Down-Regulation of the Serum Stimulatory Components of the Insulin-like Growth Factor (IGF) System (IGF-I, IGF-II, IGF Binding Protein [BP]-3, and IGFBP-5) in Age-Related (Type II) Femoral Neck Osteoporosis

Authors

  • Steven Boonen,

    1. Leuven University Center for Metabolic Bone Diseases, Katholieke Universiteit Leuven, Leuven, Belgium
    2. Arthritis and Metabolic Bone Disease Research Unit, Katholieke Universiteit Leuven, Leuven, Belgium
    3. Laboratory for Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Subburaman Mohan,

    Corresponding author
    1. Department of Biochemistry, Loma Linda University, Loma Linda, California, U.S.A.
    2. Department of Medicine, Loma Linda University, Loma Linda, California, U.S.A.
    3. Department of Physiology, Loma Linda University, Loma Linda, California, U.S.A.
    4. Musculoskeletal Disease Center, Jerry L. Pettis VA Medical Center, Loma Linda, California, U.S.A.
    • Address reprint requests to: Subburaman Mohan, Ph.D. Research Service (151) Jerry L. Pettis VA Medical Center 11201 Benton Street Loma Linda, CA 92357 U.S.A.
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  • Jan Dequeker,

    1. Arthritis and Metabolic Bone Disease Research Unit, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Jeroen Aerssens,

    1. Arthritis and Metabolic Bone Disease Research Unit, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Dirk Vanderschueren,

    1. Laboratory for Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Geert Verbeke,

    1. Department of Epidemiology, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Paul Broos,

    1. Department of Traumatology and Emergency Surgery, Katholieke Universiteit Leuven, Leuven, Belgium
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  • Roger Bouillon,

    1. Laboratory for Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium
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  • David J. Baylink

    1. Department of Biochemistry, Loma Linda University, Loma Linda, California, U.S.A.
    2. Department of Medicine, Loma Linda University, Loma Linda, California, U.S.A.
    3. Musculoskeletal Disease Center, Jerry L. Pettis VA Medical Center, Loma Linda, California, U.S.A.
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  • The data have been partially presented at the 1996 Annual Meeting of the American Society for Bone and Mineral Research, Seattle, Washington, U.S.A.

Abstract

Both a decrease in bone formation and an increase in bone resorption have been implicated in the pathogenesis of age-related (type II) femoral neck osteoporosis. While the increase in the bone resorption rate has been shown to be partially related to secondary hyperparathyroidism, the mechanisms underlying the decline in bone formation have not yet been identified. The aim of the present study was to test the hypothesis that the bone formation deficit associated with type II osteoporosis might be due to secondary hyperparathyroidism and/or to a deficiency of the insulin-like growth factor (IGF) system. Circulating concentrations of IGF-I, IGF-II, IGF binding protein (IGFBP)-3, IGFBP-4, IGFBP-5, 25-hydroxycholecalciferol (25(OH)D3), and intact parathyroid hormone (PTH) were measured in 50 elderly women after sustaining a hip fracture and in 50 healthy age-matched controls. In addition, serum levels of osteocalcin (OC), skeletal alkaline phosphatase, and N-terminal procollagen peptide and urinary pyridinium cross-links were determined as markers of bone remodeling, and bone mineral density (BMD) was assessed at the proximal femur. In the patient group, serum was drawn within 18 h of the fracture and prior to surgery. Circulating protein concentrations did not change over this time frame. No difference was found between mean IGFBP-4 serum levels in the two groups studied, while mean levels of IGF-I, IGF-II, IGFBP-3, IGFBP-5, 25(OH)D3, and markers of bone formation were significantly lower (p < 0.006) in patients as compared with healthy subjects. Serum PTH and urinary pyridinium cross-links, however, were markedly increased (p < 0.001) in the osteoporotic group. In pooled data from the normal and osteoporotic populations, age-adjusted multiple regression models based on IGF-I, IGF-II, IGFBP-3, and IGFBP-5 were found to be highly predictive of serum OC (R2 = 19%, p < 0.001) and BMD of femoral neck (R2 = 49%, p < 0.0001), consistent with an effect of the anabolic IGF components on overall bone formation rate. Similar models based on 25(OH)D3 and PTH, however, were statistically unrelated to OC. To address further the potential impact of trauma on circulating IGF system components, we measured IGF system component levels in 10 male patients within 18 h following tibial fracture and in 10 age-matched normal male subjects. There was no significant difference in serum level of any of the IGF system components between the two groups. Although limited by its cross-sectional design, the present study suggests that, in addition to bone resorption resulting from secondary hyperparathyroidism, impaired bone formation associated with deficiency of the IGF system might predispose elderly women to fragility fracture of the proximal femur.

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