Candidate Urine Peptide Biomarkers for IgA Nephropathy: Where Are We Now?

The Feasibility of Targeted Magnetic Iron Oxide Nanoagent for Noninvasive IgA Nephropathy Diagnosis

IgA nephropathy is the most common glomerular disease in the world and has become a serious threat to human health. Accurate and non-invasive molecular imaging to detect and recognize the IgA nephropathy is critical for the subsequent timely treatment; otherwise, it may progress to end-stage renal disease and lead to glomerular dysfunction. In this study, we have developed a sensitive, specific, and biocompatible integrin αvβ3-targeted superparamagnetic Fe₃O₄ nanoparticles (NPs) for the noninvasive magnetic resonance imaging (MRI) of integrin αvβ3, which is overexpressed in glomerular mesangial region of IgA nephropathy. The rat model of IgA nephropathy was successfully established and verified by biochemical tests and histological staining. Meanwhile, the clinical ¹⁸F-AlF-NOTA-PRGD2 probe molecule was utilized to visualize and further confirmed the IgA nephropathy in vivo via positron emission computed tomography. Subsequently, the Fe₃O₄ NPs were conjugated with arginine–glycine–aspartic acid (RGD) molecules (Fe₃O₄-RGD), and their integrin αvβ3-targeted T2-weighted imaging (T2WI) potential has been carefully evaluated. The Fe₃O₄-RGD demonstrated great relaxation in vivo. The T2WI signal of renal layers in the targeted group at 3 h after intravenous injection of Fe₃O₄-RGD was distinctly lower than baseline, indicating MRI signal decreased in the established IgA nephropathy rat model. Moreover, the TEM characterization and Prussian blue staining confirmed that the Fe₃O₄-RGD was located at the region of glomerulus and tubular interstitium. Moreover, no obvious signal decreased was detected in the untargeted Fe₃O₄ treated and normal groups. Collectively, our results establish the possibility of Fe₃O₄-RGD serving as a feasible MRI agent for the noninvasive diagnosis of IgA nephropathy.

Clinical characteristics of inflammatory bowel disease patients with immunoglobulin A nephropathy

Background/Aims

Inflammatory bowel disease (IBD) is a chronic inflammation of the gastrointestinal tract. Some patients with this condition have been reported to present with immunoglobulin A nephropathy (IgAN), a renal complication that can cause end-stage renal failure, but the frequency of this comorbidity has not been described. Thus, the aim of this study was to investigate the frequency of IgAN in patients with IBD.

Methods

This study included 620 patients with IBD (338 with ulcerative colitis [UC] and 282 with Crohn’s disease [CD]) from the Hiroshima University Hospital outpatient department. IgAN cases were identified from medical interviews, blood examinations (serum immunoglobulin A), and urinalyses (occult blood, proteinuria). Definitive IgAN cases were diagnosed by renal biopsies, while those detected through the clinical course and test results, but not clinically recommended for renal biopsy, were defined as suspected IgAN.

Results

We analyzed 427 cases meeting the inclusion criteria (220 with UC and 207 with CD). The incidence of IgAN across all patients with IBD was 3.0%. The frequency of IgAN was significantly higher in patients with CD (11/207, 5.3%) than in those with UC (2/220, 0.9%) (P< 0.01). Moreover, a significant correlation was found between CD patients with ileostomy or colostomy and a diagnosis of IgAN.

Conclusions

Patients with IBD present a high incidence of IgAN, especially those with CD who have undergone ileostomy or colostomy.

Differential expression of peptides serves as an indicator of IgA nephropathy in pediatric patients

Peptide profiles change significantly with aging and peptide biomarkers discovered in adult patients may not be suitable for the evaluation of pediatric patients. The present study was designed to explore alterations in the serum peptidome profile of pediatric patients with IgA nephropathy (IgAN). A total of 17 children diagnosed with IgAN were recruited as the experimental group, 11 sex-matched healthy children were recruited as a healthy control group and 18 sex-matched children with other glomerular diseases were recruited as a disease control group. Serum peptides of each subject were enriched and analyzed by liquid chromatography with tandem mass spectrometry and the subsequently identified IgAN-specific peptides were evaluated using Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analysis. Subsequently, the function of the IgAN-specific peptides was predicted via sequence comparison with other known functional bioactive peptides. A total of 123 peptides with a fold change >2 (P<0.05) and 48 peptides with a fold change >5 (P<0.05) were identified to be differentially expressed between the pediatric IgAN group and the two other groups. Consequently, two putative peptides that may have bioactive effects in the pathogenesis of IgAN in pediatric patients were identified. The serum peptidome profile of pediatric patients with IgAN was significantly different from the disease control group and the healthy control group. These differentially expressed peptides may serve as biomarkers for the minimally invasive diagnosis of pediatric patients with IgAN. Additionally, the potential bioactive peptides specifically expressed in pediatric IgAN patients that were identified in this study may lay a foundation for exploring new therapies for IgAN, such as the creation of novel peptide drugs.

Formalin-fixed paraffin-embedded renal biopsy tissues: an underexploited biospecimen resource for gene expression profiling in IgA nephropathy

Primary IgA nephropathy (IgAN) diagnosis is based on IgA-dominant glomerular deposits and histological scoring is done on formalin-fixed paraffin embedded tissue (FFPE) sections using the Oxford classification. Our aim was to use this underexploited resource to extract RNA and identify genes that characterize active (endocapillary–extracapillary proliferations) and chronic (tubulo-interstitial) renal lesions in total renal cortex. RNA was extracted from archival FFPE renal biopsies of 52 IgAN patients, 22 non-IgAN and normal renal tissue of 7 kidney living donors (KLD) as controls. Genome-wide gene expression profiles were obtained and biomarker identification was carried out comparing gene expression signatures a subset of IgAN patients with active (N = 8), and chronic (N = 12) renal lesions versus non-IgAN and KLD. Bioinformatic analysis identified transcripts for active (DEFA4,TNFAIP6,FAR2) and chronic (LTB,CXCL6, ITGAX) renal lesions that were validated by RT-PCR and IHC. Finally, two of them (TNFAIP6 for active and CXCL6 for chronic) were confirmed in the urine of an independent cohort of IgAN patients compared with non-IgAN patients and controls. We have integrated transcriptomics with histomorphological scores, identified specific gene expression changes using the invaluable repository of archival renal biopsies and discovered two urinary biomarkers that may be used for specific clinical decision making.

Use of gas chromatography mass spectrometry to elucidate metabolites predicting the phenotypes of IgA nephropathy in hyper IgA mice

IgA nephropathy, a common chronic kidney disease, has various possible outcomes. Therefore, the identification of novel prognostic biomarkers is needed. To this purpose, we used gas chromatography mass spectrometry to search for metabolites capable of predicting the phenotypes of IgA nephropathy in hyper IgA (HIGA) mice, an established model mice for IgA nephropathy. We measured the plasma metabolite levels in 12- and 22-week-old mice, prior to the manifestation of IgA nephropathy phenotypes, and statistically investigated the associations between these metabolites and the phenotypes of IgA nephropathy, such as the urine protein levels and histological phenotypes of the kidney at 32 weeks. We observed that in plasma samples collected from 12- and 22-week-old HIGA mice, the urinary protein levels were significantly associated with 8 and 10 metabolites, the glomerular cellular component levels were significantly associated with 8 and 7 metabolites, and the mesangial substrate levels were significantly associated with 8 and 8 metabolites, respectively. Among the candidate metabolites associated with the phenotypes of IgA nephropathy, coniferyl alcohol levels were significantly higher in HIGA mice at all of the 12, 22, and 32 weeks of age. Since this study was an observational study, we could not elucidate the underlying mechanisms; however, we were able to identify new candidate metabolites, such as coniferyl alcohol, as being potentially involved in the pathogenesis of IgA nephropathy. These results might help to develop novel laboratory tests and therapeutic reagents for IgA nephropathy in the future.