SAT-255 Evaluation of Uncoupling Protein 1 and Fibroblast Growth Factor 21 in Obese Adolescents

Abstract: Brown adipose tissue (BAT) has recently gained scientific interest for its functional capacity to burn excess energy. Fibroblast growth factor 21 (FGF 21) targets BAT where it stimulates mitochondrial inner membrane protein Uncoupling Protein 1 (UCP 1) gene expression, and thus promotes glucose oxidation and energy expenditure. Circulating FGF 21 levels, however, were found to be elevated in obesity in some adult studies. There are only a few studies in children and the results are controversial. We aimed to detect FGF 21 and UCP 1 levels in obese adolescents, and investigate their relation to obesity parameters and degree of obesity, insulin secretion and sensitivity, circulating parameters of lipid metabolism including free fatty acids (FFA), inflammation markers as well as non-alcoholic fatty liver disease (NAFLD) and metabolic syndrome (MS). 64 obese adolescents according to Cole criteria and a control group of 86 lean adolescents with similar age, sex and stage of puberty were included in our study. Serum FGF 21, UCP 1 and metabolic parameters were measured after an overnight fast. Enzyme-Linked Immunosorbent Assay (ELISA) method (BioTek™ ELx800™ Absorbance Microplate Readers, Winooski, Vermont, U.S.A.) was used to determine FGF 21, UCP 1 and FFA levels. Metabolic syndrome diagnosis was based on International Diabetes Federation 2007 criteria. Obese adolescents showed higher blood pressure, fasting insulin, HOMA-IR, total cholesterol, LDL, triglyceride and lower HDL levels than the controls (p<0.001; p<0.001; p<0.001; p<0.001; p<0.001; p<0.001; p=0.006 respectively), however there was no significant difference in terms of FGF 21 and UCP 1 levels between the two groups. Free fatty acids and UCP 1 levels were positively correlated in obese and control groups separately and in the combination group (r=0,453; p<0,001, r=0,693; p<0,001, r=0,592; p<0,001 respectively). FGF 21 was negatively correlated with body weight (r=-0,420; p=0,001), body weight SDS (r=-0,273; p=0,029), BMI (r=-0,332; p=0,007), waist circumference (r=-0,280; p=0,025), hip circumference (r=-0,248; p=0,048), systolic (r=-0,287; p=0,021) and diastolic blood pressure (r=-0,411; p=0,001) but not correlated with fasting insulin, HOMA-IR and lipids in obese adolescents. Obese adolescents with and without MS or NAFLD did not differ significantly with respect to their FGF 21 concentrations. Our findings suggest an association of FGF 21 with the degree of obesity in obese adolescents. There is a relationship between FFA and UCP 1 which is consistent with the knowledge that FFA are physiological stimulants of UCP 1. Futher investigations are needed to evaluate the importance of our results.