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Bone. 2015 Mar;72:137-47. doi: 10.1016/j.bone.2014.11.017. Epub 2014 Nov 26.

Improvement of the skeletal and dental hypophosphatasia phenotype in Alpl-/- mice by administration of soluble (non-targeted) chimeric alkaline phosphatase.

Author information

1
Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA.
2
Laboratory of Oral Connective Tissue Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD, USA.
3
Department of Orthodontics and Pediatric Dentistry, School of Dentistry, University of Michigan, Ann Arbor, MI, USA.
4
AM-Pharma B.V., Bunnik, The Netherlands.
5
Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA 92037, USA. Electronic address: millan@sanfordburnham.org.

Abstract

Hypophosphatasia (HPP) results from ALPL gene mutations, which lead to a deficiency of tissue-nonspecific alkaline phosphatase (TNAP), and accumulation of inorganic pyrophosphate, a potent inhibitor of mineralization that is also a natural substrate of TNAP, in the extracellular space. HPP causes mineralization disorders including soft bones (rickets or osteomalacia) and defects in teeth and periodontal tissues. Enzyme replacement therapy using mineral-targeting recombinant TNAP has proven effective in preventing skeletal and dental defects in TNAP knockout (Alpl(-/-)) mice, a model for life-threatening HPP. Here, we show that the administration of a soluble, intestinal-like chimeric alkaline phosphatase (ChimAP) improves the manifestations of HPP in Alpl(-/-) mice. Mice received daily subcutaneous injections of ChimAP at doses of 1, 8 or 16 mg/kg, from birth for up to 53 days. Lifespan and body weight of Alpl(-/-) mice were normalized, and vitamin B6-associated seizures were absent with 16 mg/kg/day of ChimAP. Radiographs, μCT and histological analyses documented improved mineralization in cortical and trabecular bone and secondary ossification centers in long bones of ChimAP16-treated mice. There was no evidence of craniosynostosis in the ChimAP16-treated mice and we did not detect ectopic calcification by radiography and histology in the aortas, stomachs, kidneys or lungs in any of the treatment groups. Molar tooth development and function improved with the highest ChimAP dose, including enamel, dentin, and tooth morphology. Cementum remained deficient and alveolar bone mineralization was reduced compared to controls, though ChimAP-treated Alpl(-/-) mice featured periodontal attachment and retained teeth. This study provides the first evidence for the pharmacological efficacy of ChimAP for use in the treatment of skeletal and dental manifestations of HPP.

KEYWORDS:

Craniosynostosis; Enzyme replacement; Hypophosphatasia; Osteomalacia; Rickets; Seizures

PMID:
25433339
PMCID:
PMC4283789
DOI:
10.1016/j.bone.2014.11.017
[Indexed for MEDLINE]
Free PMC Article

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