Abstract
Amorphous calcium phosphate was found to be a major mineral component of skeletal tissue by X-ray diffraction techniques. This non-crystalline bone mineral phase can be converted into crystalline apatitein vitro upon exposure to water for a prolonged period of time. The amorphous calcium phosphate content of whole rat femur, tibia-fibula and calvarium decreases as the crystalline apatite content of these bones increases with advancing age. In addition, hypophysectomized whole rat femora contain more amorphous bone mineral than do normal controls. No significant differences in amorphous/crystalline bone mineral composition exist between control and denervated whole rat femora during disuse osteoporosis. However, rachitic chick bone contains more amorphous calcium phosphate than does normal bone tissue, regardless of the manner in which the disease state is reached. Moreover, alterations in chick bone lipid and mucopolysaccharide content coincide with corresponding alterations in the amorphous/crystalline mineral content of the tissue. It is suggested that amorphous calcium phosphate is the first mineral deposited during the calcification process and that the amorphous bone mineral fraction can act as a metabolically active, metastable precursor of crystalline bone apatite. It is further suggested that the amorphous calcium phosphate fraction of bone mineral may also exist in a stabilized form.
Résumé
L'analyse de diffraction par rayons X a montré que le phosphate de calcium amorphe est un des principaux constituants du squelette. Cette phase solide, non cristallisée de l'os peut se transformer en apatite cristalline in vitro après avoir été en contact avec de l'eau pendant une période suffisamment longue. Chez le rat, la teneur en phosphate de calcium amorphe des fémurs, tibias, péronés et des calottes crâniennes décroît, alors que la teneur en apatite cristalline de ces os croît, avec l'âge. De plus. les fémurs de rats hypophysectomisés contiennent une plus grande proportion de minéral osseux sous forme amorphe que ceux de témoins normaux. En ce qui concerne la proportion de minéral amorphe et cristallin dans l'ostéoporose d'immobilisation, on n'observe pas de différence significative entre des fémurs dénervés et des os témoins. Cependant, l'os de poulets rachitiques contient plus de phosphate de calcium amorphe que le tissu osseux de poulets sains, quelle que soit la manière dont on a provoqué le rachitisme. De plus, des modification de la teneur de l'os de poulet en lipides et en mucopolysaccharides correspondent à des modifications du rapport entre minéral amorphe et cristallin de l'os. Nous suggérons que le phosphate de calcium amorphe est la première forme minérale déposée au cours de la calcification et que la fraction amorphe est un précurseur métaboliquement actif et métastable de l'apatite cristalline: Il semble d'autre part que le phosphate de calcium amorphe peut également exister sous une forme stable.
Zusammenfassung
Das amorphe Calciumphosphat wurde mittels Röntgenstrahlendiffraktionsmethoden als eine der wichtigsten Komponenten des Knochengewebes erkannt. Dieser nicht kristallisierte Teil des Knochenminerals kann in vitro durch Wassereinwirkung während längerer Zeit in kristallines Apatit umgewandelt werden. Bei Ratten nimmt der Gehalt an amorphem Calciumphosphat der ganzen Femora, Tibia, Fibula und Calvaria mit zunehmendem Alter ab, während der Gehalt an kristallinem Apatit steigt. Dazu enthalten die Femora von hypophysektomierten Ratten mehr amorphes Knochenmineral als die von normalen Tieren. Es besteht kein signifikanter Unterschied im relativen Gehalt von amorphem und kristallinem Knochenmineral zwischen Kontroll- und denervierten Rattenfemora bei Immobilisationsosteoporose. Jedoch enthalten Knochen von rachitischen Hühnern, ungeachtet auf welche Art die Krankheit hervorgerufen wurde, mehr amorphes Calciumphosphat als normales Knochengewebe. Ferner stimmen die Veränderungen des Lipids- und Mucopolysaccharidgehaltes der Hühnerknochen mit entsprechenden Veränderungen im Gehalt an amorphem und kristallinem Mineral des Gewebes überein. Es wird vorgeschlagen, daß amorphes Calciumphosphat das erste Mineral ist, welches während des Verkalkungsprozesses abgelagert wird, und daß dieser Anteil an amorphem Knochenmineral als ein metabolisch aktiver, metastabiler Vorgänger des kristallinen Knochenapatites wirken kann. Dieser amorphe Calciumphosphatanteil des Knochenminerals könnte auch in einer stabilen Form vorkommen.
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This work was supported in part by PHS Grant DE-10945 from the National Institute of Dental Research, U.S.A. Publication No. 24 from the Laboratory of Ultrastructural Biochemistry.
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Termine, J.D., Posner, A.S. Amorphous/crystalline interrelationships in bone mineral. Calc. Tis Res. 1, 8–23 (1967). https://doi.org/10.1007/BF02008070
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DOI: https://doi.org/10.1007/BF02008070