Chronic graft loss: dealing with the vascular alterations in solid organ transplantation

Macrophage Infiltration Detected at MR Imaging in Rat Kidney Allografts: Early Marker of Chronic Rejection?

PURPOSE

To evaluate detection of iron-loaded macrophages at magnetic resonance (MR) imaging as a noninvasive means to monitor early signs of chronic allograft rejection in the life-supporting Fisher-to-Lewis rat kidney transplantation model.

MATERIALS AND METHODS

Experiments followed the Swiss federal regulations of animal protection. Male Fisher (n = 37) and Lewis (n = 77) rats were used. After removal of a native recipient kidney and transplantation of a donor kidney, the recipient rat's contralateral kidney was removed. Allografts and control syngeneic grafts comprised, respectively, kidneys from Fisher and Lewis donors transplanted into Lewis rats. Recipients were imaged by using a gradient-echo MR sequence 24 hours after intravenous administration of superparamagnetic iron oxide (SPIO) particles. Biochemical analyses of blood and urine, as well as assessments of Banff scores (reference standard for histologic classification of graft rejection), were performed. Statistical tests used were analysis of variance for multiple comparisons with Bonferroni tests, Mann-Whitney tests, and Pearson correlations with Bonferroni corrections.

RESULTS

A SPIO dose-dependent decrease in cortical MR signal intensity occurred in allografts between 8 and 16 weeks after transplantation. A strong significant negative correlation (P = .005 for 0.3 mL/kg SPIO dose, P = .003 for 1.0 mL/kg SPIO dose) was found between MR signal intensity and Banff scores, which deteriorated over the experimental period. Proteinuria occurred at 16 weeks. Blood and urine creatinine levels remained unchanged up to week 28.

CONCLUSION

This MR imaging method is more robust than the usually adopted creatinine clearance method for the detection of early signs of allograft chronic rejection in the Fisher-to-Lewis rat kidney transplantation model.

Rapamycin rescue therapy in patients after kidney transplantation: first clinical experience

This study was aimed at analysing rapamycin (RAPA) rescue therapy with calcineurin inhibitor (CNI) withdrawal in renal transplant patients primarily presenting with CNI-nephrotoxicity (CNI-Neph), chronic allograft nephropathy (CAN) without [CAN(a)] and with histological changes suggestive of chronic rejection [CAN(b)]. In 36 patient with CNI-Neph (n = 6), CAN(b) (n = 21), CAN(a) (n = 7), and others (n = 2) RAPA therapy was started 4.4-115 months (median 30.6 months) after renal transplantation. During a follow up of 3-33 months (median 19 months) parameters of kidney function were recorded. Three patients on haemodialysis did not show any recovery of graft function. Of the remaining 33 patients renal function improved in 22 (66.7%), was stable in three (9%) but deteriorated in eight (24%) patients, of whom seven (21%) required haemodialysis thereafter. Success rate of RAPA therapy differed with respect to the histological diagnosis: 70% in CAN(b), 80% in CNI-Neph and 33% in CAN(a). Furthermore, in patients with creatinine levels above 400 mum (n = 6) graft function rarely improved (n = 2, 33%). The RAPA rescue therapy with CNI withdrawal appears promising in a special cohort of patients with chronic renal allograft dysfunction even late after transplantation.

Early withdrawal of cyclosporine A improves 1-year kidney graft structure and function in sirolimus-treated patients

BACKGROUND

Chronic allograft nephropathy (CAN) represents the most common cause of late graft loss. Nephrotoxicity from chronic use of calcineurin inhibitors (CNI) has the potential to contribute to CAN. The present investigation aimed to evaluate the impact of early CNI withdrawal on kidney graft function and structure at 1 year in sirolimus (SRL)-treated patients.

METHODS

Forty consecutive kidney transplant recipients were initially treated with corticosteroids, cyclosporine A (CsA), and SRL (2 mg/day). After 3 months, patients were randomly assigned to either continue the same treatment (group I) or to withdraw CsA and continue SRL (group II). All patients underwent kidney graft biopsy immediately after graft reperfusion (0-hr biopsy) and 12 months after engraftment.

RESULTS

Baseline graft biopsy showed a higher degree of renal damage in group II patients (total score, 4+/-1.6 vs. 2+/-0.9; P<0.05). Twelve months after engraftment, CAN was diagnosed in 55% of all patients, of whom 64% were in group I and 36% in group II. CAN lesions were scored as moderate to severe in 90% of group I patients but only 32% of group II patients (P<0.05). A vascular score greater than or equal to 2 occurred in 90% of group I patients and in 38% of group II patients (P<0.05). At 1 year, group I patients showed a significantly worse kidney graft function (serum creatinine, 2.0+/-0.3 vs. 1.3+/-0.3 mg/dL; creatinine clearance, 54+/-14 vs. 66+/-17 mL/min; both P<0.002).

CONCLUSIONS

These results suggest that early withdrawal of CsA is a safe option, which allows a significant reduction of chronic histologic damage, particularly vascular injury, of cadaveric kidney allografts.

Macrophage labeling by SPIO as an early marker of allograft chronic rejection in a rat model of kidney transplantation

Anatomical and functional information (renography, perfusion) was obtained by MRI in a life-supporting transplantation model, in which Lewis rats received kidneys from Fisher 344 donors. Renography and perfusion analyses were carried out with Gd-DOTA and small particles of iron oxide (SPIO), respectively. Starting 12 weeks posttransplantation, images from grafts of untreated recipients exhibited distinctive signal attenuation in the cortex. Animals treated with cyclosporin (Sandimmune Neoral; Novartis Pharma, Basel, Switzerland) to prevent acute rejection showed a signal attenuation in the cortex at 33 weeks posttransplantation, while kidneys from rats treated additionally with everolimus (Certican; Novartis), a rapamycin derivative, had no changes in anatomical appearance. A significant negative correlation was found between the MRI cortical signal intensity and the histologically determined iron content in macrophages located in the cortex. Renography revealed a significantly reduced functionality of the kidneys of untreated controls 33 weeks after transplantation, while no significant changes in perfusion were observed in any group of rats. These results suggest the feasibility, by labeling macrophages with SPIO, of detecting signs of graft rejection significantly earlier than when changes in function occur. Monitoring early changes associated with chronic rejection can have an impact in preclinical studies by shortening the duration of the experimental period and by facilitating the investigation of novel immunomodulatory therapies for transplantation.

Cold storage preservation and warm ischaemic injury to isolated arterial segments: endothelial cell injury

Injury to endothelial cells is thought to be important to the development of the vascular lesion of chronic rejection. It was the aim of this study to develop a semiquantitative method to assess endothelial injury in arterial grafts and to document the injury produced by cold storage preservation and additional warm ischaemia. Twelve- and 24-h cold preservation of rat aortic segments, together with an additional 1 h of warm ischaemia, were assessed. Electron micrographs of representative endothelial cells were scored for cytoplasmic, nuclear and mitochondrial injury. The overall injury score was obtained by addition of the individual scores. Storage for up to 24 h in University of Wisconsin (UW) and Terasaki did not produce any injury. Twenty-four hours of storage in Euro-Collins resulted in endothelial cell death. Injury occurred after 12 h of storage in Ross, Collins and normal saline, and the injury increased following 24 h of storage. One hour of warm ischaemia did not increase the injury. Injury to endothelial cells varies with the preservation solution used and the time of cold storage, so that both the type of solution and the storage time should be taken into account in clinical studies looking at the influence of cold ischaemia time and graft outcome.

Endothelial targeting with C1-inhibitor reduces complement activation in vitro and during ex vivo reperfusion of pig liver

Tissue damage during cold storage and reperfusion remains a major obstacle to wider use of transplantation. Vascular endothelial cells and complement activation are thought to be involved in the inflammatory reactions following reperfusion, so endothelial targeting of complement inhibitors is of great interest. Using an in vitro model of human umbilical vein endothelial cells (HUVEC) cold storage and an animal model of ex vivo liver reperfusion after cold ischaemia, we assessed the effect of C1-INH on cell functions and liver damage. We found that in vitro C1-INH bound to HUVEC in a manner depending on the duration of cold storage. Cell-bound C1-INH was functionally active since retained the ability to inhibit exogenous C1s. To assess the ability of cell-bound C1-INH to prevent complement activation during organ reperfusion, we added C1-INH to the preservation solution in an animal model of extracorporeal liver reperfusion. Ex vivo liver reperfusion after 8 h of cold ischaemia resulted in plasma C3 activation and reduction of total serum haemolytic activity, and at tissue level deposition of C3 associated with variable level of inflammatory cell infiltration and tissue damage. These findings were reduced when livers were stored in preservation solution containing C1-INH. Immunohistochemical analysis of C1-INH-treated livers showed immunoreactivity localized on the sinusoidal pole of the liver trabeculae, linked to sinusoidal endothelium, so it is likely that the protective effect was due to C1-INH retained by the livers. These results suggest that adding C1-INH to the preservation solution may be useful to reduce complement activation and tissue injury during the reperfusion of an ischaemic liver.

MCMV induces neointima in IFN-gammaR-/- mice: intimal cell apoptosis and persistent proliferation of myofibroblasts

BACKGROUND

CMV infections have been linked to vasculopathies like atherosclerosis and Scleroderma. CMV infects vascular endothelium with intermittent shedding of the virus and the development of latency.

METHODS

We adopted a model of arteritis, developed by Presti et al. (1998), triggered by murine cytomegalovirus (MCMV) infection. Our studies focused on neointima formation. Groups of mice include: 1) immunocompetent 129S, 2) immunocompetent 129S receiving whole body irradiation and MCMV, 3) IFN-gammaR-/- receiving MCMV, and 4) IFN-gammaR-/- receiving MCMV and whole body irradiation.

RESULTS

Mice were inoculated with MCMV (5 x 10(4) or 1 x 10(5) PFU's) by i.p. injection; hearts and abdominal aortas were collected and histopathology evaluated. Infected immunocompetent animals exhibited widespread perivascular inflammation, which subsided by 8 weeks. Intimal pathology was not observed in any control group. Immunocompetent animals receiving MCMV and irradiation developed mild to moderate intimal lesions associated with medial and adventitial inflammation. IFN-gammaR-/- mice infected for 4 months and receiving whole body irradiation 2 months after infection developed pathology characterized by extensive adventitial and medial infiltrate and significant neointima, suggesting that infection and immunosuppression were co-requisites of neointima formation. Immunohistochemical analysis revealed myofibroblasts as a major component of neointima. The disease is characterized by up-regulation of growth factors (TGF-beta1, PDGF-A and B). Apoptosis was detected in the intimal layer of affected aortas. Active proliferation of myofibroblasts and infiltrating cells was also detected.

CONCLUSION

These results indicate that CMV infections may lead to intimal injury that results in the formation of neointima characteristic of autoimmune vasculopathies.

Renal allograft vasculopathy: ultrasound findings in a non-human primate model of chronic rejection

The purpose was to determine whether decreased cortical flow detected with power Doppler (PD) ultrasound in renal allografts in cynomolgus monkeys marks the presence or onset of chronic renal allograft vasculopathy. The 2D grey scale and PD ultrasound findings of 24 consecutively implanted non-life-supporting renal allografts in cynomolgus monkeys that underwent either 24 h (n=15) or 48 h (n=9) cold ischaemia times were recorded and compared with the results of histology performed every 2 weeks post-operatively. 13 allografts developed vasculopathies, 10 of which had PD scores equal to 1 (severe reduction of cortical flow). A PD score of 1 occurred in only one instance in the group of allografts without vasculopathies and this was due to necrosis. Allografts without vasculopathies otherwise had either PD scores of 3 (normal flow; n=2) or 2 (reduced flow; n=4). Allografts subjected to 48 h cold ischaemia times were smaller than those with 24 h cold ischaemia times (significant at weeks 5-11, p<0.05), but a reduction in graft size associated with vasculopathies occurred infrequently. In conclusion, the finding of reduced renal cortical flow detected by PD ultrasound during serial examination of non-life-supporting renal allografts is highly supportive of a diagnosis of graft vasculopathy due to arteriolar intimal proliferation, and illustrates an excellent method of monitoring changes in cortical perfusion in allografts in animal models. The combination of findings of reduced or absent cortical flow together with severe graft enlargement is highly suggestive of the presence of not only vasculopathies but also tissue damage and degeneration.

From anatomy to the target: contributions of magnetic resonance imaging to preclinical pharmaceutical research

In recent years, in vivo magnetic resonance (MR) methods have become established tools in the drug discovery and development process. In this article, the role of MR imaging (MRI) in the preclinical evaluation of drugs in animal models of diseases is illustrated on the basis of selected examples. The individual sections are devoted to applications of anatomic, physiologic, and "molecular" imaging providing, respectively, structural-morphological, functional, and target-specific information. The impact of these developments upon clinical drug evaluation is also briefly addressed. The main advantages of MRI are versatility, allowing a comprehensive characterization of a disease state and of the corresponding drug intervention; high spatial resolution; and noninvasiveness, enabling repeated measurements. Successful applications in drug discovery exploit one or several of these aspects. Additionally, MRI is contributing to strengthen the link between preclinical and clinical drug research.

MRI and ultrasonographic detection of morphologic and hemodynamic changes in chronic renal allograft rejection in the rat

PURPOSE

The purpose of this study is to describe the sonographic, MRI, and histopathologic findings in a rat model of chronic renal allograft rejection.

MATERIALS AND METHODS

Allogeneic renal grafts (male DA kidney into male Lewis rat with unilateral nephrectomy, N = 27) and syngeneic renal grafts (male Lewis kidney into male Lewis rat, N = 19) were examined serially with ultrasound, MRI, and histology.

RESULTS

Nonparametric Spearman rank correlation showed significance between the histologic score and the following parameters: the MRI score (r(s) = 0.91, P < 0.01, N = 46), the ultrasound score (r(s) = 0.9, P < 0.01, N = 46), the power Doppler score (r(s) = 0.86, P < 0.01, N = 46), and the MRI perfusion (r(s) = -0.80, P < 0.01, N = 45). Positive correlations were also found between the MRI volume estimations (graft r(s) = 0.49, P < 0.01, N = 46; native r(s) = 0.59, P < 0.01, N = 46), and the ultrasound volume estimations (graft r(s) = 0.39, P < 0.01, N = 45; native r(s) = 0.64, P < 0.01, N = 46) as well as with actual graft weight.

CONCLUSIONS

This study shows that both MRI and ultrasound can provide complementary, accurate information compared to histology in regard to the alterations in anatomy and hemodynamic changes associated with chronic allograft nephropathy.

The role of magnetic resonance imaging and spectroscopy in transplantation: from animal models to man

Critical success factors in solid organ and vascular transplantation are the assessment of graft status/viability as well as stringent monitoring of transplant recipients, preferentially using noninvasive techniques. This review addresses the application of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the field of transplantation. The first section is devoted to the description of the main MR techniques used for monitoring the status of the graft noninvasively. Subsequently, the role of MRI/MRS in the analysis of the viability of organs for transplantation is discussed. Since chronic rejection remains a major difficulty, development of new therapies is still ongoing. Thus, the third part is devoted to the use of MRI/MRS for monitoring graft rejection in animal models of transplantation. This is followed by a discussion of clinical studies of transplantation involving MRI/MRS. Finally, a general appraisal is made on available imaging techniques for the non-invasive characterization of grafts in situ, highlighting the role of MR methods in the field of transplantation.

Complete loss of functional smooth muscle cells precedes vascular remodeling in rat aorta allografts

BACKGROUND

The functional consequences of vascular remodeling in rat aorta allografts were studied at different times after transplantation (Tx).

METHODS

At days 1, 3, 7, 14, 28, and 56 after Tx, rat aorta allografts (Dark Agouti [DA]-to-Lewis) were mounted as isolated organs, and their contractile properties tested with phenylephrine, KCl, or endothelin-1. Controls were native DA-aortae and DA-syngeneic grafts. Changes in alpha smooth muscle actin and morphology were assessed by immunoblotting and histology.

RESULTS

PostTx syngeneic grafts presented similar functional and morphological properties to native aortae. In allografts, no morphological changes was detected at day 7 after Tx, but phenylephrine-induced vasoconstriction was reduced by 60%. Signs of medial smooth muscle cell (SMC) loss and adventitial inflammation were observed at day 14 after Tx, without neointima formation. A complete loss of contractile property was observed at day 28 after Tx in association with a 75% decrease in alpha-SMC actin, severe adventitial inflammation, and reduced medial cellularity. At this time, neointima was restricted to both edges of allografts. At day 56 after Tx, allografts were also not functional and exhibited neointima on their entire length. All these changes were prevented by treating recipients with cyclosporine (7.5 mg/kg/day).

CONCLUSION

These results indicate that, after Tx, the contractile property of rat aorta allografts is altered before manifest vascular remodeling. Because this can be prevented by cyclosporine, it most likely reflects an acute rejection of SMC. These results also show that vascular graft dysfunction can be used to monitor the development of rejection in the rat aorta allograft model.

Analysis of the reversibility of chronic liver allograft rejection implications for a staging schema

In contrast to all other vascularized organ allografts, chronic rejection (CR) of the liver is potentially reversible. We therefore studied demographic, perioperative, biochemical, and histologic features associated with reversibility or progression to graft failure. Using very stringent clinical and histological criteria, we identified a subgroup of 23 of 916 patients receiving primary liver allografts with CR from the Liver Transplantation Database. Of these, 13 experienced graft failure as a result of CR, and 10 patients recovered to normal histology or liver injury test results. Male-to-female sex mismatch (p = 0.07), younger recipient age (p = 0.09), younger donor age (p = 0.06), white-to-white race match (p = 0.09), primary diagnosis of biliary atresia (p = 0.02), and cold ischemia time of more than 12 hours (p = 0.02) were associated with graft failure. Patients who eventually recovered from CR were more likely to have acute rejection within the first 2 weeks (70% vs 23%; p = 0.04), had a higher number of acute rejection episodes (p = 0.08), and were more likely to have been treated with OKT3 (90% vs 46%, p = 0.07). Although overlap existed in the histopathologic findings between the patients whose grafts failed and those who recovered, those patients who developed bile duct loss in more than 50% of the portal tracts (p < 0.01), severe (bridging) perivenular fibrosis (p = 0.05), and the presence of foam cell clusters (p = 0.06) were more likely to require retransplantation. In contrast to other solid organ allografts, CR of the liver is not an irreversible process. These findings can be used to understand the evolution of CR and to design a biologically correct and clinically relevant staging system.