Growth factor delivery for bone tissue repair: an update.

Growth factors (GFs) are endogenous proteins capable of acting on cell-surface receptors and directing cellular activities involved in the regeneration of new bone tissue. The specific actions and long-term effects of GFs on bone-forming cells have resulted in exploration of their potential for clinical bone repair. The concerted efforts have led to the recent approval of two GFs, bone morphogenetic protein-2 and osteogenic protein-1, for clinical bone repair, and human parathryroid hormone (1-34) for augmentation of systemic bone mass.

Imparting mineral affinity to fetuin by bisphosphonate conjugation: a comparison of three bisphosphonate conjugation schemes.

Protein conjugation to bisphosphonic acids (BPs), such as 1-amino-1,1-diphosphonate methane (aminoBP) and 3,5-di(ethylamino-2,2-bisphosphono)benzoic acid (diBP), was proposed as a foundation for bone-specific delivery of protein therapeutics. This study was performed to directly compare the mineral affinity of protein-BP conjugates prepared by three different approaches. Fetuin, serving as a model protein, was derivatized with BPs by the following approaches: (i) by attaching the aminoBPs onto protein lysines using succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SMCC); (ii) by attaching the aminoBPs onto protein carbohydrates using 4-(maleimidomethyl)-cyclohexane-1-carboxyl-hydrazide (MMCCH), and (iii) by conjugating diBP to protein lysines using the carbodiimide chemistry.

A comparison of mineral affinity of bisphosphonate-protein conjugates constructed with disulfide and thioether linkages.

Chemical conjugation of bisphosphonates (BPs) to therapeutic proteins is an effective means to impart mineral affinity to proteins. Such conjugates can be implanted with mineral-based matrices to control the local delivery kinetics of the proteins. BPs linked to proteins with reversible (i.

Designing proteins for bone targeting.

Protein-based therapeutic agents intended for bone diseases should ideally exhibit a high affinity to bone tissue, so that their systemic administration will result in specific delivery to bone with minimal distribution to extra-skeletal sites. This was shown possible in the authors' lab by modifying a desired protein with bisphosphonates (BPs) that exhibit an exceptionally high affinity to the bone-mineral hydroxyapatite. In this review, we explore the potential applications of that concept by summarizing the bone diseases and candidate proteins that will benefit from the proposed bone delivery approach.

The ectopic study of tissue-engineered bone with hBMP-4 gene modified bone marrow stromal cells in rabbits.

Background: Tissue-engineering techniques combined with gene therapy have been recently reported to improve osteogenesis. In this study, tissue-engineered bone constructed by human Bone Morphogenetic Protein 4 (hBMP-4) gene-modified bone marrow stromal cells (bMSCs) was explored in an ectopic bone formation model in rabbits.

Methods: A pEGFP-hBMP-4 mammalian plasmid (EGFP: Enhanced Green Fluorescent Protein) was constructed by subcloning techniques.

A di(bisphosphonic acid) for protein coupling and targeting to bone.

Proteins intended for treatment of bone diseases should ideally exhibit a high bone affinity, so that they are preferentially deposited to bones after systemic administration. This can be achieved by combining molecules having a high affinity to bone with the proteins. Bisphosphonates (BPs) are chemical analogs of pyrophosphate that possess exceptional bone mineral affinity.

Imparting bone mineral affinity to osteogenic proteins through heparin-bisphosphonate conjugates.

Although numerous growth factors can promote the regeneration of bone upon parenteral administration, all exhibit undesirable side-effects that prevent their clinical utility. These side-effects arise due to the growth factors' inherent lack of bone affinity. The goal of this study was to develop a means to enhance the bone mineral affinity of osteogenic growth factors so as to minimize their extra-skeletal distribution.

Systemic bone formation with weekly PTH administration in ovariectomized rats.

Purpose: Weekly subcutaneous administration of 0 (vehicle), 10 and 80 microg/kg doses of human parathyroid hormone (1-34) [PTH (1-34)] were compared based on their capacity to induce systemic formation of bone in 9 month-old ovariectomized (OVX) Sprague-Dawley rats.

Methods: Changes elicited at bone tissue after 4 weeks of treatment were assessed using dual x-ray absorptiometry, micro-computed tomography (microCT), and ashing.

Results: The 10 microg/kg dose led to a significant increase (p<0.

Impact of tether length on bone mineral affinity of protein-bisphosphonate conjugates.

Purpose: To determine the effect of tether length on bone mineral affinity of fetuin-bisphosphonate conjugates.

Methods: 1-Amino-1,1-diphosphonate methane (aminoBP) was conjugated onto the lysine residues of fetuin by using five different crosslinkers that varied in length. Both the conjugation efficiency (i.

Imparting bone affinity to glycoproteins through the conjugation of bisphosphonates.

Purpose: To develop a novel means of conjugating bisphosphonates onto the carbohydrate moieties of glycoproteins to enhance protein affinity to bone.

Methods: 1-Amino-1,1-diphosphonate methane (aminoBP) was conjugated onto the carbohydrate moietites of oxidized fetuin by using 4-(maleimidomethyl)cyclohexane-1-carboxyl-hydrazide (MMCCH). Bone affinity of the resulting conjugates was compared to proteins obtained from another means of conjugation, whereby aminoBP was conjugated onto fetuin's lysine moieties by using succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxylate (SMCC).