Whole-body inhalation of nano-sized carbon black: a surrogate model of military burn pit exposure

Abstract

Objective: Chronic multisymptom illness (CMI) is an idiopathic disease affecting thousands of U.S. Veterans exposed to open-air burn pits emitting aerosolized particulate matter (PM) while serving in Central and Southwest Asia and Africa. Exposure to burn pit PM can result in profound biologic consequences including chronic fatigue, impaired cognition, and respiratory diseases. Dysregulated or unresolved inflammation is a possible underlying mechanism for CMI onset. We describe a rat model of whole-body inhalation exposure using carbon black nanoparticles (CB) as a surrogate for military burn pit-related exposure. Using this model, we measured biomarkers of inflammation in multiple tissues.

Results: Male Sprague Dawley rats were exposed to CB aerosols by whole body inhalation (6 ± 0.83 mg/m³). Proinflammatory biomarkers were measured in multiple tissues including arteries, brain, lung, and plasma. Biomarkers of cardiovascular injury were also assayed in plasma. CB inhalation exposure increased CMI-related proinflammatory biomarkers such as IFN-γ and TNFα in multiple tissue samples. CB exposure also induced cardiovascular injury markers (adiponectin, MCP1, sE-Selectin, sICam-1 and TIMP1) in plasma. These findings support the validity of our animal exposure model for studies of burn pit-induced CMI. Future studies will model more complex toxicant mixtures as documented at multiple burn pit sites.

Keywords: Burn Pit Exposure; Carbon Black; Chronic Multisymptom Illness; Cytokines; Environmental Exposure; Inflammation; Inhalation toxicology; Nanoparticle.

Fig. 1

CB nanoparticle characterization and deposition in lung. A CB particle characterization table and real-time mass concentration measurements (mg/m³) of the CB aerosols during an inhalation exposure for 6 h for a target concentration of 6 mg/m³. Data represent an average of three exposures. B Particle size distribution of the carbon black aerosol measured from the exposure chamber using a high resolution electrical low-pressure impactor (ELPI +). A log-normal fit of the distributions resulted in a count median diameter (CMD) of 67 nm with a geometric standard deviation (GSD) of 2.13 nm. Inset: representative image of CB particles. Scale bar 500 nm. C Particle size distribution of the CB aerosol measured from the exposure chamber with a cascade impactor (Nano-MOUDI). A log-normal fit of the distribution resulted in a mass median aerodynamic diameter of 975 nm with a GSD of 2.47 nm. D TEM and SEM images of CB agglomerate collected on a TEM grid from the exposure 6 mg/m³ chamber

Fig. 2

Pro-inflammatory and vascular injury biomarker analysis in rat tissues. Changes in tissue biomarkers of inflammation between control (white bars) and CB6 (grey bars) exposed rats are shown for all 4 tissues; vascular injury biomarkers are shown for plasma. A Artery. B Brain. C Lung. D Plasma. Data are represented as means ± SEM. Significance is denoted as: * p < 0.05, ** p < 0.005, *** p < 0.0005, ****p < 0.0001; ns, not significant at threshold of p < 0.05