Cytokine responses of human lung cells (BEAS-2B) treated with micron-sized and nanoparticles of metal oxides compared to soil dusts

Interactions of nanoparticles with pulmonary structures and cellular responses

Combustion-derived and synthetic nano-sized particles (NSP) have gained considerable interest among pulmonary researchers and clinicians for two main reasons. 1) Inhalation exposure to combustion-derived NSP was associated with increased pulmonary and cardiovascular morbidity and mortality as suggested by epidemiological studies. Experimental evidence has provided a mechanistic picture of the adverse health effects associated with inhalation of combustion-derived and synthetic NSP. 2) The toxicological potential of NSP contrasts with the potential application of synthetic NSP in technological as well as medicinal settings, with the latter including the use of NSP as diagnostics or therapeutics. To shed light on this paradox, this article aims to highlight recent findings about the interaction of inhaled NSP with the structures of the respiratory tract including surfactant, alveolar macrophages, and epithelial cells. Cellular responses to NSP exposure include the generation of reactive oxygen species and the induction of an inflammatory response. Furthermore, this review places special emphasis on methodological differences between experimental studies and the caveats associated with the dose metrics and points out ways to overcome inherent methodological problems.

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.

Effects of cell type and culture media on Interleukin-6 secretion in response to environmental particles

Cultured lung cells provide an alternative to animal exposures for comparing the effects of different types of air pollution particles. Studies of particulate matter in vitro have reported proinflammatory cytokine signaling in response to many types of environmental particles, but there have been few studies comparing identical treatments in multiple cell types or identical cells with alternative cell culture protocols. We compared soil-derived, diesel, coal fly ash, titanium dioxide, and kaolin particles along with soluble vanadium and lipopolysaccharide, applied to airway-derived cells grown in submerged culture. Cell types included A549, BEAS-2B, RAW 264.7, and primary macrophages. The cell culture models (specific combinations of cell types and culture conditions) were reproducibly different in the cytokine signaling responses to the suite of treatments. Further, Interleukin-6 (IL-6) response to the treatments changed when the same cells, BEAS-2B, were grown in KGM versus LHC-9 media or in media containing bovine serum. The effect of changing media composition was reversible over multiple changes of media type. Other variables tested included culture well size and degree of confluence. The observation that sensitivity of a cell type to environmental agonists can be manipulated by modifying culture conditions suggests a novel approach for studying biochemical mechanisms of particle toxicity.

Neuropeptide processing in regional brain slices: effect of conformation and sequence

The central enzymatic stability of des-enkephalin-gamma-endorphin and its synthetic analogs [cycloN alpha 6, C delta 11]beta-endorphin-[6-17] and [Pro7, Lys(Ac)9]-beta-endorphin[6-17] was studied in vitro using a newly developed, regionally dissected rat brain slice, time course incubation procedure. Tissue slice viability was estimated as the ability of the brain slice to take up or release gamma-[3H]aminobutyric acid after high K+ stimulation. Results demonstrated stability of uptake/release up to 5 hr of incubation, suggesting tissue viability over this period. The estimated half-life of peptides based on the results obtained in our incubation protocol suggest that the peptides studied are metabolized at different rates in the individual brain regions tested. A good correlation exists between the high enzyme activity of neutral endopeptidase (EC 3.4.24.11) and the rapid degradation of des-enkephalin-gamma-endorphin and [cycloN alpha 6, C delata 11]beta-endorphin-[6-17] in caudate putamen. Proline substitution combined with lysine acetylation appears to improve resistance to enzymatic metabolism in caudate putamen and hypothalamus. However, cyclization of des-enkephalin-gamma-endorphin forming an amide bond between the alpha-NH2 of the N-terminal threonine and the gamma-COOH of glutamic acid did not improve peptide stability in any brain region tested. The present study has shown that the brain slice technique is a valid and unique approach to study neuropeptide metabolism in small, discrete regions of rat brain where peptides, peptidases and receptors are colocalized and that specific structural modifications can improve peptide stability.