Variability in Bioreactivity Linked to Changes in Size and Zeta Potential of Diesel Exhaust Particles in Human Immune Cells

Abstract

Acting as fuel combustion catalysts to increase fuel economy, cerium dioxide (ceria, CeO2) nanoparticles have been used in Europe as diesel fuel additives (Envirox™). We attempted to examine the effects of particles emitted from a diesel engine burning either diesel (diesel exhaust particles, DEP) or diesel doped with various concentrations of CeO2 (DEP-Env) on innate immune responses in THP-1 and primary human peripheral blood mononuclear cells (PBMC). Batches of DEP and DEP-Env were obtained on three separate occasions using identical collection and extraction protocols with the aim of determining the reproducibility of particles generated at different times. However, we observed significant differences in size and surface charge (zeta potential) of the DEP and DEP-Env across the three batches. We also observed that exposure of THP-1 cells and PBMC to identical concentrations of DEP and DEP-Env from the three batches resulted in statistically significant differences in bioreactivity as determined by IL-1β, TNF-α, IL-6, IFN-γ, and IL-12p40 mRNA (by qRT-PCR) and protein expression (by ELISPOT assays). Importantly, bioreactivity was noted in very tight ranges of DEP size (60 to 120 nm) and zeta potential (−37 to −41 mV). Thus, these physical properties of DEP and DEP-Env were found to be the primary determinants of the bioreactivity measured in this study. Our findings also point to the potential risk of over- or under- estimation of expected bioreactivity effects (and by inference of public health risks) from bulk DEP use without taking into account potential batch-to-batch variations in physical (and possibly chemical) properties.

Air Pollution Particulate Matter Alters Antimycobacterial Respiratory Epithelium Innate Immunity

“…Interestingly, as shown here, PM 10 , which contained much less endotoxin than PM 2.5 , inhibited HBD-2 production in all concentrations used (Fig. 2), suggesting that the size and composition of PM components influence biological responses in human cells (46).…”

Effects of a nanoceria fuel additive on the physicochemical properties of diesel exhaust particles

“…22 The current study did not provide clear evidence that DEP toxicity would be altered via altered zeta potential due to the addition of Envirox TM in the fuel.…”

“…Given that these physicochemical properties are important determinants of particle toxicity, it is anticipated that using nanoceria additives to diesel fuel would alter the toxicity of the emitted DEP in various ways. 22,40,43 For example, the increased organized structure and decreased oxidative potential might decrease the bioreactivity of DEP, while reduced particle size may increase the diffusion rate of particles within and across the lung and decrease clearance rate in the lung, thereby increasing overall bioreactivity and toxicity. 27,44 Hence, the impact on the overall DEP bioreactivity and toxicity is hard to predict solely based on physiochemical property changes observed in the present study.…”

“…This dilution and sonication procedure was appropriate for making DEP suspension solutions for toxicological testing. 15 The samples were placed in the center of the sonicator to get maximal sonication power. For each batch of the DEP (0x, 0.1x, 1x, and 10x), particles in 3 sets of the suspensions were measured in parallel to obtain averages and standard deviations.…”

“…Sarkar and colleagues also reported a similar tendency with zeta potential changing from -40.3 mV to -31 mV as Envirox TM concentration increased from 0x to10x. 22 Several factors including media pH, particle size, morphology, and composition may affect zeta potentials. 23 In this study all of these factors besides media pH were changed to different degrees, which made the trend in zeta potential as a function of Envirox TM concentration not as clear and not consistent even across the two replicate samples.…”