Confocal Raman Spectroscopy Analysis Of Normal And Malignant Gastric Tissues

Gastric cancer is one of the most common occurring malignant tumors globally, whichendangers human health seriously. The incidence and mortality of gastric cancer varies indifferent countries worldwide, and China is one of the highest countries. The incidence andmortality of gastric cancer in our country is more than twice the world average. It is knownthat the prognosis and therapeutic effect of gastric cancer are closely related to cancerstaging at treatment. Early diagnosis is recognized as the crucial approach in improvingsurvival. Presently, most detection methods of gastric cancer can be available based onobvious tissue morphological structure alterations. Thus, early detection and diagnosis ofgastric cancer are of great difficulty. Currently, pathological biopsy guided by endoscopy isrecognized as the “gold standard”, but this method is invasive and impractical in real-timescreening. What’s more, selection of biopsy lesions is depended on physician’s subjectivejudgment. Raman spectroscopy is a vibrational spectroscopic method based on inelasticscattering of light. Laser-confocal Raman Spectroscopy is a rapid, none-destructive, in-situand highly sensitive spectroscopy technique. It can get rid of the interference from water,and detect subtle cellular biochemical changes as well. Internal components of tissuecontain various molecules such as nucleic acids, lipids, proteins and so on. Raman spectraof tissue is produced by the vibrations of various chemical bonds like C=C, N-H, C=O,benzene ring within these molecules. Structural conformation, relative content, electronicenvironment and internal chemical bonds of DNA, amino acids, lipids can all be changedaccompanying with cell malignant transformation, which generate characteristic Ramanspectrum. We investigated both normal and malignant gastric tissues. Through analyzingthe significance of spectral difference between cancer and normal ones, we could not onlyfurther confirm its value in discriminating cancer from normal, but also explore themolecular and biochemical changes associated with canceration. Our study provided a validfoundation for Raman spectroscopy in both application in clinical early diagnosis andinvestigation of mechanism underlying tumorigenesis in stomach.Methods: Gastric cancer tissues were collected either from surgery or from biopsy during gastroscopy. Confocal Raman spectroscopy with an excitation wavelength of785nm was applied in tissue measurement. Average Raman spectrum, average Raman shifts,ratio of relative peak intensity of normal and malignant gastric tissues were calculatedrespectively. Two Independent Sample t-Test was used to analyze the ratio of relative peakintensity between normal and cancer. Meanwhile, its value in differentiating normal fromcancer was also measured. Assignments of Raman peaks were acquired from publishedreferences. At last, biochemical transformation of molecules during gastric cancerdevelopment was also studied through analyzing the assigments of characteristic Ramanpeaks.Results: Raman spectrum from malignant gastric tissues was obviously different fromthat of normal ones. Gastric tissue has plenty of Raman peaks, which mainly located at800-1800cm-1. Compared with normal ones, the shape, position, intensity, number of Ramancharacteristic peaks from malignant gastric tissue have changed:1) Some characteristicpeaks shifted to higher or lower wave number to various degrees, some decreased orincreased respectively, some were newly added while others were absent. All the alterationssuggested that in malignant gastric tissues: content of nucleic acids increased; structure ofnucleic acids tended to be loose; content of unsaturated fatty acids and Carotenoidincreased; composition of protein changed; content of collagen decreased; conformation ofHistones tended to be more stable; more Tryptophan may be buried and then located inhydrophobic environment.2) Some ratio of relative peak intensity of normal andmalignant gastric tissue were significantly different, such as I1088cm-1/I1207cm-1、I1585cm-1/I854（855）cm-1、 I1585cm-1、I1527cm-1and so on, which provided a accuracy of66.7%-87.1%,sensitivity of66.7%-83.3%and specificity of66.7%-89.5%in discriminating cancer fromnormal.Conclusion: Raman spectroscopy provides an effective approach to gastric cancerresearch. It can not only differentiate gastric cancer from normal through spectrum analysis,but also explore the cellular metabolism, molecular and biochemical alteration associatedwith carcinomatous transformation. Raman spectroscopy has great applying potential infundamental mechanism research, clinical detection as well as diagnosis of gastric cancer. Itis of great hope for Raman spectroscopy to be the ideal “optical biopsy”.