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 ultraviol et resonance Raman (UVRR) spectroscopy to analyze normal and neoplastic col on tissue. Ultraviolet light at 251 nm, generated from the third harmonic o f a Titanium:Sapphire laser, was used to irradiate the surfaces of surgical ly resected human colon specimens from six patients, five clinically diagno sed with adenocarcinoma, and one with familial adenomatous polyposis. All g rossly neoplastic samples found to contain mucosal dysplasia or invasive ad enocarcinoma upon histologic evaluation, were analyzed in parallel with nor mal tissue obtained from the same specimen and located at least 1 cm away f rom grossly neoplastic tissue. The colon spectra were modeled as a linear c ombination 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 solu tions, where relative concentrations of free nucleotides and DNA were quant ified with <10% error. Of the 11 neoplastic samples studied from the 6 spec imens, 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 contai ning only dysplasia, and three of the five samples containing invasive aden ocarcinoma. Lower A was present in all five samples containing invasive can cer, and in three of the six samples containing only dysplasia. This lower level of A corroborates previously published biochemistry work showing a lo wer level of total adenylates in tumor homogenates compared with normal tis sue. Our data indicate that surface UVRR may provide unique information abo ut site-to-site changes in cellular metabolites during colon carcinogenesis .