Glycosaminoglycans increase levels of free and bioactive IGF-I in vitro.
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.
Møller
Anne Vestergård
AV
Medical Research Laboratories, Clinical Institute and Medical Department M (Diabetes and Endocrinology), Aarhus University Hospital, Nørrebrogade, DK-8000 Aarhus C, Denmark.
Jørgensen
Søren Peter
SP
Chen
Jian-Wen
JW
Larnkjaer
Anni
A
Ledet
Thomas
T
Flyvbjerg
Allan
A
Frystyk
Jan
J
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
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