S34 Reduced alveolar macrophage HSD-1 activity is associated with impaired efferocytosis and greater mortality in ARDS patients

Abstract

Introduction The role of alveolar macrophages (AMs) in ARDS pathogenesis is unclear. Our previous work with ARDS patients has shown that cortisol:cortisone ratios are significantly lower in bronchoalveolar lavage fluid (BALF) compared to plasma, indicating dysregulated alveolar steroid metabolism. AMs normally express 11β hydroxysteroid dehydrogenase type 1 (HSD-1) which converts cortisone to cortisol. We investigated whether AM HSD-1 activity is decreased in ARDS and the relationship with mortality and AM function. Methods AMs were isolated from the BALF of ventilated ICU patients with ARDS (n=24) or Sepsis (n=12, control group at risk of ARDS). AMs were used in efferocytosis and phagocytosis assays; using labelled apoptotic neutrophils or pHrodo particles (E. Coli and S. Aureus) respectively. Thin layer chromatography assays measured AM HSD-1 reductase activity. BAL neutrophils were assessed for apoptosis and viability using flow cytometry. Results AMs had significantly lower HSD-1 reductase activity in ARDS compared to sepsis (0.102 vs 0.966 pM/hr, p=0.038). ARDS patients who died during admission had significantly lower AM HSD-1 reductase activity compared to survivors (0.0585 vs 0.566 pM/hr, p=0.0189, figure 1). AM efferocytic index was significantly impaired in ARDS compared to sepsis (4.95% vs 24.3%, p=0.0001). Direct correlation is seen between AM HSD-1 activity and efferocytic index, across both patient groups (R2=0.6249, p=0.0195). A greater proportion of BAL neutrophils were apoptotic in ARDS compared to Sepsis (39.2% vs 19%, p=0.04). No significant difference in AM phagocytic index was seen between ARDS and Sepsis. Conclusions ARDS onset is associated with decreased AM HSD-1 reductase activity. Cortisol stimulates efferocytosis,1 therefore reduced AM HSD-1 reductase activity may cause the impaired efferocytosis we observed. This impaired efferocytosis likely contributes to the alveolar accumulation of apoptotic neutrophils we observed. These persistent apoptotic neutrophils likely undergo secondary necrosis, causing the prolonged inflammation seen in ARDS. This may explain why lower AM HSD-1 reductase activity is associated with greater mortality in ARDS. Therapeutic strategies to upregulate alveolar HSD-1 activity may restore AM efferocytosis function, decrease inflammation, and reduce mortality in ARDS. Work to modify HSD-1 activity in vivo is ongoing using transgenic mesenchymal stem cells which overexpress HSD-1. Reference 1. PMID: 22615206.