Gastrointestinal tract exposure to particles and DNA damage in animals: A review of studies before, during and after the peak of nanotoxicology

Humans ingest particles and fibers on daily basis. Non-digestible carbohydrates are beneficial to health and food additives are considered safe. However, titanium dioxide (E171) has been banned in the European Union because the European Food Safety Authority no longer considers it non-genotoxic. Ingestion of microplastics and nanoplastics are novel exposures; their potential hazardous effects to humans have been under the radar for many years. In this review, we have assessed the association between oral exposure to man-made particles/fibers and genotoxicity in gastrointestinal tract cells and secondary tissues. We identified a total of 137 studies on oral exposure to particles and fibers. This was reduced to 49 papers with sufficient quality and relevance, including exposures to asbestos, diesel exhaust particles, titanium dioxide, silver nanoparticles, zinc oxide, synthetic amorphous silica and certain other nanomaterials. Nineteen studies show positive results, 25 studies show null results, and 5 papers show equivocal results on genotoxicity. Recent studies seem to show null effects, whereas there is a higher proportion of positive genotoxicity results in early studies. Genotoxic effects seem to cluster in studies on diesel exhaust particles and titanium dioxide, whereas studies on silver nanoparticles, zinc oxide and synthetic amorphous silica seem to show mainly null effects. The most widely used genotoxic tests are the alkaline comet assay and micronucleus assay. There are relatively few results on genotoxicity using reliable measurements of oxidatively damaged DNA, DNA double strand breaks (γH2AX assay) and mutations. In general, evidence suggest that oral exposure to particles and fibers is associated with genotoxicity in animals.

Pleural inflammatory response, mesothelin content and DNA damage in mice at one-year after intra-pleural carbon nanotube administration

Many in vitro and in vivo studies have shown that exposure to carbon nanotubes (CNTs) is associated with inflammation, oxidative stress and genotoxicity, although there is a paucity of studies on these effects in the pleural cavity. In the present study, we investigated adverse outcomes of pleural exposure to multi-walled CNTs (MWCNT-7, NM-401 and NM-403) and single-walled CNTs (NM-411). Female C57BL/6 mice were exposed to 0.2 or 5 µg of CNTs by intra-pleural injection and sacrificed one-year post-exposure. Exposure to long and straight types of MWCNTs (i.e. MWCNT-7 and NM-401) was associated with decreased number of macrophages and increased number of neutrophils and eosinophils in pleural lavage fluid. Increased protein content in the pleural lavage fluid was also observed in mice exposed to MWCNT-7 and NM-401. The concentration of mesothelin was increased in mice exposed to MWCNT-7 and NM-411. Levels of DNA strand breaks and DNA oxidation damage, measured by the comet assay, were unaltered in cells from pleural scrape. Extra-pleural effects were seen in CNT exposed mice, including enlarged and pigmented mediastinal lymph nodes (all four types of CNTs), pericardial plaques (MWCNT-7 and NM-401), macroscopic abnormalities on the liver (MWCNT-7) and ovaries/uterus (NM-411). In conclusion, the results demonstrate that intra-pleural exposure to long and straight MWCNTs is associated with adverse outcomes. Certain observations such as increased content of mesothelin in pleural lavage fluid and ovarian/uterine abnormalities in mice exposed to NM-411 suggests that exposure to SWCNTs may also be associated with some adverse outcomes.

Nanoplastics from ground polyethylene terephthalate food containers: Genotoxicity in human lung epithelial A549 cells

The ubiquitous pollution of plastic particles in most environmental matrices leads to concern about any potential adverse effects on human health. Most studies on the toxicological effect of nanoplastics has focused on standard particles of polystyrene. In reality humans are exposed to a large variety of different types and sizes of plastic material via oral intake and inhalation. In this study, we investigated the effect of polyethylene terephthalate (PET) nanoplastic particles from ground food containers from a supermarket. The aim was to investigate a possible link between exposure to PET nanoplastics and genotoxic response in a cell model of the human airway epithelial (A549) cells. Further, we investigated the combined effect of PET and chemicals known to alter the cellular redox state, as a model of partially compromised antioxidant defense system. DNA damage was assessed by the alkaline comet assay. The ground PET nanoplastics have a mean hydrodynamic diameter of 136 nm in water. The results showed that PET exposure led to increased reactive oxygen species production (approximately 30 % increase compared to unexposed cells). In addition, exposure to PET nanoplastic increased the level of DNA strand breaks (net increase = 0.10 lesions/106 base pair, 95 % confidence interval: 0.01, 0.18 lesions/106 base pair). Pre- or post-exposure to hydrogen peroxide or buthionine sulfoximine did not lead to a higher level of DNA damage. Overall, the study shows that exposure to PET nanoplastics increases both intracellular reactive oxygen production and DNA damage in A549 cells.

Comparison of acute phase response in mice after inhalation and intratracheal instillation of molybdenum disulphide and tungsten particles

Inhalation studies are the gold standard for assessing the toxicity of airborne materials. They require considerable time, special equipment, and large amounts of test material. Intratracheal instillation is considered a screening and hazard assessment tool as it is simple, quick, allows control of the applied dose, and requires less test material. The particle-induced pulmonary inflammation and acute phase response in mice caused by intratracheal instillation or inhalation of molybdenum disulphide or tungsten particles were compared. End points included neutrophil numbers in bronchoalveolar lavage fluid, Saa3 mRNA levels in lung tissue and Saa1 mRNA levels in liver tissue, and SAA3 plasma protein. Acute phase response was used as a biomarker for the risk of cardiovascular disease. Intratracheal instillation of molybdenum disulphide or tungsten particles did not produce pulmonary inflammation, while molybdenum disulphide particles induced pulmonary acute phase response with both exposure methods and systemic acute phase response after intratracheal instillation. Inhalation and intratracheal instillation showed similar dose-response relationships for pulmonary and systemic acute phase response when molybdenum disulphide was expressed as dosed surface area. Both exposure methods showed similar responses for molybdenum disulphide and tungsten, suggesting that intratracheal instillation can be used for screening particle-induced acute phase response and thereby particle-induced cardiovascular disease.

Genotoxicity by rapeseed methyl ester and hydrogenated vegetable oil combustion exhaust products in lung epithelial (A549) cells

Biofuel is an attractive substitute for petrodiesel because of its lower environmental footprint. For instance, the polycyclic aromatic hydrocarbons (PAH) emission per fuel energy content is lower for rapeseed methyl ester (RME) than for petrodiesel. This study assesses genotoxicity by extractable organic matter (EOM) of exhaust particles from the combustion of petrodiesel, RME, and hydrogenated vegetable oil (HVO) in lung epithelial (A549) cells. Genotoxicity was assessed as DNA strand breaks by the alkaline comet assay. EOM from the combustion of petrodiesel and RME generated the same level of DNA strand breaks based on the equal concentration of total PAH (i.e. net increases of 0.13 [95% confidence interval (CI): 0.002, 0.25, and 0.12 [95% CI: 0.01, 0.24] lesions per million base pairs, respectively). In comparison, the positive control (etoposide) generated a much higher level of DNA strand breaks (i.e. 0.84, 95% CI: 0.72, 0.97) lesions per million base pairs. Relatively low concentrations of EOM from RME and HVO combustion particles (<116 ng/ml total PAH) did not cause DNA strand breaks in A549 cells, whereas benzo[a]pyrene and PAH-rich EOM from petrodiesel combusted using low oxygen inlet concentration were genotoxic. The genotoxicity was attributed to high molecular weight PAH isomers with 5-6 rings. In summary, the results show that EOM from the combustion of petrodiesel and RME generate the same level of DNA strand breaks on an equal total PAH basis. However, the genotoxic hazard of engine exhaust from on-road vehicles is lower for RME than petrodiesel because of lower PAH emission per fuel energy content.

Exposure to nanoplastic particles and DNA damage in mammalian cells

There is concern about human exposure to nanoplastics from intentional use or degradation of plastics in the environment. This review assesses genotoxic effects of nanoplastics, defined as particles with a primary size of less than 1000 nm. The majority of results on genotoxicity come from studies on polystyrene (PS) particles in mammalian cell cultures. Most studies have measured DNA strand breaks (standard comet assay), oxidatively damaged DNA (Fpg-modified comet assay) and micronuclei. Twenty-nine out of 60 results have shown statistically significant genotoxic effects by PS exposure in cell cultures. A statistical analysis indicates that especially modified PS particles are genotoxic (odds ratio = 8.6, 95 % CI: 1.6, 46) and immune cells seems to be more sensitive to genotoxicity than other cell types such as epithelial cells (odds ratio = 8.0, 95 % CI: 1.6, 39). On the contrary, there is not a clear association between statistically significant effects in genotoxicity tests and the primary size of PS particles, (i.e. smaller versus larger than 100 nm) or between the type of genotoxic endpoint (i.e. repairable versus permanent DNA lesions). Three studies of PS particle exposure in animals have shown increased level of DNA strand breaks in leukocytes and prefrontal cortex cells. Nanoplastics from polyethylene, propylene, polyvinyl chloride and polyethylene terephthalate have been investigated in very few studies and it is currently not possible to draw conclusion about their genotoxic hazard. In summary, there is some evidence suggesting that PS particles may be genotoxic in mammalian cells.

Acute phase response following pulmonary exposure to soluble and insoluble metal oxide nanomaterials in mice

BACKGROUND

Acute phase response (APR) is characterized by a change in concentration of different proteins, including C-reactive protein and serum amyloid A (SAA) that can be linked to both exposure to metal oxide nanomaterials and risk of cardiovascular diseases. In this study, we intratracheally exposed mice to ZnO, CuO, Al₂O₃, SnO₂ and TiO₂ and carbon black (Printex 90) nanomaterials with a wide range in phagolysosomal solubility. We subsequently assessed neutrophil numbers, protein and lactate dehydrogenase activity in bronchoalveolar lavage fluid, Saa3 and Saa1 mRNA levels in lung and liver tissue, respectively, and SAA3 and SAA1/2 in plasma. Endpoints were analyzed 1 and 28 days after exposure, including histopathology of lung and liver tissues.

RESULTS

All nanomaterials induced pulmonary inflammation after 1 day, and exposure to ZnO, CuO, SnO₂, TiO₂ and Printex 90 increased Saa3 mRNA levels in lungs and Saa1 mRNA levels in liver. Additionally, CuO, SnO₂, TiO₂ and Printex 90 increased plasma levels of SAA3 and SAA1/2. Acute phase response was predicted by deposited surface area for insoluble metal oxides, 1 and 28 days post-exposure.

CONCLUSION

Soluble and insoluble metal oxides induced dose-dependent APR with different time dependency. Neutrophil influx, Saa3 mRNA levels in lung tissue and plasma SAA3 levels correlated across all studied nanomaterials, suggesting that these endpoints can be used as biomarkers of acute phase response and cardiovascular disease risk following exposure to soluble and insoluble particles.

Genotoxicity of Particles From Grinded Plastic Items in Caco-2 and HepG2 Cells

Large plastic litters degrade in the environment to micro- and nanoplastics, which may then enter the food chain and lead to human exposure by ingestion. The present study explored ways to obtain nanoplastic particles from real-life food containers. The first set of experiments gave rise to polypropylene nanoplastic suspensions with a hydrodynamic particle size range between 100 and 600 nm, whereas the same grinding process of polyethylene terephthalate (PET) produced suspensions of particles with a primary size between 100 and 300 nm. The exposure did not cause cytotoxicity measured by the lactate dehydrogenase (LDH) and water soluble tetrazolium 1 (WST-1) assays in Caco-2 and HepG2 cells. Nanoplastics of transparent PET food containers produced a modest concentration-dependent increase in DNA strand breaks, measured by the alkaline comet assay [net induction of 0.28 lesions/10⁶ bp at the highest concentration (95% CI: 0.04; 0.51 lesions/10⁶ base pair)]. The exposure to nanoplastics from transparent polypropylene food containers was also positively associated with DNA strand breaks [i.e., net induction of 0.10 lesions/10⁶ base pair (95% CI: −0.04; 0.23 lesions/10⁶ base pair)] at the highest concentration. Nanoplastics from grinding of black colored PET food containers demonstrated no effect on HepG2 and Caco-2 cells in terms of cytotoxicity, reactive oxygen species production or changes in cell cycle distribution. The net induction of DNA strand breaks was 0.43 lesions/10⁶ bp (95% CI: 0.09; 0.78 lesions/10⁶ bp) at the highest concentration of nanoplastics from black PET food containers. Collectively, the results indicate that exposure to nanoplastics from real-life consumer products can cause genotoxicity in cell cultures.

Biomarkers of DNA Oxidation Products: Links to Exposure and Disease in Public Health Studies

Environmental exposure can increase the production of reactive oxygen species and deplete cellular antioxidants in humans, resulting in oxidatively generated damage to DNA that is both a useful biomarker of oxidative stress and indicator of carcinogenic hazard. Methods of oxidatively damaged DNA analysis have been developed and used in public health research since the 1990s. Advanced techniques detect specific lesions, but they might not be applicable to complex matrixes (e.g., tissues), small sample volume, and large-scale studies. The most reliable methods are characterized by (1) detecting relevant DNA oxidation products (e.g., premutagenic lesions), (2) not harboring technical problems, (3) being applicable to complex biological mixtures, and (4) having the ability to process a large number of samples in a reasonable period of time. Most effort has been devoted to the measurements of 8-oxo-7,8-dihydro-2'-deoxyguanine (8-oxodG), which can be analyzed by chromatographic, enzymic, and antibody-based methods. Results from validation trials have shown that certain chromatographic and enzymic assays (namely the comet assay) are superior techniques. The enzyme-modified comet assay has been popular because it is technically simpler than chromatographic assays. It is widely used in public health studies on environmental exposures such as outdoor air pollution. Validated biomarker assays on oxidatively damaged DNA have been used to fill knowledge gaps between findings in prospective cohort studies and hazards from contemporary sources of air pollution exposures. Results from each of these research fields feed into public health research as approaches to conduct primary prevention of diseases caused by environmental or occupational agents.

Inhalation of hydrogenated vegetable oil combustion exhaust and genotoxicity responses in humans

Biofuels from vegetable oils or animal fats are considered to be more sustainable than petroleum-derived diesel fuel. In this study, we have assessed the effect of hydrogenated vegetable oil (HVO) exhaust on levels of DNA damage in peripheral blood mononuclear cells (PBMCs) as primary outcome, and oxidative stress and inflammation as mediators of genotoxicity. In a randomized cross-over study, healthy humans were exposed to filtered air, inorganic salt particles, exhausts from combustion of HVO in engines with aftertreatment [i.e. emission with nitrogen oxides and low amounts of particulate matter less than 2.5 µm (approximately 1 µg/m³)], or without aftertreatment (i.e. emission with nitrogen oxides and 93 ± 13 µg/m³ of PM_2.5). The subjects were exposed for 3 h and blood samples were collected before, within 1 h after the exposure and 24 h after. None of the exposures caused generation of DNA strand breaks and oxidatively damaged DNA, or affected gene expression of factors related to DNA repair (Ogg1), antioxidant defense (Hmox1) or pro-inflammatory cytokines (Ccl2, Il8 and Tnfa) in PBMCs. The results from this study indicate that short-term HVO exhaust exposure is not associated with genotoxic hazard in humans.

Cell medium-dependent dynamic modulation of size and structural transformations of binary phospholipid/ω-3 fatty acid liquid crystalline nano-self-assemblies: Implications in interpretation of cell uptake studies

Lyotropic non-lamellar liquid crystalline (LLC) nanoparticles, with their tunable structural features and capability of loading a wide range of drugs and reporter probes, are emerging as versatile injectable nanopharmaceuticals. Secondary emulsifiers, such as Pluronic block copolymers, are commonly used for colloidal stabilization of LLC nanoparticles, but their inclusion often compromises the biological safety (e.g., poor hemocompatibility and enhanced cytotoxicity) of the formulation. Here, we introduce a library of colloidally stable, structurally tunable, and pH-responsive lamellar and non-lamellar liquid crystalline nanoparticles from binary mixtures of a phospholipid (phosphatidylglycerol) and three types of omega-3 fatty acids (ω-3 PUFAs), prepared in the absence of a secondary emulsifier and organic solvents. We study formulation size distribution, morphological heterogeneity, and the arrangement of their internal self-assembled architectures by nanoparticle tracking analysis, synchrotron small-angle X-ray scattering, and cryo-transmission electron microscopy. The results show the influence of type and concentration of ω-3 PUFAs in nanoparticle structural transitions spanning from a lamellar (L_α) phase to inverse discontinuous (micellar) cubic Fd3m and hexagonal phase (H₂) phases, respectively. We further report on cell-culture medium-dependent dynamic fluctuations in nanoparticle size, number and morphology, and simultaneously monitor uptake kinetics in two human cell lines. We discuss the role of these multiparametric biophysical transformations on nanoparticle-cell interaction kinetics and internalization mechanisms. Collectively, our findings contribute to the understanding of fundamental steps that are imperative for improved engineering of LLC nanoparticles with necessary attributes for pharmaceutical development.

Genotoxicity of multi-walled carbon nanotube reference materials in mammalian cells and animals

Carbon nanotubes (CNTs) were the first nanomaterials to be evaluated by the International Agency for Research on Cancer (IARC). The categorization as possibly carcinogenic agent to humans was only applicable to multi-walled carbon nanotubes called MWCNT-7. Other types of CNTs were not classifiable because of missing data and it was not possible to pinpoint unique CNT characteristics that cause cancer. Importantly, the European Commission's Joint Research Centre (JRC) has established a repository of industrially manufactured nanomaterials that encompasses at least four well-characterized MWCNTs called NM-400 to NM-403 (original JRC code). This review summarizes the genotoxic effects of these JRC materials and MWCNT-7. The review consists of 36 publications with results on cell culture experiments (22 publications), animal models (9 publications) or both (5 publications). As compared to the publications in the IARC monograph on CNTs, the current database represents a significant increase as there is only an overlap of 8 publications. However, the results come mainly from cell cultures and/or measurements of DNA strand breaks by the comet assay and the micronucleus assay (82 out of 97 outcomes). A meta-analysis of cell culture studies on DNA strand breaks showed a genotoxic response by MWCNT-7, less consistent effect by NM-400 and NM-402, and least consistent effect by NM-401 and NM-403. Results from other in vitro tests indicate strongest evidence of genotoxicity for MWCNT-7. There are too few observations from animal models and humans to make general conclusions about genotoxicity.

Inflammatory response, reactive oxygen species production and DNA damage in mice after intrapleural exposure to carbon nanotubes

Carbon nanotubes (CNTs) are speculated to cause mesothelioma by persistent inflammation, oxidative stress, tissue injury and genotoxicity. To investigate pleural response to CNTs, we exposed C57BL/6 mice by intrapleural injection of 0.2 or 5 µg multi-walled CNTs (MWCNT-7, NM-401 and NM-403) or single-walled CNTs (NM-411). Inflammatory response, cellular reactive oxygen species (ROS) production of pleural lavage cells and genotoxicity in cells from the mesothelial surface were assessed at day 1 and 90 after the exposure. Long and rigid types of MWCNTs (MWCNT-7 and NM-401) caused acute inflammation, characterized by influx of macrophages, neutrophils and eosinophils into the pleural cavity. The inflammation was still evident at 90 days after the exposure, although it had reduced dramatically. The cellular ROS production was increased at day 90 after the exposure to MWCNT-7 and NM-401. The short and tangled type of MWCNT (i.e. NM-403) did not cause pleural inflammation or ROS production in pleural fluid cells. The exposure to NM-411 did not cause consistent inflammation responses or cellular ROS production. Levels of DNA strand breaks and DNA oxidation damage were unaltered, except for NM-411-exposed mice that had increased level of DNA strand breaks at 90 days after the exposure. In conclusion, the long and rigid CNTs caused prolonged inflammatory response and increased ROS production in pleural lavage cells, yet it was not reflected in higher levels of DNA damage in pleural tissue.

Reactive oxygen species production, genotoxicity and telomere length in FE1-Muta™Mouse lung epithelial cells exposed to carbon nanotubes

Carbon nanotubes (CNTs) are fiber-like nanomaterials, which are used in various applications with possible exposure to humans. The genotoxicity and carcinogenic potential of CNTs remain to be fully understood. This study assessed the genotoxicity of three different multi-walled carbon nanotubes (MWCNTs) (MWCNT-7, NM-401 and NM-403) and one single-walled carbon nanotube (SWCNT) (NM-411) in FE1-Muta™Mouse lung epithelial (MML) cells using the alkaline comet assay. With the 2',7'-dichlorodihydrofluorescein diacetate fluorescent probe, we assessed the effect of CNT-exposure on the intracellular production of reactive oxygen species (ROS). We measured the effect of a 10-week CNT exposure on telomere length using quantitative PCR. Two of the included MWCNTs (NM-401 and MWCNT-7) and the SWCNT (NM-411) caused a significant increase in the level of DNA damage at concentrations up to 40 µg/ml (all concentrations pooled, p < 0.05), but no concentration-response relationships were found. All of the CNTs caused an increase in intracellular ROS production compared to unexposed cells (p_trend < 0.05). Results from the long-term exposure showed longer telomere length in cells exposed to MWCNTs compared to unexposed cells (p < 0.01). In conclusion, our results indicated that the included CNTs cause ROS production and DNA strand breaks in FE1-MML cells. Moreover, the MWCNTs, but not the SWCNT, had an impact on telomere length in a long-term exposure scenario.

Simultaneous Cross-Linking and Cross-Polymerization of Enzyme Responsive Polyethylene Glycol Nanogels in Confined Aqueous Droplets for Reduction of Low-Density Lipoprotein Oxidation

A key initiating step in atherosclerosis is the accumulation and retention of apolipoprotein B complexing lipoproteins within the artery walls. In this work, we address this exact initiating mechanism of atherosclerosis, which results from the oxidation of low-density lipoproteins (oxLDL) using therapeutic nanogels. We present the development of biocompatible polyethylene glycol (PEG) cross-linked nanogels formed from a single simultaneous cross-linking and co-polymerization step in water without the requirement for an organic solvent, high temperature, or shear stress. The nanogel synthesis also incorporates in situ noncovalent electrostatically driven template polymerization around an innate anti-inflammatory and anti-oxidizing paraoxonase-1 (PON-1) enzyme payload-the release of which is triggered because of matrix metalloproteinase responsive elements instilled in the PEG cross-linker monomer. The results obtained demonstrate the potential of triggered release of the PON-1 enzyme and its efficacy against the production of ox-LDL, and therefore a reduction in macrophage foam cell and reactive oxygen species formation.

Assessment of reactive oxygen species production and genotoxicity of rare earth mining dust: Implications for public health and mining management

Mining rare earth elements (REEs) can release large amounts of metal(loid)-rich dust, which can pose significant health risks to local residents. However, compared to other types of particulates, toxicity of mining dust has been largely overlooked. To provide experimental evidence on toxicity of REE mine dust, the study assessed the oxidative stress potential and genotoxicity of inhalable particles collected in a REE mining area, and associated toxicological response with source compositions. Both source types (i.e., mine and tailing area) and distances from source (i.e., industrial and residential areas) were considered when selecting the 44 sampling sites. The particle samples contained 2.3-3.5 folds higher concentrations of tested metal(loid)s than background concentrations in soil. Specially, elevated Fe, REEs, Cd, Pb were found. In spite of low cytotoxicity in lung epithelial A549 cells, there was increased cellular ROS production by of particle exposure. Samples with higher mining-originated source contributions (Provenance Index <0.3) had higher cellular ROS production (1.72 fold, 95%CI: 1.66-1.79 fold) than samples with lower mining contributions (1.58 fold, 95%CI: 1.52-1.65 fold). The factors soil (~46%), mine (~22%), and heavy metal (~20%) sources were recognized by source apportionment analysis as the main contributors to cellular ROS production; importantly, mine and heavy metal sources counted more in industrial samples. While samples generated genotoxicity, there were no differences in DNA damage between the location groups of sampling. Collectively, the results indicate that particles in mining areas may cause ROS production and DNA damage in lung cells depending on mine dust. Coupled with the long-range transportation potential of mine dust, safety measures on open pit and dust disposal sites should be adopted.

Inflammation, oxidative stress and genotoxicity responses to biodiesel emissions in cultured mammalian cells and animals

Biodiesel fuels are alternatives to petrodiesel, especially in the transport sector where they have lower carbon footprint. Notwithstanding the environmental benefit, biodiesel fuels may have other toxicological properties than petrodiesel. Particulate matter (PM) from petrodiesel causes cancer in the lung as a consequence of delivery of genotoxic polycyclic aromatic hydrocarbons, oxidative stress and inflammation. We have reviewed articles from 2002 to 2019 (50% of the articles since 2015) that have described toxicological effects in terms of genotoxicity, oxidative stress and inflammation of biodiesel exhaust exposure in humans, animals and cell cultures. The studies have assessed first generation biodiesel from different feedstock (e.g. rapeseed and soy), certain second generation fuels (e.g. waste oil), and hydrogenated vegetable oil. It is not possible to rank the potency of toxicological effects of specific biodiesel fuels. However, exposure to biodiesel exhaust causes oxidative stress, inflammation and genotoxicity in cell cultures. Three studies in animals have not indicated genotoxicity in lung tissue. The database on oxidative stress and inflammation in animal studies is larger (13 studies); ten studies have reported increased levels of oxidative stress biomarkers or inflammation, although the effects have been modest in most studies. The cell culture and animal studies have not consistently shown a different potency in effect between biodiesel and petrodiesel exhausts. Both increased and decreased potency have been reported, which might be due to differences in feedstock or combustion conditions. In conclusion, combustion products from biodiesel and petrodiesel fuel may evoke similar toxicological effects on genotoxicity, oxidative stress and inflammation.

Effect of combustion-derived particles on genotoxicity and telomere length: A study on human cells and exposed populations

Particulate matter (PM) from combustion processes has been associated with oxidative stress to DNA, whereas effects related to telomere dysfunction are less investigated. We collected air-borne PM from a passenger cabin of a diesel-propelled train and at a training facility for smoke diving exercises. Effects on oxidative stress biomarkers, genotoxicity measured by the comet assay and telomere length in PM-exposed A549 cells were compared with the genotoxicity and telomere length in peripheral blood mononuclear cells (PBMCs) from human volunteers exposed to the same aerosol source. Although elevated levels of DNA strand breaks and oxidatively damaged DNA in terms of Fpg-sensitive sites were observed in PBMCs from exposed humans, the PM collected at same locations did not cause genotoxicity in the comet assay in A549 cells. Nevertheless, A549 cells displayed telomere length shortening after four weeks exposure to PM. This is in line with slightly shorter telomere length in PBMCs from exposed humans, although it was not statistically significant. In conclusion, the results indicate that genotoxic potency measured by the comet assay of PM in A549 cells may not predict genotoxicity in exposed humans, whereas telomere length measurements may be a novel indicator of genotoxic stress in cell cultures and humans.

Breast Milk-Derived Extracellular Vesicles Enriched in Exosomes From Mothers With Type 1 Diabetes Contain Aberrant Levels of microRNAs

The breast milk plays a crucial role in shaping the initial intestinal microbiota and mucosal immunity of the infant. Interestingly, breastfeeding has proven to be protective against the early onset of immune-mediated diseases including type 1 diabetes. Studies have shown that exosomes from human breast milk are enriched in immune-modulating miRNAs suggesting that exosomal miRNAs (exomiRs) transferred to the infant could play a critical role in the development of the infant's immune system. We extracted exomiRs from breast milk of 52 lactating mothers (26 mothers with type 1 diabetes and 26 healthy mothers), to identify any differences in the exomiR content between the two groups. Small RNA-sequencing was performed to identify known and novel miRNAs in both groups. A total of 631 exomiRs were detected by small RNA sequencing including immune-related miRNAs such as hsa-let-7c, hsa-miR-21, hsa-miR-34a, hsa-miR-146b, and hsa-miR-200b. In addition, ~200 novel miRNAs were identified in both type 1 diabetes and control samples. Among the known miRNAs, nine exomiR's were found differentially expressed in mothers with type 1 diabetes compared to healthy mothers. The highly up-regulated miRNAs, hsa-miR-4497, and hsa-miR-3178, increased lipopolysaccharide-induced expression and secretion of tumor necrosis factor α (TNFα) in human monocytes. The up-regulated miRNA target genes were significantly enriched for longevity-regulating pathways and FoxO signaling. Our findings suggest a role of breast milk-derived exomiRs in modulating the infant's immune system.

Health effects of exposure to diesel exhaust in diesel-powered trains

BACKGROUND

Short-term controlled exposure to diesel exhaust (DE) in chamber studies have shown mixed results on lung and systemic effects. There is a paucity of studies on well-characterized real-life DE exposure in humans. In the present study, 29 healthy volunteers were exposed to DE while sitting as passengers in diesel-powered trains. Exposure in electric trains was used as control scenario. Each train scenario consisted of three consecutive days (6 h/day) ending with biomarker samplings.

RESULTS

Combustion-derived air pollutants were considerably higher in the passenger carriages of diesel trains compared with electric trains. The concentrations of black carbon and ultrafine particles were 8.5 μg/m³ and 1.2-1.8 × 10⁵ particles/cm³ higher, respectively, in diesel as compared to electric trains. Net increases of NOx and NO₂ concentrations were 317 μg/m³ and 36 μg/m³. Exposure to DE was associated with reduced lung function and increased levels of DNA strand breaks in peripheral blood mononuclear cells (PBMCs), whereas there were unaltered levels of oxidatively damaged DNA, soluble cell adhesion molecules, acute phase proteins in blood and urinary excretion of metabolites of polycyclic aromatic hydrocarbons. Also the microvascular function was unaltered. An increase in the low frequency of heart rate variability measures was observed, whereas time-domain measures were unaltered.

CONCLUSION

Exposure to DE inside diesel-powered trains for 3 days was associated with reduced lung function and systemic effects in terms of altered heart rate variability and increased levels of DNA strand breaks in PBMCs compared with electric trains.

TRIAL REGISTRATION

ClinicalTrials.Gov ( NCT03104387 ). Registered on March 23rd 2017.

Inhalation of House Dust and Ozone Alters Systemic Levels of Endothelial Progenitor Cells, Oxidative Stress, and Inflammation in Elderly Subjects

Ambient air pollution including ozone and especially particulate matter represents important causes of cardiovascular disease. However, there is limited knowledge on indoor air dust with respect to this risk and the potential interactions between dust and ozone. Here, we exposed 23 healthy elderly subjects for 5.5 h, to either clean air, house dust at 275 µg/m3 (diameter < 2.5 µm), ozone at 100 ppb or combined house dust and ozone in a double-blinded randomized cross-over study. The combined house dust and ozone exposure was associated with a 48% (95% CI 24%-65%) decrease as compared with the clean air exposure, in CD34+KDR+ late endothelial progenitor cells (EPCs) per leukocyte in the blood shortly after exposure, whereas none of the single exposures resulted in a significant effect. The combined exposure also increased reactive oxygen species production capacity in granulocytes and monocytes as well as an up-regulation of interleukin-8 mRNA levels in leukocytes. Ozone alone reduced the gene expression of tumor necrosis factor and C-C motif chemokine ligand 2, while dust alone showed no effects. The combined exposure to house dust and ozone also reduced levels of oxidized purines in DNA consistent with concomitant up-regulation of mRNA of the repair enzyme 8-oxoguanine DNA glycosylase. The reduction in late EPCs can be an indicator of cardiovascular risk caused by the combination of pulmonary oxidative stress induced by ozone and the inflammatory potential of the house dust. These data were corroborated with in vitro findings from exposed human macrophages and endothelial cells.

Exposure to Air Pollution inside Electric and Diesel-Powered Passenger Trains

Diesel-powered trains are used worldwide for passenger transport. The present study aimed to assess air pollution concentrations in passenger cars from diesel and electric trains. Personal exposure monitoring (6-7 h per day) was carried out for 49 days on diesel and 22 days on electric trains. Diesel trains had higher concentrations of all the assessed air pollution components. Average increases (and fold differences) in passenger cars of diesel trains compared with electric trains were for ultrafine particles 212 000 particles/cm³ (35-fold), black carbon 8.3 μg/m³ (6-fold), NO _x 316 μg/m³ (8-fold), NO₂ 38 μg/m³ (3-fold), PM_2.5 34 μg/m³ (2-fold), and benzo( a)pyrene 0.14 ng/m³ (6-fold). From time-series data, the pull and push movement modes, the engine in use, and the distance to the locomotive influenced the concentrations inside the diesel trains. In conclusion, concentrations of all air pollutants were significantly elevated in passenger cars in diesel trains compared to electric trains.

Hepatic Hazard Assessment of Silver Nanoparticle Exposure in Healthy and Chronically Alcohol Fed Mice

Silver (Ag) nanoparticles (NPs) are currently among one of the most widely used nanomaterials. This in turn, implies an increased risk of human and environmental exposure. Alcohol abuse is a global issue with millions of people in the general population affected by the associated adverse effects. The excessive consumption of alcohol is a prominent cause of chronic liver disease which manifest in multiple disorders. In this study, the adverse health effects of Ag NP exposure were investigated in models of alcoholic hepatic disease in vitro and in vivo. The data showed that Ag NP induced hepatic health effects were aggravated in the alcohol pretreated mice in comparison to controls with regards to an organ specific inflammatory response, changes in blood biochemistry, acute phase response and hepatic pathology. In addition, alcoholic disease influenced the organ's ability for recovery post-NP challenge. Additionally, it is demonstrated that the in vivo data correlated well with in vitro findings where ethanol pretreatment of hepatocytes resulted in significantly increased inflammatory response post-Ag NP exposure. To the best of our knowledge this is the first study of its kind to investigate nano-sized material-induced hepatic pathology in models representative of susceptible individuals (those with pre-existing alcohol liver disease) within the population. This is an area of research in the field of nanotoxicology, and in particular with regard to NP risk assessment that is almost entirely overlooked.

Neurotensin, substance P, and insulin enhance cell migration

Neurotensin, substance P, and insulin have been demonstrated to improve wound healing in vivo. However, the mechanism behind their effect is still not fully understood. This study investigates the effects leading to enhanced scratch closure by these peptides in vitro. The skin keratinocyte cell line, HaCaT, was used to test scratch closure effects of the peptides and alterations of cytokine levels. HUVEC cells were used to test the angiogenic effect of the peptides. Furthermore, clinical isolates of Staphylococcus lugdunensis were used to examine the potential antimicrobial activity of each peptide. Our results demonstrate that neurotensin, substance P, and insulin had significant migratory effects in scratch assays were neurotensin had the lowest effect. Furthermore, we investigated use of the peptides in combination. When substance P was used in combination with neurotensin, the cell migratory capacity was decreased, and the peptides showed a negative correlation (r = -0.298, P < .001). Neurotensin and insulin significantly increased levels of monocyte chemoattractant protein-1 (P < .001) secreted from white blood cells, whereas substance P showed a tendency. Interestingly, neurotensin increased the level of monocyte chemoattractant protein-1 significantly compared to substance P (P < .01). Additionally, the peptides decreased TNFα mRNA levels (P < .001) in HaCaT cells, whereas only neurotensin and insulin decreased IL-8 mRNA (P < .001) but had no significant effect on IL-6 mRNA levels. Surprisingly, substance P increased IL-6 mRNA 9-fold (P < .001). Furthermore, we demonstrate that the peptides increased angiogenesis in the HUVEC cells (P < .001). Finally, S. lugdunensis isolates were not susceptible to the peptides. We demonstrate that the peptides worked differently on HaCaT cells, but substance P acted differently than neurotensin on cytokine levels expression as well as on migration of HaCaT cells. On the contrary, neurotensin and insulin worked similarly. All of these aspects are crucial for proper wound healing, and the results suggest multiple mechanisms for wound-healing properties of these peptides.

Hepatic toxicity assessment of cationic liposome exposure in healthy and chronic alcohol fed mice

The utilisation of nanoparticles as the means of targeted delivery of therapeutics and/or imaging agents could greatly enhance the specific transport of biologically active payloads to target tissues while avoiding or reducing undesired side-effects. To allow for this to become a reality, the question of potential toxicological effects needs to be addressed. In the present investigation, a cationic liposome with prospective for medical applications was constructed and thoroughly assessed for any material-induced hepatic adverse effects in vivo − in healthy and alcoholic hepatic disease models and in vitro − (HepG2 cells). The data demonstrated that intravenous injection of liposomes did not cause any significant in vivo hepatic toxicity (inflammation, alterations in blood parameters, anti-oxidant depletion, acute phase response and histopathology) at doses of 200 μg per mouse in either healthy or chronically alcohol fed mice. Additionally, the in vitro material-induced adverse effects (cytotoxicity, inflammation or albumin secretion) were all also minimal. The data from this study demonstrated that the intravenous injection of cationic liposomes does not cause hepatic toxicity. This investigation is important as it investigates the toxicity of a nano-sized material in a model of alcoholic hepatic disease in vitro and in vivo. This is an area of research in the field of nanotoxicology that is currently almost entirely overlooked.

Repair activity of oxidatively damaged DNA and telomere length in human lung epithelial cells after exposure to multi-walled carbon nanotubes

One type of carbon nanotubes (CNTs) (MWCNT-7, from Mitsui) has been classified as probably carcinogenic to humans, however insufficient data does not warrant the same classification for other types of CNTs. Experimental data indicate that CNT exposure can result in oxidative stress and DNA damage in cultured cells, whereas these materials appear to induce low or no mutagenicity. Therefore, the present study aimed to investigate whether in vitro exposure of cultured airway epithelial cells (A549) to multi-walled CNTs (MWCNTs) could increase the DNA repair activity of oxidatively damaged DNA and drive the cells toward replicative senescence, assessed by attrition of telomeres. To investigate this, H₂O₂ and KBrO₃ were used to induce DNA damage in the cells and the effect of pre-exposure to MWCNT tested for a change in repair activity inside the cells or in the extract of treated cells. The effect of MWCNT exposure on telomere length was investigated for concentration and time response. We report a significantly increased repair activity in A549 cells exposed to MWCNTs compared to non-exposed cells, suggesting that DNA repair activity may be influenced by exposure to MWCNTs. The telomere length was decreased at times longer than 24h, but this decrease was not concentration dependent. The results suggest that the seemingly low mutagenicity of CNTs in cultured cells may be associated with an increased DNA repair activity and a replicative senescence, which may counteract the manifestation of DNA lesions to mutations.

In vitro toxicity of cationic micelles and liposomes in cultured human hepatocyte (HepG2) and lung epithelial (A549) cell lines

The aim of this study was to compare the effects of cationic micelle and liposome drug delivery systems on liver and lung cells in a toxicological in vitro screening model, with observations on cytotoxicity and genotoxicity. A screening battery was established for assessment of a broad range of parameters related to adverse effects. Clear concentration response effects were observed related to impairment of mitochondrial function, membrane integrity and oxidative stress markers, but no effect was observed on genotoxicity. The adverse effects were highest for the liposomes. The High Content Screening seems optimal for initial screening of adverse effects, and combined with standard cytotoxicity measurements initial screening can be performed for predictive toxicological screening.

Applications of the comet assay in particle toxicology: air pollution and engineered nanomaterials exposure

Exposure to ambient air particles is associated with elevated levels of DNA strand breaks (SBs) and endonuclease III, formamidopyrimidine DNA glycosylase (FPG) and oxoguanine DNA glycosylase-sensitive sites in cell cultures, animals and humans. In both animals and cell cultures, increases in SB and in oxidatively damaged DNA are seen after exposure to a range of engineered nanomaterials (ENMs), including carbon black, carbon nanotubes, fullerene C60, ZnO, silver and gold. Exposure to TiO2 has generated mixed data with regard to SB and oxidatively damaged DNA in cell cultures. Nanosilica does not seem to be associated with generation of FPG-sensitive sites in cell cultures, while large differences in SB generation between studies have been noted. Single-dose airway exposure to nanosized carbon black and multi-walled carbon nanotubes in animal models seems to be associated with elevated DNA damage levels in lung tissue in comparison to similar exposure to TiO2 and fullerene C60. Oral exposure has been associated with augmented DNA damage levels in cells of internal organs, although the doses have been typically very high. Intraveneous and intraperitoneal injection of ENMs have shown contradictory results dependent on the type of ENM and dose in each set of experiments. In conclusion, the exposure to both combustion-derived particles and ENMs is associated with increased levels of DNA damage in the comet assay. Particle size, composition and crystal structure of ENM are considered important determinants of toxicity, whereas their combined contributions to genotoxicity in the comet assay are yet to be thoroughly investigated.

Automobile diesel exhaust particles induce lipid droplet formation in macrophages in vitro

Exposure to diesel exhaust particles (DEP) has been associated with adverse cardiopulmonary health effects, which may be related to dysregulation of lipid metabolism and formation of macrophage foam cells. In this study, THP-1 derived macrophages were exposed to an automobile generated DEP (A-DEP) for 24h to study lipid droplet formation and possible mechanisms. The results show that A-DEP did not induce cytotoxicity. The production of reactive oxygen species was only significantly increased after exposure for 3h, but not 24h. Intracellular level of reduced glutathione was increased after 24h exposure. These results combined indicate an adaptive response to oxidative stress. Exposure to A-DEP was associated with significantly increased formation of lipid droplets, as well as changes in lysosomal function, assessed as reduced LysoTracker staining. In conclusion, these results indicated that exposure to A-DEP may induce formation of lipid droplets in macrophages in vitro possibly via lysosomal dysfunction.

Monocyte adhesion induced by multi-walled carbon nanotubes and palmitic acid in endothelial cells and alveolar-endothelial co-cultures

Free palmitic acid (PA) is a potential pro-atherogenic stimulus that may aggravate particle-mediated cardiovascular health effects. We hypothesized that the presence of PA can aggravate oxidative stress and endothelial activation induced by multi-walled carbon nanotube (MWCNT) exposure in vitro. We investigated the interaction between direct exposure to MWCNTs and PA on THP-1 monocyte adhesion to human umbilical vein endothelial cells (HUVECs), as well as on indirect exposure in an alveolar-endothelial co-culture model with A549 cells and THP-1-derived macrophages exposed in inserts and the effect measured in the lower chamber on HUVECs and THP-1 cells. The exposure to MWCNTs, including a short (NM400) and long (NM402) type of entangled fibers, was associated with elevated levels of reactive oxygen species as well as a decrease in the intracellular glutathione concentration in HUVEC and A549 monocultures. Both effects were found to be independent of the presence of PA. MWCNT exposure significantly increased THP-1 monocyte adhesion to HUVECs, and co-exposure to PA aggravated the NM400-mediated adhesion but decreased the NM402-mediated adhesion. For the co-cultures, the exposure of A549 cells did not promote THP-1 adhesion to HUVECs in the lower chamber. When THP-1 macrophages were present on the cell culture inserts, there was a modest increase in the adhesion and an increase in interleukin-6 and interleukin-8 levels in the lower chamber whereas no tumor necrosis factor was detected. Overall, this study showed that direct exposure of HUVECs to MWCNTs was associated with oxidative stress and monocyte adhesion and the presence of PA increased the adhesion when exposed to NM400.

Measurement of oxidative damage to DNA in nanomaterial exposed cells and animals

Increased levels of oxidatively damaged DNA have been documented in studies of metal, metal oxide, carbon-based and ceramic engineered nanomaterials (ENMs). In particular, 8-oxo-7,8-dihydroguanine-2'-deoxyguanosine (8-oxodG) is widely assessed as a DNA nucleobase oxidation product, measured by chromatographic assays, antibody-based methods or the comet assay with DNA repair enzymes. However, spurious oxidation of DNA has been a problem in certain studies applying chromatographic assays, yielding high baseline levels of 8-oxodG. Antibody-based assays detect high 8-oxodG baseline levels, related to cross-reactivity with other molecules in cells. This review provides an overview of efforts to reliably detect oxidatively damaged DNA and a critical assessment of the published studies on DNA damage levels. Animal studies with high baseline levels of oxidatively damaged DNA are more likely to show positive associations between exposure to ENMs and oxidized DNA in tissue than studies showing acceptable baseline levels (odds ratio = 12.1, 95% confidence interval: 1.2-124). Nevertheless, reliable studies indicate that intratracheal instillation of nanosized carbon black is associated with increased levels of oxidatively damaged DNA in lung tissue. Oral exposure to nanosized carbon black, TiO2 , carbon nanotubes and ZnO is associated with elevated levels of oxidatively damaged DNA in tissues. These observations are supported by cell culture studies showing concentration-dependent associations between ENM exposure and oxidatively damaged DNA measured by the comet assay. Cell culture studies show relatively high variation in the ability of ENMs to oxidatively damage DNA; hence, it is currently impossible to group ENMs according to their DNA damaging potential.

Polyethylenimine architecture-dependent metabolic imprints and perturbation of cellular redox homeostasis

Polyethylenimines (PEIs) are among the most efficient polycationic non-viral transfectants. PEI architecture and size not only modulate transfection efficiency, but also cytotoxicity. However, the underlying mechanisms of PEI-induced multifaceted cell damage and death are largely unknown. Here, we demonstrate that the central mechanisms of PEI architecture- and size-dependent perturbations of integrated cellular metabolomics involve destabilization of plasma membrane and mitochondrial membranes with consequences on mitochondrial oxidative phosphorylation (OXPHOS), glycolytic flux and redox homeostasis that ultimately modulate cell death. In comparison to linear PEI, the branched architectures induced greater plasma membrane destabilization and were more detrimental to glycolytic activity and OXPHOS capacity as well as being a more potent inhibitor of the cytochrome c oxidase. Accordingly, the branched architectures caused a greater lactate dehydrogenase (LDH) and ATP depletion, activated AMP kinase (AMPK) and disturbed redox homeostasis through diminished availability of nicotinamide adenine dinucleotide phosphate (NADPH), reduced antioxidant capacity of glutathione (GSH) and increased burden of reactive oxygen species (ROS). The differences in metabolic and redox imprints were further reflected in the transfection performance of the polycations, but co-treatment with the GSH precursor N-acetyl-cysteine (NAC) counteracted redox dysregulation and increased the number of viable transfected cells. Integrated biomembrane integrity and metabolomic analysis provides a rapid approach for mechanistic understanding of multifactorial polycation-mediated cytotoxicity, and could form the basis for combinatorial throughput platforms for improved design and selection of safer polymeric vectors.

Synergistic effects of zinc oxide nanoparticles and Fatty acids on toxicity to caco-2 cells

Fatty acids exposure may increase sensitivity of intestinal epithelial cells to cytotoxic effects of zinc oxide (ZnO) nanoparticles (NPs). This study evaluated the synergistic effects of ZnO NPs and palmitic acid (PA) or free fatty acids (FFAs) mixture (oleic/PA 2:1) on toxicity to human colon epithelial (Caco-2) cells. The ZnO NPs exposure concentration dependently induced cytotoxicity to Caco-2 cells showing as reduced proliferation and activity measured by 3 different assays. PA exposure induced cytotoxicity, and coexposure to ZnO NPs and PA showed the largest cytotoxic effects. The presence of FFAs mixture did not affect the ZnO NPs-induced cytotoxicity. Filtration of freshly prepared suspension of NPs through a 0.45-µm pore size membrane significantly reduced the cytotoxicity, indicating a role of concentration or size of particles in cytotoxic effects. The ZnO NPs and PA coexposure induced production of mitochondrial reactive oxygen species (mROS) but not intracellular ROS production, whereas FFAs mixture exposure did not induce mROS and inhibited intracellular ROS. Both ZnO NPs and fatty acids (PA and FFAs mixture) promoted lysosomal destabilization, which was not correlated with cytotoxicity. These results indicated that PA can enhance ZnO NPs-induced cytotoxicity probably by the augmentation of mROS production, whereas FFAs mixture did not affect ROS production. Synergistic effects between ZnO NPs and fatty acids may be important when considering NPs toxicity via oral exposure.

Hepatic toxicology following single and multiple exposure of engineered nanomaterials utilising a novel primary human 3D liver microtissue model

Background

The liver has a crucial role in metabolic homeostasis as well as being the principal detoxification centre of the body, removing xenobiotics and waste products which could potentially include some nanomaterials (NM). With the ever increasing public and occupational exposure associated with accumulative production of nanomaterials, there is an urgent need to consider the possibility of detrimental health consequences of engineered NM exposure. It has been shown that exposure via inhalation, intratracheal instillation or ingestion can result in NM translocation to the liver. Traditional in vitro or ex vivo hepatic nanotoxicology models are often limiting and/or troublesome (i.e. reduced metabolism enzymes, lacking important cell populations, unstable with very high variability, etc.).

Methods

In order to rectify these issues and for the very first time we have utilised a 3D human liver microtissue model to investigate the toxicological effects associated with a single or multiple exposure of a panel of engineered NMs (Ag, ZnO, MWCNT and a positively charged TiO₂).

Results

Here we demonstrate that the repeated exposure of the NMs is more damaging to the liver tissue as in comparison to a single exposure with the adverse effects more significant following treatment with the Ag and ZnO as compared with the TiO₂ and MWCNT NMs (in terms of cytotoxicity, cytokine secretion, lipid peroxidation and genotoxicity).

Conclusions

Overall, this study demonstrates that the human microtissue model utilised herein is an excellent candidate for replacement of traditional in vitro single cell hepatic models and further progression of liver nanotoxicology.

Carbon black nanoparticles promote endothelial activation and lipid accumulation in macrophages independently of intracellular ROS production

Exposure to nanoparticles (NPs) may cause vascular effects including endothelial dysfunction and foam cell formation, with oxidative stress and inflammation as supposed central mechanisms. We investigated oxidative stress, endothelial dysfunction and lipid accumulation caused by nano-sized carbon black (CB) exposure in cultured human umbilical vein endothelial cells (HUVECs), THP-1 (monocytes) and THP-1 derived macrophages (THP-1a). The proliferation of HUVECs or co-cultures of HUVECs and THP-1 cells were unaffected by CB exposure, whereas there was increased cytotoxicity, assessed by the LDH and WST-1 assays, especially in THP-1 and THP-1a cells. The CB exposure decreased the glutathione (GSH) content in THP-1 and THP-1a cells, whereas GSH was increased in HUVECs. The reactive oxygen species (ROS) production was increased in all cell types after CB exposure. A reduction of the intracellular GSH concentration by buthionine sulfoximine (BSO) pre-treatment further increased the CB-induced ROS production in THP-1 cells and HUVECs. The expression of adhesion molecules ICAM-1 and VCAM-1, but not adhesion of THP-1 to HUVECs or culture dishes, was elevated by CB exposure, whereas these effects were unaffected by BSO pre-treatment. qRT-PCR showed increased VCAM1 expression, but no change in GCLM and HMOX1 expression in CB-exposed HUVECs. Pre-exposure to CB induced lipid accumulation in THP-1a cells, which was not affected by the presence of the antioxidant N-acetylcysteine. In addition, the concentrations of CB to induce lipid accumulation were lower than the concentrations to promote intracellular ROS production in THP-1a cells. In conclusion, exposure to nano-sized CB induced endothelial dysfunction and foam cell formation, which was not dependent on intracellular ROS production.

In vivo toxicity of cationic micelles and liposomes

This study investigated toxicity of nanocarriers comprised of cationic polymer and lipid components often used in gene and drug delivery, formulated as cationic micelles and liposomes. Rats were injected intravenously with 10, 25 or 100 mg/kg and sacrificed after 24 or 48 h, or 24 h after the last of three intravenous injections of 100 mg/kg every other day. Histological evaluation of liver, lung and spleen, clinical chemistry parameters, and hematology indicated little effect of treatment. DNA strand breaks were increased in the lung and spleen. Further, in the dose response study we found unaltered expression levels of genes in the antioxidant response (HMOX1) and repair of oxidized nucleobases (OGG1), whereas expression levels of cytokines (IL6, CXCL2 and CCL2) were elevated in lung, spleen or liver. The results indicate that assessment of genotoxicity and gene expression add information on toxicity of nanocarriers, which is not obtained by histology and hematology.

FROM THE CLINICAL EDITOR

This study investigates the toxicity of cationic micelles and liposomes utilized as nanocarriers in gene and drug delivery, demonstrating its effects on the lungs, spleen and liver.

Oxidatively damaged DNA in animals exposed to particles

Exposure to combustion-derived particles, quartz and asbestos is associated with increased levels of oxidized and mutagenic DNA lesions. The aim of this survey was to critically assess the measurements of oxidatively damaged DNA as marker of particle-induced genotoxicity in animal tissues. Publications based on non-optimal assays of 8-oxo-7,8-dihydroguanine by antibodies and/or unrealistically high levels of 8-oxo-7,8-dihydroguanine (suggesting experimental problems due to spurious oxidation of DNA) reported more induction of DNA damage after exposure to particles than did the publications based on optimal methods. The majority of studies have used single intracavitary administration or inhalation with dose rates exceeding the pulmonary overload threshold, resulting in cytotoxicity and inflammation. It is unclear whether this is relevant for the much lower human exposure levels. Still, there was linear dose-response relationship for 8-oxo-7,8-dihydroguanine in lung tissue without obvious signs of a threshold. The dose-response function was also dependent on chemical composition and other characteristics of the administered particles, whereas dependence on species and strain could not be equivocally determined. Roles of cytotoxicity or inflammation for oxidatively induced DNA damage could not be documented or refuted. Studies on exposure to particles in the gastrointestinal tract showed consistently increased levels of 8-oxo-7,8-dihydroguanine in the liver. Collectively, there is evidence from animal experimental models that both pulmonary and gastrointestinal tract exposure to particles are associated with elevated levels of oxidatively damaged DNA in the lung and internal organs. However, there is a paucity of studies on pulmonary exposure to low doses of particles that are relevant for hazard/risk assessment.