Evidence for a hydroxyapatite precursor in regenerating cyprinid scales

Abstract

Summary Collagen matrices, mineralized with calcium phosphates in a hydroxyapatite phase, are generally found in skeletal tissues. However, mechanisms of biomineral formation and regulation are still poorly understood. Elasmoid scales are part of the dermal skeleton and regenerate quickly when damaged or lost. This makes the scale a convenient target to study mineral compostion and formation. The X‐ray diffractogram of the mineral layer of carp scales only show speaks corresponding with hydroxyapatite. Energy‐dispersive X‐ray spectroscopy (EDX) during scanning electron microscopy identifies the elements calcium and phosphorus, which are restricted to the external layer of the scale. In contrast with various other species, calcium phosphate crystals are not present in the elasmodine layer. The clean boundary between calcified and uncalcified matrix suggests that subsequental mineralization of the elasmodine layer is inhibited. Quantification of the calcium and phosphorus content allows definition of a calcium/phosphorus ratio, which is indicative ofthe crystalline phase of the minerals. Through accurate measurements of total calcium and phosphorus (by ICP‐MS) in zebrafish scales, different ratios were found for newly formed (regenerating) scales compared to ontogenetic or completely regenerated scales. This shows that the mineral is not at first deposited as hydroxyapatite, but in a precursor phase. Although the nature of the phase remains to be established, this first analysis shows that cyprinids scales can easily be used to gain insights in the dynamics of biomineralization.

Zebrafish (Danio rerio) in calcium-poor water mobilise calcium and phosphorus from scales

“…As the metabolism of calcium and phosphorus are tightly coupled, it may not come as a surprise that we found decreased phosphorus contents in scales of calcium‐restricted fish. Calcium and inorganic phosphate (Pi) are the two main constituents of calcium hydroxyapatite, the main mineral of which the scale is composed (De Vrieze et al., ). Magnesium whitlockite (Ca 9 (MgFe)(PO 4 ) 6 PO 3 OH) is a less usual form of calcium phosphate; we measured Mg since Ca/P ratios in scales indicate towards presence of whitlockite.…”

“…Precipitation of calcium phosphates, in the adult scale predominantly in the form of calcium hydroxyapatite (De Vrieze et al., ), is restricted to the outer (episquamal) layer of the elasmoid scale. Further located on the episquamal side are mono‐ and multinucleated osteoclasts (De Vrieze et al., ).…”

Influence of Prednisolone and Alendronate on the de novo Mineralization of Zebrafish Caudal Fin

“…On the other hand, lower mineral availability, represented by decreased Ca/P ratios, could be more influenced by both PN and ALN. (43) This is shown by the significant lower mineral ratios found in the bones of fish after the intake of PN and the narrow difference between the proximal and distal parts of bones…”

Magnetically Induced Crystal Alignment of Calcium Hydrogen Phosphate Dihydrate

“…Calcium hydrogen phosphate dihydrate (CHPD; CaHPO 4 •2H 2 O), commonly known as the mineral brushite, is a type of calcium phosphate that exhibits higher nucleation rate and lower stability under physiological conditions compared to other calcium phosphate phases (Giocondi et al, 2010;Tamimi et al, 2012). Moreover, CHPD is proposed as one of the possible precursor materials for calcification of hydroxylapatite in natural hard tissues and is proven to be highly biocompatible (Bigi et al, 1988;Vrieze et al, 2012;Wondee et al, 2010;Kumta et al, 2005). The above mentioned properties can trigger pathological mineralization, such as kidney stones, dental caries and plaque, but can also work greatly beneficial in fabricating resorbable biomaterials for tissue engineering (Krambeck et al, 2010;Scudiero et al, 1999;Prasad & Kamath, 2013;Cheng & Pritzker, 1983;Kaufman & Kleinberg, 1973;Kuznetsov et al, 2013).…”