Role of basement membrane collagen and elastin in the autofluorescence spectra of the colon

Background: Autofluorescence can be used to detect neoplasia in the colon. Two known fluorophores, collagen and elastin, are probably partly responsible for colonic emission spectra. Their contribution to colonic autofluorescence was investigated. Methods: Autofluorescence spectra of normal, dysplastic, and malignant colonic tissue were studied by using excitation wavelengths from 280 nm to 350 nm. The wavelengths of peak emission and their widths at half maximum intensity were measured. Similar measurements were performed on collagen types I, III, IV, V, IX, and elastin. Colonic spectra were compared to those of collagen and elastin. Spectral differences between collagen types IV (basement membrane) I, III, V, and IX were studied. Results: Four major emission peaks were noted whose wavelength of peak emission and full widths at half maximum intensity were independent of tissue histology. The emission spectra of type IV collagen differed markedly from that of nonbasement membrane collagens and elastin. Conclusions: Type IV (basement membrane) collagen is most likely responsible for the emission peak at 365 nm. The spectra of basement membrane collagen and not other types of collagen should be used in studies of epithelial tissue spectra. Elastin did not appear to be responsible for any of the four autofluorescence peaks observed in colonic tissue.