Efficient Clearance of Inhaled Nanoparticles Depends on Strong Adhesion to the Epithelium: The Role of Hydrophilicity, Coating, Size, and Shape
Date
2023-09-14
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Abstract
Health alerts regarding high levels of fine particles in ambient air are increasingly common, reflecting a significant worldwide crisis. These particles contribute substantially to premature death, a problem only expected to grow. Among these, nanoparticles pose a particular threat, linked to respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, and cancer as well as extrapulmonary effects. The health implications of nanoparticles differ, rendering simple particle concentration nearly meaningless. In this thesis, we focused on understanding the accumulation of nanoparticles in the lung, which is a critical aspect of their toxicity. We developed in-vitro assays to predict whether particles remain in the alveolar lumen to be cleared through alveolar and airway pathways, and which particles traverse the alveolar epithelium to induce interstitial lung disease or enter the blood and lymphatic vessels to cause systemic effects. We hypothesized that the fate of inhaled nanoparticles in the alveolar lung primarily depends on their adhesion strength to alveolar epithelium and the physical/chemical characteristics of the particle. To test this, we employed atomic force microscopy (AFM) for adhesion force measurement, transmission electron microscopy (TEM) to correlate adhesion strength to nanoparticle uptake, and confocal laser scanning microscopy (CLSM) to study nanoparticle translocation. Characteristics of nanoparticles, including protein corona coating, alveolar surfactant coating, hydrophobicity/hydrophilicity, size and geometry were studied in the presence or absence of pharmacological blockers to determine endocytic mechanism(s) involved in the interaction with the epithelium. Results showed that the adhesion of nanoparticles to the epithelial cells was an active process, and the strength of adhesion to the epithelium correlated directly to their uptake and transcytosis. Amorphous silica nanoparticles (ASN) with 15 nm in diameter were found to adhere strongly and translocate across the epithelium, whereas nanocarbon black particles 15 nm in diameter (nCB15) exhibited weak adhesion and remained in the alveolar lumen. Interestingly, commonly studied zeta potential had no influence on the interaction, whereas particle coating with surfactant increased their potential to accumulate in the alveolar lumen. Rendering ASN particles hydrophobic reduced their adhesion to the epithelium. The size of nanoparticles was linked to how cells perceived nanoparticles, with particles larger than 150 nm being endocytosed in a clathrin-enhanced mechanism, while particles less than 150 nm were taken up in a caveolin-enhanced mechanism. The epithelium did not show a preferred endocytic mechanism with respect to clathrin or caveolin for silica nanorods (SNR) yet showed a cytotoxic response to these elongated particles. This work contributes to the development of an effective framework for assessing the potential risks of inhaled nanoparticles, and our novel approach of categorization can support public health policies aiming to reduce exposure to nanoparticles in various environments.
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Inhaled nanoparticles, Adhesion force, Single cell force spectroscopy, Nanoparticle fate, Nanoparticle properties, Nanoparticle endocytosis, Nanoparticle exocytosis, Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Total Internal Reflection Fluorescence Microscopy (TIRF), Nanoparticle accumulation and categorization
Citation
Bogari, N. N. (2023). Efficient clearance of inhaled nanoparticles depends on strong adhesion to the epithelium: the role of hydrophilicity, coating, size, and shape (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.