Objective: To study the mechanisms of N-acetylcysteine (NAC) in the inhibition of proliferation and collagen synthesis of human pulmonary fibroblasts.
Methods: The human pulmonary fibroblasts (HFB) were primarily cultured in complete medium of DMEM/F12, with the cell line A549 derived from alveolar epithelia as the control. Different concentrations of NAC were administrated, with or without stimulation by TGF-beta(1) for 24 h. The cell proliferations were tested by methylthiazolyltetrazolium (MTT) and cell cycle detected with flow cytometer. The mRNA expression of type I procollagen was tested with RT-PCR. Proteins of cyclin E, alpha-SMA and STAT-3 were detected with Western blotting.
Results: The proliferation of HFB was inhibited significantly by NAC at different concentrations (5, 10, 20 and 40 mmol/L). NAC had no effects on proliferation of A549 at a dose of 20 mmol/L. The cell proportion in G(0)/G(1) phase was increased by NAC at different concentrations (10, 20 and 40 mmol/L), while the changes in S-phase ratio were decreased significantly. Procollagen type Isynthesis was increased by TGF-beta(1) significantly. NAC showed inhibition on procollagen type I synthesis before or after stimulation with TGF-beta(1). Expression of protein cyclin E and alpha-SMA was significantly induced by TGF-beta(1), the relative indensity being 0.98 +/- 0.09 and 1.56 +/- 0.23 respectively. Induction of cyclin E by TGF-beta(1) was attenuated significantly by NAC 20 mmol/L (0.52 +/- 0.04). But alpha-SMA was not changed by NAC 20 mmol/L (1.63 +/- 0.20). Stimulation with TGF-beta(1) and NAC had no effects on expression of STAT-3.
Conclusions: Inhibition on proliferation of HFB by NAC may be through the attenuation of cyclin E. Differentiation of fibroblasts into myofibroblasts was inhibited by NAC through inhibition on alpha-SMA. NAC directly inhibited collagen synthesis.