To Örebro University

Introduction: Ghrelin is a growth hormone-releasing acylated peptide stimulating the appetite, mainly produced in the stomach, and with an important role in pubertal development (1). Two ghrelin forms have been described, acylated (AG) and desacylated (DAG), but it is debated whether DAG is an active hormone or a degradation product of AG (2). Our aim was to evaluate the effects of adding the protease inhibitor 4-(2-aminoethyl) benzenesufonyl fluoride hydrochloride (AEBSF) to sampling tubes and acidification of plasma on levels of AG and DAG in girls with suspected central precocious puberty (CPP).

Methods: 13 girls aged 6.6 to 10.1 years with suspected CPP undergoing a gonadotropin-releasing hormone stimulation test during 2015-2017 at the Departments of Paediatrics, at Örebro or Uppsala University Hospital were included. Blood samples were collected at 0 min in precooled EDTA tubes with or without AEBSF at a final concentration of 2mg/ml. After cold centrifugation, HCl at a final concentration of 50 μmol/l, was added to 50% of the plasma tubes containing AEBSF. The AG and DAG concentrations were measured by ELISA kits. Comparison was performed using one-way ANOVA for repeated measurements.

Results: The mean plasma AG levels were significantly higher after the addition of AEBSF only (650.9 +/- 257.1 pg/ml) or AEBSF+HCl (681.2 +/- 299 pg/ml) compared to the concentrations without additives (247.6 +/- 123.4 pg/ml, p<0.01 for both comparisons). There was no significant difference between the AG levels after AEBSF and AEBSF+HCl addition. The plasma levels of DAG were significantly lower after the addition of AEBSF+HCl (69.3 +/- 30.6 pg/ml) and even further lowered after the addition of AEBSF only (56.3+/- 30.9 pg/ml) compared to the concentrations of DAG in tubes without any additives (149.9 +/- 73.7 pg/ml, p < 0.01 for both comparisons).

Discussion: Due to the unstable nature of AG, special procedures are required for accurate measurement of its plasma levels in children, including the use of a protease inhibitor like AEBSF. However, DAG was still measurable indicating that it may not only be a degradation product of AG. 1. Kojima M, Kangawa K. Ghrelin: structure and function. Physiol Rev. 2005;85(2):495-522.2. Blatnik M, Soderstrom CI, Dysinger M, Fraser SA. Prandial ghrelin attenuation provides evidence that des-acyl ghrelin may be an artifact of sample handling in human plasma. Bio-analysis. 2012;4(20):2447-55.