The putative role of MALDI-MSI in the study of Membranous Nephropathy.

Membranous Nephropathy (MN) is an immunocomplex mediated renal disease that represents one of the most frequent glomerulopathies worldwide. This glomerular disease can manifest as primary (idiopathic) or secondary and this distinction is crucial when choosing the most appropriate course of treatment. In secondary cases, the best strategy involves treating the underlying disease, whereas in primary forms, the identification of confirmatory markers of the idiopathic etiology underlining the process is requested by clinicians. Among those currently reported, the positivity to circulating antigens (PLA2R, IgG4 and THSD7A) was demonstrated in approximately 75% of iMN patients, while approximately 1 in 4 patients with iMN still lack a putative diagnostic marker. Ultimately, the discovery of biomarkers to help further stratify these two different forms of glomerulopathy seems mandatory. Here, MALDI-MSI was applied to FFPE renal biopsies from histologically diagnosed primary and secondary MN patients (n=20) in order to detect alterations in their tissue proteome. MALDI-MSI was able to generate molecular signatures of primary and secondary MN, with one particular signal (m/z 1459), identified as Serine/threonine-protein kinase MRCK gamma, being over-expressed in the glomeruli of primary MN patients with respect to secondary MN. Furthermore, a number of signals that could differentiate the different forms of iMN that were positive to PLA2R or IgG4 were detected, as well as a further set of signals (m/z 1094, 1116, 1381 and 1459) that could distinguish these patients from those who were negative to both. These signals could potentially represent future targets for the further stratification of iMN patients. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

PICC insertion and veins of the arm size variation during dialysis treatment: A prospective observational study.

BACKGROUND: Peripherally Inserted Central Catheters play an increasingly important role in Central Venous Access Devices. However, the use of these devices should be carefully considered in specific situations such as central catheterisation in patients with chronic kidney disease. When evaluating the feasibility of placement for a patient undergoing dialysis, the relationship between changes in circulating volume before and after dialysis treatment, and potential variations in the size of deep veins in the upper limbs, should be considered. MATERIALS: Upper limb veins, specifically the basilic or brachial veins, were identified and measured before and after dialysis treatment. Patient data and weight loss data during dialysis treatment were also collected. Linear regression analysis was performed to assess the correlation between the variables. RESULTS: The average variation in vein size for the entire sample was +0.17 ± 0.43 mm. The mean volume removed was 2.2 ± 0.8 l. In subgroup 1 (fluid volume loss <2000 ml), the population experienced a decrease in the measured vein size after dialysis. In subgroup 2 (fluid volume loss ⩾2000 ml), the population experienced an increase in the measured vein size after dialysis. CONCLUSIONS: Upper arm vascular access placement in dialysed patients with fluid removal of less than 2000 ml should be performed after the dialysis session. Conversely, in dialysed patients with fluid removal of more than 2000 ml, where a significant increase in vein size was observed, vascular access placement should be performed before the dialysis session when the veins are smaller. Additionally, it should be noted that in patients with chronic kidney disease, the venous system of the upper limbs should be preserved as much as possible to prevent thrombosis and stenosis in potential arteriovenous fistula creation.

MALDI-MSI Pilot Study Highlights Glomerular Deposits of Macrophage Migration Inhibitory Factor as a Possible Indicator of Response to Therapy in Membranous Nephropathy.

PURPOSE: Membranous nephropathy (MN) is the most frequent cause of nephrotic syndrome in adults and the disease course is characterized by the "rule of third", with one-third of patients experiencing complete remission and the remaining experiencing relapses or progression of the disease. Additionally, the therapeutic approach is not standardized, leading to further heterogeneity in terms of response and outcome. EXPERIMENTAL DESIGN: In this pilot study, MALDI-MSI analysis is performed on renal biopsies (n = 13) obtained from two homogeneous groups of patients, which differentially responded to the immunosuppressive treatments (Ponticelli regimen). RESULTS: A signal at m/z 1303 displays the greatest discriminatory power when comparing the two groups and is observed to be of higher intensity in the glomeruli of the non-responding patients. The corresponding tryptic peptide is identified as macrophage migration inhibitory factor (MIF). CONCLUSIONS AND CLINICAL RELEVANCE: Despite much effort being made in recent years to understand the pathogenesis of MN, a biomarker able to predict the outcome of these patients following therapeutic treatment is still lacking. Here, a protein (MIF), verified by immunohistochemistry, that can differentiate between these MN patients and could be a valuable starting point for a further study focused on verifying its predictive role in therapy response is highlighted.

High Spatial Resolution MALDI-MS Imaging in the Study of Membranous Nephropathy.

PURPOSE: Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) technology has advanced rapidly during recent years with the development of instruments equipped with low-diameter lasers that are suitable for high spatial resolution imaging. This may provide significant advantages in certain fields of molecular pathology where more specific protein fingerprints of individual cell types are required, such as renal pathology. EXPERIMENTAL DESIGN: Here MALDI-MSI analysis of a cohort of membranous nephropathy (MN) patients is performed among which patients either responded favorably (R; n = 6), or unfavorably (NR; n = 4), to immunosuppressive treatment (Ponticelli Regimen), employing a 10 µm laser spot diameter. RESULTS: Specific tryptic peptide profiles of the different cellular regions within the glomerulus can be generated, similarly for the epithelial cells belonging to the proximal and distal tubules. Conversely, specific glomerular and sub-glomerular profiles cannot be obtained while using the pixel size performed in previous studies (50 µm). Furthermore, two proteins are highlighted, sonic hedgehog and α-smooth muscle actin, whose signal intensity and spatial localization within the sub-glomerular and tubulointerstitial compartments differ between treatment responders and non-responders. CONCLUSIONS AND CLINICAL RELEVANCE: The present study exemplifies the advantage of using high spatial resolution MALDI-MSI for the study of MN and highlights that such findings have the potential to provide complementary support in the routine prognostic assessment of MN patients.

Clinicopathological characteristics of typical and atypical anti-glomerular basement membrane nephritis.

Anti-glomerular basement membrane (GBM) antibody disease is a rare pathological condition that mainly involves renal and/or pulmonary parenchyma. It is characterized by the presence of circulating anti-GBM antibodies accompanied by a linear deposition of immunoglobulins (Ig) detected through immunofluorescence (IF) technique and typical signs and symptoms of organ dysfunction, such as rapidly progressive glomerulonephritis (RPGN) and pulmonary hemorrhage (PH). However, recently atypical forms of anti-GBM disease have been described and the presence of overlapping diseases contributed to make its diagnosis challenging. In this review will be discussed the entire spectrum of renal anti-GBM related conditions, focusing the attention on the differences in terms of pathogenesis, diagnosis and therapy of these disparate entities.