Cyclosporine versus tacrolimus (FK 506) for prevention of cardiac allograft vasculopathy

Cardiovascular toxicities by calcineurin inhibitors: Cellular mechanisms behind clinical manifestations

Calcineurin inhibitors (CNI), including cyclosporine A (CsA) and tacrolimus (TAC), are cornerstones of immunosuppressive therapy in solid organ transplant recipients. While extensively recognized for their capacity to induce nephrotoxicity, hypertension, and dyslipidemia, emerging reports suggest potential direct cardiovascular toxicities associated with CNI. Evidence from both in vitro and in vivo studies has demonstrated direct cardiotoxic impact of CNI, manifesting itself as induction of cardiomyocyte apoptosis, enhanced oxidative stress, inflammatory cell infiltration, and cardiac fibrosis. CNI enhances cellular apoptosis through CaSR via activation of the p38 MAPK pathway and deactivation of the ERK pathway, and enhancement of miR-377 axis. Although CNI could attenuate cardiac hypertrophy in certain animal models, CNI concurrently impaired systolic function, enhanced cardiac fibrosis, and increased the risk of heart failure. Evidence from in vivo studies demonstrated that CNI prolong the duration of action potentials through a decrease in potassium current. CNI also exerted direct effects on endothelial cell injury, inducing apoptosis and enhancing oxidative stress. CNI may induce vascular inflammation through TLR4 via MyD88 and TRIF pathways. In addition, CNI affects vascular function by impairing endothelial-dependent vasodilation and promoting vasoconstriction. Clinical studies in transplant patients also revealed an increased incidence of cardiac remodeling. However, the evidence is constrained by the limited number of participants and potential confounding factors. Several studies indicate differing cardiovascular toxicity profiles between CsA and TAC, and these could be potentially due to their different interactions with calcineurin subunits and calcineurin-independent effects. Further studies are needed to clarify these mechanisms to improve cardiovascular outcomes for transplant patients with CNI.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

The pharmaceutical management of cardiac allograft vasculopathy after heart transplantation

INTRODUCTION

Cardiac allograft vasculopathy (CAV) is a major limitation to long-term survival after heart transplantation. Its peculiar pathophysiology involves multifactorial pathways including immune-mediated and metabolic risk factors, which are associated with the development of specific pathological lesions. The often diffuse and chronic nature of the disease reduces the effectiveness of revascularization procedures, and pharmacological prevention of the disease is the sole therapeutic approach with some proven efficacy.

AREAS COVERED

In this article, after briefly outlining the risk factors for CAV, the authors revise the potential pharmacological approaches that may reduce the burden of CAV. While several therapies have shown convincing efficacy in terms of CAV prevention diagnosed by coronary imaging, very few have been reported to improve prognosis with any meaningful level of evidence.

EXPERT OPINION

The authors believe that a customizable approach is necessary for clinical practice given the currently available evidence. Furthermore, it is important, in the future, to address the glaring therapeutic gap of an effective treatment against donor-specific antibodies, whose effect on endothelial injury is currently one of the major mechanisms of CAV development and for which no pharmacological treatment is currently available.

Outcomes and survival following heart retransplantation for cardiac allograft failure: a systematic review and meta-analysis

Background

Long-term efficacy of heart retransplantation (RTx) for end-stage cardiac allograft failure remains unclear given the limited worldwide experience and is an important question to elucidate given the shortage of donor organs. The aim of this systematic review was to examine the outcomes of RTx in patients with cardiac allograft failure.

Methods

Electronic search was performed to identify all studies in the English literature assessing RTx for cardiac allograft failure. All identified articles were systematically assessed for inclusion and exclusion criteria.

Results

Eleven studies were included for analysis, with a total of 7,791 patients. A total of 7,446 patients underwent primary heart transplantation (HTx) whereas 345 patients underwent RTx with average time from primary HTx to RTx interval of 5.03 years (95% CI: 3.13-6.94 years). There were 35.2% of patients received RTx within 30 days of primary transplant. Early mortality was significantly higher among RTx patients (RTx 28.2% vs. HTx 11.2%, P<0.001) whereas survival was significantly higher among HTx patients when compared to RTx patients at 1 year (HTx 81.8% vs. RTx 59.1%, P<0.001), 2 years (HTx 77.9% vs. RTx 53.6%, P<0.001), 3 years (HTx 76.1% vs. RTx 49.8%, P<0.001), 5 years (HTx 68.8% vs. RTx 41.4%, P<0.001) and 10 years (HTx 53.9% vs. RTx 31.7%, P<0.001). There were no significant differences between HTx and RTx in terms of freedom from rejection at 1 year (HTx 61.0% vs. RTx 53.7%, P=0.43), 2 years (HTx 63.8% vs. RTx 53.7%, P=0.26), 3 years (HTx 62.9% vs. RTx 51.9%, P=0.30) and 5 years (HTx 61.0% vs. RTx 51.9%, P=0.36).

Conclusions

Patients who underwent heart RTx had a significant lower survival when compared to those who only underwent primary HTx. There were no significant differences in post-transplantation freedom from rejection. Careful patient selection and perioperative care can make heart RTx a viable option for selected recipients.

Medication management of cardiac allograft vasculopathy after heart transplantation

Cardiac allograft vasculopathy (CAV) is a common complication following heart transplantation (HT), resulting in diminished graft survival. The preferred strategy for preventing CAV is optimal medical management; however, for patients who develop CAV, delaying disease progression through effective medication management is equally important. A review of the literature regarding medication management of CAV was conducted via a search of the MEDLINE database. Studies were included if they were published in English, conducted in humans ≥ 18 years of age or older, and used noninvestigational medications. Immunosuppressive medications such as the antiproliferative mycophenolate, the calcineurin inhibitor tacrolimus, and the proliferation signal inhibitors sirolimus and everolimus have been shown to prevent the development of CAV. Certain cardiovascular medications, such as HMG-CoA reductase inhibitors (statins), gemfibrozil, calcium channel blockers, and angiotensin-converting enzyme inhibitors, have also demonstrated efficacy in preventing this disease process. Prevention of CAV has also been observed with prophylaxis against cytomegalovirus infection and antioxidant medications. Despite being commonly used in HT patients, neither antiplatelet agents nor glycemic control have proved effective at preventing CAV. Only sirolimus has been shown to arrest the progress of existing CAV.

Tacrolimus versus cyclosporine microemulsion for heart transplant recipients: a meta-analysis

BACKGROUND

Tacrolimus and cyclosporine microemulsion are the 2 major immunosuppressants for heart transplantation. Several studies have compared these 2 drugs, but the outcomes were not consistent. This meta-analysis of randomized controlled trials compared the beneficial and harmful effects of tacrolimus and microemulsion cyclosporine for heart transplant recipients.

METHODS

Electronic databases and manual bibliography searches were conducted. A meta-analysis was performed of all randomized controlled trials comparing tacrolimus with cyclosporine microemulsion as primary immunosuppression for heart transplant recipients. Data for mortality, acute rejection, withdrawals, and adverse events were extracted. The combined results of the data of the randomized controlled trials were summarized as relative risk with 95% confidence intervals.

RESULTS

The study assessed 7 randomized controlled trials including 885 patients. There was no difference in mortality at 1 year between recipients treated with tacrolimus and cyclosporine microemulsion. Tacrolimus-treated patients had less acute rejection risk at 6 months and 1 year. Fewer patients stopped tacrolimus than cyclosporine microemulsion. The rate of new-onset diabetes mellitus requiring insulin treatment was higher with tacrolimus. More post-transplantation hypertension occurred with cyclosporine microemulsion. The groups had comparable incidences of malignancy and renal failure needing dialysis.

CONCLUSIONS

The use of tacrolimus as primary immunosuppressant for heart transplant recipients results in comparable survival and a significant reduction in acute rejection compared with cyclosporine microemulsion.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.

Treatment of allograft vasculopathy in heart transplantation

Cardiac allograft vasculopathy remains one of the main causes of morbidity and mortality after heart transplantation, although its impact is becoming somewhat smaller as prophylactic measures are implemented. Advances in the understanding of the molecular and cellular mechanisms involved in the genesis and development of cardiac allograft vasculopathy are opening ways for new diagnostic and therapeutic strategies. Successful prophylaxis of the early stages of the disease has been demonstrated with the use of newer immunosuppressive agents, such as sirolimus and everolimus, that will probably be included in future protocols. For most patients with established cardiac allograft vasculopathy, currently available revascularisation methods and retransplantation are not appropriate options. Antiproliferative agents could provide significant improvement in terms of symptom relief and prognosis, but their definite value must be proven in well-designed trials.

Contemporary concepts in prevention and treatment of cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV), is characterized by heterogeneous proliferative thickening of the vascular intima of the cardiac allograft vasculature. Since its presentation is commonly clinically silent, early diagnosis and preventative therapy are critical. Preventative therapy including optimization of immunosuppressive therapy and treatment of comorbidities associated with CAV progression must be initiated early since most of the intimal thickening occurs during the first year posttransplant. Long-term use of calcineurin inhibitors is associated with a high incidence of chronic renal disease and also contributes to hyperlipidemia and hypertension, all of which may exacerbate CAV. In addition, statins, antihypertensive agents and anti-CMV agents all have demonstrated benefits in reducing CAV. Once established, the limited treatment options include nonpharmacologic interventions such as retransplantation, percutaneous coronary interventions, coronary artery bypass grafting, transmyocardial laser revascularization and heparin-induced/mediated extracorporeal LDL plasmapheresis (HELP). As the use of new assessment tools increases our understanding of this disease, better preventative and treatment strategies are evolving.

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.

Five-year results of a randomized, single-center study of tacrolimus vs microemulsion cyclosporine in heart transplant patients

BACKGROUND

Previous multicenter, randomized trials, lacking standardized post-transplant protocols, have compared tacrolimus (Tac) and cyclosporine (CyA, Sandimmune) and demonstrated similar outcomes with some different adverse effects. The microemulsion form of CyA (mCyA, Neoral) has replaced Sandimmune CyA as the more widely utilized CyA formulation. This is the first 5-year follow-up study of a large, single-center trial (n = 67) under a standardized post-transplant protocol comparing Tac and mCyA.

METHODS

Sixty-seven heart transplant patients were randomized to Tac (n = 33) or mCyA (n = 34), both in combination with corticosteroids and azathioprine without cytolytic induction. Five-year end-points included survival, Grade > or = 3A or treated rejection, angiographic cardiac allograft vasculopathy (CAV; any lesion > or = 30% stenosis), renal dysfunction (creatinine > or = 2.0 mg/dl), use of two or more anti-hypertensive medications, percent diabetic and lipid levels.

RESULTS

Five-year survival, freedom from Grade > or = 3A or any treated rejection and angiographic CAV, mean cholesterol level and percent diabetic were similar between the two groups. The Tac group had a significantly lower 5-year mean triglyceride level (Tac 97 +/- 34 vs mCyA 175 +/- 103 mg/dl, p = 0.011) and average serum creatinine level (Tac 1.2 +/- 0.5 mg/dl vs mCyA 1.5 +/- 0.4 mg/dl, p = 0.044). There was a trend toward fewer patients requiring two or more anti-hypertensive drugs in the Tac group (Tac 33% vs mCyA 59%, p = 0.065).

CONCLUSIONS

Tac and mCyA appear to be comparable with regard to 5-year survival, freedom from rejection and CAV. However, compared with mCyA, Tac appears to reduce the adverse effect profile for hypertriglyceridemia and renal dysfunction and the need for hypertensive medications.

Lipid profiles in pediatric thoracic transplant recipients are determined by their immunosuppressive regimens

BACKGROUND

Controversy exists over the pattern of lipidemic effects from calcineurin inhibitors and prednisone. We report an extensive longitudinal study of lipid profiles in pediatric thoracic transplant recipients.

METHODS

Serial fasting lipids of subjects from a single pediatric center, along with their immunosuppressive regimens, were examined. Groups were analyzed according to cyclosporine- or tacrolimus-based immunosuppression in addition to whether prednisone was used as adjunctive therapy.

RESULTS

Of a total of 119 subjects, 85 were and remained on tacrolimus (TAC), 13 remained on cyclosporine (CSA), 4 switched from TAC to CSA, and 17 switched from CSA to TAC. The median age at transplant was 100 months, and the latest follow-up was 48 months. The CSA Group had higher lipid levels than the TAC Group, and levels changed minimally over time. At 1 year, TAC vs CSA total cholesterol was 153 vs 186 mg/dl (p = 0.002), low-density lipoprotein (LDL) cholesterol was 92 vs 117 (p = 0.09), and high-density lipoprotein (HDL) cholesterol was 42 vs 48 (p = NS), respectively. At the latest follow-up, the TAC vs CSA cholesterol was 143 vs 180 mg/dl (p = 0.001), LDL was 84 vs 115 (p = 0.001), and HDL was 42 vs 41 (p = NS). Profiles of subjects that switched agents reflected the agent used (e.g., higher total cholesterol, LDL, and HDL while on cyclosporine). Sub-group analysis showed prednisone augmented the hyperlipidemic effects.

CONCLUSION

Hyperlipidemia is common in pediatric thoracic transplant patients and persists over time. It is more pronounced in cyclosporine subjects and is further elevated with prednisone. These findings indicate the need for close monitoring, and consideration for intervention, especially in high-risk sub-groups.

From clinical trials to clinical practice: an overview of Certican (everolimus) in heart transplantation

Cardiac allograft vasculopathy (CAV) is the primary cause of late morbidity and mortality in heart transplant patients and remains a major challenge to further improvements in long-term graft survival in this population. Clearly, there is a need for immunosuppressive regimens that reduce the risk of CAV. Certican (everolimus) is a proliferation signal inhibitor developed for the prevention of acute and chronic rejection after solid-organ transplantation. Pre-clinical studies suggest that everolimus prevents vascular remodeling and neointimal proliferation, which are key components of CAV. In a pivotal trial in heart transplantation, everolimus at 1.5 or 3.0 mg plus standard-dose cyclosporine (CsA; Neoral) and corticosteroids demonstrated superior efficacy to azathioprine (AZA) by decreasing the incidence of biopsy-proven acute rejection (BPAR) and the composite end-point, efficacy failure. Importantly, in this trial, everolimus was also associated with a significant reduction in both the incidence and severity of CAV in recipients of heart transplants. Furthermore, cytomegalovirus (CMV) infection rates were significantly lower with everolimus than with AZA. The study suggests that everolimus has the ability to target the primary causes of chronic allograft dysfunction by reducing acute rejection and CMV infection, and preventing CAV. Moreover, these findings indicate that use of everolimus as part of the primary immunosuppression regimen, could provide a major benefit for heart transplant patients, offering a real hope of alleviating CAV in the long term. Few large-scale trials have been conducted in heart transplant patients, so their value must therefore be maximized with findings being effectively translated into clinical practice.

A decade experience of cardiac retransplantation in adult recipients

BACKGROUND

Cardiac retransplantation is considered to be the best therapeutic option for a failing cardiac allograft. However, poor outcomes with retransplantation have previously been reported, a factor that raises important ethical, logistic and financial issues given the limited organ donor supply.

METHODS

Seven hundred sixty-six adult patients underwent cardiac transplantation for end-stage heart failure at our institution from 1992 to 2002. Of these, 41 (5.4%) were retransplants. Variables examined included recipient and donor demographics, indications for retransplant, comorbidities, cytomegalovirus (CMV) serology status, left ventricular assist device use before transplant, donor ischemic time, rate of early mortality (within 30 days), and post-transplantation survival rate.

RESULTS

Indications for cardiac retransplant were transplant-related coronary artery disease in 37, acute rejection in 3, and other causes in 1. The mean interval between transplantation and retransplantation was 5.9 +/- 3.4 years. Baseline characteristics such as recipient age, gender, CMV serology status, and donor age were similar in the primary transplant and retransplant groups. Early mortality after transplantation was comparable between the 2 groups, but post-transplant survival was significantly lower in retransplant patients compared with primary transplants with 1-, 3-, 5-, and 7-year actuarial survival rates of 72.2%, 66.3%, 47.5%, and 40.7% vs. 85.1%, 79.2%, 72.9%, and 66.8%, respectively (p < 0.001).

CONCLUSIONS

Cardiac retransplantation offers short-term outcomes similar to primary transplantation but lower long-term survival rates. Non-retransplant surgical options should also be considered in these patients. Careful patient selection and risk-assessment is necessary to govern appropriate allocation of limited donor organs.

Cardiac allograft vasculopathy after heart transplantation: risk factors and management

Cardiovascular disease post-transplant, particularly ischemic heart disease, is a significant problem for all transplant recipients. The major risk factors-smoking, obesity, diabetes, dyslipidemia and hypertension-are often more prevalent in heart transplant populations than in the general population. One of the main risk factors influencing graft loss and patient survival is cardiac allograft vasculopathy (CAV). Because CAV affects between 30% and 60% of cardiac transplant recipients within 5 years of surgery, prevention is a key focus for cardiac transplant teams today. CAV is caused by both immunologic mechanisms (e.g., acute rejection and anti-HLA antibodies) and non-immunologic mechanisms relating to the transplant itself or the recipient (e.g., donor age, hypertension, hyperlipidemia and pre-existing diabetes) or to the side effects often associated with immunosuppression with calcineurin inhibitors or corticosteroids (e.g., cytomegalovirus infection, nephrotoxicity and new-onset diabetes after transplantation). The calcineurin inhibitors, cyclosporine and tacrolimus, effectively prevent acute rejection, but do not prevent the development of CAV. CAV prevention will require a combined approach of new adjunct immunosuppressant agents (e.g., the proliferation signal inhibitors) and reduction in cardiovascular risk. Hypertension, hyperlipidemia and diabetes are also associated with the immunosuppression required to prevent organ rejection. Some studies have shown that hypertension is present more frequently in cyclosporine-treated patients than in tacrolimus-treated patients and that tacrolimus may be associated with a more favorable lipid profile. On the other hand, tacrolimus may be more diabetogenic than cyclosporine with current data suggesting a trend but no statistically significant supporting evidence. New-onset diabetes after transplantation is at times difficult to manage and may be an important determinant along with hypertension and hyperlipidemia of ischemic heart disease, cerebrovascular disease and peripheral vascular disease. The choice of calcineurin inhibitor for an immunosuppressive regimen in heart transplantation should consider the associated relative cardiovascular risks.

Calcineurin inhibitors in heart transplantation

The use of calcineurin inhibitors (CNIs; cyclosporine and tacrolimus) has dramatically increased medium-term life expectancy after heart transplantation but has had only limited impact on long-term outcomes for heart transplant recipients. The original oil-based formulation of cyclosporine has been superceded by a microemulsion formulation (Neoral), which has more predictable pharmacokinetics and allows more precise dose-tailoring. Cyclosporine microemulsion and tacrolimus (Prograf) have a similar efficacy in the prevention of acute rejection of heart transplants, but their use is accompanied by nephrotoxicity and by cardiovascular side effects. The efficacy of immunosuppression can be improved by adjunctive therapy, such as azathioprine, mycophenolate mofetil (MMF; Cellcept), corticosteroids, and induction therapy. One of the most important predictors of patient mortality at >5 years after heart transplantation is cardiac allograft vasculopathy (CAV)/late graft failure, which accounts for 31% of deaths. Neither cyclosporine nor tacrolimus have been shown to prevent the development of CAV. In terms of efficacy, MMF provides a modest advantage over azathioprine in preventing CAV, and the combination of cyclosporine plus MMF results in significantly lower mortality than cyclosporine plus azathioprine. Overall, CNIs have multiple cardiovascular side effects, such as hypertension, hyperlipidemia and new-onset diabetes after transplantation, although cyclosporine and tacrolimus have somewhat different cardiovascular side-effect profiles. The challenge in choosing the best immunosuppressive regimen is to balance efficacy and safety to optimize graft and patient survival over the course of many decades. Because cyclosporine and tacrolimus have similar efficacy against acute rejection the choice of CNI for heart transplant recipients should be based on the relative risk of cardiovascular and renal side effects.

Inhibitors of Calcineurin

Before the early 1980s, patient and allograft survival for solid organ transplant recipients was dismal. By 1983, the first calcineurin blocker, cyclosporine (Sandimmun), had been introduced, and outcomes were dramatically improved. However, cyclosporine macroemulsion had suboptimal pharmacokinetics, significant drug interactions, and several adverse effects, including nephrotoxicity, neurotoxicity, hyperlipidemia, and hypertension. Recent advances with cyclosporine include the introduction of modified dosage formulations: Neoral, a microemulsion, and several generic microemulsion products. The potent second-generation calcineurin blocker tacrolimus (Prograf) was introduced in 1994 and has become the drug of choice for several types of transplant recipients. Although tacrolimus has improved pharmacokinetics and therapeutic drugmonitoring parameters, it has adverse effects such as nephrotoxicity, neurotoxicity, and diabetes. Thus, current immunosuppressive regimens implementing calcineurin blockers often involve additional immunosuppressive agents to “spare” the use of these agents, minimizing their adverse effects. This article reviews the mechanisms of action, pharmacokinetics, clinical use, therapeutic drug monitoring, drug interactions, adverse effects, and dosing of cyclosporine and tacrolimus in solid organ transplant recipients.

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.

FK506 vs. cyclosporin. Pathologic findings in 1067 endomyocardial biopsies

INTRODUCTION

Whether FK506 or cyclosporin is better for chronic immunosuppression in heart transplant patients has been debated. We examined endomyocardial biopsies from patients treated with these two drugs to determine if there was a difference in frequency of histologic cellular rejection episodes and Quilty lesions. The Quilty lesion (AKA cyclosporin effect) may be an atypical form of rejection, and is thought to be related to the use of cyclosporin immunosuppression.

METHODS

We reviewed 1067 endomyocardial biopsies from 65 patients who were assigned FK506 or cyclosporin after heart transplantation.

RESULTS

The number of episodes of rejection (162 FK506 vs. 145 cyclosporin) was the same. However, when compared to cyclosporin treatment, FK506 was associated with significantly more Quilty A lesions and fewer Quilty B lesions.

CONCLUSION

FK506 appears to prevent some Quilty A lesions from progressing to Quilty B lesions. Since Quilty B lesion is associated with myocyte injury and Quilty A is not, this effect of FK506 could be associated with improved long-term graft function.

Pediatric heart transplantation

Heart transplantation is now a treatment option with good outcome for infants and children with end-stage heart failure or complex, inoperable congenital cardiac defects. One-year and 5-year actuarial survival rates are high, approximately 75% and 65%, respectively, with overall patient survival half-life greater than 10 years. To date, survival has been improving as a result of reducing early mortality. Further reductions in late mortality, in part because of graft coronary artery disease and rejection, will allow achievement of the goal of decades-long survival. Quality of life in surviving children, as judged by activity, is usually "normal." Somatic growth is usually at the low normal range but linear growth can be reduced. Of infant recipients, 85% evaluated at 6 years of age or older were in an age-appropriate grade level. Long-term management of childhood heart recipients requires the collaboration of transplant physicians, given the increasing number of immunosuppressive agents and the balance between rejection and infection. Currently, recipients are maintained on immunosuppressive medications that target calcineurin (eg, cyclosporine, tacrolimus), lymphocyte proliferation (eg, azathioprine, mycophenolate mofetil [MMF], sirolimus) and, in some instances antiinflammatory corticosteroids. Emerging evidence now suggests a favorable immunologic opportunity for transplantation in childhood and, conversely, a higher mortality rate in children who have had prior cardiac surgery. Further studies are needed to define age-dependent factors that are likely to play a role in graft survival and possible graft-specific tolerance (eg, optimal conditions for tolerance induction and how immunosuppressive regimens should be changed with maturation of the immune system). As late outcomes continue to improve, the need for donor organs likely will increase, as transplantation affords a better quality and duration of life for children with complex congenital heart disease, otherwise facing a future of multiple palliative operations and chronic heart failure.

Transplant Coronary Vasculopathy

Because the transplanted heart is denervated, classic angina as a symptom of allograft coronary vasculopathy rarely is perceived. Any cardiac transplant patients who presents with decreased exercise capacity, shortness of breath, or syncope should be assessed thoroughly. Unfortunately, the initial presenting symptom of transplant vasculopathy may be acute myocardial infarction, heart failure, or even sudden death. Patients should be evaluated on an annual basis for the presence of transplant coronary vasculopathy in addition to when clinical suspicion warrants. Coronary angiography has been the main modality of invasive assessment, although it is insensitive. Recently, intracoronary ultrasound has been used in conjunction with angiography to detect the first evidence of transplant vasculopathy, manifested as thickening of the intimal layer of the vessel wall due to smooth muscle cell proliferation, which ultimately leads to luminal narrowing. Patients with evidence of vasculopathy should undergo functional evaluation with dobutamine echocardiography to document ischemic burden. Preventive measures include traditional coronary risk factor modification. Patients are started on statins early in the post-transplantation period and hypertension is treated aggressively using calcium channel blockers and angiotensin-converting enzyme (ACE) inhibitors. Because of their deleterious metabolic effects, steroids may be withdrawn under close surveillance for rejection. After transplant vasculopathy has developed, it is difficult to treat and options are limited. Patients with discrete luminal obstructions may undergo angioplasty, stenting, or coronary artery bypass. However, these procedures are palliative, and the only definitive therapy is retransplantation.

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

Immunosuppression may have an important impact on early graft coronary endothelial injury. We investigated functional and morphologic coronary alterations, myocardial expression, and cardiac release of possible mediators of allograft vasculopathy within 6 months after cardiac transplantation with respect to different immunosuppressive regimens. Epicardial and microvascular endothelium-dependent and endothelium-independent vasomotor function and epicardial intimal thickening were measured in 8 transplant recipients treated with cyclosporin A (CyA), azathioprine, and prednisone (group 1), 9 transplant recipients treated with tacrolimus (TKL), azathioprine, and prednisone (group 2), and 14 patients treated with TKL, mycophenolate mofetil (MMF), and prednisone (group 3). The gene expressions of inducible and endothelial nitric oxide synthase (iNOS and eNOS), endothelin-1, prostacyclinsynthase, and thromboxansynthase were analyzed in endomyocardial biopsy specimens using semiquantitative reverse transcription polymerase chain reaction. Transcardiac cytokine release, endothelin-1, and nitrate-release were determined from plasma samples. Epicardial endothelial dysfunction (vasoconstriction to acetylcholine > 10%) and microvascular smooth muscle cell dysfunction (flow velocity increase to adenosine and nifedipine < 2.0) were enhanced in heart transplant recipients immunosuppressed with TKL, azathioprine, and prednisone. The prevalence of epicardial dysfunction was 78% in group 2 versus 44% and 46% in group 1 and 3 (p < 0.05), respectively. The prevalence of microvascular dysfunction was 56% in group 2 versus 13% and 7% in group 1 and 3 (p < 0.02), respectively. Coronary vasomotor dysfunction was associated with increased myocardial iNOS expression (p < 0.05), decreased eNOS expression (p < 0.05), and enhanced cardiac immunoreactive interleukin-6 (p < 0.01). Coronary intimal thickening was not different between the groups. The combination of TKL and MMF appears to be superior to TKL and azathioprine (and comparable to CyA and azathioprine) concerning preservation of early coronary vasomotor function, eNOS expression, iNOS suppression as well as cardiac interleukin-6 release. This may have an important impact on subsequent development of transplant coronary atherosclerosis.