The role of novel biomarkers in childhood idiopathic nephrotic syndrome: a narrative review of published evidence

Two histological subtypes of idiopathic nephrotic syndrome are commonly recognized in children, namely minimal change nephropathy and focal segmental glomerulosclerosis. Children with minimal change nephropathy (the majority of whom are steroid-sensitive) and focal segmental glomerulosclerosis (the majority of whom are steroid-resistant) require early identification in order to ensure appropriate therapeutic intervention and better outcome. Although renal biopsy and histology remain the ideal diagnostic steps to identify these histological subtypes, reports indicate that serum and urinary biomarkers are now being utilized in the investigation of childhood idiopathic nephrotic syndrome. This paper aims to review the diagnostic and prognostic utility of novel biomarkers in childhood idiopathic nephrotic syndrome and to highlight their role in differentiating steroid-sensitive nephrotic syndrome (SRNS) from steroid-resistant nephrotic syndrome (SSNS). Using the terms “idiopathic nephrotic syndrome,” “children,” and “biomarkers” the PubMed database was searched for relevant studies related to the topic. Biomarkers such as adiponectin, neopterin, β2-microglobulin, and N-acetyl-β-D glucosaminidase were reported as diagnostic markers. In addition to neopterin and N-acetyl-β-D glucosaminidase, urine vitamin D-binding protein and α1β-glycoprotein were shown to differentiate SRNS from SSNS while N-acetyl-β-D glucosaminidase and β2-microglobulin could predict steroid responsiveness and renal outcome in SRNS. Although progress has been made in demonstrating the diagnostic and prognostic utility of these biomarkers, their limited availability in most laboratories has precluded a complete paradigm shift from the conventional renal biopsy. Nevertheless, further longitudinal studies are required to establish their usefulness as noninvasive predictors of disease response to immunosuppressive therapy.

A Quantitative Proteomic Analysis of Urine from Gamma-Irradiated Non-Human Primates

The molecular effects of total body gamma-irradiation exposure are of critical importance as large populations of people could be exposed either by terrorists, nuclear blast, or medical therapy. In this study, we aimed to identify changes in the urine proteome using a non-human primate model system, Rhesus macaque, in order to characterize effects of acute radiation syndrome following whole body irradiation (Co-60) at 6.7 Gy and 7.4 Gy with a twelve day observation period. The urine proteome is potentially a valuable and non-invasive diagnostic for radiation exposure. Using high-resolution mass spectrometry, we identified 2346 proteins in the urine proteome. We show proteins involved in disease, cell adhesion, and metabolic pathway were significantly changed upon exposure to differing levels and durations of radiation exposure. Cell damage increased at a faster rate at 7.4 Gy compared with 6.7 Gy exposures. We report sets of proteins that are putative biomarkers of time- and dose-dependent radiation exposure. The proteomic study presented here is a comprehensive analysis of the urine proteome following radiation exposure.

Predictive urinary biomarkers for steroid-resistant and steroid-sensitive focal segmental glomerulosclerosis using high resolution mass spectrometry and multivariate statistical analysis

Background

Focal segmental glomerulosclerosis (FSGS) is a glomerular scarring disease diagnosed mostly by kidney biopsy. Since there is currently no diagnostic test that can accurately predict steroid responsiveness in FSGS, prediction of the responsiveness of patients to steroid therapy with noninvasive means has become a critical issue. In the present study urinary proteomics was used as a noninvasive tool to discover potential predictive biomarkers.

Methods

Urinary proteome of 10 patients (n = 6 steroid-sensitive, n = 4 steroid-resistant) with biopsy proven FSGS was analyzed using nano-LC-MS/MS and supervised multivariate statistical analysis was performed.

Results

Twenty one proteins were identified as discriminating species among which apolipoprotein A-1 and Matrix-remodeling protein 8 had the most drastic fold changes being over- and underrepresented, respectively, in steroid sensitive compared to steroid resistant urine samples. Gene ontology enrichment analysis revealed acute inflammatory response as the dominant biological process.

Conclusion

The obtained results suggest a panel of predictive biomarkers for FSGS. Proteins involved in the inflammatory response are shown to be implicated in the responsiveness. As a tool for biomarker discovery, urinary proteomics is especially fruitful in the area of prediction of responsiveness to drugs. Further validation of these biomarkers is however needed.

Urinary sediment miRNA levels in adult nephrotic syndrome

BACKGROUND

MicroRNAs are a group of non-coding RNA molecules that play important roles in the pathogenesis of various kidney diseases. We investigate the urinary sediment miRNA levels of adult patients with nephrotic syndrome.

METHODS

We study 20 patients with diabetic glomerulosclerosis (DGS), 21 with minimal change nephropathy (MCN) or focal glomerulosclerosis (FGS), 23 with membranous nephropathy (MGN), and 10 healthy controls. Urinary sediment miRNA levels are quantified.

RESULTS

Urinary sediment miR-29a, miR-192, and miR-200c levels were significantly different between diagnosis groups. Post hoc analysis showed that urinary miR-638 level was significantly lower in all causes of nephrotic syndrome than healthy controls, while the DGS group had lower urinary miR-192 level than other diagnosis groups. In contrast, the MCN/FGS group had higher urinary miR-200c level than other diagnosis groups. For each specific pathology group, urinary level of several miRNA targets significantly correlated with kidney function and histological scarring.

CONCLUSIONS

Urinary miR-29a, miR-192 and miR-200c levels have characteristic alterations among patients with different causes of nephrotic syndrome. Our results suggest that urinary miRNA levels have the potential of being developed as the diagnosis tool and marker of disease severity in adult nephrotic syndrome.

Screening for urinary biomarkers of steroid-resistant nephrotic syndrome in children

The present study aimed to screen for urinary biomarkers of steroid-resistant nephrotic syndrome (SRNS) in children. These biomarkers were divided into three groups, the control, the steroid-sensitive nephrotic syndrome (SSNS) and the SRNS groups, which were composed of 45, 32 and 9 children, respectively. Urine samples were obtained and analyzed using Au-chips. Compared with the control group, the peak intensities of four proteins, measured using mass-to-charge ratios, were significantly increased in the primary nephrotic syndrome (PNS; SSNS and SRNS combined) group (P<0.01). The intensity of three and one peaks increased significantly in the SSNS and SRNS groups, respectively, compared with the control (P<0.01). Compared with the SRNS group, the intensity of one protein peak increased in the SSNS group (P<0.01). The diagnostic model was established based on these four protein peaks. The sensitivity and specificity of the model were 88.89 and 93.75%, respectively. Four differentially expressed proteins may consequently serve as urinary biomarkers for SRNS in children.

GLCCI1 single nucleotide polymorphisms in pediatric nephrotic syndrome

BACKGROUND

Empiric steroid therapy is the first-line therapy for pediatric nephrotic syndrome, but treatment response is variable. There are few predictors of steroid-responsiveness, although evidence for genetic factors does exist. Single nucleotide polymorphisms (SNPs) have been recently identified in the promoter region of glucocorticoid-induced transcript 1 gene (GLCCI1) which affect steroid-responsiveness in asthmatic patients. Independently, GLCCI1 was identified as a podocyte protein, the loss of which disrupts the function of the glomerular filtration barrier. We therefore examined whether SNPs associated with the steroid-responsive expression of GLCCI1 might predict steroid-responsiveness in nephrotic syndrome.

CASE-DIAGNOSIS/TREATMENT

A cohort of 211 pediatric patients with nephrotic syndrome and 102 controls were genotyped; among the cases, 117 were initial steroid responders, while 94 did not respond to oral steroids. No statistically significant differences were noted among the groups, although there was a trend based on the comparison of the small subgroups of steroid-responsive and non-responsive patients with biopsy-proven minimal change disease.

CONCLUSIONS

While larger cohorts are needed to ascertain the possibility of a small effect of GLCCI1 SNPs on the steroid-responsiveness of nephrotic syndrome, the GLCCI1 SNPs associated with steroid-responsiveness in asthmatic patients are unlikely to have a clinically actionable impact in pediatric nephrotic syndrome.

The urine proteome for radiation biodosimetry: effect of total body vs. local kidney irradiation

Victims of nuclear accidents or radiological terrorism are likely to receive varying doses of ionizing radiation inhomogeneously distributed over the body. Early biomarkers may be useful in determining organ-specific doses due to total body irradiation (TBI) or partial body irradiation. The authors used liquid chromatography and mass spectrometry to compare the effect of TBI and local kidney irradiation (LKI) on the rat urine proteome using a single 10-Gy dose of x-rays. Both TBI and LKI altered the urinary protein profile within 24 h with noticeable differences in gene ontology categories. Some proteins, including fetuin-B, tissue kallikrein, beta-glucuronidase, vitamin D-dependent calcium binding protein and chondroitin sulfate proteoglycan NG2, were detected only in the TBI group. Some other proteins, including major urinary protein-1, RNA binding protein 19, neuron navigator, Dapper homolog 3, WD repeat and FYVE domain containing protein 3, sorting nexin-8, ankycorbin and aquaporin were detected only in the LKI group. Protease inhibitors and kidney proteins were more abundant (fraction of total scans) in the LKI group. Urine protein (Up) and creatinine (Uc) (Up/Uc) ratios and urinary albumin abundance decreased in both TBI and LKI groups. Several markers of acute kidney injury were not detectable in either irradiated group. Present data indicate that abundance and number of proteins may follow opposite trends. These novel findings demonstrate intriguing differences between TBI and LKI, and suggest that urine proteome may be useful in determining organ-specific changes caused by partial body irradiation.