Coronary vasomotor dysfunction in the cardiac allograft: impact of different immunosuppressive regimens

Mycophenolate Mofetil and Rapamycin Induce Apoptosis in the Human Monocytic U937 Cell Line Through Two Different Pathways

Transplant vasculopathy may be considered as an accelerated form of atherosclerosis resulting in chronic rejection of vascularized allografts. After organ transplantation, a diffuse intimal thickening is observed, leading to the development of an atherosclerosis plaque due to a significant monocyte infiltration. This results from a chronic inflammatory process induced by the immune response. In this study, we investigated the impact of two immunosuppressive drugs used in therapy initiated after organ transplantation, mycophenolate mofetil, and rapamycin, on the apoptotic response of monocytes induced or not by oxidized LDL. Here we show the pro-apoptotic effect of these two drugs through two distinct signaling pathways and we highlight a synergistic effect of rapamycin on apoptosis induced by oxidized LDL. In conclusion, since immunosuppressive therapy using mycophenolate mofetil or rapamycin can increase the cell death in a monocyte cell line, this treatment could exert similar effects on human monocytes in transplant patients, and thus, prevent transplant vasculopathy, atherosclerosis development, and chronic allograft rejection. J. Cell. Biochem. 118: 3480-3487, 2017. © 2017 Wiley Periodicals, Inc.

Expression of NO Synthase Under Medication with Cyclosporine A, Mycophenolate Mofetil, and Tacrolimus during Development of Transplant Vasculopathy on Rat Cardiac Allograft

OBJECTIVE

The transplant vasculopathy as a sign of chronic graft rejection affects both the epicardial and the intramyocardial arteries of the graft. This is at least partially mediated by NO synthases. The aim of this study was to assess possible protective effects of cyclosporine A (CsA), tacrolimus (FK506), and mycophenolate mofetil (MMF) on the expression of NO synthases in an experimental transplant rat model.

AIMS

Heart transplantation was performed in 322 rats. These were randomly assigned to four equal groups (control, CsA, FK506, MMF). Recipients were monitored up to 60 days after transplantation, while transplanted hearts were recovered at certain time points for analysis. Expression and staining intensity for endothelial nitric oxide synthases (e-nos) and inducible nitric oxide synthases (i-nos) were analyzed in epicardial and intramyocardial vessels in each group.

RESULTS

All employed drugs led to a significant reduction of expression or staining intensity of i-nos and e-nos. MMF was most effective in reduction in expression of both NO synthases.

CONCLUSIONS

These results imply that all described drugs prevent endothelial impairment induced by toxicity of NO and thereby prevent transplant vasculopathy. MMF seems to be the most effective drug.

Mycophenolate Mofetil and Atherosclerosis: Results of Animal and Human Studies

The immunosuppressive agent mycophenolate mofetil (MMF) has beneficial effects in cardiac transplant patients beyond the suppression of tissue rejection. Patients with regimens containing MMF experience diminished intimal thickening and cardiac allograft vasculopathy compared to patients treated with azathioprine. Studies have shown that diet-induced atherosclerosis (a related vasculopathy) is a chronic inflammatory process, and so MMF has also been used to reduce atherosclerosis in a rabbit model of hyperlipidemia. These data hold out the intriguing possibility that MMF might be a viable primary or secondary preventive agent in people at significant risk for atherosclerosis.

Status of the endothelium-derived hyperpolarizing factor pathway in coronary arteries after heterotopic heart transplantation

BACKGROUND

After the first year of transplantation, the major limitation to long-term survival is the development of graft coronary vasculopathy, characterized by a pathologic activation of the endothelium with an attendant loss of its regulatory properties on homeostasis of the vascular wall. The present study was designed to evaluate the integrity of coronary vascular relaxations attributed to the endothelium-derived hyperpolarizing factor (EDHF) and to study hyperpolarization of smooth muscle cells after heterotopic heart transplantation.

METHODS

Six weeks after heart transplantation in a porcine model, vascular reactivity studies of control, native and allograft epicardial coronary artery rings were performed in standard organ chamber experiments. Moreover, membrane potential measurements were made with intracellular microelectrodes in rings of native and allograft coronary arteries.

RESULTS

There was a significant decrease in endothelium-dependent relaxations to 5-hydroxytryptamine (5-HT), high doses of bradykinin (BK) alone and BK plus N-omega-nitro-L-arginine (L-NNA) in rings from allograft compared to native, whereas the variation was significantly increased in response to cromakalim, a K(+)-ATP channel opener. Electrical and mechanical recordings showed no alteration in the resting membrane potential of smooth muscle cells, depolarization during contraction to prostaglandin F(2alpha) (PGF(2alpha)), or hyperpolarization in the presence of BK + L-NNA in rings of allograft vs native.

CONCLUSIONS

In this swine model of heart transplantation, part of the reduction in endothelium-dependent relaxations to BK may be attributed to an alteration in the activity of EDHF. This impairment of EDHF-mediated relaxations may compound the endothelial dysfunction preceding the development of coronary graft vasculopathy.

Mycophenolate Acid Inhibits Endothelial NAD(P)H Oxidase Activity and Superoxide Formation by a Rac1-Dependent Mechanism

Endothelial dysfunction precedes hypertension and atherosclerosis and predicts cardiac allograft vasculopathy and death in heart transplant recipients. Endothelial overproduction of reactive oxygen species, such as superoxide anions produced by NAD(P)H oxidase, induces endothelial dysfunction. Because immunosuppressive drugs have been associated with increased reactive oxygen species production and endothelial dysfunction, we sought to elucidate the underlying mechanisms. Reactive oxygen species, release of superoxide anions, and NAD(P)H oxidase activity were studied in human umbilical vein endothelial cells and in polymorphonuclear neutrophils. Gp91ds- tat was used to specifically block NAD(P)H oxidase. Transcriptional activation of different subunits of NAD(P)H oxidase was assessed by real-time RT-PCR. Rac1 subunit translocation and activation were studied by membrane fractionation and pull-down assays. Calcineurin inhibitors significantly increased endothelial superoxide anions production because of NAD(P)H oxidase, whereas mycophenolate acid (MPA) blocked it. MPA also attenuated the respiratory burst induced by neutrophil NAD(P)H oxidase. Because transcriptional activation of NAD(P)H oxidase was not affected, but addition of guanosine restored endothelial superoxide anions formation after MPA treatment, we speculate that the inhibitory effect of MPA was mediated by depletion of cellular guanosine triphosphate content. This prevented activation of Rac1 and, thus, of endothelial NAD(P)H oxidase. Because all heart transplant recipients are at risk for cardiac allograft vasculopathy development, these differential effects of immunosuppressants on endothelial oxidative stress should be considered in the choice of immunosuppressive drugs.

Allograft vasculopathy versus atherosclerosis

Over the last 4 decades, heart transplantation (HTx) has evolved as a mainstream therapy for heart failure. Approximately half of patients needing HTx have organ failure consequent to atherosclerosis. Despite advances in immunosuppressive drugs, long-term success of HTx is limited by the development of a particular type of coronary atherosclerosis, referred to as cardiac allograft vasculopathy (CAV). Although the exact pathogenesis of CAV remains to be established, there is strong evidence that CAV involves immunologic mechanisms operating in a milieu of nonimmunologic risk factors. The immunologic events constitute the principal initiating stimuli, resulting in endothelial injury and dysfunction, altered endothelial permeability, with consequent myointimal hyperplasia and extracellular matrix synthesis. Lipid accumulation in allograft arteries is prominent, with lipoprotein entrapment in the subendothelial tissue, through interactions with proteoglycans. The apparent endothelial "intactness" in human coronary arteries of the transplanted heart suggest that permeability and function of the endothelial barrier altered. Various insults to the vascular bed result in vascular smooth muscle cell (SMC) activation. Activated SMCs migrate from the media into the intima, proliferate, and elaborate cytokines and extracellular matrix proteins, resulting in luminal narrowing and impaired vascular function. Arteriosclerosis is a broad term that is used to encompass all diseases that lead to arterial hardening, including native atherosclerosis, postangioplasty restenosis, vein bypass graft occlusion, and CAV. These diseases exhibit many similarities; however, they are distinct from one another in numerous ways as well. The present review summarizes the current understanding of the risk factors and the pathophysiological similarities and differences between CAV and atherosclerosis.

Coronary endothelial vasomotor function and vascular remodeling in heart transplant recipients randomized for tacrolimus or cyclosporine immunosuppression

OBJECTIVES

This study aimed to compare changes in coronary endothelial function, systemic endothelin-1 (ET-1) levels, and vascular remodeling in heart transplant recipients randomized to cyclosporin A (CyA) or tacrolimus (Tac) immunosuppression.

BACKGROUND

Functional endothelial abnormalities and intimal thickening are sensitive measures of early cardiac allograft vasculopathy (CAV).

METHODS

The randomized, prospective study was performed in two groups of 22 patients, maintained on Tac or CyA and mycophenolate mofetil immunosuppression, 1 and 12 months after heart transplantation. We investigated epicardial luminal diameter, coronary blood flow velocity, and ET-1 plasma levels at 1 and 12 months after transplantation. Structural coronary alterations were determined using intravascular ultrasound.

RESULTS

Epicardial vasomotor function at baseline and during follow-up was comparable between the groups. Deterioration of microvascular endothelial function during follow-up was significantly enhanced in the CyA versus Tac group (p < 0.05). Circulating ET-1 concentration increased in the CyA group but significantly decreased over time in the Tac group (CyA +17% vs. Tac -25%; p < 0.05). The time-dependent increase in mean intimal area was significantly enhanced in the CyA versus Tac group, whereas the vessel area significantly increased during follow-up in the Tac compared with the CyA group.

CONCLUSIONS

Epicardial endothelial function is comparable between CyA- and Tac-treated patients. Microvascular endothelial function deteriorates more in CyA-treated patients, a finding that correlates with enhanced ET-1 concentration and an increased intimal area during follow-up. The mean vessel area in the Tac group increased over time, indicating positive vascular remodeling. Tac is superior to CyA with respect to microvascular endothelial function, intimal thickening, and vascular remodeling.

Dendritic cell adhesion is enhanced on endothelial cells preexposed to calcineurin inhibitors

Chronic rejection remains a major complication in solid organ transplantation. Host alloreactive T cells (TC) can be activated by donor dendritic cells (DCs; direct allorecognition) or by recipient DCs (indirect allorecognition). A fundamental aspect of DC function is vascular invasion to present donor antigens to recipient naive TC in secondary lymphoid organs. We investigated the impact of calcineurin inhibitors on DC binding and transmigration to allogeneic human microvascular endothelial cells (ECs) with and without blocking of specific adhesion molecules. Recipient immature DCs were generated by culturing CD14 human peripheral blood monocytes with GM-CSF and IL-4. DC adhesion and transmigration were investigated on allogeneic ECs preincubated with increasing concentrations of cyclosporine and tacrolimus. Experiments were repeated in the presence of blocking antibodies against LFA-1, PECAM-1, VCAM-1, and ICAM-1. Endothelial stimulation with cyclosporine A (100 and 300 ng/mL) and tacrolimus (15 ng/mL) significantly enhanced DC-EC adhesion and transmigration (P<0.01). LFA-1 blockade on DCs significantly reduced cyclosporine- and tacrolimus-induced DC adhesion (P<0.001). VCAM-1 blockade on ECs partially reversed cyclosporine-induced DC adhesion (P<0.001), whereas DC adhesion under tacrolimus exposure was significantly decreased by ICAM-1 (P<0.01) and PECAM-1 (P<0.001) blockade. DC binding and transmigration on allogeneic ECs exposed to calcineurin inhibitors is concentration-dependently increased. Different adhesion molecule patterns on ECs are responsible for enhanced DC invasion under cyclosporine and tacrolimus exposure. We speculate that long-term immunosuppression mediates enhanced invasion of recipient DCs to the donor organ and therefore may aggravate chronic rejection.

Review of Major Clinical Trials with Mycophenolate Mofetil in Cardiac Transplantation

Over the past 10 years, the addition of mycophenolate mofetil (MMF) to combination immunosuppressive regimens in cardiac transplant patients has resulted in significant outcomes benefits. Randomized trials and other studies have demonstrated that the use of MMF is associated with a decreased risk of rejection and improved survival. This article will provide an overview of these trials, as well as those evaluating MMF in renal-sparing regimens and in pediatric cardiac transplant recipients. In addition, emerging evidence demonstrating that MMF may provide long-term benefits in reducing cardiac allograft vasculopathy and those evaluating the role of MMF therapeutic drug monitoring in cardiac transplant recipients will be discussed.

Three-year results of a randomized, double-blind, controlled trial of mycophenolate mofetil versus azathioprine in cardiac transplant recipients

BACKGROUND

This study reports the 36-month results of a randomized, double-blind, active-controlled trial of mycophenolate mofetil (MMF) vs azathioprine (AZA) in heart transplant patients.

METHODS

Patients were randomized at the time of transplant to receive MMF (1,500 mg twice a day, N = 327) or AZA (1.5 to 3 mg/kg in 4 daily doses, N = 323) in addition to cyclosporine and corticosteroids; 289 patients in each group received study drug. Data were analyzed in all randomized patients (enrolled) and in patients who received study medications (treated). Clinical and graft assessments continued for 36 months.

RESULTS

For the co-primary end-point, 53 of 289 (18.3%) AZA-treated patients either died or received another transplant compared with 34 of 289 (11.8%) MMF-treated patients (p < 0.01). Time to re-transplantation or patient death was significantly shorter for AZA- than MMF-treated patients (p = 0.029). In patients undergoing intravascular ultrasound, the change in mean maximal intimal thickness was less for the MMF group than for the AZA group (0.06 +/- 0.03 mm vs 0.13 +/- 0.03 mm, respectively; p = 0.056). No significant differences between treatments were observed in quantitative coronary angiographic measurements of transplant coronary vasculopathy. Congestive heart failure, atrial arrhythmia and leukopenia were more common in the AZA group, whereas diarrhea, esophagitis, Herpes simplex, Herpes zoster and cytomegalovirus (CMV) tissue invasion were more common in MMF-treated patients.

CONCLUSION

MMF reduces mortality and graft loss up to 36 months after transplantation.

A model of prediction system for adverse cardiovascular reactions by calcineurin inhibitors among patients with renal transplants using gene-based single-nucleotide polymorphisms

The application of pharmacogenomic information to diagnostic assays is expected to improve the prediction of drug efficacy and toxicity, leading to appropriate therapeutic regimens for individual patients. Cardiovascular events are common and severe adverse drug reactions (ADRs) among transplant patients treated with calcineurin inhibitors (CNIs). We conducted case-control association studies using 50,947 gene-based single-nucleotide polymorphisms (SNPs) to identify genetic variations that might be associated with cardiovascular risk factors in 72 renal transplant recipients with CNI therapy. The overall incidence of cardiovascular events was 13.9% (10/72) among patients receiving cyclosporine or tacrolimus; arrhythmias in six patients (8.3%), ischemic heart diseases in two patients (2.8%), and heart failure in two patients (2.8%). On the basis of results of the genome-wide association studies, we attempted to establish a scoring system to predict individual risks for cardiovascular toxicity of cyclosporine and tacrolimus. Estimation of the predictive performance was carried out by the use of internal leave-one-out cross-validation test. When we combined arrhythmia, ischemic heart disease and heart failure cases as subjects with a cardiotoxicity phenotype, nine of ten ADR patients and 50 of 62 non-ADR patients were correctly classified into the respective categories using the top eight SNPs. In addition, the proportion of individuals in the control population (n=246) with scores over the cut-off (11.0%) was close to the cardiovascular ADR frequency (8.3%) among renal transplant patients in the previous clinical study. Our results open the possibility that prediction of CNI-induced cardiovascular complications can lead to better prognosis and quality of life among kidney-transplant patients, and to improved immunosuppressive regimens.

Peripheral Expansion of Circulating T-Helper 1 Cells Predicts Coronary Endothelial Dysfunction After Cardiac Transplantation

OBJECTIVE

We sought to assess the importance of Th1 cells for the development of cardiac allograft vasculopathy.

BACKGROUND

Despite improvements in immunosuppressive regimens, chronic rejection still represents one of the leading causes of death beyond the first year after heart transplantation. Chronic rejection is characterized by the development of transplant vasculopathy. The exact mechanisms initiating and promoting this form of arteriosclerosis in the human setting remain unclear.

METHODS

In order to assess the role of T lymphocytes we characterized differentiated T-cell subsets in 32 transplant recipients early after transplantation using RT-PCR, flow cytometry and immunhistochemistry and matched these findings with endothelial function testing as an early clinical indicator of transplant vasculopathy.

RESULTS

Allograft endothelial dysfunction (ED) was defined as a compromised coronary flow reserve to acetylcholine (CFVR<2 in 8 of 32 transplant recipients). In these patients, mRNA transcript levels for the T-helper (Th)1 signature cytokines interferon (INF)-gamma (p<0.0001) and interleukin (IL)-2 (p<0.005) and STAT4 (Th1 transcription factor, p<0,05) were significantly higher than in the remaining 24 patients with normal endothelial function. This correlated with a significant increase in circulating CD3(+)/IFN-gamma(+)-T-cells (28.6 +/- 4.4% vs 8.7 +/- 5.6%; p<0.0001). In contrast, transcript levels for the Th2 signature cytokines (IL-4, IL-10) and STAT6 (Th2 transcription factor) did not differ significantly between the two groups.

CONCLUSIONS

Peripheral expansion of circulating Th1 but not Th2 cells predicts coronary ED after cardiac transplantation. Therefore, quantification of circulating T cells might be a diagnostic tool to predict development of ED in patients after heart transplantation.

The impact of immunosuppression on endothelial function

Endothelial dysfunction is an early marker for transplant atherosclerosis. Potential mechanisms for allograft endothelial dysfunction include stimulation of alloimmune-dependent pathways, ischemia/reperfusion injury, metabolic alterations, chronic infections, as well as direct endothelial cell activation by immunosuppressive drugs. Thus far, no study has directly compared different immunosuppressive drugs with respect to their potential to modulate endothelial function under normoxic and hypoxic conditions. We examined human microvascular endothelial cells (HMEC-1) in vitro after stimulation with therapeutic concentrations of methylprednisolone (MP), mycophenolic acid (MMF), cyclosporine A (CS), rapamycin (Rapa), and tacrolimus (Tac) to designate the corresponding induction of oxidative stress, apoptosis, metabolic activity, proliferation, endothelin (ET-1) release, and nitric oxide (NO) production. HMEC-1 stimulation with CS, MMF, and Rapa resulted in a stronger induction of oxidative stress compared with MP and Tac. Induction of oxidative stress by immunosuppressives correlated with metabolic activity and apoptosis. Low- and high-dose MMF significantly inhibited cell proliferation under hypoxic conditions, whereas low-dose CS and MP increased endothelial cell proliferation. ET-1 release was significantly elevated by Rapa, Tac, and MP. NO production was significantly enhanced by all immunosuppressive drugs except Tac. Quality and quantity of immunosuppression modify endothelial function and lead to a dose-dependent and oxygenation-state-related endothelial activation. MP and MMF induced minor changes in endothelial function compared with CS, Rapa, and Tac.

Cyclosporine-induced coronary endothelial dysfunction: is tetrahydrobiopterin the solution?

BACKGROUND

Coronary endothelial dysfunction after heart transplantation is predictive of cardiac allograft vasculopathy. Immunosuppressive drugs, particularly cyclosporine may contribute to this dysfunction by a direct effect. Tetrahydrobiopterin (BH(4)) is a potent antioxidant and an essential cofactor of nitric oxide biosynthesis. The purpose of this study was to investigate whether BH(4) could reverse the endothelial dysfunction induced by cyclosporine.

METHODS

A previously described in vitro model of drug incubation in Krebs-bicarbonate solution (4 degrees C, 48 hours) of porcine epicardial coronary arteries was used. Coronary endothelial function studies were performed in organ chamber experiments after incubation with cyclosporine (10(-4) mol/L) in the presence or absence of 6-methyltetrahydropterin (MH(4) [0.1 mol/L], a BH(4) analog) to assess its effect on the cyclosporine-induced endothelial dysfunction.

RESULTS

The average doses of PGF2(alpha) required to attain 50% of the maximal contraction to KCl was significantly lower (P < .001) in the cyclosporine group (8.6 +/- 1.94 x 10(-6) mol/L) compared to the control group (24.8 +/- 5.2 x 10(-6) mol/L). Exposure to cyclosporine induced a significant decrease in endothelium-dependent relaxations to serotonin (5HT) (% E(max) [5HT]: 77% +/- 4%; P < .05). Addition of MH(4) significantly reversed this impaired response (% E(max) [5HT]: 62% +/- 4%; P < .05). No alterations of relaxation were observed with bradykinin in both groups. Endothelium-independent relaxations to sodium nitroprussiate were fully preserved.

CONCLUSIONS

These results suggest a significant protective role of BH(4) on coronary endothelial function following exposure to cyclosporine, which could reduce the incidence of endothelial dysfunction and cardiac allograft vasculopathy following cardiac transplantation.

Mycophenolate mofetil vs. azathioprine is associated with decreased acute rejection, late acute rejection, and risk for cardiovascular death in renal transplant recipients with pre-transplant diabetes

Outcomes specifically in mycophenolate mofetil (MMF)-treated diabetic renal transplant patients have not been previously reported. This study compared acute rejection (AR), late acute rejection (LAR), patient survival [and specifically death from cardiovascular (CV), infectious and malignant causes], incidence of post-transplant malignancies, and graft loss in MMF- or azathioprine (AZA)-treated renal transplant patients with pre-transplant diabetes. Outcomes were compared between MMF- (n = 14 144) and AZA- (n = 3001) treated diabetic patients using the Scientific Registry of Transplant Recipients data on all U.S. adult renal transplants performed between 1995 and 2002. Statistical analyses included Kaplan-Meier survival analysis, Cox multivariable regression and chi-square tests. MMF patients had less AR compared with AZA-treated patients (23.5% vs. 28.3%, p < 0.001) and less risk for LAR over 4 yr [hazard ratio (HR): 0.64, 95% CI 0.44, 0.92; p = 0.02]. While time to any-cause death did not differ between the groups, MMF treatment was associated with a 20% decreased risk of CV death (HR: 0.80, 95% CI 0.67, 0.97; p = 0.020) compared with AZA treatment. MMF patients also had a lower incidence of malignancies than AZA patients (2.2% vs. 3.7%, p < 0.001). These results suggest treatment with MMF compared with treatment with AZA in diabetic transplant patients is associated with less AR, less risk of LAR, a decreased risk of CV death, and a lower incidence of malignancies.

Evidence for a role of toll-like receptor 4 in development of chronic allograft rejection after cardiac transplantation

BACKGROUND

Long-term success of cardiac transplantation is limited by various forms of graft rejection. The specific mechanisms initiating and controlling these highly specialized immune processes remain unclear so far.

METHODS

To investigate the role of innate immunity in the development of allograft rejection, we assessed toll-like receptor (TLR)4 expression and typical downstream effects of TLR signaling (B7-1, interleukin [IL]-12, tumor necrosis factor [TNF]-alpha) in circulating CD14+ monocytes in 38 transplant recipients 1 to 3 years and in 10 transplant recipients 6 to 10 years after transplantation and compared them with 20 healthy controls using reverse transcription polymerase chain reaction, flow cytometry, and enzyme-linked immunoadsorbent assay. The results were matched with endothelial function testing as an early clinical indicator of transplant vasculopathy early after transplantation.

RESULTS

Allograft endothelial dysfunction (ED) was defined as a compromised coronary flow reserve (CFVR) to acetylcholine (CFVR<2 in 13 of 38 transplant recipients). In these patients, mRNA transcript levels for TLR4 (P<0.05) and surface expression of TLR4 (P<0.005) and B7-1 (P<0.05) on circulating monocytes as well as secretion of IL-12 (P<0.02) and TNF-alpha (P<0.05) were significantly higher than in the remaining 25 patients without ED. Compared with the controls, recipients late after transplantation did not show significantly elevated levels of TLR4 or dependent mediators. These results were compared with mRNA levels in a mice model of acute and chronic rejection. Rejecting mice exhibited elevated mRNA levels for mTLR4 and mB7-1.

CONCLUSIONS

Our results suggest activation of innate immunity in heart-transplant recipients through TLR4 contributes to the development of chronic rejection after cardiac transplantation.

Long-term follow-up of brachytherapy for treatment of allograft in-stent restenosis

The experience of brachytherapy in the treatment of in-stent restenosis of allograft arteries is limited. We present two cases of in-stent restenosis treated with brachytherapy with favorable angiographic follow-up at 10 months in one patient and at 17 months in the other.

Cardiac allograft vasculopathy: central role of endothelial injury leading to transplant "atheroma"

Endothelial injury plays a central role in the pathophysiologic mechanisms underlying cardiac allograft vasculopathy (CAV). Although the accelerated course of CAV and its localization to the allograft support an important role for the alloimmune response, there is considerable evidence implicating lipoprotein abnormalities, metabolic disturbances, viral infections, and systemic inflammation in the process. This multifactorial basis for CAV may be put into a pathophysiologic context in which endothelial cell injury is the triggering event that initiates and drives the proliferative and fibrotic processes characteristic of CAV. In the transplant setting, endothelial cell injury is induced by multiple factors, including brain death, ischemia-reperfusion, alloimmune responses, and viral infections. Once initiated, propagation of the proliferative processes that ultimately lead to vascular occlusion is enhanced by the abnormal metabolic environment of elevated lipoproteins and insulin resistance encountered in most patients. This review examines the evidence for the role of potential triggers of endothelial injury in the pathophysiology of CAV and discusses the central role of the nitric oxide pathway in the disease process.

Cardiac allograft vasculopathy and dysregulation of the NO synthase pathway

Cardiac allograft vasculopathy is the most aggressive form of atherosclerosis in humans and is the leading cause of death after the first year of heart transplantation. Endothelial dysfunction is a major contributing factor to the acceleration of coronary vascular disease in these individuals. A reflection of this endothelial dysfunction is the severe impairment in endothelium-dependent vasodilation that occurs early after transplantation. The etiology of this allograft endothelial alteration is multifactorial and may include preexisting atherosclerosis of the graft vessels, reperfusion injury during transplantation, denervation, disruption of the lymphatic system, and acute and chronic immune injury, as well as traditional risk factors for coronary artery disease (hyperlipidemia, diabetes, hypertension, or hyperhomocysteinemia) and pathogens, such as cytomegalovirus. The alteration in endothelial function affects vasomotor tone of the coronary arteries. Evidence indicates that there may be an impairment of endothelial production and/or activity of NO. Because NO is a potent vasodilator, its deficiency would explain the abnormal vasomotor tone in these individuals. In addition, because NO inhibits key processes in vascular inflammation and atherosclerosis, its absence may contribute to the acceleration of transplant vascular disease. Recent studies from our group and others have shed light on the mechanisms of endothelial dysfunction and its importance in cardiac allograft vasculopathy. In addition, the alteration in endothelial function contributes to vascular inflammation and progression of the disease.

Simvastatin treatment is associated with improvement in coronary endothelial function and decreased cytokine activation in patients after heart transplantation

OBJECTIVES

This study was designed to assess the association between 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibition, coronary endothelial function and cytokine activation in heart transplant recipients without angiographically detectable disease.

BACKGROUND

Coronary endothelial dysfunction contributes to cardiac allograft vasculopathy. The vasoprotective effects of statins in heart transplant recipients may include restoration of endothelial function and suppression of allograft inflammatory activity.

METHODS

Heart transplant recipients (one to three years after heart transplant) were divided into three groups based on the total cholesterol levels: group 1 (n = 21), patients with a history of hypercholesterolemia adequately controlled with simvastatin; group 2 (n = 19), patients with hypercholesterolemia not adequately treated with simvastatin; and group 3 (n = 40), patients without hypercholesterolemia. Coronary vasomotor function and intimal thickness as well as coronary sinus and aortic cytokine concentrations (tumor necrosis factor [TNF]-alpha, interleukin [IL]-6 and soluble IL-2 receptor) were investigated. In a prospective one-year follow-up study, changes in coronary endothelial function and cytokine levels were compared between 11 hypercholesterolemic patients treated with simvastatin and 9 controls.

RESULTS

Epicardial and microvascular endothelial functions were better in groups 1 and 3 than they were in group 2 (p < 0.01 and p < 0.05). Transcardiac IL-6 and TNF-alpha gradients were significantly increased in groups 2 and 3 compared with group 1 (IL-6: p < 0.05; TNF-alpha: p < 0.01). Plaque areas were significantly increased in groups 1 and 2 (p < 0.05 vs. group 3), whereas lumen area was increased in group 2 compared with group 1 (p < 0.05), demonstrating adaptive vascular remodeling. In patients treated with simvastatin, coronary endothelial function and cardiac cytokine activity significantly improved during the one-year follow-up.

CONCLUSIONS

Inhibition of allograft inflammatory activity and attenuation of the coronary endothelial dysfunction observed in cardiac transplant recipients during treatment with simvastatin may represent an important mechanism by which HMG-CoA reductase inhibitors protect against the development of cardiac allograft vasculopathy.