Fluoroquinolones directly drive mitochondrial hyperpolarisation and modulate iNOS expression in monocyte derived macrophage populations

Introduction The fluoroquinolone levofloxacin is often selected for use prophylactically as well as during respiratory infections. However, studies on how these antibiotics may alter innate immunity, as opposed to their bactericidal activity, are limited. Materials &Methods We employed a murine model of therapeutically relevant antibiotic dosing to investigate the effect of prophylactic levofloxacin treatment on innate immunity. Results We observed mild pathology at the barrier sites of both the lung and colon in terms of alveolar space and goblet cell numbers respectively. Although we saw no alteration in lung immune populations of neutrophils, eosinophils or dendritic cells, we did see heightened expression of macrophage inducible nitric oxide synthase (iNOS). Interestingly this was only present in the shorter-lived CD206- interstitial macrophage subset and not observed in the long-lived resident alveolar population. Within the large intestine levofloxacin also targeted iNOS expression in the shorter-lived TIM4-CD4+ population, but conversely inhibiting expression in the microbially rich colon. We therefore utilised the bone marrow derived macrophage system, devoid of microbial interactions and demonstrated that levofloxacin had a direct effect on driving iNOS expression and increasing phagocytosis, but only when present in developing macrophages and not mature macrophage populations. Our macrophage observations were replicated in ciprofloxacin, but not doxycycline treated animals, indicating a fluoroquinolone specific action. Mechanistically, fluoroquinolone treatment was associated with mitochondrial hyperpolarisation, indicating a direct alteration of macrophage immunity via off target effects. Conclusion Collectively, this study demonstrates a direct action of fluoroquinolones on macrophage immunity which should be considered when selecting antibiotics for tissue specific and prophylactic use.