Identification of Particles in Exhaled Air Using Mass Spectrometry

Abstract

Bronchiolitis obliterans syndrome (BOS) as a form of chronic lung allograft dysfunction is a limiting factor to the survival of lung transplant recipients. Detection and monitoring of chronic rejection is hampered by a lack of clinically available markers. Particles in exhaled air (PExA) is proposed as a noninvasive means of potentially identifying and observing BOS patients. This pilot study aims to capture the range of exhaled particles expected in human samples and identify possible candidate markers. The PExA device collects exhaled air using a two-way valve that allows subjects to inhale filtered air and exhale air into a reservoir from which an optical particle counter counts and sizes entering particles. Particles are collected according to their inertia and those above a threshold impact onto a plate, collecting onto a membrane of polytetrafluoroethylene. Total accumulated mass can be measured by the PExA device. Samples were obtained from two healthy subjects (1 combined 600 ng sample and 200 ng from each) and from five patients with lung pathology (1 grouped sample of 600 ng from three patients and 200 ng samples from two unique patients). The samples were analyzed via liquid chromatography-mass spectrometry on an Orbitrap Fusion Lumos mass spectrometer coupled to an easy-nLC1200 liquid chromatography system. The fifty most abundant proteins identified by mass spectrometry represented a breadth of biological function and a variety of localizations. Ten could be traced to immunological system processes and included a number of immunoglobulin constant regions. Sixteen of these most abundant proteins could be found in the extracellular region. A number are components of the plasma, including serotransferrin and annexin proteins. Fifteen proteins were found in greater abundance in the healthy subjects compared to patients while two (haptoglobin and gasdermin-A) were notable for a lower abundance in the patients. The PExA device presents as a novel method for non-invasive analysis of lung transplant patients with the potential to monitor developing chronic rejection. This pilot study characterizes the range of proteins identified from samples across subjects and serves as a basis for the exploration of markers in chronic rejection patients. This work establishes a method for the ongoing effort to use PExA to identify and monitor BOS in lung transplant recipients.