Calcium ions and osteoclastogenesis initiate the induction of bone formation by coral-derived macroporous constructs

Authors

  • Roland M Klar,

    1. Bone Research Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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  • Raquel Duarte,

    1. Department of Internal Medicine, University of the Witwatersrand, Johannesburg, South Africa
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  • Therese Dix-Peek,

    1. Department of Internal Medicine, University of the Witwatersrand, Johannesburg, South Africa
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  • Caroline Dickens,

    1. Department of Internal Medicine, University of the Witwatersrand, Johannesburg, South Africa
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  • Carlo Ferretti,

    1. Bone Research Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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  • Ugo Ripamonti

    Corresponding author
    1. Bone Research Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
    • Correspondence to: Ugo RIPAMONTI, M.D., Ph.D., Bone Research Laboratory, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown, Johannesburg 2193, South Africa.

      Tel.: +27 11 717 2144

      Fax: + 27 11 717 2300

      E-mail: ugo.ripamonti@wits.ac.za

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Abstract

Coral-derived calcium carbonate/hydroxyapatite macroporous constructs of the genus Goniopora with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) initiate the induction of bone formation. Which are the molecular signals that initiate pattern formation and the induction of bone formation? To evaluate the role of released calcium ions and osteoclastogenesis, 7% HA/CC was pre-loaded with either 500 μg of the calcium channel blocker, verapamil hydrochloride, or 240 μg of the osteoclast inhibitor, biphosphonate zoledronate, and implanted in the rectus abdominis muscle of six adult Chacma baboons Papio ursinus. Generated tissues on days 15, 60 and 90 were analysed by histomorphometry and qRT-PCR. On day 15, up-regulation of type IV collagen characterized all the implanted constructs correlating with vascular invasion. Zoledronate-treated specimens showed an important delay in tissue patterning and morphogenesis with limited bone formation. Osteoclastic inhibition yielded minimal, if any, bone formation by induction. 7% HA/CC pre-loaded with the Ca++ channel blocker verapamil hydrochloride strongly inhibited the induction of bone formation. Down-regulation of bone morphogenetic protein-2 (BMP-2) together with up-regulation of Noggin genes correlated with limited bone formation in 7% HA/CC pre-loaded with either verapamil or zoledronate, indicating that the induction of bone formation by coral-derived macroporous constructs is via the BMPs pathway. The spontaneous induction of bone formation is initiated by a local peak of Ca++ activating stem cell differentiation and the induction of bone formation.

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