Multiparametric luminescence lifetime imaging: a new diagnostic tool to follow up bioenergetic alterations during PDT

Altered bioenergetic metabolism is a common property during tumor development and neurological disorders. It is often accompanied by a switch from oxidative phosphorylation (OXPHOS) to glycolysis and vice versa. Depending on the energy metabolism of the cells they become more oxidized (when there is more OXPHOS) or more reduced (more glycolysis). Various algorithms have been developed to correlate the metabolic state of the cells with the fluorescence lifetimes of coenzymes such as NAD(P)H and FAD and with the relative contributions of their decaying components. However, as observed in a variety of investigations, the situation is complex and the result is influenced by parameters like oxidative stress, pH or viscosity, influencing the lifetime of NAD(P)H. Also for FAD the situation is not unambiguous, taking into account that both FMN and FAD are involved in the complexes of the mitochondrial respiratory system, leading to different lifetime results. Besides, oxygen concentration and consumption has to be taken into account. Within this talk the various aspects of bioenergetic alterations will be discussed and new sophisticated methods will be presented such as correlated FLIM (fluorescence lifetime imaging) and PLIM (phosphorescence lifetime imaging) to follow up disease development and responses, for example during photodynamic therapy (PDT). Correlated FLIM/PLIM aims to provide important insights in new theranostic procedures.