Oxidative stress and Nrf2 expression in peripheral blood mononuclear cells derived from COPD patients: an observational longitudinal study

Background: A persistent low inflammatory-oxidative status and the inadequacy of the antioxidant nuclear factor-E2-related factor 2 (Nrf2) have been implicated in chronic obstructive pulmonary disease (COPD) progression. Therefore this study was aimed to assess the association between lung function decline and oxidative-inflammatory markers and Nrf2 signaling pathway expression in peripheral blood mononuclear cells (PBMCs) over time.

Methods: 33 mild-moderate COPD outpatients (mean age 66.9 ± 6.9 years) were age-sex matched with 37 no-COPD subjects. A clinical evaluation, blood sampling tests and a spirometry were performed at baseline and after a mean follow-up of 49.7 ± 6.9 months.

Results: In COPD, compared to no-COPD, we found a faster lung function decline at follow-up. Although similar prevalence of smoking, hypertension, diabetes and dyslipidemia, systemic markers of inflammation (hs-CRP and white blood cells, WBCs) and oxidative stress (8-isoprostane) were significantly increased in COPD at follow-up, while the antioxidant glutathione (GSH) was significantly reduced. Moreover the expression of Nrf2 and of Nrf2-related genes heme oxygenase (HO)-1 and glutamate-cysteine ligase catalytic (GCLC) subunit in PBMCS were significantly down-regulated in COPD at follow-up, whereas no changes were observed in no-COPD. The percent variation (Δ) of FEV₁ detected after the follow-up in COPD patients was directly correlated with ΔNrf2 (r = 0.826 p < 0.001), ΔHO-1 (r = 0.820, p < 0.001) and ΔGCLC (r = 0.840, p < 0.001). Moreover ΔFEV₁ was also directly correlated with ΔGSH (r = 0.595, p < 0.01) and inversely correlated with Δ8-iso (r = - 0.587, p < 0.01) and with baseline smoking history (r = - 0.39, p < 0.03). No correlation was found between ΔFEV₁, ΔCRP and ΔWBCs. By means of hierarchical stepwise multiple linear regression, taking into account other baseline key factors related to FEV₁, ΔNrf2, ΔHO-1and ΔGCLC were found to be significant predictors of ΔFEV₁, explaining 89.5% of its variance.

Conclusions: Although our results must be confirmed in larger trial they suggest that the down-regulation of Nrf2/ARE gene expression in PBMCs may be one of the determinants of FEV₁ decline and of COPD progression. Therefore the future possibility to counteract Nrf2 decline in COPD patients may help in reducing the negative effects of the oxidative stress-induced progression of the disease.