title: Association of Osteoprotegerin with Obesity, Insulin Resistance and Non-Alcoholic Fatty Liver Disease in Children.
abstract: BACKGROUND
  Osteoprotegerin (OPG) is a member of the tumor necrosis factor superfamily. Reduced OPG levels are related to obesity, insulin resistance, and non-alcoholic fatty liver disease (NAFLD).
  
  
  OBJECTIVE
  The aim of this study was to evaluate the relationship between OPG levels, obesity, insulin resistance, and NAFLD in pediatric patients.
  
  
  METHODS
  This was a prospective, cross-sectional, controlled study that was conducted in the department of pediatrics at Bagcilar training and research hospital in Istanbul, Turkey, between April and August 2015. The study was performed on 107 children with obesity and 37 controls aged 5 - 17 years. In the obese subset, 62 patients had NAFLD. Homeostatic model assessment-insulin resistance (HOMA-IR) was used to calculate insulin resistance. Insulin resistance was defined as a HOMA-IR value greater than 2.5. Plasma OPG levels were measured using enzyme-linked immunosorbent assays. NAFLD was diagnosed by hepatic ultrasound.
  
  
  RESULTS
  The mean age was 11.25 ± 3.38 years in the patient group and 10.41 ± 3.15 years in the control group. The OPG level in the obese group with the mean of 55.20 ± 24.55 pg/mL (median = 48.81 pg/mL) was significantly lower than that in the control group with the mean of 70.78 ± 33.41 pg/mL (median = 64.57 pg/mL) (P = 0.0001). The optimal cut-off point (sensitivity, specificity) of the OPG level for the diagnosis of obesity was ≤ 46, 19 pg/mL. According to logistic regression analysis, fasting insulin (P = 0.036) and OPG (P = 0.01) levels were most affected by obesity. In the obese patients, who had HOMA-IR < 2.5, the mean level of OPG was 58.91 ± 6.88729 pg/mL (median = 49.55). In the obese patients, who had HOMA-IR ≥ 2.5, the mean level of OPG was 54.19 ± 22.21 pg/mL (median = 48.47). No significant correlations were found between OPG and HOMA-IR (P = 0.791). No statistically significant difference was observed in the mean OPG between patients with hepatosteatosis (mean = 54.55 ± 25.01 pg/mL) (median = 49.46) and those without the disease (56.30 ± 24.02 pg/mL) (mean = 48.34) (P = 0.089).
  
  
  CONCLUSIONS
  We confirmed that serum OPG concentrations reduce in obese children. However, no correlation was identified between OPG and insulin resistance. OPG levels are not meaningful in the diagnosis of NAFLD in children with obesity.
authors.affiliation: Bagcilar Training and Research Hospital, Department of Pediatrics, Istanbul, Turkey.
authors.forename: Meltem
authors.initials: M
authors.lastname: Erol
authors.affiliation: Bagcilar Training and Research Hospital, Department of Pediatrics, Istanbul, Turkey.
authors.forename: Ozlem
authors.initials: O
authors.lastname: Bostan Gayret
authors.affiliation: Bagcilar Training and Research Hospital, Department of Pediatric Allergy, Istanbul, Turkey.
authors.forename: Hikmet
authors.initials: H
authors.lastname: Tekin Nacaroglu
authors.affiliation: Bagcilar Training and Research Hospital, Department of Pediatrics, Istanbul, Turkey.
authors.forename: Ozgul
authors.initials: O
authors.lastname: Yigit
authors.affiliation: Bagcilar Training and Research Hospital, Department of Biochemistry, Istanbul, Turkey.
authors.forename: Oguzhan
authors.initials: O
authors.lastname: Zengi
authors.affiliation: Bagcilar Training and Research Hospital, Department of Radiology, Istanbul, Turkey.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Salih Akkurt
authors.affiliation: Department of Pediatric Nephology, Koc University Hospital, Istanbul, Turkey.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Tasdemir
keywords: Children; Insulin Resistance; Non-Alcoholic Fatty Liver Disease; Obesity; Osteoprotegerin