Comparison of cytotoxicity and membrane efflux pump inhibition in HepG2 cells induced by single-walled carbon nanotubes with different length and functional groups.

Environmental risk of single-walled carbon nanotubes (SWCNTs) is receiving increasing attentions owing to their wide study and application. However, little is known on the influence of length and functional groups on SWCNT cytotoxicity. In this study, six types of SWCNTs with different functional groups (pristine, carboxyl group and hydroxyl group) and lengths (1-3 µm and 5-30 µm) were chosen. Cytotoxicities in human hepatoma HepG2 cells induced by these SWCNTs were compared based on cell viability, oxidative stress, plasma membrane fluidity and ABC transporter activity assays. Results showed that all the SWCNTs decreased cell viability of HepG2, increased intracellular reactive oxygen species (ROS) level, and damaged plasma membrane in a concentration-dependent manner. Long SWCNTs had stronger cytotoxic effects than short SWCNTs, which might be due to weaker aggregation for the long SWCNTs. Functionalization changed the toxic effects of the SWCNTs, and different influence was found between long SWCNTs and short SWCNTs. Moreover, the six types of SWCNTs at low concentrations changed plasma membrane fluidity, inhibited transmembrane ABC transporter (efflux pump) activity, and acted as chemosensitizer to improve the sensitivity of cells to arsenic, indicating the chemosensitive effect should be considered as toxic endpoint of SWCNTs. Comparison of different toxic endpoints among the six types of SWCNTs showed that short hydroxyl-SWCNT might be safer than other SWCNTs. This study provides insights into toxicities of SWCNTs, which is of great value for the risk assessment and application of SWCNTs.

Memory effect of arsenic-induced cellular response and its influences on toxicity of titanium dioxide nanoparticle.

Toxicity of arsenic (As) has been widely characterized. However, few studies focus on whether cell responses induced by As at nontoxic concentration could be inherited and further change cell tolerance to another pollutant. In this study, human A549 and HeLa cells were exposed to As at nontoxic concentrations for 10 or 15 passages, then the cells were recovered in the cell medium without As. At 25th passage, residual As in both type of cells was completely removed through the recovery process. And no abnormity in cell viability was identified in both type of cells between control and As-treated groups. Above results indicated that As exposure-recovery treatment had limited influence on phenotype of the cells. However, gene expression profiles determined by high-throughput sequencing showed that As exposure-recovery treatment induced similar expression modification of genes related to inflammation, oxidative stress and epigenetic modulation in the A549 and HeLa cells after recovery of 10 or 15 passages, indicating that As-induced cellular responses have been partially memorized at transcriptional level. The memory effect might play key roles in increased tolerance of the A549 and HeLa cells to adverse effects (cell viability, intracellular reactive oxygen species (ROS) generation and plasma membrane damage) induced by titanium dioxide nanoparticles (as representative pollutant). This study shed new lights on toxic effects induced by As at nontoxic concentration, which is useful for risk assessment of combined effects of As and other pollutants.

Cytotoxicity and Efflux Pump Inhibition Induced by Molybdenum Disulfide and Boron Nitride Nanomaterials with Sheetlike Structure.

Sheetlike molybdenum disulfide (MoS2) and boron nitride (BN) nanomaterials have attracted attention in the past few years due to their unique material properties. However, information on adverse effects and their underlying mechanisms for sheetlike MoS2 and BN nanomaterials is rare. In this study, cytotoxicities of sheetlike MoS2 and BN nanomaterials on human hepatoma HepG2 cells were systematically investigated at different toxic end points. Results showed that MoS2 and BN nanomaterials decreased cell viability at 30 µg/mL and induced adverse effects on intracellular ROS generation (≥2 µg/mL), mitochondrial depolarization (≥4 µg/mL), and membrane integrity (≥8 µg/mL for MoS2 and ≥2 µg/mL for BN). Furthermore, this study first found that low exposure concentrations (0.2-2 µg/mL) of MoS2 and BN nanomaterials could increase plasma membrane fluidity and inhibit transmembrane ATP binding cassette (ABC) efflux transporter activity, which make both nanomaterials act as a chemosensitizer (increasing arsenic toxicity). Damage to plasma membrane and release of soluble Mo or B species might be two reasons that both nanomaterials inhibit efflux pump activities. This study provides a systematic understanding of the cytotoxicity of sheetlike MoS2 and BN nanomaterials at different exposure levels, which is important for their safe use.

Hepatic transcriptomic responses in mice exposed to arsenic and different fat diet.

Chronic exposure to inorganic arsenic (iAs) or a high-fat diet (HFD) can produce liver injury. However, effects of HFD on risk assessment of iAs in drinking water are unclear. In this study, we examined how HFD and iAs interact to alter iAs-induced liver injury in C57BL/6 mice. Mice fed low-fat diet (LFD) or HFD were exposed to 3 mg/L iAs or deionized water for 10 weeks. Results showed that HFD changed intake and excretion of iAs by mice. Then, HFD increased the amount of iAs-induced hepatic DNA damage and amplified changes in pathways related to cell death and growth, signal transduction, lipid metabolism, and insulin signaling. Compared to gene expression profiles caused by iAs alone or HFD alone, insulin signaling pathway might play important roles in the interactive effects of iAs and HFD. Our data suggest that HFD increases sensitivity of mice to iAs in drinking water, resulting in increased hepatotoxicity. This study highlight that HFD might enhance the risk of iAs hepatotoxicity in iAs-polluted regions. The diet should be considered during risk assessment of iAs in drinking water.

Comparison of Cytotoxicity and Inhibition of Membrane ABC Transporters Induced by MWCNTs with Different Length and Functional Groups.

Experimental studies indicate that multiwalled carbon nanotubes (MWCNTs) have the potential to induce cytotoxicity. However, the reports are often inconsistent and even contradictory. Additionally, adverse effects of MWCNTs at low concentration are not well understood. In this study, we systemically compared adverse effects of six MWCNTs including pristine MWCNTs, hydroxyl-MWCNTs and carboxyl-MWCNTs of two different lengths (0.5-2 µm and 10-30 µm) on human hepatoma cell line HepG2. Results showed that MWCNTs induced cytotoxicity by increasing reactive oxygen species (ROS) generation and damaging cell function. Pristine short MWCNTs induced higher cytotoxicity than pristine long MWCNTs. Functionalization increased cytotoxicity of long MWCNTs, but reduced cytotoxicity of short MWCNTs. Further, our results indicated that the six MWCNTs, at nontoxic concentration, might not be environmentally safe as they inhibited ABC transporters' efflux capabilities. This inhibition was observed even at very low concentrations, which were 40-1000 times lower than their effective concentrations on cytotoxicity. The inhibition of ABC transporters significantly increased cytotoxicity of arsenic, a known substrate of ABC transporters, indicating a chemosensitizing effect of MWCNTs. Plasma membrane damage was likely the mechanism by which the six MWCNTs inhibited ABC transporter activity. This study provides insight into risk assessments of low levels of MWCNTs in the environment.