The thiocyanate analog selenocyanate is a more potent antimicrobial pro-drug that also is selectively detoxified by the host

• Type of Material: Article
• Authors: Brian J. Day, National Jewish Health; Preston E. Bratcher, National Jewish Health; Joshua Chandler, Emory University; Matthew B. Kilgore, Emory University; Elysia Min, National Jewish Health; John J. LiPuma, University of Michigan, Ann Arbor; Robert J. Hondal, University of Vermont; David P. Nichols, University of Washington
• Language: English
• Date: 2020-01-01
• Publisher: ELSEVIER
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: 2019
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.freeradbiomed.2019.11.016
• Title of Journal or Parent Work: Free Radical Biology and Medicine
• Volume: 146
• Start Page: 324
• End Page: 332
• Grant/Funding Information: This work was supported by a Cystic Fibrosis Foundation Research Grant (BJD and DPN) and NIH R01 HL14146 (BJD and RJH).
• Keywords: Anti-Infective Agents; Hypohalous acids; Animals; Cyanates; Prodrugs; Pseudomonas aeruginosa; Thiocyanates; Burkholderia cepacia complex; Antimicrobials; Innate immunity; Methicillin-Resistant Staphylococcus aureus; Cystic fibrosis; Host defense; Staphylococcus aureus; Haloperoxidases; Selenium Compounds; Anti-Bacterial Agents; Humans
• Research Categories: Health Sciences, Medicine and Surgery; Health Sciences, Immunology; Biology, Microbiology

Abstract

A hallmark of cystic fibrosis (CF) lung pathology is an increased susceptibility to pulmonary infections. Thiocyanate (–SCN) is an endogenous component of the innate immunity's peroxidase system that converts –SCN to the antimicrobial agent hypothiocyanite (HOSCN). We have previously shown that the host thioredoxin reductase (TrxR), but not the pathogen's TrxR, can selectively detoxify HOSCN thereby decreasing inflammation and oxidative stress. We tested whether the –SCN analog selenocyanate (–SeCN) shares these properties against several clinical CF bacterial isolates. We examined oxidant production from a lactoperoxidase (LPO) system using –SeCN as a potential substrate. The LPO system generated an oxidant similar in nature to HOSCN and consistent with being HOSeCN. The rate of oxidant generation using –SeCN was significantly less than seen for −SCN. An LPO system was used to generate HOSCN or HOSeCN and compared for antimicrobial activity during in situ exposure of clinical CF isolates of P. aeruginosa (PA), B. cepacia complex (BCC), and methicillin-resistant S. aureus (MRSA) obtained from CF sputum samples. Bacterial viability was assessed by colony forming units. Selective detoxification of HOSeCN was determined by comparing its metabolism by mammalian thioredoxin reductase (TrxR) to bacterial TrxR following the consumption of NADPH. We also assessed potential toxicity of equivalent HOSeCN generation, which demonstrated in situ antimicrobial activity, in human bronchial epithelial cells with a cell viability assay. The –SeCN/HOSeCN system was much more potent than –SCN/HOSCN system at killing PA, BCC and MRSA isolates. The −SeCN/HOSeCN system was more effective at killing –SCN/HOSCN resistant isolates. Mammalian TrxR selectively detoxified HOSeCN whereas the bacterial TrxR enzyme showed little activity. Human bronchial epithelial cells exposed to equivalent flux of HOSeCN that killed several CF pathogens showed no decrease in viability. –SeCN may be an effective therapeutic for the treatment of CF lung pathogens that are difficult to treat with current antibiotics.