A panel of four plasma amino acids is a promising biomarker for newly diagnosed bladder cancer.

Background Metastasis and recurrence are the main causes of death in post-operative bladder cancer (BC), emphasizing the importance of exploring early-stage diagnostic markers. Serum biomarkers constitute a promising diagnostic approach for asymptomatic stage cancer as they are non-invasive, have high accuracy and low cost. Aims To correlate concentrations of plasma amino acids with BC progression to assess their utility as an early-stage diagnostic. Methods Newly diagnosed BC patients (n=95) and normal controls (n=96) were recruited during the period from 1 December 2018 to 30 December 2020. General and food frequency questionnaires established their basic information and dietary intake data. Venous blood samples were collected from fasting subjects and used to detect levels of plasma amino acids by liquid chromatography-mass spectrometry. Verification was performed on the GSE13507 transcriptome gene expression matrix of BC from Gene Expression Omnibus (GEO) database. Results Eleven amino acids have been identified as altered in the plasma of newly diagnosed BC patients compared to controls (P < 0.05). Adjusted by gender, education, smoking and other factors, plasma ornithine level (OR = 0.256, 95% CI: 0.104 ∼ 0.630) is a protective factor for BC, plasma levels of methionine (OR = 3.460, 95% CI: 1.384 ∼ 8.651), arginine (OR = 3.851, 95% CI: 1.542 ∼ 9.616), and glutamate (OR = 3.813, 95% CI: 1.543 ∼ 9.419) are all risk factors for BC. ROC analysis demonstrated that the combination of plasma ornithine, methionine, arginine and glutamate could accurately diagnose BC (AUC = 0.84, 95% CI: 0.747 ∼ 0.833). In addition, the mRNA level of arginase 1 was decreased (P < 0.05), while the inducible nitric oxide synthase was increased significantly, which may be linked with the disturbance of arginine metabolism in BC patients. Further analysis of GEO database confirmed the role of arginine metabolism. Conclusion A biomarker panel containing four amino acids may provide a feasible strategy for the early diagnosis of BC. However, further validation is required through prospective studies.