Organic dust, causing both oxidative stress and Nrf2 activation, is phagocytized by bronchial epithelial cells

Abstract

Inhalation of organic dust (OD) from swine confinement facilities leads to pulmonary inflammation, airway hyperresponsiveness, and oxidative stress. In mice, pretreatment with a hydroxyl radical scavenger prevents airway inflammation and airway hyperresponsiveness (AHR) induced by OD exposure. We sought to determine a mechanism by which OD could induce oxidative stress in bronchial epithelial cells. Human bronchial epithelial cells (BEAS-2B or NHBE) were treated with various concentrations of OD, followed by evaluation of intracellular oxidative stress using 2′,7′–dichlorofluorescein diacetate (DCFDA). After stimulation with OD, gene expression of antioxidant genes was assessed by real-time quantitative PCR followed by quantification of Nrf2 nuclear translocation using a luciferase reporter assay. Phagocytic markers (CD36 and CD68) were analyzed by FACS. Cells were treated with an actin inhibitor, cytochalasin D, before OD exposure and evaluated for Nrf2 nuclear translocation and DCFDA. Mice were pretreated with sulforaphane, the Nrf2 activator, before OD exposure and evaluated for pulmonary inflammation and airway reactivity. OD induced a time- and concentration-dependent increase in DCFDA. mRNA expression levels of Nrf2-dependent genes and Nrf2 nuclear translocation were increased after OD exposure. OD exposure increased the expression of CD68 and CD36. Cytochalasin D prevented oxidative stress and Nrf2 nuclear translocation after OD. Pretreatment with sulforaphane prevented OD-induced inflammation and AHR while increasing the uptake of OD in bronchial epithelial cells. Bronchial epithelial cells can phagocytose OD, resulting in an increase in endogenous oxidative stress. Nrf2-dependent mechanisms mediate the antioxidant response to OD.

Nrf2 Activation Protects Against Organic Dust and Hydrogen Sulfide Exposure Induced Epithelial Barrier Loss and K. pneumoniae Invasion

“…When we pre-treated NHBE cells or PCLS with RTA-408, it increased the Nrf2 levels in H 2 S exposed NHBE cells (both mRNA and protein) and all three exposures of PCLS model (protein data) along with an increased expression of the downstream target genes indicating the therapeutic potential of RTA-408 mediated activation of Nrf2 pathway. Our observations are in line with the findings of McGovern et al., who reported that sulforaphane (Nrf2 activator) pre-treatment in OD exposed BEAS-2B cells had higher expression of nqo1, hox1 as compared to sulforaphane pre-treated controls ( McGovern et al., 2019 ). He et al., explains how Nrf2 mediated upregulation of the cytoprotective genes reduce reactive nitrogen species (3NT) levels ( He and Ma, 2012 ).…”

Sulforaphane Inhibits Foam Cell Formation and Atherosclerosis via Mechanisms Involving the Modulation of Macrophage Cholesterol Transport and the Related Phenotype

“…Interestingly, reduced lipid deposition and CD36 levels in the kidneys were detected in an SFN-treated unilateral ureteral obstruction-induced renal damage rat model [75]. Nevertheless, the limited reports on the impact of SFN on CD36 are inconsistent [76][77][78][79][80]. Accumulating evidence has shown that SFN could improve the capacity of macrophages to phagocytose, clear, or kill various pathogens.…”

New Insights into the Nrf-2/HO-1 Signaling Axis and Its Application in Pediatric Respiratory Diseases

“…Zhang et al observed that Nrf2 activation could improve O 3 -induced asthma by suppressing ROS and Th17 cells [48]. McGovern et al recently revealed that some organic dust causing Nrf2 activation can be taken up by bronchial epithelial cells [49].…”