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)

The insulin-like growth factor-I gene and osteoporosis: A critical appraisal

“…After birth, the patient grew poorly and had low BMD, confirming the central role of IGF-I in postnatal growth, as suggested in the somatomedin hypothesis (Salmon and Daughaday, 1957). Interestingly, the patient's serum IGFBP-3 and ALS concentrations were normal-findings in support of recent studies showing that these peptides are controlled independently of IGF-I in humans (Gargosky et al, 1993;Hardouin et al, 1989;Zapf et al, 1989;Baxter, 1990). However, a similar skeletal phenotype was recently reported for a human mutation in ALS, the major carrier protein for IGFBP-3 and IGF-I (Domene et al, 2004).…”

Differential regulation of tissue insulin-like growth factor-binding protein (IGFBP)-3, IGF-I and IGF type 1 receptor mRNA levels, and serum IGF-I and IGFBP concentrations by growth hormone and IGF-I

“…An indirect response to GH has also been investigated by Chin et al (1994) who reported that GH receptor mRNA was absent from IGFBP-3 expressing cells in the liver. However, studies in man are more equivocal; Gargosky et al (1993) reported an inability of IGF-I to increase circulating IGFBP-3 concentrations in GH receptor-deficient patients and Kupfer et al (1993) observed a decline in IGFBP-3 and ALS concentrations in response to IGF-I in calorically-restncted normal adults. These discrepancies can be explained in part by consider¬ ation of IGFBP-3 stability, the half-life of IGFBP-3 being longer when in the ternary than binary complex (Dai & Baxter 1994).…”

“…1986) but it is not clear whether this is due to the primary GH deficiency or to the subsequent lack of IGF-I. Studies in which GH or IGF-I have been administered to humans and rats have not yielded consist¬ ent changes in blood IGFBP-3 concentrations (Gargosky et al 1993). It is therefore important to identify the major source(s) of blood IGFBP-3 and to characterize key factors regulating its synthesis.…”

The GH–IGF–IGFBP axis is changed in Turner syndrome: Partial normalization by HRT

“…Serum IGFBP-3 was measured by an immunoradiometric assay (IRMA) (Diagnostic System Laboratories Inc., Webster, TX, USA), and ALS by RIA (Bioclone Australia, Marrickville, Australia). In order to determine the distribution of IGFBP-3 in the 150 kDa ternary complex and the non-ternary complex bound fraction, 200 lL of serum from each patient/control was exposed to size-exclusion chromatography at neutral pH as previously described [19], followed by determination of the IGFBP profile by Western ligand blotting (WLB) [20,21], and finally measurement of the IGFBP-3 concentration by IRMA as described above. The column which was used for size-exclusion chromatography was calibrated with proteins of known molecular weight (thyroglobulin (670 kDa), gamma-globulin (158 kDa), ovalbumin (44 kDa), myoglobin (17 kDa), and cyanocobalamin (1.4 kDa); all from Bio-Rad, Melville; NY, USA).…”