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P. Pastoureau, B. Merle and P. D. Delmas

Abstract. We developed a sensitive and specific radioimmunoassay for ovine bone gla-protein (osteocalcin) using a polyclonal rabbit antibody raised against ovine bone gla-protein. Bone from lambs was extracted in 0.5 mol/l EDTA and desalted on Sephadex G-25. Bone gla-protein was purified by gel filtration chromatography over Sephadex G-100 and ion-exchange chromatography on DEAE-Sephadex A-25. The protein, subjected to monodimensional electrophoresis migrated as a single spot in SDS PAGE with the same apparent molecular weight of 12 kD as bovine bone gla-protein. The amino acid composition of purified bone gla-protein was in agreement with a previous publication. The competitive RIA uses 125I-labelled bone gla-protein as a tracer and a complex of a second antibody and polyethylene glycol to separate free and antibody-bound 125I-labelled bone gla-protein. The intra- and inter-assay variations are less than 6 and 10%, respectively. There is no reactivity of our antisera with dog sera. The cross-reactivity is only partial with calf and human sera and complete with ovine sera. We measured bone gla-protein levels in serum of 96 normal male sheep of different ages. Serum bone gla-protein rapidly and significantly (P <0.001) decreased from 535 ± 169 μg/l at birth, to 240 ± 43 μg/l at 45 days, 152 ± 44 μg/l at 90 days, and 5.9 ± 0.7 μg/l at 7 years of age. In addition, bone gla-protein levels at birth were higher in normal birth weight than in hypotrophic lambs with low birth weight (535 ± 169 vs 271 ± 156 μg/l, P< 0.001). Furthermore, lambs raised outside in free conditions tended to have higher serum bone gla-protein levels than lambs raised under shelter (194 ± 53 vs 137 ± 34 μg/l), suggesting a role of breeding factors such as diet or relative immobilization on bone gla-protein levels. These results emphasize the interest of a RIA for the bone-specific protein bone gla-protein as a potential tool for experimental studies on skeletal growth and bone remodelling in a large animal.

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A Chaitou, S Boutroy, N Vilayphiou, A Varennes, M Richard, S Blaizot, F Munoz, P D Delmas, J Goudable, R Chapurlat and P Szulc

Objective

In the elderly, vitamin D deficit, low calcium intake, and impaired bone microarchitecture are associated with higher risk of hip fracture. We assessed the association of bone microarchitecture with calcium intake and serum concentrations of 25-hydroxycholecalciferol (25OHD) and parathyroid hormone (PTH) in men.

Design

Cross-sectional analysis was performed in 1064 men aged 20–87 years not taking vitamin D or calcium supplements.

Methods

Daily calcium intake was assessed using a food frequency questionnaire. Bone microarchitecture was assessed at distal radius and tibia by high-resolution peripheral quantitative computed tomography. We measured serum and urinary levels of biochemical bone turnover markers (BTMs). Statistical models were adjusted for age, weight, height, and glomerular filtration rate.

Results

In 500 men aged <65 years, lower 25OHD levels and low calcium intake were associated with lower trabecular volumetric bone mineral density (Dtrab) at the distal tibia, due to lower trabecular number (Tb.N). Low calcium intake was associated with lower cortical thickness (Ct.Th). Higher PTH level was associated with higher BTM levels. In 563 men aged ≥65 years, the highest PTH quartile was associated with lower Ct.Th (tibia), lower Dtrab (both sites), and lower Tb.N (radius) compared with the lowest quartile. Low calcium intake was associated with lower Tb.N and more heterogenous trabecular distribution. BTM positively correlated with the PTH concentration.

Conclusion

In older men, elevated PTH concentration is associated with high bone turnover, poor trabecular microarchitecture (radius and tibia), and, at the distal tibia, lower Ct.Th. Low calcium intake is associated with lower Tb.N and more heterogenous trabecular distribution.