Analysis of nucleotides and aromatic amino acids in normal and neoplastic colon mucosa by ultraviolet resonance raman spectroscopy

The objective of this study was to explore the potential of using ultraviolet resonance Raman (UVRR) spectroscopy to analyze normal and neoplastic colon tissue. Ultraviolet light at 251 nm, generated from the third harmonic of a Titanium:Sapphire laser, was used to irradiate the surfaces of surgically resected human colon specimens from six patients, five clinically diagnosed with adenocarcinoma, and one with familial adenomatous polyposis. All grossly neoplastic samples found to contain mucosal dysplasia or invasive adenocarcinoma upon histologic evaluation, were analyzed in parallel with normal tissue obtained from the same specimen and located at least 1 cm away from grossly neoplastic tissue. The colon spectra were modeled as a linear combination of nucleotide, aromatic amino acid, and lipid lineshapes, using chemical standards as a reference. Nucleotide and amino acid contributions to the UVRR spectra were quantified by a least squares minimization method. The least squares minimization spectral model was verified in aqueous solutions, where relative concentrations of free nucleotides and DNA were quantified with <10% error. Of the 11 neoplastic samples studied from the 6 specimens, 10 showed either a lower amino acid/nucleotide ratio, a lower level of adenyl (A) signal, or both when compared with their normal counterpart. Lower amino acid/nucleotide ratio was present in five of six samples containing only dysplasia, and three of the five samples containing invasive adenocarcinoma. Lower A was present in all five samples containing invasive cancer, and in three of the six samples containing only dysplasia. This lower level of A corroborates previously published biochemistry work showing a lower level of total adenylates in tumor homogenates compared with normal tissue. Our data indicate that surface UVRR may provide unique information about site-to-site changes in cellular metabolites during colon carcinogenesis.