Bone strength: current concepts

Comparative anti-osteoporotic properties of the leaves and roots of Marantodes pumilum var. alata in postmenopausal rat model

Background

Marantodes pumilum var. alata (MPva), popularly known as Kacip Fatimah, is widely used to maintain female reproductive health, facilitate post-partum recovery and manage symptoms of menopause and osteoporosis in South-East Asia. This study aims to further evaluate the osteoprotective potential of MPva in view of reports of its bone-protective properties in postmenopausal condition.

Methods

Thirty female Sprague-Dawley rats were sorted into 5 groups (n = 6) namely: MPv (leaf treatment); MPr (root treatment); ERT (estrogen treatment); OVXC (untreated ovariectomized control) and Sham (untreated sham-operated control). All rats (except the Sham) were ovariectomized to induce a state of estrogen deficiency that simulates menopause. Two weeks after ovariectomy, the rats were treated for 8 weeks with oral gavages of estrogen and plant extracts. The ERT group received 64.5 μg/kg/day dose of estrogen while MPv and MPr groups received 20 mg/kg/day dose of leaf and root extracts, respectively. At the end of treatment, left femora were excised from euthanized rats and investigated for changes in bone micro-architecture, mineral density, and biomechanical properties.

Results

Bone volume fraction, degree of anisotropy and structure-model-index of bone were significantly improved (p < 0.05) in the MPv group compared to OVXC. Breaking force and maximum stress of bone were also significantly higher (p < 0.05) in the MPv group compared to the OVXC.

Conclusion

Treatment with MPva leaf protected bone microarchitecture and density against osteoporosis-related changes in postmenopausal rats. Similar to estrogen, the protective effects of MPva leaf translated into better-enhanced bone mechanical properties compared to the root treatment.

Skeletal macro- and microstructure adaptations in men undergoing arduous military training

PURPOSE

Short periods of basic military training increase the density and size of the tibia, but the adaptive response of bone microarchitecture, a key component of bone strength, is not fully understood.

METHODS

Tibial volumetric bone mineral density (vBMD), geometry, microarchitecture and mechanical properties were measured using high-resolution peripheral quantitative computed tomography in 43 male British Army infantry recruits (mean ± SD, age 21 ± 3 years, height 1.76 ± 0.06 m, body mass 76.5 ± 9.4 kg). Bilateral scans were performed at the distal tibia at the start (week 1) and end (week 13) of basic military training. Concurrent measures were obtained for whole-body areal bone mineral density (aBMD) using DXA, and markers of bone metabolism (βCTX, P1NP, PTH, total 25(OH)D and ACa) from venous blood.

RESULTS

Training increased areal BMD for total body (1.4%) and arms (5.2%) (P ≤ 0.031), but not legs and trunk (P ≥ 0.094). Training increased trabecular (1.3 to 1.9%) and cortical vBMD (0.6 to 0.9%), trabecular volume (1.3 to 1.9%), cortical thickness (3.2 to 5.2%) and cortical area (2.6 to 2.8%), and reduced trabecular area (-0.4 to -0.5%) in both legs (P < 0.001). No changes in trabecular number, thickness and separation, cortical porosity, stiffness or failure load were observed (P ≥ 0.188). βCTX decreased (-0.11 μg∙l^-1, P < 0.001) and total 25(OH)D increased (9.4 nmol∙l^-1, P = 0.029), but no differences in P1NP, PTH or ACa were observed between timepoints (P ≥ 0.233).

CONCLUSION

A short period of basic military training increased density and altered geometry of the distal tibia in male military recruits. The osteogenic effects of basic military training are likely due to an increase in unaccustomed, dynamic and high-impact loading.

The Effect of Calcium Deficiency on Bone Properties in Growing Rats

Background:

In this work, the study of the physicochemical properties of the rat bones that were fed under severe and moderate calcium depletion was carried out. Calcium depletion is a common problem in the diet of the third world.

Objective:

Three calcium levels: 5000, 2500, and 1039 mg/kg, were used in the diets to evaluate the influence of calcium deficiency on the bone quality by post-mortem tests.

Methods:

Inductive Coupled Plasma was used to study the elemental chemical composition of the bones; X-ray diffraction evaluated the bone structure and crystallinity; the microstructure and architecture were investigated using scanning electron microscopy; thermogravimetric analysis assessed the ratio between organic and inorganic phases of bones. All of these results were correlated with flexion and compression test determining the biomechanical properties to evaluate the bone quality.

Results:

The results showed that severe calcium depletion (75% depletion, 1039 mg/kg) was a critical factor in the unsuitable mineralization process responsible for the deterioration of bone quality. Bone architecture with delicate trabeculae caused the poor mechanical response. For moderate calcium depletion (50% of the request, 2500 mg/kg), the bone quality and its mechanical behavior showed less deterioration in comparison with bones of severe calcium depletion diet.

Conclusion:

By using this animal model, the effect of calcium depletion in bone mineralization in rats was understood and can be extrapolated for humans.

X-ray densitometric indices of proximal phalanx, medial phalanx and ungular pelvic limb bones as criteria for age diagnosis of cattle in forensic veterinary expertise

Morphological parameters of biological material are extremely informative in diagnostic studies, in particular, to determine the species, sex, time of death, the term of burial. The most informative object for these tasks is the skeleton, because changes in the bones are stored for a long time, while soft tissue is subjected to rotting. Bone tissue is the most durable, but at the same time, it is very labile and reacts to all metabolic processes in the body. The object of the study was proximal phalanx, medial phalanx and ungular bone of the pelvic limb of cattle ranging in age from newborn to 12 years old. Radiography of the proximal phalanx, medial phalanx and ungular bones of the pelvic limb was performed on the Arman apparatus. The bones were subjected to X-ray in the lateromedial projection. The inner and outer sections of the tubular bone were determined. The mathematical modeling of the interaction of X-rays and the cortical layer of bones of fingers (proximal phalanx, medial phalanx and ungular) of cattle was carried out in this work. It is established that this process is described by Bouger's law. The physico-mathematical model of proximal phalanx, medial phalanx and ungular bones has been calculated, on the basis of which it was possible to calculate the X-ray densitometric indices of these bones of cattle. The age features of dynamics of X-ray densitometric indices of the proximal phalanx, medial phalanx and ungular bones were established and a method of determining the age of cattle according to this criterion was proposed. A mathematical model for the proximal phalanx, medial phalanx and ungular bones of the pelvic limbs of cattle that can be applied in X-ray densitometry uses: for the average third proximal phalanx – section of heterogeneous tubular structure modeled by a semicircle; for a medial phalanx bone – a section of a triangular shape; for the ungular bone – a heterogeneous structure, the plantar surface is inscribed in a rectangle. The process of interaction of X-rays with the bone structure of the examined pelvic limb bones can be described by Bouguer's law. The developed mathematical modeling of this interaction and the algorithm for its analysis is the basis for determining the age of cattle for X-ray densitometric indices of the proximal phalanx, medial phalanx and ungular bones of pelvic limbs. By X-ray densitometry of the proximal phalanx and medial phalanx bones of the pelvic limbs extremities one can diagnose the age of bovine animals from birth to 5 years, but according to ungular bones – from birth to 10 years. X-ray densitometry of medial phalanx and ungular bones of pelvic limbs can be used for diagnosing bovine cattle in a complex with other morphological, chemical and physical methods of investigation.

The effect of peripheral nervous system in growing bone biomechanics. An experimental study

Objective

There are several factors which affect bone growth. One of them is the peripheralnervous system whose effect on the biomechanics has not been extensively studied. The purpose of this study is to assess the effect of peripheral nervous system in bone biomechanics in an experimental rat model.

Materials & methods

27 male Wistar rats were used. In all animals, the roots of the right brachial plexus were dissected and after that the animals were divided into three groups A, B and C. The animals were sacrificed six, nine, and twelve months respectively after the denervation. Both humerus were resected and biomechanical analysis was performed.

Results

According to the findings of the present study the denervated bones sustain less loading before fracture and they become also more elastic. Additionally, in greater time after denervation plastic deformity is noticed.

Conclusion

Apart from structural changes, the peripheral nerves are responsible for biomechanic changes in the bones such the greater elasticity of the bone and the reduced strength.

Postmortem change in bone biomechanical properties: Loss of plasticity

Bone is a hierarchical composite material composed primarily of collagen molecules, mineral crystals, and water. The mineral phase confers strength and stiffness while the organic matrix provides toughness. As a result, living bone is very capable of absorbing energy and resisting fracture. After death, the bone often becomes dehydrated and the collagen degrades causing greater stiffness and reduced toughness. These changes in mechanical properties are augmented due to the combined effects of water loss and collagen degradation. As a result, bone becomes more brittle postmortem, which causes the changes in fracture characteristics that are commonly used to estimate the timing of the fracture. However, because the loss of moisture and collagen degradation are influenced by taphonomic conditions, anthropologist must use caution when interpreting the timing of fractures based solely on fracture characteristics. As part of this special volume on hard tissue alterations associated with trauma, the aim of this article is to provide an overview of the mechanical changes that occur in bone postmortem and summarize major works in bone biology and anthropology examining the cause and timing of plasticity loss in bone after death.

Is bone loss a physiological cost of reproduction in the Great fruit-eating bat Artibeus lituratus?

During mammalian pregnancy and lactation, the maternal demand for calcium is increased to satisfy fetus and newborn skeletal growth. In addition to the dietary intake, females use the calcium contained in their bones to supply this increased demand, leading to a decrease in maternal bone mineral content. In reproductive insectivorous female bats, bone loss has been described as a physiological cost of reproduction, due to the reported increased risk of bone fracture. This physiological cost may be the mechanism underlying the conflict between increasing litter size and maintaining wing skeletal integrity, which would help to explain the small litter size of most bat species. If bone loss is a linking cost between reproduction and survival in bats, and most bat species have small litter sizes, one would expect to find a loss of bone and an increasing probability of bone fracture during pregnancy and lactation in other non-insectivorous bats. In this study, we tested for the existence of this cost in the Great-fruit eating bat, Artibeus lituratus. We analyzed trabecular structure, bone strength and bone mineral content for the humerus bone, hypothesizing that bone loss during reproduction in females would increase the risk of fracture. Our results showed a decrease of 22-31% in bone trabecular area in lactating females, rapidly compensated following weaning. Bone strength did not differ among reproductive and non-reproductive groups and seems to be more influenced by bone organic components rather than mineral contents. Since we observed bone loss during reproduction yet the humerus strength seems to be unaffected, we suggest that bone loss may not represent a physiological cost during reproduction for this frugivorous bat.

An Evidence-Based Review: The Effects of Malaysian Traditional Herbs on Osteoporotic Rat Models

Osteoporosis is considered a silent disease, the early symptoms of which often go unrecognised. Osteoporosis causes bone loss, reduces mineralised density, and inevitably leads to bone fracture. Hormonal deficiencies due to aging or drug induction are also frequently attributed to osteoporosis. Nevertheless, the phytochemical content of natural plants has been proven to significantly reduce osteoporotic conditions. A systematic review was conducted by this study to identify research specifically on the effects of Malaysian herbs such as Piper sarmentosum, Eurycoma longifolia and Labisia pumila on osteoporotic bone changes. This review consisted of a comprehensive search of five databases for the effects of specific herbs on osteoporotic bone change. These databases were Web of Science (WOS), Medline, Scopus, ScienceDirect and PubMed. The articles were selected throughout the years, were limited to the English language and fully documented. Duplication, irrelevant titles, different herbs and in vitro studies were excluded, including those that are not original research papers. A total of 399 potential studies were identified, but only 21 samples were accepted based on the inclusion and exclusion criteria. Six of the twenty one studies were on Piper sarmentosum, six on Eurycoma longifolia, and the remaining nine studies were on Labisia pumila. Overall, in three of the studies a glucocorticoid-induced model was used, while in 12 of the studies an ovariectomised model was used, and for the other six studies an orchidectomised model was used as the osteoporotic model. All of the studies reported varied results based on the type of herbs used, but in comparison to Eurycoma longifolia, Piper sarmentosum and Labisia pumila recorded better anti-osteoporotic effects, while the majority of studies on Eurycoma longifolia were unable to preserve bone strength.

A Thoroughbred racehorse with a unicortical palmar lateral condylar fracture returned to training 14 days after surgery: a hypothesis on the role of a single bone screw on crack propagation

A 2-year-old Thoroughbred racehorse had LF lameness that began post high-speed exercise and persisted for two days before the horse once again became sound. Diagnostic analgesia localized the lameness to the LF distal metacarpus, and a standing MRI identified a unicortical condylar fracture. A single 5.5 mm cortical screw was placed in lag fashion. The horse began hand walking at 14 days, racetrack jogging at 30 days, and racing at 5 months after the day of surgery. Placement of a single lag screw ahead of the tip of the crack in unicortical condylar fracture may be useful for reducing the recovery period for horses returning to training and racing.

Regulation of Wnt signaling by physical exercise in the cell biological processes of the locomotor system

In the past decade, researches on Wnt signaling in cell biology have made remarkable progress regarding our understanding of embryonic development, bone formation, muscle injury and repair, neurogenesis, and tumorigenesis. The study also showed that physical activity can reverse age-dependent decline in skeletal muscle, preventing osteoporosis, regenerative neurogenesis, hippocampal function, cognitive ability, and neuromuscular junction formation, and the age-dependent recession is highly correlated with Wnt signaling pathways. However, how the biological processes in cell and physical activity during/following exercise affect the Wnt signaling path of the locomotor system is largely unknown. In this study, we first briefly introduce the important features of the cellular biological processes of exercise in the locomotor system. Then, we discuss Wnt signaling and review the very few studies that have examined Wnt signaling pathways in cellular biological processes of the locomotor system during physical exercise.

Comparison of Proximal Femoral Geometry and Risk Factors between Femoral Neck Fractures and Femoral Intertrochanteric Fractures in an Elderly Chinese Population

Background

Few studies have investigated the differences in proximal femoral geometry and risk factors between patients with different types of hip fracture, especially in elderly Chinese. This study aimed to assess the differences in proximal femoral geometry parameters between patients with femoral neck fractures and patients with intertrochanteric fractures to provide guidance for individualized customized prosthesis and accurate reconstruction of proximal femurs in elderly Chinese patients.

Methods

We retrospectively studied the electronic medical records of 198 elderly patients over 65 years of age who were admitted to the orthopedic department with hip fractures between January 2017 and December 2017 in The Third Hospital, Hebei Medical University. Age, fracture site, gender, and proximal femoral geometry parameters (neck shaft angle [NSA], center edge angle [CEA], femoral head diameter [FHD], femoral neck diameter [FND], femoral neck axial length [FNAL], hip axial length [HAL], and femoral shaft diameter [FSD]) were recorded. Student's t-test was used to compare the continuous variables, Chi-square test was used to analyze categorical variables, and multiple logistic stepwise regression analysis was used to evaluate the influencing factors of hip fracture type.

Results

Statistically significant differences in NSA (137.63 ± 4.56° vs. 132.07 ± 4.17°, t = 1.598, P < 0.001), CEA (37.62 ± 6.77° vs. 43.11 ± 7.09°, t = 5.597, P < 0.001), FND (35.21 ± 3.25 mm vs. 34.09 ± 3.82 mm, t = 2.233, P = 0.027), and FNAL (99.30 ± 7.91 mm vs. 103.58 ± 8.39 mm, t = 3.715, P < 0.001) were found between the femoral neck fracture group and femoral intertrochanteric fracture group. FHD, FND, FSD, HAL, and FNAL were different between sexes (all P < 0.001). The greater NSA was the risk factor for femoral neck fractures (odds ratio [OR]: 0.70, P < 0.001), greater CEA and longer FNAL were risk factors for femoral intertrochanteric fractures (OR: 1.15, 1.17, all P < 0.001), and greater FND was a protective factor for femoral intertrochanteric fractures (OR: 0.74, P < 0.001).

Conclusions

We demonstrate differences in geometric morphological parameters of the proximal femur in different hip fracture types, as well as an effect of sex. These differences should be considered in the selection of prostheses for fracture internal fixation and hip replacements. These data could help guide the design of individualized customized prostheses and improve the accurate reconstruction of the proximal femur for elderly Chinese hip fracture patients.

Early Evidence for Northern Salmonid Fisheries Discovered using Novel Mineral Proxies

Salmonid resources currently foster socioeconomic prosperity in several nations, yet their importance to many ancient circumpolar societies is poorly understood due to insufficient fish bone preservation at archaeological sites. As a result, there are serious gaps in our knowledge concerning the antiquity of northern salmonid fisheries and their impacts on shaping biodiversity, hunter-gatherer adaptations, and human-ecological networks. The interdisciplinary study presented here demonstrates that calcium-magnesium phosphate minerals formed in burned salmonid bones can preserve at ancient northern sites, thus informing on the early utilization of these resources despite the absence of morphologically classifiable bones. The minerals whitlockite and beta magnesium tricalcium phosphate were identified in rare morphologically classifiable Atlantic salmonid bones from three Mid-Holocene sites in Finland. Large amounts of beta magnesium tricalcium phosphate were also experimentally formed by burning modern Atlantic salmonid and brown trout bones. Our results demonstrate the value of these minerals as proxies for ancient northern salmonid fishing. Specifically, the whitlockite mineral was discovered in hearth sediments from the 5,600 year old Yli-Ii Kierikinkangas site on the Iijoki River in northern Finland. Our fine sieving and mineralogical analyses of these sediments, along with zooarchaeological identification of recovered bone fragments, have confirmed for the first time that the people living at this village did incorporate salmonids into their economies, thus providing new evidence for early estuary/riverine fisheries in northern Finland.

Mandibular shape in farmed Arctic foxes (Vulpes lagopus) exposed to persistent organic pollutants

We investigated if dietary exposure to persistent organic pollutants (POPs) affect mandibular asymmetry and periodontal disease in paired male-siblings of Arctic foxes (Vulpes lagopus). During ontogeny, one group of siblings was exposed to the complexed POP mixture in naturally contaminated minke whale (Balaenoptere acutorostarta) blubber (n = 10), while another group was given wet feed based on pig (Sus scrofa) fat as a control (n = 11). The ∑POP concentrations were 802 ng/g ww in the whale-based feed compared to 24 ng/g ww in the control diet. We conducted a two-dimensional geometric morphometric (GM) analysis of mandibular shape and asymmetry in the foxes and compared the two groups. The analyses showed that directional asymmetry was higher than fluctuating asymmetry in both groups and that mandibular shape differed significantly between the exposed and control group based on discriminant function analysis (T² = 58.52, p = 0.04, 1000 permutations). We also found a non-significantly higher incidence of periodontal disease (two-way ANOVA: p = 0.43) and greater severity of sub-canine alveolar bone deterioration similar to periodontitis (two-way ANOVA: p = 0.3) in the POP-exposed group. Based on these results, it is possible that dietary exposure to a complexed POP mixture lead to changes in jaw morphology in Arctic foxes. This study suggests that extrinsic factors, such as dietary exposure to POPs, may affect mandibular shape and health in a way that could be harmful to wild Arctic populations. Therefore, further studies using GM analysis as an alternative to traditional morphometric methods should be conducted for wild Arctic fox populations exposed to environmental contaminants.

Women with fracture, unidentified by FRAX, but identified by cortical porosity, have a set of characteristics that contribute to their increased fracture risk beyond high FRAX score and high cortical porosity

The Fracture Risk Assessment Tool (FRAX) is widely used to identify individuals at increased risk for fracture. However, cortical porosity is associated with risk for fracture independent of FRAX and is reported to improve the net reclassification of fracture cases. We wanted to test the hypothesis that women with fracture who are unidentified by high FRAX score, but identified by high cortical porosity, have a set of characteristics that contribute to their fracture risk beyond high FRAX score and high cortical porosity. We quantified FRAX score with femoral neck areal bone mineral density (FN aBMD), and femoral subtrochanteric architecture, in 211 postmenopausal women aged 54-94 years with non-vertebral fractures, and 232 fracture-free controls in Tromsø, Norway, using StrAx software. Of 211 fracture cases, FRAX score > 20% identified 53 women (sensitivity 25.1% and specificity 93.5%), while cortical porosity cut-off > 80th percentile identified 61 women (sensitivity 28.9% and specificity 87.9%). The 43 (20.4%) additional fracture cases identified by high cortical porosity alone, had lower FRAX score (12.3 vs. 26.2%) than those identified by FRAX alone, they were younger, had higher FN aBMD (806 vs. 738 mg/cm²), and fewer had a prior fracture (23.3 vs. 62.9%), all p < 0.05. They had higher cortical porosity (48.7 vs. 42.1%), thinner cortices (3.75 vs. 4.12 mm), lower cortical and total volumetric BMD (942 vs. 1053 and 586 vs. 699 mg HA/cm³), larger medullary and total cross-sectional areas (245 vs. 190 and 669 vs. 593 mm²), and higher cross-sectional moment of inertia (2619 vs. 2388 cm⁴) all p < 0.001. When the fracture cases and controls with high cortical porosity were compared, cases had higher cortical porosity, lower cortical vBMD, lower total vBMD, smaller cortical CSA/Total CSA, larger medullary CSA and larger total CSA than controls (all p ≤ 0.05). Thus, fracture cases, unidentified by FRAX, but identified by cortical porosity, had an architecture where the positive impact of larger bone size did not offset the negative effect of thinner cortices with increased porosity. A measurement of cortical porosity may be a marker of other characteristics that capture additional fracture risk components, not captured by FRAX.

Cortical bone quality affectations and their strength impact analysis using holographic interferometry

It is now accepted that bone strength is a complex property determined mainly by three factors: quantity, quality and turnover of the bone itself. Most of the patients who experience fractures due to fragility could never develop affectations related to bone mass density (i.e. osteoporosis). In this work, the effect of secondary bone strength affectations are analyzed by simulating the degradation of one or more principal components (organic and inorganic) while they are inspected with a nondestructive optical technique. From the results obtained, a strong correlation among the hydroxyapatite, collagen and water is found that determines the bone strength.

Age-dependent bone loss and recovery during hindlimb unloading and subsequent reloading in rats

Background

Bone structure and strength are rapidly lost during conditions of decreased mechanical loading, and aged bones have a diminished ability to adapt to increased mechanical loading. This is a concern for older patients that experience periods of limited mobility or bed rest, but the acute effects of disuse on the bones of aged patients have not been thoroughly described. Previous animal studies have primarily examined the effect of mechanical unloading on young animals. Those that have studied aged animals have exclusively focused on bone loss during unloading and not bone recovery during subsequent reloading. In this study, we investigated the effect of decreased mechanical loading and subsequent reloading on bone using a hindlimb unloading model in Adult (9 month old) and Aged (28 month old) male rats.

Methods

Animals from both age groups were subjected to 14 days of hindlimb unloading followed by up to 7 days of reloading. Additional Aged rats were subjected to 7 days of forced treadmill exercise during reloading or a total of 28 days of reloading. Trabecular and cortical bone structure of the femur were quantified using ex vivo micro-computed tomography (μCT), and mechanical properties were quantified with mechanical testing.

Results

We found that Adult rats had substantially decreased trabecular bone volume fraction (BV/TV) following unloading (− 27%) while Aged animals did not exhibit significant bone loss following unloading. However, Aged animals had lower trabecular BV/TV after 3 days of reloading (− 20% compared to baseline), while trabecular BV/TV of Adult rats was not different from baseline values after 3 days of reloading. Trabecular BV/TV of Aged animals remained lower than control animals even with exercise during 7 days of reloading and after 28 days of reloading.

Conclusions

These data suggest that aged bone is less responsive to both increased and decreased mechanical loading, and that acute periods of disuse may leave older subjects with a long-term deficit in trabecular bone mass. These finding indicate the need for therapeutic strategies to improve the skeletal health of elderly patients during periods of disuse.

Emerging concepts in the epidemiology, pathophysiology, and clinical care of osteoporosis across the menopausal transition

Bone loss in women accelerates during perimenopause, and continues into old age. To-date, there has been little progress made in stratifying for fracture risk in premenopausal and early postmenopausal women. Epidemiologic data suggests that changes in serum FSH could predict decrements in bone mass during peri- and postmenopause. In bone, FSH stimulates osteoclast formation by releasing osteoclastogenic cytokines. Here, we address the evidence for bone loss across the menopausal transition, discuss strategies for detection and treatment of early postmenopausal osteoporosis, and describe the role FSH plays in physiology and likely in pathophysiology of early postmenopausal bone loss.

Unraveling the compromised biomechanical performance of type 2 diabetes- and Roux-en-Y gastric bypass bone by linking mechanical-structural and physico-chemical properties

Type 2 diabetes mellitus (T2DM) is a metabolic disorder associated with obesity and hyperglycemia. Roux-en-Y gastric bypass (RYGB) surgery is a common treatment for severely obese patients and T2DM. Both RYGB and T2DM are linked to increased skeletal fragility, though the exact mechanisms are poorly understood. Our aim was to characterize the structural, mechanical and compositional properties of bones from diet-induced obese and RYGB-treated obese (bypass) mice to elucidate which the exact factors are contributing to the increased skeletal fragility. To achieve this, a combinatory approach including microfocus X-ray computed tomography, 3-point bending, finite element modeling and Raman spectroscopy, was used. Compared to aged-matched lean controls, the obese mice displayed decreased cortical thickness, trabecular bone loss, decreased stiffness and increased Young’s modulus. For the bypass mice, these alterations were even more pronounced, and additionally they showed low mineral-to-matrix ratio in the cortical endosteal area. Accumulation of the advanced glycation end-product (AGE) pentosidine was found in the cortex of obese and bypass groups and this accumulation was correlated with an increased Young’s modulus. In conclusion, we found that the increased fracture risk in T2DM- and post-RYGB bones is mainly driven by accumulation of AGEs and macro-structural alterations, generating biomechanical dysfunctionality.

Quantitative imaging techniques for the assessment of osteoporosis and sarcopenia

Bone and muscle are two deeply interconnected organs and a strong relationship between them exists in their development and maintenance. The peak of both bone and muscle mass is achieved in early adulthood, followed by a progressive decline after the age of 40. The increase in life expectancy in developed countries resulted in an increase of degenerative diseases affecting the musculoskeletal system. Osteoporosis and sarcopenia represent a major cause of morbidity and mortality in the elderly population and are associated with a significant increase in healthcare costs. Several imaging techniques are currently available for the non-invasive investigation of bone and muscle mass and quality. Conventional radiology, dual energy X-ray absorptiometry (DXA), computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound often play a complementary role in the study of osteoporosis and sarcopenia, depicting different aspects of the same pathology. This paper presents the different imaging modalities currently used for the investigation of bone and muscle mass and quality in osteoporosis and sarcopenia with special emphasis on the clinical applications and limitations of each technique and with the intent to provide interesting insights into recent advances in the field of conventional imaging, novel high-resolution techniques and fracture risk.

Chronic arsenicosis and cadmium exposure in wild snowshoe hares (Lepus americanus) breeding near Yellowknife, Northwest Territories (Canada), part 2: Manifestation of bone abnormalities and osteoporosis

Various bone abnormalities, including osteoporosis, have been associated with chronic arsenic and cadmium exposure in experimental animal models, but information regarding the bone pathology of wild population of small mammals breeding in contaminated environment is limited. This present study was conducted to comparatively assess the prevalence and pattern of skeletal abnormalities in free ranging snowshoe hares inhabiting an area heavily contaminated by arsenic and other trace metals, near the vicinity of the abandoned Giant mine, and in a reference location approximately 20km from the city of Yellowknife, Northwest Territories, Canada. The femur and vertebrae of snowshoe hares from the mine area and reference location were subjected to bone densitometry examination and biomechanical testing using dual energy X-ray absorptiometry (DXA) and 3-point bending test. t-test results indicated that femoral densitometry parameters such as bone mineral density (BMD) (p=0.5), bone mineral content (BMC) (p=0.675), bone area (BA) (p=0.978) and tissue area (TA) (p=0.549) were not significantly different between locations. All densitometry parameters of the vertebrae (BMD, BA and TA) differed between locations (p<0.05), except for BMC (p=0.951) which showed no significant difference between the two locations. Vertebrae from the mine area also showed relatively lower BA and TA compared to the reference location. A constellation of skeletal abnormalities were also observed along the axial and appendicular bones respectively. Specifically, growth defects, osteoporosis, cortical fractures, sclerosis, and cyst like changes were commonly observed in the femurs and vertebrae of hares from both locations. With respect to biomechanical properties, only bone stiffness and peak load tended to be relatively reduced in specimens from the mine area, whereas work to failure was notably increased in specimens from the reference site compared to those from the mine area. Taken together, the results of this preliminary study suggest that chronic concomitant exposure to arsenic and cadmium may be involved in the etiology of various bone abnormalities, including osteoporosis in wild population of snowshoe hares from the Yellowknife area. The result presented in this study represent the first evaluation of osteological effects in free-ranging furbearers (snowshoe hares) diagnosed with arsenicosis, and concomitantly exposed to environmental levels of cadmium.

Updating osteoimmunology: regulation of bone cells by innate and adaptive immunity

Osteoimmunology encompasses all aspects of the cross-regulation of bone and the immune system, including various cell types, signalling pathways, cytokines and chemokines, under both homeostatic and pathogenic conditions. A number of key areas are of increasing interest and relevance to osteoimmunology researchers. Although rheumatoid arthritis has long been recognized as one of the most common autoimmune diseases to affect bone integrity, researchers have focused increased attention on understanding how molecular triggers and innate signalling pathways (such as Toll-like receptors and purinergic signalling pathways) related to pathogenic and/or commensal microbiota are relevant to bone biology and rheumatic diseases. Additionally, although most discussions relating to osteoimmune regulation of homeostasis and disease have focused on the effects of adaptive immune responses on bone, evidence exists of the regulation of immune cells by bone cells, a concept that is consistent with the established role of the bone marrow in the development and homeostasis of the immune system. The active regulation of immune cells by bone cells is an interesting emerging component of investigations that seek to understand how to control immune-associated diseases of the bone and joints.

Skeletal Muscle as an Endocrine Organ: The Role of Myokines in Exercise Adaptations

Exercise stimulates the release of proteins with autocrine, paracrine, or endocrine functions produced in skeletal muscle, termed myokines. Based on the current state of knowledge, the major physiological function of myokines is to protect the functionality and to enhance the exercise capacity of skeletal muscle. Myokines control adaptive processes in skeletal muscle by acting as paracrine regulators of fuel oxidation, hypertrophy, angiogenesis, inflammatory processes, and regulation of the extracellular matrix. Endocrine functions attributed to myokines are involved in body weight regulation, low-grade inflammation, insulin sensitivity, suppression of tumor growth, and improvement of cognitive function. Muscle-derived regulatory RNAs and metabolites, as well as the design of modified myokines, are promising novel directions for treatment of chronic diseases.

Elevated Levels of Peripheral Kynurenine Decrease Bone Strength in Rats with Chronic Kidney Disease

The diagnosis and treatment of bone disorders in patients with chronic kidney disease (CKD) represent a clinical challenge. CKD leads to mineral and bone complications starting early in the course of renal failure. Recently, we have observed the positive relationship between intensified central kynurenine turnover and bone strength in rats with subtotal 5/6 nephrectomy (5/6 Nx)-induced CKD. The aim of the present study was to determine the association between peripheral kynurenine pathway metabolites and bone strength in rats with 5/6 Nx-induced CKD. The animals were sacrificed 1 and 3 months after 5/6 Nx or sham operation. Nephrectomized rats presented higher concentrations of serum creatinine, urea nitrogen, and parathyroid hormone both 1 and 3 months after nephrectomy. These animals revealed higher concentrations of kynurenine and 3-hydroxykynurenine in the serum and higher gene expression of aryl hydrocarbon receptor (AhR) as a physiological receptor for kynurenine and AhR-dependent cytochrome in the bone tissue. Furthermore, nephrectomy significantly increased the number of osteoclasts in the bone without affecting their resorptive activity measured in serum. These changes were particularly evident in rats 1 month after 5/6 Nx. The main bone biomechanical parameters of the tibia were unchanged between nephrectomized and sham-operated rats but were significantly increased in older compared to younger animals. A similar trend was observed for geometrical parameters measured with calipers, bone mineral density based on Archimedes' method and image of bone microarchitecture obtained from micro-computed tomography analyses of tibial cortical bone. In nephrectomized animals, peripheral kynurenine levels correlated negatively with the main parameters of bone biomechanics, bone geometry, and bone mineral density values. In conclusion, our data suggest that CKD-induced elevated levels of peripheral kynurenine cause pathological changes in bone structure via AhR pathway. This finding opens new opportunities for the treatment/prevention of osteoporosis in CKD.

Recombinant sclerostin antagonizes effects of ex vivo mechanical loading in trabecular bone and increases osteocyte lacunar size

Sclerostin has emerged as an important regulator of bone mass. We have shown that sclerostin can act by targeting late osteoblasts/osteocytes to inhibit bone mineralization and to upregulate osteocyte expression of catabolic factors, resulting in osteocytic osteolysis. Here we sought to examine the effect of exogenous sclerostin on osteocytes in trabecular bone mechanically loaded ex vivo. Bovine trabecular bone cores, with bone marrow removed, were inserted into individual chambers and subjected to daily episodes of dynamic loading. Cores were perfused with either osteogenic media alone or media containing human recombinant sclerostin (rhSCL) (50 ng/ml). Loaded control bone increased in apparent stiffness over time compared with unloaded bone, and this was abrogated in the presence of rhSCL. Loaded bone showed an increase in calcein uptake as a surrogate of mineral accretion, compared with unloaded bone, in which this was substantially inhibited by rhSCL treatment. Sclerostin treatment induced a significant increase in the ionized calcium concentration in the perfusate and the release of β-CTX at several time points, an increased mean osteocyte lacunar size, indicative of osteocytic osteolysis, and the expression of catabolism-related genes. Human primary osteocyte-like cultures treated with rhSCL also released β-CTX from their matrix. These results suggest that osteocytes contribute directly to bone mineral accretion, and to the mechanical properties of bone. Moreover, it appears that sclerostin, acting on osteocytes, can negate this effect by modulating the dimensions of the lacunocanalicular porosity and the composition of the periosteocyte matrix.

HIGH-IMPACT DROP EXERCISE ALTERS MECHANICAL PROPERTIES IN OSTEOPENIC BONE

ABSTRACT Introduction: Osteopenia is a reversible condition and precedes osteoporosis. Physical activity and mechanical loading appear to play an important role in the regulation of bone homeostasis, without the side effects of targeted drug therapy. However, there is controversy as to which type of stimulus promotes more effective adaptations with respect to mechanical properties of bones. Objective: To investigate the effects of high-impact drop training on bone structure after ovariectomy-induced osteopenia in 40 10-week-old female Wistar rats. Methods: Twenty female rats (prevention program) were randomly assigned into two groups (n=10): Ovariectomized sedentary (OVXs), and OVX trained (OVX+Dropt). OVX+Dropt animals began training 3 days after surgery. Another twenty female rats (treatment program) were randomly assigned to two other groups (n=10): Ovariectomized sedentary (OVXs), and OVX trained (OVX+Dropt). OVX+Dropt animals began training 60 days after surgery. The rats in the trained groups were dropped from 40 cm height 20 times/day, 5 days/week over a period of 12 weeks period. At the end, the biomechanical tests were analyzed. Results: The final load and stiffness of the left tibia in the trained groups were higher than in the sedentary groups (p<0.05). Conclusions: Dropping exercise induced favorable changes in bone mechanical properties. High-impact drop exercise is effective to prevent bone loss after ovariectomy even when osteopenia is already established.

Development of a novel method for the strengthening and toughening of irradiation-sterilized bone allografts

Reconstruction of large skeletal defects is a significant and challenging issue. Bone allografts are often used for such reconstructions. However, sterilizing bone allografts by using γ-irradiation, damages collagen and causes the bone to become weak, brittle and less fatigue resistant. In a previous study, we successfully protected the mechanical properties of human cortical bone by conducting a pre-treatment with ribose, a natural and biocompatible agent. This study focuses on examining possible mechanisms by which ribose might protect the bone. We examined the mechanical properties, crosslinking, connectivity and free radical scavenging potentials of the ribose treatment. Human cortical bone beams were treated with varying concentration of ribose (0.06-1.2 M) and γ-irradiation before testing them in 3-point bending. The connectivity and amounts of crosslinking were determined with Hydrothermal-Isometric-Tension testing and High-Performance-Liquid-Chromatography, respectively. The free radical content was measured using Electron Paramagnetic Resonance. Ribose pre-treatment improved the mechanical properties of irradiation sterilized human bone in a pre-treatment concentration-dependent manner. The 1.2 M pre-treatment provided >100% of ultimate strength of normal controls and protected 76% of the work-to-fracture (toughness) lost in the irradiated controls. Similarly, the ribose pre-treatment improved the thermo-mechanical properties of irradiation-sterilized human bone collagen in a concentration-dependent manner. Greater free radical content and pentosidine content were modified in the ribose treated bone. This study shows that the mechanical properties of irradiation-sterilized cortical bone allografts can be protected by incubating the bone in a ribose solution prior to irradiation.

Micro-computed tomography assisted distal femur metaphyseal blunt punch compression for determining trabecular bone strength in mice

Shorter generation time and the power of genetic manipulation make mice an ideal model system to study bone biology as well as bone diseases. However their small size presents a challenge to perform strength measurements, particularly of the weight-bearing cancellous bone in the murine long bones. We recently developed an improved method to measure the axial compressive strength of the cancellous bone in the distal femur metaphysis in mice. Transverse micro-computed tomography image slices that are 7µm thick were used to locate the position where the epiphysis-metaphysis transition occurs. This enabled the removal of the distal femur epiphysis at the exact transition point exposing the full extent of metaphyseal trabecular bone, allowing more accurate and consistent measurement of its strength. When applied to a murine model system consisting of five month old male wild-type (WT) and Ca(2+)/calmodulin dependent protein kinase kinase 2 (CaMKK2) knockout (KO) Camkk2(-/-) mice that possess recorded differences in trabecular bone volume, data collected using this method showed good correlation between bone volume fraction and strength of trabecular bone. In combination with micro-computed tomography and histology, this method will provide a comprehensive and consistent assessment of the microarchitecture and tissue strength of the cancellous bone in murine mouse models.

Jumping exercise preserves bone mineral density and mechanical properties in osteopenic ovariectomized rats even following established osteopenia

The effects of jump training on bone structure before and after ovariectomy-induced osteopenia in rats were investigated. Jumping exercise induced favorable changes in bone mineral density, bone mechanical properties, and bone formation/resorption markers. This exercise is effective to prevent bone loss after ovariectomy even when osteopenia is already established.

INTRODUCTION

The present study investigated the effects of jump training on bone structure before and after ovariectomy-induced osteopenia in 80 10-week-old Wistar rats.

METHODS

Forty rats (prevention program) were randomly allocated to one of four equal groups (n = 10): sham-operated sedentary (SHAM-SEDp), ovariectomized (OVX) sedentary (OVX-SEDp), sham-operated exercised (SHAM-EXp), and OVX exercised (OVX-EXp). SHAM-EXp and OVX-EXp animals began training 3 days after surgery. Another 40 rats (treatment program) were randomly allocated into another four groups (n = 10): sham-operated sedentary (SHAM-SEDt), OVX sedentary (OVX-SEDt), sham-operated exercised (SHAM-EXt), and OVX exercised (OVX-EXt). SHAM-EXt and OVX-EXt animals began training 60 days after surgery. The rats in the exercised groups jumped 20 times/day, 5 days/week, to a height of 40 cm for 12 weeks. At the end of the experimental period, serum osteocalcin, follicle-stimulating hormone (FSH) dosage, dual X-ray absorptiometry (DXA), histomorphometry, and biomechanical tests were analyzed.

RESULTS

The OVX groups showed higher values of FSH and body weight (p < 0.05). DXA showed that jump training significantly increased bone mineral density of the femur and fifth lumbar vertebra (p < 0.05). The stiffness of the left femur and fifth lumbar vertebra in the exercised groups was greater than that of the sedentary groups (p < 0.05). Ovariectomy induced significant difference in bone volume (BV/TV, percent), trabecular separation (Tb.Sp, micrometer), and trabecular number (Tb.N, per millimeter) (p < 0.05) compared to sham operation. Jump training in the OVX group induced significant differences in BV/TV, Tb.Sp, and Tb.N and decreased osteoblast number per bone perimeter (p < 0.05) compared with OVX nontraining, in the prevention groups. Osteocalcin dosage showed higher values in the exercised groups (p < 0.05).

CONCLUSIONS

Jumping exercise induced favorable changes in bone mineral density, bone mechanical properties, and bone formation/resorption markers. Jump training is effective to prevent bone loss after ovariectomy even when osteopenia is already established.

Intrinsic material property differences in bone tissue from patients suffering low-trauma osteoporotic fractures, compared to matched non-fracturing women

Osteoporotic (low-trauma) fractures are a significant public health problem. Over 50% of women over 50yrs. of age will suffer an osteoporotic fracture in their remaining lifetimes. While current therapies reduce skeletal fracture risk by maintaining or increasing bone density, additional information is needed that includes the intrinsic material strength properties of bone tissue to help develop better treatments, since measurements of bone density account for no more than ~50% of fracture risk. The hypothesis tested here is that postmenopausal women who have sustained osteoporotic fractures have reduced bone quality, as indicated with measures of intrinsic material properties compared to those who have not fractured. Transiliac biopsies (N=120) were collected from fracturing (N=60, Cases) and non-fracturing postmenopausal women (N=60, age- and BMD-matched Controls) to measure intrinsic material properties using the nano-indentation technique. Each biopsy specimen was embedded in epoxy resin and then ground, polished and used for the nano-indentation testing. After calibration, multiple indentations were made using quasi-static (hardness, modulus) and dynamic (storage and loss moduli) testing protocols. Multiple indentations allowed the median and variance to be computed for each type of measurement for each specimen. Cases were found to have significantly lower median values for cortical hardness and indentation modulus. In addition, cases showed significantly less within-specimen variability in cortical modulus, cortical hardness, cortical storage modulus and trabecular hardness, and more within-specimen variability in trabecular loss modulus. Multivariate modeling indicated the presence of significant independent mechanical effects of cortical loss modulus, along with variability of cortical storage modulus, cortical loss modulus, and trabecular hardness. These results suggest mechanical heterogeneity of bone tissue may contribute to fracture resistance. Although the magnitudes of differences in the intrinsic properties were not overwhelming, this is the first comprehensive study to investigate, and compare the intrinsic properties of bone tissue in fracturing and non-fracturing postmenopausal women.

Simple additive manufacturing of an osteoconductive ceramic using suspension melt extrusion

OBJECTIVE

Craniofacial bone trauma is a leading reason for surgery at most hospitals. Large pieces of destroyed or resected bone are often replaced with non-resorbable and stock implants, and these are associated with a variety of problems. This paper explores the use of a novel fatty acid/calcium phosphate suspension melt for simple additive manufacturing of ceramic tricalcium phosphate implants.

METHODS

A wide variety of non-aqueous liquids were tested to determine the formulation of a storable 3D printable tricalcium phosphate suspension ink, and only fatty acid-based inks were found to work. A heated stearic acid-tricalcium phosphate suspension melt was then 3D printed, carbonized and sintered, yielding implants with controllable macroporosities. Their microstructure, compressive strength and chemical purity were analyzed with electron microscopy, mechanical testing and Raman spectroscopy, respectively. Mesenchymal stem cell culture was used to assess their osteoconductivity as defined by collagen deposition, alkaline phosphatase secretion and de-novo mineralization.

RESULTS

After a rapid sintering process, the implants retained their pre-sintering shape with open pores. They possessed clinically relevant mechanical strength and were chemically pure. They supported adhesion of mesenchymal stem cells, and these were able to deposit collagen onto the implants, secrete alkaline phosphatase and further mineralize the ceramic.

SIGNIFICANCE

The tricalcium phosphate/fatty acid ink described here and its 3D printing may be sufficiently simple and effective to enable rapid, on-demand and in-hospital fabrication of individualized ceramic implants that allow clinicians to use them for treatment of bone trauma.

Bone structure and function in male C57BL/6 mice: Effects of a high-fat Western-style diet with or without trace minerals

PURPOSE

Osteoporosis occurs in both women and men, but most of what we know about the condition comes from studies in females. The present study examined bone structure and function over an 18-month period in male C57BL/6 mice maintained on either a rodent chow diet (AIN76A) or a high-fat, Western-style diet (HFWD). Effects of mineral supplementation were assessed in both diets.

METHODS

Trabecular and cortical bone structure in femora and vertebrae were assessed by micro-CT analysis. Following this, bone stiffness and strength measurements were made. Finally, bone levels of several cationic trace elements were quantified, and serum biomarkers of bone metabolism evaluated.

RESULTS

Bone loss occurred over time in both diets but was more rapid and extensive in mice on the HFWD. Dietary mineral supplementation reduced bone loss in both diets and increased bone stiffness in the femora and bone stiffness and strength in the vertebrae. Bone content of strontium was increased in response to mineral supplementation in both diets.

CONCLUSIONS

Bone loss was more severe in mice on the HFWD and mineral supplementation mitigated the effects of the HFWD. In comparison to previous findings with female C57BL/6 mice, the present studies indicate that males are more sensitive to diet and benefited from a healthy diet (AIN76A), while females lost as much bone on the healthy diet as on the HFWD. Male mice benefited from mineral supplementation, just as females did in the previous study.

The Association between Elevated Levels of Peripheral Serotonin and Its Metabolite - 5-Hydroxyindoleacetic Acid and Bone Strength and Metabolism in Growing Rats with Mild Experimental Chronic Kidney Disease

Chronic kidney disease (CKD) is associated with disturbances in bone strength and metabolism. The alterations of the serotonergic system are also observed in CKD. We used the 5/6 nephrectomy model of CKD to assess the impact of peripheral serotonin and its metabolite– 5-hydroxyindoleacetic acid on bone biomechanical properties and metabolism in growing rats. The animals were sacrificed one and three months after nephrectomy. Biomechanical properties were determined on two different bone types: the cortical bone of the femoral diaphysis using three-point bending test and the mixed cortico-trabecular bone by the bending test of the femoral neck. Biomechanical tests revealed preserved cortical bone strength, whereas work to fracture (W) and yield load (F_y) of mixed cortico-trabecular bone were significantly lower in CKD compared to controls. Serum activity of alkaline phosphatase (ALP), a bone formation marker, and tartrate-resistant acid phosphatase (TRACP 5b) reflecting bone resorption, were similar in CKD and controls. ALP was associated with lower femoral stiffness and strength, and higher displacements and W. TRACP 5b was inversely associated with cortical F_u and W. The elevated peripheral serotonergic system in CKD was: inversely associated with stiffness but positively related to the displacements and W; inversely associated with cortical F_y but positively correlated with this parameter in cortico-trabecular bone; inversely associated with ALP in controls but positively correlated with this biomarker in CKD animals. In conclusion, this study demonstrates the distinct effect of mild degree of CKD on bone strength in rapidly growing rats. The impaired renal function affects the peripheral serotonin metabolism, which in turn may influence the strength and metabolism of bones in these rats. This relationship seems to be beneficial on the biomechanical properties of the cortico-trabecular bone, whereas the cortical bone strength can be potentially reduced.

7T MRI of distal radius trabecular bone microarchitecture: How trabecular bone quality varies depending on distance from end-of-bone

PURPOSE

To use 7T magnetic resonance imaging (MRI) to determine how trabecular bone microarchitecture varies at the epiphysis, metaphysis, and diaphysis of the distal radius.

MATERIALS AND METHODS

The distal radius of 24 females (mean age = 56 years, range = 24-78 years) was scanned on a 7T MRI using a 3D fast low-angle shot sequence (0.169 × 0.169 × 1 mm). Digital topological analysis was applied at the epiphysis, metaphysis, and diaphysis to compute: total trabecular bone volume; trabecular thickness, number, connectivity, and erosion index (a measure of network resorption). Differences and correlations were assessed using standard statistical methods.

RESULTS

The metaphysis and epiphysis had 83-123% greater total bone volume and 14-16% greater trabecular number than the diaphysis (both P < 0.0001). The erosion index was significantly higher at the diaphysis than the metaphysis and epiphysis (both P < 0.01). The most elderly volunteers had lower trabecular number (<66 years mean 0.29 ± 0.01; ≥66 years, 0.27 ± 0.02, P < 0.05) and higher erosion index (<66 years mean 1.18 ± 0.17; age ≥66 years, mean 1.42 ± 0.46, P < 0.05) at the epiphysis; differences not detected by total trabecular bone volume.

CONCLUSION

7T MRI reveals trabecular bone microarchitecture varies depending on scan location at the end-of-bone, being of overall higher quality distally (epiphysis) than proximally (diaphysis). Age-related differences in trabecular microarchitecture can be detected by 7T MRI. The results highlight the potential sensitivity of 7T MRI to microarchitectural differences and the potential importance of standardizing scan location for future clinical studies of fracture risk or treatment response.

LEVEL OF EVIDENCE

3 J. Magn. Reson. Imaging 2017;45:872-878.

Does Secondary Renal Osteopathy Exist in Companion Animals?

Secondary renal hyperparathyroidism is an inevitable consequence of chronic kidney disease. In human patients, the disease is associated with decreased bone quality and increased fracture risk. Recent evidence suggests that bone quality is also decreased in companion animals, more pronouncedly in cats compared with dogs, likely because of a longer disease course. The clinical significance of these findings is yet to be determined. However, clinicians should keep in mind that animals with chronic kidney disease have decreased bone quality and increased fracture risk.

Improved Mobilization of Exogenous Mesenchymal Stem Cells to Bone for Fracture Healing and Sex Difference

Mesenchymal stem cell (MSC) transplantation has been tested in animal and clinical fracture studies. We have developed a bone-seeking compound, LLP2A-Alendronate (LLP2A-Ale) that augments MSC homing to bone. The purpose of this study was to determine whether treatment with LLP2A-Ale or a combination of LLP2A-Ale and MSCs would accelerate bone healing in a mouse closed fracture model and if the effects are sex dependent. A right mid-femur fracture was induced in two-month-old osterix-mCherry (Osx-mCherry) male and female reporter mice. The mice were subsequently treated with placebo, LLP2A-Ale (500 μg/kg, IV), MSCs derived from wild-type female Osx-mCherry adipose tissue (ADSC, 3 x 10⁵ , IV) or ADSC + LLP2A-Ale. In phosphate buffered saline-treated mice, females had higher systemic and surface-based bone formation than males. However, male mice formed a larger callus and had higher volumetric bone mineral density and bone strength than females. LLP2A-Ale treatment increased exogenous MSC homing to the fracture gaps, enhanced incorporation of these cells into callus formation, and stimulated endochondral bone formation. Additionally, higher engraftment of exogenous MSCs in fracture gaps seemed to contribute to overall fracture healing and improved bone strength. These effects were sex-independent. There was a sex-difference in the rate of fracture healing. ADSC and LLP2A-Ale combination treatment was superior to on callus formation, which was independent of sex. Increased mobilization of exogenous MSCs to fracture sites accelerated endochondral bone formation and enhanced bone tissue regeneration. Stem Cells 2016;34:2587-2600.

Liver-derived IGF-I regulates cortical bone mass but is dispensable for the osteogenic response to mechanical loading in female mice

Low circulating IGF-I is associated with increased fracture risk. Conditional depletion of IGF-I produced in osteoblasts or osteocytes inhibits the bone anabolic effect of mechanical loading. Here, we determined the role of endocrine IGF-I for the osteogenic response to mechanical loading in young adult and old female mice with adult, liver-specific IGF-I inactivation (LI-IGF-I(-/-) mice, serum IGF-I reduced by ≈70%) and control mice. The right tibia was subjected to short periods of axial cyclic compressive loading three times/wk for 2 wk, and measurements were performed using microcomputed tomography and mechanical testing by three-point bending. In the nonloaded left tibia, the LI-IGF-I(-/-) mice had lower cortical bone area and increased cortical porosity, resulting in reduced bone mechanical strength compared with the controls. Mechanical loading induced a similar response in LI-IGF-I(-/-) and control mice in terms of cortical bone area and trabecular bone volume fraction. In fact, mechanical loading produced a more marked increase in cortical bone mechanical strength, which was associated with a less marked increase in cortical porosity, in the LI-IGF-I(-/-) mice compared with the control mice. In conclusion, liver-derived IGF-I regulates cortical bone mass, cortical porosity, and mechanical strength under normal (nonloaded) conditions. However, despite an ∼70% reduction in circulating IGF-I, the osteogenic response to mechanical loading was not attenuated in the LI-IGF-I(-/-) mice.

Bone mechanical properties and changes with osteoporosis

This review will define the role of collagen and within-bone heterogeneity and elaborate the importance of trabecular and cortical architecture with regard to their effect on the mechanical strength of bone. For each of these factors, the changes seen with osteoporosis and ageing will be described and how they can compromise strength and eventually lead to bone fragility.

A 3D vascularized bone remodeling model combining osteoblasts and osteoclasts in a CaP nanoparticle-enriched matrix

AIM

We aimed to establish a 3D vascularized in vitro bone remodeling model.

MATERIALS & METHODS

Human umbilical endothelial cells (HUVECs), bone marrow mesenchymal stem cells (BMSCs), and osteoblast (OBs) and osteoclast (OCs) precursors were embedded in collagen/fibrin hydrogels enriched with calcium phosphate nanoparticles (CaPn). We assessed vasculogenesis in HUVEC-BMSC coculture, osteogenesis with OBs, osteoclastogenesis with OCs, and, ultimately, cell interplay in tetraculture.

RESULTS

HUVECs developed a robust microvascular network and BMSCs differentiated into mural cells. Noteworthy, OB and OC differentiation was increased by their reciprocal coculture and by CaPn, and even more by the combination of the tetraculture and CaPn.

CONCLUSION

We successfully developed a vascularized 3D bone remodeling model, whereby cells interacted and exerted their specific function.

Bone strength in children: understanding basic bone biomechanics

The term 'bone strength' is often used to explain why some children's bones fracture while others do not. Bone strength describes the general integrity of bone; a complex organ with multiple structural levels and an array of biomechanical properties. Key biomechanical properties of bone include stiffness, toughness, ductility and mechanical strength. When measured in bone tissue, these properties are known as the intrinsic biomechanical properties of bone, while the extrinsic biomechanical properties reflect the structural behaviour of a whole bone. The fine balance between various and often opposing intrinsic and extrinsic biomechanical properties of bone is crucial for fracture resistance. When clinically evaluating a child with a fracture, an understanding of basic bone biomechanics helps determine the likely mechanism of injury and whether underlying reduced fracture resistance exists.

Myostatin deficiency partially rescues the bone phenotype of osteogenesis imperfecta model mice

Mice with osteogenesis imperfecta (+/oim), a disorder of bone fragility, were bred to mice with muscle over growth to test whether increasing muscle mass genetically would improve bone quality and strength. The results demonstrate that femora from mice carrying both mutations have greater mechanical integrity than their +/oim littermates.

INTRODUCTION

Osteogenesis imperfecta is a heritable connective tissue disorder due primarily to mutations in the type I collagen genes resulting in skeletal deformity and fragility. Currently, there is no cure, and therapeutic strategies encompass the use of antiresorptive pharmaceuticals and surgical bracing, with limited success and significant potential for adverse effects. Bone, a mechanosensing organ, can respond to high mechanical loads by increasing new bone formation and altering bone geometry to withstand increased forces. Skeletal muscle is a major source of physiological loading on bone, and bone strength is proportional to muscle mass.

METHODS

To test the hypothesis that congenic increases in muscle mass in the osteogenesis imperfecta murine model mouse (oim) will improve their compromised bone quality and strength, heterozygous (+/oim) mice were bred to mice deficient in myostatin (+/mstn), a negative regulator of muscle growth. The resulting adult offspring were evaluated for hindlimb muscle mass, and bone microarchitecture, physiochemistry, and biomechanical integrity.

RESULTS

+/oim mice deficient in myostatin (+/mstn +/oim) were generated and demonstrated that myostatin deficiency increased body weight, muscle mass, and biomechanical strength in +/mstn +/oim mice as compared to +/oim mice. Additionally, myostatin deficiency altered the physiochemical properties of the +/oim bone but did not alter bone remodeling.

CONCLUSIONS

Myostatin deficiency partially improved the reduced femoral bone biomechanical strength of adult +/oim mice by increasing muscle mass with concomitant improvements in bone microarchitecture and physiochemical properties.