Strontium and Bone Nanostructure in Normal and Ovariectomized Rats Investigated by Scanning Small-Angle X-Ray Scattering

Abstract

The effect of SrCl(2) treatment on bone nanostructure in a rat ovariectomy model was studied using scanning small-angle X-ray scattering (sSAXS). Twelve 6-month-old female Wistar rats were used. Six animals were ovariectomized (+ovx) and six were left intact after sham surgery (-ovx). Six animals, three +ovx and three -ovx, were treated with 4 mmol SrCl(2) (aq)/kg/day (+Sr), whereas the remaining six received placebo (-Sr) for 140 days. Rats were labeled with flourochromes at days 7, 126, and 136. Femoral cross sections were studied using fluorescence microscopy, scanning electron microscopy including energy-dispersive X-ray analysis, and sSAXS. The SAXS data comprised about 5,500 measurements and provided information about mineral crystal thickness and orientation in new and old bone. The newly formed bone contained higher levels of Sr(2+) in +Sr than in -Sr animals, indicating that the Sr(2+) was incorporated into the new bone. Mineral plates were significantly thicker in old bone, 2.62 nm (95% CI 2.58-2.66), than in new bone, 2.41 nm (95% CI 2.36-2.46). Surprisingly, mineral plates in new bone were significantly thicker (2.52 [95% CI 2.47-2.57] nm vs. 2.41 [95% CI 2.36-2.46] nm, P = 0.017) in +ovx rats than in -ovx rats. However, no significant effect of SrCl(2) on mineral plate thicknesses in new bone was observed. The statistical model yielded estimates of the difference in bone mineral plate thickness induced by Sr. The estimated effect of Sr was -0.09 (95% CI -0.21 to 0.03) and 0.02 (95% CI -0.10 to 0.14) nm for new bone in -ovx and +ovx rats, respectively.

Characterising Bone Material Composition and Structure in the Ovariectomized (OVX) Rat Model of Osteoporosis

“…profile [10]. Dimensions of the mineral crystals are assumed to be of finite thickness, T, along one dimension and infinite in the other two dimensions, i.e.…”

“…where is a scale factor dependent on specimen thickness, mineral content and scattering contrast [10].…”

“…Measurements can be position-resolved with a resolution similar to that of the beam dimensions. Few publications exist on the implementation of SAXS in the OVX rat model but these are somewhat inconsistent in their findings [9,10,7,11].…”

“…Mineral volume fraction of bone is both species and site dependent with documented values varying between 30 to 55% as determined by ash weight/dry weight ratios, energy dispersive x-ray spectroscopy or quantitative backscattered electron imaging [15]. An alternative approach in determining the mean crystal thickness parameter is that suggested by Bünger et al, which relies on iterative curve fitting to the radially averaged one dimensional SAXS pattern I(q) [10]. Significantly, this method is independent of any assumptions on bone mineral content.…”

“…Significantly, this method is independent of any assumptions on bone mineral content. Limited adoption of iterative curve fitting exists in the literature with, to our knowledge, only a sole publication on its implementation in the OVX rat model [10]. However, this study was restricted to a sample size of n = 3 [10].…”