Nanomaterial exposure, toxicity, and impact on human health.

The use of engineered nanomaterials (ENM) has grown after the turn of the 21st century. Also, the production of ENM has globally grown, and exposure of workers especially via the lungs to ENM has increased. This review tackles with effects of ENM on workers' health because occupational environment is the main source of exposure to ENM. Assessment of exposure to ENM is demanding, and today there are no occupational exposure level (OEL) for ENM. This is partly due to challenges of such measurements, and in part to the unknown causality between ENM metrics and effects. There are also marked gaps in systematic knowledge on ENM hazards. Human health surveys of exposed workers, or human field studies have not identified specific effects of ENM linking them with a specific exposure. There is, however, a consensus that material characteristics such as size, and chemistry influence effects of ENM. Available data suggest that multiwalled carbon nanotubes (MWCNT) affect the immunological system and cause inflammation of the lungs, or signs of asthma whereas carbon nanofibers (CNF) may cause interstitial fibrosis. Metallic and metal oxide nanoparticles together with MWCNT induce genotoxicity, and a given type of MWCNT has been identified as a possible human carcinogen. Currently, lack of understanding of mechanisms of effects of ENM renders assessment of hazards and risks of ENM material-by-material a necessity. The so called "omics" approaches utilizing ENM-induced alterations in gene and protein expression may be useful in the development of a new paradigm for ENM hazard and risk assessment. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

A call for action: Improve reporting of research studies to increase the scientific basis for regulatory decision-making.

This is a call for action to scientific journals to introduce reporting requirements for toxicity and ecotoxicity studies. Such reporting requirements will support the use of peer-reviewed research studies in regulatory decision-making. Moreover, this could improve the reliability and reproducibility of published studies in general and make better use of the resources spent in research.

A theoretical approach for a weighted assessment of the mutagenic potential of nanomaterials.

Several approaches have recently been proposed for predicting the potential hazard and risk to human health of engineered nanomaterials (NMs). Here, we present a theoretical approach to assess the mutagenic potential of NMs, which could be incorporated into risk assessment tools. Following the weight of evidence approach recommended for chemicals, we describe criteria for evaluating and weighting existing literature information, based on current knowledge on the relevance and limitations of genotoxicity and mutagenicity assays used in testing NMs. The relevant assays are then categorized according to the genotoxic events detected in three categories: DNA damage, gene mutations and chromosomal damage - the former weighing lower than the two latter ones, since unrepairable alterations have more weight than those depicting primary DNA damage that can still be repaired. Besides, evidence from in vivo tests are given a higher weight than data coming from in vitro tests, because animal studies can more accurately predict secondary genotoxicity. Although studies conducted according to validated protocols have greater weight, studies that do not comply with conventional test guidelines are also considered, trying to make use of all available information for each NM. A threshold of agreement among studies belonging to the same category is required to consider this category positive or negative for mutagenicity. The final outcome is a statement on the mutagenic potential of the nanoform and the uncertainty of this evaluation. Finally, we discuss new methods and possible improvements in current assays that could be incorporated in future guidelines.

A comparison of REACH-derived no-effect levels for workers with EU indicative occupational exposure limit values and national limit values in Finland.

The purpose of occupational exposure limits values (OELs) is to regulate exposure to chemicals and minimize the risk of health effects at work. National authorities are responsible for the setting and updating of national OELs. In addition, the EU sets indicative occupational exposure limit values (IOELVs), which have to be considered by the Member States. Under the new European legislation on chemicals (REACH), manufacturers and importers are obliged to establish derived no-effect levels (DNELs) for chemicals that are manufactured or imported in quantities >10 tonnes per year. Chemical safety data sheets must report both OELs and the DNEL values, if such have been set. This may cause confusion at workplaces, especially if the values differ from each other. In this study, we explored how EU IOELVs and Finnish national OELs [Haitallisiksi tunnetut pitoisuudet (HTP) values] correlate with worker inhalation DNELs for substances registered under REACH. The long-term DNEL value for workers (inhalation) was identical to the corresponding IOELV for the majority of the substances (64/87 cases). Comparison of DNELs with HTP values revealed that the values were identical or close to each other in 159 cases (49%), whereas the DNEL was considerably higher in 69 cases, and considerably lower in 87 cases. Examples of cases with high differences between Finnish national OELs and DNELs are given. However, as the DNELs were not systematically lower than the OELs, the default assessment factors suggested by REACH technical guidance had obviously not been used in many of the REACH registrations.

Wood dusts induce the production of reactive oxygen species and caspase-3 activity in human bronchial epithelial cells.

Wood dusts are associated with several respiratory symptoms, e.g. impaired lung function and asthma, in exposed workers. However, despite the evidence from epidemiological studies, the underlying mechanisms are not well understood. In the present study, we investigated different wood dusts for their capacity to induce cytotoxicity and production of radical oxygen species (ROS) as well as activation of the apoptotic caspase-3 enzyme in human bronchial epithelial cells (BEAS-2B). Dusts from three different tree species widely used in wood industry were studied; birch and oak represented hardwood species, and pine a common softwood species. All the experiments were carried out in three different concentrations (10, 50, and 500 microg/ml) and the analysis was performed after 0.5, 2, 6, and 24h exposure. All wood dusts studied were cytotoxic to human bronchial epithelial cells in a dose-dependent manner after 2 and 6h treatment. Exposure to pine, birch, or oak dust had a significant stimulating effect on the production of ROS. Also an induction in caspase-3 protease activity, one of the central components of the apoptotic cascade, was seen in BEAS-2B cells after 2 and 6h exposure to each of the wood dusts studied. In summary, we demonstrate that dusts from pine, birch and oak are cytotoxic, able to increase the production of ROS and the apoptotic response in human broncho-epithelial cells in vitro. Thus, our current data suggest oxidative stress by ROS as an important mechanism likely to function in wood dust related pulmonary toxicity although details of the cellular targets and cell-particle interactions remain to be solved. It is though tempting to speculate that redox-regulated transcription factors such as NFkappaB or AP-1 may play a role in this wood dust-evoked process leading to apparently induced apoptosis of target cells.

Polycyclic aromatic hydrocarbon (PAH) metabolizing enzyme activities in human lung, and their inducibility by exposure to naphthalene, phenanthrene, pyrene, chrysene, and benzo(a)pyrene as shown in the rat lung and liver.

In order to survey changes and activities in the polycyclic aromatic hydrocarbon (PAH)-metabolizing enzymes implicated in lung cancer susceptibility studies, we investigated enzyme induction by 2-5-ring-sized 'biomarker' PAHs in rat liver and lung, and the activities in five human lung specimens. Naphthalene, phenanthrene, pyrene, chrysene, and benzo[a]pyrene (BaP) were administered to rats for 3 days (25-128 mg/kg/day) and the responses compared with those of model inducers. PAH treatment increased the CYP1A-catalyzed activity of pyrene 1-hydroxylation and 7-ethoxyresorufin O-deethylation in rat liver by up to 28- and 279-fold, and in rat lung by up to 22- and 51-fold, respectively. 1-Naphthol (hUGT1A6), 1-hydroxypyrene (hUGT1A6/1A9), and entacapone (hUGT1A9) are markers of PAH-glucuronidating human uridine diphosphate-glucuronosyltransferases (UGT). These activities increased up to 6.4-fold in rat liver and up to 1.9-fold in rat lung. NADPH:quinone oxidoreductase 1 (NQO1) and glutathione S-transferase activities increased up to 5.3- and 1.6-fold (liver), and up to 4.4- and 1.4-fold (lung), respectively. CYP1A showed the best liver-to-lung relationship (R (2 )=( )0.90). The inducing efficiency by PAHs differed extensively: control 60-fold), many times greater than the experimental (inducible/constitutive) variation in the rat. Kinetics of 1-hydroxypyrene glucuronidation showed two low-K (m) forms both in rat and human lung. Since the 2-4-ring PAHs (major constituents) were poor enzyme inducers, it appears that the PAH-metabolizing pathways are mainly induced by BaP-type minor constituents. Gene-environmental interactions which magnify polymorphic variability in pulmonary bioactivation/detoxification capacity probably play a key role in individual susceptibility to (or protection against) chemically induced lung cancer. Hence, human exposure to PAH mixtures with high content of BaP-type hydrocarbons confers a potentially higher health risk than PAH mixtures with low content of procarcinogens.

Interactive effects of methyl tertiary-butyl ether (MTBE) and tertiary-amyl methyl ether (TAME), ethanol and some drugs: Triglyceridemia, liver toxicity and induction of CYP (2E1, 2B1) and phase II enzymes in female Wistar rats.

The abilities of the gasoline additives methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME) to cause liver damage following oral administration, dosed alone or in combination with model hepatotoxins, were investigated in the rat. Inducibility of liver drug-metabolizing enzyme activities was also studied. Exposure to these ethers (10-20mmol/kg) for 3 days resulted in hepatomegaly (13-30%) and induction of cytochrome P450 (CYP) activity towards N-nitrosodimethylamine (NDMAD), 7-pentoxyresorufin (PROD), and 7-ethoxyresorufin (EROD). Immunoinhibition assays with monoclonal antibodies showed that the ethers were equipotent as inducers of CYP2E1 activity (2-fold increase) but not of CYP2B1, which was elevated up to 260-fold in TAME-treated rats but only by 20-fold in MTBE rats. A slight or no modifying effect was observed on the NADPH:quinone oxidoreductase (NQO1), glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UGT) activities. Alanine aminotransaminase (ALT) and aspartate aminotransaminase (AST) were elevated in blood plasma after administration of the ethers. No dramatic enhancement of liver damage could be detected by plasma enzyme analysis (ALT, AST, alkaline phosphatase, γ-glutamyltransferase) following ether administration (13.5mmol/kg) to rats pretreated with mildly hepatotoxic dosages of ethanol, pyrazole, phenobarbital, acetaminophen (paracetamol), or 13-cis-retinoic acid (13-cis-RA or isotretinoin). Plasma triglycerides increased in TAME-treated rats (1.7-fold) and in all 13-cis-RA-treated groups (2.1-2.8-fold). The findings that MTBE and TAME exhibited a clear but differential inducing effect on two ether-metabolizing CYP forms (2E1 and 2B1) with no marked effect on phase II activities may reflect the importance of these pathways in vivo. The observation that only TAME by itself induced hypertriglyceridemia while acetaminophen- and 13-cis-RA-induced hypertriglyceridemia were aggravated by both ethers, points to differences in their effects on lipid metabolism. TAME was clearly a more potent CNS depressant than MTBE. There was no marked potentiation of drug/chemical-induced acute liver damage either by MTBE or TAME.

Fumonisin B1-induced apoptosis in neuroblastoma, glioblastoma and hypothalamic cell lines.

Fumonisin B(1) (FB(1)) is a mycotoxin produced by Fusarium verticilliodes, which commonly infects corn across the world. Fusarium fungi may also be found in moisture-damaged buildings. In this study, we investigated the role of apoptosis in the toxicity of FB(1) in four different cell lines. Activation of caspase-3-like protease, DNA fragmentation and expression of p53 and Bcl-2 family proteins were studied in mouse GT1-7 hypothalamic, rat C6 glioblastoma, human U-118MG glioblastoma, and human SH-SY5Y neuroblastoma cells exposed to 0.1-100microM FB(1) for 0-144h. Caspase-3-like protease activity increased in all cell lines, except SH-SY5Y, at 48-144h, and internucleosomal DNA fragmentation occurred in all of the cell lines, pointing to a role for apoptosis in the toxicity of FB(1). However, the expressions of p53 or pro- or antiapoptotic Bcl-2 family proteins (Bax, Bcl-2, Bcl-X(L) and Mcl-1) were not affected in any of the cell lines even after prolonged exposure to FB(1) at high doses. The results of this study, together with the results of our previous studies, provide evidence that FB(1) is a potential neurotoxin, but that the toxicity of FB(1) varies between different cell lines. The sensitivity of these cell lines towards FB(1) is as follows: U-118MG>GT1-7>C6>SH-SY5Y cells. These results are consistent with the assumption that cells of glial origin may be more sensitive towards FB(1) than cells of neural origin.

Oxidative stress induced by fumonisin B1 in continuous human and rodent neural cell cultures.

Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium verticillioides, which is a common infectant of corn and other cereal grains. Of concern to human health is also a possible airborne exposure to FB1-producing strains of F. verticillioides, which may grow in moisture-damaged buildings. In this study, we have characterized oxidative stress-related parameters induced by FB1 in three different neural cell lines, human SH-SY5Y neuroblastoma, rat C6 glioblastoma and mouse GT1-7 hypothalamic cells. The cells were exposed to graded doses of FB1 between 0.1 and 100 microM for 0-144 h after which the production of reactive oxygen species (ROS), lipid peroxidation, intracellular glutathione (GSH) levels and cell viability were measured. FB1 caused a dose-dependent increase of ROS production in C6 glioblastoma and GT1-7 hypothalamic cells but was without an effect in SH-SY5Y cells. Decreased GSH levels, increased MDA-formation, indicative of lipid peroxidation and necrotic cell death were observed in all cell lines after incubation with FB1. These findings indicate that FB1 induces oxidative stress in human, rat and mouse neural cell cultures.

Fumonisin B1-induced toxicity and oxidative damage in U-118MG glioblastoma cells.

The mycotoxin fumonisin B1 (FB1) is produced by Fusarium verticillioides, which commonly infects corn and other agricultural products. Fusarium species are also a frequent finding in moisture-damaged buildings, causing possible human exposure to FB1. FB1 is neurotoxic and carcinogenic in a number of animal species. In this study, we have investigated the effects of FB1 on human U-118MG glioblastoma cells. The production of reactive oxygen species (ROS), lipid peroxidation, intracellular reduced glutathione (GSH) levels, cell viability, caspase-3-like protease activity and DNA fragmentation were studied in cells exposed to 0.01-100 microM FB1 for 0.5-144 h. FB1 increased lipid peroxidation and the production of ROS in U-118MG cells, showing significant effects after culture times from 48 to 144 h at dose levels of 10 or 100 microM FB1. These effects were accompanied by changes in the GSH levels and cell viability, which decreased significantly after incubating the cells for 48-144 h with the toxin. Signs of apoptosis were indicated by increased caspase-3-like protease activity and internucleosomal DNA fragmentation. Thus, oxidative stress and apoptosis may be involved in the neurotoxicity induced by FB1.