The internalization of three types of carbon nanoparticles by HeLa cells in vitro

We have found activated carbon nanoparticles (ACNP) can be used as carriers of nanodrug delivery systems to treat cervical cancer. But how ACNP to enter into the HeLa cell, how to distribute, translocate and, metabolize and develop therapeutic effects has been unknown. In this paper, we invested the action of ACNP on HaLa cells in comparison with single walled carbon nanotubes (SWCNT) and quantum dots (QDs) in vitro.

The effects of the nanoparticles on the HeLa cells were observed by tetrazolium bromide reduction (MTT) assay, lactate dehydrogenase leakage determination (LDH), flow cytometry, apoptotic rate, DNA comet assay. The morphological influences of nanoparticles on HeLa cells were observed with inverted microscope and atomic force microscopy (AFM); The mechanism of across cell membrane translocation of ACNP, SWCNT and QDs was investigated by treating the cells with endocytosis inhibitors and 4 °C low temperature.

The three nanoparticles can inhibit the proliferation of HeLa cells in time- and concentration-dependent manners. Under the light microscope, the volume of HeLa cells treated by ACNP and SWCNT became smaller than that of control group. ACNP and SWCNT can induce HeLa cells shrinkage, weaken cell adhesion and increase the number of free cells in culture media. Under AFM, ACNP caused ill-defined cell membranes and membrane rupture; SWCNT caused cell shrinkage, reduced adhesion properties and "collapse-like" structure; QDs induced cell surface roughness and cell membrane folds. There are many irregular depressions in the cells. Flow cytometry showed that the three nanoparticles induced apoptosis of Hela cells. Electrophoresis showed the three nanoparticles induced DNA damage. Transmission electron microscopy(TEM) revealed that ACNP can pass through the cell membrane into the cytoplasm and further into the nucleus, causing disappearance of surface microvilli, mitochondrial swelling and nuclear shrinkage; SWCNT can enter into HeLa cells in the medium without inhibitors under room temperature, inducing cell and nuclear shrinkage, SWCNT was not found in the HeLa cells treated by inhibitors and low temperature; QDs was found accumulated in the cell membranes and can also cause swelling of mitochondria and increase cytoplasmic vacuoles.

The three kinds of nanoparticles can inhibit the growth and cause apoptosis of HeLa cells; the mechanism may be nuclear DNA damage and increased membrane permeability; The internalization of SWCNT by HeLa cells is energy dependent while the internalization of ACNP is independent of energy. The DNA damage effects of ACNP may be realized through two ways, one of which is to injure cell membranes and the other is to act on DNA directly. QDs damage DNA mainly through the action of cell membranes.