ABSTRACT
Time-resolved fluorescence spectrometry is a highly valuable technological tool to detect and characterize mitochondrial metabolic oxidative changes by means of endogenous fluorescence (Chorvat and Chorvatova, Laser Phys Lett 6: 175-193, 2009). Here, we describe the detection and measurement of endogenous mitochondrial NAD(P)H (nicotinamide adenine dinucleotide (phosphate)) fluorescence directly in living cultured cells using fluorescence lifetime spectrometry imaging after excitation with 405 nm picosecond (ps) laser. Time-correlated single photon counting (TCSPC) method is employed.
Subject(s)
Mitochondria/metabolism , NADP/metabolism , Oxidation-Reduction , Spectrometry, Fluorescence/methods , Cell Line , Cell Survival , Electron Transport , Humans , Image Processing, Computer-Assisted , Microscopy, Fluorescence/methodsABSTRACT
Early detection of cancer is crucial for the successful diagnostics of its presence and its subsequent treatment. To improve cancer detection, we tested the progressive multimodal optical imaging of U87MG cells in culture. A combination of steady-state spectroscopic methods with the time-resolved approach provides a new insight into the native metabolism when focused on endogenous tissue fluorescence. In this contribution, we evaluated the metabolic state of living U87MG cancer cells in culture by means of endogenous flavin fluorescence. Confocal microscopy and time-resolved fluorescence imaging were employed to gather spectrally and time-resolved images of the flavin fluorescence. We observed that flavin fluorescence in U87MG cells was predominantly localized outside the cell nucleus in mitochondria, while exhibiting a spectral maximum under 500 nm and fluorescence lifetimes under 1.4 ns, suggesting the presence of bound flavins. In some cells, flavin fluorescence was also detected inside the cell nuclei in the nucleoli, exhibiting longer fluorescence lifetimes and a red-shifted spectral maximum, pointing to the presence of free flavin. Extra-nuclear flavin fluorescence was diminished by 2-deoxyglucose, but failed to increase with 2,4-dinitrophenol, the uncoupler of oxidative phosphorylation, indicating that the cells use glycolysis, rather than oxidative phosphorylation for functioning. These gathered data are the first step toward monitoring the metabolic state of U87MG cancer cells.
