title: Glycosaminoglycans increase levels of free and bioactive IGF-I in vitro.
abstract: BACKGROUND
  It is unclear how IGFs become separated from their IGF-binding proteins (IGFBPs) in vivo. However, the IGFBPs possess binding sites for glycosaminoglycans (GAGs) and interaction with GAGs alters IGFBP ligand affinity. Accordingly, GAGs may control IGF bioavailability. To test this hypothesis, we investigated the effect of GAGs on serum levels of free and bioactive IGF-I, total IGF-I, and IGFBPs in vitro.
  
  
  METHODS
  Serum was incubated with increasing concentrations of six different GAGs (heparin, tinzaparin (Innohep), dermatan sulfate, heparan sulfate, non-anticoagulant (nac) heparin, and nac low-molecular weight heparin). To investigate for reversibility, heparin was co-incubated with protamine sulfate (PS). Finally, the effect of heparin was studied in serum from pregnant and post partum women, normal subjects and patients with type 1 diabetes.
  
  
  RESULTS
  All GAGs increased free IGF-I in a dose-dependent manner (P<0.0001), whereas total IGF-I and IGFBP levels remained unchanged. However, the potency of the GAGs differed significantly (P<0.0001) and did not relate to their anti-coagulating activity. The effect of heparin on free IGF-I was fully reversed by PS. Heparin increased free and bioactive IGF-I in all tested sera (P<0.0001), but the increase was most pronounced in samples from pregnant women (P<0.0001).
  
  
  CONCLUSIONS
  All tested GAGs stimulated the release of free and bioactive IGF-I in several types of serum, most likely by reversible interaction with the IGFBPs. The effect was most pronounced in pregnancy sera, which are characterized by extensive IGFBP-3 proteolysis. Our findings support the view that GAGs localized in the vessel wall and attached to the extracellular matrix control IGF-I tissue accessibility and bioactivity.
authors.affiliation: Medical Research Laboratories, Clinical Institute and Medical Department M (Diabetes and Endocrinology), Aarhus University Hospital, Nørrebrogade, DK-8000 Aarhus C, Denmark.
authors.forename: Anne Vestergård
authors.initials: AV
authors.lastname: Møller
authors.forename: Søren Peter
authors.initials: SP
authors.lastname: Jørgensen
authors.forename: Jian-Wen
authors.initials: JW
authors.lastname: Chen
authors.forename: Anni
authors.initials: A
authors.lastname: Larnkjaer
authors.forename: Thomas
authors.initials: T
authors.lastname: Ledet
authors.forename: Allan
authors.initials: A
authors.lastname: Flyvbjerg
authors.forename: Jan
authors.initials: J
authors.lastname: Frystyk
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000494:pharmacology; D003871:Dermatan Sulfate / Q000494:pharmacology; D005260:Female; D005343:Fibrinolytic Agents / Q000494:pharmacology; D006025:Glycosaminoglycans / Q000494:pharmacology*; D006493:Heparin / Q000494:pharmacology; D006495:Heparin, Low-Molecular-Weight / Q000494:pharmacology; D006497:Heparan Sulfate / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D016014:Linear Models; D011247:Pregnancy / Q000097:blood*; D000078222:Tinzaparin
chemical_list: D000925:Anticoagulants; D003871:Dermatan Sulfate; D005343:Fibrinolytic Agents; D006025:Glycosaminoglycans; D006493:Heparin; D006495:Heparin, Low-Molecular-Weight; D006497:Heparan Sulfate; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D000078222:Tinzaparin