Synthesis of truncated analogues of preptin-(1-16), and investigation of their ability to stimulate osteoblast proliferation

Authors

Renata Kowalczyk, Sung H. Yang, Margaret A. Brimble, Karen E. Callon, Maureen Watson, Young-Eun Park, Jillian Cornish

Abstract

Preptin, a 34-amino acid residue peptide hormone is co-secreted with insulin from the β-pancreatic cells and is active in fuel metabolism. We have previously established that a shorter fragment of preptin, namely preptin-(1-16), stimulates bone growth by proliferation and increasing the survival rate of osteoblasts. This was demonstrated in both in vitro and in vivo models. These findings suggest that preptin-(1-16) could play an important role in the anabolic therapy of osteoporosis. However, due to the large size of the peptide it is not an ideal therapeutic agent. The aim of this study was to identify the shortest preptin analogue that retains or even increases the bone anabolic activity as compared to the parent preptin-(1-16) peptide. Truncations were made in a methodical manner from both the N-terminus and the C-terminus of the peptide, and the effect of these deletions on the resulting biological activity was assessed. In order to improve the enzymatic stability of the shortest yet active analogue identified, ruthenium-catalysed ring closing metathesis was used to generate a macrocyclic peptide using allylglycine residues as handles for ring formation. We have successfully identified a short 8-amino acid preptin (1-8) fragment that retains an anabolic effect on the proliferation of primary rat osteoblasts and enhances bone nodule formation. Preptin (1-8) is a useful lead compound for the development of orally active therapeutics for the treatment of osteoporosis.

Link To Article

http://dx.doi.org/10.1016/j.bmc.2014.05.026

Trends in trabecular architecture and bone mineral density distribution in 152 individuals aged 30-90 years

Authors

T. Koehne, E. Vettorazzi, N. Küsters, R. Lüneburg, B. Kahl-Nieke, K. Püschel, M. Amling, B. Busse

Abstract

The strength of trabecular bone depends on its microarchitecture and its tissue level properties. However, the interrelation between these two determinants of bone quality and their relation to age remains to be clarified. Iliac crest bone cores (n = 152) from individuals aged 30-90 years were analyzed by quantitative backscattered electron imaging. Univariate and multivariate analyses were conducted to determine whether epidemiological parameters (age, sex or BMI), structural histomorphometrical variables (BV/TV, Tb.Th, Tb.N and Tb.Sp) and osteoid-related indices (OV/BV, OS/BS or O.Th) predict the degree of bone mineralization. While sex and BMI were not associated with bone mineralization, age was positively correlated with the most frequently occurring calcium concentrations (Ca peak), the percentage of highly mineralized bone areas (Ca high) and, in the case of adjusted co-variates, also the mean calcium content (Ca mean). Bone volume fraction and trabecular thickness were both negatively correlated with Ca mean. However, trabecular thickness was additionally associated with Ca peak, Ca high as well as the amount of low mineralized bone (Ca low) and was the only structural parameter predicting bone mineralization independent of age. Furthermore, our analyses demonstrated that osteoid variables - within a normal range (<2 % OV/BV) - were significantly associated with all mineralization parameters and represent the only predictor for the mineralization heterogeneity (Ca width). Taken together, we showed that elevated trabecular bone mineralization correlates with aging and bone loss. However, these associations are attributable to trabecular thinning that comes along with high bone mineralization due to the loss of low mineralized bone surfaces. Therefore, we demonstrated that the degree of areally resolved bone mineral is primarily associated with the amount of physiological osteoid present and the thickness of mineralized bone in trabeculae.

Link To Article

http://dx.doi.org/10.1016/j.bone.2014.05.010

The Role of Muscle Loading on Bone (Re)modeling at the Developing Enthesis

Authors

Alexander M. Tatara, Justin H. Lipner, Rosalina Das, H. Mike Kim, Nikunj Patel, Eleni Ntouvali, Matthew J. Silva, Stavros Thomopoulos

Abstract

Muscle forces are necessary for the development and maintenance of a mineralized skeleton. Removal of loads leads to malformed bones and impaired musculoskeletal function due to changes in bone (re)modeling. In the current study, the development of a mineralized junction at the interface between muscle and bone was examined under normal and impaired loading conditions. Unilateral mouse rotator cuff muscles were paralyzed using botulinum toxin A at birth. Control groups consisted of contralateral shoulders injected with saline and a separate group of normal mice. It was hypothesized that muscle unloading would suppress bone formation and enhance bone resorption at the enthesis, and that the unloading-induced bony defects could be rescued by suppressing osteoclast activity. In order to modulate osteoclast activity, mice were injected with the bisphosphonate alendronate. Bone formation was measured at the tendon enthesis using alizarin and calcein fluorescent labeling of bone surfaces followed by quantitative histomorphometry of histologic sections. Bone volume and architecture was measured using micro computed tomography. Osteoclast surface was determined via quantitative histomorphometry of tartrate resistant acid phosphatase stained histologic sections. Muscle unloading resulted in delayed initiation of endochondral ossification at the enthesis, but did not impair bone formation rate. Unloading led to severe defects in bone volume and trabecular bone architecture. These defects were partially rescued by suppression of osteoclast activity through alendronate treatment, and the effect of alendronate was dose dependent. Similarly, bone formation rate was increased with increasing alendronate dose across loading groups. The bony defects caused by unloading were therefore likely due to maintained high osteoclast activity, which normally decreases from neonatal through mature timepoints. These results have important implications for the treatment of muscle unloading conditions such as neonatal brachial plexus palsy, which results in shoulder paralysis at birth and subsequent defects in the rotator cuff enthesis and humeral head.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0097375

A novel one-pot process for near-net-shape fabrication of open-porous resorbable hydroxyapatite/protein composites and in vivo assessment

Authors

Berit Mueller, Dietmar Koch, Rainer Lutz, Karl A. Schlegel, Laura Treccani, Kurosch Rezwan

Abstract

We present a mild one-pot freeze gelation process for fabricating near-net, complex-shaped hydroxyapatite scaffolds and to directly incorporating active proteins during scaffold processing. In particular, the direct protein incorporation enables a simultaneous adjustment and control of scaffold microstructure, porosity, resorbability and enhancement of initial mechanical and handling stability. Two proteins, serum albumin and lysozyme, are selected and their effect on scaffold stability and microstructure investigated by biaxial strength tests, electron microscopy, and mercury intrusion porosimetry. The resulting hydroxyapatite/protein composites feature adjustable porosities from 50 % to 70 % and a mechanical strength ranging from 2 to 6 MPa comparable to that of human spongiosa without any sintering step. Scaffold degradation behaviour and protein release are assessed by in vitro studies. A preliminary in vivo assessment of scaffold biocompatibility and resorption behaviour in adult domestic pigs is discussed. After implantation, composites were resorbed up to 50 % after only 4 weeks and up to 65 % after 8 weeks. In addition, 14 % new bone formation after 4 weeks and 37 % after 8 weeks were detected. All these investigations demonstrate the outstanding suitability of the one-pot-process to create, in a customisable and reliable way, biocompatible scaffolds with sufficient mechanical strength for handling and surgical insertion, and for potential use as biodegradable bone substitutes and versatile platform for local drug delivery.

Link To Article

http://dx.doi.org/10.1016/j.msec.2014.05.017

Mechanical Load Increases in Bone Formation Via a Sclerostin-Independent Pathway

Authors

A Morse, MM McDonald, NH Kelly, KM Melville, A Schindeler, I Kramer, M Kneissel, MCH van der Meulen, and DG Little

Abstract

Sclerostin, encoded by the Sost gene, is an important negative regulator of bone formation that has been proposed to have a key role in regulating the response to mechanical loading. To investigate the effect of long-term Sclerostin deficiency on mechanotransduction in bone, we performed experiments on unloaded or loaded tibiae of 10 week old female Sost-/- and wild type mice. Unloading was induced via 0.5U BTX injections into the right quadriceps and calf muscles, causing muscle paralysis and limb disuse. On a separate group of mice, increased loading was performed on the left tibiae through unilateral cyclic axial compression of equivalent strains (+1200µe) at 1200 cycles/day, 5days/week. Another cohort of mice receiving equivalent loads (-9.0N) also were assessed. Contralateral tibiae served as normal load controls. Loaded/unloaded and normal load tibiae were assessed at day 14 for bone volume (BV) and formation changes. Loss of BV was seen in the unloaded tibiae of wild type mice, but BV was not different between normal load and unloaded Sost-/- tibiae. An increase in BV was seen in the loaded tibiae of wild type and Sost-/- mice over their normal load controls. The increased BV was associated with significantly increased mid-shaft periosteal MS/BS, MAR and BFR/BS, and endosteal MAR and BFR/BS. Notably, loading induced a greater increase in periosteal MAR and BFR/BS in Sost-/- mice than in wild type controls. Thus, long-term Sclerostin deficiency inhibits the bone loss normally induced with decreased mechanical load, but can augment the increase in bone formation with increased load.

Link To Article

http://dx.doi.org/10.1002/jbmr.2278

Ablation of Osteopontin Improves the Skeletal Phenotype of Phospho1-/- Mice

Authors

Manisha C. Yadav PhD., Carmen Huesa PhD., Sonoko Narisawa PhD., Marc F. Hoylaerts PhD., Alain Moreau PhD., Colin Farquharson PhD. and José Luis Millán PhD

Abstract

PHOSPHO1 and tissue-nonspecific alkaline phosphatase (TNAP) have non-redundant functions during skeletal mineralization. While TNAP deficiency (Alpl-/- mice) leads to hypophosphatasia, caused by accumulation of the mineralization inhibitor inorganic pyrophosphate (PPi), comparably elevated levels of PPi in Phospho1-/- mice do not explain their stunted growth, spontaneous fractures, bowed long bones, osteomalacia, and scoliosis. We have previously shown that elevated PPi in Alpl-/- mice is accompanied by elevated osteopontin (OPN), another potent mineralization inhibitor, and that the amount of OPN correlates with the severity of hypophosphatasia in mice. Here we demonstrate that plasma OPN is elevated and OPN expression is upregulated in the skeleton, particularly in the vertebrae, of Phospho1-/- mice. Liquid chromatography/tandem mass spectrometry showed an increased proportion of phosphorylated OPN (p-OPN) peptides in Phospho1-/- mice, suggesting that accumulation of p-OPN causes the skeletal abnormalities in Phospho1-/- mice. We also show that ablation of the OPN gene, Spp1, leads to improvements in the skeletal phenotype in Phospho1-/- as they age. In particular, their scoliosis is ameliorated at 1 month of age and is completely rescued at 3 months of age. There is also improvement in the long bone defects characteristic of Phospho1-/- mice at 3 months of age. Mineralization assays comparing [Phospho1-/-; Spp1-/-], Phospho1-/- and Spp1-/- chondrocytes display corrected mineralization by the double knockout cells. Expression of chondrocyte differentiation markers was also normalized in the [Phospho1-/-; Spp1-/-] mice. Thus, while Alpl and Phospho1 deficiencies lead to similar skeletal phenotypes and comparable changes in the expression levels of PPi and OPN, there is a clear dissociation in the hierarchical roles of these potent inhibitors of mineralization, with elevated PPi and elevated p-OPN levels causing the respective skeletal phenotypes in Alpl-/- and Phospho1-/- mice.

Link To Article

http://dx.doi.org/10.1002/jbmr.2281