Analysis of the metabolic deterioration of ex vivo skin from ischemic necrosis through the imaging of intracellular NAD(P)H by multiphoton tomography and fluorescence lifetime imaging microscopy.

Ex vivo human skin has been used extensively for cosmeceutical and drug delivery studies, transplantable skin allografts, or skin flaps. However, it has a half-life of a few days due to ischemic necrosis. Traditional methods of assessing viability can be time-consuming and provide limited metabolic information. Using multiphoton tomography and fluorescence lifetime imaging (MPT-FLIM) we assess ischemic necrosis of ex vivo skin by NAD(P)H autofluorescence intensity and fluorescence lifetime. Ex vivo skin is stored in the presence and absence of nutrient media (Dulbecco Modified Eagle Medium) at -20, 4, and 37 degrees C and room temperature over a 7-day time course to establish different rates of metabolic deterioration. At higher temperatures we observe a decrease in NAD(P)H autofluorescence, higher image noise, and a significant increase in the average fluorescence lifetime (tau(m)) from approximately 1000 to 2000 ps. Additionally, significant distortions in NAD(P)H fluorescence lifetime histograms correspond to the reduction in autofluorescence. Skin kept at 4 degrees C, with or without media, showed the least change. Our findings suggest that MPT-FLIM enables useful noninvasive optical biopsies to monitor the metabolic state and deterioration of human skin for research and clinical purposes.