Micro-MRI methods to detect renal cysts in mice

BACKGROUND: Mouse models of disease, especially using transgenic and knockout technologies, are powerful tools to analyze the molecular basis of disease. We recently reported that a new dynamic micro-MRI method with dendrimer-based contrast agents can visualize renal structure and function in normal living mice and mice with acute renal failure. While MRI contrast enhancement is useful for detecting functional impairment of the kidneys, this technology has limitations in assessing morphologic changes, particularly cystic disease, because contrast-enhanced micro-MRI depicts cysts as low-intensity areas that cannot be distinguished from fibrotic foci. METHODS: In the current study, we evaluated if micro-MRI employing a new three-dimensional MR hydrography signal sequence [three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA)] can visualize chronic cystic changes without any contrast agents. RESULTS: We were able to positively depict multiple renal cortical cysts of approximately 0.2 mm diameter in a mouse model of sickle cell disease and observe serial changes of renal cysts (>0.2 mm diameter) in cyclooxygenase-2 (COX-2) knockout mice during a 21/2-month period. Some cysts decreased in size over time. CONCLUSIONS: Micro-MRI with 3D-FIESTA can depict cyst formation in the diseased kidneys of living mice without injection of contrast agents.     

Detection and localization of proteinuria by dynamic contrast-enhanced magnetic resonance imaging using MS325

After renal transplantation, persistent glomerular disease affecting the native kidneys typically causes albuminuria, at least for a period of time, making it difficult to determine in a noninvasive fashion whether proteinuria originates in the native kidneys or the renal allograft. To address this problem, dynamic contrast-enhanced magnetic resonance imaging (MRI) using gadolinium (Gd)-based albumin-bound blood pool contrast agent (MS325) to localize proteinuria was investigated. Glomerular proteinuria was induced in Sprague-Dawley rats by intravenous injection of puromycin aminonucleoside (PAN), whereas control rats received physiologic saline vehicle. Both groups of animals underwent a 40-min dynamic contrast-enhanced MRI using radio frequency spoiled gradient echo imaging sequence after injection of Gd-labeled MS325. Contrast uptake and clearance curves for cortex and medulla were determined from acquired MR images. Compared with controls, proteinuric rats exhibited significantly lower elimination rate constants. The use of gadopentetate dimeglumine (Gd-DTPA) as a contrast agent showed smaller and less specific differences between proteinuric and control groups. In rats with one proteinuric kidney (PAN-treated) and one normal kidney (transplanted from a normal rat), MRI using MS325 was able to differentiate between the two kidneys. The results suggest that MRI with an albumin-bound blood pool contrast agent may be a useful noninvasive way to localize proteinuria. If this technique can be successfully applied in human patients, it may allow for the localization of proteinuria after kidney transplant and thereby provide a noninvasive way to detect disease affecting the renal allograft.     

Magnetic resonance imaging as a sole method for the morphological and functional evaluation of live kidney donors

OBJECTIVE: To evaluate gadolinium-enhanced dynamic magnetic resonance imaging (MRI) as the sole method for the anatomical and functional assessment of potential live-kidney donors. SUBJECTS AND METHODS: The study included 50 consecutive kidney donors; in addition to routine donor evaluation, the kidney was imaged with Gd-enhanced dynamic MRI, which was also used for selectively determining the glomerular filtration rate (GFR) of each kidney. All donors had a m99Tc-mercaptoacetyltriglycine (MAG3) renal scan as the reference standard to measure GFR. The anatomical results of MRI were compared with the findings at donor nephrectomy, and the GFR estimated from MRI compared with that from MAG3 scintigraphy. RESULTS: MR angiography had 100% sensitivity, 94% specificity and 96% overall accuracy for detecting the number of renal arteries, and 100% sensitivity, 98% specificity and 98% overall accuracy for the number of renal veins. There was a close correlation (r = 0.54, P < 0.01) between the GFR of each kidney estimated by MRI or MAG3. For the right and left kidneys the mean isotope clearance was not significantly different from that of mean MRI clearance. MR urography allowed visualization of the urinary tract and the detection of any abnormality. CONCLUSION: Gd-enhanced dynamic MRI can provide accurate information about the anatomy of the urinary tract and vasculature of the kidney, and can be used to accurately estimate the selective GFR of each kidney. Therefore, we recommend MRI as a single imaging diagnostic method for assessing potential live kidney donors.     

Role of protein kinase C in cisplatin nephrotoxicity

BACKGROUND: Cisplatin is widely used in cancer treatment. The major disadvantage of this antitumor agent is its nephrotoxicity. The mechanism of cisplatin-induced nephrotoxicity has not been clarified. Recent evidence suggests protein kinase C (PKC)-related signal transduction pathways may modulate cisplatin-induced cytotoxicity. METHODS: The effect of cisplatin administration on PKC expression in the kidney and the effect of a PKC inhibitor on cisplatin-induced renal impairment were investigated in rats. RESULTS: A single intraperitoneal injection of 8 mg/kg cisplatin induced remarkable damage in the proximal tubules located in the outer medulla, which was associated with impaired renal function, within 48 h. An immunoblotting study revealed marked expression of alpha-PKC in membrane fractions of medullary tubules prepared from cisplatin-treated rats. In addition, pretreatment with the PKC inhibitor (H-7) protected kidneys from cisplatin-induced damage. CONCLUSIONS: These findings suggest that the nephrotoxic effects of cisplatin may, in part, be related to PKC activation in the renal tubules.     

Dendrimer-enhanced MRI as a diagnostic and prognostic biomarker of sepsis-induced acute renal failure in aged mice

BACKGROUND: Acute renal failure (ARF) induced by sepsis has a high mortality. In an aged mouse model of sepsis-induced ARF we have previously shown that renal injury occurs before serum creatinine is elevated. Development of a noninvasive biomarker that could diagnose renal dysfunction early in sepsis and monitor the response to therapy would be very valuable. METHODS: We performed magnetic resonance imaging (MRI) with gadolinium-based G4 dendrimer intravenous contrast in a fluid- and antibiotic-treated cecal ligation and puncture (CLP) sepsis model in aged mice. Imaging was also performed in a mouse volume depletion model and in models of ARF induced by ischemia/reperfusion (I/R) and cisplatin. RESULTS: Twenty hours post-CLP, aged mice had a distinct pattern of renal injury using dendrimer-enhanced MRI. This pattern was different from renal injury induced by either cisplatin or I/R. Prerenal azotemia induced by volume depletion was distinguished from sepsis by dendrimer-enhanced MRI. Dendrimer-enhanced MRI detected renal dysfunction 6 hours post-CLP, a time when serum creatinine was still normal. Ethyl pyruvate reversed the renal dysfunction detected by dendrimer-enhanced MRI at 20 hours, but not at 6 hours post-CLP. The appearance of renal dysfunction on dendrimer-enhanced MRI at 6 hours post-CLP predicted the length of survival. CONCLUSION: Dendrimer-enhanced MRI is a novel biomarker that provides information for the early diagnosis, drug responsiveness, and prognosis of sepsis-induced ARF.     

Dynamic MR imaging of kidneys perfused with EOB-Gd-DTPA

Gandolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) is a hepatobiliary contrast agent for MRI. It was reported that Gd-EOB-DTPA is useful to detect liver tumors and differentially diagnose benign and malignant pathologies in the liver. Since Gd-EOB-DTPA partially accumulates in the hepatocytes and bile via various transporters after intravenous injection, signal intensity in the liver increases on T1-weighted images. The signal intensity of the liver after Gd-EOB-DTPA injection depends on the Gd-EOB-DTPA uptake by hepatocytes and bile excretion. It is known tha the Gd-EOB-DTPA accumulating in the kidney is excreted to the urine through glomerular filtration. Because Gd-DTPA is concentrated in the renal tubules after being filtered at the Bowman's capsule, and since it is neither secreted nor reabsorbed the concentrating and diluting function of the renal tubules can be studied by imaging techniques. since renal function can be evaluated with Gd-EOB-DTPA can also be used to evaluate renal function. Eith the development of MRI equipment and rapid imaging techniques, temporal resolution had improved greatly. However, no previous study has been carried out on renal function using Gd-EOB-DTPA dynamic MR study that was correlated with estimated glomerular filtration rate (eGFR) and stage of chronic kidney disease (CKD) in the Japan Association of chronic kidney disease initiative.     

Evaluation of renal function with dynamic Gd-DTPA-enhanced magnetic resonance imaging after shock wave lithotripsy]

It has already been reported that MR imaging is a superior imaging technique to detect minute anatomical changes in the kidney after ESWL. However, the morphological abnormalities found by MR imaging do not necessarily mean deterioration of the renal function. The purpose of this study is to assess the morphological changes in the kidney and changes in renal function after the ESWL treatment by dynamic MR imaging. A total of 16 patients underwent axial MR imaging before and after ESWL. Dynamic MR was also performed on 11 patients of them within 24 hours after ESWL, and both before and after ESWL in the remaining 5 patients. Eight kidneys showed morphological abnormalities on T1-weight images, and 4 of them showed loss of corticomedullary demarcation. Furthermore, the first MR imaging after injection of GdDTPA revealed focal areas of decreased signal intensity in only 2 of these 4 patients who showed loss of corticomedullary demarcation on previous MR images. However, the second MR imaging 6 months after ESWL showed no abnormality in either of them. The percent contrast of signal intensity increase to fat signal intensity was one minute after GdDTPA injection compared before and after ESWL in 5 of the 16 patients. The values before and after ESWL revealed no statistically significant difference, and no patient showed any remarkable decrease of signal intensity after ESWL. These results suggest that loss of corticomedullary demarcation after ESWL does not necessarily reflect damage to the renal function and that the shock-wave exposure causes no permanent damage to the renal function but only temporary impairment.     

Clinical value of new rapid nuclear magnetic resonance tomography in preoperative assessment of hypernephroma. A prospective comparative study of CT and MR

The new technique of rapid magnetic resonance imaging (MRI) with a paramagnetic contrast agent provides excellent imaging of the kidneys and their lesions. MR imaging of this anatomical region at short breath holding intervals matches the well-known quality of computed tomography (CT) for the first time. MR and CT studies were performed on 36 patients with proven renal cell carcinoma. Different investigators evaluated the staging of the tumor by means of both techniques in a prospective study. In all patients a radical nephrectomy was performed. Surgical and pathological findings were compared. Though little difference was found in diagnostic value between the two systems, MRI results concerning the T-stage were better. Venous invasion was clearly shown by MRI without the use of contrast medium. Furthermore, sagittal and transaxial images provided a more direct assessment of the extent of the tumor and its demarcation to healthy parenchyma. Thus, MRI is helpful in planning of the surgical approach when organ-sparing excision of renal tumors is to be performed.     

Use of urography by magnetic resonance for the study of the urinary apparatus versus conventional urography

Conventional urography (IVU) is an essential examination for the assessment of urinary tract but it is not free of complications, such as adverse reactions to contrast agents used (vasovagal and anaphylactic reactions), neurotoxicity, nephrotoxicity, as well as the damage due to the ionizing irradiation applied to the patient. For this reason, alternative imaging techniques such as magnetic resonance (MR) urography or uro-resonance have been developed.Objective:We present a case study assessing the diagnostic accuracy, specificity and sensitivity of uro-resonance and IVU as a morphological and functional examination of the urinary tract; and a quality study of the urographic images obtained with MR versus IVU.Materials and methods:150 patients have submited to a MR study, 63 of them with an IVU study already performed, acquiring high-intensity signals at T2 corresponding to abdominal and retroperitoneal fluid, initially using furosemide at low doses and, in a final study, administering gadolinium at a rate of 0.1 mg/Kg. The test was indicated in patients with antecedents of adverse reactions to iodine contrast, acute or chronic kidney failure, functional cancellation of the kidneys, pregnant patients and those in paediatric age. The capacity of diagnosis of urinary obstruction and the aetiology of this obstruction of both tests was studied, as well as the quality of the images obtained by the urographic study using MR.Results:High resolution images were obtained of all the upper urinary tracts using MR, especially in the renal pelvis, without artefacts caused by peristalsis or intestinal fluid interposition. In 83.3% of cases, examinations revealed urological pathology. The diagnostic accuracy of the involvement cause of the urinary tract was 83.3%, with a sensitivity of 89.6%, a specificity of 69.2%, a positive predictive value of 86.6% and a negative predictive value of 75%.Conclusion:MR urography is a high sensitive technique for the study of urinary tract, used as an alternative to conventional urography particularly in cases of the contraindication of ionizing radiation or allergy to the contrast agent, as well as in patients with renal failure, and offers a wider morphological and functional study, with a high image quality, able to displace conventional examinations in the short or medium term.     

Ultrasmall superparamagnetic iron oxides (USPIOs): a future alternative magnetic resonance (MR) contrast agent for patients at risk for nephrogenic systemic fibrosis (NSF)?

Gadolinium (Gd) based contrast agents (GBCAs) in magnetic resonance imaging (MRI) are used in daily clinical practice and appear safe in most patients; however, nephrogenic systemic fibrosis (NSF) is a recently recognized severe complication associated with GBCAs. It affects primarily patients with renal disease, such as stage 4 or 5 chronic kidney disease (CKD; glomerular filtration rate <30 ml/min per 1.73 m(2)), acute kidney injury, or kidney and liver transplant recipients with kidney dysfunction. Contrast-enhanced MRI and computed tomography (CT) scans provide important clinical information and influence patient management. An alternative contrast agent is needed to obtain adequate imaging results while avoiding the risk of NSF in this vulnerable patient group. One potential alternative is ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, which provide enhancement characteristics similar to GBCAs. We review our experience in approximately 150 patients on the potential benefits of the USPIOs ferumoxtran-10 and ferumoxytol. We focus on central nervous system (CNS) MRI but also review imaging of other vascular beds. Safety studies, including USPIO administration (ferumoxytol) as iron supplement therapy in CKD patients on and not on dialysis, suggest that decreased kidney function does not alter the safety profile. We conclude that for both CNS MR imaging and MR angiography, USPIO agents like ferumoxytol are a viable option for patients at risk for NSF.     

Cisplatin-induced oxidative stress stimulates renal Fas ligand shedding

Acute kidney injury (AKI), a significant complication of cisplatin chemotherapy is associated with reactive oxygen species (ROS)-dependent renal cell death, but the cellular targets of ROS in cisplatin nephrotoxicity are not fully resolved. Here, we investigated cisplatin-induced oxidative renal damage and tested the hypothesis that ROS-dependent shedding of death activator Fas ligand (FasL) occurs in cisplatin nephropathy. We show that intraperitoneal injection of sulfobutyl ether-β-cyclodextrin (Captisol?)-solubilized cisplatin elevated the level of lipid peroxidation product malondialdehyde in mouse kidneys and urinary concentration of oxidative DNA damage biomarker 8-hydroxy-2′-deoxyguanosine. Cisplatin increased mouse kidney-to-body weight ratio and the plasma or urinary levels of predictive biomarkers of AKI, including creatinine, blood urea nitrogen, microalbumin, neutrophil gelatinase-associated lipocalin, and cystatin C. Histological analysis and dUTP nick end labeling of kidney sections indicated tubular injury and renal apoptosis, respectively in cisplatin-treated mice. Whereas the plasma concentration of soluble FasL (sFasL) was unaltered, urinary sFasL was increased ～4-fold in cisplatin-treated mice. Real-time quantitative live-cell imaging and lactate dehydrogenase assay showed that cisplatin stimulated caspase 3/7 activation and cytotoxicity in a human proximal tubule epithelial cell line which were attenuated by inhibitors of the FasL/Fas system and poly [ADP-ribose] polymerase-1. Moreover, TEMPOL, an intracellular free radical scavenger mitigated cisplatin-induced renal oxidative stress and injury, AKI biomarker and urinary sFasL elevation, and proximal tubule cell death. Our findings indicate that cisplatin-induced oxidative stress triggers the shedding of membrane-bound FasL to sFasL in the kidney. We demonstrate that cisplatin elicits nephrotoxicity by promoting FasL/Fas-dependent oxidative renal tubular cell death.     

胰、肾联合移植后的磁共振扫描监测

目的 探讨磁共振技术在胰，肾联合移植术后的应用价值。方法 用磁共振自旋回波序列，磁共振胰胆管成像和磁共振尿路成像。动态增强三维增强快速扰向梯度回波磁共振血管成像和三维相位对比法磁共振血流成像对5例接受胰，肾联合移植术的患者进行监测。分析各序列图像特点。结果 常规磁共振平扫可观察移植胰腺和肾的形态特征。自旋回波T1加权像增强序列可反映移植体的强化程度；磁共振胰胆管成像及磁共振尿路成像可直观反映胰管，肾盏，肾盂及输尿管情况，三维磁共振血流成像可较好的显示血管及移植体循环情况。结论 正确完善的磁共振扫描方法可客观反映移植体的形态及功能，是移植术后监测移植体的有效方法。     

A novel contrast-induced acute kidney injury mouse model based on low-osmolar contrast medium

The contrast-induced acute kidney injury (CI-AKI) has been becoming the third common cause of hospital-acquired acute kidney injury. An ideal animal model is essential for understanding the pathophysiology of CI-AKI. Previous CI-AKI studies were mostly performed on rats with high-osmolar contrast medium (HOCM), which is unsuitable for transgenic researches. This study provides a novel, efficient and reproducible CI-AKI model which was developed in mouse by administrating a low-osmolar contrast medium (LOCM). First of all, we applied the frequently used pretreatments (uninephrectomy and water deprivation), which combined with HOCM on rats could induce CI-AKI, on mice with LOCM. Secondly, we attempted to find a novel pretreatment suitable for mouse and LOCM by combining two classic pretreatments(uninephrectomy, water deprivation and furosemide administration). Finally, we evaluate the kidney damage of the novel model. We found that this mouse model possessed a significant reduction in renal function, severe renal tissue damage, and increased renal tubular cells apoptosis, indicating that LOCM is a feasible inducer for CI-AKI mice model. Taken together, we found that uninephrectomy (UPHT) combined with 24 h water deprivation and furosemide administration 20 min before LOCM (iohexol, 10 ml/kg) application is a feasible pretreatment to establish a novel CI-AKI mouse model.     

Reduced renal prepro-epidermal growth factor mRNA and decreased EGF excretion in ARF

Levels of prepro epidermal growth factor (EGF) mRNA in renal cortical tissue and urinary EGF excretion have been determined during cisplatin and ischemia-induced acute renal failure in the rat. Northern analysis of polyadenylated RNAs of kidney cortical tissue showed diminished renal preproEGF mRNA in rats injected with cisplatin (5 mg/kg). The decrease in preproEGF mRNA occurred as early as 12 hours in the kidney and persisted for at least three days after cisplatin injection. The submandibular gland, a major site of EGF synthesis, contained normal levels of preproEGF mRNA. Transplatin, a non-nephrotoxic isomer of cisplatin, did not reduce renal preproEGF mRNA levels. Northern analysis of polyadenylated RNAs of kidney cortical tissue 24 hours after a 50 minute period of renal pedicle clamping also showed reduced preproEGF mRNA levels. By contrast, cisplatin increased renal c-fos mRNA. Urinary EGF excretion was also reduced after cisplatin and ischemia and the decrease in EGF excretion correlated significantly with the degree of renal failure. The data show that nephrotoxic and ischemic renal cell injury reduces preproEGF mRNA and urinary EGF excretion. Reduced preproEGF mRNA and diminished EGF excretion may be important in the functional and regenerative responses to renal injury.     

High-resolution magnetic resonance imaging using gadolinium-based contrast agent for atherosclerotic carotid plaque

BACKGROUND: Early detection of vulnerable plaques at risk of causing thromboembolic events is very important, and many investigators report the usefulness of high-resolution MRI. The purpose of this study was to determine whether the detection of atherosclerotic carotid plaques can be enhanced after administration of contrast agents and, if so, to evaluate the potential for functional information. METHODS: We studied 9 patients (10 subjects) who underwent a high-resolution MRI examination using a gadolinium-based contrast agent before CEA. Pre- and postcontrast-enhanced T1-weighted images were reviewed, and their histopathologic characteristics evaluated in the corresponding tissue slices. RESULTS: Strong contrast enhancement patterns were found in 6 of 10 subjects. For 5 of 6 subjects, many microvessels with inflammatory cells or intraplaque hemorrhages were demonstrated in their corresponding tissue slices. Contrast enhancement patterns were noted to be focal, diffuse, and along the luminal surface or the vessel adventitial boundary. Moreover, some plaques were clearly demonstrated by using contrast agent, and others were clearly divided into fibrous and lipid regions. CONCLUSION: Gadolinium-based contrast agent can penetrate human atherosclerotic carotid plaques. The extent or size of neovascularization and the endothelial permeability are likely related to the mechanism of enhancement, and contrast-enhanced MRI may be essential for the identification of plaque neovascularization which is an important factor of vulnerable plaques. In addition to morphologic information, with the functional information provided using various contrast agents, we may expect a more correct diagnosis of carotid plaques at risk of causing thromboembolic events.     

Cisplatin-induced nephrotoxicity is mediated by tumor necrosis factor-alpha produced by renal parenchymal cells

Cisplatin is a chemotherapeutic agent that induces tumor necrosis factor-alpha (TNF-alpha) production in many cell types with unfortunate renal toxicity. We sought to determine the contributions of renal parenchymal cells and bone marrow-derived immune cells to the pathogenesis of cisplatin-induced renal injury in vivo. To do this we created chimeric mice in which the bone marrow was ablated and replaced with donor bone marrow cells from wild-type or from TNF-alpha knockout mice. Six weeks after reconstitution, the chimeric mice were treated with cisplatin and renal structural and functional parameters were measured. Chimeras with kidneys of wild-type animals all developed significant renal failure after 72 h of cisplatin treatment regardless of the immune cell source. Chimeras with kidneys of TNF-alpha knockout mice showed significantly less renal dysfunction (blood urea nitrogen, serum creatinine, and glomerular filtration rate), renal histologic injury, and serum TNF-alpha levels; again regardless of the immune cell source. Urinary excretion of several proinflammatory cytokines was lower in the wild-type bone marrow-knockout kidney chimera mouse than in wild-type background mice. Our results indicate that a substantial portion of circulating and urinary TNF-alpha is derived from nonimmune cells after cisplatin administration. We conclude that the production of TNF-alpha by renal parenchymal cells, rather than by bone marrow-derived infiltrating immune cells, is responsible for cisplatin-induced nephrotoxicity.     

Modern imaging modalities in renal disease: CT and MRI

Considerable technical advances have been made in computed tomography (CT) and magnetic resonance imaging (MRI) over the last 10 years. Both modalities allow for high-resolution imaging of the entire abdomen before as well as during the arterial and parenchymal perfusion phase after intravenous contrast medium administration. Multiplanar reconstructions of the three-dimensional source data sets yield views in any spatial orientation. Maximum intensity projections enable the generation of CT or MR angiographies as well as CT or MR urographies from delayed images. Thus, both modalities today allow for comprehensive diagnostic evaluation of renal disease by a single examination comprising detailed visualization of the parenchyma as well as of arterial and venous vessels and assessment of excretion. CT and MRI thus enable efficient preoperative diagnostic assessment in particular in patients with renal masses.     

Uptake and metabolism of cisplatin by rat kidney

Cisplatin, an effective antineoplastic agent, is toxic to the kidney. Since the kidney's vulnerability to cisplatin may originate in its ability to accumulate and retain platinum to a greater degree than other organs, we studied the characteristics of the renal accumulation of platinum and investigated the nature of intracellular platinum. Cisplatin and ethylenediamminedichloroplatinum, nephrotoxic and antineoplastic liganded platinum compounds, were concentrated in rat renal cortical slices fivefold above medium concentration. Platinum uptake was energy- and temperature-dependent and could be inhibited by drugs which inhibit base transport. The organic anions para-aminohippurate and pyrazinoate did not reduce renal slice platinum uptake. Unbound platinum in the blood and urine was predominantly cisplatin but unbound platinum in kidney cytosol was not. This latter compound, in contrast to cisplatin, was not active as a mutagen. These studies suggest that the kidney accumulates platinum in part by transport or specific binding to the base transport system in the kidney and biotransforms it intracellularly. Unbound platinum in the cell is not cisplatin and may no longer be toxic.     

Multiphoton Intravital Microscopy of the Transplanted Mouse Kidney

Graft outcomes after kidney transplantation continue to be adversely affected by ischemia‐reperfusion injury and rejection. High‐resolution, real‐time imaging of the transplanted kidney could shed valuable insights into these dynamic processes, but such methodology has not been established. Here we describe a technique for intravital imaging of the transplanted mouse kidney using multiphoton fluorescence microscopy. The technique enabled real‐time, high‐resolution imaging and quantitation of renal filtration, cell death, leukocyte adhesion and capillary blood flow after transplantation. Using this technique, we found that brief graft ischemia associated with the transplantation procedure led to a rapid decline in renal filtration accompanied by a significant increase in microvascular leakage and renal tubular epithelial cell death within the first 3 h after transplantation. No significant changes in leukocyte adhesion or capillary blood flow were observed during the same time period. This report establishes multiphoton fluorescence microscopy as a sensitive tool for simultaneously studying functional and structural perturbations that occur in the mouse kidney after transplantation and for investigating the migration of leukocytes to the graft.     

Magnetic Resonance Imaging of Transplanted Mouse Islets Labeled With Chitosan-Coated Superparamagnetic Iron Oxide Nanoparticles

Although only 10% of islet recipients maintain insulin independence, 80% of them are C-peptide positive at 5 years after transplantation. To better understand the fate of transplanted islets, a magnetic resonance imaging (MRI) technique has been used to detect Feridex-labeled islet grafts in rodents. In this study, we used a novel MRI contrast agent, chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles, to monitor mouse islet grafts. Male inbred C57BL/6 mice were used as donors and recipients of islet transplantation. The islet cytotoxicity was evaluated by fluorescein diacetate and propidium iodide staining for RAW cells incubated with CSPIO. After being incubated overnight with and without CSPIO (10 mg/mL), 300 islets were transplanted under the left kidney capsule of each mouse. After transplantation, 3.0-Tesla MRI of the recipients was performed biweekly until 19 weeks. At the end of study, the islet graft was removed for insulin and Prussian blue staining. The cell death rates in RAW cells did not increase with increasing CSPIO concentrations or incubation time. The grafts of CSPIO-labeled islets were visualized on MRI scans as distinct hypointense spots homogeneously located at the upper pole of left kidney. Their MRI signal was 30%-50% that of control islets and was maintained throughout the follow-up period. At 18 weeks, the histology of CSPIO-labeled islet graft revealed the insulin- and iron-stained areas to be almost identical. Our results indicate that isolated mouse islets labeled with CSPIO nanoparticles can be effectively and safely imaged by using MRI as long as 18 weeks after transplantation.