Effects of Chinese green tea on cigarette smoke-induced lung inflammation, oxidative stress and protease activity in rats

Abstract

INTRODUCTION: Chronic obstructive pulmonary disease (COPD) is a progressively destructive airway disease mainly caused by smoking. Systemic and lung inflammation persists in COPD patients even after smoking cessation. Chronic inflammation and/or oxidative stress cause lung damage due to the release of destructive proteases such as matrix metalloproteinases (MMPs)-2/9/12. Chinese green tea is thought to have both anti-inflammatory and anti-oxidative effects in different systems. This study is to address whether cigarette smoke (CS) exposure would induce lung inflammation, oxidative stress and MMPs activity, and whether Chinese green tea would reverse such effects. METHODS: Sprague-Dawley rats were divided into four groups, i.e. sham air (SA), 4% CS, 2% Lung Chen tea plus SA or 4% CS. Exposure to sham air or 4% CS was performed for 1h/day for 56 days in ventilated smoking chambers. Lung tissues and bronchoalveolar lavage fluid (BALF) were obtained from rats sacrificed 24h after last CS exposure. The protein levels of pro-inflammatory cytokines/chemokines were determined by ELISA. The MMP activity was assessed by gelatin and casein zymography respectively. Local oxidative damage was determined by staining lung sections with anti-8-oxo-dG antibody and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG) in lung homogenates. RESULTS: Elevation of interleukin (IL)-1b/-6, interferon (IFN)-g and cytokine induced neutrophil chemoattractant (CINC)-1 was observed in lung after CS exposure. MMP-12 activity was increased in BALF in CS-exposed rats. There were no differences between SA or CS exposure in MMP-2/-9 activities in BALF. Pretreatment of Chinese green tea reversed local DNA oxidation and IL-6 elevation (1.48 ± 0.25 vs 0.67 ± 0.14 ng/mg protein, for CS and Tea/CS respectively; p < 0.01) but did not affect other pro-inflammatory cytokines/chemokines and MMP-12 activity. CONCLUSION: Our data demonstrated that cigarette smoke exposure led to lung inflammation, local oxidative stress and elevation of protease activity in our rat model. These results support that Chinese green tea might be beneficial to smoke-induced local oxidative damage and inflammation.