Development of a Novel Simulation Reactor for Chronic Exposure to Atmospheric Particulate Matter

Animal models of chronic obstructive pulmonary disease and their role in drug discovery and development: a critical review

INTRODUCTION

The use of laboratory animals is essential to understand the mechanisms underlying COPD and to discover and evaluate new drugs. However, the complex changes associated with the disease in humans are difficult to fully replicate in animal models.

AREAS COVERED

This review examines the most recent literature on animal models of COPD and their implications for drug discovery and development.

EXPERT OPINION

Recent advances in animal models include the introduction of transgenic mice with an increased propensity to develop COPD-associated features, such as emphysema, and animals exposed to relevant environmental agents other than cigarette smoke, in particular biomass smoke and other air pollutants. Other animal species, including zebrafish, pigs, ferrets and non-human primates, are also increasingly being used to gain insights into human COPD. Furthermore, three-dimensional organoids and humanized mouse models are emerging as technologies for evaluating novel therapeutics in more human-like models. However, despite these advances, no model has yet fully captured the heterogeneity and progression of COPD as observed in humans. Therefore, further research is needed to develop improved models incorporating humanized elements in experimental animals, that may better predict therapeutic responses in clinic settings and accelerate the development of new treatments for this debilitating disease.

Chronic Exposure to Secondary Organic Aerosols Causes Lung Tissue Damage

Recently, secondary organic aerosols (SOAs) emerged as a predominant component of fine particulate matter. However, the pathogenic mechanism(s) of SOAs are still poorly understood. Herein, we show that chronic exposure of mice to SOAs resulted in lung inflammation and tissue destruction. Histological analyses found lung airspace enlargement associated with massive inflammatory cell recruitment predominated by macrophages. Concomitant with such cell influx, our results found changes in the levels of a series of inflammatory mediators in response to SOA. Interestingly, we observed that the expression of the genes encoding for TNF-α and IL-6 increased significantly after one month of exposure to SOAs; mediators that have been largely documented to play a role in chronic pulmonary inflammatory pathologies. Cell culture studies confirmed these in vivo findings. Of importance as well, our study indicates increased matrix metalloproteinase proteolytic activity suggesting its contribution to lung tissue inflammation and degradation. Our work represents the first in vivo study, which reports that chronic exposure to SOAs leads to lung inflammation and tissue injury. Thus, we hope that these data will foster new studies to enhance our understanding of the underlying pathogenic mechanisms of SOAs and perhaps help in the design of therapeutic strategies against SOA-mediated lung injury.

Weight loss and abnormal lung inflammation in mice chronically exposed to secondary organic aerosols

Secondary organic aerosols (SOAs) have emerged recently as a major component of fine particulate matter. Cell culture studies revealed a role for SOAs in cell oxidative stress, toxicity and inflammation and only a few studies investigated short-term SOA exposure in animal models. Here, mice were chronically exposed to naphthalene-derived SOAs for one and two months. Weight monitoring indicated a marked mass loss, especially in females, following chronic exposure to SOAs. Significantly, a cytokine antibody microarray approach revealed SOA-induced abnormal lung inflammation similar to that seen in cigarette smoke-induced chronic obstructive pulmonary disease (COPD). This in vivo study testifies to the pathogenic role of sub-chronic SOA exposure on human health.

Pathogenic Mechanisms of Secondary Organic Aerosols

Air pollution represents a major health problem and an economic burden. In recent years, advances in air pollution research has allowed particle fractionation and identification of secondary organic aerosol (SOA). SOA is formed from either biogenic or anthropogenic emissions, through a mass transfer from the gaseous mass to the particulate phase in the atmosphere. They can have deleterious impact on health and the mortality of individuals with chronic inflammatory diseases. The pleiotropic effects of SOA could involve different and interconnected pathogenic mechanisms ranging from oxidative stress, inflammation, and immune system dysfunction. The purpose of this review is to present recent findings about SOA pathogenic roles and potential underlying mechanisms focusing on the lungs; the latter being the primary exposed organ to atmospheric pollutants.

Proteome-wide effects of naphthalene-derived secondary organic aerosol in BEAS-2B cells are caused by short-lived unsaturated carbonyls

Exposure to air pollution causes adverse health outcomes, but the toxicity mechanisms remain unclear. Here, we investigated the dynamic toxicities of naphthalene-derived secondary organic aerosol (NSOA) in a human bronchial epithelial cell line (BEAS-2B) and identified the chemical components responsible for toxicities. The chemical composition of NSOA was found to vary with six simulated atmospheric aging conditions (C₁-C₆), as characterized by high-resolution mass spectrometry and ion mobility mass spectrometry. Global proteome profiling reveals dynamic evolution in toxicity: Stronger proteome-wide impacts were detected in fresh NSOA, but the effects declined along with atmospheric aging. While Nrf2-regulated proteins (e.g., NQO1) were significantly up-regulated, the majority (78 to 97%) of proteins from inflammation and other pathways were down-regulated by NSOA exposure (e.g., Rho GTPases). This pattern is distinct from the reactive oxygen species (ROS)-mediated toxicity pathway, and an alternative cysteine reaction pathway was revealed by the decreased abundance of proteins (e.g., MT1X) prone to posttranslational thiol modification. This pathway was further validated by observing decreased Nrf2 response in reporter cells, after preincubating NSOA with cysteine. Ethynyl-naphthalene probe was employed to confirm the alkylation of cellular proteome thiols on the proteome-wide level by fresh NSOA via in-gel fluorescence imaging. Nontarget analysis identified several unsaturated carbonyls, including naphthoquinones and hydroxylated naphthoquinones, as the toxic components responsible for cysteine reactivity. Our study provides insights into the dynamic toxicities of NSOA during atmospheric aging and identifies short-lived unsaturated carbonyls as the predominant toxic components at the posttranslational level.

Soluble Wood Smoke Extract Promotes Barrier Dysfunction in Alveolar Epithelial Cells through a MAPK Signaling Pathway

Wildfire smoke induces acute pulmonary distress and is of particular concern to risk groups such as the sick and elderly. Wood smoke (WS) contains many of the same toxic compounds as those found in cigarette smoke (CS) including polycyclic aromatic hydrocarbons, carbon monoxide, and free radicals. CS is a well-established risk factor for respiratory diseases such as asthma and COPD. Limited studies investigating the biological effects of WS on the airway epithelium have been performed. Using a cell culture-based model, we assessed the effects of a WS-infused solution on alveolar epithelial barrier function, cell migration, and survival. The average geometric mean of particles in the WS was 178 nm. GC/MS analysis of the WS solution identified phenolic and cellulosic compounds. WS exposure resulted in a significant reduction in barrier function, which peaked after 24 hours of continuous exposure. The junctional protein E-cadherin showed a prominent reduction in response to increasing concentrations of WS. Furthermore, WS significantly repressed cell migration following injury to the cell monolayer. There was no difference in cell viability following WS exposure. Mechanistically, WS exposure induced activation of the p44/42, but not p38, MAPK signaling pathway, and inhibition of p44/42 phosphorylation prevented the disruption of barrier function and loss of E-cadherin staining. Thus, WS may contribute to the breakdown of alveolar structure and function through a p44/42 MAPK-dependent pathway and may lead to the development and/or exacerbation of respiratory pathologies with chronic exposure.

Establishment and characterization of a multi-purpose large animal exposure chamber for investigating health effects

Air pollution poses a significant threat to the environment and human health. Most in vivo health studies conducted regarding air pollutants, including particulate matter (PM) and gas phase pollutants, have been either through traditional medical intranasal treatment or using a tiny chamber, which limit animal activities. In this study, we designed and tested a large, whole-body, multiple animal exposure chamber with uniform dispersion and exposure stability for animal studies. The chamber simultaneously controls particle size distribution and PM mass concentration. Two different methods were used to generate aerosol suspension through either soluble material (Alternaria extract), liquid particle suspension (nanosilica solution), or dry powder (silica powder). We demonstrate that the chamber system provides well controlled and characterized whole animal exposures, where dosage is by inhalation of particulate matter.

Continuous Inhalation Exposure to Fungal Allergen Particulates Induces Lung Inflammation While Reducing Innate Immune Molecule Expression in the Brainstem

Continuous exposure to aerosolized fine (particle size ≤2.5 µm) and ultrafine (particle size ≤0.1 µm) particulates can trigger innate inflammatory responses in the lung and brain depending on particle composition. Most studies of manmade toxicants use inhalation exposure routes, whereas most studies of allergens use soluble solutions administered via intranasal or injection routes. Here, we tested whether continuous inhalation exposure to aerosolized Alternaria alternata particulates (a common fungal allergen associated with asthma) would induce innate inflammatory responses in the lung and brain. By designing a new environmental chamber able to control particle size distribution and mass concentration, we continuously exposed adult mice to aerosolized ultrafine Alternaria particulates for 96 hr. Despite induction of innate immune responses in the lung, induction of innate immune responses in whole brain samples was not detected by quantitative polymerase chain reaction or flow cytometry. However, exposure did trigger decreases in Arginase 1, inducible nitric oxide synthase, and tumor necrosis factor alpha mRNA in the brainstem samples containing the central nervous system respiratory circuit (the dorsal respiratory group, ventral respiratory group, and the pre-Bötzinger and Bötzinger complexes). In addition, a significant decrease in the percentage of Toll-like receptor 2-expressing brainstem microglia was detected by flow cytometry. Histologic analysis revealed a significant decrease in Iba1 but not glial fibrillary acidic protein immunoreactivity in both the brainstem and the hippocampus. Together these data indicate that inhalation exposure to a natural fungal allergen under conditions sufficient to induce lung inflammation surprisingly causes reductions in baseline expression of select innate immune molecules (similar to that observed during endotoxin tolerance) in the region of the central nervous system controlling respiration.