The effect of GH therapy on the immunoreactive forms and distribution of IGFBP-3, IGF-I, the acid-labile subunit, and growth rate in GH-deficient children

We have previously shown that the major correlates of growth following growth hormone (GH) therapy in growth hormone-deficient (GHD) children are changes in circulating insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (IGFBP-3), suggesting a synergistic interaction between IGF-I and IGFBP-3 (1). The first aim of this project was to examine the molecular forms of IGFBP-3 and the acid-labile subunit (ALS), and to assess the changes in these molecular forms during GH administration to GHD children. Plasma samples from prepubertal GHD patients, prior to therapy and during the first year of GH treatment, were subjected to Western ligand and immunoblot analysis. Densitometric analysis of Western ligand blotting (WLB) showed a 76% increase in IGFBP-3 (p=0.02), but a 56% decrease in 36-kDa IGFBP-2 (p=0.03) during GH therapy. Western immunoblot (WIB) analysis of IGFBP-3 revealed the presence of intact (40- to 45-kDa doublet) as well as a proteolyzed (28-kDa) form of IGFBP-3 in the serum of GHD and healthy children. Both immunoreactive forms of IGFBP-3 increased by 64% during GH therapy (intactp=0.003; proteolyzedp=0.0001). WIB analysis of the ALS showed an 84-to 86-kDa doublet, which increased by 41% with GH therapy (p=0.01). The response to GH therapy, as measured by the height velocity standard deviation score (SDS) adjusted for bone age, correlated with the percent change in total IGFBP-3 (r=0.772,p=0.002 by WIB), intact IGFBP-3 (r=0.845,p=0.0005 by WLB;r=0.541,p-0.05 by WIB), and proteolyzed IGFBP-3 (r=0.703,p=0.007), as well as with the percent change in ALS (r=0.813,p=0.014).