High Levels of Aromatic Amino Acids in Gastric Juice during the Early Stages of Gastric Cancer Progression

Background: Early-stage gastric cancer is mostly asymptomatic and can easily be missed easily by conventional gastroscopy. Currently, there are no useful biomarkers for the early detection of gastric cancer, and their identification of biomarkers is urgently needed. Methods: Gastric juice was obtained from 185 subjects that were divided into three groups: non-neoplastic gastric disease (NGD), advanced gastric cancer and early gastric cancer (EGC). The levels of aromatic amino acids in the gastric juice were quantitated using high-performance liquid chromatography. Results: The median values (25th to 75th percentile) of tyrosine, phenylalanine and tryptophan in the gastric juice were 3.8 (1.7-7.5) mu g/ml, 5.3 (2.3-9.9) mu g/ml and 1.0 (0.4-2.8) mu g/ml in NGD; 19.4 (5.8-72.4) mu g/ml, 24.6 (11.5-73.7) mu g/ml and 8.3 (2.1-28.0) mu g/ml in EGC. Higher levels of tyrosine, phenylalanine and tryptophan in the gastric juice were observed in individuals of EGC groups compared those of the NGD group (NGD vs. EGC, P<0.0001). For the detection of EGC, the areas under the receiver operating characteristic curves (AUCs) of each biomarker were as follows: tyrosine, 0.790 [95% confidence interval (CI), 0.703-0.877]; phenylalanine, 0.831 (95% CI, 0.750-0.911); and tryptophan, 0.819 (95% CI, 0.739-0.900). The sensitivity and specificity of phenylalanine were 75.5% and 81.4%, respectively, for detection of EGC. A multiple logistic regression analysis showed that high levels of aromatic amino acids in the gastric juice were associated with gastric cancer (adjusted beta coefficients ranged from 1.801 to 4.414, P<0.001). Conclusion: Increased levels of tyrosine, phenylalanine and tryptophan in the gastric juice samples were detected in the early phase of gastric carcinogenesis. Thus, tyrosine, phenylalanine and tryptophan in gastric juice could be used as biomarkers for the early detection of gastric cancer. A gastric juice analysis is an efficient, economical and convenient method for screening early gastric cancer development in the general population.