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Oral Presentations, Invited Speakers
Abstracts I-1 to I-29
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THE ROLE OF BONE QUALITY IN THE PATHOPHYSIOLOGY OF OSTEOPOROSIS M. L. Bouxsein Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center & Harvard Medical School, Boston, USA The first Consensus Conference on Osteoporosis of the new millennium proposed a new definition of osteoporosis as 'a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture.' In this statement, bone density and bone quality were cited as primary contributors to bone strength. Whereas a precise definition of bone quality remains elusive, evidence is mounting to support the concept that characteristics independent of bone density, such as trabecular architecture, bone turnover, the organic and inorganic composition of bone matrix, damage accumulation, and cell viability, may be important in the pathophysiology of osteoporosis and in the mechanisms that underlie the anti-fracture effects of osteoporosis therapies. For example, the concept of bone quality has been invoked to explain observations from clinical trials that small changes in BMD result in greater than predicted reductions in fracture risk, that therapy-induced changes in BMD explain only a small proportion of the variance in fracture risk reduction, and that reductions in fracture risk are evident long before changes in BMD are observed. Ultimately, the effect of these potential contributors to bone quality must be reflected in the mechanical behavior of bone. In this presentation, the ways in which these factors may contribute to bone strength will be described, with an emphasis on discussing several plausible mechanisms by which osteoporosis therapies may affect bone strength, and therefore fracture risk, independently or synergistically with their effects on bone density. PREDICTION OF OSTEOPOROTIC FRACTURES BY CLINICAL RISK FACTOR ANALYSIS C. E. De Laet1*, H. A. P. Pols2 1Institute for Medical Technology Assessment, Erasmus Medical Center, Rotterdam, The Netherlands 2Dept of Internal Medicine, Erasmus Medical Center, Rotterdam, The Netherlands Although it is believed that most fractures occurring in the elderly are related to osteoporosis, the most important fractures are those of the hip, wrist and vertebrae. In most areas in the world osteoporotic fractures occur more frequently in women than in men. For targeting therapeutic interventions the crucial question is not to diagnose osteoporosis, but to evaluate fracture risk. Fracture risk assessment can be based on the use of Clinical Risk Factors (CRF's), on an assessment of the quantity or quality of bone for example by bone mineral density (BMD), or on a combination of both. A large number of risk factors for osteoporotic fractures have been identified. In most studies age, BMD, previous fractures steroid use and frailty related parameters are strong predictors of a future osteoporotic fracture. Between men and women no large differences appear to exist in the predictive power of these risk factors For the Dutch osteoporosis guidelines we evaluated the 10-year fracture risk. Based on evidence from literature we proposed a simple risk score based on 5 easy to use risk indicators and calculated, taking into account mortality, 10-year fracture risk for hip, wrist and vertebral fractures at several ages. Moreover, we integrated the effect on quality of life of several fracture types in one score using the concept of hip fracture equivalents. When based on this 'a priori' risk an intervention is considered, an additional assessment of bone metabolism (BMD, ultrasound, bone turnover markers) can be carried out. It is clear that epidemiology is not restricted anymore to the description of the size of the problem, but also contributes to a better understanding of the aetiology of osteoporosis in both men and women. Currently a worldwide effort to find reliable and consistent clinical risk factors for fractures is underway through a meta-analysis of several large cohort studies. The results can then be used to evaluate medium term fracture risk in specific populations and validate the current risk scores. INTERACTIONS BETWEEN RANKL, TNF-ALPHA AND TNF-BETA IN THE REGULATION OF OSTEOCLAST FORMATION AND FUNCTION T. J. Chambers St George's Hospital Medical School, London, UK It has been known for many years that osteoclasts derive from M-CSF-dependent precursors of the mononuclear phagocyte series, and that their formation and function are regulated by cells of the osteoblastic lineage. There has recently been an explosion of information concerning the molecular basis for this regulation. Osteoblastic cells express M-CSF, which is required for proliferation, survival, and the induction of RANK in precursors. Osteoblastic cells induce osteoclastic differentiation and resorptive activity through expression of RANKL. Osteoclastic regulation is assisted through secretion by osteoblastic and other cells of osteoprotegerin (OPG), a soluble decoy receptor for RANKL. TGF-beta appears to be an essential cofactor for osteoclast formation. Thus, TGF-beta not only powerfully synergizes with RANKL, but osteoclast formation is abolished by soluble TGF-beta receptors. TGF-beta seems to act partly by preventing the development of resistance to OCL-induction that otherwise occurs when precursors are incubated in M-CSF, and opposes the ability of agents such as IFN-gamma to induce alternative macrophagic lineages. TGF-beta also suppresses apoptosis in osteoclasts. Surprisingly, not only RANKL but TNF-alpha can induce osteoclast formation in-vitro, especially in the presence of TGF-beta. Thus, TNF-alpha can induce inflammatory/cytocidal macrophages or osteoclasts, depending upon the presence or absence of cofactors such as interferons or TGF-beta. This suggests a model in which lineage is activated by RANKL/TNF-alpha, but determined by the cofactors. TNF-alpha enhances bone resorption by several pathways. Not only does it induce RANKL in osteoblastic cells, and directly stimulate osteoclastic differentiation in precursors, but it also stimulates bone resorption in mature osteoclasts, in the absence of osteoblastic cells. TNF-alpha is equipotent with RANKL for this action. Interestingly, TNF activates osteoclasts at concentrations an order of magnitude below those required for osteoclastic differentiation. Moreover, TNF-alpha strongly synergizes with RANKL, such that miniscule concentrations of TNF-alpha are sufficient to substantially augment osteoclast activation. The extreme sensitivity of osteoclasts to activation by TNF-alpha, suggests that the most sensitive osteolytic response of bone to TNF-alpha is through activation of existing osteoclasts; and the strong synergy with RANKL provides a mechanism whereby increased osteolysis can be achieved without disturbance to the underlying pattern of osteoclastic localisation. THE MEVALONATE PATHWAY IN OSTEOCLAST SIGNALLING M. J. Rogers*, F. P. Coxon Dept of Medicine & Therapeutics, University of Aberdeen, UK The mevalonate pathway is responsible for the synthesis of cholesterol and a variety of isoprenoid lipids (such as farnesyl diphosphate/FPP and geranylgeranyldiphosphate/GGPP). FPP and GGPP are substrates for prenyl:protein transferases that attach the isoprenoid lipid onto the C-terminus of small GTPases. The latter are a large family of highly conserved proteins that act as molecular switches. The binding of GTP causes allosteric changes that allow interaction with effector proteins (eg protein kinases), thereby activating mutiple downstream signalling pathways. Post-translational prenylation of small GTPases with a farnesyl or geranylgeranyl group is essential for their correct function since it allows association with subcellular membranes and, in some cases, interaction with other proteins. Recently, the importance of prenylated small GTPases in osteoclasts was highlighted by the discovery that nitrogen-containing bisphosphonates (N-BPs) are potent inhibitors of FPP synthase. Inhibition of this enzyme causes loss of FPP and, indirectly, GGPP, thereby inhibiting prenylation of small GTPases. In particular, geranylgeranylated GTPases appear to be essential in osteoclasts, since restoring geranylgeranylation, but not farnesylation, rescues osteoclasts from the effects of N-BPs. Furthermore, the effects of N-BPs on osteoclasts are mimicked in vitro by GGT8, a selective inhibitor of protein geranylgeranylation. The role of geranylgeranylated GTPases in osteoclasts is poorly understood, although they are probably fundamental for the intracellular control of osteoclast activity. For example, the Rho family GTPases (Rho, Rac and Cdc42) are involved in cytoskeletal organisation. In osteoclasts, inhibition of Rho or Rac function prevents the formation of podosomes and F-actin rings and inhibits resorption, although the exact signalling pathways upstream and downstream are largely unclear. Cdc42 appears to regulate podosome assembly in other cell types but its role in osteoclasts is unknown. Rab GTPases, the largest subfamily, are involved in membrane and vesicular trafficking. Rab7 is localised to the ruffled border, and antisense inhibition of Rab7 disrupts ruffled border formation and inhibits bone resorption. The roles of other Rab proteins in osteoclasts are unknown, although specific inhibition of Rab prenylation inhibits resorption and causes morphological changes in the osteoclast membrane. The mevalonate pathway is therefore of fundamental importance in osteoclasts for providing metabolites necessary for the correct function of small GTPase signalling proteins. Inhibition of this pathway is the basis for existing and potentially novel anti-resorptive agents. OSTEOGENESIS IMPERFECTA: PATHOPHYSIOLOGY AND MANAGEMENT F. H. Glorieux Shriners Hospital for Children and McGill University, Montreal, Canada Osteogenesis imperfecta (OI) is a heritable disorder characterized by increased bone fragility. Four different types are commonly distinguished that range from a mild condition (type I) to a lethal one (type II). Types III and IV are the severe forms surviving the neonatal period. In most cases, there is a reduction in the production of normal type I collagen or the synthesis of abnormal collagen as a result of mutations in the type I collagen genes. There are instances, however, where alterations in bone matrix components, other than type I collagen, are the likely basic abnormalities. We have identified three such discrete types by histomorphometric evaluation (type V and VI) and linkage analysis (type VII). They provide evidence for the as yet poorly understood complexity of the phenotype-genotype correlations in OI. In all severe forms, histologic and densitometric evaluations have documented an increase in osteoclastic activity and a reduction in the formation of new bone. We thus designed studies to assess the effects of bisphosphonate (potent inhibitors of bone resorption) treatment in children with severe OI. Pamidronate administered intravenously at 2-4 month intervals resulted in significant increase in bone mineral density, decrease in chronic pain and fracture incidence, and improved mobility and ambulation. Patients received annual doses of 9-16 mg/kg. There was no adverse effects on growth, fracture healing or bone modeling. The benefits observed were more marked in children under 2 years of age, with reshaping of vertebral bodies and long bones, probably correlated to rapid skeletal growth in the young infant. The major impact on bone is cortical thickening, with the long term effect on remodeling remaining to be evaluated. Although not a cure for OI, this therapeutic approach is the first one that permits to significantly alter the natural course of events in severe OI, characterized by relentless progression of crippling deformities and chronic pain. This approach will remain the therapy of choice until targeted gene therapy will become a reality. THE MUTATIONAL SPECTRUM OF HUMAN MALIGNANT AUTOSOMAL RECESSIVE OSTEOPETROSIS A. Frattini1, C. Sobacchi1, P. Orchard2, I. Tezcan3, P. Vezzoni1, I. Baric4, S. Dupuis-Girod5, A. Musio1, M. Mirolo1, A. Villa1* 1Institute of Biomedical Technologies, CNR, Segrate (MI), Italy 2Department of Pediatrics, Division of Bone Marrow Transplantation, University of Minnesota, Minneapolis, Minnesota, USA 3Hacettepe University Children's Hospital, Ankara, Turkey 4Department of Pediatrics, University Hospital Center, Zagreb, Croatia 5Unite d'Immonulogie et d'Hematologie Pediatriques, Hopital Necker-Enfant Malades, Paris, France Human malignant infantile osteopetrosis (arOP) is a genetically heterogenous autosomal recessive disorder of bone metabolism, which, if untreated, has a fatal outcome. Most human arOP patients have normal to elevated number of osteoclasts in bone biopsies, suggesting that osteopetrosis is due to a defect in genes affecting the function and not the differentiation of osteoclasts. This notion has been recently supported by the finding of a defect in the vacuolar proton pump (VPP) in about 50% of the patients and by the demonstration that ClC-7, a chloride channel which acts in concert with the VPP, was mutated in one of 12 families studied. These data confirm that acidification is the most sensitive step in bone resorption. Our group, as well as others have recently found that mutations in the ATP6i gene, encoding the a3 subunit of the VPP, are responsible for a subset of arOP. By sequencing the ATP6i gene in arOP patients from 44 unrelated families with a worldwide distribution we have now confirmed that ATP6i mutations are responsible for approximately one-half of patients affected by arOP. The vast majority of these mutations (40 out of 42 alleles, including 7 deletions, 2 insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles. In addition, we have also analysed 9 unrelated arOP patients from Costa Rica, where this disease is apparently much more frequent than elsewhere. All these patients bore either or both of two missense mutations (G405R and R444L) in amino acid residues evolutionary conserved from yeast to humans. The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born. We also examined whether ClC-7 gene is mutated in our ATP6i-independent arOP patients. Our results suggest that this gene is only rarely responsible for arOP. This study contributes to the determination of genetic heterogeneity of arOP and allows further delineation of the other genetic defects causing this severe condition. FIBRODYSPLASIA OSSIFICANS PROGRESSIVA: CLUES TO THE FORMATION OF A HETEROTOPIC SKELETON F. S. Kaplan*, J. Ahn, L. Serrano de la Pena, E. M. Shore School of Medicine, University of Pennsylvania, Philadelphia, USA Fibrodysplasia ossificans progressiva (FOP), a rare autosomal dominant genetic disorder, is the most disabling form of heterotopic ossification in humans. FOP is characterized by anterior-patterning malformations of the great toes and by progressive induction of endochondral osteogenesis at ectopic sites. Bone morphogenetic protein 4 (BMP4) mRNA and protein are uniquely over-expressed in lymphocytes and lesional cells from patients who have FOP. New findings suggest that defects in the BMP4 pathway in FOP cells severely limit their ability to express multiple BMP antagonists in response to a BMP4 stimulus. The BMP4 gene is not mutated in FOP, and the BMP4 locus has been excluded from linkage to the condition. These data suggest that the primary defect in FOP is not in the BMP4 gene itself, but in a component of the BMP4 pathway or interacting pathway that leads to resistance of BMP4 antagonist expression. Our data suggest that a loss of negative feedback due to an insufficient BMP antagonist response may account in part for increased BMP4 activity in FOP. Such a defect suggests the loss of a critical negative feedback mechanism by which cells normally regulate the magnitude and boundaries of ambient morphogenetic signals. These findings from a disabling human disease illustrate the importance of a critical balance between an inductive morphogen and its secreted antagonists in the formation of an ectopic organ system and suggest the potential of BMP antagonist-based strategies in the therapy of FOP. 11BETA-HYDROXYSTEROID DEHYDROGENASE IN GLUCOCORTICOID SIGNALLING IN BONE M. Hewison*, M. S. Cooper, P. M. Stewart Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham B15 2TH, UK Glucocorticoids play an essential role in skeletal development but are detrimental in excess. Despite this, relatively little is known about the molecular mechanisms involved in determining the sensitivity of bone cells to glucocorticoids. Susceptibility to the bone-specific effects of glucocorticoids correlates only weakly with circulating hormone levels or target cell glucocorticoid receptor (GR) expression. We have therefore proposed that tissue-specific 'prereceptor' regulation may act as a pivotal determinant of the impact of glucocorticoids on bone. Previous studies have shown that in several tissues glucocorticoid action is dependent on the expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) isozymes, which interconvert active cortisol and inactive cortisone. 11beta-HSD1 is located in tissues which express relatively high levels of GR such as liver and adipose where it functions by increasing local concentrations of cortisol. 11beta-HSD2 is located predominantly in tissues with high mineralocorticoid receptor (MR) expression such as kidney and colon. In these tissues 11beta-HSD2 acts to protect the MR from illicit occupancy by cortisol by metabolising it to cortisone. Immunohistochemical, Western blot and RT-PCR analyses of normal human bone and primary osteoblast cultures showed predominant expression of 11beta-HSD1. Conversely, fetal bone and osteosarcoma cells exhibited predominant 11beta-HSD2 expression. In each case the presence of an isozyme was associated with GR expression. Subsequent enzyme activity studies have shown that primary cultures of human osteoblasts are able to synthesise cortisol from cortisone. This was potently stimulated by inflammatory cytokines such as TNFalpha and IL-1, suggesting a role for 11beta-HSD1 as a modulator of inflammatory responses. Paradoxically, osteoblast 11beta-HSD1 activity was also stimulated by therapeutic corticosteroids such as prednisone and prednisolone. Functional studies in vitro using stable transfectant models have shown that the major impact of 11beta-HSD isozymes is on osteoblast proliferation, with 11beta-HSD1 being antiproliferative and 11beta-HSD2 proproliferative. However, studies using an 11beta-HSD inhibitor suggest that altered bone resorption may be the chief consequence of 11beta-HSD1 action in vivo. These data confirm that prereceptor regulation is a crucial determinant of the impact of glucocorticoids on bone. In particular, 11beta-HSD1 may play an important role in the pathophysiology of steroid-induced bone disease. ANALYSIS OF THE REGULATION OF BONE FORMATION BY LEPTIN G. Karsenty Baylor College of Medicine, Houston, TX, USA We have shown earlier that leptin regulates following its binding to hypothalamic receptors. This initial study however did not provide any clues about the molecular mechanisms accounting for this action of leptin. In an effort to analyze how leptin can regulate bone formation in vivo we asked three questions. The first question is what is the identity of the neurons controlling bone formation. We performed chemical leisoning in wild-type mice followed by leptin infusion in the third ventricle to answer this question. This allowed us to identify a population of hypothalamic neurons that act as the central center of bone formation. To determine how leptin signals to this center we generated various transgenic mouse models expressing leptin either in ob/and in liver as well or mice overexpressing leptin receptors. Results of the analysis of these mice will be presented at the meeting. Finally, we followed several different approaches to determine the nature and the identity of the mediators of leptin action on bone formation. These investigations indicated that one group of molecules are responsible for this action. This part of the investigation will also be presented at the meeting. THE BIOCHEMICAL AND CELLULAR CHARACTERIZATION OF SCLEROSTIN, THE CAUSATIVE GENE FOR SCLEROSTEOSIS J. A. Latham Gene Function and Target Validation, Celltech R&D Inc, Bothell WA, USA Sclerosteosis is a recessive disorder restricted to the skeleton that afflicts patients with excessive bone matrix deposition. The matrix material, both cortical and cancellous, is extremely strong and of superior quality. This disease provides an excellent opportunity through the application of the drug surrogate hypothesis for the identification of therapeutic targets for use in treating diseases associated with low bone mass. In this strategy, the combination of recessive genetics inferring loss of function and a restricted phenotype converse from the diseased population, provides a direct route to a therapeutic intervention opportunity. Positional cloning methods have identified the causative gene, which has been called Sclerostin, a novel family member of the soluble BMP antagonists. This group of proteins, which includes Chordin, Noggin, Cerberus and Gremlin, form high affinity noncovalent complexes with BMPs. These protein/protein complexes perturb the signaling property of the BMP and therefore act to suppress the mitogenic properties of this protein. Data will be presented that describes the characterization of this gene product in biochemical and cellular systems with an eye to understanding the role of the gene in bone matrix deposition and its applicability in treating osteoporosis. ROLE OF FOS PROTEINS IN OSTEOBLAST DIFFERENTIATION AND FUNCTION E. F. Wagner, et al. Research Institute of Molecular Pathology (I.M.P.), Dr. Bohr-Gasse 7, A-1030 Vienna, Austria Fos proteins are transcription factors belonging to the AP-1 complex, which acts like a biosensor for many cells and is causally involved in many developmental processes, but also in cell differentiation and disease. One of the four members of the Fos proteins is c-Fos, which is a key regulator of bone development (1). Transgenic mice expressing exogenous c-Fos develop bone tumors, characterised by transformation of osteoblasts. In contrast, mice lacking c-Fos are osteopetrotic due to a differentiation block in bone resorbing osteoclasts (2). We were also interested to study how c-Fos and its related protein Fra-1, which is c-Fos inducible, control osteoblast proliferation and osteoclast differentiation (3). Gene deletion experiments in mice demonstrated that Fra-1 is an essential gene for development (4) and genetic rescue experiments suggest that Fra-1 is not essential for osteoblast and osteoclast differentiation. However, transgenic mice overexpressing Fra-1 develop the bone disease osteosclerosis, which is due to increased bone formation (5). The primary cause of the disease in Fra-1 transgenic mice is an osteoblast differentiation defect, although the transgenic osteoclasts are hyperactive in vitro. To test whether Fra-1 can substitute for c-Fos, we generated knock-in mice that express Fra-1 in place of c-Fos. Fra-1 rescues c-Fos dependent functions in bone development, which appeared to be gene-dosage dependent (6). However, Fra-1 failed to substitute for c-Fos in inducing expression of target genes in vitro. We are using these systems to identify novel Fos target genes by microarrays and with the help of bone-specific conditional alleles of c-Fos and Fra-1, we are studying the molecular mechanisms how Fos proteins govern bone cell development and differentiation. 1. Wagner, E.F. and Karsenty, G. (2001) Genetic control of skeletal development. Curr Opin. Genetics & Development, 11, 527-533. 2. Grigoriadis, A.E., Wang, Z.-Q., Cecchini, M.G., Hofstetter, W., Felix, R., Fleisch H.A. and Wagner, E.F. (1994) c-Fos is a key regulator of osteoclast/ macrophage lineage determination and bone remodelling. Science 266, 443-448. 3. Matsuo, K., Owens, J.M., Tonko, M., Elliot, C. Chambers, T.J. and Wagner, E.F. (2000) Osteoclast differentiation by the c-Fos target gene Fra-1, Nature Genetics 24, 184-187. 4. Schreiber, M., Wang, Z.Q., Jochum W., Fetka, I. Elliott, C. and Wagner, E.F. (2000). Placental vascularization requires the AP-1 component Fra1. Development 127, 4937-4948. 5. Jochum, W., David, J.P., Elliot, C., Wutz, A., Plenk, H., Matsuo, K. and Wagner, E.F. (2000) Increased bone formation in transgenic mice expressing the transcription factor Fra-1, Nature Medicine 6, 980-984. 6. Fleischmann, A., Hafezi, F., Elliott, C., Remé, C.E., Rüther, U. and Wagner, E.F. (2000). Fra-1 replaces c-Fos-dependent functions in mice. Genes & Development 14, 2695-2700. QUANTITATIVE ULTRASOUND: METHODS AND CLINICAL APPLICATIONS C. C. Glüer*, R. Barkmann Medizinische Physik, Diagnostische Radiologie, Universitätsklinikum Kiel, Germany Quantitative Ultrasound (QUS) approaches have been developed for the assessment of bone status in osteoporosis and other skeletal disorders. Today a number of different QUS devices are commercially available that assess partially different aspects of bone status. One needs to recognise the difference between the measurement parameters Speed of Sound (SOS) and Broadband Ultrasound Attenuation (BUA), the different measurement sites (calcaneus, finger phalanges, and radius) and the different technologies employed (transverse transmission, axial transmission). For example, one could expect substantial differences between BUA results at a trabecular weight bearing bone measured in transverse transmission and SOS measured at a cortical non weight bearing bone measured in axial transmission. Today the main area for use of QUS approaches is the assessment of a fracture risk. For use in monitoring and diagnosis, further studies and methodological clarification to determine diagnostic criteria suitable for peripheral devices are required. Special applications, e.g. in paediatrics or rheumatology, have been investigated with promising results. In clinical practice, adequate and regularly performed quality assurance measures and in-depth knowledge about the general and device specific limitations of the approach used are of substantial importance. When used appropriately, QUS devices can play an important role in the assessment of bone status. Ultrasound interaction with bone is strongly affected by bone mass but also by other factors related to elasticity and strength of bone. Bone microstructure and material properties both have been shown to affect QUS parameters. PERIPHERAL OR CENTRAL DENSITOMETRY: DOES IT MATTER WHICH TECHNIQUE WE USE? I. Fogelman*, G. M. Blake GKT Medical School, Guy's Hospital, London, UK Over the past decade, bone density scans have assumed an essential role in the diagnosis of osteoporosis. Although dual X-ray absorptiometry (DXA) scans of the central skeleton remain widely used, a variety of different types of equipment for measuring peripheral sites is now available. However, the poor correlation between different types of measurement and a lack of consensus on how results from peripheral sites should be interpreted have proved a barrier to the more widespread use of these devices. These issues prompt the following questions: Which technique best identifies patients at risk of fracture? What approaches to scan interpretation ensure the closest agreement between different methods? Does it matter if different patients are selected for treatment on the basis of different techniques? The relative risk (RR) of fracture derived from prospective studies is a key parameter for comparing the clinical value of different techniques. Recent reports confirm the advantages of hip bone mineral density compared with peripheral measurements for predicting hip fracture risk, although for fractures at other sites the differences are inconclusive. Using receiver operating characteristic curves, we show that the guidelines adopted for scan interpretation are of crucial importance for ensuring that the information is used effectively. The closest agreement between different techniques is achieved by setting thresholds for peripheral devices that target either the same percentage of the population or the same percentage of future fracture cases as femur DXA. Different methods select different groups of individuals from the total pool of patients who will later sustain a fracture, with the most successful technique being the one with the largest RR value. The emphasis placed by many studies on validating new techniques by studying their correlation with DXA may lead to the clinical value of peripheral devices being underestimated when the key datum is the RR value inferred from prospective fracture studies. ADVANCED IMAGING OF BONE MACRO AND MICRO STRUCTURE H. K. Genant Osteoporosis and Arthritis Research Group, University of California, San Francisco CA, USA In the past decade, considerable progress has been made in the development of methods for assessing the skeleton noninvasively so that osteoporosis can be detected early, its progression and response to therapy carefully monitored, or the risk of fracture effectively ascertained. Bone mineral density (BMD) of the peripheral, central or entire skeleton as well as the trabecular or cortical bone envelopes can now be evaluated with a high degree of accuracy and precision and the strength of bone and the propensity to fracture can be reliably estimated. Noninvasive and/or nondestructive techniques are capable of providing macro or micro structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, numerous studies indicate that bone strength is only partially explained by BMD. Quantitative assessment of macrostructural characteristics such as geometry, and microstructural features such as relative trabecular volume, trabecular spacing and connectivity may improve our ability to estimate bone strength. The methods available for quantitatively assessing macrostructure include (besides conventional radiographs, which are not considered here) computed tomography, and particularly volumetric quantitative computed tomography (vQCT). Methods for assessing microstructure of trabecular bone noninvasively and/or nondestructively include high resolution computed tomography (hrCT), micro computed tomography (µCT), high resolution magnetic resonance (hrMR), and micro magnetic resonance µMR. Volumetric QCT, hrCT and hrMR are generally applicable in vivo, and µCT and µMR are principally applicable in vitro. From a clinical perspective, the challenges for bone imaging include balancing the relative advantages of simple bone densitometry versus the more complex architectural features of bone or similarly the deeper research requirements versus the broader clinical needs. The considerable potential biological differences between the peripheral appendicular skeleton and the central axial skeleton must be further examined. Finally, the relative merits of these sophisticated imaging techniques have to be weighed with respect to their applications as diagnostic procedures requiring high accuracy or reliability versus their monitoring applications requiring high precision or reproducibility. PROSPECTS FOR CARTILAGE ENGINEERING A. P. Hollander1*, W. Z. Kafienah1, S. C. Dickinson1, T. J. Sims1, I. Martin2, M. D. Barker3, A. Frazer3 1Academic Rheumatology, University of Bristol, Bristol, UK 2Department of Surgery, University of Basel, Basel, Switzerland 3Division of Genomic Medicine, Sheffield University, Sheffield, UK There have been significant advances in the techniques required for successful tissue engineering of cartilage. However a number of challenges remain to be resolved in advance of clinical application. Cartilage engineering to date has mostly relied on the use of cells isolated from young animals. There have been few attempts at developing a clinically useful methodology. An autologous cell source will be essential for the treatment of cartilage lesions, however the clinical use of human chondrocytes for tissue engineering will require expansion of cell numbers from a small donor site biopsy. Therefore clinical application will be limited by the chondrogenic potential of cells after proliferation. We have now demonstrated that adult human articular chondrocytes that have been expanded in monolayer culture and then used for cartilage engineering have poor chondrogenic potential. In contrast, adult nasal septum chondrocytes are relatively effective when used under identical conditions. We therefore propose that nasal chondrocytes should be used to repair articular cartilage lesions. An alternative would be to use autologous mesenchymal stem cells and promote their differentiation to chondrocytes, however a key challenge will be to avoid the generation of hypertrophic chondrocytes, which may result in calcification of cartilage at the articular surface. Techniques must be developed to ensure that implanted engineered cartilage integrates well with the surrounding natural tissue. In order to achieve short-term mechanical stability it may be necessary to engineer osteochondral implants that can be inserted into the subchondral bone. Subsequent integration of implant with surrounding cartilage must involve migration of chondrocytes between the two surfaces and techniques for enhancing this process are under development. Successful clinical trials of implanted engineered cartilage must include effective outcome measures. In addition to a range of clinical assessment techniques, it will be essential to use quantitative methods for analysing follow-up biopsies taken months or years after implantation. We have developed methods for determining the specific collagen content as well as collagen crosslink maturity in very small tissue biopsies. In summary, the technique of cartilage engineering is now advanced enough that we must consider how to use it successfully in the clinical setting. PROSPECTS FOR CELL ENGINEERING IN BONE REPAIR A. K. Smith Osiris Therapeutics, Inc., Baltimore MD, USA Human mesenchymal stem cells (MSCs) can be isolated and expanded ex vivo as a non-differentiated adult stem cell population. These cells are capable of multilineage differentiation into diverse tissue types such as bone marrow stromal cells, bone, adipose tissue, cartilage, tendon and ligament and muscle. Osiris Therapeutics has evaluated the potential to use cryopreserved MSCs attached to matrix materials for their combined ability to repair critically sized bone defects. Matrix materials evaluated include hydroxyapatite/tricalcium phosphate composites as well as modified allograft bone. Preclinical studies have demonstrated successful bone repair in large critical gap osteoperiosteal defects in canine and non-human primate models. Results from the animal studies show inclusion of MSCs results in superior bone formation compared to matrix alone which showed incomplete healing. Other issues associated with use of matrix alone included suboptimal integration with the host bone tissue and/or lack of mechanical integrity. Preclinical animal studies have also demonstrated the potential to use an allogeneic MSC preparation in tissue engineering. Studies show that bone formation is accomplished to the same extent using allogeneic MSCs, in the absence of any immunosuppression, as is seen with autologous MSCs. There is no evidence of either a cellular or humoral immune response to the allogeneic MSCs in preclinical animal studies even with multiple delivery of MSC doses. MSCs can be cryopreserved and successfully stored for long periods of time. The combined storage potential and the ability to achieve equivalent efficacy with an allogeneic MSC observations support the potential to use allogeneic MSC preparations support the potential for an 'off-the-shelf' or 'universal' MSC product for tissue engineering applications. Clinical studies are currently underway for bone repair using an MSC matrix combination. Preclinical models have also demonstrated regenerative potential for use of MSCs in the arthritic knee joint, where these cells repair damaged meniscus and retard articular cartilage and subchondral bone damage. MSCs have also been successfully used in preclinical studies to treat cardiac infarct and in human clinical trials for improved hematopoietic transplantation support. Preclinical and previous human clinical data support the safe and widespread potential of adult-derived hMSCs in regenerative medicine. THE REPAIR OF SKELETAL DEFECTS WITH BMPS T. A. Einhorn Boston University School of Medicine, 720 Harrison Avenue, Boston MA, USA Bone has the capacity to undergo regeneration as part of a repair process. While bone regeneration may involve several independent molecular events, a key regulator of bone regeneration is the TGF-b superfamily of molecules which include the bone morphogenetic proteins (BMPs). In addition to identifying specific molecules and cloning them for biotechnology applications, the receptors and signal transduction pathways of BMPs have also been elucidated. Although much more can be learned regarding the biology of bone regeneration and, in particular, BMP-induced osteogenesis, technology in this field has advanced to the point where clinical applications have already been made. The use of recombinant BMP-2 and BMP-7, in several types of delivery systems, and in several animal models, has suggested that recombinant gene technology may lead to the application of BMPs in the repair and restoration of skeletal defects, and in the treatment of degenerative conditions of the spine. Clinical studies on the application of BMP-2 in fresh fractures of the tibia, and BMP-7 in tibial nonunions have yielded impressive results. Indeed, BMP-7 (known as osteogenic protein-1; OP-1) is now available for clinical use in the treatment of nonunions in several European countries as well as Australia. More recently, the US Food and Drug Administration has issued an HDE (Humanitarian Device Exception) for the use of OP-1 in the treatment of recalcitrant nonunions of long bones. Future investigations on the clinical applicability of BMPs will concentrate on improved clinical experimental design and the development of novel carriers for enhanced delivery of the active molecules. In particular, the role of gene therapy in the delivery of BMP in patients should be explored. The few reports that have demonstrated enhanced bone regeneration when BMP-2 is delivered in an adenoviral vector have been impressive. Innovative methods for gene delivery could yield safe and effective therapies within the foreseeable future. MANAGEMENT OF CANCER ASSOCIATED BONE DISEASES: NEW DEVELOPMENTS R. E. Coleman Cancer Research Centre, Weston Park Hospital, Sheffield, UK The bisphosphonates are an important class of agents for the treatment of metastatic bone disease. Randomised controlled trials have clearly demonstrated that bisphosphonate treatment is effective in reducing skeletal morbidity in breast cancer and multiple myeloma. Attention is now focussing on when to start treatment and how long to continue, as well as the use of bone markers to predict those patients most likely to benefit. At present clodronate, usually given orally, and infusions of pamidronate are the two most widely used bisphosphonates in oncology. New more potent bisphosphonates are now available and could be expected to simplify treatment and possibly improve the therapeutic effectiveness of bisphosphonate therapy. Zoledronic acid (Zometa™) is the most potent, and has shown superior efficacy in hypercalcaemia of malignancy. Three large (n=>3000) phase III trials in treatment of bone metastases have been completed. In patients with multiple myeloma and breast cancer patients, non-inferiority of zoledronic acid compared with pamidronate has been confirmed, with advantages in terms of convenience and some of the secondary endpoints. Importantly, in placebo-controlled trials, a reduction in skeletal complications has been shown in other solid tumours affecting bone including prostate cancer, confirming the role of bisphosphonates across the range of tumours affecting bone. Although many studies indicate that bisphosphonates prevent the development of metastatic bone disease in animals, the clinical role of prophylactic bisphosphonates in early breast cancer is not defined. Three studies with oral clodronate have been published, two of them showing a protective effect on the development of bone metastases and improved survival, and one suggesting a disadvantage to the use of adjuvant clodronate. Further large adjuvant trials with clodronate and zoledronate are in progress. Recently, the biological importance of the RANK-OPG system has been defined. Osteoprotogerin (OPG), has been identified as a decoy receptor to RANK ligand, inhibiting the osteoclast stimulatory effects of this molecule. Phase I studies of synthetic OPG are complete and open up a range of new therapeutic avenues for metastatic bone disease. OSTEOMALACIA TUMOURS, RICKETS AND NOVEL BONE-RENAL MOLECULAR PATHWAYS P. S. N. Rowe University of Texas Health Science Center at San Antonio, Molecular Medicine, Institute for Drug Development CTRC,14960 Omicron Drive San Antonio, TX 78245, USA Oncogenic hypophosphatemic osteomalacia (OHO), X-linked hypophosphatemic rickets (HYP) and autosomal dominant hypophosphatemic rickets (ADHR) are characterized by rachitic and osteomalacic bone defects, hypophosphatemia, abnormal renal phosphate (Pi) handling, and renal defects in vitamin D metabolism. Also, all three diseases (familial and tumor), are associated with primary or secondary secretion of novel uncharacterized factors (phosphatonins), that have direct impact on pathophysiology. HYP is primarily caused by a defective novel zinc-metalloendopeptidase (PHEX). This has prompted a search for a putative PHEX phosphatonin-substrate (PTN). PHEX is thought to either activate or inactivate PTN(s) initiating a regulatory bone-renal Pi cascade. Physiology experiments in Hyp-mouse models support the PTN model and indicate that PTN(s) are circulating osteoblast-derived factor(s). Moreover, the apparent overlapping pathophysiology between HYP and OHO suggests that OHO-tumours may secrete inappropriately processed form(s) of PTN. Candidate PTNs have been discovered and these molecules could potentially play major roles in the mineralisation of osteoid, renal phosphate handling and cancer metastasis to bone. Fibroblast-growth-factor (FGF23) is an example of a good PTN candidate. Activating mutations in specific FGF23 C-terminal residues occur in patients with ADHR and the protein is expressed in some OHO-tumours. Also, CHO-cells expressing FGF23 cause rickets when heterotransplanted into nude mice. Interestingly no FGF23 inhibition of Pi-uptake occurs in-vitro in renal cell-lines and FGF23 is not expressed in bone. Another good PTN candidate, MEPE, is a novel glycosylated protein with RGD/ASARM motifs and is a member of the SIBLING proteins (DMP-1, OPN, DSPP, BSP-I). This protein was cloned from OHO-tumours and is not expressed in non-phosphaturic tumours. MEPE is found in plasma and is expressed in osteoblasts/osteocytes in rodents and humans. MEPE and PHEX are developmentally co-expressed in osteoblasts. Also, MEPE expression is markedly increased during osteoblast-mediated matrix mineralisation and vastly elevated levels occur in bone and osteoblasts derived from Hyp mice. MEPE peptides inhibit phosphate uptake in human renal cell-lines and alter vitamin D metabolism. Moreover, MEPE peptides increase bone mineralisation in bone organ-culture and increase osteoblast numbers. Further experimentation is needed to unravel the abundance of factors and molecular-interactions involved in the regulation of Pi and the mineralisation of osteoid. TREASURE YOUR EXCEPTIONS: MAPPING HUMAN SKELETAL DYSPLASIAS C. A. Francomano National Institute on Aging, Baltimore MD, USA The human skeletal dysplasias are a genetically and clinically diverse group of disorders, representing over 200 distinct conditions. Knowledge of the genes underlying this widely diverse group of disorders has the potential to inform our understanding of the genetic and biochemical pathways critical to skeletal growth and development. It is likely that many of the genes found to cause the rare skeletal dysplasias also play a role in the pathogenesis of more common disorders of skeletogenesis and skeletal aging. To date, over 70 loci known to cause skeletal phenotypes have been mapped. These include loci encoding structural proteins of the extracellular matrix, enzymes involved in the modification of the structural proteins, molecules involved in signal transduction, and genes encoding regulatory proteins and RNA products. Current methodology and tools to further analyze the pathogenesis of these conditions will be presented, including the Skeletal Gene Database, a searchable listing of all genes known to be involved in skeletal growth and development. This database includes genes from 11 different bone libraries represented in the National Center for Biotechnology Informatics databases, with a total of 28,218 expressed sequence tags (ESTs) represented. To illustrate many of the issues involved in mapping and analyzing the skeletal dysplasias, this presentation will focus on the family of disorders caused by mutations in Fibroblast Growth Factor Receptor 3 (FGFR3). Clinical and molecular features of this family of disorders, which includes achondroplasia, hypochondroplasia, thanatophoric dysplasia, and Severe Achondroplasia with Acanthosis Nigricans and Developmental Delay (SADDAN) will be discussed. The pivotal role of the Human Genome Project in allowing investigators to move from a map location to a disease gene will be illustrated using the example of achondroplasia. The role of microarrays, genomic and proteomic approaches to further understanding pathogenesis will be presented. The utility of animal models to dissecting molecular pathways will also be discussed. Finally, an overview of the utility of knowledge about skeletal dysplasias and how that knowledge may be applied to understanding more common disorders of skeletal growth and development will be presented. PROGRESS IN MAPPING OSTEOPOROSIS GENES IN MICE R. F. Klein Oregon Health & Science University and Portland VA Medical Center, Portland, Oregon, USA Osteoporosis is one of the most common bone and mineral disorders in both aging men and women. Susceptibility to osteoporosis appears to involve the interaction of multiple environmental and genetic factors. Considerable past research has centered on the influence of reproductive, nutritional and/or life-style factors on the development of osteoporosis. With the advent of new molecular genetic approaches, the focus of research has recently shifted towards genetic factors. The number, location and effects of the individual genes contributing to osteoporosis risk are all unknown. The extreme difficulty of dissecting out environmental factors from genetic ones in humans has motivated the investigation of animal models. Recent analyses of inbred strain databases are beginning to reveal important aspects of the genetic regulation of bone mass acquisition and maintenance. Advances in genetic mapping of complex traits, such as quantitative trait locus (QTL) mapping, are especially promising. A major strength of this approach is that it enables the provisional identification of candidate genes in the absence of any prior hypothesis about the mechanism by which the phenotype is expressed. QTL mapping offers an attractive interface between forward and reverse genetics. As candidate genes are identified as having important skeletal functions, the tools of molecular biology will allow the genetic diversity underlying their expression and function to be more fully examined. Discoveries made with animal models can often set the stage for skeletal research in human subjects to augment the results from animals and confirm their relevance to our own species. Perhaps the most versatile aspect of animal model systems is in their use as a proving ground for hypotheses regarding the genetic as well as the epigenetic basis of osteoporosis. Old ideas regarding disease mechanisms can now be rigorously tested in vivo, and perhaps more importantly, provocative new concepts can emerge. HARVESTING BIOLOGICAL DATA USING BIOINFORMATICS: PREDICTION OF HUMAN DISEASE GENES J. A. M. Leunissen1,2*, M. A. van Driel1, K. Cuelenaere2, P. Neerincx1, G. H. Degenhart1, H. G. Brunner3 1CMBI, University of Nijmegen, Nijmegen, Netherlands 2Dalicon BV, Nijmegen, Netherlands 3Human Genetics, UMCN, Nijmegen, Netherlands We have developed a tool integrating different genetic web-based databases in order to quickly generate a list of candidate genes for human diseases. Given a cytogenetic localisation and phenotypic data for input, the tool extracts gene names from several distributed databases and returns only genes that match the two prerequisites. The system provides researchers of human genetic diseases with plausible candidate genes based on phenotype as well as genotype. The tool is written in Perl and has a modular set-up; new genetic databases can easily be added, as long as the database supports a 'bulk query' strategy, i.e. being able to return all known or appropriate gene names in one query. The power of the tool is based upon the fact that gene names are mostly standardised, thus allowing them to be used as unique identifiers when integrating search results. Several filters are included in order to allow man to mouse homologies to be included in the search strategies. Notably, an 'Oxford grid' is constructed to query the relevant sections of mouse genetic databases, and a list of gene synonyms is included to deal with gene naming inconsistencies between human and mouse. Recent additions include EST database searching to verify the expression location 'experimentally', and the use of pathway databases to be able to include those genes where the relationship between expression profile and localisation is indirect, i.e. linked through a common pathway. In its present form the program is mainly suited for syndromes, for which it is valid to assume that the disease gene has an aberrant or absent gene expression in the affected tissues. Through the addition of pathway information, as well as by expanding the number of databases, we will increase both its sensitivity and its versatility. APPLICATION OF PROTEOMICS TO ELUCIDATE MECHANISMS OF DISEASE L. C. Lawrie1,2*, G. I. Murray2, J. E. Fothergill1 1Dept. of Molecular & Cell Biology, University of Aberdeen, Scotland, UK 2Dept. of Pathology, University of Aberdeen, Scotland, UK Proteomics offers a powerful analytical tool for the post-genomic era. Proteome is the word used to describe the total protein complement expressed by an organism, a cell, or a tissue type. By studying the differences in protein expression profiles between normal and disease/treated samples proteomics can be used to elucidate molecular mechanisms of disease, to identify diagnostic markers or therapeutic targets and also to provide an understanding of the mechanisms of drug toxicity. The first part of this presentation will describe the basic principles involved in proteomic analysis including the separation and visualisation of proteins by 2D gel electrophoresis, followed by the characterisation and identification of these proteins by mass spectrometry and database searching. The second part of the presentation will concentrate on the application of proteomics in oncology. Cancer is characterised by multiple genetic abnormalities. Some of these are crucial to the development of individual types of cancer, whereas others appear to be the consequence of tumour development. It is important to characterise the functional consequences of these gene changes in terms of protein expression, to elucidate more fully the processes of tumour development and progression and also the response of established tumours to therapy. There is a need to identify biomarkers of cancer risk, of early diagnosis, and of disease progression, and to pinpoint targets for therapeutic intervention, diagnosis, or imaging. It is also important to develop methods of cancer classification which more accurately predict the clinical behaviour of tumours. The application of proteomics is expected to have a major impact on oncology, both for our understanding of tumour development and progression, and in providing improved diagnosis and treatment. PROBING GENE FUNCTION BY TRANSGENIC APPROACHES M. F. Young CSDB, National Institute of Dental Research, NIH, Bethesda, MD, USA Genetically engineered mice are critical tools to uncover the function of a protein in mineralized tissue. At the same time they provide valuable experimental models for prevalent calcified tissue diseases such as osteoporosis, osteoarthritis and ectopic calcification. They can also be used to study the function of a protein in the context of external influences such as impact (running), hormone imbalance, nutritional variation or pharmaceutical intervention. Technical advances in cell and molecular biology have resulted in a corresponding increase in the ways that mice can be genetically altered. The goal of the workshop will be to present a brief outline of the types of transgenic mice available with emphasis on the concepts and techniques used to create them. The advantages and disadvantages of each type of genetic alteration will be addressed. Examples from the literature and from the author's own experience will be used to illustrate key points such as ways to circumvent gene redundancy or lethality. The workshop will discuss conventional transgenics that contain genes 'driven' by a promoter either ectopically or, in a tissue specific fashion. The multi-faceted nature of creating mice with a single gene deficiency using gene targeting and homologous recombination (knockout or KO) will be detailed. Despite the technical power of the gene targeting method it is restricted by the fact that some genes when knocked out from conception are lethal. Although these observations clearly show the importance of a protein, they limit examining its function later in life. In this regard, new techniques developed to abrogate genes at a specific time and location in vivo will be discussed. The ways that one can determine the function of a gene in any tissue for which a specific promoter is available will be presented. A new development in this area is to combine spatial specificity with controlled temporal reduction using chemicals that can be injected into the genetically engineered mutant mice. The workshop will conclude with commentary on the newest advances in calcified tissue research using transgenic strategies. BONE CELLS' RESPONSES TO MECHANICAL STRAIN: IMPLICATIONS FOR POSTMENOPAUSAL OSTEOPOROSIS L. E. Lanyon Royal Veterinary College, London, UK Bones' ability to withstand load-bearing without damage is achieved and maintained by a homeostatic mechanism in which bone cells adjust bone architecture to control the strains engendered by functional loading. The mechano-responsive cells are most likely osteocytes and osteoblasts. The increased fracture incidence characteristic of post-menopausal osteoporosis is associated with a decline in bone mass despite continued functional activity. This implies reduced responsiveness to the increased strains which the bone loss should engender. In cultures of rat primary osteoblasts, and in ROS 17/2.8 cells, both a short period of strain and estrogen stimulate proliferation. The size of the proliferative response to strain and estrogen together equals the addition of the two individual maximal responses separately. The estrogen antagonist ICI 182,780 reduces, and tamoxifen abolishes the proliferative response to strain and reduces that due to estrogen. In human primary osteoblasts and in TE85 cells ICI 182,780 similarly blocks strain-related proliferation but tamoxifen does not. In rat primary osteoblasts and ROS17/2.8 cells estrogen and strain cause phosphorylation of serine 118 in the amino terminal of ERalpha which is the consensus phosphorylation site for MAPK. This response is eliminated by inhibitors of ERK-1 and ERK-2, the immediate upstream activators of MAPK. In ROS cells increasing ERalpha number by transfection increases the proliferation stimulated by both estrogen and strain, both of which are inhibited by ICI 182,780. Strain and estrogen also both upregulate ERE activity which is also blocked by ICI. In osteoblast-like cells early proliferative responses to strain and estrogen appear to involve the MAPK pathway, Estrogen Receptor alpha and EREs. At the cell level strain and estrogen neither enhance nor obstruct each other's effects on osteoblast proliferation although different interactions may occur at the tissue and organ level. Proliferation of osteoblasts is only one of resident bone cells' adaptive responses to strain but it may be representative of others. The etiology of post-menopausal osteoporosis could be explained by less effective strain-related control of bone architecture associated with the down-regulation of ER number which others have reported to follow the withdrawal of estrogen. WHAT TYPE OF EXERCISE PROTECTS THE SKELETON? A. Heinonen UKK Institute for Health Promotion Research, Tampere, Finland In human exercise studies the changes in bone mass are small, and local rather than generalised, and the attainable changes take place slowly. Different exercise modalities and sports load the skeleton at different sites and different ways, and thus the training response may vary. In terms of skeletal loading, weightlifting, for instance, creates extreme torques in the upper extremities whereas the lower extremities experience large compressive stresses. The bone mass values of the intensively training female and male weightlifters (i.e., high-magnitude loading) were more than 10% higher than those of comparable referents in the previous studies. However, prospective weight-training studies have demonstrated only small to moderate (0.8-3.8%) gain in regional bone mineral mass. The most commonly practised sports that involves a large number of repetitive loading is running and walking. However, the difference is not as great as between athletes in strength sports and control subjects. Nevertheless, earlier randomised controlled clinical trials have shown that multi-exercise endurance training at a relatively high intensity maintained bone mass at the femoral neck and lumbar spine in healthy postmenopausal women. Previous studies have reported that athletes engaged in sports producing high strain rates via versatile impact-type movements have much higher bone mass (9-40%), geometry and structure (the largest differences over 50%) than their sedentary controls. Adaptation to this loading seemed to occur in a site-specific fashion by gross-geometric changes, structural or architectural changes or by their combination. Clinical trials also support the high-impact loading concept. In our recent randomised controlled study, we showed that the 18-month high impact training (jumping) resulted in significant increase (1.4-3.7%) in bone mass in the loaded sites. Cumulative evidence shows that the important components of osteocenic exercise stimulus are high-impact and high-magnitude loading in versatile movements. Greater differences in BMC and BMD between playing and non-playing arm sites in squash and tennis supports the osteogenic value of high-impact loading. When the loading magnitude is low, as may occur in the elderly, the number of loading cycles becomes more important. In the elderly, progressive strength training is likely to be safe and may be effective in reducing the risk factors for falling, although having less effect on BMD. IDENTIFYING PATIENTS WHO NEED TREATMENT FOR OSTEOPOROSIS J. A. Kanis WHO Collaborating Centre for Metabolic Bone Diseases, University of Sheffield Medical School, Sheffield, UK In the past 10 years there have been significant advances in the field of osteoporosis, including the development of diagnostic techniques, a greater understanding of the pathogenesis of osteoporosis and the evolution of effective treatments. There are, however, large gaps in our ability to implement effective therapeutic strategies. Strategies may be based on a global approach where the intention is to shift the distribution of bone mineral density (BMD) in the whole population, for example by the promotion of exercise, smoking cessation or manipulating the dietary intake of calcium. However, evidence for the efficacy of such approaches is lacking, and their feasibility has never been tested. The alternative approach is the 'high risk' strategy whereby segments of the population most at risk are targeted for intervention, for example, mass population screening of women at the time of the menopause. There are many reasons why this is not feasible at present. A particular problem with BMD is that despite its high specificity, its sensitivity (detection rate) for fracture outcomes is low over most reasonable assumptions. For this reason, treatment strategies need to take into account the risk factors that operate independently of BMD and thereby enhance the predictive value of the test. These factors include age, family history of hip fracture, prior fragility fracture, high rates of bone turnover, low body mass index and neuromuscular incompetence. The presence of such factors increases fracture risk over and above that which can be explained on the basis of BMD. Therefore, diagnostic thresholds differ from intervention thresholds. Intervention thresholds should be based on the absolute risk of the clinically significant outcomes. Fracture risk is optimally determined as a fracture probability over a relatively long time-frame (eg 10 years). The setting of intervention thresholds is ultimately dependent upon health economic considerations that have been evaluated in the Swedish population. These require modification in different countries to take account of different costs and risks that vary markedly in different regions of the world. OSTEOPOROSIS TREATMENT WITH PARATHYROID HORMONE R. Neer Massachusetts General Hospital, Boston, MA 02114, USA Anti-resorptive agents rarely cure osteoporosis, because bone formation is too slow, and such drugs slow it even more. Agents that stimulate bone formation may overcome this limitation. Human parathyroid hormone (hPTH) and its amino-terminal fragments and analogs increase bone formation, and can increase bone mass and strength in animals. The new bone produced by hPTH treatment is histologically, chemically, and mechanically normal. There have now been more than 14 prospective clinical trials of hPTH-(1-34) or hPTH-(1-84) in osteoporotic women or men. In a randomized placebo-controlled multi-national trial in 1,637 postmenopausal women with a prior vertebral fracture, hPTH-(1-34) reduced the risk of a first additional vertebral fracture 61-69%, and reduced the risk of a first new non-vertebral fracture 50%, while increasing bone mineral density (BMD) 9-13% in the spine, 3-6% in the femoral neck, and 2-4% in the total body, and decreasing forearm cortical BMD non-progressively by 1-2%. These fracture reductions exceed those reported for anti-resorptive agents. In prospective, randomized, direct comparisons, hPTH-(1-34) also increases spine and hip BMD substantially more than alendronate or hormone replacement therapy in postmenopausal osteoporotic women. In osteoporotic men, hPTH-(1-34) increases spine and hip BMD more than anti-resorptive drugs are reported to do. hPTH routinely cures estrogen-deficiency osteoporosis in rodents, but does so far less often in humans, in part because humans cannot tolerate the high hPTH doses needed in rodents. Combining hPTH with an anti-resorptive drug might overcome this limitation, and might also enhance the effectiveness of hPTH in humans. Several clinical trials are now exploring this possibility. In humans hPTH has no major adverse effects and causes only minor side effects. In rodents, high doses of hPTH cause marked osteosclerosis, and nearly life-long high-dose hPTH treatment causes osteosarcomas. Neither complication has been observed in humans treated with hPTH or its amino-terminal fragments or analogs, nor is the incidence of this rare malignancy increased in humans with primary or secondary hyperparathyroidism. In the near future, hPTH may be marketed as a treatment for established osteoporosis. STATINS AND BONE: MYTH OR REALITY? T. D. Spector St Thomas' Hospital, London, UK The actions of statins on serum cholesterol concentrations are well documented and are associated with decreased cardiovascular events and death. In late 1999 experimental work produced the unexpected finding that statins may/could stimulate bone formation when administered locally to bony sites or when given systemically in rats. A number of other animal studies have confirmed an effect of most but not all statins. Since these findings a number of epidemiological studies have been published recently that explore the effects of statin use on bone mineral density (BMD) and fracture risk in humans. These studies have produced mixed results even disagreeing in the same dataset. Whilst unequivocal evidence for a therapeutic effect in the doses used in humans is lacking, many statins do influence bone via a number of potential pathways including stimulating osteoblasts, inhibiting osteoclasts, altering apoptosis, angiogenesis, and inhibiting inflammation. Understanding these mechanisms should prove helpful in new therapeutic approaches and understanding of osteoporosis. |
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