Particle coating alters mucociliary transit in excised rat trachea: A synchrotron X-ray imaging study

Mark Gardner,Martin Donnelley,Kaye Morgan,Alexandra Mccarron,David Parsons

doi:10.1038/s41598-019-47465-1

Abstract

We have previously developed non-invasive in vivo mucociliary transport (MCT) monitoring methods using synchrotron phase contrast X-ray imaging (PCXI) to evaluate potential therapies for cystic fibrosis (CF). However, previous in vivo measurements of MCT velocity using this method were lower than those from alternate methods. We hypothesise this was due to the surface chemistry of the uncoated particles. We investigated the effect of particle surface coating on MCT marker performance by measuring the velocity of uncoated, positively-charged (aminated; NH2), and negatively-charged (carboxylated; COOH) particles. The effect of aerosolised hypertonic saline (HS) was also investigated, as previous in vivo measurements showed HS significantly increased MCT rate. PCXI experiments were performed using an ex vivo rat tracheal imaging setup. Prior to aerosol delivery there was little movement of the uncoated particles, whilst the NH2 and COOH particles moved with MCT rates similar to those previously reported. After application of HS the uncoated and COOH particle velocity increased and NH2 decreased. This experiment validated the use of COOH particles as MCT marker particles over the uncoated and NH2 coated particles. Our results suggest that future experiments measuring MCT using synchrotron PCXI should use COOH coated marker particles for more accurate MCT quantification.

Highlights

The mucociliary transport (MCT) system is an important part of the body’s immune system, enabling pathogens, inflammatory cells and foreign particles that are inhaled into the lungs to become captured in the mucus, transported up the airways and trachea, and swallowed and excreted or coughed clear[1]
Particle surface chemistry and charge are thought to play an important role in mucin aggregation[19,20] with MCT rate measurement studies typically performed using particles with a carboxyl-coating[21,22] We hypothesise that altering our MCT assessment method to utilise carboxyl coated beads instead of uncoated beads will allow for a measured MCT marker velocity that is closer to MCT rates measured using alternate methods
The measured MCT rate increased for COOH coated particles with the addition of hypertonic saline (HS) aerosol to the airway, when compared to the baseline MCT rate for the COOH particles

Summary

Introduction

The mucociliary transport (MCT) system is an important part of the body’s immune system, enabling pathogens, inflammatory cells and foreign particles that are inhaled into the lungs to become captured in the mucus, transported up the airways and trachea, and swallowed and excreted or coughed clear[1]. Previous MCT assessments in animal models have used a range of methodologies Examples of these include computed tomographic (CT) imaging to assess the motion of individual large 350 μm tantalum disks in pig airways[6]; gamma scintigraphy to quantify the bulk clearance of radiolabelled particles from the mouse nose[7]; and a dissecting microscope and filter to assess the trans-tracheal bulk motion of fluorescent particles[8]. Our previous PCXI studies used uncoated high refractive index (HRI) glass beads[10,11,16] MCT marker particles These beads are visible using PCXI, and have extremely uniform size, shape and surface properties, which we hypothesised would result in relatively uniform MCT behaviour. Improved performance of the MCT marker particles will allow for further investigations into the dynamic effect of HS on airway surface rehydration and MCT rate in a range of CF animal models

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Conclusion