Biomedical subjects

Christian Alexandre

Publications and source records attributed to Christian Alexandre.

12 recordsLinked to original sources

PubMed2005

Leptin modulates both resorption and formation while preventing disuse-induced bone loss in tail-suspended female rats.

In vitro studies have demonstrated leptin-positive effects on the osteoblast lineage and negative effects on osteoclastogenesis. Therefore, we tested the hypothesis that leptin may prevent tail-suspension-induced bone loss characterized by an uncoupling pattern of bone remodeling, through both mechanisms. Female rats were randomly tail-suspended or not and treated either with ip administration of leptin or vehicle for 3, 7, and 14 d. As measured by dual energy x-ray absorptiometry, tail-suspension induced a progressive decrease in tibia-metaphysis bone mineral density, which was prevented by leptin. Histomorphometry showed that this was related to the prevention of the transient increase in osteoclast number observed with suspension at d 7. These effects could be mediated by the receptor activator of nuclear factor kappaB-ligand (RANKL)/osteoprotegerin (OPG) pathway since we observed using direct RT-PCR, a suspension-induced increase in RANKL gene expression in proximal tibia at d 3, which was counterbalanced by leptin administration with a similar 3-fold increase in OPG expression and a RANKL to OPG ratio close to nonsuspended conditions. In addition, leptin prevented the decrease in bone formation rate induced by tail-suspension at d 14. The latter could be related to the role of leptin in mediating the reciprocal differentiation between adipocytes and osteoblasts, because leptin concurrently blunted the disuse-induced increase in bone marrow adipogenesis. In summary, these data suggest that peripheral administration of leptin could prevent disuse-induced bone loss through, first, a major inhibitory effect on bone resorption and, second, a delayed effect preventing the decrease in bone formation.

Animals↗

PubMed2005

Androgens and bone metabolism.

The gradual reductions in bone mass and skeletal calcium density seen throughout adulthood occur in parallel with changes in the production of bioactive sex hormones in both men and women. The long-held belief that osteoporosis is dependent on androgens in men and estrogens in women has been challenged by recent reports of osteoporosis in young men with normal testosterone levels but extremely low estrogen levels. A review of the literature indicates that estrogens have a far greater influence on bone mass than do androgens. This may suggest new approaches to the treatment of male osteoporosis. Furthermore, osteoporosis induced by prostate cancer treatment should receive greater medical attention.

Adult↗

PubMed2005

Cancellous bone structure of iliac crest biopsies following 370 days of head-down bed rest.

INTRODUCTION: Static bone histomorphometry was applied to existing iliac bone sections originating from a 370-d 5 degrees head-down bed rest experiment. This bed rest experiment is the longest ever to have been conducted. We hypothesized that bed rest would decrease cancellous bone volume fraction and that this effect would be reversed by countermeasures. METHODS: Eight healthy male subjects underwent 370 d of 5 degrees head-down bed rest. Three subjects were treated with bisphosphonate (Xidifon, potassium salt of ethane-1-hydroxy-1-disphosphonate, EHDP) combined with an exercise regimen (1-2 h x d(-1)) for the entire study period. Five subjects underwent 120 d of bed rest without countermeasures followed by 250 d of bed rest with the exercise regimen. Transiliac bone biopsies were obtained either at baseline and day 366, or at baseline, day 116, and day 366 at alternating sides of the ileum. Static histomorphometry was performed using a computerized method. RESULTS: The 120 d of head-down bed rest without countermeasures resulted in decreased bone volume fraction BV/TV (-6.3%, p = 0.046) and trabecular number (Tb.N; -10.2%, p = 0.080) and increased trabecular separation (Tb.Sp; 14.7%, p = 0.020), whereas the 250 d of subsequent head-down bed rest with exercise treatment prevented further significant deterioration of the histomorphometric measures. DISCUSSION: The 120 d of 5 degrees head-down bed rest without countermeasures induced significant deterioration of iliac crest cancellous bone histomorphometric properties. On average, the countermeasures consisting of either bisphosphonate and exercise, or exercise alone were able to either prevent or stop immobilization-induced changes of the iliac cancellous bone structure.

Adult↗

PubMed2004

Increase of both angiogenesis and bone mass in response to exercise depends on VEGF.

UNLABELLED: Physiological angiogenesis during bone remodeling is undefined. Treadmill-running rats displayed bone marrow angiogenesis concomitant with bone formation increase and resorption decrease and upregulation of VEGF and its R1 receptor mRNA in proximal tibia. VEGF blockade over 5 weeks of training fully prevented the exercise-induced bone mass gain. INTRODUCTION: We investigated the role of vascular endothelial growth factor (VEGF) and angiogenesis in the osteogenic response to exercise. MATERIALS AND METHODS: Nine-week-old male Wistar rats were treadmill-trained at 60% Vo(2max) for various periods. Bone and vascular histomorphometry was performed after 2- and 5-week experiments. On-line RT PCR for VEGF and its receptors R1 and R2 was done after a 10-day experiment. In the 5-week experiment, running rats received either a VEGF inhibitory antibody or a placebo. RESULTS: After 2 weeks, tibial BMD did not change; however, vessel number in the proximal metaphysis increased by 20% in running versus sedentary rats. In running rats, vessel number correlated positively (r = 0.88) with bone formation rate and negatively (r = -0.85) with active resorption surfaces. After 10 days of training, upregulation of VEGF and VEGF receptor R1 mRNA was detected in periosteum and metaphyseal bone. VEGF blockade in 5-week trained rats fully prevented the exercise-induced increase in metaphyseal BMD (9%) and cancellous bone volume (BV/TV; 25%), as well as the increased vessel number (25%). In 5-week placebo-treated running rats, bone formation rate returned to initial values, whereas osteoclastic surfaces continued to decline compared with both sedentary and anti-VEGF-treated running rats. CONCLUSION: VEGF signaling-mediated bone angiogenesis is tightly related to exercise-induced bone cellular uncoupling and is indispensable for bone gain induced by exercise.

Animals↗

PubMed2004

Interactions between estrogen and mechanical strain effects on U2OS human osteosarcoma cells are not influenced by estrogen receptor type.

Estrogens (E) and mechanical strain (MS) exert direct effects on osteoblast activity, with good evidence of interactions between their respective effects. Osteoblasts express both forms of estrogen receptors (ER) ERalpha and ERbeta, and previous studies have suggested a specific role for each receptor. Therefore, our working hypothesis was that the interactions between E and MS on osteoblast activity vary depending on which ER is preferentially activated. Using human osteosarcoma cells U2OS stably transfected either with ERalpha or ERbeta, we evaluated the effects of cyclical cell loading on a F-3000 Flexercell Strain Unit (1.5% elongation, 10 min/day) in presence of estradiol (E2) 10(-8) M or not. The original U2OS cell line, which does not express ER, was characterized by low alkaline phosphatase (AP) activity. In both U2OS-ERalpha and U2OS-ERbeta cell lines, MS induced similar increases in AP activity and gene expression as measured by real-time quantitative RT-PCR, and a decrease in type I collagen gene expression. MS and E2 had a synergistic effect on AP activity as compared to each stimulus alone. No change in proliferation rate was observed. Neither proliferation nor differentiation of the original U2OS cell line was altered by strain or E2. In summary, our data showing differences in response to MS between the U2OS with no ER expression and the U2OS-ERalpha or -ERbeta cell lines provide additional evidence that ER plays a critical role in mechanotransduction. However, we were not able to demonstrate that interactions between E and MS were dependent on ER type in U2OS osteosarcoma cells.

Alkaline Phosphatase↗

PubMed2003

Lower bone cellular activities in male and female mature C3H/HeJ mice are associated with higher bone mass and different pyridinium crosslink profiles compared to C57BL/6J mice.

The female inbred strains of C3H/HeJ (C3H) and C57BL/6J mice (B6), having high and low femoral peak bone mass, respectively, were proposed as models for studying the genetic regulation of bone mass. Here, we compared the known bone phenotype, in 4.5-month-old C3H versus B6 mice, in both genders. Femoral bone mineral content, trabecular bone mass, and thickness at the distal metaphysis were higher in C3H mice. In the long bones, deoxypyridinoline content was lower and pyridinoline/deoxypyridinoline ratios were greater in C3H. Intrafibrillar collagen packing is different not only within strains but also within sexes. Bone resorption activity, evaluated by urinary pyridinium crosslinks and active resorption surfaces in the femoral metaphysis, was lower in C3H. Bone formation activity, evaluated by serum osteocalcin and alkaline phosphatase (ALP) levels, as well as histomorphometric indices of bone formation in the femoral metaphysis and the cortical tibia, was lower in C3H. Conversely, the ALP- and Von Kossa-positive colony-forming units were more numerous in bone marrow cell cultures originating from male C3H. In both strains, resorption and formation activities were lower in males than in females. In C3H, males had lower bone mass than females whereas the opposite was seen in B6. In conclusion, we found that the lower cellular activities in C3H were associated with high cancellous bone mass and pyridinium crosslink levels, which might account for the more mineralized bone in C3H mice compared to that in B6 mice.

Amino Acids↗

PubMed2003

Focal contacts organization in osteoblastic cells under microgravity and cyclic deformation conditions.

We compared quantitatively vinculin-related adhesion parameters in osteoblastic cells submitted to opposite mechanical stresses, i.e., low deformation and frequency strain regimens (stretch condition) and microgravity exposure (relaxed condition). Cyclic deformation induced a biphasic response comprising new focal contacts formation followed by their clustering in ROS cells. Microgravity exposure induced a reduction in focal contact number and clustering in ROS cells. We previously demonstrated that 1% cyclic deformations at 0.05 Hz during a daily 10 min episode over 7 days stimulated ROS 17/2.8 growth as compared to static culture whereas relaxed ROS proliferated similarly to static culture (BC). To evaluate whether the proliferation (stretch) or the survival (relaxed) status of ROS cells influences focal contact organization, we inhibited ERKs proliferative-dependent pathway. Inhibition of proliferation by PD98059 was overcome although not fully restored by stretch. Furthermore stretch-induced clustering of vinculin-positive contacts still occurs in the presence of ERKs inhibitor, whereas the increase in focal contact number is abolished. In conclusion, we showed that focal contacts are mechanoeffectors and that hyper-mechanical stimulation could up regulate focal contacts size as compared to hypo-mechanical that down regulate clusterization.

Adaptation, Physiological↗

PubMed2003

Tail suspension induces bone loss in skeletally mature mice in the C57BL/6J strain but not in the C3H/HeJ strain.

We assessed the effects of tail-suspension in two skeletal genetic backgrounds, the high C3H/HeJ (C3H) and low C57BL/6J (B6) bone masses inbred mice (male, 4-months old). Cancellous bone mass and structural parameters were evaluated in distal femoral metaphysis by three dimensional microcomputed tomography. Bone cellular activities were evaluated by histomorphometry and measurements of alkaline phosphatase activity (ALP) and osteocalcin in blood and deoxypyridinoline (D-pyr) in urine. In C3H mice, 2- and 3-week unloading experiments were performed. After an early and transient decrease in body weight, a 2-week suspension period resulted in stimulation of both bone formation rate by 45% and active osteoclastic surfaces by 19%. D-pyr did not change, but ALP and osteocalcin levels increased by 18% and 72%, respectively, in 2-week suspended mice, and osteocalcin remained elevated by 30% in the 3-week suspended mice. Such cellular modifications allowed the C3H mice to maintain their initial bone mass and trabecular structural parameters even after a 3-week suspension period. In B6 mice, 1- and 2-week unloading experiments were performed. Tail suspension resulted in decreased body weight during the first days followed by an incomplete recovery during the second week of unloading. The resorption activity was unaffected by any suspension time period, whereas a decrease of 42.5% in bone formation rate and of 21.5% in ALP were seen by the end of the first week of suspension, both values being restored after a 2-week suspension period. At this latter time, trabeculae were thinner, leading to a 24.5% cancellous bone loss. Trabecular number and connectivity, rod-plate index, and degree of anisotropy were not modified. We concluded that C3H mice constituted a unique model in which genetic background overwhelmed the usual effects of reduced biomechanical usage in bone, whereas B6 mice, compared with the standardized rat model, offered an alternative model of bone loss in a mature skeleton.

Animals↗

PubMed2003

Noninvasive in vivo monitoring of bone architecture alterations in hindlimb-unloaded female rats using novel three-dimensional microcomputed tomography.

UNLABELLED: We tested a novel microcomputed tomograph designed to longitudinally and noninvasively monitor bone alterations in hindlimb-unloaded female rats at a resolution of 26 microm over a period of 3 weeks. This prototype has a potential to detect three-dimensional trabecular microarchitectural changes induced by growth and unloading. INTRODUCTION: Until now, data concerning structural changes of cancellous bone have only been available after necropsy of animals. In this study, we tested a novel microcomputed tomography (microCT) technique designed to monitor such changes repeatedly at a resolution of 26 microm with an acquisition time of about 10 minutes to map the entire proximal tibial metaphysis. MATERIALS AND METHODS: Four-month-old female Wistar rats were randomized to seven groups of 10 animals to be either tail-suspended or to act as controls. MicroCT and DXA measurements were performed at 0, 7, 14, and 23 days in suspended and control rats. One group was killed at each of these time points, and bone samples were processed for histomorphometry and ex vivo microCT. RESULTS: We verified that a good correlation was obtained between two-dimensional bone parameters evaluated in longitudinal tibial sections either by histomorphometry or microCT and microCT parameters obtained from either in vivo or ex vivo tibias. The longitudinal survey allowed earlier detection of both growth and unloading-related bone changes than the transverse survey. In controls, aging induced denser bones, reorganization of the trabecular network toward a more oriented plate-like structure, and an isotropic pattern. Unloading first inhibited cortical and cancellous bone growth and then induced bone loss characterized by fewer trabeculae, reduced connectivity density, and enhanced structure model index (SMI), revealing a lighter cancellous structure with development of rod-like characteristics. CONCLUSION: We show for the first time that this microCT prototype has a great potential to accurately, repeatedly, reliably, and rapidly investigate alterations of three-dimensional trabecular microarchitecture.

Absorptiometry, Photon↗

PubMed2002

MAP and src kinases control the induction of AP-1 members in response to changes in mechanical environment in osteoblastic cells.

The activating protein-1 (AP-1) complex plays a critical role in bone physiology, including its response to strain. We studied gene expression and nuclear translocation kinetics of the seven AP-1 members, after substrate deformation (Flexcell) or simulated microgravity (Clinostat), in osteoblastic ROS17/2.8 cells. Gene expression and nuclear translocation of all the AP-1 members were induced, under both conditions, with differences in their kinetics, except fosB mRNA in the Clinostat. Downregulation of protein kinase C (PKC) and COX1/2 or inhibition of ERK1/2, p38(MAPK) or src kinases had no major effect on AP-1 mRNA expression in the Flexcell. In contrast, ERK1/2, p38(MAPK) and src kinases treatment blocked nuclear translocation of almost all the AP-1 members in both models, except Fra-1, JunD after deformation and Fra-1, JunB after clinorotation. Thus, changes in the osteoblastic mechanical environment induced a dramatic induction of most of the AP-1 members with specific kinetics and involved MAPK and src kinase pathways, which differed whether the cells were stretched or clinorotated.

Active Transport, Cell Nucleus↗

PubMed2002

High-resolution three-dimensional micro-computed tomography detects bone loss and changes in trabecular architecture early: comparison with DEXA and bone histomorphometry in a rat model of disuse osteoporosis.

RATIONALE AND OBJECTIVES: The ability of three-dimensional micro-computed tomography (3D-microCT) to detect changes in a rat model of disuse osteoporosis was evaluated and compared with two reference techniques: dual x-ray absorptiometry (DEXA) for bone mass, and bone histomorphometry (BHM) for bone mass and trabecular micro-architecture. METHODS: Forty-two rats were divided into controls or were hindlimb unloaded for 7, 13, and 23 days. DEXA bone mineral density measurements were performed on right tibiae. Then, after plastic embedding, bone volume (BV/TV) and trabecular (Tb)-derived parameters of trabecular bone architecture (Tb Th, thickness; Tb N, number) were measured with BHM. 3D-microCT measurements of BV/TV, Tb Th, and Tb N were carried out on left tibiae. RESULTS: Unloaded rats lost bone in a time-dependent manner. DEXA and 3D-microCT detected bone loss earlier than BHM. The decreases in Tb Th and Tb N were observed at day 13 only with 3D-microCT (P < 0.05 and P < 0.01, respectively). All bone mass and architectural parameters measured with the three techniques correlated significantly (0.59, 0.89, P < 0.001), except Tb Th. CONCLUSIONS: 3D-microCT is a valid technique for bone mass and micro-architecture measurements in this rat model of disuse osteoporosis.

Absorptiometry, Photon↗

PubMedDate not supplied

Focal contact clustering in osteoblastic cells under mechanical stresses: microgravity and cyclic deformation.

We quantitatively compared vinculin-related adhesion parameters in osteoblastic cells submitted to two opposing mechanical stresses: low deformation and frequency strain regimens (stretch conditions) and microgravity exposure (relaxed conditions). In both ROS 17/2.8 cells and rat primary osteoblastic cells, 1% cyclic deformations at 0.05 Hz for 10 min per day for seven days stimulated cell growth compared to static culture conditions, while relaxed ROS cells proliferated in a similar way to static cultures (BC). We studied the short-term (up to 24 h) adaptation of focal contact reorganization under these two conditions. Cyclic deformation induced a biphasic response comprising the formation of new focal contacts followed by clustering of these focal contacts in both ROS cells and primary osteoblasts. Microgravity exposure induced a reduction in focal contact number and clustering in ROS cells. To evaluate whether the proliferation (stretch) or survival (relaxed) status of ROS cells influences focal contact organization, we inhibited the ERK proliferative-dependent pathway. Inhibition of proliferation by PD98059 was partially reversed, but not fully restored by stretch. Stretch-induced clustering of vinculin-positive contacts also persisted in the presence of PD98059, whereas the increase in focal contact number was abolished. In conclusion, we show that focal contacts are mechanoeffectors, and we suggest that their morphologic organization might serve as a discriminant functional parameter between survival and proliferation status in ROS 17/2.8 osteoblastic cells.

Adaptation, Physiological↗