Mineral Changes in Osteoporosis

Abstract

Bone mineral composition, crystallinity, and bone mineral content of osteoporotic patients are different from those of normal subjects. We review the evidence that these mineralization parameters contribute to the strength (fracture resistance) of bone and the methods that have been used to examine them. A specific example is provided from analysis of biopsies from the Multiple Outcomes in Raloxifene Evaluation trial. For the analyses, randomly selected biopsies from placebo, low-dose, and high-dose groups (n = 5 per group) obtained at time zero and 2 years after treatment were examined by infrared imaging spectroscopy. In all cases, comparable increases in mineral content were found, but there were no significant variations in mineral crystallinity.Osteoporosis is a devastating disease that affects more than 10 million people in the United States, with annual costs in excess of 13.5 billion dollars. 123 According to the US Surgeon General's Report, 123 by the year 2020 1/2 of all Americans older than 50 years will be at risk of an osteoporotic fragility fracture. Osteoporosis is characterized by low bone mass and structural deterioration of bone, leading to bone fragility and an increased tendency to fracture. Fracture resistance is determined by the strength of the bone, which in turn depends on its geometric properties (size, shape, and connectivity), the activities of the cells in the tissue, and the material properties of the tissue. 36,73,109 The material properties of bone include the mineral content, 73 mineral composition and mineral crystal size, 27 and matrix content and composition. 35 The most frequently used clinical indication of osteoporosis and fracture risk, bone mineral density (BMD), is also the most readily accessible non-invasive measure of bone mineral content. 85 The purpose of this review is to describe the additional properties that may be predictive of mechanical strength obtained by analyses of bone tissue specimens. Methods of analysis and recent data obtained by these methods also are reviewed to show how material properties are altered in osteoporosis.Specific questions addressed are how the composition of bone is altered in osteoporosis; how mineral crystal composition and size vary in osteoporosis; how spectroscopic analyses can be used to characterize these alterations in properties with high spatial resolution; and how therapies currently in clinical use affect these properties. The Composition of BoneBone is a composite consisting, in decreasing order, of mineral (an analogue of geologic hydroxyapatite [HA]), an organic matrix, cells, and water. 14 The organic matrix predominately Correspondence to:

Towards new material biomarkers for fracture risk

“…The <00ℓ> coherence length was found to be lower for the fracture group than the non-fracture group (p = 0.020). This is surprising and counter to previous FTIR studies [18,34]. However, a possible mechanism to consolidate our view with others is to consider that in OP apatite the carbonate ions preferentially replace those phosphate ions within the most shallow potential wells i.e.…”

“…This suggests greater carbonate content in the fracture material in comparison to the non-fracture material and/ or less phosphate. A higher carbonate to phosphate ratio in the fracture material is consistent with previous studies [18,28,34]. This increase is consistent with the data reported here, where a~11% increase in the carbonate to phosphate ratio was observed for the fracture material.…”

“…Perhaps of most relevance are those reports detailing differences between osteoporotic and 'normal' tissues, although inconsistencies are frequent. For example, reports such as those of Thompson et al [17] and Faibish and Boskey [34] suggested an increase in crystallite size in osteoporotic tissue. However, these two reports differ in conclusions regarding the crystal chemistry;…”

“…Thompson suggested a decrease in carbonate [17], while Faibish and Boskey [34] argued for an increase when comparing osteoporotic to normal bone. An increase in both crystallite size and carbonate content was reported by Gadeleta et al [18].…”

Infrared spectroscopy indicates altered bone turnover and remodeling activity in renal osteodystrophy

“…Carbonate-to-phosphate ratio has been suggested previously to be related to the size of the mineral crystals in the bone tissue. (30,33) Based on this study and previous findings, this ratio seems also to be related to bone remodeling rate and turnover, as measured by histomorphometry.As the ''gold standard,'' bone histomorphometry is a valuable and well-established clinical and research tool for studying the effects of treatment, etiology, and pathogenesis of metabolic bone diseases. (34) It provides information on bone volume and bone remodeling activity, for example, cells, osteoid formation, resorption, and mineralization.…”