The use of proliferation signal inhibitors in the prevention and treatment of allograft vasculopathy in heart transplantation

Rapamycin Decreases the Osteogenic Response in Aortic Valve Interstitial Cells Through the Stat3 Pathway

BACKGROUND

Calcific aortic valve disease (CAVD) is an age-related and slowly progressive valvular disorder. We have previously found that the increased inflammatory and osteogenic responses to Toll-like receptor 4 (TLR4) stimulation is correlated with lower signal transducer and activator of transcription 3 (Stat3) activity in aortic valve interstitial cells (AVICs). Rapamycin, a drug used clinically, induces feedback activation of Akt. Akt in turn may upregulate Stat3. Therefore we hypothesized that rapamycin will decrease TLR4-induced osteogenic response in human AVICs through modulation of Stat3 activity.

METHODS

AVICs were isolated from normal valves taken from the explanted hearts of patients undergoing transplantation. Cells were treated with TLR4 ligand lipopolysaccharide (LPS) or rapamycin, or both. The osteogenic markers runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), and bone morphogenetic protein 2 (BMP-2), as well as activation of Stat3 and its associated signaling molecules, were analyzed.

RESULTS

LPS induces the expression of RUNX2, ALP, and BMP-2. Rapamycin decreased both the baseline and LPS-induced expression of RUNX2, ALP, and BMP-2. Rapamycin also decreased calcium deposit formation. Rapamycin activated both Stat3 and Akt in AVICs. Suppression of Akt resulted in abolishment of Stat3 activation. Inhibition of Stat3 enhanced expression of RUNX2, ALP, and BMP-2 at baseline and in response to LPS.

CONCLUSIONS

Rapamycin inhibits TLR4-induced osteogenic responses in AVICs by activation of Stat3 through Akt. Rapamycin may alleviate inflammation-induced initiation and progression of CAVD.

Twelve-month efficacy and safety of the conversion to everolimus in maintenance heart transplant recipients

AIM: To determine the clinical reasons for conversion to everolimus (EVL) and long-term outcomes in heart transplant (HT) recipients.

METHODS: A retrospective 12-mo study has been carried out in 14 Spanish centres to assess the efficacy and safety of conversion to EVL in maintenance HT recipients.

RESULTS: Two hundred and twenty-two patients were included (mean age: 53 ± 10.5 years; mean time from HT: 8.1 ± 4.5 years). The most common reasons for conversion were nephrotoxicity (30%), chronic allograft vasculopathy (20%) and neoplasms (17%). The doses and mean levels of EVL at baseline (conversion to EVL) and after one year were 1.3 ± 0.3 and 1.2 ± 0.6 mg/d and 6.4 ± 3.4 and 5.6 ± 2.5 ng/mL, respectively. The percentage of patients receiving calcineurin inhibitors (CNIs) at baseline and on the final visit was 95% and 65%, respectively. The doses and mean levels of CNIs decreased between baseline and month 12 from 142.2 ± 51.6 to 98.0 ± 39.4 mg/d (P < 0.001) and from 126.1 ± 50.9 to 89.2 ± 47.7 ng/mL (P < 0.001), respectively, for cyclosporine, and from 2.9 ± 1.8 to 2.6 ± 1.9 mg/d and from 8.3 ± 4.0 to 6.5 ± 2.7 ng/mL (P = 0.011) for tacrolimus. In the subgroup of patients converted because of nephrotoxicity, creatinine clearance increased from 34.9 ± 10.1 to 40.4 ± 14.4 mL/min (P < 0.001). There were 37 episodes of acute rejection in 24 patients (11%). The most frequent adverse events were oedemas (12%), infections (9%) and gastrointestinal problems (6%). EVL was suspended in 44 patients (20%). Since the database was closed at the end of the study, no further follow-up data is available.

CONCLUSION: Conversion to EVL in maintenance HT recipients allowed minimisation or suspension of the CNIs, with improved kidney function in the patients with nephrotoxicity, after 12 mo.

Everolimus and sirolimus in transplantation-related but different

INTRODUCTION

The inhibitors of the mammalian target of rapamycin (mTOR) sirolimus and everolimus are used not only as immunosuppressants after organ transplantation in combination with calcineurin inhibitors (CNIs) but also as proliferation signal inhibitors coated on drug-eluting stents and in cancer therapy. Notwithstanding their related chemical structures, both have distinct pharmacokinetic, pharmacodynamic and toxicodynamic properties.

AREAS COVERED

The additional hydroxyethyl group at the C(40) of the everolimus molecule results in different tissue and subcellular distribution, different affinities to active drug transporters and drug-metabolizing enzymes as well as differences in drug-target protein interactions including a much higher potency in terms of interacting with the mTOR complex 2 than sirolimus. Said mechanistic differences as well as differences found in clinical trials in transplant patients are reviewed.

EXPERT OPINION

In comparison to sirolimus, everolimus has higher bioavailability, a shorter terminal half-life, different blood metabolite patterns, the potential to antagonize the negative effects of CNIs on neuronal and kidney cell metabolism (which sirolimus enhances), the ability to stimulate mitochondrial oxidation (which sirolimus inhibits) and to reduce vascular inflammation to a greater extent. A head-to-head, randomized trial comparing the safety and tolerability of these two mTOR inhibitors in solid organ transplant recipients is merited.

Cardiac allograft vasculopathy: a donor or recipient induced pathology?

Cardiac allograft vasculopathy (CAV) is one of the main causes of late-stage heart failure after heart transplantation. CAV is characterized by concentric luminal narrowing of the coronary arteries, but the exact pathogenesis of CAV is still not unraveled. Many researchers show evidence of an allogeneic immune response of the recipient, whereas others show contrasting results in which donor-derived cells induce an immune response against the graft. In addition, fibrosis of the neo-intima can be induced by recipient-derived circulating cells or donor-derived cells. In this review, both donor and recipient sides of the story are described to obtain better insight in the pathogenesis of CAV. Dual outcomes were found regarding the contribution of donor and recipient cells in the initiation of the immune response and the development of fibrosis during CAV. Future research could focus more on the potential synergistic interaction of donor and recipient cells leading to CAV.

Rejection after conversion to a proliferation signal inhibitor in chronic heart transplantation

We sought to determine the incidence, risk factors, and consequences of acute rejection (AR) after conversion from a calcineurin inhibitor (CNI) to a proliferation signal inhibitor (PSI) in maintenance heart transplantation. Relevant clinical data were retrospectively obtained for 284 long-term heart transplant recipients from nine centers in whom CNIs were replaced with a PSI (sirolimus or everolimus) between October 2001 and March 2009. The rejection rate at one yr was 8.3%, stabilizing to 2% per year thereafter. The incidence rate after conversion (4.9 per 100 patient-years) was significantly higher than that observed on CNI therapy in the pre-conversion period (2.2 per 100 patient-years). By multivariate analysis, rejection risk was associated with a history of late AR prior to PSI conversion, early conversion (<5 yr) after transplantation and age <50 yr at the time of conversion. Use of mycophenolate mofetil was a protective factor. Post-conversion rejection did not significantly influence the evolution of left ventricular ejection fraction, renal function, or mortality during further follow-up. Conversion to a CNI-free immunosuppression based on a PSI results in an increased risk of AR. Awareness of the clinical determinants of post-conversion rejection could help to refine the current PSI conversion strategies.

Rapamycin protects against myocardial ischemia-reperfusion injury through JAK2-STAT3 signaling pathway

Rapamycin (Sirolimus®) is used to prevent rejection of transplanted organs and coronary restenosis. We reported that rapamycin induced cardioprotection against ischemia-reperfusion (I/R) injury through opening of mitochondrial K(ATP) channels. However, signaling mechanisms in rapamycin-induced cardioprotection are currently unknown. Considering that STAT3 is protective in the heart, we investigated the potential role of this transcription factor in rapamycin-induced protection against (I/R) injury. Adult male ICR mice were treated with rapamycin (0.25mg/kg, i.p.) or vehicle (DMSO) with/without inhibitor of JAK2 (AG-490) or STAT3 (stattic). One hour later, the hearts were subjected to I/R either in Langendorff mode or in situ ligation of left coronary artery. Additionally, primary murine cardiomyocytes were subjected to simulated ischemia-reoxygenation (SI/RO) injury in vitro. For in situ targeted knockdown of STAT3, lentiviral vector containing short hairpin RNA was injected into the left ventricle 3 weeks prior to initiating I/R injury. Infarct size, cardiac function, and cardiomyocyte necrosis and apoptosis were assessed. Rapamycin reduced infarct size, improved cardiac function following I/R, and limited cardiomyocyte necrosis as well as apoptosis following SI/RO which were blocked by AG-490 and stattic. In situ knock-down of STAT3 attenuated rapamycin-induced protection against I/R injury. Rapamycin triggered unique cardioprotective signaling including phosphorylation of ERK, STAT3, eNOS and glycogen synthase kinase-3ß in concert with increased prosurvival Bcl-2 to Bax ratio. Our data suggest that JAK2-STAT3 signaling plays an essential role in rapamycin-induced cardioprotection. We propose that rapamycin is a novel and clinically relevant pharmacological strategy to target STAT3 activation for treatment of myocardial infarction.

Virtual histology assessment of cardiac allograft vasculopathy following introduction of everolimus--results of a multicenter trial

In this 12-month multicenter Scandinavian study, 78 maintenance heart transplant (HTx) recipients randomized to everolimus with reduced calcineurin inhibitor (CNI) exposure or continued standard CNI-therapy underwent matched virtual histology (VH) examination to evaluate morphological progression of cardiac allograft vasculopathy (CAV). Parallel measurement of a range of inflammatory markers was also performed. A similar rate of quantitative CAV progression was observed in the everolimus (n = 30) and standard CNI group (n = 48) (plaque index 1.9 ± 3.8% and 1.6 ± 3.9%, respectively; p = 0.65). However, VH analysis revealed a significant increase in calcified (2.4 ± 4.0 vs. 0.3 ± 3.1%; p = 0.02) and necrotic component (6.5 ± 8.5 vs. 1.1 ± 8.6%; p = 0.01) among everolimus patients compared to controls. The increase in necrotic and calcified components was most prominent in everolimus patients with time since HTx >5.1 years and was accompanied by a significant increase in levels of von Willebrand (vWF) factor (p = 0.04) and vascular cell adhesion molecule (VCAM) (p = 0.03). Conversion to everolimus and reduced CNI is associated with a significant increase in calcified and necrotic intimal components and is more prominent in patients with a longer time since HTx. A significant increase in vWF and VCAM accompanied these qualitative changes and the prognostic implication of these findings requires further investigation.

Everolimus in clinical practice in long-term liver transplantation: an observational study

INTRODUCTION

Everolimus, a mammalian target of rapamycin (mTOR) inhibitor, has been used in acute and chronic treatment of kidney and heart transplants. There is scarce information regarding its use in liver transplant recipients, although everolimus may be a useful alternative for selected cases.

OBJECTIVE

The objective of this study was to study the clinical, biochemical, and pathological features of patients to whom everolimus was added based upon defined clinical profiles.

STUDY DESIGN

This study was prospective observational ongoing study to evaluate the effectiveness and safety of everolimus alone or in combination with low doses of a calcineurin inhibitor (CNI). Chronic liver transplant recipients without contraindications to everolimus were defined based upon 7 profiles of complications. The initial everolimus dose (0.25 mg every 12 hours) was overlapped during conversion, measuring blood levels and evaluating clinical tolerance. Routine monitoring was performed to obtain immunosuppressant blood levels near the lower limit of the therapeutic range.

RESULTS

The 35 patients' including 17 men and 18 women, had an overall mean age of 61 ± 10 years with a mean follow-up of 34 months. The everolimus treatment lasted 20 months (range, 6-60). The indication for everolimus conversion were as follows: renal insufficiency (45.7%), no response to hepatitis C virus (HCV) treatment (42.9%), autoimmune hepatitis associated with interferon (8.5%), de novo autoimmune hepatitis (25.5%), de novo tumor (37.1%), neurotoxicity (14.3%), or side effects to rapamycin treatment (5.7%). Patients may have presented more than one indication. Effectiveness was assessed based upon improved liver (48.6%) or renal function (31.25% with renal insufficiency) or withdrawal of prednisone (100% of 10 patients receiving prednisone). CNI was withdrawn from 48.6% of patients due to de novo tumors or neurotoxicity. The side effect were as follows: anemia, leukopenia, or thrombocytopenia (11.4%) or dyslipidemia (27.3%). The survival rate was 94.3%.

CONCLUSIONS

Administration of everolimus to chronic liver transplants enhanced therapeutic options in the long term recipients when applied for predefined clinical indications and administrated with dose adjustments based on serial monitoring of exposure.

Everolimus: a proliferation signal inhibitor with clinical applications in organ transplantation, oncology, and cardiology

Everolimus, a proliferation signal inhibitor in the mammalian target of rapamycin (mTOR) drug class, has many clinical applications, including in organ transplantation, oncology, and cardiology. It currently has United States Food and Drug Administration (FDA) approval for prophylaxis against rejection in de novo renal transplant recipients, treatment of renal cell carcinoma, and use as a drug-eluting stent. To review the pharmacology, pharmacokinetics, efficacy, and safety of everolimus, we performed a search of the MEDLINE database (January 1997-April 2010) for all English-language articles of in vitro and in vivo studies that evaluated everolimus, as well as abstracts from recent scientific meetings and the manufacturer. In transplantation, everolimus demonstrates immunosuppressive properties and has been used to prevent acute rejection in cardiac, liver, lung, and renal transplant recipients. It appears that this agent may be potent enough to allow for the minimization or removal of calcineurin inhibitors in the long-term management of renal transplant recipients. In oncology, everolimus has been proven effective for the management of treatment-resistant renal cell carcinoma. In cardiology, everolimus is available as a drug-coated stent and is used in percutaneous coronary interventions for prevention of restenosis. In transplant recipients and patients with renal cell carcinoma, everolimus appears to have an extensive adverse-event profile. The pharmacologic properties of everolimus differentiate this agent from other drugs used in these clinical areas, and its pharmacokinetic properties differentiate it from sirolimus.

Clinical recommendations for the use of everolimus in heart transplantation

Proliferation signal inhibitors (PSIs), everolimus (EVL), and sirolimus are a group of immunosuppressor agents indicated for the prevention of acute rejection in adult heart transplant recipients. Proliferation signal inhibitors have a mechanism of action with both immunosuppressive and antiproliferative effects, representing an especially interesting treatment option for the prevention and management of some specific conditions in heart transplant population, such as graft vasculopathy or malignancies. Proliferation signal inhibitors have been observed to work synergistically with calcineurin inhibitors (CNIs). Data from clinical trials and from the growing clinical experience show that when administered concomitantly with CNIs, PSIs allow significant dose reductions of the latter without loss of efficacy, a fact that has been associated with stabilization or significant improvement in renal function in patients with CNI-induced nephrotoxicity. The purpose of this article was to review the current knowledge of the role of PSIs in heart transplantation to provide recommendations for the proper use of EVL in cardiac transplant recipients, including indications, treatment regimens, monitoring, and management of the adverse events.

Effect of antibodies on endothelium

Patients developing posttransplant antibodies against HLA and non-HLA antigens expressed by the endothelium of the graft undergo more frequent episodes of rejection and have decreased long-term graft survival. Antibodies against the endothelium can alter/damage the cells of the graft through several mechanisms. Historically, antibodies were thought to elicit endothelial cell injury via complement-dependent mechanisms. New research has shown that antibodies can also contribute to the process of transplant rejection by stimulating proinflammatory and proproliferation signals. Antibody ligation leads to several functional alterations in EC including Weibel Palade body exocytosis, leukocyte recruitment, growth factor expression and cell proliferation. In contrast, under certain circumstances, antibodies may induce prosurvival signals and graft accommodation. The signaling events regulating accommodation vs. rejection appear to be influenced by the specificity and concentration of the anti-HLA antibody and the degree of molecular aggregation. Knowledge of the HLA and non-HLA antibody-mediated signaling pathways has the potential to identify new therapeutic targets to promote accommodation and prevent acute and chronic antibody-mediated rejection.

Human leukocyte antigen antibodies in chronic transplant vasculopathy-mechanisms and pathways

Transplant recipients exhibiting posttransplant antibodies are at a higher risk for acute and chronic antibody mediated rejection (AMR). The primary alloantigens recognized by antibodies in recipients with AMR are the highly polymorphic HLA class I and class II molecules expressed on the surface of the endothelial cells (ECs) of the graft. Traditionally, anti-HLA antibodies were thought to mediate graft injury through complement-dependent mechanisms. However, recent studies indicate that antibodies can also contribute to alterations in EC function through complement-independent mechanisms by transducing intracellular signals. Anti-HLA antibodies transduce signals that are both pro-inflammatory and pro-proliferative suggesting mechanistic roles in acute and chronic AMR.