Human Sputum Proteomics: Advancing Non-Invasive Diagnosis of Respiratory Diseases with Enhanced Biomarker Analysis Methods

Abstract

Many ailments can be diagnosed while they are asymptomatic, meaning that the patient has no signs or symptoms of a progressing disease. If caught in their initial stage of formation, these disorders can be effectively treated, leading to successful outcomes; curative therapies can halt illnesses from advancing, thus improving the quality of life and long-term survival of the patient. Still, cutting-edge upgrades in precision technologies are necessary for early, reliable, affordable, and rapid disease detection, but also vital for the well-being of people and the future of global public health. The emerging role and utility of non-invasive and repeatable diagnostic test approaches for the detection of health conditions have been exemplified by liquid biopsies based on genomic biomarkers. As such, biological fluids permit any measurable molecular indicator or signature (e.g., proteins) to provide valuable information on an individual’s wellness and/or disease. Among the bodily secretions used for non-invasive diagnostics is sputum, a complex viscous gel-like biopolymeric network that has gained growing recognition as a rich source of biomarkers of airway infections and pulmonary diseases, and serves as a determinant to reveal other illnesses. As per the World Health Organization, the burden of respiratory conditions is exacerbated by factors ranging from considerable subjection to air pollution and occupational contaminants to tobacco smoking and second-hand smoke, in addition to poor socio-economic status. Due to the likely increase in these determinants, respiratory tract ailments are on the rise, affecting the health of many individuals, in addition to putting stress on healthcare facilities and services worldwide. The aim of this study was to perform a narrative review of sputum constituents with an emphasis on proteins and glycoproteins assessed as possible biomarkers of lung and other organ diseases. A search was conducted using mucus, sputum proteomics, sputum biomarkers, and point-of-care testing as keywords employing Google, PubMed (MEDLINE), and Web of Science, selecting the most referenced and related papers of the last decade. We, therefore, highlight the need to use expectorated or induced sputum specimens as a routine sample source for testing valuable protein biomarkers to diagnose these chronic disorders, predict inflammation and disease progression, as well as monitor the effectiveness of treatments. Further, we discuss the urgent need for fast and reliable point-of-care methods to detect and quantify crucial protein biomarkers in sputum specimens, and the limitations faced when dealing with their complex matrices.