Transport of AOPP-Albumin into Human Alveolar Epithelial A549 Cells

Purpose. Alveolar clearance of proteins, such as albumin, plays an essential role in recovery from lung injuries. Albumin is known to be oxidized by reactive oxygen species (ROS), leading to generation of advanced oxidation protein products (AOPP)-albumin in the alveolar lining fluid. In this study, we aimed to characterize the uptake of FITC-labeled AOPP-albumin (FITC-AOPP-albumin) into human alveolar epithelial cell line, A549. Methods. FITC-AOPP-albumin uptake into A549 cells and its effect of ROS generation was evaluated using fluorescence spectrometer and flow cytometry, respectively. Results. FITC-AOPP-albumin was taken up by A549 cells in a time- and temperature-dependent fashion, and showed saturation kinetics with a K-m value of 0.37 mg/mL. The uptake of FITC-AOPP-albumin was suppressed by phenylarsine oxide, a clathrin-mediated endocytosis inhibitor, but not by indomethacin and nystatin, caveolae-mediated endocytosis inhibitors, or 5-(N-ethyl-N-isopropyl) amiloride, a macropinocytosis inhibitor. AOPP-albumin induced ROS generation in A549 cells, suggesting that alveolar clearance of AOPP-albumin should be important to prevent further ROS generation. Conclusion. AOPP-albumin is transported into alveolar epithelial cells through clathrin-mediated endocytosis, which may be important to prevent further ROS generation.