Is It Necessary to Add Aprotinin Before Measuring The Level of Irisin in Serum and Plasma Samples ?

Irisin is a myokine with 112 aminoacids and its level is regulated by peroxisome proliferator-activated receptor-γ coactivator1-α (PGC1-α). It is released into blood circulation from skeletal muscle tissue after a proteolytic cleavage of extracellular domain of Fibronectin type III domain-containing protein 5 (FNDC5), a type I integral membrain protein. Aprotinin is a polivalent serin protease inhibitor. It is added to sample solutions such as serum, plasma or tissue extracts in order to inhibit serine proteases found in the sample medium. So, degradation of the proteins to be measured can be prevented. These study has been made to get a preliminary information in order to see if any irisin loss could be seen in these samples which are frequently needed to be kept at -80°C for a long time. For this purpose, blood samples have been taken from 10 men and 10 women volunteers with ages between 25-40 and aprotinin has been added to the plasma and the serum samples and have been kept at -80°C for 3 months. At the end of 3 months, irisin levels of these samples with aprotinin and without aprotinin have been determined by ELISA. Statistical analysis of the results has shown an insignificant differance between the plasma samples with or without aprotinin (p=0.525) and a significant decrease between the serum samples with and without aprotinin (p=0.009). In conclusion, with the results of this study, no net decision could have been achieved to add aprotinin to the samples for irisin determination with ELISA in plasma and serum kept at -80°C for about 3 months.