Article

Site specific increase in heterogeneity of trabecular bone tissue mineral during oestrogen deficiency.

Bioengineering Sciences Research Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, United Kingdom.
European cells & materials (Impact Factor: 4.89). 01/2011; 21:396-406.
Source: PubMed

ABSTRACT Although osteoporosis reduces overall bone mass causing bone fragility, recent studies report that the remaining bone tissue is significantly stiffer. Preliminary studies indicate that alterations in bone tissue mineral content might explain these changes, albeit that other studies report conflicting observations. The objective of this study is to quantify whether the distribution of bone tissue mineral is altered during oestrogen deficiency. Individual trabeculae were harvested from the proximal femur of 7 ovariectomised sheep (OVX), sacrificed 12 months post-surgery, and 5 age-matched controls. Mineral content (wt% Ca) was determined using a quantitative backscattered scanning electron microscopy imaging approach. Mineral heterogeneity within individual trabeculae was compared by calculating the full width at half maximum (FWHM) of mineral density distributions. Mean calcium content, the spatial distribution of mineral within trabeculae and the inter-trabecular variation between regions of proximal femora were also compared. Oestrogen deficiency increased mineral heterogeneity within individual trabeculae compared to healthy controls, as measured by FWHM (3.57 ± 0.68 vs. 3.17 ± 0.36 wt% Ca, p = 0.04). In particular mineral variability increased between superficial and deep regions of trabeculae of OVX animals (p = 0.04). Interestingly, mineralisation variability between greater and lesser trochanters (i.e. intertrochanteric fracture line) was increased in OVX compared to CON, as indicated by a greater % difference in the standard deviation of trabecular mineral content (77.11 ± 11.70 vs. 45.64 ± 23.70 %, p = 0.03). Such changes are undetectable by evaluating the mean mineral content of bone tissue, but may contribute to changes in bone mechanical strength following osteoporotic bone loss.

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Available from: Fergal J. O’Brien, Jul 23, 2014
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    ABSTRACT: The quantity and distribution of bone tissue mineral are key determinants of bone strength. Recent research revealed altered mineral distribution within sheep femora following estrogen deficiency. Rapid increases in bone remodeling occur at the onset of estrogen deficiency and abate over time. Therefore, altered tissue mineralization might be a transient characteristic of osteoporosis. Bisphosphonates reduce fracture incidence by 40–60% but increases in bone mineral density are insufficient to explain such changes. In this study the hypotheses that bone tissue mineralization is altered over prolonged estrogen depletion and bisphosphonate treatment were tested. Quantitative backscattered imaging (qBEI) was used to quantify bone mineral density distribution (BMDD) parameters (mean, FWHM) in trabeculae from the proximal femora of an ovariectomized sheep model that underwent estrogen deficiency for 31 months, an ovariectomized group administered with Zoledronic acid and age-matched controls. To assess the effects of normal ageing and prolonged estrogen deficiency, data were compared to BMDD data from sheep that were estrogen deficient for 12 months and age-matched controls. This study reports that normal ageing increases mean mineralization and mineral heterogeneity at a trabecular level. In contrast, prolonged estrogen deficiency leads to significantly decreased mean mineralization and further exacerbates increases in mineral heterogeneity. Interestingly, ZOL treatment of OVX sheep significantly reduced tissue mineral variability, both at a trabecular level and between femoral regions. Together, these findings indicate that ZOL treatment acts to reverse the increased mineral heterogeneity occurring during estrogen deficiency, which may contribute to its capacity to reduce osteoporotic fractures.
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