| Nanobiology as a newly emerging multidisciplinary fused science has introduced a new dimension to research endeavor and a range of technologies in biology. However, the mechanisms underlying cell uptake of nanoparticles remain obscure. The characteristic size in the nanoscale, which is equivalent to the size of some biological macromolecules (such as DNA, proteins, etc.), nanoparticles would possess some unknown biological effects on the biological systems. Extensive studies need to be carried out to detect the interaction between nanoparticles and biological systems, providing robust evidence for the application of nanoparticles in life science. In our study, superparamagnetic iron oxide nanoparticles (SPION) and multi-walled carbon nanotubes had been chosen to study, the cellular influences and the potential molecular mechanisms were investigated.As one of the prospective nanoparticles candidates, SPION have been focused on in several nanomedical fields. Here, we reported that the internalization of SPION into a macrophage-like cell line RAW264.7 was in a time-and concentration-dependent manner to some degree. The internalized SPION were mainly found in the cytoplasmic vesicles, with no localization in the endoplasmic reticulum, mitochondria and nucleus. Moreover, the RAW264.7 cellular uptake was via an energy-dependent process that was suggestive of endocytosis. By blocking various endocytic pathways, we demonstrated that multiple endocytic processes were involved including clathrin-and caveolae-mediated endocytosis, macropinocytosis and scavenger receptor-mediated phagocytosis. Our data showed that nanoparticle endocytosis is therefore not mediated by a unique signaling pathway in a giving cell type.Meanwhile, the present study investigated the internalization of SPION in three cell models with different phagocytic capacity using transmission electron microscopy and energy dispersive spectrometer analysis. The results showed that the iron element was the nanoparticles composition in the cytoplasm of RAW264.7 cells but not in the red blood cells. SPION could be uptaken by RAW264.7 (with strong phagocytic capacity) and the 3T3-L1 cell (with weak phagocytic capacity), but not by red blood cells (with no phagocytic capacity), suggesting that different internalization pathways could be chosen for the nanoparticles cellular uptake in different cell types. The internalization occurred much more quickly in RAW264.7 cells than 3T3-L1 cells.The potential applications of SPION in several nanomedical fields have attracted intense interests, but the intracellular trail, the final fate and the biological effect of the internalized iron oxide nanoparticles have not been clearly elucidated. Here we showed that the internalized SPION had no effect on the cell viability, ROS induction and mitochondrial membrane potential dysfunction, possessing well biocompatible characteristics in RAW264.7 cells. Moreover, three kinds of possible metabolic fate for the internalized SPION in RAW264.7 cells were speculated:first, the internalized SPION are distributed to daughter cells; second, the internalized SPION are degraded in the lysosome and free iron was released into the intracellular iron metabolic pool; third, the intact iron oxide nanoparticles could be exocytosed out of cells. In addition, the internalized SPION indeed affected the intracellular iron metabolism in RAW264.7 cell, inducing an up-regulation of ferritin light chain at both protein and mRNA level, and ferroportinl at the mRNA level. The central player in the intracellular iron metabolism iron regulatory protein 2 has no degradation opposite to the hypothesis. The results in the present study provided evidences for the consideration of biological safety of SPION administered as contrast agents or drug delivery tools.Intense interest in the applications of nanomaterials for drug delivery, diagnostic or imaging tests and regenerative medicine has been generated because of the nanoscale size of such materials. Among the nanomaterials, carbon nanotube has been the focus of extensive researches as a potential player in nanobiotechnology. However, the nature or mechanism by which carbon nanotubes interact with cells or specifically ion channels is largely unknown. Ion channels transduce electrical signals in excitable cells and they therefore play critical roles in many physiological systems. A notable example of ion channels that plays an essential role in physiology is potassium channels that are involved in the repolarization of action potentials in excitable cells. Functional abnormality of these K+channels contribute to disturbance of action potential repolarization and inability to reset the resting potential properly and thus leading to dysfunction of an organ.In our previous study, we observed that carboxyl-terminated multi-walled carbon nanotubes (MWCNTs, length 300-800nm, inner diameter 10-20nm and outer diameter 40-50nm) act as antagonists of three types of potassium channels as assessed by whole-cell patch clamp electrophysiology on undifferentiated pheochromocytoma (PC 12) cells. Moreover, the possible signal pathway through which the MWCNTs have impact on the K+ channels was further explored. Oxidative stress could develop as a cellular response to hazardous materials or endogenous adverse metabolite and could also be a potential downstream effect pathway by which nanotubes affect ion channels. The physiological effects of oxidative stress include the production of reactive oxygen species (ROS), increasing of [Ca2+]i and decreasing of the mitochondrial membrane potential (⊿Ψm). However, MWCNTs did not significantly change the expression levels of ROS and did not alter the⊿Ψm in PC 12 cells. MWCNTs also did not significantly change the level of intracellular free calcium. These results suggest that oxidative stress was not involved in MWCNTs suppression of Ito, IK and IK1 current densities. Nonetheless, the suppression of potassium currents by MWCNTs will impact on electrical signaling of excitable cells such as neurons and muscles. As such, the potential side effects of nanotubes on potassium channels should be examined before they are used as a delivery tool in vivo.
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