Free insulin‐like growth factors (IGF‐I and IGF‐II) in human serum

FEBS Letters

Skjærbæk, Christian¹  Dinesen, Bo²  Ørskov, Hans¹  Frystyk, Jan¹ 

[1] Institute of Experimental Clinical Research, Medical Research Laboratories, Aarhus University Hospital, Nørrebrogade 44, DK-8000 Aarhus, Denmark;Steno Diabetes Center, Gentofte, Denmark

关键词: IGF-I;    IGF-II;    Ultrafiltration;    IGFBP;    Immunoassay;   

DOI  :  10.1016/0014-5793(94)00602-4

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Using ultrafiltration by centrifugation we have isolated the free, unbound fractions of insulin-like growth factor I and II (free IGF-I and IGF-II) in human serum. In this way near in vivo conditions could be maintained before and during isolation. The recovery was 80 to 100% in the ultrafiltrates, which contained no detectable amounts of IGF-binding proteins (IGFBPs) as measured by Western ligand blotting and IGFBP-1 and IGFBP-3 immunoassays. The concentration of free peptides was measured in two ultrasensitive non-competitive IGF-I and IGF-II time-resolved fluoroimmunoassays. We found that (i) equilibrium between free and protein-complexed IGF was strongly dependent on re-establishment of in vivo conditions (temperature, pH, ionic milieu and dilution); (ii) metabolic events (glucose load and fasting) caused significant changes in free IGF-I and IGF-II levels without concomitant changes in total circulating levels of IGFs; (iii) in 49 healthy adult subjects (20 to above 60 years) free IGF-I was inversely related to age and ranged from 950 ± 150 ng/l (mean ± S.E.M.) (20–30 years) to 410 ± 70 ng/l (⪢ 60 years). The relative percentage was, however, unchanged, being 0.38 ± 0.02% of total IGF-I. In contrast, free IGF-II was independent of age, being 1,480 ± 80 ng/l (∼0.20 ± 0.01% of total IGF-II).

【 授权许可】

Unknown