Rapid Test Can Identify a Key Driver of Severe Asthma by Tracking Protein Signatures

Researchers have developed a new rapid sputum-based test that can identify the presence of a key driver of severe asthma, white blood cells. A simple, rapid testing device has the potential to detect key drivers of respiratory diseases, including asthma, and would improve accessibility and efficiency in identifying patients with asthma.

The full experimental study is published in Angewandte Chemie International Edition.¹

In this study, researchers aimed to develop a new sputum-based lateral flow device (LFD), similar to that of a rapid COVID-19 test, that can quickly and accurately identify eosinophils in complex biological samples, such as sputum, by tracking their protein signatures.

John Brennan, PhD

“This is what our collaboration set out to achieve,” said John Brennan, PhD, director of McMaster University’s Biointerfaces Institute and senior study author, in a statement.² “This test and others like it can have the kind of lasting, meaningful impact that will improve or even save many lives.”

White blood cells, otherwise known as eosinophils, are known to play a role in many airways diseases, including chronic cough, chronic obstructive pulmonary disease (COPD), and certain forms of vasculitis and bronchiectasis. Measurements of eosinophil peroxidase (EPX) are the most abundant and specific of eosinophil cationic proteins and a reliable identifier of eosinophil number and activity.

The researchers developed a protein-targeting element known as a DNAzyme and modified it into the rapid test. Although DNAzymes have primarily been used for detecting metals or bacterial targets, the researchers believed the new platform could be adapted to identify any material of biological origin by detecting its protein signature.

A modified version of the test acted as a bridging strand to allow capture of complimentary DNA (cDNA) modified gold nanoparticles (GNPs) onto a DNA-modified test line to identify measurements of EPX.

Thirty-eight sputum samples from patients or healthy donors were obtained using saline-induction or spontaneous expectorant. Healthy donors included nonsmokers with no known respiratory disease, infection, or symptoms who had not received any vaccination in the prior 8 weeks.

To compare the rapid test results to gold standard sputum cytometry results, the sputum plugs were collected and processed to created 2 sputum samples. One of the samples was centrifuged to remove cellular debris and the other for use with the LFD.

The DNAzyme-based LFD and fluorescence assay for detection of EPX showed good resistance to mammalian nucleases and high sensitivity and selectivity against other eosinophil proteins, including eosinophil cationic protein and eosinophil-derived neurotoxin, and neutrophil proteins, including myeloperoxidase. Furthermore, these assays were validated with patient sputum levels, reaching 100% clinical sensitivity and 96% specificity within 45 minutes.

However, the researchers acknowledge that further work needs to be done to evaluate the rapid test in a clinical setting.

Parameswaran Nair, MD, PhD

“A rapid test to detect eosinophilia would help clinicians make decisions about using drugs, such as steroids or new biologics for patients with severe asthma, and other lung diseases associated with eosinophilia, such as severe cough, and COPD,” said Parameswaran Nair, MD, PhD, professor of medicine at McMaster University and co-author of the study, in a statement.² “It would also help to limit the unnecessary use of antibiotics.”

References

1. Ali MM, Mukherjee M, Radford K, et al. A rapid sputum‐based lateral flow assay for airway eosinophilia using an RNA‐cleaving DNAzyme selected for Eosinophil peroxidase. Angew Chem Int Ed Engl. Published online July 21, 2023. doi:10.1002/anie.202307451

2. While resolving a key asthma challenge, Hamilton researchers also create a new method to detect proteins in body fluids and other materials. News release. EurekAlert! August 1, 2023. Accessed August 23, 2023. https://www.eurekalert.org/news-releases/997344