The high molecular weight insulin-like growth factor-binding protein complex: epitope mapping, immunoassay, and preliminary clinical evaluation.
Measurements of insulin-like growth factor I(IGF-I), IGF-binding protein-3 (IGFBP-3), and the acid-labile subunit (ALS) are important in assessing the GH-IGF axis. As nearly all IGF-I, IGFBP-3, and ALS circulate in a GH-dependent ternary protein complex, direct determination of the complex may be of significant analytical and clinical importance. We evaluated a panel of monoclonal antibodies (mAb) to human IGFBP-3 and classified them into four groups (G-1 to G-4). G-1 antibodies recognized epitopes that mapped at or near IGFBP-3 ligand (IGF)-binding site. This region overlapped with the G-2 defined region, which, in turn, overlapped with G-3 epitopes defined by one antibody (mAb 3). Only G-1 and G-3 antibodies paired without interference. mAb 9 recognized a conformational epitope (G-4), and mAb 10 was nonreactive. In pairwise mixed antibody evaluation, mAbs in G-2 and G-3 showed simultaneous binding to serum IGFBP-3 complexes in combination with an anti-IGF-I or an anti-ALS antibody. On this basis, two novel enzyme-linked immunosorbent assays (ELISAs) involving IGFBP-3/IGF-I (ELISA-1) and IGFBP-3/ALS (ELISA-2) recognition partners were developed, both demonstrating acceptable analytical performance characteristics. IGFBP-3 complexes measured by ELISA-1 and -2 in samples from normal individuals and subjects with GH deficiency, acromegaly, and GH receptor deficiency more tightly correlated with IGF-I, IGFBP-3, and ALS than IGF-II. ELISA-1 determinations were comparatively more age dependent and, in comparison to ELISA-2, showed better discriminations among the various sample groups, particularly among GH receptor deficiency, normal, and GH deficiency subjects. The development of IGFBP-3 complex ELISAs may simplify diagnostic applications and facilitate investigations of the physiological relevance of the ternary complex formation.
Khosravi
J
J
Diagnostics Systems Laboratories, Inc., Toronto, Ontario, Canada.
Diamandi
A
A
Mistry
J
J
Krischna
R G
RG
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D005260:Female; D006801:Humans; D007223:Infant; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis* / Q000276:immunology; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D007335:Insulin-Like Growth Factor II / Q000032:analysis; D008875:Middle Aged; D008970:Molecular Weight; D011986:Receptors, Somatotropin / Q000172:deficiency
D018972:Insulin-Like Growth Factor Binding Protein 3; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II