Germ-Free C57BL/6 Mice Have Increased Bone Mass and Altered Matrix Properties but Not Decreased Bone Fracture Resistance

Gut microbiota and microbial metabolites for osteoporosis

Osteoporosis is an age-related bone metabolic disease. As an essential endocrine organ, the skeletal system is intricately connected with extraosseous organs. The crosstalk between bones and other organs supports this view. In recent years, the link between the gut microecology and bone metabolism has become an important research topic, both in preclinical studies and in clinical trials. Many studies have shown that skeletal changes are accompanied by changes in the composition and structure of the gut microbiota (GM). At the same time, natural or artificial interventions targeting the GM can subsequently affect bone metabolism. Moreover, microbiome-related metabolites may have important effects on bone metabolism. We aim to review the relationships among the GM, microbial metabolites, and bone metabolism and to summarize the potential mechanisms involved and the theory of the gut‒bone axis. We also describe existing bottlenecks in laboratory studies, as well as existing challenges in clinical settings, and propose possible future research directions.

Impact of different 3D regions of interest on quantifying dynamic lumbar vertebral microstructure in ovariectomized rats-a micro-CT study

Introduction

The selection of regions of interest (ROIs) is crucial for accurate microcomputed tomography (micro-CT) analysis. Distinct ROI selection methods exist for lumbar vertebras in osteoporotic animal model research. However, whether different ROIs directly affect the results of quantitative micro-CT-based microarchitectural data is still unknown. This study aimed to compare the diagnostic accuracy of two commonly used ROIs of lumbar vertebras in ovariectomized (OVX) rats at different time points.

Methods

Rats were randomly divided into the baseline group, the sham/OVX-operated groups, with 12- or 24-weeks sham (Sham 12w or Sham 24w)/12- or 24-weeks (OVX 12w or OVX 24w)-operated group (n = 6 in every group). The fifth lumbar vertebras were collected and scanned using micro-CT. Quantitative analyses of bone microarchitecture parameters were conducted separately for the central ROI (ROI 1) and overall ROI (ROI 2).

Results

The results indicated that the Tb.N of baseline group rats for ROI 1 was significantly lower than that for ROI 2. The Tb.Th of rats of the Sham 12w and Sham 24w groups was significantly increased compared to that of the baseline group rats using the ROI 2 analysis. The bone mineral density (BMD) and bone volume fraction (BV/TV) were significantly lower by the ROI 1 than by the ROI 2 in all groups. The BMD and BV/TV also showed a significant reduction at 24 weeks postoperatively compared with those at 12 weeks postoperatively. Bland-Altman analysis showed good consistency between the two different ROI selection methods.

Conclusion

This study found that capturing peripheral trabeculas (overall ROI) does not explain the increased Tb.Th in healthy mice and decreased Tb.N in OVX mice; both findings indicate that this is evident in both ROI. Moreover, this study suggested the potential value of the central ROI (effective and quicker) for evaluating osteoporosis of the lumbar vertebras in OVX rats and provides a basis for analyzing the morphological changes of lumbar trabecular.

Optimizing number of Raman spectra using an artificial neural network guided Monte Carlo simulation approach to analyze human cortical bone

This study presents a novel methodology for optimizing the number of Raman spectra required per sample for human bone compositional analysis. The methodology integrates Artificial Neural Network (ANN) and Monte Carlo Simulation (MCS). We demonstrate the robustness of ANN in enabling prediction of Raman spectroscopy-based bone quality properties even with limited spectral inputs. The ANN algorithms tailored to individual sex and age groups, which enhance the specificity and accuracy of predictions in bone quality properties. In addition, ANN guided MCS systematically explores the variability and uncertainty inherent in different sample sizes and spectral datasets, leading to the identification of an optimal number of spectra per sample for characterizing human bone tissues. The findings suggest that as low as 2 spectra are sufficient for biochemical analysis of bone, with R2 values between real and predicted values of v1/PO4/Amide I and ∼I1670/I1640 ratios, ranging from 0.60 to 0.89. Our results also suggest that up to 8 spectra could be optimal when balancing other factors. This optimized approach streamlines experimental workflows, reduces data and acquisition costs. Additionally, our study highlights the potential for advancing Raman spectroscopy in bone research through the innovative integration of ANN-guided probabilistic modeling techniques. This research could significantly contribute to the broader landscape of bone quality analyses by establishing a precedent for optimizing the number of Raman spectra with sophisticated computational tools. It also sets a novel platform for future optimization studies in Raman spectroscopy applications in biomedical field.

Exercise ameliorates osteopenia in mice via intestinal microbial-mediated bile acid metabolism pathway

Rationale: Physical exercise is essential for skeletal integrity and bone health. The gut microbiome, as a pivotal modulator of overall physiologic states, is closely associated with skeletal homeostasis and bone metabolism. However, the potential role of intestinal microbiota in the exercise-mediated bone gain remains unclear. Methods: We conducted microbiota depletion and fecal microbiota transplantation (FMT) in ovariectomy (OVX) mice and aged mice to investigate whether the transfer of gut ecological traits could confer the exercise-induced bone protective effects. The study analyzed the gut microbiota and metabolic profiles via 16S rRNA gene sequencing and LC-MS untargeted metabolomics to identify key microbial communities and metabolites responsible for bone protection. Transcriptome sequencing and RNA interference were employed to explore the molecular mechanisms. Results: We found that gut microbiota depletion hindered the osteogenic benefits of exercise, and FMT from exercised osteoporotic mice effectively mitigated osteopenia. Comprehensive profiling of the microbiome and metabolome revealed that the exercise-matched FMT reshaped intestinal microecology and metabolic landscape. Notably, alterations in bile acid metabolism, specifically the enrichment of taurine and ursodeoxycholic acid, mediated the protective effects on bone mass. Mechanistically, FMT from exercised mice activated the apelin signaling pathway and restored the bone-fat balance in recipient MSCs. Conclusion: Our study underscored the important role of the microbiota-metabolic axis in the exercise-mediated bone gain, heralding a potential breakthrough in the treatment of osteoporosis.

Increased cancellous bone mass accompanies decreased cortical bone mineral density and higher axial deformation in femurs of leptin-deficient obese mice

INTRODUCTION

Leptin is a pleiotropic hormone that regulates food intake and energy homeostasis with enigmatic effects on bone development. It is unclear if leptin promotes or inhibits bone growth. The aim of this study was to characterize the micro-architecture and mechanical competence of femur bones of leptin-deficient mice.

MATERIALS AND METHODS

Right femur bones of 15-week old C57BL/6 (n = 9) and leptin-deficient (ob/ob, n = 9) mice were analyzed. Whole bones were scanned using micro-CT and morphometric parameters of the cortex and trabeculae were assessed. Elastic moduli were determined from microindentations in midshaft cross-sections. Mineral densities were determined using quantitative backscatter scanning electron microscopy. 3D models of the distal femur metaphysis, cleared from trabecular bone, were meshed and used for finite element simulations of axial loading to identify straining differences between ob/ob and C57BL/6 controls.

RESULTS

Compared with C57BL/6 controls, ob/ob mice had significantly shorter bones. ob/ob mice showed significantly increased cancellous bone volume and trabecular thickness. qBEI quantified a ∼7% lower mineral density in ob/ob mice in the distal femur metaphysis. Indentation demonstrated a significantly reduced Young's modulus of 12.14 [9.67, 16.56 IQR] GPa for ob/ob mice compared to 23.12 [20.70, 26.57 IQR] GPa in C57BL/6 mice. FEA revealed greater deformation of cortical bone in ob/ob as compared to C57BL/6 mice.

CONCLUSION

Leptin deficient ob/ob mice have a softer cortical bone in the distal femur metaphysis but an excessive amount of cancellous bone, possibly as a response to increased deformation of the bones during axial loading. Both FEA and direct X-ray and electron microscopy imaging suggest that the morphology and micro-architecture of ob/ob mice have inferior biomechanical properties suggestive of a reduced mechanical competence.

A systematic framework for understanding the microbiome in human health and disease: from basic principles to clinical translation

The human microbiome is a complex and dynamic system that plays important roles in human health and disease. However, there remain limitations and theoretical gaps in our current understanding of the intricate relationship between microbes and humans. In this narrative review, we integrate the knowledge and insights from various fields, including anatomy, physiology, immunology, histology, genetics, and evolution, to propose a systematic framework. It introduces key concepts such as the 'innate and adaptive genomes', which enhance genetic and evolutionary comprehension of the human genome. The 'germ-free syndrome' challenges the traditional 'microbes as pathogens' view, advocating for the necessity of microbes for health. The 'slave tissue' concept underscores the symbiotic intricacies between human tissues and their microbial counterparts, highlighting the dynamic health implications of microbial interactions. 'Acquired microbial immunity' positions the microbiome as an adjunct to human immune systems, providing a rationale for probiotic therapies and prudent antibiotic use. The 'homeostatic reprogramming hypothesis' integrates the microbiome into the internal environment theory, potentially explaining the change in homeostatic indicators post-industrialization. The 'cell-microbe co-ecology model' elucidates the symbiotic regulation affecting cellular balance, while the 'meta-host model' broadens the host definition to include symbiotic microbes. The 'health-illness conversion model' encapsulates the innate and adaptive genomes' interplay and dysbiosis patterns. The aim here is to provide a more focused and coherent understanding of microbiome and highlight future research avenues that could lead to a more effective and efficient healthcare system.

Aging decreases osteocyte peri-lacunar-canalicular system turnover in female C57BL/6JN mice

Osteocytes engage in bone resorption and mineralization surrounding their expansive lacunar-canalicular system (LCS) through peri-LCS turnover. However, fundamental questions persist about where, when, and how often osteocytes engage in peri-LCS turnover and how these processes change with aging. Furthermore, whether peri-LCS turnover is associated with natural variation in cortical tissue strain remains unexplored. To address these questions, we utilized confocal scanning microscopy, immunohistochemistry, and scanning electron microscopy to characterize osteocyte peri-LCS turnover in the cortical (mid-diaphysis) and cancellous (metaphysis) regions of femurs from young adult (5 mo) and early-old-age (22 mo) female C57BL/6JN mice. LCS bone mineralization was measured by the presence of perilacunar fluorochrome labels. LCS bone resorption was measured by immunohistochemical marker of bone resorption. The dynamics of peri-LCS turnover were estimated from serial fluorochrome labeling, where each mouse was administered two labels between 2 and 16 days before euthanasia. Osteocyte participation in mineralizing their surroundings is highly abundant in both cortical and cancellous bone of young adult mice but significantly decreases with aging. LCS bone resorption also decreases with aging. Aging has a greater impact on peri-LCS turnover dynamics in cancellous bone than in cortical bone. Lacunae with recent peri-LCS turnover are larger in both age groups. While peri-LCS turnover is associated with variation in tissue strain between cortical quadrants and intracortical location for 22 mo mice, these associations were not seen for 5 mo mice. The impact of aging on decreasing peri-LCS turnover may have significant implications for bone quality and mechanosensation.

Lactobacilli and Their Fermented Foods as a Promising Strategy for Enhancing Bone Mineral Density: A Review

Lactobacilli fermentation possesses special nutritional and health values to food, especially in improving diseases related to the gut microbiota such as osteoporosis risk. Previous research indicates that lactobacilli-fermented foods have the potential to enhance the bone mineral density (BMD), as suggested by some clinical studies. Nonetheless, there is currently a lack of comprehensive summaries of the effects and potential mechanisms of lactobacilli-fermented foods on BMD. This review summarizes findings from preclinical and clinical studies, revealing that lactobacilli possess the potential to mitigate age-related and secondary factor-induced bone loss. Furthermore, these findings imply that lactobacilli are likely mediated through the modulation of bone remodeling via gut inflammation-related pathways. Additionally, lactobacilli fermentation may augment calcium accessibility through directly promoting calcium absorption or modifying food constituents. Considering the escalating global health challenge of bone-related issues among the elderly population, this review may offer a valuable reference for the development of food strategies aimed at preventing osteoporosis.

Effects of high dose aspartame-based sweetener on the gut microbiota and bone strength in young and aged mice

In a recent study examining the effects of manipulating the gut microbiome on bone, a control group of mice in which the microbiome was altered using a non-caloric, aspartame-based sweetener resulted in whole bone strength being 40% greater than expected from geometry alone, implicating enhanced bone tissue strength. However, the study was not designed to detect changes in bone in this control group and was limited to young male mice. Here we report a replication study examining how changes in the gut microbiome caused by aspartame-based sweetener influence bone. Male and female C57Bl/6 J mice were untreated or treated with a high dose of sweetener (10 g/L) in their drinking water from either 1 to 4 mo of age (young cohort; n = 80) or 1 to 22 mo of age (aged cohort; n = 52). Sweetener did not replicate the modifications to the gut microbiome observed in the initial study and did not result in an increase in bone tissue strength in either sex at either age. Aged male mice dosed with sweetener had larger bones (+17% femur section modulus, p<.001) and greater whole bone strength (+22%, p=.006) but the increased whole bone strength was explained by the associated increase in body mass (+9%, p<.001). No differences in body mass, whole bone strength, or femoral geometry were associated with sweetener dosing in males from the young cohort or females at either age. As we were unable to replicate the gut microbiota observed in the initial experiment, it remains unclear if changes in the gut microbiome can enhance bone tissue strength. Although prior work studying gut microbiome-induced changes in bone with oral antibiotics has been highly repeatable, the current study highlights the variability of nutritional manipulations of the gut microbiota in mice.

Chronic pancreatitis-associated metabolic bone diseases: epidemiology, mechanisms, and clinical advances

Chronic pancreatitis (CP) is a progressive inflammatory disease with an increasing global prevalence. In recent years, a strong association between CP and metabolic bone diseases (MBDs), especially osteoporosis, has been identified, attracting significant attention in the research field. Epidemiological data suggest a rising trend in the incidence of MBDs among CP patients. Notably, recent studies have highlighted a profound interplay between CP and altered nutritional and immune profiles, offering insights into its linkage with MBDs. At the molecular level, CP introduces a series of biochemical disturbances that compromise bone homeostasis. One critical observation is the disrupted metabolism of vitamin D and vitamin K, both essential micronutrients for maintaining bone integrity, in CP patients. In this review, we provide physio-pathological perspectives on the development and mechanisms of CP-related MBDs. We also outline some of the latest therapeutic strategies for treating patients with CP-associated MBDs, including stem cell transplantation, monoclonal antibodies, and probiotic therapy. In summary, CP-associated MBDs represent a rising medical challenge, involving multiple tissues and organs, complex disease mechanisms, and diverse treatment approaches. More in-depth studies are required to understand the complex interplay between CP and MBDs to facilitate the development of more specific and effective therapeutic approaches.

Rapamycin does not alter bone microarchitecture or material properties quality in young-adult and aged female C57BL/6 mice

Advancing age is the strongest risk factor for osteoporosis and skeletal fragility. Rapamycin is an FDA-approved immunosuppressant that inhibits the mechanistic target of rapamycin (mTOR) complex, extends lifespan, and protects against aging-related diseases in multiple species; however, the impact of rapamycin on skeletal tissue is incompletely understood. We evaluated the effects of a short-term, low-dosage, interval rapamycin treatment on bone microarchitecture and strength in young-adult (3 mo old) and aged female (20 mo old) C57BL/6 mice. Rapamycin (2 mg/kg body mass) was administered via intraperitoneal injection 1×/5 d for a duration of 8 wk; this treatment regimen has been shown to induce geroprotective effects while minimizing the side effects associated with higher rapamycin dosages and/or more frequent or prolonged delivery schedules. Aged femurs exhibited lower cancellous bone mineral density, volume, trabecular connectivity density and number, higher trabecular thickness and spacing, and lower cortical thickness compared to young-adult mice. Rapamycin had no impact on assessed microCT parameters. Flexural testing of the femur revealed that both yield strength and ultimate strength were lower in aged mice compared to young-adult mice. There were no effects of rapamycin on these or other measures of bone biomechanics. Age, but not rapamycin, altered local and global measures of bone turnover. These data demonstrate that short-term, low-dosage interval rapamycin treatment does not negatively or positively impact the skeleton of young-adult and aged mice.

Aging effects on osteoclast progenitor dynamics affect variability in bone turnover via feedback regulation

Bone turnover markers (BTMs) are commonly used in osteoporosis treatment as indicators of cell activities of bone-resorbing osteoclasts and bone-forming osteoblasts. The wide variability in their values due to multiple factors, such as aging and diseases, makes it difficult for physicians to utilize them for clinical decision-making. The progenitors of osteoclasts and osteoblasts are indispensable for a comprehensive interpretation of the variability in BTM values because these upstream progenitors strongly regulate the downstream cell activities of bone turnover. However, understanding the complex interactions among the multiple populations of bone cells is challenging. In this study, we aimed to gain a fundamental understanding of the mechanism by which the progenitor dynamics affect the variability in bone turnover through in silico experiments by exploring the cell dynamics with aging effects on osteoporosis. Negative feedback control driven by the consumptive loss of progenitors prevents rapid bone loss due to excessive bone turnover, and through feedback regulation, aging effects on osteoclast differentiation and osteoclast progenitor proliferation cause variability in the osteoclast and osteoblast activity balance and its temporal transition. By expressing the variability in the bone turnover status, our model describes the individualities of patients based on their clinical backgrounds. Therefore, our model could play a powerful role in assisting tailored treatment and has the potential to resolve the various health problems associated with osteoporosis worldwide.