In vitro synthesis and microscopic structural change of fetuin-A/calcium phosphate composite nanoparticles during phase transition process

Abstract

Calciprotein particles (CPP), found in the blood, are composite nanoparticles consisting of the protein fetuin-A and solid-phase calcium phosphate. Among these, amorphous CPP (a-CPP), composed of fetuin-A/amorphous calcium phosphate nanoparticles, are non-pathogenic. In contrast, crystalline CPP (c-CPP), which contain calcium phosphate crystals and result from the agglomeration of a-CPP, are known to cause inflammation and vascular calcification. We have developed an in vitro synthesis method for CPP and studied the phase transition process from a-CPP to c-CPP. This study evaluates the influence of atmospheric carbon dioxide on this transition by examining microscopic structures using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and infrared spectroscopy. We found that the transition from a-CPP to c-CPP was significantly accelerated by atmospheric carbon dioxide. This phenomenon can be attributed to the formation of carbonate-containing hydroxyapatite, which is expected to have a highly symmetric hexagonal structure conducive to crystal growth.