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

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.

Enzyme replacement for craniofacial skeletal defects and craniosynostosis in murine hypophosphatasia

“…Alternatively, this finding could indicate that compensators for TNAP exist that function to influence both bone mineralization and craniosynostosis. A previous study showed that the skulls of Alpl −/− mice treated with 16 mg/kg/day of recombinant soluble alkaline phosphatase appeared similar to those of Alp +/+ mice [48]. Future studies will be needed to determine if mineral-targeting of TNAP alters efficacy for preventing craniosynostosis, as compared directly to treatment with soluble forms of alkaline phosphatase.…”

Hypophosphatasia: diagnosis and clinical signs – a dental surgeon perspective

“…Spectacular improvements in terms of survival, skeletal manifestation (including healing of rickets), pulmonary function, and growth were reported when asfotase alfa was studied in young children with very severe perinatal or infantile HPP. Other treatments, such as other enzyme replacement therapy or even gene therapy, have also been investigated in animal models.…”

<b><i>Galla chinensis </i></b>Compounds Remineralize Enamel Caries Lesions in a Rat Model

“…After scanning, three-dimensional images of the mandibles were reconstructed, and a fixed threshold of 5,500 Hounsfield units was used to discriminate enamel and dentin [Gasque et al, 2015]. The enamel volumes of the first molars were computed on an Inveon MM Platform (model 5001).…”