[Recommendations for the healthcare of patients with FOP]

BACKGROUND

Fibrodysplasia ossificans progressiva (FOP) is a very rare, severe genetic disorder triggered by a gain-of-function mutation in the ACVR1 gene that codes for the type I bone morphogenetic protein (BMP) receptor ACVR1 (activin A receptor-type 1), also known as ALK2 (activin receptor-like kinase-2). It leads to the onset and progression of heterotopic ossification (HO) in soft and connective tissue. HO is often preceded by episodes of soft tissue swelling or flare-ups. Flare-ups, characteristic of FOP, may be induced by trauma, infection, vaccination, or other medications, as well as surgical procedures or may occur spontaneously. As patients age, they develop severe mobility limitations due to progressive HO formation, including immobility, causing a shortened life expectancy. FOP's first characteristic clinical sign is the congenital malformation of one or both big toes with valgus axis deviation, which is present in almost all patients. To confirm the diagnosis, molecular genetic analysis of the ACVR1 gene is possible.

AIM OF THE RECOMMENDATIONS

This white paper aims to provide an overview of the necessary prerequisites and conditions for the care of patients with FOP and positively contribute to patients with FOP by improving the overall availability of knowledge. To achieve this, relevant aspects of the care of the very rare disease FOP are presented, from the initial diagnosis to the care in regular care based on the authors' knowledge (German FOP network) and the international FOP Treatment Guidelines. The recommendations presented here are addressed to all actors and decision-makers in the health care system and are also intended to inform patients and the public.

Activation of beta-adrenergic receptor signaling prevents glucocorticoid-induced obesity and adipose tissue dysfunction in male mice

Elevated serum concentrations of glucocorticoids (GCs) result in excessive lipid accumulation in white adipose tissue (WAT) as well as dysfunction of thermogenic brown adipose tissue (BAT) - ultimately leading to the development of obesity and metabolic disease. Here, we hypothesized that activation of the sympathetic nervous system either via cold exposure or use of a selective β3-adrenergic receptor (β3-AR) agonist alleviates the adverse metabolic effects of chronic GC exposure in rodents. To this end, male 10-week-old C57BL/6NRj mice were treated with corticosterone via drinking water or placebo for 4 weeks while being maintained at 29°C (thermoneutrality), 22°C (room temperature) or 13°C (cold temperature); in a follow-up study mice received a selective β3-AR agonist or placebo with and without corticosterone while maintained at room temperature. Body weight and food intake were monitored throughout the study. Histological and molecular analyses were performed on white and brown adipose depots. Cold exposure not only preserved the thermogenic function of brown adipose tissue, but also reversed GC-induced lipid accumulation in white adipose tissue and corrected GC-driven obesity, hyperinsulinemia and hyperglycemia. The metabolic benefits of cold exposure were associated with enhanced sympathetic activity in adipose tissue, thus potentially linking an increase in sympathetic signaling to the observed metabolic benefits. In line with this concept, chronic administration of a selective β3-AR agonist reproduced the beneficial metabolic effects of cold adaption during exposure to exogenous GCs. This preclinical study demonstrates the potential of β3-AR as a therapeutic target in the management and prevention of GC-induced metabolic disease.

Targeting transforming growth factor- β (TGF-β) for treatment of osteogenesis imperfecta

BACKGROUND

Currently, there is no disease-specific therapy for osteogenesis imperfecta (OI). Preclinical studies have shown that excessive TGF-β signaling is a driver of pathogenesis in OI. Here, we evaluated TGF-β signaling in children with OI and translated this discovery by conducting a phase 1 clinical trial of TGF-β inhibition in adults with OI.

METHODS

Histology and RNASeq were performed on bones obtained from children affected (n=10) and unaffected (n=4) by OI. Gene Ontology (GO) enrichment assay, gene set enrichment analysis (GSEA), and Ingenuity Pathway Analysis (IPA) were used to identify key dysregulated pathways. Reverse-phase protein array (RPPA), Western blot (WB), and Immunohistochemistry (IHC) were performed to evaluate changes at the protein level. A phase 1 study with a single administration of fresolimumab, a pan-anti-TGF-β neutralizing antibody, was conducted in 8 adults with OI. Safety and effects of fresolimumab on bone remodeling markers and lumbar spine areal bone mineral density (LS aBMD) were assessed.

RESULTS

OI bone demonstrated woven structure, increased osteocyte density, high turnover, and reduced bone maturation. SMAD phosphorylation was the most significantly up-regulated GO molecular event. GSEA identified TGF-β pathway as top activated signaling pathway in OI. IPA showed that TGF-β was the most significant activated upstream regulator mediating the global changes identified in OI bone. Treatment with fresolimumab was well-tolerated and associated with increase in LS aBMD in participants with OI type IV, while those with more severe OI type III and VIII had unchanged or decreased LS aBMD.

CONCLUSIONS

Our data confirm that TGF-β signaling is a driver pathogenic mechanism in OI bone and that anti-TGF-β therapy could be a potential disease-specific therapy with dose-dependent effects on bone mass and turnover.

TRIAL REGISTRATION

NCT03064074 FUNDING. This work was supported by the Brittle Bone Disorders Consortium (BBDC) (U54AR068069). The BBDC is a part of the National Center for Advancing Translational Science's (NCATS') RDCRN. The BBDC is funded through a collaboration between the Office of Rare Disease Research (ORDR) of NCATS, National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institute of Dental and Craniofacial Research (NIDCR), National Institute of Mental Health (NIMH) and National Institute of Child Health and Human Development (NICHD). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. The BBDC was also supported by the OI Foundation. The work was supported by The Clinical Translational Core of BCM IDDRC (P50HD103555) from the Eunice Kennedy Shriver NICHD. Funding from the USDA/ARS under Cooperative Agreement No. 58-6250-6-001 also facilitated analysis for the study procedures. The contents of this publication do not necessarily reflect the views or policies of the USDA, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government. The study was supported by a research agreement with Sanofi Genzyme.

COPB2 loss of function causes a coatopathy with osteoporosis and developmental delay

Coatomer complexes function in the sorting and trafficking of proteins between subcellular organelles. Pathogenic variants in coatomer subunits or associated factors have been reported in multi-systemic disorders, i.e., coatopathies, that can affect the skeletal and central nervous systems. We have identified loss-of-function variants in COPB2, a component of the coatomer complex I (COPI), in individuals presenting with osteoporosis, fractures, and developmental delay of variable severity. Electron microscopy of COPB2-deficient subjects' fibroblasts showed dilated endoplasmic reticulum (ER) with granular material, prominent rough ER, and vacuoles, consistent with an intracellular trafficking defect. We studied the effect of COPB2 deficiency on collagen trafficking because of the critical role of collagen secretion in bone biology. COPB2 siRNA-treated fibroblasts showed delayed collagen secretion with retention of type I collagen in the ER and Golgi and altered distribution of Golgi markers. copb2-null zebrafish embryos showed retention of type II collagen, disorganization of the ER and Golgi, and early larval lethality. Copb2+/- mice exhibited low bone mass, and consistent with the findings in human cells and zebrafish, studies in Copb2+/- mouse fibroblasts suggest ER stress and a Golgi defect. Interestingly, ascorbic acid treatment partially rescued the zebrafish developmental phenotype and the cellular phenotype in Copb2+/- mouse fibroblasts. This work identifies a form of coatopathy due to COPB2 haploinsufficiency, explores a potential therapeutic approach for this disorder, and highlights the role of the COPI complex as a regulator of skeletal homeostasis.

Identification of Functionally Distinct Mx1+αSMA+ Periosteal Skeletal Stem Cells

The periosteum is critical for bone maintenance and healing. However, the in vivo identity and specific regulatory mechanisms of adult periosteum-resident skeletal stem cells are unknown. Here, we report animal models that selectively and durably label postnatal Mx1+αSMA+ periosteal stem cells (P-SSCs) and establish that P-SSCs are a long-term repopulating, functionally distinct SSC subset responsible for lifelong generation of periosteal osteoblasts. P-SSCs rapidly migrate toward an injury site, supply osteoblasts and chondrocytes, and recover new periosteum. Notably, P-SSCs specifically express CCL5 receptors, CCR3 and CCR5. Real-time intravital imaging revealed that the treatment with CCL5 induces P-SSC migration in vivo and bone healing, while CCL5/CCR5 deletion, CCR5 inhibition, or local P-SSC ablation reduces osteoblast number and delays bone healing. Human periosteal cells express CCR5 and undergo CCL5-mediated migration. Thus, the adult periosteum maintains genetically distinct SSC subsets with a CCL5-dependent migratory mechanism required for bone maintenance and injury repair.

A global Slc7a7 knockout mouse model demonstrates characteristic phenotypes of human lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an inborn error of cationic amino acid (arginine, lysine, ornithine) transport caused by biallelic pathogenic variants in SLC7A7, which encodes the light subunit of the y+LAT1 transporter. Treatments for the complications of LPI, including growth failure, renal disease, pulmonary alveolar proteinosis, autoimmune disorders and osteoporosis, are limited. Given the early lethality of the only published global Slc7a7 knockout mouse model, a viable animal model to investigate global SLC7A7 deficiency is needed. Hence, we generated two mouse models with global Slc7a7 deficiency (Slc7a7em1Lbu/em1Lbu; Slc7a7Lbu/Lbu and Slc7a7em1(IMPC)Bay/em1(IMPC)Bay; Slc7a7Bay/Bay) using CRISPR/Cas9 technology by introducing a deletion of exons 3 and 4. Perinatal lethality was observed in Slc7a7Lbu/Lbu and Slc7a7Bay/Bay mice on the C57BL/6 and C57BL/6NJ inbred genetic backgrounds, respectively. We noted improved survival of Slc7a7Lbu/Lbu mice on the 129 Sv/Ev × C57BL/6 F2 background, but postnatal growth failure occurred. Consistent with human LPI, these Slc7a7Lbu/Lbu mice exhibited reduced plasma and increased urinary concentrations of the cationic amino acids. Histopathological assessment revealed loss of brush border and lipid vacuolation in the renal cortex of Slc7a7Lbu/Lbu mice, which combined with aminoaciduria suggests proximal tubular dysfunction. Micro-computed tomography of L4 vertebrae and skeletal radiographs showed delayed skeletal development and suggested decreased mineralization in Slc7a7Lbu/Lbu mice, respectively. In addition to delayed skeletal development and delayed development in the kidneys, the lungs and liver were observed based on histopathological assessment. Overall, our Slc7a7Lbu/Lbu mouse model on the F2 mixed background recapitulates multiple human LPI phenotypes and may be useful for future studies of LPI pathology.

A multicenter study to evaluate pulmonary function in osteogenesis imperfecta

Pulmonary complications are a significant cause for morbidity and mortality in osteogenesis imperfecta (OI). However, to date, there have been few studies that have systematically evaluated pulmonary function in individuals with OI. We analyzed spirometry measurements, including forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1 ), in a large cohort of individuals with OI (n = 217) enrolled in a multicenter, observational study. We show that individuals with the more severe form of the disease, OI type III, have significantly reduced FVC and FEV1 which do not follow the expected trends of the normal population. We also show that "normalization" of FVC and FEV1 using general population data to generate percent predicted values underestimates the pulmonary involvement in OI. Within each subtype of OI, we used linear mixed models to find potential correlations between FEV1 and FVC with the clinical variables including mobility, bisphosphonate use, and scoliosis. Our results are an important step in understanding the extent of pulmonary involvement in individuals with OI and for developing pulmonary endpoints for use in the routine patient care as well as in the investigation of new therapies.

TGF-β Family Signaling in Mesenchymal Differentiation

Mesenchymal stem cells (MSCs) can differentiate into several lineages during development and also contribute to tissue homeostasis and regeneration, although the requirements for both may be distinct. MSC lineage commitment and progression in differentiation are regulated by members of the transforming growth factor-β (TGF-β) family. This review focuses on the roles of TGF-β family signaling in mesenchymal lineage commitment and differentiation into osteoblasts, chondrocytes, myoblasts, adipocytes, and tenocytes. We summarize the reported findings of cell culture studies, animal models, and interactions with other signaling pathways and highlight how aberrations in TGF-β family signaling can drive human disease by affecting mesenchymal differentiation.

Genetic causes and mechanisms of Osteogenesis Imperfecta

Osteogenesis Imperfecta (OI) is a genetic disorder characterized by various clinical features including bone deformities, low bone mass, brittle bones, and connective tissue manifestations. The predominant cause of OI is due to mutations in the two genes that encode type I collagen. However, recent advances in sequencing technology has led to the discovery of novel genes that are implicated in recessive and dominant OI. These include genes that regulate the post-translational modification, secretion and processing of type I collagen as well as those required for osteoblast differentiation and bone mineralization. As such, OI has become a spectrum of genetic disorders informing about the determinants of both bone quantity and quality. Here we summarize the known genetic causes of OI, animal models that recapitulate the human disease and mechanisms that underlie disease pathogenesis. Additionally, we discuss the effects of disrupted collagen networks on extracellular matrix signaling and its impact on disease progression.

Fkbp10 Deletion in Osteoblasts Leads to Qualitative Defects in Bone

Osteogenesis imperfecta (OI), also known as brittle bone disease, displays a spectrum of clinical severity from mild (OI type I) to severe early lethality (OI type II), with clinical features including low bone mass, fractures, and deformities. Mutations in the FK506 Binding Protein 10 (FKBP10), gene encoding the 65-kDa protein FKBP65, cause a recessive form of OI and Bruck syndrome, the latter being characterized by joint contractures in addition to low bone mass. We previously showed that Fkbp10 expression is limited to bone, tendon, and ligaments in postnatal tissues. Furthermore, in both patients and Fkbp10 knockout mice, collagen telopeptide hydroxylysine crosslinking is dramatically reduced. To further characterize the bone specific contributions of Fkbp10, we conditionally ablated FKBP65 in Fkbp10^fl/fl mice (Mus musculus; C57BL/6) using the osteoblast-specific Col1a1 2.3-kb Cre recombinase. Using μCT, histomorphometry and quantitative backscattered electron imaging, we found minimal alterations in the quantity of bone and no differences in the degree of bone matrix mineralization in this model. However, mass spectroscopy (MS) of bone collagen demonstrated a decrease in mature, hydroxylysine-aldehyde crosslinking. Furthermore, bone of mutant mice exhibits a reduction in mineral-to-matrix ratio and in crystal size as shown by Raman spectroscopy and small-angle X-ray scattering, respectively. Importantly, abnormalities in bone quality were associated with impaired bone biomechanical strength in mutant femurs compared with those of wild-type littermates. Taken together, these data suggest that the altered collagen crosslinking through Fkbp10 ablation in osteoblasts primarily leads to a qualitative defect in the skeleton. © 2017 American Society for Bone and Mineral Research.

Correlations Between Bone Mechanical Properties and Bone Composition Parameters in Mouse Models of Dominant and Recessive Osteogenesis Imperfecta and the Response to Anti-TGF-β Treatment

Osteogenesis imperfecta (OI) is a group of genetic disorders characterized by brittle bones that are prone to fracture. Although previous studies in animal models investigated the mechanical properties and material composition of OI bone, little work has been conducted to statistically correlate these parameters to identify key compositional contributors to the impaired bone mechanical behaviors in OI. Further, although increased TGF-β signaling has been demonstrated as a contributing mechanism to the bone pathology in OI models, the relationship between mechanical properties and bone composition after anti-TGF-β treatment in OI has not been studied. Here, we performed follow-up analyses of femurs collected in an earlier study from OI mice with and without anti-TGF-β treatment from both recessive (Crtap^-/- ) and dominant (Col1a2^+/P.G610C ) OI mouse models and WT mice. Mechanical properties were determined using three-point bending tests and evaluated for statistical correlation with molecular composition in bone tissue assessed by Raman spectroscopy. Statistical regression analysis was conducted to determine significant compositional determinants of mechanical integrity. Interestingly, we found differences in the relationships between bone composition and mechanical properties and in the response to anti-TGF-β treatment. Femurs of both OI models exhibited increased brittleness, which was associated with reduced collagen content and carbonate substitution. In the Col1a2^+/P.G610C femurs, reduced hydroxyapatite crystallinity was also found to be associated with increased brittleness, and increased mineral-to-collagen ratio was correlated with increased ultimate strength, elastic modulus, and bone brittleness. In both models of OI, regression analysis demonstrated that collagen content was an important predictor of the increased brittleness. In summary, this work provides new insights into the relationships between bone composition and material properties in models of OI, identifies key bone compositional parameters that correlate with the impaired mechanical integrity of OI bone, and explores the effects of anti-TGF-β treatment on bone-quality parameters in these models. © 2016 American Society for Bone and Mineral Research.

Pharmacological and biological therapeutic strategies for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a connective tissue disorder characterized by bone fragility, low bone mass, and bone deformities. The majority of cases are caused by autosomal dominant pathogenic variants in the COL1A1 and COL1A2 genes that encode type I collagen, the major component of the bone matrix. The remaining cases are caused by autosomal recessively or dominantly inherited mutations in genes that are involved in the post-translational modification of type I collagen, act as type I collagen chaperones, or are members of the signaling pathways that regulate bone homeostasis. The main goals of treatment in OI are to decrease fracture incidence, relieve bone pain, and promote mobility and growth. This requires a multi-disciplinary approach, utilizing pharmacological interventions, physical therapy, orthopedic surgery, and monitoring nutrition with appropriate calcium and vitamin D supplementation. Bisphosphonate therapy, which has become the mainstay of treatment in OI, has proven beneficial in increasing bone mass, and to some extent reducing fracture risk. However, the response to treatment is not as robust as is seen in osteoporosis, and it seems less effective in certain types of OI, and in adult OI patients as compared to most pediatric cases. New pharmacological treatments are currently being developed, including anti-resorptive agents, anabolic treatment, and gene- and cell-therapy approaches. These therapies are under different stages of investigation from the bench-side, to pre-clinical and clinical trials. In this review, we will summarize the recent findings regarding the pharmacological and biological strategies for the treatment of patients with OI. © 2016 Wiley Periodicals, Inc.

Sclerostin Antibody Treatment Improves the Bone Phenotype of Crtap(-/-) Mice, a Model of Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is characterized by low bone mass, poor bone quality, and fractures. Standard treatment for OI patients is limited to bisphosphonates, which only incompletely correct the bone phenotype, and seem to be less effective in adults. Sclerostin-neutralizing antibodies (Scl-Ab) have been shown to be beneficial in animal models of osteoporosis, and dominant OI resulting from mutations in the genes encoding type I collagen. However, Scl-Ab treatment has not been studied in models of recessive OI. Cartilage-associated protein (CRTAP) is involved in posttranslational type I collagen modification, and its loss of function results in recessive OI. In this study, we treated 1-week-old and 6-week-old Crtap(-/-) mice with Scl-Ab for 6 weeks (25 mg/kg, s.c., twice per week), to determine the effects on the bone phenotype in models of "pediatric" and "young adult" recessive OI. Vehicle-treated Crtap(-/-) and wild-type (WT) mice served as controls. Compared with control Crtap(-/-) mice, micro-computed tomography (μCT) analyses showed significant increases in bone volume and improved trabecular microarchitecture in Scl-Ab-treated Crtap(-/-) mice in both age cohorts, in both vertebrae and femurs. Additionally, Scl-Ab improved femoral cortical parameters in both age cohorts. Biomechanical testing showed that Scl-Ab improved parameters of whole-bone strength in Crtap(-/-) mice, with more robust effects in the week 6 to 12 cohort, but did not affect the increased bone brittleness. Additionally, Scl-Ab normalized the increased osteoclast numbers, stimulated bone formation rate (week 6 to 12 cohort only), but did not affect osteocyte density. Overall, our findings suggest that Scl-Ab treatment may be beneficial in the treatment of recessive OI caused by defects in collagen posttranslational modification. © 2015 American Society for Bone and Mineral Research.

Excessive transforming growth factor-β signaling is a common mechanism in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder, in both a dominant and recessive manner, of connective tissue characterized by brittle bones, fractures and extraskeletal manifestations. How structural mutations of type I collagen (dominant OI) or of its post-translational modification machinery (recessive OI) can cause abnormal quality and quantity of bone is poorly understood. Notably, the clinical overlap between dominant and recessive forms of OI suggests common molecular pathomechanisms. Here, we show that excessive transforming growth factor-β (TGF-β) signaling is a mechanism of OI in both recessive (Crtap(-/-)) and dominant (Col1a2(tm1.1Mcbr)) OI mouse models. In the skeleton, we find higher expression of TGF-β target genes, higher ratio of phosphorylated Smad2 to total Smad2 protein and higher in vivo Smad2 reporter activity. Moreover, the type I collagen of Crtap(-/-) mice shows reduced binding to the small leucine-rich proteoglycan decorin, a known regulator of TGF-β activity. Anti-TGF-β treatment using the neutralizing antibody 1D11 corrects the bone phenotype in both forms of OI and improves the lung abnormalities in Crtap(-/-) mice. Hence, altered TGF-β matrix-cell signaling is a primary mechanism in the pathogenesis of OI and could be a promising target for the treatment of OI.

Differential effects of collagen prolyl 3-hydroxylation on skeletal tissues

Mutations in the genes encoding cartilage associated protein (CRTAP) and prolyl 3-hydroxylase 1 (P3H1 encoded by LEPRE1) were the first identified causes of recessive Osteogenesis Imperfecta (OI). These proteins, together with cyclophilin B (encoded by PPIB), form a complex that 3-hydroxylates a single proline residue on the α1(I) chain (Pro986) and has cis/trans isomerase (PPIase) activity essential for proper collagen folding. Recent data suggest that prolyl 3-hydroxylation of Pro986 is not required for the structural stability of collagen; however, the absence of this post-translational modification may disrupt protein-protein interactions integral for proper collagen folding and lead to collagen over-modification. P3H1 and CRTAP stabilize each other and absence of one results in degradation of the other. Hence, hypomorphic or loss of function mutations of either gene cause loss of the whole complex and its associated functions. The relative contribution of losing this complex's 3-hydroxylation versus PPIase and collagen chaperone activities to the phenotype of recessive OI is unknown. To distinguish between these functions, we generated knock-in mice carrying a single amino acid substitution in the catalytic site of P3h1 (Lepre1^H662A). This substitution abolished P3h1 activity but retained ability to form a complex with Crtap and thus the collagen chaperone function. Knock-in mice showed absence of prolyl 3-hydroxylation at Pro986 of the α1(I) and α1(II) collagen chains but no significant over-modification at other collagen residues. They were normal in appearance, had no growth defects and normal cartilage growth plate histology but showed decreased trabecular bone mass. This new mouse model recapitulates elements of the bone phenotype of OI but not the cartilage and growth phenotypes caused by loss of the prolyl 3-hydroxylation complex. Our observations suggest differential tissue consequences due to selective inactivation of P3H1 hydroxylase activity versus complete ablation of the prolyl 3-hydroxylation complex.

The prolyl 3-hydroxylase complex serves to hydroxylate a single residue in type I collagen and also serves as a collagen chaperone. The complex is comprised of prolyl 3-hydroxylase 1, cartilage associated protein, and cyclophilin B. Mutations have been identified in the genes encoding the complex members in patients with recessive Osteogenesis Imperfecta. Recent data suggest that prolyl 3-hydroxylation of collagen does not alter the stability of collagen but may rather mediate protein-protein interactions. Additionally, the collagen chaperoning function of the complex is an important rate limiting step in the modification of type I collagen. Irrespective of whether patients with mutations in the genes encoding the members of the prolyl 3-hydroxylase complex have hypomorphic or complete loss of function alleles, either circumstance leads to the loss of both functions of the prolyl 3-hydroxylase complex. Thus, it is unknown how collagen chaperoning and/or hydroxylation affect bone and cartilage homeostasis. In this study, we generated a mouse model lacking the prolyl 3-hydroxylation activity of the complex while maintaining the chaperoning function. We found that the hydroxylase mutant mice have normal cartilage and normal cortical bone but decreased trabecular bone, suggesting that there is a differential requirement for hydroxylation in different tissues.

Strontium enhances osseointegration of calcium phosphate cement: a histomorphometric pilot study in ovariectomized rats

BACKGROUND

Calcium phosphate cements are used frequently in orthopedic and dental surgeries. Strontium-containing drugs serve as systemic osteoblast-activating medication in various clinical settings promoting mechanical stability of the osteoporotic bone.

METHODS

Strontium-containing calcium phosphate cement (SPC) and calcium phosphate cement (CPC) were compared regarding their local and systemic effects on bone tissue in a standard animal model for osteoporotic bone. A bone defect was created in the distal femoral metaphysis of 60 ovariectomized Sprague-Dawley rats. CPC and SPC were used to fill the defects in 30 rats in each group. Local effects were assessed by histomorphometry at the implant site. Systemic effects were assessed by bone mineral density (BMD) measurements at the contralateral femur and the spine.

RESULTS

Faster osseointegration and more new bone formation were found for SPC as compared to CPC implant sites. SPC implants exhibited more cracks than CPC implants, allowing more bone formation within the implant. Contralateral femur BMD and spine BMD did not differ significantly between the groups.

CONCLUSIONS

The addition of strontium to calcium phosphate stimulates bone formation in and around the implant. Systemic release of strontium from the SPC implants did not lead to sufficiently high serum strontium levels to induce significant systemic effects on bone mass in this rat model.

Mutations in SERPINF1 cause osteogenesis imperfecta type VI

Osteogenesis imperfecta (OI) is a spectrum of genetic disorders characterized by bone fragility. It is caused by dominant mutations affecting the synthesis and/or structure of type I procollagen or by recessively inherited mutations in genes responsible for the posttranslational processing/trafficking of type I procollagen. Recessive OI type VI is unique among OI types in that it is characterized by an increased amount of unmineralized osteoid, thereby suggesting a distinct disease mechanism. In a large consanguineous family with OI type VI, we performed homozygosity mapping and next-generation sequencing of the candidate gene region to isolate and identify the causative gene. We describe loss of function mutations in serpin peptidase inhibitor, clade F, member 1 (SERPINF1) in two affected members of this family and in an additional unrelated patient with OI type VI. SERPINF1 encodes pigment epithelium-derived factor. Hence, loss of pigment epithelium-derived factor function constitutes a novel mechanism for OI and shows its involvement in bone mineralization.

Osteoplastic procedures for the treatment of vertebral complications in multiple myeloma patients

Pain induced by vertebral fracture in multiple myeloma can be treated by an osteoplastic procedure. The magnitude of the pain reduction by the procedure depends on the presence of additional causes for pain as spondylosis deformans, osteochondrosis, stenosis of the spinal canal, or intervertebral nerve compression. To identify additional reasons for pain apart from a vertebral fracture-induced pain, a detailed preoperative analysis of the patients complaints is crucial for the outcome after an osteoplastic procedure. In addition, the technical aspects for performing the procedure and potential complications have to be considered as well as the stability of the cortical bone of the respective vertebral body. A complete collapse of the vertebra (vertebra plana) is an unfavorable situation for any osteoplastic procedure. In case of inflammatory or infectious vertebral lesions (e.g. spondylodiscitis) osteoplastic procedures are contraindicated. An interdisciplinary discussion of the individual case among oncologists, radiotherapists, trauma/spien surgeons, radiologists, and osteologists/endocrinologists is a prerequisite for the identification of patients who will truly benefit from an osteoplastic procedure and to avoid overtreatment of the patient and economical exploitation of healthcare providers.

Vertebroplasty and kyphoplasty - inefficient treatments for degenerative spine disease

Osteoporotic vertebral fractures and pathological vertebral lesions are frequent clinical situations causing severe back pain. The pharmacological treatment of the underlying disease and the analgetic treatment of the associated back pain usually do not rid the patient's back pain completely and are insufficient to prevent the fracture-weakened vertebral body from further fracturing with long term consequences for the biomechanical competence of the entire spine. In the last 10 years the minimal invasive treatment options vertebroplasty (VP) and balloon kyphoplasty (BK) have spread quickly because these procedures appeared to be promising treatments to stop the fracture and vertebral lesion associated back pain and to internally stabilize a fractured vertebral body. Numerous published reports on VP and BK appeared to support the notion of an immediate and lasting pain reduction after VP and BK in additon to a prevention of further fracturing of the treated vertebrae. The first three randomized controlled and partly blinded trials have been published this year. Two of these trials demonstrate that VP does not result in a better pain control than a sham operation whereas BK was shown to reduce back pain due to verterbal fractures for at least 12 months. Considering that more than 1.5 million people world-wide have been treated with VP and BK until now this work discusses the recent trials and suggests clinical and academic consequences on the basis of the most recent evidence.

The intravertebral vacuum phenomen as specific sign of osteonecrosis in vertebral compression fractures: results from a radiological and histological study

This study investigated the prevalence of the intravertebral vacuum phenomenon (IVP) and osteonecroses in vertebral compression fractures (VCFs). We therefore performed an histological analysis of biopsies obtained from VCFs prior to balloon kyphoplasty. Computed tomography (CT) scans were reviewed regarding the presence of an IVP (i.e. cleft sign, Kümmell disease). We reviewed the data of 266 consecutive patients treated by balloon kyphoplasty in 501 procedures from 2002 to 2004. From 180 patients (68%) we obtained adequate bone tissue for histological evaluation. Biopsy specimens were analysed regarding the presence of osteoporosis, infection, malignancy and osteonecrosis. CT scans of all 180 patients were reviewed for presence of an IVP. Histological examination revealed 135 (75%) osteoporoses, 20 (11%) neoplasms, 12 (7%) trauma cases and 13 (7%) osteonecroses. An IVP was present in 12 (7%) patients. There was a significant association of osteonecrosis and IVP (P < 0.0001). Eleven of 12 patients with a vacuum phenomenon showed an osteonecrosis on histology, whereas 11 of 13 patients with osteonecrosis showed an IVP on CT. The IVP is a specific sign of osteonecrosis in vertebral compression fractures (sensitivity 85%, specificity 99%, positive predictive value 91%). Our findings strongly support the thesis that an IVP indicates local bone ischemia associated with a non-healing vertebral collapse and pseudarthrosis.

[Balloon kyphoplasty in the therapy of vertebral fractures]

Approximately 500,000 vertebral fractures occur as a result of osteoporosis every year in Europe. One third of the patients thus affected complain of severe back pain and seek treatment. In the past, the treatment of such fractures was limited to conservative methods, such as the use of braces and analgesics and long-term immobilisation followed by physiotherapy. Since 1998 balloon kyphoplasty, a minimally invasive procedure, has also been available for their treatment. During balloon kyphoplasty a balloon system is introduced into a fractured vertebral body to achieve bitranspedicular augmentation, after which low-viscosity bone cement is injected into the vertebral body, where it sets very quickly. In general the patient can be fully mobilized 24-48 h after the procedure and in most cases the symptoms are then considerably attenuated; many patients are actually free of pain. Published studies and our own experience indicate that balloon kyphoplasty is a safe method of treating painful vertebral compression fractures sustained in various ways and that complications are rare with this procedure.

[Balloon kyphoplasty in the treatment of vertebral fractures]

Approximately 500,000 vertebral fractures occur as a result of osteoporosis every year in Europe. One third of the patients thus affected complain of severe back pain and seek treatment. In the past, the treatment of such fractures was limited to conservative methods, such as the use of braces and analgesics and long-term immobilisation followed by physiotherapy. Since 1998 balloon kyphoplasty, a minimally invasive procedure, has also been available for their treatment. During balloon kyphoplasty a balloon system is introduced into the fractured vertebral body to achieve bitranspedicular augmentation, after which low-viscosity bone cement is injected into the vertebral body, where it sets very quickly. In general the patient can be fully mobilized 24-48 h after the procedure and in most cases the symptoms are then considerably attenuated; many patients are actually free of pain. Published studies and our own experience indicate that balloon kyphoplasty is a safe method of treating painful vertebral compression fractures sustained in various ways and that complications are rare with this procedure.

[Balloon kyphoplasty in the treatment of back pain]

BACKGROUND

Experience of just under 5 years has shown that balloon kyphoplasty can be just as successfully employed as the longer-stablished vertebroplasty for the treatment of back pain due to recent or prior osteoporotic fractures as well as new traumatic fractures.

MATERIAL AND METHOD

Among 345 patients with a total of 690 treated vertebral bodies, the change in pain symptomatology was analyzed for a follow-up period of 12 months in 40 study patients who underwent kyphoplasty and a control group of 20 patients. In addition, the pain experienced by a further 29 patients with new traumatic vertebral body fractures was monitored over a 12-month period. These fractures were partly managed by fixateur interne alone and by a combination of fixateur interne and kyphoplasty.

RESULTS

The 40 patients treated by kyphoplasty had a baseline VAS score of 26.2+/-2.00, which increased to 44.4+/-3.11 after 12 months, while the respective scores for the control group were 33.6+/-4.21 and 34.3+/-4.35. In the 29 patients with new traumatic vertebral body fractures, the initial VAS score was 62 and after 12 months a distinct reduction of pain was noted with a score of 20 (100 = maximum pain, 0 = no pain). The number of times that the 40 patients managed by kyphoplasty had to consult their general practitioner was significantly reduced by the pain therapy.

CONCLUSION

Balloon kyphoplasty verifiably improved the pain symptomatology after vertebral fracture over a period of 12 months. Comparison with the control group, which received the same osteoporosis drug therapy, confirmed the effect of this minimally invasive treatment form.

[Therapeutic management of acromegaly]

BACKGROUND

Only 60% of the patients with acromegaly are biochemically cured (growth hormone [GH] nadir < 1.0 microg/l after an oral glucose load, normalized age- and gender-matched insulin-like growth factor-1 [IGF-1] levels) after transsphenoidal surgery of the pituitary gland. In the absence of a remission there are effective pharmacological treatment regimens available which are able to lower GH and IGF-1 serum levels.

THERAPEUTIC STRATEGIES

Somatostatin analogs, a GH receptor antagonist and dopamine agonists have been shown to alleviate the comorbid features and to normalize GH and IGF-1 levels.

CASE REPORTS

In this overview six case reports are presented to highlight the current pharmacological treatment options and to propose an algorithm for the clinical routine in patients with persisting acromegaly.

CONCLUSION

Transsphenoidal surgery is the treatment of choice for the initial management of acromegaly. In the absence of a remission there are effective pharmacological treatment regimens available among which somatostatin analogs are recommended as the first-line treatment.

Osseous integration of calcium phosphate in osteoporotic vertebral fractures after kyphoplasty: initial results from a clinical and experimental pilot study

INTRODUCTION

This study evaluated the radiological changes at the bone-cement interface of calcium phosphate cement (CPC) and polymethylmethacrylate (PMMA) 12 months after kyphoplasty. In a pilot experiment, we additionally performed a histomorphometric analysis in osteopenic foxhounds to analyze the process of osseous integration of CPC and PMMA.

METHODS

Twenty postmenopausal female patients with 46 vertebral compression fractures (VCF) were treated by kyphoplasty, utilizing CPC (N=28) or PMMA (N=18) for intravertebral stabilization. After a 12-month follow-up, we measured the density changes of border voxels at the bone-cement interface by computed tomography (CT) using dedicated software algorithms. We defined the border-voxel density (BVD) as a parameter of cement resorption at the interface. We also investigated the bone-implant interface in three osteopenic foxhounds by histomorphometry 3, 6, and 12 months after cement implantation.

RESULTS

Twelve months after kyphoplasty, only CPC showed a significant decrease of the BVD compared to PMMA (p<0.01), indicating a slow progress of resorption at the interface. Histomorphometry of the dog vertebrae showed near total bone coverage of CPC implants, whereas the PMMA surface exhibited only 30% direct bone contact (p<0.01). We also observed a time-dependent increase in the number of discernable osteons close to the interface of CPC, but no bone tissue within PMMA (p<0.01).

CONCLUSIONS

The decrease of the BVD 12 months after kyphoplasty may indicate osseous integration of CPC by: (1) the ingrowth of bone tissue and (2) osteonal penetration close to the interface.

Endothelin-1 Levels in Patients with Paget's Disease of Bone

A locally accelerated bone turnover is the pathophysiological basis of Paget's disease of bone (PD) and may result in severe bone deformations and pain. Affected bone sites are hypervascularized. Secreted endothelial products such as endothelin-1 (ET-1), influence bone metabolism. We investigated a possible correlation between ET-1 plasma concentrations and bone metabolism in patients with PD and whether ET-1 plasma levels are regulated by i. v. bisphosphonate treatment. Plasma ET-1 levels were determined in 22 patients with PD and found to be significantly (p = 0.006) elevated (0.75 +/- 0.48 fmol/ml) compared to 19 healthy controls (0.20 +/- 0.24 fmol/ml). In a group of five patients with PD, plasma ET-1 levels were determined before and after treatment with i. v. pamidronate. On the average, ET-1 levels decreased by 21 % after pamidronate infusions (p = 0.045). The results suggest that bone metabolism in pagetic bone affects endothelial cell metabolism and may also be modulated by endothelial cell products. ET-1 plasma levels may indicate PD activity.

No association of the 94T/G polymorphism in the adiponectin gene with diabetic complications

AIM

This study examined a possible association of the T/G polymorphism at nucleotide 94 in the adiponectin gene with the prevalence of diabetic complications.

METHODS

The study was performed in 696 patients with type 1 diabetes and type 2 diabetes. Genotyping was performed by means of polymerase chain reaction and subsequent cleavage by using SmaI restriction endonuclease.

RESULTS

The 94G/G genotype was significantly more prevalent in patients with type 2 diabetes (2.2%) than in type 1 diabetics (0.0%) (p = 0.02), whereas no differences were found for frequencies of the 94T/T and the 94G/T genotypes, respectively. In patients with type 1 diabetes, 45 of 239 patients were heterozygous for the 94T/G polymorphism (carrier rate (CR): 18.8%; allele frequency (AF): 0.094). In type 2 diabetics, 71 of 457 patients were heterozygous and 10 patients were homozygous for the 94G/G genotype (CR: 17.7%; AF: 0.10). No association with diabetic nephropathy, diabetic neuropathy or diabetic retinopathy was found for either genotype in patients with type 1 and type 2 diabetes.

CONCLUSIONS

The 94T/G polymorphism in the adiponectin gene is not associated with diabetic complications. The significance of a higher prevalence of the G allele in type 2, compared to type 1 diabetes remains to be clarified.

CT volumetry of intravertebral cement after kyphoplasty. Comparison of polymethylmethacrylate and calcium phosphate in a 12-month follow-up

This study was intended to measure the volume of intravertebral cement after balloon kyphoplasty with high resolution computed tomography (CT) and dedicated software. Volume changes of biocompatible calcium phosphate cement (CPC) were detected during a follow-up of 12 months. Measurements were compared with a control group of patients treated with polymethylmethacrylate (PMMA). Twenty-three vertebrae (14 CPC, 9 PMMA) of 12 patients were examined with CT using an identical imaging protocol. Dedicated software was used to quantify intravertebral cement volume in subvoxel resolution by analyzing each cement implant with a density-weighted algorithm. The mean volume reduction of CPC was 0.08 ml after 12 months, which corresponds to an absorption rate of 2 vol%. However, the difference did not reach significance level (P>0.05). The mean error estimate was 0.005 ml, indicating excellent precision of the method. CT volumetry appears a precise tool for measurement of intravertebral cement volume. CT volumetry offers the possibility of in vivo measurement of CPC resorption.

Die Wertigkeit der Ballonkyphoplastie bei der osteoporotischen Wirbelkörperfraktur

BACKGROUND DATA

Patients with osteoporotic vertebral compression fractures frequently complain of pain and a loss of function and mobility. Such fractures are associated with an increased mortality. The common treatment with bed rest, bracing or osteosynthesis does not lead to satisfying results. With two new surgical techniques, vertebroplasty and kyphoplasty, an internal stabilisation of osteoporotic vertebral fractures is possible.

METHODS

All patients were treated by kyphoplasty. With a minimal invasive dorsal approach, an inflatable bone tamp is placed in the fractured vertebral body. This tamp can restore the vertebral body height and create a cavity, which is filled with bone cement under low pressure. The advantage of kyphoplasty compared to vertebroplasty is the restoration of the vertebral height and a decreased cement leakage rate. We performed a prospective, interdisciplinary study with a follow-up of 12 months. We treated 192 vertebral fractures in 102 patients. Augmentation was performed with polymethylmethacrylate in 138 cases and with a new injectable calcium phosphate-cement in 54 vertebral bodies. Outcome data were obtained with two different spine-scores and by the radiomorphometric evaluation of x-rays before and after treatment.

RESULTS

We noticed a significant improvement in pain and function in 89% of the patients. All patients showed a regain of vertebral height of on average 17%. In 7% of all treated vertebral bodies, we noticed cement leakage, which was, however, far below the rates published for vertebroplasty (20-70%). There were two complications, bleeding due to an unknown coagulopathy and a violation of the myelon by malpunction.

CONCLUSION

Kyphoplasty is a reliable and minimally invasive method for stabilizing fractured osteoporotic vertebral bodies. Improvement of pain and function and a regain in height of the treated vertebral body can be accomplished.

Kyphoplastie und Vertebroplastie bei Frakturen im hohen Lebensalter

Kyphoplasty and vertebroplasty are two minimally invasive percutaneous techniques used for treatment of osteoporotic vertebral compression fractures in the thoracic and lumbar spine. The injection of polymethylmetacrylate (PMMA) is often a final attempt at therapeutic treatment of complications due to such fractures. Vertebroplasty involves injection of cement via one or both pedicles under high pressure, thus filling and stabilizing the vertebra without reduction of fracture. Extravertebral cement leakage is a common complication: an intact posterior wall normally prevents cement leakage into the epidural space. Kyphoplasty involves transpedicular inflation of balloon tamps, thus creating a cavity which is then filled with PMMA under low pressure. Restoration of vertebral height is possible and the potential for extravertebral cement leakage lessened.