Introduction
Adropin is a new hormone which improves lipid metabolism and plays an important role in the vascular protection. Adropin is an amino acid peptide that is present in endothelial cells, where it increases nitric oxide by upregulating endothelial nitric oxide (NO) synthase and vascular endothelial growth factor receptor 2 as well as protein kinase B and extracellular signal-regulated kinases 1/2 14, 17. The current study aims to determine the effect of high-intensity interval training (HIIT) on adropin and NO metabolites in overweight men.  
Materials and Methods
This is a quasi-experimental study with a pre-test/post-test design. Participants were 32 overweight men (Mean±SD age: 30.5±3.07 years, BMI: 27.93±4.2 kg/m2). They were randomly divided into two groups; HIIT (n=16) and control (n=16). The HIIT group performed 8 weeks of HIIT (3 days per week) at 20 sessions of 30 s with a 13-scond interval between each session. Body composition assessments were performed using a bioelectrical impedance analyzer. Fasting blood samples were taken from the median cubital vein of all participants before and after the training. Blood samples were then centrifuged at 3000×g for 7 minutes and maintained at -70°C. Then, blood samples were thawed at room temperature and analyzed using a microplate reader and ELISA kits. The data analysis was done by repeated-measures ANOVA. The significance level was set at P<0.05. 
Results
The body fat percentage was significantly reduced in the HIIT group compared to the pre-test results (P< 0.05). There was a significant increase in peak oxygen consumption in the HIIT group compared to the control group and pre-test values (P<0.05). There was a significant difference in Adropin level between HIIT and control groups (0.88±0.256; 95% CI: 0.26-1.5 ng/mL). There was also a significant difference in NO metabolites between the two groups (7.5±3.03; 95% CI: 0.85-14.15 ng/mL). There was a positive relationship between the levels of Adropin and NO metabolites in overweight men (r=0.498, P=0.0001).  
Discussion
Among the main vascular endothelial dysfunction-related mechanisms, reduced NO bioavailability has a main role in the endothelium vasodilation decrease which associated with many pathologies such as hypertension, diabetes mellitus, atherosclerosis, and heart failure. Our findings showed that body fat percentage and lipid profile were improved following HIIT in overweight men. It seems that HIIT can attenuate cardiovascular diseases by increasing Adropin and NO levels. In addition, it may improve cardiovascular fitness (VO2max) and body composition of men with overweight.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the ethical committee of the University of Tehran (Code: IR.UT.REC.1395007). All procedures were in accordance with the guidelines outlined in the declaration of Helsinki. 

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
The authors contributed equally to preparing this article.

Conflicts of interest
The authors declare no conflict of interest.

Acknowledgements
The authors would like to thank all participants for their cooperation. 


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