Sputum plasminogen activator inhibitor-1 elevation by oxidative stress-dependent nuclear factor-κB activation in COPD

Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of fibrinolysis at sites of vascular injury and thrombus formation. Recently, sputum PAI-1 was reported to be elevated in COPD. However, the mechanism of PAI-1 elevation in COPD has yet to be clarified. Here, we show that PAI-1 elevation in COPD is closely associated with oxidative stress-induced nuclear factor κB (NF-κB) activation.

Patients and control subjects were recruited from the outpatient department of Royal Brompton Hospital, local general practice, and the National Heart and Lung Institute. Sputum samples were obtained, and sputum sample processing was performed to obtain sputum supernatants and sputum macrophages.

The mean PAI-1 level in COPD sputum (1.92 ± 3.11 ng/mL, n = 32) was higher than that of both age-matched smokers without COPD (0.48 ± 0.63 ng/mL, n = 11) and healthy nonsmokers (0.55 ± 1.11 ng/mL, n = 9). Sputum PAI-1 significantly correlated with sputum malondialdehyde (MDA) in COPD (r = 0.59, P < .001). In addition, NF-κB activity in sputum macrophages (three control and seven COPD subjects) significantly correlated with both sputum PAI-1 (r = 0.72, P < .05) and sputum MDA (r = 0.78, P < .01). An in vitro study showed that both hydrogen peroxide and cigarette smoke-conditioned medium induced PAI-1 production in A549 cells, and the production was inhibited by an inhibitor of I κB kinase-β in a concentration-dependent manner. Furthermore, histone deacetylase 2 (HDAC2) knockdown by RNA interference, a mimic of oxidative-stress-dependent HDAC2 reduction, enhanced tumor necrosis factor-α-induced PAI-1 induction (half maximal effective concentration [EC50], 0.64 ± 0.19 ng/mL in HDAC2-KD, 7.64 ± 3.70 ng/mL in control) concomitant with enhancement of NF-κB p65 acetylation and NF-κB DNA-binding activity.

Oxidative stress, directly or indirectly via HDAC reduction, plays a role in PAI-1 expression in COPD via activation of NF- κ B.