Platelet activation in heart transplant recipients

Early Use of Aspirin for Coronary Allograft Prophylaxis in Heart Transplant Recipients

BACKGROUND

Coronary allograft vasculopathy (CAV) remains a significant cause of morbidity and mortality after heart transplantation. The use of aspirin for CAV prophylaxis has recently garnered interest as a possible therapeutic adjunct in this setting.

METHODS

This 2-center retrospective cohort study included 372 patients who underwent heart transplantation between January 2009 and March 2018 and were stratified according to the commencement of aspirin during their index transplant admission. The primary outcome was the development of moderate or severe CAV (International Society for Heart and Lung Transplantation grade ≥2) at surveillance coronary angiography. Secondary endpoints included mortality at follow-up.

RESULTS

There were no differences in age, sex, and cause of heart failure. In the early aspirin group, the preponderant risk factors included use of ventricular assist devices, pretransplant smoking, and mild or moderate rejection. Multivariable analyses to assess for independent predictors of CAV development and mortality demonstrated that aspirin was associated with reduced mortality (adjusted hazard ratio = 0.19; 95% confidence interval, 0.08-0.47, P < 0.01) and a trend toward a protective effect against the development of moderate or severe CAV (adjusted hazard ratio = 0.24; 95% confidence interval, 0.54-1.19; P = 0.08).

CONCLUSIONS

In this retrospective risk-adjusted 2-center cohort study, early aspirin administration was associated with reduced risk of death and a trend toward a protective effect against CAV development. These findings warrant validation in prospective randomized trials.

Platelet-to-Albumin Ratio: The Prognostic Utility in the Prediction of 2-Month Postoperative Heart Transplant Complications

BACKGROUND

The platelet-to-albumin ratio (PAR), leucocyte-to-albumin ratio (LAR), neutrophil percentage-to-albumin ratio (NPAR), and monocyte-to-albumin ratio (MAR) represent easily reproducible markers, which may predict the outcomes in various diseases. Early postoperative complications might appear after heart transplantation, such as infections, diabetes mellitus type 2 (DM2), acute graft rejection, and atrial fibrillation (AFib).

OBJECTIVE

The aim of our study was to investigate the PAR, LAR, NPAR, and MAR values before and after heart transplantation, and the associations of the preoperative levels of these markers with the presence of postoperative complications in first two months after surgery.

METHODS

Our retrospective research was directed from May 2014 to January 2021, with a total number of 38 patients being included. We used cut-off values for the ratios from previously published studies, as well as our own determination of these levels by using a receiver operating characteristic (ROC) curve.

RESULTS

By ROC analysis, the optimal preoperative PAR cut-off value was 38.84 (AUC: 0.771, p = 0.0039), with 83.3% sensitivity, and 75.0% specificity. Applying a Chi square (χ²) test, PAR > 38.84 represented an independent risk factor for complications, regardless of cause, and postoperative infections.

CONCLUSIONS

Preoperative PAR > 38.84 was a risk factor of developing complications of any cause, and postoperative infections in the first two months after heart transplantation.

Cardiac allograft vasculopathy: current review and future research directions

Cardiac allograft vasculopathy (CAV) is a pathologic immune-mediated remodelling of the vasculature in transplanted hearts and, by impairing perfusion, is the major cause of late graft loss. Although best understood following cardiac transplantation, similar forms of allograft vasculopathy occur in other vascularized organ grafts and some features of CAV may be shared with other immune-mediated vasculopathies. Here, we describe the incidence and diagnosis, the nature of the vascular remodelling, immune and non-immune contributions to pathogenesis, current therapies, and future areas of research in CAV.

Association of Aspirin Treatment With Cardiac Allograft Vasculopathy Progression and Adverse Outcomes After Heart Transplantation

BACKGROUND

Enhanced platelet reactivity may play a role in cardiac allograft vasculopathy (CAV) progression. The use of antiplatelet agents after heart transplantation (HT) has been inconsistent and although aspirin (ASA) is often a part of the medication regimen after HT, limited evidence is available on its benefit.

METHODS AND RESULTS

CAV progression was assessed by measuring the difference in plaque volume and plaque index between the last follow-up and the baseline coronary intravascular ultrasound examination. Overall, 529 HT recipients were retrospectively analyzed (337 had ≥2 intravascular ultrasound studies). The progression in plaque volume (P = .007) and plaque index (P = .002) was significantly attenuated among patients treated with early ASA (within the first year after HT). Over a 6.7-year follow-up, all-cause mortality was lower with early ASA compared with late or no ASA use (P < .001). No cardiac deaths were observed in the early ASA group, and the risk of CAV-related graft dysfunction was significantly lower in this group (P = .03). However, the composite of all CAV-related events (cardiac death, CAV-related graft dysfunction, or coronary angioplasty) was not significantly different between the groups (P = .16).

CONCLUSIONS

Early ASA use after HT may delay CAV progression and decrease mortality and CAV-related graft dysfunction, but does not seem to affect overall CAV-associated events.

The effect of antiplatelet therapy on survival and cardiac allograft vasculopathy following heart transplantation: A systematic review and meta-analysis

Cardiac allograft vasculopathy (CAV) is mediated by endothelial inflammation, platelet activation and thrombosis. Antiplatelet therapy may prevent the development of CAV. This systematic review and meta-analysis summarizes and appraises the evidence on the effect of antiplatelet therapy after heart transplantation (HT). CENTRAL(Ovid), MEDLINE(Ovid), Embase(Ovid) were searched from inception until April 30, 2020. Outcomes included CAV, all-cause mortality, and CAV-related mortality. Data were pooled using random-effects models. Seven observational studies including 2023 patients, mean age 52 years, 22% female, 47% with ischemic cardiomyopathy followed over a mean 7.1 years proved eligible. All studies compared acetylsalicylic acid (ASA) to no treatment and were at serious risk of bias. Data from 1911 patients in 6 studies were pooled in the meta-analyses. The evidence is very uncertain about the effect of ASA on all-cause or CAV-related mortality. ASA may reduce the development of CAV (RR 0.75, 95% CI: 0.44-1.29) based on very low certainty evidence. Two studies that conducted propensity-weighted analyses showed further reduction in CAV with ASA (HR 0.31, 95% CI: 0.13-0.74). In conclusion, there is limited evidence that ASA may reduce the development of CAV. Definitive resolution of the impact of antiplatelet therapy on CAV and mortality will require randomized clinical trials.

Cardiac Allograft Vasculopathy: The Enduring Enemy of Cardiac Transplantation

Cardiac allograft vasculopathy remains a major limiting factor in the long-term survival of the heart transplant recipient. Our understanding of its pathogenesis is continuously evolving as advances in imaging modalities have allowed a direct window into the natural history of the disease. Innovation in diagnostic modalities has spurred the proliferation of prognostic tools and biomarkers. And in parallel, pharmacological advances have emerged that have helped ameliorate the disease's progressive course.

Consequences of Retained Defibrillator and Pacemaker Leads After Heart Transplantation-An Underrecognized Problem

BACKGROUND

Cardiovascular implantable electronic devices (CIEDs) are common in patients undergoing heart transplantation (HT), and complete removal is not always possible at the time of transplantation.

METHODS

We retrospectively assessed the frequency of retained CIED leads and clinical consequences in consecutive HT patients from 2013 to 2016. Clinical outcomes included bacteremia, upper-extremity deep venous thrombosis (UEDVT), lead migration, and inability to perform magnetic resonance imaging (MRI).

RESULTS

A total of 138 patients (55 ± 11 years of age, 76% male) were identified; 37 (27%) had retained lead fragments (RLFs) at discharge. Patients with RLFs were older, had longer lead implantation time before HT, and a higher prevalence of dual-coil CIED leads compared with those without RLFs (P < .05 for all). Lead implantation time was identified as an independent predictor for RLFs (P < .05). Patients with RLFs had a higher frequency of DVT compared with the non-RLF group during the 1-year study period (42% vs 21%; P < .04). There was no difference in bacteremia. Fourteen patients (38%) could not undergo clinically indicated MRI.

CONCLUSION

RLFs after HT occur commonly and are associated with a higher rate of UEDVT and limit the use of MRI. Although no significant difference was found in the rates of bacteremia between the groups, this finding might be explained by the overall low incidence. Patients with risk factors for RLFs should be identified before transplantation, and complete lead removal should be considered with a multidisciplinary approach.

The incidence of aspirin resistance in heart transplantation recipients

Introduction

Coronary allograft vasculopathy can cause as many deaths as infections or rejection episodes within 3 years following heart transplantation.

Aim

To compare the aspirin resistance rate in an allograft heart transplantation population and in a control group by laboratory tests including the Aspirin-Resistant Patients Identification Test (ASPItest).

Material and methods

A total of 24 heart recipients (20 men and 4 women) at a mean age of 48 ±13 years who underwent routine clinical follow-up were consecutively enrolled in group 1. The control group consisted of 24 patients (19 men and 5 women) at a mean age of 64 ±7 years waiting for coronary artery bypass grafting in our department. All patients were treated with a standard dose of 75 mg aspirin (ASA) daily.

Results

Aspirin resistance was evaluated by the Multiplate platelet function test. The ASPItest revealed a mean value of 27 ±22 U in the transplant group. Results above 30 U were obtained in 8 (34%) patients, with a mean value of 50.3 ±20.6 U, indicating aspirin resistance. In the control group ASPItest results above 30 U were obtained in 5 (20%) patients, with a mean value of 43.3 ±6.4 U.

Conclusions

There is a high incidence (34% vs. 20%, NS) of ASA resistance in heart transplantation recipients and in the general population, respectively.

Platelets: versatile modifiers of innate and adaptive immune responses to transplants

PURPOSE OF REVIEW

Over the last decade there has been mounting experimental data demonstrating that platelets contribute to acute vascular inflammation and atherosclerosis. This review focuses on recent findings that link platelets to inflammatory responses of relevance to transplants.

RECENT FINDINGS

Although it has been known that platelets modify vascular inflammation by secretion of soluble mediators and release of microparticles, new aspects of these mechanisms are being defined. For example, platelet-derived CCL5 not only functions in homomers, but also forms more potent heteromers with platelet factor 4 (PF4; CXCL4). This heteromer formation can be inhibited with small molecules. New findings also demonstrate heterologous interactions of platelet microparticles with leukocytes that may increase their range of impact. By attaching to neutrophils, platelet microparticles appear to migrate out of blood vessels and into other compartments where they stimulate secretion of cytokines. Contact of platelets with extracellular matrix also can result in cleavage of hyaluronan into fragments that serve as an endogenous danger signal.

SUMMARY

Recent findings have expanded the range of interactions by which platelets can modify innate and adaptive immune responses to transplants.

Combination of clopidogrel and everolimus dramatically reduced the development of transplant arteriosclerosis in murine aortic allografts

Our group has shown that platelet inhibition with clopidogrel, an antagonist of the P2Y12 adenosine diphosphate receptor on platelets, reduced the formation of transplant arteriosclerosis. The aim of this study was to investigate whether a combination of cyclosporin or everolimus with clopidogrel has a beneficial effect on the development of transplant arteriosclerosis. Fully MHC mismatched C57Bl/6 (H2(b)) donor aortas were transplanted into CBA.J (H2(k)) recipients and mice received either clopidogrel alone (1 mg/kg/day) or in combination with cyclosporin (2 mg/kg/day) or everolimus (0.05 mg/kg/day). Grafts were analysed by histology and morphometry on day 30 after transplantation. In mice treated with clopidogrel alone, transplant arteriosclerosis was significantly reduced [intima proliferation 56 +/- 11% vs. 81 +/- 7% (control)/n = 7]. Daily application of everolimus reduced the development of transplant arteriosclerosis compared with untreated controls [intima proliferation of 29 +/- 9% vs. 81 +/- 7% (control)/n = 7]. Strikingly, combination of clopidogrel and everolimus almost abolished the formation of transplant arteriosclerosis [intima proliferation: 11 +/- 8% vs. 81 +/- 7% (control)/n = 7]. By contrast, combination of cyclosporin and clopidogrel compared with clopidogrel alone showed no additive effect. These results demonstrate that combination of platelet- and mammalian target of Rapamycin-inhibition can dramatically reduce the development of transplant arteriosclerosis.

Activation of platelets by Aspergillus fumigatus and potential role of platelets in the immunopathogenesis of Aspergillosis

Aspergillus fumigatus is the most frequent cause of invasive mold infections worldwide. Platelets contribute to inflammation and promote thrombosis, characteristically seen in aspergillosis, and might be involved both in antifungal defense and in the histopathological process. In the experiments reported here, in vitro activation of platelets by conidia, swollen conidia, and hyphae from A. fumigatus was assessed by flow cytometry and enzyme immunoassays. THP-1 monocytes and human monocytes with and without platelets were cultured with hyphae from A. fumigatus, and the release of interleukin-8 (IL-8) was measured by enzyme immunoassays. A. fumigatus potently induced the expression of CD62-p and CD63 and the release of CD40 ligand, RANTES, and Dickkopf homolog 1 in platelets, with particularly enhancing effects of hyphae compared with conidia. The hypha-mediated activation of platelets further enhanced the release of IL-8 both in THP-1 monocytes and in human adherent monocytes. In conclusion, we have found that A. fumigatus is a potent inducer of platelet-mediated inflammation, potentially promoting protective as well as harmful responses during aspergillosis.

Involvement of platelet activation by P2Y12 receptor in the development of transplant arteriosclerosis in mice

BACKGROUND

Although activated platelets influence inflammation by intraplatelet mediators in transplantation, their mechanism of involvement in the progression of transplant arteriosclerosis has not yet been elucidated. We, therefore, investigated this question using P2Y12 receptor knockout (KO) mice, in which platelets cannot be aggregated by adenosine diphosphate stimulation.

METHODS

Carotid arteries from 129X1 mice were orthotopically transplanted into wild-type or KO mice in a minor antigen(s)-mismatched strain combination. No immunosuppression was used. Grafts were harvested at 7, 14, 28, and 56 days after transplantation for morphometry and immunohistology. Fluorescence-activated cell sorting and quantitative real-time reverse-transcriptase polymerase chain reaction were performed at 7 and 14 days after transplantation.

RESULTS

The intima/media ratio of grafts in KO mice was significantly reduced compared with wild-type mice at 14, 28, and 56 days after transplantation. Fluorescence-activated cell sorting analysis showed a significant reduction of platelet CD154 expression and platelet-leukocyte aggregates in KO mice at 14 days after transplantation. Additionally, levels of intercellular adhesion molecule-1 and CD40 mRNA, and numbers of intercellular adhesion molecule-1- or CD40-positive cells in the grafts were lower in KO mice at 7 and 14 days after transplantation. These reductions resulted in a significant attenuation of CD45-positive leukocytes adhering to the graft vessel wall in KO mice at 14 days after transplantation.

CONCLUSION

Diminished platelet function by P2Y12 receptor deficiency attenuates initiation and strongly inhibits progression of transplant arteriosclerosis in mice by diminishing adhesion molecule expression and leukocyte accumulation in the grafts during the early phase after transplantation.

Attenuation of transplant arteriosclerosis with clopidogrel is associated with a reduction of infiltrating dendritic cells and macrophages in murine aortic allografts

BACKGROUND

Monotherapy with clopidogrel reduced the formation of transplant arteriosclerosis in a murine aortic allograft model. However, the underlying immunologic mechanisms are still unknown.

METHODS

Fully major histocompatibility complex-mismatched C57BL/6 (H2b) donor aortas were transplanted into CBA.J (H2k) recipients and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel, an antagonist of the P2Y12 ADP receptor on platelets, or control saline for 30 days. Blood was analyzed for changes in adhesion molecule and sCD40L concentrations by ELISA. Grafts were analyzed by histology, morphometry, and immunofluorescence on day 30 after transplantation. Intragraft cytokine mRNA production was analyzed by reverse-transcriptase polymerase chain reaction on day 14 after transplantation.

RESULTS

Treatment with clopidogrel resulted in significantly decreased blood concentrations of sCD40L and P-selectin after transplantation. Cellular analysis of the aortic transplant revealed fewer numbers of infiltrating dendritic cells (CD205+) and macrophages (F4/80+) after application of clopidogrel, whereas T-cells within the graft were unaltered. In addition cellular P-/E-selectin, ICAM-1, and platelet-derived-growth-factor (PDGF)-beta surface expression were significantly reduced as compared with untreated controls. Intragraft mRNA expression confirmed these results and showed significant lower production of P-/E-selectin, ICAM-1, and PDGF-beta after treatment with clopidogrel. Antiglycoprotein-Ib and antiglycoprotein VI had no beneficial effect on the development of transplant arteriosclerosis.

CONCLUSION

This report shows that application of clopidogrel after transplantation results in a reduction in adhesion molecule expression within the blood and transplant tissue and is associated with reduced transendothelial migration of dendritic cells and macrophages within the vascular wall.

Trapidil decreases the aggregation of platelets from heart transplant recipients ex vivo

Heart transplant recipients show platelet hyperaggregability, which may be related to the incidence of graft vasculopathy. We investigated whether trapidil can inhibit the aggregation of platelets from these patients. Platelet count, mean platelet volume (MPV), and adenosine diphosphate (ADP)-induced platelet aggregation were determined in 18 heart transplant recipients and 12 healthy subjects. Additionally, platelet-rich plasma from the patients was incubated with trapidil or with saline, prior to measuring ADP-induced aggregation. The MPV was significantly greater in patients compared to controls (9.4+/-1.1 vs 8.5+/-0.7 fL; P=.01), and ADP-induced platelet aggregation was significantly increased in patients compared to controls (81.2%+/-13.1% vs 69.6%+/-16.2%; P=.04, respectively). The trapidil-treated samples showed significantly decreased platelet aggregation compared to the control samples (24.2%+/-12.6% vs 66.7%+/-11.7%; P<.001). Platelets from heart transplant recipients showed an increased MPV and increased ADP-induced aggregation. Trapidil effectively reduced the ADP-induced aggregation ex vivo.

Gene Expression Profiles and B-Type Natriuretic Peptide Elevation in Heart Transplantation

Background— B-type natriuretic peptide (BNP) is chronically elevated in heart transplantation and reflects diastolic dysfunction, cardiac allograft vasculopathy, and poor late outcome. This investigation studied peripheral gene expression signatures of elevated BNP concentrations in clinically quiescent heart transplant recipients in an effort to elucidate molecular correlates beyond hemodynamic perturbations.

Methods and Results— We performed gene microarray analysis in peripheral blood mononuclear cells of 28 heart transplant recipients with clinical quiescence (absence of dyspnea or fatigue; normal left ventricular ejection fraction [EF >55%]; ISHLT biopsy score 0 or 1A; and normal hemodynamics [RAP <7 mm Hg, PCWP ≤15 mm Hg, and CI ≥2.5 L/min per m 2 ]). BNP levels were performed using the Triage B-type Natriuretic Peptide test (Biosite Diagnostics Inc, San Diego, Calif) and median BNP concentration was 165 pg/mL. Seventy-eight probes (of 7370) mapped to 54 unique genes were significantly correlated with BNP concentrations ( P <0.001). Of these, the strongest correlated genes ( P <0.0001) were in the domains of gelsolin (actin cytoskeleton), matrix metallopeptidases (collagen degradation), platelet function, and immune activity (human leukocyte antigen system, heat shock protein, mast cell, and B-cell lineage).

Conclusions— In the clinically quiescent heart transplant recipient, an elevated BNP concentration is associated with molecular patterns that point to ongoing active cardiac structural remodeling, vascular injury, inflammation, and alloimmune processes. Thus, these findings allude to the notion that BNP elevation is not merely a hemodynamic marker but should be considered reflective of integrated processes that determine the balance between active cardiac allograft injury and repair.

Clopidogrel reduces the development of transplant arteriosclerosis

BACKGROUND

Transplant arteriosclerosis, the hallmark feature of chronic rejection, is still the major limiting factor for the long-term success of heart transplantation. Platelets have been implicated to play a role in the pathogenesis of this disease. Therefore the aim of this study was to investigate whether platelet inhibition alone has a positive effect on the development of transplant arteriosclerosis.

METHODS

Fully major histocompatibility complex-mismatched C57BL/6 (H2(b)) donor aortas were transplanted into CBA (H2(k)) recipients, and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel or control saline as a daily intraperitoneal injection for 30 days. Blood was analyzed on days 2, 7, 14, and 30 by using a platelet aggregation test (adenosine diphosphate) for effectiveness of the treatment. Grafts were analyzed by means of histology and morphometry on day 30 after transplantation.

RESULTS

When mice were treated daily with 1 mg/kg clopidogrel in the absence of any other immunosuppression, transplant arteriosclerosis was significantly reduced compared with that seen in saline-treated control animals (intimal proliferation of 66% +/- 9% [1 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 7, P < or = .03). Daily application of 10 mg/kg and 20 mg/kg clopidogrel also significantly reduced the development of transplant arteriosclerosis compared with that seen in control animals (intimal proliferation of 61% +/- 11% [10 mg/kg clopidogrel] vs 54% +/- 10% [20 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 8, P < or = .003). There was, however, no additional beneficial effect when compared with mice treated with 1 mg/kg clopidogrel (P = .06). Isografts did not show any signs of vascular lesions on day 30 after transplantation.

CONCLUSION

These results demonstrate that monotherapy with clopidogrel can effectively reduce the formation of transplant arteriosclerosis in a murine aortic allograft model.