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Development and clinical evaluation of a novel immunoassay for the binary complex of IGF-I and IGF-binding protein-1 in human serum.
Frystyk, Jan; Højlund, Kurt; Rasmussen, Kirsten Nyborg; Jørgensen, Søren Peter; Wildner-Christensen, Mette; Ørskov, Hans.
Affiliation
  • Frystyk J; Medical Research Laboratories, Aarhus University Hospital, DK-8000 Aarhus C, Denmark. jan@frystyk.dk
J Clin Endocrinol Metab ; 87(1): 260-6, 2002 Jan.
Article in En | MEDLINE | ID: mdl-11788656
Correlation studies have suggested that IGF-binding protein (IGFBP)-1 is a dynamic regulator of free IGF-I. To further study this, we developed a monoclonal immunofluorometric assay specific for the binary complex of IGF-I and IGFBP-1 in human serum. An IGFBP-1 antibody, which recognizes all phospho-forms of IGFBP-1, was used for coating. An europium-labeled IGF-I antibody served as tracer. Assay incubation was performed at conditions approaching those in vivo (i.e. pH 7.4, 37 C). The assay was highly specific: no signal was obtained unless both IGF-I and IGFBP-1 were present and neither IGFBP-2, -3, -4, nor IGF-II caused any cross-reaction. The linear standard curve covered 3 orders of magnitude, and within and in-between assay coefficients of variation were less than 5 and 15%, respectively. To study the dynamic relationship between free IGF-I and binary complex formation, seven healthy subjects were fasted for 72 h. Samples were collected every 3 h. During fasting, free IGF-I was reduced by two thirds (P < 0.0001). IGFBP-1 and the binary complex increased in parallel (P < 0.0001), and levels correlated positively in all subjects (0.89 < or = r < or = 0.98; P < 0.0001). Free IGF-I correlated inversely with IGFBP-1 (-0.81 < or = r < or = -0.48; 0.0001 < or = P < or = 0.05) and the binary complex (-0.79 < or = r < or = -0.41; 0.0001 < or = P < or = 0.05). To study overnight fasting levels, we compared healthy controls and patients with type 1 diabetes and chronic renal failure (n = 10), because these patients show profound alterations in their IGF-system. In both groups, the binary complex was increased about 2.5-fold (P < 0.0001), whereas IGFBP-1 was increased by 5- to 6-fold (P < 0.0001). Accordingly, free IGF-I was severely reduced (P < 0.0001). In conclusion, the assay enables us to study the role of IGFBP-1 as a dynamic regulator of free IGF-I. Our results clearly show that IGFBP-1 and free IGF-I are tightly associated peptides. Furthermore, it has now become possible to compare levels of IGF-I carried within the binary complex IGFBP-1:IGF-I in different (patho-) physiological conditions.
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Collection: 01-internacional Database: MEDLINE Main subject: Insulin-Like Growth Factor I / Fluoroimmunoassay / Insulin-Like Growth Factor Binding Protein 1 Limits: Adult / Humans / Male / Middle aged Language: En Journal: J Clin Endocrinol Metab Year: 2002 Document type: Article Affiliation country: Denmark Country of publication: United States
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Collection: 01-internacional Database: MEDLINE Main subject: Insulin-Like Growth Factor I / Fluoroimmunoassay / Insulin-Like Growth Factor Binding Protein 1 Limits: Adult / Humans / Male / Middle aged Language: En Journal: J Clin Endocrinol Metab Year: 2002 Document type: Article Affiliation country: Denmark Country of publication: United States