Organ and tissue level properties are more sensitive to age than osteocyte lacunar characteristics in rat cortical bone

Modeling and remodeling induce significant changes of bone structure and mechanical properties with age. Therefore, it is important to gain knowledge of the processes taking place in bone over time. The rat is a widely used animal model, where much data has been accumulated on age-related changes of bone on the organ and tissue level, whereas features on the nano- and micrometer scale are much less explored. We investigated the age-related development of organ and tissue level bone properties such as bone volume, bone mineral density, and load to fracture and correlated these with osteocyte lacunar properties in rat cortical bone. Femora of 14 to 42-week-old female Wistar rats were investigated using multiple complementary techniques including X-ray micro-computed tomography and biomechanical testing. The body weight, femoral length, aBMD, load to fracture, tissue volume, bone volume, and tissue density were found to increase rapidly with age at 14-30 weeks. At the age of 30-42 weeks, the growth rate appeared to decrease. However, no accompanying changes were found in osteocyte lacunar properties such as lacunar volume, ellipsoidal radii, lacunar stretch, lacunar oblateness, or lacunar orientation with animal age. Hence, the evolution of organ and tissue level properties with age in rat cortical bone is not accompanied by related changes in osteocyte lacunar properties. This suggests that bone microstructure and bone matrix material properties and not the geometric properties of the osteocyte lacunar network are main determinants of the properties of the bone on larger length scales

Polychromatic neutron phase contrast imaging of weakly absorbing samples enabled by phase retrieval

We demonstrate the use of a phase retrieval technique for propagation-based phase contrast neutron imaging with a polychromatic beam. This enables imaging samples with low absorption contrast and/or improving the signal-to-noise ratio to facilitate e.g. time resolved measurements. A metal sample, designed to be close to a pure phase object, and a bone sample with canals partially filled with D2O were used for demonstrating the technique. These samples were imaged with a polychromatic neutron beam followed by phase retrieval. For both samples the signal-to-noise ratio were significantly improved and in case of the bone sample, the phase retrieval allowed for separation of bone and D2O, which is important for example for in situ flow experiments. The use of deuteration-contrast avoids the use of chemical contrast enhancement and makes neutron imaging an interesting complementary method to X-ray imaging of bone

Parathyroid hormone PTH(1–34) increases the volume, mineral content, and mechanical properties of regenerated mineralizing tissue after distraction osteogenesis in rabbits

Background and purpose Parathyroid hormone (PTH) has attracted considerable interest as a bone anabolic agent. Recently, it has been suggested that PTH can also enhance bone repair after fracture and distraction osteogenesis. We analyzed bone density and strength of the newly regenerated mineralized tissue after intermittent treatment with PTH in rabbits, which undergo Haversian bone remodeling similar to that in humans

Expression of Bcl-2 and Bax in Mouse Renal Tubules during Kidney Development

Bcl-2 and Bax play an important role in apoptosis regulation, as well as in cell adhesion and migration during kidney morphogenesis, which is structurally and functionally related to mitochondria. In order to elucidate the role of Bcl-2 and Bax during kidney development, it is essential to establish the exact location of their expression in the kidney. The present study localized their expression during kidney development. Kidneys from embryonic (E) 16-, 17-, 18-day-old mouse fetuses, and postnatal (P) 1-, 3-, 5-, 7-, 14-, 21-day-old pups were embedded in Epon. Semi-thin serial sections from two E17 kidneys underwent computer assisted 3D tubule tracing. The tracing was combined with a newly developed immunohistochemical technique, which enables immunohistochemistry on glutaraldehyde fixated plastic embedded sections. Thereby, the microstructure could be described in detail, and the immunochemistry can be performed using exactly the same sections. The study showed that Bcl-2 and Bax were strongly expressed in mature proximal convoluted tubules at all time points, less strongly expressed in proximal straight tubules, and only weakly in immature proximal tubules and distal tubules. No expression was detected in ureteric bud and other earlier developing structures, such as comma bodies, S shaped bodies, glomeruli, etc. Tubules expressing Bcl-2 only were occasionally observed. The present study showed that, during kidney development, Bcl-2 and Bax are expressed differently in the proximal and distal tubules, although these two tubule segments are almost equally equipped with mitochondria. The functional significance of the different expression of Bcl-2 and Bax in proximal and distal tubules is unknown. However, the findings of the present study suggest that the mitochondrial function differs between mature proximal tubules and in the rest of the tubules. The function of Bcl-2 and Bax during tubulogenesis still needs to be investigated

Short-term glucocorticoid excess blunts abaloparatide-induced increase in femoral bone mass and strength in mice

Abstract Glucocorticoids (GCs), such as prednisolone, are widely used to treat inflammatory diseases. Continuously long-term or high dose treatment with GCs is one of the most common causes of secondary osteoporosis and is associated with sarcopenia and increased risk of debilitating osteoporotic fragility fractures. Abaloparatide (ABL) is a potent parathyroid hormone-related peptide analog, which can increase bone mineral density (aBMD), improve trabecular microarchitecture, and increase bone strength. The present study aimed to investigate whether GC excess blunts the osteoanabolic effect of ABL. Sixty 12–13-week-old female RjOrl:SWISS mice were allocated to the following groups: Baseline, Control, ABL, GC, and GC + ABL. ABL was administered as subcutaneous injections (100 μg/kg), while GC was delivered by subcutaneous implantation of a 60-days slow-release prednisolone-pellet (10 mg). The study lasted four weeks. GC induced a substantial reduction in muscle mass, trabecular mineral apposition rate (MAR) and bone formation rate (BFR/BS), and endocortical MAR compared with Control, but did not alter the trabecular microarchitecture or bone strength. In mice not receiving GC, ABL increased aBMD, bone mineral content (BMC), cortical and trabecular microarchitecture, mineralizing surface (MS/BS), MAR, BFR/BS, and bone strength compared with Control. However, when administered concomitantly with GC, the osteoanabolic effect of ABL on BMC, cortical morphology, and cortical bone strength was blunted. In conclusion, at cortical bone sites, the osteoanabolic effect of ABL is generally blunted by short-term GC excess

The effect of oral dabigatran etexilate on bone density, strength, and microstructure in healthy mice

Thrombin is a key component in the coagulation cascade where it converts factor V, VIII, XI, and fibrinogen. In addition to the abundant production of thrombin in the liver, osteoclasts synthesize and secrete thrombin as well. Osteoblasts express thrombin receptors, and it has been reported that thrombin stimulates the expression of RANKL relatively to OPG, resulting in greater osteoclast activation and bone degradation. Pradaxa (dabigatran etexilate, DE) is a new anticoagulant, which has recently been approved for clinical use. DE is a direct thrombin inhibitor with potential to modulate the RANKL/OPG ratio and thereby limit osteoclast activation and bone degradation. The purpose of the study was to investigate whether DE can increase bone density, bone strength, and bone microstructure in healthy male and female mice and to investigate whether the effect of DE is sex-dependent. Twenty-eight 14-week-old male C57BL/6 mice were stratified by weight into 4 groups: 1. Control 3weeks; 2. DE 3weeks; 3. Control 6weeks; 4. DE 6weeks. An identical study design was applied to twenty-four 14-week-old female C57BL/6 mice. Chow mixed with DE was offered ad libitum, resulting in a dose of 1.70mgDE/g body weight and 1.52mgDE/g body weight, to female and male mice, respectively. The animals were euthanized after 3 or 6weeks. Bone mineral density (aBMD) and bone mineral content (BMC) were evaluated with DEXA, 3D microstructural properties were determined with μCT, bone strength was determined with mechanical testing, and bone formation and resorption was evaluated with bone histomorphometry. In female mice, DE resulted in significant higher tibial aBMD values after 6weeks of intervention. Furthermore, DE significantly increased tibial diaphyseal cortical bone area and tissue area, which was accompanied by significantly increased strength of the tibial shaft. DE had no effect on femoral cortical bone or on femoral and vertebral trabecular 3D microstructure. Finally, bone histomorphometry showed that DE had no effect on MS/BS or Oc.S/BS. In male mice, no bone positive effects of DE were found in any of the parameters investigated. In conclusion, intervention with DE may result in a weak positive site specific effect at tibial cortical bone in female mice, and importantly, no major deleterious effects of DE on bone tissue were seen in either female or male mice despite the relatively high dose of DE used. Keywords: Blood clotting, μCT, Dabigatran etexilate, Bone formatio