Potential application of CuSO4 the reduction of lipofuscin autofluorescence in formalin-fixed paraffin-embedded tissue

The fluorescent pigment lipofuscin accumulates within the cytoplasm of cells of most of the organs. Because of its broad excitation and emission spectra, the presence of lipofuscin autofluorescence complicates the use of fluorescence microscopy. In this study, we examined chemical treatments of tissue sections with two concentration of CuSO4 for their ability to reduce or eliminate lipofuscin-like autofluorescence without adversely affecting other fluorescent labels. We found that 4mM CuSO4 in 50 mM ammonium acetate buffer mildly eliminated lipofuscin autofluorescence in sections of human tonsil or mouse synovial tissue, whereas, at higher concentration (10mM) the autofluorescence was almost completely abolished. We found that this treatment had no effect on the fluorescence intensity of target tissue. We conclude that treatment of tissue with CuSO4 provides a reasonable compromise between reduction of lipofuscin-like fluorescence and maintenance of specific fluorescent labels.