Antimicrobial properties of Gallium Protoporphyrin in COPD

Abstract

<b>Aims and Objectives:</b> Colonisation with Non-typeable <i>Haemophilus influenzae</i> (NTHi) is common in COPD. Iron is required by bacteria for nutrition. Gallium is imported into bacteria using iron import proteins. Gallium cannot fulfill key metabolic functions, causing bactericidal effects. We tested the efficacy of gallium compounds as antimicrobials against NTHi, and their ability to reduce NTHi induced inflammation in macrophages. <b>Methods:</b> NTHi was cultured with the free iron analogue gallium nitrate (GaN) and the heme iron analogue gallium protoporphyrin (GaPP) (0.5 - 4 μM; 24 hours). Growth of NTHi reference strain (NCTC 12699) and 6 clinical isolates from COPD patients (including antibiotic resistant isolates) was assessed by optical density, and viability by Miles Misra. Monocyte derived macrophages (MDMs) from healthy non-smokers (n=6) were exposed to NTHi cultured with either GaN or GaPP. Cytokine gene expression and protein secretion were measured by qPCR and ELISA. MDMs were treated with GaPP before or after NTHi exposure. Viable intracellular NTHi was assessed by gentamicin protection assay. <b>Results:</b> NTHi growth and viability were reduced by GaPP but not GaN. GaPP inhibited growth of COPD isolates (4 μM: 87% reduction). MDM cytokine gene expression and protein secretion (TNFα, IL-6 and CXCL8) in response to NTHi was reduced (65.3 %, 78.7% and 85.8% reduction for gene expression, respectively) when cultured with GaPP 4 μM. GaPP reduced intracellular viability of NTHi in macrophages. <b>Conclusions:</b> GaPP is an effective antimicrobial for NTHi while GaN showed no effect on NTHi growth or viability. Culture of NTHi with GaPP also reduced the pro-inflammatory cytokine response and intracellular bacterial viability in MDMs.