Richard Marsell

Circulating Fibroblast Growth Factor-23 Is Associated With Fat Mass and Dyslipidemia in Two Independent Cohorts of Elderly Individuals

Objective—Disturbances in mineral metabolism define an increased cardiovascular risk in patients with chronic kidney disease. Fibroblast growth factor-23 (FGF23) is a circulating regulator of phosphate and vitamin D metabolism and has recently been implicated as a putative pathogenic factor in cardiovascular disease. Because other members of the FGF family play a role in lipid and glucose metabolism, we hypothesized that FGF23 would associate with metabolic factors that predispose to an increased cardiovascular risk. The goal of this study was to investigate the relationship between FGF23 and metabolic cardiovascular risk factors in the community. Methods and Results—Relationships between serum FGF23 and body mass index (BMI), waist circumference, waist-to-hip ratio, serum lipids, and fat mass were examined in 2 community-based, cross-sectional cohorts of elderly whites (Osteoporotic Fractures in Men Study: 964 men aged 75±3.2; Prospective Investigation of the Vasculature in Uppsala Seniors study: 946 men and women aged 70). In both cohorts, FGF23 associated negatively with high-density lipoprotein and apolipoprotein A1 (7% to 21% decrease per 1-SD increase in log FGF23; P<0.01) and positively with triglycerides (11% to 14% per 1-SD increase in log FGF23; P<0.01). A 1-SD increase in log FGF23 was associated with a 7% to 20% increase in BMI, waist circumference, and waist-to-hip ratio and a 7% to 18% increase in trunk and total body fat mass (P<0.01) as determined by whole-body dual x-ray absorptiometry. FGF23 levels were higher in subjects with the metabolic syndrome compared with those without (46.4 versus 41.2 pg/mL; P<0.05) and associated with an increased risk of having the metabolic syndrome (OR per 1-SD increase in log FGF23, 1.21; 95% CI, 1.04 to 1.40; P<0.05). Conclusion—We report for the first time on associations between circulating FGF23, fat mass, and adverse lipid metabolism resembling the metabolic syndrome, potentially representing a novel pathway(s) linking high FGF23 to an increased cardiovascular risk.

Fibroblast growth factor-23 is associated with parathyroid hormone and renal function in a population-based cohort of elderly men

OBJECTIVE Fibroblast growth factor-23 (FGF23) is a circulating factor involved in phosphate (Pi) and vitamin D metabolism. Serum FGF23 is increased at later stages of chronic kidney disease due to chronic hyperphosphatemia and decreased renal clearance. Recent studies also indicate that FGF23 may directly regulate the expression of parathyroid hormone (PTH) in vitro. Therefore, the objective of the current study was to determine the relationship between FGF23, PTH, and other biochemistries in vivo in subjects with no history of renal disease. DESIGN Serum biochemistries were measured in a subsample of the population-based Swedish part of the MrOS study. In total, 1000 Caucasian men aged 70-80 years were randomly selected from the population. METHODS Intact FGF23, Pi, calcium, albumin, estimated glomerular filtration rate (eGFR, calculated from cystatin C), PTH, and 25(OH)D3 were measured. Association studies were performed using linear univariate and multivariate regression analyses. RESULTS The median FGF23 level was 36.6 pg/ml, ranging from 0.63 to 957 pg/ml. There was a significant correlation between log FGF23 and eGFR (r=-0.21; P<0.00001) and log PTH (r=0.13; P<0.001). These variables remained as independent predictors of FGF23 in multivariate analysis. In addition, log PTH (beta=0.082; P<0.05) and eGFR (beta=-0.090; P<0.05) were associated with log FGF23 in subjects with eGFR>60 ml/min. Only eGFR (beta=-0.35; P<0.0001) remained as a predictor of log FGF23 in subjects with eGFR<60 ml/min. CONCLUSIONS Serum FGF23 and PTH are associated in vivo, supporting recent findings that FGF23 directly regulates PTH expression in vitro. Additionally, eGFR is associated with FGF23 in subjects with normal or mildly impaired renal function, indicating that GFR may modulate FGF23 levels independent of serum Pi.

Amelioration of the premature ageing-like features of Fgf-23 knockout mice by genetically restoring the systemic actions of FGF-23

Genetic ablation of fibroblast growth factor 23 from mice (Fgf‐23−/−) results in a short lifespan with numerous abnormal biochemical and morphological features. Such features include kyphosis, hypogonadism and associated infertility, osteopenia, pulmonary emphysema, severe vascular and soft tissue calcifications, and generalized atrophy of various tissues. To determine whether these widespread anomalies in Fgf‐23−/− mice can be ameliorated by genetically restoring the systemic actions of FGF‐23, we generated Fgf‐23−/− mice expressing the human FGF‐23 transgene in osteoblasts under the control of the 2.3 kb α1(I) collagen promoter (Fgf‐23−/− /hFGF‐23‐Tg double mutants). This novel mouse model is completely void of all endogenous Fgf‐23 activity, but produces human FGF‐23 in bone cells that is subsequently released into the circulation. Our results suggest that lack of Fgf‐23 activities results in extensive premature ageing‐like features and early mortality of Fgf‐23−/− mice, while restoring the systemic effects of FGF‐23 significantly ameliorates these phenotypes, with the resultant effect being improved growth, restored fertility, and significantly prolonged survival of double mutants. With regard to their serum biochemistry, double mutants reversed the severe hyperphosphataemia, hypercalcaemia, and hypervitaminosis D found in Fgf‐23−/− littermates; rather, double mutants show hypophosphataemia and normal serum 1,25‐dihydroxyvitamin D3 levels similar to pure FGF‐23 Tg mice. These changes were associated with reduced renal expression of NaPi2a and 1α‐hydroxylase, compared to Fgf‐23−/− mice. FGF‐23 acts to prevent widespread abnormal features by acting systemically to regulate phosphate homeostasis and vitamin D metabolism. This novel mouse model provides us with an in vivo tool to study the systemic effects of FGF‐23 in regulating mineral ion metabolism and preventing multiple abnormal phenotypes without the interference of native Fgf‐23. Copyright

Bisphosphonate-linked hyaluronic acid hydrogel sequesters and enzymatically releases active bone morphogenetic protein-2 for induction of osteogenic differentiation.

Regeneration of bone by delivery of bone morphogenetic proteins (BMPs) from implantable scaffolds is a promising alternative to the existing autologous bone grafting procedures. Hydrogels are used extensively in biomaterials as delivery systems for different growth factors. However, a controlled release of the growth factors is necessary to induce bone formation, which can be accomplished by various chemical functionalities. Herein we demonstrate that functionalization of a hyaluronan (HA) hydrogel with covalently linked bisphosphonate (BP) ligands provides efficient sequestering of BMP-2 in the resulting HA-BP hydrogel. The HA-BP hydrogel was investigated in comparison with its analogue lacking BP groups (HA hydrogel). While HA hydrogel released 100% of BMP-2 over two weeks, less than 10% of BMP-2 was released from the HA-BP hydrogel for the same time. We demonstrate that the sequestered growth factor can still be released by enzymatic degradation of the HA-BP hydrogel. Most importantly, entrapment of BMP-2 in HA-BP hydrogel preserves the growth factor bioactivity, which was confirmed by induction of osteogenic differentiation of mesenchymal stem cells (MSCs) after the cells incubation with the enzymatic digest of the hydrogel. At the same time, the hydrogels degradation products were not toxic to MSCs and osteoblasts. Furthermore, BP-functionalization of HA hydrogels promotes adhesion of the cells to the surface of HA hydrogel. Altogether, the present findings indicate that covalent grafting of HA hydrogel with BP groups can alter the clinical effects of BMPs in bone tissue regeneration.

GSK-3 inhibition by an orally active small molecule increases bone mass in rats☆

Glycogen synthase kinase 3β (GSK-3β) actions are central in the canonical Wnt pathway, important in many biological processes and a potential drug target for treating several diseases. It is appreciated that a balanced Wnt canonical signaling is crucial for the maintenance of normal bone mass. In this study we investigated the effects of a potent orally active GSK-3 inhibitor, AZD2858, on bone mass in rats. Treatment (1 μM) of human osteoblast cells with AZD2858 in vitro increased β-catenin levels after a short period of time. In rats, oral AZD2858 treatment caused a dose-dependent increase in trabecular bone mass compared to control after a two-week treatment with a maximum effect at a dose of 20 mg/kg once daily (total BMC: 172% of control; p<0.001). A small but significant effect was also seen at cortical sites (total BMC: 111% of control; p<0.001). Biomechanical testing demonstrated an increase in both vertebral compression strength at a dose of 20 mg/kg once daily (Load at failure: 370% of control, p<0.001) and diaphyseal strength of femora subjected to a three point bending test (Load at failure: 115% of control; p<0.01). Furthermore, histomorphometry showed a dramatic increase in bone formation indices, and serum markers of both bone formation (Osteocalcin, 146% of control; p<0.001) and resorption (CTX, 189% of control; p<0.001) were elevated. Our conclusion is that a GSK-3 inhibitor drug may prove effective as an anabolic strategy in the treatment of diseases characterized by low bone mass, since AZD2858 has extensive bone building effects at predominantly trabecular sites.

Rats treated with AZD2858, a GSK3 inhibitor, heal fractures rapidly without endochondral bone formation

Fracture healing is a complex interplay between endochondral and intramembranous bone formation processes. The canonical Wnt/β-catenin pathway enhances new bone formation and may play a role in fracture healing. Glycogen synthase kinase 3β (GSK3β) is a key regulator of β-catenin degradation. In this study, we investigate the effects of AZD2858, an orally bioactive GSK3 inhibitor, on fracture healing. Femoral fractures were produced in rats after the insertion of a femoral nail. The rats were treated with oral administration of AZD2858 at a dose of 30 μmol/kg (20mg/kg) daily for up to 3 weeks, while control animals were administered vehicle. At 4days, and at 1, 2 and 3 weeks, histological analysis was performed, and at the 2 and 3 week time points, we performed peripheral quantitative computed tomography (pQCT), X-rays, and four-point bending tests. Peripheral QCT showed an increase in both mineral density (of 28% at 2 weeks and 38% at 3weeks) and mineral content (of 81% at 2 weeks and 93% at 3 weeks) in the calluses from AZD2858 treated animals as compared to vehicle treated animals. Histological analysis demonstrated that rats treated with GSK3 inhibitor healed their fractures rapidly, but without the pre-formation of cartilage tissue. Furthermore, four-point bending tests of fractured femora from animals treated for 2 and 3 weeks showed an increase in strength in treated animals compared to their vehicle-treated controls. In conclusion, AZD2858, a potent GSK3 inhibitor, has a substantial impact on fracture healing. The fractures healed with a bony callus without an obvious endochondral component, suggesting that AZD2858 drives mesenchymal cells into the osteoblastic pathway. This leads to direct bone repair in an unstable fracture milieu.

The phosphate regulating hormone fibroblast growth factor‐23

Over the last decade, the regulation of phosphate (Pi) homeostasis has been under intense investigation. By utilizing modern biochemical and genetic tools, the pathophysiological mechanisms behind several known hereditary and acquired hypo‐ and hyperphosphatemic diseases have been clarified. The results of these efforts have opened new insights into the causes of Pi dysregulation and hereby also the physiological mechanisms determining Pi homeostasis. Although several potential Pi‐regulating proteins have been discovered and investigated, current data strongly argues for fibroblast growth factor‐23 (FGF23), a hormonal factor produced in bone, as a particularly important regulator of Pi homeostasis. In this article, we review the discovery of the FGF23 protein, as well as its biochemistry, localization of production, receptor specificity and mechanisms of action.

Non-invasive tri-modal visualisation via PET/SPECT/μCT of recombinant human bone morphogenetic protein-2 retention and associated bone regeneration: A proof of concept

ABSTRACT Bone morphogenetic proteins (BMPs) are vital for bone and cartilage formation, where bone morphogenetic protein‐2 (BMP‐2) is acknowledged as a growth factor in osteoblast differentiation. However, uncontrolled delivery may result in adverse clinical effects. In this study we investigated the possibility for longitudinal and non‐invasive monitoring of implanted [125I]BMP‐2 retention and its relation to ossification at the site of implantation. A unilateral critically sized femoral defect was produced in the left limb of rats while the right femur was retained intact as a paired reference control. The defect was filled with a hyaluronan hydrogel with 25% hydroxyapatite alone (carrier control; n=2) or combined with a mixture of [125I]BMP‐2 (150&mgr;g/ml; n=4). Bone formation was monitored using micro computed tomography (&mgr;CT) scans at 1, 3, 5, 7, 9 and 12weeks. The retention of [125I]BMP‐2 was assessed with single photon emission computed tomography (SPECT), and the bone healing process was followed with sodium fluoride (Na18F) using positron emission tomography (PET) at day 3 and at week 2, 4, and 6. A rapid burst release of [125I]BMP‐2 was detected via SPECT. This was followed by a progressive increase in uptake levels of [18F]fluoride depicted by PET imaging that was confirmed as bone formation via &mgr;CT. We propose that this functional, non‐invasive imaging method allows tri‐modal visualisation of the release of BMP‐2 and the following in vivo response. We suggest that the potential of this novel technique could be considered for preclinical evaluation of novel smart materials on bone regeneration.