Monitoring cellular metabolism with fluorescence lifetime of reduced nicotinamide adenine dinucleotide

Formulation of oxidative phosphorylation and its first observation by means of fluorescence spectroscopy in the 1960s led to the acceptance of bioenergetics as a new field of studies. The new discipline grew fast with the increasing number of papers, related to the energy generation in mitochondria, advancement of the instrumentation, and improvement of observation techniques. As such, fluorescence lifetime imaging microscopy (FLIM) has gained popularity as a sensitive technique to monitor the functional/conformational states of nicotinamide adenine dinucleotide reduced (NADH)-one of the main compounds of oxidative phosphorylation. We hereby review the development and current application of cellular metabolism observation via NADH FLIM, illustrating it with the examples of both physiological (cell density, apoptosis, necrosis) and pathological states (inhibition of the electron transfer chain).