Distribution of collagen cross-links in normal human trabecular bone

Tumor removal limits prostate cancer cell dissemination in bone and osteoblasts induce cancer cell dormancy through focal adhesion kinase

BACKGROUND

Disseminated tumor cells (DTCs) can enter a dormant state and cause no symptoms in cancer patients. On the other hand, the dormant DTCs can reactivate and cause metastases progression and lethal relapses. In prostate cancer (PCa), relapse can happen after curative treatments such as primary tumor removal. The impact of surgical removal on PCa dissemination and dormancy remains elusive. Furthermore, as dormant DTCs are asymptomatic, dormancy-induction can be an operational cure for preventing metastases and relapse of PCa patients.

METHODS

We used a PCa subcutaneous xenograft model and species-specific PCR to survey the DTCs in various organs at different time points of tumor growth and in response to tumor removal. We developed in vitro 2D and 3D co-culture models to recapitulate the dormant DTCs in the bone microenvironment. Proliferation assays, fluorescent cell cycle reporter, qRT-PCR, and Western Blot were used to characterize the dormancy phenotype. We performed RNA sequencing to determine the dormancy signature of PCa. A drug repurposing algorithm was applied to predict dormancy-inducing drugs and a top candidate was validated for the efficacy and the mechanism of dormancy induction.

RESULTS

We found DTCs in almost all mouse organs examined, including bones, at week 2 post-tumor cell injections. Surgical removal of the primary tumor reduced the overall DTC abundance, but the DTCs were enriched only in the bones. We found that osteoblasts, but not other cells of the bones, induced PCa cell dormancy. RNA-Seq revealed the suppression of mitochondrial-related biological processes in osteoblast-induced dormant PCa cells. Importantly, the mitochondrial-related biological processes were found up-regulated in both circulating tumor cells and bone metastases from PCa patients' data. We predicted and validated the dormancy-mimicking effect of PF-562,271 (PF-271), an inhibitor of focal adhesion kinase (FAK) in vitro. Decreased FAK phosphorylation and increased nuclear translocation were found in both co-cultured and PF-271-treated C4-2B cells, suggesting that FAK plays a key role in osteoblast-induced PCa dormancy.

CONCLUSIONS

Our study provides the first insights into how primary tumor removal enriches PCa cell dissemination in the bones, defines a unique osteoblast-induced PCa dormancy signature, and identifies FAK as a PCa cell dormancy gatekeeper.

Cooperative Calcium Phosphate Deposition on Collagen-Inspired Short Peptide Nanofibers for Application in Bone Tissue Engineering

In recent years, immense attention has been devoted over the production of osteoinductive materials. To this direction, collagen has a dominant role in developing hard tissues and plays a crucial role in the biomineralization of these tissues. Here, we demonstrated for the first time the potential of the shortest molecular pentapeptide domain inspired from collagen toward mineralizing hydroxyapatite on peptide fibers to develop bone-filling material. Our simplistic approach adapted the easy and facile route of introducing the metal ions onto the peptide nanofibers, displaying adsorbed glutamate onto the surface. This negatively charged surface further induces the nucleation of the crystalline growth of hydroxyapatite. Interestingly, nucleation and growth of the hydroxyapatite crystals lead to the formation of a self-supporting hydrogel to construct a suitable interface for cellular interactions. Furthermore, microscopic and spectroscopic investigations revealed the crystalline growth of the hydroxyapatite onto peptide fibers. The physical properties were also influenced by this crystalline deposition, as evident from the hierarchical organization leading to hydrogels with enhanced mechanical stiffness and improved thermal stability of the scaffold. Furthermore, the mineralized peptide fibers were highly compatible with osteoblast cells and showed increased cellular biomarkers production, which further reinforced the potential application toward effectively fabricating the grafts for bone tissue engineering.

Fracture in Patients with Normal Bone Mineral Density: An Evaluation of the American Orthopaedic Association's Own the Bone Registry

BACKGROUND

Fractures often occur in patients with normal dual x-ray absorptiometry (DXA)-measured bone mineral density (BMD). DXA does not consider clinical fracture risk factors or bone quality. We hypothesized that patients with normal BMD who sustain a fracture have other characteristics suggesting abnormal bone and an elevated fracture risk requiring additional bone health evaluation and potential anti-osteoporotic treatment.

METHODS

A total of 7,219 patients who were ≥50 years of age, had sustained a fracture from July 2016 to July 2021, and had DXA data in the American Orthopaedic Association's Own the Bone (AOA OTB) registry were included in this study. The index and prior fracture site data were obtained. BMD status was classified by the World Health Organization T-score criteria. The Fracture Risk Assessment Tool (FRAX) scores with and without BMD were calculated in patients with normal BMD. An elevated risk was defined as a major osteoporotic fracture risk of ≥20% or a hip fracture risk of ≥3%.

RESULTS

The mean patient age (and standard deviation) was 70.8 ± 9.71 years, 84% of patients were female, and 92% of patients were Caucasian. Normal BMD was present in 8.6% of patients. The index fracture was a major osteoporotic fracture in 68.6% of patients with normal BMD and 75.6% of patients with osteoporosis. The most common site for index and prior fractures other than major osteoporotic fractures was the foot and ankle; of patients with normal BMD, 13.9% had this as the most common index site and 17.4% had this as the most common prior site. The FRAX risk calculated without BMD was elevated in 72.9% of patients with normal BMD, and the FRAX risk calculated with BMD was elevated in 12.0% of patients.

CONCLUSIONS

Most patients with a fracture and normal BMD met indications, including a prior fracture or elevated FRAX risk, for anti-osteoporotic therapies. Most patients were Caucasian and therefore potentially had a higher baseline fracture risk. The FRAX risk calculated without BMD was elevated more often than the FRAX risk with BMD, implying that clinical risk factors, which highlight multiple opportunities for non-pharmacologic secondary fracture prevention, should be considered along with DXA. Fractures other than major osteoporotic fractures were more common in patients with normal BMD, suggesting that minor fractures in adults who are ≥50 years of age should be considered sentinel events warranting further evaluation. Surgeons must recognize that other important risk factors apart from BMD may help to guide further bone health evaluation.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Clinical risk factor status in patients with vertebral fracture but normal bone mineral density

BACKGROUND CONTEXT

Normal bone mineral density (BMD) as measured by dual-energy x-ray absorptiometry (DXA) is present in approximately 10% of older adults with fracture. BMD alone does not evaluate bone quality or clinical risk factors, and therefore, may not adequately capture a patient's fracture risk. Thus, despite a normal DXA-measured BMD, the underlying bone may be abnormal, suggesting that further bone health evaluation, and potentially, pharmacologic treatment may be warranted.

PURPOSE

To determine the prevalence of normal BMD, clinical fracture risk factors, and quantitative risk of fracture using the Fracture Risk Assessment Tool (FRAX) in vertebral fracture patients with normal BMD enrolled in the Own the Bone registry, thus facilitating identification of those who meet criteria for anti-osteoporosis therapy.

STUDY DESIGN/SETTING

Retrospective, national registry-based cohort.

PATIENT SAMPLE

From July 2016 to July 2021, 1,807 patients age ≥50 who sustained a vertebral fracture and had DXA data available from within 2 years prior to enrollment in the American Orthopaedic Association's Own the Bone (AOA OTB) registry were included.

OUTCOME MEASURES

World Health Organization (WHO) DXA T-score based bone classification criteria; FRAX risk scores of major osteoporotic fracture or hip fracture.

METHODS

Demographic data, prior fracture site, and clinical fracture risk factors were collected. BMD status was classified by the WHO T-score criteria: ≥ -1.0 normal, -1.1 to -2.4 osteopenia, and ≤ -2.5 osteoporosis, with low bone mass including either osteopenia or osteoporosis. In normal BMD patients, FRAX scores were calculated with and without BMD, with the treatment threshold defined as a major osteoporotic fracture risk ≥20% or hip fracture risk ≥3%.

RESULTS

Mean±SD age was 72.0±9.7, 78.1% were female, and 92.4% were Caucasian. Normal BMD was present in 7.9%. Clinical fracture risk factors including alcohol use ≥3 units/day and history of ≥2 falls in the year prior to enrollment were more common in normal BMD (11.2% and 28%, respectively) compared to low bone mass patients (3.4% and 25.2%, respectively). A prior vertebral fracture had occurred in 49.5% with normal BMD compared to 45.8% with low bone mass, while a prior non-major osteoporotic fracture occurred in 28.9% and 29.3% of normal BMD and low bone mass patients, respectively. In normal BMD patients, either a prior fracture or FRAX risk with BMD meeting treatment thresholds was present in 85%.

CONCLUSIONS

Clear indications for receipt of pharmacologic therapy, ie, prior fracture or elevated fracture risk, were present in most patients with vertebral fracture and normal BMD enrolled in the AOA OTB. Prior non-major osteoporotic fractures were common and may be useful indicators of underlying bone disease. Surgeons must recognize that other important risk factors apart from BMD may indicate poor bone health, and thus, help guide further bone health evaluation.

Controlled mechanical early loads improve bone quality and quantity around implants: An in vivo experimental study

OBJECTIVES

This study aimed to investigate the effects of early loads on bone quality and quantity around implants and to compare the effects of early loads on bone quality and quantity with the effects of conventional loads.

MATERIALS AND METHODS

Grade IV-titanium implants with buttress threads were placed in rat maxillary bone 4 weeks after extraction of first molars. A controlled mechanical load (10 N, 3 Hz, 1,800 cycles, 2 days/week) was started via the implants 1 and 3 weeks after implant placement for 2 weeks (early and conventional loads, respectively). Bone quality, defined as distribution of bone cells, types and orientation of collagen fibers, and production of semaphorin3A, its receptor neuropilin-1, and sclerostin, were quantitatively evaluated.

RESULTS

Early loads substantially and positively affected bone quality by changing the preferential alignment of collagen fibers with increased production of type I and III collagens, semaphorin3A, and neuropilin-1, increased osteoblast numbers, decreased production of sclerostin, and decreased osteoclast numbers both inside and outside the implant threads, when compared with non-loaded conditions. Conventional loads changed bone quality around implants slightly. Interestingly, early loads had significantly stronger effects on bone quality and quantity based on the evaluation parameters than conventional loads.

CONCLUSIONS

This is the first report to provide scientific evidence for load initiation time based on both bone quality and quantity around implants. These new findings show that implants with buttress threads transmitted early loads optimally to bone tissue by improving bone quality and quantity inside and outside the implant threads.

Phosphorylated Serine-Modified Polyamidoamine Dendrimer as an Osteoid Surface-Targeting Drug Carrier

The aim of this study was to develop a polyethylene glycol (PEG)-conjugated third-generation polyamidoamine dendrimer (PAMAM) with phosphorylated serine as an osteoid surface-targeting drug carrier for the treatment of bone diseases. We conjugated PAMAM backbones to l-serine and obtained Ser-PAMAM. Then, phosphoric acid and PEG were covalently bound to the Ser-PAMAM to generate PEGylated phosphorylated Ser-PAMAM (PEG-phosSer-PAMAM). Using osteoblast-like cells (MC3T3-E1 cells) cultured in 3D collagen gels, we showed that phosSer-PAMAM adsorbed both the hydroxyapatite and type I collagen components of the bone matrix. Fourier transform infrared spectroscopy analysis indicated that the phosphoryl side chains of phosSer-PAMAM formed electrostatic interactions and hydrogen bonds with the anionic amino acid residues of type I collagen. Mice were intravenously injected with the foregoing molecules, and a tissue distribution study disclosed that the lower limb bone took up about twice as much ¹¹¹In-labeled PEG-phosSer-PAMAM as ¹¹¹In-labeled nonphosphorylated PEG-Ser-PAMAM or unmodified PAMAM. An intrabone distribution experiment showed that fluorescein isothiocyanate (FITC)-labeled PEG-phosSer-PAMAM accumulated on the osteoid surfaces, which is associated with bone pathogenesis such as skeletal dysplasias and osteoporosis to a far greater extent than nonphosphorylated PEG-Ser-PAMAM. Our findings indicated that PEG-phosSer-PAMAM is a promising carrier for efficient drug targeting to osteoid surfaces.

Selenium nanoparticles stimulate osteoblast differentiation via BMP-2/MAPKs/β-catenin pathway in diabetic osteoporosis

Aim: To evaluate whether selenium nanoparticles (SeNPs) can stimulate bone formation and inhibit the bone loss involved in hyperglycemia-induced osteoporosis. Methods: Rat osteoblastic UMR-106 cells were used for in vitro studies and female Sprague–Dawley rats were used for type 2 diabetes-associated osteoporosis in vivo study. Results: In vitro studies show that SeNPs promote osteoblast differentiation via modulating alkaline phosphatase (ALP) activity, and promoting calcium nodule formation and collagen content. The authors also provide evidence regarding the involvement of the BMP-2/MAPKs/β-catenin pathway in preventing diabetic osteoporosis. Further, in vivo and ex vivo studies suggested that SeNPs can preserve mechanical and microstructural properties of bone. Conclusion: To the best of our knowledge, this study provides the first evidence regarding the therapeutic benefits of SeNPs in preventing diabetes-associated bone fragility.

Regenerative Medicine Technologies to Treat Dental, Oral, and Craniofacial Defects

Additive manufacturing (AM) is the automated production of three-dimensional (3D) structures through successive layer-by-layer deposition of materials directed by computer-aided-design (CAD) software. While current clinical procedures that aim to reconstruct hard and soft tissue defects resulting from periodontal disease, congenital or acquired pathology, and maxillofacial trauma often utilize mass-produced biomaterials created for a variety of surgical indications, AM represents a paradigm shift in manufacturing at the individual patient level. Computer-aided systems employ algorithms to design customized, image-based scaffolds with high external shape complexity and spatial patterning of internal architecture guided by topology optimization. 3D bioprinting and surface modification techniques further enhance scaffold functionalization and osteogenic potential through the incorporation of viable cells, bioactive molecules, biomimetic materials and vectors for transgene expression within the layered architecture. These computational design features enable fabrication of tissue engineering constructs with highly tailored mechanical, structural, and biochemical properties for bone. This review examines key properties of scaffold design, bioresorbable bone scaffolds produced by AM processes, and clinical applications of these regenerative technologies. AM is transforming the field of personalized dental medicine and has great potential to improve regenerative outcomes in patient care.

Impact microindentation measurements correlate with cortical bone material properties measured by Fourier transform infrared imaging in humans

Bone Material Strength index (BMSi) measured by Impact Microindentation is generally lower in subjects with fragility fractures independently of BMD values. We recently reported that in humans, BMSi values are strongly associated with material properties of subperiosteal mineralized bone surface (local mineral content, nanoporosity, pyridinoline content). In the present study we investigated the relationship of BMSi with material properties of the whole bone cortex, by analyzing thin sections of iliac crest biopsies (N = 12) from patients with different skeletal disorders and a wide range of BMD with or without fractures, by Fourier transform infrared imaging (FTIRI). The calculated parameters were: i) mineral and organic matrix content and their ratio (MM), ii) mineral maturity/crystallinity (MMC) and iii) the ratio of pyridinoline (Pyd) and divalent collagen cross-links (XLR). Results were expressed as images, which were converted to histogram distributions. For each histogram the characteristics recorded were: mean value, mode (most often occurring value), skewness, and kurtosis and their association with BMSi values was examined by correlation analysis. BMSi values were significantly correlated only with MM mean and mode values (r = 0.736, p = 0.0063, and r = 0.855, p = 0.0004, respectively), and with XLR mode values (r = -0.632, p = 0.0274). The results of the present study demonstrate that BMSi values are strongly associated with MM, a metric that corrects the mineral content for the organic matrix content, and may also depend on organic matrix quality. These and our previous observations strongly suggest that BMSi assesses material properties of cortical bone.

LOX gene polymorphisms are associated with osteoporotic vertebral compression fracture in postmenopausal Chinese women

INTRODUCTION

Collagen cross-linking, which is regulated by lysyl oxidase (LOX), plays critical roles in bone mechanical strength. LOX can influence bone remodeling by modulating osteoblast and osteoclast activity. This study aimed to explore the effect of LOX gene polymorphisms on osteoporotic fractures susceptibility in postmenopausal Chinese women.

METHODS

This was a prospective study of postmenopausal women who visited the outpatient and community clinics of the local Hospital. Five tagging single nucleotide polymorphisms (SNPs) in the LOX gene were determined. Bone mineral density (BMD) was measured at the lumbar spine, femoral neck, and hip using dual-energy X-ray absorptiometry. Fractures were confirmed by X-ray and divided into: vertebral compression fracture (OVCF) and non-OVCF (all other fractures).

RESULTS

This study included 602 patients with non-traumatic fractures and 1343 healthy volunteers. The rs1800449 was significantly associated with vertebral compression fracture (OVCF) after adjusting for age and BMI (P = 0.012). Compared with subjects with the GG genotype, the risk of having OVCF was 1.28 and 1.74, respectively for subjects with the GA and AA genotypes (P = 0.043 and P = 0.018). A recessive genetic model showed that carriers of the AA genotype had higher fracture risk compared to G carriers (GA and GG genotypes) (P = 0.015). The rs2288393 SNP exhibited marginally significant association with OVCF (P = 0.051). Haplotype analyses corroborated our single SNP results: both haplotype CGA and CCG contained rs10519694, rs2288393, and rs1800449, and were significant associated with OVCF (P = 0.048 and P = 0.032, respectively). On the other hand, we found no evidence of an association of LOX gene allelic variants with either BMD or non-OVCF (all P > 0.05).

CONCLUSION

The results suggest that genetic polymorphisms in LOX may contribute to susceptibility to OVCF in Chinese postmenopausal women.

Skin Ultrasound Measurement as a Potential Marker of Bone Quality: A Prospective Pilot Study of Patients undergoing Lumbar Spinal Fusion

Bone mineral density (BMD) is not the sole predictor of fracture development. Qualitative markers including bone collagen maturity contribute to bone fragility. Bone and related type I collagen containing connective tissues degenerate in parallel fashion. With aging, changes in skin collagen content and quality have been observed that can be detected on ultrasound (US) as a decrease in dermal thickness and an increase in reticular layer echogenicity. We hypothesized that US dermal thickness and echogenicity correlate with bone collagen maturity. Data of 43 prospectively enrolled patients (mean age 61 years, 24 females), who underwent instrumented, posterior lumbar fusion was analyzed. Besides preoperative quantitative computed tomography (QCT) and skin US measurements, intraoperative bone biopsies were obtained and analyzed with Fourier-transform infrared spectroscopy. Among men, there was no correlation between US measurements and collagen maturity. Among women, dermal layer thickness correlated negatively with collagen maturity in trabecular bone of the iliac crest (r = -0.51, p = 0.01) and vertebra (r = -0.59, p = 0.01) as well as in cortical bone of the iliac crest (r = -0.50, p = 0.02) and vertebra (r = -0.50, p = 0.04). In addition, echogenicity correlated positively with collagen maturity in trabecular vertebral bone (r = 0.59, p = 0.01). In both genders, US measurements showed no correlation with QCT BMD. In summary, ultrasound skin parameters are associated with bone quality factors such as collagen maturity, rather than bone quantity (BMD). Ultrasound of the skin may thereby be an easy and accessible take off point for diagnosis of bone collagen maturity and connective tissue degeneration in the future. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2508-2515, 2019.

Biomechanical and Bone Material Properties of Schnurri-3 Null Mice

Schnurri‐3 (Shn3) is an essential regulator of postnatal skeletal remodeling. Shn3‐deficient mice (Shn3–/–) have high bone mass; however, their bone mechanical and material properties have not been investigated to date. We performed three‐point bending of femora, compression tests of L3 vertebrae. We also measured intrinsic material properties, including bone mineralization density distribution (BMDD) and osteocyte lacunae section (OLS) characteristics by quantitative backscatter electron imaging, as well as collagen cross‐linking by Fourier transform infrared microspectroscopy of femora from Shn3–/– and WT mice at different ages (6 weeks, 4 months, and 18 months). Moreover, computer modeling was performed for the interpretation of the BMDD outcomes. Femora and L3 vertebrae from Shn3–/– aged 6 weeks revealed increased ultimate force (2.2‐ and 3.2‐fold, p < .01, respectively). Mineralized bone volume at the distal femoral metaphysis was about twofold (at 6 weeks) to eightfold (at 4 and 18 months of age) in Shn3–/– (p < .001). Compared with WT, the average degree of trabecular bone mineralization was similar at 6 weeks, but increased at 4 and 18 months of age (+12.6% and +7.7%, p < .01, respectively) in Shn3–/–. The analysis of OLS characteristics revealed a higher OLS area for Shn3–/– versus WT at all ages (+16%, +23%, +21%, respectively, p < .01). The collagen cross‐link ratio was similar between groups. We conclude that femora and vertebrae from Shn3–/– had higher ultimate force in mechanical testing. Computer modeling demonstrated that in cases of highly increased bone volume, the average degree of bone matrix mineralization can be higher than in WT bone, which was actually measured in the older Shn3–/– groups. The area of 2D osteocyte lacunae sections was also increased in Shn3‐deficiency, which could only partly be explained by larger remnant areas of primary cortical bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Fourier Transform Infrared Imaging of Bone

Fourier transform infrared imaging (FTIRI) is a technique that can be used to analyze the material properties of bone using tissue sections. This chapter describes the basic principles of FTIR and the methods for capturing and analyzing FTIR images in bone sections.

Irradiation-Induced Compositional Effects on Human Bone After Extracorporeal Therapy for Bone Sarcoma

The present study investigates Raman scattering of human bone irradiated with 50 Gy single dose during therapeutic treatment of Ewing and Osteosarcoma. Bone quality was evaluated via mineral-to-matrix ratio, degree of crystallinity, change in amount of calcium, and carbonate substitution. Alteration in collagen and its cross-links was quantified through second-derivative deconvolution of Amide I peak. A dose of 50 Gy radiation leads to almost 50% loss of mineral content, while maintaining mineral crystallinity, and small changes in carbonate substitution. Deconvolution of Amide I suggested modifications in collagen structure via increase in amount of enzymatic trivalent cross-linking (p < 0.05). Overall irradiation led to detrimental effect on bone quality via changes in its composition, consequently reducing its elastic modulus with increased plasticity. The study thus quantifies effect of single-dose 50 Gy radiation on human bone, which in turn is necessary for designing improved radiation dosage during ECRT and for better understanding post-operative care.

Identification of Pyridinoline Trivalent Collagen Cross-Links by Raman Microspectroscopy

Intermolecular cross-linking of bone collagen is intimately related to the way collagen molecules are arranged in a fibril, imparts certain mechanical properties to the fibril, and may be involved in the initiation of mineralization. Raman microspectroscopy allows the analysis of minimally processed bone blocks and provides simultaneous information on both the mineral and organic matrix (mainly type I collagen) components, with a spatial resolution of ~1 μm. The aim of the present study was to validate Raman spectroscopic parameters describing one of the major mineralizing type I trivalent cross-links, namely pyridinoline (PYD). To achieve this, a series of collagen cross-linked peptides with known PYD content (as determined by HPLC analysis), human bone, porcine skin, predentin and dentin animal model tissues were analyzed by Raman microspectroscopy. The results of the present study confirm that it is feasible to monitor PYD trivalent collagen cross-links by Raman spectroscopic analysis in mineralized tissues, exclusively through a Raman band ~1660 wavenumbers. This allows determination of the relative PYD content in undecalcified bone tissues with a spatial resolution of ~1 μm, thus enabling correlations with histologic and histomorphometric parameters.

Effects of losartan treatment on the physicochemical properties of diabetic rat bone

Inhibitors of the renin-angiotensin system used to treat several diseases have also been shown to be effective on bone tissue, suggesting that angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may reduce fracture risk. The present study investigated the effects of losartan on the physicochemical and biomechanical properties of diabetic rat bone. Losartan (5 mg/kg/day) was administered via oral gavage for 12 weeks. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry. Whole femurs were tested under tension to evaluate the biomechanical properties of bone. The physicochemical properties of bone were analyzed by Fourier transform infrared spectroscopy. Although losartan did not recover decreases in the BMD of diabetic bone, it recovered the physicochemical (mineral and collagen matrix) properties of diabetic rat bone. Furthermore, losartan also recovered ultimate tensile strength of diabetic rat femurs. Losartan, an angiotensin II type 1 receptor blocker, has a therapeutic effect on the physicochemical properties of diabetic bone resulting in improvement of bone strength at the material level. Therefore, specific inhibition of this pathway at the receptor level shows potential as a therapeutic target for diabetic patients suffering from bone diseases such as osteopenia.

Novel anatomic adaptation of cortical bone to meet increased mineral demands of reproduction

The goal of this study was to investigate the effects of reproductive adaptations to mineral homeostasis on the skeleton in a mouse model of compromised mineral homeostasis compared to adaptations in control, unaffected mice. During pregnancy, maternal adaptations to high mineral demand include more than doubling intestinal calcium absorption by increasing calcitriol production. However, calcitriol biosynthesis is impaired in HYP mice, a murine model of X-linked hypophosphatemia (XLH). In addition, there is a paucity of mineralized trabecular bone, a primary target of bone resorption during pregnancy and lactation. Because the highest density of mineral is in mature cortical bone, we hypothesized that mineral demand is met by utilizing intracortical mineral reserves. Indeed, analysis of HYP mice revealed dramatic increases in intracortical porosity characterized by elevated serum PTH and type-I collagen matrix-degrading enzyme MMP-13. We discovered an increase in carbonate ion substitution in the bone mineral matrix during pregnancy and lactation of HYP mice, suggesting an alternative mechanism of bone remodeling that maintains maternal bone mass during periods of high mineral demand. This phenomenon is not restricted to XLH, as increased carbonate in the mineral matrix also occurred in wild-type mice during lactation. Taken together, these data suggest that increased intracortical perilacunar mineral turnover also contributes to maintaining phosphate levels during periods of high mineral demand. Understanding the mechanisms of skeletal contribution to mineral homeostasis is important to improving the treatment and prevention of fracture risk and bone fragility for female patients with XLH, but also provides important insight into the role and unique adaptations of the maternal skeleton to the demands of fetal development and the needs of postnatal nutrition.

Combined treatment with minodronate and vitamin C increases bone mineral density and strength in vitamin C-deficient rats

Objectives

Reduced bone quality caused by vitamin C deficiency in older persons may lead to incidental fragility fractures during bisphosphonate treatment, although bisphosphonate increases bone mineral density (BMD). This study aimed to evaluate the effects of minodronate and ascorbic acid (Aa) on BMD, bone quality, and bone strength in Aa-deficient osteogenic disorder Shionogi (ODS) rats.

Methods

Six-month-old ODS rats were divided into four groups (n = 20 per group): (1) Aa supplementation (Aa⁺); (2) Aa-deficient (Aa⁻); (3) Aa supplementation and minodronate administration (Aa⁺ + Mino); and (4) Aa-deficient and minodronate administration (Aa⁻ + Mino). BMD, bone strength, bone histomorphometry, and bone quality determined using Fourier transform infrared spectroscopy imaging (FTIRI) were evaluated after 4 and 8 weeks.

Results

BMD was significantly higher in the Aa⁺ + Mino group than in the Aa⁻ group (p < 0.05). Bone strength was significantly higher in the Aa⁺ and Aa⁺ + Mino groups than in the Aa⁻ group (p < 0.05). Furthermore, bone strength was significantly higher in the Aa⁺ + Mino group than in the Aa⁻ + Mino group (p < 0.05). Minodronate treatment irrespective of Aa supplementation significantly decreased bone resorption compared with the Aa⁺ and Aa⁻ groups (p < 0.05). No significant differences in the parameters evaluated by FTIRI were observed between the groups.

Conclusions

Aa supplementation improved bone strength in ODS rats. Combined treatment with minodronate and Aa, but not minodronate alone, improved bone strength and increased BMD. Aa is required for bone health because it is essential for osteoblast differentiation.

Aging Versus Postmenopausal Osteoporosis: Bone Composition and Maturation Kinetics at Actively-Forming Trabecular Surfaces of Female Subjects Aged 1 to 84 Years

Bone strength depends on the amount of bone, typically expressed as bone mineral density (BMD), determined by dual-energy X-ray absorptiometry (DXA), and on bone quality. Bone quality is a multifactorial entity including bone structural and material compositional properties. The purpose of the present study was to examine whether bone material composition properties at actively-forming trabecular bone surfaces in health are dependent on subject age, and to contrast them with postmenopausal osteoporosis patients. To achieve this, we analyzed by Raman microspectroscopy iliac crest biopsy samples from healthy subjects aged 1.5 to 45.7 years, paired biopsy samples from females before and immediately after menopause aged 46.7 to 53.6 years, and biopsy samples from placebo-treated postmenopausal osteoporotic patients aged 66 to 84 years. The monitored parameters were as follows: the mineral/matrix ratio; the mineral maturity/crystallinity (MMC); nanoporosity; the glycosaminoglycan (GAG) content; the lipid content; and the pyridinoline (Pyd) content. The results indicate that these bone quality parameters in healthy, actively-forming trabecular bone surfaces are dependent on subject age at constant tissue age, suggesting that with advancing age the kinetics of maturation (either accumulation, or posttranslational modifications, or both) change. For most parameters, the extrapolation of models fitted to the individual age dependence of bone in healthy individuals was in rough agreement with their values in postmenopausal osteoporotic patients, except for MMC, lipid, and Pyd content. Among these three, Pyd content showed the greatest deviation between healthy aging and disease, highlighting its potential to be used as a discriminating factor.

Altered material properties are responsible for bone fragility in rats with chronic kidney injury

Chronic kidney disease (CKD) is associated with an increased risk of fragility fractures, but the underlying pathophysiological mechanism remains obscure. We performed an in vivo experimental study to examine the roles of uremia and abnormal mineral/parathyroid metabolism in the development of bone metabolic abnormalities in uremic rats. Male Sprague-Dawley rats were divided into four groups, comprising sham operation (high turnover bone control=HTB-Cont), 5/6-nephrectomy (high turnover bone nephrectomized=HTB-Nx), thyroparathyroidectomy (low turnover bone control=LTB-Cont), and thyroparathyroidectomy plus 5/6 nephrectomy (low turnover bone nephrectomized=LTB-Nx), and maintained for 16 weeks. Uremia was successfully created in the LTB-Nx and HTB-Nx groups, while hyperparathyroidism was only found in the HTB-Nx group. Cancellous bone histomorphometry revealed significantly higher bone turnover in the HTB-Nx group than in the LTB-Nx group. Storage modulus at 1 Hz and tan delta in cortical bone of the femur, which represent the viscoelastic mechanical properties, were significantly lower in both Nx groups than in the Cont groups regardless of bone metabolism. Pentosidine-to-matrix ratio was increased and crystallinity was decreased in both Nx groups regardless of bone turnover. Mineral-to-matrix ratio was significantly decreased in the HTB-Nx group, but increased in the LTB-Nx group. Enzymatic collagen crosslinks were decreased in the HTB-Nx group. The degree of orientation of the c-axis in carbonated hydroxyapatite (biological apatite=BAp) crystallites was decreased in both Nx groups regardless of bone metabolism. Stepwise multivariate regression revealed that pentosodine-to-matrix ratio and BAp preferential c-axis orientation were significantly associated with storage modulus and tan delta. In conclusion, bone elastic mechanical properties deteriorated regardless of bone metabolism or bone mass in rats with chronic kidney injury. Various changes in bone mineral properties were associated with CKD, including abnormal parathyroid function, impaired bone turnover, and uremia associated with the accumulation of uremic toxins, were responsible for these changes. Pentosidine-to-matrix ratio and BAp orientation at position 5 were the two meaningful determinants of elastic bone mechanical strength, and both factors were associated with the severity of uremia, but not parathyroid function or bone metabolism. These two factors may account for the increased bone fragility among CKD patients.

Prediction of local ultimate strain and toughness of trabecular bone tissue by Raman material composition analysis

Clinical studies indicate that bone mineral density correlates with fracture risk at the population level but does not correlate with individual fracture risk well. Current research aims to better understand the failure mechanism of bone and to identify key determinants of bone quality, thus improving fracture risk prediction. To get a better understanding of bone strength, it is important to analyze tissue-level properties not influenced by macro- or microarchitectural factors. The aim of this pilot study was to identify whether and to what extent material properties are correlated with mechanical properties at the tissue level. The influence of macro- or microarchitectural factors was excluded by testing individual trabeculae. Previously reported data of mechanical parameters measured in single trabeculae under tension and bending and its compositional properties measured by Raman spectroscopy was evaluated. Linear and multivariate regressions show that bone matrix quality but not quantity was significantly and independently correlated with the tissue-level ultimate strain and postyield work (r = 0.65–0.94). Principal component analysis extracted three independent components explaining 86% of the total variance, representing elastic, yield, and ultimate components according to the included mechanical parameters. Some matrix parameters were both included in the ultimate component, indicating that the variation in ultimate strain and postyield work could be largely explained by Raman-derived compositional parameters.

Fourier transform Infrared spectroscopic characterization of mineralizing type I collagen enzymatic trivalent cross-links

The most abundant protein of bone's organic matrix is collagen. One of its most important properties is its cross-linking pattern, which is responsible for the fibrillar matrices' mechanical properties such as tensile strength and viscoelasticity. We have previously described a spectroscopic method based on the resolution of the Amide I and II Fourier transform Infrared (FTIR) bands to their underlying constituent peaks, which allows the determination of divalent and pyridinoline (PYD) collagen cross-links in mineralized thin bone tissue sections with a spatial resolution of ~6.3 μm. In the present study, we used FTIR analysis of a series of biochemically characterized collagen peptides, as well as skin, dentin, and predentin, to examine the potential reasons underlying discrepancies between two different analytical methodologies specifically related to spectral processing. The results identified a novel distinct FTIR underlying peak at ~1,680 cm(-1), correlated with deoxypyridinoline (DPD) content. Furthermore, the two different methods of spectral resolution result in widely different results, while only the method employing well-established spectroscopic routines for spectral resolution provided biologically relevant results, confirming our earlier studies relating the area of the underlying 1,660 cm(-1) with PYD content. The results of the present study describe a new peak that may be used to determine DPD content, confirm our earlier report relating spectroscopic parameters to PYD content, and highlight the importance of the selected spectral resolution methodology.

The microstructural and biomechanical development of the condylar bone: a review

BACKGROUND

Bone constantly strives for optimal architecture. Mandibular condyle, which is subjected to various mechanical loads forcing it to be highly adaptive, has a unique structure and a relatively high remodelling rate. Despite the eminent clinical relevance of mandibular condyle, literature on its structural and biomechanical development and on the mechanical role of its mineralized and non-mineralized bone components is scarce.

OBJECTIVE

The aim of the present review is to provide a brief introduction to basic bone mechanics and a synopsis of the growth and development of human mandibular condyle. Subsequently, the current ideas on the relationship between the structural and biomechanical properties of bone in general and of mandibular condyle in particular are reviewed. Finally, up-to-date knowledge from fundamental bone research will be blended with the current knowledge relevant to clinical dentistry, above all orthodontics.

METHODS

A comprehensive literature study was performed with an emphasis on recent and innovative work focusing on the interaction between microarchitectural and micromechanical properties of bone.

CONCLUSIONS

Mandibular condyle is a bone structure with a high bone turnover rate. Mechanical properties of mandibular condyle improve during adolescence and are optimal during adulthood. Local mineralization degree might not be a decisive determinant of the local bone tissue stiffness as was believed hitherto. Bone collagen and its cross links play a role in toughness and tensile strength of bone but not in its compressive properties. Clinical procedures might affect mandibular condyle, which is highly reactive to changes in its mechanical environment.

Photoacoustic FTIR spectroscopic study of undisturbed human cortical bone

Chemical pretreatment has been the prevailing sample preparation procedure for infrared (IR) spectroscopic studies on bone. However, experiments have indicated that chemical pretreatment can potentially affect the interactions between the components. Typically the IR techniques have involved transmission experiments. Here we report experimental studies using photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). As a nondestructive technique, PA-FTIR can detect absorbance spectrum from a sample at controllable sampling depth and with little or no sample preparation. Additionally, the coupling inert gas, helium, which is utilized in the PA-FTIR system, can inhibit bacteria growth of bone by displacing oxygen. Therefore, we used this technique to study the undisturbed human cortical bone. It is found that photoacoustic mode (linear-scan, LS-PA-FTIR) can obtain basically similar spectra of bone as compared to the traditional transmission mode, but it seems more sensitive to amide III and ν(2) carbonate bands. The ν(3) phosphate band is indicative of detailed mineral structure and symmetry of native bone. The PA-FTIR depth profiling experiments on human cortical bone also indicate the influence of water on OH band and the cutting effects on amide I and mineral bands. Our results indicate that phosphate ion geometry appears less symmetric in its undisturbed state as detected by the PA-FTIR as compared to higher symmetry observed using transmission techniques on disturbed samples. Moreover, the PA-FTIR spectra indicate a band at 1747 cm(-1) possibly resulting from CO stretching of lipids, cholesterol esters, and triglycerides from the arteries. Comparison of the spectra in transverse and longitudinal cross-sections demonstrates that, the surface area of the longitudinal section bone appears to have more organic matrix exposed and with higher mineral stoichiometry.

Mechanisms of bone fragility in a mouse model of glucocorticoid-treated rheumatoid arthritis: implications for insufficiency fracture risk

OBJECTIVE

Glucocorticoid (GC) therapy is associated with increased risk of fracture in patients with rheumatoid arthritis (RA). To elucidate the cause of this increased risk, we examined the effects of chronic erosive inflammatory arthritis and GC treatment on bone quality, structure, and biomechanical properties in a murine model.

METHODS

Mice with established arthritis and expressing human tumor necrosis factor α (TNFα) transgene (Tg) and their wild-type (WT) littermates were continually treated with GC (prednisolone 5 mg/kg/day via subcutaneous controlled-release pellet) or placebo for 14, 28, or 42 days. Microstructure, biomechanical properties, chemical composition, and morphology of the tibiae and lumbar vertebral bodies were assessed by micro-computed tomography, biomechanical testing, Raman spectroscopy, and histology, respectively. Serum markers of bone turnover were also determined.

RESULTS

TNF-Tg and GC treatment additively decreased mechanical strength and stiffness in both the tibiae and the vertebral bodies. GC treatment in the TNF-Tg mice increased the ductility of tibiae under torsional loading. These changes were associated with significant alterations in the biochemical and structural composition of the mineral and organic components of the bone matrix, a decrease in osteoblast activity and bone formation, and an increase in osteoclast activity.

CONCLUSION

Our findings indicate that the concomitant decrease in bone strength and increase in bone ductility associated with chronic inflammation and GC therapy, coupled with the significant changes in the bone quality and structure, may increase the susceptibility of the bone to failure under low-energy loading. This may explain the mechanism of symptomatic insufficiency fractures in patients with RA receiving GC therapy who do not have radiographic manifestations of fracture.

Bone material properties in premenopausal women with idiopathic osteoporosis

Idiopathic osteoporosis (IOP) in premenopausal women is characterized by fragility fractures at low or normal bone mineral density (BMD) in otherwise healthy women with normal gonadal function. Histomorphometric analysis of transiliac bone biopsy samples has revealed microarchitectural deterioration of cancellous bone and thinner cortices. To examine bone material quality, we measured the bone mineralization density distribution (BMDD) in biopsy samples by quantitative backscattered electron imaging (qBEI), and mineral/matrix ratio, mineral crystallinity/maturity, relative proteoglycan content, and collagen cross-link ratio at actively bone forming trabecular surfaces by Raman microspectroscopy and Fourier transform infrared microspectroscopy (FTIRM) techniques. The study groups included: premenopausal women with idiopathic fractures (IOP, n = 45), or idiopathic low BMD (Z-score ≤ -2.0 at spine and/or hip) but no fractures (ILBMD, n = 19), and healthy controls (CONTROL, n = 38). BMDD of cancellous bone showed slightly lower mineral content in IOP (both the average degree of mineralization of cancellous bone [Cn.Ca(Mean) ] and mode calcium concentration [Cn.Ca(Peak) ] are 1.4% lower) and in ILBMD (both are 1.6% lower, p < 0.05) versus CONTROL, but no difference between IOP and ILBMD. Similar differences were found when affected groups were combined versus CONTROL. The differences remained significant after adjustment for cancellous mineralizing surface (MS/BS), suggesting that the reduced mineralization of bone matrix cannot be completely accounted for by differences in bone turnover. Raman microspectroscopy and FTIRM analysis at forming bone surfaces showed no differences between combined IOP/ILBMD groups versus CONTROL, with the exceptions of increased proteoglycan content per mineral content and increased collagen cross-link ratio. When the two affected subgroups were considered individually, mineral/matrix ratio and collagen cross-link ratio were higher in IOP than ILBMD. In conclusion, our findings suggest that bone material properties differ between premenopausal women with IOP/ILBMD and normal controls. In particular, the altered collagen properties at sites of active bone formation support the hypothesis that affected women have osteoblast dysfunction that may play a role in bone fragility.

Effects of alendronate and risedronate on bone material properties in actively forming trabecular bone surfaces

We used Raman and Fourier transform infrared microspectroscopy (FTIRM) analysis to examine the intrinsic bone material properties at actively bone-forming trabecular surfaces in iliac crest biopsies from women with postmenopausal osteoporosis (PMO) who were treated with either alendronate (ALN) or risedronate (RIS). At eight study sites, women were identified who had postmenopausal osteoporosis (PMO), were at least 5 years postmenopause, and had been on long-term therapy (either 3-5 years or >5 years) with daily or weekly ALN or RIS. Following standard tetracycline labeling, biopsies were collected from 102 women (33 treated with ALN for 3-5 years [ALN-3], 35 with ALN for >5 years [ALN-5], 26 with RIS for 3-5 years [RIS-3], and 8 with RIS for >5 years [RIS-5]) and were analyzed at anatomical areas of similar tissue age in bone-forming areas (within the fluorescent double labels). The following outcomes were monitored and reported: mineral to matrix ratio (corresponding to ash weight), relative proteoglycan content (regulating mineralization commencement), mineral maturity (indicative of the mineral crystallite chemistry and stoichiometry, and having a direct bearing on crystallite shape and size), and the ratio of two of the major enzymatic collagen cross-links (pyridinoline/divalent). In RIS-5 there was a significant decrease in the relative proteoglycan content (-5.83% compared to ALN-5), while in both RIS-3 and RIS-5 there was significantly lower mineral maturity/crystallinity (-6.78% and -13.68% versus ALN-3 and ALN-5, respectively), and pyridinoline/divalent collagen cross-link ratio (-23.09% and -41.85% versus ALN-3 and ALN-5, respectively). The results of the present study indicate that ALN and RIS exert differential effects on the intrinsic bone material properties at actively bone-forming trabecular surfaces.

Fourier transform infrared imaging of bone

Fourier transform infrared imaging (FTIRI) is a technique that can be used to analyze the material properties of bone using tissue sections. In this chapter I describe the basic principles of FTIR and the methods for capturing and analyzing FTIR images in bone sections.

Lathyrism-induced alterations in collagen cross-links influence the mechanical properties of bone material without affecting the mineral

In the present study a rat animal model of lathyrism was employed to decipher whether anatomically confined alterations in collagen cross-links are sufficient to influence the mechanical properties of whole bone. Animal experiments were performed under an ethics committee approved protocol. Sixty-four female (47 day old) rats of equivalent weights were divided into four groups (16 per group): Controls were fed a semi-synthetic diet containing 0.6% calcium and 0.6% phosphorus for 2 or 4 weeks and β-APN treated animals were fed additionally with β-aminopropionitrile (0.1% dry weight). At the end of this period the rats in the four groups were sacrificed, and L2-L6 vertebra were collected. Collagen cross-links were determined by both biochemical and spectroscopic (Fourier transform infrared imaging (FTIRI)) analyses. Mineral content and distribution (BMDD) were determined by quantitative backscattered electron imaging (qBEI), and mineral maturity/crystallinity by FTIRI techniques. Micro-CT was used to describe the architectural properties. Mechanical performance of whole bone as well as of bone matrix material was tested by vertebral compression tests and by nano-indentation, respectively. The data of the present study indicate that β-APN treatment changed whole vertebra properties compared to non-treated rats, including collagen cross-links pattern, trabecular bone volume to tissue ratio and trabecular thickness, which were all decreased (p<0.05). Further, compression tests revealed a significant negative impact of β-APN treatment on maximal force to failure and energy to failure, while stiffness was not influenced. Bone mineral density distribution (BMDD) was not altered either. At the material level, β-APN treated rats exhibited increased Pyd/Divalent cross-link ratios in areas confined to a newly formed bone. Moreover, nano-indentation experiments showed that the E-modulus and hardness were reduced only in newly formed bone areas under the influence of β-APN, despite a similar mineral content. In conclusion the results emphasize the pivotal role of collagen cross-links in the determination of bone quality and mechanical integrity. However, in this rat animal model of lathyrism, the coupled alterations of tissue structural properties make it difficult to weigh the contribution of the anatomically confined material changes to the overall mechanical performance of whole bone. Interestingly, the collagen cross-link ratio in bone forming areas had the same profile as seen in actively bone forming trabecular surfaces in human iliac crest biopsies of osteoporotic patients.

Infrared assessment of bone quality: a review

BACKGROUND

Bone strength depends on both bone quantity and quality. The former is routinely estimated in clinical settings through bone mineral density measurements but not the latter. Bone quality encompasses the structural and material properties of bone. Although its importance is appreciated, its contribution in determining bone strength has been difficult to precisely quantify partly because it is multifactorial and requires investigation of all bone hierarchical levels. Fourier transform infrared spectroscopy provides one way to explore these levels.

QUESTIONS/PURPOSES

The purposes of our review were to (1) provide a brief overview of Fourier transform infrared spectroscopy as a way to establish bone quality, (2) review the major bone material parameters determined from Fourier transform infrared spectroscopy, and (3) review the role of Fourier transform infrared microspectroscopic analysis in establishing bone quality.

METHODS

We used the ISI Web of Knowledge database initially to identify articles containing the Boolean term "infrared" AND "bone." We then focused on articles on infrared spectroscopy in bone-related journals.

RESULTS

Infrared spectroscopy provides information on bone material properties. Their microspectroscopic versions allow one to establish these properties as a function of anatomic location, mineralization extent, and bone metabolic activity. It provides answers pertaining to the contribution of mineral to matrix ratio, mineral maturity, mineral carbonate substitution, and collagen crosslinks to bone strength. Alterations of bone material properties have been identified in disease (especially osteoporosis) not attainable by other techniques.

CONCLUSIONS

Infrared spectroscopic analysis is a powerful tool for establishing the important material properties contributing to bone strength and thus has helped better understand changes in fragile bone.

Mineral composition is altered by osteoblast expression of an engineered G(s)-coupled receptor

Activation of the G(s) G protein-coupled receptor Rs1 in osteoblasts increases bone mineral density by 5- to 15-fold in mice and recapitulates histologic aspects of fibrous dysplasia of the bone. However, the effects of constitutive G(s) signaling on bone tissue quality are not known. The goal of this study was to determine bone tissue quality in mice resulting from osteoblast-specific constitutive G(s) activation, by the complementary techniques of FTIR spectroscopy and synchrotron radiation micro-computed tomography (SRμCT). Col1(2.3)-tTA/TetO-Rs1 double transgenic (DT) mice, which showed osteoblast-specific constitutive G(s) signaling activity by the Rs1 receptor, were created. Femora and calvariae of DT and wild-type (WT) mice (6 and 15 weeks old) were analyzed by FTIR spectroscopy. WT and DT femora (3 and 9 weeks old) were imaged by SRμCT. Mineral-to-matrix ratio was 25% lower (P = 0.010), carbonate-to-phosphate ratio was 20% higher (P = 0.025), crystallinity was 4% lower (P = 0.004), and cross-link ratio was 11% lower (P = 0.025) in 6-week DT bone. Differences persisted in 15-week animals. Quantitative SRμCT analysis revealed substantial differences in mean values and heterogeneity of tissue mineral density (TMD). TMD values were 1,156 ± 100 and 711 ± 251 mg/cm(3) (mean ± SD) in WT and DT femoral diaphyses, respectively, at 3 weeks. Similar differences were found in 9-week animals. These results demonstrate that continuous G(s) activation in murine osteoblasts leads to deposition of immature bone tissue with reduced mineralization. Our findings suggest that bone tissue quality may be an important contributor to increased fracture risk in fibrous dysplasia patients.

Effects of risedronate in Runx2 overexpressing mice, an animal model for evaluation of treatment effects on bone quality and fractures

Young mice overexpressing Runx2 specifically in cells of the osteoblastic lineage failed to gain bone mass and exhibited a dramatic increase in bone resorption, leading to severe osteopenia and spontaneous vertebral fractures. The objective of the current study was to determine whether treatment with a bisphosphonate (risedronate, Ris), which reduces fractures in postmenopausal as well as in juvenile osteoporosis, was able to improve bone quality and reduce vertebral fractures in mice overexpressing Runx2. Four-week-old female Runx2 mice received Ris at 2 and 10 μg/kg subcutaneously twice a week for 12 weeks. Runx2 and wild-type mice received vehicle (Veh) as control. We measured the number of new fractures by X-ray and bone mineral density (BMD) by DEXA. We evaluated bone quality by histomorphometry, micro-CT, and Fourier transform infrared imaging (FTIRI). Ris at 20 μg/kg weekly significantly reduced the average number of new vertebral fractures compared to controls. This was accompanied by significantly increased BMD, increased trabecular bone volume, and reduced bone remodeling (seen in indices of bone resorption and formation) in the vertebrae and femoral metaphysis compared to Runx2 Veh. At the femur, Ris also increased cortical thickness. Changes in collagen cross-linking seen on FTIRI confirmed that Runx2 mice have accelerated bone turnover and showed that Ris affects the collagen cross-link ratio at both forming and resorbing sites. In conclusion, young mice overexpressing Runx2 have high bone turnover-induced osteopenia and spontaneous fractures. Ris at 20 μg/kg weekly induced an increase in bone mass, changes in bone microarchitecture, and decreased vertebral fractures.

The role of apoptosis in mineralizing murine versus avian micromass culture systems

Chondrocyte apoptosis is thought to be an important step in the calcification of cartilage in vivo; however, there are conflicting reports as to whether or not this apoptosis is a necessary precursor to mineralization. The goal of this study was to determine whether or not apoptosis is necessary for mineralization in an in vitro murine micromass model of endochondral ossification. C3H10T1/2 murine mesenchymal stem cells were plated in micromass culture in the presence of 4 mM inorganic phosphate with the addition of the apoptogens, camptothecin, or staurosporine, to induce apoptosis. The rate and total accumulation of mineralization was measured with (45)Ca uptake. In these studies, both apoptogens increased the rate of mineralization, with staurosporine increasing (45)Ca accumulation by about 2.5 times that of controls and camptothecin increasing total amounts of mineralization about 1.5 times that of controls. Inhibiting cell apoptosis with the caspase inhibitor, ZVAD-fmk, to prevent apoptosis, caused slower rates of (45)Ca uptake; however, total amounts of (45)Ca accumulation reached the same values by day 30 of culture. FTIR data showed mineralization in all samples treated with 4 mM inorganic phosphate, with the highest mineral to matrix ratios in the camptothecin treated samples.

Infrared spectroscopy reveals both qualitative and quantitative differences in equine subchondral bone during maturation

The collagen phase in bone is known to undergo major changes during growth and maturation. The objective of this study is to clarify whether Fourier transform infrared (FTIR) microspectroscopy, coupled with cluster analysis, can detect quantitative and qualitative changes in the collagen matrix of subchondral bone in horses during maturation and growth. Equine subchondral bone samples (n = 29) from the proximal joint surface of the first phalanx are prepared from two sites subjected to different loading conditions. Three age groups are studied: newborn (0 days old), immature (5 to 11 months old), and adult (6 to 10 years old) horses. Spatial collagen content and collagen cross-link ratio are quantified from the spectra. Additionally, normalized second derivative spectra of samples are clustered using the k-means clustering algorithm. In quantitative analysis, collagen content in the subchondral bone increases rapidly between the newborn and immature horses. The collagen cross-link ratio increases significantly with age. In qualitative analysis, clustering is able to separate newborn and adult samples into two different groups. The immature samples display some nonhomogeneity. In conclusion, this is the first study showing that FTIR spectral imaging combined with clustering techniques can detect quantitative and qualitative changes in the collagen matrix of subchondral bone during growth and maturation.

The role of mineral content in determining the micromechanical properties of discrete trabecular bone remodeling packets

In trabecular bone, each remodeling event results in the resorption and/or formation of discrete structural units called 'packets'. These remodeling packets represent a fundamental level of bone's structural hierarchy at which to investigate composition and mechanical behaviors. The objective of this study was to apply the complementary techniques of quantitative backscattered electron microscopy (qBSEM) and nanoindentation to investigate inter-relationships between packet mineralization, elastic modulus, contact hardness and plastic deformation resistance. Indentation arrays were performed across nine trabecular spicules from 3 human donors; these spicules were then imaged using qBSEM, and discretized into their composite remodeling packets (127 in total). Packets were classified spatially as peripheral or central, and mean contact hardness, plastic deformation resistance, elastic modulus and calcium content calculated for each. Inter-relationships between measured parameters were analysed using linear regression analyses, and dependence on location assessed using Student's t-tests. Significant positive correlations were found between all mechanical parameters and calcium content. Elastic modulus and contact hardness were significantly correlated, however elastic modulus and plastic deformation resistance were not. Calcium content, contact hardness and elastic modulus were all significantly higher for central packets than for peripheral, confirming that packet mineral content contributes to micromechanical heterogeneity within individual trabecular spicules. Plastic deformation resistance, however, showed no such regional dependence, indicating that the plastic deformation properties in particular, are determined not only by mineral content, but also by the organic matrix and interactions between these two components.

Infrared spectroscopy indicates altered bone turnover and remodeling activity in renal osteodystrophy

Renal osteodystrophy alters metabolic activity and remodeling rate of bone and also may lead to different bone composition. The objective of this study was to characterize the composition of bone in high-turnover renal osteodystrophy patients by means of Fourier transform infrared spectroscopic imaging (FTIRI). Iliac crest biopsies from healthy bone (n = 11) and patients with renal osteodystrophy (ROD, n = 11) were used in this study. The ROD samples were from patients with hyperparathyroid disease. By using FTIRI, phosphate-to-amide I ratio (mineral-to-matrix ratio), carbonate-to-phosphate ratio, and carbonate-to-amide I ratio (turnover rate/remodeling activity), as well as the collagen cross-link ratio (collagen maturity), were quantified. Histomorphometric analyses were conducted for comparison. The ROD samples showed significantly lower carbonate-to-phosphate (p < .01) and carbonate-to-amide I (p < .001) ratios. The spatial variation across the trabeculae highlighted a significantly lower degree of mineralization (p < .05) at the edges of the trabeculae in the ROD samples than in normal bone. Statistically significant linear correlations were found between histomorphometric parameters related to bone-remodeling activity and number of bone cells and FTIRI-calculated parameters based on carbonate-to-phosphate and carbonate-to-amide I ratios. Hence the results suggested that FTIRI parameters related to carbonate may be indicative of turnover and remodeling rate of bone.

Raloxifene ameliorates detrimental enzymatic and nonenzymatic collagen cross-links and bone strength in rabbits with hyperhomocysteinemia

We demonstrate a reduction in enzymatic divalent immature and trivalent pyridinium cross-links and an increase in the nonenzymatic cross-link, pentosidine (Pen), in rabbits with methionine (Met)-induced hyperhomocysteinemia. Such detrimental cross-link formation in bone was ameliorated by raloxifene (RLX) treatment.

INTRODUCTION

Collagen cross-links are determinants of bone quality. Homocysteine (Hcys) interferes with collagen cross-linking. Because RLX is thought to ameliorate bone quality, we investigated whether RLX ameliorated hyperhomocysteinemia-induced cross-link abnormalities using a Met-rich diet rabbit model.

METHODS

We divided New Zealand white rabbits into six groups (n = 6 per group): baseline control, sham operation, sham + 1% Met diet, ovariectomy (OVX), 1% Met diet + OVX, OVX + RLX (10 mg/kg/day), and 1% Met diet + OVX + RLX. RLX was administered for 16 weeks. We measured the amount of enzymatic immature and mature pyridinium cross-links and the nonenzymatic cross-link, Pen, and correlated the cross-link content to bone strength.

RESULTS

Hcys levels were significantly higher in the Met diet groups than in the normal diet groups. Met-fed rabbits with or without OVX showed a significant reduction of enzymatic cross-links, whereas an increase in Pen was observed in Met-fed rabbits with OVX. The cross-link content of the RLX-treated Met-fed rabbits with OVX was restored to similar levels as the sham group, accompanied by an improvement of bone strength.

CONCLUSION

These results demonstrate that hyperhomocysteinemia reduced bone strength via a reduction of enzymatic cross-links and an increase of nonenzymatic cross-links. RLX may ameliorate hyperhomocysteinemia-induced detrimental cross-linking in rabbits with OVX and may improve bone strength via the amelioration of collagen cross-links.

Differentiation and mineralization of murine mesenchymal C3H10T1/2 cells in micromass culture

The murine mesenchymal cell line, C3H10T1/2 in micromass culture undergoes chondrogenic differentiation with the addition of BMP-2. This study compares the use of BMP-2 vs. insulin, transferrin, and sodium selenite (ITS) to create a chondrogenic micromass cell culture system that models cartilage calcification in the presence of 4mM inorganic phosphate. BMP-2 treated cultures showed more intense alcian blue staining for proteoglycans than ITS treated cultures at early time points. Both ITS and BMP-2 treated cultures showed similar mineral deposition in cultures treated with 4mM phosphate via von Kossa staining, however FTIR spectroscopy of cultures showed different matrix properties. ITS treated cultures produced matrix that more closely resembled mouse calcified cartilage by FTIR analysis. (45)Ca uptake curves showed delayed onset of mineralization in cultures treated with BMP-2, however they had an increased rate of mineralization (initial slope of (45)Ca uptake curve) when compared to the cultures treated with ITS. Immunohistochemistry showed the presence of both collagens type I and type II in BMP-2 and ITS treated control (1mM inorganic phosphate) and mineralizing cultures. BMP-2 treated mineralizing cultures displayed more intense staining for collagen type II than all other cultures. Collagen type X staining was detected at Day 9 only in mineralizing cultures treated with ITS. Western blotting of Day 9 cultures confirmed the presence of collagen type X in the mineralizing ITS cultures, and also showed very small amounts of collagen type X in BMP-2 treated cultures and control ITS cultures. By Day 16 all cultures stained positive for collagen type X. These data suggest that BMP-2 induces a more chondrogenic phenotype, while ITS treatment favors maturation and hypertrophy of the chondrocytes in the murine micromass cultures.

Collagen cross-links as a determinant of bone quality: a possible explanation for bone fragility in aging, osteoporosis, and diabetes mellitus

Collagen cross-linking, a major post-translational modification of collagen, plays important roles in the biological and biomechanical features of bone. Collagen cross-links can be divided into lysyl hydroxylase and lysyloxidase-mediated enzymatic immature divalent cross-links,mature trivalent pyridinoline and pyrrole cross-links, and glycation- or oxidation-induced non-enzymatic cross-links(advanced glycation end products) such as glucosepane and pentosidine. These types of cross-links differ in the mechanism of formation and in function. Material properties of newly synthesized collagen matrix may differ in tissue maturity and senescence from older matrix in terms of crosslink formation. Additionally, newly synthesized matrix in osteoporotic patients or diabetic patients may not necessarily be as well-made as age-matched healthy subjects. Data have accumulated that collagen cross-link formation affects not only the mineralization process but also microdamage formation. Consequently, collagen cross-linking is thought to affect the mechanical properties of bone. Furthermore,recent basic and clinical investigations of collagen cross-links seem to face a new era. For instance, serum or urine pentosidine levels are now being used to estimate future fracture risk in osteoporosis and diabetes. In this review, we describe age-related changes in collagen cross-links in bone and abnormalities of cross-links in osteoporosis and diabetes that have been reported in the literature.

Spatial variation in osteonal bone properties relative to tissue and animal age

Little is known about osteonal bone mineral and matrix properties, although these properties are of major importance for the understanding of bone alterations related to age and bone diseases such as osteoporosis. During aging, bone undergoes modifications that compromise their structural integrity as shown clinically by the increase of fracture incidence with age. Based on Fourier transform infrared (FTIR) analysis from baboons between 0 and 32 yr of age, consistent systematic variations in bone properties as a function of tissue age are reported within osteons. The patterns observed were independent of animal age and positively correlated with bone tissue elastic behavior measured by nano-indentation. As long as tissue age is expressed as a percentage of the entire osteon radius, osteonal analyses can be used to characterize disease changes independent of the size of the osteon. These mineral and matrix analyses can be used to explain bone fragility. The mineral content (mineral-to-matrix ratio) was correlated with the animal age in both old (interstitial) and newly formed bone tissue, showing for the first time that age-related changes in BMC can be explain by an alteration in the mineralization process itself and not only by an imbalance in the remodeling process.

Bone matrix quality and plasma homocysteine levels

It has recently been reported in the clinical literature that blood homocysteine levels correlate well with fracture risk, although a couple of reports exist to the opposite. Bone strength depends on both bone quantity and quality. The purpose of the present study was to investigate possible correlations between plasma homocysteine levels and bone material properties (Bone Mineral Density Distribution; BMDD, and collagen cross-link ratio). In the present study, femoral heads from subjects (N=19, females, age range 70-95 years old) with known homocysteine plasma levels were investigated. The bone material was collected during hemiarthroplasty surgery. We have determined collagen cross-link ratio and bone mineralization density distribution (BMDD) in bone tissue from patients with acute femoral neck fractures, by Fourier Transform Infrared Imaging (FTIRI) and quantitative Backscattered Electron Imaging (qBEI), respectively. The collagen cross-link ratio that was spectroscopically determined was pyridinoline/divalent cross-links (pyr/divalent). The BMDD variables quantified were: CaMean: the weighted mean calcium concentration; CaPeak: the most frequent Ca concentration; CaWidth: the width of the distribution, a measure of the mineralization homogeneity; CaLow: the percentage of bone area that is mineralized below the 5th percentile in the reference range; CaHigh: the percentage of bone area that is mineralized above the 95th percentile in the reference range. There was a significant correlation between plasma homocysteine levels and collagen cross-link ratio in areas of primary mineralized bone (p<0.0001), unlike the case of trabecular bone surfaces undergoing resorption (p>0.05). On the other hand there was no correlation in any of the BMDD parameters and plasma homocysteine levels (p>0.05). The results are consistent with the known effect of homocysteine on collagen post-translational modifications. These changes were independent of bone mineral characteristics. The results of the present study offer a mechanism by which homocysteine affects bone quality, but caution should be exercised since all patients examined had sustained fracture.

Spectroscopic markers of bone quality in alendronate-treated postmenopausal women

Comparison of infrared spectroscopic images of sections from biopsies of placebo-treated post-menopausal women and women treated for 3 years with 10 mg/day alendronate demonstrated significant increases in cortical bone mineral content, no alterations in other spectroscopic markers of "bone quality," but a decrease in tissue heterogeneity.

METHODS

The material properties of thick sections from iliac crest biopsies of seven alendronate-treated women were compared to those from ten comparably aged post-menopausal women without bone disease, using infrared spectroscopic imaging at approximately 7 microm spatial resolution. Parameters evaluated were mineral/matrix ratio, crystallinity, carbonate/amide I ratio, and collagen maturity. The line widths at half maximum of the pixel histograms for each parameter were used as measures of heterogeneity.

RESULTS

The mineral content (mineral/matrix ratio) in the cortical bone of the treated women's biopsies was higher than that in the untreated control women. Crystallinity, carbonate/protein, and collagen maturity indices were not significantly altered; however, the pixel distribution was significantly narrowed for all cortical and trabecular parameters with the exception of collagen maturity in the alendronate treatment group.

CONCLUSIONS

The increases in mineral density and decreased fracture risk associated with bisphosphonate treatment may be counterbalanced by a decrease in tissue heterogeneity, which could impair tissue mechanical properties. These consistent data suggest that alendronate treatment, while increasing the bone mass, decreases the tissue heterogeneity.

Bone quality determined by Fourier transform infrared imaging analysis in mild primary hyperparathyroidism

CONTEXT

Mild primary hyperparathyroidism (PHPT) is characterized by asymptomatic hypercalcemia, most commonly in the absence of classical signs and symptoms. Hence, there is need to characterize this disorder with particular attention to the skeleton.

DESIGN

We determined the ratio of pyridinium and dehydrodihydroxylysinonorleucine collagen cross-links in 46 iliac crest bone biopsies from patients with PHPT (14 men, aged 28-68 yr; 32 women, aged 26-74 yr) by Fourier transform infrared imaging. The results were compared with previously reported collagen cross-links ratio determined in iliac crest biopsies from normal subjects.

RESULTS

PHPT patients exhibited significantly lower pyridinium to dehydrodihydroxylysinonorleucine collagen cross-links ratio, compared with normal controls. Parathyroidectomy restored values to those comparable with normal controls. Moreover, the differences among PHPT subjects were gender dependent, with female PHPT patients having a statistically significant lower ratio, compared with either male PHPT patients or normal controls. Comparison of the obtained outcomes with histomorphometry showed that the collagen cross-link ratio was strongly correlated with rate of bone formation, and mineralizing surface, in individual patients. This ratio was also correlated with bone mineralization density distribution parameters obtained in the same patients. The strongest correlations were with bone mineralization density distribution variables reflecting heterogeneity of mineralization and primary mineralization parameters.

CONCLUSIONS

The results are consistent with the high turnover state manifested in PHPT patients. Reduced collagen cross-link ratio in patients with PHPT would be expected to reduce the stiffness of bone tissue. These observations provide a more complete assessment of bone material properties in this disorder.

Collagen maturity, glycation induced-pentosidine, and mineralization are increased following 3-year treatment with incadronate in dogs

Collagen cross-linking is a determinant of bone quality. A three-year treatment of bisphosphonate-incadronate disodium-in beagles increased degree of mineralization, collagen maturity, and pentosidine, a compound with advanced glycation end products. The treatment had no effect on the total amount of enzymatic cross-link formation.

INTRODUCTION

Collagen cross-linking is a determinant of bone quality. Recently, we reported that long-term treatment with bisphosphonate increased microdamage accumulation. The aim of this study was to clarify the effect of a three-year treatment with bisphosphonate on degree of mineralization and immature and mature enzymatic cross-links and non-enzymatic collagen cross-link, pentosidine, in cortical bone in the same dogs.

METHODS

Twenty-nine 1-year-old beagles (15 males, 14 females) were divided into three groups that daily were given vehicle or incadronate at doses of 0.3 or 0.6 mg/kg/day orally for three years. A cortex of a rib was fractionated into low- and high-density portions. The contents of calcium, phosphorus, enzymatic immature and mature cross-links, and the non-enzymatic glycation product pentosidine were determined in each fraction.

RESULTS

Calcium, phosphorus, and pentosidine contents and the ratio of mature to immature cross-links increased significantly with incadronate in a dose-dependent manner, but the total amount of enzymatic cross-links was unchanged. The pentosidine content correlated inversely with cortical activation frequency (p < 0.01).

CONCLUSION

Long-term suppression of bone remodeling by bisphosphonate increases degree of mineralization, collagen maturity, and non-enzymatic cross-linking.

Bone architecture: collagen structure and calcium/phosphorus maps

Bone collagen structure in normal and pathological tissues is presented using techniques of thin section transmission electron microscopy and morphometry. In pathological tissue, deviations from normal fine structure are reflected in abnormal arrangements of collagen fibrils and abnormalities in fibril diameter. The relationships between these bone structural changes and the skeletal calcium/phosphorus ratio are discussed. Calcium/phosphorus ratio is measured by X-ray absorptiometry and computed microtomography.

Bisphosphonates alter trabecular bone collagen cross-linking and isomerization in beagle dog vertebra

Changes in organic matrix may contribute to the anti-fracture efficacy of anti-remodeling agents. Following one year of treatment in beagle dogs, bisphosphonates alter the organic matrix of vertebral trabecular bone, while raloxifene had no effect. These results show that pharmacological suppression of turnover alters the organic matrix component of bone.

INTRODUCTION

The collagen matrix contributes significantly to a bone's fracture resistance yet the effects of anti-remodeling agents on collagen properties are unclear. The goal of this study was to assess changes in collagen cross-linking and isomerization following anti-remodeling treatment.

METHODS

Skeletally mature female beagles were treated for one year with oral doses of vehicle (VEH), risedronate (RIS; 3 doses), alendronate (ALN; 3 doses), or raloxifene (RAL; 2 doses). The middle dose of RIS and ALN and the lower dose of RAL approximate doses used for treatment of post menopausal osteoporosis. Vertebral trabecular bone matrix was assessed for collagen isomerization (ratio of alpha/beta C-telopeptide [CTX]), enzymatic (pyridinoline [PYD] and deoxypyridinoline [DPD]), and non-enzymatic (pentosidine [PEN]) cross-links.

RESULTS

All doses of both RIS and ALN increased PEN (+34-58%) and the ratio of PYD/DPD (+14-26%), and decreased the ratio of alpha/beta CTX (-29-56%) compared to VEH. RAL did not alter any collagen parameters. Bone turnover rate was significantly correlated to PEN (R = -0.664), alpha/beta CTX (R = 0.586), and PYD/DPD (R = -0.470).

CONCLUSIONS

Bisphosphonate treatment significantly alters properties of bone collagen suggesting a contribution of the organic matrix to the anti-fracture efficacy of this drug class.