Fluorescence spectroscopy of mouse organs using ultraviolet excitation: Towards assessment of organ viability for transplantation

Identifying diseases and evaluating tissue function and viability can be performed by subjective or objective methods. However, subjective techniques may be inaccurate and non-optical objective techniques may be relatively expensive and time-consuming. Then, these techniques may not be suitable for clinical applications that require immediate assessment and intervention. Fluorescence spectroscopy (FS) is one of the optical techniques with great potential for medical diagnostics and surgical guidance. This potential is associated to the possibility of label-free techniques biochemical sensitivity without contrast agents. For clinical applications, fluorescence can be used to assess biomolecular content of respiratory metabolism involving NAD(P)H and FAD. In addition, changes in collagen, elastin, porphyrin, pyridoxine, and tryptophan content can potentially be detected. One way to collect epifluorescence signals from superficial tissue layers is using ultraviolet (UV) excitation. In this study, we used UV excitation FS to investigate the effect of temperature variation (from 0 to 25 degrees Celsius) on tissue autofluorescence. The measurements reproducibility was assessed by variations of the spectral shape accounted by the calculation of the Pearson correlation coefficient for each pair of measurements. Overall, fluorescence measurements were more reproducible at 25°C compared to 0°C. Liver showed lowest fluorescence variability (most homogeneous organ) regarding results from both 300 nm and 340 nm excitations. We report temperature and wavelength-dependent spectral changes due to the tissue thawing by calculating the difference between normalized UVEFS measurements at 0°C and 25°C. Observed differences may be attributed to blood absorption and NADH fluorescence emission. Our results can be used to increase the database of tissue fluorescence spectra using UV excitation for future reference to choose targeted wavelengths in fluorescence instrumentation. Furthermore, our study illustrates expected fluorescence variations during the assessment of organs viability for transplantation, especially due to cold preservation.