Antioxidant Activity Mediates Pirfenidone Antifibrotic Effects in Human Pulmonary Vascular Smooth Muscle Cells Exposed to Sera of Idiopathic Pulmonary Fibrosis Patients

Abstract

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease characterized by an exacerbated fibrotic response. Although molecular and cellular determinants involved in the onset and progression of this devastating disease are largely unknown, an aberrant remodeling of the pulmonary vasculature appears to have implications in IPF pathogenesis. Here, we demonstrated for the first time that an increase of reactive oxygen species (ROS) generation induced by sera from IPF patients drives both collagen type I deposition and proliferation of primary human pulmonary artery smooth muscle cells (HPASMCs). IPF sera-induced cellular effects were significantly blunted in cells exposed to the NADPH oxidase inhibitor diphenyleneiodonium (DPI) proving the causative role of ROS and suggesting their potential cellular source. Contrary to IPF naive patients, sera from Pirfenidone-treated IPF patients failed to significantly induce both ROS generation and collagen synthesis in HPASMCs, mechanistically implicating antioxidant properties as the basis for the in vivo effect of this drug.

Figure 1

(a-b) Real-time assessment of intracellular ROS production and collagen I synthesis in HPASMCs exposed to sera of IPF patients. (a) Before stimulation, subconfluent human pulmonary artery smooth muscle cells (HPASMCs) were loaded with 10 μM of H₂-DCFDA and then cultured in basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD). Variations in intracellular ROS levels were kinetically determined in a 5-hour time-course (a randomly selected representative experiment is reported) and values at 2 hours (steady state) were used in the future comparisons. Fluorescence data were normalized for protein content and expressed as relative fluorescence units (RFUs). (b) Before stimulation, subconfluent HPASMCs were transduced with lentiviral particles obtained from the COL1A1-LV-tGFP and EF1α-LV-FP602 lentivectors and then cultured in basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD). Variations of COL1 promoter activation were kinetically followed for 10 hours (a randomly selected representative experiment is reported) and values at 8 hours (steady state) were used in the future comparison. Data are normalized for transduction efficiency by reporting the ratio of COL1A1-LV-tGFP to EF1α-LV-FP602 relative fluorescence units (RFUs).

Figure 2

(a-b) Effects of IPF sera on HPASMC intracellular ROS levels. Before stimulation, subconfluent human pulmonary artery smooth muscle cells (HPASMCs) were loaded with 10 μM of H₂-DCFDA, then cultured in basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD). (b) In selected experiments, cells were pretreated for 60 min with the NADPH oxidase inhibitor diphenyleneiodonium (DPI) before exposure to the sera. (a-b) Data represent the variations of intracellular ROS levels after 2 hours of sera stimulation. Fluorescence data were normalized for protein content and expressed as relative fluorescence units (RFUs). P value indicating that the significance is reported in the figure.

Figure 3

(a-b) Effects of IPF sera on HPASMC collagen I production. (a) Before stimulation, subconfluent HPASMCs were transduced with lentiviral particles obtained from the COL1A1-LV-tGFP and EF1α-LV-FP602 lentivectors and then cultured in basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD). Data represent the collagen I promoter activity after 8 hours of sera stimulation. Data are normalized for transduction efficiency by reporting the ratio of COL1A1-LV-tGFP to EF1α-LV-FP602 relative fluorescence units (RFUs). (b) Subconfluent HPASMCs were stimulated for 48 hrs with basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD) and processed for collagen I quantification as reported in the Materials and Methods. In selected experiments, cells were pretreated for 60 min with the NADPH oxidase inhibitor diphenyleneiodonium (DPI) before exposure to the sera. Data are expressed as ng/ml collagen protein. P value indicating that the significance is reported in the figure.

Figure 4

(a-b) Effects of IPF sera on HPASMC proliferation. Subconfluent HPASMCs were cultured for 48 hours in basal medium containing 10% (v/v) of sera from idiopathic pulmonary fibrosis (IPF), sera from idiopathic pulmonary fibrosis patients treated for 24 weeks with Pirfenidone (IPF + D), and healthy donors (HD). In selected experiments, cells were pretreated for 60 min with the NADPH oxidase inhibitor diphenyleneiodonium (DPI) before exposure to the sera. Data are expressed as ng/ml collagen protein. (a-b) Data are expressed as relative light units/sec (RLU/s). P value indicating that the significance is reported in the figure.