title: 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.
abstract: We have previously reported that adult GH receptor-deficient (GHRD) patients treated subcutaneously with recombinant human insulin-like growth factor (IGF)-I have increased serum IGF-I levels and decreased IGF-II levels, whereas IGF-binding protein-3 (IGFBP-3) levels were unchanged. To further investigate the effects of IGF-I administration upon the IGF-IGFBP axis in GHRD, we have examined: 1) the molecular distribution of IGF-I and IGF-II among the IGFBPs; 2) the composition and distribution of the IGFBPs, in particular IGFBP-3; and 3) the acid labile subunit (ALS). Serum samples from adult GHRD patients who were treated sc with recombinant human IGF-I (40 micrograms/kg, sc, twice a day) or from normal Ecuadorian adults were incubated with [125I]IGF-II and subjected to neutral size-exclusion chromatography. The fractions were then subjected to Western ligand blot, Western immunoblot, IGFBP-3 RIA, and IGF RIAs. Serum of healthy adults incorporated [125I]IGF-II into the 150- and 44-kilodalton (kDa) IGFBP region. The 150-kDa IGFBP region contained most of the circulating IGFBP-3, whereas the 44-kDa IGFBP region contained mainly IGFBP-1, 2, and 4. The 150-kDa region also contained a unique 28-kDa immunoreactive form of IGFBP-3, which was not detectable by Western ligand blot. Endogenous IGF-I and IGF-II were distributed equally in the 150- and 44-kDa IGFBP regions. Sera from GHRD patients mainly incorporated [125I]IGF-II into the 44-kDa IGFBP region. Similar to control sera, the 150-kDa IGFBP region contained IGFBP-3, albeit at lower concentrations. The 44-kDa IGFBP region contained all IGFBPs including 50% of the total immunoreactive IGFBP-3. The two immunoreactive forms of IGFBP 3 (40- to 45-kDa doublet and 28-kDa band) were present in both IGFBP regions. The IGF size-distribution study revealed that the 150-kDa IGFBP region carried half of the circulating endogenous IGF-I, but only 30% of the IGF-II. Concentrations of the ALS were consistently low. Administration of IGF-I to GHRD patients was unable to increase concentrations of the molecular forms of IGFBP-3, correct the aberrant distribution of IGFs among the IGFBPs, or increase serum concentrations of ALS. In conclusion, we have found two forms of IGFBP-3 associated with IGF and ALS, which are capable of forming the ternary 150-kDa complex in healthy adult serum. The ratio of these two forms of IGFBP-3 and their distribution in serum was different between GHRD and control patients.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Pediatrics, Stanford University School of Medicine, California 94305.
authors.forename: S E
authors.initials: SE
authors.lastname: Gargosky
authors.forename: K F
authors.initials: KF
authors.lastname: Wilson
authors.forename: P J
authors.initials: PJ
authors.lastname: Fielder
authors.forename: M A
authors.initials: MA
authors.lastname: Vaccarello
authors.forename: J
authors.initials: J
authors.lastname: Guevara-Aguirre
authors.forename: F B
authors.initials: FB
authors.lastname: Diamond
authors.forename: R C
authors.initials: RC
authors.lastname: Baxter
authors.forename: A L
authors.initials: AL
authors.lastname: Rosenbloom
authors.forename: R G
authors.initials: RG
authors.lastname: Rosenfeld
mesh_terms: D000328:Adult; D002352:Carrier Proteins / Q000097:blood*; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000627:therapeutic use*; D007335:Insulin-Like Growth Factor II / Q000032:analysis*; D008297:Male; D011986:Receptors, Somatotropin / Q000172:deficiency*; D011994:Recombinant Proteins / Q000627:therapeutic use
chemical_list: D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II