Macura, Slobodan I

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.

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.

ABSTRACT Brain atrophy is a common feature of numerous neurologic diseases in which the role of neuroinflammation remains ill‐defined. In this study, we evaluated the contribution of major histocompatibility complex class I molecules to brain atrophy in Theiler's murine encephalomyelitis virus (TMEV)–infected transgenic FVB mice that express the D b class I molecule. FVB/D b and wild‐type FVB mice were evaluated for changes in neuroinflammation, virus clearance, neuropathology, and development of brain atrophy via T2‐weighted MRI and subsequent 3‐dimensional volumetric analysis. Significant brain atrophy and hippocampal neuronal loss were observed in TMEV‐infected FVB/D b mice, but not in wild‐type FVB mice. Brain atrophy was observed at 1 mo postinfection and persisted through the 4‐mo observation period. Of importance, virus‐infected FVB/D b mice elicited a strong CD8 T‐cell response toward the immunodominant D b ‐restricted TMEV‐derived peptide, VP2 121–130 , and cleared TMEV from the CNS. In addition, immunofluorescence revealed CD8 T cells near virus‐infected neurons; therefore, we hypothesize that class I restricted CD8 T‐cell responses promote development of brain atrophy. This model provides an opportunity to analyze the contribution of immune cells to brain atrophy in a system where persistent virus infection and demyelination are not factors in long‐term neuropathology.—Huseby Kelcher, A. M., Atanga, P. A., Gamez, J. D., Cumba Garcia, L. M., Teclaw, S. J., Pavelko, K. D., Macura, S. I., Johnson, A. J. Brain atrophy in picornavirus‐infected FVB mice is dependent on the H‐2Db class I molecule. FASEB J. 31, 2267–2275 (2017). www.fasebj.org

PurposeNoninvasive imaging techniques that quantify renal tissue composition are needed to more accurately ascertain prognosis and monitor disease progression in polycystic kidney disease (PKD). Given the success of magnetization transfer (MT) imaging to characterize various tissue remodeling pathologies, it was tested on a murine model of autosomal dominant PKD.MethodsC57Bl/6 Pkd1 R3277C mice at 9, 12, and 15 months were imaged with a 16.4T MR imaging system. Images were acquired without and with RF saturation in order to calculate MT ratio (MTR) maps. Following imaging, the mice were euthanized and kidney sections were analyzed for cystic and fibrotic indices, which were compared with statistical parameters of the MTR maps.ResultsThe MTR‐derived mean, median, 25th percentile, skewness, and kurtosis were all closely related to indices of renal pathology, including kidney weight/body weight, cystic index, and percent of remaining parenchyma. The correlation between MTR and histology‐derived cystic and fibrotic changes was R2 = 0.84 and R2 = 0.70, respectively.ConclusionMT imaging provides a new, noninvasive means of measuring tissue remodeling PKD changes and may be better suited for characterizing renal impairment compared with conventional MR techniques. Magn Reson Med 75:1466–1473, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance.