Effects of static or dynamic mechanical stresses on osteoblast phenotype expression in three-dimensional contractile collagen gels

Studies performed at tissular (three-dimensional, 3-D) or cellular (two-dimensional, 2-D) levels showed that the loading pattern plays a crucial role in the osteoblastic physiology. In this study, we attempted to investigate the response of a 3-D osteoblastic culture submitted to either no external stress or static or dynamic stresses. Rat osteosarcoma cells (ROS 17/2.8) were embedded within collagen type I lattices and studied for 3 weeks. Entrapment and proliferation of cells within the hydrated collagen gel resulted in the generation of contractile forces, which led to contraction of the collagen gel. We used this ability to evaluate the influence of three modes of mechanical stresses on the cell proliferation and differentiation: (1) the freely retracted gels (FRG) were floating in the medium, (2) the tense gels (TG) were stretched statically and isometrically, with contraction prevented in the longitudinal axis, and (3) the dynamic gels (DG) were floating gels submitted to periodic stresses (50 or 25 rpm frequency). Gels showed maximum contraction at day 12 in 50 rpm DG, followed by 25 rpm DG, then FRG (88%, 81%, 70%, respectively) and at day 16 in TG (33%). The proliferation rate was greater in TG than in FRG (+52%) but remained low in both DGs. Gel dimensions were related to the collagen concentration and on a minor extent to cell number. Cells in DG appeared rounder and larger than in other conditions. In TG, cells were elongated and oriented primarily along the tension axis. Scanning electron microscopy (SEM) showed that tension exerted by cells in TG led to reorientation of collagen fibers which, in turn, determined the spatial orientation and morphology of the cells. Transmission electron microscopy (TEM) performed at maximum proliferation showed a vast majority of cells with a distended well-developed RER filled with granular material and numerous mitochondria. Alkaline phosphatase activity peaked close to the proliferation peak in FRG, whereas in TG, a biphasic curve was observed with a small peak at day 4 and the main peak at day 16. In DG, this activity was lower than in the two other conditions. A similar time course was observed for alkaline phosphatase gene expression as assessed by Northern blots. Regardless of the conditions, osteocalcin level showed a triphasic pattern: a first increase at day 2, followed by a decrease from day 4 to 14, and a second increase above initial values at day 18. Microanalysis-x indicated that mineralization occurred after 14 days and TEM showed crystals within the matrix. We showed that static and dynamic mechanical stresses, in concert with 3-D collagen matrices, played a significant role on the phenotypic modulation of osteoblast-like cells. This experimental model provided a tool to investigate the significance and the mechanisms of mechanical activity of the 3-D cultured osteoblast-like cells.

Bisphosphonate effects in rat unloaded hindlimb bone loss model: three-dimensional microcomputed tomographic, histomorphometric, and densitometric analyses

The effects of antiresorptive drugs on bone loss remain unclear. Using three-dimensional microtomography, dual X-ray/densitometry, and histomorphometry, we evaluated tiludronate effects in the bone loss model of immobilization in tail-suspended rats after 7, 13, and 23 days. Seventy-eight 12-week-old Wistar male rats were assigned to 13 groups: 1 baseline group, and for each time point, 1 control group treated with vehicle and three tail-suspended groups treated with either tiludronate (0.5 or 5 mg/kg) or vehicle, administered s. c. every other day, during the last week before sacrifice. In primary spongiosa (ISP), immobilization-induced bone loss plateaued after day 7 and was prevented by tiludronate. In secondary spongiosa (IISP), bone loss appeared at day 13 with a decrease in trabecular thickness and trabecular number (Tb.N) as assessed by three-dimensional microtomography. Osteoclastic parameters did not differ in tail-suspended rats versus control rats, whereas bone formation showed a biphasic pattern: after a marked decrease at day 7, osteoblastic activity and recruitment normalized at days 13 and 23, respectively. At day 23, the 80% decrease in bone mass was fully prevented by high-dose tiludronate with an increase in Tb.N without preventing trabecular thinning. In summary, at day 7, tiludronate prevented bone loss in ISP. After day 13, tiludronate prevented bone loss in ISP and IISP despite a further decrease in bone formation. Thus, the preventive effects of tiludronate in this model may be related to the alteration in bone modeling with an increase in Tb.N in ISP and subsequently in IISP.

[Action of bisphosphonates on malignant osteolysis]

MECHANISM OF BONE DESTRUCTION IN MALIGNANT OSTEOLYSIS: Many mechanisms have been described to explain the excessive osteoclastic activity: local stimulation factors (cytokines, lymphokines) are mainly found in breast cancer of myeloma; a general stimulation factor (PTH rP) is found predominantly in lung cancer, head and neck cancer and in cancer of the kidney or ovary. CONTRIBUTION OF BISPHOSPHONATES: The use of bisphosphonates is warranted to counteract the overactivity of the osteoclasts in humans, especially since these drugs could have a direct effect on cancer cells and also have their own therapeutic effect. There are four objectives for using bisphosphonates in cancer patients: lowering serum calcium levels, pain relief, treatment and prevention of bone metastasis. Four bisphosphonates have marketing approval in France for this indication. PROVEN AND TO BE PROVEN EFFECTS: The serum calcium lowering effect and the curative effect for the treatment of bone metastasis are well documented for all four formulations which all meet the clinical requirements for marketing approval. The preventive effect on the development of secondary bone localizations of primary cancers remains to be demonstrated and will require extensive testing in humans. There is however room for hope of substantial progress in cancerology.

Effects of centrifuging at 2g on rat long bone metaphyses

Hypergravity may be considered as a means of counteracting the deleterious effects of microgravity on bone tissue. The effects of exposure to 4 days of hypergravity provided by centrifuging, on bone tissue were studied using histomorphometry. Young 53-day-old male Sprague Dawley rats were randomly divided into a centrifuged group (2g, n = 10), a rotated group (ROTATE, n = 6) of rats exposed to 1.03 g placed in cages near the centre of rotation of the centrifuge and a stationary control group (CONTROL, n = 10). The body mass of the 2g rats was decreased by this experience by 16% compared to CONTROL. The width of the tibial growth plate of 2g was decreased. In two out of ten 2g rats, the hypertrophic zone was injured. In both the tibial and humeral primary (1 degrees ) spongiosae, a reduced 1 degrees spongiosa width (-35% and -24%, ROTATE versus CONTROL respectively; -37% and -41%, 2g versus CONTROL respectively) associated with bone gain (+27% for tibia and humerus ROTATE versus CONTROL; + 16% and +20%, 2g versus CONTROL respectively) was observed in both ROTATE and 2g. In the tibial secondary (2 degrees) spongiosa, bone mass was increased in the 2g (+13% 2g versus CONTROL) rats due to thicker trabeculae, but was decreased in ROTATE rats (-12% versus CONTROL) due to thinner trabeculae. The parameters of formation and resorption activities were stimulated in the 2g and ROTATE groups, the formation activity being more enhanced in 2g. No structural changes were observed in the humeral 2 degrees spongiosa in any of the groups. Numeral bone formation parameters were decreased in 2g and ROTATE but resorption activity was increased in 2g and decreased in ROTATE compared to CONTROL. In conclusion, as early as the 4th day, 2g hypergravity induced reduced endochondral bone formation and increased cancellous bone mass. Rotation led to mixed results including reduced endochondral bone formation, increased bone volume in the 1 degrees spongiosa and bone loss in the 2 degrees spongiosa.

Engrailed and hedgehog make the range of Wingless asymmetric in Drosophila embryos

In many instances, remote signaling involves the transport of secreted molecules. Here, we examine the spread of Wingless within the embryonic epidermis of Drosophila. Using two assays for Wingless activity (specification of naked cuticle and repression of rhomboid transcription), we found that Wingless acts at a different range in the anterior and posterior directions. We show that this asymmetry follows in part from differential distribution of the Wingless protein. Transport or stability is reduced within engrailed-expressing cells, and farther posteriorward Wingless movement is blocked at the presumptive segment boundary and perhaps beyond. We demonstrate the role of hedgehog in the formation of this barrier.

A case of Schnitzler's syndrome with nodular regenerative hyperplasia of the liver

Schnitzler's syndrome is a rare condition of urticaria, macroglobulinemia, and sclerotic bone lesions. We report a case in a 70-year-old man in whom inflammatory polyarthralgia was followed by a nonpruritic urticarial eruption with a moderate decline in general health. Laboratory tests showed inflammation and a modest isolated peak of monoclonal IgM kappa. There was no evidence of Waldenström macroglobulinemia. Schnitzler's syndrome was considered. However, an ultrasound scan of the abdomen done because of mild gamma-glutamyl-transferase elevation disclosed multiple hepatic lesions. The liver histology showed incipient nodular regenerative hyperplasia. Only about 30 cases of Schnitzler's syndrome have been reported since the seminal description in 1972. Hepatic involvement was a common but nonspecific finding, and we found no cases with nodular regenerative hyperplasia. However, this abnormality is often found in patients with autoimmune or hematological disorders. The pathogenesis of Schnitzler's syndrome remains unknown, but the possibility of progression to a hematological malignancy requires prolonged follow-up.

Recurrence of vertebral fracture with cyclical etidronate therapy in osteoporosis: histomorphometry and X-Ray microanalysis evaluation

In an open prospective study, we evaluated differences between patients with (wRVF group) and without recurrence of vertebral fracture (woRVF group) during cyclical etidronate therapy for osteoporosis. Thirty-two patients (age 64 +/- 1.8 years) characterized by at least one osteoporotic VF were treated during 1 year. At baseline, body mass index was significantly lower (23.3 +/- 0.6 vs. 26.9 +/- 1.0 kg/m2, p< 0.05), the number of previous VFs was higher (4.0 +/- 0. 4 vs. 2.4 +/- 0.4, NS), and patients were older in the wRVF group as compared with the woRVF group (67.8 +/- 3 vs. 62.6+/- 2.2 year, NS). Trabecular bone volume (11.6 +/- 1.2 vs. 15 +/- 0.9%, p< 0.05) and trabecular number (1.06 +/- 0.08 vs. 1.27 +/- 0.05, p < 0.05) were significantly lower in the wRVF group. None of the baseline resorptive variables differed, whereas the bone formation rate (BFR) was 2-fold lower in the wRVF group (p< 0. 05). After 1 year of treatment, osteoclast number, active eroded surfaces, and resorption depth dramatically decreased in both groups (p< 0. 01). To a lesser extent, the mineral apposition rate and serum alkaline phosphatase level were significantly reduced (p< 0.05). No impaired mineralization was observed. Using X-ray microanalysis, we found no abnormality in bone mineral but a significant increase of the calcium/phosphorus ratio during treatment in the wRVF group. Our results demonstrate that recurrence of VFs within the first year of cyclical etidronate therapy was related neither to a lack of histologic response to the treatment nor induction of an abnormality of mineralization. VFs were more likely in the presence of a decreased BFR and lower trabecular connectivity, providing support for treating osteoporotic patients with etidronate early in the course of the disease.

Energy and substrate metabolism during a 42-day bed-rest in a head-down tilt position in humans

Microgravity-induced changes in body composition (decrease in muscle mass and increase in fat mass) and energy metabolism were studied in seven healthy male subjects during a 42-day bed-rest in a head-down tilt (HDT) position. Resting energy expenditure (REE), fat and glucose oxidation were estimated by indirect calorimetry on days 0, +8 and +40 of the HDT period. Assessments were performed both in post-absorptive conditions and following two identical test meals given at 3-h intervals. Body composition (dual x-ray absorptiometry) was measured on days 0, +27, +42. Mean post-absorptive lipid oxidation decreased from 53 (SEM 8) mg x min(-1) (day 0) to 32 (SEM 10) mg x min(-1) (day 8, P = 0.04) and 36 (SEM 8) mg x min(-1) (day 40, P = 0.06). Mean post-absorptive glucose oxidation rose from 126 (SEM 15) mg x min(-1) (day 0) to 164 (SEM 14) mg x min(-1) (day 8, P = 0.04) and 160 (SEM 20) mg x min(-1) (day 40, P = 0.07). Mean fat-free mass (FFM) decreased between days 0 and 42 [58.0 (SEM 1.8) kg and 55.3 (SEM 1.7) kg, P < 0.01] while fat mass increased without reaching statistical significance. The mean REE decreased from 1688 (SEM 50) kcal x day(-1) to 1589 (SEM 42) kcal x day(-1) (P = 0.056). Changes in REE were accounted for by changes in FFM. Mean energy intake decreased from 2532 (SEM 43) kcal x day(-1) to 2237 (SEM 50) kcal x day(-1) (day 40, P < 0.01) with only a minor decrease in the proportion of fat. We concluded that changes in fat oxidation at the whole body level can be found during HDT experiments. These changes were related to the decrease in FFM and could have promoted positive fat balance hence an increase in fat mass.

Rotating-wall vessels, promising bioreactors for osteoblastic cell culture: comparison with other 3D conditions

Osteoblastic cells cultured on microcarriers in bioreactors are a potentially useful tool to reproduce the in vivo three-dimensional (3D) bone network. The aim is to compare different types of 3D and two-dimensional (2D) osteoblastic culture. ROS17/2.8 cells are cultured in a bioreactor (rotating-wall vessel) or in two kinds of control (3D petri dish, 3D Percoll) and on two types of microcarrier (Cytodex 3 and Biosilon). Growth and morphology are determined by cell count and SEM, and differentiation is determined by dosage of alkaline phosphatase (ALP) activity and northern blots (ALP and osteocalcin (OC)). SEM shows that Biosilon microcarriers are the best substrate. Proliferation in the RWV and 3D petri dish is still in the exponential phase, whereas growth in the 2D culture reaches a plateau after eight days of culture. ALP activity and the ALP and OC mRNA levels are similar at day 8 for both the RWV and 3D petri dish. However, at day 10, cells are more differentiated in the RWV. The study shows that osteoblasts are both proliferate and differentiate in 3D structures. A BrDU immunocytochemical approach shows that only the cells in the periphery of the aggregates proliferate. Therefore the bioreactor may be a suitable tissue culture model for investigation of growth and differentiation processes in tissue engineering.

[Osteoarticular Mycobacterium xenopi infection]

BACKGROUND

Mycobacterium xenopi is a potential pathogen for man and can cause bone and joint infections, particularly spondylodiscitis. Most cases of infection occur in fragilized patients and are found more and more often in AIDS patients.

CASE REPORT

A 41-year-old HIV+ woman developed cervical spondylodiscitis due to Mycobacterium xenopi infection. The strain was isolated from a discovertebral biopsy and was resistant to several antibiotics. Outcome was unfavorable.

DISCUSSION

Most of the cases reported to date have involved spondylodiscitis of the thoracic or lumbar spine. To our knowledge, this is the first report of cervical spondylodiscitis dut to Mycobacterium xenopi in an HIV+ patient. Antibiotic combinations using fluoroquinolones and new macrolides are usually prescribed. Such protocols may provide cure of these opportunistic infections in immunodeficient patients.

Effects of gravitational changes on the bone system in vitro and in vivo

Spaceflight data obtained on bone cells, rodents, and humans are beginning to shed light on the importance of gravitational loading on the skeletal system. The space environment is a relevant model to explore the bone cell response to minimal strains. However, whether there is a direct effect of gravity on the cell rather than changes related to lack of convection forces in cell cultures performed in microgravity is unknown. In vitro studies carried out using osteoblastic cell cultures in space show changes in cell shape, suggesting that cell attachment structures as well as cytoskeleton reorganization might be involved. Valuable information is expected from in vitro models of an increase or decrease in mechanical stress in order to identify the different pathways of mechanoreception and mechanotransduction in the osteoblastic lineage. Results obtained from both humans and rodents after spaceflights indicated that bone mass changes are site specific rather than evenly distributed throughout the skeleton, thus emphasizing the need to perform measurements at different bone sites: weight- and non-weight-bearing bones, and cancellous and cortical envelopes. Bone mass measurements and biochemical parameters of bone remodeling are currently under evaluation in cosmonauts. Histomorphometric studies of bones from rats after space missions of various periods provided the time course of the cancellous bone cellular events: transient increase in resorption and sustained decrease in bone formation. The underlying bone loss occurred first in weight-bearing bones and later in less weight-bearing bones. During the postflight period, time required to recover the lost bone was greater than the mission length. Thus, the postflight period deserves more attention than it is currently receiving. On earth, the rat tail-suspension model is currently used to mimic spaceflight-induced bone loss. Data from the model confirmed the impairment of osteoblastic activity and showed an alteration in osteoblast recruitment with skeletal unloading. However, this model needs to be further validated.

Bone formation and resorption biological markers in cosmonauts during and after a 180-day space flight (Euromir 95)

Long-term spaceflights induce bone loss as a result of profound modifications of bone remodeling, the modalities of which remain unknown in humans. We measured intact parathyroid hormone (PTH) and serum calcium; for bone formation, serum concentrations of bone alkaline phosphatase (BAP), intact osteocalcin (iBGP), and type 1 procollagen propeptide (PICP); for resorption, urinary concentrations (normalized by creatinine) of procollagen C-telopeptide (CTX), free and bound deoxypyridinoline (F and B D-Pyr), and Pyr in a 36-year-old cosmonaut (RTO), before (days -180, -60, and -15), during (from days 10 to 178, n = 12), and after (days +7, +15, +25, and +90) a 180-day spaceflight, in another cosmonaut (ASW) before and after the flight. Flight PTH tended to decrease by 48% and postflight PTH increased by 98%. During the flight, BAP, iBGP, and PICP decreased by 27%, 38%, and 28% respectively in CM1, and increased by 54%, 35%, and 78% after the flight. F D-Pyr and CTX increased by 54% and 78% during the flight and decreased by 29% and 40% after the flight, respectively. We showed for the first time in humans that microgravity induced an uncoupling of bone remodeling between formation and resorption that could account for bone loss.

Can an osteoporotic vertebral fracture cause compression of the spinal cord or cauda equina

A 78-year-old woman developed an osteoporotic fracture of L2 followed two months later by spinal cord compression. Imaging study findings suggested a malignancy but a biopsy showed osteonecrosis, of which there was no evidence on the imaging studies. Osteonecrosis may be the cause of neurologic compromise associated with osteoporotic vertebral fractures.

Space-related bone mineral redistribution and lack of bone mass recovery after reambulation in young rats

This study reports the effects of a 14-day spaceflight followed by a 14-day reambulation period on bones of 56-day-old male rats compared with synchronous (S) and vivarium (V) control animals. Femur, tibia, and humerus bone mineral densities (BMD); bone calcium and phosphorus concentrations ([Ca2+] and [P]), measured by X-ray microanalysis (XRM), on tibia, vertebra, and calvaria; and histomorphometric data on proximal primary and secondary spongiosae (I and II SP, respectively) of the tibia and humerus were measured. After the flight in flown rats (compared with S), BMD was lower in the distal femur and remained similar to S in humerus and tibia, [Ca2+] and [P] were lower in tibia II SP and higher in calvaria, tibia I SP width and II SP bone volume were lower, resorption was markedly higher in tibia II SP, and no difference in formation parameters was observed. After reambulation, BMD was lower in long bones of both flight and S groups compared with V. Bone loss appeared in humeral II SP and worsened in tibial II SP in flown rats. Tibial formation parameters were higher in flown rats compared with V and S, indicating the onset of an active recovery. Tibial XRM [Ca2+] and [P] in flown rats remained below control levels.

Hindlimb unloading in rat decreases preosteoblast proliferation assessed in vivo with BrdU incorporation

Immobilization affects bone formation. However, the mechanisms regulating the decrease in osteoblast recruitment remain unclear. The aim of our study was to determine in vivo osteoblastic proliferation after short-term immobilization among the different bone compartments. Twelve Wistar 5-wk-old rats were assigned to two groups: six tail-suspended animals for 6 days and their six age-related controls. Osmotic minipumps, each containing 40 mg of bromodeoxyuridine (BrdU), were implanted intraperitoneally at day 4 until euthanasia. Histomorphometric measurements found a significantly lower bone volume in primary (ISP, -22%) and secondary spongiosa (IISP, -37%) in unloaded rats compared with their age-related controls. BrdU immunohistochemistry showed that the proliferation capacity of osteogenic precursors in ISP (-29%) and preosteoblasts in IISP (-80%) and in periosteum as well as bone marrow cells (-40%) was lowered by unloading. We demonstrated in vivo for the first time that 6-day tail suspension induced a significant decrease in proliferation of periosteal and trabecular preosteoblasts in ISP and IISP as well as in bone marrow cells.

Effects of intermittent or continuous gravitational stresses on cell-matrix adhesion: quantitative analysis of focal contacts in osteoblastic ROS 17/2.8 cells

The relationship between cell morphology and cell metabolism and the role of mechanical load in bone remodeling is well known. Mechanical stimulation induces changes in the shape of osteoblasts, probably mediated by reorganization of focal contacts. We studied the influence of gravity (Gz) variations occurring during parabolic flight on osteoblast focal adhesion of ROS 17/2.8 osteosarcoma cells subjected to 15 or 30 parabolic flights. Significant flight-induced shape changes consisted of decreased cell area associated with focal contact plaque reorganization. Identical durations of continuous mechanical stress induced by centrifugation (2 Gz) or clinorotation (Gz randomization) had no major effect on cell focal adhesion. ROS 17/2.8 G2/M synchronization by treatment with nocodazole inhibited the flight-induced decrease in adhesion parameters. We concluded that ROS 17/2.8 cells are sensitive to Gz switches and that their adaptation is at least dependent on microtubule function.

Pre-osteoblastic proliferation assessed with BrdU in undecalcified, Epon-embedded adult rat trabecular bone

We evaluated bromodeoxyuridine (BrdU) immunohistochemistry in undecalcified adult rat tibiae to study cell kinetics in various bone compartments: primary and secondary spongiosae, periosteum, and bone marrow. Several regimens of BrdU administration were tested (i.p. injections and osmotic minipumps). We compared LR White resin, methylmethacrylate, and Epon-araldite embedding, microwave irradiation for antigen retrieval, several concentrations of sodium ethoxide for deplastification, and various DNA denaturation procedures. Paraffin-embedded decalcified tibiae and Epon-embedded bowel were used as positive controls. The best results were obtained in rats labeled with 40 mg of BrdU for 72 hr using osmotic minipumps. The procedure using a Microprobe system in Eponembedded bone tissue with a sodium ethoxide concentration of 50% for two intervals of 20 min provided the best staining quality and tissue preservation. Labeled pre-osteoblastic cells and bone marrow cells could be counted. Epon embedding allowed preservation of tetracycline double labeling performed 1 to 5 days before sacrifice. The number of labeled pre-osteoblastic cells was correlated with the double-labeled surface area measured histomorphometrically.

Effects of 1- and 6-month spaceflight on bone mass and biochemistry in two humans

The bone mineral density and the biochemical parameters exploring bone cell activities were analyzed in two cosmonauts who spent 1 and 6 months, respectively, in the Russian MIR station. Measurements were performed before the flight, after the flight, and after a recovery period. At the end of the first month, peripheral QCT measurements indicated a slight decrease of trabecular bone mass in the distal tibial metaphysis. However, after 6 months of spaceflight, a more marked loss of trabecular and cortical bones was observed in the tibia, and was still significant after 6 month recovery in the trabecular compartment, whereas a decrease was no longer observed in the cortical envelope. No change was observed in either compartment of the distal radius at any time. Ultrasound BUA of the calcaneus was greatly reduced by the first month, followed by a more dramatic decrease after month 6. Ultrasound SOS detected no change. Parameters reflecting bone formation activity appeared to be depressed after both missions. In contrast, no dramatic change in resorption parameters was observed, except for a trend toward an increase in pyridinoline. In conclusion, the lower weight-bearing bones appeared more sensitive than the upper ones in terms of spaceflight-induced bone loss. This probably explained the absence of marked systemic biochemical data changes. This study further suggests that recovery in the tibial trabecular compartment 6 months after landing was not completed after a 6 month mission.