Inhibition of Myeloperoxidase Activity in Cystic Fibrosis Sputum by Peptide Inhibitor of Complement C1 (PIC1)

• Published in: PloS one 2017-01, Vol.12 (1), p.e0170203-e0170203
• Main Authors: Hair, Pamela S, Sass, Laura A, Krishna, Neel K, Cunnion, Kenji M
• Format: Article
• Language: English
• Subjects: Acids; Aniline Compounds - metabolism; Antioxidants; Antioxidants - metabolism; Benzidines - metabolism; Biochemistry; Biology and Life Sciences; Cardiovascular disease; Children & youth; Complement C1 Inhibitor Protein - metabolism; Complement component C1; Complement system; Cystic fibrosis; Cystic Fibrosis - enzymology; Fluids; Genetic aspects; Heme; Heme - metabolism; Humans; Hypochlorous acid; Immunology; Inflammation; Inhibitors; Lungs; Medical research; Medical schools; Medicine and Health Sciences; Neutrophils; Neutrophils - metabolism; Oxidation; Oxidation-Reduction; Pediatrics; Peptides; Peroxidase; Peroxidase - antagonists & inhibitors; Peroxidase - metabolism; Physical Sciences; Rodents; Spectral analysis; Sputum; Sputum - enzymology; Substrate inhibition; Substrates; Valence
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0170203

Myeloperoxidase is the major peroxidase enzyme in neutrophil granules and implicated in contributing to inflammatory lung damage in cystic fibrosis. Free myeloperoxidase is present in cystic fibrosis lung fluid and generates hypochlorous acid. Here we report a new inhibitor of myeloperoxidase activity, Peptide Inhibitor of Complement C1 (PIC1). Using TMB as the oxidizing substrate, PIC1 inhibited myeloperoxidase activity in cystic fibrosis sputum soluble fractions by an average of a 3.4-fold decrease (P = 0.02). PIC1 also dose-dependently inhibited myeloperoxidase activity in a neutrophil lysate or purified myeloperoxidase by up to 28-fold (P < 0.001). PIC1 inhibited myeloperoxidase activity similarly, on a molar basis, as the specific myeloperoxidase inhibitor 4-Aminobenzoic acid hydrazide (ABAH) for various oxidizing substrates. PIC1 was able to protect the heme ring of myeloperoxidase from destruction by NaOCl, assayed by spectral analysis. PIC1 incubated with oxidized TMB reversed the oxidation state of TMB, as measured by absorbance at 450 nm, with a 20-fold reduction in oxidized TMB (P = 0.02). This result was consistent with an antioxidant mechanism for PIC1. In summary, PIC1 inhibits the peroxidase activity of myeloperoxidase in CF sputum likely via an antioxidant mechanism.