Urinary Nephrin and Podocalyxin Levels as Predictors of Pre-eclampsia in High-Risk Pregnant Women

Abstract

Introduction: Pre-eclampsia (PE) is characterized by new-onset hypertension and proteinuria. Damage of podocyte cells has been reported in pre-eclamptic women, thus podocyte specific proteins such as nephrin and podocalyxin could be useful biomarkers in PE. Aim: To investigate the role of urinary nephrin (u-nephrin) and urinary podocalyxin (u-PDX) levels in predicting PE in women with a high-risk pregnancy. Materials and methods: We included 101 pregnant women in this study and allocated them into three groups: group 1 included pregnant women at high risk of developing PE (n=41), group 2 - pregnant women with PE (n=30), and group 3 was the controls including healthy pregnant women (n=30). The inclusion criteria for women with PE were de novo hypertension >140/90 mm Hg, proteinuria >300 mg/24 hours, and presence of edema after 20 weeks of gestation, while the exclusion criteria were a history of renal diseases and pregnant women younger than 18. Inclusion criteria for the group of women with a high-risk pregnancy was gestational week >15, a history of PE in a previous pregnancy, pre-existing diabetes type 1 or 2, pre-existing hypertension, multiple gestations, prior placental abruption, obesity women, nulliparity, maternal age >35 years, and a family history of PE. The study was conducted from March 2016 to May 2017 in the Medical Faculty at the Institute of Medical and Experimental Biochemistry in Skopje. Urine samples were used to measure the nephrin and podocalyxin levels using immunoenzyme assay, creatinine and microalbumin. Blood samples were collected for biochemical analyses. Results: U-nephrin levels were elevated in 96.7% of women with PE, and 73% of women with a high-risk pregnancy. U-PDX levels were elevated in 63% of the women with PE and 100% of the women with a high-risk pregnancy. U-nephrin and u-PDX levels were significantly increased in women with a high-risk pregnancy and women with PE compared with a control group (p<0.001). A significant difference was found between the subgroups of pregnant women classified according to gestational age in their u-nephrin and u-PDX levels. There was a significant positive correlation between the levels of both markers and glomerular filtration rate, and significant negative correlation between the levels of both markers and gestational age. ROC analysis revealed that the cut-off value of 304.6 ng/ml of u-nephrin had a sensitivity (Se) of 96.7%, specificity (Sp) of 96.7% (for both Se and Sp 95% confidence interval (CI) 82.8-99.9), while the cut-off value of 59.5 ng/ml of u-PDX had a sensitivity of 100% and Sp of 93.3% (Se - 95% CI 88.4-100, Sp - 95% CI 77.9-99.2), in distinguishing women with PE and healthy pregnancies. Both markers showed excellent clinical utility (CUI≥0.81), for u-nephrin (CUI+ and CUI− is 0.934), for u-PDX (CUI+ is 0.938; CUI− is 0.933). Conclusions: U-nephrin and U-PDX levels could be useful as predictors of PE in women with a high-risk pregnancy.

Urinary nephrin—a potential marker of early glomerular injury: a systematic review and meta-analysis

“…All studies determining urinary nephrin showed that it increased significantly in patients with increased levels of albumin in urine [24,36]. Likewise, other studies have also shown that urinary nephrin increased linearly with the progression of the disease, this suggests that quantification of nephrin could be a useful biomarker of glomerular injury progression [25,47,49].…”

“…Therefore, an important aspect to include in a meta-analysis such as this is the heterogeneity in diagnostic accuracy of the methods employed by the various studies. ELISA was the method of choice in most studies (n = 11) for the detection of nephrinuria in PE and nephropathies [20,24,25,31,32,36,43,45,[48][49][50]. Interestingly these assays demonstrated improved sensitivity (0.89) and specificity (0.73) and therefore diagnostic accuracy (AUC-SROC = 0.92) for determining urinary nephrin compared to RT-PCR [44,46,47].…”

“…An analysis of the 15 selected studies revealed that all studies aimed to investigate urinary nephrin as an early indicator of glomerular damage in both acute and chronic conditions. Eight studies utilised urinary nephrin for predicting PE [20,25,27,31,32,[43][44][45], six studies utilised urinary nephrin for predicting nephropathy [24,36,[46][47][48][49], and one study utilised urinary nephrin for predicting glomerulopathy/ glomerular injury [50]. Most of the studies used Enzyme Linked Immunosorbent Assay (ELISA) (n = 11) and the remaining used Real Time-Polymerase Chain Reaction (RT-PCR) (n = 3), and Western Blotting (WB) (n = 1) to determine the concentration of urinary nephrin.…”

“…A nationwide cohort study revealed that there is a strong association between PE and later glomerular injury [35], while another study also showed glomerular injury in diabetic nephropathy [24]. These studies revealed that glomerular injury may occur irrespective of proteinuria, that nephrinuria is often detected prior to proteinuria/albuminuria, and that urine nephrin levels correlate with disease severity [25,28,36]. To date, no study has systematically reviewed and analysed the diagnostic accuracy of urinary nephrin for determining glomerular injury in patients with acute and chronic renal injury.…”

“…However, to date, no biomarker has been identified for early detection of acute glomerular injury [22,23]. Recent studies have suggested that podocyte proteins may be a better marker for detection of early glomerular injury [24][25][26][27]. A number of studies have found nephrin to be a promising early marker of glomerular injury [24,[28][29][30][31][32].…”