Spine bone texture assessed by trabecular bone score (TBS) predicts osteoporotic fractures in men: The Manitoba Bone Density Program.

INTRODUCTION: One quarter of osteoporotic fractures occur in men. TBS, a gray-level measurement derived from lumbar spine DXA image texture, is related to microarchitecture and fracture risk independently of BMD. Previous studies reported the ability of spine TBS to predict osteoporotic fractures in women. Our aim was to evaluate the ability of TBS to predict clinical osteoporotic fractures in men. METHODS: 3620 men aged ≥50 (mean 67.6years) at the time of baseline DXA (femoral neck, spine) were identified from a database (Province of Manitoba, Canada). Health service records were assessed for the presence of non-traumatic osteoporotic fracture after BMD testing. Lumbar spine TBS was derived from spine DXA blinded to clinical parameters and outcomes. We used Cox proportional hazard regression to analyze time to first fracture adjusted for clinical risk factors (FRAX without BMD), osteoporosis treatment and BMD (hip or spine). RESULTS: Mean followup was 4.5years. 183 (5.1%) men sustain major osteoporotic fractures (MOF), 91 (2.5%) clinical vertebral fractures (CVF), and 46 (1.3%) hip fractures (HF). Correlation between spine BMD and spine TBS was modest (r=0.31), less than correlation between spine and hip BMD (r=0.63). Significantly lower spine TBS were found in fracture versus non-fracture men for MOF (p<0.001), HF (p<0.001) and CVF (p=0.003). Area under the receiver operating characteristic curve (AUC) for incident fracture discrimination with TBS was significantly better than chance (MOF AUC=0.59, p<0.001; HF AUC=0.67, p<0.001; CVF AUC=0.57, p=0.032). TBS predicted MOF and HF (but not CVF) in models adjusted for FRAX without BMD and osteoporosis treatment. TBS remained a predictor of HF (but not MOF) after further adjustment for hip BMD or spine BMD. CONCLUSION: We observed that spine TBS predicted MOF and HF independently of the clinical FRAX score, HF independently of FRAX and BMD in men. Studies with more incident fractures are needed to confirm these findings.

Partnership for fragility bone fracture care provision and prevention program (P4Bones): study protocol for a secondary fracture prevention pragmatic controlled trial.

ABSTRACT: BACKGROUND: Fractures associated with bone fragility in older adults signal the potential for secondary fracture. Fragility fractures often precipitate further decline in health and loss of mobility, with high associated costs for patients, families, society and the healthcare system. Promptly initiating a coordinated, comprehensive pharmacological bone health and falls prevention program post-fracture may improve osteoporosis treatment compliance; and reduce rates of falls and secondary fractures, and associated morbidity, mortality and costs.Methods/design: This pragmatic, controlled trial at 11 hospital sites in eight regions in Quebec, Canada, will recruit community-dwelling patients over age 50 who have sustained a fragility fracture to an intervention coordinated program or to standard care, according to the site. Site study coordinators will identify and recruit 1,596 participants for each study arm. Coordinators at intervention sites will facilitate continuity of care for bone health, and arrange fall prevention programs including physical exercise. The intervention teams include medical bone specialists, primary care physicians, pharmacists, nurses, rehabilitation clinicians, and community program organizers.The primary outcome of this study is the incidence of secondary fragility fractures within an 18-month follow-up period. Secondary outcomes include initiation and compliance with bone health medication; time to first fall and number of clinically significant falls; fall-related hospitalization and mortality; physical activity; quality of life; fragility fracture-related costs; admission to a long term care facility; participants' perceptions of care integration, expectations and satisfaction with the program; and participants' compliance with the fall prevention program. Finally, professionals at intervention sites will participate in focus groups to identify barriers and facilitating factors for the integrated fragility fracture prevention program.This integrated program will facilitate knowledge translation and dissemination via the following: involvement of various collaborators during the development and set-up of the integrated program; distribution of pamphlets about osteoporosis and fall prevention strategies to primary care physicians in the intervention group and patients in the control group; participation in evaluation activities; and eventual dissemination of study results.Study/trial registration: Clinical Trial.Gov NCT01745068Study ID number: CIHR grant # 267395.

Revisiting sodium and water reabsorption with functional genomics tools.

PURPOSE OF REVIEW: The kidney plays an essential role in maintaining sodium and water balance, thereby controlling the volume and osmolarity of the extracellular body fluids, the blood volume and the blood pressure. The final adjustment of sodium and water reabsorption in the kidney takes place in cells of the distal part of the nephron in which a set of apical and basolateral transporters participate in vectorial sodium and water transport from the tubular lumen to the interstitium and, finally, to the general circulation. According to a current model, the activity and/or cell-surface expression of these transporters is/are under the control of a gene network composed of the hormonally regulated, as well as constitutively expressed, genes. It is proposed that this gene network may include new candidate genes for salt- and water-losing syndromes and for salt-sensitive hypertension. A new generation of functional genomics techniques have recently been applied to the characterization of this gene network. The purpose of this review is to summarize these studies and to discuss the potential of the different techniques for characterization of the renal transcriptome. RECENT FINDINGS: Recently, DNA microarrays and serial analysis of gene expression have been applied to characterize the kidney transcriptome in different in-vivo and in-vitro models. In these studies, a set of new interesting genes potentially involved in the regulation of sodium and water reabsorption by the kidney have been identified and are currently under detailed investigation. SUMMARY: Characterization of the kidney transcriptome is greatly expanding our knowledge of the gene networks involved in multiple kidney functions, including the maintenance of sodium and water homeostasis.

Spine trabecular bone score subsequent to bone mineral density improves fracture discrimination in women.

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is used to diagnose osteoporosis and assess fracture risk. However, DXA cannot evaluate trabecular microarchitecture. This study used a novel software program (TBS iNsight; Med-Imaps, Geneva, Switzerland) to estimate bone texture (trabecular bone score [TBS]) from standard spine DXA images. We hypothesized that TBS assessment would differentiate women with low trauma fracture from those without. In this study, TBS was performed blinded to fracture status on existing research DXA lumbar spine (LS) images from 429 women. Mean participant age was 71.3 yr, and 158 had prior fractures. The correlation between LS BMD and TBS was low (r = 0.28), suggesting these parameters reflect different bone properties. Age- and body mass index-adjusted odds ratios (ORs) ranged from 1.36 to 1.63 for LS or hip BMD in discriminating women with low trauma nonvertebral and vertebral fractures. TBS demonstrated ORs from 2.46 to 2.49 for these respective fractures; these remained significant after lowest BMD T-score adjustment (OR = 2.38 and 2.44). Seventy-three percent of all fractures occurred in women without osteoporosis (BMD T-score > -2.5); 72% of these women had a TBS score below the median, thereby appropriately classified them as being at increased risk. In conclusion, TBS assessment enhances DXA by evaluating trabecular pattern and identifying individuals with vertebral or low trauma fracture. TBS identifies 66-70% of women with fracture who were not classified with osteoporosis by BMD alone.

Bone propeller flap: a staged procedure.

The ideal reconstruction technique for complex defects of the lower limb consists of replacing tissue with similar tissue in an attempt to achieve a good functional result. A 23-year-old white male sustained a crush injury with a grade IIIB open ankle dislocation. After open reduction and fixation, the patient developed severe osteomyelitis at the tibiotalar joint requiring a staged and radical debridement with a substantial combined soft tissue and bony defect over the distal tibia, fibula, and talus area. The reconstructive approach consisted of a modified model of the propeller flap, implementing the spare part concept in a 2-stage procedure using a prefabricated and vascularized "double-barrel" fibular graft. At 17 months postoperatively, a plain radiograph showed bony union with complete and stable coverage of the soft tissue defect. The patient was fully weightbearing. In conclusion, there is evidence to suggest that the established concept of a soft tissue propeller flap can be implemented on bone.

Proliferative and Osteogenic Differentiation Potentials of Human Fetal Bone Cells

BACKGROUND. Human primary fetal bone cells (hFBC) are being characterized for use in bone tissue regeneration. Unlike human mesenchymal stem cells (hMSC), hFBC are partially differentiated with high expansion and regeneration potential. To date, proliferative and osteoblastic differentiation capacities of fetal bone cells remain poorly examined. The goal of this study was to define an environmental culture conditions for optimal proliferation and production of extracellular bone matrix leading to efficient bone repair. METHODS. Human primary FBC derived from our dedicated, consistent banks of bone cells comprising several fetal donors. For proliferation study, monolayer cultures of both cell types were expanded in DMEM or α- MEM media. Osteoblastic differentiation potentials of both hFBC and hMSC were evaluated through RT-PCR. Regulation of osteogenic differentiation by protein ligands Wnt3a and Wnt5a was studied by ALP enzymatic activity measurement. RESULTS. Evaluation of the proliferation rate demonstrated that hFBC proliferated more rapidly in α-MEM medium. Regarding growth factors that could stimulate cell proliferation rate, we observed that PDGF, FGF2 and Wnt3a had positive effects on proliferation of hFBC. Gene expression analysis demonstrated a higher expression of runx2 in hFBC cultured in basal conditions, which was was similar than that was observed in hMSC in osteoinductive culture conditions. Expression of sox9 was very low in hBFC and hMSC, compared to expression observed in fetal cartilage cells. Looking at osteogenic differentiation capacity, ALP activity was positively regulated byWnt5awhen hFBCwere cultured inα-MEM, but not in DMEM. Conversely, Wnt3a was shown to block the effect of osteogenic inductors on differentiation of both cell types. CONCLUSION. Data presented in this study indicate that the proliferation and differentiation of fetal and mesenchymal stem cells is optimal in α- MEM. Evidence for a pre-differentiated state of hBFC was given by extracellular matrix spontaneous mineralization as well as by higher ALP activity levels observed for these cells in baseline culture conditions, in comparison with hMSC. As we showed that, in vitro, hFBC express a higher capacity to differentiate in osteoblasts, they represent an attractive and promising prospect for fundamental research, and specifically for a new generation of skeletal tissue engineering.

Effects of anti-resorptive agents on trabecular bone score (TBS) in older women.

We evaluated the longitudinal effects of anti-resorptive agents (534 treated women vs. 1,150 untreated) on lumbar spine bone mineral density (BMD) and trabecular bone score (TBS). TBS was responsive to treatment in women over age 50. The treatment-related increase in TBS was less than the increase in BMD, which is consistent with bone texture preservation. INTRODUCTION: In addition to inducing an increase in BMD, anti-resorptive agents also help to preserve bone architecture. TBS, a new gray-level texture measurement, correlates with 3D parameters of bone micro-architecture independent of BMD. Our objective was to evaluate the longitudinal effects of anti-resorptive agents on lumbar spine BMD and TBS. METHODS: Women (≥50 years), from the BMD program database for the province of Manitoba, Canada, who had not received any anti-resorptive drug prior to their initial dual X-ray absorptiometry (DXA) exam were divided into two groups: untreated, those without any anti-resorptive drug over the course of follow-up, and treated, those with a non-estrogen anti-resorptive drug (86 % bisphosphonates, 10 % raloxifene, and 4 % calcitonin). Lumbar spine TBS was calculated for each lumbar spine DXA examination. Changes in TBS and BMD between baseline and follow-up (mean follow-up 3.7 years), expressed in percentage per year, were compared between the two groups. RESULTS: A total of 1,150 untreated women and 534 treated women met the inclusion criteria. Only a weak correlation was seen between BMD and TBS in either group. Significant intergroup differences in BMD change and TBS change were observed over the course of follow-up (p < 0.001). Similar mean decreases in BMD and TBS (-0.36 %/year and -0.31 %/year, respectively) were seen for untreated subjects (both p < 0.001). Conversely, treated subjects exhibited a significant mean increase in BMD (+1.86 %/year, p < 0.002) and TBS (+0.20 %/year, p < 0.001). CONCLUSION: TBS is responsive to treatment with non-estrogen anti-resorptive drug therapy in women over age 50. The treatment-related increase in TBS is less than the increase in BMD, which is consistent with bone texture preservation.

TBS (Trabecular Bone Score) is More Sensitive Than BMD to Diabetes-Related Fracture Risk

Background:Type 2 diabetes (T2D) is associated with increased fracture risk but paradoxically greater BMD. TBS (trabecular bone score), a novel grey-level texture measurement extracted from DXA images, correlates with 3D parameters of bone micro-architecture. We evaluated the ability of lumbar spine (LS) TBS to account for the increased fracture risk in diabetes. Methods:29,407 women ≥50 years at the time of baseline hip and spine DXA were identified from a database containing all clinical BMD results for the Province of Manitoba, Canada. 2,356 of the women satisfied a well-validated definition for diabetes, the vast majority of whom (>90%) would have T2D. LS L14 TBS was derived for each spine DXA examination blinded to clinical parameters and outcomes. Health service records were assessed for incident non-traumatic major osteoporotic fracture codes (mean follow-up 4.7 years). Results:In linear regression adjusted for FRAX risk factors (age,BMI, glucocorticoids, prior major fracture, rheumatoid arthritis, COPD as a smoking proxy, alcohol abuse) and osteoporosis therapy, diabetes was associated with higher BMD for LS, femoral neck and total hip but lower LS TBS (all p<0.001). Similar results were seen after excluding obese subjects withBMI>30. In logistic regression (Figure), the adjusted odds ratio (OR) for a skeletal measurement in the lowest vs highest tertile was less than 1 for all BMD measurements but increased for LS TBS (adjusted OR 2.61, 95%CI 2.30-2.97). Major osteoporotic fractures were identified in 175 (7.4%) with and 1,493 (5.5%) without diabetes (p < 0.001). LS TBS predicted fractures in those with diabetes (adjusted HR 1.27, 95%CI 1.10-1.46) and without diabetes (HR 1.31, 95%CI 1.24-1.38). LS TBS was an independent predictor of fracture (p<0.05) when further adjusted for BMD (LS, femoral neck or total hip). The explanatory effect of diabetes in the fracture prediction model was greatly reduced when LS TBS was added to the model (indicating that TBS captured a large portion of the diabetes-associated risk), but was paradoxically increased from adding any of the BMD measurements. Conclusions:Lumbar spine TBS is sensitive to skeletal deterioration in postmenopausal women with diabetes, whereas BMD is paradoxically greater. LS TBS predicts osteoporotic fractures in those with diabetes, and captures a large portion of the diabetes-associated fracture risk. Combining LS TBS with BMD incrementally improves fracture prediction.

Bone mineral density (BMD), micro-architecture estimation (TBS) and vertebral fracture assessment (VFA) extracted from a single DXA device in combination with clinical risk factors improve significantly the identification of women at high risk of fracture.

Osteoporosis (OP) is a systemic skeletal disease characterized by a low bone mineral density (BMD) and a micro-architectural (MA) deterioration. Clinical risk factors (CRF) are often used as a MA approximation. MA is yet evaluable in daily practice by the trabecular bone score (TBS) measure. TBS is very simple to obtain, by reanalyzing a lumbar DXA-scan. TBS has proven to have diagnosis and prognosis values, partially independent of CRF and BMD. The aim of the OsteoLaus cohort is to combine in daily practice the CRF and the information given by DXA (BMD, TBS and vertebral fracture assessment (VFA)) to better identify women at high fracture risk. The OsteoLaus cohort (1400 women 50 to 80 years living in Lausanne, Switzerland) started in 2010. This study is derived from the cohort COLAUS who started in Lausanne in 2003. The main goal of COLAUS is to obtain information on the epidemiology and genetic determinants of cardiovascular risk in 6700 men and women. CRF for OP, bone ultrasound of the heel, lumbar spine and hip BMD, VFA by DXA and MA evaluation by TBS are recorded in OsteoLaus. Preliminary results are reported. We included 631 women: mean age 67.4 ± 6.7 years, BMI 26.1 ± 4.6, mean lumbar spine BMD 0.943 ± 0.168 (T-score − 1.4 SD), and TBS 1.271 ± 0.103. As expected, correlation between BMD and site matched TBS is low (r2 = 0.16). Prevalence of VFx grade 2/3, major OP Fx and all OP Fx is 8.4%, 17.0% and 26.0% respectively. Age- and BMI-adjusted ORs (per SD decrease) are 1.8 (1.2-2.5), 1.6 (1.2-2.1), and 1.3 (1.1-1.6) for BMD for the different categories of fractures and 2.0 (1.4-3.0), 1.9 (1.4-2.5), and 1.4 (1.1-1.7) for TBS respectively. Only 32 to 37% of women with OP Fx have a BMD < − 2.5 SD or a TBS < 1.200. If we combine a BMD < − 2.5 SD or a TBS < 1.200, 54 to 60% of women with an osteoporotic Fx are identified. As in the already published studies, these preliminary results confirm the partial independence between BMD and TBS. More importantly, a combination of TBS subsequent to BMD increases significantly the identification of women with prevalent OP Fx which would have been misclassified by BMD alone. For the first time we are able to have complementary information about fracture (VFA), density (BMD), micro- and macro architecture (TBS and HAS) from a simple, low ionizing radiation and cheap device: DXA. Such complementary information is very useful for the patient in the daily practice and moreover will likely have an impact on cost effectiveness analysis.

Bone marrow-derived cells are implicated as a source of lymphatic endothelial progenitors in human breast cancer.

Bone marrow-derived endothelial progenitor cells (EPCs) infiltrate into sites of neovascularization in adult tissues and mature into functional blood endothelial cells (BECs) during a process called vasculogenesis. Human marrow-derived EPCs have recently been reported to display a mixed myeloid and lymphatic endothelial cell (LEC) phenotype during inflammation-induced angiogenesis; however, their role in cancer remains poorly understood. We report the in vitro differentiation of human cord blood CD133(+)CD34(+) progenitors into podoplanin(+) cells expressing both myeloid markers (CD11b, CD14) and the canonical LEC markers vascular endothelium growth factor receptor 3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and prospero homeobox 1 (PROX-1). These podoplanin(+) cells displayed sprouting behavior comparable to that of LECs in vitro and a dual hemangiogenic and lymphangiogenic activity in vivo in an endothelial cell sprouting assay and corneal vascularization assay, respectively. Furthermore, these cells expressed vascular endothelium growth factor (VEGF) family members A, -C, and -D. Thus, bone-marrow derived EPCs stimulate hemangiogenesis and lymphangiogenesis through their ability to differentiate into LECs and to produce angiogenic factors. Importantly, plasma from patients with breast cancer induced differentiation of CD34(+) cord blood progenitors into hemangiogenic and lymphangiogenic CD11b(+) myeloid cells, whereas plasma from healthy women did not have this effect. Consistent with these findings, circulating CD11b(+) cells from breast cancer patients, but not from healthy women, displayed a similar dual angiogenic activity. Taken together, our results show that marrow-derived EPCs become hemangiogenic and lymphangiogenic upon exposure to cancer plasma. These newly identified functions of bone-marrow derived EPCs are expected to influence the diagnosis and treatment of breast cancer.

Role of CLOCK and circadian rhythms in calcium homeostasis

Le maintien d'une concentration sanguine constante de calcium est d'une importance cruciale et trois organes participent à la balance calcique normale : les reins, les intestins et les os. La concentration plasmatique de calcium est strictement régulée par l'hormone parathyroïdienne (PTH) et par la vitamine D. Des variations circadiennes de la PTH, de la vitamine D ainsi que du calcium plasmatique ont été décrites précédemment chez l'humain ainsi que chez le rat. Ces rythmes de PTH dans le sérum sont importants pour la régulation du remodelage de l'os. En effet, il a été montré chez les souris C57BL/6J que des injections de PTH une fois par jour mènent à une augmentation de la densité minérale de l'os alors que l'infusion en continu de PTH est associée à une diminution de cette densité. La vitamine D joue également un rôle fondamental dans la physiologie osseuse, car un déficit en vitamine D peut conduire à une ostéomalacie. Cependant la fonction des oscillations de vitamine D au niveau de l'homéostasie osseuse reste inconnue. L'horloge circadienne est un système interne de contrôle biologique du temps générant des rythmes de 24 heures dans l'expression des gènes, ainsi que dans la physiologie et le comportement. Ce contrôle s'opère par des boucles rétroactives positives et négatives de l'expression de gènes circadiens tels que CLOCK, BMAL1, CRY1 et 2 ou PERI et 2. Dans ce travail, nous avons émis l'hypothèse que l'homéostasie calcique est sous le contrôle de l'horloge circadienne. Dans un premier temps, nous avons montré chez les souris C57BL/6J des variations journalières des concentrations de calcium, de PTH et de vitamine D dans le sang, ainsi que de calcium dans les urines. Nous avons également démontré des changements au niveau de l'expression rénale des gènes importants dans l'homéostasie du calcium, tant au niveau de l'ARN messager que des protéines. Ensuite, pour analyser le rôle du système de l'horloge circadienne dans l'homéostasie du calcium, nous avons étudié des souris dans lesquelles a été supprimé le gène CLOCK crucial pour la fonction de l'horloge et nous avons comparé ces souris à des souris de type sauvage de même portée. Les souris CLOCK-I- étaient hypercalciuriques à chaque moment de la journée. Cependant le rythme circadien de l'excrétion de calcium était préservé. Le taux de calcium plasmatique ne différait pas entre les génotypes, mais les souris CLOCK -/- ne montraient pas de variations journalières de ce paramètre. Une perte du rythme journalier était également observée pour les niveaux de vitamine D, perte qui pourrait être une cause de l'altération de la micro-architecture osseuse révélée chez les souris CLOCK-/-. En effet, ces souris montrent une diminution du nombre de trabécules, de leur volume ainsi que de leur surface, ce qui suggère la présence d'ostéoporose. Nous avons également trouvé que le rythme de l'expression de l'ARN messager de CYP27B1 était aboli dans les reins des souris CLOCK -/-, ce qui peut expliquer l'altération du rythme de la vitamine D. Les taux sanguins de PTH étaient comparables entre les souris CLOCK -/- et de type sauvage. Dans les reins, une augmentation de l'expression de l'ARN messager de TRPV5 et NCX1 a été constatée, ce qui suggérerait une augmentation de la réabsorption de calcium dans le tubule convoluté distal et dans le tubule connecteur. Dans les intestins, la réabsorption calcique était diminuée, chez les souris CLOCK-I-, fait confirmé par une diminution des niveaux d'ARN messager de TRPV6 et PMCAL. En résumé, la suppression du gène CLOCK chez les souris a conduit à une hypercalciurie, une altération du rythme des taux plasmatiques de calcium et de vitamine D et à une détérioration de l'architecture osseuse. Pour conclure, ces résultats montrent que l'horloge circadienne est essentielle à l'homéostasie calcique ainsi qu'à la physiologie des os. - L'ostéoporose affecte environ 22 millions de femmes et 5.5 millions d'hommes en Europe, réduisant significativement leur qualité de vie et a causé 3.5 millions de nouvelles fractures en 2010. Les dépenses totales liées à ces fractures ont atteint 37 milliards d'euro et ce coût devrait augmenter de 25% d'ici à 2025. Le nombre de nouvelles fractures dues à l'ostéoporose à travers le monde est estimé à environ 1000 par heure. Parmi les causes de l'ostéoporose, le déficit én calcium et/ou en vitamine D joue un rôle important, mais il existe également des causes génétiques ou liées à des facteurs comme les hormones sexuelles (estrogènes, testostérone), l'âge, le tabac, le poids corporel, certains médicaments,... La vie est rythmique : ceci est dû à l'alternance naturelle du jour et de la nuit et de ses effets sur le corps. La prise alimentaire, par exemple, est un processus qui a lieu pendant la phase active, qui est prévisible (il se produit toujours au même moment) et qui peut être anticipé par le corps. Pour cela, une horloge interne est présente dans chaque cellule du corps et est synchronisée par la lumière du jour, entre autres stimuli. Cette horloge indique la phase du jour et régule l'expression de gènes impliqués dans les différents processus qui nécessitent une anticipation. Pendant mon travail de thèse, je me suis demandé si des îythmes circadiens (c'est-à-dire d'une durée d'environ 24 heures et indépendants des stimuli externes) étaient observables'pour les gènes régulant les flux de calcium dans le corps et si l'interruption de ces rythmes pouvait mener à des altérations de la qualité de l'os. J'ai d'abord travaillé avec des souris normales et j'ai pu montrer la présence de rythmes au niveau du calcium sanguin et urinaire, mais également au niveau des hormones et gènes qui contrôlent le métabolisme du calcium dans le corps, comme la vitamine D et l'hormone parathyroidienne. De manière intéressante, j'ai observé que la plupart de ces gènes ont un rythme synchronisé. J'ai ensuite utilisé un modèle de souris dans lequel l'horloge interne a été génétiquement invalidée et j'ai montré que ces souris présentent une augmentation de leur excrétion urinaire de calcium et un rythme circadien altéré de la vitamine D dans le sang. Ces souris absorbent aussi moins bien le calcium intestinal et présentent une ostéoporose marquée. Ce travail montre donc que l'horloge interne est nécessaire pour établir un rythme circadiens de certains facteurs influant les flux de calcium dans l'organisme, comme la vitamine D, et que la perturbation de ces rythmes mène à une dérégulation du métabolisme osseux. Ainsi, la perturbation de l'horloge interne peut causer une ostéoporose et une hypercalciurie qui pourraient aboutir à la formation de fractures et de calculs rénaux. L'extrapolation de ces observations chez l'homme ou à des changements plus subtiles des rythmes circadiens, comme le décalage horaire, restent à montrer. Cette recherche a démontré que les rythmes circadiens des mécanismes de régulation des flux de calcium dans l'organisme sont essentiels au maintien d'un squelette normal et suggère que les perturbations des rythmes circadiens pourraient être une nouvelle cause de l'ostéoporose. - Maintaining constant calcium concentration in the plasma is of a crucial importance and three organs participate in normal calcium balance - kidney, gut and bone. Plasma calcium concentration is strictly regulated by parathyroid hormone (PTH) and vitamin D. Circadian variations of PTH, vitamin D and plasma calcium were previously described in humans, as well as in rats. Rhythms in serum PTH are important for balanced bone remodelling. Indeed in C57BL/6J mice, PTH injection once per day leads to an increase in bone mineral density (BMD), whilst continuous infusion is associated with decreased BMD. Vitamin D also plays a crucial role in bone physiology, since the deficiency in vitamin D can lead to rickets/osteomalacia. However, the role of vitamin D rhythms in bone homeostasis remains unknown. The circadian clock is an. internal time-keeping system generating rhythms in gene expression with 24h periodicity, in physiology and in behaviour. It is operated by positive- and negative-feedback loops of circadian genes, such as CLOCK, BMAL1, CRY1 and 2 or PERI and 2. In this work, we hypothesized, that calcium homeostasis is under the control of the circadian clock. First, we showed daily variations in urinary calcium and serum calcium, PTH and l,25(OH)2 vitamin D, together with renal mRNA and protein levels of genes involved in calcium homeostasis in C57BL/6J mice. Second, and to investigate the role of the circadian clock system in calcium handling, we studied mice lacking the gene CLOCK crucial for fonction of the clock system and compared them to the WT littermates. CLOCK-/- mice were hypercalciuric at all timepoints of the day. However, the circadian rhythm of calcium excretion was preserved. Serum calcium levels did not differ between the genotypes, but CLOCK-/- mice did not exhibit daily variation for this parameter. Loss of rhythm was observed also for serum l,25(OH)2 vitamin D levels, which may be one of the causes of altered bone microarchitecture that was revealed in CLOCK-/- mice. They displayed increased trabecular separation and decreased trabecular number, trabecular bone volume and trabecular bone surface, suggestive of osteoporosis. We found that the rhythm of the mRNA expression of CYP27B1 was abolished in the kidney of CLOCK-/- mice, which could induce the altered rhythm of l,25(OH)2 vitamin. Serum PTH levels were comparable between CLOCK-/- and WT mice. In the kidney, increased mRNA expression of TRPV5 and NCX1 suggests increased calcium reabsorption in the distal convoluted and connecting tubule. In the gut, intestinal calcium absorption was decreased in CLOCK¬/- mice, confirmed by decreased mRNA levels of TRPV6 and PMCA1. In summary, deletion of the CLOCK gene in mice conducts to hypercalciuria, alteration of the rhythm in serum calcium and l,25(OH)2D levels, and impainnent of their bone microarchitecture. In conclusion, these data show that the circadian clock system is essential in calcium homeostasis and bone physiology.

Alkaline mineral water lowers bone resorption even in calcium sufficiency: alkaline mineral water and bone metabolism.

BACKGROUND: Dietary acid charge enhances bone loss. Bicarbonate or alkali diet decreases bone resorption in humans. We compared the effect of an alkaline mineral water, rich in bicarbonate, with that of an acid one, rich in calcium only, on bone markers, in young women with a normal calcium intake. METHODS: This study compared water A (per litre: 520 mg Ca, 291 mg HCO(3)(-), 1160 mg SO(4)(-), Potential Renal Acid load (PRAL) +9.2 mEq) with water B (per litre: 547 mg Ca, 2172 mg HCO(3)(-), 9 mg SO(4)(-), PRAL -11.2 mEq). 30 female dieticians aged 26.3 yrs (SD 7.3) were randomized into two groups, followed an identical weighed, balanced diet (965 mg Ca) and drank 1.5 l/d of the assigned water. Changes in blood and urine electrolytes, C-telopeptides (CTX), urinary pH and bicarbonate, and serum PTH were measured after 2 and 4 weeks. RESULTS: The two groups were not different at baseline, and showed a similar increase in urinary calcium excretion. Urinary pH and bicarbonate excretion increased with water B, but not with water A. PTH (p=0.022) and S-CTX (p=0.023) decreased with water B but not with water A. CONCLUSION: In calcium sufficiency, the acid calcium-rich water had no effect on bone resorption, while the alkaline water rich in bicarbonate led to a significant decrease of PTH and of S-CTX.

Trabecular Bone Score (TBS)--A Novel Method to Evaluate Bone Microarchitectural Texture in Patients With Primary Hyperparathyroidism.

Context: In the milder form of primary hyperparathyroidism (PHPT), cancellous bone, represented by areal bone mineral density at the lumbar spine by dual-energy x-ray absorptiometry (DXA), is preserved. This finding is in contrast to high-resolution peripheral quantitative computed tomography (HRpQCT) results of abnormal trabecular microstructure and epidemiological evidence for increased overall fracture risk in PHPT. Because DXA does not directly measure trabecular bone and HRpQCT is not widely available, we used trabecular bone score (TBS), a novel gray-level textural analysis applied to spine DXA images, to estimate indirectly trabecular microarchitecture. Objective: The purpose of this study was to assess TBS from spine DXA images in relation to HRpQCT indices and bone stiffness in radius and tibia in PHPT. Design and Setting: This was a cross-sectional study conducted in a referral center. Patients: Participants were 22 postmenopausal women with PHPT. Main Outcome Measures: Outcomes measured were areal bone mineral density by DXA, TBS indices derived from DXA images, HRpQCT standard measures, and bone stiffness assessed by finite element analysis at distal radius and tibia. Results: TBS in PHPT was low at 1.24, representing abnormal trabecular microstructure (normal ≥1.35). TBS was correlated with whole bone stiffness and all HRpQCT indices, except for trabecular thickness and trabecular stiffness at the radius. At the tibia, correlations were observed between TBS and volumetric densities, cortical thickness, trabecular bone volume, and whole bone stiffness. TBS correlated with all indices of trabecular microarchitecture, except trabecular thickness, after adjustment for body weight. Conclusion: TBS, a measurement technology readily available by DXA, shows promise in the clinical assessment of trabecular microstructure in PHPT.