Pyridoxine deficiency affects biomechanical properties of chick tibial bone

Leg disorders in broiler chickens: a review of current knowledge

Ensuring improved leg health is an important prerequisite for broilers to achieve optimal production performance and welfare status. Broiler leg disease is characterized by leg muscle weakness, leg bone deformation, joint cysts, arthritis, femoral head necrosis, and other symptoms that result in lameness or paralysis. These conditions significantly affect movement, feeding and broiler growth performance. Nowadays, the high incidence of leg abnormalities in broiler chickens has become an important issue that hampers the development of broiler farming. Therefore, it is imperative to prevent leg diseases and improve the health of broiler legs. This review mainly discusses the current prevalence of broiler leg diseases and describes the risk factors, diagnosis, and prevention of leg diseases to provide a scientific basis for addressing broiler leg health problems.

Hypophosphatasia: Vitamin B6 status of affected children and adults

Hypophosphatasia (HPP) is the heritable dento-osseous disease caused by loss-of-function mutation(s) of the gene ALPL that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP is a cell-surface homodimeric phosphomonoester phosphohydrolase expressed in healthy people especially in the skeleton, liver, kidneys, and developing teeth. In HPP, diminished TNSALP activity leads to extracellular accumulation of its natural substrates including inorganic pyrophosphate (PPi), an inhibitor of mineralization, and pyridoxal 5'-phosphate (PLP), the principal circulating form of vitamin B₆ (B₆). Autosomal dominant and autosomal recessive inheritance involving >450 usually missense defects scattered throughout ALPL largely explains the remarkably broad-ranging severity of this inborn-error-of-metabolism. In 1985 when we identified elevated plasma PLP as a biochemical hallmark of HPP, all 14 investigated affected children and adults had markedly increased PLP levels. However, pyridoxal (PL), the dephosphorylated form of PLP that enters cells to cofactor many enzymatic reactions, was not low but often inexplicably elevated. Levels of pyridoxic acid (PA), the B₆ degradation product quantified to assess B₆ sufficiency, were unremarkable. Canonical signs or symptoms of B₆ deficiency or toxicity were absent. B₆-dependent seizures in infants with life-threatening HPP were later explained by their profound deficiency of TNSALP activity blocking PLP dephosphorylation to PL and diminishing gamma-aminobutyric acid synthesis in the brain. Now, there is speculation that altered B₆ metabolism causes further clinical complications in HPP. Herein, we assessed the plasma PL and PA levels accompanying previously reported elevated plasma PLP concentrations in 150 children and adolescents with HPP. Their mean (SD) plasma PL level was nearly double the mean for our healthy pediatric controls: 66.7 (59.0) nM versus 37.1 (22.2) nM (P < 0.0001), respectively. Their PA levels were broader than our pediatric control range, but their mean value was normal; 40.2 (25.1) nM versus 39.3 (9.9) nM (P = 0.7793), respectively. In contrast, adults with HPP often had plasma PL and PA levels suggestive of dietary B₆ insufficiency. We discuss why the B₆ levels of our pediatric patients with HPP would not cause B₆ toxicity or deficiency, whereas in affected adults dietary B₆ insufficiency can develop.

Adequate intake and supplementation of B vitamins, in particular folic acid, can play a protective role in bone health

In vitro and animal model studies have shown that B vitamins (VB) deficiency have negative consequences on bone, as a result of direct or mediated activity of hyperhomocysteinemia. However, there are still no precise indications regarding a possible VB role in order to maintain bone health. So, the aim of this narrative review was to consider the state of the art on correlation between VB dietary intake, blood levels and supplementation and bone health (bone mineral density (BMD), bone turnover markers and fractures risk) in humans. This review included 29 eligible studies. Considering VB blood levels, the 14 studies considered have shown that low serum folate can be a factor risk for reduced BMD and fractures in elderly, particularly women; no independent association was found for other VB. Studies that evaluate relationship between VB dietary intake and BMD are only 2; one, conducted on 1869 women, demonstrated a positive effect of folate intake on BMD, another demonstrated a dose-dependent inverse relationship between vitamin B6 dietary intake and risk of hip fracture, but only for 35298 female participants. Regarding the relationship between BV supplementation and bone health (9 studies with only VB and 4 with other nutrients), all studies that considered patients with hyperhomocysteinemia or with low folate blood levels, are in agreement in demonstrating that folate supplementation (500mcg-5mg) is useful in improving BMD. In conclusion, a request for folate and homocysteine blood levels in elderly patients with osteopenia/osteoporosis is mandatory. For patients with hyperhomocysteinemia or with low folate blood levels, folate supplementation (500mcg-5mg) is crucial.

Dietary betaine reduces plasma homocysteine concentrations and improves bone strength in laying hens

1. This study tested the hypothesis that the methyl-donor properties of betaine could reduce homocysteine concentrations, which has been recognised in a previous genetics study to be linked to bone quality. This was combined with phytase treatment, as phosphorus is critical for bone mineralisation.2. Using a 2 × 2 factorial arrangement, a total of 1920 Lohmann LSL-lite chickens housed as 24 replicates of 20 chickens were fed one of four diets containing dietary betaine (0 or 1000 mg/kg) and phytase (300 or 1000 FTU/kg) from one day old until end-of-lay. Blood and bone samples were collected at 45 and 70 weeks of age.3. Hens fed betaine had lower plasma homocysteine level (P < 0.05), higher tibia breaking strength (P < 0.05) and higher tibia bone density (P < 0.05).4. Egg production and quality was excellent throughout the study and were not affected by the dietary treatments.5. The addition of dietary betaine was successful at reducing plasma homocysteine concentrations and improving bone strength in laying hens, which could be used as an intervention to alleviate welfare concerns.

Association between serum vitamin B6 concentration and risk of osteoporosis in the middle-aged and older people in China: a cross-sectional study

OBJECTIVE

To determine the relationship between serum vitamin B₆ (Vit B₆) concentration and the status of bone mineral density and identify the relationship between serum Vit B6 and bone metabolism parameters in middle-aged and older people in China.

DESIGN

The present study was a cross-sectional study within the framework of an ongoing prospective population-based cohort study.

SETTING AND PARTICIPANTS

A total of 1829 residents (men ≥50 years and women ≥45 years) from two subdistricts were recruited from July 2015 to February 2016 in Shanghai, China.

MEASURES

Recruited residents were grouped (control, osteopenia and osteoporosis) according to their lumbar spine bone mineral density, measured through dual-energy X-ray absorptiometry. Serum Vit B₆ concentrations, bone turnover marker concentrations and calcium and phosphorus metabolism parameters were assessed.

RESULTS

No significant linear trend between serum Vit B₆ concentrations and lumbar bone mass was observed in the men. In the women, the average osteoporosis risk was 61% higher at serum Vit B₆ concentrations of <19.2 μg/L than at those of >26.9 μg/L (OR 1.61, 95% CI 1.00 to 2.58). However, there was no significance after controlling of serum 25-hydroxy-vitamin D concentration and parathyroid hormone concentration, respectively. In the osteoporotic women, the serum Vit B₆ concentration was significantly negatively correlated to concentrations of bone turnover marker including N-terminal propeptide of type I collagen, β-C-terminal telopeptide of type I collagen and osteocalcin. It was also positively related to the serum 25-hydroxy-vitamin D concentration and inversely related to the serum parathyroid hormone concentration.

CONCLUSIONS

A relatively low serum Vit B₆ concentration, even in the normal range, may be a risk factor for osteoporosis in postmenopausal women, which is dependent on serum 25-hydroxy-vitamin D concentration and parathyroid hormone concentration.

TRIAL REGISTRATION NUMBER

NCT02958020; Post-results.

Vibrational spectroscopic techniques to assess bone quality

Although musculoskeletal diseases such as osteoporosis are diagnosed and treatment outcome is evaluated based mainly on routine clinical outcomes of bone mineral density (BMD) by DXA and biochemical markers, it is recognized that these two indicators, as valuable as they have proven to be in the everyday clinical practice, do not fully account for manifested bone strength. Thus, the term bone quality was introduced, to complement considerations based on bone turnover rates and BMD. Bone quality is an "umbrella" term that incorporates the structural and material/compositional characteristics of bone tissue. Vibrational spectroscopic techniques such as Fourier transform infrared microspectroscopy (FTIRM) and imaging (FTIRI), and Raman spectroscopy, are suitable analytical tools for the determination of bone quality as they provide simultaneous, quantitative, and qualitative information on all main bone tissue components (mineral, organic matrix, tissue water), in a spatially resolved manner. Moreover, the results of such analyses may be readily combined with the outcomes of other techniques such as histology/histomorphometry, small angle X-ray scattering, quantitative backscattered electron imaging, and nanoindentation.

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.

Fragility Fracture Incidence in Chronic Obstructive Pulmonary Disease (COPD) Patients Associates With Nanoporosity, Mineral/Matrix Ratio, and Pyridinoline Content at Actively Bone-Forming Trabecular Surfaces

Chronic obstructive pulmonary disease (COPD) is associated with low areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) and altered microstructure by bone histomorphometry and micro-computed tomography. Nevertheless, not all COPD patients sustain fragility fractures. In the present study, we used Raman microspectroscopic analysis to determine bone compositional properties at actively forming trabecular surfaces (based on double fluorescent labels) in iliac crest biopsies from 19 postmenopausal COPD patients (aged 62.1 ± 7.3 years). Additionally, we analyzed trabecular geometrical centers, representing tissue much older than the forming surfaces. Eight of the patients had sustained fragility fractures, and 13 had received treatment with inhaled glucocorticoids. None of the patients had taken oral glucocorticoids. The monitored parameters were mineral/matrix ratio (MM), nanoporosity, and relative glycosaminoglycan (GAG), lipid, and pyridinoline contents (PYD). There were no significant differences between the glucocorticoid-treated patients and those who did not receive any. On the other hand, COPD patients sustaining fragility fractures had significantly lower nanoporosity and higher MM and PYD values compared with COPD patients without fragility fractures. To the best of our knowledge, this is the first study to discriminate between fracture and non-fracture COPD patients based on differences in the material properties of bone matrix. Given that these bone material compositional differences are evident close to the cement line (a major bone interface), they may contribute to the inferior bone toughness and coupled with the lower lumbar spine bone mineral density values result in the fragility fractures prevalent in these patients. © 2016 American Society for Bone and Mineral Research.

The supramolecular structure of bone: X-ray scattering analysis and lateral structure modeling

The evolution of vertebrates required a key development in supramolecular evolution: internally mineralized collagen fibrils. In bone, collagen molecules and mineral crystals form a nanocomposite material comparable to cast iron in tensile strength, but several times lighter and more flexible. Current understanding of the internal nanoscale structure of collagen fibrils, derived from studies of rat tail tendon (RTT), does not explain how nucleation and growth of mineral crystals can occur inside a collagen fibril. Experimental obstacles encountered in studying bone have prevented a solution to this problem for several decades. This report presents a lateral packing model for collagen molecules in bone fibrils, based on the unprecedented observation of multiple resolved equatorial reflections for bone tissue using synchrotron small-angle X-ray scattering (SAXS; ∼1 nm resolution). The deduced structure for pre-mineralized bone fibrils includes features that are not present in RTT: spatially discrete microfibrils. The data are consistent with bone microfibrils similar to pentagonal Smith microfibrils, but are not consistent with the (nondiscrete) quasi-hexagonal microfibrils reported for RTT. These results indicate that collagen fibrils in bone and tendon differ in their internal structure in a manner that allows bone fibrils, but not tendon fibrils, to internally mineralize. In addition, the unique pattern of collagen cross-link types and quantities in mineralized tissues can be can be accounted for, in structural/functional terms, based on a discrete microfibril model.

Evidence for a Role for Nanoporosity and Pyridinoline Content in Human Mild Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous connective tissue disorder characterized by bone fragility that arises from decreased bone mass and abnormalities in bone material quality. OI type I represents the milder form of the disease and according to the original Sillence classification is characterized by minimal skeletal deformities and near-normal stature. Raman microspectroscopy is a vibrational spectroscopic technique that allows the determination of bone material properties in bone biopsy blocks with a spatial resolution of ∼1 µm, as a function of tissue age. In the present study, we used Raman microspectroscopy to evaluate bone material quality in transiliac bone biopsies from children with a mild form of OI, either attributable to collagen haploinsufficiency OI type I (OI-Quant; n = 11) or aberrant collagen structure (OI-Qual; n = 5), as a function of tissue age, and compared it against the previously published values established in a cohort of biopsies from healthy children (n = 54, ages 1 to 23 years). The results indicated significant differences in bone material compositional characteristics between OI-Quant patients and healthy controls, whereas fewer were evident in the OI-Qual patients. Differences in both subgroups of OI compared with healthy children were evident for nanoporosity, mineral maturity/crystallinity as determined by maxima of the v1 PO4 Raman band, and pyridinoline (albeit in different direction) content. These alterations in bone material compositional properties most likely contribute to the bone fragility characterizing this disease. © 2016 American Society for Bone and Mineral Research.

B-vitamins and bone health--a review of the current evidence

Because of ongoing global ageing, there is a rapid worldwide increase in incidence of osteoporotic fractures and the resultant morbidity and mortality associated with these fractures are expected to create a substantial economic burden. Dietary modification is one effective approach for prevention of osteoporosis in the general population. Recently, B vitamins have been investigated for their possible roles in bone health in human studies. In this review, we provide different lines of evidence and potential mechanisms of individual B vitamin in influencing bone structure, bone quality, bone mass and fracture risk from published peer-reviewed articles. These data support a possible protective role of B vitamins, particularly, B2, B6, folate and B12, in bone health. However, results from the clinical trials have not been promising in supporting the efficacy of B vitamin supplementation in fracture reduction. Future research should continue to investigate the underlying mechanistic pathways and consider interventional studies using dietary regimens with vitamin B enriched foods to avoid potential adverse effects of high-dose vitamin B supplementation. In addition, observational and interventional studies conducted in Asia are limited and thus require more attention due to a steep rise of osteoporosis and hip fracture incidence projected in this part of the world.

Effects of long-term alendronate treatment on postmenopausal osteoporosis bone material properties

Raman microspectroscopic analysis of iliac crest from patients that were treated with alendronate (ALN) for 10 years revealed minimal, transient alterations in bone material properties confined to actively forming bone surfaces compared to patients that were on ALN for 5 years. These changes were not encountered in the bulk tissue.

INTRODUCTION

Alendronate (ALN) and other bisphosphonates (BPs) are the most widely prescribed therapy for postmenopausal osteoporosis. Despite their overall excellent safety record and efficacy in reducing fractures, questions have been raised regarding potential detrimental effects that may be related to prolonged bone turnover reduction, although no definite cause-effect relationship has been established to date. The purpose of the present study was to evaluate bone material properties in patients that were receiving ALN for 5 or 10 years.

METHODS

Raman microspectroscopic analysis was used to analyze iliac crest biopsies from postmenopausal women with osteoporosis who had been treated with ALN for 5 years and were then re-randomized to placebo (PBO, N = 14), 5 mg/day ALN (N = 10), or 10 mg/day ALN (N = 6) for another 5 years. The parameters monitored and expressed as a function of tissue age were (i) the mineral/matrix ratio (MM), (ii) the relative proteoglycan content (PG), (iii) the relative lipid content (LPD), (iv) the mineral maturity/crystallinity (MMC), and (v) the relative pyridinoline content (PYD).

RESULTS

The obtained data indicate that 10-year ALN use results in minimal, transient bone tissue composition changes compared to use for 5 years, confined to actively forming trabecular surfaces, implying potential differences in bone matrix maturation that nevertheless did not result in differences of these values in bulk tissue.

CONCLUSIONS

The data suggest that prolonged reduction in bone turnover during 10 years of therapy with ALN by itself is unlikely to be associated with adverse effects on bone material properties.

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.

Vibrational spectroscopic imaging for the evaluation of matrix and mineral chemistry

Metabolic bone diseases manifesting fragility fractures (such as osteoporosis) are routinely diagnosed based on bone mineral density (BMD) measurements, and the effect of various therapies also evaluated based on the same outcome. Although useful, it is well recognized that this metric does not fully account for either fracture incidence or the effect of various therapies on fracture incidence, thus, the emergence of bone quality as a contributing factor in the determination of bone strength. Infrared and Raman vibrational spectroscopic techniques are particularly well-suited for the determination of bone quality as they provide quantitative and qualitative information of the mineral and organic matrix bone components, simultaneously. Through the use of microspectroscopic techniques, this information is available in a spatially resolved manner, thus, the outcomes may be easily correlated with outcomes from techniques such as histology, histomorphometry, and nanoindentation, linking metabolic status with material properties.

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.

Collagen modifications in postmenopausal osteoporosis: advanced glycation endproducts may affect bone volume, structure and quality

The classic model of postmenopausal osteoporosis (PM-OP) starts with the depletion of estrogen, which in turn stimulates imbalanced bone remodeling, resulting in loss of bone mass/volume. Clinically, this leads to fractures because of structural weakness. Recent work has begun to provide a more complete picture of the mechanisms of PM-OP involving oxidative stress and collagen modifications known as advanced glycation endproducts (AGEs). On one hand, AGEs may drive imbalanced bone remodeling through signaling mediated by the receptor for AGEs (RAGE), stimulating resorption and inhibiting formation. On the other hand, AGEs are associated with degraded bone material quality. Oxidative stress promotes the formation of AGEs, inhibits normal enzymatically derived crosslinking and can degrade collagen structure, thereby reducing fracture resistance. Notably, there are multiple positive feedback loops that can exacerbate the mechanisms of PM-OP associated with oxidative stress and AGEs. Anti-oxidant therapies may have the potential to inhibit the oxidative stress based mechanisms of this disease.

Transmenopausal changes in trabecular bone quality

Bone strength depends on its amount and quality. Bone quality includes its structural and material properties. Bone material properties are dependent on bone turnover rates. Remodeling rates are significantly increased immediately after menopause. In the present study, we used Raman microspectroscopic analysis of double iliac crest biopsies with a spatial resolution of 1 µm obtained before and immediately after menopause (1 year after cessation of menses) in healthy females to investigate changes in material properties attributable to menopause. In particular, the mineral/matrix ratio, the relative proteoglycan and lipid content, the mineral maturity/crystallinity, and the relative pyridinoline collagen cross-link content were determined in trabecular bone as a function of surface metabolic activity and tissue age. The results indicate that significant changes (specifically in mineral/matrix ratio) were evident at active bone forming surfaces, whereas the relative proteoglycan content was altered at resorbing surfaces. These changes were not accompanied by altered mineral content or quality as monitored by Raman microspectroscopic analysis.

B-vitamins and bone in health and disease: the current evidence

Osteoporosis, a metabolic skeletal disease characterised by decreased bone mass and increased fracture risk, is a growing public health problem. Among the various risk factors for osteoporosis, calcium and vitamin D have well-established protective roles, but it is likely that other nutritional factors are also implicated. This review will explore the emerging evidence supporting a role for certain B-vitamins, homocysteine and the 677 C → T polymorphism in the gene encoding the folate-metabolising enzyme methylenetetrahydrofolate reductase, in bone health and disease. The evidence, however, is not entirely consistent and as yet no clear mechanism has been defined to explain the potential link between B-vitamins and bone health. Coeliac disease, a common condition of malabsorption, induced by gluten ingestion in genetically susceptible individuals, is associated with an increased risk both of osteoporosis and inadequate B-vitamin status. Given the growing body of evidence linking low bone mineral density and/or increased fracture risk with low B-vitamin status and elevated homocysteine, optimal B-vitamin status may play an important protective role against osteoporosis in coeliac disease; to date, no trial has addressed this possible link.

Update on nutrients involved in maintaining healthy bone

Osteoporosis is a leading cause of morbidity and mortality in the elderly and influences quality of life, as well as life expectancy. Currently, there is a growing interest among the medical scientists in search of specific nutrients and/or bioactive compounds of natural origin for the prevention of disease and maintenance of bone health. Although calcium and vitamin D have been the primary focus of nutritional prevention of osteoporosis, a recent research has clarified the importance of several additional nutrients and food constituents. Based on this review of the literature, supplementation with vitamins B, C, K, and silicon could be recommended for proper maintenance of bone health, although further clinical studies are needed. The results of studies on long-chain polyunsaturated fatty acids, potassium, magnesium, copper, selenium, and strontium are not conclusive, although studies in vitro and in animal models are interesting and promising.

The ratio 1660/1690 cm(-1) measured by infrared microspectroscopy is not specific of enzymatic collagen cross-links in bone tissue

In postmenopausal osteoporosis, an impairment in enzymatic cross-links (ECL) occurs, leading in part to a decline in bone biomechanical properties. Biochemical methods by high performance liquid chromatography (HPLC) are currently used to measure ECL. Another method has been proposed, by Fourier Transform InfraRed Imaging (FTIRI), to measure a mature PYD/immature DHLNL cross-links ratio, using the 1660/1690 cm⁻¹ area ratio in the amide I band. However, in bone, the amide I band composition is complex (collagens, non-collagenous proteins, water vibrations) and the 1660/1690 cm⁻¹ by FTIRI has never been directly correlated with the PYD/DHLNL by HPLC. A study design using lathyritic rats, characterized by a decrease in the formation of ECL due to the inhibition of lysyl oxidase, was used in order to determine the evolution of 1660/1690 cm⁻¹ by FTIR Microspectroscopy in bone tissue and compare to the ECL quantified by HPLC. The actual amount of ECL was quantified by HPLC on cortical bone from control and lathyritic rats. The lathyritic group exhibited a decrease of 78% of pyridinoline content compared to the control group. The 1660/1690 cm⁻¹ area ratio was increased within center bone compared to inner bone, and this was also correlated with an increase in both mineral maturity and mineralization index. However, no difference in the 1660/1690 cm⁻¹ ratio was found between control and lathyritic rats. Those results were confirmed by principal component analysis performed on multispectral infrared images. In bovine bone, in which PYD was physically destructed by UV-photolysis, the PYD/DHLNL (measured by HPLC) was strongly decreased, whereas the 1660/1690 cm⁻¹ was unmodified. In conclusion, the 1660/1690 cm⁻¹ is not related to the PYD/DHLNL ratio, but increased with age of bone mineral, suggesting that a modification of this ratio could be mainly due to a modification of the collagen secondary structure related to the mineralization process.

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.

Enhancement of calcium/vitamin d supplement efficacy by administering concomitantly three key nutrients essential to bone collagen matrix for the treatment of osteopenia in middle-aged women: a one-year follow-up

Two vitamins and proline (CB₆Pro), three nutrients essential for bone collagen, were used in combination to a 1000 mg calcium/250 IU vitamin D (Ca/D) daily supplement to treat osteopenia as a preventive measure against osteoporosis later in life. Middle-aged women not using estrogen were screened for osteopenia using the WHO criteria and divided into three groups (n = 20 each): 1) placebo healthy controls with normal bone mineral density (BMD); 2) control Ca/D-treated osteopenic patients; and 3) Ca/D + CB₆Pro-treated osteopenic patients. The three groups were comparable at baseline except for BMD. After one-year treatment, cortical diaphyseal BMD remained constant in each group, but trabecular bone loss persisted (at 5 lumbar sites) in osteopenic group 2. No further bone loss was detected in osteopenic group 3. A loss of 2% was evidenced in the placebo group at one lumbar site. Markers of bone formation (which increase in coupling to resorption) decreased significantly in both osteopenic groups. Although biomarkers of resorption did not change, hormone (PTH and 1,25(OH)₂D₃)-induced osteoclastic activity was significantly reduced. No decline in BMD occurred at any bone site in osteopenic group 3, highlighting the importance of improving the quality of bone matrix concomitantly to mineral replacement.

Homocysteine levels and risk of hip fracture in postmenopausal women

BACKGROUND

Recent studies suggest that high homocysteine levels are associated with an increased risk of fractures. Homocysteine levels are known to be influenced by vitamin B and folate supply or status, and poor renal function can result in higher levels independent of nutritional adequacy.

OBJECTIVE

The aim of the study was to determine the associations between fasting homocysteine levels and incident hip fractures, and the effects of other factors on hip fracture risk.

DESIGN

We conducted a case-control study in the Women's Health Initiative Observational Study, a study of postmenopausal women (n = 93,676) recruited in the United States. We selected 400 incident cases of hip fracture and 400 controls matched on age, ethnicity, and blood draw date among women not on osteoporosis therapies. Outcome measures included physician-adjudicated, incident hip fractures. Baseline lifestyle and nutritional questionnaires were performed.

RESULTS

The risk of hip fracture increased 1.38-fold [95% confidence interval (CI), 1.14, 1.66] for each sd increase in serum homocysteine level after adjustment for fracture risk factors. This association was not affected by adjustment for dietary folate, B6, or B12 intake, but it diminished after adjustment for cystatin-C level (odds ratio, 1.08; 95% CI, 0.66-1.79), a measure of renal function not affected by muscle mass. Among women in the highest quartile of homocysteine and cystatin-C compared to those without elevations in either biomarker, the risk of hip fracture was substantially elevated (odds ratio, 2.8; 95% CI, 1.61-4.87).

CONCLUSIONS

This study indicates that high homocysteine levels are associated with an increased risk of hip fracture, which could be accounted for by poor renal function.

Bone tissue and hyperhomocysteinemia

Bone tissue quality is determined not only by multiple architectural variables, but also by the mechanical properties of collagen type 1. Homocysteinuria is a genetic disease whose manifestations include severe hyperhomocysteinemia and decreased bone strength. The effects of smaller homocysteine elevations on bone tissue are difficult to demonstrate in clinical studies. Studies in animals and in humans suggest that homocysteine may weaken collagen crosslinks and, if present in large amounts, interfere with bone remodeling. Whether routine homocysteine assays should be performed to detect bone frailty remains unclear. In clinical practice, the focus should be on identifying patients with potential causes of homocysteine elevation (e.g., medications), who should then be given vitamin D and folic acid supplementation if needed. This approach may improve not only bone health, but also vascular and general health.

Effects of PTH and alendronate on type I collagen isomerization in postmenopausal women with osteoporosis: the PaTH study

Fracture efficacy of PTH and alendronate (ALN) is only partly explained by changes in BMD, and bone collagen properties have been suggested to play a role. We analyzed the effects of PTH(1-84) and ALN on urinary alphaalpha/betabeta CTX ratio, a marker of type I collagen isomerization and maturation in postmenopausal women with osteoporosis. In the first year of the previously published PaTH study, postmenopausal women with osteoporosis were assigned to PTH(1-84) (100 microg/d; n = 119), ALN (10 mg/d; n = 60), or PTH and ALN together (n = 59). We analyzed patients on ALN alone (n = 60) and a similar number of patients assigned to PTH alone (n = 63). During the second year, women on PTH in the first year were reallocated to placebo (n = 31) or ALN (n = 32) and women with ALN continued on ALN. During the first year, there was no significant change in alphaalpha/betabeta CTX ratio with PTH or ALN. At 24 mo, there was a marked increase of the alphaalpha/betabeta CTX ratio in women who had received PTH during the first year, followed by a second year of placebo (median: +45.5, p < 0.001) or ALN (+55.2%, p < 0.001). Conversely, the alphaalpha/betabeta CTX ratio only slightly increased (+16%, p < 0.05) after 2 yr of continued ALN. In conclusion, treatment with PTH(1-84) for 1 yr followed by 1 yr of placebo or ALN may be associated with decreased type I collagen isomerization. The influence of these biochemical changes of type I collagen on bone fracture resistance remains to be studied.

Plasma B vitamins, homocysteine, and their relation with bone loss and hip fracture in elderly men and women

CONTEXT

Elevated homocysteine is a strong risk factor for osteoporotic fractures among elders, yet it may be a marker for low B-vitamin status.

OBJECTIVE

Our objective was to examine the associations of plasma concentrations of folate, vitamin B12, vitamin B6, and homocysteine with bone loss and hip fracture risk in elderly men and women.

DESIGN

This was a longitudinal follow-up study of the Framingham Osteoporosis Study.

SETTING

Community dwelling residents of Framingham, MA, were included in the study.

PARTICIPANTS

A total of 1002 men and women (mean age 75 yr) was included in the study.

MAIN OUTCOME MEASURES

Baseline (1987-1989) blood samples were used to categorize participants into plasma B-vitamin (normal, low, deficient) and homocysteine (normal, high) groups. Femoral neck bone mineral density (BMD) measured at baseline and 4-yr follow-up was used to calculate annual percent BMD change. Incident hip fracture was assessed from baseline through 2003.

RESULTS

Multivariable-adjusted mean bone loss was inversely associated with vitamin B6 (P for trend 0.01). Vitamins B12 and B6 were inversely associated with hip fracture risk (all P for trend < 0.05), yet associations were somewhat attenuated and not significant after controlling for baseline BMD, serum vitamin D, and homocysteine. Participants with high homocysteine (>14 micromol/liter) had approximately 70% higher hip fracture risk after adjusting for folate and vitamin B6, but this association was attenuated after controlling for vitamin B12 (hazard ratio = 1.49; 95% confidence interval 0.91, 2.46).

CONCLUSIONS

Low B-vitamin concentration may be a risk factor for decreased bone health, yet does not fully explain the relation between elevated homocysteine and hip fracture. Thus, homocysteine is not merely a marker for low B-vitamin status.

Collagen cross-linking influences osteoblastic differentiation

Osteoblasts synthesize collagen matrix, which itself regulates the differentiation of precursor cells into mature osteoblasts. They express lysyl oxidase (LOX), which is involved in the collagen cross-linking process. Lathyrogens, like ss-aminopropionitrile (ssAPN), inhibit the formation of a stable matrix. The aim of the present study was to investigate the influence of cross-linking on osteoblastic differentiation. MC3T3-E1 cells were seeded and treated with or without 400 muM ssAPN for 1 week. Thereafter, living cells were removed and, on this extracellular matrix, new MC3T3-E1 cells were seeded and cultured for 1 week without ssAPN. RNA was isolated, and expression of specific marker genes was determined by quantitative reverse transcription-polymerase chain reaction. Changes in specific cross-links after ssAPN treatment were measured with Fourier-transform infrared spectroscopy. The collagen matrix that formed showed a significant reduction of two major cross-links of bone collagen, deH-DHLNL and pyr, compared to control cultures. Gene expression studies showed an increase of collagen alpha1 (I) (COL1A1) to 150%. Expression of LOX and osteocalcin (OCN) mRNA was significantly downregulated to about 75%. When fresh MC3T3-E1 cells were seeded on this altered matrix without ssAPN, COL1A1 mRNA expression was upregulated (140%), OCN was downregulated (60%), and LOX mRNA expression remained unaffected. These results indicate that ssAPN treatment not only disrupts collagen cross-link formation but also affects osteoblastic activity and expression. In conclusion, the disrupted matrix produced in the presence of lathyrogen influences, even in its absence, the expression of osteoblastic genes.

Stimulation of osteoclast activity by low B-vitamin concentrations

BACKGROUND

Homocysteine (HCY) has recently been linked to fragility fractures. Moreover, HCY activates osteoclasts (OC). Elevated HCY concentrations are mainly caused by folate, vitamin B12 (B12) and B6 (B6) deficiencies. We hypothesized that folate, B12 and B6 deficiencies stimulate OC activity.

MATERIALS AND METHODS

OC were cultured from peripheral blood mononuclear cells (10 healthy male donors, 34+/-5 years) for 20 days. Culture medium was conditioned with decreasing concentrations of folate, B12 and B6 (in combination or variation of only one vitamin) starting at physiologic concentrations. Moreover, we tested increasing concentrations of HCY. OC activity was measured by dentine resorption activity (DRA), tartrate-resistant acid phosphatase (TRAP) and cathepsin K (CK) activity.

RESULTS

The combined reduction of folate, B12 and B6 stimulated DRA up to 211% (p<0.001). This observation was confirmed by TRAP (maximum increase 24%, p<0.001) and CK (maximum increase 24%, p<0.001). Reduction of only one vitamin stimulated DRA up to 250% (folate: maximum increase 248%, p<0.018; B12: maximum increase 252%, p<0.001, B6: maximum increase 247%, p<0.001). However, only for folate this effect could be confirmed by TRAP (maximum increase 33%, p<0.001). HCY stimulated DRA up to 395% (p<0.001). TRAP (maximum increase 49%, p<0.001) and CK analyses confirmed this observation (maximum increase 50%, p<0.001).

CONCLUSION

Our results demonstrate a strong stimulatory effect of low concentrations of folate, B12 and B6 on OC activity, suggesting a mechanistic role of low B-vitamin concentrations for bone degradation. Consequently, OC stimulation by low folate, B12 and B6 concentrations could be an important adverse factor for bone health.

B vitamins, homocysteine, and bone disease: epidemiology and pathophysiology

Observational studies indicate that mildly elevated homocysteine is a strong risk factor for osteoporotic fracture, yet there is no clear biologic mechanism for an effect of homocysteine on bone. The association could instead be attributed to B vitamins (folate, vitamin B(12), vitamin B(6)), as low levels of these nutrients are the primary determinants of homocysteine and may be associated with lower bone quality. Discovery of a direct effect of homocysteine or B vitamins on bone would be important in terms of interventions, as these factors can be modified with changes in diet or supplementation. This article reviews the connections of homocysteine and B vitamins to measures of bone quality and osteoporotic fracture. Although the literature suggests that these factors may be associated with bone health, most of the epidemiologic studies are observational, limiting conclusions regarding causality. More controlled -trials are needed to determine whether treatment with B vitamins would reduce fracture rates among community-dwelling cohorts.

Régime méditerranéen et ostéoporose

As a result of the demographic shift towards an ageing population, all industrialized countries face a growing prevalence of chronic age-related conditions, particularly osteoporosis. This multifaceted disease is defined as "a systemic skeletal disorder" characterised by low bone mass and micro-architectural deterioration of bone tissue, which results in increased bone fragility and susceptibility to fracture. Two main categories have been suggested: post-menopausal and senile osteoporosis. The prevention of osteoporosis through dietary means is especially challenging in technologically advanced societies. Indeed, within Europe, conspicuous differences are encountered in the severity of osteoporosis, the lowest incidence being reported in the Mediterranean area. The beneficial effect is attributed mainly to specific eating pattern. These food items contain a complex array of naturally occurring bioactive molecules with antioxidant, anti-inflammatory and alkalinising properties, that may contribute to the bone-sparing effect of Mediterranean diet.

Accretion of bone quantity and quality in the developing mouse skeleton

In this work, we found that bone mineral formation proceeded very rapidly in mice by 1 day of age, where the degree of mineralization, the tissue mineral density, and the mineral crystallinity reached 36%, 51%, and 87% of the adult values, respectively. However, even though significant mineralization had occurred, the elastic modulus of 1-day-old bone was only 14% of its adult value, indicating that the intrinsic stiffening of the bone lags considerably behind the initial mineral formation.

INTRODUCTION

To meet the mechanical challenges during early development, the skeleton requires the rapid accretion of bone quality and bone quantity. Here, we describe early bone development in the mouse skeleton and test the hypothesis that specific compositional properties determine the stiffness of the tissue.

MATERIALS AND METHODS

Tibias of female BALB mice were harvested at eight time-points (n = 4 each) distributed between 1 and 40 days of age and subjected to morphometric (muCT), chemical (Fourier transform infrared microspectroscopy), and mechanical (nanoindentation) analyses. Tibias of 450-day-old mice served as fully mineralized control specimens.

RESULTS

Bone growth proceeded very rapidly; at 1 day of age, the degree of mineralization (phosphate/protein ratio), the density of mineralized bone (TMD), and mineral crystallinity had reached 36%, 51%, and 87% of the adult (450 days) values, respectively. Spatially, the variability in mineralization across the mid-diaphysis was very high for the early time-points and declined over time. In contrast to the notable changes in mineralization, carbonate substitution into the mineral lattice (carbonate/phosphate ratio) and collagen cross-linking did not show any significant changes over this time period. Even though significant mineralization had occurred, the elastic modulus of 1-day-old bone was only 14% of the adult value and increased to 89% (of its adult value) after 40 days. Between samples of different time-points, significant positive correlations were observed between the elastic modulus and TMD (r(2) = 0.84), phosphate/protein ratio (r(2) = 0.59), and crystallinity (r(2) = 0.23), whereas collagen cross-linking showed a small but significant negative correlation (r(2) = 0.15).

CONCLUSIONS

These data indicate that specific chemical and morphometric properties modulate bone's stiffness during early growth. The intrinsic stiffening of the bone, however, lags considerably behind the initial mineral formation, emphasizing the importance of bone mineral quality for optimizing matrix integrity.

Low vitamin B6, and not plasma homocysteine concentration, as risk factor for abdominal aortic aneurysm: a retrospective case-control study

BACKGROUND

Hyperhomocysteinemia has been associated with vascular disease in many epidemiologic studies, but only a few have reported on the relation between hyperhomocysteinemia and aneurysms of the abdominal aorta (AAAs). Although these studies showed higher homocysteine concentrations in patients with AAA than in controls, little attention had been given to possible confounding factors. Most patients with AAA are of older age, have an impaired renal function, and have other risk factors for cardiovascular disease. This matched case-control study investigated the relation between homocysteine concentration (before and after methionine loading) and AAA, taking into account possible confounders such as age, sex, and concentrations of creatinine and B vitamins.

METHODS

Patients with a history of AAA were recruited from the outpatient clinic; 60% had already undergone surgery for their AAA. They were asked to invite a friend or neighbor to participate as a control subject (age-matched and sex-matched). Concentrations of homocysteine, vitamin B6, vitamin B12, folate, and creatinine were determined in the fasting state, and blood was taken for methylenetetrahydrofolate reductase (MTHFR) mutation analysis. Six hours after oral methionine loading, the postmethionine load homocysteine concentration was determined.

RESULTS

Univariate analysis showed an odds ratio (OR) of 2.2 (95% confidence interval (CI), 0.9 to 5.5) for the risk of AAA for the highest quartile of homocysteine concentration. After adjustment for creatinine, the OR was markedly reduced to 1.24 (95% CI, 0.42 to 3.66), and this risk further attenuated in the multivariate analysis. Univariate analysis of the B vitamins showed an increased risk of AAA for the bottom quartile of vitamin B6 (OR, 3.75; 95% CI, 1.22 to 11.54), which even increased after adjustments. The relative risk associated with the MTHFR 677TT polymorphism was 2.1 (95% CI, 0.9 to 5.3).

CONCLUSION

Vitamin B6, but not homocysteine, is an independent risk factor for AAA. The role of vitamin B6 in the pathogenesis of AAA needs to be further elucidated.

FT-IR imaging of native and tissue-engineered bone and cartilage

Fourier transform infrared (FT-IR) imaging and microspectroscopy have been extensively applied to the analyses of tissues in health and disease. Spatially resolved mid-IR data has provided insights into molecular changes that occur in diseases of connective or collagen-based tissues, including, osteoporosis, osteogenesis imperfecta, osteopetrosis and pathologic calcifications. These techniques have also been used to probe chemical changes associated with load, disuse, and micro-damage in bone, and with degradation and repair in cartilage. This review summarizes the applications of FT-IR microscopy and imaging for analyses of bone and cartilage in healthy and diseased tissues, and illustrates the application of these techniques for the characterization of tissue-engineered bone and cartilage.

Contribution of the advanced glycation end product pentosidine and of maturation of type I collagen to compressive biomechanical properties of human lumbar vertebrae

Collagen characteristics contribute to bone biomechanical properties. Yet, few studies have analyzed the independent contributions of bone mineral density (BMD) and post-translational modifications of type I collagen to whole bone strength. Thus, the aim of this study was to determine the relative contributions of BMD and both enzymatic and non-enzymatic collagen crosslink concentration to the biomechanical properties of human vertebrae. Nineteen L3 vertebrae were collected after necropsy (age 26-93; 10 males, 9 females). BMD of the vertebral body was measured by DXA, and the vertebrae were compressed to failure to assess the stiffness, failure load and work to fracture. After mechanical testing, the concentration of both enzymatic crosslinks pyridinoline (PYD), and deoxypyridinoline (DPD) as well as, and the non-enzymatic crosslinks pentosidine (PEN) were analyzed in trabecular and cortical bone by reversed-phase HPLC. The extent of aspartic acid isomerization of type I collagen C telopeptide (CTX) was evaluated by ELISA of native (alpha CTX) and isomerized (beta CTX) forms. BMD was significantly positively related with stiffness (R(2) = 0.74; P < 0.0001), failure load (R(2) = 0.69; P < 0.0001) and work to fracture (R(2) = 0.44; P = 0.002). Bivariate regression analysis showed no association between collagen traits and biomechanical properties. However, in a multiple regression model, BMD and trabecular PEN were both significantly associated with failure load and work to fracture (multiple R(2) = 0.83, P = 0.001 and R(2) = 0.67, P = 0.001, respectively). Similarly, BMD and trabecular alpha/beta CTX ratio were both associated with stiffness (multiple R(2) = 0.83, P = 0.015). These findings indicate that post-translational modifications of type I collagen have an impact on skeletal fragility.

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

INTRODUCTION

Diabetes is associated with an increased risk of fracture, although type 2 diabetes is often characterized by normal bone mineral density (BMD). Enzymatic and glycation-induced non-enzymatic cross-links play important roles in the expression of bone strength. The serum vitamin B6 concentration is lower in patients with diabetes than in healthy controls. The aim our study was to see if spontaneously diabetic WBN/Kob rats in the pre- and post-onset of diabetes would serve as a suitable model for studying the pathogenesis of the susceptibility to fracture in diabetes without the reduction of bone mineral density. Seventy male WBN/Kob rats were obtained at the ages of 1 to 18 months.

METHODS

Seventy normal male Wistar rats were used as the non-diabetic, age-matched control. The contents of enzymatic cross-links (dihydroxylysinonorleucine, hydroxylysinonorleucine, lysinonorleucine, pyridinoline and deoxypyridinoline) and non-enzymatic cross-links (pentosidine) were determined in femoral bone. We also analyzed the serum concentration of vitamin B6 (pyridoxal and pyridoxamine), femoral BMD and a three-point bending test of the femur.

RESULTS

A low level of serum vitamin B6 was associated with a decrease in enzymatic crosslinking in bone during the subclinical diabetes stage. After the onset of diabetes, there was a steady decrease in enzymatic cross-links and a steep increase in pentosidine. Furthermore, impaired bone mechanical properties in the WBN/Kob rats despite the lack of reduction in BMD coincided with impaired enzymatic cross-link formation and increases in glycation-induced pentosidine.

CONCLUSIONS

These results indicate that the alteration of enzymatic and non-enzymatic crosslinking in bone could be important for explaining the variation of fracture susceptibility in diabetes.

Bone material properties in trabecular bone from human iliac crest biopsies after 3- and 5-year treatment with risedronate

Long-term effects of risedronate on bone mineral maturity/crystallinity and collagen cross-link ratio in triple iliac crest biopsies of osteoporotic women were evaluated. In this double-blinded study, 3- and 5-year treatment with risedronate arrested the tissue aging encountered in untreated osteoporosis and in osteoporosis treated with other antiresorptives. This effect may be contributing to risedronate's antifracture efficacy.

INTRODUCTION

Risedronate is widely used in the treatment of osteoporosis. It reduces bone turnover, increases BMD, and decreases fracture risk. To date, there are no data available on the long-term effects of risedronate on bone material properties in humans.

MATERIALS AND METHODS

Osteoporotic women enrolled in the VERT-NA trial received either risedronate (5 mg/day, orally) or placebo for up to 5 years. All subjects received calcium. They also received vitamin D supplementation if deficient at baseline. Triple iliac crest biopsies were collected from a subset of these subjects at baseline, 3 years, and 5 years. Mineral maturity/crystallinity and collagen cross-link ratio was measured in these biopsies using Fourier transform infrared imaging.

RESULTS

Patients that received placebo exhibited increased mineral maturity/crystallinity and collagen cross-link ratio after 3 and 5 years compared with baseline values. On the contrary, patients that received risedronate retained baseline values in both bone material indices throughout. A more spatially detailed analysis revealed that this was achieved mainly through beneficial effects on active bone-forming areas. Surprisingly, patients that received risedronate achieved premenopausal values at bone-forming areas in both indices after 5 years of treatment.

CONCLUSION

Long-term treatment with risedronate affects bone material properties (mineral maturity/crystallinity and collagen cross-link ratio) and arrests the tissue aging apparent in untreated osteoporosis. These changes at the material level of the bone matrix may contribute to risedronate's rapid and sustained antifracture efficacy in osteoporotic patients.

Degree of mineralization-related collagen crosslinking in the femoral neck cancellous bone in cases of hip fracture and controls

Based on the present definition of osteoporosis, both bone density and quality are important factors in the determination of bone strength. Collagen crosslinking is a determinant of bone quality. Cross-links can form enzymatically by the action of lysyl oxidase or non-enzymatically, resulting in advanced glycation end products. Collagen crosslinking is affected by tissue maturation as well as the degree of mineralization. Homocysteine and vitamin B6 (pyridoxal) are also regulatory factors of collagen crosslinking. We elucidate the relationship between the degree of mineralization and collagen cross-links in cancellous bone from hip fracture cases. We also determined plasma levels of homocysteine and pyridoxal. Twenty-five female intracapsular hip fracture cases (78 +/- 6 years) and 25 age-matched postmortem controls (77 +/- 6 years) were included in this study. Collagen crosslinking was analyzed after each bone specimen was fractionated into low (1.7-2.0 g/ml) and high (>2.0 g/ml) density fractions. The content of enzymatic (immature reducible and mature nonreducible cross-links) and nonenzymatic cross-link (pentosidine) were determined. In the controls, there was no difference in total enzymatic cross-links between low and high density bone, while pentosidine content was significantly higher in high density bone. In the fracture cases, not only reduced enzymatic cross-links in high density bone and increased pentosidine in both low and high density bone, but also higher plasma homocysteine and lower pyridoxal levels were evident compared with the controls. These results indicate that detrimental crosslinking in both low and high mineralized bone result in impaired bone quality in osteoporotic patients.

Reductions in degree of mineralization and enzymatic collagen cross-links and increases in glycation-induced pentosidine in the femoral neck cortex in cases of femoral neck fracture

INTRODUCTION

Enzymatic and glycation-induced nonenzymatic cross-links play important roles in the expression of bone strength. The cross-link pattern is affected by tissue maturation and senescence. The aim of our study was to understand the distinctive posttranslational modifications of collagen in areas with different degrees of mineralization with and without hip fracture.

METHODS

Sixteen female cases of intracapsular hip fracture (78+/-6 years) and 16 age- and gender-matched postmortem controls (76+/-6 years) were included in this study. A sample of each femoral neck cortex was fractionated into low (1.7 to 2.0 g/ml) and high (>2.0 g/ml) density portions. The contents of enzymatic cross-links (dihydroxylysinonorleucine, hydroxylysinonorleucine, lysinonorleucine, pyridinoline, and deoxypyridinoline) and nonenzymatic cross-links (pentosidine) and the extent of lysine (Lys) hydroxylation were determined in each fraction.

RESULTS

In the controls, there was no significant difference in the contents of enzymatic cross-links between low- and high-mineralized bone fractions whereas pentosidine content was significantly higher in high-mineralized bone compared with low-mineralized bone (p=0.0014). When comparing enzymatic cross-link contents between controls and fracture cases, a trend toward lower (p=0.0961) cross-link content in low-mineralized bone and a significant reduction (p<0.0001) in high-mineralized bone were observed. Pentosidine content of low-mineralized bone was significantly higher in fracture cases than in controls (p<0.0001). The extent of Lys hydroxylation was significantly higher in fracture cases than in controls (p<0.001). The higher hydroxylation of Lys in collagen from fracture cases relative to controls was associated with significantly higher values of hydroxylysine-derived cross-link such that the enzymatic cross-link patterns correlated with the extent of Lys hydroxylation in the collagen molecules.

CONCLUSIONS

These results suggest that reductions in the degree of mineralization and enzymatic cross-links and excessive formation of pentosidine may play an important role in explaining poor bone quality in osteoporosis.

The role of collagen in bone strength

Bone is a complex tissue of which the principal function is to resist mechanical forces and fractures. Bone strength depends not only on the quantity of bone tissue but also on the quality, which is characterized by the geometry and the shape of bones, the microarchitecture of the trabecular bones, the turnover, the mineral, and the collagen. Different determinants of bone quality are interrelated, especially the mineral and collagen, and analysis of their specific roles in bone strength is difficult. This review describes the interactions of type I collagen with the mineral and the contribution of the orientations of the collagen fibers when the bone is submitted to mechanical forces. Different processes of maturation of collagen occur in bone, which can result either from enzymatic or nonenzymatic processes. The enzymatic process involves activation of lysyl oxidase, which leads to the formation of immature and mature crosslinks that stabilize the collagen fibrils. Two type of nonenzymatic process are described in type I collagen: the formation of advanced glycation end products due to the accumulation of reducible sugars in bone tissue, and the process of racemization and isomerization in the telopeptide of the collagen. These modifications of collagen are age-related and may impair the mechanical properties of bone. To illustrate the role of the crosslinking process of collagen in bone strength, clinical disorders associated with bone collagen abnormalities and bone fragility, such as osteogenesis imperfecta and osteoporosis, are described.

Bone mineral density, chemical composition and biomechanical properties of the tibia of female rats exposed to cadmium since weaning up to skeletal maturity

The influence of exposure to cadmium (Cd) during skeletal development on the risk of bone fractures at the stage of skeletal maturity was investigated on a female rat model of human exposure. The tibias of rats treated with 1, 5 or 50 mg Cd/l in drinking water for 3, 6, 9 and 12 months (since weaning) were used. The exposure to Cd dose- and time-dependently influenced the tibia bone mineral density (BMD) and chemical composition. In skeletally matured animals, at each level of the exposure to Cd, the BMD at the whole tibia and its diaphysis as well as the percentage of minerals content in the bone, including the content of zinc, copper and iron, were decreased compared to control. Moreover, in the 50 mg Cd/l group, the percentage of organic components content increased. The Cd-induced changes, at all levels of exposure, resulted in weakening in the yield strength and fracture strength of the tibia (a three-point bending test of the diaphysis and compression test with vertical loading) of the skeletally matured females. A very important and clinically useful finding of this study is that a decrease (even by several percent) in the tibia BMD results in weakness in the bone biomechanical properties and that the BMD may predict the risk of its fracture at the exposure to Cd. Moreover, the results together with our previous findings seem to suggest that tibia, due to higher vulnerability of its diaphysis, compared to the femoral diaphysis, to damage by Cd may be more useful than femur to investigate the effect of Cd on the cortical bone. The present study revealed that a low exposure to Cd (1 mg Cd/l), corresponding to low human environmental exposure, during the skeletal development affects the tibia mineral status leading to weakening in its mechanical properties at the skeletal maturity. The findings allow for the conclusion that environmental exposure to Cd during childhood and adolescence may enhance the risk of low BMD and fractures at adulthood.

Expression of lysyl oxidase isoforms in MC3T3-E1 osteoblastic cells

Covalent intermolecular cross-linking of collagen is initiated by the action of lysyl oxidase (LOX) on the telopeptidyl lysine and hydroxylysine residues. Recently, several LOX isoforms, i.e., LOX-like proteins 1-4 (LOXL1-4), have been identified but their specific tissue distribution and functions are still largely unknown. In this study, mRNA expression of LOX and LOXL1-4 in MC3T3-E1 osteoblastic cells was screened by RT-PCR and quantitatively analyzed by real-time PCR during cell differentiation and matrix mineralization. The results demonstrated that LOX and all LOXLs, except LOXL2, were expressed in this cell line and that the expression pattern during cell differentiation and matrix mineralization was distinct from one another. This indicates that the expression of LOX and its isoforms is highly regulated during osteoblast differentiation, suggesting their distinct roles in collagen matrix stabilization and subsequent mineralization.

Homocysteine – a newly recognised risk factor for osteoporosis

Osteoporosis is a widespread problem, which frequently has devastating health consequences through its association with fragility fractures. The total number of fractures, and hence the cost to society, will increase dramatically over the next 50years as a result of demographic changes in the number of elderly people. Thus, prevention of osteoporosis by identifying risk factors or risk indicators, as well as the development of new treatment strategies, are major issues. Recent data suggest that homocysteine (Hcy), folate, vitamin B

Effects of long-term dietary lipids on mature bone mineral content, collagen, crosslinks, and prostaglandin E2 production in Japanese quail

This study investigated the effects of long-term dietary lipids on mature bone mineral content, collagen concentration, crosslink levels, bone marrow and ex vivo prostaglandin E2 (PGE2) biosynthesis, as well as the relationship of PGE2 production to these bone formation parameters. One-month-old male Japanese quail were given a basal diet containing 1 of 4 lipid sources: soybean oil (SBO), hydrogenated soybean oil (HSBO), chicken fat (CF), or menhaden fish oil (FO) at 50 g/kg of the diet. At 8 mo of age, lipid treatments did not affect bone length, diameter, or weight in quail. Quail fed SBO or CF had significantly lower levels of mineral content in tibial bones compared with those given FO. Bone collagen level was significantly higher in quail consuming SBO than those given HSBO or CF. Collagen crosslink concentration was markedly increased in birds provided FO or HSBO compared with those fed SBO or CF. Prostaglandin E2 biosynthesis in bone organ culture and marrow were greatly increased in quail maintained on the SBO or CF diet compared with those given the FO or HSBO diet. Prostaglandin E2 production in the bone microenvironment was negatively correlated with tibial ash and collagen crosslinks but had a positive correlation with tibial collagen levels. These results support our previous findings that long-term exposure to diets high in SBO or CF impaired mature bone mechanical properties and histological characteristics. Further, the results suggest that long-term supplementation of SBO or CF in the diet had a significant adverse effect on mature bone metabolism, and that dietary lipids altered bone metabolism, perhaps partially by controlling the production of local regulatory factor in bone.