Circulation intraosseuse : de la physiologie à la pathologie

Blood flow within bones is unique in two ways: the blood circulates within a closed cavity in which pressure must remain constant, a feat achieved in part thanks to the considerable distensibility of the intraosseous vessels and, above all, veins; the intraosseous circulation allows traffic of minerals between the blood and bone tissue and sends the blood cells produced within the bone marrow into the systemic circulation. In contrast, the arterioles and capillaries within bones have the same anatomic structure as those located elsewhere in the body and are susceptible to arteriosclerosis, arteritis, or thrombosis. The mechanisms that regulate blood flow within bone are incompletely understood, probably because they are difficult to study in vivo. The cytokines and growth factors that regulate intraosseous angiogenesis also regulate bone remodeling, and close links exist between the blood supply to bone and bone formation and resorption : most diseases characterized by increased bone resorption are associated with increased bone vascularization. The vascular bud located at the center of bone multicellular units (BMUs) may determine the timing of bone resorption and bone formation. Avascular bone necrosis and bone infarction may result from acute blood vessel occlusion (thrombosis, lipid emboli, fat cell hypertrophy with compression of intraosseous capillaries), whereas arteriosclerosis may contribute to the development of osteoporosis.     

Effect of ovariectomy on intraosseous vascularization and bone remodelling in rats: Action of tiludronate

In order to study the action of tiludronate on the changes in intraosseous vascularization induced by ovariectomy, and to link these effects to those observed in bone remodelling, 30 female Sprague-Dawley rats (age 40 weeks) were studied. Ten rats were sham-operated and treated by vehicle, 10 rats were ovariec-tomized and treated by vehicle, and 10 rats were ovariectomized and treated orally with tiludronate, 0.16 mmol/kg/per day, 3 days a week for 16 weeks, from the day following ovariectomy. The rats were killed after 4 months, and a histomorphometric study and quantification of intraosseous vessels carried out on the sixth lumbar vertebra. The area of the intraosseous sinusoidal capillaries increased after ovariectomy, which also induced a moderate increase in resorption surfaces and osteoid surfaces leading to a decrease of 40% in the trabecular bone volume at the lumbar spine level. This bone mineral loss was completely prevented by tiludronate, which normalized the bone turnover. However, tiludronate was without any effect on intraosseous vascularization. These results indicate that the surface area of the intraosseous sinusoidal capillaries was correlated positively with resorption surfaces and negatively with trabecular bone volume and the number of bone trabeculae. In these experimental conditions, an inhibitor of bone resorption can exert its positive effect on bone mass without normalization of vascularization.     

Study of the intraosseous vessels of the femoral head in patients with fractures of the femoral neck or osteoarthritis of the hip

Bearing in mind earlier studies which established a link between arteriosclerosis and mineral loss, or fragility of the bones, and also our recent study showing that patients with arterial disorders of the lower limbs also suffered from osteoporosis, we carried out a histological study of the number and appearance of the intraosseous vessels and trabecular bone volume in the femoral heads of patients undergoing surgery for either fracture of the femoral neck or osteoarthritis of the hip. The number of thick-walled vessels, arterioles or arterial capillaries was significantly diminished in the femoral heads of patients with fractures of the femoral neck (p=0.007). In addition, in the latter patients, arteriosclerotic vascular lesions (rupture of the internal elastic lamina, medial thickening and fibrosis) were more frequent than in patients with osteoarthritis of hip. The possibility that, through chronic ischemia, arteriosclerosis may lead to disturbance of bone remodelling and loss of the mechanical properties of bone has not been contradicted by these findings.     

Scanning electron microscopic observation of microvascular cast changes of bone following rigid limb immobilization

This paper reported the results of scanning electron microscopic observation of microvascular cast changes of tibia following long cast immobilization of lower extremity. Beginning from 10 days after immobilization, the diameter of microvessels, particularly capillaries and sinusoids system in bone marrow, displayed severalfold enlargement compared with the control side. The changes became more obvious at 20 days. The number of sinusoids increased whereas the degree of dilatation declined at 40 days. The vessels within the epiphyseal region also showed more intense dilatation, growth of sinusoid-like structure and proliferation of sinusoidal and capillary system in marrow at 60 to 80 days. Similar changes in the cortical bone emerged as well at 80 days. The above-mentioned changes decreased at 100 days. These results pointed out that the pump effect of muscle on the blood flow in bone almost disappeared completely and disturbance of intraosseous venous drainage occurred. Under the condition of increased but unbalanced bone metabolism and turnover, the intraosseous microvascular system exhibited the described changes. Thus the total bone blood volume and the total bone blood flow increased.     

Arteriovenous shunting is not associated with venous congestion in bone. Knee tamponade studied with 15-microns and 50-microns microspheres in immature dogs

Blood flow in the hind-limb bones of 8 immature labrador dogs with unilateral knee joint tamponade at 75 percent of the mean arterial pressure was measured with 15-microns and 50-microns microspheres to determine whether or not arteriovenous shunting occurs in bone with venous congestion caused by increased outflow resistance. The intraosseous pressure was 43 percent of the mean arterial pressure in the experimental distal femoral epiphysis versus 14 percent in the control knee (P less than 0.001). No pressure changes were found in the distal femoral metaphysis. Regional blood flow with 15-microns microspheres decreased centrally in the distal femoral epiphysis and increased centrally in the proximal tibial epiphysis. Metaphyseal blood flow was largely unchanged. A net shift in the preferred embolization site of 50-microns microspheres relative to that of 15-microns microspheres from central to peripheral regions occurred within both juxtaarticular epiphyses, indicating arteriolar vasodilation, but the relation between the uptake of the two microsphere sizes was unchanged when the epiphyses and other bony flow compartments were viewed in toto. The result speaks against the hypothesis of arteriovenous shunting in intraosseous hypertension.     

Effects of variation in systemic blood pressure on intraosseous pressure, PO2, and PCO2

Several regulatory mechanisms have been shown to influence the intraosseous circulation. The influence of general hypovolemia on bone circulation and possible regulatory effects were investigated by recording the intraosseous pressure and PO2 and PCO2 continuously by mass spectrometry in rabbits. Hypovolemia was induced by repeated bleedings. The intraosseous and arterial pressures were found to be linearly related. The intraosseous PO2 already decreased after the first step of bleeding and decreased more than 50% of the initial value after an average blood loss of 40 ml. The intraosseous PCO2 showed an opposite pattern. The experimental PO2 vs. arterial pressure curves were similar to curves obtained by a computer simulation that assumes the blood flow to be proportional to the intraosseous pressure.     

Endothelial control of long bone vascular resistance.

This in vitro study investigates whether intraosseous endothelial cells can regulate long bone blood flow by secretion of vasodilator prostaglandin and EDRF (endothelium-derived relaxing factor). Canine tibia were perfused through the nutrient artery at a constant flow rate, and the increases in perfusion pressure caused by standard doses of norepinephrine were recorded first under control conditions and then during acetylcholine infusion. Acetylcholine attenuated the norepinephrine pressure responses (-62 +/- 3%). This attenuating effect of acetylcholine was partially abolished by inhibition of prostaglandin synthesis (-20 +/- 6%) and completely abolished by inhibition of EDRF synthesis (+73 +/- 43%) or combined inhibition of prostaglandin and EDRF synthesis (+134 +/- 30%). These results are statistically significant (p less than 0.0001) and suggest that both EDRF and vasodilator prostaglandin are synthesized by intraosseous endothelial cells, and can modify long bone vascular resistance. Thus, as in other organs, intraosseous endothelial cells may provide bone with an autoregulatory control mechanism and enable it to respond to a diverse group of vasodilator stimuli.     

From marrow oedema to osteonecrosis: common paths in the development of post-transplant bone pain

Osteonecrosis, the calcineurin-inhibitor-induced pain syndrome and transient marrow oedema may occur after renal transplantation, are generally painful and can be diagnosed by X-ray, radionuclide scan or magnetic resonance imaging. They share features of increased intraosseous pressure, compromised vascular supply, marrow oedema and the development of a 'bone compartment syndrome'. Glucocorticoid dosage is the most commonly implicated risk factor for osteonecrosis. Mechanisms may include the differentiation of mesenchymal stem cells to adipocytes causing increased intraosseous pressure and collapse of marrow sinusoids, as well as increased osteoblast and osteocyte apoptosis. Some of these effects may be ameliorated by lipid lowering drugs. Calcineurin-inhibitors, particularly cyclosporine, may increase the risk of osteonecrosis because of vasoconstrictive effects and sirolimus may influence the development of osteonecrosis by potentiating the effects of calcineurin inhibitors or by influencing the lipid profile. For osteonecrosis, early stages are generally managed conservatively or with core decompression sometimes accompanied by bone grafting and more recently the injection of bone morphogenic protein. The use of iloprost to improve blood flow and bisphosphonates and RANK-ligand inhibition to reduce osteoclastic resorption of remaining trabecular structures are as yet unproven strategies. Unfortunately, the rate of total hip arthroplasty remains high. For the calcineurin-inhibitor-induced pain syndrome and transient marrow oedema, calcium channel blockers, the reduction or withdrawal of calcineurin-inhibitors and core decompression have been used. Although a lack of randomized controlled trials makes management decisions difficult, early recognition of these bone pain syndromes affords the best opportunity for avoiding prolonged pain or joint replacement surgery.     

Changes in bone Pb accumulation: Cause and effect of altered bone turnover

This paper assesses the magnitude of Pb uptake in cortical and trabecular bones in healthy animals and animals with altered balance in bone turnover, and the impact of exposure to Pb on serum markers of bone formation and resorption. The results reported herein provide physiological evidence that Pb distributes differently in central compartments in Pb metabolism, such as cortical and trabecular bones, in healthy animals and animals with altered balance in bone turnover, and that exposure to Pb does have an impact on bone resorption resulting in OC-dependent osteopenia. These findings show that Pb may play a role in the etiology of osteoporosis and that its concentration in bones varies as a result of altered bone turnover characteristic of this disease, a long standing question in the field. In addition, data collected in this study are consistent with previous observations of increased half-life of Pb in bone at higher exposures. This evidence is relevant for the necessary revision of current physiologically based kinetic models for Pb in humans.     

Monocytes mediate osteoclastic bone resorption by prostaglandin production

Summary Monocytes are frequently found adjacent to active bone resorption surfaces in both physiological and pathological situations and may play a key role in bone resorption. There is strong circumstantial evidence that monocytes are precursors for osteoclasts in vivo, and recently they have been shown to resorb devitalized bone directly. The present study shows that monocytes can also resorb bone by stimulation of osteoclasts. Live fetal rodent bones prelabeled with⁴⁵Ca and cultured for 48–96 h in the presence of human monocytes or monocyte-conditioned medium released 80% more mineral than bones cultured in control medium. Bone matrix sustained comparable resorption as demonstrated by a 2-fold decrement in the extracted dry weights of the bones cultured in monocyte-conditioned medium. Histological examination of the bones cultured with monocytes or monocyte-conditioned medium showed increased osteoclast number and activity when compared with bones cultured in control medium. Known inhibitors of osteoclastic activity (phosphate 6 × 10⁻³M, cortisol 10⁻⁶M, and calcitonin 50 mU/ml) inhibited monocyte-conditioned medium-mediated bone resorption. The monocyte-conditioned medium contained sufficient prostaglandin E to account for the bone resorption. Indomethacin 10⁻⁵M added to the monocyte cultures blocked monocyte-conditioned media-induced bone resorption and prostaglandin release. These experiments suggest that monocytes stimulate osteoclastic bone resorption by prostaglandin production. Monocyte-induced bone resorption is partly reversed by inhibitors of osteoclast function. Monocyte-induced osteoclastic bone resorption may play an important role in physiologic bone remodeling and in bone destruction that occurs in chronic inflammatory diseases such as rheumatoid arthritis and periodontal disease.     

Regulating DeltaFosB expression in adult Tet-Off-DeltaFosB transgenic mice alters bone formation and bone mass.

The DeltaFosB isoforms are naturally occurring AP-1 family members that increase bone volume via a cell-autonomous effect on osteoblastic bone formation. Mice overexpressing DeltaFosB demonstrate a very high level of bone formation, resulting in a progressive osteosclerosis. Despite the linkage of bone formation and resorption in physiological systems, no alteration in bone resorption was detected in mice overexpressing DeltaFosB. To determine whether altering DeltaFosB expression can regulate bone formation independently of bone resorption in adult mice, we used the Tet-Off-inducible transgene system to induce or block transgenic DeltaFosB overexpression and thereby regulate bone formation in vivo. Overexpression of DeltaFosB after skeletal maturity increased trabecular bone volume by increasing bone formation, again without altering bone resorption, indicating that developmental DeltaFosB overexpression is not required for the osteosclerotic phenotype. Similarly, switching off DeltaFosB overexpression after osteosclerosis had developed led to a marked decrease in bone formation and loss of bone mass such that trabecular bone volume approached normal levels. Despite this dramatic reduction, no alteration in bone resorption was detected. These results clearly demonstrate that DeltaFosB regulates bone formation and bone mass in adult mice with no effect on bone resorption.     

Bone remodeling during pregnancy and post-partum assessed by metal lead levels and isotopic concentrations

Bone remodeling is normally evaluated using bone turnover markers/indices as indicators of bone resorption and formation. However, during pregnancy and post-partum, there have been inconsistent results between and within biomarkers for bone formation and resorption. These differences may relate to pregnancy-related changes in metabolism and/or hemodilution altering measured marker levels. An alternative approach to evaluating bone remodeling is to use the metal lead (Pb) concentrations and Pb isotopic compositions in blood. These measurements can also provide information on the amount of Pb that is mobilized from the maternal skeleton. Despite some similarities with accepted bone turnover markers, the Pb data demonstrate increased bone resorption throughout pregnancy that further continues post-partum independent of length of breast-feeding, dietary intake and resumption of menses. Furthermore the isotopic measurements are not affected by hemodilution. These data confirm calcium balance studies that indicate increased bone resorption throughout pregnancy and lactation. They also indicate potentially major public health implications of the transfer of maternal Pb burden to the fetus and new born.     

Bone vascularization. Anatomic and physiological considerations, surgical deductions concerning osteosynthesis procedures and vascularized bone graft

The authors report some general considerations concerning the bony anatomy and the bone blood flow. They describe the vascularization of the long bones involving arteries, veins, capillaries and lymphatic vessels. The double systemic and local control of the bone blood flow is evaluated. The local factors are numerous: autoregulation, nervous regulation as well as humoral, metabolic and cellular factors. Some surgical deductions are then discussed concerning osteosynthesis procedures and biomechanical properties of vascularized bone grafts.     

Basic fibroblast growth factor stimulates osteoclast recruitment, development, and bone pit resorption in association with angiogenesis in vivo on the chick chorioallantoic membrane and activates isolated avian osteoclast resorption in vitro.

Increased local osteoclast (OC)-mediated bone resorption coincides with angiogenesis in normal bone development and fracture repair, as well as in pathological disorders such as tumor-associated osteolysis and inflammatory-related rheumatoid arthritis or periodontal disease. Angiogenic stimulation causes recruitment, activation, adhesion, transmigration, and differentiation of hematopoietic cells which may therefore enable greater numbers of pre-OC to emigrate from the circulation and develop into bone-resorptive OCs. A chick chorioallantoic membrane (CAM) model, involving coimplantation of a stimulus in an agarose plug directly adjacent to a bone chip was used to investigate if a potent angiogenic stimulator, basic fibroblast growth factor (bFGF), could promote OC recruitment, differentiation, and resorption in vivo. Angiogenesis elicited by bFGF on the CAM was accompanied by increased OC formation and bone pit resorption (both overall and on a per OC basis) on the bone implants in vivo. In complementary in vitro assays, bFGF did not directly stimulate avian OC development from bone marrow mononuclear cell precursors, consistent with their low mRNA expression of the four avian signaling FGF receptors (FGFR)-1, FGFR-2, FGFR-3, and FGFR-like embryonic kinase (FREK). In contrast, bFGF activated isolated avian OC bone pit resorption via mechanisms inhibited by a selective cyclo-oxygenase (COX)-2 prostaglandin inhibitor (NS-398) or p42/p44 MAPK activation inhibitor (PD98059), consistent with a relatively high expression of FGFR-1 by differentiated avian OCs. Thus, bFGF may sensitively regulate local bone resorption and remodeling through direct and indirect mechanisms that promote angiogenesis and OC recruitment, formation, differentiation, and activated bone pit resorption. The potential for bFGF to coinduce angiogenesis and OC bone remodeling may find clinical applications in reconstructive surgery, fracture repair, or the treatment of avascular necrosis. Alternatively, inhibiting such bFGF-dependent processes may aid in the treatment of inflammatory-related or metastatic bone loss.     

Comparison of growth-induced resorption and denervation-induced resorption on the release of [3H]tetracycline, 45calcium, and [3H]collagen from whole bones of growing rats

The major effect of immobilization during growth is a smaller bone mass induced by either an increased bone resorption or a decreased bone formation. Using a method of analyzing radioisotopic loss of [3H]tetracycline and [3H]collagen from bone prelabeled in vivo, we compared the amount of bone resorption due to immobilization with bone resorption induced by growth. One hind limb was denervated in growing male rats, 6 weeks of age, that had been chronically prelabeled with [3H]tetracycline, 45calcium, and [3H]proline. The total radioactivity of the whole femur and tibia/fibula from the denervated limb was compared with that from bones of the control limb at 0, 1, 2, 4, and 8 weeks after denervation. The effect of growth on bone formation was measured by net increases in bone length, volume, and mass of matrix and mineral. Experimental bones had a significantly smaller volume and mass. Bone resorption was much greater during growth modeling than during denervation. The additional bone resorption induced by denervation was a small fraction (one-fourth) of the resorption induced by growth. Denervation during growth resulted in less bone being formed due to a smaller gain in matrix and mineral mass as a result of a reduction in bone formation.     

Milk ribonuclease-enriched lactoferrin induces positive effects on bone turnover markers in postmenopausal women

Summary  Current treatments for postmenopausal osteoporosis suffer from side effects. Safe and natural milk proteins, ribonuclease, and lactoferrin promote formation of new capillaries and bone formation. A ribonuclease-enriched lactoferrin supplement studied here, demonstrates significant reduction in resorption and increase in formation, towards restoring the balance of bone turnover within 6 months. Introduction  Osteoporosis, a major health issue among postmenopausal women, causes increased bone resorption and reduced bone formation. A reduction in angiogenesis could also contribute to this imbalance. Current treatments such as hormone replacement therapy and bisphosphonates have drawbacks of severe side effects. Milk ribonuclease (RNase) is known to promote angiogenesis and lactoferrin (LF) to stimulate bone formation by osteoblasts. We examine the effect of ribonuclease-enriched lactoferrin supplement on the bone health of postmenopausal women. Methods  A total of 38 healthy, postmenopausal women, aged 45 to 60 years were randomized into placebo or RNAse-enriched-LF (R-ELF) supplement groups. The bone health status was monitored by assessing bone resorption markers, serum N-telopeptides (NTx), and urine deoxypyridinoline (Dpd) crosslinks and serum bone formation markers, bone-specific alkaline phosphatase (BAP), and osteocalcin (OC). Results  R-ELF supplementation demonstrated a decrease in urine Dpd levels by 14% (19% increase for placebo) and serum NTx maintained at 24% of the baseline (41% for placebo), while serum BAP and OC levels showed a 45% and 16% elevation (25% and 5% for placebo). Conclusions  R-ELF supplementation demonstrated a statistically significant reduction in bone resorption and increase in osteoblastic bone formation, to restore the balance of bone turnover within a short period.     

EphB4 enhances the process of endochondral ossification and inhibits remodeling during bone fracture repair

Previous reports have identified a role for the tyrosine kinase receptor EphB4 and its ligand, ephrinB2, as potential mediators of both bone formation by osteoblasts and bone resorption by osteoclasts. In the present study, we examined the role of EphB4 during bone repair after traumatic injury. We performed femoral fractures with internal fixation in transgenic mice that overexpress EphB4 under the collagen type 1 promoter (Col1‐EphB4) and investigated the bone repair process up to 12 weeks postfracture. The data indicated that Col1‐EphB4 mice exhibited stiffer and stronger bones after fracture compared with wild‐type mice. The fractured bones of Col1‐EphB4 transgenic mice displayed significantly greater tissue and bone volume 2 weeks postfracture compared with that of wild‐type mice. These findings correlated with increased chondrogenesis and mineral formation within the callus site at 2 weeks postfracture, as demonstrated by increased safranin O and von Kossa staining, respectively. Interestingly, Col1‐EphB4 mice were found to possess significantly greater numbers of clonogenic mesenchymal stromal progenitor cells (CFU‐F), with an increased capacity to form mineralized nodules in vitro under osteogenic conditions, when compared with those of the wild‐type control mice. Furthermore, Col1‐EphB4 mice had significantly lower numbers of TRAP‐positive multinucleated osteoclasts within the callus site. Taken together, these observations suggest that EphB4 promotes endochondral ossification while inhibiting osteoclast development during callus formation and may represent a novel drug target for the repair of fractured bones. © 2013 American Society for Bone and Mineral Research.     

Calcium absorption and osseous organ-, tissue-, and envelope-specific changes following ovariectomy in rats

Because cancellous bone loss occurs following ovariectomy (OVX) in rats, this has become a popular model to explore therapeutic modalities for postmenopausal bone loss in humans. The purpose of this study was to determine intestinal calcium absorption in situ and organ-, tissue-, envelope-, and site-specific changes in osseous tissues at six weeks after OVX in rats using chemical, biochemical, absorptiometric, microradiographic, and morphometric methods. There were no changes in intestinal absorption of calcium, but duodenal weight per length was significantly increased in the OVX animals compared with age-matched, sham-operated controls. There was an increase in wet bone weight, but decreases in ash/dry bone weight, total bone Ca, and Ca per ash weight in the OVX animals. There were significant decreases in the OVX animals in metaphyseal bone mineral content, as determined by photon absorptiometry and metaphyseal cancellous bone volume. The perimeter to area ratio of the metaphyseal cancellous bone in the OVX animals was increased compared with controls. Endochondral growth rates were increased in the OVX animals, attributable to an increased growth plate hypertrophic cell size and rate of chondrocyte proliferation. In the OVX animals there was an increase in modeling in the formation mode of the periosteal surface at the tibio-fibular junction. Increased periosteal modeling in the formation mode was also observed in the body of the mandible, suggesting that the changes in periosteal bone formation are not strictly coupled with changes in endochondral growth. There was an increase in modeling in the resorption mode of the endocortical surface at the tibio-fibular junction in the OVX animals. There was increased bone turnover in the OVX animals compared with controls on the endosteal surface, as indicated by increases in both formation and resorption indices, including an increase in the osteoclast population. In the long bones, OVX results in larger bones due to increases in endochondral growth and modeling in the formation mode at the periosteal surfaces, with a loss of cancellous bone and total bone calcium due to increased resorption on the endocortical surfaces and turnover (increased formation and resorption) on endosteal surfaces. This study emphasizes that osseous tissue changes following OVX in rats are tissue-specific, envelop-specific, and site-specific.     

Magnetic resonance tomography in preoperative analysis of chronic post-traumatic osteomyelitis

Chronic osteomyelitis in 8 patients was studied preoperatively by magnetic resonance (MR) imaging and in part of them also by computed tomography (CT). Morphologic information about extraosseous and intraosseous changes was important for surgical planning. In long bones CT generally is superior delineating bone structures (sequestra and fragments of devitalized bone in the intramedullary cavity) and MR may be used as an adjunct for localizing extraosseous and intraosseous abscesses. In trabecular bones as the os calcis MR seems to be equivalent to CT.