Elevated mitochondrial reactive oxygen species in COPD macrophages at exacerbation

Increased reactive oxygen species (ROS) may drive pathophysiology in COPD. Excessive levels of ROS trigger signalling cascades and damage cells. Understanding the source of intracellular ROS in COPD is critical. This study examined mitochondrial ROS (mROS) levels and mitochondrial membrane potential (MMφ) in COPD macrophages (MΦ) and the effect of phagocytosis on these processes. Monocyte-derived MΦ from non-smoker (NS), smoker (S), COPD or COPD acute exacerbation (AECOPD) subjects were cultured in GM-CSF (G-MΦ) or M-CSF (M-MΦ) for 12d (n=3-15). MΦ were exposed to fluorescently labelled H.influenzae (HI) or S.pneumoniae (SP) for 4h, after which mROS were measured by mitoSOX assay, and MMφ measured by JC-1 assay. There were no differences in baseline mROS levels, or MMφ between NS, S and COPD subjects in either MΦ phenotype. Phagocytosis of HI or SP did not alter mROS or MMφ in cells from NS or S (p>0.05). However in COPD, M-MΦ phagocytosis increased mROS by ∼50% with HI and ∼80% with SP (p<0.05, p<0.01) and HI also caused a ∼40% reduction in MMφ (p<0.05). Conversely, HI caused a ∼50% increase in mROS levels in G-MΦ, (p<0.05) and caused a ∼40% reduction in MMφ (p<0.05), but this was not seen with SP. AECOPD MΦ also showed a ∼100% increase in baseline mROS in G-MΦ (p<0.05) and M-MΦ compared to stable COPD, but this was not significant. In COPD, phagocytosis leads to an increase in MΦ mROS production and drop in MMφ, and during exacerbation mROS levels are also elevated. This suggests that COPD MΦ may be unable to regulate mROS levels, which may lead to altered MΦ function. Targeting this increase in ROS, particularly at exacerbation, may be a novel therapeutic target.