Advancing our understanding of the influence of drug induced changes in the gut microbiome on bone health.

The gut microbiome has been implicated in a multitude of human diseases, with emerging evidence linking its microbial diversity to osteoporosis. This review article will explore the molecular mechanisms underlying perturbations in the gut microbiome and their influence on osteoporosis incidence in individuals with chronic diseases. The relationship between gut microbiome diversity and bone density is primarily mediated by microbiome-derived metabolites and signaling molecules. Perturbations in the gut microbiome, induced by chronic diseases can alter bacterial diversity and metabolic profiles, leading to changes in gut permeability and systemic release of metabolites. This cascade of events impacts bone mineralization and consequently bone mineral density through immune cell activation. In addition, we will discuss how orally administered medications, including antimicrobial and non-antimicrobial drugs, can exacerbate or, in some cases, treat osteoporosis. Specifically, we will review the mechanisms by which non-antimicrobial drugs disrupt the gut microbiome's diversity, physiology, and signaling, and how these events influence bone density and osteoporosis incidence. This review aims to provide a comprehensive understanding of the complex interplay between orally administered drugs, the gut microbiome, and osteoporosis, offering new insights into potential therapeutic strategies for preserving bone health.

Structural role of osteocalcin and its modification in bone fracture.

Osteocalcin (OC), an abundant non-collagenous protein in bone extracellular matrix, plays a vital role in both its biological and mechanical function. OC undergoes post-translational modification, such as glycation; however, it remains unknown whether glycation of OC affects bone's resistance to fracture. Here, for the first time, we demonstrate the formation of pentosidine, an advanced glycation end-product (AGE) cross-link on mouse OC analyzed by ultra-performance liquid chromatography. Next, we establish that the presence of OC in mouse bone matrix is associated with lower interlamellar separation (distance) and thicker bridges spanning the lamellae, both of which are critical for maintaining bone's structural integrity. Furthermore, to determine the impact of modification of OC by glycation on bone toughness, we glycated bone samples in vitro from wild-type (WT) and osteocalcin deficient (Oc-/-) mice, and compared the differences in total fluorescent AGEs and fracture toughness between the Oc -/- glycated and control mouse bones and the WT glycated and control mouse bones. We determined that glycation resulted in significantly higher AGEs in WT compared to Oc-/- mouse bones (delta-WT > delta-OC, p = 0.025). This observed change corresponded to a significant decrease in fracture toughness between WT and Oc-/- mice (delta-WT vs delta-OC, p = 0.018). Thus, we propose a molecular deformation and fracture mechanics model that corroborates our experimental findings and provides evidence to support a 37%-90% loss in energy dissipation of OC due to formation of pentosidine cross-link by glycation. We anticipate that our study will aid in elucidating the effects of a major non-collagenous bone matrix protein, osteocalcin, and its modifications on bone fragility and help identify potential therapeutic targets for maintaining skeletal health.

Clinical and sociodemographic risk factors associated with the development of second primary cancers among postmenopausal breast cancer survivors.

BACKGROUND: Advancement in breast cancer (BC) diagnosis and treatment have increased the number of long-term survivors. Consequently, primary BC survivors are at a greater risk of developing second primary cancers (SPCs). The risk factors for SPCs among BC survivors including sociodemographic characteristics, cancer treatment, comorbidities, and concurrent medications have not been comprehensively examined. The purpose of this study is to assess the incidence and clinicopathologic factors associated with risk of SPCs in BC survivors. METHODS: We analyzed 171, 311 women with early-stage primary BC diagnosed between January 2000 and December 2015 from the Medicare-linked Surveillance Epidemiology and End Results (SEER-Medicare) database. SPC was defined as any diagnosis of malignancy occurring within the study period and at least 6 months after primary BC diagnosis. Univariate analyses compared baseline characteristics between those who developed a SPC and those who did not. We evaluated the cause-specific hazard of developing a SPC in the presence of death as a competing risk. RESULTS: Of the study cohort, 21,510 (13%) of BC survivors developed a SPC and BC was the most common SPC type (28%). The median time to SPC was 44 months. Women who were white, older, and with fewer comorbidities were more likely to develop a SPC. While statins [hazard ratio (HR) 1.066 (1.023-1.110)] and anti-hypertensives [HR 1.569 (1.512-1.627)] increased the hazard of developing a SPC, aromatase inhibitor therapy [HR 0.620 (0.573-0.671)] and bisphosphonates [HR 0.905 (0.857-0.956)] were associated with a decreased hazard of developing any SPC, including non-breast SPCs. CONCLUSION: Our study shows that specific clinical factors including type of cancer treatment, medications, and comorbidities are associated with increased risk of developing SPCs among older BC survivors. These results can increase patient and clinician awareness, target cancer screening among BC survivors, as well as developing risk-adapted management strategies.

Optimizing the use of adjuvant chemotherapy in non-small cell lung cancer patients with comorbidities.

Veterans with locoregional non-small cell lung cancer (NSCLC) may benefit from adjuvant chemotherapy. However, comorbidities and other factors may impact the harms and benefits of this treatment. Here, we identified the optimal indications for adjuvant chemotherapy in Veterans with NSCLC, chronic obstructive pulmonary disease (COPD), chronic kidney disease (CKD), and/or coronary artery disease (CAD). We used data from randomized controlled trials (RCTs) and Veterans Administration (VA) databases to enhance a simulation model. Then, we conducted in-silico RCTs comparing adjuvant chemotherapy vs observation among Veterans with stage II-IIIA NSCLC. Among Veterans without COPD or CKD, adjuvant chemotherapy was the optimal strategy regardless of the presence or absence of CAD except for patients >70 years with squamous cell carcinoma. Conversely, most veterans without COPD but with CKD were optimally managed with observation. Veterans with COPD but without CKD, benefited from adjuvant chemotherapy if they were ≤70 years with stage II-IIIA adenocarcinoma or <60 years with stage II-IIIA squamous cell carcinoma. Adjuvant chemotherapy was only beneficial for Veterans with both COPD and CKD among stage II-IIIA adenocarcinoma <60 years of age. Veterans with stages II-IIIA squamous cell carcinoma, COPD, and CKD were optimally managed with observation. Many Veterans with comorbidities are optimally managed with observation post-surgical resection. However, we also identified several groups of Veterans whom the benefits of adjuvant chemotherapy outweighed the risks of early toxicity. Our findings could inform patient-provider discussions and potentially reduce physicians' uncertainty about the role of adjuvant chemotherapy in this population.

Bone matrix quality in a developing high-fat diet mouse model is altered by RAGE deletion.

Overweightness and obesity in adolescents are epidemics linked to chronic low-grade inflammation and elevated fracture risk. The increased fracture risk observed in overweight/obese adolescence contrasts the traditional concept that high body mass is protective against fracture, and thus highlights the need to determine why weight gain becomes detrimental to fracture during growth and maturity. The Receptor for Advanced Glycation End products (RAGE) is a central inflammatory regulator that can influence bone metabolism. It remains unknown how RAGE removal impacts skeletal fragility in overweightness/obesity, and whether increased fracture risk in adolescents could result from low-grade inflammation deteriorating bone quality. We characterized the multiscale structural, mechanical, and chemical properties of tibiae extracted from adolescent C57BL/6J (WT) and RAGE null (KO) mice fed either low-fat (LF) or high-fat (HF) diet for 12 weeks starting at 6 weeks of age using micro-computed tomography, strength, Raman spectroscopy, and nanoindentation. Overweight/obese WT HF mice possessed degraded mineral-crystal quality and increased matrix glycoxidation in the form of pentosidine and carboxymethyl-lysine, with HF diet in females only showing reduced cortical surface expansion and TMD independently of RAGE ablation. Furthermore, in contrast to males, HF diet in females led to more material damage and plastic deformation. RAGE KO mitigated glycoxidative matrix accumulation, preserved mineral quantity, and led to increased E/H ratio in females. Taken together, these results highlight the complex, multi-scale and sex-dependent relationships between bone quality and function under overweightness, and identifies RAGE-controlled glycoxidation as a target to potentially preserve matrix quality and mechanical integrity.

Non-Obese MKR Mouse Model of Type 2 Diabetes Reveals Skeletal Alterations in Mineralization and Material Properties.

Obesity is a common comorbidity of type 2 diabetes (T2D). Therefore, increased risk of fragility fractures in T2D is often confounded by the effects of obesity. This study was conducted to elucidate the mechanistic basis by which T2D alone leads to skeletal fragility. We hypothesized that obesity independent T2D would deteriorate bone's material quality by accumulating defects in the mineral matrix and undesired modifications in its organic matrix associated with increased oxidative stress and hyperglycemia. To test this hypothesis, we used 15-week-old male non-obese mice with engineered muscle creatine kinase promoter/human dominant negative insulin growth factor 1 (IGF-I) receptor (MKR) and FVB/N wild-type (WT) controls (n = 12/group). MKR mice exhibit reduced insulin production and loss of glycemic control leading to diabetic hyperglycemia, verified by fasting blood glucose measurements (>250 mg/dL), without an increase in body weight. MKR mice showed a significant decrease in femoral radial geometry (cortical area, moment of inertia, cortical thickness, endosteal diameter, and periosteal diameter). Bone mineral density (BMD), as assessed by micro-computed tomography (µCT), remained unchanged; however, the quality of bone mineral was altered. In contrast to controls, MKR mice had significantly increased hydroxyapatite crystal thickness, measured by small-angle X-ray scattering, and elongated c-axis length of the crystals evaluated by confocal Raman spectroscopy. There was an increase in changes in the organic matrix of MKR mice, associated with enhanced glycoxidation (carboxymethyl-lysine [CML] and pentosidine) and overall glycation (fluorescent advanced glycation end products), both of which were associated with various measures of bone fragility. Moreover, increased CML formation positively correlated with elongated mineral crystal length, supporting the role of this negatively charged side chain to attract calcium ions, promote growth of hydroxyapatite, and build a physical link between mineral and collagen. Collectively, our results show, for the first time, changes in bone matrix in a non-obese T2D model in which skeletal fragility is attributable to alterations in the mineral quality and undesired organic matrix modifications. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Influence of Metastatic Bone Lesion Type and Tumor Origin on Human Vertebral Bone Architecture, Matrix Quality, and Mechanical Properties.

Metastatic spine disease is incurable, causing increased vertebral fracture risk and severe patient morbidity. Here, we demonstrate that osteolytic, osteosclerotic, and mixed bone metastasis uniquely modify human vertebral bone architecture and quality, affecting vertebral strength and stiffness. Multivariable analysis showed bone metastasis type dominates vertebral strength and stiffness changes, with neither age nor gender having an independent effect. In osteolytic vertebrae, bone architecture rarefaction, lower tissue mineral content and connectivity, and accumulation of advanced glycation end-products (AGEs) affected low vertebral strength and stiffness. In osteosclerotic vertebrae, high trabecular number and thickness but low AGEs, suggesting a high degree of bone remodeling, yielded high vertebral strength. Our study found that bone metastasis from prostate and breast primary cancers differentially impacted the osteosclerotic bone microenvironment, yielding altered bone architecture and accumulation of AGEs. These findings indicate that therapeutic approaches should target the restoration of bone structural integrity. © 2022 American Society for Bone and Mineral Research (ASBMR).

The association of osteoporosis knowledge and beliefs with preventive behaviors in postmenopausal breast cancer survivors.

BACKGROUND: Postmenopausal breast cancer survivors (PBCS) are at increased risk of bone loss and fractures due to age-related decline of estrogen, and this risk is compounded by aromatase inhibitor cancer therapy. Several patient-level targetable risk factors can mitigate osteoporosis risk; however, adequate health behavior and risk perception in this population are underreported. The goal of this study was to evaluate osteoporosis knowledge and beliefs and assess their association with engagement in osteoporosis preventive behaviors among PBCS. METHODS: In this cross-sectional descriptive study, early stage I-IIIA PBCS (ages 55-86 years) completed the Facts on Osteoporosis Quiz, Osteoporosis Health Beliefs Scale, and Osteoporosis Preventive Behaviors questionnaires. Participants who were non-English speaking or declined to participate were excluded. Clinical and sociodemographic information were obtained from chart review and baseline questionnaire, respectively. Fisher's exact test, Student t-test, and Wilcoxon Mann-Whitney tests were used where appropriate to assess the association between knowledge and beliefs with engagement in osteoporosis preventive behaviors. RESULTS: The mean participant age was 66.1 years with 20% self-reporting as non-Hispanic White, 40% non-Hispanic Black, 27% Hispanic, and 13% other. Approximately 83% of the cohort had estrogen receptor positive breast cancer and received a bone density scan within the last six years. Osteoporosis knowledge (10.5 ± 3.4), seriousness (14.9 ± 3.8), and susceptibility (14.0 ± 3.5) mean scores were low among PBCS. Most PBCS (75%) were adherent to calcium and vitamin D supplements, but only 47% reported engagement in strength-training exercises. Married/partnered, higher osteoporosis knowledge and health motivation scores were associated with strength-training exercise. After adjustment for marital status and osteoporosis knowledge, only health motivation score remained significantly associated with strength-training exercise (OR 5.56, 95% CI 1.35-22.93). CONCLUSIONS: PBCS are highly motivated to keep a healthy lifestyle despite limited osteoporosis knowledge, perceived risk, and susceptibility. However, < 50% participated in strength-training exercise. Our findings suggest that oncologic care should include osteoporosis and fracture prevention strategies, directed at encouraging cancer survivors to increase their engagement in osteoporosis preventive behaviors, particularly strength-training exercises.

Assessing the association of diabetes with lung cancer risk.

BACKGROUND: Diabetes is a well-established risk factor for many cancers, but its relationship with lung cancer incidence remains unclear. In this study, we aimed to assess if diabetes is independently associated with lung cancer risk and histology subtype among participants in a screening study. METHODS: In a retrospective cohort study using data from the Prostate, Lung, Colorectal, and Ovarian (PLCO) study, we assessed the association of self-reported diabetes with lung cancer incidence using Poisson regression while adjusting for other established risk factors in the PLCOM2012, a validated lung cancer prediction model. The adjusted association of diabetes and lung cancer cell type was evaluated using nominal regression. Stratified analyses were also conducted according to sex, smoking history, and body mass index categories. RESULTS: Overall, 140,395 participants were included in our analysis. Diabetes was not significantly associated with lung cancer incidence [incidence rate ratio (IRR): 1.03, 95% confidence interval (CI): 0.91-1.17]. Similarly, stratified analyses also did not show significant associations between diabetes and lung cancer risk (all P values >0.05). We found no significant difference in the distribution of lung cancer histology in participants with vs. without diabetes (P=0.30). CONCLUSIONS: Diabetes was not an independent risk factor for lung cancer in a large cohort of PLCO participants. We did not observe differences in histology according to diabetes status. These results suggest that patients with diabetes do not need more aggressive lung cancer screening. Future research including more detailed metabolic parameters may further elucidate the relationship between metabolic disease and lung cancer risk.

The role of extracellular matrix phosphorylation on energy dissipation in bone.

Protein phosphorylation, critical for cellular regulatory mechanisms, is implicated in various diseases. However, it remains unknown whether heterogeneity in phosphorylation of key structural proteins alters tissue integrity and organ function. Here, osteopontin phosphorylation level declined in hypo- and hyper- phosphatemia mouse models exhibiting skeletal deformities. Phosphorylation increased cohesion between osteopontin polymers, and adhesion of osteopontin to hydroxyapatite, enhancing energy dissipation. Fracture toughness, a measure of bone's mechanical competence, increased with ex-vivo phosphorylation of wildtype mouse bones and declined with ex-vivo dephosphorylation. In osteopontin-deficient mice, global matrix phosphorylation level was not associated with toughness. Our findings suggest that phosphorylated osteopontin promotes fracture toughness in a dose-dependent manner through increased interfacial bond formation. In the absence of osteopontin, phosphorylation increases electrostatic repulsion, and likely protein alignment and interfilament distance leading to decreased fracture resistance. These mechanisms may be of importance in other connective tissues, and the key to unraveling cell-matrix interactions in diseases.

The effects of metastatic lesion on the structural determinants of bone: Current clinical and experimental approaches.

Metastatic bone disease is incurable with an associated increase in skeletal-related events, particularly a 17-50% risk of pathologic fractures. Current surgical and oncological treatments are palliative, do not reduce overall mortality, and therefore optimal management of adults at risk of pathologic fractures presents an unmet medical need. Plain radiography lacks specificity and may result in unnecessary prophylactic fixation. Radionuclide imaging techniques primarily supply information on the metabolic activity of the tumor or the bone itself. Magnetic resonance imaging and computed tomography provide excellent anatomical and structural information but do not quantitatively assess bone matrix. Research has now shifted to developing unbiased data-driven tools that can predict risk of impending fractures and guide individualized treatment decisions. This review discusses the state-of-the-art in clinical and experimental approaches for prediction of pathologic fractures with bone metastases. Alterations in bone matrix quality are associated with an age-related increase in skeletal fragility but the impact of metastases on the intrinsic material properties of bone is unclear. Engineering-based analyses are non-invasive with the capability to evaluate oncological treatments and predict failure due to the progression of metastasis. The combination of these approaches may improve our understanding of the underlying deterioration in mechanical performance.

Structural role of osteocalcin and osteopontin in energy dissipation in bone.

Non-collagenous proteins are a vital component of bone matrix. Amongst them, osteocalcin (OC) and osteopontin (OPN) hold special significance due to their intimate interaction with the mineral and collagenous matrix in bone. Both proteins have been associated with microdamage and fracture, but their structural role in energy dissipation is unclear. This study used bone tissue from genetic deficient mice lacking OC and/or OPN and subjected them to a series of creep-fatigue-creep tests. To this end, whole tibiae were loaded in four-point bending to 70% stiffness loss which captured the three characteristic phases of fatigue associated with initiation, propagation, and coalescence of microdamage. Fatigue loading preceded and followed creep tests to determine creep and dampening parameters. Microdamage in the form of linear microcracks and diffuse damage were analyzed by histology. It was shown that OC and OPN were 'activated' following stiffness loss associated with fatigue damage where they facilitated creep and dampening parameters (i.e. increased energy dissipation). More specifically, post-fatigue creep rate and dampening were significantly greater in wild-types (WTs) than genetic deficient mice (p < 0.05). These results were supported by microdamage analysis which showed significant increase in creep-associated diffuse damage formation in WTs compared to genetic deficient groups (p < 0.05). Based on these findings, we propose that during local yield events, OC and OPN rely on ionic interactions of their charged side chains and on hydrogen bonding to dissipate energy in bone.

Mechanical Characterization of Bone: State of the Art in Experimental Approaches-What Types of Experiments Do People Do and How Does One Interpret the Results?

PURPOSE OF REVIEW: The mechanical integrity of bone is determined by the direct measurement of bone mechanical properties. This article presents an overview of the current, most common, and new and upcoming experimental approaches for the mechanical characterization of bone. The key outcome variables of mechanical testing, as well as interpretations of the results in the context of bone structure and biology are also discussed. RECENT FINDINGS: Quasi-static tests are the most commonly used for determining the resistance to structural failure by a single load at the organ (whole bone) level. The resistance to crack initiation or growth by fracture toughness testing and fatigue loading offers additional and more direct characterization of tissue material properties. Non-traditional indentation techniques and in situ testing are being increasingly used to probe the material properties of bone ultrastructure. Destructive ex vivo testing or clinical surrogate measures are considered to be the gold standard for estimating fracture risk. The type of mechanical test used for a particular investigation depends on the length scale of interest, where the outcome variables are influenced by the interrelationship between bone structure and composition. Advancement in the sensitivity of mechanical characterization techniques to detect changes in bone at the levels subjected to modifications by aging, disease, and/or pharmaceutical treatment is required. As such, a number of techniques are now available to aid our understanding of the factors that contribute to fracture risk.

Osteocalcin and osteopontin influence bone morphology and mechanical properties.

Osteocalcin (OC) and osteopontin (OPN) are major non-collagenous proteins (NCPs) involved in bone matrix organization and deposition. In spite of this, it is currently unknown whether OC and OPN alter bone morphology and consequently affect bone fracture resistance. The goal of this study is to establish the role of OC and OPN in the determination of cortical bone size, shape, and mechanical properties. Our results show that Oc-/- and Opn-/- mice were no different from each other or wild type (WT) with respect to bone morphology (P > 0.1). Bones from mice lacking both NCPs (Oc-/- Opn-/- ) were shorter, with thicker cortices and larger cortical areas, compared with the WT, Oc-/- , and Opn-/- groups (P < 0.05), suggesting a synergistic role for NCPs in the determination of bone morphology. Maximum bending load was significantly different among the groups (P = 0.024), while tissue mineral density and measures of stiffness and strength were not different (P > 0.1). We conclude that the removal of both OC and OPN from bone matrix induces morphological adaptation at the structural level to maintain bone strength.