The Effect of Obesity on Serum Growth Factors, and Insulin-like Growth Factor Binding Protein-3 Proteolysis in Children with Simple Obesity / 대한소아내분비학회지

ABSTRACT

PURPOSE: In children with simple obesity, spontaneous and stimulated growth hormone (GH) secretion are diminished, but their heights usually are normal or even taller for their age and sex. The exact mechanism to explain the discrepancy between impaired GH secretion and normal height velocity has not been elucidated. In this study, we aimed to determine the level of serum growth factors, and the degree of insulin-like growth factor binding protein (IGFBP)-3 proteolysis, and to assess the alteration of the IGF system associated with accelerated or normal growth in simple obesity. METHODS: We evaluated serum growth factors, and IGFBP-3 proteolysis in 27 obese, 25 obesity risk group, and 28 age-matched control group. We measured serum levels of insulin-like growth factor (IGF)-I, IGFBP-1, -3, and free IGF-I by immuno-radiometric assay and IGFBP-3 fragment by Western immunoblotting. RESULTS: The height was taller in obese children than in lean control group. The results showed no significant difference in the level of serum total IGF-1 and IGFBP-3 between obese and normal control group. Although there was no significant difference in other components, serum free IGF-I levels were significantly increased (P<0.05) and showed positive correlation with their height in obese children (r=0.25, P<0.05). The degree of IGFBP-3 proteolysis was increased in obesity and obesity risk group compared to control group. The densities of the IGFBP-3 proteolytic fragment approximate 18 kDa also showed positive correlation with levels of free IGF-I (r=0.23, P<0.05) and height (r=0.19, P<0.05). CONCLUSION: These findings may suggest that elevated levels of serum IGFBP-3 proteolytic fragments showing decreased affinity to IGF-I result in the increase of biologically active free IGF-I, thereby maintain normal growth in the obese children.