Parallel metabolomics of urine and serum revealed systematic alteration associated with renal disease

Background: Membranous nephropathy is an important glomerular disease characterized by podocyte injury and proteinuria, but no metabolomics research was reported as yet. Here, we performed a parallel metabolomics study, based on human urine and serum, to comprehensively profile systematic metabolic alterations, identify differential metabolites, and understand the pathogenic mechanism of membranous nephropathy. Results: There were obvious metabolic distinctions between the membranous nephropathy patients with urine protein lower than 3.5 g/24h (LUPM) and those higher than 3.5 g/24h (HUPM) by PLS-DA model analysis. In total, 26 urine metabolites and 9 serum metabolites were identified to account for such differences, and the majority of metabolites was significantly increased in HUPM patients whether for urines or for serums. Combining the results of urine with serum, all differential metabolites were classified to 5 classes. This classification helps globally insight the systematic metabolic alteration before and after blood flowing through kidney. Citric acid and 4 amino acids were markedly increased only in the serum samples of HUPM patients, implying more impaired filtration function of kidneys of HUPM patients than LUPM patients. The dicarboxylic acids, phenolic acids, and cholesterol were significantly elevated only in urines of HUPM patients, suggesting more severe oxidative attacks than LUPM patients. Conclusion: Parallel metabolomics of urine and serum revealed the systematic metabolic variations associated with LUPM and HUPM patients, where HUPM patients suffered more severe injury of kidney function and oxidative stresses than LUPM patients. This research exhibited a promising application of parallel metabolomics in renal diseases.