Biochemical characterization of saliva of smoking and non-smoking patients by using Fourier-transform infrared spectroscopy

More than 90% of oral malignant neoplasms consist of squamous cell carcinoma originated from extrinsic and/or intrinsic multifactorial etiology on the epithelium of the oral mucosa. This multifactorial etiology makes early-stage cancer detection challenging due to the lack of associated oral-tissue clinical features and absence of changes on conventional cellular-imaging, serological and histopathological exams. By using a molecular-sensitive optical technique such as Fourier-transform infrared (FT-IR) spectroscopy, disease-specific biochemical changes can be detected non-destructively, non-invasively and with small sample volumes. In this study, we have used FT-IR spectroscopy to analyze saliva samples of control, smoker, and occasional smoker groups and determine their intrinsic molecular changes as well as the performance of sample differentiation by using a neural network classifier. Saliva samples were collected by spitting, homogenized and stored at -20 degrees C until analysis. Spectral data was collected in the fingerprint region (900cm(-1) to 1800cm(-1)) by using a Thermo Scientific Nicolet 6700 ATR FT-IR Spectrometer, in which 1-mu l samples were placed on the crystal without additives and left to dry completely by an average time of 5 minutes. Data pre-processing and analysis was performed on the OriginPro8.5 and Orange software. Saliva-sample classification was performed with leave-one-out validation. Correctly classified instances were 72.7% for the control group, 65.5% for occasional smokers and 75% for smokers. Sample differences were observed in the peaks at 1076cm(-1) (skeletal cis conformation of DNA and symmetric stretching of phosphate [PO2], 1403cm(-1) symmetric CH3 modes of protein methyl groups and delta sCH3 of collagen, 1451cm(-1) asymmetrical CH3 bending modes of the protein methyl groups, 1547cm(-1) of protein band, amide II, peptide and proteins amide II, and 1646cm(-1) amide I, C-5 methylated cytosine, C=O bond, C=C stretching uracil and NH2 guanine.