The effects of estrogen deficiency on cortical bone microporosity and mineralization

Abstract

Recent studies have demonstrated matrix-mineral alterations in bone tissue surrounding osteocytes in estrogen-deficient animals. While cortical bone porosity has been shown to be a contributor to the mechanical properties of bone tissue, little analysis has been done to investigate the effects of estrogen deficiency on bone's microporosities, including the vascular and osteocyte lacunar porosities. In this study we examined alterations in cortical bone microporosity, mineralization, and cancellous bone architecture due to estrogen deficiency in the ovariectomized rat model of postmenopausal osteoporosis. Twenty-week-old female Sprague-Dawley rats were subjected to either ovariectomy or sham surgery. Six weeks post-surgery tibiae were analyzed using high-resolution micro-CT, backscattered electron imaging, nanoindentation, and dynamic histomorphometry. Estrogen deficiency caused an increase in cortical bone vascular porosity, with enlarged vascular pores and little change in tissue mineral density in the proximal tibial metaphysis. Measurements of cancellous architecture corresponded to previous studies reporting a decrease in bone volume fraction, an increase in trabecular separation, and a decrease in trabecular number in the proximal tibia due to estrogen deficiency. Nanoindentation results showed no differences in matrix stiffness in osteocyte-rich areas of the proximal tibia of estrogen-deficient rats, and bone labeling and backscattered electron imaging showed no significant changes in mineralization around the vascular pores. The findings demonstrate local surface alterations of vascular pores due to estrogen deficiency. An increase in cortical vascular porosity may diminish bone strength as well as alter bone mechanotransduction via interstitial fluid flow, both of which could contribute to bone fragility during postmenopausal osteoporosis.

<p>Nobiletin-loaded micelles reduce ovariectomy-induced bone loss by suppressing osteoclastogenesis</p>

“…5 Estrogen deficiency stimulates cortical porosity and therefore forming resorption areas on the trabecular surface. 6,7 It has been recently demonstrated that osteoporosis treatment exploits on improving bone regeneration or inhibiting bone resorption. 8,9 At the cellular level, interaction and communication between the main bone-cell types, the bone-forming osteoblasts and the bone-degrading osteoclasts, organize the smallest functional unit on bone metabolism including osteogenesis which is reduced/ineffective in osteoporotic bone and the important effect of osteoclastogenesis activation.…”

Botox‐induced muscle paralysis alters intracortical porosity and osteocyte lacunar density in skeletally mature rats

“…but no three‐dimensional analysis of vascular pore changes in response to disuse has been previously reported in adult rats. Interestingly, recent work from our group has shown similar vascular canal changes in the proximal tibial metaphysis of skeletally mature rats in response to estrogen deficiency, a condition associated with the development of postmenopausal osteoporosis . An increase in vascular porosity has been shown to diminish interstitial fluid flow in the lacunar‐canalicular system, possibly altering molecular transport and the transduction of mechanical signals to the osteocytes .…”

“…Diminished loading has also been shown to induce osteocyte apoptosis that is spatially associated with recruitment of osteoclasts . Recent studies from our lab have demonstrated alterations of both the vascular and osteocyte lacunar porosities in skeletally mature rats that underwent ovariectomy, a model for postmenopausal osteoporosis . In the rat ovariectomy model, we have shown that an increase in vascular porosity reduces interstitial fluid flow due to mechanical loading, potentially altering bone mechanotransduction and negatively affecting the bone formation/resorption balance …”

“…Reconstructions were obtained with a customized back‐projection algorithm, after applying a low‐pass filter with an asymmetrical boxcar 2‐pixel kernel, and using ring artifact correction, beam‐hardening correction (40%), and a 10% threshold for defect pixel masking (NRecon v1.6; Bruker). Both scanning and reconstruction parameters have been shown in our previous studies to be optimal to enhance signal‐to‐noise ratio and image contrast . Hydroxyapatite (HA) rod‐like calibration phantoms (2‐mm diameter) with densities of 0.25 and 0.75 gHA/cm were scanned with identical parameters to convert the grayscale images to density.…”

Effect of Giving Nano Calcium Phosphate Diet on Mineral Content and Function Groups of Ovariectomy Tibia Rats

“…Several previous researchers examined the effects of ovariectomy (OVX), including causing morphometric and densitometric changes in the tibia bone [16], being overweight [17], and bone becomes porous [18]. Other researchers also have shown that OVX causes an increase in cortical bone blood vessel porosity and decreased bone mineral [19]. All things that arise because of OVX contribute to bone fragility during the process leading to osteoporosis.…”