Simon Parmentier

Extrarenal Progenitor Cells Do Not Contribute to Renal Endothelial Repair

Endothelial progenitor cells (EPCs) may be relevant contributors to endothelial cell (EC) repair in various organ systems. In this study, we investigated the potential role of EPCs in renal EC repair. We analyzed the major EPC subtypes in murine kidneys, blood, and spleens after induction of selective EC injury using the concanavalin A/anti-concanavalin A model and after ischemia/reperfusion (I/R) injury as well as the potential of extrarenal cells to substitute for injured local EC. Bone marrow transplantation (BMTx), kidney transplantation, or a combination of both were performed before EC injury to allow distinction of extrarenal or BM-derived cells from intrinsic renal cells. During endothelial regeneration, cells expressing markers of endothelial colony-forming cells (ECFCs) were the most abundant EPC subtype in kidneys, but were not detected in blood or spleen. Few cells expressing markers of EC colony-forming units (EC-CFUs) were detected. In BM chimeric mice (C57BL/6 with tandem dimer Tomato-positive [tdT+] BM cells), circulating and splenic EC-CFUs were BM-derived (tdT+), whereas cells positive for ECFC markers in kidneys were not. Indeed, most BM-derived tdT+ cells in injured kidneys were inflammatory cells. Kidneys from C57BL/6 donors transplanted into tdT+ recipients with or without prior BMTx from C57BL/6 mice were negative for BM-derived or extrarenal ECFCs. Overall, extrarenal cells did not substitute for any intrinsic ECs. These results demonstrate that endothelial repair in mouse kidneys with acute endothelial lesions depends exclusively on local mechanisms.

Injured kidney endothelium is only marginally repopulated by cells of extrarenal origin

The role of bone marrow marrow-derived cells after kidney endothelial injury is controversial. In this study, we investigated if and to what extent extrarenal cells incorporate into kidney endothelium after acute as well as during chronic endothelial injury. Fischer F-344wt (wild type) rat kidney grafts were transplanted into R26-hPAP (human placental alkaline phosphatase) transgenic Fischer F-344 recipient rats to allow identification of extrarenal cells by specific antibody staining. A severe model of renal thrombotic microangiopathy was induced via graft perfusion with antiglomerular endothelial cell (GEN) antibody and resulted in eradication of 85% of the glomerular and 69% of the peritubular endothelium (GEN group). At week 4 after injury, renal endothelial healing as well as recovery of the kidney function was seen. Endothelial chimerism was evaluated by double staining for hPAP and endothelial markers RECA-1 or JG-12. Just 0.25% of the glomerular and 0.1% of the peritubular endothelium was recipient derived. In a second experiment, chronic endothelial injury was induced by combination of kidney transplantation with 5/6 nephrectomy (5/6 Nx group). After 14 wk, only 0.86% of the peritubular and 0.05% of the glomerular endothelium was of recipient origin. In summary, despite demonstration of extensive damage and loss as well as excellent regeneration, just a minority of extrarenal cells were incorporated into kidney endothelium in rat models of acute and chronic renal endothelial cell injury. Our results highlight that kidney endothelial regeneration after specific and severe injury is almost exclusively of renal origin.

Phenytoin inhibits necroptosis

Receptor-interacting protein kinases 1 and 3 (RIPK1/3) have best been described for their role in mediating a regulated form of necrosis, referred to as necroptosis. During this process, RIPK3 phosphorylates mixed lineage kinase domain-like (MLKL) to cause plasma membrane rupture. RIPK3-deficient mice have recently been demonstrated to be protected in a series of disease models, but direct evidence for activation of necroptosis in vivo is still limited. Here, we sought to further examine the activation of necroptosis in kidney ischemia-reperfusion injury (IRI) and from TNFα-induced severe inflammatory response syndrome (SIRS), two models of RIPK3-dependent injury. In both models, MLKL-ko mice were significantly protected from injury to a degree that was slightly, but statistically significantly exceeding that of RIPK3-deficient mice. We also demonstrated, for the first time, accumulation of pMLKL in the necrotic tubules of human patients with acute kidney injury. However, our data also uncovered unexpected elevation of blood flow in MLKL-ko animals, which may be relevant to IRI and should be considered in the future. To further understand the mode of regulation of cell death by MLKL, we screened a panel of clinical plasma membrane channel blockers and we found phenytoin to inhibit necroptosis. However, we further found that phenytoin attenuated RIPK1 kinase activity in vitro, likely due to the hydantoin scaffold also present in necrostatin-1, and blocked upstream necrosome formation steps in the cells undergoing necroptosis. We further report that this clinically used anti-convulsant drug displayed protection from kidney IRI and TNFα-induces SIRS in vivo. Overall, our data reveal the relevance of RIPK3-pMLKL regulation for acute kidney injury and identifies an FDA-approved drug that may be useful for immediate clinical evaluation of inhibition of pro-death RIPK1/RIPK3 activities in human diseases.

Correction to: Phenytoin inhibits necroptosis

The name of the one of the authors was misspelt. The author’s surname is Rodriguez, not Rodriquez as originally published. This has been corrected in both the PDF and HTML versions of the Article.

The clinical relevance of necroinflammation—highlighting the importance of acute kidney injury and the adrenal glands

Necroinflammation is defined as the inflammatory response to necrotic cell death. Different necrotic cell death pathways exhibit different immune reponses, despite a comparable level of intracellular content release (referred to as damage associated molecular patterns or DAMPs). In addition to DAMP release, which is inevitably associated with necrotic cell death, the active production of pro/anti-inflammatory cytokines characterizes certain necrotic pathways. Necroptosis, ferroptosis and pyroptosis, therefore, are immunogenic to a different extent. In this review, we discuss the clinical relevance of necroinflammation highlighting potential human serum markers. We focus on the role of the adrenal glands and the lungs as central organs affected by systemic and/or local DAMP release and underline their role in intensive care medicine. In addition, data from models of acute kidney injury (AKI) and kidney transplantation have significantly shaped the field of necroinflammation and may be helpful for the understanding of the potential role of dialysis and plasma exchange to treat ongoing necroinflammation upon intensive care unit (ICU) conditions. In conclusion, we are only beginning to understand the importance of necroinflammation in diseases and transplantation, including xenotransplantation. However, given the existing efforts to develop inhibitors of necrotic cell death (ferrostatins, necrostatins, etc), we consider it likely that interference with necroinflammation reaches clinical routine in the near future.

Optimized Reference Intervals for Plasma Free Metanephrines in Patients With CKD

To the Editor: The diagnostic work-up of pheochromocytoma/paraganglioma (PPGL) among patients with chronic kidney disease (CKD) is a clinical challenge. Impaired renal elimination of catecholamines and their metabolites confounds urinary tests, while increased plasma concentrations of free metanephrines in patients with CKD also complicate interpretation of plasma tests.1, 2, 3 We therefore aimed to establish optimal reference intervals for plasma free metanephrines and 3-methoxytyramine in patients with CKD stages 3 and 4 or receiving hemodialysis (HD). This prospective multicenter study included 234 patients (79 CKD3, 48 CKD4, and 107 receiving HD) and an aged-matched reference population of 173 individuals (Table 1; Item S1). Measurements of plasma free normetanephrine, metanephrine, and 3-methoxytyramine were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS).4

Renal Sarcoidosis Mimicking Xanthogranulomatous Pyelonephritis.

A 70-year-old male patient underwent left-sided nephrectomy for signs and symptoms that were suggestive of xanthogranulomatous pyelonephritis (recurrent fever, swollen malfunctioning kidney, granulomatous inflammation in renal biopsy). Contralateral progression and workup for further symptoms finally established the diagnosis of extrapulmonary sarcoidosis. With corticosteroid and azathioprine treatment, renal function was preserved in the long term. Awareness of similarities in computed tomography imaging and histopathological findings of xanthogranulomatous pyelonephritis and renal sarcoidosis may prevent delayed diagnosis and inappropriate treatment of the latter.

A new apparatus for standardized rat kidney biopsy.

Survival biopsies are frequently applied in rat kidney disease models, but several drawbacks such as surgical kidney trauma, bleeding risk and variable loss of kidney tissue are still unsolved. Therefore, we developed an easy-to-use core biopsy instrument and evaluated whether two consecutive kidney biopsies within the same kidney can be carried out in a standardized manner. On day 0, 18 Lewis rats underwent a right nephrectomy and 9 of these rats a subsequent first biopsy of the left kidney (Bx group). 9 control rats had a sham biopsy of the left kidney (Ctrl group). On day 7, a second kidney biopsy/sham biopsy was performed. On day 42, all animals were sacrificed and their kidneys were removed for histology. Biopsy cylinders contained 57±28 glomeruli per transversal section, representing an adequate sample size. PAS staining showed that the biopsy depth was limited to the renal cortex whereas surgical tissue damage was limited to the area immediately adjacent to the taken biopsy cylinder. On day 42, the reduction of functional renal mass after two biopsies was only 5.2% and no differences of body weight, blood pressure, proteinuria, serum creatinine, glomerulosclerosis, interstitial fibrosis or number of ED-1 positive macrophages were found between both groups. In summary, our apparatus offers a safe method to perform repetitive kidney biopsies with minimal trauma and sufficient sample size and quality even in experimental disease models restricted to one single kidney.

New onset of alopecia in a young woman with end-stage renal disease

Background Hair loss is a common complain of women receiving renal replacement therapy. Apart from its emotional impact on the patient, hair loss might allude to several underlying diseases. Differential diagnoses include malnutrition, adverse effects of drugs, endocrine, inflammatory or autoimmune disorders, abnormal behaviour (trichotillomania) or tinea capitis [1]. Therefore, a thorough exploration of affected patients is constitutional.