Glycoproteomic Analysis of Bronchoalveolar Lavage (BAL) Fluid Identifies Tumor-Associated Glycoproteins from Lung Adenocarcinoma

Cytological
examination of cells from bronchoalveolar lavage (BAL)
is commonly used for the diagnosis of lung cancer. Proteins released
from lung cancer cells into BAL may serve as biomarkers for cancer
detection. In this study, N-glycoproteins in eight
cases of BAL fluid, as well as eight lung adenocarcinoma tissues and
eight tumor-matched normal lung tissues, were analyzed using the solid-phase
extraction of N-glycoprotein (SPEG), iTRAQ labeling,
and liquid chromatography tandem mass spectrometry (LC-MS/MS). Of
80 glycoproteins found in BAL specimens, 32 were identified in both
cancer BAL and cancer tissues, with levels of 25 glycoproteins showing
at least a 2-fold difference between cancer and benign BAL. Among
them, eight glycoproteins showed greater than 2-fold elevations in
cancer BAL, including Neutrophil elastase (NE), Integrin alpha-M,
Cullin-4B, Napsin A, lysosome-associated membrane protein 2 (LAMP2),
Cathepsin D, BPI fold-containing family B member 2, and Neutrophil
gelatinase-associated lipocalin. The levels of Napsin A in cancer
BAL were further verified in independently collected 39 BAL specimens
using an ELISA assay. Our study demonstrates that potential protein
biomarkers in BAL fluid can be detected and quantified.