Background Lupus nephropathy (LN) is an important cause of morbidity and mortality in patients with Systemic Lupus Erythematosus (SLE). Considering that renal biopsy is a specialized technique and not risk free, a proteomics study is proposed to determine biomarkers that may help us to differentiate patients diagnosed with SLE with and without renal involvement.

Methods We selected 12 patients with SLE and renal involvement and 14 patients with SLE without renal involvement. There were no differences between groups according to race, gender and age. The patients were classified as moderate (<500), mild (150–500) or normal (<150) level of proteinuria in the urine. A 24 hour urine sample was obtained for analysis. Proteomic analysis was conducted by label free nLC MS/MS analysis.

Results The Principal Component Analysis (PCA) revealed differences between samples from patients who have high level of proteinuria in 24 hours and patients who do not have renal involvement. Interestingly, patients with mild proteinuria correlated better with patients without renal involvement than with the severe proteinuria group. A total of 292 proteins (identified with at least two peptides with a FDR<1%) were quantified and further considered in the analysis. Consistent with the nature of the sample, the Gene Ontology (GO analysis) of the whole list of identified proteins revealed the presence of extracellular (277 proteins, p=2.25E–171) and secretion-related proteins (49 proteins, p=1.1E–09), among others. Proteins related to defensive processes were prominent among them.

Interestingly, clear differences were detected between the three subgroups of samples. The Students T-test analysis reflected the differential presence of 147 proteins (p<0.01) between patients with and without renal involvement, being 17 more abundant in the urine of the patients with renal damage, whereas 130 showed the opposite pattern. The subset of proteins whose abundance increases upon renal damage is comprised of typical highly-abundant serum proteins. In addition, differences between most closely related groups (mild proteinuria and no renal affectation) revealed differences that may be useful for a better stratification of patients.

Conclusions A different protein pattern is observed between the groups of patients, so in a more detailed study we may indicate if some of these can serve as prognostic markers for this type of patients.

Funding Source(s): No funding