Lothar Seefried

The transcriptional profile of mesenchymal stem cell populations in primary osteoporosis is distinct and shows overexpression of osteogenic inhibitors.

Primary osteoporosis is an age-related disease characterized by an imbalance in bone homeostasis. While the resorptive aspect of the disease has been studied intensely, less is known about the anabolic part of the syndrome or presumptive deficiencies in bone regeneration. Multipotent mesenchymal stem cells (MSC) are the primary source of osteogenic regeneration. In the present study we aimed to unravel whether MSC biology is directly involved in the pathophysiology of the disease and therefore performed microarray analyses of hMSC of elderly patients (79–94 years old) suffering from osteoporosis (hMSC-OP). In comparison to age-matched controls we detected profound changes in the transcriptome in hMSC-OP, e.g. enhanced mRNA expression of known osteoporosis-associated genes (LRP5, RUNX2, COL1A1) and of genes involved in osteoclastogenesis (CSF1, PTH1R), but most notably of genes coding for inhibitors of WNT and BMP signaling, such as Sclerostin and MAB21L2. These candidate genes indicate intrinsic deficiencies in self-renewal and differentiation potential in osteoporotic stem cells. We also compared both hMSC-OP and non-osteoporotic hMSC-old of elderly donors to hMSC of ∼30 years younger donors and found that the transcriptional changes acquired between the sixth and the ninth decade of life differed widely between osteoporotic and non-osteoporotic stem cells. In addition, we compared the osteoporotic transcriptome to long term-cultivated, senescent hMSC and detected some signs for pre-senescence in hMSC-OP. Our results suggest that in primary osteoporosis the transcriptomes of hMSC populations show distinct signatures and little overlap with non-osteoporotic aging, although we detected some hints for senescence-associated changes. While there are remarkable inter-individual variations as expected for polygenetic diseases, we could identify many susceptibility genes for osteoporosis known from genetic studies. We also found new candidates, e.g. MAB21L2, a novel repressor of BMP-induced transcription. Such transcriptional changes may reflect epigenetic changes, which are part of a specific osteoporosis-associated aging process.

Pulse treatment with zoledronic acid causes sustained commitment of bone marrow derived mesenchymal stem cells for osteogenic differentiation

The aminobisphosphonate zoledronic acid (ZA) is a bone seeking specific inhibitor of protein farnesylation and geranylgeranylation, which causes inhibition of osteoclast function and apoptosis. It is widely used as an osteoclast targeted antiresorptive treatment of metastatic bone disease, Pagets disease and osteoporosis. Mesenchymal stem cells (MSC) and osteoblast precursors can also be targets of bisphosphonates, but the clinical relevance of these effects is under debate. We show here that ZA in vitro causes inhibition of proliferation and induction of apoptosis in hMSC, when applied in concentrations of 20 and 50 microM for more than 24 h which can be rescued by treatment with 10 microM geranylgeranyl pyrophosphate (GGPP). However, pulse stimulation for 3 and 6 h with these concentrations and subsequent culture for up to 2 weeks under osteogenic conditions exerts sustained regulation of osteogenic marker genes in hMSC. The effect on gene regulation translates into marked enhancement of mineralization, as shown by alizarin red and alkaline phosphatase staining after 4 weeks of osteogenic culture. ZA, when applied as a pulse stimulus, might therefore also stimulate osteogenic differentiation in vivo, since muM plasma concentrations can be achieved by intravenous application of 5 mg in patients. These data set the stage for the future dissection of the effects of ZA and other aminobisphosphonates on cells beyond osteoclasts, with respect to cell differentiation in benign metabolic and to antitumor efficacy in metastatic bone diseases, as well as adverse events due to putative substance accumulation in bone during long-term treatment.

Estrogen receptor and Wnt signaling interact to regulate early gene expression in response to mechanical strain in osteoblastic cells

Bone mass homeostasis is regulated by an interaction of various factors, including growth factors, systemic hormones and mechanical loading. Two signal transduction pathways, the estrogen receptor (ER) and the Wnt/beta-catenin signal transduction pathway, have been shown to have an important role in regulating osteoblast and osteoclast function and to be involved in mechanotransduction. Therefore, dysfunction of these pathways can lead to osteoporotic bone loss. However, less is known about the modulation of gene expression by the interaction of these pathways in response to mechanical strain. We performed in vitro stretch experiments using osteoblastic MC3T3-E1 cells to study the effect of both pathways and mechanical strain on the expression of cyclooxygenase-2 (Cox-2), which is involved in the synthesis of prostaglandins, modulators of bone formation and resorption. Using specific agonists and antagonists, we demonstrated a regulation by an interaction of these pathways in mechantransduction. Estradiol (E2) had a sensitizing effect on mechanically induced Cox-2 expression, which seemed to be ligand-specific as it could be abolished using the antiestrogen ICI182,780. However, mechanical strain in the presence of Wnt signaling activators diminished both the E2 sensitizing effect and the stimulatory effect of Wnt signaling in the absence of strain. This interaction might be one regulatory mechanism by which mechanical loading exerts its role in bone mass homeostasis.

BMP12 and BMP13 gene transfer induce ligamentogenic differentiation in mesenchymal progenitor and anterior cruciate ligament cells.

BACKGROUND AIMS To date there are only very few data available on the ligamentogenic differentiation capacity of mesenchymal stromal/progenitor cells (MSC) and anterior cruciate ligament (ACL) fibroblasts. METHODS We describe the in vitro potential of MSC and ACL cells to undergo ligamentogenic differentiation upon transduction with adenoviral vectors encoding the human cDNA for bone morphogenetic protein (BMP) 12 and BMP13, also known as growth and differentiation factors (GDF) 6 and 7, respectively. RESULTS Transgene expression for at least 14 days was confirmed by Western blot analyzes. After 21 days of cell culture within collagen type I hydrogels, histochemical (hematoxylin/eosin (H&E), Azan and van Gieson), immunohistochemical and polymerase chain reaction (PCR) analyzes of the genetically modified constructs of both cell types revealed elongated, viable fibroblast-like cells embedded in a ligament-like matrix rich in collagens, vimentin, fibronectin, decorin, elastin, scleraxis, tenascin, and tenomodulin. CONCLUSIONS It appears that both MSC and ACL fibroblasts are capable of ligamentogenic differentiation with these factors. This information may aid in the development of biologic approaches to repair and restore ACL after injury.

FGF23 is a putative marker for bone healing and regeneration.

Besides numerous other factors, fibroblast growth factor receptor (FGFR) signaling is involved in fracture healing and bone remodeling. FGF23 is a phosphatonin produced by osteoblastic cells, which signals via FGFR1, thereby exerting effects in bone and kidney. We analyzed if serum FGF23 levels might be an indicator to predict fracture healing and union. FGF23 (C‐Term) was elevated on day 3 postoperatively in 55 patients sustaining an exchange of total hip implants due to aseptic loosening. A prospective study of 40 patients undergoing primary hip arthroplasty also showed elevated FGF23 (C‐Term) but no change in FGF23 (intact) levels on days 1, 4, and 10 postoperatively. Serum phosphate and phosphate clearance stayed within normal ranges. FGF23 mRNA expression in ovine callus was compared between a standard and delayed course of osteotomy healing. In the standard model, a marked increase in FGF23 mRNA expression compared to the delayed healing situation was observed. Immunohistochemical analysis showed FGF23 production of osteoblasts and granulation tissue in the fracture callus during bone healing. In conclusion, FGF23 is involved in bone healing, can be measured by a sensitive assay in peripheral blood, and is a promising candidate as an indicator for healing processes prone to reunion versus nonunion.

Clinical Aspects of Hypophosphatasia: An Update

Hypophosphatasia (HPP) is a heterogeneous rare inborn error of bone and mineral metabolism caused by mutations in the ALPL gene encoding the isoenzyme, tissue-nonspecific alkaline phosphatase (TNAP). These mutations result in a decreased level of TNAP activity and increased levels of its substrates, including inorganic pyrophosphate, pyridoxal-5′-phosphate and phosphoethanolamine. Clinical presentations are highly variable, ranging from stillbirth and absence of mineralization in severe disease to mild dental problems or osteopenia in adulthood. Further clinical symptoms include defective bone mineralization with bone deformities, recurrent fractures, chronic non-bacterial osteomyelitis, craniosynostosis, neonatal seizures, nephrocalcinosis, muscular hypotonia, failure to thrive and dental abnormalities with premature exfoliation of teeth and caries. Prognosis is very poor in severe perinatal forms with most patients dying from pulmonary complications of their skeletal disease but patients with mild phenotypes (adult form or Odonto-HPP) usually do not have a limitation in their life expectancy. Although TNAP is a ubiquitous enzyme, mostly known for its crucial role during mineralization of bone and teeth, its exact biological role in different human organs is still unclear, and the pathophysiology of symptoms due to TNAP deficiency in HPP are not understood in detail. Since inflammation and tissue destruction of the musculoskeletal system may occur in HPP, TNAP may also play an important role in controlling inflammatory processes. Recent investigations provide evidence that TNAP is also essentially involved in the development of the central nervous system and might contribute to multiple functions of the human brain. HPP can be diagnosed on clinical, biochemical and radiological criteria, and genetic testing confirms the diagnosis and is useful for genetic counseling. Since clinical symptoms are highly variable, patients should be followed up by a multidisciplinary team having experience in HPP treatment. Up to now, no curative treatment of HPP is available. Therefore, symptomatic treatment in particular with regard to pain, seizures and other metabolic phenomena is most important. However, recently, enzyme replacement therapy with a bone-targeted recombinant human TNAP molecule has been reported to improve bone mineralization, respiratory function and physical activity in severely affected infants with HPP, and further clinical trials are ongoing. Hopefully, this and other new therapeutic strategies may improve the prognosis and quality of life of patients with HPP and may contribute to our understanding of bone metabolism in general.

BPS804 Anti‐sclerostin Antibody in Adults with Moderate Osteogenesis Imperfecta: Results of a Randomized Phase 2a Trial

This 21‐week, open‐label, phase 2a trial aimed to evaluate the pharmacodynamics and safety of multiple, escalating infusions of BPS804, a neutralizing, anti‐sclerostin antibody, in adults with moderate osteogenesis imperfecta (OI). Patients received BPS804 (three escalating doses each separated by 2 weeks [5, 10, and 20 mg/kg]) or no treatment (reference group). The primary efficacy endpoints were mean changes from baseline to day 43 in: procollagen type 1 N‐terminal propeptide (P1NP), procollagen type 1 C‐terminal propeptide (P1CP), bone‐specific alkaline phosphatase (BSAP), osteocalcin (OC), and type 1 collagen cross‐linked C‐telopeptide (CTX‐1). Mean change from baseline to day 141 in lumbar spine areal bone mineral density (aBMD) was also assessed. BPS804 safety and tolerability were assessed every 2 weeks. Overall, 14 adults were enrolled (BPS804 group: n = 9, mean age 30.7 years, mean aBMD Z‐score –2.6; reference group, n = 5, mean age 27.4 years, mean aBMD Z‐score –2.2). In the BPS804 group, P1NP, P1CP, BSAP, and OC were increased by 84% (p < 0.001), 53% (p = 0.003), 59% (p < 0.001), and 44% (p = 0.012), respectively, versus baseline (reference: P1NP, +6% [p = 0.651]; P1CP, +5% [p = 0.600]; BSAP, –13% [p = 0.582]; OC, –19% [p = 0.436]). BPS804 treatment downregulated CTX‐1 by 44% from baseline (reference: –7%; significance was not tested for this biomarker), and increased aBMD by 4% (p = 0.038; reference group: +1%; p = 0.138). BPS804 was generally well tolerated. There were 32 adverse events reported in nine patients; none was suspected to be treatment‐related. There were no treatment‐related fractures. BPS804 stimulates bone formation, reduces bone resorption, and increases lumbar spine aBMD in adults with moderate OI. This paves the way for a longer‐term, phase 3 trial into the efficacy, safety, and tolerability of BPS804 in patients with OI.

Efficacy of anti-sclerostin monoclonal antibody BPS804 in adult patients with hypophosphatasia

BACKGROUND. Hypophosphatasia (HPP) is a rare genetic disorder resulting in variable alterations of bone formation and mineralization that are caused by mutations in the ALPL gene, encoding the tissue-nonspecific alkaline phosphatase (ALP) enzyme. METHODS. In this phase IIA open-label, single-center, intra-patient, dose-escalating study, adult patients with HPP received 3 ascending intravenous doses of 5, 10, and 20 mg/kg BPS804, a fully human anti-sclerostin monoclonal antibody, on days 1, 15, and 29, respectively. Patients were followed for 16 weeks after the last dose. We assessed the pharmacodynamics, pharmacokinetics, preliminary efficacy, and safety of BPS804 administrations at specified intervals during treatment and follow-up. RESULTS. Eight patients (mean age 47.8 years) were enrolled in the study (6 females, 2 males). BPS804 treatment increased mean ALP and bone-specific ALP enzymatic activity between days 2 and 29. Transient increases in the bone formation markers procollagen type-I N-terminal propeptide (PINP), osteocalcin, and parathyroid hormone as well as a transient decrease in the bone resorption marker C-telopeptide of type I collagen (CTX-1) were observed. Lumbar spine bone mineral density showed a mean increase by day 85 and at end of study. Treatment-associated adverse events were mild and transient. CONCLUSION. BPS804 treatment was well tolerated and resulted in increases in bone formation biomarkers and bone mineral density, suggesting that sclerostin inhibition could be applied to enhance bone mineral density, stability, and regeneration in non-life-threatening clinical situations in adults with HPP. TRIAL REGISTRATION. Clinicaltrials.gov NCT01406977. FUNDING. Novartis Institutes for BioMedical Research, Basel, Switzerland.

Monitoring guidance for patients with hypophosphatasia treated with asfotase alfa

Hypophosphatasia (HPP) is a rare, inherited, systemic, metabolic disorder caused by autosomal recessive mutations or a single dominant-negative mutation in the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). The disease is associated with a broad range of signs, symptoms, and complications, including impaired skeletal mineralization, altered calcium and phosphate metabolism, recurrent fractures, pain, respiratory problems, impaired growth and mobility, premature tooth loss, developmental delay, and seizures. Asfotase alfa is a human, recombinant enzyme replacement therapy that is approved in many countries for the treatment of patients with HPP. To address the unmet need for guidance in the monitoring of patients receiving asfotase alfa, an international panel of physicians with experience in diagnosing and managing HPP convened in May 2016 to discuss treatment monitoring parameters. The panel discussions focused on recommendations for assessing and monitoring patients after the decision to treat with asfotase alfa had been made and did not include recommendations for whom to treat. Based on the consensus of panel members, this review provides guidance on the monitoring of patients with HPP during treatment with asfotase alfa, including recommendations for laboratory, efficacy, and safety assessments and the frequency with which these should be performed during the course of treatment. Recommended assessments are based on patient age and include regular monitoring of biochemistry, skeletal radiographs, respiratory function, growth, pain, mobility and motor function, and quality of life. Because of the systemic presentation of HPP, a coordinated, multidisciplinary, team-based, patient-focused approach is recommended in the management of patients receiving asfotase alfa. Monitoring of efficacy and safety outcomes must be tailored to the individual patient, depending on medical history, clinical manifestations, availability of resources in the clinical setting, and the clinicians professional judgment.

Distribution of Constituents and Metabolites of Maritime Pine Bark Extract (Pycnogenol®) into Serum, Blood Cells, and Synovial Fluid of Patients with Severe Osteoarthritis: A Randomized Controlled Trial

The present randomized controlled study aimed to investigate the in vivo distribution of constituents or metabolites of the standardized maritime pine bark extract Pycnogenol®. Thirty-three patients with severe osteoarthritis scheduled for a knee arthroplasty were randomized to receive either 200 mg per day Pycnogenol® (P+) or no treatment (Co) over three weeks before surgery. Serum, blood cells, and synovial fluid samples were analyzed using liquid chromatography coupled to tandem mass spectrometry with electrospray ionization (LC-ESI/MS/MS). Considerable interindividual differences were observed indicating pronounced variability of the polyphenol pharmacokinetics. Notably, the highest polyphenol concentrations were not detected in serum. Catechin and taxifolin primarily resided within the blood cells while the microbial catechin metabolite δ-(3,4-dihydroxy-phenyl)-γ-valerolactone, ferulic, and caffeic acid were mainly present in synovial fluid samples. Taxifolin was detected in serum and synovial fluid exclusively in the P+ group. Likewise, no ferulic acid was found in serum samples of the Co group. Calculating ratios of analyte distribution in individual patients revealed a simultaneous presence of some polyphenols in serum, blood cells, and/or synovial fluid only in the P+ group. This is the first evidence that polyphenols distribute into the synovial fluid of patients with osteoarthritis which supports rationalizing the results of clinical efficacy studies.