Proliferation signal inhibitors in cardiac transplantation

Mild acute cellular rejection and development of cardiac allograft vasculopathy assessed by intravascular ultrasound and coronary angiography in heart transplant recipients-a SCHEDULE trial substudy

To evaluate the association between mild acute cellular rejection (ACR) and the development of cardiac allograft vasculopathy (CAV) after heart transplantation (HTx). Substudy of the SCHEDULE trial (n = 115), where de novo HTx recipients were randomized to (i) everolimus with early CNI elimination or (ii) CNI-based immunosuppression. Seventy-six patients (66%) were included based on matched intravascular ultrasound (IVUS) examinations at baseline and year 3 post-HTx. Biopsy-proven ACR within year 1 post-HTx was recorded and graded (1R, 2R, 3R). Development of CAV was assessed by IVUS and coronary angiography at year 3 post-HTx. Median age was 53 years (45-61), and 71% were male. ACR was recorded in 67%, and patients were grouped by rejection profile: no ACR (33%), only 1R (42%), and ≥2R (25%). Median ∆MIT (maximal intimal thickness)_BL-3Y was not significantly different between groups (P = 0.84). The incidence of CAV was 49% by IVUS and 26% by coronary angiography with no significant differences between groups. No correlation was found between number of 1R and ∆MIT_BL-3Y (r = -0.025, P = 0.83). The number of 1R was not a significant predictor of ∆MIT_BL-3Y (P = 0.58), and no significant interaction with treatment was found (P = 0.98). The burden of mild ACR was not associated with CAV development.

Heart transplantation: review

Heart transplantation is currently the definitive gold standard surgical approach in the treatment of refractory heart failure. However, the shortage of donors limits the achievement of a greater number of heart transplants, in which the use of mechanical circulatory support devices is increasing. With well-established indications and contraindications, as well as diagnosis and treatment of rejection through defined protocols of immunosuppression, the outcomes of heart transplantation are very favorable. Among early complications that can impact survival are primary graft failure, right ventricular dysfunction, rejection, and infections, whereas late complications include cardiac allograft vasculopathy and neoplasms. Despite the difficulties for heart transplantation, in particular, the shortage of donors and high mortality while on the waiting list, in Brazil, there is a great potential for both increasing effective donors and using circulatory assist devices, which can positively impact the number and outcomes of heart transplants.

Myocyte growth, repair, and oxidative stress following pediatric heart transplantation

Cardiac remodeling is associated with plasma biomarkers of fibrinogenesis, inflammation, and oxidative stress, and upregulation of mitogenic, pro-fibrotic, and apoptotic signaling pathways. Our primary objective was to evaluate biomarker and subcellular myocardial changes in pediatric heart transplant recipients. Fifty-two-week prospective, randomized (tacrolimus, Tac, vs. cyclosporine, CsA), open-label, parallel group study. Serial myocardial biopsies were probed for mitogenic and pro-inflammatory proteins. Plasma biomarkers of oxidative stress (F2α isoprostanes, nitrotyrosine), and inflammation and oxidation (hsCRP and cystatin-C) were measured. Nine of 11 randomized patients completed the study (four Tac, five CsA). Mean levels of F2α isoprostanes, hsCRP, and cystatin-C were maximal at Week 2. Peak activation of all MAP kinases in myocardial tissue was maximal at Week 10; no association was seen with rejection. Cardiac Bax/Bcl-2 levels (index of apoptosis) correlated negatively with F2α isoprostanes at Week 2 (r = -0.88) and with hsCRP at Week 52 (r = -0.67). At Week 52, hsCRP levels correlated positively with molecular indices of cardiac cell growth. We found evidence of systemic and myocardial oxidative damage and inflammation early posttransplant, which may be related to the remodeling process. Further study is needed to better understand the cardiac and systemic repair processes following pediatric heart transplantation.

Coronary microvasculopathy in heart transplantation: Consequences and therapeutic implications

Despite the progress made in the prevention and treatment of rejection of the transplanted heart, cardiac allograft vasculopathy (CAV) remains the main cause of death in late survival transplanted patients. CAV consists of a progressive diffuse intimal hyperplasia and the proliferation of vascular smooth muscle cells, ending in wall thickening of epicardial vessels, intramyocardial arteries (50-20 μm), arterioles (20-10 μm), and capillaries (< 10 μm). The etiology of CAV remains unclear; both immunologic and non-immunologic mechanisms contribute to endothelial damage with a sustained inflammatory response. The immunological factors involved are Human Leukocyte Antigen compatibility between donor and recipient, alloreactive T cells and the humoral immune system. The non-immunological factors are older donor age, ischemia-reperfusion time, hyperlipidemia and CMV infections. Diagnostic techniques that are able to assess microvascular function are lacking. Intravascular ultrasound and fractional flow reserve, when performed during coronary angiography, are able to detect epicardial coronary artery disease but are not sensitive enough to assess microvascular changes. Some authors have proposed an index of microcirculatory resistance during maximal hyperemia, which is calculated by dividing pressure by flow (distal pressure multiplied by the hyperemic mean transit time). Non-invasive methods to assess coronary physiology are stress echocardiography, coronary flow reserve by transthoracic Doppler echocardiography, single photon emission computed tomography, and perfusion cardiac magnetic resonance. In this review, we intend to analyze the mechanisms, consequences and therapeutic implications of microvascular dysfunction, including an extended citation of relevant literature data.

Benefit of early conversion from CNI-based to everolimus-based immunosuppression in heart transplantation

BACKGROUND

Calcineurin inhibitor (CNI)-induced nephrotoxicity is a feared adverse effect after heart transplantation (HTx). In patients with advanced renal failure we performed an overnight conversion from cyclosporine (CsA) to everolimus within the first year after HTx and compared changes in renal function to a similar switch performed in a group of long-term HTx survivors with 24-month follow up.

METHODS

Sixteen HTx recipients (Group 1), including 5 patients undergoing dialysis, were switched overnight from CsA to everolimus at 5.5 (range 1.3 to 8.5) months post-operatively, whereas 15 patients completed 24 months of follow-up. Fifteen long-term survivors (Group 2) were recruited at 96 (58 to 148) months post-HTx. Due to 3 withdrawals and 2 deaths, 10 of these 15 patients remained available for follow-up assessment.

RESULTS

In Group 1 patients, creatinine level improved from 211 (186 to 263) to 112 (98 to 140) mumol/liter and estimated glomerular filtration rate (eGFR) from 29 (20 to 35) to 62 (43 to 69) ml/min/1.73 m(2) (p < 0.001). In Group 2, creatinine decreased from 227 (188 to 255) to 193 (150 to 250) micromol/liter (p = 0.299), and eGFR increased from 26 (21 to 31) to 28 (22 to 35) ml/min/1.73 m(2) (p = 0.225). Four cellular rejections were treated successfully in Group 1. All together, 24 adverse events occurred.

CONCLUSIONS

These preliminary data are the first to suggest that the improvement in renal function after switching to CNI-free everolimus treatment has the greatest potential within the first year post-HTx. While we await randomized, controlled trials, it appears that conversion can be performed with acceptable safety in selected patients.

Heart Transplantation in Singapore

Introduction: The status of heart transplantation in Singapore is reviewed in this article. Materials and Methods: The database of 40 consecutive heart transplantations from July 1990 through December 2007 is reviewed retrospectively. The data is compared with the 2008 registry data of the International Society for Heart and Lung Transplantation (ISHLT). Results: The average age of recipients was 45.3 years. Ages ranged from 14 to 64 years. Ischaemic cardiomy- opathy (52.5%) and dilated cardiomyopathy (42.5%) were the major indications. From 1990 to 1999, 50% of the donors sustained brain death from road traffic accident, 25% from cerebrovascular accident and 25% from falling from height, whereas the cause of brain death in the donors from 2000 to 2007 was 33%, 47% and 9.5%, respectively. The average donor age increased from 28.3 to 38.1 years. The significant morbidities in the recipients were hypertension, cytomegalovirus (CMV) infection, cardiac allograft vasculopathy and renal dysfunction. Thirty- two required treatment for hypertension. 67.5% developed CMV disease requiring treatment. Cardiac allograft vasculopathy was diagnosed in 10. Rising creatinine levels reaching over 2.5 mg/dL was seen in 7. Three required renal dialysis. Epstein-Barr virus related lympho prolifera- tive disorder occurred in 2 patients. One patient developed adenocarcinoma of stomach. The 30-day mortality was 10% and half life was 10 years. Cardiac allograft vasculopathy and sepsis caused 41.7% of mortality each. 11.7% of the mortality was due to cerebrovascular accident. Conclusion: The status of heart transplantation in Singapore is comparable to the ISHLT registry data. Transplant provides excellent early survival of 80%; however, the expected half life is around 10 years after cardiac transplantation. The late mortality is mainly caused by cardiac allograft vasculopathy (CAV) and renal failure. More effort and research needs to be directed towards these issues to improve the long-term results. Key words: Cardiac allograft vasculopathy, Cardiac donors, Cardiac recipients, Cytomegalovirus, Lympho proliferative disorder, Renal dysfunction

Proliferation signal inhibitors and cardiac allograft vasculopathy

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is the leading cause of late morbidity and mortality in heart transplant patients and limits long-term survival. Immunosuppression following cardiac transplantation has traditionally comprised a calcineurin inhibitor in combination with mycophenolate mofetil or azathioprine and corticosteroids. This combination provides effective immunosuppression but does not prevent subsequent development of CAV. Proliferation signal inhibitors (such as sirolimus and everolimus), a new class of immunosuppressants, have recently been shown to be effective in attenuating the development of CAV following cardiac transplantation.

RECENT FINDINGS

In addition to immunosuppressive properties, proliferation signal inhibitors have important antiproliferative effects outside the immune system. Several ex-vivo and preclinical studies on animal models have demonstrated control of the vascular manifestations after cardiac transplantation. In clinical trials, proliferation signal inhibitors used as secondary immunosuppressive agents in place of azathioprine or mycophenolate prevented CAV progression and reduced the incidence of clinically significant cardiac events. Proliferation signal inhibitors are also effective as primary immunosuppressants, and, after complete calcineurin inhibitor withdrawal, mitigate the progression of CAV, improve calcineurin inhibitor-induced nephropathy and hypertension.

SUMMARY

Proliferation signal inhibitors are powerful immunosuppressive agents with antiproliferative properties that attenuate CAV and have the potential to improve long-term survival following cardiac transplantation.

mTOR regulates vascular smooth muscle cell differentiation from human bone marrow-derived mesenchymal progenitors

OBJECTIVE

Vascular smooth muscle cells (VSMCs) and circulating mesenchymal progenitor cells (MSCs) with a VSMC phenotype contribute to neointima formation and lumen loss after angioplasty and during allograft arteriosclerosis. We hypothesized that phosphoinositol-Akt-mammalian target of rapamycin-p70S6 kinase (PI3K/Akt/mTOR/p70S6K) pathway activation regulates VSMC differentiation from MSCs.

METHODS AND RESULTS

We studied effects of PI3K/Akt/mTOR signaling on phenotypic modulation of MSC and VSMC marker expression, including L-type Ca(2+) channels. Phosphorylation of Akt and p70S6K featured downregulation of VSMC markers in dedifferentiated MSCs. mTOR inhibition with rapamycin at below pharmacological concentrations blocked p70S6K phosphorylation and induced a differentiated contractile phenotype with smooth muscle (sm)-calponin, sm-alpha-actin, and SM protein 22-alpha (SM22alpha) expression. The PI3K inhibitor Ly294002 abolished Akt and p70S6K phosphorylation and reversed the dedifferentiated phenotype via induction of sm-calponin, sm-alpha-actin, SM22alpha, and myosin light chain kinase. Rapamycin acted antiproliferative without impairing MSC viability. In VSMCs, rapamycin increased a homing chemokine for MSCs, stromal cell-derived factor-1-alpha, at mRNA and protein levels. The CXCR4-mediated MSC migration toward conditioned medium of rapamycin-treated VSMCs was enhanced.

CONCLUSIONS

We describe novel pleiotropic effects of rapamycin at very low concentrations that stabilized differentiated contractile VSMCs from MSCs in addition to exerting antiproliferative and enhanced homing effects.

Induction of vascular atrophy as a novel approach to treating restenosis. A review

Regardless of the type of arterial reconstruction, luminal narrowing (stenosis or restenosis) develops in approximately one third of the vessels. In the past, the focus of research has been on the mechanisms of stenosis (intimal hyperplasia, pathologic remodeling) and pharmacologic approaches to prevention. An alternative approach is to induce intimal atrophy after luminal narrowing has developed, thus limiting treatment to only those patients that develop a problem. This approach to treat established disease by reducing wall mass through induction of cell death and extracellular matrix removal would be particularly useful for treating stenosis in synthetic bypass grafts or stented vessels, in which intimal hyperplasia is the primary mechanism of stenosis. This approach may be applicable as well to other vascular proliferative disorders, such as pulmonary hypertension and chronic transplant arteriopathy. Proof of principle has been shown in experiments with antibodies to platelet-derived growth factor (PDGF) receptors that cause neointimal regression in baboon polytetrafluoroethylene (PTFE) grafts and with angiotensin-converting enzyme inhibitors that induce medial atrophy in hypertensive arteries. Possible molecular targets could include PDGF receptors, A20, and BMP4. Further studies are needed to determine the utility of such a therapeutic approach to vascular disease.