Urinary profiles of free amino acids and metal(loid)s in testicular cancer

Testicular germ cell tumours (TGCT) are the most common malignancy in men aged 15–35 years and its incidence is increasing worldwide. Tumour markers commonly used in the diagnosis and prognosis of TGCT have limited sensitivity and specificity and additional, minimally invasive biomarkers for disease management are needed. Metabolomic-based profiling of amino acids in urine may identify changed metabolites as potential biomarkers of testicular cancer. Impaired metal(loid) homeostasis may increase susceptibility to cancer development. We compared a quantitative profile of 30 amino acids and 18 metal(loid)s in urine samples between 86 men with newly diagnosed TGCT and 68 control subjects, aged 18 to 55 years. The concentration of free amino acids was determined by GC-MS using Phenomenex EZ:faast kit for sample preparation, multi-element analysis was performed by ICP-MS, and all results were corrected for creatinine levels. Testicular cancer patients had significantly higher levels of aspartic acid (Asp), manganese (Mn) and zinc (Zn), and significantly lower levels of threonine (Thr), serine (Ser), histidine (His) and cobalt (Co) when compared to control subjects. Linear discriminant analysis using all 30 amino acids successfully separated subjects with TGCT from control subjects and the discrimination rate was 86%. Metabolic pathway analysis (MetaboAnalyst 4.0) showed that Asp, Thr, Ser, and His were related to alterations in 12 metabolic pathways and those with the highest impact were metabolism of alanine, aspartate and glutamate (0.26) and glycine, Thr and Ser (0.23). Our results indicated that disorders in the citric acid cycle, the urea cycle and amino acid metabolism play a role in the pathogenesis of testicular cancer. The impaired urinary profile of Mn, Co and Zn may be highly relevant with regard to their role in amino acids synthesis, antioxidant defense and genetic repair processes. More research is needed to verify our findings