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Sputum Proteomics in Inflammatory and Suppurative Respiratory Diseases

¹ School of Molecular and Clinical Medicine, University of Edinburgh, Western General Hospital, Edinburgh, United Kingdom

Correspondence and requests for reprints should be addressed to Professor Andrew P. Greening, M.D., F.R.C.P., Respiratory Unit Offices, 1st Floor, Anne Ferguson Building, Western General Hospital, Crewe Road, South Edinburgh EH4 2XU, UK. E-mail: a.greening{at}ed.ac.uk

Rationale: Markers of inflammatory activity are important for assessment and management of many respiratory diseases. Markers that are currently unrecognized may be more valuable than those presently believed to be useful.

Objectives: To identify potential biomarkers of suppurative and inflammatory lung disease in induced sputum samples.

Methods: Induced sputum was collected from 20 healthy control subjects, 24 patients with asthma, 24 with chronic obstructive pulmonary disease, 28 with cystic fibrosis (CF), and 19 with bronchiectasis. Twelve patients with CF had sputum sampled before and after antibiotic therapy for an infective exacerbation. The fluid phase of induced sputum was analyzed by surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectroscopy on three protein array surfaces. Some protein markers were selected for identification, and relevant ELISA assays sought. For 12 patients with CF, both SELDI-TOF and ELISA monitored changes in inflammatory responses during infective exacerbations.

Measurements and Main Results: SELDI-TOF identified potential biomarkers that differentiated each of the disease groups from healthy control subjects: at a significance of P < 0.01, there were 105 for asthma, 113 for chronic obstructive pulmonary disease, 381 for CF, and 377 for bronchiectasis. Peaks selected for protein identification yielded calgranulin A, calgranulin B, calgranulin C, Clara cell secretory protein, lysosyme c, proline rich salivary peptide, cystatin s, and hemoglobin . On treatment of an infective CF exacerbation, SELDI-TOF determined falls in levels of calgranulin A and calgranulin B that were mirrored by ELISA-measured falls in calprotectin (heterodimer of calgranulins A and B).

Conclusions: Proteomic screening of sputum yields potential biomarkers of inflammation. The early development of a clinically relevant assay from such data is demonstrated.

Key Words: biomarkers • calprotectin • cystic fibrosis

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Induced sputum cytology has been used to investigate a number of respiratory diseases, including asthma. The fluid phase is less well characterized and likely to contain undiscovered biomarkers that may be used to monitor disease. What This Study Adds to the Field High-throughput mass spectrometry identifies key biomarkers in sputum, allowing quantitative measurement with immunoassay, and potential development of new clinically applicable tests of inflammation in lung disease.