Autofluorescence characteristics of immortalized and carcinogen-transformed human bronchial epithelial cells

Tissue autofluorescence has been explored as a potential method of noninvasive pre-neoplasia (pre-malignancy) detection in the lung. Here, we report the first studies of intrinsic cellular autofluorescence from SV40 immortalized and distinct tobacco-carcinogen-transformed (malignant) human bronchial epithelial cells. These cell lines are useful models for studies seeking to distinguish between normal and pre-neoplastic human bronchial epithelial cells. The cells were characterized via spectrofluorimetry and confocal fluorescence microscopy. Spectrofluorimetry revealed that tryptophan was the dominant fluorophore. No change in tryptophan emission intensity was observed between immortalized and carcinogen-transformed cells. Confocal autofluorescence microscopy was performed using a highly sensitive, spectrometer-coupled instrument capable of limiting emission detection to specific wavelength ranges. These studies revealed two additional endogenous fluorophores, whose excitation and emission characteristics were consistent with nicotinamide adenine dinucleotide (NADH) and flavins. In immortalized human bronchial epithelial cells, the fluorescence of these species was localized to cytoplasmic granules. In contrast, the carcinogen-transformed cells showed an appreciable decrease in the fluorescence intensity of both NADH and flavins and the punctate, spatial localization of the autofluorescence was lost. The observed autofluorescence decrease was potentially the result of changes in the redox state of the fluorophores. The random cytoplasmic fluorescence pattern found in carcinogen-transformed cells may be attributed to changes in the mitochondrial morphology. The implications of these results to pre-neoplasia detection in the lung are discussed.