Background & objective: Despite the established pro-inflammatory actions of platelet activating factor (PAF) observed on chronic obstructive pulmonary disease (COPD), its action on airway remodeling has been still unclear. It has been reported that nuclear factor-kappa B (NF-kappaB) activity is necessary for ASMC proliferation. Further, PAF has been identified as the proximal inducer of NF-kappaB. The present study was thus aimed to investigate the effect of PAF on airway smooth muscle cells (ASMC) proliferation and to evaluate the potential role of NF-kappaB in this regulation.
Methods: Healthy male Sprague-Dowley rats of 6-8 wk age were used for obtaining ASMCs. 3-(4,5- dimethylthiazole-2-yl)-2,5-diphenyltetrazolium-bromide (MTT) assay was to investigate the effects of PAF on ASMC proliferation and to confirm its optimum concentration for action. Additionally, cell proliferation was also examined using cell cycle assay by flow cytometry and immunocytochemical staining for proliferating cell nuclear antigen (PCNA). And NF-kappaB DNA-binding activity was assayed by electrophoretic mobility shift assay (EMSA).
Results: PAF stimulated ASMC proliferation with its peak at 100 nM. At this optimum concentration, PAF significantly increased the cell proliferation index (PI) and the PCNA-positive rate in the ASMCs, as well as NF-kappaB DNA- binding activity. Whereas, 20 mM N-acetylcysteine (NAC) pre-treatment effectively blocked all of these events.
Interpretation & conclusion: The present findings demonstrated that PAF could promote ASMC proliferation, suggesting its potential involvement in airway remodeling. Our study also suggested the promising action of 20 mM NAC on the alleviation of airway remodeling due to direct inhibition of ASMC proliferation. The involved mechanism would be relevant to the change of NF-kappaB activation in ASMCs.