A proton nuclear magnetic resonance-based metabolomic approach in IgA nephropathy urinary profiles

Immunoglobulin A nephropathy (IgAN) is the most common form of primary glomerulonephritis worldwide. Both one-dimensional NOESY and transverse-relaxation filter CPMG NMR spectra were recorded to investigate the urine metabolome of 24 IgAN patients and to detect altered metabolic profiles in comparison with 68 healthy matched controls. The spectral data were analyzed using multivariate statistical techniques. The analysis revealed that the NMR spectra of IgAN patients were statistically different from those of the controls (P = 4 × 10-7 for 1D-NOESY and P = 2 × 10-7 for CPMG). The robustness of the determined statistical model was confirmed by its predictive performance (for the 1D-NOESY dataset: sensitivity = 67 %, specificity = 95 %; for the CPMG dataset sensitivity = 60 %, specificity = 94 %). For the first time we found metabolites, including betaine and citrate, that are differentially modulated in IgAN patients compared to controls and that may be directly involved in the pathogenesis of IgAN. These metabolites may influence, directly or indirectly, the TNF-α, a regulating factor of the Th1/Th2 cell balance that is relevant in the pathology. The involvement of metabolites such as betaine and citrate in TNF-α regulation supports the power of the identified metabolic profiles to discern IgAN from controls.