Sulforaphane improves MARCO expression, bacterial clearance and survival in post‐influenza bacterial pneumonia (145.1)

Abstract

Mechanisms that increase susceptibility for post‐influenza bacterial pneumonia include down‐regulation of the alveolar macrophage (AM) scavenger receptor MARCO by interferon‐γ (IFN‐γ), leading to diminished bacterial clearance. Since MARCO expression can be increased by NRF2 signaling, we tested whether the NRF2‐inducer sulforaphane (SFN) can up‐regulate MARCO expression and improve bacterial clearance after influenza. Human AM‐like monocyte‐derived macrophages (HMDMs) were treated with IFN‐γ (10‐50 IU/ml, 24h) to simulate influenza infection, followed by sulforaphane (SFN, 10µM) for 24h before quantitation of MARCO expression or challenge with green fluorescence protein (GFP)‐expressing S. aureus. Scanning cytometry was used to quantitate MARCO surface labeling and uptake of bacteria. C57/BL6 mice were inoculated i.n. on day 0 with 3500PFU of PR8 influenza virus, and on day 7 with 500 CFU of S. pneumoniae serotype 3. Mice were injected with SFN 25 or 50 mg/kg, or PBS daily from day 6 to 9 after influenza infection. Bacterial clearance was measured on day 1 after S. pneumoniae infection using lung lavage samples. IFN‐γ down‐regulated MARCO expression (p<0.001) of HMDMs and impaired phagocytosis of S. aureus (p<0.001, n=4). SFN added after IFN‐γ significantly improved MARCO expression (p=0.003) and S. aureus phagocytosis (p=0.05), an effect that was inhibited by scavenger receptor blockers poly(I) (p=0.001) or MARCO blocking peptide (P<0.001). In vivo, sulforaphane‐treated mice showed improved bacterial clearance (e.g. 84%, 95% reduction in SFN‐treated mice in 2 trials) and a significantly higher survival rate compared to PBS‐treated mice (75.0% vs. 12.5%, n = 8/grp, p=0.022). Therapeutic targeting of the NRF2 pathway may be beneficial to reduce risk or severity of secondary bacterial pneumonia after influenza.Grant Funding Source: Supported by ES00002