Diacetyl Vapor Inhalation Induces Mixed, Granulocytic Lung Inflammation with Increased CD4+CD25+ T Cells in the Rat.

Emma L House,Angela M Groves,So-Young Kim,Ravi S Misra,Eric Hernady,Matthew D Mcgraw,Carl J Johnston

doi:10.3390/toxics9120359

Emma L House, Angela M Groves + Show 5 more

Open Access

https://doi.org/10.3390/toxics9120359

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Journal: Toxics	Publication Date: Dec 20, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: University of Rochester Medical Center

Abstract

Diacetyl (DA) is a highly reactive alpha diketone associated with flavoring-related lung disease. In rodents, acute DA vapor exposure can initiate an airway-centric, inflammatory response. However, this immune response has yet to be fully characterized in the context of flavoring-related lung disease progression. The following studies were designed to characterize the different T cell populations within the lung following repetitive DA vapor exposures. Sprague-Dawley rats were exposed to 200 parts-per-million DA vapor for 5 consecutive days × 6 h/day. Lung tissue and bronchoalveolar lavage fluid (BALF) were analyzed for changes in histology by H&E and Trichrome stain, T cell markers by flow cytometry, total BALF cell counts and differentials, BALF IL17a and total protein immediately, 1 and 2 weeks post-exposure. Lung histology and BALF cell composition demonstrated mixed, granulocytic lung inflammation with bronchial lymphoid aggregates at all time points in DA-exposed lungs compared to air controls. While no significant change was seen in percent lung CD3+, CD4+, or CD8+ T cells, a significant increase in lung CD4+CD25+ T cells developed at 1 week that persisted at 2 weeks post-exposure. Further characterization of this CD4+CD25+ T cell population identified Foxp3+ T cells at 1 week that failed to persist at 2 weeks. Conversely, BALF IL-17a increased significantly at 2 weeks in DA-exposed rats compared to air controls. Lung CD4+CD25+ T cells and BALF IL17a correlated directly with BALF total protein and inversely with rat oxygen saturations. Repetitive DA vapor exposure at occupationally relevant concentrations induced mixed, granulocytic lung inflammation with increased CD4+CD25+ T cells in the rat lung.

Highlights

bronchiolitis obliterans (BO) is defined by histopathology with significant small airways, or bronchiolar, remodeling consisting of sub-epithelial collagen deposition and subsequent airway lumen occlusion due to circumferential narrowing [6]
Rat lungs were evaluated by histology for airways inflammation immediately after exposure (Day 5), 1 week post-exposure (Day 12) and 2 weeks post-exposure (Day 19); Figure 1
By Day 19, thickening of the bronchial walls with deposition of sub-epithelial, extracellular matrix was seen on hematoxylin and eosin (H&E) (Day 19, Figure 1d, arrows) and Masson’s Trichrome (Figure S1)

Summary

Introduction

Due to its low boiling point (88 ◦ C), DA frequently enters the vapor phase during the production process. DA is highly reactive due to its inherent chemical properties. It has two strong electrophilic carbonyl moieties that can and non-enzymatically modify nearby nucleophilic residues in adjacent cellular proteins [4]. These two chemical properties make DA a significant respiratory hazard. Over the past two decades, DA vapor exposures has been well associated with the fibrotic lung disease known as bronchiolitis obliterans (BO), labeled as “flavoring-related lung disease” [5]. BO is defined by histopathology with significant small airways, or bronchiolar, remodeling consisting of sub-epithelial collagen deposition and subsequent airway lumen occlusion due to circumferential narrowing [6]

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