Background and study aims: The reason for the difference in fluorescence between normal and diseased tissues (carcinoma and adenoma) in the colon observed on autofluorescence endoscopy is unclear, flavins, NADPH and collagen being regarded as possible major sources of fluorescence. The purpose of this study was to identify the reason for this difference in fluorescence.
Patients and methods: Samples of human colonic tissues (adenoma: n = 6, cancer: n = 11, normal: n = 11) were obtained from resected specimens. The flavin content of human colonic tissue was measured by high performance liquid chromatography. Fluorescence microscopy under blue light excitation (400-440 nm) was performed using frozen sections of normal, adenomatous and cancerous tissues, and examining them for the presence and characteristics of fluorescence.
Results: The flavin content of normal and diseased tissue was not significantly different. Fluorescence microscopy of normal colonic tissue revealed strong fluorescence in the submucosal layer, which corresponded to collagen. Tissue fluorescence did not decrease in reducing agent or acid solution. No difference in fluorescence was detected in normal mucosa, adenoma or cancerous tissue on fluorescence microscopy. These findings indicate that flavins and NADPH do not affect tissue fluorescence, and that submucosal collagen is the main source of tissue fluorescence in the colon.
Conclusion: The reason for the decreased fluorescence in diseased tissues appears to be a decrease in collagen fluorescence due to the screening effect of mucosal thickening or replacement of submucosa by cancer cells.