Transmembrane delivery of aggregated [Gd@C82(OH)22]n nanoparticles.

We investigated whether multi-hydroxyl metallofullerenes can penetrate into erythrocyte and whether this potential transmembrane delivery requires aggregated nanostructure of these particles. The metal atom encapsulated in metallofullerenes was used as a quantitative marker to investigate body distribution of aggregated nanoparticles in cytomembrane and cytoplasm. Image of atomic force microscopy (AFM) and assay of inductively coupled plasma-mass spectrometry (ICP-MS) suggested that aggregated [Gd@C82(OH)22]n particles traversed through cytomembrane into cytoplasm. Aggregated Gd nanostructure belonged to small sphere with average diameter of 22.4 +/- 0.5 nm. For pristine Gd@C82 molecule, due to the electron donation from Gd atom, the distribution of electrons on the surface of carbon cage was localized. The electrophilic additive reaction of polyhydroxyl on the surface of Gd@C82 was directly affected by local distribution of electrons. This resulted in local distribution of hydroxyls on the surface of Gd nanoparticles. Local distribution of hydroxyls brought about polar and nonpolar domains on particle surface, which induced Gd@C82(OH)22 to be amphiphilic molecule with due hydrophilic and hydrophobic properties. Amphiphilic properties of these molecules promoted their mutual aggregation in water. In the process of aggregation, amphiphilic properties of aggregated nanoparticles were well maintained, and besides, hydrophilic and hydrophobic domains were also regularly distributed on the surface of [Gd@C82(OH)22]n particles. The amphiphilic nanoparticles attached externally to cytomembrane of erythrocyte might be effectively driven by hydrophobic effect when they directly contacted cytomembrane of erythrocyte. The number of [Gd@C82(OH)22]n nanoparticles attached to cytomembrane reached up to a certain critical threshold, a significant curvature tension of membrane would occur. The shape of cell was accordingly changed. Increased membrane tension triggered the sudden opening of specific pores as a result of cytmembrane response to nanoparitcle effect and the [Gd@C82(OH)22]n nanoparticles gained entry to cell via these pores. This process was biologically independent of caveolar-mediated endocytosis or transportation pathway via ion channels.