(174b) Whole Genome Microarray Analysis of Wistar Rats Real-Life Exposure to PM2.5 and PM1 Ambient Particles and Correlation to Specific Water-Soluble Metals

The current study aimed to explore the differential gene expression in Wistar rats, after exposure to PM_2.5 and PM₁ ambient air particles for an eight-week period. In parallel, filtered PM2.5and PM1 was collected in separate samplers. Gene expression analysis after microarrays analysis showed significantly altered gene expression of several immunological markers. The preliminary results of the study show that natural exposure to PM2.5 and PM1induced airway and lung inflammation and moreover it triggers a T-helper type 2 inflammatory (Th2) response upregulating the gene expression of interleukin-4 (IL-4), IL-5, IL-13 and IL-25. Interleukins 5 and 13 can lead to eosinophilia and goblet cell hyperplasia and both play an important role at the immune response in mucosal sites such as the airway epithelium of the upper respiratory tract. In addition, gene expression analysis revealed pathway activation of the aryl hydrocarbon receptor (AhR), which is a ligand-dependent transcription factor that is involved in the detection of intracellular changes and sensing oxygen and redox potentials. Finally, high concentrations of Fe, Mn and Zn for both particle size analysis were shown after PM-component analysis and high concentration of Cu at PM2.5.

Introduction

Particulate matter (PM) is one of the most important environmental issues in Europe. Various sizes of PM are suspended in the atmosphere and contributes to ambient air pollution¹. The toxicity caused by PM2.5 and PM1 is a combination of effect of particles, adsorbed toxic pollutants, biological components such as endotoxin, pollen, fungal spores, viruses, and bacteria, polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs) and heavy metals². Up till now there is no study that analyzed the differential gene expression after natural exposure to PM2.5 and PM1. In order to understand the biological mechanisms triggered by PM2.5 and PM1 exposure and lead to airway inflammation, in this study, we aimed to evaluate the following hypotheses: (1) How the natural exposure to PM2.5 and PM1 in Wistar rats can alter the gene expression after whole genome analysis in comparison to the control group; (2) What is the type of immune response triggered after exposure to PM2.5 and PM1; (3) How altered gene expression in rats after exposure to PM2.5 and PM1 from a traffic-related area would correlate with the concentrations of other measured components such as PAHs and heavy metals.

Methodology and Results

An eight-week exposure campaign was carried out within October and February 2019 - 2020 in a location in the urban area of Thessaloniki. The urban background site is located in the Kalamaria district of Easter Thessaloniki. Briefly, nine 10-week old Wistar rats were randomly separated in three groups (PM2.5, PM1, control) in modified plexiglass cages that were connected to Tecora samplers with an operational flow rate of 2.3 m³ h^-1 of filtered air. In parallel, while the experiment was running another two samplers were used to collect PM2.5 and PM1 samples on PTFE filters (pall Corporation, 47 mm diameter) for 24 h. After animal euthanasia blood and tissues were collected for microarray gene expression analysis using a SureScan array from Agilent. GC/MS/MS was used to determine and quantify the composition of metals. PM-component analysis showed high concentrations of Fe, Mn and Zn for both particle size analysis and in addition high concentration of Cu at PM2.5. Preliminary results showed a significant two-fold up-regulation in expression of genes related to interleukins connected to a Th2 inflammatory response such as IL-4, IL-5, IL-13 and IL-25. In addition, genes related to the AhR-pathway and to oxidative stress where up-regulated.

Conclusions

Besides the increased amount of research, we are still lacking knowledge on the biological mechanisms triggered by exposure to PM2.5 and PM1 ambient air particles. In the current study, a whole-body natural exposure of Wistar rats to PM2.5 and PM1 was performed for eight weeks. Preliminary results of gene expression analysis showed an up-regulation of a Th2 inflammatory response. Still further research needs to be performed to elucidate further the biological mechanisms triggered after exposure to PM2.5 and PM1. The authors of this study suggest that if the concentration of the aforementioned water-soluble metals exceeded 12 ng/m3, emergency visits due to child asthma showed a statistically significant increase. This limit was exceeded for both PM1 (25,36 ng/m3) and PM2,5 (36,84 ng/m3) samples. This fact suggests that there is a possible health risk due to metal concentration levels in the studied areas.

Acknowledgement

This work was supported by the Operation Programme (ESPA) in Human Resources Development, Education and Learning Co-funded by Greece and the European Union. Number of Scholarship: 95382

References

1. Ljubimova J. Y et al: Coarse particulate matter (PM2.5–10) in Los Angeles Basin air induces expression of inflammation and cancer biomarkers in rat brains. Scientific Reports 2018, 8:5708
2. Wang H. et al: The acute airway inflammation induced by PM2.5 exposure and the treatment of essential oils in Balb/c mice. Scientific Reports 2018, 7:44256