Proteinuria is Associated with Urinary Loss of Cubilin and Vitamin D-Binding Protein in Patients with Preeclampsia

Women with preeclampsia (PE) form a vulnerable group for vitamin D3 deficiency. Reabsorption of vitamin D3 occurs in the proximal tubule after being endocytosed in combination with DBP (vitamin D binding protein) by the megalin/cubilin receptor. Because proteinuria promotes tubule injury and dysfunction, we hypothesized that the proteinuria present in PE could promote the loss of these components into the urine. Twenty preeclamptic patients and ten normal pregnant women with a gestational age greater than 20 weeks composed three groups: NC, normotensive control pregnant patients; PE, non-proteinuric preeclamptic patients; and PPE, preeclamptic patients with proteinuria. When proteinuria was absent, preeclampsia was diagnosed accordingly to the American College of Obstetricians and Gynecologists’ (ACOG) guideline. The presence of 24-hour proteinuria equal to or greater than 300 mg was considered to form the PPE group. Urinary cubilin, megalin, and DBP were measured by ELISA and normalized by urinary creatinine. Regarding gestational age, there was no difference between the groups. NC group had arterial pressure within normal values, whereas PE and PPE groups had a significant increase (p < 0.01). As expected, PPE group presented elevated ACR (p < 0.05), accompanied by large amounts of cubilin and DBP in the urine (p < 0.05 vs. NC and PE). No difference was found in urinary megalin. PPE patients showed more chance of shedding cubilin into the urine compared to non-proteinuric patients (odds ratio 12.7 (1.2–136.3). In conclusion, this study further tightens the relationship between PE and vitamin D(3) deficiency, since proteinuria present in PE induces the loss of molecules responsible for renal tubular vitamin D(3) reabsorption for subsequent activation. Combined with other factors, the proteinuria may intensify vitamin D(3) deficiency in PE.