Citations

Objectives Magnetization transfer imaging is a novel noninvasive tool for the detection of kidney fibrosis, but its association with kidney function and hemodynamics is unclear. Renovascular disease (RVD) associated with metabolic derangements elicits renal fibrosis and is often unresponsive to percutaneous transluminal angioplasty (PTRA), but tools to predict therapeutic success are unavailable. We hypothesized that magnetization transfer imaging predicts kidney recovery after PTRA in swine with unilateral RVD. Materials and Methods Stenotic kidney (STK) and contralateral kidney magnetization transfer ratios (MTRs; M t/M 0) were measured at 3.0-T magnetic resonance imaging, at offset frequencies of 600 and 1000 Hz, before and 1 month post-PTRA in 7 RVD pigs. Stenotic kidney MTR was correlated to renal perfusion, renal blood flow (RBF), and glomerular filtration rate (GFR), determined using multidetector computed tomography and with ex vivo renal fibrosis (trichrome staining). Untreated RVD (n = 6) and normal pigs (n = 7) served as controls. Results Renovascular disease induced hypertension and renal dysfunction. Blood pressure and renal perfusion were unchanged post-PTRA, but GFR and RBF increased. Baseline cortical STK-MTR predicted post-PTRA renal perfusion and RBF, and MTR changes associated inversely with changes in perfusion and normalized GFR. Stenotic kidney MTR at 600 Hz showed closer association with renal parameters, but both frequencies predicted post-PTRA cortical fibrosis. Conclusions Renal STK-MTR, particularly at 600 Hz offset, is sensitive to hemodynamic changes after PTRA in swine RVD and capable of noninvasively predicting post-PTRA kidney perfusion, RBF, and fibrosis. Therefore, STK-MTR may be a valuable tool to predict renal hemodynamic and functional recovery, as well as residual kidney fibrosis after revascularization in RVD.

AbstractEffective therapeutic strategies are needed to preserve renal function in patients with atherosclerotic renal artery stenosis (ARAS). Low‐energy shockwave therapy (SW) and adipose tissue‐derived mesenchymal stem/stromal cells (MSCs) both stimulate angiogenesis repair of stenotic kidney injury. This study tested the hypothesis that intrarenal delivery of adipose tissue‐derived MSCs would enhance the capability of SW to preserve stenotic kidney function and structure. Twenty‐two pigs were studied after 16 weeks of ARAS, ARAS treated with a SW regimen (bi‐weekly for 3 weeks) with or without subsequent intrarenal delivery of adipose tissue‐derived MSCs and controls. Four weeks after treatment, single‐kidney renal blood flow (RBF) before and after infusion of acetylcholine, glomerular filtration rate (GFR), and oxygenation were assessed in vivo and the renal microcirculation, fibrosis, and oxidative stress ex vivo. Mean arterial pressure remained higher in ARAS, ARAS + SW, and ARAS + SW + MSC compared with normal. Both SW and SW + MSC similarly elevated the decreased stenotic kidney GFR and RBF observed in ARAS to normal levels. Yet, SW + MSC significantly improved RBF response to acetylcholine in ARAS, and attenuated capillary loss and oxidative stress more than SW alone. Density of larger microvessels was similarly increased by both interventions. Therefore, although significant changes in functional outcomes were not observed in a short period of time, adjunct MSCs enhanced pro‐angiogenic effect of SW to improve renal microvascular outcomes, suggesting this as an effective stratege for long‐term management of renovascular disease.

Cellular senescence, a permanent arrest of cell proliferation, is characterized by a senescence-associated secretory phenotype (SASP), which reinforces senescence and exerts noxious effects on adjacent cells. Recent studies have suggested that transplanting small numbers of senescent cells suffices to provoke tissue inflammation. We hypothesized that senescent cells can directly augment renal injury. Primary scattered tubular-like cells (STCs) acquired from pig kidneys were irradiated by 10 Gy of cesium radiation, and 3 wk later cells were characterized for levels of senescence and SASP markers. Control or senescent STCs were then prelabeled and injected (5 × 105 cells) into the aorta of C57BL/6J mice. Four weeks later, renal oxygenation was studied in vivo using 16.4-T magnetic resonance imaging and function by plasma creatinine level. Renal markers of SASP, fibrosis, and microvascular density were evaluated ex vivo. Per flow cytometry, irradiation induced senescence in 80–99% of STCs, which showed increased gene expression of senescence and SASP markers, senescence-associated β-galactosidase staining, and cytokine levels (especially IL-6) secreted in conditioned medium. Four weeks after injection, cells were detected engrafted in the mouse kidneys with no evidence for rejection. Plasma creatinine and renal tissue hypoxia increased in senescent compared with control cells. Senescent kidneys were more fibrotic, with fewer CD31+ endothelial cells, and showed upregulation of IL-6 gene expression. Therefore, exogenously delivered senescent renal STCs directly injure healthy mouse kidneys. Additional studies are needed to determine the role of endogenous cellular senescence in the pathogenesis of kidney injury and evaluate the utility of senolytic therapy.

Objectives Multiparametric renal magnetic resonance imaging (MRI), including diffusion-weighted imaging, magnetic resonance elastography, and magnetization transfer imaging (MTI), is valuable in the noninvasive assessment of renal fibrosis. However, hemodynamic changes in diseased kidneys may impede their ability to measure renal fibrosis. Because MTI assesses directly tissue content of macromolecules, we test the hypothesis that MTI would be insensitive to renal hemodynamic changes in swine kidneys with acute graded ischemia. Materials and Methods Seven domestic pigs underwent placement of an inflatable silicone cuff around the right renal artery to induce graded renal ischemia. Multiparametric MRI was performed at baseline, 50%, 75%, and 100% renal artery stenosis as well as reperfusion. Measurements included regional perfusion, R2*, apparent diffusion coefficient (ADC), stiffness, and magnetization transfer ratio (MTR) using arterial spin-labeled MRI, blood oxygenation–dependent MRI, diffusion-weighted imaging, magnetic resonance elastography, and MTI, respectively. Histology was performed to rule out renal fibrosis. Results During graded ischemia, decreases in renal perfusion were accompanied with elevated R2*, decreased ADC, and stiffness, whereas no statistically significant changes were observed in the MTR. No fibrosis was detected by histology. After release of the obstruction, renal perfusion showed only partial recovery, associated with return of kidney R2*, ADC, and stiffness to baseline levels, whereas cortical MTR decreased slightly. Conclusions Renal MTI is insensitive to decreases in renal perfusion and may offer reliable assessment of renal structural changes.

The rodent model of folic acid (FA)-induced acute kidney injury (AKI) provides a useful model for studying human AKI, but little is known about longitudinal changes in renal hemodynamics and evolution of renal fibrosis in vivo. In this work, we aimed to longitudinally assess renal structural and functional changes using multiparametric magnetic resonance imaging (MRI). Ten adult mice were injected with FA, after which a multiparametric MRI was used to measure kidney volume, hypoxia index R2*, magnetization transfer ratio (MTR), perfusion, T1, and glomerular filtration rate (GFR) at 2 wk posttreatment. Then five mice were euthanized for histology, and the other five underwent MRI again at 4 wk, followed by histology. Control mice ( n = 5) were injected with vehicle and studied with MRI at 2 wk. Trichrome and hematoxylin-eosin staining were performed to assess FA-induced tissue injuries. Whereas kidney size and oxygenation showed progressive deterioration, a transient impairment in renal perfusion and normalized GFR slightly improved by 4 wk. Kidney fluid content, as reflected by T1, was prominent at 2 wk and tended to regress at 4 wk, consistent with observed tubular dilation. Trichrome staining revealed patchy necrosis and mild interstitial fibrosis at 2 wk, which exacerbated at 4 wk. MTR detected increased fibrosis at 4 wk. In conclusion, multiparametric MRI captured the longitudinal progression in kidney damage evolving within the first month after treatment with folic acid and may provide a useful tool for assessment of therapeutic strategies.

Background Ossabaw pigs are unique miniature swine with genetic predisposition to develop metabolic syndrome and coronary atherosclerosis after extended periods receiving atherogenic diets. We have hypothesized that transgenic Ossabaw swine expressing chimp PCSK9 (proprotein convertase subtilisin‐like/kexin type 9) containing the D374Y gain of function would develop familial hypercholesterolemia and coronary artery plaques more rapidly than Landrace swine with the same transgene. Methods and Results Ossabaw and Landrace PCSK9 gain‐of‐function founders were generated by Sleeping Beauty transposition and cloning. Histopathologic findings in the Ossabaw founder animal showed more advanced plaques and higher stenosis than in the Landrace founder, underscoring the Ossabaw genetic predisposition to atherosclerosis. We chose to further characterize the Ossabaw PCSK9 gain‐of‐function animals receiving standard or atherogenic diets in a 6‐month longitudinal study using computed tomography, magnetic resonance (MR) imaging, intravascular ultrasound, and optical coherence tomography, followed by pathological analysis of atherosclerosis focused on the coronary arteries. The Ossabaw model was consistently hypercholesterolemic, with or without dietary challenge, and by 6 months had consistent and diffuse fibrofatty or fibroatheromatous plaques with necrosis, overlying fibrous caps, and calcification in up to 10% of coronary plaques. Conclusions The Ossabaw PCSK9 gain‐of‐function model provides consistent and robust disease development in a time frame that is practical for use in preclinical therapeutic evaluation to drive innovation. Although no animal model perfectly mimics the human condition, this genetic large‐animal model is a novel tool for testing therapeutic interventions in the context of developing and advanced coronary artery disease.

Abstract Mesenchymal stem cells (MSC) have been experimentally used for kidney repair, but modest retention limits their efficacy. Cell-surface coating allows modulating MSC homing and interaction with target cells. We coated mouse adipose tissue-derived MSC with antibodies directed against kidney injury molecule-1 (ab-KIM1), which is upregulated in injured kidneys, and tested the hypothesis that this would enhance their therapeutic effects in ischemic kidney injury. Untreated MSC, ab-KIM1-coated MSC (KIM-MSC), or vehicle, were injected systemically into the carotid artery of 2-kidneys, 1-clip mice 2 weeks after surgery. MSC retention in different organs was explored 24 hours, 48 hours, or 2 weeks after injection. Renal volume, perfusion, and oxygenation were studied 2 weeks after injection using magnetic resonance imaging in vivo, and renal inflammation, apoptosis, capillary density, and fibrosis ex vivo. The ab-KIM1 coating had little effect on MSC viability or proliferation. The stenotic kidney showed upregulated KIM1 expression, selective homing, and greater retention of KIM-MSC compared to untreated MSC and compared to other organs. KIM-MSC-injected mice improved renal perfusion and capillary density, and attenuated oxidative damage, apoptosis, and fibrosis compared to mice treated with vehicle or with native MSC. In conclusion, MSC coating with ab-KIM1 increased their retention in the ischemic kidney and enhanced their therapeutic efficacy. This novel method may be useful to selectively target injured kidneys, and supports further development of strategies to enhance cell-based treatment of ischemic kidney injury.

PurposeDynamic manganese‐enhanced MRI (MEMRI) allows assessment of tissue viability by tracing manganese uptake. We aimed to develop a rapid T1 mapping method for dynamic MEMRI to facilitate assessments of murine kidney viability.MethodsA multi‐slice saturation recovery fast spin echo (MSRFSE) was developed, validated, and subsequently applied in dynamic MEMRI at 16.4T on ischemic mouse kidneys after 4 weeks of unilateral renal artery stenosis (RAS). Baseline T1 values and post‐contrast R1 (1/T1) changes were measured in cortex (CO), outer (OSOM), inner (ISOM) strips of outer medulla, and inner medulla (IM).ResultsValidation studies showed strong agreement between MSRFSE and an established saturation recovery Look‐Locker method. Baseline T1 (s) increased in the stenotic kidney CO (2.10 [1.95–2.56] vs. 1.88 [1.81–2.00], P = 0.0317) and OSOM (2.17 [2.05–2.33] vs. 1.96 [1.87–2.00], P = 0.0075) but remained unchanged in ISOM and IM. This method allowed a temporal resolution of 1.43 min in dynamic MEMRI. Mn2+ uptake and retention decreased in stenotic kidneys, particularly in the OSOM (ΔR1: 0.48 [0.38–0.56] vs. 0.64 [0.61–0.69] s−1, P < 0.0001).ConclusionDynamic MEMRI by MSRFSE detected decreased cellular viability and discerned the regional responses to RAS. This technique may provide a valuable tool for noninvasive evaluation of renal viability. Magn Reson Med 80:190–199, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

PurposeTo develop and validate a method for measuring murine single‐kidney glomerular filtration rate (GFR) using dynamic contrast‐enhanced MRI (DCE‐MRI).MethodsThis prospective study was approved by the Institutional Animal Care and Use Committee. A fast longitudinal relaxation time (T1) measurement method was implemented to capture gadolinium dynamics (1 s/scan), and a modified two‐compartment model was developed to quantify GFR as well as renal perfusion using 16.4T MRI in mice 2 weeks after unilateral renal artery stenosis (RAS, n = 6) or sham (n = 8) surgeries. This approach was validated by comparing model‐derived GFR and perfusion to those obtained by fluorescein isothiocyanante (FITC)‐inulin clearance and arterial spin labeling (ASL), respectively, using the Pearson's and Spearman's rank correlations and Bland‐Altman analysis.ResultsThe compartmental model provided a good fitting to measured gadolinium dynamics in both normal and RAS kidneys. The proposed DCE‐MRI method offered assessment of single‐kidney GFR and perfusion, comparable to the FITC‐inulin clearance (Pearson's correlation coefficient r = 0.95 and Spearman's correlation coefficient ρ = 0.94, P < 0.0001, and mean difference −7.0 ± 11.0 μL/min) and ASL (r = 0.92 and ρ = 0.84, P < 0.0001, and mean difference 4.4 ± 66.1 mL/100 g/min) methods.ConclusionThe proposed DCE‐MRI method may be useful for reliable noninvasive measurements of single‐kidney GFR and perfusion in mice. Magn Reson Med 79:2935–2943, 2018. © 2017 International Society for Magnetic Resonance in Medicine.