Emo, JA; Bennett, JA; Bauer, SM; Meednu, N; Rezaee, F; Oberdorster, G; Rangasamy, T; Georas, S
Introduction: Exposure to ambient particulate matter (PM) is increasingly linked with both asthma incidence and severity. Mechanisms by which PM increases risks of developing asthma are not known, but may involve the ability of inhaled PM to act as an inhaled adjuvant. PM induces oxidative stress in its target cells, which is counteracted by genes induced by the antioxidant transcription factor nuclear erythroid related factor 2 (Nrf2). We used a mouse model to test the hypothesis that Nrf2 protected mice from the adjuvant effects of inhaled PM.
Methods: Wild-type (WT) and Nrf2 gene-targeted knock-out (KO) mice on the Balb/c background were exposed to 100 μg of ovalbumin (Ova, Grade V, Sigma) in 50 microliters sterile saline alone or together with an aqueous slurry of PM from outdoor Baltimore air (60 μg) on days 0 and 6 by oropharyngeal aspiration (sensitization). On day 13, mice were exposed to 1% Ova aerosol alone (challenge), and then sacrificed on day 15 for bronchoalveolar lavage (BAL) cell counts, differentials, and histologic analysis of lungs. The PM used in these studies has been extensively characterized (J All Clin Immunol 119:488). Animals were sensitized, challenged analyzed in a blinded fashion.
Results: The numbers of BAL cells recovered from WT and Nrf2 KO mice were not significantly different at baseline or following sensitization with Ova alone. In contrast, BAL cell counts were significantly higher in Nrf2 KO mice sensitized with Ova plus PM as adjuvant, and challenged once with Ova, compared to WT controls (7.6±1.6 vs. 5.5±1.1 x 105 total cells, mean±SEM, n=8, p=0.02). As expected based on a single Ova challenge, BAL cell differentials revealed only a modest degree of inflammation in both strains, with a tendency towards higher percentages of neutrophils in Nrf2 KO compared to WT littermates (2.9 vs. 1.3 %, mean±SEM, n=8, p=0.2), and lung tissue inflammation was only modestly enhanced in both strains using this protocol.
Conclusions: Nrf2 protects mice from the inhaled adjuvant effects of PM during sensitization with a model allergen. Future studies using repeated allergen challenge and investigating the molecular and cellular mechanisms involved should enhance our understanding of the link between PM and asthma incidence. Nrf2 may be a novel susceptibility gene for asthma.
This abstract is funded by: NIH HL071933, Pilot Project funding from the Rochester EPA PM Center.
