THE 24/25-KDA SERUM INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN IS INCREASED IN ELDERLY WOMEN WITH HIP AND SPINE FRACTURES

Fractures of the hip in elderly women represent a clinical syndrome (age-related osteoporosis) often marked by decreased calcium absorption and secondary hyperparathyroidism. We studied 13 elderly women with fractures of the hip and spine and 18 healthy similarly aged control women to determine whether serum insulin-like growth factor-I (IGF-I) or its carrier binding proteins (IGFBPs) were altered in this syndrome. Serum IGF-I concentrations were not different in the two groups (P = 0.50), but immunoreactive PTH was significantly higher in the fracture group (58.50 +/- 8.20 vs. 13.50 +/- 2.70 ng/L; P < 0.003). Binding of [I-125]IGF-I to IGFBP-3, IGFPB-2, and IGFPB-1, measured by ligand blotting, was not statistically different in the 2 groups, but binding intensities for the serum 24/25-kDa IGFPB were approximately 2.5 times greater in fracture women than control women (P < 0.0005). In data pooled from both groups, PTH correlated strongly (r = 0.70; P < 0.0001) with the relative binding intensities for the 24/25-kDa IGFPB. Based on previous work, we speculate that production of the 24/25-kDa IGFPB, which in vitro is known to inhibit IGF-I and IGF-II-mediated osteoblast function, may be stimulated by PTH in patients with the syndrome of age-related osteoporosis.