Fasting Insulin and Alanine Amino Transferase, but not FGF21, Were Independent Parameters Related with Irisin Increment after Intensive Aerobic Exercising

Abstract

Background: Irisin is a protein cleaved from fibronectin type III domain-containing protein 5 and has been implicated in the beneficial effects of exercise. However, it is unknown which factors contribute to irisin increment after intensive exercising in humans. This study aimed to assess independent factors related with serum irisin after 2 weeks of supervised physical activity in young sedentary healthy women. Design and Methods: We developed a comparative, interventional, longitudinal, and prospective study at a third-level specialty health center. Between March 2010 and August 2011, 82 sedentary young adult women, without chronic diseases or regular medical treatments, were recruited. A total of 38 women fulfilled selection criteria, and irisin concentrations were quantified before and after the intervention. Independent factors related with irisin increment were evaluated according to mild to moderate and vigorous intensity of physical activity. A supervised treadmill exercise test following the Bruce's protocol was conducted from Monday to Friday during 2 weeks. In addition, anthropometric measurements were taken, and fibroblast growth factor 21 (FGF21), glucose, insulin, and liver transaminases were measured. Results: Intensity of exercising was directly related to irisin (p = 0.02) and FGF21 (p = 0.01) serum levels. However, an independent and significant relationship between FGF21 and irisin was not confirmed. A novel association was found between alanine aminotransferase (ALT) and irisin, showing a positive and significant correlation (r = 0.37, p = 0.02). The association was particularly strong with higher intensity of aerobic exercising (r = 0.64, p = 0.01). Linear regression model adjusted for glucose and body mass index confirmed an independent association between ALT and irisin and also between insulin and irisin (adjusted R² = 0.12, p = 0.04). Such association increased after grouping in moderate to vigorous physical activity intensity (adjusted R² = 0.46, F = 4.7, p = 0.03). Conclusions: Serum irisin and FGF21 levels significantly increased after 2 weeks of supervised physical activity. However, only fasting insulin and ALT, but not FGF21, were independent parameters explaining irisin increment, mainly after moderate to vigorous exercising.

The Role of Irisin in Exercise-Mediated Bone Health

“…Some resistance trainings during early life improve BMD and bone structural properties, and have a direct preventive effect on bone diseases in later life ( Gomez-Bruton et al, 2017 ), and irisin also plays a key role in this process ( Elizondo-Montemayor et al, 2018 ). Although different types of exercise training have conflicting results on irisin, most studies suggest that high-moderate intensity ( Tsuchiya et al, 2014 ; Rashti et al, 2019 ; Torre-Saldana et al, 2019 ) and resistance exercises ( Nygaard et al, 2015 ; Tsuchiya et al, 2015 ; Kim et al, 2016 ) lead to more significantly enhanced in irisin level, and improve bone loss in patients with osteoporosis ( Watson et al, 2019 ). This means that irisin has become a new target in promoting bone health, and the possibility of treating some bone diseases.…”

Long-Term Effect of Exercise on Irisin Blood Levels—Systematic Review and Meta-Analysis

“…Several kinds of physical exercise increased irisin blood levels among healthy people as well. High-intensity interval training increased irisin in young, healthy males [41,60] and healthy young adults [43], military aerobic training [48] increased irisin blood levels in young, healthy males and one study with a single group design found a significant increase in irisin in young females after treadmill exercise [37]. On the other hand, cycle ergometer-sprint training, consecutive training [77] as well as indoor running [64] led to a decrease of irisin blood levels in young, healthy males, and the same effect was found after basketball training in healthy children [39] or after taekwondo training in obese children [70].…”

Exercise-Induced Fibroblast Growth Factor-21: A Systematic Review and Meta-Analysis

“…Of the 72 studies, 24 were excluded after title and abstract review, and the original text of 48 studies was reviewed. After screening the studies according to the inclusion criteria, 38 studies were excluded, and finally, 10 studies were selected ( Figure 1 ) [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”

“…The quality of four studies [ 29 , 30 , 33 , 35 ] was assessed using the RoB tool, and the results were as follows: random sequence generation (low, 1; uncertain, 2; high, 1), allocation concealment (low, 1; uncertain, 3), blinding of participants and personnel (low, 1; uncertain, 3), blinding outcome assessment (low, 1; uncertain, 3), incomplete outcome data (low, 3; high, 1), selective reporting (low, 4), and other biases (low, 1; uncertain, 2; high, 1) ( Figure 2 ). Four studies [ 26 , 27 , 28 , 31 , 32 , 34 ] were assessed by the RoBANS, and the results were as follows: selection of participants (low, 4; uncertain, 1; high, 1), confounding variables (low, 1; uncertain, 4; high, 1), measurement of exposure (low, 5; uncertain, 1), blinding of outcome assessments (low, 4; uncertain, 2), incomplete outcome data (low, 5; uncertain, 1), and selective outcome reporting (low, 5; uncertain, 1) ( Table 1 ).…”

“… Forest plot of within-group comparisons of exercise-induced changes in fibroblast growth factor-21 levels [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Keihanian et al, 2019(a) [ 29 ]—resistance exercise; Keihanian et al, 2019(b) [ 29 ]—aerobic exercise; Shabkhiz et al, 2021(a) [ 30 ]—participants without type 2 diabetes; Shabkhiz et al, 2021(b) [ 30 ]—participants with type 2 diabetes.…”