Update on imaging-based diagnosis of acute renal allograft rejection.

Kidney transplantation is the preferred treatment for patients with end-stage renal disease. Despite effective immunosuppressants, acute allograft rejections pose a major threat to graft survival. In early stages, acute rejections are still potentially reversible, and early detection is crucial to initiate the necessary treatment options and to prevent further graft dysfunction or even loss of the complete graft. Currently, invasive core needle biopsy is the reference standard to diagnose acute rejection. However, biopsies carry the risk of graft injuries and cannot be immediately performed on patients receiving anticoagulation drugs. Therefore, non-invasive assessment of the whole organ for specific and rapid detection of acute allograft rejection is desirable. We herein provide a review summarizing current imaging-based approaches for non-invasive diagnosis of acute renal allograft rejection.

SPECT- and PET-based approaches for noninvasive diagnosis of acute renal allograft rejection.

Molecular imaging techniques such as single photon emission computed tomography (SPECT) or positron emission tomography are promising tools for noninvasive diagnosis of acute allograft rejection (AR). Given the importance of renal transplantation and the limitation of available donors, detailed analysis of factors that affect transplant survival is important. Episodes of acute allograft rejection are a negative prognostic factor for long-term graft survival. Invasive core needle biopsies are still the "goldstandard" in rejection diagnostics. Nevertheless, they are cumbersome to the patient and carry the risk of significant graft injury. Notably, they cannot be performed on patients taking anticoagulant drugs. Therefore, a noninvasive tool assessing the whole organ for specific and fast detection of acute allograft rejection is desirable. We herein review SPECT- and PET-based approaches for noninvasive molecular imaging-based diagnostics of acute transplant rejection.

PET with 18F-FDG-labeled T lymphocytes for diagnosis of acute rat renal allograft rejection.

UNLABELLED: We proposed small-animal PET with (18)F-FDG-labeled T lymphocytes as a new method for image-based diagnosis of acute allogeneic renal transplant rejection (AR) established in a rat model. METHODS: One and 2 h after tail vein injection of 30 × 10(6) ex vivo (18)F-FDG-labeled human T cells into male 10-wk-old uninephrectomized, allogeneically transplanted rats (aTX; Lewis-brown Norway [LBN] to Lewis), whole-body radioactivity distribution was assessed in vivo by small-animal PET (postoperative day 4), and percentage injected dose (%ID) as a parameter of T-cell infiltration was assessed and compared between graft and native kidney. In vivo results were confirmed by autoradiography and staining of human CD3 after postmortem dissection. Syngeneically transplanted rats (sTX) (LBN to LBN), rats with ischemia-reperfusion injury (IRI) (45-min warm ischemia), and rats subjected to acute cyclosporine A (CSA) toxicity (50 mg/kg for 2 d intraperitoneally) served as controls. RESULTS: The accumulation of labeled cells was significantly elevated in allografts with AR (1.07 ± 0.28 %ID), compared with native control kidneys (0.49 ± 0.18 %ID) (P < 0.0001). No differences were found among native controls, sTX, CSA toxicity, and kidneys with IRI. In vivo uptake of (18)F-FDG cells measured in the PET scanner correlated with results obtained by autoradiography, histologic evaluation, and polymerase chain reaction. CONCLUSION: We proposed graft PET imaging using (18)F-FDG-labeled T cells as a new option to detect rat renal AR with a low dose of (18)F-FDG in a noninvasive, fast, and specific manner in rats.

Non-invasive imaging of acute allograft rejection after rat renal transplantation using 18F-FDG PET.

The number of patients with end-stage renal disease, and the number of kidney allograft recipients continuously increases. Episodes of acute cellular allograft rejection (AR) are a negative prognostic factor for long-term allograft survival, and its timely diagnosis is crucial for allograft function (1). At present, AR can only be definitely diagnosed by core-needle biopsy, which, as an invasive method, bares significant risk of graft injury or even loss. Moreover, biopsies are not feasible in patients taking anticoagulant drugs and the limited sampling site of this technique may result in false negative results if the AR is focal or patchy. As a consequence, this gave rise to an ongoing search for new AR detection methods, which often has to be done in animals including the use of various transplantation models. Since the early 60s rat renal transplantation is a well-established experimental method for the examination and analysis of AR (2). We herein present in addition small animal positron emission tomography (PET) using (18)F-fluorodeoxyglucose (FDG) to assess AR in an allogeneic uninephrectomized rat renal transplantation model and propose graft FDG-PET imaging as a new option for a non-invasive, specific and early diagnosis of AR also for the human situation (3). Further, this method can be applied for follow-up to improve monitoring of transplant rejection (4).

Strategies for non-invasive molecular imaging of acute allograft rejection by gamma scintigraphy and positron emission tomography.

The number of patients necessitating treatment for end-stage organ failure, and therefore, the number of allograft recipients, increases. Despite the introduction of new and effective immunosuppressive drugs, acute cellular graft rejection (AR) is still a major risk for graft survival. Hence, early detection and treatment of AR is crucial to limit the inflammatory process and preserve the function of the transplant. Nowadays, AR can only be definitively diagnosed by biopsy. As an invasive procedure, biopsy carries the risk of significant graft injury and is not feasible in patients taking anticoagulant medication. Moreover, limited sampling site (randomly taken exceedingly small portions of tissue) may lead to false negative results, i.e., when rejection is focal or patchy. Thus, in diagnostics, entirely image-based methods would be superior. As AR is characterized by recruitment of activated leukocytes into the transplant several diagnostic strategies exist. We herein review the current approaches (experimental and clinical scenarios with a special focus on renal AR) in noninvasive molecular imaging-based diagnostics of acute AR using either single photon (gamma) imaging or positron emission tomography.

Hydroxyfasudil-mediated inhibition of ROCK1 and ROCK2 improves kidney function in rat renal acute ischemia-reperfusion injury.

Renal ischemia-reperfusion (IR) injury (IRI) is a common and important trigger of acute renal injury (AKI). It is inevitably linked to transplantation. Involving both, the innate and the adaptive immune response, IRI causes subsequent sterile inflammation. Attraction to and transmigration of immune cells into the interstitium is associated with increased vascular permeability and loss of endothelial and tubular epithelial cell integrity. Considering the important role of cytoskeletal reorganization, mainly regulated by RhoGTPases, in the development of IRI we hypothesized that a preventive, selective inhibition of the Rho effector Rho-associated coiled coil containing protein kinase (ROCK) by hydroxyfasudil may improve renal IRI outcome. Using an IRI-based animal model of AKI in male Sprague Dawley rats, animals treated with hydroxyfasudil showed reduced proteinuria and polyuria as well as increased urine osmolarity when compared with sham-treated animals. In addition, renal perfusion (as assessed by (18)F-fluoride Positron Emission Tomography (PET)), creatinine- and urea-clearances improved significantly. Moreover, endothelial leakage and renal inflammation was significantly reduced as determined by histology, (18)F-fluordesoxyglucose-microautoradiography, Evans Blue, and real-time PCR analysis. We conclude from our study that ROCK-inhibition by hydroxyfasudil significantly improves kidney function in a rat model of acute renal IRI and is therefore a potential new therapeutic option in humans.

Potential of noninvasive serial assessment of acute renal allograft rejection by 18F-FDG PET to monitor treatment efficiency.

UNLABELLED: We propose (18)F-FDG PET as a method to monitor acute rejection of allogeneic renal transplants in a rat model. METHODS: Allogeneically transplanted (aTX) rats (binephrectomized Lewis-brown Norway to Lewis) served as the renal transplant model. aTX rats treated with cyclosporine A (CSA) served as a therapy monitoring group. Healthy control rats, rats with acute CSA nephrotoxicity, rats with acute tubular necrosis, syngeneically transplanted (sTX) rats, and aTX rats treated with CSA since postoperative day 0 served as controls. After surgery, renal glucose metabolism was assessed in vivo serially up to postoperative day 7 by performing small-animal PET 3 h after intravenous injection of 30 MBq of (18)F-FDG. Mean radioactivity (cps/mm(3) of tissue) was measured and the percentage injected dose calculated. Results were confirmed by histologic, functional, and autoradiographic analysis. RESULTS: Renal (18)F-FDG uptake was significantly elevated at postoperative day 4 in aTX rats, when compared with control, sTX, acute tubular necrosis, or CSA-treated rats (P < 0.05). In vivo (18)F-FDG uptake correlated with the results of autoradiography and with inflammatory infiltrates observed on histologic examination. Notably, (18)F-FDG PET assessed the response to therapy 48 h earlier than the time at which serum creatinine decreased and when histologic examination still showed signs of allograft rejection. In aTX rats, the CSA-susceptible graft infiltrate was dominated by activated cytotoxic T cells and monocytes/macrophages. CONCLUSION: (18)F-FDG PET is an option to noninvasively assess early response to therapy in rat renal allograft rejection.

Small-animal PET: a promising, non-invasive tool in pre-clinical research.

Today, non-invasive imaging techniques are significantly contributing to the understanding of molecular processes in vivo. Positron emission tomography (PET) is a scintigraphic medical imaging modality that uses radiolabelled molecules (tracers), provides quantitative tomographic images and allows non-invasive assessment of the biodistribution of radioactive substances in vivo. The assessment of pathological glucose metabolism is the clinically best-established application of PET today; however, a multitude of different tracers are available to assess diverse physiological processes. The growing interest in pre-clinical imaging studies, in biological and medical basic research, as well as in pharmaceutical research, has fostered the recent growth in small-animal PET. Small-animal PET can be applied to enable the transfer from molecular findings in vitro to in vivo applications in humans, from bench to bed side.

Non-invasive imaging of acute renal allograft rejection in rats using small animal F-FDG-PET.

BACKGROUND: At present, renal grafts are the most common solid organ transplants world-wide. Given the importance of renal transplantation and the limitation of available donor kidneys, detailed analysis of factors that affect transplant survival are important. Despite the introduction of new and effective immunosuppressive drugs, acute cellular graft rejection (AR) is still a major risk for graft survival. Nowadays, AR can only be definitively by renal biopsy. However, biopsies carry a risk of renal transplant injury and loss. Most important, they can not be performed in patients taking anticoagulant drugs. METHODOLOGY/PRINCIPAL FINDINGS: We present a non-invasive, entirely image-based method to assess AR in an allogeneic rat renal transplantation model using small animal positron emission tomography (PET) and (18)F-fluorodeoxyglucose (FDG). 3 h after i.v. injection of 30 MBq FDG into adult uni-nephrectomized, allogeneically transplanted rats, tissue radioactivity of renal parenchyma was assessed in vivo by a small animal PET-scanner (post operative day (POD) 1,2,4, and 7) and post mortem dissection. The mean radioactivity (cps/mm(3) tissue) as well as the percent injected dose (%ID) was compared between graft and native reference kidney. Results were confirmed by histological and autoradiographic analysis. Healthy rats, rats with acute CSA nephrotoxicity, with acute tubular necrosis, and syngeneically transplanted rats served as controls. FDG-uptake was significantly elevated only in allogeneic grafts from POD 1 on when compared to the native kidney (%ID graft POD 1: 0.54+/-0.06; POD 2: 0.58+/-0.12; POD 4: 0.81+/-0.06; POD 7: 0.77+/-0.1; CTR: 0.22+/-0.01, n = 3-28). Renal FDG-uptake in vivo correlated with the results obtained by micro-autoradiography and the degree of inflammatory infiltrates observed in histology. CONCLUSIONS/SIGNIFICANCE: We propose that graft FDG-PET imaging is a new option to non-invasively, specifically, early detect, and follow-up acute renal rejection. This method is potentially useful to improve post-transplant rejection monitoring.

Dynamic 18F-fluoride small animal PET to noninvasively assess renal function in rats.

PURPOSE: Renal function can be quantified by both laboratory and scintigraphic methods. In the case of small animal diagnostics, scintigraphic image-based methods are ideal since they can assess split renal function, work noninvasively, and can be repeated. The aim of this study is to validate a (18)F-PET-based method to quantify renal function in rats. MATERIALS AND METHODS: Fluoride clearance was calculated from a dynamic whole body listmode acquisition of 60 min length in a small animal PET scanner following an i.v. injection of 15 MBq (18)F-fluoride. Volumes of interest (VOIs) were placed in the left ventricle and the bladder as well as traced around the kidney contours. The respective time-activity curves (TAC) were calculated. The renal (18)F-clearance was calculated by the ratio of the total renal excreted activity (bladder VOI) and the integral of the blood TAC. PET-derived renal function was validated by intraindividual measurements of creatinine clearance (n = 23), urea clearance (n = 23), and tubular excretion rate (TER-MAG3). The split renal function was derived from the injection of the clinically available radionuclide (99m)Tc-mercaptotriglycine by blood sampling and planar renography (n = 8). RESULTS: In all animals studied, PET revealed high-quality TACs. PET-derived renal fluoride clearance was linearly correlated with intraindividual laboratory measures (PET vs. creatinine: r = 0.78; PET vs. urea: r = 0.73; PET vs. TER-MAG3: r = 0.73). Split function was comparable ((18)F-PET vs. MAG3-renography: r = 0.98). PET-derived measures were highly reproducible. CONCLUSIONS: (18)F-PET is able to noninvasively assess renal function in rats and provides a significant potential for serial studies in different experimental scenarios.

The superior prognostic value of humoral factors compared with molecular proliferation markers in renal cell carcinoma.

BACKGROUND: The American Joint Committee on Cancer and the Union Internationale Contre le Cancer have acknowledged routine laboratory parameters, such as serum calcium, alkaline phosphatase, hemoglobin, and the erythrocyte sedimentation rate (ESR), as predictors of survival in patients with renal cell carcinoma. The predictive value of these parameters compared with proliferation markers, such as Ki-67, proliferating cell nuclear antigen (PCNA), topoisomerase II-alpha, and p100, has not been determined. METHODS: Forty-eight consecutive patients who underwent nephrectomy for nonmetastatic renal cell carcinoma between 1990 and 1994 were observed up to 120 months postoperatively. Ten of 48 patients developed tumor progression 6-69 months after surgery. Routine preoperative laboratory parameters as well as tumor-specific data were assessed. Findings were compared with tumor proliferation indices, which were obtained by immunohistochemical staining for nuclear antigens Ki-67, PCNA, topoisomerase II-alpha, and p100 in paraffin embedded tumor tissue. RESULTS: Univariate and multivariate statistical analyses demonstrated superiority of routine laboratory values compared with tumor proliferation indices in predicting progression-free survival and disease-specific death. The best predictor after tumor size and symptomatic presentation was ESR (P < 0.0001), with ESR values > 70 mm at 2 hours indicating a significantly poorer prognosis. Only the proliferation marker Ki-67 reached univariate significance at a threshold of 7%. CONCLUSIONS: Routine laboratory parameters, such as alkaline phosphatase, lactate dehydrogenase, thrombocyte count, and especially ESR, provided superior long-term prognostic information for patients with nonmetastatic renal cell carcinoma compared with the molecular tumor proliferation markers Ki-67, PCNA, topoisomerase II-alpha, and p100.