In search of the most relevant parameter for quantifying lung inflammatory response to nanoparticle exposure: particle number, surface area, or what?

[Health effects of nanoparticles and nanomaterials (II) methods for measurement of nanoparticles and their presence in the air]

The mass concentrations of airborne particles in the atmospheric, indoor, and industrial environments are regulated by air quality standards. Epidemiological studies show that there are significant positive correlations between particle mass concentrations and adverse health effects. In this context nanoparticles in the air, which are defined as particles with a diameter (Dp) of less than 50 nm or 100 nm for engineered ones, are gaining increasing attention despite a small contribution to the mass of total airborn particles. Contrary to the mass concentration the number concentrations of atmospheric nanoparticles are quite high in most cases. Moreover there is limited toxicological information on nanoparticles, although the deposition rate of nanoparticles in the respiratory region is known to be relatively high. Accordingly there are a lot of debates about what metric is best to depict the size distribution of nanoparticles, number, surface area, or mass. In this paper, we report methods for measurement of nanoparticles on the basis of those metrics. We also report sources of nanoparticle in the environment and occupational settings. The high number concentration of nanoparticles of 20-30 nm modal diameters have been documented at roadsides. Diesel-powered vehicles are major sources of those nanoparticles in the urban atmosphere. Engineered nanoparticles generate in some occupational settings in the handling processes such as bagging and cleaning with vacuum cleaners.

Nominal and effective dosimetry of silica nanoparticles in cytotoxicity assays

Because of their small size and large specific surface area (SA), insoluble nanoparticles are almost not affected by the gravitational force and are generally formulated in stable suspensions or sols. This raises, however, a potential difficulty in in vitro assay systems in which cells adhering to the bottom of a culture vessel may not be exposed to the majority of nanoparticles in suspension. J. G. Teeguarden et al., 2007, Toxicol. Sci. 95, 300-312 have recently addressed this issue theoretically, emphasizing the need to characterize the effective dose (mass or number or SA dose of particles that affect the cells) which, according to their model based on sedimentation and gravitation forces, might only represent a very small fraction of the nominal dose. We hypothesized, in contrast, that because of convection forces that usually develop in sols, the majority of the particles may reach the target cells and exert their potential toxicity. To address this issue, we exposed three different cell lines (A549 epithelial cells, EAHY926 endothelial cells, and J774 monocyte-macrophages) to a monodisperse suspension of Stöber silica nanoparticles (SNP) in three different laboratories. Four different end points (lacticodehydrogenase [LDH] release, LDH cell content, tetrazolium salt (MTT), and crystal violet staining) were used to assess the cell response to nanoparticles. We found, in all cell lines and for all end points, that the cellular response was determined by the total mass/number/SA of particles as well as their concentration. Practically, for a given volume of dispersion, both parameters are of course intimately interdependent. We conclude that the nominal dose remains the most appropriate metric for in vitro toxicity testing of insoluble SNP dispersed in aqueous medium. This observation has important bearings on the experimental design and the interpretation of in vitro toxicological studies with nanoparticles.

[Health effects of nanoparticles and nanomaterials (I) recent oveview of health effects of nanoparticles]

Recently, the impact of nanoparticles and nanomaterials on health and environmental effects has become a big issue. There are two types of nanoparticles to be considered in hygiene science; environmental nanopartcles emitted from automobiles and manufactured nanoparticles such as fullerenes, carbon nanobutbes, and ultrafine metals/metal oxides. These very fine particles are potentially health threatening, because they are supposed to be highly permeable in the lung and skin tissues and small enough to evade phagocytosis by reticuloendothelial system. The dose metrics are critical to evaluate toxicity of nanoparticles, because the surface-based rather than weight-based concentration has been reported to correlate well with effects and endopoints of nanoparticles. Research on environmental nanoparticles should be done as a part of research for fine particles or particulate materials less than 2.5 microm (PM2.5). Variety of materials, such as carbon, metals, and metal oxides, are included in manufactured nanoparticles. Moreover, some of manomaterials are generated in the shape of fiber and sheet. Thus, we should focus more on nano-specific biological interactions and tissue permeability to investigate health effects of manufactured nanoparticles. In this report trend in health effects of nanoparticles is overviewed.

Cytotoxicity and inflammatory potential of soot particles of low-emission diesel engines

We evaluated, in vitro, the inflammatory and cytotoxic potential of soot particles from current low-emission (Euro IV) diesel engines toward human peripheral blood monocyte-derived macrophage cells. The result is surprising. At the same mass concentration, soot particles produced under low-emission conditions exhibit a much highertoxic and inflammatory potential than particles from an old diesel engine operating under black smoke conditions. This effect is assigned to the defective surface structure of Euro IV diesel soot, rendering it highly active. Our findings indicate that the reduction of soot emission in terms of mass does not automatically lead to a reduction of the toxic effects toward humans when the structure and functionality of the soot is changed, and thereby the biological accessibility and inflammatory potential of soot is increased.

Differential binding of cytokines to environmentally relevant particles: a possible source for misinterpretation of in vitro results?

Inflammation is considered as a key event in adverse health effects associated with exposure to ambient particulate matter. The inflammatory potential of particles is often compared using in vitro cell systems, where the particle-induced release of pro-inflammatory cytokines is measured. A major concern in these assays is the potential of particles to bind cytokines, which may lead to an underestimation of the inflammatory potential. We therefore investigated the cytokine binding to a selection of particle samples, including particles collected from outdoor sources (wood combustion, traffic) and particles commonly used to model environmental sources (ultrafine carbon black, diesel, quartz), for a range of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6, IL-8). Furthermore, the influence of serum proteins and particle- and cytokine concentrations on the cytokine binding was studied. Cytokines primarily bound to carbonaceous particles (up to 85%), not to mineral particles. Furthermore, depending on the type of cytokine, the cytokine binding could be reduced partly or completely by adding serum proteins to the cell growth medium or particle suspensions. Based on these observations we recommend either to adjust culturing and exposure conditions to prevent cytokine binding, or to adjust the measured cytokine release by application of correction factors obtained from cytokine binding experiments.

Considerations on occupational medical surveillance in employees handling nanoparticles

OBJECTIVES

The use of engineered nanoparticles not only offers new technical perspectives but also raises questions regarding possible health aspects for producers and users. Nanoparticles may, just by virtue of their size, exert biological effects unrelated to the chemicals they are composed of. These considerations, and results from experimental animal studies suggesting that engineered nanomaterials may pose a health hazard to employees, all underscore the need for preventive measures. In this context, the need for, the feasibility, and the appropriateness of targeted occupational medical surveillance are currently subject to debate.

METHODS

We compared established concepts for the development of occupational medical surveillance programs to existing knowledge on exposures in workplaces and on health effects of nanomaterials.

RESULTS

A variety of potential effect parameters have been proposed for medical surveillance of exposed personnel, such as heart rate variability, blood-clotting parameters, pro-inflammatory cytokines, etc. None of these parameters are specific, most are not validated as individual health risk indicators, and some require sophisticated equipment not routinely available. Against this background, BASF currently puts specific weight on risk assessment and exposure control in workplaces. Particle emissions are primarily avoided by manufacturing in closed systems or using effective extraction systems. Appropriate personal protective equipment has been defined for such operations where an exposure potential cannot be excluded.

CONCLUSIONS

While there is presently no evidence-based foundation for "nano-specific" occupational medical screening, one can perform general medical screening with methods targeted at some of the health outcomes under discussion. The results of such examinations can provide a basis for future epidemiologic studies. Therefore, the establishment of exposure registries to enable the conduct of large-scale multi-centric prospective epidemiologic studies is recommended.

What do we (need to) know about the kinetic properties of nanoparticles in the body?

Nowadays the development and applications of nanotechnology are of major importance in both industrial and consumer areas. However, the knowledge on human exposure and possible toxicity of nanotechnology products is limited. To understand the mechanism of toxicity, thorough knowledge of the toxicokinetic properties of nanoparticles is warranted. There is a need for information on the absorption, distribution, metabolism and excretion (ADME) of nanoparticles and validated detection methods of these man-made nanoparticles. Determination of the ADME properties of nanoparticles requires specialised detection methods in different biological matrices (e.g. blood and organs). In this paper, the current knowledge on the kinetic properties of nanoparticles is reviewed. Moreover, knowledge gaps from a kinetic point of view (detection, dose, ADME processes) are identified.