Synthetic amorphous magnesium-substituted calcium phosphate: silent constructs that trap macromolecules for intracellular delivery

Amorphous magnesium-substituted calcium phosphate (AMCP) nanoparticles form constitutively in large numbers in the gastrointestinal tract. Collective evidence indicates that they trap luminal macromolecules, such as bacterial and dietary protein antigen, delivering this cargo to mucosal antigen presenting cells. Here using a precise synthetic mimetic of the AMCP nanomineral, we studied whether trapping of macromolecules by AMCP modulates signalling of the macromolecule itself. Based upon whole genome transcriptomic analyses and using peptidoglycan as a macromolecule, we showed that neither AMCP nanomineral itself regulated any gene, nor did it modify any gene regulation by peptidoglycan. We conclude that synthetic AMCP nanomineral can deliver macromolecular cargo intracellularly without affecting gene transcription. Peripheral blood mononuclear cells (PBMC) were isolated from 7 subjects and further enriched for monocytes by Percoll density gradient centrifugation. Protein-containing (bovine serum albumin at 500 µg/ml), synthetic amorphous magnesium-substituted calcium phosphate nanoparticles were prepared in the absence (AMCP) or presence (AMCP/sPg) of 50 µg/ml soluble, purified peptidoglycan from Escherichia coli. Monocyte-enriched PBMC were stimulated for 3 hr with synthetic AMCP or AMCP/sPg nanoparticles (both diluted 1:9 in tissue culture medium) or with 4 µg/ml soluble peptidoglycan (sPg) or with vehicle control. Cells were subsequently recovered and subjected to genome-wide gene expression analysis.