title: The sequestration of hydroxyapatite nanoparticles by human monocyte-macrophages in a compartment that allows free diffusion with the extracellular environment.
abstract: Calcium phosphate and hydroxyapatite nanoparticles are extensively researched for medical applications, including bone implant materials, DNA and SiRNA delivery vectors and slow release vaccines. Elucidating the mechanisms by which cells internalize nanoparticles is fundamental for their long-term exploitation. In this study, we demonstrate that hydrophilic hydroxyapatite nanoparticles are sequestered within a specialized compartment called SCC (surface-connected compartment). This membrane-bound compartment is an elaborate labyrinth-like structure directly connected to the extracellular space. This continuity is demonstrated by in vivo 2-photon microscopy of ionic calcium using both cell-permeable and cell-impermeable dyes and by 3-D reconstructions from serial block-face SEM of fixed cells. Previously, this compartment was thought to be initiated specifically by exposure of macrophages to hydrophobic nanoparticles. However, we show that the SCC can be triggered by a much wider range of nanoparticles. Furthermore, we demonstrate its formation in A549 human lung epithelial cells, which are considerably less phagocytic than macrophages. EDX shows that extensive amounts of hydroxyapatite nanoparticles can be sequestered in this manner. We propose that SCC formation may be a means to remove large amounts of foreign material from the extracellular space, followed by slow degradation, may be to avoid excessive damage to surrounding cells or tissues.
authors: Multi-Imaging Centre, Dept. of Physiology, Development and Neuroscience, Anatomy Building, Cambridge University, Cambridge CB2 3DY, UK.
authors: Michael
authors: M
authors: Motskin
authors: Karin H
authors: KH
authors: Müller
authors: Christel
authors: C
authors: Genoud
authors: Alexander G
authors: AG
authors: Monteith
authors: Jeremy N
authors: JN
authors: Skepper
mesh_terms: D002118:Calcium / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D002451:Cell Compartmentation; D045744:Cell Line, Tumor; D002470:Cell Survival; D003102:Colloids; D004058:Diffusion; D017886:Durapatite / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007091:Image Processing, Computer-Assisted; D051907:Lysosomal Membrane Proteins / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D018613:Microscopy, Confocal; D036641:Microscopy, Fluorescence, Multiphoton; D009000:Monocytes / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D044367:Phase Transition; D013052:Spectrometry, X-Ray Emission; D033921:Vesicular Transport Proteins / Q000378:metabolism; D052118:Lysosomal-Associated Membrane Protein 1
chemical_list: D002118:Calcium; D002402:Cathepsin D; D003102:Colloids; D017886:Durapatite; D051907:Lysosomal Membrane Proteins; D033921:Vesicular Transport Proteins; C489116:LAMP1 protein, human; D052118:Lysosomal-Associated Membrane Protein 1; C093846:early endosome antigen 1