Role of collagen enzymatic and glycation induced cross-links as a determinant of bone quality in spontaneously diabetic WBN/Kob rats

Obesity and insulinopenic type 2 diabetes differentially impact, bone phenotype, bone marrow adipose tissue, and serum levels of the cathelicidin-related antimicrobial peptide in mice

Obesity is a risk factor of developing type 2 diabetes (T2D) and metabolic complications, through systemic inflammation and insulin resistance. It has also been associated with increased bone marrow adipocytes along with increased bone fragility and fracture risk. However, the differential effects of obesity and T2D on bone fragility remain unclear. The cathelicidin-related antimicrobial peptide (CRAMP) is a multifunctional modulator of the innate immunity that has emerged as biomarker of cardiometabolic diseases. The aims of this study were i) to assess the differential impact between hyperinsulinemic obesity versus insulinopenic T2D, on bone phenotype and bone marrow adipose tissue (BMAT), and ii) to analyse the link with CRAMP expression and its circulating levels in the context of obesity and T2D. We used C57BL/6 J male mice models of obesity induced by high-fat diet (HFD), and of insulinopenic T2D induced by streptozotocin (STZ) treatment combined with HFD, reflecting the metabolic heterogeneity of the diseases. As compared to low-fat diet (LFD) control group after 16 weeks of feeding, the HFD mice exhibit a significant weight gain, moderate hyperglycaemia, impaired glucose tolerance and insulin sensitivity, and significant increase in serum insulin levels. This hyperinsulinemic obesity led to decreased trabecular (Tb.Th) and cortical thickness (Ct.Th) in the tibia, associated with significant BMAT expansion, in addition to increased subcutaneaous (SCAT) and visceral adipose tissue (VAT). No changes were observed in the circulating levels of CRAMP peptide neither in other bone parameters. While, STZ treatment in HFD/STZ group induced a more severe hyperglycaemia, glucose intolerance and insulin resistance, and hypoinsulinemia. We also observed a negative effect on the expansion of both SCAT and VAT, as well as lower increase in BMAT as compared to HFD group. However, these mice with insulinopenic T2D exhibit early decrease in trabecular number (Tb.N) in proximal tibia, progressively from 8 to 16 weeks of protocol, and impaired femoral biomechanical stiffness. These alterations are also accompanied with decreased circulating levels of the CRAMP peptide in the HFD/STZ mice. The CRAMP mRNA levels decreased in VAT of both HFD and HFD/STZ groups. Overall, these results provide novel insights into the differential negative impact of obesity versus T2D on bone microenvironment, and suggest a link between hyperglycaemia-induced bone quality alterations during insulinopenia, and impaired regulation of the cathelicidin peptide of the innate immunity. Further investigations are needed to elucidate this relationship.

UTE MRI technical developments and applications in osteoporosis: a review

Osteoporosis (OP) is a metabolic bone disease that affects more than 10 million people in the USA and leads to over two million fractures every year. The disease results in serious long-term disability and death in a large number of patients. Bone mineral density (BMD) measurement is the current standard in assessing fracture risk; however, the majority of fractures cannot be explained by BMD alone. Bone is a composite material of mineral, organic matrix, and water. While bone mineral provides stiffness and strength, collagen provides ductility and the ability to absorb energy before fracturing, and water provides viscoelasticity and poroelasticity. These bone components are arranged in a complex hierarchical structure. Both material composition and physical structure contribute to the unique strength of bone. The contribution of mineral to bone's mechanical properties has dominated scientific thinking for decades, partly because collagen and water are inaccessible using X-ray based techniques. Accurate evaluation of bone requires information about its components (mineral, collagen, water) and structure (cortical porosity, trabecular microstructure), which are all important in maintaining the mechanical integrity of bone. Magnetic resonance imaging (MRI) is routinely used to diagnose soft tissue diseases, but bone is "invisible" with clinical MRI due to its short transverse relaxation time. This review article discusses using ultrashort echo time (UTE) sequences to evaluate bone composition and structure. Both morphological and quantitative UTE MRI techniques are introduced. Their applications in osteoporosis are also briefly discussed. These UTE-MRI advancements hold great potential for improving the diagnosis and management of osteoporosis and other metabolic bone diseases by providing a more comprehensive assessment of bone quantity and quality.

NLRP3 blockade by MCC950 suppressed osteoclastogenesis via NF-κB/c-Fos/NFATc1 signal pathway and alleviated bone loss in diabetes mellitus

Obesity and type 2 diabetes mellitus (T2DM) are linked to osteoporosis development, with obesity being a significant risk factor for T2DM. T2DM patients with obesity exhibit a higher fracture rate and often have a poor prognosis post-fracture. To address the urgent need for understanding the mechanisms of diabetic osteoporosis (DOP), research is ongoing to explore how obesity and T2DM impact bone metabolism. The NLRP3 inflammasome has been implicated in the pathogenesis of osteoporosis, and MCC950, an NLRP3 inflammasome inhibitor, has shown promise in various diseases but its role in osteoporosis remains unexplored. In this study, BMMs and BMSCs were isolated and cultured to investigate the effects of MCC950 on bone metabolism, and DOP model was used to evaluate the efficacy of MCC950 in vivo. The study demonstrated that MCC950 treatment inhibited osteoclast differentiation, reduced bone resorption capacity in BMMs without suppression for osteoblast differentiation from BMSCs. Additionally, MCC950 suppressed the activation of the NF-κB signaling pathway and downregulated key factors associated with osteoclast differentiation. Additionally, MCC950 alleviated bone loss in DOP mouse. These findings suggest that MCC950, by targeting the NLRP3 inflammasome, may have a protective role in preventing osteoporosis induced by T2DM with obesity. The study highlights the potential therapeutic implications of MCC950 in managing diabetic osteoporosis and calls for further research to explore its clinical application in high-risk patient populations.

In vivo glycation-interplay between oxidant and carbonyl stress in bone

Metabolic syndromes (eg, obesity, type 2 diabetes (T2D), atherosclerosis, and neurodegenerative diseases) and aging, they all have a strong component of carbonyl and reductive-oxidative (redox) stress. Reactive carbonyl (RCS) and oxidant (ROS) stress species are commonly generated as products or byproducts of cellular metabolism or are derived from the environment. RCS and ROS can play a dual role in living organisms. Some RCS and ROS function as signaling molecules, which control cellular defenses against biological and environmental assaults. However, due to their high reactivity, RCS and ROS inadvertently interact with different cellular and extracellular components, which can lead to the formation of undesired posttranslational modifications of bone matrix proteins. These are advanced glycation (AGEs) and glycoxidation (AGOEs) end products generated in vivo by non-enzymatic amino-carbonyl reactions. In this review, metabolic processes involved in generation of AGEs and AGOEs within and on protein surfaces including extracellular bone matrix are discussed from the perspective of cellular metabolism and biochemistry of certain metabolic syndromes. The impact of AGEs and AGOEs on some characteristics of mineral is also discussed. Different therapeutic approaches with the potential to prevent the formation of RCS, ROS, and the resulting formation of AGEs and AGOEs driven by these chemicals are also briefly reviewed. These are antioxidants, scavenging agents of reactive species, and newly emerging technologies for the development of synthetic detoxifying systems. Further research in the area of in vivo glycation and glycoxidation should lead to the development of diverse new strategies for halting the progression of metabolic complications before irreversible damage to body tissues materializes.

An improved linear systems model of hydrothermal isometric tension testing to aid in assessing bone collagen quality: Effects of ribation and type-2 diabetes

This study sought to further develop and validate a previously proposed physics-based model that maps denaturation kinetics from differential scanning calorimetry (DSC) to the isometric tension generated during hydrothermal isometric tension (HIT) testing of collagenous tissues. The primary objectives of this study were to verify and validate two physics-based model parameters: α, which indicates the amount of instantaneous isometric tension developed per unit of collagen denaturation, and β, which captures the proportionality between temperature and the generated isometric tension post denaturation initiation. These parameters were used as measures of bone collagen quality, employing data from HIT and DSC testing of human bone collagen from two previous studies. Additionally, given the physical basis of the model, the study aimed to further validate Max.Slope, the rate of change in isometric tensile stress with change in temperature, as an independent measure of collagen network connectivity. Max.Slope has previously been positively correlated with measures of cortical bone fracture resistance. Towards this verification and validation, the hypotheses were a) that α would correlate strongly with HIT denaturation temperature, Td, and the enthalpy of melting (ΔH) from DSC, and b) that β would correlate positively and strongly with Max.Slope. The model was employed in the analysis of HIT-DSC data from the testing of demineralized bone collagen isolated from cadaveric human femurs in two prior studies. In one study, data were collected from HIT-DSC testing of cortical bone collagen from 74 donors. Among them, 38 had a history of type 2 diabetes +/- chronic kidney disease, while the remaining 36 had no history of T2D again with or without CKD. Cortical bone specimens were extracted from the lateral mid-shaft. The second study involved 15 donor femora, with four cortical bone specimens extracted from each. Of these four, two specimens underwent a 4-week incubation in 0.1 M ribose at 37 °C to induce non-enzymatic ribation and advanced glycation endproducts, while the other two served as non-ribated controls. The examination involved investigating correlations between the model parameters α and β and various measures, such as Max.Slope, Td, ΔH, age, and duration of type 2 diabetes. The results revealed positive correlations between the model parameter β and Max.Slope (r = 0.55-0.58). The parameter α was found to be associated with Td, but also sensitive to the shape of the HIT curve around Td resulting in difficulties with variability and interpretation. As a result, while both hypotheses are confirmed, Max.Slope and β are better indicators of bone collagen quality because they are measures of the connectivity or, more generally, the integrity of the bone collagen network.

Bone Fragility in Diabetes and its Management: A Narrative Review

Bone fragility is a serious yet under-recognised complication of diabetes mellitus (DM) that is associated with significant morbidity and mortality. Multiple complex pathophysiological mechanisms mediating bone fragility amongst DM patients have been proposed and identified. Fracture risk in both type 1 diabetes (T1D) and type 2 diabetes (T2D) continues to be understated and underestimated by conventional risk assessment tools, posing an additional challenge to the identification of at-risk patients who may benefit from earlier intervention or preventive strategies. Over the years, an increasing body of evidence has demonstrated the efficacy of osteo-pharmacological agents in managing skeletal fragility in DM. This review seeks to elaborate on the risk of bone fragility in DM, the underlying pathogenesis and skeletal alterations, the approach to fracture risk assessment in DM, management strategies and therapeutic options.

Bone metabolism in diabetes: a clinician's guide to understanding the bone-glucose interplay

Skeletal fragility is an increasingly recognised, but poorly understood, complication of both type 1 and type 2 diabetes. Fracture risk varies according to skeletal site and diabetes-related characteristics. Post-fracture outcomes, including mortality risk, are worse in those with diabetes, placing these people at significant risk. Each fracture therefore represents a sentinel event that warrants targeted management. However, diabetes is a very heterogeneous condition with complex interactions between multiple co-existing, and highly correlated, factors that preclude a clear assessment of the independent clinical markers and pathophysiological drivers for diabetic osteopathy. Additionally, fracture risk calculators and routinely used clinical bone measurements generally underestimate fracture risk in people with diabetes. In the absence of dedicated prospective studies including detailed bone and metabolic characteristics, optimal management centres around selecting treatments that minimise skeletal and metabolic harm. This review summarises the clinical landscape of diabetic osteopathy and outlines the interplay between metabolic and skeletal health. The underlying pathophysiology of skeletal fragility in diabetes and a rationale for considering a diabetes-based paradigm in assessing and managing diabetic bone disease will be discussed.

Antidiabetic Agents and Bone Quality: A Focus on Glycation End Products and Incretin Pathway Modulations

Diabetes mellitus is associated with inadequate bone health and quality and heightened susceptibility to fractures, even in patients with normal or elevated bone mineral density. Elevated advanced glycation end-products (AGEs) and a suppressed incretin pathway are among the mechanisms through which diabetes affects the bone. Accordingly, the present review aimed to investigate the effects of antidiabetic medications on bone quality, primarily through AGEs and the incretin pathway. Google Scholar, Cochrane Library, and PubMed were used to examine related studies until February 2024. Antidiabetic medications influence AGEs and the incretin pathway directly or indirectly. Certain antidiabetic drugs including metformin, glucagon-like peptide-1 receptor agonists (GLP-1RA), dipeptidyl-peptidase-4 (DDP-4) inhibitors, α-glucosidase inhibitors (AGIs), sodium-glucose co-transporter-2 inhibitors, and thiazolidinediones (TZDs), directly affect AGEs through multiple mechanisms. These mechanisms include decreasing the formation of AGEs and the expression of AGEs receptor (RAGE) in tissue and increasing serum soluble RAGE levels, resulting in the reduced action of AGEs. Similarly, metformin, GLP-1RA, DDP-4 inhibitors, AGIs, and TZDs may enhance incretin hormones directly by increasing their production or suppressing their metabolism. Additionally, these medications could influence AGEs and the incretin pathway indirectly by enhancing glycemic control. In contrast, sulfonylureas have not demonstrated any obvious effects on AGEs or the incretin pathway. Considering their favorable effects on AGEs and the incretin pathway, a suitable selection of antidiabetic drugs may facilitate more protective effects on the bone in diabetic patients.

Increased AGE Cross-Linking Reduces the Mechanical Properties of Osteons

The osteon is the primary structural component of bone, contributing significantly to its unique toughness and strength. Despite extensive research on osteonal structure, the properties of osteons have not been fully investigated, particularly within the context of bone fragility diseases like type 2 diabetes mellitus (T2DM). This study aims to isolate osteons from bovine bone, simulate the effects of increased advanced glycation end-products (AGEs) in T2DM through ribosylation, and evaluate the mechanical properties of isolated osteons. Osteons extracted from the posterior section of bovine femur mid-diaphysis were processed to achieve a sub-millimeter scale for microscale imaging. Subsequently, synchrotron radiation micro-computed tomography was employed to precisely localize and isolate the osteon internally. While comparable elastic properties were observed between control and ribosylated osteons, the presence of AGEs led to decreased strain to failure. Young's modulus was quantified (9.9 ± 4.9 GPa and 8.7 ± 3 GPa, respectively), aligning closely with existing literature. This study presents a novel method for the extraction and isolation of osteons from bone and shows the detrimental effect of AGEs at the osteonal level.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11837-024-06716-x.

Roles of collagen cross-links and osteon collagen/lamellar morphotypes in equine third metacarpals in tension and compression tests

Many bones experience bending, placing one side in net compression and the other in net tension. Because bone mechanical properties are relatively reduced in tension compared with compression, adaptations are needed to reduce fracture risk. Several toughening mechanisms exist in bone, yet little is known of the influences of secondary osteon collagen/lamellar 'morphotypes' and potential interplay with intermolecular collagen cross-links (CCLs) in prevalent/predominant tension- and compression-loaded regions. Paired third metacarpals (MC3s) from 10 adult horses were prepared for mechanical testing. From one MC3/pair, 5 mm cubes were tested in compression at several mid-shaft locations. From contralateral bones, dumbbell-shaped specimens were tested in tension. Hence, habitual/natural tension- and compression-loaded regions were tested in both modes. Data included: elastic modulus, yield and ultimate strength, and energy absorption (toughness). Fragments of tested specimens were examined for predominant collagen fiber orientation (CFO; representing osteonal and non-osteonal bone), osteon morphotype score (MTS, representing osteonal CFO), mineralization, porosity and other histological characteristics. As a consequence of insufficient material from tension-tested specimens, CCLs were only examined in compression-tested specimens (HP, hydroxylysylpyridinoline; LP, lysylpyridinoline; PE, pentosidine). Among CCLs, only LP and HP/LP correlated significantly with mechanical parameters: LP with energy absorption, HP/LP with elastic modulus (both r=0.4). HP/LP showed a trend with energy absorption (r=-0.3, P=0.08). HP/LP more strongly correlated with osteon density and mineralization than CFO or MTS. Predominant CFO more strongly correlated with energy absorption than MTS in both testing modes. In general, CFO was found to be relatively prominent in affecting regional toughness in these equine MC3s in compression and tension.

The impact of chronic obstructive pulmonary disease on bone strength

Chronic obstructive pulmonary disease (COPD) is a lifestyle-related disease that develops in middle-aged and older adults, often due to smoking habits, and has been noted to cause bone fragility. COPD is a risk factor for osteoporosis and fragility fracture, and a high prevalence of osteoporosis and incidence of vertebral fractures have been shown in patients with COPD. Findings of lung tissue analysis in patients with COPD are primarily emphysema with a loss of alveolar septal walls, and the severity of pulmonary emphysema is negatively correlated with thoracic spine bone mineral density (BMD). On the other hand, epidemiological studies on COPD and fracture risk have reported a BMD-independent increase in fracture risk; however, verification in animal models and human bone biopsy samples has been slow, and the essential pathogenesis has not been elucidated. The detailed pathological/molecular mechanisms of musculoskeletal complications in patients with COPD are unknown, and basic research is needed to elucidate the mechanisms. This paper discusses the impacts of COPD on bone strength, focusing on findings in animal models in terms of bone microstructure, bone metabolic dynamics, and material properties.

Bone Health in Patients With Type 2 Diabetes

The association between type 2 diabetes mellitus (T2DM) and skeletal fragility is complex, with effects on bone at the cellular, molecular, and biomechanical levels. As a result, people with T2DM, compared to those without, are at increased risk of fracture, despite often having preserved bone mineral density (BMD) on dual-energy x-ray absorptiometry (DXA). Maladaptive skeletal loading and changes in bone architecture (particularly cortical porosity and low cortical volumes, the hallmark of diabetic osteopathy) are not apparent on routine DXA. Alternative imaging modalities, including quantitative computed tomography and trabecular bone score, allow for noninvasive visualization of cortical and trabecular compartments and may be useful in identifying those at risk for fractures. Current fracture risk calculators underestimate fracture risk in T2DM, partly due to their reliance on BMD. As a result, individuals with T2DM, who are at high risk of fracture, may be overlooked for commencement of osteoporosis therapy. Rather, management of skeletal health in T2DM should include consideration of treatment initiation at lower BMD thresholds, the use of adjusted fracture risk calculators, and consideration of metabolic and nonskeletal risk factors. Antidiabetic medications have differing effects on the skeleton and treatment choice should consider the bone impacts in those at risk for fracture. T2DM poses a unique challenge when it comes to assessing bone health and fracture risk. This article discusses the clinical burden and presentation of skeletal disease in T2DM. Two clinical cases are presented to illustrate a clinical approach in assessing and managing fracture risk in these patients.

Effects of aging and diabetes on the deformation mechanisms and molecular structural characteristics of collagen fibrils under daily activity

Crosslinking plays an important role in collagen-based tissues since it affects mechanical behavior and tissue metabolism. Aging and diabetes affect the type and density of crosslinking, effectively altering tissue properties. However, most studies focus on these effects under large stress rather than daily activities. We focus on the deformation mechanisms and structural change at the binding sites for integrins, proteoglycans, and collagenase in collagen fibrils using a fully atomistic model. We show that high-connectivity enzymatic crosslinking (our "HC" model, representing normal tissues) and advanced-glycation end-products (our "Glucosepane" model, which increase in diabetes) result in uniform deformation under daily activity, but low-connectivity enzymatic crosslinking (our "LC" model, representing aging tissues) does not. In particular, the HC model displays more sliding, which may explain the ability of healthy tissues to absorb more strain energy. In contrast, AGEs induce instability in the structures near the binding sites, which would affect the tissue metabolism of the collagen molecule. Our results provide important insights into the molecular mechanisms of collagen and a possible explanation for the role of crosslinking in tissues undergoing daily activity.

Plasma undercarboxylated osteocalcin dynamics with glycemic stress reflects insulin sensitivity and beta-cell function in humans with and without T2DM

This study aimed to better understand the relationship between bone-related biomarkers and nutrient stress in the context of metabolic health. We investigated plasma osteocalcin (OC) during an oral glucose challenge and experimental hyperinsulinemia in Type 2 diabetes (T2DM) and lean healthy controls (LHC). Older individuals with obesity and T2DM (n = 9) and young LHCs (n = 9) underwent a 75g oral glucose tolerance test (OGTT) and a 40 mU/m2/min hyperinsulinemic-euglycemic clamp. Plasma undercarboxylated OC (ucOC) and total OC were measured at baseline, 60mins, and 120mins of the OGTT and clamp via ELISA. In addition, plasma alkaline phosphatase (ALP), leptin, adiponectin, Vitamin D and insulin were measured and indices of insulin sensitivity and β-cell function were derived. The T2DM group had lower (p<0.05) ucOC and ucOC:total OC ratio than LHC during both the OGTT and clamp. Further, baseline ucOC was positively correlated to indices of β-cell function and negatively correlated to indices of insulin resistance when both groups were combined (all p<0.05). Suppression of OC observed in T2DM may be related to glucose intolerance and insulin resistance. Similarly, our data suggest that the observed phenotypic differences between groups are likely a product of long-term glucose dysregulation rather than acute flux in glucose or insulin.

Combining Raman Microspectroscopy and X-ray Microcomputed Tomography for the Study of Bone Quality in Apolipoprotein-Deficient Animal Models

Raman microspectroscopy and X-ray microcomputed tomography (micro-CT) were used for assessment of the quality of the femur and tibia bones in apolipoprotein-deficient mice compared to control littermates. The cortical and trabecular bone was investigated separately. Raman spectra revealed no differences in the bioapatite-to-collagenous matrix ratio of the cortical bone. The quantities of calcium and collagen, which were measured using atomic absorption spectrometry and thermogravimetric analysis, respectively, were also found to be equal in the two groups. Density and morphometric parameters, which were measured using micro-CT, verified the cortical mineral stability. Bone quality indices were measured using Raman spectra. A decreased collagen crosslink (trivalent-to-divalent) ratio revealed delayed maturation of the collagen network. Such a decrease has been reported in the literature to be connected to decreased bone strength. For the trabecular bone, micro-CT revealed severe osteoporosis in the knock-out group, which was evident from a decreased mineral density, trabecular thickness and increased bone surface/volume ratio. The trabecular bone was not accessible for Raman spectroscopy. According to these results, the cortical and trabecular femur bone is expected to exhibit proneness to fracturing, each for a different reason. A combination of the two techniques was regarded as necessary for an overall assessment of bone quality.

A pilot study: effect of irisin on trabecular bone in a streptozotocin-induced animal model of type 1 diabetic osteopathy utilizing a micro-CT

Background

Osteoporosis is a significant co-morbidity of type 1 diabetes mellitus (DM1) leading to increased fracture risk. Exercise-induced hormone 'irisin' in low dosage has been shown to have a beneficial effect on bone metabolism by increasing osteoblast differentiation and reducing osteoclast maturation, and inhibiting apoptosis and inflammation. We investigated the role of irisin in treating diabetic osteopathy by observing its effect on trabecular bone.

Methods

DM1 was induced by intraperitoneal injection of streptozotocin 60 mg/kg body weight. Irisin in low dosage (5 µg twice a week for 6 weeks I/P) was injected into half of the control and 4-week diabetic male Wistar rats. Animals were sacrificed six months after induction of diabetes. The trabecular bone in the femoral head and neck was analyzed using a micro-CT technique. Bone turnover markers were measured using ELISA, Western blot, and RT-PCR techniques.

Results

It was found that DM1 deteriorates the trabecular bone microstructure by increasing trabecular separation (Tb-Sp) and decreasing trabecular thickness (Tb-Th), bone volume fraction (BV/TV), and bone mineral density (BMD). Irisin treatment positively affects bone quality by increasing trabecular number p < 0.05 and improves the BMD, Tb-Sp, and BV/TV by 21-28%. The deterioration in bone microarchitecture is mainly attributed to decreased bone formation observed as low osteocalcin and high sclerostin levels in diabetic bone samples p < 0.001. The irisin treatment significantly suppressed the serum and bone sclerostin levels p < 0.001, increased the serum CTX1 levels p < 0.05, and also showed non-significant improvement in osteocalcin levels.

Conclusions

This is the first pilot study to our knowledge that shows that a low dose of irisin marginally improves the trabecular bone in DM1 and is an effective peptide in reducing sclerostin levels.

Increased tissue modulus and hardness in the TallyHO mouse model of early onset type 2 diabetes mellitus

Individuals with type 2 diabetes mellitus (T2DM) have a higher fracture risk compared to those without T2DM despite having higher bone mineral density (BMD). Thus, T2DM may alter other aspects of resistance to fracture beyond BMD such as bone geometry, microarchitecture, and tissue material properties. We characterized the skeletal phenotype and assessed the effects of hyperglycemia on bone tissue mechanical and compositional properties in the TallyHO mouse model of early-onset T2DM using nanoindentation and Raman spectroscopy. Femurs and tibias were harvested from male TallyHO and C57Bl/6J mice at 26 weeks of age. The minimum moment of inertia assessed by micro-computed tomography was smaller (-26%) and cortical porosity was greater (+490%) in TallyHO femora compared to controls. In three-point bending tests to failure, the femoral ultimate moment and stiffness did not differ but post-yield displacement was lower (-35%) in the TallyHO mice relative to that in C57Bl/6J age-matched controls after adjusting for body mass. The cortical bone in the tibia of TallyHO mice was stiffer and harder, as indicated by greater mean tissue nanoindentation modulus (+22%) and hardness (+22%) compared to controls. Raman spectroscopic mineral:matrix ratio and crystallinity were greater in TallyHO tibiae than in C57Bl/6J tibiae (mineral:matrix +10%, p < 0.05; crystallinity +0.41%, p < 0.10). Our regression model indicated that greater values of crystallinity and collagen maturity were associated with reduced ductility observed in the femora of the TallyHO mice. The maintenance of structural stiffness and strength of TallyHO mouse femora despite reduced geometric resistance to bending could potentially be explained by increased tissue modulus and hardness, as observed at the tibia. Finally, with worsening glycemic control, tissue hardness and crystallinity increased, and bone ductility decreased in TallyHO mice. Our study suggests that these material factors may be sentinels of bone embrittlement in adolescents with T2DM.

Assessment of muscle mass and bone density in elderly patients with type 2 diabetes mellitus depending on the level of glycated hemoglobin

Aim to assess the prevalence of low muscle mass and low bone density in elderly patients with type 2 diabetes (T2DM), depending on the level of glycated hemoglobin (HbA1c). Material and methods.The study included 187 patients (mean age 65.16 4.31 years), who were tested for fasting blood glucose, HbA1c, osteocalcin (OC), procollagen type 1 N-terminal propeptide (P1NP), C-terminal type I collagen telopeptides (B-CTX), 25-hydroxyvitamin D, body composition and bone mineral density. Results.The prevalence of low muscle mass, osteopenia, and osteoporosis in elderly patients with T2DM was 35.8%, 38.5%, and 30.5%, respectively. The prevalence of low muscle mass was significantly higher in women with HbA1c 9.0% (p =0.035). Osteopenia and osteoporosis prevailed in men with HbA1c 9.0% (p=0.007 and p=0.048, respectively). The appendicular skeletal muscle index (ASMI), bone mineral content (BMC) and bone mineral density (BMD) of the lumbar spine, BMC and BMD of the thigh were significantly reduced in the osteoporosis and osteopenia groups (p0.05); while B-CTX, P1NP were significantly increased. In men, both ASMI (p=0.007) and P1NP levels (p=0.001) were important risk factors for osteopenia/osteoporosis, and in women such risk factor was ASMI (p=0.019). Conclusion.In T2DM patients, the high HbA1c levels were associated with higher rates of low muscle mass in women and osteoporosis in men, and ASMI was a risk factor for osteoporosis in both sexes.

Longitudinal alterations in bone morphometry, mechanical integrity and composition in Type-2 diabetes in a Zucker diabetic fatty (ZDF) rat

Individuals with Type-2 Diabetes (T2D) have an increased risk of bone fracture, without a reduction in bone mineral density. It is hypothesised that the hyperglycaemic state caused by T2D forms an excess of Advanced Glycated End-products (AGEs) in the organic matrix of bone, which are thought to stiffen the collagen network and lead to impaired mechanical properties. However, the mechanisms are not well understood. This study aimed to investigate the geometrical, structural and material properties of diabetic cortical bone during the development and progression of T2D in ZDF (fa/fa) rats at 12-, 26- and 46-weeks of age. Longitudinal bone growth was impaired as early as 12-weeks of age and by 46-weeks bone size was significantly reduced in ZDF (fa/fa) rats versus controls (fa/+). Diabetic rats had significant structural deficits, such as bending rigidity, ultimate moment and energy-to-failure measured via three-point bend testing. Tissue material properties, measured by taking bone geometry into account, were altered as the disease progressed, with significant reductions in yield and ultimate strength for ZDF (fa/fa) rats at 46-weeks. FTIR analysis on cortical bone powder demonstrated that the tissue material deficits coincided with changes in tissue composition, in ZDF (fa/fa) rats with long-term diabetes having a reduced carbonate:phosphate ratio and increased acid phosphate content when compared to age-matched controls, indicative of an altered bone turnover process. AGE accumulation, measured via fluorescent assays, was higher in the skin of ZDF (fa/fa) rats with long-term T2D, bone AGEs did not differ between strains and neither AGEs correlated with bone strength. In conclusion, bone fragility in the diabetic ZDF (fa/fa) rats likely occurs through a multifactorial mechanism influenced initially by impaired bone growth and development and proceeding to an altered bone turnover process that reduces bone quality and impairs biomechanical properties as the disease progresses.

Bone collagen quality in lumbar fusion patients: the association between volumetric bone mineral density and advanced glycation endproducts

PURPOSE

The sole determination of volumetric bone mineral density (vBMD) is insufficient to evaluate overall bone integrity. The accumulation of advanced glycation endproducts (AGEs) stiffens and embrittles collagen fibers. Despite the important role of AGEs in bone aging, the relationship between AGEs and vBMD is poorly understood. We hypothesized that an accumulation of AGEs, a marker of impaired bone quality, is related to decreased vBMD.

METHODS

Prospectively collected data of 127 patients undergoing lumbar fusion were analyzed. Quantitative computed tomography (QCT) measurements were performed at the lumbar spine. Intraoperative bone biopsies were obtained and analyzed with confocal fluorescence microscopy for fluorescent AGEs, both trabecular and cortical. Spearman's correlation coefficients were calculated to examine relationships between vBMD and fAGEs, stratified by sex. Multivariable linear regression analysis with adjustments for age, sex, body mass index (BMI), race, diabetes mellitus and HbA1c was used to investigate associations between vBMD and fAGEs.

RESULTS

One-hundred and twenty-seven patients (51.2% female, 61.2 years, BMI of 28.7 kg/m2) with 107 bone biopsies were included in the final analysis, excluding patients on anti-osteoporotic drug therapy. In the univariate analysis, cortical fAGEs increased with decreasing vBMD at (r = -0.301; p = 0.030), but only in men. In the multivariable analysis, trabecular fAGEs increased with decreasing vBMD after adjusting for age, sex, BMI, race, diabetes mellitus and HbA1c (β = 0.99;95%CI=(0.994,1.000); p = 0.04).

CONCLUSION

QCT-derived vBMD measurements were found to be inversely associated with trabecular fAGEs. Our results enhance the understanding of bone integrity by suggesting that spine surgery patients with decreased bone quantity may also have poorer bone quality.

Association between bone marrow lesions and bone mineral density of the proximal tibia in end-stage osteoarthritic knees

This retrospective cross-sectional study investigated the association between bone marrow lesions (BMLs) and bone mineral density (BMD) in the proximal tibia of end-stage osteoarthritic knees from a large patient sample. Overall, 1308 end-stage osteoarthritic knees were enrolled before total knee arthroplasty. The preoperative range of motion was recorded. Bone mineral density in the medial tibial plateau (MTP), lateral tibial plateau (LTP), and metaphysis were measured using dual-energy X-ray absorptiometry. The MTP/LTP, MTP/metaphysis, and LTP/metaphysis ratios were calculated. BMLs were scored using a whole-organ magnetic resonance imaging scoring system. The relationship between BMD and BML scores was investigated using linear regression analysis. The highest BMD was 0.787 ± 0.176 g/cm² at the MTP, followed by 0.676 ± 0.180 g/cm² and 0.572 ± 0.145 g/cm² at the metaphysis and LTP, respectively. The prevalence of BMLs was 90.4% and 24.2% in the MTP and LTP, respectively. In women, higher BML scores at the MTP were positively correlated with the BMD of the MTP (p < 0.001, r = 0.278), MTP/LTP (p < 0.001, r = 0.267), and MTP/metaphysis ratios (p < 0.001, r = 0.243). Regression analysis showed that higher BML scores in the MTP were correlated with higher BMD in the MTP (p < 0.001) and lower BMD in the LTP (p < 0.001). High BML scores in the MTP were positively associated with high BMD in the MTP, which also induced the medial to lateral imbalance of BMD in the proximal tibia.

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.

Biomineralization inspired 3D printed bioactive glass nanocomposite scaffolds orchestrate diabetic bone regeneration by remodeling micromilieu

Type II diabetes mellitus (TIIDM) remains a challenging clinical issue for both dentists and orthopedists. By virtue of persistent hyperglycemia and altered host metabolism, the pathologic diabetic micromilieu with chronic inflammation, advanced glycation end products accumulation, and attenuated biomineralization severely impairs bone regeneration efficiency. Aiming to "remodel" the pathologic diabetic micromilieu, we 3D-printed bioscaffolds composed of Sr-containing mesoporous bioactive glass nanoparticles (Sr-MBGNs) and gelatin methacrylate (GelMA). Sr-MBGNs act as a biomineralization precursor embedded in the GelMA-simulated extracellular matrix and release Sr, Ca, and Si ions enhancing osteogenic, angiogenic, and immunomodulatory properties. In addition to angiogenic and anti-inflammatory outcomes, this innovative design reveals that the nanocomposites can modulate extracellular matrix reconstruction and simulate biomineralization by activating lysyl oxidase to form healthy enzymatic crosslinked collagen, promoting cell focal adhesion, modulating osteoblast differentiation, and boosting the release of OCN, the noncollagenous proteins (intrafibrillar mineralization dependent), and thus orchestrating osteogenesis through the Kindlin-2/PTH1R/OCN axis. This 3D-printed bioscaffold provides a multifunctional biomineralization-inspired system that remodels the "barren" diabetic microenvironment and sheds light on the new bone regeneration approaches for TIIDM.

Increased Advanced Glycation Endproducts, Stiffness, and Hardness in Iliac Crest Bone From Postmenopausal Women With Type 2 Diabetes Mellitus on Insulin

Individuals with type 2 diabetes mellitus (T2DM) have a greater risk of bone fracture compared with those with normal glucose tolerance (NGT). In contrast, individuals with impaired glucose tolerance (IGT) have a lower or similar risk of fracture. Our objective was to understand how progressive glycemic derangement affects advanced glycation endproduct (AGE) content, composition, and mechanical properties of iliac bone from postmenopausal women with NGT (n = 35, age = 65 ± 7 years, HbA1c = 5.8% ± 0.3%), IGT (n = 26, age = 64 ± 5 years, HbA1c = 6.0% ± 0.4%), and T2DM on insulin (n = 25, age = 64 ± 6 years, HbA1c = 9.1% ± 2.2%). AGEs were assessed in all samples using high-performance liquid chromatography to measure pentosidine and in NGT/T2DM samples using multiphoton microscopy to spatially resolve the density of fluorescent AGEs (fAGEs). A subset of samples (n = 14 NGT, n = 14 T2DM) was analyzed with nanoindentation and Raman microscopy. Bone tissue from the T2DM group had greater concentrations of (i) pentosidine versus IGT (cortical +24%, p = 0.087; trabecular +35%, p = 0.007) and versus NGT (cortical +40%, p = 0.003; trabecular +35%, p = 0.004) and (ii) fAGE cross-link density versus NGT (cortical +71%, p < 0.001; trabecular +44%, p < 0.001). Bone pentosidine content in the IGT group was lower than in the T2DM group and did not differ from the NGT group, indicating that the greater AGE content observed in T2DM occurs with progressive diabetes. Individuals with T2DM on metformin had lower cortical bone pentosidine compared with individuals not on metformin (-35%, p = 0.017). Cortical bone from the T2DM group was stiffer (+9%, p = 0.021) and harder (+8%, p = 0.039) versus the NGT group. Bone tissue AGEs, which embrittle bone, increased with worsening glycemic control assessed by HbA1c (Pen: R2  = 0.28, p < 0.001; fAGE density: R2  = 0.30, p < 0.001). These relationships suggest a potential mechanism by which bone fragility may increase despite greater tissue stiffness and hardness in individuals with T2DM; our results suggest that it occurs in the transition from IGT to overt T2DM. © 2022 American Society for Bone and Mineral Research (ASBMR).

Dermal ultrasound measurements for bone quality assessment : An investigation of advanced glycation endproducts derived from confocal fluorescence microscopy

Bone quality is increasingly being recognized in the assessment of fracture risk. Nonenzymatic collagen cross-linking with the accumulation of advanced glycation end products stiffens and embrittles collagen fibers thus increasing bone fragility. Echogenicity is an ultrasound (US) parameter that provides information regarding the skin collagen structure. We hypothesized that both skin and bone collagen degrade in parallel fashion. Prospectively collected data of 110 patients undergoing posterior lumbar fusion was analyzed. Preoperative skin US measurements were performed in the lumbar region to assess dermal thickness and echogenicity. Intraoperative bone biopsies from the posterior superior iliac spine were obtained and analyzed with confocal fluorescence microscopy for fluorescent advanced glycation endproducts (fAGEs). Pearson's correlation was calculated to examine relationships between  (1) US and fAGEs, and (2) age and fAGEs stratified by sex. Multivariable linear regression analysis with adjustments for age, sex, body mass index (BMI), diabetes mellitus, and hemoglobin A1c (HbA1c) was used to investigate associations between US and fAGEs. One hundred and ten patients (51.9% female, 61.6 years, BMI 29.8 kg/m2 ) were included in the analysis. In the univariate analysis cortical and trabecular fAGEs decreased with age, but only in women (cortical: r = -0.32, p = 0.031; trabecular: r = -0.32; p = 0.031). After adjusting for age, sex, BMI, diabetes mellitus, and HbA1c, lower dermal (β = 1.01; p = 0.012) and subcutaneous (β = 1.01; p = 0.021) echogenicity increased with increasing cortical fAGEs and lower dermal echogenicity increased with increasing trabecular fAGEs (β = 1.01; p = 0.021). This is the first study demonstrating significant associations between skin US measurements and in vivo bone quality parameters in lumbar fusion patients. As a noninvasive assessment tool, skin US measurements might be incorporated into future practice to investigate bone quality in spine surgery patients.

Contributors to impaired bone health in type 2 diabetes

Type 2 diabetes (T2D) is associated with numerous complications, including increased risk of fragility fractures, despite seemingly protective factors [e.g., normal bone mineral density and increased body mass index(BMI)]. However, fracture risk in T2D is underestimated by current fracture risk calculators. Importantly, post-fracture mortality is worse in T2D following any fracture, highlighting the importance of identifying high-risk patients that may benefit from targeted management. Several diabetes-related factors are associated with increased fracture risk, including exogenous insulin therapy, vascular complications, and poor glycaemic control, although detailed comprehensive studies to identify the independent contributions of these factors are lacking. The underlying pathophysiological mechanisms are complex and multifactorial, with different factors contributing during the course of T2D disease. These include obesity, hyperinsulinaemia, hyperglycaemia, accumulation of advanced glycation end products, and vascular supply affecting bone-cell function and survival and bone-matrix composition. This review summarises the current understanding of the contributors to impaired bone health in T2D, and proposes an updated approach to managing these patients.

Effects of Incretin Pathway Elements on Bone Properties

Introduction The effects of incretin-based drugs, such as receptor agonists of glucagon-like peptide-1 and inhibitors of dipeptidyl peptidase-4, on bone metabolism are not completely clear yet. The aim of this study is to compare the effects of glucagon-like peptide-1 and inhibitors of dipeptidyl peptidase-4 on the bone to see how different elements of the incretin pathway affect bone quality in terms of biomechanical properties, bone turnover, and mineral properties. Materials and methods Forty 10-week-old Wistar rats were divided into four groups: a control group, a control diabetic group, a diabetic group treated with sitagliptin, and a diabetic group treated with exenatide. Type 2 diabetes was simulated by dietary manipulation in addition to low-dose streptozotocin, and then two different incretin-based drugs were administered. The rats were sacrificed after five weeks of therapeutic treatment. Their serum was analyzed with the enzyme-linked immunosorbent assay (ELISA) method for basic bone turnover markers, and their right femur was subjected to a three-point bending test. Finally, Hematoxylin & Eosin staining, in addition to Raman spectroscopy, were employed to access the collagen and mineral properties of the bone. Results Both incretin-based drugs reduced osteoclast function; however, they were not able to restore osteoblastic function to normal. The net effect on bone strength was surprising: bone elasticity was restored by the antidiabetic treatment, but bone strength deteriorated. Exenatide had a slightly more pronounced effect, which, although not significant, points to the direction that dipeptidyl peptidase-4 (DPP4) may be a linking factor between reduced osteoclastic function and reduced bone formation, as suggested by the literature. Conclusion DPP4 receptors seem to be one of the links between reduced osteoclast function and reduced bone remodeling, so DPP4 inhibition can be more detrimental to the bone than glucagon-like peptide-1 (GLP-1) receptor agonists.

Histological assessment of cortical bone changes in diabetic rats

BACKGROUND

Diabetes mellitus weakens bone strength due to deterioration of bone quality; however, the histological mechanisms are still unknown. We hypothesized that histological assessment of cortical bone would enable us to determine the cause of the bone strength reduction associated with diabetes mellitus. Our aim was to evaluate the histomorphometric changes of cortical bone associated with deterioration of intrinsic bone properties and bone quality in diabetes mellitus.

METHODS

We compared the outcomes of mechanical tests, bone mineral density measured using micro-computed tomography, and histological assessments, by applying Villanueva's bone stain, to the tibial bones of 40-week-old diabetic and control male rats.

RESULTS

With respect to mechanical testing, the maximum load and energy absorption were significantly lower in the diabetic than in the control group, although fracture displacement and stiffness were not significantly different between the two groups. Bone mineral density was significantly higher in the diabetic group than in the control group. Bone histomorphometry revealed that the diabetic rats had fewer osteocytes, greater cortical porosity, and increased mineralization in cortical bone compared with the control group.

CONCLUSIONS

Increased mineralization of the cortical bone with greater cortical porosity leads to a weakening of bone strength in diabetes mellitus.

The extracellular matrix of human bone marrow adipocytes and glucose concentration differentially alter mineralization quality without impairing osteoblastogenesis

Bone marrow adipocytes (BMAds) accrue in various states of osteoporosis and interfere with bone remodeling through the secretion of various factors. However, involvement of the extracellular matrix (ECM) produced by BMAds in the impairment of bone marrow mesenchymal stromal cell (BM-MSC) osteoblastogenesis has received little attention. In type 2 diabetes (T2D), skeletal fragility is associated with several changes in bone quality that are incompletely understood, and BMAd quantity increases in relationship to poor glycemic control. Considering their altered phenotype in this pathophysiological context, we aimed to determine the contribution of the ECM of mature BMAds to osteoblastogenesis and mineralization quality in the context of chronic hyperglycemia.

Human BM-MSCs were differentiated for 21 days in adipogenic medium containing either a normoglycemic (LG, 5.5 mM) or a high glucose concentration (HG, 25 mM). The ECM laid down by BMAds were devitalized through cell removal to examine their impact on the proliferation and differentiation of BM-MSCs toward osteoblastogenesis in LG and HG conditions. Compared to control plates, both adipocyte ECMs promoted cell adhesion and proliferation. As shown by the unmodified RUNX2 and osteocalcin mRNA levels, BM-MSC commitment in osteoblastogenesis was hampered by neither the hyperglycemic condition nor the adipocyte matrices. However, adipocyte ECMs or HG condition altered the mineralization phase with perturbed expression levels of type 1 collagen, MGP and osteopontin. Despite higher ALP activity, mineralization levels per cell were decreased for osteoblasts grown on adipocyte ECMs compared to controls. Raman spectrometry revealed that culturing on adipocyte matrices specifically prevents type-B carbonate substitution and favors collagen crosslinking, in contrast to exposure to HG concentration alone. Moreover, the mineral to organic ratio was disrupted according to the presence of adipocyte ECM and the glucose concentration used for adipocyte or osteoblast culture. HG concentration and adipocyte ECM lead to different defects in mineralization quality, recapitulating contradictory changes reported in T2D osteoporosis.

Our study shows that ECMs from BMAds do not impair osteoblastogenesis but alter both the quantity and quality of mineralization partly in a glucose concentration-dependent manner. This finding sheds light on the involvement of BMAds, which should be considered in the compromised bone quality of T2D and osteoporosis patients more generally.

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Glucose level alters the Extracellular Matrix composition of Bone Marrow adipocytes.

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Osteoblastogenesis on adipocyte ECMs is unaltered but produced less mineral amount.

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The quality of the mineral is altered differently by adipocyte ECMs or glucose levels.

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The presence of BM adipocytes should be valued in damaged osteoporosis bone quality.

Advanced glycation end products and bone - How do we measure them and how do they correlate with bone mineral density and fractures? A systematic review and evaluation of precision of measures

The role of advanced glycation end products (AGEs) in bone fragility especially in diabetic bone disease is increasingly recognized and researched. As skeletal frailty in diabetes does not correlate to bone mineral density (BMD) in the same way as in postmenopausal osteoporosis, BMD may not be a suitable measure of bone quality in persons with diabetes. Abundant research exists upon the effect of AGEs on bone, and though full understanding of the mechanisms of actions does not yet exist, there is little doubt of the clinical relevance. Thus, the measurement of AGEs as well as possible treatment effects on AGEs have become issues of interest. The aim of this report is to summarize results of measurements of AGEs. It consists of a systematic review of the existing literature on AGE measurements in clinical research, an evaluation of the precision of skin autofluorescence (SAF) measurement by AGE Reader® (Diagnoptics), and a short commentary on treatment of osteoporosis in patients with and without diabetes with respects to AGEs. We conclude that various AGE measures correlate well, both fluorescent and non-fluorescent and in different tissues, and that more than one target of measure may be used. However, pentosidine has shown good correlation with both bone measures and fracture risk in existing literature and results on SAF as a surrogate measurement is promising as some corresponding associations with fracture risk and bone measures are reported. As SAF measurements performed with the AGE Reader® display high precision and allow for a totally noninvasive procedure, conducting AGE measurements using this method has great potential and further research of its applicability is encouraged.

Collagen cross-link profiles and mineral are different between the mandible and femur with site specific response to perturbed collagen

Compromises to collagen and mineral lead to a decrease in whole bone quantity and quality in a variety of systemic diseases, yet, clinically, disease manifestations differ between craniofacial and long bones. Collagen alterations can occur through post-translational modification via lysyl oxidase (LOX), which catalyzes enzymatic collagen cross-link formation, as well as through non-enzymatic advanced glycation end products (AGEs) such as pentosidine and carboxymethyl-lysine (CML). Characterization of the cross-links and AGEs, and comparison of the mineral and collagen modifications in craniofacial and long bones represent a critical gap in knowledge. However, alterations to either the mineral or collagen in bone may contribute to disease progression and, subsequently, the anatomical site dependence of a variety of diseases. Therefore, we hypothesized that collagen cross-links and AGEs differ between craniofacial and long bones and that altered collagen cross-linking reduces mineral quality in an anatomic location dependent. To study the effects of cross-link inhibition on mineralization between anatomical sites, beta-aminoproprionitrile (BAPN) was administered to rapidly growing, 5-8 week-old male mice. BAPN is a dose-dependent inhibitor of LOX that pharmacologically alters enzymatic cross-link formation. Long bones (femora) and craniofacial bones (mandibles) were compared for mineral quantity and quality, collagen cross-link and AGE profiles, and tissue level mechanics, as well as the response to altered cross-links via BAPN. A highly sensitive liquid chromatography/mass spectrometry (LC-MS) method was developed which allowed for quantification of site-dependent accumulation of the advanced glycation end-product, carboxymethyl-lysine (CML). CML was ∼8.3× higher in the mandible than the femur. The mandible had significantly higher collagen maturation, mineral crystallinity, and Young's modulus, but lower carbonation, than the femur. BAPN also had anatomic specific effects, leading to significant decreases in mature cross-links in the mandible, and an increase in mineral carbonation in the femur. This differential response of both the mineral and collagen composition to BAPN between the mandible and femur highlights the need to further understand how inherent compositional differences in collagen and mineral contribute to anatomic-site specific manifestations of disease in both craniofacial and long bones.

Association Between Vitamin A Intake and Disease Severity in Early-Onset Heterotopic Ossification of the Posterior Longitudinal Ligament of the Spine

STUDY DESIGN

A sex- and age-matched case-control study and a cross-sectional study.

OBJECTIVE

In our previous study, patients with early-onset (<50 years of age) ossification of the posterior longitudinal ligament (OPLL) had distinct features such as morbid obesity, a high prevalence of lifestyle-related diseases, and diffuse ossified lesions mainly affecting the thoracic spine. Our goals were to determine whether early-onset OPLL patients have unbalanced dietary habits and to identify nutritional factors associated with OPLL exacerbation.

METHODS

In Study 1, the simple brief-type self-administered diet history questionnaire (BDHQ) was used to compare nutrient intake levels of early-onset OPLL patients (n = 13) with those of sex- and age-matched non-OPLL controls (n = 39) or with those of common OPLL (onset age ≥ 50 years, n = 62). In Study 2, serological validation was conducted for thoracic OPLL patients (n = 77) and non-OPLL controls (n = 101) in a nationwide multicenter study in Japan.

RESULTS

The BDHQ showed that the early-onset OPLL patients had significantly lower intakes of vitamins A and B6 than non-OPLL controls. These results were validated by lower serum vitamins A and B6 levels in the early-onset thoracic OPLL patients. The severity of OPLL negatively correlated with serum vitamin A levels in male early-onset OPLL patients. The multiple regression analysis revealed that the severity of thoracic OPLL had an association with onset age and serum vitamin A level.

CONCLUSIONS

Vitamin A deficiency resulting from unbalanced dietary habits is associated with exacerbation of male early-onset OPLL.

Causative or associative: A critical review of the role of advanced glycation end-products in bone fragility

The accumulation of advanced glycation end-products (AGEs) in the organic matrix of bone with aging and chronic disease such as diabetes is thought to increase fracture risk independently of bone mass. However, to date, there has not been a clinical trial to determine whether inhibiting the accumulation of AGEs is effective in preventing low-energy, fragility fractures. Moreover, unlike with cardiovascular or kidney disease, there are also no pre-clinical studies demonstrating that AGE inhibitors or breakers can prevent the age- or diabetes-related decrease in the ability of bone to resist fracture. In this review, we critically examine the case for a long-standing hypothesis that AGE accumulation in bone tissue degrades the toughening mechanisms by which bone resists fracture. Prior research into the role of AGEs in bone has primarily measured pentosidine, an AGE crosslink, or bulk fluorescence of hydrolysates of bone. While significant correlations exist between these measurements and mechanical properties of bone, multiple AGEs are both non-fluorescent and non-crosslinking. Since clinical studies are equivocal on whether circulating pentosidine is an indicator of elevated fracture risk, there needs to be a more complete understanding of the different types of AGEs including non-crosslinking adducts and multiple non-enzymatic crosslinks in bone extracellular matrix and their specific contributions to hindering fracture resistance (biophysical and biological). By doing so, effective strategies to target AGE accumulation in bone with minimal side effects could be investigated in pre-clinical and clinical studies that aim to prevent fragility fractures in conditions that bone mass is not the underlying culprit.

Advanced Glycation End Products, Bone Health, and Diabetes Mellitus

Advanced glycation end products (AGEs), the compounds resulting from the non-enzymatic glycosylation between reducing sugars and proteins, are derived from food or produced de novo. Over time, more and more endogenous and exogenous AGEs accumulate in various organs such as the liver, kidneys, muscle, and bone, threatening human health. Among these organs, bone is most widely reported. AGEs accumulating in bone reduce bone strength by participating in bone structure formation and breaking bone homeostasis by binding their receptors to alter the proliferation, differentiation, and apoptosis of cells involved in bone remodeling. In this review, we summarize the research about the effects of AGEs on bone health and highlight their associations with bone health in diabetes patients to provide some clues toward the discovery of new treatment and prevention strategies for bone-related diseases caused by AGEs.

Aging exacerbates the morphological and mechanical response of mineralized collagen fibrils in murine cortical bone to disuse

Mineralized collagen fibrils (MCFs) are the fundamental building blocks of bone tissue and contribute significantly to the mechanical behavior of bone. However, it is still largely unknown how the collagen network in bone responds to aging and the disuse normally accompanying it. Utilizing atomic force microscopy, nanoindentation and Raman spectroscopy, age-related alterations in the microstructure and mechanical properties of murine cortical tibia at multiple scales were investigated in this study. The potential difference in the responses of bone to disuse at different ages was studied. The results indicated that the age- and disuse-related alterations in bone initiate from MCFs in the bone matrix. The D-periodic spacing, radial elastic modulus of a single MCF and the mineral-to-matrix ratio on the cortical bone surface were larger in aged mice than in adult mice. Disuse, on the other hand, mainly has a major influence on aged mice, particularly on the morphology and mechanical properties of MCFs, but it only has modest effects on adult bone. These findings revealed insights into the morphological and mechanical adaptation of mineralized collagen fibrils in murine cortical bone to aging and disuse. STATEMENT OF SIGNIFICANCE: Bone is a complex structured composite material consisting of an interwoven framework of collagen fibrils reinforced by mineral particles and embedded in an extrafibrillar mineralized matrix. Utilizing atomic force microscopy, nanoindentation and Raman spectroscopy, this study suggests that the effects of aging, as well as the accompanying disuse, on the morphology and mechanical properties of bone initiate from the mineralized collagen fibril level. More interestingly, the MCF in the bone of aged mice seems to be more sensitive to disuse than that in adult mice. These findings significantly further the current understanding of the adaptation process of bone to aging at the mineralized collagen fibril level and provide direct insights into the physiological response of bone to aging and the abnormal mechanical environment.

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.

Advanced Glycation End Products: Do They Impair Bone Health in Diabetes?

In diabetes mellitus (DM), there is increased formation and accumulation of advanced glycation end products (AGEs), which represent a heterogeneous class of molecules produced by non-enzymatic glycation of various molecules during long-term hyperglycaemia. Several studies have examined the role of AGEs in DM complications. Accumulating evidence suggests that AGEs affect bone metabolism. New knowledge indicates that they may play a role in bone disease among DM subjects. More data are now needed to clarify their role and to explore new AGEs-based therapeutic options for optimal bone health in DM.

High glucose-induced inhibition of osteoblast like MC3T3-E1 differentiation promotes mitochondrial perturbations

Diabetes mellitus is a metabolic disorder that causes health concerns worldwide. Patients with diabetes exhibit multisystemic symptoms, including loss of bone quality over time. The progressive deterioration of bone promotes failure to withstand damage and increases the risk of fractures. Much of the molecular and metabolic mechanism(s) in diabetic bone remains unclear. In vitro studies suggest that hyperglycemia inhibits mineralization, affecting bone formation and function. In this study, inhibition of osteoblast differentiation was induced using hyperglycemia to assess whether high glucose promotes mitochondrial impairment along with altered bone matrix formation. It was hypothesized that bone energy metabolism would be altered in these cells as calcium deposition, a key phase for bone function, is suppressed. Early passages of osteoblast like MC3T3-E1 cells were differentiated under normal and high glucose conditions. To investigate osteoblast differentiation, we quantified calcium accumulation by alizarin red staining and analyzed immunoblots of key proteins. To assess mitochondrial function, we quantified mitochondrial DNA (mtDNA), detected expression and function of key proteins from the Tricarboxylic (TCA) cycle, measured mitochondrial respiration, and fuel oxidation of alternative nutrients. Results confirmed previous work showing that mineralization was inhibited and AKT expression was reduced in high glucose-treated bone cells. Unexpectedly, high glucose-treated osteoblast cells utilize both mitochondrial respiration and glycolysis to maintain energy demands with partial help of fatty acid for reliance of baseline bioenergetics. These metabolic shifts suggest that hyperglycemia maintain bone metabolic needs in an early differentiated state concurrent to the inhibition in bone matrix formation.

Functions and Mechanisms of Pro-Lysyl Oxidase Processing in Cancers and Eye Pathologies with a Focus on Diabetic Retinopathy

Lysyl oxidases are multifunctional proteins derived from five lysyl oxidase paralogues (LOX) and lysyl oxidase-like 1 through lysyl oxidase-like 4 (LOXL1-LOXL4). All participate in the biosynthesis of and maturation of connective tissues by catalyzing the oxidative deamination of lysine residues in collagens and elastin, which ultimately results in the development of cross-links required to function. In addition, the five LOX genes have been linked to fibrosis and cancer when overexpressed, while tumor suppression by the propeptide derived from pro-LOX has been documented. Similarly, in diabetic retinopathy, LOX overexpression, activity, and elevated LOX propeptide have been documented. The proteolytic processing of pro-forms of the respective proteins is beginning to draw attention as the resultant peptides appear to exhibit their own biological activities. In this review we focus on the LOX paralogue, and what is known regarding its extracellular biosynthetic processing and the still incomplete knowledge regarding the activities and mechanisms of the released lysyl oxidase propeptide (LOX-PP). In addition, a summary of the roles of both LOX and LOX-PP in diabetic retinopathy, and brief mentions of the roles for LOX and closely related LOXL1 in glaucoma, and keratoconus, respectively, are included.

Bone Microarchitecture and Strength in Long-Standing Type 1 Diabetes

Type 1 diabetes (T1DM) is associated with an increased fracture risk, specifically at nonvertebral sites. The influence of glycemic control and microvascular disease on skeletal health in long-standing T1DM remains largely unknown. We aimed to assess areal (aBMD) and volumetric bone mineral density (vBMD), bone microarchitecture, bone turnover, and estimated bone strength in patients with long-standing T1DM, defined as disease duration ≥25 years. We recruited 59 patients with T1DM (disease duration 37.7 ± 9.0 years; age 59.9 ± 9.9 years.; body mass index [BMI] 25.5 ± 3.7 kg/m² ; 5-year median glycated hemoglobin [HbA1c] 7.1% [IQR 6.82-7.40]) and 77 nondiabetic controls. Dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HRpQCT) at the ultradistal radius and tibia, and biochemical markers of bone turnover were assessed. Group comparisons were performed after adjustment for age, gender, and BMI. Patients with T1DM had lower aBMD at the hip (p < 0.001), distal radius (p = 0.01), lumbar spine (p = 0.04), and femoral neck (p = 0.05) as compared to controls. Cross-linked C-telopeptide (CTX), a marker of bone resorption, was significantly lower in T1DM (p = 0.005). At the distal radius there were no significant differences in vBMD and bone microarchitecture between both groups. In contrast, patients with T1DM had lower cortical thickness (estimate [95% confidence interval]: -0.14 [-0.24, -0.05], p < 0.01) and lower cortical vBMD (-28.66 [-54.38, -2.93], p = 0.03) at the ultradistal tibia. Bone strength and bone stiffness at the tibia, determined by homogenized finite element modeling, were significantly reduced in T1DM compared to controls. Both the altered cortical microarchitecture and decreased bone strength and stiffness were dependent on the presence of diabetic peripheral neuropathy. In addition to a reduced aBMD and decreased bone resorption, long-standing, well-controlled T1DM is associated with a cortical bone deficit at the ultradistal tibia with reduced bone strength and stiffness. Diabetic neuropathy was found to be a determinant of cortical bone structure and bone strength at the tibia, potentially contributing to the increased nonvertebral fracture risk. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Exploring the Mechanical Properties and Performance of Type-I Collagen at Various Length Scales: A Progress Report

Collagen is the basic protein of animal tissues and has a complex hierarchical structure. It plays a crucial role in maintaining the mechanical and structural stability of biological tissues. Over the years, it has become a material of interest in the biomedical industries thanks to its excellent biocompatibility and biodegradability and low antigenicity. Despite its significance, the mechanical properties and performance of pure collagen have been never reviewed. In this work, the emphasis is on the mechanics of collagen at different hierarchical levels and its long-term mechanical performance. In addition, the effect of hydration, important for various applications, was considered throughout the study because of its dramatic influence on the mechanics of collagen. Furthermore, the discrepancies in reports of the mechanical properties of collagenous tissues (basically composed of 20-30% collagen fibres) and those of pure collagen are discussed.

Prediction of Femoral Strength Based on Bone Density and Biochemical Markers in Elderly Men With Type 2 Diabetes Mellitus

Purpose: Effects of bone density, bone turnover and advanced glycation end products (AGEs) on femoral strength (FS) are still unclear in patients with type 2 diabetes mellitus (T2DM). This study aims to assess and predict femoral strength and its influencing factors in elderly men with T2DM. Methods: T2DM patients (n = 10, mean age, 66.98 years) and age-matched controls (n = 8, mean age, 60.38 years) were recruited. Femoral bone mineral density (BMD) and serum biochemical indices of all subjects were measured. FS was evaluated through finite element analysis based on quantitative computed tomography. Multiple linear regression was performed to obtain the best predictive models of FS and to analyze the ability of predictors of FS in both groups. Results: FS (p = 0.034), HbA1c (p = 0.000) and fasting blood glucose (p = 0.000) levels of T2DM group were significantly higher than those of control group; however, the P1NP level (p = 0.034) was significantly lower. FS was positively correlated with femoral neck T score (FNTS) (r = 0.794, p < 0.01; r = 0.881, p < 0.01) in both groups. FS was correlated with age (r = -0.750, p < 0.05) and pentosidine (r = -0.673, p < 0.05) in T2DM group. According to multiple linear regression, FNTS and P1NP both contributed to FS in two groups. P1NP significantly improved the prediction of FS in both groups, but significant effect of FNTS on predicting FS was only presented in control group. Furthermore, pentosidine, age and HbA1c all played significant roles in predicting FS of T2DM. Conclusion: Femoral strength was higher in elderly men with T2DM, which might be caused by higher BMD and lower bone turnover rate. Moreover, besides BMD and bone formation level, AGEs, blood glucose and age might significantly impact the prediction of femoral strength in T2DM.

Bone fragility in diabetes: novel concepts and clinical implications

Increased fracture risk represents an emerging and severe complication of diabetes. The resulting prolonged immobility and hospitalisations can lead to substantial morbidity and mortality. In type 1 diabetes, bone mass and bone strength are reduced, resulting in up to a five-times greater risk of fractures throughout life. In type 2 diabetes, fracture risk is increased despite a normal bone mass. Conventional dual-energy x-ray absorptiometry might underestimate fracture risk, but can be improved by applying specific adjustments. Bone fragility in diabetes can result from cellular abnormalities, matrix interactions, immune and vascular changes, and musculoskeletal maladaptation to chronic hyperglycaemia. This Review summarises how the bone microenvironment responds to type 1 and type 2 diabetes, and the mechanisms underlying fragility fractures. We describe the value of novel imaging technologies and the clinical utility of biomarkers, and discuss current and future therapeutic approaches that protect bone health in people with diabetes.

The Association between Accumulation of Toxic Advanced Glycation End-Products and Cytotoxic Effect in MC3T3-E1 Cells

In diabetic patients, the metabolism of excess glucose increases the toxicity of the aldehyde group of sugar. Aldehydes, including glyceraldehyde (GA), react with intracellular proteins to form advanced glycation end-products (AGEs), which deteriorate bone quality and cause osteoporosis. One of the causes of osteoporotic fractures is impaired osteoblast osteogenesis; however, the cytotoxic effects of aldehydes and the subsequent formation of AGEs in osteoblasts have not yet been examined in detail. Therefore, the present study investigated the cytotoxicity of intracellular GA and GA-derived AGEs, named toxic AGEs (TAGE), in the mouse osteoblastic cell line MC3T3-E1. Treatment with GA induced MC3T3-E1 cell death, which was accompanied by TAGE modifications in several intracellular proteins. Furthermore, the downregulated expression of Runx2, a transcription factor essential for osteoblast differentiation, and collagen correlated with the accumulation of TAGE. The GA treatment also reduced the normal protein levels of collagen in cells, suggesting that collagen may be modified by TAGE and form an abnormal structure. Collectively, the present results show for the first time that GA and TAGE exert cytotoxic effects in osteoblasts, inhibit osteoblastic differentiation, and decrease the amount of normal collagen. The suppression of GA production and associated accumulation of TAGE has potential as a novel therapeutic target for osteoporosis under hyperglycemic conditions.

Advanced glycation end products promote osteoporosis by inducing ferroptosis in osteoblasts

Advanced glycation end products (AGEs) have been widely reported to play an important role in osteoporosis (OP), particularly in diabetes-related OP. The aim of the present study was to investigate the effect of AGEs on osteoblast function and the underlying mechanisms. The level of bone mineral density (BMD), serum AGEs and fasting blood glucose (FBG) was measured in patients with OP and healthy individuals, and the correlation between AGE levels and BMD or FBG was then analyzed. For the in vitro experiments, the hFOB1.19 osteoblast cell line was cultured in medium containing AGEs and serum from healthy individuals or patients with OP, and with or without type-2 diabetes mellitus (T2DM). Cell proliferation, differentiation, mineralization, apoptosis and ferroptosis were evaluated using Cell Counting Kit-8 and alkaline phosphatase (ALP) assays, Alizarin red and TUNEL staining, iron indicator, lipid peroxidation tests and western blot analysis, respectively. In a separate set of experiments, the ferroptosis inhibitor, deferoxamine (DFO), was also added to the culture medium of cells treated with AGEs and serum from patients with OP and T2DM. The results demonstrated that patients with OP had a higher level of serum AGEs and FBG compared with that in healthy individuals. The level of serum AGEs in patients with OP was negatively correlated with BMD, but was positively correlated with FBG. In addition, AGEs and serum from patients with OP markedly inhibited hFOB1.19 cell proliferation, ALP production and mineralized nodule formation. Apoptosis and ferroptosis were significantly promoted by AGEs and serum from patients with OP. Moreover, serum from OP patients with T2DM caused stronger effect than that from OP patients with normal FBG. However, DFO reversed the effects induced by AGEs and serum from patients with OP and T2DM on hFOB1.19 cells. Collectively, AGEs could disrupt the functions of osteoblasts by inducing cell ferroptosis, thus contributing to OP.

Differential risk of fracture attributable to type 2 diabetes mellitus according to skeletal site

BACKGROUND

Impaired bone quality, especially related to accumulation of advanced glycation end-products (AGEs) and higher incidence of falls contribute substantially to a higher risk of fracture associated with type 2 diabetes mellitus (T2DM). These factors may predispose to fractures more at skeletal sites where impaired bone toughness and falls play a larger pathogenic role (such as hip fractures) compared to skeletal sites where they are less important (such as vertebral fractures).

OBJECTIVE

To determine if the associations of T2DM with prevalent and incident vertebral fractures are as strong as they are for hip and other non-vertebral fractures.

METHODS

Amongst 80,238 individuals in the Manitoba Bone Density Program database (mean [SD] age 64.4 [11.1] years, 89.8% female, 8676 with diagnosed T2DM) with a baseline BMD test (1996-2016), we estimated hazard ratios (HRs) for incident clinical fracture at different skeletal sites in those with compared to those without T2DM using Cox proportional hazards models over a mean (SD) 9.0 (5.0) year follow-up period. We also estimated odds ratios for prevalent vertebral fracture on VFA images amongst 9594 individuals (mean [SD] 76 [6.8] years, 1185 with T2DM diagnosis at time of DXA-VFA) and for prior clinical fractures at different skeletal sites using logistic regression models.

RESULTS

After multivariable adjustment, T2DM was associated with incident hip (HR 1.63, 95% CI 1.44 to 1.85) and proximal humerus fractures (HR 1.59, 95% CI 1.39 to 1.83), but was not associated with incident forearm fracture (HR 1.00, 95% CI 0.86 to 1.17) and only weakly with incident clinical vertebral fracture (HR 1.16, 95% CI 1.01 to 1.33). Similarly, T2DM was associated with prior hip (OR 1.78, 95% CI 1.21 to 2.61) and prior proximal humerus fracture (OR 1.31, 95% CI 1.02 to 1.68) but not with prior forearm (OR 0.89, 95% CI 0.74 to 1.06) or prevalent vertebral fracture on VFA images (OR 0.91, 95% CI 0.77 to 1.08).

CONCLUSION

T2DM is a stronger risk factor for hip and proximal humerus fractures than for vertebral and wrist fractures. Further research is warranted to determine if the known differences in falls and/or bone quality between T2DM and age-related osteoporosis account for these differential associations.

Inhibitory Effects of Astaxanthin on CML-HSA-Induced Inflammatory and RANKL-Induced Osteoclastogenic Gene Expression in RAW 264.7 Cells

Objective: Elevated levels of serum N^ε-carboxymethyllysine (CML), a well-known advanced glycation end-product (AGE), were observed in patients with inflammation or osteoporosis. Astaxanthin was reported to possess anti-inflammatory and antioxidant effects. In the present study, we investigated the effects of commercially available dietary supplement AstaReal ACT^R (ASR) capsule content as astaxanthin on CML-HSA-induced inflammatory and receptor activator of nuclear factor-kappa-Β ligand (RANKL)-induced osteoclastogenic gene expression. Methods: RAW 264.7 murine macrophage cells were stimulated with CML-HSA to trigger inflammatory gene expression and treated with either a vehicle control or varied concentrations of astaxanthin. Inflammatory gene expression was measured using an enzyme-linked immunosorbent assay (ELISA) or qPCR. We triggered osteoclastogenesis using RANKL, and osteoclastogenic gene expression was measured through tartrate-resistant acid phosphatase (TRAP) activity, staining, immunofluorescence, and qPCR analyses. Results: CML-HSA showed a stimulatory effect on inflammatory gene expression, and astaxanthin reduced the expression by at least two-fold. The levels of autoinflammatory gene expression were reduced by astaxanthin. The RANKL-induced osteoclastogenesis was significantly inhibited by astaxanthin, with reductions in the activation of nuclear factor-κB (NF-κB), the expression of NFATc1 (nuclear factor of activated T cells 1), multinucleated cell formation, and the expression of mature osteoclast marker genes. Conclusion: Astaxanthin has potential as a remedy for CML-HSA-induced inflammation and RANKL-induced excessive bone loss.

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.

Relations Between Bone Quantity, Microarchitecture, and Collagen Cross-links on Mechanics Following In Vivo Irradiation in Mice

Humans are exposed to ionizing radiation via spaceflight or cancer radiotherapy, and exposure from radiotherapy is known to increase risk of skeletal fractures. Although irradiation can reduce trabecular bone mass, alter trabecular microarchitecture, and increase collagen cross‐linking, the relative contributions of these effects to any loss of mechanical integrity remain unclear. To provide insight, while addressing both the monotonic strength and cyclic‐loading fatigue life, we conducted total‐body, acute, gamma‐irradiation experiments on skeletally mature (17‐week‐old) C57BL/6J male mice (n = 84). Mice were administered doses of either 0 Gy (sham), 1 Gy (motivated by cumulative exposures from a Mars mission), or 5 Gy (motivated by clinical therapy regimens) with retrieval of the lumbar vertebrae at either a short‐term (11‐day) or long‐term (12‐week) time point after exposure. Micro‐computed tomography was used to assess trabecular and cortical quantity and architecture, biochemical composition assays were used to assess collagen quality, and mechanical testing was performed to evaluate vertebral compressive strength and fatigue life. At 11 days post‐exposure, 5 Gy irradiation significantly reduced trabecular mass (p < 0.001), altered microarchitecture (eg, connectivity density p < 0.001), and increased collagen cross‐links (p < 0.001). Despite these changes, vertebral strength (p = 0.745) and fatigue life (p = 0.332) remained unaltered. At 12 weeks after 5 Gy exposure, the trends in trabecular bone persisted; in addition, regardless of irradiation, cortical thickness (p < 0.01) and fatigue life (p < 0.01) decreased. These results demonstrate that the highly significant effects of 5 Gy total‐body irradiation on the trabecular bone morphology and collagen cross‐links did not translate into detectable effects on vertebral mechanics. The only mechanical deficits observed were associated with aging. Together, these vertebral results suggest that for spaceflight, irradiation alone will likely not alter failure properties, and for radiotherapy, more investigations that include post‐exposure time as a positive control and testing of both failure modalities are needed to determine the cause of increased fracture risk. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by US Government employees and their work is in the public domain in the USA.