Accelerated Graft Arteriosclerosis Research Articles

Antibody and Complement in Transplant Vasculopathy

Advances in immunosuppression have decreased the incidence of acute rejection, but the development of vasculopathy in the coronary arteries of transplants continues to limit the survival of cardiac allografts. Transplant vasculopathy has also been referred to as accelerated graft arteriosclerosis because it has features of arteriosclerosis, but it is limited to the graft and develops over a period of months to years. Although the pathological features of transplant vasculopathy are well defined, the causative mechanisms are not completely understood. This review focuses on the mechanisms by which antibody and complement can cause or contribute to coronary vasculopathy in cardiac transplants. Antibodies and complement can have independent effects, but the combination of antibodies and complement with inflammatory cells has greater pathogenic potential for the endothelial and smooth muscle cells of the coronary arteries. For example, stimulation through receptors for IgG or complement split products can activate macrophages, but stimulation through combinations of these receptors generates synergistic results. Together, antibodies and complement efficiently integrate the activation of endothelial cells, platelets, and macrophages, which are 3 of the primary components in the pathogenesis of transplant vasculopathy. Recent findings indicate that antibodies and complement produced within the transplant may contribute to vascular pathology in some transplants. Acute rejection caused by antibodies and complement has been treated by combinations of plasmapheresis, intravenous gamma-globulin and monoclonal antibodies to CD20 on B lymphocytes. The effect of these treatment modalities on the development of coronary vasculopathy is unknown.

Inhibition of accelerated graft arteriosclerosis by gene transfer of soluble fibroblast growth factor receptor-1 in rat aortic transplants.

Because increased fibroblast growth factor-1 (FGF-1) and FGF receptor (FGFR) expression correlate with the development of accelerated graft arteriosclerosis in transplanted human hearts, this study sought to determine whether local gene transfer of soluble FGFR-1, capable of binding both FGF-1 and FGF-2, could blunt the development of accelerated graft arteriosclerosis in the rat aortic transplant model. A construct encoding the FGFR-1 ectodomain, capable of neutralizing FGF-2 action, was expressed in rat aortic allografts, using adenoviral gene transfer at the time of transplantation. Neointima formation was inhibited in aortic allografts transduced with soluble FGFR-1, compared with allografts transduced with Null virus. FGFs play a causal role in the development of accelerated graft arteriosclerosis in the rat aortic transplant model. Targeted interruption of FGF function could potentially reduce neointima formation in patients with heart and kidney transplants.

Usefulness of decreased levels of d-dimer in predicting progressive accelerated graft arteriosclerosis

The classic metabolic risk factors for atherosclerosis such as hypercholesterolemia, hypertriglyceridemia, low high-density lipoprotein cholesterol, and diabetes mellitus are only weakly associated with the development of arteriosclerosis in coronary arteries of donor hearts after cardiac transplantation.1 Similarly, multiple nonimmune factors including donor age, sex, sex mismatch, pretransplant diagnosis, ischemic time, post-transplant hypertension, body mass index, and cytomegalovirus infection are not associated with the development of graft stenosis.2 A limitation of accelerated arteriosclerosis to the transplanted heart suggests that immune mechanisms may be involved because it is a form of vascular rejection. However, human leukocyte antigen class I or II mismatching does not appear to correlate with the subsequent development of graft stenosis.3 Fibrin deposition plays a role in the development and progression of atherosclerosis.4,5 Endothelial deposition of fibrin can be increased either by increased thrombotic activity or impaired fibrinolysis. Depletion of arteriolar tissue plasminogen activator measured by endomyocardial biopsy has been associated with the subsequent development of graft stenosis.6 There is also evidence from cross-sectional studies that elevation of both plasminogen activators and inhibitors is associated with accelerated graft arteriosclerosis.7,8 This study examines prospectively if plasma markers of thrombosis, fibrinolysis, or platelet activation can predict the development of accelerated graft arteriosclerosis.

Correlation of chlamydia pneumoniae infection and severity of accelerated graft arteriosclerosis after cardiac transplantation.

Chlamydia pneumoniae has been associated with atherosclerosis, although its role in the process is not clearly defined. Heart transplant recipients are known to have high titers of antibodies to C. pneumoniae, and the organism has been recovered from the coronary arteries of both transplant recipients and donors. This study evaluated association between C. pneumoniae infection and accelerated graft arteriosclerosis (AGA), also known as cardiac allograft vasculopathy (CAV), after cardiac transplantation. A case-control study was performed with 54 heart transplant recipients at the Johns Hopkins Hospital. Severe cases had >50% luminal narrowing on cardiac catheterization, mild cases <50% narrowing, and controls were free of arteriosclerotic disease. Blood specimens were examined for C. pneumoniae serology and DNA detection by polymerase chain reaction (PCR) assays. For every twofold increase in geometric mean C. pneumoniae immunoglobulin (Ig)G titer, the odds ratio for severe AGA versus controls was 3.13 (P=0.03) and for mild AGA versus control patients was 1.61 (P=0.45). On Kaplan-Meier survival analysis there was a nonsignificant trend toward faster development of CAV in patients with higher C. pneumoniae antibody titers. Overall, 29% of heart transplant patients evaluated had evidence of circulating C. pneumoniae DNA by PCR, without a statistical difference between groups. C. pneumoniae IgG titer correlates with severity of allograft arteriosclerosis after cardiac transplantation. Circulating C. pneumoniae DNA is detectable by PCR in up to 30% of cardiac transplant recipients, but this does not correlate with severity of allograft vasculopathy.

Inducible nitric oxide synthase inhibition of weibel-palade body release in cardiac transplant rejection.

Inducible nitric oxide synthase (iNOS, or NOS2) reduces the severity of accelerated graft arteriosclerosis (AGA) in transplanted organs, although the precise mechanism is unclear. We transplanted wild-type murine hearts into either wild-type or NOS2-null recipient mice; we then measured cardiac allograft survival and analyzed tissue sections by immunohistochemistry. We have confirmed that NOS2 increases cardiac allograft survival. We now show that there is less inflammation of cardiac allografts in wild-type hosts than in NOS2-null hosts. Furthermore, staining for von Willebrand factor reveals that the presence of NOS2 is correlated with the presence of Weibel-Palade bodies inside endothelial cells, whereas the absence of NOS2 is correlated with the release of Weibel-Palade bodies. Weibel-Palade bodies contain mediators that promote thrombosis and inflammation. Therefore, nitric oxide (NO) may stabilize the vessel wall and prevent endothelial activation in part by inhibiting the release of the contents of Weibel-Palade bodies. Prevention of Weibel-Palade body release might be a mechanism by which NO protects the vessel wall from inflammatory disorders such as atherosclerosis or graft arteriosclerosis.

Capillary endothelia and cardiomyocytes differ in vulnerability to ischemia/reperfusion during clinical heart transplantation.

The development of accelerated graft arteriosclerosis is a major cause of late death after orthotopic heart transplantation. The influence and the extent of peritransplant injury, especially of cardiomyocyte or capillary endothelial cell edema is discussed. A morphometric ultrastructural analysis of myocardial biopsies from 29 donor hearts (21 male, age 34+/-11 years) was performed. Right ventricular biopsies were obtained before cardioplegia (A), immediately following cardioplegia (B) (Custodiol, Dr. F. Köhler Chemie GmbH, Alsbach-Hähnlein, Germany), before implantation (C), after 30 (D) or 60 (E) min of reperfusion and 1 week after transplantation (F). Mean ischemic time was 185+/-68 min. Quantitative electron microscopy was carried out in five samples per heart and time point and in 30 test fields per sample by 'random systematic sampling' and 'point and intersection counting'. As parameters for cell edema the volume density of myofibrils in cardiomyocytes and the mean barrier thickness of capillary endothelia were analyzed. P-values of less than 0.05 were regarded as significant. Significant differences in contrast to the previous values are marked by *. The volume density of myofibrils (vol.%) was as follows: (B) 63.6+/-3.2, (C) 61.8+/-3.2, (D) 62.9+/-3.2, (E) 63.6+/-4.5. The mean barrier thickness (nm) was as follows: (A) 353+/-21, (B) 376+/-59, (C) 416+/-71*, (D) 473+/-45*; (E) 453+/-50*, (F) 379+/-39. Apart from a generally accepted edema of cardiomyocytes a relevant capillary endothelial cell edema develops during clinical heart transplantation. In contrast to cardiomyocytes the cell edema of endothelia shows a more pronounced and significant progression during cold ischemia and early reperfusion. After 60 min of reperfusion it is still significantly more pronounced than at the onset of ischemia. After 1 week there are no statistical differences compared to the initial values. Thus, an edema of capillary endothelia probably will trigger inhomogeneities in capillary perfusion. Peritransplant injury of endothelia may contribute to the later development of accelerated allograft arteriosclerosis.

Accelerated graft arteriosclerosis in cardiac transplants: complement activation promotes progression of lesions from medium to large arteries.

A critical role for the terminal components of complement (C5b-C9) has been demonstrated previously in acute allograft rejection with the use of C6-deficient PVG congenic rat strains. The C6 deficiency prevents the formation of membrane attack complex (MAC) by C5b-C9. Hearts transplanted from PVG.1A (RT1a) rats are rejected acutely (7-9 days) by fully MHC-incompatible C6-sufficient PVG.1L (RT11) recipients, but they survive significantly longer in untreated C6-deficient PVG.1L recipients (19 to >60 days). To investigate the contribution of MAC to chronic rejection and accelerated graft arteriosclerosis (AGA) in long-term cardiac allografts, hearts were transplanted heterotopically from PVG.1A donors to C6-sufficient and C6-deficient PVG.1L hosts that were treated with cyclosporine 15 mg/kg/day for 14 days after cardiac grafting. Alloantibody responses in hosts were measured by flow cytometry at 4, 8, 12, and 16 weeks after transplantation. Vigorously contracting grafts were removed at 60 days (n=5) and at 90-128 days (n=12) after surgery for morphological evaluation. Computerized planimetry measurements were made in complete cross-sections of grafts on all assessable arteries larger than 16 microns in diameter. The survival of most (six of seven) cardiac allografts in C6-deficient recipients was prolonged by cyclosporine treatment to greater than 90 days. In contrast, 14 of 25 hearts that were transplanted to C6-sufficient recipients were rejected between 21 and 84 days with severe vascular injury. AGA, defined as smooth muscle cells forming a neointima inside the internal elastic lamina and luminal compromise, affected a greater percentage of arteries in C6-sufficient than in C6-deficient recipients. AGA developed earlier and more frequently in arteries of medium (<100 micron) diameter than those of large diameter in both C6-sufficient and C6-deficient recipients. Serial sections demonstrated the lesions in medium arteries to be located adjacent to the smooth muscle sphincters at the junction of arteriolar branches. These results demonstrate that MAC promotes the pathogenesis of AGA in long-term cardiac allografts.

Terminal complement proteins in mediating processes of accelerated graft arteriosclerosis in cardiac transplants

Terminal complement proteins in mediating processes of accelerated graft arteriosclerosis in cardiac transplants

Murine model of accelerated graft arteriosclerosis in primed recipients

Murine model of accelerated graft arteriosclerosis in primed recipients

Expression of NF-kappaB and cytokines in chronic rejection of transplanted murine heart.

The heart transplantation-associated accelerated graft arteriosclerosis (AGAS) is one of the major causes of cardiac allograft failure. We investigated the early time-course of expresssion patterns of cytokines, transcription factor, and its inhibitor in the intraabdominally transplanted mice hearts that differed only in the D locus of class I histocompatibility antigen. The allograft hearts were harvested at 1-3, 5, 7, 14, 28, and 42 days after the transplantation, and the expressions of NF-kappaB/I-kappaB and cytokines (TNF-alpha, INF-gamma) were examined in these specimens. The expressions of TNF-alpha and INF-gamma were observed on day 1, peaking on day 5 and 7, respectively. Activated NF-kappaB (p65) expression was present on the cytoplasm and perinuclear area in the endothelial cells of coronary arteries on day 1. The peak of translocation of NF-B from cytoplasm to nucleus appeared on day 5 in the endothelial cells, myocytes, and leukocytes within the vessels, and remained elevated until day 42. The I-kappaB expression gradually increased from day 1 until day 5, but a remarkable decrease was detected on day 7. Our data suggest that the increased expressions of NF-kappaB/I-kappaB and cytokines (TNF-alpha, INF-gamma) play an important role in inducing immune responses in the donor allograft heart and hence the blockage of the expressions might be mandatory to avoid a potential graft failure.

Fas-mediated apoptosis in accelerated graft arteriosclerosis.

Pathological conditions have been recognized where vessel destruction is a prominent feature of the pathogenic process. One such condition consists of the chronic rejection of blood vessels in transplanted solid organs. Accelerated graft arteriosclerosis (AGA) is a multifactorial process characterized by the concentric proliferation of smooth muscle cells (SMCs) within the intima of the vessel wall of transplanted organs. Proliferation of SMCs within the intima corresponds to a response of these cells to injury. In situations like restenosis post-angioplasty, the mechanism of injury: the mechanical disruption of the tunica media, is evident. However, in the case of AGA, the mechanism of injury has remained elusive. In this report, we provide evidence that injury to SMCs in AGA vessels requires an intact Fas pathway. The resulting damage to the tunica media and internal elastic lamina, in turn, might trigger the proliferation of intimal smooth muscle cells that appear to be less sensitive to Fas mediated killing, particularly when supported by a favorable context of inflammatory cytokines and growth factors, as it is the case in AGA. This pathogenic process results in a absolute loss of functional blood vessels that is not being compensated by an efficient angiogenic response.

Influence of MHC class I and class II (mis)matching between donor and recipient on the cytomegalovirus induced accelerated graft arteriosclerosis in a rat aorta transplant model

Influence of MHC class I and class II (mis)matching between donor and recipient on the cytomegalovirus induced accelerated graft arteriosclerosis in a rat aorta transplant model

T-cell costimulatory blockade in experimental chronic cardiac allograft rejection: effects of cyclosporine and donor antigen.

Chronic rejection is a T cell-dependent process and blockade of the CD28-B7 T-cell costimulatory activation pathway by the fusion protein CTLA4Ig has been shown to prevent the development of accelerated graft arteriosclerosis in a rat model of chronic cardiac allograft rejection. The effectiveness of T-cell costimulatory blockade at preventing chronic allograft rejection in a clinically relevant model in combination with cyclosporine therapy has not been investigated. Using the well-established LEW into F334 heterotopic cardiac allograft model, we show that when cyclosporine is administered in combination with CTLA4Ig, it abrogates the previously demonstrated protective effect of CTLA4Ig in preventing chronic allograft rejection. Long-term surviving allografts from animals treated with a combination of cyclosporine and CTLA4Ig had a mean vascular luminal occlusion of 42.2%, affecting more than 90% of graft vessels due to accelerated arteriosclerosis. This was associated with up-regulation of intragraft expression of mRNA for CD4, the costimulatory molecule B7, the T-cell cytokine interferon-gamma, monocyte chemoattractant protein-1, and the fibrogenic growth factor transforming growth factor-beta; all have been previously shown to be associated with development of chronic rejection in this model. In comparison, the addition of donor splenocytes to the combination of CTLA4Ig and cyclosporine therapy protocol significantly reduced the amount of arteriosclerosis; mean vascular luminal occlusion was 11.3%, affecting approximately 50% of vessels. This was associated with decreased intragraft expression of CD4, B7, interferon-gamma, monocyte chemoattractant protein-1, and transforming growth factor-beta. These data indicate that the mechanism of action of CTLA4Ig in attenuating chronic rejection is cyclosporine sensitive, and that strategies implying combination of CTLA4Ig and cyclosporine may not be clinically desirable. Administration of donor antigen may be necessary if CTLA4Ig and cyclosporine are to be combined, to prevent the process of chronic rejection.

The WAF 1-mediated p53 growth-suppressor pathway is intact in the coronary arteries of heart transplant recipients

It has been suggested that the interaction of cytomegalovirus (CMV) with the p53 tumor suppressor gene product plays a role in the development of coronary artery restenosis after angioplasty. CMV nucleic acids have been observed in the coronary arteries of allografted hearts, suggesting a possible role for the interaction of CMV with p53 in the development of accelerated graft arteriosclerosis in transplant recipients. Formalin-fixed, paraffin-embedded sections of coronary arteries from 19 transplanted hearts were immunostained for the p53 gene product using Target Unmasking Fluid (TUF) - mediated immunohistochemistry and the anti-p53 antibodies CM1 and D07. Fresh-frozen sections of coronary arteries were also available from six of the 19 hearts, and these fresh-frozen sections were immunostained for the p53 gene product with the D07 antibody and for WAF1 using the anti-WAF1 antibody EA10. Focal and weak staining for p53 was observed in smooth muscle and endothelial cells in two of 19 vessels, whereas the remaining 17 did not stain. CMV nucleic acids were previously shown in six of 13 of these hearts by in situ hybridization. The fresh-frozen sections of coronary arteries also did not stain for p53, but the smooth muscle cells in these vessels did stain intensely for WAF1. These results suggest three possibilities: (1) CMV-p53 interactions are not important in the development of accelerated graft arteriosclerosis; or (2) there is an interaction, but it is transient and not detectable at the time points examined in this study; or (3) there is an interaction, but binding of CMV to p53 leads to accelerated degradation of p53, as occurs with HPV-E6. The expression of WAF1 further suggests that the WAF1-mediated antiproliferative signal is intact in these vessels.

CARDIAC TRANSPLANTATION IN THE RAT

Cardiac transplantation between inbred rat strains that differ for weak histocompatibility antigens is associated with the development of arteriosclerosis in the arteries of the donor graft myocardium. The lesions are seen in donor/recipient pairs that differ for both MHC and non-MHC histocompatibility antigens that apparently stimulate a low-level, chronic rejection of the donor heart graft. The arteriosclerosis associated with this chronic rejection consists of a diffuse, concentric proliferation of the intima and pathologically resembles the lesions observed in the coronary arteries of long-term human cardiac graft recipients. We have recently examined the influence of positive and negative manipulation of the host immune response on the development of the graft arteriosclerosis. Our results demonstrate that delayed harvest of the cardiac grafts or immunization with donor skin grafts or splenic lymphocytes increases the sensitivity of the recipient to the donor heart grafts--and, under conditions that allow for the long-term survival of the graft--increases the severity of the arteriosclerotic lesions. Alternatively, suppression of the host immune responses with cyclosporine or FK506, substantially reduces the arteriosclerotic changes. These results suggest that control of accelerated graft arteriosclerosis in long-term human cardiac recipient may require more careful and effective immunosuppression of the allograft reaction.

Combined heart-lung transplantation for end-stage Eisenmenger’s syndrome

Between May, 1981, and December, 1984, thirteen combined heart-lung transplants were performed in 12 patients for the treatment of Eisenmenger's syndrome. The age range of the recipients was 22 to 42 years. Two patients had undergone previous open cardiac operations; in addition, one had had closure of a persistent ductus arteriosus, one an open lung biopsy, one a pulmonary artery banding, and one patient received a second heart-lung transplant after 3 years. Four recipients died before hospital discharge, one at operation and three at 4, 10, and 33 days after operation. Early symptomatic results and cardiopulmonary function were excellent in all of the survivors. Two patients died 14 and 15 months after transplantation of accelerated graft arteriosclerosis and respiratory failure, respectively, and six remain alive 7 to 44 months after transplantation. Four of these surviving patients and the two patients who died late subsequently had major pulmonary complications. Symptoms included progressive breathlessness, cough (often productive), and fever with physical signs of diffuse crepitations and expiratory rhonchi. Serial pulmonary function tests showed progressive obstructive physiology in all six patients with superimposed restrictive defects in four. Histologic examination of tissue from open lung biopsy or autopsy displayed bronchiolitis obliterans in five of these patients, one of whom required retransplantation. It is possible that these late changes are the result of rejection, since similar changes in one other patient have now been reversed with augmented immunosuppression. Further understanding of the causes and manifestations of late pulmonary deterioration should improve the late functional results of this operation for Eisenmenger's syndrome.

PATHOGENESIS AND PREVENTION OF GRAFT ARTERIOSCLEROSIS IN AN EXPERIMENTAL HEART TRANSPLANT MODEL

Accelerated graft arteriosclerosis is a major cause of death in human heart transplantation. Despite many investigations, the pathogenesis of this disease remains undetermined and its control inadequate. In this study using a rat heart transplant model and cyclosporin A, a new immunosuppressant, acute rejection was prevented but arteriosclerotic-like vessel disease still developed consistently as early as 20 days postoperatively. The combination of cyclosporin A and dipyridamole prevented the development of this vessel disease in transplanted hearts at 20 and 50 days postoperatively. Sulfinpyrazone and cyclosporin A reduced but did not prevent the disease. These findings suggest that immunologically induced graft arteriosclerosis can be prevented in transplanted rat hearts by the combination of cyclosporin A and dipyridamole.