Bone quality in diabetes

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.

Comparative analysis of ventricular stiffness across species

Investigating ventricular diastolic properties is crucial for understanding the physiological cardiac functions in organisms and unraveling the pathological mechanisms of cardiovascular disorders. Ventricular stiffness, a fundamental parameter that defines ventricular diastolic functions in chordates, is typically analyzed using the end-diastolic pressure-volume relationship (EDPVR). However, comparing ventricular stiffness accurately across chambers of varying maximum volume capacities has been a long-standing challenge. As one of the solutions to this problem, we propose calculating a relative ventricular stiffness index by applying an exponential approximation formula to the EDPVR plot data of the relationship between ventricular pressure and values of normalized ventricular volume by the ventricular weight. This article reviews the potential, utility, and limitations of using normalized EDPVR analysis in recent studies. Herein, we measured and ranked ventricular stiffness in differently sized and shaped chambers using ex vivo ventricular pressure-volume analysis data from four animals: Wistar rats, red-eared slider turtles, masu salmon, and cherry salmon. Furthermore, we have discussed the mechanical effects of intracellular and extracellular viscoelastic components, Titin (Connectin) filaments, collagens, physiological sarcomere length, and other factors that govern ventricular stiffness. Our review provides insights into the comparison of ventricular stiffness in different-sized ventricles between heterologous and homologous species, including non-model organisms.

Effect of a single dose of zoledronic acid on bone mineral density and trabecular bone score in Indian postmenopausal osteoporotic women with and without type 2 diabetes mellitus - A prospective cohort pilot study

PURPOSE

The objectives were to study the effect of a single dose of intravenous (IV) zoledronic acid (ZA) on changes in bone mineral density (BMD) (lumbar spine (LS), hip, & distal forearm), trabecular bone score (TBS) and bone turnover markers (BTMs) in postmenopausal osteoporotic women with and without diabetes over 12 months.

METHODS

Patients were divided into two groups: type 2 diabetes mellitus (T2DM) (n = 40) and non-DM (n = 40). Both groups received a single dose of 4 mg IV ZA at baseline. The BMD with TBS and BTMs (β-CTX, sclerostin, P1NP) were measured at baseline, six months, and 12 months.

RESULTS

At baseline, BMD in all three sites was similar in both groups. T2DM patients were older and had lower BTMs than non-DM patients. The mean increase in LS-BMD (gram/cm2) at 12 months in T2DM and the non-DM group was 3.6 ± 4.7% and 6.2 ± 4.7 %, respectively (P = 0.01). However, the age adjusted mean difference in LS BMD increment between two groups at one year was - 2.86 % (-5.02% to -0.69%), P = 0.01. There was a comparable change in BMD at other two sites, BTMs, and TBS in both the groups over one year follow-up.

CONCLUSION

The gain in the LS-BMD was significantly lower in T2DM group compared to non-DM subjects over 12 months after a single IV infusion of 4 mg ZA. The explanation for this could be low bone turnover in diabetes subjects at baseline.

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.

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.

Cellular and Molecular Mechanisms Associating Obesity to Bone Loss

Obesity is an alarming disease that favors the upset of other illnesses and enhances mortality. It is spreading fast worldwide may affect more than 1 billion people by 2030. The imbalance between excessive food ingestion and less energy expenditure leads to pathological adipose tissue expansion, characterized by increased production of proinflammatory mediators with harmful interferences in the whole organism. Bone tissue is one of those target tissues in obesity. Bone is a mineralized connective tissue that is constantly renewed to maintain its mechanical properties. Osteoblasts are responsible for extracellular matrix synthesis, while osteoclasts resorb damaged bone, and the osteocytes have a regulatory role in this process, releasing growth factors and other proteins. A balanced activity among these actors is necessary for healthy bone remodeling. In obesity, several mechanisms may trigger incorrect remodeling, increasing bone resorption to the detriment of bone formation rates. Thus, excessive weight gain may represent higher bone fragility and fracture risk. This review highlights recent insights on the central mechanisms related to obesity-associated abnormal bone. Publications from the last ten years have shown that the main molecular mechanisms associated with obesity and bone loss involve: proinflammatory adipokines and osteokines production, oxidative stress, non-coding RNA interference, insulin resistance, and changes in gut microbiota. The data collection unveils new targets for prevention and putative therapeutic tools against unbalancing bone metabolism during obesity.

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.

Effect of Teriparatide on Bone Mineral Density and Trabecular Bone Score in Type 2 Diabetic Patients with Osteoporosis: A Retrospective Cohort Study

The BMDs of the lumbar spine, whole femur, and femoral neck and TBS were measured. Change in BMD or TBS was defined as the BMD or TBS at follow-up, performed 1 year after baseline, minus baseline BMD or TBS. Results: This retrospective cohort study included 93 patients, of whom 52 received no medication, 26 received bisphosphonates, and 15 received weekly teriparatide. BMD of the lumbar spine increased in all three groups. There was no change in BMD of the whole femur and femoral neck in the no medication and bisphosphonates groups, whereas the BMD of the whole femur (from 0.73 (0.15) to 0.74 (0.15) g/cm², p = 0.011) and femoral neck (from 0.59 (0.16) to 0.60 (0.16) g/cm², p = 0.011) in the teriparatide group increased. The change in BMD of the femoral neck (no medication; −0.002 (0.034) g/cm², bisphosphonates; −0.0001 (0.024) g/cm², and teriparatide; 0.017 (0.022) g/cm², p = 0.091) or TBS (no medication; −0.007 (0.051), bisphosphonates; −0.058 (0.258), and teriparatide; 0.021 (0.044), p = 0.191) in the teriparatide group tended to be higher than that in the other groups, although there was no statistically significant difference. Conclusions: Teriparatide increased the BMD of the femoral neck and TBS in osteoporosis patients with type 2 diabetes mellitus, compared to bisphosphonates and no medication.

Lycopene Improves Bone Quality and Regulates AGE/RAGE/NF-кB Signaling Pathway in High-Fat Diet-Induced Obese Mice

Objective. This study was aimed at examining the effects of lycopene on bone metabolism in high-fat diet (HFD)- induced obese mice and to identify the potential underlying mechanisms. Methods. Mice were fed a HFD for 12 weeks and then continue with or without lycopene intervention (15 mg/kg) for additional 10 weeks. The effects of lycopene on blood glucose and lipid metabolism, as well as serum levels of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and malondialdehyde (MDA) were determined by biochemical assays. Bone histomorphological features and osteoclast activity were assessed by hematoxylin/eosin and tartrate-resistant acid phosphatase staining. Bone microstructure at the proximal tibial metaphysis and diaphysis was determined by microcomputed tomography. Tibial biomechanical strength and material profiles were measured by a three-point bending assay and Fourier transform infrared spectroscopy. Protein expressions involved in the AGE/RAGE/NF-кB signaling pathway were determined by western blot and/or immunohistochemical staining. Results. Lycopene consumption reduced body weight gain and improved blood glucose and lipid metabolism in HFD-induced obese mice. In addition, lycopene treatment preserved bone biomechanical strength, material profiles, and microarchitecture in obese mice. Moreover, these alterations were associated with an increase in serum levels of T-AOC and SOD, and a decline in serum levels of MDA, as well as a reduction of AGEs, RAGE, cathepsin K, and p-NF-кBp65 and NF-кBp65 expressions in the femurs and tibias of obese mice. Conclusion. Lycopene may improve bone quality through its antioxidant properties, which may be linked with the regulation of the AGE/RAGE/NF-кB signaling pathway in obese mice. These results suggest that lycopene consumption may be beneficial for the management of obesity-induced osteoporosis.

Investigation of Mechanical, Material, and Compositional Determinants of Human Trabecular Bone Quality in Type 2 Diabetes

CONTEXT

Increased bone fragility and reduced energy absorption to fracture associated with type 2 diabetes (T2D) cannot be explained by bone mineral density alone. This study, for the first time, reports on alterations in bone tissue's material properties obtained from individuals with diabetes and known fragility fracture status.

OBJECTIVE

To investigate the role of T2D in altering biomechanical, microstructural, and compositional properties of bone in individuals with fragility fracture.

METHODS

Femoral head bone tissue specimens were collected from patients who underwent replacement surgery for fragility hip fracture. Trabecular bone quality parameters were compared in samples of 2 groups, nondiabetic (n = 40) and diabetic (n = 30), with a mean duration of disease 7.5 ± 2.8 years.

RESULTS

No significant difference was observed in aBMD between the groups. Bone volume fraction (BV/TV) was lower in the diabetic group due to fewer and thinner trabeculae. The apparent-level toughness and postyield energy were lower in those with diabetes. Tissue-level (nanoindentation) modulus and hardness were lower in this group. Compositional differences in the diabetic group included lower mineral:matrix, wider mineral crystals, and bone collagen modifications-higher total fluorescent advanced glycation end-products (fAGEs), higher nonenzymatic cross-link ratio (NE-xLR), and altered secondary structure (amide bands). There was a strong inverse correlation between NE-xLR and postyield strain, fAGEs and postyield energy, and fAGEs and toughness.

CONCLUSION

The current study is novel in examining bone tissue in T2D following first hip fragility fracture. Our findings provide evidence of hyperglycemia's detrimental effects on trabecular bone quality at multiple scales leading to lower energy absorption and toughness indicative of increased propensity to bone fragility.

Associations of Circulating Osteoglycin With Bone Parameters and Metabolic Markers in Patients With Diabetes

Objective

Circulating osteoglycin may facilitate the crosstalk between bone and pancreas to empower adaptation of bone mass to whole body energy balance. We aimed to examine whether osteoglycin is associated with bone and metabolic parameters and if osteoglycin levels differ between patients with type 1 and 2 diabetes (T1D and T2D).

Design and methods

A cross-sectional study of 190 patients with diabetes mellitus and stable hemoglobin A1c (HbA1c) (97 T1D and 93 T2D) was conducted. S-osteoglycin was analyzed by ELISA. Unpaired t-tests were performed to test differences between patients with T1D and T2D and linear regression analyses were performed to investigate associations between osteoglycin, glycemic markers, bone turnover markers and characteristics.

Results

S-osteoglycin did not differ between patients with T1D and T2D (p=0.10). No associations were present between osteoglycin and age, gender, microvascular complications, HbA1c, or plasma glucose in T1D or T2D patients (p>0.05 for all). S-osteoglycin was not associated with levels of bone turnover markers (C-terminal cross-linked telopeptide of type-I collagen (CTX), P-procollagen type 1 amino terminal propeptide (P1NP), P-osteocalcin (OC), P-sclerostin, S-osteoprotegerin (OPG) or S-Receptor Activator of Nuclear factor Kappa beta Ligand (RANKL)) in neither T1D or T2D patients (p>0.05 for all).

Conclusion

Osteoglycin levels were similar in T1D and T2D patients. Osteoglycin did not correlate with glucose, HbA1c or any other biochemical marker of bone turnover. Thus, we did not find evidence supporting the existence of an osteoglycin-bone-pancreas axis.

Clinical Trial Registration

ClinicalTrials.gov, identifier NCT01870557.

Lactate Dehydrogenase Inhibition With Oxamate Exerts Bone Anabolic Effect

Cellular bioenergetics is a promising new therapeutic target in aging, cancer, and diabetes because these pathologies are characterized by a shift from oxidative to glycolytic metabolism. We have previously reported such glycolytic shift in aged bone as a major contributor to bone loss in mice. We and others also showed the importance of oxidative phosphorylation (OxPhos) for osteoblast differentiation. It is therefore reasonable to propose that stimulation of OxPhos will have bone anabolic effect. One strategy widely used in cancer research to stimulate OxPhos is inhibition of glycolysis. In this work, we aimed to evaluate the safety and efficacy of pharmacological inhibition of glycolysis to stimulate OxPhos and promote osteoblast bone-forming function and bone anabolism. We tested a range of glycolytic inhibitors including 2-deoxyglucose, dichloroacetate, 3-bromopyruvate, and oxamate. Of all the studied inhibitors, only a lactate dehydrogenase (LDH) inhibitor, oxamate, did not show any toxicity in either undifferentiated osteoprogenitors or osteoinduced cells in vitro. Oxamate stimulated both OxPhos and osteoblast differentiation in osteoprogenitors. In vivo, oxamate improved bone mineral density, cortical bone architecture, and bone biomechanical strength in both young and aged C57BL/6J male mice. Oxamate also increased bone formation by osteoblasts without affecting bone resorption. In sum, our work provided a proof of concept for the use of anti-glycolytic strategies in bone and identified a small molecule LDH inhibitor, oxamate, as a safe and efficient bone anabolic agent. © 2020 American Society for Bone and Mineral Research (ASBMR).

Development of HFD-Fed/Low-Dose STZ-Treated Female Sprague-Dawley Rat Model to Investigate Diabetic Bone Fragility at Different Organization Levels

Type 2 diabetes (T2D) adversely affects the normal functioning, intrinsic material properties, and structural integrity of many tissues, and bone fragility is one of them. To simulate human T2D and to investigate diabetic bone fragility, many rodent diabetic models have been developed. Still, an outbred genetically normal nonobese diabetic rat model is not available that can better simulate the disease characteristics of nonobese T2D patients, who have a high prevalence in Asia. In this study, we used a combination treatment of high-fat diet (4 weeks, 58% kcal as fat) and low-dose streptozotocin (STZ; 35 mg/kg i.p. at the end of the fourth week) to develop T2D in female Sprague-Dawley (SD) rats. After 8 weeks of the establishment of the T2D model, the femoral bones were excised after euthanizing rats (animal age approximately 21 to 22 weeks; n = 10 with T2D, n = 10 without diabetes). The bone microstructure (μCT), mechanical, and material properties (three-point bending, cyclic reference point indentation, nanoindentation), mean mineral crystallite size (XRD), bone composition (mineral-to-matrix ratio, nonenzymatic cross-link ratio [NE-xLR], Fourier transform-infrared microspectroscopy), and total fluorescent advanced glycation end products were analyzed. We found that diabetic bone had reduced whole-bone strength and compromised structural properties (μCT). The NE-xLRs were elevated in the T2D group, and strongly and negatively correlated with postyield displacement, which suggests bone fragility was caused by a lack of glycation control. Along with that, the decreased mineral-to-matrix ratio and modulus, increased indentation distance increase, and wider mineral crystallite size in the T2D group were evidence that the diabetic bone composition and material properties had changed, and bone became weaker with a tendency to easily fracture. Altogether, this model simulates the natural history and metabolic characteristics of late-stage T2D (insulin resistance and as disease progress develops, hypoinsulinemia) for nonobese young (and/or adolescent) T2D patients (Asians) and provides potential evidence of diabetic bone fragility at various organization levels. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Pathophysiology and Management of Type 2 Diabetes Mellitus Bone Fragility

Individuals with type 2 diabetes mellitus (T2DM) have an increased risk of bone fragility fractures compared to nondiabetic subjects. This increased fracture risk may occur despite normal or even increased values of bone mineral density (BMD), and poor bone quality is suggested to contribute to skeletal fragility in this population. These concepts explain why the only evaluation of BMD could not be considered an adequate tool for evaluating the risk of fracture in the individual T2DM patient. Unfortunately, nowadays, the bone quality could not be reliably evaluated in the routine clinical practice. On the other hand, getting further insight on the pathogenesis of T2DM-related bone fragility could consent to ameliorate both the detection of the patients at risk for fracture and their appropriate treatment. The pathophysiological mechanisms underlying the increased risk of fragility fractures in a T2DM population are complex. Indeed, in T2DM, bone health is negatively affected by several factors, such as inflammatory cytokines, muscle-derived hormones, incretins, hydrogen sulfide (H2S) production and cortisol secretion, peripheral activation, and sensitivity. All these factors may alter bone formation and resorption, collagen formation, and bone marrow adiposity, ultimately leading to reduced bone strength. Additional factors such as hypoglycemia and the consequent increased propensity for falls and the direct effects on bone and mineral metabolism of certain antidiabetic medications may contribute to the increased fracture risk in this population. The purpose of this review is to summarize the literature evidence that faces the pathophysiological mechanisms underlying bone fragility in T2DM patients.

Impact of Diabetes Mellitus on Bone Health

Long-term exposure to a diabetic environment leads to changes in bone metabolism and impaired bone micro-architecture through a variety of mechanisms on molecular and structural levels. These changes predispose the bone to an increased fracture risk and impaired osseus healing. In a clinical practice, adequate control of diabetes mellitus is essential for preventing detrimental effects on bone health. Alternative fracture risk assessment tools may be needed to accurately determine fracture risk in patients living with diabetes mellitus. Currently, there is no conclusive model explaining the mechanism of action of diabetes mellitus on bone health, particularly in view of progenitor cells. In this review, the best available literature on the impact of diabetes mellitus on bone health in vitro and in vivo is summarised with an emphasis on future translational research opportunities in this field.

Insulin Receptor deletion in S100a4-lineage cells accelerates age-related bone loss

Type I and Type II Diabetes dramatically impair skeletal health. Altered Insulin Receptor (IR) signaling is a common feature of both diseases, and insulin has potent bone anabolic functions. Several previous studies have demonstrated that loss of IR in bone cells results in disrupted bone homeostasis during early post-natal growth. Here we have deleted IR in S100a4-lineage cells (IRcKO^S100a4) and assessed the effects on bone homeostasis in both young (15 weeks) and older adult (48 weeks) mice. S100a4-Cre has previously been shown to target the perichondrium during bone development, and here we show that S100a4 is expressed by adult trabecular and cortical bone cells, and that S100a4-Cre effectively targets adult bone, resulting in efficient deletion of IRβ. Deletion of IRβ in S100a4-lineage cells does not affect initial bone acquisition or homeostasis with no changes in cortical, trabecular or mechanical properties at 15-weeks of age, relative to wild type (WT) littermates. However, by 48-weeks of age, IRcKO^S100a4 mice display substantial declines in trabecular bone volume, bone volume fraction and torsional rigidity, relative to age-matched WT controls. This work establishes the utility of using S100a4-cre to target bone and demonstrates that IRβ in S100a4-lineage cells is required for maintenance of bone homeostasis in adult mice.

[Selective signaling pathway via feeding-related ciliary GPCR, melanin-concentrating hormone receptor 1]

G-protein-coupled receptors (GPCRs), which constitute a highly diverse family of seven transmembrane receptors, respond to external signals and regulate a variety of cellular and physiological processes. GPCRs are encoded by about 800 different genes in human and they represent the largest family of drug targets in clinical trials, which accounts for about 30% of approved drugs acting on 108 unique GPCRs. Signaling through GPCRs can be optimized by enriching receptors, selective binding partners, and downstream effectors in discrete cellular environment. The primary cilium is a ubiquitous organelle that functions as a sensory antenna for surrounding physical and chemical stimuli. Primary cilium's compartment is as little as 1/10,000th of the total cell volume. Therefore, the ciliary membrane is highly enriched for specific signaling molecules, allowing the primary cilium to organize signaling in a highly ordered microenvironment. Recently, a set of non-olfactory GPCRs such as somatostatin receptor 3 and melanin-concentrating hormone receptor 1 (MCHR1) have been found to be selectively targeted to cilia on several mammalian cell types including neuronal cells both in vitro and in vivo approaches. Moreover, investigations into the pathophysiology have implicated GPCR ciliary signaling in a number of developmental and cellular pathways. Thus, cilia are now considered as an increasingly important connection for GPCR signaling. This review summarizes our current understanding of the signaling pathways though ciliary GPCR, especially feeding- and mood-related GPCR MCHR1, along with specific biological phenomenon as cilia length shortening.

Type 1 Diabetes and Bone Fragility: Links and Risks

Type 1 diabetes (T1D) is associated with an increased fracture risk, which is present at young and old age. Reductions in bone mineral density do not explain the increased fracture risk. Novel scanning modalities suggest that structural deficits may contribute to the increased fracture risk. Furthermore, T1D may due to insulinopenia be a state of low bone turnover. However, diabetes complications and comorbidities may influence fracture risk. Patients with T1D are fearful of falls. The diabetes related complications, hypoglycemic events, and antihypertensive treatment may all lead to falls. Thus, the increased fracture risk in T1D seems to be multifactorial, and earlier intervention with antiosteoporotic medication and focus on fall prevention is needed. This systematic review addresses the epidemiology of fractures and osteoporosis in patients with T1D and the factors that influence fracture risk.

Advanced Glycation End Products and esRAGE Are Associated With Bone Turnover and Incidence of Hip Fracture in Older Men

BACKGROUND

Diabetes mellitus is associated with increased fracture risk despite preservation of bone density and reduced bone turnover.

AIMS

We tested the hypothesis that circulating advanced glycation end products (AGEs) and endogenous secretory receptor for AGEs (esRAGE) differentially modulate bone turnover and predict fracture risk in older men.

PARTICIPANTS

A total of 3384 community-dwelling men aged 70 to 89 years.

METHODS

Collagen type I C-terminal cross-linked telopeptide, N-terminal propeptide of type I collagen (P1NP), and total osteocalcin (TOC) were assayed using immunoassay and undercarboxylated osteocalcin (ucOC) following hydroxyapatite binding. Plasma N-carboxymethyllysine (CML) and esRAGE were assayed using immunoassay. Methylglyoxal and glyoxal were assayed using mass spectrometry. Incident hip fractures were ascertained.

RESULTS

Median age was 76.3 years (interquartile range, 74.2 to 79.1 years). Plasma CML was measured in 3011 men, methylglyoxal and glyoxal in 766 men, and esRAGE in 748 men. Plasma CML, methylglyoxal, glyoxal, and esRAGE were similar in men without and with diabetes (all P > 0.05). CML was positively associated with fasting glucose (r = 0.06, P < 0.001), and esRAGE was inversely associated (r = -0.08, P = 0.045). esRAGE was positively associated with bone formation (P1NP, r = 0.17, P < 0.001; ucOC, r = 0.11, P = 0.008; TOC, r = 0.16, P < 0.001). Incident hip fractures occurred in 106 men during follow-up. Men with CML in the third quartile of values had reduced incidence of hip fracture compared with men in the lowest quartile (hazard ratio, 0.49; 95% CI, 0.24 to 0.99; P = 0.045).

CONCLUSIONS

Glycemia associates positively with CML and reciprocally with esRAGE in older men. Circulating esRAGE modulates bone turnover in older men, whereas CML predicts incidence of hip fracture.

Differential effects of high-fat diet and exercise training on bone and energy metabolism

Bone microarchitecture and strength are impaired by obesity and physical inactivity, but the underlying molecular regulation of bone metabolism in response to these factors is not well understood. Therefore, we analyzed bone and energy metabolism in male mice fed a high-fat or standard chow diet for 12 weeks with or without free access to running wheels. High-fat diet (HFD) mimicked the human condition of obesity and insulin resistance, including symptoms such as elevated serum glucose and insulin levels and reduced insulin-stimulated glucose uptake into muscle and adipose tissue. Interestingly, HFD also decreased (-44%) glucose uptake into bone marrow. Bone mass was reduced (-45%) by HFD due to a diminished (-45%) bone remodeling rate. Bone matrix quality aspects, such as biomechanical stability, were additionally decreased. Concurrently, the bone marrow adiposity increased (+63%) in response to a HFD. Further, we detected elevated expression of the Wnt signaling inhibitor dickkopf-1 (Dkk-1, +42%) in mice fed a HFD, but this was not reflected in serum samples obtained from obese humans. In mice, exercise attenuated the adverse effects of HFD by reversing the glucose uptake into bone marrow, improving the bone mass and bone matrix quality while decreasing the bone marrow adiposity. This data shows that exercise prevents some, but not all of the negative effects of HFD on bone health and suggests that insulin signaling in bone marrow and Dkk-1 signaling may be involved in the pathogenesis of bone loss induced by HFD.

Skeletal Fragility in Type 2 Diabetes Mellitus

Type 2 diabetes (T2D) is associated with an increased risk of fracture, which has been reported in several epidemiological studies. However, bone mineral density in T2D is increased and underestimates the fracture risk. Common risk factors for fracture do not fully explain the increased fracture risk observed in patients with T2D. We propose that the pathogenesis of increased fracture risk in T2D is due to low bone turnover caused by osteocyte dysfunction resulting in bone microcracks and fractures. Increased levels of sclerostin may mediate the low bone turnover and may be a novel marker of increased fracture risk, although further research is needed. An impaired incretin response in T2D may also affect bone turnover. Accumulation of advanced glycosylation endproducts may also impair bone strength. Concerning antidiabetic medication, the glitazones are detrimental to bone health and associated with increased fracture risk, and the sulphonylureas may increase fracture risk by causing hypoglycemia. So far, the results on the effect of other antidiabetics are ambiguous. No specific guideline for the management of bone disease in T2D is available and current evidence on the effects of antiosteoporotic medication in T2D is sparse. The aim of this review is to collate current evidence of the pathogenesis, detection and treatment of diabetic bone disease.

Real-world antidiabetic drug use and fracture risk in 12,277 patients with type 2 diabetes mellitus: a nested case-control study

We conducted a nested case-control study to study the association between antidiabetic treatments (alone or in combination) use and fracture risk among incident type 2 Diabetes mellitus patients. We found an increased risk of bone fracture with insulin therapy compared to metformin monotherapy.

INTRODUCTION

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fragility fractures, to which antidiabetic therapies may contribute. We aimed to characterize the risk of fracture associated with different antidiabetic treatments as usually prescribed to T2DM patients in actual practice conditions.

METHODS

A case-control study was nested within a cohort of incident T2DM patients registered in 2006-2012 in the Information System for Research Development in Primary Care (Catalan acronym, SIDIAP), a database which includes records for > 5.5 million patients in Catalonia (Spain). Each case (incident major osteoporotic fracture) was risk-set matched with up to five same-sex controls by calendar year of T2DM diagnosis and year of birth (± 10 years). Study exposure included previous use of all antidiabetic medications (alone or in combination), as dispensed in the 6 months before the index date, with metformin (MTF) monotherapy, the most commonly used drug, as a reference group (active comparator).

RESULTS

Data on 12,277 T2DM patients (2049 cases and 10,228 controls) were analyzed. Insulin use was associated with increased fracture risk (adjusted OR 1.63 (95% CI 1.30-2.04)), as was the combination of MTF and sulfonylurea (SU) (adjusted OR 1.29 (1.07-1.56)), compared with MTF monotherapy. Sensitivity analyses suggest possible causality for insulin therapy but not for the MTF + SU combination association. No significant association was found with any other antidiabetic medications.

CONCLUSIONS

Insulin monotherapy was associated with an increased fracture risk compared to MTF monotherapy in T2DM patients. Fracture risk should be taken into account when starting a glucose-lowering drug as part of T2DM treatment.

Association of Decreased Handgrip Strength with Reduced Cortical Thickness in Japanese Female Patients with Type 2 Diabetes Mellitus

LD-100, a quantitative ultrasonic device, allows us to measure cortical thickness (CoTh). Patients with type 2 diabetes mellitus (T2DM) show high prevalence of sarcopenia. This study aimed to clarify the association of handgrip strength (HGS) with cortical porosis, a major risk for fracture of DM. CoTh and trabecular bone mineral density (TrBMD) at the 5.5% distal radius were assessed in T2DM female patients (n = 122) and non-DM female controls (n = 704) by LD-100. T2DM patients aged older 40 years showed significantly lower HGS and CoTh, but not TrBMD, than non-DM counterparts. Although HGS was significantly and positively correlated with CoTh and TrBMD in T2DM patients, multivariate analysis revealed HGS as an independent factor positively associated with CoTh, but not TrBMD, in T2DM patients, suggesting the preferential association of HGS with cortical, but not trabecular, bone component in T2DM female patients. In conclusion, the present study demonstrated an early decline of HGS in T2DM female patients as compared with non-DM healthy controls after the age of 40 years, which is independently associated with thinner CoTh, but not TrBMD in T2DM patients, and thus suggested that reduced muscle strength associated with DM might be a major factor for cortical porosis development in DM patients.

Diet quality and osteosarcopenic obesity in community-dwelling adults 50 years and older

OBJECTIVES

To examine the association between diet quality and osteosarcopenic obesity (OSO), low bone and muscle mass with concurrent high fat mass, in middle-aged and older adults.

STUDY DESIGN

Data were from a cross-sectional study of 2579 men and 3550 women aged 50 years and older who completed the Korea National Health and Nutritional Examination Survey from 2008 to 2010.

MAIN OUTCOME MEASURES

Data were collected using 24-h dietary recall, and diet quality was determined by the Diet Quality Index-International (DQI-I), on which higher scores denote better quality. Body composition was evaluated by dual-energy x-ray absorptiometry. The association between dietary quality and the number of body composition abnormalities (including OSO) was analyzed by multinomial logistic regression, adjusting for covariates.

RESULTS

In women, after controlling for covariates, higher scores on the DQI-I were associated with a significantly lower number of phenotypes associated with adverse body composition. Those in the highest tertile group of DQI-I were less likely to have OSO compared with those in the lowest tertile (odds ratio=0.54, 95% confidence interval: 0.32-0.92). In men, DQI-I scores were not associated with the number of body composition abnormalities.

CONCLUSIONS

Middle-aged and older women who eat a healthier diet, as determined by a high DQI-I score, are less likely to have multiple body composition abnormalities.

Nanoindentation time-dependent deformation/recovery suggestive of methylglyoxal induced glycation in calcified nodules

Although empirical findings have indicated increase in bone fracture risk in type 2 diabetes patients, that has yet to be proven by results obtained at the material level. Here, we report evidence showing nanoscale time-dependent deformation/recovery of in vitro calcified nodules mimicking bone turnover in type 2 diabetes in respect to methylglyoxal (MG)-induced glycation. Nanoindentation test results revealed that calcified nodules cultured with MG did not show adequate dimensional recovery, despite a large creep rate during constant load indentation testing. This lesser recovery is likely based on the linear matrix polymerization network formed by advanced glycation end products (AGEs) as a secondary product of MG. Since elevated serum MG and abnormal bone turnover related to the amount of AGEs are observed in cases of type 2 diabetes, this time-dependent behavior may be one of the factors of the bone fracture mechanism at the material level in affected patients.

Insulin use and Excess Fracture Risk in Patients with Type 2 Diabetes: A Propensity-Matched cohort analysis

Despite normal to high bone mineral density, patients with type 2 diabetes (T2DM) have an increased fracture risk. T2DM medications could partially account for this excess risk. The aim of this study was to assess the association between insulin use and bone fracture risk in T2DM patients. A population-based matched cohort study based on a primary care records database validated for research use (Catalonia, Spain) was performed. Propensity score (PS) for insulin use was calculated using logistic regression including predefined predictors of fractures. A total of 2,979 insulin users and 14,895 non-users were observed for a median of 1.42 and 4.58 years respectively. Major fracture rates were 11.2/1,000 person-years for insulin users, compared with 8.3/1,000 among non-users. Matched models confirmed a significant association, with an adjusted subhazard ratio (adj SHR) of 1.38 [95% CI 1.06 to 1.80] for major fractures. No differences between types of insulin or different regimens were found. Estimated number needed to harm (fracture) was 82 (95% CI 32 to 416). Insulin use appears to be associated with a 38% excess fracture risk among T2DM patients in the early stages of the disease. Fracture risk should be included among the considerations to initiate insulin treatment.

The Prevalence and Risk Factors of Osteoporosis among a Saudi Female Diabetic Population

AIM:

This study aimed to assess the prevalence and determinants of osteoporosis [lumbar spine (LS) and femoral neck (FN)] among patients with type 2 diabetes at King Salman Hospital.

MATERIALS AND METHODS:

One hundred seventy patients with type 2 diabetes were enrolled in this cross-sectional study in the period from the 1st of January until the 1st of July 2015. Patient selection was based on self-report of the previous diagnosis by a physician, being on an antidiabetic agent, or a fasting glucose of 126 mg/dl as per the American Diabetes Association criteria. A dual energy X-ray absorptiometry scan with the bone mineral density (BMD) categorization based on the WHO cut of levels of T-scores and determination of vitamin D levels were performed. A detailed questionnaire was used to collect demographic data.

RESULTS:

Out of 170 participants, 50 (29.4%) were diagnosed as having osteoporosis, while 68 (40%) were diagnosed with osteopenia. Age was determined as a risk factor for a decreased BMD in patients with osteopenia (odds ratio (OR) = 1.1, 95% confidence interval (CI) = (1.0-1.1), p = 0.039) and osteoporosis (OR = 1.1, CI = 1.0-1.2, p < 0.001). Similarly, oral hypoglycemic agents (OHA) increased the risk of decreased BMD in osteopenia (OR = 2.6; CI = 1.0-6.7; p = 0.023) as well as osteoporosis, (OR = 3.8; CI = 1.3-10.9; p = 0.013), while vitamin D deficiency increased the risk of osteopenia OR = 3.0; CI = 1.2-7.2; p = 0.012). Increased BMI decreased the risk of both osteopenia and osteoporosis (OR = 0.9; CI = 0.9-0.99; p = 0.031 vs. OR = 0.9; CI = 0.80-0.95; p = 0.003).

CONCLUSION:

Advanced age, OHA and vitamin D deficiency are determinants of decreased BMD in Saudi women with type 2 diabetes, while an increased BMI protects against low BMD.

Pathophysiology of Bone Fragility in Patients with Diabetes

It has been well established that bone fragility is one of the chronic complications of diabetes mellitus, and both type 1 and type 2 diabetes are risk factors for fragility fractures. Diabetes may negatively affect bone health by unbalancing several pathways: bone formation, bone resorption, collagen formation, inflammatory cytokine, muscular and incretin system, bone marrow adiposity and calcium metabolism. The purpose of this narrative review is to explore the current understanding of pathophysiological pathways underlying bone fragility in diabetics. In particular, the review will focus on the peculiar cellular and molecular system impairment that may lead to increased risk of fracture in type 1 and type 2 diabetes.

Zinc Up-Regulates Insulin Secretion from β Cell-Like Cells Derived from Stem Cells from Human Exfoliated Deciduous Tooth (SHED)

Stem cells from human exfoliated deciduous tooth (SHED) offer several advantages over other stem cell sources. Using SHED, we examined the roles of zinc and the zinc uptake transporter ZIP8 (Zrt- and irt-like protein 8) while inducing SHED into insulin secreting β cell-like stem cells (i.e., SHED-β cells). We observed that ZIP8 expression increased as SHED differentiated into SHED-β cells, and that zinc supplementation at day 10 increased the levels of most pancreatic β cell markers-particularly Insulin and glucose transporter 2 (GLUT2). We confirmed that SHED-β cells produce insulin successfully. In addition, we note that zinc supplementation significantly increases insulin secretion with a significant elevation of ZIP8 transporters in SHED-β cells. We conclude that SHED can be converted into insulin-secreting β cell-like cells as zinc concentration in the cytosol is elevated. Insulin production by SHED-β cells can be regulated via modulation of zinc concentration in the media as ZIP8 expression in the SHED-β cells increases.

Enzymatic and non-enzymatic functions of the lysyl oxidase family in bone

Advances in the understanding of the biological roles of the lysyl oxidase family of enzyme proteins in bone structure and function are reviewed. This family of proteins is well-known as catalyzing the final reaction required for cross-linking of collagens and elastin. Novel emerging roles for these proteins in the phenotypic development of progenitor cells and in angiogenesis are highlighted and which point to enzymatic and non-enzymatic roles for this family in bone development and homeostasis and in disease. The explosion of interest in the lysyl oxidase family in the cancer field highlights the need to have a better understanding of the functions of this protein family in normal and abnormal connective tissue homeostasis at fundamental molecular and cellular levels including in mineralized tissues.

Transient Intermittent Hypoxia Exposure Disrupts Neonatal Bone Strength

A brief intermittent hypoxia (IH, ambient O2 levels alternating between room air and 12% O2) for 1 h immediately after birth resulted in pancreatic islet dysfunction associated with zinc deficiency as previously reported. We hypothesized that IH exposure modulates zinc homeostasis in bone as well, which leads to increased bone fragility. To test this hypothesis, we used neonatal rats and human osteoblasts (HObs). To examine IH influences on osteoblasts devoid of neural influences, we quantified amounts of alkaline phosphatase and mineralization in IH-treated HObs. Bones harvested from IH-treated animals showed significantly reduced hardness and elasticity. The IH group also showed discretely decreased levels of alkaline phosphatase and mineralization amounts. The IH group showed a decreased expression of ZIP8 or Zrt and Irt-like protein 8 (a zinc uptake transporter), Runx2 (or Runt-related transcription factor 2, a master protein in bone formation), Collagen-1 (a major protein comprising the extracellular matrix of the bone), osteocalcin, and zinc content. When zinc was eliminated from the media containing HObs using a zinc chelate and added later with zinc sulfate, Runx2, ZIP8, and osteocalcin expression decreased first, and recovered with zinc supplementation. Adenovirus-mediated ZIP8 over-expression in osteoblasts increased mineralization significantly as well. We conclude that IH impairs zinc homeostasis in bones and osteoblasts, and that such disturbances decrease bone strength, which can be recovered by zinc supplementation.

Bone Marrow Adipose Tissue: To Be or Not To Be a Typical Adipose Tissue?

Bone marrow adipose tissue (BMAT) emerges as a distinct fat depot whose importance has been proved in the bone-fat interaction. Indeed, it is well recognized that adipokines and free fatty acids released by adipocytes can directly or indirectly interfere with cells of bone remodeling or hematopoiesis. In pathological states, such as osteoporosis, each of adipose tissues - subcutaneous white adipose tissue (WAT), visceral WAT, brown adipose tissue (BAT), and BMAT - is differently associated with bone mineral density (BMD) variations. However, compared with the other fat depots, BMAT displays striking features that makes it a substantial actor in bone alterations. BMAT quantity is well associated with BMD loss in aging, menopause, and other metabolic conditions, such as anorexia nervosa. Consequently, BMAT is sensed as a relevant marker of a compromised bone integrity. However, analyses of BMAT development in metabolic diseases (obesity and diabetes) are scarce and should be, thus, more systematically addressed to better apprehend the bone modifications in that pathophysiological contexts. Moreover, bone marrow (BM) adipogenesis occurs throughout the whole life at different rates. Following an ordered spatiotemporal expansion, BMAT has turned to be a heterogeneous fat depot whose adipocytes diverge in their phenotype and their response to stimuli according to their location in bone and BM. In vitro, in vivo, and clinical studies point to a detrimental role of BM adipocytes (BMAs) throughout the release of paracrine factors that modulate osteoblast and/or osteoclast formation and function. However, the anatomical dissemination and the difficulties to access BMAs still hamper our understanding of the relative contribution of BMAT secretions compared with those of peripheral adipose tissues. A further characterization of the phenotype and the functional regulation of BMAs are ever more required. Based on currently available data and comparison with other fat tissues, this review addresses the originality of the BMAT with regard to its development, anatomy, metabolic properties, and response to physiological cues.

Energy Metabolism in Mesenchymal Stem Cells During Osteogenic Differentiation

There is emerging interest in stem cell energy metabolism and its effect on differentiation. Bioenergetic changes in differentiating bone marrow mesenchymal stem cells (MSCs) are poorly understood and were the focus of our study. Using bioenergetic profiling and transcriptomics, we have established that MSCs activate the mitochondrial process of oxidative phosphorylation (OxPhos) during osteogenic differentiation, but they maintain levels of glycolysis similar to undifferentiated cells. Consistent with their glycolytic phenotype, undifferentiated MSCs have high levels of hypoxia-inducible factor 1 (HIF-1). Osteogenically induced MSCs downregulate HIF-1 and this downregulation is required for activation of OxPhos. In summary, our work provides important insights on MSC bioenergetics and proposes a HIF-based mechanism of regulation of mitochondrial OxPhos in MSCs.

Diabetes and bone: biological and environmental factors

PURPOSE OF REVIEW

Type 1 and type 2 diabetes mellitus are known to increase fracture risk. It is known that type 1 diabetes mellitus is associated with lower bone mineral density, but for type 2 diabetes mellitus, the real risk of increasing osteoporotic fractures is not explained by bone mineral density, which was found to be normal or paradoxically higher than controls in several studies, thus claiming for further investigations. This review summarizes some of the newest findings about factors that contribute to bone alterations in diabetic patients.

RECENT FINDINGS

Most recent evidences showed that bone of diabetic patients presents a cortical porosity which is not captured by the bidimensional densitometric measurements as performed by dual energy X-ray absorptiometry. Other studies investigated bone matrix searching for molecular mechanisms underlying the reduced bone strength in diabetic patients. The loss of bone biomechanical properties in diabetes has been associated to the glycated collagen matrix induced by hyperglycemia. Other studies analyzed the effect on bone microarchitecture of the most common antidiabetic drugs.

SUMMARY

Disease management of fracture risk in diabetic patients needs new methodologies of assessment that also take into account bone quality and evaluation of clinical risk factors, including balance, visual, and neurological impairments.

Diabetes mellitus affects the biomechanical function of the callus and the expression of TGF-beta1 and BMP2 in an early stage of fracture healing

Transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2) are important regulators of bone repair and regeneration. In this study, we examined whether TGF-β1 and BMP-2 expressions were delayed during bone healing in type 1 diabetes mellitus. Tibial fractures were created in 95 diabetic and 95 control adult male Wistar rats of 10 weeks of age. At 1, 2, 3, 4, and 5 weeks after fracture induction, five rats were sacrificed from each group. The expressions of TGF-β1 and BMP2 in the fractured tibias were measured by immunohistochemistry and quantitative reverse-transcription polymerase chain reaction, weekly for the first 5 weeks post-fracture. Mechanical parameters (bending rigidity, torsional rigidity, destruction torque) of the healing bones were also assessed at 3, 4, and 5 weeks post-fracture, after the rats were sacrificed. The bending rigidity, torsional rigidity and destruction torque of the two groups increased continuously during the healing process. The diabetes group had lower mean values for bending rigidity, torsional rigidity and destruction torque compared with the control group (P<0.05). TGF-β1 and BMP-2 expression were significantly lower (P<0.05) in the control group than in the diabetes group at postoperative weeks 1, 2, and 3. Peak levels of TGF-β1 and BMP-2 expression were delayed by 1 week in the diabetes group compared with the control group. Our results demonstrate that there was a delayed recovery in the biomechanical function of the fractured bones in diabetic rats. This delay may be associated with a delayed expression of the growth factors TGF-β1 and BMP-2.

Cannabidiol, a Major Non-Psychotropic Cannabis Constituent Enhances Fracture Healing and Stimulates Lysyl Hydroxylase Activity in Osteoblasts

Cannabinoid ligands regulate bone mass, but skeletal effects of cannabis (marijuana and hashish) have not been reported. Bone fractures are highly prevalent, involving prolonged immobilization and discomfort. Here we report that the major non-psychoactive cannabis constituent, cannabidiol (CBD), enhances the biomechanical properties of healing rat mid-femoral fractures. The maximal load and work-to-failure, but not the stiffness, of femurs from rats given a mixture of CBD and Δ(9) -tetrahydrocannabinol (THC) for 8 weeks were markedly increased by CBD. This effect is not shared by THC (the psychoactive component of cannabis), but THC potentiates the CBD stimulated work-to-failure at 6 weeks postfracture followed by attenuation of the CBD effect at 8 weeks. Using micro-computed tomography (μCT), the fracture callus size was transiently reduced by either CBD or THC 4 weeks after fracture but reached control level after 6 and 8 weeks. The callus material density was unaffected by CBD and/or THC. By contrast, CBD stimulated mRNA expression of Plod1 in primary osteoblast cultures, encoding an enzyme that catalyzes lysine hydroxylation, which is in turn involved in collagen crosslinking and stabilization. Using Fourier transform infrared (FTIR) spectroscopy we confirmed the increase in collagen crosslink ratio by CBD, which is likely to contribute to the improved biomechanical properties of the fracture callus. Taken together, these data show that CBD leads to improvement in fracture healing and demonstrate the critical mechanical role of collagen crosslinking enzymes.

A direct role of collagen glycation in bone fracture

Non-enzymatic glycation (NEG) is an age-related process accelerated by diseases like diabetes, and causes the accumulation of advanced glycation end-products (AGEs). NEG-mediated modification of bone's organic matrix, principally collagen type-I, has been implicated in impairing skeletal physiology and mechanics. Here, we present evidence, from in vitro and in vivo models, and establish a causal relationship between collagen glycation and alterations in bone fracture at multiple length scales. Through atomic force spectroscopy, we established that NEG impairs collagen's ability to dissipate energy. Mechanical testing of in vitro glycated human bone specimen revealed that AGE accumulation due to NEG dramatically reduces the capacity of organic and mineralized matrix to creep and caused bone to fracture under impact at low levels of strain (3000-5000 μstrain) typically associated with fall. Fracture mechanics tests of NEG modified human cortical bone of varying ages, and their age-matched controls revealed that NEG disrupted microcracking based toughening mechanisms and reduced bone propagation and initiation fracture toughness across all age groups. A comprehensive mechanistic model, based on experimental and modeling data, was developed to explain how NEG and AGEs are causal to, and predictive of bone fragility. Furthermore, fracture mechanics and indentation testing on diabetic mice bones revealed that diabetes mediated NEG severely disrupts bone matrix quality in vivo. Finally, we show that AGEs are predictive of bone quality in aging humans and have diagnostic applications in fracture risk.

Dietary protein derived from dried bonito fish improves type-2 diabetes mellitus-induced bone frailty in Goto-Kakizaki rats

Type-2 diabetes mellitus (T2DM) induces bone frailty. Protein and polyunsaturated fatty acids (PUFA) contained in fish can be effective in enhancing bone quality, but the bone developing effect of fish protein containing less PUFA has not been evaluated in young animals with T2DM. We prepared a bonito fish (BF) and defatted BF (DBF) and hypothesized that protein contained in BF and DBF would be effective for mitigating the effects of T2DM-induced bone frailty. We mainly evaluated the effect of dietary BF and DBF on bone and apparent calcium absorption in young Goto-Kakizaki (GK) rats with T2DM. GK rats were divided into 3 groups based on diets (casein, BF, and DBF) and fed with each diet for 6 wk. Wistar rats were fed with the casein diet as a non-T2DM control. Bone mass, bone strength, apparent calcium absorption, and serum biochemical parameters were determined. The dry weight and strength of the femurs were lower in the GK rats than in the Wistar rats fed with the casein diet. Dietary intake of the BF and DBF diets enhanced the maximum load and dry weight of the femurs and suppressed the serum alkaline phosphatase activity although the apparent calcium absorption was lower in the GK rats fed with the BF and DBF diets than in those fed with the casein diet. These parameters were not different between the rats fed with the BF and DBF diets. Our data suggest that protein contained in the BF and DBF diets improved T2DM-induced bone frailty.

Type 1 diabetes and osteoporosis: from molecular pathways to bone phenotype

The link between type 1 diabetes mellitus (DM1) and osteoporosis, identified decades ago, has gained attention in recent years. While a number of cellular mechanisms have been postulated to mediate this association, it is now established that defects in osteoblast differentiation and activity are the main culprits underlying bone fragility in DM1. Other contributing factors include an accumulation of advanced glycation end products (AGEs) and the development of diabetes complications (such as neuropathy and hypoglycemia), which cause further decline in bone mineral density (BMD), worsening geometric properties within bone, and increased fall risk. As a result, patients with DM1 have a 6.9-fold increased incidence of hip fracture compared to controls. Despite this increased fracture risk, bone fragility remains an underappreciated complication of DM1 and is not addressed in most diabetes guidelines. There is also a lack of data regarding the efficacy of therapeutic strategies to treat osteoporosis in this patient population. Together, our current understanding of bone fragility in DM1 calls for an update of diabetes guidelines, better screening tools, and further research into the use of therapeutic strategies in this patient population.

Insights into bone fragility in diabetes: the crucial role of bone quality on skeletal strength

Meta-analyses have revealed that the relative risk of hip fractures in patients with type 1 and type 2 diabetes mellitus is higher than that in non-diabetic subjects. The risk of fracture in patients with diabetes mellitus increases along with a decrease in bone mineral density (BMD) similarly to those in non-diabetic patients. However, the observed risk of fracture is higher than expected one by BMD in both type 1 and type 2 diabetic patients, indicating that precise estimation of bone fragility by BMD values in patients with diabetes is difficult. Bone strength consists of BMD and bone quality, for this reason, poor bone quality is a most suitable and explicable cause for elevated fracture risk in this population. This bone fragility observed in patients with diabetes mellitus is caused by unique pathogenesis in diabetes, suggesting that osteoporosis in diabetic patients may be one of the diabetic complications and that specific diagnostic criteria for this osteoporosis is required. Bone quality indicators closely related to bone fragility are required to be identified to establish a diagnostic method for osteoporosis in patients with diabetes mellitus.

Pediatric reference Raman data for material characteristics of iliac trabecular bone

Bone material characteristics are important contributors in the determination of bone strength. Raman spectroscopic analysis provides information on mineral/matrix ratio, mineral maturity/crystallinity, relative pyridinoline (Pyd) collagen cross-link content, relative proteoglycan content and relative lipid content. However, published reference data are available only for adults. The purpose of the present study was to establish reference data of Raman outcomes pertaining to bone quality in trabecular bone for children and young adults. To this end, tissue age defined Raman microspectroscopic analysis was performed on bone samples from 54 individuals between 1.5 and 23 years with no metabolic bone disease, which have been previously used to establish histomorphometric and bone mineralization density distribution reference values. Four distinct tissue ages, three well defined by the fluorescent double labels representing early stages of bone formation and tissue maturation (days 3, 12, 20 of tissue mineralization) and a fourth representing old mature tissue at the geometrical center of the trabeculae, were analyzed. In general, significant dependencies of the measured parameters on tissue age were found, while at any given tissue age, sex and subject age were not confounders. Specifically, mineral/matrix ratio, mineral maturity/crystallinity index and relative pyridinoline collagen cross-link content index increased by 485%, 20% and 14%, respectively between days 3 and 20. The relative proteoglycan content index was unchanged between days 3 and 20 but was elevated in the old tissue compared to young tissue by 121%. The relative lipid content decreased within days 3 to 20 by -22%. Thus, the method allows not only the monitoring of material characteristics at a specific tissue age but also the kinetics of tissue maturation as well. The established reference Raman database will serve as sensitive tool to diagnose disturbances in material characteristics of pediatric bone biopsy samples.

A novel function for lysyl oxidase in pluripotent mesenchymal cell proliferation and relevance to inflammation-associated osteopenia

Lysyl oxidase is a multifunctional enzyme required for collagen biosynthesis. Various growth factors regulate lysyl oxidase during osteoblast differentiation, subject to modulation by cytokines such as TNF-α in inflammatory osteopenic disorders including diabetic bone disease. Canonical Wnt signaling promotes osteoblast development. Here we investigated the effect of Wnt3a and TNF-α on lysyl oxidase expression in pluripotent C3H10T1/2 cells, bone marrow stromal cells, and committed osteoblasts. Lysyl oxidase was up-regulated by a transcriptional mechanism 3-fold in C3H10T1/2 cells, and 2.5-fold in bone marrow stromal cells. A putative functional TCF/LEF element was identified in the lysyl oxidase promoter. Interestingly, lysyl oxidase was not up-regulated in committed primary rat calvarial- or MC3T3-E1 osteoblasts. TNF-α down-regulated lysyl oxidase both in Wnt3a-treated and in non-treated C3H10T1/2 cells by a post-transcriptional mechanism mediated by miR203. Non-differentiated cells do not produce a collagen matrix; thus, a novel biological role for lysyl oxidase in pluripotent cells was investigated. Lysyl oxidase shRNAs effectively silenced lysyl oxidase expression, and suppressed the growth of C3H10T1/2 cells by 50%, and blocked osteoblast differentiation. We propose that interference with lysyl oxidase expression under excess inflammatory conditions such as those that occur in diabetes, osteoporosis, or rheumatoid arthritis can result in a diminished pool of pluripotent cells which ultimately contributes to osteopenia.

Biochemical markers of bone turnover in diabetes patients--a meta-analysis, and a methodological study on the effects of glucose on bone markers

This study examined whether markers of bone turnover differ between individuals with and without diabetes. Bone markers showed heterogeneity between studies and were discrepant for markers of bone creation and markers of bone degradation. Bone markers may be of lesser value in diabetes due to heterogeneity.

INTRODUCTION

The aim of this meta-analysis was to compare existing literature regarding changes in bone markers among diabetics compared to healthy controls. To exclude that blood glucose levels among diabetes patients could influence the assays used for determining bone turnover markers, a methodological study was performed.

METHODS

Medline at Pubmed Embase, Cinahl, Svemed+, Cochrane library, and Bibliotek.dk was searched in August 2012. The studies should examine biochemical bone turnover among diabetes patients in comparison to controls in an observational design. In the methodological study, fasting blood samples were drawn from two individuals. Glucose was added to the blood samples in different concentrations and OC, CTX, and procollagen type 1 amino terminal propeptide were measured after 0, 1, 2, and 3 h.

RESULTS

Twenty-two papers fulfilled the criteria for the meta-analysis. From the pooled data in the meta-analysis, the bone markers osteocalcin (OC) (-1.15 ng/ml [-1.78,-0.52]) and C-terminal cross-linked telopeptide (CTX) (-0.14 ng/ml [-0.22, -0.05]) were significantly lower among diabetes patients than non-diabetes patients, however other markers did not differ. All markers displayed very high heterogeneity by I2 statistics. In the methodological study, the addition of glucose did not significantly change the bone markers neither by level of glucose nor with increasing incubation time.

CONCLUSION

The dissociative pattern of biochemical bone markers of bone formation and bone resorption present in diabetes patients is thus not caused by glucose per se but may be modulated by unknown factors associated with diabetes mellitus.

Insights into reference point indentation involving human cortical bone: sensitivity to tissue anisotropy and mechanical behavior

Reference point indentation (RPI) is a microindentation technique involving 20 cycles of loading in "force-control" that can directly assess a patient׳s bone tissue properties. Even though preliminary clinical studies indicate a capability for fracture discrimination, little is known about what mechanical behavior the various RPI properties characterize and how these properties relate to traditional mechanical properties of bone. To address this, the present study investigated the sensitivity of RPI properties to anatomical location and tissue organization as well as examined to what extent RPI measurements explain the intrinsic mechanical properties of human cortical bone. Multiple indents with a target force of 10N were done in 2 orthogonal directions (longitudinal and transverse) per quadrant (anterior, medial, posterior, and lateral) of the femoral mid-shaft acquired from 26 donors (25-101 years old). Additional RPI measurements were acquired for 3 orthogonal directions (medial only). Independent of age, most RPI properties did not vary among these locations, but they did exhibit transverse isotropy such that resistance to indentation is greater in the longitudinal (axial) direction than in the transverse direction (radial or circumferential). Next, beam specimens (~2mm×5mm×40mm) were extracted from the medial cortex of femoral mid-shafts, acquired from 34 donors (21-99 years old). After monotonically loading the specimens in three-point bending to failure, RPI properties were acquired from an adjacent region outside the span. Indent direction was orthogonal to the bending axis. A significant inverse relationship was found between resistance to indentation and the apparent-level mechanical properties. Indentation distance increase (IDI) and a linear combination of IDI and the loading slope, averaged over cycles 3 through 20, provided the best explanation of the variance in ultimate stress (r(2)=0.25, p=0.003) and toughness (r(2)=0.35, p=0.004), respectively. With a transverse isotropic behavior akin to tissue hardness and modulus as determined by micro- and nano-indentation and a significant association with toughness, RPI properties are likely influenced by both elastic and plastic behavior of bone tissue.