Urinary podocalyxin and nephrin levels as biomarkers in lupus nephritis patients: Relation to renal involvement and disease activity

Aim of the workTo evaluate the impact of systemic lupus erythematosus (SLE) on urinary levels of podocalyxin and nephrin and to determine their relationship to renal biopsy and disease activity in lupus nephritis (LN) patients.Patients and methodsThe study included 50 LN patients with their renal biopsy classified according to the international society of nephrology. Disease activity was determined using the British Isles Lupus Assessment Group (BILAG). All patients underwent clinical and laboratory evaluation. Urine samples were collected for the assessment of urinary podocalyxin (UPx) and nephrin (UN) by ELISA and for the estimation of protein (UP) and creatinine (Cr) concentrations. The UPx:Cr, UN:Cr and UP:Cr ratios were calculated.ResultsUrinary levels of podocalyxin (593.8 ± 282.2 ng/ml), nephrin (304.1 ± 236.8 ng/ml) and protein (2.36 ± 0.56 g/l) were significantly higher, while urinary creatinine levels (101.4 ± 28.7 mg/l) lower in LN patients compared to control (38.1 ± 9 ng/ml, 19.2 ± 4.1 ng/ml, 0.34 ± 0.13 g/l and 155.4 ± 26.7 mg/l; p = 0.0008, p = 0.0003, p = 0.00002 and 0.0009, respectively). Consequently, UNCr, UPxCr and UPCr ratios were significantly higher in patients compared to control. There was a significant correlation of the estimated ratios with the LN class and with the BILAG scores being most significant with UPx:Cr ratio. ROC curve and regression analyses defined UPx:Cr ratio as the specific significant predictor of pathological LN grade.ConclusionSLE deleteriously affects fine glomerular structure as reflected by increased urinary levels of podocyte-related proteins; podocalyxin and nephrin. Urinary podocalyxin/creatinine ratio significantly predicts the pathological impact of SLE on the kidney and could be used as a non-invasive marker for such effect and its progression.