THE COMPOSITION AND DISTRIBUTION OF INSULIN-LIKE GROWTH-FACTORS (IGFS) AND IGF-BINDING PROTEINS (IGFBPS) IN THE SERUM OF GROWTH-HORMONE RECEPTOR-DEFICIENT PATIENTS - EFFECTS OF IGF-I THERAPY ON IGFBP-3

We have previously reported that adult GH receptor-deficient (GHRD) pa tients treated subcutaneously with recombinant human insulin-like grow th factor (IGF)-I have increased serum IGF-I levels and decreased IGF- II levels, whereas IGF-binding protein-3 (IGFBP-3) levels were unchang ed. To further investigate the effects of IGF-I administration upon th e IGF-IGFBP axis in GHRD, we have examined: 1) the molecular distribut ion of IGF-I and IGF-II among the IGFBPs; 2) the composition and distr ibution of the IGFBPs, in particular IGFBP-3; and 3) the acid labile s ubunit (ALS). Serum samples from adult GHRD patients who were treated sc with recombinant human IGF-I (40 mu g/kg, sc, twice a day) or from normal Ecuadorian adults were incubated with [I-125]IGF-II and subject ed to neutral size-exclusion chromatography. The fractions were then s ubjected to Western ligand blot, Western immunoblot, IGFBP-3 RIA, and IGF RIAs. Serum of healthy adults incorporated [I-125]IGF-II into the 150- and 44-kilodalton (kDa) IGFBP region. The 150-kDa IGFBP region co ntained most of the circulating IGFBP-3, whereas the 44-kDa IGFBP regi on contained mainly IGFBP-1, 2, and 4. The 150-kDa region also contain ed a unique 28-kDa immunoreactive form of IGFBP-3, which was not detec table by Western ligand blot. Endogenous IGF-I and IGF-II were distrib uted equally in the 150- and 44-kDa IGFBP regions. Sera from GHRD pati ents mainly incorporated [I-125]IGF-II into the 44-kDa IGFBP region. S imilar to control sera, the 150-kDa IGFBP region contained IGFBP-3, al beit at lower concentrations. The 44-kDa IGFBP region contained all IG FBPs including 50% of the total immunoreactive IGFBP-3. The two immuno reactive forms of IGFBP 3 (40- to 45-kDa doublet and 28-kDa band) were present in both IGFBP regions. The IGF size-distribution study reveal ed that the 150-kDa IGFBP region carried half of the circulating endog enous IGF-I, but only 30% of the IGF-II. Concentrations of the ALS wer e consistently low. Administration of IGF-I to GHRD patients was unabl e to increase concentrations of the molecular forms of IGFBP-3, correc t the aberrant distribution of IGFs among the IGFBPs, or increase seru m concentrations of ALS. In conclusion, we have found two forms of IGF BP-3 associated with IGF and ALS, which are capable of forming the ter nary 150-kDa complex in healthy adult serum. The ratio of these two fo rms of IGFBP-3 and their distribution in serum was different between G HRD and control patients. These data may provide an explanation for th e altered IGF distribution also observed in GHRD patients. Furthermore , we have found that the administration of IGF-I to patients with GHRD failed to elevate total IGF levels or to increase IGFBP-3 or ALS leve ls in the circulation.