The phosphorylation status of insulin-like growth factor-binding protein-1in prepubertal obese children

Objective: We measured the total and nonphosphorylated insulin-like growth factor-binding protein (IGFBP)-1 concentrations in obese children to determ ine the effect of obesity on the status of IGFBP-1 phosphorylation. We also measured the serum levels of insulin, total and free IGF-I, and IGFBP-3 to investigate their relationships to the IGFBP-1 phosphorylation status in o bese subjects. Subjects and methods: Nineteen prepubertal obese and 15 age-matched control children were included in the study. The serum levels of total and nonphos phorylated IGFBP-1 were determined by noncompetitive RIAs. Results: The serum levels of total and nonphosphorylated IGFBP-1 were signi ficantly lower in the obese group (48.7 +/- 5.6 mu g/l, P < 0.001 and 11.1 +/- 1.9 mu g/l, P < 0.01 respectively) than in the controls (86.7 +/- 9.0 m u g/l and 25.8 +/- 6.2 mu g/l respectively). However, the ratio of nonphosp horylated IGFBP-1 to total IGFBP-1 did not differ significantly between the obese and control groups. The circulating free IGF-I level was significant ly higher in the obese children than in the controls (P < 0.05), while the serum levels of insulin, total IGF-I and IGFBP-3 were not significantly dif ferent between the two groups. A stepwise regression analysis of the combin ed group revealed that only the total IGFBP-1 level was an independent pred ictor of the free IGF-I concentration (P < 0.001). Conclusion: The present study shows that both total and nonphosphorylated I GFBP-1 concentrations are decreased in obese children and the increased fre e IGF-I level in obese children is related to the reduced total IGFBP-1 lev el, but unrelated to the change in the IGFBP-1 phosphorylation status.