Physicochemical and biological properties of biomimetic mineralo-protein nanoparticles formed spontaneously in biological fluids

Recent studies indicate that mineral nanoparticles (NPs) form spontaneously in human body fluids. These biological NPs represent mineral precursors that are associated with ectopic calcifications seen in various human diseases. However, the parameters that control the formation of mineral NPs and their possible effects on human cells remain poorly understood. Here a nanomaterial approach to study the formation of biomimetic calcium phosphate NPs comparable to their physiological counterparts is described. Particle sizing using dynamic light scattering reveals that serum and ion concentrations within the physiological range yield NPs below 100 nm in diameter. While the particles are phagocytosed by macrophages in a size-independent manner, only large particles or NP aggregates in the micrometer range induce cellular responses that include production of mitochondrial reactive oxygen species, caspase-1 activation, and secretion of interleukin-1β (IL-1β). A comprehensive proteomic analysis reveals that the particle-bound proteins are similar in terms of their identity and number, regardless of particle size, suggesting that protein adsorption is independent of particle size and curvature. In conclusion, the conditions underlying the formation of mineralo-protein particles are similar to the ones that form in vivo. While mineral NPs do not activate immune cells, they may become pro-inflammatory and contribute to pathological processes once they aggregate and form larger mineral particles. The properties of biological mineralo-protein nanoparticles that form spontaneously in human body fluids are described. Concentrations of serum and precipitating ions near physiological levels produce small biomimetic nanoparticles that grow steadily in size but that retain a similar protein profile irrespective of size. These biological mineral particles are phagocytosed by immune cells and they activate pro-inflammatory responses in a size-dependent manner.