Podocytes in the urine may be a useful marker of disease activity in diabetic nephropathy. Trandolapril may be effective for podocyte injury.

Aims/objectiveNephropathy, a major complication of diabetes, is the leading cause of end-stage renal disease. Recent studies have demonstrated that podocyte injury is involved in the onset of and progression to renal insufficiency. Here, we describe a novel, highly sensitive ELISA for detecting urinary podocalyxin, a glycoconjugate on the podocyte apical surface that indicates podocyte injury, particularly in the early phase of diabetic nephropathy.MethodsUrine samples from patients with glomerular diseases (n = 142) and type 2 diabetes (n = 71) were used to quantify urinary podocalyxin by ELISA. Urine samples were obtained from 69 healthy controls for whom laboratory data were within normal values. Podocalyxin was detected in urine by immunofluorescence, immunoelectron microscopy and western blotting.ResultsMorphologically, urinary podocalyxin was present as a vesicular structure; western blotting showed it as a positive band at 165–170 kDa. Levels of urinary podocalyxin were elevated in patients with various glomerular diseases and patients with diabetes. In patients with diabetes, urinary podocalyxin was higher than the cut-off value in 53.8% patients at the normoalbuminuric stage, 64.7% at the microalbuminuric stage and 66.7% at the macroalbuminuric stage. Positive correlations were observed between urinary podocalyxin levels and HbA1c, urinary β2 microglobulin, α1 microglobulin and urinary N-acetyl-β-d-glucosaminidase, although urinary podocalyxin levels were not correlated with other laboratory markers such as blood pressure, lipid level, serum creatinine, estimated GFR or proteinuria.Conclusions/interpretationUrinary podocalyxin may be a useful biomarker for detecting early podocyte injury in patients with diabetes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-012-2661-7) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

T he podocyte is a highly differentiated cell that has characteristic interdigitating foot processes that cover the outer surface of the glomerular basement membrane (GBM) in the kidney (1). The turnover rate of podocytes is very low under normal and various pathologic conditions compared with that of other glomerular cells (2,3). Meanwhile, podocytes contribute to the hydraulic permeability of the glomerulus and play a crucial role as a filter for macromolecules (1). Because of these biologic and morphologic characteristics of podocytes, injuries to podocytes are accompanied by characteristic changes in morphology, as observed by electron microscopy (EM), including effacement of foot processes, microvillous transformation, and occasional detachment from the GBM (4 -7). In several immunologic and nonimmunologic forms of glomerulonephritis, the podocyte is the primary target of injury (8,9). Podocyte injury is also a key event leading to glomerular sclerosis. Recent studies have revealed that the denuded GBM left behind after a podocyte becomes detached and subsequently adheres to parietal epithelial cells, resulting in the formation of a synechia of the glomerular tuft to Bowman's capsule, which represents the earliest stage of segmental sclerosis (10,11).We recently demonstrated the presence of podocytes and their cell fragments in the urinary sediment of patients with glomerular diseases, in an immunofluorescence (IF) study using a specific monoclonal antibody against podocalyxin (PCX), a glycoprotein that is prominently expressed on podocytes (12). Quantification of urinary podocytes has clinical significance in its ability to predict acute glomerular lesions (13). In addition to urinary podocytes, urine sediments from nephritic patients contain PCX-positive granular structures (PPGS) in or around the urine casts. We hypothesized that these structures represent urinary podocytes and their cell debris. We subsequently found that PPGS are excreted in the urine in far greater numbers compared with urinary podocytes. However, because we also found PPGS in the urine of patients without any urinary podocytes, we questioned whether these structures truly represent cell debris from detached podocytes. Thus, the purpose of the present study was to trace PPGS to their origin immunohistochemically. Materials and Methods Patients, Urine Samples, and Kidney SpecimensUrine samples voided in the morning were obtained from 50 healthy children and adolescents (25 male and 25 female; mean age, 12.3 yr; range, 3 to 20 yr) and 53 patients with active glomerulonephritis or nephrotic syndrome (29 male and 24 female; mean age, 11.3 yr; range,

The significance of the presence of podocytes in the urine was studied in various renal diseases in children. The podocytes were detected by immunofluorescence using monoclonal antibodies against the podocalyxin that is present on the surface of podocytes which serves as a glycocalyx. They were scored according to the numbers per partitioned area on cytospun urine sediments. Urine podocytes were absent in normal control, nonglomerular diseases such as urinary tract infection and nonglomerular hematuria, and glomerular, noninflammatory diseases such as minimal change nephrotic syndrome and membranous nephropathy. Conversely, the excretion of podocytes in the urine were detected in various glomerular, inflammatory diseases. A significantly higher level of the podocyte score was found in the acute state of glomerular diseases which was defined as within 6 months after disease onset. Positive correlations were obtained between the presence of urinary podocytes and the histological features of active extracapillary changes and mesangial proliferation. Urinary podocytes were examined monthly for 12 months in 7 cases with IgA nephropathy and 2 cases with Henoch-Schönlein purpura nephritis, and a consistently higher urinary podocyte score was observed in the patients with histological progression. The scoring of urinary podocytes was found to be useful clinically, as a diagnostic tool for glomerular or nonglomerular diseases, inflammatory or noninflammatory diseases, a marker for the estimation of the severity of active glomerular injury and also as a predictor of disease progression.

Recent studies have revealed that podocytopenia leads to glomerular scarring and that the loss of podocytes into the urine may be a cause of podocytopenia. The purpose of this study was to examine whether serial examinations of urinary podocytes (u-podo) could be a useful predictor of disease progression in children with glomerulonephritis. Urine samples and renal biopsy specimens from 20 patients (10 males and 10 females; mean age 11.8 yr; range 4 to 24 yr) with IgA nephropathy (n ‫؍‬ 17) and Henoch-Schö nlein purpura nephritis (n ‫؍‬ 3) were analyzed. Forty-four renal biopsies were performed on 20 patients. Proteinuria (g/d per 1.73 m 2 ), hematuria (score), and u-podo (cells/ml) were examined twice a month in 24 intervals between two biopsies (mean 16.7 mo; range 4 to 58 mo) and average and cumulative values were determined for the intervals. Renal histologic changes were scored on the basis of acute intracapillary, acute extracapillary, acute tubulointerstitial, chronic intracapillary, chronic extracapillary, and chronic tubulointerstitial lesions, as well as glomerulosclerosis. It was found that hematuria, proteinuria, u-podo, and acute lesion scores decreased during the intervals examined, whereas chronic lesion scores increased. Changes in acute histology scores correlated well with hematuria, proteinuria, and u-podo excretion, whereas chronic histology scores and glomerulosclerosis both correlated well with cumulative u-podo excretion. Patients with severe histologic progression of disease also had persistent u-podo excretion. These findings provide additional data to support a potential causative role for prolonged urinary loss of podocytes in disease progression in children with IgA nephropathy and Henoch-Schö nlein purpura nephritis.