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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 64  |  Issue : 3  |  Page : 129-134

Exercise in the cold causes greater irisin release but may not be enough for adropin


1 Faculty of Sport Sciences, Erzurum Technical University, Erzurum, Turkey
2 Department of Medical Biochemistry, Faculty of Medicine, University of Health Sciences, Erzurum, Turkey
3 Department of Biochemistry, Erzurum Regional Research and Training Hospital, Erzurum, Turkey

Date of Submission03-Jan-2021
Date of Decision28-Mar-2021
Date of Acceptance03-May-2021
Date of Web Publication14-Jun-2021

Correspondence Address:
Mr. Cebrail Gencoglu
Faculty of Sport Sciences, Erzurum Technical University, Erzurum
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/cjp.cjp_2_21

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  Abstract 


When irisin and adropin were discovered, it was popularly hoped that they would become therapies for metabolic disorders that threaten global health. However, contradictory results have been reported in the subsequent period. Irisin, induced by exercise or cold exposure, is believed to be a myokine that causes the browning of adipose tissue thus increasing energy expenditure. Adropin is thought to be beneficial for health by regulating blood flow, capillary density, and playing an active role in glucose and insulin homeostasis. However, there were no experimental studies investigating the simultaneous effect of exercise and cold exposure in humans. The purpose of this study was to investigate irisin and adropin responses in young healthy individuals performing aerobic exercise in different environmental temperatures. Twenty-seven young, healthy individuals participated in this study. Participants performed 40 min of aerobic running exercise in environmental temperatures of 0°C, 12°C, and 24°C. Venous blood samples were taken pre- and post-exercise. Irisin and adropin levels were analyzed using an enzyme-linked immunosorbent assay. The principal findings showed that while serum irisin concentrations significantly increased after aerobic exercise was performed at an environmental temperature of 0°C, there was no significant difference between pre- and post-exercise recordings for physical activity performed at 12°C and 24°C. Adropin concentrations, however, remained unchanged between pre- and post-exercise at 0°C, 12°C, and 24°C. Interestingly, the exercise at 0°C caused an increase in adropin (12.5%), but this amount was not enough to be a statistically significant result. The findings of this study suggest that aerobic exercise in a cold environment causes greater irisin release. However, the combined effect of exercise and cold exposure may not be enough to statistically increase adropin level.

Keywords: Adipokine, cold exposure, energy expenditure, environmental temperature, myokine


How to cite this article:
Ulupinar S, Ozbay S, Gencoglu C, Altinkaynak K, Sebin E, Oymak B. Exercise in the cold causes greater irisin release but may not be enough for adropin. Chin J Physiol 2021;64:129-34

How to cite this URL:
Ulupinar S, Ozbay S, Gencoglu C, Altinkaynak K, Sebin E, Oymak B. Exercise in the cold causes greater irisin release but may not be enough for adropin. Chin J Physiol [serial online] 2021 [cited 2021 Jul 28];64:129-34. Available from: https://www.cjphysiology.org/text.asp?2021/64/3/129/318373




  Introduction Top


Studies on metabolic disorders have increased exponentially, and the investigations that have been conducted have attempted to develop strategies promoting energy expenditure through the remodeling of the molecular mechanisms of the skeletal muscles.[1],[2],[3] Exercise and cold exposure are well-known metabolic stimulants that have proven their effectiveness in preventing many obesity-related health problems.[4],[5],[6],[7] With the discovery of exercise-induced hormones and adipokines, recent investigations have indicated the positive effects of adipose modulation and energy metabolism in addition to past evidence showing that exercise improves muscle strength and endurance.[8],[9],[10] Furthermore, evidence revealing the effect of cold exposure on these mediators has created an infrastructure for combining exercise and cold stress factors under experimental conditions.[5],[11],[12],[13]

Emerging findings have suggested that irisin can be effective in brown adipose tissue (BAT) activation.[14] Irisin, a peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α) dependent myokine, is produced by proteolytic cleavage of the fibronectin type III domain-containing protein 5, and it has been shown that irisin concentration increases in blood circulation in response to aerobic exercise.[9],[15],[16],[17] Skeletal muscles are considered to be the main source of irisin secretion, both at rest and during exercise.[18] Studies have reported that the concentration of fatty acids is affected by exercise and cold, and irisin shows similar responses to these two stress events.[5],[6],[19],[20] However, while an acute and transient increase in irisin levels following aerobic exercise appears to be the most valid outcome, there are still some issues that remain unclear.

Kumar et al. first isolated adropin in 2008 and suggested that it could play an important role in lipid metabolism.[8],[21] Shortly after the discovery, adropin was reported as a peptide hormone playing an active role in preventing adiposity, insulin resistance, and impaired glucose tolerance. It is thus considered to serve as a regulator in metabolic homeostasis.[8],[21],[22] Previous studies indicated that elevated adropin concentration in circulation reduced the insulin resistance and glucose intolerance that occurs in response to metabolic stress.[8],[22],[23] Celik et al. found that adropin levels were significantly lower in patients with cardiac syndrome x[24] and St-Onge indicated that low serum adropin concentration was associated with coronary atherosclerosis.[25] Fujie et al.[26] suggested that aerobic exercise intervention significantly elevated serum adropin levels and adropin may improve arterial stiffness. After these promising findings, interest in how adropin can be increased and used for therapeutic purposes has stimulated further scientific study.[27],[28]

Although the initial researches following the discovery of irisin and adropin was presented as a promising approach to the prevention of health-threatening major diseases such as obesity and type 2 diabetes, some mechanisms associated with the hormones are still obscure. Moreover, many contradictory results, especially regarding irisin, have been observed in subsequent studies.[9],[16],[29],[30],[31],[32] Further, although it has been reported that there is 100% identity between human and murine irisin and adropin amino acid sequences, recent studies have emphasized that the transferability of data from rats to human should be questioned.[16],[30],[33] Hence, it is clear that experimental research involving humans is required to reveal the effects of exercise and cold exposure on irisin and adropin. We hypothesized that if exercise and cold exposure factors were applied simultaneously, the responses of irisin and adropin hormones may be greater. Therefore, this study aimed to investigate the serum irisin and adropin responses to aerobic exercises performed at different environmental temperatures in humans.


  Materials and Methods Top


Subjects

Twenty-seven healthy, young individuals (age = 20.6 ± 1.8 years; height = 174.1 ± 8.5 cm; weight = 64.4 ± 8.6 kg; n = 27; 10 females and 17 males) participated in this trial. The inclusion criteria were as follows: 18–25 years of age, no chronic medical condition requiring regular prescription medication. The exclusion criteria were as follows: cold sensitivity, being a professional athlete, undertaking regular aerobic exercise, being in a special diet program, and taking any supplement. This study was conducted according to the Declaration of Helsinki. All participants were informed about possible risks related to experimental procedures and written informed consent was obtained prior to participation in the study. The research protocol was approved by the Ethics Committee of Erzurum Research Training Hospital (Erzurum BEAH KAEK 37732058-514.10, 2019/01-12).

Experimental protocols

Participants performed 40 min of aerobic running exercises at three different temperatures (0°C, 12°C, and 24°C). Each session was separated by 48 h. Blood samples were collected at normal room temperature (22°C) and participants were not allowed to wait before exercising in cold environmental temperatures. The participants started with 5 min of warming and were asked to reach a 70% maximum heart rate (HRmax). Upon reaching their target heart rate, participants were asked to maintain it for 40 min.[34] The intensity of running was calculated according to the formula proposed by Karvonen, Kentala, and Mustala:[35]

Target HRzone = ([HRmax − HR resting] × % intensity) + HR resting

To control running speed during the exercises, HR was measured simultaneously by the telemetric HR monitor (S610i, Polar Electro Oy, Kempele, Finland).[36] Participants were asked to perform the exercises after 3–4 h fasting, maintain their normal daily meal routines, and not use any stimulant or supplement during the study period. Each participant undertook the exercises between 16:00 and 17:00. Exercises were performed at an indoor sports facility. Appropriate temperatures were set before exercising commenced, using the air conditioning system. Participants dressed as they wished at 12°C and 24°C. However, at 0°C, they wore three layers of clothing: an inner layer (in contact with the skin) that did not readily absorb moisture but wicked it to other layers (lightweight polyester or polypropylene), a middle layer that provided primary insulation (polyester fleece or wool), and an outer layer that maximized moisture transfer to the environment.[37]

Biochemical measures

To measure irisin and adropin concentrations, 10 mL samples of venous blood were taken from the antecubital vein in aprotinin-containing tubes pre- and post-exercise. The serum was separated immediately by centrifuging at 4000 rpm at 4°C for 5 min. The samples were then frozen and stored at −80°C until each participant completed all exercises. Irisin and adropin concentrations were measured using a commercially available enzyme immunoassay kit (Human irisin enzyme-linked immunosorbent assay [ELISA] kit 201-12-5328, SunRed, China; Human adropin ELISA kit 201-12-2015, SunRed, China). Intra- and inter-assay coefficients of variation of 10.0% and 12.0%, respectively, were recorded. The irisin and adropin levels in the samples were analyzed in a double-blind fashion.

Statistical analysis

Statistical analysis was performed using the statistical software (IBM SPSS Statistics for Windows, Version 21.0, Armonk, NY, USA). All data were presented as means ± standard deviation (SD). Repeated measures two-way analysis of variance (ANOVA) was the method chosen to express the time (pre- and post-exercise) and temperature interactions (0°C, 12°C, and 24°C). Repeated measures one-way ANOVA was used to determine the magnitude of irisin and adropin increases at the different environmental temperatures. The assumptions of sphericity were assessed by Mauchly's test. Whenever an assumption was violated, corrections were made. Specifically, if the epsilon (ε) value was < 0.75, Greenhouse–Geisser correction was applied. If ε was > 0.75, Huynh–Feldt correction was applied to the degree of freedom. A value of P < 0.05 was accepted as statistically significant. In addition, effect sizes for the changes of pre- and post-exercise were calculated using Cohen's d[38] and classified according to Hopkins.[39]


  Results Top


Serum irisin concentrations were measured before and after the aerobic exercises performed at different environmental temperatures. While the change in irisin level after exercise at 0°C had a small effect size, the effect of exercises performed at 12°C and 24°C was not statistically significant and had trivial effect sizes [Table 1].
Table 1: Irisin concentrations (ng/mL) pre- and post-exercises (n=27)

Click here to view


Two-way ANOVA showed that a significant interaction between temperature (factor 1: 0°C, 12°C, and 24°C) and aerobic exercise (factor 2: baseline and post-exercise) occurred. There was a significant difference in serum irisin levels between pre- and post-exercise at 0°C, whereas there was no significant difference at 12°C and 24°C [[Figure 1], left panel]. Further, one-way ANOVA showed a significant difference in irisin elevation from baseline. Pairwise comparisons indicated that irisin increase at 0°C was greater than at 24°C (P = 0.007) but there was no significant difference between 0°C and 12°C (P = 0.153).
Figure 1: Graphical display of irisin concentrations pre- and post-exercises (left panel) and net change from baseline (right panel). *Significantly different from pre-exercises value; Significant interaction between temperature (0°C, 12°C, and 24°C) and exercise (pre- and post-); #Significantly different from 24°C. np2: partial eta squared, line indicates the median, and boxes indicate the interquartile range.

Click here to view


There was no significant difference between before and after aerobic exercise serum adropin levels at 0°C, 12°C, and 24°C [Table 2], and no interaction between temperature and exercise was recorded [Figure 2]. The adropin increase (12.5%) at 0°C did not show a statistically significant result.
Figure 2: Graphical display of adropin concentrations pre- and post-exercises (left panel) and net change from baseline (right panel). Np2: partial eta squared, line indicates the median, and boxes indicate the interquartile range.

Click here to view
Table 2: Adropin concentrations (ng/mL) pre- and post-exercises (n=27)

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  Discussion Top


This is the first study to investigate the combined effect of aerobic exercise and cold exposure on serum irisin and adropin levels in humans. Consistent with our experimental hypotheses, the main finding indicated that serum irisin concentration significantly increased after aerobic exercise performed at an environmental temperature of 0°C. However, no significant difference between pre- and post-exercise at 12°C and 24°C was observed. Contrary to our hypothesis, aerobic exercise did not cause any statistically significant change in adropin responses at any temperature. Although the exercise at 0°C caused an increase in adropin at the rate of 12.5%, this increase was not enough to be statistically significant.

Irisin, in recent years, has been reported to play a role in BAT thermogenic activity and has gained attention as an aerobic exercise hormone.[5],[33],[40] What has made irisin so popular in such a short time is the fact that increases in serum irisin level can promote energy expenditure without changes in food intake and/or activity level. Irisin is thought to serve as the first messenger in the process that increases thermogenic capacity in adipose tissue.[41] A wealth of findings has revealed that irisin concentration increases postexercise in animal models. Brenmoehl et al.[29] reported an increase in irisin level immediately after treadmill exercise in mice. In addition, some studies demonstrated that elevated irisin concentration decreased body weight and improved glucose homeostasis in mice.[42],[43] However, some contradictory results indicated that regular exercise performed by humans and rats did not cause a change in irisin levels.[44],[45] Thus, irisin has appeared as an aerobic exercise hormone, at least in mice, but it is clear that further investigation is needed to prove that it has a beneficial effect in humans.

Following the discovery of irisin, research has shown it to be a source of hope in the treatment of metabolic disorders that threaten global health. Many studies have been conducted on humans. Kim et al.[46] found a positive relationship between serum irisin concentration and muscle mass. Kim et al.[46] also noted a negative relationship between serum irisin concentration and fat mass. Anastasilakis et al.[47] showed that irisin levels increased following 30 min of aerobic exercise. Anastasilakis et al.[47] performed a similar experimental design to our study in terms of aerobic exercise duration (30 min vs. 40 min) and age group (20.0 ± 0.1 vs. 20.6 ± 1.8 years) and showed an increase in irisin concentrations by 4.4%. In our study, the increase in the irisin concentrations at 12°C and 24°C was <3%. However, the exercise performed at 0°C caused an increase of 19%. Anastasilakis et al.[47] reported a partial increase in the irisin level after aerobic exercise in young healthy individuals. Our study, however, also showed that this increase may be greater when exercise is performed in a cold environment.

Qiu et al.[40] reported that serum irisin levels were significantly increased in young, healthy individuals (both trained and untrained subjects) following 50 min of aerobic cycling exercise. When graded, exhaustive exercises in both running and cycling modes were applied; serum irisin levels also significantly increased in both cases. The authors showed that irisin responses did not differ according to training status or exercise mechanics (running or cycling). Unfortunately, however, like many studies in the literature, the mentioned study did not test the effect of cold on irisin. Our study may help to fill this gap in the literature.

Kraemer et al.[15] investigated the effect of prolonged exercise (90 min of treadmill exercise) on irisin concentrations in young people. They revealed that by the 54th min of a 90-min treadmill exercise, irisin concentrations significantly increased in both men and women. However, Kraemer et al.[15] also indicated that both immediately after 90 min of exercise and 20 min after the cessation of exercise, irisin concentrations did not elevate. Thus, the authors indicated that while aerobic exercise increased irisin level, irisin did not continue to rise when exercise duration was excessively extended. Considering the above-mentioned studies,[15],[40],[47] it is clear that factors such as training status, gender, movement mechanics, or excessive prolongation of exercise are not effective in raising irisin levels higher than the irisin elevation caused by aerobic exercise. Contrary to these studies, our study suggests that when aerobic exercise and cold exposure are combined, increases in irisin can be gained.

There are numerous studies in the literature based on the knowledge that irisin is induced by exercise. However, there is still limited information concerning the combination of cold and exercise. McMillan and White[14] reported that acute or repeated mild cold exposures of 17°C–19°C improved BAT activity in humans, and they pointed out that this was a remarkable method for increasing metabolic rate. Lee et al.[5] indicated that irisin release increased significantly in both humans and rodents due to cold-exposure. Further, they measured the resting energy expenditure of 10 participants at 27, 19, 16, 14, and 12°C, and found 1.488, 1.731, 1.926, 2.100, and 2.235 (kcal/day), respectively. The authors showed that cold environmental temperatures cause greater resting energy expenditure. Coker et al.[48] measured the serum irisin concentrations of eight healthy adults during a Yukon Arctic Ultra event. The event, considered to be the longest and coldest ultra-endurance race in the world, covered a distance of 430 miles with temperatures ranging from − 45°C to − 8°C. Coker et al.[48] indicated that the cold exposure and extreme physical exertion promoted significant increases in serum irisin levels among participants. Thus, given the findings of the aforementioned studies, aerobic exercise does appear to contribute to increased irisin levels when performed in cold environmental temperatures. The present study supports them with similar results.

Adropin, another peptide hormone, is thought to be related to exercise and effective in preventing metabolic disorders. Glück et al.[49] suggested that the production of irisin and adropin peptides causes a reduction in body mass, in turn affecting energy metabolism. Ganesh Kumar et al.[22] showed that adropin levels were negatively correlated with age and body mass index, and age-adjusted adropin levels were higher in males than females. Fujie et al.[50] indicated that aging reduces serum levels of adropin, whereas aerobic exercise significantly increases adropin in mice. Although these studies provide a scientific basis for the positive effects of adropin, experimental designs examining, in particular, the factors that may cause adropin increase in humans have been limited.

Alizadeh et al.[23] investigated the effect of 30 min of aerobic exercise on adropin, glucose, and insulin resistance in 24 overweight women. While it was found that aerobic exercise was effective against insulin resistance, it was not effective concerning glucose and adropin. Similarly, another study[11] showed that exercise performed under both indoor (21°C to 25°C) and outdoor (−5°C to 5°C) conditions did not have a significant effect on adropin responses. In fact, in our study, although the exercise performed at 0°C caused an increase of 12.5%, this difference was not statistically significant. In support of these studies, our investigation showed that aerobic exercise did not lead to a significant, acute change in adropin levels. It is possible that a regular physical activity is required to observe the effect of aerobic exercise on adropin, while the effect on irisin is acute and transient. It is clear that many studies involving different designs are needed to elucidate the unclear issues surrounding these peptide hormones.

We hypothesized that adropin responses to all exercise sessions would increase. Furthermore, we conjectured that adropin response to exercise performed at an environmental temperature of 0°C would be greater than for that performed at 12°C and 24°C. Analysis showed that the effects of exercise and cold exposure (0°C) increased adropin concentrations by 12.5%, but this result was not statistically significant. However, it is known that statistical significance value is extremely sensitive to sample size and standard error.[51],[52] The large SDs of the adropin values in our study may have been responsible for preventing the results from reaching the significance threshold. In addition, the amount of increase (12.5%) can be considered clinically important and there is a high potential for reaching a significant result if the sample size is increased in future studies. This study has provided a basic foundation for clinical evaluation and for deciding whether the research is reproducible. Moreover, while the number of research trials examining the combinations of cold exposure and exercise on adropin is still very limited, we suggest that this study can contribute to the gap in the relevant literature and that future research with a similar design should be conducted.

The fact that our study did not include 40 min of cold exposure without exercise could be considered a limitation of the research. Forty minutes of cold exposure without exercise would have provided the opportunity to compare only the exercise effect, only the cold exposure, and then the combined effect of these two factors on human physiology. We felt, however, that 40 min of cold exposure without exercise had no practical validity. As the major requirement is to exercise, (because exercise has numerous proven benefits), our main purpose was to examine whether irisin and adropin responses increase when physical activity is performed in a cold environment.


  Conclusion Top


The present study indicated that aerobic exercise or cold exposure has no acute effect on adropin. Conversely, however, this research suggested that the combined effect of aerobic exercise and cold exposure (0°C) increased the irisin level in healthy, young participants. Nevertheless, it was observed that aerobic exercises performed at a mild (12°C) or normal temperature (24°C) may not be sufficient to increase irisin concentrations.

Undoubtedly, further studies are needed to confirm the promising results of irisin and adropin. It is critical to determine whether the beneficial effects of irisin and adropin on mice also apply to humans. Although cold exposure is reported to be another inductor of irisin, the literature on human trials is still lacking. Consequently, future studies are required to not only understand the optimal environmental temperature and exercise components that increase irisin and adropin levels but also to investigate the physiological mechanisms related to the effects of exercise and cold exposure.

Acknowledgment

The authors would like to thank the participants for their enthusiastic participation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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