Pathogenesis of cigarette smoke-induced chronic obstructive pulmonary disease and therapeutic effects of glucocorticoids and N-acetylcysteine in rats.

BACKGROUND

T lymphocytes and matrix metalloproteinase (MMP) play an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). However, the details of the mechanisms involved are unclear. The aims of this study were to investigate the changes in interferon-gamma (IFN-gamma), interleukin-4 (IL-4), MMP-9, MMP-12 and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels in a smoke-induced COPD rat model and the therapeutic effects of glucocorticoids and N-acetylcysteine.

METHODS

Male Wistar rats were exposed to cigarette smoke for 3.5 months. Budesonide or N-acetylcysteine was given in the last month. Lung function was measured at the end of the study. IL-4 and IFN-gamma levels were then determined in bronchoalveolar lavage fluid and lung tissue samples by enzyme-linked immunosorbent assay. The expression of MMP-9, MMP-12 and TIMP-1 mRNA in lung tissue was determined by RT-PCR.

RESULTS

In comparison with the control group, rats exposed to smoke had a significant increase in IL-4 and MMP-12 levels and a significant decrease in IFN-gamma levels. In addition, the IL-4/IFN-gamma ratio and MMP-12/TIMP-1 ratio were both higher. At the same time, the ratio of forced expiratory volume in 0.3 second to forced vital capacity (FEV(0.3)/FVC) and dynamic compliance (C(dyn)) decreased and expiratory resistance (Re) increased. By measuring pulmonary mean linear intercept and mean alveolar numbers, obvious emphysematous changes were observed in the smoke exposed group. After treatment with budesonide, IL-4 and MMP-12 decreased and IFN-gamma increased. The IL-4/IFN-gamma ratio returned to normal, though the MMP-12/TIMP-1 ratio remained unchanged. FEV(0.3)/FVC was significantly higher and Re was significantly lower than that in untreated smoke exposed rats. No significant differences were found in pulmonary mean linear intercept and mean alveolar numbers. After treatment with N-acetylcysteine, IFN-gamma increased and the IL-4/IFN-gamma ratio decreased. The MMP-12/TIMP-1 ratio remained unchanged. Re and C(dyn) both improved obviously. No significant differences were found in pulmonary mean linear intercept and mean alveolar numbers. Correlation analysis indicated that IL-4 levels in lung tissue correlated negatively with FEV(0.3)/FVC (r = -0.53, P = 0.001), IFN-gamma levels in lung tissue correlated negatively with Re (r = -0.63, P = 0.000) and positively with C(dyn) (r = 0.44, P = 0.009), and that the IL-4/IFN-gamma ratio correlated negatively with FEV(0.3)/FVC (r = -0.44, P = 0.010) and C(dyn) (r = -0.42, P = 0.015) and positively with Re (r = 0.58, P = 0.000). Finally, MMP-12 correlated negatively with FEV(0.3)/FVC (r = -0.36, P = 0.026).

CONCLUSIONS

Cigarette smoke exposure increases IL-4 levels and decreases IFN-gamma levels. This may be the result of smoke-induced changes in lung function. Budesonide can mitigate the changes in IL-4 and IFN-gamma levels induced by smoke exposure. N-acetylcysteine has no effect on IL-4, but increases IFN-gamma levels and brings the IL-4/IFN-gamma ratio back to normal. Cigarette smoke can also promote MMP-12 gene expression and elevate the MMP-12/TIMP-1 ratio. This effect may play a role in smoke-induced emphysema. Budesonide and N-acetylcysteine do not alter the MMP-12/TIMP-1 ratio in this study when given in the late phase of smoke exposure.