Patients with chronic kidney disease (CKD) have increased risk of fractures, yet the optimal treatment is unknown. In secondary analyses of large randomized trials, bisphosphonates have been shown to improve bone mineral density and reduce fractures. However, bisphosphonates are currently not recommended in patients with advanced kidney disease due to concern about over-suppressing bone remodeling, which may increase the risk of developing arterial calcification. In the present study we used a naturally occurring rat model of CKD with secondary hyperparathyroidism, the Cy/+ rat, and compared the efficacy of treatment with zoledronic acid, calcium given in water to simulate a phosphate binder, and the combination of calcium and zoledronic acid. Animals were treated beginning at 25 weeks of age (approximately 30% of normal renal function) and followed for ten weeks. The results demonstrate that both zoledronic acid and calcium improved bone volume by microCT and both equally suppressed mineral apposition rate, bone formation rate, and mineralizing surface of trabecular bone. In contrast, only calcium treatment with or without zoledronic acid improved cortical porosity and cortical biomechanical properties (ultimate load and stiffness) and lowered parathyroid hormone (PTH). However, only calcium treatment led to the adverse effects of increased arterial calcification and fibroblast growth factor 23 (FGF23). These results suggest zoledronic acid may improve trabecular bone volume in CKD in the presence of secondary hyperparathyroidism, but does not benefit extraskeletal calcification or cortical biomechanical properties. Calcium effectively reduces PTH and benefits both cortical and trabecular bone yet increases the degree of extra skeletal calcification.

Traditional bone mechanical testing techniques require excised bone and destructive sample preparation. Recently, a cyclic-microindentation technique, reference-point indentation (RPI), was described that allows bone to be tested in a clinical setting, permitting the analysis of changes to bone material properties over time. Because this is a new technique, it has not been clear how the measurements generated by RPI are related to the material properties of bone measured by standard techniques. In this paper, we describe our experience with the RPI technique, and correlate the results obtained by RPI with those of traditional mechanical testing, namely 3-point bending and axial compression. Using different animal models, we report that apparent bone material toughness obtained from 3-point bending and axial compression is inversely correlated with the indentation distance increase (IDI) obtained from RPI with r2 values ranging from 0.50 to 0.57. We also show that conditions or treatments previously shown to cause differences in toughness, including diabetes and bisphosphonate treatment, had significantly different IDI values compared to controls. Collectively these results provide a starting point for understanding how RPI relates to traditional mechanical testing results.

Prehensile-tailed platyrrhines (atelines and Cebus) and procyonids (Potos) display bony tail features that have been functionally and adaptively linked to their prehensile behaviors, particularly the need to resist relatively greater bending and torsional stresses associated with supporting their body weight during suspensory postures. We compared fiber architecture of the mm. intertransversarii caudae (ITC), the prime tail lateral flexors/rotators, in 40 individuals distributed across 8 platyrrhine and 2 procyonid genera, divided into one of two groups: prehensile or nonprehensile. We tested the hypothesis that prehensile-tailed taxa exhibit relatively greater physiologic cross-sectional areas (PCSAs) to maintain tail suspensory postures for extended periods. As an architectural tradeoff of maximizing force, we also predicted prehensile-tailed taxa would exhibit relatively shorter, more pinnate fibers, and a lower mass to tetanic tension ratio (Mass/P O ). Prehensile-tailed taxa have relatively higher PCSAs in all tail regions, indicating their capacity to generate relatively greater maximum muscle forces compared to nonprehensile-tailed taxa. Contrary to our predictions, there are no group differences in pinnation angles, fiber lengths or M/P O ratios. Therefore, the relatively greater prehensile PCSAs are driven largely by relative increase in muscle mass. These findings suggest that relatively greater ITC PCSAs can be functionally linked to the need for prehensile-tailed taxa to suspend and support their body weight during arboreal behaviors. Moreover, maximizing ITC force production may not come at the expense of muscle excursion/ contraction velocity. One advantage of this architectural configuration is it facilitates suspension of the body while simultaneously maximizing tail contact with the substrate. Anat Rec, 292:827-841, 2009.

The prehensile tail may have evolved twice (in parallel) in New World monkeys (platyrrhines), suggesting it is an effective adaptation to negotiating arboreal habitats. Yet, despite the obvious importance of the prehensile tail for balance, feeding behavior, and locomotion, the structural differences between prehensile and nonprehensile tails are poorly understood. Previous studies showed that some linear measurements of caudal vertebrae are capable of distinguishing prehensile from nonprehensile tails but only in the distal parts of the vertebral sequence. This study examines structural properties of the tail with external measurements that are selected to better approximate resistance to bending/torsion while also examining vertebral cross-sectional geometry with computed tomography-a direct measure of resistance to bending/torsion. Specifically, this study tests the hypotheses that the caudal vertebrae (and the tail as a whole) of prehensile-tailed platyrrhines are structured to resist higher torsional and bending stresses than their functional analogues in nonprehensile-tailed platyrrhines, and that the predicted differences become more drastic further distally within the sequence. Results of this study indicate that prehensile and nonprehensile tails are structured differently. Prehensile tails are characterized by longer proximal tail regions than nonprehensile tails. Furthermore, the hemal processes (the distal attachment for the primary tail flexors) of prehensile tail vertebrae are better developed and can distinguish prehensile from nonprehensile tails better than traditionally used external measurements. Finally, results confirm predictions that prehensile tail caudal vertebrae are capable of withstanding higher torsional and bending stresses than their nonprehensile tail counterparts, and that these disparities become more pronounced further distally within the sequence. Anat Rec,

Chronic Kidney Disease (CKD) is associated with abnormalities in bone quantity and quality leading to increased fractures. Recent studies suggest abnormalities of Wnt signaling in animal models of CKD and elevated sclerostin levels in patients with CKD. The goal of this study was to evaluate the effectiveness of anti-sclerostin antibody treatment in an animal model of progressive CKD with low and high parathyroid hormone (PTH) levels. Cy/+ male rats (CKD) were treated without or with calcium in the drinking water at 25 weeks of age to stratify the animals into high PTH and low PTH groups, respectively, by 30 weeks. Animals were then treated with anti-sclerostin antibody at 100 mg/kg IV weekly for 5 doses, a single 20 ug/kg subcutaneous dose of zoledronic acid, or no treatment and sacrificed at 35 weeks. As a positive control, the efficacy of anti-sclerostin antibody treatment was also evaluated in normal littermates. The results demonstrated that the CKD animals with high PTH had lower calcium, higher phosphorus, and lower FGF23 compared to the CKD animals with low PTH. Treatment with anti-sclerostin Ab had no effect on any of the biochemistries, while zoledronic acid lowered dkk-1 levels. The anti-sclerostin antibody increased trabecular BV/TV., trabecular mineralization surface, in animals with low, but not high, PTH. Neither anti-sclerostin antibody nor zoledronic acid improved biomechanical properties in the animals. Cortical porosity was severe in high PTH animals and unaffected by either treatment. In contrast, in normal animals treated with anti-sclerostin antibody, there was an improvement in bone volume, cortical geometry, and biomechanical properties. In summary, this is the first study to test the efficacy of anti-sclerostin Ab treatment on animals with advanced CKD. We found efficacy in improving bone properties only when the PTH levels were low.

Skeletal muscle atrophy and impaired muscle function are associated with lower health-related quality of life, and greater disability and mortality risk in those with chronic kidney disease (CKD). However, the pathogenesis of skeletal dysfunction in CKD is unknown. We used a slow progressing, naturally occurring, CKD rat model (Cy/+ rat) with hormonal abnormalities consistent with clinical presentations of CKD to study skeletal muscle signaling. The CKD rats demonstrated augmented skeletal muscle regeneration with higher activation and differentiation signals in muscle cells (i.e. lower Pax-7; higher MyoD and myogenin RNA expression). However, there was also higher expression of proteolytic markers (Atrogin-1 and MuRF-1) in CKD muscle relative to normal. CKD animals had higher indices of oxidative stress compared to normal, evident by elevated plasma levels of an oxidative stress marker, 8-hydroxy-2' -deoxyguanosine (8-OHdG), increased muscle expression of succinate dehydrogenase (SDH) and Nox4 and altered mitochondria morphology. Furthermore, we show significantly higher serum levels of myostatin and expression of myostatin in skeletal muscle of CKD animals compared to normal. Taken together, these data show aberrant regeneration and proteolytic signaling that is associated with oxidative stress and high levels of myostatin in the setting of CKD. These changes likely play a role in the compromised skeletal muscle function that exists in CKD.

Although the gold standard for determining bones’ mechanical integrity is the direct measure of mechanical properties, clinical evaluation has long relied on surrogates of mechanical properties for assessment of fracture risk. Nearly a decade ago, reference point indentation (RPI) emerged as an innovative way to potentially assess mechanical properties of bone in vivo. Beginning with the BioDent device, and then followed by the newer generation OsteoProbe, this RPI technology has emerged in several papers. In this review we overview the technology and some important details about the two devices. We also highlight select key studies, focused specifically on the in vivo application of these devices, as a way of synthesizing where the technology stands in 2015. The BioDent machine has been shown, in two clinical reports, to be able to differentiate fracture versus non-fracture patient populations and in preclinical studies to detect treatment effects that are consistent with those quantified using traditional mechanical tests. The OsteoProbe appears able to separate clinical cohorts yet there exists a lack of clarity regarding details of testing, which suggests more rigorous work needs to be undertaken with this machine. Taken together, RPI technology has shown promising results, yet much more work is needed to determine if its theoretical potential to assess mechanical properties in vivo can be realized.

Raloxifene treatment has been shown previously to positively affect bone mechanical properties following 1 year of treatment in skeletally mature dogs. Reference point indentation (RPI) can be used for in vivo assessment of mechanical properties and has been shown to produce values that are highly correlated with properties derived from traditional mechanical testing. The goal of this study was to use RPI to determine if raloxifene-induced alterations in mechanical properties occurred after 6 months of treatment. Twelve skeletally mature female beagle dogs were treated for 6 months with oral doses of saline vehicle (VEH, 1 ml/kg/day) or a clinically relevant dose of raloxifene (RAL, 0.5 mg/kg/day). At 6 months, all animals underwent in vivo RPI (10 N force, 10 cycles) of the anterior tibial midshaft. RPI data were analyzed using a custom MATLAB program, designed to provide cycle-by-cycle data from the RPI test and validated against the manufacturer-provided software. Indentation distance increase (IDI), a parameter that is inversely related to bone toughness, was significantly lower in RAL-treated animals compared to VEH (− 16.5%), suggesting increased bone toughness. Energy absorption within the first cycle was significantly lower with RAL compared to VEH (− 21%). These data build on previous work that has documented positive effects of raloxifene on material properties by showing that these changes exist after 6 months.