Revealing a new mode of sensitization induced by mechanical circulatory support devices: Impact of anti-AT1 R antibodies

Bariatric surgery modulates plasma levels of antibodies against angiotensin II type 1 and endothelin 1 type A receptor in severe obesity

PURPOSE

The contribution of endothelial-targeted autoantibodies against the angiotensin II type 1 receptor (anti-AT1R) and the anti-endothelin 1 type A receptor (anti-ETAR1) has been proposed in the development of cardiovascular diseases. However, no data have been reported yet in obesity. In this observational study we evaluated the relationship between anthropometric and metabolic parameters and anti-AT1R and anti-ETAR1 concentrations in a cohort of patients with severe obesity and associated comorbidities undergoing bariatric surgery.

METHODS

Clinical evaluation and metabolic assessment were performed in 36 subjects referring to our Center for the Study and Integrated Treatment of Obesity at the University Hospital of Padova. Circulating inflammatory adipocytokines and the endothelial dysfunction marker asymmetric dimethylarginine (ADMA) were evaluated; plasma levels of anti-AT1R and anti-ETAR1 were also determined. 10 normal-weight subjects were considered as a control group. 29 patients out of 36 were re-evaluated after surgery.

RESULTS

With respect to normal-weight controls patients showed significantly higher plasma levels of anti-AT1R (28 ± 20.4 vs 13.5 ± 2.8 U/mL, p < 0.005) and ADMA (0.8 ± 0.1 vs 0.54 ± 0.08 uM/L, p < 0.0001) but not anti-ETAR1 (14.2 ± 1.3 vs 13.3 ± 2 U/mL, p = 0.1). Anti-AT1R concentration showed an increasing trend with the worsening of glycemic status, while the presence of arterial hypertension among the patients did not affect autoantibodies levels. One year after surgery, a significant improvement in body weight and metabolic and inflammatory parameters was observed, along with a significant reduction of anti-AT1R (28.1 ± 20.4 U/mL vs 22.6 ± 16 U/mL, p < 0.05) and anti-ETAR1 (14.2 ± 1.3 U/L vs 13 ± 1.6 U/L, p < 0.01).

CONCLUSIONS

Subjects with obesity present higher plasma levels of anti-AT1R which are more related to glycemic profile than blood pressure levels, and are reduced by bariatric surgery. Considering the detrimental effects of these autoantibodies on vascular health, they should be assessed as potential biomarkers in obesity and metabolic diseases.

Association of MICA and AT1R antibodies with antibody-mediated rejection and cardiac allograft vasculopathy in a pediatric heart transplant recipient

BACKGROUND

Recipient antibodies against mismatched donor-specific human leukocyte antigens (HLA) are known to be associated with antibody-mediated rejection (AMR), posing increased risks of cardiac allograft vasculopathy (CAV), graft dysfunction, and graft loss after heart transplant (HTx). However, the impact of non-HLA antibodies on HTx outcome is not yet well defined.

CASE DESCRIPTION

Here we report a case of a pediatric patient, who was retransplanted after developing CAV in his first heart allograft. Five years post 2nd HTx, the patient presented with graft dysfunction and mild rejection (ACR 1R, AMR 1H, C4d Neg) in the cardiac biopsy in the absence of HLA donor-specific antibodies (DSAs). We detected strong antibodies against non-HLA antigens, including angiotensin II receptor type 1 (AT1R) and donor-specific MHC class I chain-related gene A (MICA), in the patient's serum that were implicated in the AMR and accelerated CAV of his second allograft, and likely played a role in the loss of his first allograft as well.

CONCLUSION

This case report underscores the clinical relevance of non-HLA antibodies in heart transplantation and highlights the value of incorporating these tests in the immunological risk assessment and post-transplant monitoring of HTx recipients.

Angiotensin II Type 1 Receptor Antibody-mediated Rejection Following Orthotopic Heart Transplant: A Single-center Experience

BACKGROUND

Antibody-mediated rejection (AMR) following orthotopic heart transplant (OHT) causes significant morbidity and mortality. There are limited data on antibodies to the angiotensin II type 1 receptor antibody (AT1R-Ab) causing rejection following OHT.

METHODS

This is a retrospective, single-center study that presents our 2-y experience with a series of 11 patients with evidence of nonspecific graft dysfunction and pathologic levels of AT1R-Ab. The clinical outcomes and treatments were compared to a group of 10 patients, also with evidence of nonspecific graft dysfunction, but who had nonsignificant AT1R-Ab titers.

RESULTS

The mean age of the AT1R-Ab cohort was 52% and 73% were bridged to transplant with an left ventricular assist device. The average left ventricular ejection fraction at presentation was 45%, and most were not on an angiotensin receptor blocker (ARB). Endomyocardial biopsies in those with elevated AT1R-Ab levels frequently showed reactive endothelium/endocardium without C4d or intravascular CD68 staining. Ten patients (91%) were started on an ARB. Other therapies included plasmapheresis and IVIg (64%), with 4 patients also receiving rituximab. Most patients had symptom improvement, but minimal change in graft function at an average 6 mo of follow-up.

CONCLUSIONS

The role of AT1R-Ab-mediated rejection in OHT recipients remains poorly understood. More than half of patients at our center who presented with graft dysfunction in the absence of acute cellular rejection or AMR were found to have elevated AT1R-Ab titers. Empiric AMR treatment in conjunction with ARB therapy may improve patient outcomes. Future studies are needed to better define the optimal treatment modalities for ATR1-Ab-mediated AMR.

Antibodies against Angiotensin II Type 1 and Endothelin 1 Type A Receptors in Cardiovascular Pathologies

Angiotensin II receptor type 1 (AT1R) and endothelin-1 receptor type A (ETAR) are G-protein-coupled receptors (GPCRs) expressed on the surface of a great variety of cells: immune cells, vascular smooth cells, endothelial cells, and fibroblasts express ETAR and AT1R, which are activated by endothelin 1 (ET1) and angiotensin II (AngII), respectively. Certain autoantibodies are specific for these receptors and can regulate their function, thus being known as functional autoantibodies. The function of these antibodies is similar to that of natural ligands, and it involves not only vasoconstriction, but also the secretion of proinflammatory cytokines (such as interleukin-6 (IL6), IL8 and TNF-α), collagen production by fibroblasts, and reactive oxygen species (ROS) release by fibroblasts and neutrophils. The role of autoantibodies against AT1R and ETAR (AT1R-AAs and ETAR-AAs, respectively) is well described in the pathogenesis of many medical conditions (e.g., systemic sclerosis (SSc) and SSc-associated pulmonary hypertension, cystic fibrosis, and allograft dysfunction), but their implications in cardiovascular diseases are still unclear. This review summarizes the current evidence regarding the effects of AT1R-AAs and ETAR-AAs in cardiovascular pathologies, highlighting their roles in heart transplantation and mechanical circulatory support, preeclampsia, and acute coronary syndromes.

Prevalence of AT1R antibody (AT1R-Ab) among Malaysian multi-ethnic population

BACKGROUND

Angiotensin II type 1 receptor antibody (AT1R-Ab) is a non-HLA antibody that has been reported to cause antibody-mediated rejection and graft loss in kidney transplantation. The prevalence of positive AT1R-Ab varies between 8% and 18% in different regions. Thus, this study aims to determine the prevalence of AT1R-Ab among the Malaysian population.

METHODOLOGY

All sera for AT1R-Ab were collected at the University Malaya Medical Centre (UMMC), Kuala Lumpur, Malaysia. The sera were centrifuged and kept refrigerated at -80 °C before being transported to the South Australian Transplantation and Immunogenetics Laboratory (SATIS). Enzyme-linked immunosorbent assay kit (One Lambda) was used for the detection of AT1R-Ab, and it was performed according to the manufacturer's instructions. The level of >17.1 U/mL was considered to be AT1R-Ab positive; 10.0-17.1 U/mL at risk, and <10.0 U/mL negative.

RESULTS

A total of 115 samples were collected from 99 patients pre and post-kidney transplant recipients. From the pre-transplant sera (n = 68) 17.7% were positive, 35.3% were at risk and 47.0% were negative. The positive AT1R-Ab cohort were relatively younger, with a mean age of 34.7 ± 8.3 years old and statistically significant, with a p-value of 0.028. Among the sera that were tested positive, 19.0% were from the Chinese ethnicity, 6.7% from Malay and 16.7% from Indian. There was no difference in the rejection episodes, persistent or de novo HLA-DSA, and graft function between the group (AT1R-Ab negative vs AT1R-Ab at risk and positive) and the results were consistent in a model adjusted for all potential confounders.

CONCLUSION

The prevalence of positive (>17.1 U/mL) pre-transplant AT1R-Ab was 17.7% and 35.3% were at risk (10.0-17.1 U/mL) in our pre-transplant cohort.

Non-HLA Abs in Solid Organ Transplantation

The role of anti-HLA antibodies in solid organ rejection is well established and these antibodies are routinely monitored both in patients in the waiting list and in the post-transplant setting. More recently, the presence of other antibodies directed towards non-HLA antigens, or the so-called minor histocompatibility antigens, has drawn the attention of the transplant community; however, their possible involvement in the graft outcome remains uncertain. These antibodies have been described to possibly have a role in rejection and allograft failure. This review focuses on the most studied non-HLA antibodies and their association with different clinical outcomes considered in solid organ transplantation with the aim of clarifying their clinical implication and potential relevance for routine testing.

Elevated AT1R Antibody and Morbidity in Patients Bridged to Heart Transplant Using Continuous Flow Left Ventricular Assist Devices

BACKGROUND

We studied longitudinal levels of angiotensin-II type 1 receptor antibody (AT1R-Ab) and their effects on adverse events (death, treated rejection and cardiac allograft vasculopathy) in patients who were bridged to heart transplant using a continuous flow left ventricular assist device (LVAD).

METHODS AND RESULTS

Sera of 77 patients bridged to heart transplant (from 2009 to 2017) were tested for AT1R-Ab and CRP before and after LVAD. Elevated AT1R-Ab was defined as >10.0 U/mL. The median follow-up after transplant was 3.6 years (interquartile range, 2.2-5.6 years). After LVAD, AT1R-Ab levels increased from baseline and remained elevated until transplant. Freedom from adverse events at 5 years was lower in those with elevated AT1R-Ab levels at time of transplant. In an adjusted, multivariable Cox analysis, an AT1R-Ab level of >10 U/mL was associated with developing the primary end point (adjusted hazard ratio 3.4, 95% confidence interval 1.2-9.2, P = .017). Although C-reactive protein levels were high before and after LVAD placement, C-reactive protein did not correlate with AT1R-Ab.

CONCLUSIONS

In LVAD patients bridged to heart transplant, an increased AT1R-Ab level at time of transplant was associated with poor outcomes after heart transplant. Post-LVAD AT1R-Ab elevations were not correlated with serum markers of systemic inflammation. Larger studies are needed to examine the pathologic role of AT1R-Ab in heart transplant.

Is There a Role for Natural Antibodies in Rejection Following Transplantation?

Antibody-mediated rejection continues to hinder long-term survival of solid organ allografts. Natural antibodies (Nabs) with polyreactive and autoreactive properties have recently emerged as potential contributors to antibody-mediated graft rejection. This review discusses Nabs, their functions in health and disease, their significance in rejection following kidney, heart, and lung transplantation, and their implication in serum reactivity to key antigens associated with rejection. Finally, potential effector mechanisms of Nabs in the context of transplantation are explored.

Impact and production of Non-HLA-specific antibodies in solid organ transplantation

Organ transplantation is an effective way to treat end-stage organ disease. Extending the graft survival is one of the major goals in the modern era of organ transplantation. However, long-term graft survival has not significantly improved in recent years despite the improvement of patient management and advancement of immunosuppression regimen. Antibody-mediated rejection is a major obstacle for long-term graft survival. Donor human leucocyte antigen (HLA)-specific antibodies were initially identified as a major cause for antibody-mediated rejection. Recently, with the development of solid-phase-based assay reagents, the contribution of non-HLA antibodies in organ transplantation starts to be appreciated. Here, we review the role of most studied non-HLA antibodies, including angiotensin II type 1 receptor (AT₁ R), K-α-tubulin and vimentin antibodies, in the solid organ transplant, and discuss the possible mechanism by which these antibodies are stimulated.

Combined Heart and Kidney Transplantation: Clinical Experience in 100 Consecutive Patients

Background

Combined heart and kidney transplantation (HKTx) is performed in patients with severe heart failure and advanced renal insufficiency. We analyzed the long‐term survival after HKTx, the influence of age and dialysis status, the rates of cardiac rejection, and the influence of sensitization.

Methods and Results

From June 1992 to December 2016, we performed 100 HKTx procedures. We compared older (≥60 years, n=53) with younger (<60 years, n=47) recipients, and recipients on preoperative dialysis (n=49) and not on dialysis (n=51). We analyzed actuarial freedom from any cardiac rejection, acute cellular rejection, and antibody‐mediated rejection, and survival rates by sensitized status with panel‐reactive antibody levels <10%, 10% to 50%, and >50%, and compared these survival rates with those from the United Network for Organ Sharing database. There was no difference in 15‐year survival between the 2 age groups (35±12.4% and 49±17.3%, ≥60 versus <60 years; P=0.45). There was no difference in 15‐year survival between the dialysis and nondialysis groups (44±13.4% and 37±15.2%, P=0.95). Actuarial freedom from any cardiac rejection (acute cellular rejection>0 or antibody‐mediated rejection>0) was 92±2.8% and 84±3.8%, acute cellular rejection (≥2R/3A) 98±1.5% and 94±2.5%, and antibody‐mediated rejection (≥1) 96±2.1% and 93±2.6% at 30 days and 1 year after HKTx. There was no difference in the 5‐year survival among recipients by sensitization status with panel‐reactive antibody levels <10%, 10% to 50%, and >50% (82±5.9%, 83±10.8%, and 92±8.0%; P=0.55). There was no difference in 15‐year survival after HKTx between the United Network for Organ Sharing database and our center (38±3.2% and 40±10.1%, respectively; P=0.45).

Conclusions

HKTx is safe to perform in patients 60 years and older or younger than 60 years and with or without dialysis dependence, with excellent outcomes. The degree of panel‐reactive antibody sensitization did not appear to affect survival after HKTx.

Hyperacute graft dysfunction in an orthotopic heart transplant in the presence of non-HLA antibodies

Antibody-mediated rejection (AMR) in heart transplants in the absence of anti-HLA donor-specific antibody (DSA) is not well studied or documented. This case reviews hyperacute fulminant graft dysfunction suspected to be mediated by non-HLA antibodies. After cross clamp removal, the patient developed severe pulmonary edema, profound coagulopathy, and biventricular failure. The patient's presumed AMR, cardiogenic shock, and coagulopathy were treated with extracorporeal membrane oxygenation (ECMO), plasmapheresis, intravenous immunoglobulin (IVIG), multiple blood products, and prothrombin complex concentrate. The recipient was 0% panel-reactive antibody (PRA), ABO, and crossmatch compatible. Intraoperative biopsy sample revealed a thrombotic process suggestive of a coagulation pathway activated by AMR; however, no C4d deposition was detected. Postmortem biopsies also suggested AMR. Retrospective testing of the patient's pretransplant serum revealed strong antiangiotensin II type 1 receptor (AT1R) antibodies and a strongly positive endothelial cell crossmatch. Anti-AT1R antibodies are known to be AT1 receptor agonists and may trigger inflammation and activate the extrinsic coagulation pathway. Given the potential effects of signaling through the AT1R, the patient's preexisting anti-AT1R antibodies and procoagulant therapy may have adversely affected the patient's clinical course.

Controversies in the Postoperative Management of the Critically Ill Heart Transplant Patient

Heart transplant recipients are susceptible to a number of complications in the immediate postoperative period. Despite advances in surgical techniques, mechanical circulatory support (MCS), and immunosuppression, evidence supporting optimal management strategies of the critically ill transplant patient is lacking on many fronts. This review identifies some of these controversies with the aim of stimulating further discussion and development into these gray areas.