Xiaomei Liu

Cytotoxicity and mitochondrial damage caused by silica nanoparticles.

Amorphous silica nanoparticles are widely applied in many fields. But the adverse effects of silica nanoparticle exposure were unclear. The present study investigated the cytotoxicity and mitochondrial damage of silica nanoparticles exposure in hepatocellular carcinoma cell line (HepG2). The cells were treated with 43 nm non-modified amorphous silica nanoparticles which dispersed in serum-free DMEM at concentrations of 0, 25, 50, 100 and 200 μg/mL for 3 and 24 h. The results showed that the silica nanoparticles could lead to increasing cellular reactive oxygen species (ROS) production for 3 and 24 h exposure. Moreover, the oxidative stress induced by the particles could play an important role of the mitochondrial membrane damage and the cell apoptosis. It indicated that apoptosis through mitochondrial pathway mediated by oxidative stress was a potential mechanism of cytotoxicity induced by silica nanoparticles. The particles could enter the cells through different pathways and dispersed in cytoplasm and deposited inside mitochondria. Mitochondria were the major organelles for the cytotoxicity of silica nanoparticles exposure. Mitochondrial damage was related to the oxidative stress and the direct injurious effect of nanoparticles. It can be considered as the potential mechanism for the cytotoxic effects of amorphous silica nanoparticles.

Size-dependent cytotoxicity of amorphous silica nanoparticles in human hepatoma HepG2 cells

The purpose of this study is to compare the potential cytotoxicity induced by amorphous silica particles with different sizes. The effects of one fine particle (498 nm) and three nanoparticles (68, 43, and 19 nm) on cultured human hepatoma (HepG2) cells were investigated by detecting morphological changes, cell viability, cytomembrane integrity, DNA damage, cell cycle distribution, and apoptosis after the cells were treated with 100 μg/mL of four silica particles for 24h. The results indicated that in HepG2 cells, the cytotoxicity generated by silica particles strongly depended on the particle size, and smaller silica particle possessed higher toxic effect. In order to further elucidate the possible mechanisms of cell injuries, intracellular reactive oxygen species (ROS) was measured. Increased ROS level was also observed in a size dependent way. However, the result showed the fine particle did not promote intracellular ROS level significantly, while cell injuries were detected in this treated group. Thus, our data demonstrated that exposure to different sizes of silica particles resulted in a size dependent cytotoxicity in cultured HepG2 cells, and ROS generation should be one possible damage pathway but might not be completely responsible for the toxic effect produced by silica particles.

Silica nanoparticles induce autophagy and autophagic cell death in HepG2 cells triggered by reactive oxygen species

Silica nanoparticles (SNPs) are becoming favorable carriers for drug delivery or gene therapy, and in turn, the toxic effect of SNPs on biological systems is gaining attention. Currently, autophagy is recognized as an emerging toxicity mechanism triggered by nanomaterials, yet there have been scarcely research about the mechanisms of autophagy and autophagic cell death associated with SNPs. In this study, we verified the activation of SNPs-induced autophagy via the MDC-staining and LC3-I/LC3-II conversion, resulted in a dose-dependent manner. The typically morphological characteristics (autophagosomes and autolysosomes) of the autophagy process were observed in TEM ultrastructural analysis. In addition, the autophagic cell death was evaluated by cellular co-staining assay. And the underlying mechanisms of autophagy and autophagic cell death were performed using the intracellular ROS detection, autophagy inhibitor and ROS scavenger. Results showed that the elevated ROS level was in line with the increasing of autophagy activation, while both the 3-MA and NAC inhibitors effectively suppressed the autophagy and cell death induced by SNPs. In summary, our findings demonstrated that the SNPs-induced autophagy and autophagic cell death were triggered by the ROS generation in HepG2 cells, suggesting that exposure to SNPs could be a potential hazardous factor for maintaining cellular homeostasis.

Realumination of dealuminated zeolites Y

H 4 EDTA- and SiCl 4 -vapor-dealuminated zeolite Y were realuminated with aqueous solutions of NaAlO 2 and NaOH. The products were characterized by using XRD, MAS n.m.r., FTi.r. , and second-derivative FTi.r. techniques. The results clearly show that insertion of aluminum species into the frameworks of the zeolites occurs through the occupancy of the structural vacancies present in the dealuminated zeolites Y and/or through substitution of aluminum species for the framework silicon atoms. Effects of alkalinity of the solution and concentration of NaAlO 2 on realumination were also investigated.

Multinucleation and cell dysfunction induced by amorphous silica nanoparticles in an L-02 human hepatic cell line.

Silica nanoparticles (SNPs) are one of the most important nanomaterials, and have been widely used in a variety of fields. Therefore, their effects on human health and the environment have been addressed in a number of studies. In this work, the effects of amorphous SNPs were investigated with regard to multinucleation in L-02 human hepatic cells. Our results show that L-02 cells had an abnormally high incidence of multinucleation upon exposure to silica, that increased in a dose-dependent manner. Propidium iodide staining showed that multinucleated cells were arrested in G2/M phase of the cell cycle. Increased multinucleation in L-02 cells was associated with increased generation of cellular reactive oxygen species and mitochondrial damage on flow cytometry and confocal microscopy, which might have led to failure of cytokinesis in these cells. Further, SNPs inhibited cell growth and induced apoptosis in exposed cells. Taken together, our findings demonstrate that multinucleation in L-02 human hepatic cells might be a failure to undergo cytokinesis or cell fusion in response to SNPs, and the increase in cellular reactive oxygen species could be responsible for the apoptosis seen in both mononuclear cells and multinucleated cells.

Inhibition of gap junction intercellular communication is involved in silica nanoparticles-induced H9c2 cardiomyocytes apoptosis via the mitochondrial pathway.

Gap junction intercellular communication (GJIC) between cardiomyocytes is essential for synchronous heart contraction and relies on connexin-containing channels. Connexin 43 (Cx43) is a major component involved in GJIC in heart tissue, and its abnormal expression is closely associated with various cardiac diseases. Silica nanoparticles (SNPs) are known to induce cardiovascular toxicity. However, the mechanisms through which GJIC plays a role in cardiomyocytes apoptosis induced by SNPs remain unknown. The aim of the present study is to determine whether SNPs-decreased GJIC promotes apoptosis in rat cardiomyocytes cell line (H9c2 cells) via the mitochondrial pathway using CCK-8 Kit, scrape-loading dye transfer technique, Annexin V/PI double-staining assays, and Western blot analysis. The results showed that SNPs elicited cytotoxicity in H9c2 cells in a time- and concentration-dependent manner. SNPs also reduced GJIC in H9c2 cells in a concentration-dependent manner through downregulation of Cx43 and upregulation of P-Cx43. Inhibition of gap junctions by gap junction blocker carbenoxolone disodium resulted in decreased survival and increased apoptosis, whereas enhancement of the gap junctions by retinoic acid led to enhanced survival but decreased apoptosis. Furthermore, SNPs-induced apoptosis through the disrupted functional gap junction was correlated with abnormal expressions of the proteins involved in the mitochondrial pathway-related apoptosis such as Bcl-2/Bax, cytochrome C, Caspase-9, and Caspase-3. Taken together, our results provide the first evidence that SNPs-decreased GJIC promotes apoptosis in cardiomyocytes via the mitochondrial pathway. In addition, downregulation of GJIC by SNPs in cardiomyocytes is mediated through downregulation of Cx43 and upregulation of P-Cx43. These results suggest that in rat cardiomyocytes cell line, GJIC plays a protective role in SNPs-induced apoptosis and that GJIC may be one of the targets for SNPs-induced biological effects.

Enhancement of Antiproliferative and Proapoptotic Effects of Cadmium Chloride Combined with hSmac in Hepatocellular Carcinoma Cells

Background: To study the effects of cadmium chloride (CdCl2) combined with hSmac on the proliferation and apoptosis of hepatocellular carcinoma cells, i.e. SMMC-7721. Methods: SMMC-7721 cells were transfected with pcDNA3.1+-hSmac using a lipofectamine-mediated method, and then cell viability was detected by MTT assay after exposure to 10, 20, and 30 µmol/l CdCl2. Apoptosis was determined by both acridine orange-ethidium bromide staining and flow cytometry, and expressions of caspase-3, caspase-9, and cytochrome c by Western blot. Results: CdCl2 had cytotoxicity to SMMC-7721 cells, and it could inhibit proliferation in a dose-dependent manner and induce apoptosis; hSmac could inhibit proliferation and induce apoptosis independently in SMMC-7721 cells. Furthermore, cotreatment with CdCl2 and hSmac could enhance antiproliferative and proapoptotic effects in SMMC-7721 cells. Conclusions: hSmac could enhance the cytotoxicity of CdCl2.