Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells

Lena Kastl, Daniel Sasse, Verena Wulf, Raimo Hartmann, Josif Mircheski, Christiane Ranke, Susana Carregal-Romero, José Antonio Martínez-López, Rafael Fernández-Chacón, Wolfgang J. Parak, Hans Peter Elsasser, Pilar Riveragil*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.

Original languageEnglish
Pages (from-to)6605-6618
Number of pages14
JournalACS Nano
Issue number8
StatePublished - 27 Aug 2013
Externally publishedYes


  • actin cytoskeleton
  • cancer cells
  • caveolin-mediated uptake
  • clathrin-mediated uptake
  • colloids
  • endosomes
  • intracellular localization
  • layer-by-layer assembly
  • lipid rafts
  • lysosomes
  • macropinocytosis
  • mechanisms of internalization
  • phagocytosis
  • pharmacological inhibitors
  • polyelectrolyte multilayer capsules


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