacity [18] shown to be a therapeutic in the treatment of osteoporosis, sarcopenia, and metabolic syndrome [18]. We examined the baseline and change of circulating irisin after an acute bout of WBV at the beginning of the study (week 0) and after 6 weeks of WBV training (week 6).
2.
Methods
2.1.
Exercise
Healthy untrained females (n = 14, age 24.3 ± 2.6 years, BMI 20.4 ± 1.8 kg/m2, mean ± SD) participated in a 6-week program of WBV training with two sessions per week. Each session consisted of seven isometric exercises (Galileo 2000, Novotec, Germany) as follows: squat with the knees flexed at 120°, squat with the knees flexed at 100°, one-leg squat on each leg with the knee flexed at 120°, wide-stance squat with the knees flexed at 100°, elbow flex, triceps dip, and push-up on elbows. Vibration frequency was 16, 19, and 21 Hz (increased during training). Vibration amplitude was 2.5 mm during the first four weeks and 5 mm during the last two weeks. The duration of each training session increased progressively every two weeks from 11 to 18.5 min. Blood samples were collected before and within 5 min after the end of the first and last training session for the preparation of serum. For lactate measurement, 14 μL of blood was immediately hemolyzed with 140 μL of 0.3 mol/L HClO4. All procedures were in accordance with the Code of Ethics of the Aristotle University of Thessaloniki and the Helsinki declaration, and all participants provided written informed consent.
2.2.
Biochemical measurements
Irisin was measured using a previously validated ELISA (#EK067-52, Phoenix Pharmaceuticals, Burlingame, CA) [10,12]. Interleukin-6 (IL-6) was measured with ELISA (R&D Systems, Minneapolis, MN). Lactate was measured according to an enzymic method from Sigma Diagnostics (data sheet of product number L3916, lactic dehydrogenase). Creatine kinase was measured using an automated analyzer (Hitachi cobas c311; Roche Diagnostics, Indianapolis, IN). Insulin, insulin-like growth factor 1 (IGF1), and insulin-like growth factor binding
Tabl e 1a – Basel ine b ioche mical and ho rmo nal parameters before and after a 6-week program of wholebody bilateral vibration training (n = 14).
Irisin (ng/mL) IL-6 (pg/mL) Lactate (mmol/L) Creatine kinase (U/L) Glucose (mmol/L) Insulin (μIU/mL) IGF1 (ng/mL) IGFBP3 (μg/mL) Cortisol (nmol/L) Testosterone (nmol/L) Growth hormone (mU/L) Uric acid (mmol/L)
Week 0
Week 6
P
804.7 ± 333.6 1.4 ± 0.2 1.8 ± 0.7 60.0 ± 27.5 6.0 ± 1.2 9.0 ± 2.2 248.3 ± 61.8 8.4 (4.3–29.3) 228.5 ± 80.8 3.6 ± 1.4 1.7 (0.7–15.4) 0.2 ± 0.1
790.5 ± 339.1 0.9 ± 0.3 1.3 ± 0.5 57.5 ± 25.4 6.5 ± 1.0 5.8 ± 1.3 217.6 ± 55.6 39.5 (4.9–48.8) 348.4 ± 106.6 4.1 ± 1.2 1.2 (0.4–2.0) 0.2 ± 0.1
0.77 0.02 0.56 0.46 0.14 0.20 < 0.01 < 0.01 0.69 0.10 0.51 0.72
protein 3 (IGFBP3) were measured by Immulite 1000 (Siemens Healthcare Diagnostics, Norwood, MA). Glucose and uric acid were measured with kits from Centronic (Wartenberg, Germany). Cortisol, testosterone, and growth hormone were measured by kits from DRG (Marburg, Germany).
2.3.
Statistical analysis
Data are expressed as means ± SD or median (interquartile range). Differences in baseline or percentage change in hormone levels were determined with paired t test or Wilcoxon signed rank test, as appropriate. Changes in irisin levels with acute exercise and training were examined with 2way repeated-measures ANOVA. Spearman’s correlation coefficients were calculated to correlate irisin baseline levels or percentage changes with other parameters. Analyses were performed with the SPSS and P values below 0.05 were considered significant.
Table 1b – Percent change of biochemical and hormonal parameters by acute bout of whole-body bilateral vibration exercise at week 0 and week 6 i.e. after 6 weeks of training (n = 14).
Irisin IL-6 Lactate Creatine kinase Glucose Insulin IGF1 IGFBP3 Cortisol Testosterone Growth hormone Uric acid
Week 0
Week 6
P
9.5 ± 11.9 −0.1 ± 12.4 166.9 ± 103.2 7.8 ± 11.0 3.9 ± 17.1 180.4 ± 72.3 3.3 ± 10.8 6.8 (3.8–26.8) −13.5 ± 12.4 10.0 ± 20.1 176.2 (37.6–1064.5) −10.0 ± 21.2
18.1 ± 9.7 22.7 ± 6.1 292.3 ± 139.3 9.0 ± 12.8 2.0 ± 13.6 28.9 ± 28.1 10.2 ± 8.9 4.2 (2.5–7.7) 2.6 ± 24.6 4.0 ± 25.3 458.3 (86.8–1528.1) −7.9 ± 27.5
0.05 0.03 0.01 0.72 0.65 0.12 0.02 0.18 0.07 0.30 0.22 0.83
Data are means ± SD or median (interquartile range). P values are from paired t test or Wilcoxon signed rank test comparing the relative increases at the two time points. IL-6: interleukin-6, IGF1: insulin-like growth factor 1, IGFBP3: insulin-like growth factor binding protein 3.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
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M ET ABOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
3.
Results
Baseline irisin concentration before and 6 weeks after WBV training To study the effect of long term exercise on basal irisin in humans, circulating irisin was examined at baseline and 6 weeks after WBV training. After 6 weeks of WBV training, circulating levels did not differ from baseline (week 0) levels (Table 1a). IL-6 and IGF1 levels were significantly decreased, whereas IGFBP3 levels were increased after six weeks of WBV training. Change in irisin levels after acute exercise at baseline and 6 weeks after WBV training Studies, including ours, have reported that acute, not chronic, exercise increases circulating irisin levels [14,16]. Blood lactate after a single bout of WBV was approximately 5 mmol/L, indicating a moderate exercise intensity. At week 0, the first bout of WBV significantly increased circulating irisin levels by 9.5% (Table 1b). At the end of 6 weeks of WBV training, although there was no change in the resting irisin level, the degree of irisin increase after the last bout of exercise tended to be higher compared to that at the baseline (18.1%, P = 0.05). IL-6, lactate, and IGF1 exhibited a similar pattern. Creatine kinase levels did not change with exercise, suggesting that irisin upregulation was not due to muscle damage. The results of repeated measures ANOVA showed that irisin levels were significantly increased by acute exercise and there was a marginal interaction of exercise training and acute exercise (P = 0.05). On the other hand, there was no significant interaction between exercise training and acute exercise in terms of IL-6 and lactate levels. Correlation between circulating irisin and other hormonal variables Correlation analysis between baseline circulating irisin and other variables showed that irisin levels had a tendency for positive correlation with IGF1/IGFBP3 (r = 0.35, P = 0.07) ratio and negative correlation with IGFBP3 (r = -0.34, P = 0.08) but did not reach statistical significance (Table 2). Correlation analysis between the exercise-induced change in irisin levels and other variables showed that cortisol levels were positively correlated with irisin levels. Interestingly, baseline testosterone levels were negatively correlated and percent change in testosterone levels was marginally positively correlated with baseline irisin and percent change in irisin levels, repectively.
4.
Discussion
We report herein that an acute bout of WBV significantly increases circulating irisin, whereas WBV training does not alter the baseline irisin in humans. Despite unaltered basal irisin levels, the exercise-induced increase in irisin tended to be higher after 6 weeks of WBV training. This result is of marginal statistical significance but, if confirmed, is in contrast to our previous study where the irisin response to acute running bouts was lost after 8 weeks of sprint training i.e. when the muscle had improved its metabolic status, as evidenced by unaltered intramuscular ATP levels in response to acute sprinting exercise [12]. The different results could
Table 2 – Correlation analysis between irisin and other variables.
IL-6 Lactate Creatine kinase Glucose Insulin IGF1 IGFBP3 IGF1/IGFBP3 Cortisol Testosterone Growth hormone Uric acid
r baseline
P baseline
r% change
P% change
−0.26 0.23 0.10 −0.07 0.18 0.12 −0.34 0.35 0.14 −0.40 ⁎ 0.29 0.06
0.38 0.25 0.62 0.72 0.36 0.54 0.08 0.07 0.48 0.04 0.13 0.76
0.03 0.24 0.22 −0.03 −0.14 0.23 −0.12 0.31 0.41 ⁎ 0.38 −0.07 −0.03
0.92 0.23 0.26 0.89 0.52 0.25 0.55 0.11 0.04 0.06 0.73 0.88
Correlation coefficients and P values were calculated using Spearman correlation analysis. Baseline: correlation between irisin and other variables at baseline (pre-exercise). %Change: correlation between irisin and other variables in their percent change after acute bout of whole-body bilateral vibration exercise. IL-6: interleukin-6, IGF1: insulin-like growth factor 1, IGFBP3: insulinlike growth factor binding protein 3. ⁎ Statistically significant.
have derived from either biological variability (age, gender, etc.) or from differences in exercise type and intensity. WBV is usually low in intensity and thus may not adequately follow the training principle of overload which is vital in terms of the long-term effects of exercise [18,19]. Nevertheless, the increase in percent change of irisin after training imply not only that WBV can effectively turn on the myokine response but also that increased irisin can partly be responsible for the beneficial effects of WBV. Whether there is a relation between chronic exercise and the irisin response needs to be further examined. Interestingly, a recent report has suggested that circulating irisin positively correlates with shivering activity in humans exposed to a cold environment [20]. Shivering generates heat through involuntary muscle contractions, and therefore the irisin increase is likely due to release from muscle as a part of the thermogenic process. WBV, which induces forced vibration of muscle, may mimic shivering and thus thermogenesis, which may explain the significant rise in irisin levels despite the low intensity of the exercise. Overall, WBV training did not affect baseline levels of the hormones measured. However, the IGF1 and testosterone percent increases had a similar pattern with irisin. This is in line with our previous findings in middle-aged women [12], which imply that IGF1 and testosterone may be related to irisin. Of note, the irisin levels in this study were higher compared to those in middle-aged women [10], where the same kit was used. The different levels could be due to interassay variability, but this also raises the possibility that the irisin response to exercise may differ depending on age. Whether elderly subjects with lower irisin levels have more sensitive or impaired responses needs to be elucidated in future studies.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
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ME TA BOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
In conclusion, we show that vibration exercise acutely increases circulating irisin levels. Further study is needed to assess whether this response applies to males also and what the physiological impact of the increased irisin is on metabolism.
Acknowledgments J.Y.H. researched data and wrote the manuscript. V.M., A.S., and A.K. researched data and reviewed the manuscript. C.M. designed the studies, supervised laboratory measurements and reviewed/edited the manuscript.
REFERENCES
[1] Bostrom P, Wu J, Jedrychowski MP, Korde A, Ye L, Lo JC, et al. A pgc1-alpha-dependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature 2012;481 (7382):463–8. [2] Crujeiras AB, Zulet MA, Lopez-Legarrea P, de la Iglesia R, Pardo M, Carreira MC, et al. Association between circulating irisin levels and the promotion of insulin resistance during the weight maintenance period after a dietary weightlowering program in obese patients. Metabolism 2014;63(4):520–31. [3] Moon HS, Dincer F, Mantzoros CS. Pharmacological concentrations of irisin increase cell proliferation without influencing markers of neurite outgrowth and synaptogenesis in mouse h19-7 hippocampal cell lines. Metabolism 2013;62(8):1131–6. [4] Moon HS, Mantzoros CS. Regulation of cell proliferation and malignant potential by irisin in endometrial, colon, thyroid and esophageal cancer cell lines. Metabolism 2014;63 (2):188–93. [5] Park KH, Zaichenko L, Peter P, Davis CR, Crowell JA, Mantzoros CS, et al. Diet quality is associated with circulating c-reactive protein but not irisin levels in humans. Metabolism 2014;63(2):233–41. [6] Polyzos SA, Kountouras J, Anastasilakis AD, Geladari EV, Mantzoros CS. Irisin in patients with nonalcoholic fatty liver disease. Metabolism 2014;63(2):207–17.
[7] Roberts MD, Bayless DS, Company JM, Jenkins NT, Padilla J, Childs TE, et al. Elevated skeletal muscle irisin precursor fndc5 mrna in obese oletf rats. Metabolism 2013;62(8):1052–6. [8] Swick AG, Orena S, O'Connor A. Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass. Metabolism 2013;62(8):1070–3. [9] Tanisawa K, Taniguchi H, Sun X, Ito T, Cao ZB, Sakamoto S, et al. Common single nucleotide polymorphisms in the fndc5 gene are associated with glucose metabolism but do not affect serum irisin levels in Japanese men with low fitness levels. Metabolism 2014;63(4):574–83. [10] Bostrom PA, Fernandez-Real JM, Mantzoros C. Irisin in humans: recent advances and questions for future research. Metabolism 2014;63(2):178–80. [11] Polyzos SA, Kountouras J, Shields K, Mantzoros CS. Irisin: a renaissance in metabolism? Metabolism 2013;62(8):1037–44. [12] Huh JY, Panagiotou G, Mougios V, Brinkoetter M, Vamvini MT, Schneider BE, et al. Fndc5 and irisin in humans: I. Predictors of circulating concentrations in serum and plasma and II. Mrna expression and circulating concentrations in response to weight loss and exercise. Metabolism 2012;61(12):1725–38. [13] Timmons JA, Baar K, Davidsen PK, Atherton PJ. Is irisin a human exercise gene? Nature 2012;488(7413):E9-10 [discussion E-1]. [14] Pekkala S, Wiklund P, Hulmi JJ, et al. Are skeletal muscle fndc5 gene expression and irisin release regulated by exercise and related to health? J Physiol 2013;591(Pt 21):5393–400. [15] Hecksteden A, Wegmann M, Steffen A, et al. Irisin and exercise training in humans — results from a randomized controlled training trial. BMC Med 2013;11(1):235. [16] Norheim F, Langleite TM, Hjorth M, et al. The effects of acute and chronic exercise on pgc-1alpha, irisin and browning of subcutaneous adipose tissue in human. FEBS J 2014;281(3):739–49. [17] Kraemer RR, Shockett P, Webb ND, et al. A transient elevated irisin blood concentration in response to prolonged, moderate aerobic exercise in young men and women. Horm Metab Res 2014;46(2):150–4. [18] Rittweger J. Vibration as an exercise modality: how it may work, and what its potential might be. Eur J Appl Physiol 2010;108(5):877–904. [19] Cochrane DJ. Is vibration exercise a useful addition to a weight management program? Scand J Med Sci Sports 2012;22(6):705–13. [20] Lee P, Linderman JD, Smith S, et al. Irisin and fgf21 are cold-induced endocrine activators of brown fat function in humans. Cell Metab 2014;19(2):302–9.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
Available online at www.sciencedirect.com
Metabolism www.metabolismjournal.com
Brief Report
Irisin in response to acute and chronic whole-body vibration exercise in humans☆,☆☆ Joo Young Huh a,⁎, 1 , Vassilis Mougios b, 1 , Athanasios Skraparlis b , Athanasios Kabasakalis b , Christos S. Mantzoros a a b
Section of Endocrinology, Boston VA Healthcare System, Harvard Medical School, Boston, MA School of Physical Education and Sports Science, Aristotle University of Thessaloniki, Thessaloniki, Greece
A R T I C LE I N FO Article history:
AB S T R A C T Objective. Irisin is a recently identified myokine, suggested to mediate the beneficial
Received 7 March 2014
effects of exercise by inducing browning of white adipocytes and thus increasing energy
Accepted 2 April 2014
expenditure. In humans, the regulation of irisin by exercise is not completely understood. We investigated the effect of acute and chronic whole-body vibration exercise, a moderate-
Keywords:
intensity exercise that resembles shivering, on circulating irisin levels in young
Irisin
healthy subjects. Materials/Methods. Healthy untrained females participated in a 6-week program of whole-
FNDC5 Whole body vibration exercise
body vibration exercise training. Blood was drawn before and immediately after an acute
Myokine
bout of exercise at baseline (week 0) and after 6 weeks of training. Results. The resting irisin levels were not different at baseline (week 0) and after 6 weeks of training. At both 0 and 6 weeks of training, an acute bout of vibration exercise significantly elevated circulating irisin levels by 9.5% and 18.1%, respectively (p = 0.05 for the percent change of irisin levels). Conclusions. Acute bouts of whole-body vibration exercise are effective in increasing circulating irisin levels but chronic training does not change levels of baseline irisin levels in humans. © 2014 Elsevier Inc. All rights reserved.
1.
Introduction
Irisin, a recently discovered myokine, is suggested to mediate beneficial effects of exercise by inducing browning in adipose tissue [1]. In mice, overexpression of irisin precursor, fibro-
nectin type III domain-containing protein 5 (FNDC5), resulted in mitigation of diet-induced insulin resistance [1]. Irisin has also been shown to be related to various physiological and pathophysiological conditions in mice and humans [2–9]. Therefore, irisin is an attractive target for the treatment of
Abbreviations: FNDC5, fibronectin type III domain-containing protein 5; WBV, whole body vibration exercise; IGF1, insulin-like growth factor 1; IGFBP3, insulin-like growth factor binding protein 3; IL-6, interleukin-6. ☆ Grant Support: Award from the Clinical Science Research and Development Service of the VA Office of Research and Development. ☆☆ Disclosure statement: The authors have nothing to disclose. ⁎ Corresponding author at: Harvard Medical School, Boston, MA 02215, USA. Tel.: +1 617 667 2839; fax: + 1 617 667 2896. E-mail address: [email protected] (J.Y. Huh). 1 The authors have contributed equally to this work. http://dx.doi.org/10.1016/j.metabol.2014.04.001 0026-0495/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
2
ME TA BOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
obesity and related metabolic disorders [10,11]. We have previously shown that acute bout of high-intensity exercise can induce irisin secretion in humans [12]. Although prior studies have failed to observe increased irisin levels in response to chronic, habitual exercise [13–15], several others have confirmed the increased circulating irisin in response to acute bouts of exercise, mainly employing treadmill or bicycle exercise [14–17]. It remains to be clarified whether other types of exercise can increase irisin acutely or after a period of training, and whether the increased irisin would be a result of cleavage of extracellular part of FNDC5 and/or release of intracellular irisin into the circulation, for example, by muscle damage. Here, we examine the effect of whole body vibration exercise (WBV) on circulating irisin levels. WBV is a moderateintensity exercise employing low amplitude and low frequency mechanical stimulation to improve muscle capacity [18] shown to be a therapeutic in the treatment of osteoporosis, sarcopenia, and metabolic syndrome [18]. We examined the baseline and change of circulating irisin after an acute bout of WBV at the beginning of the study (week 0) and after 6 weeks of WBV training (week 6).
2.
Methods
2.1.
Exercise
Healthy untrained females (n = 14, age 24.3 ± 2.6 years, BMI 20.4 ± 1.8 kg/m2, mean ± SD) participated in a 6-week program of WBV training with two sessions per week. Each session consisted of seven isometric exercises (Galileo 2000, Novotec, Germany) as follows: squat with the knees flexed at 120°, squat with the knees flexed at 100°, one-leg squat on each leg with the knee flexed at 120°, wide-stance squat with the knees flexed at 100°, elbow flex, triceps dip, and push-up on elbows. Vibration frequency was 16, 19, and 21 Hz (increased during training). Vibration amplitude was 2.5 mm during the first four weeks and 5 mm during the last two weeks. The duration of each training session increased progressively every two weeks from 11 to 18.5 min. Blood samples were collected before and within 5 min after the end of the first and last training session for the preparation of serum. For lactate measurement, 14 μL of blood was immediately hemolyzed with 140 μL of 0.3 mol/L HClO4. All procedures were in accordance with the Code of Ethics of the Aristotle University of Thessaloniki and the Helsinki declaration, and all participants provided written informed consent.
2.2.
Biochemical measurements
Irisin was measured using a previously validated ELISA (#EK067-52, Phoenix Pharmaceuticals, Burlingame, CA) [10,12]. Interleukin-6 (IL-6) was measured with ELISA (R&D Systems, Minneapolis, MN). Lactate was measured according to an enzymic method from Sigma Diagnostics (data sheet of product number L3916, lactic dehydrogenase). Creatine kinase was measured using an automated analyzer (Hitachi cobas c311; Roche Diagnostics, Indianapolis, IN). Insulin, insulin-like growth factor 1 (IGF1), and insulin-like growth factor binding
Tabl e 1a – Basel ine b ioche mical and ho rmo nal parameters before and after a 6-week program of wholebody bilateral vibration training (n = 14).
Irisin (ng/mL) IL-6 (pg/mL) Lactate (mmol/L) Creatine kinase (U/L) Glucose (mmol/L) Insulin (μIU/mL) IGF1 (ng/mL) IGFBP3 (μg/mL) Cortisol (nmol/L) Testosterone (nmol/L) Growth hormone (mU/L) Uric acid (mmol/L)
Week 0
Week 6
P
804.7 ± 333.6 1.4 ± 0.2 1.8 ± 0.7 60.0 ± 27.5 6.0 ± 1.2 9.0 ± 2.2 248.3 ± 61.8 8.4 (4.3–29.3) 228.5 ± 80.8 3.6 ± 1.4 1.7 (0.7–15.4) 0.2 ± 0.1
790.5 ± 339.1 0.9 ± 0.3 1.3 ± 0.5 57.5 ± 25.4 6.5 ± 1.0 5.8 ± 1.3 217.6 ± 55.6 39.5 (4.9–48.8) 348.4 ± 106.6 4.1 ± 1.2 1.2 (0.4–2.0) 0.2 ± 0.1
0.77 0.02 0.56 0.46 0.14 0.20 < 0.01 < 0.01 0.69 0.10 0.51 0.72
protein 3 (IGFBP3) were measured by Immulite 1000 (Siemens Healthcare Diagnostics, Norwood, MA). Glucose and uric acid were measured with kits from Centronic (Wartenberg, Germany). Cortisol, testosterone, and growth hormone were measured by kits from DRG (Marburg, Germany).
2.3.
Statistical analysis
Data are expressed as means ± SD or median (interquartile range). Differences in baseline or percentage change in hormone levels were determined with paired t test or Wilcoxon signed rank test, as appropriate. Changes in irisin levels with acute exercise and training were examined with 2way repeated-measures ANOVA. Spearman’s correlation coefficients were calculated to correlate irisin baseline levels or percentage changes with other parameters. Analyses were performed with the SPSS and P values below 0.05 were considered significant.
Table 1b – Percent change of biochemical and hormonal parameters by acute bout of whole-body bilateral vibration exercise at week 0 and week 6 i.e. after 6 weeks of training (n = 14).
Irisin IL-6 Lactate Creatine kinase Glucose Insulin IGF1 IGFBP3 Cortisol Testosterone Growth hormone Uric acid
Week 0
Week 6
P
9.5 ± 11.9 −0.1 ± 12.4 166.9 ± 103.2 7.8 ± 11.0 3.9 ± 17.1 180.4 ± 72.3 3.3 ± 10.8 6.8 (3.8–26.8) −13.5 ± 12.4 10.0 ± 20.1 176.2 (37.6–1064.5) −10.0 ± 21.2
18.1 ± 9.7 22.7 ± 6.1 292.3 ± 139.3 9.0 ± 12.8 2.0 ± 13.6 28.9 ± 28.1 10.2 ± 8.9 4.2 (2.5–7.7) 2.6 ± 24.6 4.0 ± 25.3 458.3 (86.8–1528.1) −7.9 ± 27.5
0.05 0.03 0.01 0.72 0.65 0.12 0.02 0.18 0.07 0.30 0.22 0.83
Data are means ± SD or median (interquartile range). P values are from paired t test or Wilcoxon signed rank test comparing the relative increases at the two time points. IL-6: interleukin-6, IGF1: insulin-like growth factor 1, IGFBP3: insulin-like growth factor binding protein 3.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
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M ET ABOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
3.
Results
Baseline irisin concentration before and 6 weeks after WBV training To study the effect of long term exercise on basal irisin in humans, circulating irisin was examined at baseline and 6 weeks after WBV training. After 6 weeks of WBV training, circulating levels did not differ from baseline (week 0) levels (Table 1a). IL-6 and IGF1 levels were significantly decreased, whereas IGFBP3 levels were increased after six weeks of WBV training. Change in irisin levels after acute exercise at baseline and 6 weeks after WBV training Studies, including ours, have reported that acute, not chronic, exercise increases circulating irisin levels [14,16]. Blood lactate after a single bout of WBV was approximately 5 mmol/L, indicating a moderate exercise intensity. At week 0, the first bout of WBV significantly increased circulating irisin levels by 9.5% (Table 1b). At the end of 6 weeks of WBV training, although there was no change in the resting irisin level, the degree of irisin increase after the last bout of exercise tended to be higher compared to that at the baseline (18.1%, P = 0.05). IL-6, lactate, and IGF1 exhibited a similar pattern. Creatine kinase levels did not change with exercise, suggesting that irisin upregulation was not due to muscle damage. The results of repeated measures ANOVA showed that irisin levels were significantly increased by acute exercise and there was a marginal interaction of exercise training and acute exercise (P = 0.05). On the other hand, there was no significant interaction between exercise training and acute exercise in terms of IL-6 and lactate levels. Correlation between circulating irisin and other hormonal variables Correlation analysis between baseline circulating irisin and other variables showed that irisin levels had a tendency for positive correlation with IGF1/IGFBP3 (r = 0.35, P = 0.07) ratio and negative correlation with IGFBP3 (r = -0.34, P = 0.08) but did not reach statistical significance (Table 2). Correlation analysis between the exercise-induced change in irisin levels and other variables showed that cortisol levels were positively correlated with irisin levels. Interestingly, baseline testosterone levels were negatively correlated and percent change in testosterone levels was marginally positively correlated with baseline irisin and percent change in irisin levels, repectively.
4.
Discussion
We report herein that an acute bout of WBV significantly increases circulating irisin, whereas WBV training does not alter the baseline irisin in humans. Despite unaltered basal irisin levels, the exercise-induced increase in irisin tended to be higher after 6 weeks of WBV training. This result is of marginal statistical significance but, if confirmed, is in contrast to our previous study where the irisin response to acute running bouts was lost after 8 weeks of sprint training i.e. when the muscle had improved its metabolic status, as evidenced by unaltered intramuscular ATP levels in response to acute sprinting exercise [12]. The different results could
Table 2 – Correlation analysis between irisin and other variables.
IL-6 Lactate Creatine kinase Glucose Insulin IGF1 IGFBP3 IGF1/IGFBP3 Cortisol Testosterone Growth hormone Uric acid
r baseline
P baseline
r% change
P% change
−0.26 0.23 0.10 −0.07 0.18 0.12 −0.34 0.35 0.14 −0.40 ⁎ 0.29 0.06
0.38 0.25 0.62 0.72 0.36 0.54 0.08 0.07 0.48 0.04 0.13 0.76
0.03 0.24 0.22 −0.03 −0.14 0.23 −0.12 0.31 0.41 ⁎ 0.38 −0.07 −0.03
0.92 0.23 0.26 0.89 0.52 0.25 0.55 0.11 0.04 0.06 0.73 0.88
Correlation coefficients and P values were calculated using Spearman correlation analysis. Baseline: correlation between irisin and other variables at baseline (pre-exercise). %Change: correlation between irisin and other variables in their percent change after acute bout of whole-body bilateral vibration exercise. IL-6: interleukin-6, IGF1: insulin-like growth factor 1, IGFBP3: insulinlike growth factor binding protein 3. ⁎ Statistically significant.
have derived from either biological variability (age, gender, etc.) or from differences in exercise type and intensity. WBV is usually low in intensity and thus may not adequately follow the training principle of overload which is vital in terms of the long-term effects of exercise [18,19]. Nevertheless, the increase in percent change of irisin after training imply not only that WBV can effectively turn on the myokine response but also that increased irisin can partly be responsible for the beneficial effects of WBV. Whether there is a relation between chronic exercise and the irisin response needs to be further examined. Interestingly, a recent report has suggested that circulating irisin positively correlates with shivering activity in humans exposed to a cold environment [20]. Shivering generates heat through involuntary muscle contractions, and therefore the irisin increase is likely due to release from muscle as a part of the thermogenic process. WBV, which induces forced vibration of muscle, may mimic shivering and thus thermogenesis, which may explain the significant rise in irisin levels despite the low intensity of the exercise. Overall, WBV training did not affect baseline levels of the hormones measured. However, the IGF1 and testosterone percent increases had a similar pattern with irisin. This is in line with our previous findings in middle-aged women [12], which imply that IGF1 and testosterone may be related to irisin. Of note, the irisin levels in this study were higher compared to those in middle-aged women [10], where the same kit was used. The different levels could be due to interassay variability, but this also raises the possibility that the irisin response to exercise may differ depending on age. Whether elderly subjects with lower irisin levels have more sensitive or impaired responses needs to be elucidated in future studies.
Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001
4
ME TA BOL I SM CL IN I CA L A N D E XP E RI ME N TAL XX ( 2 0 14 ) XXX–X XX
In conclusion, we show that vibration exercise acutely increases circulating irisin levels. Further study is needed to assess whether this response applies to males also and what the physiological impact of the increased irisin is on metabolism.
Acknowledgments J.Y.H. researched data and wrote the manuscript. V.M., A.S., and A.K. researched data and reviewed the manuscript. C.M. designed the studies, supervised laboratory measurements and reviewed/edited the manuscript.
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Please cite this article as: Huh JY, et al, Irisin in response to acute and chronic whole-body vibration exercise in humans, Metabolism (2014), http://dx.doi.org/10.1016/j.metabol.2014.04.001