FGF23 and Cardiovascular Structure and Function in Advanced Chronic Kidney Disease.

Background: Fibroblast growth factor 23 (FGF23) is a bone-derived phosphatonin that is elevated in chronic kidney disease (CKD) and has been implicated in the development of cardiovascular disease. It is unknown whether elevated FGF23 in CKD is associated with impaired cardiovascular functional capacity, as assessed by maximum exercise oxygen consumption (VO2Max). We sought to determine whether FGF23 is associated with cardiovascular functional capacity in patients with advanced CKD and after improvement of VO2Max by kidney transplantation. Methods: We performed secondary analysis of 235 patients from the Cardiopulmonary Exercise Testing in Renal Failure and After Kidney Transplantation (CAPER) cohort, which recruited patients with stage 5 CKD who underwent kidney transplantation or were waitlisted and hypertensive controls. All patients underwent cardiopulmonary exercise testing (CPET) and echocardiography and were followed longitudinally for 1 year after study enrollment. Results: Patients across FGF23 quartiles differed in BMI (P=0.004) and mean arterial pressure (P<0.001) but did not significantly differ in sex (P=0.5) or age (P=0.08) compared with patients with lower levels of FGF23. Patients with higher FGF23 levels had impaired VO2Max (Q1: 24.2±4.8 ml/min per kilogram; Q4: 18.6±5.2 ml/min per kilogram; P<0.001), greater left ventricular mass index (LVMI; P<0.001), reduced HR at peak exercise (P<0.001), and maximal workload (P<0.001). Kidney transplantation conferred a significant decline in FGF23 at 2 months (P<0.001) before improvement in VO2Max at 1 year (P=0.008). Multivariable regression modeling revealed that changes in FGF23 was significantly associated with VO2Max in advanced CKD (P<0.001) and after improvement after kidney transplantation (P=0.006). FGF23 was associated with LVMI before kidney transplantation (P=0.003), however this association was lost after adjustment for dialysis status (P=0.4). FGF23 was not associated with LVMI after kidney transplantation in all models. Conclusions: FGF23 levels are associated with alterations in cardiovascular functional capacity in advanced CKD and after kidney transplantation. FGF23 is only associated with structural cardiac adaptations in advanced CKD but this was modified by dialysis status, and was not associated after kidney transplantation.

Myocardial Cytoskeletal Adaptations in Advanced Kidney Disease.

Background The myocardial cytoskeleton functions as the fundamental framework critical for organelle function, bioenergetics and myocardial remodeling. To date, impairment of the myocardial cytoskeleton occurring in the failing heart in patients with advanced chronic kidney disease has been largely undescribed. Methods and Results We conducted a 3-arm cross-sectional cohort study of explanted human heart tissues from patients who are dependent on hemodialysis (n=19), hypertension (n=10) with preserved renal function, and healthy controls (n=21). Left ventricular tissues were subjected to pathologic examination and next-generation RNA sequencing. Mechanistic and interference RNA studies utilizing in vitro human cardiac fibroblast models were performed. Left ventricular tissues from patients undergoing hemodialysis exhibited increased myocardial wall thickness and significantly greater fibrosis compared with hypertension patients (P<0.05) and control (P<0.01). Transcriptomic analysis revealed that the focal adhesion pathway was significantly enriched in hearts from patients undergoing hemodialysis. Hearts from patients undergoing hemodialysis exhibited dysregulated components of the focal adhesion pathway including reduced ß-actin (P<0.01), ß-tubulin (P<0.01), vimentin (P<0.05), and increased expression of vinculin (P<0.05) compared with controls. Cytoskeletal adaptations in hearts from the hemodialysis group were associated with impaired mitochondrial bioenergetics, including dysregulated mitochondrial dynamics and fusion, and loss of cell survival pathways. Mechanistic studies revealed that cytoskeletal changes can be driven by uremic and metabolic abnormalities of chronic kidney disease, in vitro. Furthermore, focal adhesion kinase silencing via interference RNA suppressed major cytoskeletal proteins synergistically with mineral stressors found in chronic kidney disease in vitro. Conclusions Myocardial failure in advanced chronic kidney disease is characterized by impairment of the cytoskeleton involving disruption of the focal adhesion pathway, mitochondrial failure, and loss of cell survival pathways.

Transplant renal artery and vein occlusion evaluated with ferumoxytol-enhanced magnetic resonance angiography.

BACKGROUND: Compromise of the transplanted vasculature accompanying a kidney allograft can lead to graft failure if not diagnosed and treated expeditiously. Location of the vascular defect in the transplant renal artery or vein is difficult to anticipate, given the variety of etiologies. However, early diagnosis can anticipate further progression of kidney allograft dysfunction. Ferumoxytol-enhanced magnetic resonance angiography (FeMRA) can precisely localize lesions in both the transplant renal artery and vein and provide a comprehensive survey of the vascular conduits of concern. It avoids complications of kidney injury associated with intravenous iodinated contrast that may amplify a diagnosis of delayed graft function or further impair an allograft already compromised by donor-derived vascular disease. METHODS: We report a case of concomitant and irreversible proximal transplant renal artery and vein stenosis diagnosed by FeMRA and treated with surgical intervention. RESULTS AND CONCLUSIONS: FeMRA offers a rapid, non-invasive approach to simultaneously diagnose compromised blood flow through the transplant artery and or vein in preparation for definitive correction of the defect.

Clinical Significance of Renal Allograft Urothelial Thickening Identified by Ultrasound.

OBJECTIVES: To assess the etiology and clinical implications of ultrasound (US)-diagnosed urothelial thickening (UT) in renal transplants. METHODS: Patients with renal transplants who had UT diagnosed by US from January 2000 to December 2018 were retrospectively identified and compared to patients with transplants without UT scanned during the study period. Medical records were reviewed for demographics, US findings, pathologic results, laboratory values, and clinical outcomes and compared between groups by Fisher exact and t tests. RESULTS: A total of 143 patients with UT and 128 controls comprised our cohorts. The patient age in the UT group versus controls (mean ± SD, 50.2 ± 16.5 versus 51.2 ± 15.3 years) and the time since transplant (2.9 ± 4.2 versus 2.4 ± 5.8 years) were similar. Patients with UT were more likely to be female than controls (76 of 143 [53.1%] versus 53 of 128 [41.4%]; P = .07), but the difference was not statistically significant, and patients with UT were more likely to have indwelling stents (31 of 143 [21.7%] versus 9 of 128 [7.0%]; P = .001) and hydronephrosis (25 of 143 [17.4%] versus 11 of 128 [8.6%]; P = .03). At biopsy, rejection and vascular sclerosis were more likely in patients with UT compared to controls (24 of 25 [49.0%] versus 11 of 43 [25.6%]; P = .031; 42 of 49 [85.7%] versus 22 of 43 [51.2%]; P = .0005, respectively), whereas acute tubular necrosis was similar. The sensitivity (50.0%) and specificity (74.4%) of UT for rejection were low. CONCLUSIONS: Urothelial thickening correlates with US findings of urinary obstruction and indwelling stents, suggesting a possible mechanical component to UT's etiology. Although transplant rejection and vascular sclerosis were more frequent at biopsy in the UT group than controls, UT had low sensitivity and specificity for rejection.

Eculizumab discontinuation in atypical haemolytic uraemic syndrome: TMA recurrence risk and renal outcomes.

Background: Eculizumab modifies the course of disease in patients with atypical haemolytic uraemic syndrome (aHUS), but data evaluating whether eculizumab discontinuation is safe are limited. Methods: Patients enrolled in the Global aHUS Registry who received ≥1 month of eculizumab before discontinuing, demonstrated haematologic or renal response prior to discontinuation and had ≥6 months of follow-up were analysed. The primary endpoint was the proportion of patients suffering from thrombotic microangiopathy (TMA) recurrence after eculizumab discontinuation. Additional endpoints included: estimated glomerular filtration rate changes following eculizumab discontinuation to last available follow-up; number of TMA recurrences; time to TMA recurrence; proportion of patients restarting eculizumab; and changes in renal function. Results: We analysed 151 patients with clinically diagnosed aHUS who had evidence of haematologic or renal response to eculizumab, before discontinuing. Thirty-three (22%) experienced a TMA recurrence. Univariate analysis revealed that patients with an increased risk of TMA recurrence after discontinuing eculizumab were those with a history of extrarenal manifestations prior to initiating eculizumab, pathogenic variants or a family history of aHUS. Multivariate analysis showed an increased risk of TMA recurrence in patients with pathogenic variants and a family history of aHUS. Twelve (8%) patients progressed to end-stage renal disease after eculizumab discontinuation; seven (5%) patients eventually received a kidney transplant. Forty (27%) patients experienced an extrarenal manifestation of aHUS after eculizumab discontinuation. Conclusions: Eculizumab discontinuation in patients with aHUS is not without risk, potentially leading to TMA recurrence and renal failure. A thorough assessment of risk factors prior to the decision to discontinue eculizumab is essential.

Alternative Diagnostic Strategy for the Assessment and Treatment of Pulmonary Embolus: A Case Series.

INTRODUCTION: Ferumoxytol-enhanced magnetic resonance angiography (FeMRA) can be used as an alternate and safe method to diagnose patients with compromised renal function who present with acute pulmonary embolus in the emergency department (ED) setting. CASE REPORT: A 62-year old man with a history of renal transplant and lymphoproliferative disease described new onset of breathlessness. His clinical symptoms were suggestive of pulmonary embolus. He underwent FeMRA in the ED to avoid exposure to intravenous iodinated contrast. FeMRA demonstrated a left main pulmonary artery embolus, which extended to the left interlobar pulmonary artery. Afterward, the patient initiated anticoagulation therapy. With preserved renal function he was able to continue his outpatient chemotherapy regimen. CONCLUSION: This case highlights a safe imaging technique for emergency physicians to diagnose pulmonary embolus and subsequently guide anticoagulation therapy for patients in whom use of conventional contrast is contraindicated.

miR-218 Expressed in Endothelial Progenitor Cells Contributes to the Development and Repair of the Kidney Microvasculature.

Ischemia due to hypoperfusion is one of the most common forms of acute kidney injury. We hypothesized that kidney hypoxia initiates the up-regulation of miR-218 expression in endothelial progenitor cells (EPCs) to guide endocapillary repair. Murine renal artery-derived EPCs (CD34+/CD105-) showed down-regulation of mmu-Mir218-5p/U6 RNA ratio after ischemic injury, while in human renal arteries, MIR218-5p expression was up-regulated after ischemic injury. MIR218 expression was clarified in cell culture experiments in which increases in both SLIT3 and MIR218-2-5p expressions were observed after 5 minutes of hypoxia. ROBO1 transcript, a downstream target of MIR218-2-5p, showed inverse expression to MIR218-2-5p. EPCs transfected with a MIR218-5p inhibitor in three-dimensional normoxic culture showed premature capillary formation. Organized progenitor cell movement was reconstituted when cells were co-transfected with Dicer siRNA and low-dose Mir218-5p mimic. A Mir218-2 knockout was generated to assess the significance of miR-218-2 in a mammalian model. Mir218-2-5p expression was decreased in Mir218-2-/- embryos at E16.5. Mir218-2-/- decreased CD34+ angioblasts in the ureteric bud at E16.5 and were nonviable. Mir218-2+/- decreased peritubular capillary density at postnatal day 14 and increased serum creatinine after ischemia in adult mice. Systemic injection of miR-218-5p decreased serum creatinine after injury. These experiments demonstrate that miR-218 expression can be triggered by hypoxia and modulates EPC migration in the kidney.

Eculizumab Use for Kidney Transplantation in Patients With a Diagnosis of Atypical Hemolytic Uremic Syndrome.

INTRODUCTION: Recurrence of atypical hemolytic uremic syndrome (aHUS) in renal allografts is common, leading to dialysis and graft failure. Pretransplant versus posttransplant initiation of eculizumab treatment in patients with aHUS has not been rigorously investigated. We hypothesized eculizumab pretransplant would reduce dialysis incidence posttransplant. METHODS: Of patients enrolled in the Global aHUS Registry (n = 1549), 344 had ≥1 kidney transplant. Of these, 188 had received eculizumab. Eighty-eight patients (47%) were diagnosed with aHUS and received eculizumab before, and during, their most recent transplant (group 1). A total of 100 patients (53%; group 2) initiated eculizumab posttransplantation. This second group was subdivided into those diagnosed with aHUS before (n = 52; group 2a) or after (n = 48; group 2b) their most recent transplant. RESULTS: Within 5 years of transplantation, 47 patients required dialysis; the risk of dialysis after transplantation was significantly increased in group 2b (hazard ratio [HR] 4.6; confidence interval [CI] 1.7-12.4) but not 2a (HR 2.3; CI 0.9-6.2). Graft function within 6 months of transplantation was significantly better in group 1 (median estimated glomerular filtration rate of 60.6 ml/min per 1.73 m2) compared with 31.5 and 9.6 ml/min per 1.73 m2 in groups 2a (P = 0.004) and 2b (P = 0.0001), respectively. One meningococcal infection (resolved with treatment) and 3 deaths (deemed unrelated to eculizumab) were reported. CONCLUSIONS: Outcomes for transplant patients with aHUS treated with eculizumab were improved compared with previous reports of patients with aHUS not treated with eculizumab. Our findings suggest delayed aHUS diagnosis and therefore treatment is associated with an increased risk of dialysis posttransplantation and reduced allograft function.

Von Mises Strain as a Risk Marker for Vulnerability of Carotid Plaque: Preliminary Clinical Evaluation of Cerebral Infarction.

Non-invasive assessment of carotid artery plaque vulnerability is a key issue for cerebrovascular disease. This study investigates Von Mises strain imaging in patients by relating Von Mises strain to cerebral infarction presentation. Ultrasonography was performed in patients evaluated for carotid artery stenosis. Strains were estimated by a flow-driven diffusion method and least-squares regression applying Kalman filtering. Von Mises strains ɛVMsys and ɛVMdia were calculated by averaging four or five cardiac cycles in systole and diastole, respectively. Von Mises strain (peak, coefficient of variance, skewness and kurtosis) in patients with cerebral infarction was compared with that in the control group. Higher Von Mises peak strain localized to echolucent areas on B-mode imaging. Higher peak strain was found in patients with cerebral infarction compared with the control group (p = 0.02 for ɛVMdia and p = 0.001 for ɛVMsys). The area under the receiver operating characteristic curve for peak ɛVMsys was 0.761 (p = 0.001) with high sensitivity and specificity. Peak strain also correlated with homocysteine (r = 0.345, p = 0.007, for ɛVMdia; r = 0.287, p = 0.036, for ɛVMsys) and hypersensitive C-reactive protein (r = 0.399, p = 0.043, for ɛVMdia; r = 0.195, p = 0.034, for ɛVMsys) levels. The coefficient of variance, skewness and kurtosis of ɛVMdia or ɛVMsys were also associated with homocysteine levels. In conclusion, this study indicates that peak Von Mises strain is a potential clinical risk marker for carotid plaque vulnerability and cerebral infarction.

Pre-clinical model of severe glutathione peroxidase-3 deficiency and chronic kidney disease results in coronary artery thrombosis and depressed left ventricular function.

Background: Chronic kidney disease (CKD) patients have deficient levels of glutathione peroxidase-3 (GPx3). We hypothesized that GPx3 deficiency may lead to cardiovascular disease in the presence of chronic kidney disease due to an accumulation of reactive oxygen species and decreased microvascular perfusion of the myocardium. Methods. To isolate the exclusive effect of GPx3 deficiency in kidney disease-induced cardiac disease, we studied the GPx3 knockout mouse strain (GPx3-/-) in the setting of surgery-induced CKD. Results. Ribonucleic acid (RNA) microarray screening of non-stimulated GPx3-/- heart tissue show increased expression of genes associated with cardiomyopathy including myh7, plac9, serpine1 and cd74 compared with wild-type (WT) controls. GPx3-/- mice underwent surgically induced renal mass reduction to generate a model of CKD. GPx3-/- + CKD mice underwent echocardiography 4 weeks after injury. Fractional shortening (FS) was decreased to 32.9 ± 5.8% in GPx3-/- + CKD compared to 62.0% ± 10.3 in WT + CKD (P < 0.001). Platelet aggregates were increased in the myocardium of GPx3-/- + CKD. Asymmetric dimethylarginine (ADMA) levels were increased in both GPx3-/- + CKD and WT+ CKD. ADMA stimulated spontaneous platelet aggregation more quickly in washed platelets from GPx3-/-. In vitro platelet aggregation was enhanced in samples from GPx3-/- + CKD. Platelet aggregation in GPx3-/- + CKD samples was mitigated after in vivo administration of ebselen, a glutathione peroxidase mimetic. FS improved in GPx3-/- + CKD mice after ebselen treatment. Conclusion: These results suggest GPx3 deficiency is a substantive contributing factor to the development of kidney disease-induced cardiac disease.

Breaking down the complement system: a review and update on novel therapies.

PURPOSE OF REVIEW: The complement system represents one of the more primitive forms of innate immunity. It has increasingly been found to contribute to pathologies in the native and transplanted kidney. We provide a concise review of the physiology of the complement cascade, and discuss current and upcoming complement-based therapies. RECENT FINDINGS: Current agents in clinical use either bind to complement components directly or prevent complement from binding to antibodies affixed to the endothelial surface. These include C1 esterase inhibitors, anti-C5 mAbs, anti-CD20 mAbs, and proteasome inhibitors. Treatment continues to show efficacy in the atypical hemolytic uremic syndrome and antibody-mediated rejection. Promising agents not currently available include CCX168, TP10, AMY-101, factor D inhibitors, coversin, and compstatin. Several new trials are targeting complement inhibition to treat antineutrophilic cystoplasmic antibody (ANCA)-associated vasculitis, C3 glomerulopathy, thrombotic microangiopathy, and IgA nephropathy. New agents for the treatment of the atypical hemolytic uremic syndrome are also in development. SUMMARY: Complement-based therapies are being considered for targeted therapy in the atypical hemolytic uremic syndrome and antibody-mediated rejection, C3 glomerulopathy, and ANCA-associated vasculitis. A few agents are currently in use as orphan drugs. A number of other drugs are in clinical trials and, overall, are showing promising preliminary results.

Human vascular progenitor cells derived from renal arteries are endothelial-like and assist in the repair of injured renal capillary networks.

Vascular progenitor cells show promise for the treatment of microvasculature endothelial injury. We investigated the function of renal artery progenitor cells derived from radical nephrectomy patients, in animal models of acute ischemic and hyperperfusion injuries. Present in human adventitia, CD34positive/CD105negative cells were clonal and expressed transcription factors Sox2/Oct4 as well as surface markers CXCR4 (CD184)/KDR(CD309) consistent with endothelial progenitor cells. Termed renal artery-derived vascular progenitor cells (RAPC), injected cells were associated with decreased serum creatinine after ischemia/reperfusion, reduced albuminuria after hyperperfusion, and improved blood flow in both models. A small population of RAPC integrated with the renal microvasculature following either experimental injury. At a cellular level, RAPC promoted local endothelial migration in co-culture. Profiling of RAPC microRNA identified high levels of miRNA 218; also found at high levels in exosomes isolated from RAPC conditioned media after cell contact for 24 hours. After hydrogen peroxide-induced endothelial injury, RAPC exosomes harbored Robo-1 transcript; a gene known to be regulated by mir218. Such exosomes enhanced endothelial cell migration in culture in the absence of RAPC. Thus, our work shows the feasibility of pre-emptive pro-angiogenic progenitor cell procurement from a targeted patient population and potential therapeutic use in the form of autologous cell transplantation.

Ferumoxytol-Enhanced Magnetic Resonance Imaging in Late-Stage CKD.

Ferumoxytol is a superparamagnetic iron oxide particle encapsulated by a semisynthetic carbohydrate with properties that can be used by the nephrologist for diagnosis and therapy. Ferumoxytol is approved by the US Food and Drug Administration for treating iron deficiency anemia in the setting of chronic kidney disease, but not for clinical diagnostic imaging. It has gained appeal as a magnetic resonance imaging contrast agent in patients with estimated glomerular filtration rates < 30mL/min/1.73m(2) in whom gadolinium-based contrast magnetic resonance imaging agents are relatively contraindicated because of the association with gadolinium deposition and nephrogenic systemic fibrosis. Ferumoxytol metabolism is not dependent on kidney function, but rather is removed from the circulation by the reticuloendothelial system of the liver, spleen, and bone marrow. Additionally, the prolonged intravascular half-life (>14 hours) of ferumoxytol allows for longer image acquisition and repeat imaging, if necessary. In patients with contraindications for gadolinium contrast agents, ferumoxytol is an alternative agent for vascular assessment, including patency and course.

Modelling kidney disease with CRISPR-mutant kidney organoids derived from human pluripotent epiblast spheroids.

Human-pluripotent-stem-cell-derived kidney cells (hPSC-KCs) have important potential for disease modelling and regeneration. Whether the hPSC-KCs can reconstitute tissue-specific phenotypes is currently unknown. Here we show that hPSC-KCs self-organize into kidney organoids that functionally recapitulate tissue-specific epithelial physiology, including disease phenotypes after genome editing. In three-dimensional cultures, epiblast-stage hPSCs form spheroids surrounding hollow, amniotic-like cavities. GSK3ß inhibition differentiates spheroids into segmented, nephron-like kidney organoids containing cell populations with characteristics of proximal tubules, podocytes and endothelium. Tubules accumulate dextran and methotrexate transport cargoes, and express kidney injury molecule-1 after nephrotoxic chemical injury. CRISPR/Cas9 knockout of podocalyxin causes junctional organization defects in podocyte-like cells. Knockout of the polycystic kidney disease genes PKD1 or PKD2 induces cyst formation from kidney tubules. All of these functional phenotypes are distinct from effects in epiblast spheroids, indicating that they are tissue specific. Our findings establish a reproducible, versatile three-dimensional framework for human epithelial disease modelling and regenerative medicine applications.

RGS4 inhibits angiotensin II signaling and macrophage localization during renal reperfusion injury independent of vasospasm.

Vascular inflammation is a major contributor to the severity of acute kidney injury. In the context of vasospasm-independent reperfusion injury we studied the potential anti-inflammatory role of the Gα-related RGS protein, RGS4. Transgenic RGS4 mice were resistant to 25 min injury, although post-ischemic renal arteriolar diameter was equal to the wild type early after injury. A 10 min unilateral injury was performed to study reperfusion without vasospasm. Eighteen hours after injury, blood flow was decreased in the inner cortex of wild-type mice with preservation of tubular architecture. Angiotensin II levels in the kidneys of wild-type and transgenic mice were elevated in a sub-vasoconstrictive range 12 and 18 h after injury. Angiotensin II stimulated pre-glomerular vascular smooth muscle cells (VSMCs) to secrete the macrophage chemoattractant RANTES, a process decreased by angiotensin II R2 (AT2) inhibition. However, RANTES increased when RGS4 expression was suppressed implicating Gα protein activation in an AT2-RGS4-dependent pathway. RGS4 function, specific to VSMC, was tested in a conditional VSMC-specific RGS4 knockout showing high macrophage density by T2 MRI compared with transgenic and non-transgenic mice after the 10 min injury. Arteriolar diameter of this knockout was unchanged at successive time points after injury. Thus, RGS4 expression, specific to renal VSMC, inhibits angiotensin II-mediated cytokine signaling and macrophage recruitment during reperfusion, distinct from vasomotor regulation.